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Journal articles on the topic 'Molecular open-shells'
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1
Gottlieb, Alex D., John D. Head, and Dennis Perusse. "Natural molecular shells as open subsystems of small molecules." International Journal of Quantum Chemistry 111, no. 15 (January 19, 2011): 4158–73. http://dx.doi.org/10.1002/qua.22980.
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Rudzikas, Z. B. "Many-Body Problems. Atomic Configurations with Several Open Shells." Physica Scripta 35, no. 5 (May 1, 1987): 628–32. http://dx.doi.org/10.1088/0031-8949/35/5/003.
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Fromherz, Peter, and Diether Ruppel. "Lipid vesicle formation: the transition from open disks to closed shells." FEBS Letters 179, no. 1 (January 1, 1985): 155–59. http://dx.doi.org/10.1016/0014-5793(85)80211-8.
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Bartsch, M., H. Geesmann, G. F. Hanne, and J. Kessler. "Asymmetric scattering of polarized electrons from atoms with closed and open shells." Journal of Physics B: Atomic, Molecular and Optical Physics 25, no. 7 (April 14, 1992): 1511–26. http://dx.doi.org/10.1088/0953-4075/25/7/021.
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Nekhoroshkov, Pavel, Inga Zinicovscaia, Dmitry Nikolayev, Tatiana Lychagina, Alexey Pakhnevich, Nikita Yushin, and Jacques Bezuidenhout. "Effect of the Elemental Content of Shells of the Bivalve Mollusks (Mytilus galloprovincialis) from Saldanha Bay (South Africa) on Their Crystallographic Texture." Biology 10, no. 11 (October 25, 2021): 1093. http://dx.doi.org/10.3390/biology10111093.
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A both wild and farmed mussels in natural conditions, anthropogenic inputs are usually reflected in the increase of the content of specific elements. To determine the possible effect of the elemental patterns of farmed and wild mussels (Mytilus galloprovincialis) collected in the Saldanha Bay area (South Africa) on the crystallographic texture of the shells, the content of 20 elements in shells and 24 in the soft tissue of mussels was determined by neutron activation analysis. The crystallographic texture of mussel shells was analyzed using time-of-flight neutron diffraction. The wild mussels from open ocean site live in stressful natural conditions and contain higher amounts of the majority of determined elements in comparison with mussels farmed in closed water areas with anthropogenic loadings. The changes between the maximums of the same pole figures of the three samples are in the range of variability identified for the genus Mytilus. The content of Cl, Sr, and I was the highest in mussels from the open ocean site, which is reflected by the lowest mass/length ratio. The determined crystallographic textures of mussels are relatively stable as shown in the analyzed pole figures despite the concentrations of Na, Mg, Cl, Br, Sr, and I in shells, which significantly differ for wild and farmed mussels. The stability of the crystallographic texture that we observed suggests that it can be used as a reference model, where if a very different texture is determined, increased attention to the ecological situation should be paid.
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Argenziano, Rita, Federica Moccia, Rodolfo Esposito, Gerardino D’Errico, Lucia Panzella, and Alessandra Napolitano. "Recovery of Lignins with Potent Antioxidant Properties from Shells of Edible Nuts by a Green Ball Milling/Deep Eutectic Solvent (DES)-Based Protocol." Antioxidants 11, no. 10 (September 21, 2022): 1860. http://dx.doi.org/10.3390/antiox11101860.
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Lignins are phenolic polymers endowed with potent antioxidant properties that are finding increasing applications in a variety of fields. Consequently, there is a growing need for easily available and sustainable sources, as well as for green extraction methodologies of these compounds. Herein, a ball milling/deep eutectic solvent (DES)-based treatment is reported as an efficient strategy for the recovery of antioxidant lignins from the shells of edible nuts, namely chestnuts, hazelnuts, peanuts, pecan nuts, and pistachios. In particular, preliminarily ball-milled shells were treated with 1:2 mol/mol choline chloride:lactic acid at 120 °C for 24 h, and the extracted material was recovered in 19–27% w/w yields after precipitation by the addition of 0.01 M HCl. Extensive spectroscopic and chromatographic analysis allowed for confirmation that the main phenolic constituents present in the shell extracts were lignins, accompanied by small amounts (0.9% w/w) of ellagic acid, in the case of chestnut shells. The recovered samples exhibited very promising antioxidant properties, particularly in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay (EC50 values ranging from 0.03 to 0.19 mg/mL). These results open new perspectives for the valorization of nut shells as green sources of lignins for applications as antioxidants, e.g., in the biomedical, food, and/or cosmetic sector.
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Martins, Michael, Kai Godehusen, Tobias Richter, Philippe Wernet, and Peter Zimmermann. "Open shells and multi-electron interactions: core level photoionization of the 3d metal atoms." Journal of Physics B: Atomic, Molecular and Optical Physics 39, no. 5 (February 6, 2006): R79—R125. http://dx.doi.org/10.1088/0953-4075/39/5/r01.
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Tomašových, Adam, and Susan M. Kidwell. "Nineteenth-century collapse of a benthic marine ecosystem on the open continental shelf." Proceedings of the Royal Society B: Biological Sciences 284, no. 1856 (June 7, 2017): 20170328. http://dx.doi.org/10.1098/rspb.2017.0328.
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The soft-sediment seafloor of the open continental shelf is among the least-known biomes on Earth, despite its high diversity and importance to fisheries and biogeochemical cycling. Abundant dead shells of epifaunal suspension-feeding terebratulid brachiopods ( Laqueus ) and scallops on the now-muddy mainland continental shelf of southern California reveal the recent, previously unsuspected extirpation of an extensive offshore shell-gravel ecosystem, evidently driven by anthropogenic siltation. Living populations of attached epifauna, which formerly existed in a middle- and outer-shelf mosaic with patches of trophically diverse muds, are restricted today to rocky seafloor along the shelf edge and to the sandier shelves of offshore islands. Geological age-dating of 190 dead brachiopod shells shows that (i) no shells have been produced on the mainland shelf within the last 100 years, (ii) their shell production declined steeply during the nineteenth century, and (iii) they had formerly been present continuously for at least 4 kyr. This loss, sufficiently rapid (less than or equal to 100 years) and thorough to represent an ecosystem collapse, coincides with intensification of alluvial-plain land use in the nineteenth century, particularly livestock grazing. Extirpation was complete by the start of twentieth-century urbanization, warming, bottom fishing and scientific surveys. The loss of this filter-feeding fauna and the new spatial homogeneity and dominance of deposit- and detritus-feeders would have altered ecosystem functioning by reducing habitat heterogeneity and seawater filtering. This discovery, attesting to the power of this geological approach to recent ecological transitions, also strongly increases the spatial scope attributable to the negative effects of siltation, and suggests that it has been under-recognized on continental shelves elsewhere as a legacy of coastal land use.
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Plakhutin, B. N., A. V. Arbuznikov, and A. B. Trofimov. "Coupling coefficients for systems with two open electronic shells: Transition metal ions with pM dN configuration." International Journal of Quantum Chemistry 45, no. 4 (1993): 363–83. http://dx.doi.org/10.1002/qua.560450404.
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Graniero, Lauren E., Ethan L. Grossman, and Aaron O’Dea. "Stable isotopes in bivalves as indicators of nutrient source in coastal waters in the Bocas del Toro Archipelago, Panama." PeerJ 4 (August 2, 2016): e2278. http://dx.doi.org/10.7717/peerj.2278.
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To examine N-isotope ratios (15N/14N) in tissues and shell organic matrix of bivalves as a proxy for natural and anthropogenic nutrient fluxes in coastal environments,Pinctada imbricata,Isognomon alatus, andBrachidontes exustusbivalves were live-collected and analyzed from eight sites in Bocas del Toro, Panama. Sites represent a variety of coastal environments, including more urbanized, uninhabited, riverine, and oceanic sites. Growth under differing environmental conditions is confirmed byδ18O values, with open ocean Escudo de Veraguas shells yielding the highest averageδ18O (−1.0‰) value and freshwater endmember Rio Guarumo the lowest (−1.7‰). At all sites there is no single dominant source of organic matter contributing to bivalveδ15N andδ13C values. Bivalveδ15N andδ13C values likely represent a mixture of mangrove and seagrass N and C, although terrestrial sources cannot be ruled out. Despite hydrographic differences between end-members, we see minimalδ15N andδ13C difference between bivalves from the river-influenced Rio Guarumo site and those from the oceanic Escudo de Veraguas site, with no evidence for N from open-ocean phytoplankton in the latter. Populated sites yield relative15N enrichments suggestive of anthropogenic nutrient input, but lowδ15N values overall make this interpretation equivocal. Lastly,δ15N values of tissue and shell organic matrix correlate significantly for pterioideansP. imbricataandI. alatus. Thus for these species, N isotope studies of historical and fossil shells should provide records of ecology of past environments.
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Oleynichenko, Alexander V., Andréi Zaitsevskii, Leonid V. Skripnikov, and Ephraim Eliav. "Relativistic Fock Space Coupled Cluster Method for Many-Electron Systems: Non-Perturbative Account for Connected Triple Excitations." Symmetry 12, no. 7 (July 2, 2020): 1101. http://dx.doi.org/10.3390/sym12071101.
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The Fock space relativistic coupled cluster method (FS-RCC) is one of the most promising tools of electronic structure modeling for atomic and molecular systems containing heavy nuclei. Until recently, capabilities of the FS-RCC method were severely restricted by the fact that only single and double excitations in the exponential parametrization of the wave operator were considered. We report the design and the first computer implementation of FS-RCC schemes with full and simplified non-perturbative account for triple excitations in the cluster operator. Numerical stability of the new computational scheme and thus its applicability to a wide variety of molecular electronic states is ensured using the dynamic shift technique combined with the extrapolation to zero-shift limit. Pilot applications to atomic (Tl, Pb) and molecular (TlH) systems reported in the paper indicate that the breakthrough in accuracy and predictive power of the electronic structure calculations for heavy-element compounds can be achieved. Moreover, the described approach can provide a firm basis for high-precision modeling of heavy molecular systems with several open shells, including actinide compounds.
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Bóna, Miklós, and Meera Sitharam. "The Influence of Symmetry on the Probability of Assembly Pathways for Icosahedral Viral Shells." Computational and Mathematical Methods in Medicine 9, no. 3-4 (2008): 295–302. http://dx.doi.org/10.1080/17486700802168411.
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This paper motivates and sets up the mathematical framework for a new program of investigation: to isolate and clarify the precise influence of symmetry on the probability space of assembly pathways that successfully lead to icosahedral viral shells. Several tractable open questions are posed. Besides its virology motivation, the topic is of independent mathematical interest for studying constructions of symmetric polyhedra. Preliminary results are presented: a natural, structural classification of subsets of facets ofT= 1 polyhedra, based on their stabilizing subgroups of the icosahedral group; and a theorem that uses symmetry to formalize why increasing depth increases the numeracy (and hence probability) of an assembly pathway type (or symmetry class) for aT= 1 viral shell.
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Karen Martínez, A., and Ericson López. "On the low star formation rate in Saggitarius C." Journal of Physics: Conference Series 2238, no. 1 (April 1, 2022): 012008. http://dx.doi.org/10.1088/1742-6596/2238/1/012008.
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Abstract The Central Molecular Zone (CMZ) contains approximately 10% of the total molecular gas in the Galaxy concentrated in turbulent and dense molecular clouds. The fact that the star formation rate is low in CMZ is an open question, since there is a large amount of dense gas clouds where star formation could have started. Sagittarius (Sgr) C is the only known star formation region located in the western side of the CMZ. The main goal of our study was to find out the dominant physical conditions of Sgr C and how they could affect the process of star formation in the CMZ. We studied the dust emission toward Sgr C using infrared data. Using radio data we also studied the kinematic temperature, star formation rate surface density and cloud morphology of Sgr C. Our study showed a dust temperature T d of approximately 19 K toward Sgr C, which is in agreement with values estimated in other clouds of the CMZ and the Galactic plane. A high kinetic temperature higher than 58 K was determined toward Sgr C, which plays an important role in the cloud fragmentation and subsequent star formation. Based on our radio analysis we found a star formation rate surface density of ∑ SFR = 4 × 10-3 M ⊙yr-1 kpc -2 which is lower than in others molecular clouds of the Galaxy. Finally, the HCO + emission reveals the presence of cavities and shells in regions where there is no evidence of star formation. These shells could be related to cloud shocks believed to take place in Sgr C. It is thought that cloud shocks may have triggered star formation in other sites of the Galaxy, which is not observed in Sgr C. A comparison between physical conditions in Sgr C with those of high star formation sources could allow to find the parameters that suppress the birth of stars in this region of the Galactic Center.
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Thakur, Abhishek Kumar, Krishna Muralidharan, Thomas J. Zega, and L. M. Ziurys. "A nanometric window on fullerene formation in the interstellar medium: Insights from molecular dynamics studies." Journal of Chemical Physics 156, no. 15 (April 21, 2022): 154704. http://dx.doi.org/10.1063/5.0069166.
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Understanding the fundamental mechanisms that underlie the synthesis of fullerene molecules in the interstellar medium (ISM) and in the environments of astrophysical objects is an open question. In this regard, using classical molecular dynamics, we demonstrate the possibility of in situ formation of fullerene molecules, such as C60 from graphite, which is known to occur in the ISM, in particular, circumstellar environments. Specifically, when graphite is subjected to thermal and mechanical stimuli that are typical of circumstellar shells, we find that the graphite sheet edges undergo significant restructuring and curling, leading to edge-induced interlayer-interactions and formation of mechanically strained five-membered-ring structural units. These units serve as precursors for the formation of fullerene structures, such as pristine and metastable C60 molecules. The pathways leading to molecular C60 formation consist of a series of steps that involve bond-breakage and subsequent local rearrangement of atoms, with the activation energy barriers of the rate-limiting step(s) being comparable to the energetics of Stone–Wales rearrangement reactions. The identified chemical pathways provide fundamental insights into the mechanisms that underlie C60 formation. Moreover, they clearly demonstrate that top-down synthesis of C60 from graphitic sources is a viable synthesis route at conditions pertaining to circumstellar matter.
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Guseinov, I. I., B. A. Mamedov, M. Ertürk, H. Aksu, and E. Şahin. "Application of combined Hartree-Fock-Roothaan theory to atoms with an arbitrary number of closed and open shells of any symmetry." Few-Body Systems 41, no. 3-4 (October 30, 2007): 211–20. http://dx.doi.org/10.1007/s00601-007-0179-1.
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Youcefi, Fatma, Ali Riazi, Meriem Mokhtar, Tefiani Choukri, and Khaouani Naima. "Physicochemical Characterization and In-Vitro Antimicrobial Activity of Chitosan Extracted from Shrimp Shells Waste from Beni Saf Sea, Algeria." South Asian Journal of Experimental Biology 7, no. 3 (March 8, 2018): 122–29. http://dx.doi.org/10.38150/sajeb.7(3).p122-129.
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Chitosan is the most abundant natural organic polymer in nature. Its positive charge and its molecular arrangement confer interesting properties on the plane food, pharmaceutical, medical, cosmetic, water treatment. The present study was undertaken to study the physiochemical parameters and the in vitro antimicrobial activity of chitosan extracted from shrimp shells waste. The molecular weight of chitosan is 1414.33±16.99 kDa with, the percent of Ash 0,345±0,040 %, moisture is 2,98 ±0,13 % , and protein is 0.3 ±0,041 %.Chitosan produced (5 %) was also characterized with Fourier Transform Infrared Spectroscopy (FTIR) the spectrum of the chitosan sample from the shell recorded 16 peaks in the range of 689.40/cm and 3430.02 /cm. The antibacterial and antifungul activities of chitosan were examined against Escherichia coli ATCC10536, Pseudomonas aeruginosa ATCC 27853, Listeria monocytogenes ATCC7644, Staphylococcus aureus ATCC29213, Aspergillus niger ATCC 16888 and Candida albicans ATCC 10231 by agar wells diffusion the tests inhibitions zones diameters were 49,74± 0,75 , 54,35±0,93 , 42,27±1,07 , 32,95±0,28 and 53,73±0,64mm respectively. The minimum inhibitory concentration (MIC) using a broth microdilution method against tested microorganisms was ranging from 008% to 1.22%. These results open interesting perspectives of the chitosan. It can be used as new biomaterial with utility in many industrial areas.
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Gomez, John A., Mahlet Molla, Alejandro J. Garza, Thomas M. Henderson, and Gustavo E. Scuseria. "Assessing combinations of singlet-paired coupled cluster and density functional theory for treating electron correlation in closed and open shells." Molecular Physics 118, no. 4 (May 15, 2019): 1615144. http://dx.doi.org/10.1080/00268976.2019.1615144.
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Bachiller, R., P. J. Huggins, P. Cox, and T. Forveille. "The Spatio-Kinematic Structure of the CO Envelopes in Evolved Planetary Nebulae." Symposium - International Astronomical Union 155 (1993): 224. http://dx.doi.org/10.1017/s007418090017086x.
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We report high angular resolution mapping of the CO (J=2→1 and 1→0) lines in three evolved planetary nebulae (PNe): NGC 6781, NGC 6772, and VV47. The CO 2→1 observations of the ring-like nebula NGC 6781 provide the most detailed map to date of the kinematic structure of a PN envelope. The data are well explained with a model consisting of a thin, clumpy, ellipsoidal shell, which is open at the ends and is expanding with a velocity proportional to distance from the star. The molecular shell of NGC 6772 appears similar, but the gas is more confined to an equatorial ring and is much more incomplete. The molecular gas in VV 47 is in two clumpy lobes, which are likely to be the only surviving molecular condensations from an earlier, more extended equatorial distribution of the same kind. The average CO excitation temperature of these PNe is found to be >23 K from the CO 2→1/1→0 line ratio, and the mass of molecular gas is estimated to be 0.1, 0.02, and 0.002 M⊙ in NGC 6781, NGC 6772, and VV 47, respectively. It appears that the ring-like PNe are formed from the dissociation and ionization of neutral ellipsoidal shells; destruction of the envelope begins with the rapid ionization of the least dense polar caps, and continues until the densest molecular material at the nebular waist is fully ionized.
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Diao, Jiasheng, and Miriam S. Hasson. "Crystal Structure of Butyrate Kinase 2 from Thermotoga maritima, a Member of the ASKHA Superfamily of Phosphotransferases." Journal of Bacteriology 191, no. 8 (February 6, 2009): 2521–29. http://dx.doi.org/10.1128/jb.00906-08.
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ABSTRACT The enzymatic transfer of phosphoryl groups is central to the control of many cellular processes. One of the phosphoryl transfer mechanisms, that of acetate kinase, is not completely understood. Besides better understanding of the mechanism of acetate kinase, knowledge of the structure of butyrate kinase 2 (Buk2) will aid in the interpretation of active-site structure and provide information on the structural basis of substrate specificity. The gene buk2 from Thermotoga maritima encodes a member of the ASKHA (acetate and sugar kinases/heat shock cognate/actin) superfamily of phosphotransferases. The encoded protein Buk2 catalyzes the phosphorylation of butyrate and isobutyrate. We have determined the 2.5-Å crystal structure of Buk2 complexed with (β,γ-methylene) adenosine 5′-triphosphate. Buk2 folds like an open-shelled clam, with each of the two domains representing one of the two shells. In the open active-site cleft between the N- and C-terminal domains, the active-site residues consist of two histidines, two arginines, and a cluster of hydrophobic residues. The ATP binding region of Buk2 in the C-terminal domain consists of abundant glycines for nucleotide binding, and the ATP binding motif is similar to those of other members of the ASKHA superfamily. The enzyme exists as an octamer, in which four disulfide bonds form between intermolecular cysteines. Sequence alignment and structure superposition identify the simplicity of the monomeric Buk2 structure, a probable substrate binding site, the key residues in catalyzing phosphoryl transfer, and the substrate specificity differences among Buk2, acetate, and propionate kinases. The possible enzyme mechanisms are discussed.
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Liu, Jiaman, Yuqing Liu, Xiaofeng He, Bo Teng, and Jacqui M. McRae. "Valonea Tannin: Tyrosinase Inhibition Activity, Structural Elucidation and Insights into the Inhibition Mechanism." Molecules 26, no. 9 (May 7, 2021): 2747. http://dx.doi.org/10.3390/molecules26092747.
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Valonea tannin is a natural product readily extracted from acorn shells that has been suggested to have potential skin whitening properties. This study investigated the tyrosinase inhibition activity of extracted valonea tannin and the associated structure–function activity. Nuclear magnetic resonance spectroscopy and molecular weight analysis with gel permeation chromatography revealed that valonea tannin could be characterized as a hydrolysable tannin with galloyl, hexahydroxydiphenoyl and open formed-glucose moieties and an average molecular weight of 3042 ± 15 Da. Tyrosinase inhibition assays demonstrated that valonea tannin was 334 times more effective than gallic acid and 3.4 times more effective than tannic acid, which may relate to the larger molecular size. Kinetic studies of the inhibition reactions indicated that valonea tannin provided tyrosinase inhibition through mixed competitive–uncompetitive way. Stern–Volmer fitted fluorescence quenching analysis, isothermal titration calorimetry analysis and in silico molecule docking showed valonea tannin non-selectively bound to the surface of tyrosinase via hydrogen bonds and hydrophobic interactions. Inductively coupled plasma-optical emission spectroscopy and free radical scavenging assays indicated the valonea tannin had copper ion chelating and antioxidant ability, which may also contribute to inhibition activity. These results demonstrated the structure–function activity of valonea tannin as a highly effective natural tyrosinase inhibitor that may have commercial application in dermatological medicines or cosmetic products.
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Wang, Shang, Yan Xu, and Xiao-Wei Yu. "Micro-Aqueous Organic System: A Neglected Model in Computational Lipase Design?" Biomolecules 11, no. 6 (June 7, 2021): 848. http://dx.doi.org/10.3390/biom11060848.
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Water content is an important factor in lipase-catalyzed reactions in organic media but is frequently ignored in the study of lipases by molecular dynamics (MD) simulation. In this study, Candida antarctica lipase B, Candida rugosa lipase and Rhizopus chinensis lipase were used as research models to explore the mechanisms of lipase in micro-aqueous organic solvent (MAOS) media. MD simulations indicated that lipases in MAOS systems showed unique conformations distinguished from those seen in non-aqueous organic solvent systems. The position of water molecules aggregated on the protein surface in MAOS media is the major determinant of the unique conformations of lipases and particularly impacts the distribution of hydrophilic and hydrophobic amino acids on the lipase surface. Additionally, two maxima were observed in the water-lipase radial distribution function in MAOS systems, implying the formation of two water shells around lipase in these systems. The energy landscapes of lipases along solvent accessible areas of catalytic residues and the minimum energy path indicated the dynamic open states of lipases in MAOS systems differ from those in other solvent environments. This study confirmed the necessity of considering the influence of the microenvironment on MD simulations of lipase-catalyzed reactions in organic media.
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Strelko, V. V., and Yu I. Gorlov. "Influence of electronic states of nanographs in carbon microcrystallines on surface chemistry of activated charcoal varieties." Surface 13(28) (December 30, 2021): 15–38. http://dx.doi.org/10.15407/surface.2021.13.015.
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In this paper, the nature of the chemical activity of pyrolyzed nanostructured carbon materials (PNCM), in particular active carbon (AC), in reactions of electron transfer considered from a single position, reflecting the priority role of paramagnetic centers and edge defunctionaled carbon atoms of carbon microcristallites (CMC) due to pyrolysis of precursors. Clusters in the form of polycyclic aromatic hydrocarbons with open (OES) and closed (CES) electronic shells containing terminal hydrogen atoms (or their vacancies) and different terminal functional groups depending on specific model reactions of radical recombination, combination, replacement and elimination were used to model of nanographenes (NG) and CM. Quantum-chemical calculations of molecular models of NG and CMC and heat effects of model reactions were performed in frames of the density functional theory (DFT) using extended valence-splitted basis 6-31G(d) with full geometry optimization of concrete molecules, ions, radicals and NG models. The energies of boundary orbitals were calculated by means of the restricted Hartry-Fock method for objects with closed (RHF) and open (ROHF) electronic shells. The total energies of small negative ions (HOO-, HO-) and anion-radical О2•‾) were given as the sum of calculated total energies of these compounds and their experimental electron affinities. The estimation of probability of considered chemical transformations was carried out on the base on the well-known Bell-Evans-Polyani principle about the inverse correlation of the thermal effects of reactions and its activation energies. It is shown that the energy gap ΔЕ (energy difference of boundary orbitals levels) in simulated nanographens should depend on a number of factors: the periphery structure of models, its size and shape, the number and nature of various structural defects, electronic states of NG. When considering possible chemical transformations on the AC surface, rectangular models of NG were used, for which the simple classification by type and number of edge structural elements of the carbon lattice was proposed. Quantum chemical calculations of molecular models of NG and CNC and the energy of model reactions in frames of DTF showed that the chemisorption of free radicals (3O2 and N•O), as recombination at free radical centers (FRC), should occur with significant heat effects. Such calculations give reason to believe that FRC play an important role in formation of the functional cover on the periphery of NG in CMC of studied materials. On the base of of cluster models of active carbon with OES new ideas about possible reactions mechanisms of radical-anion О2•‾ formation and decomposition of hydrogen peroxide on the surface of active carbon are offered. Explanation of increased activity of AC reduced by hydrogen in H2O2 decomposition is given. It is shown that these PNCM models, as first of all AC, allow to adequately describe their semiconductor nature and acid-base properties of such materials.
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Brunner, M., M. Maercker, M. Mecina, T. Khouri, and F. Kerschbaum. "Modelling the carbon AGB star R Sculptoris." Astronomy & Astrophysics 614 (June 2018): A17. http://dx.doi.org/10.1051/0004-6361/201732065.
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Context. On the asymptotic giant branch (AGB), Sun-like stars lose a large portion of their mass in an intensive wind and enrich the surrounding interstellar medium with nuclear processed stellar material in the form of molecular gas and dust. For a number of carbon-rich AGB stars, thin detached shells of gas and dust have been observed. These shells are formed during brief periods of increased mass loss and expansion velocity during a thermal pulse, and open up the possibility to study the mass-loss history of thermally pulsing AGB stars. Aims. We study the properties of dust grains in the detached shell around the carbon AGB star R Scl and aim to quantify the influence of the dust grain properties on the shape of the spectral energy distribution (SED) and the derived dust shell mass. Methods. We modelled the SED of the circumstellar dust emission and compared the models to observations, including new observations of Herschel/PACS and SPIRE (infrared) and APEX/LABOCA (sub-millimeter). We derived present-day mass-loss rates and detached shell masses for a variation of dust grain properties (opacities, chemical composition, grain size, and grain geometry) to quantify the influence of changing dust properties to the derived shell mass. Results. The best-fitting mass-loss parameters are a present-day dust mass-loss rate of 2 × 10−10 M⊙ yr−1 and a detached shell dust mass of (2.9 ± 0.3) × 10−5 M⊙. Compared to similar studies, the uncertainty on the dust mass is reduced by a factor of 4. We find that the size of the grains dominates the shape of the SED, while the estimated dust shell mass is most strongly affected by the geometry of the dust grains. Additionally, we find a significant sub-millimeter excess that cannot be reproduced by any of the models, but is most likely not of thermal origin.
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Wootten, Alwyn. "The Structure of Dense Cloud Cores." International Astronomical Union Colloquium 120 (1989): 210–14. http://dx.doi.org/10.1017/s0252921100023757.
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Open slit spectra of planetary nebulae, in which images of the object are recorded in the light of several spectral lines on a single plate, have long proven a useful diagnostic of nebular properties and morphology. Fortunately, the reasonably simple structure of most planetaries greatly aids interpretation of the images. The dust-enshrouded mass-losing asymptotic giant branch stars from which planetaries evolve have now also been imaged at millimeter wavelengths. These high-resolution images have demonstrated the role of photochemistry in molding the composition of circumstellar shells. This powerful techinique is less well-developed as a tool for analyzing the structure of localized density concentrations in molecular clouds, the cores in which stars form. Even pre-astral cores, in which stars have not yet formed, may have an extended and intricate geometry which renders mapping tedious and masks their true structure. Their basic pre-astral structure may be complexly contorted by the character and extent of star formation within them. How, then, does our perception of the structure of a core depend upon the line in whose light it is imaged? Which lines optimally determine physical structure? How should chemical differences, perceived by comparisons of images in different lines, be used to determine the physical characteristics of a core?
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Yamaguchi, Klenicy K. L., David S. Dias, Carlos Victor Lamarão, Karen F. A. Castelo, Max S. Lima, Ananda S. Antonio, Attilio Converti, Emerson S. Lima, and Valdir F. Veiga-Junior. "Amazonian Bacuri (Platonia insignis Mart.) Fruit Waste Valorisation Using Response Surface Methodology." Biomolecules 11, no. 12 (November 25, 2021): 1767. http://dx.doi.org/10.3390/biom11121767.
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Bacuri (Platonia insignis Mart) is a species from the Clusiaceae genus. Its fruit pulp is commonly used in South America in several food products, such as beverages, ice cream and candies. Only the pulp of the fruit is used, and the peels and seeds are considered waste from these industries. As a trioxygenated xanthone source, this species is of high interest for bioproduct development. This work evaluated the mesocarp and epicarp of bacuri fruits through different extraction methods and experimental conditions (pH, temperature and solvent) in order to determine the most effective method for converting this agro-industrial waste in a value-added bioproduct. Open-column procedures and HPLC and NMR experiments were performed to evaluate the chemical composition of the extracts, along with total phenols, total flavonoids and antioxidant activities (sequestration of the DPPH and ABTS radicals). A factorial design and response surface methodology were used. The best extraction conditions of substances with antioxidant properties were maceration at 50 °C with 100% ethanol as solvent for mesocarp extracts, and acidic sonication in 100% ethanol for epicarp extracts, with an excellent phenolic profile and antioxidant capacities. The main compounds isolated were the prenylated benzophenones garcinielliptone FC (epicarp) and 30-epi-cambogin (mesocarp). This is the first study analysing the performance of extraction methods within bacuri agro-industrial waste. Results demonstrated that shells and seeds of bacuri can be used as phenolic-rich bioproducts obtained by a simple extraction method, increasing the value chain of this fruit.
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Mamedov, B. A., and E. Çopuroğlu. "The study of the action of self-friction field on the atom and molecular structures by using combined Hartree-Fock-Roothaan theory for closed and open shells of any symmetry." Journal of Molecular Structure 1114 (June 2016): 144–55. http://dx.doi.org/10.1016/j.molstruc.2016.02.044.
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Ewart, Heather, Peter Tickle, Robert Nudds, William Sellers, Dane Crossley, and Jonathan Codd. "Mediterranean Spur-Thighed Tortoises (Testudo graeca) Have Optimal Speeds at Which They Can Minimise the Metabolic Cost of Transport, on a Treadmill." Biology 11, no. 7 (July 13, 2022): 1052. http://dx.doi.org/10.3390/biology11071052.
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Tortoises are famed for their slow locomotion, which is in part related to their herbivorous diet and the constraints imposed by their protective shells. For most animals, the metabolic cost of transport (CoT) is close to the value predicted for their body mass. Testudines appear to be an exception to this rule, as previous studies indicate that, for their body mass, they are economical walkers. The metabolic efficiency of their terrestrial locomotion is explainable by their walking gait biomechanics and the specialisation of their limb muscle physiology, which embodies a predominance of energy-efficient slow-twitch type I muscle fibres. However, there are only two published experimental reports of the energetics of locomotion in tortoises, and these data show high variability. Here, Mediterranean spur-thighed tortoises (Testudo graeca) were trained to walk on a treadmill. Open-flow respirometry and high-speed filming were simultaneously used to measure the metabolic cost of transport and to quantify limb kinematics, respectively. Our data support the low cost of transport previously reported and demonstrate a novel curvilinear relationship to speed in Testudines, suggesting tortoises have an energetically optimal speed range over which they can move in order to minimise the metabolic cost of transport.
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MacFarlane, J. J., P. Wang, J. E. Bailey, T. A. Mehlhorn, and R. J. Dukart. "Plasma diagnostics using Kα satellite emission spectroscopy in light ion beam fusion experiments." Laser and Particle Beams 13, no. 2 (June 1995): 231–41. http://dx.doi.org/10.1017/s0263034600009356.
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Kα satellite spectroscopy can be a valuable technique for diagnosing conditions in high energy density plasmas. Kα emission lines are produced in intense light ion beam plasma interaction experiments as 2p electrons fill partially open Is shells created by the ion beam. In this paper, we present results from collisional-radiative equilibrium (CRE) calculations which show how Kα emission spectroscopy can be used to determine target plasma conditions in intense lithium beam experiments on Particle Beam Fusion Accelerator-II (PBFAII) at Sandia National Laboratories. In these experiments, 8–10 MeV lithium beams with intensities of 1–2 TW/cm2 irradiate planar multilayer targets containing a thin Al tracer. Kα emission spectra are measured using an X-ray crystal spectrometer with a resolution of λ/∆λ = 1200. The spectra are analyzed using a CRE model in which multilevel (NL ∼ 103) statistical equilibrium equations are solved self-consistently with the radiation field and beam properties to determine atomic level populations. Atomic level-dependent fluorescence yields and ion-impact ionization cross sections are used in computing the emission spectra. We present results showing the sensitivity of the Kα emission spectrum to temperature and density of the Al tracer. We also discuss the dependence of measured spectra on the X-ray crystal spectral resolution, and how additional diagnostic information could be obtained using multiple tracers of similar atomic number.
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Bose, Aneesh P. H., Johannes Windorfer, Alex Böhm, Fabrizia Ronco, Adrian Indermaur, Walter Salzburger, and Alex Jordan. "Structural manipulations of a shelter resource reveal underlying preference functions in a shell-dwelling cichlid fish." Proceedings of the Royal Society B: Biological Sciences 287, no. 1927 (May 20, 2020): 20200127. http://dx.doi.org/10.1098/rspb.2020.0127.
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Many animals can modify the environments in which they live, thereby changing the selection pressures they experience. A common example of such niche construction is the use, creation or modification of environmental resources for use as nests or shelters. Because these resources often have correlated structural elements, it can be difficult to disentangle the relative contribution of these elements to resource choice, and the preference functions underlying niche-construction behaviour remain hidden. Here, we present an experimental paradigm that uses 3D scanning, modelling and printing to create replicas of structures that differ with respect to key structural attributes. We show that a niche-constructing, shell-dwelling cichlid fish, Neolamprologus multifasciatus , has strong open-ended preference functions for exaggerated shell replicas. Fish preferred shells that were fully intact and either enlarged, lengthened or had widened apertures. Shell intactness was the most important structural attribute, followed by shell length, then aperture width. We disentangle the relative roles of different shell attributes, which are tightly correlated in the wild, but nevertheless differentially influence shelter choice and therefore niche construction in this species. We highlight the broad utility of our approach when compared with more traditional methods (e.g. two-choice tasks) for studying animal decision-making in a range of contexts.
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Yi, Kaijun, Zhiyuan Liu, and Rui Zhu. "Multi-resonant metamaterials based on self-sensing piezoelectric patches and digital circuits for broadband isolation of elastic wave transmission." Smart Materials and Structures 31, no. 1 (December 10, 2021): 015042. http://dx.doi.org/10.1088/1361-665x/ac3b1f.
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Abstract This paper proposes a general method to design multi-resonant piezoelectric metamaterials. Such metamaterials contain periodically distributed piezoelectric patches bonded on the surfaces of a host structure. The patches are shunted with digital circuits and working on self-sensing mode. A transfer function to be implemented in the digital circiots is designed to realize multi-resonance. The transfer function is derived only using the parameters of the patches. Consequently, it can be used to realize any type of multi-resonant metamaterial structures, like beams, plates and shells. The mechanism of generating multi-bandgaps by the transfer function is explained by analytically studying the effective bending stiffness of a multi-resonant piezo-metamaterial plate. It is shown that the transfer function induces multiple frequency ranges in which the effective bending stiffness becomes negative, consequently results in multiple bandgaps. The characteristics of these bandgaps are investigated, coupling and merging phenomena between them are observed and analyzed. Isolation effects of vibration transmission (elastic wave) in the metamaterials at multiple line frequencies or within a broad frequency band are numerically verified in frequency domain. Further time domain simulations accounting for the full dynamics of the metamaterials with digital circuits are also performed, stability and functionality of the metamaterials are demonstrated. The proposed multi-resonant piezoelectric metamaterials may open new opportunities in vibration mitigation of transport vehicles and underwater equipment.
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Williams, A., M. Cusack, and J. O. Buckman. "Chemico–structural phylogeny of the discinoid brachiopod shell." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 353, no. 1378 (December 29, 1998): 2005–38. http://dx.doi.org/10.1098/rstb.1998.0350.
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Stratiform shells of living discinids are composed of membranous laminae and variously aggregated, protein–coated granules of apatitic francolite supported by proteinaceous and chitinous nets in glycosaminoglycans (GAGs) to form laminae in rhythmic sets. The succession is like that of living lingulids but differs significantly in the structure of the periostracum, the nature of baculate sets and in its organic composition. In particular, discinids have a higher level of amino acids although with relatively lower acidic and higher basic concentrations; and their overall lower organic content is owing to lower levels of hydrophilic components, like GAGs and chitin. The organic constituents are not completely degraded during fossilization; but data are presently too meagre to distinguish between linguloid and discinoid ancestries. Many differences among three of the four described extant genera emanate from transformations with a long geological history. Pelagodiscus is characterized by regular, concentric rheomorphic folding (fila) of the flexible periostracum and the plastic primary layer and by sporadically developed hemispherical imprints of periostracal vesicles. Both features are more strikingly developed in Palaeozoic discinids. In the oldest discinid, the Ordovician Schizotreta , and the younger Orbiculoidea and related genera, vesicles were persistent, hexagonal close–packed arrays fading out over fila. They must have differed in composition, however, as the larger vesicles of Schizotreta were simple (possibly mucinous), whereas the smaller vesicles of Orbiculoidea and younger genera were composites of thickly coated spheroids, possibly of lipoproteins, which survive as disaggregated relicts in Pelagodiscus . Baculate sets within the secondary layer are also less well developed in living discinids, being incipient in Pelagodiscus and restricted to the dorsal valve of Discinisca . The trellised rods (baculi) with proteinaceous cores are composed of pinacoids or prisms of apatite, depending on whether they are supported by chitinous nets or proteinaceous strands in GAGs. This differentiation occurred in Schizotreta but in that stock (and Trematis ) the baculate set is symmetrical with baculi subtended between compact laminae, whereas in younger and post–Palaeozoic species the outer bounding lamina(e) of the set is normally membranous and/or stratified. The most striking synapomorphy of living discinids is the intravesicular secretion of organsiliceous tablets with a crystalline habit within the larval outer epithelium and their exocytosis as a close– or open–packed, transient, biomineral cover for larvae. Canals, on the other hand, are homologous with those pervading lingulid shells. Both systems interconnect with chitinous and proteinaceous sets and have probably always served as vertical struts in an organic scaffolding supporting the stratiform successions. A phylogenetic analysis based mainly on shell structure confirms the discinoids as the sister group of the linguloids but, contrary to current taxonomic practice, also supports the inclusion of acrotretoids within a ‘discinoid’ clade as a sister group to the discinids.
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Dziomber, Laura, Walter G. Joyce, and Christian Foth. "The ecomorphology of the shell of extant turtles and its applications for fossil turtles." PeerJ 8 (December 22, 2020): e10490. http://dx.doi.org/10.7717/peerj.10490.
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Turtles are a successful clade of reptiles that originated in the Late Triassic. The group adapted during its evolution to different types of environments, ranging from dry land to ponds, rivers, and the open ocean, and survived all Mesozoic and Cenozoic extinction events. The body of turtles is characterized by a shell, which has been hypothesized to have several biological roles, like protection, thermal and pH regulation, but also to be adapted in its shape to the ecology of the animal. However, only few studies have investigated the relationships between shell shape and ecology in a global context or clarified if shape can be used to diagnose habitat preferences in fossil representatives. Here, we assembled a three-dimensional dataset of 69 extant turtles and three fossils, in particular, the Late Triassic Proganochelys quenstedtii and Proterochersis robusta and the Late Jurassic Plesiochelys bigleri to test explicitly for a relationship between shell shape and ecology. 3D models were obtained using surface scanning and photogrammetry. The general shape of the shells was captured using geometric morphometrics. The habitat ecology of extant turtles was classified using the webbing of their forelimbs as a proxy. Principal component analysis (PCA) highlights much overlap between habitat groups. Discriminant analyses suggests significant differences between extant terrestrial turtles, extant fully aquatic (i.e., marine and riverine) turtles, and an unspecialized assemblage that includes extant turtles from all habitats, mostly freshwater aquatic forms. The paleoecology of the three fossil species cannot be determined with confidence, as all three fall within the unspecialized category, even if Plesiochelys bigleri plots closer to fully aquatic turtles, while the two Triassic species group closer to extant terrestrial forms. Although the shape of the shell of turtles indeed contains an ecological signal, it is overall too weak to uncover using shell shape in paleoecological studies, at least with the methods we selected.
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REID, DAVID G. "The genus Echinolittorina Habe, 1956 (Gastropoda: Littorinidae) in the Indo-West Pacific Ocean." Zootaxa 1420, no. 1 (March 8, 2007): 1–161. http://dx.doi.org/10.11646/zootaxa.1420.1.1.
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The phylogeny of the genus Echinolittorina, and phylogeography of some of its members, have previously been examined using molecular data, so that species can now be defined by a combination of phylogenetic, morphological and geographical criteria. The 26 species recognized in the Indo-West Pacific biogeographical region form a monophyletic group, here defined as the subgenus Granulilittorina Habe & Kosuge, 1966. Morphological descriptions are provided for these 26 species, including details of shell, pigmentation of headfoot, reproductive anatomy, spermatozoa, egg capsules and radulae. Diagnoses include reference to mitochondrial gene sequences (COI). A key is based on shells, tentacle pigmentation, penial shape and geographical distribution. Seven new species are described: E. marisrubri, E. omanensis, E. austrotrochoides, E. marquesensis, E. wallaceana, E. tricincta, E. philippinensis. Three name changes are proposed: E. malaccana (Philippi, 1847) and E. cecillei (Philippi, 1851) are valid names for two members of the former ‘E. trochoides’ group; E. biangulata (von Martens, 1897) replaces ‘E. quadricincta’. Full synonymies are given for all taxa, and the taxonomic, evolutionary and ecological literature reviewed. Distribution maps are based on examination of 1701 samples and reliable literature records. The contrast between continental and oceanic distribution patterns is emphasized; one clade of five species and two additional species are shown to have an association with upwelling areas. All species are known (or predicted from protoconch size and oviduct anatomy) to have planktotrophic development, and rare extralimital records suggest a maximum open-water dispersal distance of 1000–2100 km. The most useful morphological characters for identification are the shell, penial shape and copulatory bursa in the pallial oviduct. Sister species can be morphologically similar, but are almost always entirely allopatric, so that distributional information is important for identification. Substantial intraspecific variation is present in the shell shape and sculpture of most species; where there is a pronounced geographical pattern this may have a genetic basis, but ecophenotypic effects are also implicated, e.g. by predictable associations in some species of strongly nodulose sculpture with limestone substrates and with dry habitats where growth rate may be slow. Morphological characters are superimposed on a molecular phylogeny to demonstrate the synapomorphies of clades. This is essentially a morphostatic radiation of largely allopatric species with little morphological differentiation; ecological divergence is limited to specialization to oceanic, continental or upwelling areas and to small differences in zonation level.
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Karpenko, O. S., V. V. Lobanov, and M. T. Kartel. "C1s core-level binding energy shift dependence from carbon atoms position in graphenenanoflakes C96 and polycyclic aromatic hydrocarbon C96H24: a dft study." SURFACE 14(29) (December 30, 2022): 63–77. http://dx.doi.org/10.15407/surface.2022.14.063.
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The hexagon-shape graphene nanoflakes (GNFs) limited by zigzag edges only (with doubly and triply coordinated atoms) have unique increased reactivity. Despite the high systems symmetry (D6h) the Carbon atoms in GNFs occupy non-equivalent positions. Can such physical and chemical characteristics of GNFs, which depend of the atom position in the cluster, definition? This characteristic together with the simplicity of its calculation makes it possible to predict the properties of nanoflakes obtained from GNFs by introducing single and multiatomic vacancies into them or by replacing Carbon atoms with electron withdrawing and electron donating atoms. This characteristic includes the C1s core-level binding energy shifts, the maxima of which characterize the C atoms of a certain type. The proposed work is devoted to quantum chemical calculations of the electronic density of states (DOS) of pristine hexagon-shape GNF C96 (multiplicity, M=5), their saturated counterpart –polycyclic aromatic hydrocarbon(PAH) C96H24 (M=1) and their derivatives with one and two single vacancies in the ground electronic state (GES). All calculations were performed using the density functional theory (DFT) method with the involvement of the valence-split basis set 6-31G (d,p). Systems with open shells were considered using the UB3LYP exchange-correlation functional. The obtained spectra were fitted using Gaussian curve fitting program to determine the binding energy for each peak. The Gaussian function distribution of the theoretically calculated C1s core-level binding energy shifts of GNFs testified the presence of six peaks, each of which refers to a certain type of Carbon atoms. The C1s peak with the highest binding energy (-285.57 eV) is caused by contributions from the doubly coordinated edge cyclic chain (ECC) Carbon atoms. The C1s orbitals of the central hexagon (CHex) atoms and the first cyclic chain (FCC) atoms form delocalized molecular orbitals (MOs) in different parts of the cluster. The analogous spectrum of PAH C96H24 is slightly shifted to the region of lower binding energies and contains only two well-defined peaks. The peak with a higher binding energy (-284.36 eV) is generated by the 1s states of the CHex atoms and the atoms of the FCC, which are bounded to the CHex atoms. The electronic DOS difference in C1s core-level spectra of GNF C96 (M=5) and their saturated counterpart PAH C96H24 is established due to the presence of two weakly bounded π-systems in GNF and common conjugated system in PAH. The electronic DOS of defect-containing cluster C96-1(1) (M=3) (one CHex atom has been removed from the C96nanoflake) is generated by the C1s core-level atoms of the second cyclic chain (SCC), which are located at the different distances from the center of the nanoflake. The peak of the lowest intensity (-284.63 eV) appears in the spectrum as a reflection of the appearance of doubly coordinated Carbon atoms surrounding the single vacancy in the C96-1(1) nanoflake. The analysis of the electronic DOS of the C1s core-level spectrum of the C96-2(1) nanoflakeis shown, that doubly coordinated Carbon atoms, concentrated around two single vacancies, are essentially non-equivalent. If the MO with the lowest binding energy is localized on two of them – the MO with the highest binding energy is localized on the third atoms (one around each single vacancy). The electronic C1s core-level DOS spectrum of defect-containing molecular systems with one C96-1(1)H24 and two C96‑2(1)H24 single vacancies are similar to the analogous spectrum of PAH C96H24. In the first of them – one additional maximum appears due to C1s atoms surrounding the single vacancy. In the second – there are two additional maxima, each of which is generated by C1s core-level atoms adjacent to individual vacancies.
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Kang, Homan, Sinyoung Jeong, Jin-Kyoung Yang, Ahla Jo, Hyunmi Lee, Eun Hae Heo, Dae Hong Jeong, Bong-Hyun Jun, Hyejin Chang, and Yoon-Sik Lee. "Template-Assisted Plasmonic Nanogap Shells for Highly Enhanced Detection of Cancer Biomarkers." International Journal of Molecular Sciences 22, no. 4 (February 10, 2021): 1752. http://dx.doi.org/10.3390/ijms22041752.
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We present a template-assisted method for synthesizing nanogap shell structures for biomolecular detections based on surface-enhanced Raman scattering. The interior nanogap-containing a silver shell structure, referred to as a silver nanogap shell (Ag NGS), was fabricated on silver nanoparticles (Ag NPs)-coated silica, by adsorbing small aromatic thiol molecules on the Ag NPs. The Ag NGSs showed a high enhancement factor and good signal uniformity, using 785-nm excitation. We performed in vitro immunoassays using a prostate-specific antigen as a model cancer biomarker with a detection limit of 2 pg/mL. To demonstrate the versatility of Ag NGS nanoprobes, extracellular duplex surface-enhanced Raman scattering (SERS) imaging was also performed to evaluate the co-expression of cancer biomarkers, human epidermal growth factor-2 (HER2) and epidermal growth factor receptor (EGFR), in a non-small cell lung cancer cell line (H522). Developing highly sensitive Ag NGS nanoprobes that enable multiplex biomolecular detection and imaging can open up new possibilities for point-of-care diagnostics and provide appropriate treatment options and prognosis.
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Arm, Jakub, Tomas Benesl, Petr Marcon, Zdenek Bradac, Tizian Schröder, Alexander Belyaev, Thomas Werner, et al. "Automated Design and Integration of Asset Administration Shells in Components of Industry 4.0." Sensors 21, no. 6 (March 12, 2021): 2004. http://dx.doi.org/10.3390/s21062004.
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One of the central concepts in the principles of Industry 4.0 relates to the methodology for designing and implementing the digital shell of the manufacturing process components. This concept, the Asset Administration Shell (AAS), embodies a systematically formed, standardized data envelope of a concrete component within Industry 4.0. The paper discusses the AAS in terms of its structure, its components, the sub-models that form a substantial part of the shell’s content, and its communication protocols (Open Platform Communication—Unified Architecture (OPC UA) and MQTT) or SW interfaces enabling vertical and horizontal communication to involve other components and levels of management systems. Using a case study of a virtual assembly line that integrates AASs into the technological process, the authors present a comprehensive analysis centered on forming AASs for individual components. In the given context, the manual AAS creation mode exploiting framework-based automated generation, which forms the AAS via a configuration wizard, is assessed. Another outcome consists of the activation of a virtual assembly line connected to real AASs, a step that allows us verify the properties of the distributed manufacturing management. Moreover, a discrete event system was modeled for the case study, enabling the effective application of the Industry 4.0 solution.
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Azarov, S., V. Sydorenko, and O. Zadunaj. "EVALUATION OF EXPLOSIVE RISK IN THE PROCESS STORAGE OF WELDED NUCLEAR FUEL." Bulletin of Lviv State University of Life Safety, no. 18 (December 31, 2018): 81–87. http://dx.doi.org/10.32447/20784643.18.2018.08.
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At present, at the Chornobyl NPP, the main building of the general-purpose storage system for spent nuclear fuel is the "wet type" storage of spent nuclear fuel number 1 (SNF-1), designed for receiving and storing spent nuclear fuel. In the light of the post-Fukushima events, the task of increasing the explosion and fire safety is a priority direction of the Chornobyl NPP operation. SNF-1 should meet the current requirements of safety regulatory documents, both under normal operating conditions and during emergency situations. Among the emergencies that are likely to occur in the SNF-1 repository, the occurrence and development of fire in the interior space of reinforced concrete blocks should be considered. This condition is conditioned by the extraordinary importance of this radiation-hazardous object. An explosion on SNF-1 may occur, mainly due to violation of the rules of operation and fire safety, as well as in the event of malfunctions or failures of individual systems. Thus, the problem of providing explosion and fire safety on SNF-1 is extremely relevant.
The purpose of this work was to calculate the study of the formation of radionuclide hydrogen and its explosion in the premises of SNF-1.
Methods. Measurement, comparison, system analysis, physical and mathematical modeling.
Results. The main purpose of ensuring the explosion and fire danger of SNF-1 is to prevent the uncontrolled development of nuclear reactions and the spread of radiation. In the case of irradiation of water with low ionization radiation (for example, by gamma rays), the formation of radicals prevails, whereas for radiation with high ionization density (for example, α- and β-particles, splinters of division), the formation of molecules becomes more important. In a nuclear reactor where there are different types of radiation (γ-rays and high-energy protons formed during interaction with neutrons), both of these reactions take place simultaneously. Radicals H and OH are extremely reactive substances that are rapidly interconnected with the products formed as a result of the reaction. In the case of radioactive contamination of water in open containers filled with air and does not contain any active acceptors of OH radicals at appreciable concentrations, the observed hydrogen output is usually equal to 0.1-0.2 molecules/100 eV, which is significantly less the initial release of hydrogen formation. The larger the vessel in height, the greater the likelihood of this reaction compared with the likelihood of removing hydrogen from the liquid phase. But if we organize a non-equilibrium open system by forcing the removal of hydrogen from water, for example, by bubbling an inert gas, then the rate of its removal will exceed the rate of chemical decomposition. In this case, the hydrogen yield will increase and at the boundary it will be equal to the initial yield (unless, of course, there are no impurities of organic substances in the water, the radiolysis of which leads to the formation of molecular hydrogen). Therefore, to calculate the rate of formation of radio-hydrogen hydrogen in the reservoir basin water, the initial yield is used, that is, the maximum possible rate of hydrogen generation is calculated. Since the radioisotopes of water in the basin are mainly due to gamma radiation (beta and alpha radiation are delayed by the shells of the fuel assemblies and their energy is transferred to heat), the initial yield of the radiolytic formation of hydrogen is 0.45 molecules/100 eV. Under normal operation of SNF-1 in the basement area, the accumulation of radioactive hydrogen is eliminated at the expense of the work of the exhaust ventilation system of the surface area. The main factors determining the conditions for the formation of an explosive gas mixture based on hydrogen are the amount of stored spent fuel and the volume of water and air in the space where spent SNF is stored. The calculation is made from all sources of γ-radiation with a uniform distribution by source volume. For calculation, the main radionuclide composition of fuel in the lower beam of the fuel element was used in the case of holding 20 years and the burning depth of 24 MW×day/kg. The estimated value of the power absorbed by the water in terms of the total spent fuel, is I=1,098×1024 eV/(m3/h). The failures of the equipment of the complex of the storage system, caused by both external and internal events, which lead to failures of the ventilation system of the surface of the basin, can lead to the accumulation of radio-hydrogen hydrogen in the air volume of SNF-1 premises in the absence of ventilation systems. The break in the operation of the ventilation system, during which it is theoretically possible to achieve the lower limit of the explosive concentration of hydrogen, may be 12 days. In order to ensure explosion-proof safety in the pool of pools, it is necessary that the concentration of radiolytic hydrogen in the air be lower than the lower concentration limit of hydrogen explosion in a mixture with air (~ 4% of volume) with a stockrate of 10. Thus, the concentration of hydrogen should not exceed 0.4% of the permissible concentration of hydrogen in the air to exclude the formation of an explosive mixture with oxygen. For the case of placing all spent nuclear fuel (21284 units) in the compartments of the catchment pool 1-5, W(H2)=1.34 Hm3/h. Thus, the reasonable time of inactivity of the ventilation system will be no more than 7 days. In order to ensure that the concentration of radical hydrogen above the surface of the pool does not exceed 0.4% of the volume, the blowdown must be 250 times higher than the hydrogen generation rate, that is, the flow of air blown over the pool (ventilation) to ensure explosion-proof safety must be equal to g=250 W(H2), m3/year. The temperature of self-ignition of hydrogen in the presence of water vapor is 970 K, and the explosive properties of the hydrogen mixture are characterized by an outbreak of 4.12–75% of the volume. The degree of damage to building structures of the building of SNF-1 will be determined by the deformations and destruction that they received during the explosion of hydrogen. The formation of shock loads during an accidental explosion is directly determined by the number (volume) of stoichiometric ratios of hydrogen with the vapor and the limits of hydrogen ignition. Conclusion. Thus, the presented methodology for the estimation of the formation of radiolithic hydrogen and its possible explosion in the premises of SNF-1 allows, within the framework of a conservative approach, to conduct an explosion safety assessment and the consequences of an accidental explosion of radioactive hydrogen.
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Lathiotakis, N. N., N. Helbig, and E. K. U. Gross. "Open shells in reduced-density-matrix-functional theory." Physical Review A 72, no. 3 (September 19, 2005). http://dx.doi.org/10.1103/physreva.72.030501.
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Dzuba, V. A., and V. V. Flambaum. "Core-valence correlations for atoms with open shells." Physical Review A 75, no. 5 (May 11, 2007). http://dx.doi.org/10.1103/physreva.75.052504.
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Ghan, R., T. Shutava, A. Patel, V. John, and Y. Lvov. "Layer-by-Layer Engineered Microreactors for Bio-Polymerization of 4-(2-aminoethyl) phenol hydrochloride." MRS Proceedings 782 (2003). http://dx.doi.org/10.1557/proc-782-a5.43.
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ABSTRACTThis study presents the results of polymerization of phenol to yield fluorescent polymer encapsulated within shells fabricated via layer-by-layer (L-b-L) assembly. Hollow polyelectrolyte microcapsules (shells) were prepared using weakly cross-linked melamine formaldehyde (MF) particles. Dissolution of the MF cores was achieved by changing the pH of the solution. Horseradish peroxidase (HRP), the catalyzing enzyme, was loaded in these capsules by taking advantage of the “open/close” mechanism of the capsules by altering the pH. The empty shells were then suspended in a concentrated solution of monomer. Since the monomer is a low molecular weight species, it freely permeates through the polyion wall into the shells. Addition of aliquots of hydrogen peroxide initiated the polymerization reaction and the polymer formed from the ensuing reaction was confined in the shells due to its high molecular weight. The model used for demonstrating this synthesis is polymerization of 4-(2-aminoethyl) phenol hydrochloride commonly known as tyramine hydrochloride to its corresponding polymeric form by reacting it with hydrogen peroxide. Fluorescence spectrometry (FS), confocal laser scanning microscopy (CLSM), and atomic force microscopy (AFM) were the characterization methods employed to confirm polymerization in situ shells.
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"Chitin, Chitosan, and Submicron-Sized Chitosan Particles Prepared from Scylla serrata Shells." Materials International 2, no. 2 (April 14, 2020): 139–49. http://dx.doi.org/10.33263/materials22.139149.
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Extraction of chitin from mud crab (Scylla serrata) shells, involving demineralization and deproteinization, and deacetylation of the extracted chitin to form chitosan were investigated. The mud crab chitin and chitosan were obtained with a good yield (16.8% and 84.7% based on dried weight basis). The physicochemical properties, functional groups, molecular weight, and degree of acetylation of the chitin and chitosan were characterized. The surface morphology, the orientation arrangement of polysaccharide strands, and crystallinity of the chitin and chitosan prepared from the mud crab shells were investigated. SEM, FTIR, and XRD analyses demonstrated that the chitin consists of micron-sized fibrils, belonging to α from with the crystallinity of 60.1%. The chitosan has a viscosity-average molecular weight of 6.83 kDa with the degree of acetylation being 9.6% and the crystallinity of 73.8%. The chitosan was successfully fabricated into submicron-sized particles using top-down ionotropic gelation, microwave, and microemulsion methods, employing sodium tripolyphosphate, potassium persulfate, and glutaraldehyde as reagents, respectively. Overall, the results indicated that the preparation of chitin, chitosan, and submicron-sized chitosan particles from mud crab shells could open the opportunity for the value-added seafood waste to be utilized in a wide range of practical applications.
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Cameron, Robert, Małgorzata Ożgo, Michal Horsák, and Zdzislaw Bogucki. "At the north-eastern extremity: variation in Cepaea nemoralis around Gdańsk, northern Poland." Biologia 66, no. 6 (January 1, 2011). http://dx.doi.org/10.2478/s11756-011-0128-9.
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AbstractVariation in the shell colour and banding polymorphism in the land snail Cepaea nemoralis was studied in 260 populations in the region of Gdańsk, northern Poland. Unlike in other regions of Poland, many populations contain brown shells. Populations from shaded habitats have higher frequencies of brown than those from open and intermediate habitats, largely at the expense of yellow shells. Nearly all brown shells are also unbanded. Apart from this disequilibrium, banding morphs among yellow and pink shells show no relationship to habitat. There are no broad geographical trends in morph-frequencies, but there are very strong correlations among populations very close together, revealed both by pairwise analysis and Moran’s I. Principal Component Analyses show that these correlations relate to overall genetic similarity at the loci involved. The populations are at the north-eastern limits of the species’ range; habitats are mostly anthropogenic, and comparisons with studies in two urban areas (Wrocław, SW Poland, and Sheffield, central England) suggest that the patterns of variation seen are a product of human transport of propagules followed by local dispersal. The effect of habitat here is much less marked than in regions much further west, but it indicates that natural selection has occurred.
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Trofimov, Yu A., A. S. Minakov, N. A. Krylov, and R. G. Efremov. "Structural Mechanism of Ionic Conductivity of the TRPV1 Channel." Doklady Biochemistry and Biophysics, January 18, 2023. http://dx.doi.org/10.1134/s1607672922600245.
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Abstract The so-called “hydrophobic gating” is widely discussed as a putative mechanism to control water and ion conduction via ion channels. This effect can occur in narrow areas of the channels pore lined by non-polar residues. In the closed state of the channel, such regions may spontaneously transit to a dehydrated state to block water and ions transport without full pore occlusion. In the open state, the hydrophobic gate is wide enough to provide sustainable hydration and conduction. Apparently, the transport through the open hydrophobic gate may by facilitated by some polar residues that assist polar/charged substances to overcome the energy barrier created by nonpolar environment. In this work, we investigated the behavior of Na+ ions and their hydration shells in the open pore of the rat TRPV1 ion channel by molecular dynamics simulations. We show that polar protein groups coordinate water molecules in such a way as to restore the hydration shell of ions in the hydrophobic gate that ensures ion transport through the gate in a fully hydrated state.
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"Attosecond Photoionization Dynamics: from Molecules over Clusters to the Liquid Phase." CHIMIA 76, no. 6 (June 29, 2022): 520. http://dx.doi.org/10.2533/chimia.2022.520.
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Photoionization is a process taking place on attosecond time scales. How its properties evolve from isolated particles to the condensed phase is an open question of both fundamental and practical relevance. Here, we review recent work that has advanced the study of photoionization dynamics from atoms to molecules, clusters and the liquid phase. The first measurements of molecular photoionization delays have revealed the attosecond dynamics of electron emission from a molecular shape resonance and their sensitivity to the molecular potential. Using electron-ion coincidence spectroscopy these measurements have been extended from isolated molecules to clusters. A continuous increase of the delays with the water-cluster size has been observed up to a size of 4-5 molecules, followed by a saturation towards larger clusters. Comparison with calculations has revealed a correlation of the time delay with the spatial extension of the created electron hole. Using cylindrical liquid-microjet techniques, these measurements have also been extended to liquid water, revealing a delay relative to isolated water molecules that was very similar to the largest water clusters studied. Detailed modeling based on Monte-Carlo simulations confirmed that these delays are dominated by the contributions of the first two solvation shells, which agrees with the results of the cluster measurements. These combined results open the perspective of experimentally characterizing the delocalization of electronic wave functions in complex systems and studying their evolution on attosecond time scales.
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Mendoza, Carlos I., and David Reguera. "Shape selection and mis-assembly in viral capsid formation by elastic frustration." eLife 9 (April 21, 2020). http://dx.doi.org/10.7554/elife.52525.
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The successful assembly of a closed protein shell (or capsid) is a key step in the replication of viruses and in the production of artificial viral cages for bio/nanotechnological applications. During self-assembly, the favorable binding energy competes with the energetic cost of the growing edge and the elastic stresses generated due to the curvature of the capsid. As a result, incomplete structures such as open caps, cylindrical or ribbon-shaped shells may emerge, preventing the successful replication of viruses. Using elasticity theory and coarse-grained simulations, we analyze the conditions required for these processes to occur and their significance for empty virus self-assembly. We find that the outcome of the assembly can be recast into a universal phase diagram showing that viruses with high mechanical resistance cannot be self-assembled directly as spherical structures. The results of our study justify the need of a maturation step and suggest promising routes to hinder viral infections by inducing mis-assembly.
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Sulpis, Olivier, Priyanka Agrawal, Mariette Wolthers, Guy Munhoven, Matthew Walker, and Jack J. Middelburg. "Aragonite dissolution protects calcite at the seafloor." Nature Communications 13, no. 1 (March 1, 2022). http://dx.doi.org/10.1038/s41467-022-28711-z.
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AbstractIn the open ocean, calcium carbonates are mainly found in two mineral forms. Calcite, the least soluble, is widespread at the seafloor, while aragonite, the more soluble, is rarely preserved in marine sediments. Despite its greater solubility, research has shown that aragonite, whose contribution to global pelagic calcification could be at par with that of calcite, is able to reach the deep-ocean. If large quantities of aragonite settle and dissolve at the seafloor, this represents a large source of alkalinity that buffers the deep ocean and favours the preservation of less soluble calcite, acting as a deep-sea, carbonate version of galvanization. Here, we investigate the role of aragonite dissolution on the early diagenesis of calcite-rich sediments using a novel 3D, micrometric-scale reactive-transport model combined with 3D, X-ray tomography structures of natural aragonite and calcite shells. Results highlight the important role of diffusive transport in benthic calcium carbonate dissolution, in agreement with recent work. We show that, locally, aragonite fluxes to the seafloor could be sufficient to suppress calcite dissolution in the top layer of the seabed, possibly causing calcite recrystallization. As aragonite producers are particularly vulnerable to ocean acidification, the proposed galvanizing effect of aragonite could be weakened in the future, and calcite dissolution at the sediment-water interface will have to cover a greater share of CO2 neutralization.
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"A Particular Case of Asymptotic Formulas for Exchange Energy between Two Long-Range Interacting Atoms with Open Valence Shells of Any Type: Application to the Ground State of Alkali Dimers." Journal of Molecular Spectroscopy 175, no. 2 (February 1996): 441–44. http://dx.doi.org/10.1006/jmsp.1996.0050.
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Kimbrough, John H., J. Thomas Cribbs, and Linda L. McCarter. "Homologous c-di-GMP-Binding Scr Transcription Factors Orchestrate Biofilm Development in Vibrio parahaemolyticus." Journal of Bacteriology 202, no. 6 (January 13, 2020). http://dx.doi.org/10.1128/jb.00723-19.
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ABSTRACT The marine bacterium and human pathogen Vibrio parahaemolyticus rapidly colonizes surfaces by using swarming motility and forming robust biofilms. Entering one of the two colonization programs, swarming motility or sessility, involves differential regulation of many genes, resulting in a dramatic shift in physiology and behavior. V. parahaemolyticus has evolved complex regulation to control these two processes that have opposing outcomes. One mechanism relies on the balance of the second messenger c-di-GMP, where high c-di-GMP favors biofilm formation. V. parahaemolyticus possesses four homologous regulators, the Scr transcription factors, that belong in a Vibrio-specific family of W[F/L/M][T/S]R motif transcriptional regulators, some members of which have been demonstrated to bind c-di-GMP. In this work, we explore the role of these Scr regulators in biofilm development. We show that each protein binds c-di-GMP, that this binding requires a critical R in the binding motif, and that the biofilm-relevant activities of CpsQ, CpsS, and ScrO but not ScrP are dependent upon second messenger binding. ScrO and CpsQ are the primary drivers of biofilm formation, as biofilms are eliminated when both of these regulators are absent. ScrO is most important for capsule expression. CpsQ is most important for RTX-matrix protein expression, although it contributes to capsule expression when c-di-GMP levels are high. Both regulators contribute to O-antigen ligase expression. ScrP works oppositely in a minor role to repress the ligase gene. CpsS plays a regulatory checkpointing role by negatively modulating expression of these biofilm-pertinent genes under fluctuating c-di-GMP conditions. Our work further elucidates the multifactorial network that contributes to biofilm development in V. parahaemolyticus. IMPORTANCE Vibrio parahaemolyticus can inhabit open ocean, chitinous shells, and the human gut. Such varied habitats and the transitions between them require adaptable regulatory networks controlling energetically expensive behaviors, including swarming motility and biofilm formation, which are promoted by low and high concentrations of the signaling molecule c-di-GMP, respectively. Here, we describe four homologous c-di-GMP-binding Scr transcription factors in V. parahaemolyticus. Members of this family of regulators are present in many vibrios, yet their numbers and the natures of their activities differ across species. Our work highlights the distinctive roles that these transcription factors play in dynamically controlling biofilm formation and architecture in V. parahaemolyticus and serves as a powerful example of regulatory network evolution and diversification.
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Ramos-Silva, Paula, Mari-Lee Odendaal, Deborah Wall-Palmer, Lisette Mekkes, and Katja T. C. A. Peijnenburg. "Transcriptomic Responses of Adult Versus Juvenile Atlantids to Ocean Acidification." Frontiers in Marine Science 9 (May 16, 2022). http://dx.doi.org/10.3389/fmars.2022.801458.
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Shelled holoplanktonic gastropods are among the most vulnerable calcifiers to ocean acidification. They inhabit the pelagic environment and build thin and transparent shells of aragonite, a metastable form of calcium carbonate. While shelled pteropods have received considerable attention and are widely regarded as bioindicators of ocean acidification, atlantids have been much less studied. In the open ocean, atlantids are uniquely positioned to address the effects of ocean acidification at distinct trophic levels. From juvenile to adult, they undergo dramatic metamorphosis. As adults they are predatory, feeding primarily on shelled pteropods, copepods and other zooplankton, while as juveniles they feed on algae. Here we investigated the transcriptome and the impact of a three-day CO2 exposure on the gene expression of adults of the atlantid Atlanta ariejansseni and compared these to results previously obtained from juveniles. Individuals were sampled in the Southern Subtropical Convergence Zone (Atlantic Ocean) and exposed to ocean chemistry simulating past (~mid-1960s), present (ambient) and future (2050) conditions. In adults we found that the changes in seawater chemistry had significantly affected the expression of genes involved in biomineralization and the immune response, although there were no significant differences in shell growth between the three conditions. In contrast, juveniles experienced substantial changes in shell growth and a broader transcriptomic response. In adults, 1170 genes had the same direction of expression in the past and future treatments when compared to the ambient. Overall, this type of response was more common in adults (8.6% of all the genes) than in juveniles (3.9%), whereas a linear response with decreasing pH was more common in juveniles (7.7%) than in adults (4.5%). Taken together, these results suggest that juveniles are more sensitive to increased acidification than adults. However, experimental limitations including short incubation times, one carboy used for each treatment and two replicates for transcriptome analysis, require us to be cautious about these conclusions. We show that distinct transcriptome profiles characterize the two life stages, with less than 50% of shared transcripts. This study provides an initial framework to understand how ocean acidification may affect the molecular and calcification responses of adult and juvenile atlantids.