Articles de revues sur le sujet « Natural Self-assembly Process »
Pour voir les autres types de publications sur ce sujet consultez le lien suivant : Natural Self-assembly Process.
Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres
Consultez les 50 meilleurs articles de revues pour votre recherche sur le sujet « Natural Self-assembly Process ».
À côté de chaque source dans la liste de références il y a un bouton « Ajouter à la bibliographie ». Cliquez sur ce bouton, et nous générerons automatiquement la référence bibliographique pour la source choisie selon votre style de citation préféré : APA, MLA, Harvard, Vancouver, Chicago, etc.
Vous pouvez aussi télécharger le texte intégral de la publication scolaire au format pdf et consulter son résumé en ligne lorsque ces informations sont inclues dans les métadonnées.
Parcourez les articles de revues sur diverses disciplines et organisez correctement votre bibliographie.
1
Pidaparti, Ramana M., David Primeaux et Brandon Saunders. « Modeling and Simulation of Biological Self-Assembly Structures from Nanoscale Entities ». Journal of Nanoscience and Nanotechnology 7, no 12 (1 décembre 2007) : 4248–53. http://dx.doi.org/10.1166/jnn.2007.863.
Texte intégralRésumé :
Many natural and biological systems are formed by the process of molecular self-assembly. Molecular self-assembly is defined as the spontaneous organization of molecules under thermodynamic equilibrium conditions into structurally well defined and rather stable arrangements. In this paper, we developed a novel computational methodology to investigate the self-assembly process of simple 1-D structures representing protein monomers into long filaments, rings, pyramids, bundles, etc. Based on the preliminary results obtained, the methodology was extended to mimic the microtubule self-assembly, which occurs in all eukaryotic cells.
2
LIANG, YUJIA, YONG XIE, ZHENING ZHU, YINGLU JI, XIAOCHUN WU et QIAN LIU. « SELF-ASSEMBLY OF GOLD NANORODS ON WRINKLED TEMPLATE ». Nano 09, no 07 (octobre 2014) : 1450076. http://dx.doi.org/10.1142/s1793292014500763.
Texte intégralRésumé :
Self-assembly of nanoparticles has attracted more attention in the last decade due to their potential applications in many fields, such as sensors, surface-enhanced Raman scattering (SERS) substrate and optical/plasmonic components. Wrinkles, as one kind of common natural surface, are used to be a template/substrate in microfluidic sieves and solar cells. In this work, a wrinkled template with depth of about 200 nm and period of 1.64 μm is used for modulating the self-assembly process of gold nanorods (GNRs) to obtain patterned self-assemblies for potential application. In order to fully reflect the role of the wrinkled template in the self-assembly, the templates are placed uprightly in the GNRs solution to intensify the interplay between the wrinkled surface and nanorods. The self-assembly process is carried out in a climate chamber, where the temperature and humidity can be controlled programmingly to modulate the self-assembly conditions. The experimental results show that for the fixed wrinkled template, an obvious effect on the self-assembly is at the temperature range from 30°C to 50°C. Nematic, curved (mostly are end-to-end) and transition mode can be obtained. According to humidity, GNRs tend to form the nematic fashion in humidity lower than 60%, and the curved fashion in a higher humidity.
3
Gabora, Liane, et Mike Steel. « An evolutionary process without variation and selection ». Journal of The Royal Society Interface 18, no 180 (juillet 2021) : 20210334. http://dx.doi.org/10.1098/rsif.2021.0334.
Texte intégralRésumé :
Natural selection successfully explains how organisms accumulate adaptive change despite that traits acquired over a lifetime are eliminated at the end of each generation. However, in some domains that exhibit cumulative, adaptive change—e.g. cultural evolution, and earliest life—acquired traits are retained; these domains do not face the problem that Darwin’s theory was designed to solve. Lack of transmission of acquired traits occurs when germ cells are protected from environmental change, due to a self-assembly code used in two distinct ways: (i) actively interpreted during development to generate a soma, and (ii) passively copied without interpretation during reproduction to generate germ cells. Early life and cultural evolution appear not to involve a self-assembly code used in these two ways. We suggest that cumulative, adaptive change in these domains is due to a lower-fidelity evolutionary process, and model it using reflexively autocatalytic and foodset-generated networks. We refer to this more primitive evolutionary process as self–other reorganization (SOR) because it involves internal self-organizing and self-maintaining processes within entities, as well as interaction between entities. SOR encompasses learning but in general operates across groups. We discuss the relationship between SOR and Lamarckism, and illustrate a special case of SOR without variation.
4
Astanov, Salikh Khusenovich, et Siddiq Kakhkharovich Kakhkharov. « SPECTROSCOPIC STUDY OF THE PROCESS OF HYPOCHROMIC EFFECT IN SOL T IN SOLUTIONS OF N UTIONS OF NATURAL D TURAL DYES AND VI YES AND VITAMIN B2 AMIN B2 ». Scientific Reports of Bukhara State University 4, no 3 (26 juin 2020) : 21–27. http://dx.doi.org/10.52297/2181-1466/2020/4/3/11.
Texte intégralRésumé :
The process of self-assembly of riboflavin molecules in aqueous and binary mixtures of solvents was investigated by the spectroscopic method. It was shown that during the assembly of vitamin B2 molecules, dipole-dipole interaction occurs, as a result of which resonant splitting of excited electronic levels of riboflavin molecules occurs. And the observable hypo chromic effect is due to a decrease in the intense absorption capacity of the aggregated riboflavin molecules themselves.
5
Han, Pingping, Jiafu Shi, Teng Nie, Shaohua Zhang, Xueyan Wang, Pengfei Yang, Hong Wu et Zhongyi Jiang. « Conferring Natural-Derived Porous Microspheres with Surface Multifunctionality through Facile Coordination-Enabled Self-Assembly Process ». ACS Applied Materials & ; Interfaces 8, no 12 (17 mars 2016) : 8076–85. http://dx.doi.org/10.1021/acsami.6b00335.
Texte intégral
6
Morii, Nahoko, Giyuu Kido, Hiroyuki Suzuki et Hisayuki Morii. « Annular self-assembly of DNA molecular chains occurring in natural dry process of diluted solutions ». Biopolymers 77, no 3 (2005) : 163–72. http://dx.doi.org/10.1002/bip.20203.
Texte intégral
7
Xu, P., T. Erdem et E. Eiser. « A simple approach to prepare self-assembled, nacre-inspired clay/polymer nanocomposites ». Soft Matter 16, no 23 (2020) : 5497–505. http://dx.doi.org/10.1039/c9sm01585j.
Texte intégralRésumé :
Inspired by the relationship between the ordered architecture of aragonite crystals and biopolymers found in natural nacre, we present a facile strategy to construct organic/inorganic nanocomposites with hierarchical structure via a water-evaporation driven self-assembly process.
8
González, Andrea, Sandeep Kumar Singh, Macarena Churruca et Ricardo B. Maccioni. « Alzheimer’s Disease and Tau Self-Assembly : In the Search of the Missing Link ». International Journal of Molecular Sciences 23, no 8 (10 avril 2022) : 4192. http://dx.doi.org/10.3390/ijms23084192.
Texte intégralRésumé :
Alzheimer’s disease (AD) is a multifactorial neurodegenerative disease characterized by progressive cognitive impairment, apathy, and neuropsychiatric disorders. Two main pathological hallmarks have been described: neurofibrillary tangles, consisting of tau oligomers (hyperphosphorylated tau) and Aβ plaques. The influence of protein kinases and phosphatases on the hyperphosphorylation of tau is already known. Hyperphosphorylated tau undergoes conformational changes that promote its self-assembly. However, the process involving these mechanisms is yet to be elucidated. In vitro recombinant tau can be aggregated by the action of polyanions, such as heparin, arachidonic acid, and more recently, the action of polyphosphates. However, how that process occurs in vivo is yet to be understood. In this review, searching the most accurate and updated literature on the matter, we focus on the precise molecular events linking tau modifications, its misfolding and the initiation of its pathological self-assembly. Among these, we can identify challenges regarding tau phosphorylation, the link between tau heteroarylations and the onset of its self-assembly, as well as the possible metabolic pathways involving natural polyphosphates, that may play a role in tau self-assembly.
9
Chen, Hui, Xiao Hui Wang, Dong Li, Yan Zhu Guo et Run Cang Sun. « Preparation and Characterization of Quaternary Chitosan/sodium Alginate Self-Assembled Microcapsules ». Advanced Materials Research 554-556 (juillet 2012) : 263–67. http://dx.doi.org/10.4028/www.scientific.net/amr.554-556.263.
Texte intégralRésumé :
Biocompatible quaternary chitosan/sodium alginate multilayer microcapsules were prepared by layer-by-layer (LBL) self-assembly on the template of monodispersed melamine formaldehyde resin microspheres (MF). The process of self-assembly was monitored by measuring the surface zeta-potential of colloidal particles. The particle size was determined by digital light scattering (DLS) after each deposition, and the average thickness of monolayer film was revealed to be 3.9 nm. Using rhodamine B-labeled quaternary chitosan as the positive polyelectrolyte and sodium alginate as the negative polyelectrolyte, self-assembled multilayer microcapsules with strong red-light emitting were obtained and observed with fluorescence microscope. The fluorescent microcapsules self-assembled from the biocompatible natural polysaccharides may be potentially applied in drug delivery and fluorescence diagnosis.
10
Han, Pingping, Jiafu Shi, Teng Nie, Shaohua Zhang, Xueyan Wang, Pengfei Yang, Hong Wu et Zhongyi Jiang. « Correction to Conferring Natural-Derived Porous Microspheres with Surface Multifunctionality through Facile Coordination-Enabled Self-Assembly Process ». ACS Applied Materials & ; Interfaces 8, no 23 (6 juin 2016) : 14893. http://dx.doi.org/10.1021/acsami.6b04734.
Texte intégral
11
Yang, Jie, Guang Feng Xi et Xiao Dong Zhao. « Modeling Design and Motion Simulation of a Kind of Marine Corrosion Test Device ». Applied Mechanics and Materials 80-81 (juillet 2011) : 649–53. http://dx.doi.org/10.4028/www.scientific.net/amm.80-81.649.
Texte intégralRésumé :
A set of modified marine corrosion simulation test device was designed in this study according to the characteristics of the natural marine environment, in order to study the corrosion behavior of steel materials. The natural corrosive marine environment could be simulated indoors by the device, which had advantages such as sea water self-circulation, stable wave, multi-level adjustable amplitude and frequency and so on. Components modeling, overall assembly and motion simulation were carried out by UG program, and the interference among the various components, limit position of movement and motion parameters were analyzed, effectively avoiding the problems that may arise during processing, manufacturing and assembly process.
12
Mishra, Pawan Kumar, et Adam Ekielski. « The Self-Assembly of Lignin and Its Application in Nanoparticle Synthesis : A Short Review ». Nanomaterials 9, no 2 (11 février 2019) : 243. http://dx.doi.org/10.3390/nano9020243.
Texte intégralRésumé :
Lignin serves as a significant contributor to the natural stock of non-fossilized carbon, second only to cellulose in the biosphere. In this review article, we focus on the self-assembly properties of lignin and their contribution to its effective utilization and valorization. Traditionally, investigations on self-assembly properties of lignin have aimed at understanding the lignification process of the cell wall and using it for efficient delignification for commercial purposes. In recent years (mainly the last three years), an increased number of attempts and reports of technical-lignin nanostructure synthesis with controlled particle size and morphology have been published. This has renewed the interests in the self-assembly properties of technical lignins and their possible applications. Based on the sources and processing methods of lignin, there are significant differences between its structure and properties, which is the primary obstacle in the generalized understanding of the lignin structure and the lignification process occurring within cell walls. The reported studies are also specific to source and processing methods. This work has been divided into two parts. In the first part, the aggregation propensity of lignin based on type, source and extraction method, temperature, and pH of solution is discussed. This is followed by a critical overview of non-covalent interactions and their contribution to the self-associative properties of lignin. The role of self-assembly towards the understanding of xylogenesis and nanoparticle synthesis is also discussed. A particular emphasis is placed on the interaction and forces involved that are used to explain the self-association of lignin.
13
Jia, Jingwei, Zhengke Wang, Wentao Lu, Ling Yang, Qingwen Wu, Wei Qin, Qiaoling Hu et Ben Zhong Tang. « Monitoring layer-by-layer self-assembly process of natural polyelectrolytes by fluorescent bioconjugate with aggregation-induced emission characteristic ». J. Mater. Chem. B 2, no 47 (2014) : 8406–11. http://dx.doi.org/10.1039/c4tb01158a.
Texte intégral
14
Abdelghany, A. M., A. H. Oraby, Awatif A. Hindi, Doaa M. El-Nagar et Fathia S. Alhakami. « Green synthesis of mixed metallic nanoparticles using room temperature self-assembly ». JOURNAL OF ADVANCES IN PHYSICS 13, no 2 (16 mars 2017) : 4671–77. http://dx.doi.org/10.24297/jap.v13i2.5942.
Texte intégralRésumé :
Bimetallic nanoparticles of silver (Ag) and gold (Au) were synthesized at room temperature using Curcumin. Reduction process of silver and gold ions with different molar ratios leads to production of different nanostructures including alloys and core-shells. Produced nanoparticles were characterized simultaneously with FTIR, UV/vis. spectroscopy, transmission electron microscopy (TEM), and Energy-dispersive X-ray (EDAX). UV/vis. optical absorption spectra of as synthesized nanoparticles reveals presence of surface palsmon resonance (SPR) of both silver at (425 nm) and gold at (540 nm) with small shift and broadness of gold band after mixing with resucing and capping agent in natural extract which suggest presence of bimetallic nano structure (Au/Ag). FTIR and EDAX data approve the presence of bimetallic nano structure combined with curcumin extract. TEM micrographs shows that silver and gold can be synthesized separately in the form of nano particles using curcumin extract. Synthesis of gold nano particles in presence of silver effectively enhance and control formation of bi-metallic structure.
15
Su, Lu, Jesús Mosquera, Mathijs F. J. Mabesoone, Sandra M. C. Schoenmakers, Cyprien Muller, Marle E. J. Vleugels, Shikha Dhiman, Stefan Wijker, Anja R. A. Palmans et E. W. Meijer. « Dilution-induced gel-sol-gel-sol transitions by competitive supramolecular pathways in water ». Science 377, no 6602 (8 juillet 2022) : 213–18. http://dx.doi.org/10.1126/science.abn3438.
Texte intégralRésumé :
Fascinating properties are displayed by synthetic multicomponent supramolecular systems that comprise a manifold of competitive interactions, thereby mimicking natural processes. We present the integration of two reentrant phase transitions based on an unexpected dilution-induced assembly process using supramolecular polymers and surfactants. The co-assembly of the water-soluble benzene-1,3,5-tricarboxamide (BTA-EG 4 ) and a surfactant at a specific ratio yielded small-sized aggregates. These interactions were modeled using the competition between self-sorting and co-assembly of both components. The small-sized aggregates were transformed into supramolecular polymer networks by a twofold dilution in water without changing their ratio. Kinetic experiments show the in situ growth of micrometer-long fibers in the dilution process. We were able to create systems that undergo fully reversible hydrogel-solution-hydrogel-solution transitions upon dilution by introducing another orthogonal interaction.
16
Zhang, Jie, et Steve Granick. « Natural selection in the colloid world : active chiral spirals ». Faraday Discussions 191 (2016) : 35–46. http://dx.doi.org/10.1039/c6fd00077k.
Texte intégralRésumé :
We present a model system in which to study natural selection in the colloid world. In the assembly of active Janus particles into rotating pinwheels when mixed with trace amounts of homogeneous colloids in the presence of an AC electric field, broken symmetry in the rotation direction produces spiral, chiral shapes. Locked into a central rotation point by the centre particle, the spiral arms are found to trail rotation of the overall cluster. To achieve a steady state, the spiral arms undergo an evolutionary process to coordinate their motion. Because all the particles as segments of the pinwheel arms are self-propelled, asymmetric arm lengths are tolerated. Reconfiguration of these structures can happen in various ways and various mechanisms of this directed structural change are analyzed in detail. We introduce the concept of VIP (very important particles) to express that sustainability of active structures is most sensitive to only a few particles at strategic locations in the moving self-assembled structures.
17
Wang, Heliang, Fanrong Meng, Mingyuan Yi, Lin Fang, Zhifen Wang et Shoujuan Wang. « Highly Strong and Damage-Resistant Natural Rubber Membrane via Self-Assembly and Construction of Double Network ». Membranes 12, no 10 (26 septembre 2022) : 933. http://dx.doi.org/10.3390/membranes12100933.
Texte intégralRésumé :
Natural rubber latex (NRL) is commonly employed to manufacture medical protective appliances. However, the characteristics of weakness and fragility of NRL membranes limit their further application. To achieve excellent strength and damage-resistance of the rubber membrane, this work reported a facile core–shell structure construction strategy via self-assembly with modified sodium lignosulfonate (MSLS) and NRL to create a tough membrane. The double network can be formed after introducing polyamide epichlorohydrin resin (PAE) into the NRL membrane. Specifically, the first robust MSLS-PAE network can break in advance to dissipate applied energy, thereby achieving high fracture energy and tensile strength of ~111.51 kJ m−2 and ~37 MPa, respectively, which overtakes numerous soft materials. This work facilitates more studies on latex/lignin-based products with high performance and good stability for the functional application of biopolymer.
18
Yablon, Dalia, et George Flynn. « Investigation of The Self-Assembly of Chiral Molecules At Liquidsolid Interfaces Using Scanning Tunneling Microscopy Chemical Marker Groups : Driving Forces for 2-D Separation of Chiral Species ». Microscopy and Microanalysis 7, S2 (août 2001) : 848–49. http://dx.doi.org/10.1017/s1431927600030312.
Texte intégralRésumé :
Self-assembly of molecules on surfaces is fundamentally a process whereby individual molecules, separated in the gas or liquid phase, fonn ordered arrays on a surface. The driving forces for these self-assembly processes are the attractive and repulsive interactions among the molecules themselves and between the molecular assemblies and the surface. Since physisorption causes minimal perturbation of chemical bonds, studies of physisorbed species provide an extremely convenient method for investigating issues of molecular structure, conformation, orientation and dynamics of molecules in their “natural” state. The two dimensional nature of the interface introduces constraints that can be used advantageously to separate and identify novel structures.Control and manipulation of self assembly and molecular conformation is one of the key issues often cited in efforts to develop nanotechnology initiatives for the next generation of electrical and mechanical devices. The development of molecular electronic devices based solely on organic materials will also require careful control and manipulation of molecular assemblies as well as the conformations and orientations of the molecules and functional groups within these arrays.
19
Gabora, Liane. « Epigenetic and cultural evolution are non-Darwinian ». Behavioral and Brain Sciences 30, no 4 (août 2007) : 371. http://dx.doi.org/10.1017/s0140525x07002294.
Texte intégralRésumé :
AbstractThe argument that heritable epigenetic change plays a distinct role in evolution would be strengthened through recognition that it is what bootstrapped the origin and early evolution of life, and that, like behavioral and symbolic change, it is non-Darwinian. The mathematics of natural selection, a population-level process, is limited to replication with negligible individual-level change that uses a self-assembly code.
20
Krzek, Marzena, Sander Stroobants, Pierre Gelin, Wim De Malsche et Dominique Maes. « Influence of Centrifugation and Shaking on the Self-Assembly of Lysozyme Fibrils ». Biomolecules 12, no 12 (24 novembre 2022) : 1746. http://dx.doi.org/10.3390/biom12121746.
Texte intégralRésumé :
Protein self-assembly into fibrils and oligomers plays a key role in the etiology of degenerative diseases. Several pathways for this self-assembly process have been described and shown to result in different types and ratios of final assemblies, therewith defining the effective physiological response. Known factors that influence assembly pathways are chemical conditions and the presence or lack of agitation. However, in natural and industrial systems, proteins are exposed to a sequence of different and often complex mass transfers. In this paper, we compare the effect of two fundamentally different mass transfer processes on the fibrilization process. Aggregation-prone solutions of hen egg white lysozyme were subjected to predominantly non-advective mass transfer by employing centrifugation and to advective mass transport represented by orbital shaking. In both cases, fibrilization was triggered, while in quiescent only oligomers were formed. The fibrils obtained by shaking compared to fibrils obtained through centrifugation were shorter, thicker, and more rigid. They had rod-like protofibrils as building blocks and a significantly higher β-sheet content was observed. In contrast, fibrils from centrifugation were more flexible and braided. They consisted of intertwined filaments and had low β-sheet content at the expense of random coil. To the best of our knowledge, this is the first evidence of a fibrilization pathway selectivity, with the fibrilization route determined by the mass transfer and mixing configuration (shaking versus centrifugation). This selectivity can be potentially employed for directed protein fibrilization.
21
Tian, Zi Ting. « Advances and Prospects of Self-Assembly of Nanomaterials in 1D to 4D via Electrospinning ». Key Engineering Materials 907 (21 janvier 2022) : 59–65. http://dx.doi.org/10.4028/www.scientific.net/kem.907.59.
Texte intégralRésumé :
Self-assembly is a ubiquitous process in the natural environment, and electrospinning is a simple and convenient method to fabricate nanofibers. The self-assembly of electrospun nanofibers can produce nanomaterials in one-dimension (1D), two-dimension (2D), three-dimension (3D), and even four-dimension (4D). Techniques to fabricate 1D nanomaterials have been reviewed in this paper, especially for nanofiber and nanotube. The mechanism of the fabrication of 2D nanomaterials has been also introduced which is a specific arrangement of 1D nanostructures. The applications of 2D nanomaterials have been reviewed concerning energy devices, electronic devices, and biomedicine. Additionally, 3D nanomaterials, as more complex materials, are mainly utilized in tissue engineering and some in other fields. The advantages have been highlighted to suggest the development and prospect of 4D nanomaterials. Although 4D printing technologies still remain intractable, some aspects of improvement through electrospinning are possible in terms of responsive materials and self-growth materials.
22
Van Driessche, A. E. S., L. G. Benning, J. D. Rodriguez-Blanco, M. Ossorio, P. Bots et J. M. García-Ruiz. « The Role and Implications of Bassanite as a Stable Precursor Phase to Gypsum Precipitation ». Science 336, no 6077 (5 avril 2012) : 69–72. http://dx.doi.org/10.1126/science.1215648.
Texte intégralRésumé :
Calcium sulfate minerals such as gypsum play important roles in natural and industrial processes, but their precipitation mechanisms remain largely unexplored. We used time-resolved sample quenching and high-resolution microscopy to demonstrate that gypsum forms via a three-stage process: (i) homogeneous precipitation of nanocrystalline hemihydrate bassanite below its predicted solubility, (ii) self-assembly of bassanite into elongated aggregates co-oriented along their c axis, and (iii) transformation into dihydrate gypsum. These findings indicate that a stable nanocrystalline precursor phase can form below its bulk solubility and that in the CaSO4 system, the self-assembly of nanoparticles plays a crucial role. Understanding why bassanite forms prior to gypsum can lead to more efficient anti-scaling strategies for water desalination and may help to explain the persistence of CaSO4 phases in regions of low water activity on Mars.
23
IRLE, S., G. ZHENG, Z. WANG et K. MOROKUMA. « THEORY–EXPERIMENT RELATIONSHIP OF THE "SHRINKING HOT GIANT" ROAD OF DYNAMIC FULLERENE SELF-ASSEMBLY IN HOT CARBON VAPOR ». Nano 02, no 01 (février 2007) : 21–30. http://dx.doi.org/10.1142/s1793292007000362.
Texte intégralRésumé :
Though subject to intensive studies, the formation mechanism of buckminsterfullerene C 60 and related higher fullerenes has long evaded discovery. To elucidate their atomistic self-assembly mechanism, we have performed high-temperature quantum chemical molecular dynamics simulations on carbon vapor model systems initially consisting of C 2 molecules. Our simulations reveal a coherent mechanism how highly ordered fullerene cages naturally self-assemble under nonequilibrium conditions, following a series of irreversible processes from the polymerization of C 2 molecules to vibrationally excited giant fullerenes, which then shrink by C 2 evaporation down to the smallest spherical, isolated pentagon rule obeying species C 70 and C 60 as the smallest and kinetically most stable species of the shrinking process. We show that the potential energy surface associated with giant fullerene cage growth, measured by an average cluster curvature, is downhill all the way, and in agreement with high-level energetics from density functional theory. This fullerene formation mechanism is a good example of dynamic self-assembly leading to dissipative structures far from thermodynamic equilibrium, and the "shrinking hot giant" road provides a natural explanation for the observed cage size distributions in a random optimization process consistent with several important experimental observations.
24
Mosayebi, Majid, Deborah K. Shoemark, Jordan M. Fletcher, Richard B. Sessions, Noah Linden, Derek N. Woolfson et Tanniemola B. Liverpool. « Beyond icosahedral symmetry in packings of proteins in spherical shells ». Proceedings of the National Academy of Sciences 114, no 34 (8 août 2017) : 9014–19. http://dx.doi.org/10.1073/pnas.1706825114.
Texte intégralRésumé :
The formation of quasi-spherical cages from protein building blocks is a remarkable self-assembly process in many natural systems, where a small number of elementary building blocks are assembled to build a highly symmetric icosahedral cage. In turn, this has inspired synthetic biologists to design de novo protein cages. We use simple models, on multiple scales, to investigate the self-assembly of a spherical cage, focusing on the regularity of the packing of protein-like objects on the surface. Using building blocks, which are able to pack with icosahedral symmetry, we examine how stable these highly symmetric structures are to perturbations that may arise from the interplay between flexibility of the interacting blocks and entropic effects. We find that, in the presence of those perturbations, icosahedral packing is not the most stable arrangement for a wide range of parameters; rather disordered structures are found to be the most stable. Our results suggest that (i) many designed, or even natural, protein cages may not be regular in the presence of those perturbations and (ii) optimizing those flexibilities can be a possible design strategy to obtain regular synthetic cages with full control over their surface properties.
25
Wakefield, Jennifer M. K., Robert Hampe, Richard B. Gillis, Agnes Sitterli, Gary G. Adams, Hartmut Kutzke, Thomas Heinze et Stephen E. Harding. « Aminoethyl substitution enhances the self-assembly properties of an aminocellulose as a potential archaeological wood consolidant ». European Biophysics Journal 49, no 8 (25 août 2020) : 791–98. http://dx.doi.org/10.1007/s00249-020-01451-y.
Texte intégralRésumé :
AbstractThe 6-deoxy-6-aminocelluloses—or “aminocelluloses”—are a class of synthetic natural cellulose derivatives which are mostly aqueous soluble and have excellent film-forming properties. Recent studies have connected these properties at the molecular level with protein-like self-associative behaviour for a range of aminocelluloses including a 6-deoxy-6-(ω-aminoethyl) aminocellulose AEA-1 with the association being a two-stage process—a reversible oligomerisation followed by further (semi-reversible) aggregation into larger structures. Here, we synthesise and compare a new 6-deoxy-6-(ω-aminoethyl) aminocellulose AEA-1′ with different degree of substitution with one with further alkyl derivatisation, namely 6-deoxy-6-(ω-hydroxyethyl) aminocellulose HEA-1′. As with AEA-1, sedimentation velocity and sedimentation equilibrium in the analytical ultracentrifuge still show a two-stage process for both AEA-1′ and HEA-1′, with the latter giving higher molar masses. The consequences of these properties for use as consolidants for archaeological wood are considered.
26
Jaekel, Andreas, Pascal Lill, Stephen Whitelam et Barbara Saccà. « Insights into the Structure and Energy of DNA Nanoassemblies ». Molecules 25, no 23 (24 novembre 2020) : 5466. http://dx.doi.org/10.3390/molecules25235466.
Texte intégralRésumé :
Since the pioneering work of Ned Seeman in the early 1980s, the use of the DNA molecule as a construction material experienced a rapid growth and led to the establishment of a new field of science, nowadays called structural DNA nanotechnology. Here, the self-recognition properties of DNA are employed to build micrometer-large molecular objects with nanometer-sized features, thus bridging the nano- to the microscopic world in a programmable fashion. Distinct design strategies and experimental procedures have been developed over the years, enabling the realization of extremely sophisticated structures with a level of control that approaches that of natural macromolecular assemblies. Nevertheless, our understanding of the building process, i.e., what defines the route that goes from the initial mixture of DNA strands to the final intertwined superstructure, is, in some cases, still limited. In this review, we describe the main structural and energetic features of DNA nanoconstructs, from the simple Holliday junction to more complicated DNA architectures, and present the theoretical frameworks that have been formulated until now to explain their self-assembly. Deeper insights into the underlying principles of DNA self-assembly may certainly help us to overcome current experimental challenges and foster the development of original strategies inspired to dissipative and evolutive assembly processes occurring in nature.
27
Zhuang, Hong Mei, Xiao Liang Miao, Zhi Qiang Zhao et Lei Zhang. « Application of Nano Calcium Phosphate Biomaterials and Bone Tissue Engineering on in Exercise-Induced Injury ». Advanced Materials Research 951 (mai 2014) : 109–12. http://dx.doi.org/10.4028/www.scientific.net/amr.951.109.
Texte intégralRésumé :
The formation process of nanocalcium phosphate plays a key role in natural bone tissue. In the regulation of the organic matrix, it can be directed self-assembly into specific biological minerals, and can give the bone good mechanical properties and biological activity. Bone injury is a common injury in exercise training, in view of nanocalcium phosphate has good biocompatibility and osteoinductive; it may become the ideal biomaterials used in bone tissue engineering to improve speed up the recovery of bone injury.
28
Yang, Qin. « Microstructure similarity analysis between synthetic phase-separated block copolymers and natural spider silk ». Applied and Computational Engineering 7, no 1 (21 juillet 2023) : 85–93. http://dx.doi.org/10.54254/2755-2721/7/20230357.
Texte intégralRésumé :
This papers primary purpose is to explore why the microstructure of synthetic block copolymers and natural spider silk is similar at the nanoscale. This paper analyses the main chain segments and secondary structures of natural spider silk, clarifies the aggregation order, and introduces the contribution of secondary systems to the properties of natural block copolymers. Secondly, combined with the synthesis mechanism of natural spider silk, this paper summarizes and analyzes the general process of the synthesized block copolymer. Finally, the conditions of self-assembly of artificial fragments to form the structure are analyzed by employing mean-field theory and a phase diagram. Natural and ideal synthetic spider silk block copolymers have high similarity in performance. To achieve this, scientists can only start from the primary segment to understand their arrangement order in the secondary structure. Then the influence of each block on the properties of the silk fiber is analyzed. At the same time, the size and shape of self-assembled block copolymers are controlled at the micro-scale, thereby changing their properties. The mechanism above shows that the synthesized spider silk block copolymer is similar to natural spider silk in microscopic morphology.
29
Abatchev, Gamid, Andrew Bogard, Zoe Hutchinson, Jason Ward et Daniel Fologea. « Rapid Production and Purification of Dye-Loaded Liposomes by Electrodialysis-Driven Depletion ». Membranes 11, no 6 (31 mai 2021) : 417. http://dx.doi.org/10.3390/membranes11060417.
Texte intégralRésumé :
Liposomes are spherical-shaped vesicles that enclose an aqueous milieu surrounded by bilayer or multilayer membranes formed by self-assembly of lipid molecules. They are intensively exploited as either model membranes for fundamental studies or as vehicles for delivery of active substances in vivo and in vitro. Irrespective of the method adopted for production of loaded liposomes, obtaining the final purified product is often achieved by employing multiple, time consuming steps. To alleviate this problem, we propose a simplified approach for concomitant production and purification of loaded liposomes by exploiting the Electrodialysis-Driven Depletion of charged molecules from solutions. Our investigations show that electrically-driven migration of charged detergent and dye molecules from solutions that include natural or synthetic lipid mixtures leads to rapid self-assembly of loaded, purified liposomes, as inferred from microscopy and fluorescence spectroscopy assessments. In addition, the same procedure was successfully applied for incorporating PEGylated lipids into the membranes for the purpose of enabling long-circulation times needed for potential in vivo applications. Dynamic Light Scattering analyses and comparison of electrically-formed liposomes with liposomes produced by sonication or extrusion suggest potential use for numerous in vitro and in vivo applications.
30
Khairil, Muhammad, Raisa Alatas, Dyah Fitria Kartika Sari et Mirfath. « Communication Strategy Using Da’wah Assembly to Heal Traumatised Natural Disaster Victims in Palu City ». Space and Culture, India 7, no 4 (29 mars 2020) : 228–33. http://dx.doi.org/10.20896/saci.v7i4.626.
Texte intégralRésumé :
This article discusses how Asybaalul Khairaat volunteers’ make use of the trauma healing approach via da’wah based communication strategy to tackle traumatised victims of natural disasters in a refugee camp at Palu, Indonesia. Traumatic events of natural disasters leave psychological impacts such as stress, and anxiety. In the study location, trauma healing programs are widely applied during the disaster and recovery process, with interpersonal exchanges used to increase self-motivation. Therefore, da'wah is one of the bases of the trauma healing process, provided by the Asybaalul Khairaat assembly group, which is supported by Alkhairaat scholars, such as HA. This technique aids in distributing and preaching religious values to the refugees in Alkhairaat schools. The purpose of this article, therefore, is to probe and describe the communication strategy of Asybaalul Khairaat volunteers. The qualitative method with a case study approach was used to analyse the data. At the orientation stage, they focused on the field survey, which allowed them to directly meet the victims or refugees and the initial distribution. Furthermore, humanitarian bonds were built with the attitude of positive mutual help which reflects true Islam. This was followed by the distributing of da'wah after the purchase of Islamic symbols. Finally, spontaneity and uniqueness emerged when Asybaalul Khairaat volunteers tried to demonstrate the right form of trauma healing linked to jihad in Islam by directly assisting in humanitarian activities.
31
Batasheva, Svetlana, Marina Kryuchkova, Ramil Fakhrullin, Giuseppe Cavallaro, Giuseppe Lazzara, Farida Akhatova, Läysän Nigamatzyanova, Vladimir Evtugyn, Elvira Rozhina et Rawil Fakhrullin. « Facile Fabrication of Natural Polyelectrolyte-Nanoclay Composites : Halloysite Nanotubes, Nucleotides and DNA Study ». Molecules 25, no 15 (4 août 2020) : 3557. http://dx.doi.org/10.3390/molecules25153557.
Texte intégralRésumé :
Complexation of biopolymers with halloysite nanotubes (HNTs) can greatly affect their applicability as materials building blocks. Here we have performed a systematic investigation of fabrication of halloysite nanotubes complexes with nucleotides and genomic DNA. The binding of DNA and various nucleotide species (polyAU, UMP Na2, ADP Na3, dATP Na, AMP, uridine, ATP Mg) by halloysite nanotubes was tested using UV-spectroscopy. The study revealed that binding of different nucleotides to the nanoclay varied but was low both in the presence and absence of MgCl2, while MgCl2 facilitated significantly the binding of longer molecules such as DNA and polyAU. Modification of the nanotubes with DNA and nucleotide species was further confirmed by measurements of ζ-potentials. DNA-Mg-modified nanotubes were characterized using transmission electron (TEM), atomic force (AFM) and hyperspectral microscopies. Thermogravimetric analysis corroborated the sorption of DNA by the nanotubes, and the presence of DNA on the nanotube surface was indicated by changes in the surface adhesion force measured by AFM. DNA bound by halloysite in the presence of MgCl2 could be partially released after addition of phosphate buffered saline. DNA binding and release from halloysite nanotubes was tested in the range of MgCl2 concentrations (10–100 mM). Even low MgCl2 concentrations significantly increased DNA sorption to halloysite, and the binding was leveled off at about 60 mM. DNA-Mg-modified halloysite nanotubes were used for obtaining a regular pattern on a glass surface by evaporation induced self-assembly process. The obtained spiral-like pattern was highly stable and resisted dissolution after water addition. Our results encompassing modification of non-toxic clay nanotubes with a natural polyanion DNA will find applications for construction of gene delivery vehicles and for halloysite self-assembly on various surfaces (such as skin or hair).
32
Agmon, Ilana. « Prebiotic Assembly of Cloverleaf tRNA, Its Aminoacylation and the Origin of Coding, Inferred from Acceptor Stem Coding-Triplets ». International Journal of Molecular Sciences 23, no 24 (12 décembre 2022) : 15756. http://dx.doi.org/10.3390/ijms232415756.
Texte intégralRésumé :
tRNA is a key component in life’s most fundamental process, the translation of the instructions contained in mRNA into proteins. Its role had to be executed as soon as the earliest translation emerged, but the questions of the prebiotic tRNA materialization, aminoacylation, and the origin of the coding triplets it carries are still open. Here, these questions are addressed by utilizing a distinct pattern of coding triplets highly conserved in the acceptor stems from the modern bacterial tRNAs of five early-emerging amino acids. Self-assembly of several copies of a short RNA oligonucleotide that carries a related pattern of coding triplets, via a simple and statistically feasible process, is suggested to result in a proto-tRNA model highly compatible with the cloverleaf secondary structure of the modern tRNA. Furthermore, these stem coding triplets evoke the possibility that they were involved in self-aminoacylation of proto-tRNAs prior to the emergence of the earliest synthetases, a process proposed to underlie the formation of the genetic code. Being capable of autonomous materialization and of self-aminoacylation, this verifiable model of the proto-tRNA advent adds principal components to an initial set of molecules and processes that may have led, exclusively through natural means, to the emergence of life.
33
Sandu, Ion, Claudiu Teodor Fleaca, Florian Dumitrache, Bogdan Alexandru Sava, Iuliana Urzica, Iulia Antohe, Simona Brajnicov et Marius Dumitru. « Shaping in the Third Direction ; Synthesis of Patterned Colloidal Crystals by Polyester Fabric-Guided Self-Assembly ». Polymers 13, no 23 (24 novembre 2021) : 4081. http://dx.doi.org/10.3390/polym13234081.
Texte intégralRésumé :
A polyester fabric with rectangular openings was used as a sacrificial template for the guiding of a sub-micron sphere (polystyrene (PS) and silica) aqueous colloid self-assembly process during evaporation as a patterned colloidal crystal (PCC). This simple process is also a robust one, being less sensitive to external parameters (ambient pressure, temperature, humidity, vibrations). The most interesting feature of the concave-shape-pattern unit cell (350 μm × 400 μm × 3 μm) of this crystal is the presence of triangular prisms at its border, each prism having a one-dimensional sphere array at its top edge. The high-quality ordered single layer found inside of each unit cell presents the super-prism effect and left-handed behavior. Wider yet elongated deposits with ordered walls and disordered top surfaces were formed under the fabric knots. Rectangular patterning was obtained even for 20 μm PS spheres. Polyester fabrics with other opening geometries and sizes (~300–1000 μm) or with higher fiber elasticity also allowed the formation of similar PCCs, some having curved prismatic walls. A higher colloid concentration (10–20%) induces the formation of thicker walls with fiber-negative replica morphology. Additionally, thick-wall PCCs (~100 μm) with semi-cylindrical morphology were obtained using SiO2 sub-microspheres and a wavy fabric. The colloidal pattern was used as a lithographic mask for natural lithography and as a template for the synthesis of triangular-prism-shaped inverted opals.
34
Liu, Peng, Hui Ruan, Tiantian Li, Jiaqi Chen, Fuqiu Ma, Duoqiang Pan et Wangsuo Wu. « Removal of Cu(II) Contamination from Aqueous Solution by Ethylenediamine@β-Zeolite Composite ». Molecules 26, no 4 (12 février 2021) : 978. http://dx.doi.org/10.3390/molecules26040978.
Texte intégralRésumé :
The low cost β-zeolite and ethylenediamine modified β-zeolite (EDA@β-zeolite) were prepared by self-assembly method and used for Cu(II) removal from contaminated aqueous solution. Removal ability of β-zeolite toward Cu(II) was greatly improved after ethylenediamine (EDA) modification, the removal performance was greatly affected by environmental conditions. XPS results illustrated that the amide group played important role in the removal process by forming complexes with Cu(II). The EDA@β-zeolite showed desirable recycling ability. The finding herein suggested that the proposed composite is a promising and suitable candidate for the removal of Cu(II) from contaminated natural wastewater and aquifer.
35
Wang, G. R., A. Vianelli et E. B. Goldberg. « Bacteriophage T4 Self-Assembly : In Vitro Reconstitution of Recombinant gp2 into Infectious Phage ». Journal of Bacteriology 182, no 3 (1 février 2000) : 672–79. http://dx.doi.org/10.1128/jb.182.3.672-679.2000.
Texte intégralRésumé :
ABSTRACT T4 gene 2 mutants have a pleiotropic phenotype: degradation of injected phage DNA by exonuclease V (ExoV) in therecBCD + host cell cytoplasm and a low burst size due, at least in part, to a decreased ability for head-to-tail (H-T) joining. The more N terminal the mutation, the more pronounced is the H-T joining defect. We have overexpressed and purified the recombinant gene 2 product (rgp2) to homogeneity in order to test its role in H-T joining, during in vitro reconstitution. When we mix extracts of heads from a gp2+ phage infection (H+) with tails from a gp2+ or gp2− phage infection (T+ or T−), the H-T joining is fast and all of the reconstituted phage grow equally well on cells with or without ExoV activity. When heads from gene 2 amber mutants (H−) are used, addition of rgp2 is required for H-T joining. In this case, H-T joining is slow and only about 10% of the reconstituted phage can form plaques on ExoV+ cells. When extracts of heads with different gene 2 amber mutations are mixed with extracts of tails (with a gene 2 amber mutation) in the presence of rgp2, we find that the size of the gp2 amber peptide of the head extract is inversely related to the fraction of reconstituted phage with a 2+ phenotype. We conclude that free rgp2 is biologically active and has a direct role in H-T joining but that the process is different from H-T joining promoted by natural gp2 that is incorporated into the head in vivo. Furthermore, it seems that gp2 has a domain which binds it to the head. Thus, the presence of the longer gp2am mutants (with this domain) inhibits their replacement by full-length rgp2.
36
Perni, Michele, Céline Galvagnion, Alexander Maltsev, Georg Meisl, Martin B. D. Müller, Pavan K. Challa, Julius B. Kirkegaard et al. « A natural product inhibits the initiation of α-synuclein aggregation and suppresses its toxicity ». Proceedings of the National Academy of Sciences 114, no 6 (17 janvier 2017) : E1009—E1017. http://dx.doi.org/10.1073/pnas.1610586114.
Texte intégralRésumé :
The self-assembly of α-synuclein is closely associated with Parkinson’s disease and related syndromes. We show that squalamine, a natural product with known anticancer and antiviral activity, dramatically affects α-synuclein aggregation in vitro and in vivo. We elucidate the mechanism of action of squalamine by investigating its interaction with lipid vesicles, which are known to stimulate nucleation, and find that this compound displaces α-synuclein from the surfaces of such vesicles, thereby blocking the first steps in its aggregation process. We also show that squalamine almost completely suppresses the toxicity of α-synuclein oligomers in human neuroblastoma cells by inhibiting their interactions with lipid membranes. We further examine the effects of squalamine in a Caenorhabditis elegans strain overexpressing α-synuclein, observing a dramatic reduction of α-synuclein aggregation and an almost complete elimination of muscle paralysis. These findings suggest that squalamine could be a means of therapeutic intervention in Parkinson’s disease and related conditions.
37
Iturri, Jagoba, Andreas Breitwieser, Dietmar Pum, Uwe Sleytr et José Toca-Herrera. « Electrochemical-QCMD Control over S-Layer (SbpA) Recrystallization with Fe2+ as Specific Ion for Self-Assembly Induction ». Applied Sciences 8, no 9 (25 août 2018) : 1460. http://dx.doi.org/10.3390/app8091460.
Texte intégralRésumé :
The critical role of divalent ions (M²+) in the self-assembly of SbpA S-layer proteins (from Lysinibacillus sphaericus CCM 2177) into crystalline structures has been reported in several studies. Hence, ions such as magnesium, barium, nickel and, most commonly, calcium (Ca²+) have proven to trigger both protein-protein and protein-substrate interactions involved in the two-stage non-classical pathway recrystallization followed by SbpA units. As a result, two dimensional, crystalline nanometric sheets in a highly ordered tetrameric state (p4) can be formed on top of different surfaces. The use of iron in its ferrous state (Fe2+) as self-assembly inducing candidate has been omitted so far due to its instability under aerobic conditions, tending to natural oxidation to the ferric (Fe3+) state. In this work, the potentiality of assembling fully functional S-layers from iron (II) salts (FeCl2 and FeSO4) is described for the first time. A combination of chemical (oxidation retardants) and electrical (−1 V potential) factors has been applied to effectively act against such an oxidizing trend. Formation of the respective crystalline films has been followed by means of Electrochemical Quartz Crystal Microbalance with Dissipation (EQCM-D) measurements and complementary Atomic Force Microscopy (AFM) topography studies, which prove the presence of squared lattice symmetry at the end of the recrystallization process. Both techniques, together with additional electrochemical tests performed over the ion permeability of both types of S-layer coatings formed, show the influence of the counterion chosen (chloride vs. sulphate) in the final packing and performance of the S-layer. The presence of an underlying Secondary Cell Wall Polymer (SCWP) as in the natural case contributes to pair both systems, due to the high lateral motility freedom provided by this biopolymer to SbpA units in comparison to uncoated substrates.
38
Romera, David, Pierre Couleaud, Sara H. Mejias, Antonio Aires et Aitziber L. Cortajarena. « Biomolecular templating of functional hybrid nanostructures using repeat protein scaffolds ». Biochemical Society Transactions 43, no 5 (1 octobre 2015) : 825–31. http://dx.doi.org/10.1042/bst20150077.
Texte intégralRésumé :
The precise synthesis of materials and devices with tailored complex structures and properties is a requisite for the development of the next generation of products based on nanotechnology. Nowadays, the technology for the generation of this type of devices lacks the precision to determine their properties and is accomplished mostly by ‘trial and error’ experimental approaches. The use of bottom-up approaches that rely on highly specific biomolecular interactions of small and simple components is an attractive approach for the templating of nanoscale elements. In nature, protein assemblies define complex structures and functions. Engineering novel bio-inspired assemblies by exploiting the same rules and interactions that encode the natural diversity is an emerging field that opens the door to create nanostructures with numerous potential applications in synthetic biology and nanotechnology. Self-assembly of biological molecules into defined functional structures has a tremendous potential in nano-patterning and the design of novel materials and functional devices. Molecular self-assembly is a process by which complex 3D structures with specified functions are constructed from simple molecular building blocks. Here we discuss the basis of biomolecular templating, the great potential of repeat proteins as building blocks for biomolecular templating and nano-patterning. In particular, we focus on the designed consensus tetratricopeptide repeats (CTPRs), the control on the assembly of these proteins into higher order structures and their potential as building blocks in order to generate functional nanostructures and materials.
39
Tunn, Isabell, Matthew J. Harrington et Kerstin G. Blank. « Bioinspired Histidine–Zn2+ Coordination for Tuning the Mechanical Properties of Self-Healing Coiled Coil Cross-Linked Hydrogels ». Biomimetics 4, no 1 (18 mars 2019) : 25. http://dx.doi.org/10.3390/biomimetics4010025.
Texte intégralRésumé :
Natural biopolymeric materials often possess properties superior to their individual components. In mussel byssus, reversible histidine (His)–metal coordination is a key feature, which mediates higher-order self-assembly as well as self-healing. The byssus structure, thus, serves as an excellent natural blueprint for the development of self-healing biomimetic materials with reversibly tunable mechanical properties. Inspired by byssal threads, we bioengineered His–metal coordination sites into a heterodimeric coiled coil (CC). These CC-forming peptides serve as a noncovalent cross-link for poly(ethylene glycol)-based hydrogels and participate in the formation of higher-order assemblies via intermolecular His–metal coordination as a second cross-linking mode. Raman and circular dichroism spectroscopy revealed the presence of α-helical, Zn2+ cross-linked aggregates. Using rheology, we demonstrate that the hydrogel is self-healing and that the addition of Zn2+ reversibly switches the hydrogel properties from viscoelastic to elastic. Importantly, using different Zn2+:His ratios allows for tuning the hydrogel relaxation time over nearly three orders of magnitude. This tunability is attributed to the progressive transformation of single CC cross-links into Zn2+ cross-linked aggregates; a process that is fully reversible upon addition of the metal chelator ethylenediaminetetraacetic acid. These findings reveal that His–metal coordination can be used as a versatile cross-linking mechanism for tuning the viscoelastic properties of biomimetic hydrogels.
40
Busby, Michael, Luisa De Cola, Gregg S. Kottas et Zoran Popović. « Assembling Photo- and Electroresponsive Molecules and Nano-Objects ». MRS Bulletin 32, no 7 (juillet 2007) : 556–60. http://dx.doi.org/10.1557/mrs2007.106.
Texte intégralRésumé :
The self-assembly of small molecules into large, functional nanostructures has led to the construction of supramolecular systems, both in solution and on solid substrates, with defined dimensions that display unique properties through collective interactions, much like natural systems. In this article, we show how one assembles photo- and electroluminescent molecules through coordination chemistry for the purpose of producing novel materials that can be used for displays and lighting applications. In a stepwise process, we discuss the design and synthesis of the components, their spectroscopic behavior, and finally the properties arising from the assembly. We then move from molecules to more complex systems such as zeolite L nano-objects that can be used as nanocontainers and functionalized in different ways. We show how it is possible to organize rods of micron length in a geometrically controlled manner in solution and on surfaces. The assemblies are built by coordinative bonds and are luminescent materials that can be constructed from fluorescent building blocks, with potential applications as optoelectronic materials, in analogy to their molecular counterparts.
41
REHM, Bernd H. A. « Polyester synthases : natural catalysts for plastics ». Biochemical Journal 376, no 1 (15 novembre 2003) : 15–33. http://dx.doi.org/10.1042/bj20031254.
Texte intégralRésumé :
Polyhydroxyalkanoates (PHAs) are biopolyesters composed of hydroxy fatty acids, which represent a complex class of storage polyesters. They are synthesized by a wide range of different Gram-positive and Gram-negative bacteria, as well as by some Archaea, and are deposited as insoluble cytoplasmic inclusions. Polyester synthases are the key enzymes of polyester biosynthesis and catalyse the conversion of (R)-hydroxyacyl-CoA thioesters to polyesters with the concomitant release of CoA. These soluble enzymes turn into amphipathic enzymes upon covalent catalysis of polyester-chain formation. A self-assembly process is initiated resulting in the formation of insoluble cytoplasmic inclusions with a phospholipid monolayer and covalently attached polyester synthases at the surface. Surface-attached polyester synthases show a marked increase in enzyme activity. These polyester synthases have only recently been biochemically characterized. An overview of these recent findings is provided. At present, 59 polyester synthase structural genes from 45 different bacteria have been cloned and the nucleotide sequences have been obtained. The multiple alignment of the primary structures of these polyester synthases show an overall identity of 8–96% with only eight strictly conserved amino acid residues. Polyester synthases can been assigned to four classes based on their substrate specificity and subunit composition. The current knowledge on the organization of the polyester synthase genes, and other genes encoding proteins related to PHA metabolism, is compiled. In addition, the primary structures of the 59 PHA synthases are aligned and analysed with respect to highly conserved amino acids, and biochemical features of polyester synthases are described. The proposed catalytic mechanism based on similarities to α/β-hydrolases and mutational analysis is discussed. Different threading algorithms suggest that polyester synthases belong to the α/β-hydrolase superfamily, with a conserved cysteine residue as catalytic nucleophile. This review provides a survey of the known biochemical features of these unique enzymes and their proposed catalytic mechanism.
42
Gao, Liheng, Jundan Feng, Sijun Xu, Min Shi, Lirong Yao, Lu Wang et Zhongtian Yang. « General Strategy to Prepare Single-Layered Ag–Au–Pt Nanocrystal Ternary-Coated Biomass Textiles through Polymer-Driven Self-Assembly ». Nanomaterials 10, no 3 (10 mars 2020) : 495. http://dx.doi.org/10.3390/nano10030495.
Texte intégralRésumé :
Current metal nanomaterials for developing nanofunctional textiles are mostly based on metal nanoparticles (NPs) that show aqueous instability, a tendency to aggregate, and low chemical affinity to biomass textiles, leading to low nano-metal uptake during finishing, significant declines in function, and nano-pollution. Herein, we demonstrate a strategy to transform metal (Ag, Au, and Pt) NPs into homogenous hyperbranched poly(amide-amine) (HBPAA)-encapsulated NPs showing high water solubility, oxidative resistance, and affinity to biomass materials upon surface capping with HBPAA. The proposed method represents a universal, simple, clean, and efficient self-assembly technology to produce monolayered Ag–Au–Pt ternary-coated biomass textiles. The combination of Ag, Au, and Pt NPs yields a positive potential of approximately +37.12 mV depending on the metal concentration and could simultaneously self-assemble onto natural fibers, including cotton, silk, and wool, through the one-step impregnation of textiles. Increasing the temperature and concentration of the mixture favors the self-assembly process. A mixture of 30–110 mg/L Ag, Au, and Pt NPs could nearly completely anchor onto cotton, silk, and wool textiles after impregnation at 100 °C for 1 h without chemical assistance, thereby indicating the possibility of clean production. As-prepared functional cotton, silk, and wool possessed similarly high antibacterial activities, and a mixture containing over 1500 mg/g NPs inhibited 99% of the Escherichia coli and Staphylococcus aureus in the sample textiles. The developed coating technology is simple, clean, controllable, and broadly applicable; thus, it could be potentially applied in functional textiles.
43
Kunte, Amit, Wei Zhang, Crina Paduraru, Natacha Veerapen, Liam R. Cox, Gurdyal S. Besra et Peter Cresswell. « Endoplasmic Reticulum Glycoprotein Quality Control Regulates CD1d Assembly and CD1d-mediated Antigen Presentation ». Journal of Biological Chemistry 288, no 23 (24 avril 2013) : 16391–402. http://dx.doi.org/10.1074/jbc.m113.474221.
Texte intégralRésumé :
The non-classical major histocompatibility complex (MHC) homologue CD1d presents lipid antigens to innate-like lymphocytes called natural-killer T (NKT) cells. These cells, by virtue of their broad cytokine repertoire, shape innate and adaptive immune responses. Here, we have assessed the role of endoplasmic reticulum glycoprotein quality control in CD1d assembly and function, specifically the role of a key component of the quality control machinery, the enzyme UDP glucose glycoprotein glucosyltransferase (UGT1). We observe that in UGT1-deficient cells, CD1d associates prematurely with β2-microglobulin (β2m) and is able to rapidly exit the endoplasmic reticulum. At least some of these CD1d-β2m heterodimers are shorter-lived and can be rescued by provision of a defined exogenous antigen, α-galactosylceramide. Importantly, we show that in UGT1-deficient cells the CD1d-β2m heterodimers have altered antigenicity despite the fact that their cell surface levels are unchanged. We propose that UGT1 serves as a quality control checkpoint during CD1d assembly and further suggest that UGT1-mediated quality control can shape the lipid repertoire of newly synthesized CD1d. The quality control process may play a role in ensuring stability of exported CD1d-β2m complexes, in facilitating presentation of low abundance high affinity antigens, or in preventing deleterious responses to self lipids.
44
Chang, Ho, Mu Jung Kao et Kuang Ying Lee. « Fabrication of Membrane-Electrolyte Assembly with Nanocomposite for Direct Methanol Fuel Cell ». Advanced Materials Research 566 (septembre 2012) : 386–89. http://dx.doi.org/10.4028/www.scientific.net/amr.566.386.
Texte intégralRésumé :
This study aims to deal with the preparation of membrane-electrolyte assembly (MEA) of Pt/Ru/C nanocomposite as well as connecting to a direct methanol fuel cell and using PCB process packaging to test the efficiency of the DMFC. The components assembled in DMFC are including anode flow field plates, MEA and current collector.Using PCB boards for the anode flow field plates as well as the electicity collector plates and the type of flow field plate adopts serpentine flow field. For the efficiency of DMFC, liquid motors are used to press methanol mixed solution at specific temperature into DMFC. Besides, the cathode of DMFC adopts natural-breath method with air and uses DC electronic load to activate DMFC to investigate operating voltage and further to set constant voltage to measure current to calculate the efficiency of DMFC. Initial results of I-V curve show that self-developed MEA of Pt/Ru/C nanocomposite can enhance around 0.2% current density of DMFC after being assembled like commercial MEA
45
Kabir, Anayet, Matthew Dunlop, Bishnu Acharya, Rabin Bissessur et Marya Ahmed. « Polymeric Composites with Embedded Nanocrystalline Cellulose for the Removal of Iron(II) from Contaminated Water ». Polymers 10, no 12 (12 décembre 2018) : 1377. http://dx.doi.org/10.3390/polym10121377.
Texte intégralRésumé :
The exponential increase in heavy metal usage for industrial applications has led to the limited supply of clean water for human needs. Iron is one of the examples of heavy metals, which is responsible for an unpleasant taste of water and its discoloration, and is also associated with elevated health risks if it persists in drinking water for a prolonged period of time. The adsorption of a soluble form of iron (Fe2+) from water resources is generally accomplished in the presence of natural or synthetic polymers or nanoparticles, followed by their filtration from treated water. The self-assembly of these colloidal carriers into macroarchitectures can help in achieving the facile removal of metal-chelated materials from treated water and hence can reduce the cost and improve the efficiency of the water purification process. In this study, we aim to develop a facile one-pot strategy for the synthesis of polymeric composites with embedded nanocrystalline cellulose (NCC) for the chelation of iron(II) from contaminated water. The synthesis of the polymeric composites with embedded nanoparticles was achieved by the facile coating of ionic monomers on the surface of NCC, followed by their polymerization, crosslinking, and self-assembly in the form of three-dimensional architectures at room temperature. The composites prepared were analyzed for their physiochemical properties, antifouling properties, and for their iron(II)-chelation efficacies in vitro. The results indicate that the embedded-NCC polymeric composites have antifouling properties and exhibit superior iron(II)-chelation properties at both acidic and basic conditions.
46
Rasmussen, Steen, Nils A. Baas, Bernd Mayer et Martin Nilsson. « Ansatz for Dynamical Hierarchies ». Artificial Life 7, no 4 (octobre 2001) : 329–53. http://dx.doi.org/10.1162/106454601317296988.
Texte intégralRésumé :
Complex, robust functionalities can be generated naturally in at least two ways: by the assembly of structures and by the evolution of structures. This work is concerned with spontaneous formation of structures. We define the notion of dynamical hierarchies in natural systems and show the importance of this particular kind of organization for living systems. We then define a framework that enables us to formulate, investigate, and manipulate such dynamical hierarchies. This framework allows us to simultaneously investigate different levels of description together with their interrelationship, which is necessary to understand the nature of dynamical hierarchies. Our framework is then applied to a concrete and very simple formal, physicochemical, dynamical hierarchy involving water and monomers at level one, polymers and water at level two, and micelles (polymer aggregates) and water at level three. Formulating this system as a simple two-dimensional molecular dynamics (MD) lattice gas allows us within one dynamical system to demonstrate the successive emergence of two higher levels (three levels all together) of robust structures with associated properties. Second, we demonstrate how the framework for dynamical hierarchies can be used for realistic (predictive) physicochemical simulation of molecular self-assembly and self-organization processes. We discuss the detailed process of micellation using the three-dimensional MD lattice gas. Finally, from these examples we can infer principles about formal dynamical hierarchies. We present an ansatz for how to generate robust, higher-order emergent properties in formal dynamical systems that is based on a conjecture of a necessary minimal complexity within the fundamental interacting structures once a particular simulation framework is chosen.
47
Fu, Weigui, Guoxia Li, Gaowei Zhai, Yunji Xie, Meixiu Sun, Patrick Théato, Yiping Zhao et Li Chen. « Facile Fabrication of Multi-Hydrogen Bond Self-Assembly Poly(MAAc-co-MAAm) Hydrogel Modified PVDF Ultrafiltration Membrane to Enhance Anti-Fouling Property ». Membranes 11, no 10 (30 septembre 2021) : 761. http://dx.doi.org/10.3390/membranes11100761.
Texte intégralRésumé :
In this work, a facile preparation method was proposed to reduce natural organics fouling of hydrophobic membrane via UV grafting polymerization with methacrylic acid (MAAc) and methyl acrylamide (MAAm) as hydrophilic monomers, followed by multihydrogen bond self-assembly. The resulting poly(vinylidene fluoride)-membranes were characterized with respect to monomer ratio, chemical structure and morphology, surface potential, and water contact angle, as well as water flux and organic foulants ultrafiltration property. The results indicated that the optimal membrane modified with a poly(MAAc-co-MAAm) polymer gel layer derived from a 1:1 monomer ratio exhibited superior hydrophilicity and excellent gel layer stability, even after ultrasonic treatment or soaking in acid or alkaline aqueous solution. The initial water contact angle of modified membranes was only 36.6° ± 2.9, and dropped to 0° within 13 s. Moreover, flux recovery rates (FRR) of modified membranes tested by bovine serum albumin (BSA), humic acid (HA), and sodium alginate (SA) solution, respectively, were all above 90% after one-cycle filtration (2 h), significantly higher than that of the pure membrane (70–76%). The total fouling rates (Rt) of the pure membrane for three foulants were as high as 47.8–56.2%, while the Rt values for modified membranes were less than 30.8%. Where Rt of BSA dynamic filtration was merely 10.7%. The membrane designed through grafting a thin-layer hydrophilic hydrogel possessed a robust antifouling property and stability, which offers new insights for applications in pure water treatment or protein purification.
48
Yu, Dingyi, Shenghao Cui, Liqi Chen, Shuang Zheng, Di Zhao, Xinyu Yin, Faming Yang et Jingdi Chen. « Marine-Derived Bioactive Peptides Self-Assembled Multifunctional Materials : Antioxidant and Wound Healing ». Antioxidants 12, no 6 (31 mai 2023) : 1190. http://dx.doi.org/10.3390/antiox12061190.
Texte intégralRésumé :
Peptide self-assembling materials have received significant attention from researchers in recent years, emerging as a popular field in biological, environmental, medical, and other new materials studies. In this study, we utilized controllable enzymatic hydrolysis technology (animal proteases) to obtain supramolecular peptide self-assembling materials (CAPs) from the Pacific oyster (Crassostrea gigas). We conducted physicochemical analyses to explore the pro-healing mechanisms of CAPs on skin wounds in both in vitro and in vivo experiments through a topical application. The results demonstrated that CAPs exhibit a pH-responsive behavior for self-assembly and consist of peptides ranging from 550 to 2300 Da in molecular weight, with peptide chain lengths of mainly 11–16 amino acids. In vitro experiments indicated that CAPs display a procoagulant effect, free radical scavenging activity, and promote the proliferation of HaCaTs (112.74% and 127.61%). Moreover, our in vivo experiments demonstrated that CAPs possess the ability to mitigate inflammation, boost fibroblast proliferation, and promote revascularization, which accelerates the epithelialization process. Consequently, a balanced collagen I/III ratio in the repaired tissue and the promotion of hair follicle regeneration were observed. With these remarkable findings, CAPs can be regarded as a natural and secure treatment option with high efficacy for skin wound healing. The potential of CAPs to be further developed for traceless skin wound healing is an exciting area for future research and development.
49
Wang, Yudong, Shangjie Ge-Zhang, Pingxuan Mu, Xueqing Wang, Shaoyi Li, Lingling Qiao et Hongbo Mu. « Advances in Sol-Gel-Based Superhydrophobic Coatings for Wood : A Review ». International Journal of Molecular Sciences 24, no 11 (2 juin 2023) : 9675. http://dx.doi.org/10.3390/ijms24119675.
Texte intégralRésumé :
As the focus of architecture, furniture, and other fields, wood has attracted extensive attention for its many advantages, such as environmental friendliness and excellent mechanical properties. Inspired by the wetting model of natural lotus leaves, researchers prepared superhydrophobic coatings with strong mechanical properties and good durability on the modified wood surface. The prepared superhydrophobic coating has achieved functions such as oil-water separation and self-cleaning. At present, some methods such as the sol-gel method, the etching method, graft copolymerization, and the layer-by-layer self-assembly method can be used to prepare superhydrophobic surfaces, which are widely used in biology, the textile industry, national defense, the military industry, and many other fields. However, most methods for preparing superhydrophobic coatings on wood surfaces are limited by reaction conditions and process control, with low coating preparation efficiency and insufficiently fine nanostructures. The sol-gel process is suitable for large-scale industrial production due to its simple preparation method, easy process control, and low cost. In this paper, the research progress on wood superhydrophobic coatings is summarized. Taking the sol-gel method with silicide as an example, the preparation methods of superhydrophobic coatings on wood surfaces under different acid-base catalysis processes are discussed in detail. The latest progress in the preparation of superhydrophobic coatings by the sol-gel method at home and abroad is reviewed, and the future development of superhydrophobic surfaces is prospected.
50
Wang, Jin, Ye Zhou, Jingpeng Li, Yongshun Feng, Jian Zhang, Haixia Yu et Xiaowei Zhuang. « Improved Wettability and Dimensional Stability of Bamboo Timber by Coating Graphene/Silica Composites ». International Journal of Polymer Science 2021 (16 août 2021) : 1–10. http://dx.doi.org/10.1155/2021/7053143.
Texte intégralRésumé :
Bamboo timber (BT) is a kind of natural porous material, and usually bamboo cracking and deformation are caused by the change of humidity in the environment. Inspired by the natural structure of the shell, a multilayer structure was designed to fabricate a kind of graphene/silica composite coating on the BT surface. The multilayer bamboo composite (FAS-RGO@SiO2BT) was prepared by using the self-assembly process of nanospherical silica on graphene followed by hydrophobic modification. A possible formation mechanism of FAS-RGO@SiO2BT was discussed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The FAS-RGO@SiO2BT has excellent hydrophobic properties for tea, orange juice, milk, coffee, blue ink, red wine, and green juice. Also, the FAS-RGO@ SiO2BT has an obvious hydrophobic effect on any of the various solutions with a pH of 1 to 14. In addition, after a 90-day immersion test, the water absorption rate of FAS-RGO@ SiO2BT is 9.7% and the thickness swelling rate is 0.5%. The wettability and dimensional stability of the FAS-RGO@SiO2BT are significantly improved compared to those of BT.