Articles de revues : « Molecular cation »

1

Matsumoto, Mitsuhiro, Shoki Nawate, Yohtaro Inoue, Katsuhiko Tsunashima et Hirohisa Yamada. « Ether-Functionalized Phosphonium Ionic Liquids : Molecular Dynamics, Ion Conformation, and Intermolecular Interaction ». ECS Meeting Abstracts MA2024-02, n^o 57 (22 novembre 2024) : 3818. https://doi.org/10.1149/ma2024-02573818mtgabs.

Texte intégral

Résumé :

Ionic liquids have many potential applications because they have non-flammability, high thermal stability, high ionic conductivity, and so on. Among various types of ionic liquids, quaternary-phosphonium-cation-based ionic liquids (P-ILs) have better physicochemical properties such as ionic conductivity, potential window compared with corresponding quaternary-ammonium-cation-based ionic liquids (N-ILs). Therefore, we have considered that P-ILs are better suitable for applications in electrochemical devices such as electrolytes for lithium-ion batteries than N-ILs [1]. Recently, we spectroscopically demonstrated that such higher ionic conductivity for P-ILs can be explained by weaker intermolecular interaction between anion and cation [2]. This provided us a consideration that molecular interactions are controlling factors in translational motion of ions. For deeper discussion, we focused on the ether-functionalized P-ILs displayed in the Figure 1 because ether structure in phosphonium cations enhanced ionic conductivity and investigated by pulsed field gradient NMR (PFG-NMR), Raman, and terahertz spectroscopies. Based on the PFG-NMR, we calculated transport number of each ion specie and found that transport number of P111(1O1) cation was slightly higher than that for P1113 cation. In Raman spectroscopy, we obtained enthalpy change in conformational change of anion (ΔH) and demonstrated that ΔH for P111(1O1)cation was somewhat lower than that for P1113 cation. Terahertz spectroscopy indicated the weaker intermolecular interaction of P111(1O1) cation with anion than that of P1113 cation. Despite these differences in P111X cations, such ether group effects were hardly observed in P222X cations, which would be due to the different symmetry of cation and steric hindrance. References [1] M. Matsumoto et al., (2023). Available at SSRN: http://dx.doi.org/10.2139/ssrn.4690007 [2] M. Matsumoto et al., J. Phys. Chem. B, 126, 10490 (2022). Figure 1

Styles APA, Harvard, Vancouver, ISO, etc.

2

Mu, Liuhua, Yizhou Yang, Jian Liu, Wei Du, Jige Chen, Guosheng Shi et Haiping Fang. « Hydrated cation–π interactions of π-electrons with hydrated Li+, Na+, and K+ cations ». Physical Chemistry Chemical Physics 23, n^o 27 (2021) : 14662–70. http://dx.doi.org/10.1039/d1cp01609a.

Texte intégral

Résumé :

We give two molecular pictures of hydrated cation–π interactions: graphene sheets interact directly with K⁺ and Na⁺ cations, denoted water–cation–π, while graphene sheets interact indirectly with Li⁺ cation, denoted cation–water–π.

Styles APA, Harvard, Vancouver, ISO, etc.

3

Dočkal, Jan, Martin Lísal et Filip Moučka. « Molecular dynamics of preferential adsorption in mixed alkali–halide electrolytes at graphene electrodes ». Journal of Chemical Physics 157, n^o 8 (28 août 2022) : 084704. http://dx.doi.org/10.1063/5.0097425.

Texte intégral

Résumé :

Understanding the microscopic behavior of aqueous electrolyte solutions in contact with graphene and related carbon surfaces is important in electrochemical technologies, such as capacitive deionization or supercapacitors. In this work, we focus on preferential adsorption of ions in mixed alkali–halide electrolytes containing different fractions of Li+/Na+ or Li+/K+ and/or Na+/K+ cations with Cl− anions dissolved in water. We performed molecular dynamics simulations of the solutions in contact with both neutral and positively and negatively charged graphene surfaces under ambient conditions, using the effectively polarizable force field. The simulations show that large ions are often intuitively attracted to oppositely charged electrodes. In contrast, the adsorption behavior of small ions tends to be counterintuitive. In mixed-cation solutions, one of the cations always supports the adsorption of the other cation, while the other cation weakens the adsorption of the first cation. In mixed-cation solutions containing large and small cations simultaneously, adsorption of the larger cations varies dramatically with the electrode charge in an intuitive way, while adsorption of the smaller cations changes oppositely, i.e., in a counterintuitive way. For (Li/K)Cl mixed-cation solutions, these effects allow the control of Li+ adsorption by varying the electrode charge, whereas, for LiCl single-salt solutions, Li+ adsorption is nearly independent of the electrode charge. We rationalize this cation–cation lever effect as a result of a competition between three driving forces: (i) direct graphene–ion interactions, (ii) the strong tendency of the solutions to saturate the network of non-covalent intermolecular bonds, and (iii) the tendency to suppress local charge accumulation in any region larger than typical interparticle distances. We analyze the driving forces in detail using a general method for intermolecular bonding based on spatial distribution functions and different contributions to the total charge density profiles. The analysis helps to predict whether an ion is more affected by each of the three driving forces, depending on the strength of the ion solvation shells and the compatibility between the contributions of the charge density profiles due to the ion and water molecules. This approach is general and can also be applied to other solutions under different thermodynamic conditions.

Styles APA, Harvard, Vancouver, ISO, etc.

4

Mei, Lefu, Huashang Tao, Chao He, Xuebing Xin, Libing Liao, Limei Wu et Guocheng Lv. « Cd2+Exchange for Na+and K+in the Interlayer of Montmorillonite : Experiment and Molecular Simulation ». Journal of Nanomaterials 2015 (2015) : 1–9. http://dx.doi.org/10.1155/2015/925268.

Texte intégral

Résumé :

Montmorillonite (Mt) has high cation exchange capacity and thus has been studied extensively for its cation exchange interactions with other cations. However, molecular simulations for the forces governing the cation exchange on Mt surfaces or in the interlayer spaces were limited. In this study, Mt with K+and Na+in the interlayer spaces was tested for its cation exchange with Cd2+in solution and the forces driving the cation exchange reaction were simulated by molecular simulations. The experimental results showed that Na+in Na + Mt was completely exchanged by Cd2+, while only 50% of K+in K + Mt was exchanged by Cd2+. A largerd-value was noticed for Na + Mt in comparison to K + Mt, suggesting that the interlayer space is more hydrated with Na+as the interlayer space cation. Molecular dynamic simulations revealed a larger energy decrease when Cd2+substitutes K+. However, the nice fit of the K+into the 12-coordinated interlayer space sites may restrict its hydration and thus reduce its interlayer space cation exchange capability by Cd2+.

Styles APA, Harvard, Vancouver, ISO, etc.

5

Nana Osipova, Tamar Kvernadze, Nino Burkiashvili, Leila Japaridze, Tsiala Gabelia et Eter Salukvadze. « Some molecular-sieve peculiarities of natural zeolite of Georgia ». World Journal of Advanced Research and Reviews 17, n^o 3 (30 mars 2023) : 514–19. http://dx.doi.org/10.30574/wjarr.2023.17.3.0388.

Texte intégral

Résumé :

Ion exchange property of fibrous zeolite scolecite of Georgian origin has been studied against mono (Li, Na, NH4, K Cs and Rb), divalent (Sr, Ba Ca, Mg) and transition (Cd, Cu, Mn, Zn, Co and Ni) metal cations. Selectivity series of the above cations for scolecite have been compiled. The structure of scolecite, charge and sizeof the cations (both in hydrated and dehydrated state) and cation concentration in the solution (0.1N, 0.3N, 0.5N 1.0N and 1.5N) greatly influence on the ion-exchange property and selectivity order of scolecite. Dynamic Exchange Capacity (DEC) values for the studied cations on scolecite have been calculated. Kinetics of ion exchange in dynamic conditions for the above cations has been studied. Analysis of the obtained data shows that the external diffusion processes have influence on the establishment of equilibrium between the ions on the surface and in the micro porous structure of scolesite. The time of dynamic exchange equilibrium is directly proportional to the cation radios.

Styles APA, Harvard, Vancouver, ISO, etc.

6

Avilés-Moreno, Juan Ramón, Francisco Gámez, Giel Berden, Jonathan Martens, Jos Oomens et Bruno Martínez-Haya. « Multipodal coordination and mobility of molecular cations inside the macrocycle valinomycin ». Physical Chemistry Chemical Physics 22, n^o 35 (2020) : 19725–34. http://dx.doi.org/10.1039/d0cp02996c.

Texte intégral

Résumé :

Small cations (K⁺, NH₄⁺) occupy the center of the valinomycin cavity. Bulkier cations like H₄PO₄⁺ stretch the valinomycin backbone, which adopts barrel-like and funnel-like configurations, depending on the dynamically varying position of the cation.

Styles APA, Harvard, Vancouver, ISO, etc.

7

Büchler, P. M. « The Effect of Exchangeable Cations on the Permeability of a Bentonite to Be Used in a Stabilization Pond Liner ». Water Science and Technology 22, n^o 6 (1 juin 1990) : 23–26. http://dx.doi.org/10.2166/wst.1990.0047.

Texte intégral

Résumé :

The organophilic nature of bentonites exchanged with quaternary ammonium cations is used in sanitary engineering for the adsorption of organic pollutants. This paper deals with five different quaternary ammonium cations: tetramethylammonium, trimethylstearylammonium (C18), dimethylbenzyllaurylammonium (C12), trimethylpalmitylammonium (C16) and dimethyldistearylammonium. A Brazilian bentonite was treated with the above cations and the adsorption of vinasse organics was measured through the total organic carbon present in solution. The results show that tetramethylammonium cation is the most effective of those tested to make sodium bentonite more organophilic and the behaviour follows a Freundlich isotherm. If the isotherms are plotted in milliequivalents of the cation over the weight of the sodium bentonite the present experiments did not show an appreciable difference in the quantity adsorbed. Therefore, if cost is a determining factor, low molecular weight cations should be chosen. The modified bentonites were characterized by the X-ray diffraction patterns. For high molecular weight cations the interlamelar spacing is close to 18 Å but for tetramethylammonium it is 13.5 Å. In any case the replacement of sodium by a quaternary ammonium cation increases the capacity of the clay to adsorb organic molecules.

Styles APA, Harvard, Vancouver, ISO, etc.

8

Arnold, Donald R., Xinyao Du et Jing Chen. « The effect of meta- or para-cyano substitution on the reactivity of the radical cations of arylalkenes and alkanes. Radical ions in photochemistry, Part 34 ». Canadian Journal of Chemistry 73, n^o 3 (1 mars 1995) : 307–18. http://dx.doi.org/10.1139/v95-042.

Texte intégral

Résumé :

The effect of electron-withdrawing substituents, meta- or para-cyano, on the reactivity of the radical cation of arylalkenes and alkanes has been determined. The radical cations were generated by single electron transfer (set) to an electron-accepting photosensitizer. Three reactions were studied: (i) the addition of nucleophile to the radical cation of arylalkenes, (ii) cleavage of the benzylic carbon–carbon bond of the radical cation of arylalkanes; and (iii) the deprotonation of the benzylic carbon–hydrogen bond of the radical cation of arylalkanes. The radical cations of 4-(1-phenylethenyl)benzonitrile (1b), 3-(1-phenylethenyl)benzonitrile (1c), 4-(2-methoxy-1-phenylethyl)benzonitrile (2b), 3-(2-methoxy-1-phenylethyl)benzonitrile (2c), cis- and trans-5-cyano-2-methoxy-1-phenylindane (6b-cis and -trans), and 6-cyano-3-phenylindene (7b) were generated, by single electron transfer to the lowest excited singlet state of 1,4-dicyanobenzene (3), in acetonitrile–methanol. The radical cations of 1b, 1c, and 7b react with methanol to yield the anti-Markovnikov adducts (2b, 2c, and 6b-cis and 6b-trans). The radical cations of 2b, 2c, and 6b-trans cleave at the benzylic carbon–carbon bond to give products derived from the radical and carbocation fragments. The radical cation of 6b-cis deprotonates from the benzylic position with subsequent formation of the diastereomer, 6b-trans. This behaviour can be explained/predicted on the basis of the proposed mechanisms for these reactions. Molecular orbital calculations (AM1) support the conclusions. Keywords: photosensitized, electron transfer, radical ions, radicals, molecular orbital calculations (AM1).

Styles APA, Harvard, Vancouver, ISO, etc.

9

Haaland, P., et A. Rahbee. « The molecular silane cation ». Chemical Physics Letters 114, n^o 5-6 (mars 1985) : 571–74. http://dx.doi.org/10.1016/0009-2614(85)85144-7.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

10

van Beijnen, A. J. M., R. J. M. Nolte, J. W. Zwikker et W. Drenth. « A molecular cation channel ». Recueil des Travaux Chimiques des Pays-Bas 101, n^o 11 (2 septembre 2010) : 409–10. http://dx.doi.org/10.1002/recl.19821011108.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

11

Cens, Thierry, Matthieu Rousset, Andrey Kajava et Pierre Charnet. « Molecular Determinant for Specific Ca/Ba Selectivity Profiles of Low and High Threshold Ca2+ Channels ». Journal of General Physiology 130, n^o 4 (24 septembre 2007) : 415–25. http://dx.doi.org/10.1085/jgp.200709771.

Texte intégral

Résumé :

Voltage-gated Ca2+ channels (VGCC) play a key role in many physiological functions by their high selectivity for Ca2+ over other divalent and monovalent cations in physiological situations. Divalent/monovalent selection is shared by all VGCC and is satisfactorily explained by the existence, within the pore, of a set of four conserved glutamate/aspartate residues (EEEE locus) coordinating Ca2+ ions. This locus however does not explain either the choice of Ca2+ among other divalent cations or the specific conductances encountered in the different VGCC. Our systematic analysis of high- and low-threshold VGCC currents in the presence of Ca2+ and Ba2+ reveals highly specific selectivity profiles. Sequence analysis, molecular modeling, and mutational studies identify a set of nonconserved charged residues responsible for these profiles. In HVA (high voltage activated) channels, mutations of this set modify divalent cation selectivity and channel conductance without change in divalent/monovalent selection, activation, inactivation, and kinetics properties. The CaV2.1 selectivity profile is transferred to CaV2.3 when exchanging their residues at this location. Numerical simulations suggest modification in an external Ca2+ binding site in the channel pore directly involved in the choice of Ca2+, among other divalent physiological cations, as the main permeant cation for VGCC. In LVA (low voltage activated) channels, this locus (called DCS for divalent cation selectivity) also influences divalent cation selection, but our results suggest the existence of additional determinants to fully recapitulate all the differences encountered among LVA channels. These data therefore attribute to the DCS a unique role in the specific shaping of the Ca2+ influx between the different HVA channels.

Styles APA, Harvard, Vancouver, ISO, etc.

12

Smudde, George Hc, Terry L. Slager, Charles G. Coe, James E. MacDougall et Scott J. Weigel. « DRIFTS and Raman Investigation of N2 and O2 Adsorption on Zeolites at Ambient Temperature ». Applied Spectroscopy 49, n^o 12 (décembre 1995) : 1747–55. http://dx.doi.org/10.1366/0003702953965957.

Texte intégral

Résumé :

Diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and Raman spectroscopy were used to examine N2 and O2 adsorption on cation-exchanged (K, Na, Sr, Ca, and Li) low silica X (LSX) zeolites. IR and Raman absorption bands were observed for the molecular vibration of adsorbed N2 and O2 at room temperature and atmospheric pressure. The intensity (in Kubelka-Munk units) of the IR band increased with N2 pressure and mirrored the adsorption isotherm for N2. Both O2 and N2 displayed a similar dependence of the molecular vibrational frequency on cation charge density, which suggests that both gases are interacting directly with the cations. The vibrational frequencies for adsorbed N2 and O2 were more sensitive to the cation charge density than to framework Al content. Infrared studies of N2 and O2 on mixed cation forms of LSX show that N2 interaction was localized near individual cations within the sorption cavity of the zeolite. Thus, adsorbed N2 can be used to probe accessibility of specific cations within the zeolite framework. The spectroscopic data are consistent with the theory that the stronger interaction of N2 over O2 is caused by the stronger influence of the electric field with the larger quadrupole of N2.

Styles APA, Harvard, Vancouver, ISO, etc.

13

Techau, Michala Eichner, Javier Valdez-Taubas, Jean-François Popoff, Richard Francis, Matthew Seaman et Jenefer M. Blackwell. « Evolution of Differences in Transport Function in Slc11a Family Members ». Journal of Biological Chemistry 282, n^o 49 (10 octobre 2007) : 35646–56. http://dx.doi.org/10.1074/jbc.m707057200.

Texte intégral

Résumé :

Slc11a1 (formerly Nramp1) is a proton/divalent cation transporter that regulates cation homeostasis in macrophages. Slc11a2 mediates divalent cation uptake via the gut and delivery into cells. The mode of action of the two transporters remains controversial. Heterologous expression in frog oocytes shows Slc11a2 is a symporter, whereas Slc11a1 is an antiporter fluxing divalent cations against the proton gradient. This explains why Slc11a2, but not Slc11a1, can complement EGTA sensitivity in smf1Δ/smf2Δ/smf3Δ yeast. However, some studies of transport in mammalian cells suggest Slc11a1 is a symporter. We now demonstrate that Slc11a1, but not Slc11a2, complements a divalent cation stress phenotype in bsd2Δ/rer1Δ yeast. This is the first description of a yeast complementation assay for Slc11a1 function. Given the prior demonstration in frog oocytes that Slc11a1 acts as an antiporter, the most plausible interpretation of the data is that Slc11a1 is rescuing bsd2Δ/rer1Δ yeast by exporting divalent cations. Chimaeras define the N terminus, and a segment of the protein core preceding transmembrane domain 9 through transmembrane domain 12, as important in rescuing the divalent cation stress phenotype. EGTA sensitivity and divalent cation stress phenotypes in yeast expressing Slc11a orthologues show that symport activity is ancestral. Molecular changes that mediate rescue of the divalent cation stress phenotype post-date frogs and co-evolved with Slc11a1 orthologues that regulate divalent cation homeostasis in macrophages and resistance to infection in chickens and mammals.

Styles APA, Harvard, Vancouver, ISO, etc.

14

Wright, Stephen H. « Molecular and cellular physiology of organic cation transporter 2 ». American Journal of Physiology-Renal Physiology 317, n^o 6 (1 décembre 2019) : F1669—F1679. http://dx.doi.org/10.1152/ajprenal.00422.2019.

Texte intégral

Résumé :

Organic cation transporters play a critical role in mediating the distribution of cationic pharmaceuticals. Indeed, organic cation transporter (OCT)2 is the initial step in the renal secretion of organic cations and consequently plays a defining role in establishing the pharmacokinetics of many cationic drugs. Although a hallmark of OCTs is their broad selectivity, this characteristic also makes them targets for unwanted, adverse drug-drug interactions (DDIs), making them a focus for efforts to develop models of ligand interaction that could predict and preempt these adverse interactions. This review discusses the molecular characteristics of these transporters as well as the evidence that established the OCTs as key players in the distribution of organic cations. However, the primary focus is the present understanding of the complexity of ligand interaction with OCTs, particularly OCT2, including evidence for the presence of multiple ligand-binding sites and the influence of substrate structure on the affinity of the transporter for inhibitory ligands. This leads to a discussion of the complexities associated with the development of protocols for assessing the inhibitory potential of new molecular entities to perpetrate unwanted DDIs, the criteria that should be considered in the interpretation of the results of such protocols, and the challenges associated with development of models capable of predicting unwanted DDIs.

Styles APA, Harvard, Vancouver, ISO, etc.

15

Kruk, Danuta, Elzbieta Masiewicz, Sylwia Lotarska, Roksana Markiewicz et Stefan Jurga. « Relationship between Translational and Rotational Dynamics of Alkyltriethylammonium-Based Ionic Liquids ». International Journal of Molecular Sciences 23, n^o 3 (1 février 2022) : 1688. http://dx.doi.org/10.3390/ijms23031688.

Texte intégral

Résumé :

1H spin-lattice relaxation experiments have been performed for a series of ionic liquids including bis(trifluoromethanesulfonyl)imide anion and cations of a varying alkyl chain length: triethylhexylammonium, triethyloctylammonium, decyltriethylammonium, dodecyltriethylammonium, triethyltetradecylammonium, and hexadecyltriethylammonium. The relaxation studies were carried out in abroad frequency range covering three orders of magnitude, from 10 kHz to 10 MHz, versus temperature. On the basis of a thorough, quantitative analysis of this reach data set, parameters characterizing the relative, cation-cation, translation diffusion (relative diffusion coefficients and translational correlation times), and rotational motion of the cation (rotational correlation times) were determined. Relationships between these quantities and their dependence on the alkyl chain length were discussed in comparison to analogous properties of molecular liquids. It was shown, among other findings, that the ratio between the translational and rotational correlation times is smaller than for molecular liquids and considerably dependent on temperature. Moreover, a comparison of relative and self-diffusion coefficients indicate correlated translational dynamics of the cations.

Styles APA, Harvard, Vancouver, ISO, etc.

16

Moritomo, Yutaka, et Hiroshi Tanaka. « Alkali Cation Potential and Functionality in the Nanoporous Prussian Blue Analogues ». Advances in Condensed Matter Physics 2013 (2013) : 1–9. http://dx.doi.org/10.1155/2013/539620.

Texte intégral

Résumé :

Cation and/or molecule transfer within nanoporous materials is utilized in lithium-ion secondary battery, ion exchange, hydrogen storage, molecular sensors, molecular filters, and so on. Here, we performedab initiototal energy calculation to derive the alkali cation potential in the Prussian blue analogues,AxM[Fe(CN)6]zH2O(A=Li, Na, K, Rb, and Cs;M=Co, Ni, Mn, and Cd), with jungle-gym-type nanoporous framework. The potential curves of larger cations, that is, K+, Rb+and Cs+, exhibit a barrier at the window of the host framework, while those of the smaller cations, that is, Li+and Na+, exhibit no barrier. We will discuss the useful functionalities observed in the Prussian blue analogues, that is, (a) battery properties mediated by Li+intercalation/de-intercalation, (b) electrochromism mediated by Na+transfer in all solid device, and (c) the elimination of Cs+from aqueous solution by precipitation, in terms of the alkali cation potentials.

Styles APA, Harvard, Vancouver, ISO, etc.

17

Li, Xin, Wanling Shen, Han Sun, Lingchuang Meng, Bing Wang, Chenxi Zhan et Bin Zhao. « Theoretical studies on carbon dioxide adsorption in cation-exchanged molecular sieves ». RSC Advances 10, n^o 53 (2020) : 32241–48. http://dx.doi.org/10.1039/d0ra05228k.

Texte intégral

Résumé :

Density functional theory was used to study the adsorption of CO₂ in cation-exchanged zeolite Y, ZSM-5, CHA and A. The adsorption energies and the interactions of cations on various zeolitic topologies towards CO₂ molecule was discussed.

Styles APA, Harvard, Vancouver, ISO, etc.

18

GUAN, QING-MEI, YAN HAN et ZHONG-ZHI YANG. « MOLECULAR DYNAMICS STUDIES ON Fe2+, Co2+, AND Ni2+ AQUEOUS SOLUTIONS BASED ON ABEEM/MM FLUCTUATING CHARGE MODEL ». Journal of Theoretical and Computational Chemistry 07, n^o 06 (décembre 2008) : 1187–201. http://dx.doi.org/10.1142/s0219633608004519.

Texte intégral

Résumé :

Based on atom-bond electronegativity equalization method fused into molecular mechanics (ABEEM/MM), the intermolecular potential for transition metal ion Fe 2+, Co 2+, and Ni 2+ cations in water has been derived. Parameters for the effective interaction between a cation and a water molecule were determined by reproducing the ab initio results. Many structural and dynamic properties of Fe 2+(aq.), Co 2+(aq.), and Ni 2+(aq.) were studied using these potential parameters. Strong influences of the twofold charged cations on the structures of the hydration shells and some other properties of aqueous ionic solutions are discussed and compared with the results of a previous study of alkali metal and alkaline-earth metal cations in water. At the same time, comparative study of the hydration properties of each cation is also discussed. This work demonstrates that ABEEM/MM provides a useful tool in the exploration of the hydration of transition metal cations in water.

Styles APA, Harvard, Vancouver, ISO, etc.

19

Rajegowda, H. R., B. S. Palakshamurthy, N. K. Lokanath, S. Naveen et P. Raghavendra Kumar. « Crystal structure of (2R)-1-[(methylsulfonyl)oxy]propan-2-aminium chloride : a chiral molecular salt ». Acta Crystallographica Section E Crystallographic Communications 71, n^o 10 (12 septembre 2015) : o733—o734. http://dx.doi.org/10.1107/s2056989015015972.

Texte intégral

Résumé :

In the title chiral molecular salt, C4H12NO3S+·Cl−, the cation is protonated at the N atom, producing [RNH3]+, whereRis CH3SO2OCH2C(H)CH3. The N atom in the cation issp3-hybridized. In the crystal, cations and anions are connected by strong N—H...Cl hydrogen bonds to generate edge-shared 12-membered rings of the form {...Cl...HNH}3. This pattern of hydrogen bonding gives rise to zigzag supramolecular layers in theabplane. The layers are connected into a three-dimensional architecture by C—H...O hydrogen bonds. The structure was refined as an inversion twin.

Styles APA, Harvard, Vancouver, ISO, etc.

20

Kazheva, Olga N., Enric Canadell, Grigorii G. Aleksandrov, Nataliya D. Kushch et Oleg A. Dyachenko. « Quasi-three-dimensional network of molecular interactions and electronic structure of a new organic semiconductor, ET(NCS)0.77 ». Acta Crystallographica Section B Structural Science 58, n^o 1 (24 janvier 2001) : 148–52. http://dx.doi.org/10.1107/s0108768101019322.

Texte intégral

Résumé :

The radical cation salt ET(NCS)0.77 [bis(ethylenedithio)tetrathiafulvalene thiocyanate (1/0.77)] has been prepared for the first time by electrocrystallization and its crystal and electronic structure at 110 K was investigated. The unit-cell dimensions are orthorhombic, a = 6.638 (1), b = 8.309 (2), c = 28.776 (6) Å, V = 1587.1 (6) Å3, space group Pbcm, Z = 4. The compound has a layered structure. The ET radical cations of the conducting cationic layer build stacks. In the anionic layer the thiocyanate groups form polymeric chains where they are oriented in a `head-to-tail' mode. The structure has short intermolecular contacts of the cation–cation, anion–anion and cation–anion types, which leads to the formation of a three-dimensional structure of intermolecular interactions. This phenomenon is very rare in molecular conductors. Tight binding band structure calculations suggest, however, that the interlayer interactions through the anions are weak and that the incomplete occupation of the anion sites is the reason for the activated conductivity of the salt.

Styles APA, Harvard, Vancouver, ISO, etc.

21

Wenzel, M., Y. Wu, E. Liss et E. W. Neuse. « Stabilität des Ferricinium-Kations und seine cytostatische Wirkung / Stability of Ferricinium and its Cytostatic Effect ». Zeitschrift für Naturforschung C 43, n^o 11-12 (1 décembre 1988) : 963–66. http://dx.doi.org/10.1515/znc-1988-11-1227.

Texte intégral

Résumé :

Abstract The relative stabilities of different ferricinium cations were studied in buffer or serum-containing solution and in vivo and compared with their cytostatic effects in cultures of Yoshida ascites tumor cells. Although the ferricinium cation itself was the most unstable cation compared with the dimethyl-ferricinium cation and the deuterated ferricinium derivatives it showed the highest cytostatic effect.

Styles APA, Harvard, Vancouver, ISO, etc.

22

Quezada, Gonzalo R., et Pedro G. Toledo. « Complexation of Alkali and Alkaline-Earth Metal Cations at Spodumene-Saltwater Interfaces by Molecular Simulation : Impact on Oleate Adsorption ». Minerals 11, n^o 1 (24 décembre 2020) : 12. http://dx.doi.org/10.3390/min11010012.

Texte intégral

Résumé :

Spodumene, a lithium aluminum inosilicate, is recovered by froth flotation using surfactants, so-called collectors. Therefore, the behavior and properties of the water-mineral interface in saline solutions are central. Here, molecular dynamics simulations are used to study the adsorption of alkali and alkaline-earth metal cations from concentrated solutions on the weakest (110) surface plane of negatively-charged spodumene. Results include the envelope density function of inner-sphere complexes for each cation and the density of complexes according to their adsorption contacts. Visualization of complexes for each cation is also included. Once the structure of the cation layers adsorbed on the surface of spodumene is defined, its role as a catalyst or barrier for adsorption of the spodumene collector in flotation is evaluated. The collector studied is the typical sodium oleate. The results show that oleate adsorption is poor and that the few adsorption contacts are mainly via cation bridges. The findings here indicate that molecular simulation can facilitate the search for effective collectors for environmentally sustainable spodumene flotation processes in saltwater.

Styles APA, Harvard, Vancouver, ISO, etc.

23

Tomé, L. I. N., C. S. R. Sousa, J. R. B. Gomes, O. Ferreira, J. A. P. Coutinho et S. P. Pinho. « Understanding the cation specific effects on the aqueous solubility of amino acids : from mono to polyvalent cations ». RSC Advances 5, n^o 20 (2015) : 15024–34. http://dx.doi.org/10.1039/c5ra00501a.

Texte intégral

Résumé :

Based on solubility and molecular dynamics studies, a consistent and refined molecular description of the effect of the cation on the solubility of amino acids based on specific interactions of the cations with the negatively charged moieties of the biomolecules is proposed.

Styles APA, Harvard, Vancouver, ISO, etc.

24

Mero, Angelica, Luca Guglielmero, Lorenzo Guazzelli, Felicia D’Andrea, Andrea Mezzetta et Christian Silvio Pomelli. « A Specific Interaction between Ionic Liquids’ Cations and Reichardt’s Dye ». Molecules 27, n^o 21 (25 octobre 2022) : 7205. http://dx.doi.org/10.3390/molecules27217205.

Texte intégral

Résumé :

Solvatochromic probes are often used to understand solvation environments at the molecular scale. In the case of ionic liquids constituted by an anion and a cation, which are designed and paired in order to obtain a low melting point and other desirable physicochemical properties, these two indivisible components can interact in a very different way with the probe. This is the case with one of the most common probes: Reichardt’s Dye. In the cases where the positive charge of the cation is delocalized on an aromatic ring such as imidazolium, the antibonding orbitals of the positively charged aromatic system are very similar in nature and energy to the LUMO of Reichardt’s Dye. This leads to an interesting, specific cation-probe interaction that can be used to elucidate the nature of the ionic liquids’ cations. Parallel computational and experimental investigations have been conducted to elucidate the nature of this interaction with respect to the molecular structure of the cation.

Styles APA, Harvard, Vancouver, ISO, etc.

25

Pranowo, Harno Dwi, et Chairil Anwar. « MOLECULAR MODELLING OF Mn⁺.[DBz16C5] COMPLEXES, M = Li⁺, Na⁺ AND Zn²⁺ BASED ON MNDO/d SEMIEMPIRICAL METHOD ». Indonesian Journal of Chemistry 6, n^o 2 (14 juin 2010) : 144–49. http://dx.doi.org/10.22146/ijc.21750.

Texte intégral

Résumé :

The effect of substituent on dibenzo-16-crown-5 (DBz16C5) and interaction between these crown ether with metal cations was evaluated using computational chemistry calculations. Substituens where are connected to the benzene ring on the DBz16C5 are -COOH, -Br, -COOC2H5, -CHO, -CH=CHCO2H, -CH=CHCO2C2H5 and -CH(OH)CH3. The analysis based on computational chemistry calculation using MNDO/d semi empirical method was done. The first step is structure optimization of crown ether followed by optimization of crown ether-metals cation complexes Mn+.[DBz16C5], where M is Li+, Na+ and Zn2+. Interactions of the crown ether and cation were discussed in term of the structure parameter of crown ether, atomic charges and energy interaction of the crown ether-metals cation. Electron donating groups increase the capability of crown ether to bind cation by means of induction effect, while electron withdrawing groups reduce the ability of crown ether to bind cation. Any substituent on the benzene in DBz16C5 which can be make the symmetrical form of the crown ether-metals cation complexes will increase the selectivity of the crown ether to bind the cation. Selectivity of the crown ether to bind cation also depends on the compatibility of the diameter of cation and cavity of crown ether. DBz16C5 has higher selectivity to bind the Na+ compare to the Li+ and Zn2+. Keywords: selectivity, dibenzo-16-crown-5, MNDO/d

Styles APA, Harvard, Vancouver, ISO, etc.

26

Raghavendra Kumar, P., Upereti Shailesh et B. S. Palakshamurthy. « Crystal structure of (2-chloroethyl)[2-(methylsulfanyl)benzyl]ammonium chloride ». Acta Crystallographica Section E Crystallographic Communications 71, n^o 6 (13 mai 2015) : 621–23. http://dx.doi.org/10.1107/s2056989015008221.

Texte intégral

Résumé :

In the title molecular salt, C10H15ClNS+·Cl−, the cation is [R′R"NH2]+, whereR′ is 2-MeS-C6H4CH2– andR" is –CH2CH2Cl, and the anion is Cl−. In the cation, the N atom is protonated withsp3-hybridization and with a tetrahedral geometry. In the crystal, the anions are connected to the cations through two pairs of N—H...Cl hydrogen bonds, generating a four-centred inversion dimer with anR42(8) ring motif.

Styles APA, Harvard, Vancouver, ISO, etc.

27

Wang, Ziyi, Junwu Chen, Yao Li, Kun Dong et Yinghao Yu. « EDL structure of ionic liquid-MXene-based supercapacitor and hydrogen bond role on the interface : a molecular dynamics simulation investigation ». Physical Chemistry Chemical Physics 24, n^o 10 (2022) : 5903–13. http://dx.doi.org/10.1039/d1cp05355h.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

28

Brolo, A. G., et D. E. Irish. « SERS studies of monoprotonated pyrazine (pyrazinium) cations adsorbed onto positively charged silver electrodes ». Canadian Journal of Chemistry 75, n^o 11 (1 novembre 1997) : 1643–48. http://dx.doi.org/10.1139/v97-195.

Texte intégral

Résumé :

The surface-enhanced Raman scattering (SERS) spectra of monoprotonated pyrazine cations adsorbed on silver electrodes have been measured. The molecular orientation of the pyrazinium cation is dependent on the electrode potential. At potentials more positive than −170 mV the monoprotonated pyrazine is adsorbed end-on. However, the spectral features suggest a flat orientation as the potential becomes more negative than −300 mV. Monoprotonated pyrazine cations with both orientations can coexist at potentials between these limits. The adsorption of the positive ion to a positively charged electrode is mediated by specifically adsorbed bromide ions. Keywords: SERS; monoprotonated pyrazine cation, silver electrode, pyrazinium.

Styles APA, Harvard, Vancouver, ISO, etc.

29

TEHRANI, ZAHRA ALIAKBAR, MARJAN JEBELI JAVAN, ALIREZA FATTAHI et MOHAMMAD MAHMOODI HASHEMI. « EFFECT OF CATION RADICAL FORMATION ON REACTIVITY AND ACIDITY ENHANCEMENT OF CYTOSINE NUCLEOBASE : NATURAL BOND ORBITAL AND ATOM IN MOLECULE ANALYSIS ». Journal of Theoretical and Computational Chemistry 11, n^o 02 (avril 2012) : 313–27. http://dx.doi.org/10.1142/s0219633612500228.

Texte intégral

Résumé :

The radical cations of DNA constituents generated by the ionizing radiation initiate an alteration of the bases, which is one of the main types of cytotoxic DNA lesions. These cation radical spices are known for their role in producing nucleic acid strand break. In this study, the gas-phase intrinsic chemical properties of the gaseous radical cations of cytosine and its base pair with guanine were examined by employing density functional theory (B3LYP) with the 6-311++G(d,p) basis set. Structures, geometries, adiabatic ionization energies, adiabatic electron affinities, charge distributions, molecular orbital analysis and proton-transfer process of these molecules were investigated. The influence of cation radical formation on acidities of multiple sites in cytosine molecule was investigated. Results of calculations revealed that cytosine radicals formed by deprotonation of cytosine cation radicals can exothermically abstract hydrogen atoms from thiol groups, phenol, and α-positions of amino acid. Furthermore, comparison of acidity value of N–H sites of cytosine cation radical with the known proton affinities (PA) of organic and biological molecules implied that cytosine cation radical can exothermically transfer onto basic sites of amino acids and peptides.

Styles APA, Harvard, Vancouver, ISO, etc.

30

Arnold, Donald R., et Xinyao Du. « The photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction. Part 5 : methanol–monoterpenes (α- and β-pinene, tricyclene, and nopol), 1,4-dicyanobenzene ». Canadian Journal of Chemistry 72, n^o 2 (1 février 1994) : 403–14. http://dx.doi.org/10.1139/v94-062.

Texte intégral

Résumé :

The reactivity of the radical cations of α- and β-pinene (8 and 9), tricyclene (18), and nopol (23) has been studied. The radical ions were generated, in acetonitrile–methanol (3:1), by single electron transfer (set) to the singlet excited state of 1,4-di-cyanobenzene (1). Biphenyl (3) was used as a codonor. The cyclobutane rings of the initially formed radical cations of α- and β-pinene (8+• and 9+•) cleave to distonic radical cations that react as tertiary alkyl cations and allylic radicals. The results of ab initio molecular orbital calculations (STO-3G) are consistent with the observation that the positive charge is largely associated with the tertiary alkyl moiety while the spin density is largely distributed over the allylic radical. There was no evidence, experimental or theoretical, indicative of a bonding interaction between the cationic and allylic moieties of these distonic radical cations. The cyclobutane ring cleavage is irreversible. The radical cation of tricyclene (18) also gives 1:1:1 (nucleophile:cyclopropyl:aromatic) adducts. The regio- and stereochemistry of the adducts, and the nucleophile selectivity, are all indicative of nucleophile-assisted cleavage of the radical cation (18+•). The radical cation of nopol (23+•) also cleaves to the distonic radical cation. The cyclobutane ring cleavage must be rapid; intramolecular 1,5-endo cyclization of the hydroxyl group cannot compete.

Styles APA, Harvard, Vancouver, ISO, etc.

31

Bernardi, Paolo. « Mitochondrial Transport of Cations : Channels, Exchangers, and Permeability Transition ». Physiological Reviews 79, n^o 4 (10 janvier 1999) : 1127–55. http://dx.doi.org/10.1152/physrev.1999.79.4.1127.

Texte intégral

Résumé :

This review provides a selective history of how studies of mitochondrial cation transport (K+, Na+, Ca2+) developed in relation to the major themes of research in bioenergetics. It then covers in some detail specific transport pathways for these cations, and it introduces and discusses open problems about their nature and physiological function, particularly in relation to volume regulation and Ca2+homeostasis. The review should provide the basic elements needed to understand both earlier mitochondrial literature and current problems associated with mitochondrial transport of cations and hopefully will foster new interest in the molecular definition of mitochondrial cation channels and exchangers as well as their roles in cell physiology.

Styles APA, Harvard, Vancouver, ISO, etc.

32

Nguyen, Vu D., Cameron A. McCormick, Robert A. Pascal, Joel T. Mague et Lynn V. Koplitz. « Crystal structure of 2-cyano-1-methylpyridinium bromide ». Acta Crystallographica Section E Crystallographic Communications 71, n^o 11 (17 octobre 2015) : o854—o855. http://dx.doi.org/10.1107/s2056989015019167.

Texte intégral

Résumé :

In the title molecular salt, C7H7N2+·Br−, all the non-H atoms lie on crystallographic mirror planes. The packing consists of (010) cation–anion layers, with the cations forming dimeric unitsviavery weak pairwise C—H...N interactions. Weak C—H...Br interactions link the cations to the anions.

Styles APA, Harvard, Vancouver, ISO, etc.

33

Batsanov, Stepan S. « Revised radii of the univalent Cu, Ag, Au and Tl cations ». Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 76, n^o 1 (19 décembre 2019) : 38–40. http://dx.doi.org/10.1107/s2052520619015531.

Texte intégral

Résumé :

Radii of Cu+, Ag+, Au+ and Tl+ cations are determined by the additive method from interatomic distances in molecular and/or crystalline halides, oxides, chalcogenides and cyanides with different coordinations of atoms, and then recalculated for the 6-coordination number. The averaged (from 74 structures) values of revised radii are equal to r(Cu+) = 0.74 Å, r(Ag+) = 0.99 Å, r(Au+) = 0.92 Å, r(Tl+) = 1.22 Å, which are consistent with radii calculated from direct cation–cation contacts in ultimately compressed metals.

Styles APA, Harvard, Vancouver, ISO, etc.

34

Yamuna, Thammarse S., Manpreet Kaur, Jerry P. Jasinski et H. S. Yathirajan. « Pyrimethaminium 2-{[4-(trifluoromethyl)phenyl]sulfanyl}benzoate dimethyl sulfoxide monosolvate ». Acta Crystallographica Section E Structure Reports Online 70, n^o 6 (17 mai 2014) : o683—o684. http://dx.doi.org/10.1107/s1600536814010411.

Texte intégral

Résumé :

In the cation of the title solvated molecular salt, C12H14ClN4+·C14H8F3O2S−·C2H6OS [systematic name of the cation: 2,4-diamino-5-(4-chlorophenyl)-6-ethylpyrimidin-1-ium], the dihedral angle between the planes of the pyrimidinium and 4-chlorophenyl rings is 77.2 (5)°. In the anion, the planes of the benzene rings are twisted with respect to each other by 71.5 (5)°. Disorder was modelled for the dimethyl sulfoxide solvent molecule over two set of sites in a 0.7487 (13):0.2513 (13) ratio. In the crystal, the cations are linked by inversion-generated pairs of N—H...N hydrogen bonds, with anR22(8) graph-set motif. The cation donates two N—H...O hydrogen bonds to the anion, also generating anR22(8) loop. These interactions, along with cation–solvent N—H...O hydrogen bonds, and cation–anion C—H...F, solvent–anion C—H...O and C—H...F interactions, result in a three-dimensional network.

Styles APA, Harvard, Vancouver, ISO, etc.

35

Stoyanov, Evgenii S., et Irina V. Stoyanova. « The Chloronium Cation [(C2H3)2Cl+] and Unsaturated C4-Carbocations with C=C and C≡C Bonds in Their Solid Salts and in Solutions : An H1/C13 NMR and Infrared Spectroscopic Study ». International Journal of Molecular Sciences 23, n^o 16 (14 août 2022) : 9111. http://dx.doi.org/10.3390/ijms23169111.

Texte intégral

Résumé :

Solid salts of the divinyl chloronium (C2H3)2Cl+ cation (I) and unsaturated C4H6Cl+ and C4H7+ carbocations with the highly stable CHB11Hal11− anion (Hal=F, Cl) were obtained for the first time. At 120 °C, the salt of the chloronium cation decomposes, yielding a salt of the C4H5+ cation. This thermally stable (up to 200 °C) carbocation is methyl propargyl, CH≡C-C+-H-CH3 (VI), which, according to quantum chemical calculations, should be energetically much less favorable than other isomers of the C4H7+ cations. Cation VI readily attaches HCl to the formal triple C≡C bond to form the CHCl=CH-C+H-CH3 cation (VII). In infrared spectra of cations I, VI, and VII, frequencies of C=C and C≡C stretches are significantly lower than those predicted by calculations (by 400–500 cm−1). Infrared and 1H/13C magic-angle spinning NMR spectra of solid salts of cations I and VI and high-resolution 1H/13C NMR spectra of VII in solution in SO2ClF were interpreted. On the basis of the spectroscopic data, the charge and electron density distribution in the cations are discussed.

Styles APA, Harvard, Vancouver, ISO, etc.

36

Maslen, E. N., et B. E. Etschmann. « Bonding without ionisation. » Australian Journal of Physics 53, n^o 2 (2000) : 299. http://dx.doi.org/10.1071/ph99027.

Texte intégral

Résumé :

Charges are calculated for diatomic molecules by partitioning the promolecular density with projection operators derived from free atom potentials. The promolecular charges thus obtained have physically reasonable magnitudes, which are moderately sensitive to interatomic distances and thus to bond type. Their signs are negative for cations and positive for anions. Trends in these charges correlate with subshell structure. Due to the long range of their electrostatic potentials, the cations compete successfully for electrons at the expense of the anions in the density partitioning. This implies that the cation states become overfilled when the atoms overlap, favouring a flow of electrons away from the cation towards the vacant anion states. That accounts for the positive cations and negative anions observed when molecular densities are partitioned with projection operators based on free atom electron densities.

Styles APA, Harvard, Vancouver, ISO, etc.

37

Chang, Bo Y., Seokmin Shin, Vladimir Malinovsky et Ignacio R. Sola. « The Hydrogen molecular cation as a molecular antenna ». Journal of Physics B : Atomic, Molecular and Optical Physics 48, n^o 17 (17 juillet 2015) : 174005. http://dx.doi.org/10.1088/0953-4075/48/17/174005.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

38

Glidewell, Christopher, George Ferguson, Richard M. Gregson et Alan J. Lough. « 3,6,9,16,19,22-Hexaazatricyclo[22.2.2.211,14]triconta-1(26),11(29),12,14(30),24,27-hexaene, C24H38N6, as a building block in supramolecular chemistry : structures in two and three dimensions ». Acta Crystallographica Section B Structural Science 56, n^o 2 (1 avril 2000) : 287–98. http://dx.doi.org/10.1107/s0108768199014032.

Texte intégral

Résumé :

The adduct (1) formed between the hexaaza macrocycle 3,6,9,16,19,22-hexaazatricyclo[22.2.2.211,14]triconta-1(26),11(29),12,14(30),24,27-hexaene, C24H38N6, and 4,4′-sulfonyldiphenol, O2S(C6H4OH)2, is a salt [(C24H40N6)2+]·2[(HOC6H4SO2C6H4O)−], and the adduct (2) formed by the same macrocyclic amine with 4,4′-biphenol is an aquated salt which also contains neutral biphenol molecules, [(C24H40N6)2+]·2[(HOC6H4C6H4O)−]·(HOC6H4C6H4OH).2H2O. In both compounds the cations lie across centres of inversion: there are two crystallographically distinct cation sites in (1) and the conformations of the cations occupying them are quite different. In (2) the single type of cation site is occupied by a conformationally disordered cation: the major and minor components represent two further distinct conformers. In (1) the anions are linked by O—H...O hydrogen bonds into chains, and each cation is linked by a total of six N—H...O hydrogen bonds to anions in four different chains, so linking the chains into continuous sheets. In (2) the anions and the water molecules are linked into sheets, which are further linked into a continuous three-dimensional framework by both the cations and the neutral biphenol units.

Styles APA, Harvard, Vancouver, ISO, etc.

39

Chambers, Richard D., Martin Salisbury, Glenn Apsey et Giovanni Moggi. « Remarkably stable fluorinated conjugated cations and a di-cation ». Journal of the Chemical Society, Chemical Communications, n^o 10 (1988) : 680. http://dx.doi.org/10.1039/c39880000680.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

40

Hamani, D., O. Masson et P. Thomas. « Localization and steric effect of the lone electron pair of the tellurium Te4+ cation and other cations of the p-block elements. A systematic study ». Journal of Applied Crystallography 53, n^o 5 (8 septembre 2020) : 1243–51. http://dx.doi.org/10.1107/s1600576720010031.

Texte intégral

Résumé :

A simple method has been developed based on pure geometrical concepts to localize lone pairs (LPs) of cations of the p-block elements and model their steric effect. The method was applied to 1185 structures containing LP cations in 2439 non-equivalent positions. For oxide crystal structures, it is observed that, going from bottom left to top right in the periodic table, LPs move away from the cation core and decrease in size. For a given kind of cation M*, the LP radius increases linearly with the M*–LP distance, the smallest rate being observed for Tl+ and the largest for Cl5+. The influence of the anion type was also studied in the case of the Te4+ cation. Overall, the same trends were observed. The smallest Te–LP distances and LP radii are found for anions of large size and small charge.

Styles APA, Harvard, Vancouver, ISO, etc.

41

Werst, D. W. « Radical cation-arene .pi.-molecular complexes. Thioether radical cations in aromatic solvents ». Journal of the American Chemical Society 113, n^o 11 (mai 1991) : 4345–46. http://dx.doi.org/10.1021/ja00011a056.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

42

Zhu, Quansong, Conor L. Rooney, Hadar Shema, Christina Zeng, Julien A. Panetier, Elad Gross, Hailiang Wang et Lawrence Baker. « Molecular Solvation Environment Controls the Active Site in Cation-Mediated Electrocatalytic CO₂ Reduction to Methanol ». ECS Meeting Abstracts MA2024-01, n^o 44 (9 août 2024) : 2408. http://dx.doi.org/10.1149/ma2024-01442408mtgabs.

Texte intégral

Résumé :

Electrocatalytic synthesis of higher-value products from waste molecules is an emerging technique for sustainable chemical catalysis. Heterogeneous molecular electrocatalysts are an important group of materials where the catalytic activity and selectivity can be controlled using molecularly defined active sites. Despite extensive efforts to synthesize better molecular catalysts, the effects of molecular aggregation, which dominates the interaction of the catalyst with the electrode surface as well as with the electrochemical solvation environment, are not fully understood. Using cobalt phthalocyanine (CoPc) dispersed on carbon nanotubes (CNTs) as a model system, we find that controlling the direct interaction of the molecular catalyst with cations in the electrochemical double layer (EDL) results in significantly enhanced performance for CO2 reduction (CO2RR). Specifically, molecular dispersion of the CoPc onto CNTs yields a 4-fold increase in total current density and 8-fold increase in methanol (MeOH) selectivity compared to aggregated CoPc physically mixed with the same CNT support, enabling CO2 to MeOH conversion with 42.34% Faradaic efficiency (FE). Using surface-selective sum-frequency generation (SFG) vibrational spectroscopy, direct detection of reaction intermediates reveals that the potential-dependent adsorption of two distinct CO intermediates at two types of active sites, one less active and producing mostly CO, the other more active and able to produce methanol. DFT calculations show that the CO intermediate responsible for selective MeOH production results from the direct interaction with cations present in the EDL. This interaction, which is only possible when CoPc is molecularly dispersed on the electrode surface, is responsible for the cation-assisted conversion of CO to MeOH. Control experiments using either strongly hydrated Li+, or chelated K+ by 18-crown-6-ether, which suppress MeOH formation, further confirms the important role of this interaction. Similarly significant enhancement effects are also observed for nitrate reduction reaction (NO3RR) and oxygen reduction reaction (ORR), showing that dispersing molecular catalysts into monomers states is a general design parameter required to enhance activity and selectivity by cation-assisted reaction kinetics inside the EDL.

Styles APA, Harvard, Vancouver, ISO, etc.

43

Luger, Peter, Birger Dittrich, Leonard Benecke et Hannes Sterzel. « Charge density studies on methylene blue – a potential anti-Alzheimer agent ». Zeitschrift für Naturforschung B 73, n^o 2 (23 février 2018) : 99–108. http://dx.doi.org/10.1515/znb-2017-0165.

Texte intégral

Résumé :

AbstractMotivated by the medical interest in methylene blue as potential anti-Alzheimer agent, the charge densities of three salt structures containing the methylene blue cation with nitrate (as dihydrate), chloride (as pentahydrate) and thiocyanate counter-ions were generated by application of the invariom formalism and examined. The so-obtained charge density distributions were analyzed using the QTAIM formalism to yield bond topological and atomic properties. The atomic charges on the methylene blue cation indicate a delocalized charge distribution; only a small positive charge on the sulfur atom was found. Electrostatic potentials mapped onto iso-surfaces of electron density for the cations, and for the methylene blue cations with anions, were compared. The effect of hydrogen disorder on the molecular electrostatic potential was investigated for the thiocyanate structure.

Styles APA, Harvard, Vancouver, ISO, etc.

44

Podwórny, Jacek. « XRD Based Methods of Investigation the Order - Disorder Transformation in the Spinel Structure - A Comparative Study ». Solid State Phenomena 203-204 (juin 2013) : 129–32. http://dx.doi.org/10.4028/www.scientific.net/ssp.203-204.129.

Texte intégral

Résumé :

Three synthetic and stoichiometric 2:3 type spinels (Fd3m symmetry): MgAl2O4, MgFe2O4, NiAl2O4 with a different initial structural order in cation sublattice were investigated. Investigations by means of high temperature XRPD method at temperatures ranging from 25°C to 1100°C were carried out. Diffraction patterns at each temperature in isothermal conditions were measured. For each tested spinel changes in several temperature-dependent parameters were measured: oxygen positional parameter u(T), cell edge a0(T), cation site occupancies Occ(T) in tetrahedral and octahedral positions and a cation-anion distance in tetrahedral TO(T) and octahedral MO(T) positions. Temperatures of initial order-disorder transformation were determined on the basis of the course of these dependences. Basing on changes of the cell edge a0(T), the values of thermal expansion coefficient and for spinel before and after the beginning of order-disorder transformation, respectively, were calculated. The values of measured temperature-dependent parameters were used to calculate the degree of inversion x in the spinel structure defined as the number of 3+ cations in tetrahedral sites. In each case two methods of calculating the degree of inversion from experimental data were applied. The first method involved observing the changes in sites occupancy in the cation sublattice versus temperature, which resulted in a change of diffraction lines intensities. The second method was based on observing the changes in cation-anion distances in tetra- and octahedral coordination versus temperature. The results obtained by both methods were compared, discussed and advantages and disadvantages of each of them were presented. It was shown that when atomic scattering factors of cations 2+ and 3+ in the spinel structure differ significantly, the most precise method is the one based on changes in sites occupancies versus temperature. The method based on calculation of changes in cation-anion distances is recommended when atomic scattering factors of cations differ slightly but oxygen positional parameter and cation-anion distances changes significantly during order-disorder transformation like in normal spinel structure when effective ionic radii of 2+ and 3+ cations differ significantly.

Styles APA, Harvard, Vancouver, ISO, etc.

45

Ariño, Joaquín, José Ramos et Hana Sychrová. « Alkali Metal Cation Transport and Homeostasis in Yeasts ». Microbiology and Molecular Biology Reviews 74, n^o 1 (mars 2010) : 95–120. http://dx.doi.org/10.1128/mmbr.00042-09.

Texte intégral

Résumé :

SUMMARY The maintenance of appropriate intracellular concentrations of alkali metal cations, principally K+ and Na+, is of utmost importance for living cells, since they determine cell volume, intracellular pH, and potential across the plasma membrane, among other important cellular parameters. Yeasts have developed a number of strategies to adapt to large variations in the concentrations of these cations in the environment, basically by controlling transport processes. Plasma membrane high-affinity K+ transporters allow intracellular accumulation of this cation even when it is scarce in the environment. Exposure to high concentrations of Na+ can be tolerated due to the existence of an Na+, K+-ATPase and an Na+, K+/H+-antiporter, which contribute to the potassium balance as well. Cations can also be sequestered through various antiporters into intracellular organelles, such as the vacuole. Although some uncertainties still persist, the nature of the major structural components responsible for alkali metal cation fluxes across yeast membranes has been defined within the last 20 years. In contrast, the regulatory components and their interactions are, in many cases, still unclear. Conserved signaling pathways (e.g., calcineurin and HOG) are known to participate in the regulation of influx and efflux processes at the plasma membrane level, even though the molecular details are obscure. Similarly, very little is known about the regulation of organellar transport and homeostasis of alkali metal cations. The aim of this review is to provide a comprehensive and up-to-date vision of the mechanisms responsible for alkali metal cation transport and their regulation in the model yeast Saccharomyces cerevisiae and to establish, when possible, comparisons with other yeasts and higher plants.

Styles APA, Harvard, Vancouver, ISO, etc.

46

Nguyen, Dung, Hwoi Kwon et Tsung-Yu Chen. « Divalent Cation Modulation of Ion Permeation in TMEM16 Proteins ». International Journal of Molecular Sciences 22, n^o 4 (23 février 2021) : 2209. http://dx.doi.org/10.3390/ijms22042209.

Texte intégral

Résumé :

Intracellular divalent cations control the molecular function of transmembrane protein 16 (TMEM16) family members. Both anion channels (such as TMEM16A) and phospholipid scramblases (such as TMEM16F) in this family are activated by intracellular Ca2+ in the low µM range. In addition, intracellular Ca2+ or Co2+ at mM concentrations have been shown to further potentiate the saturated Ca2+-activated current of TMEM16A. In this study, we found that all alkaline earth divalent cations in mM concentrations can generate similar potentiation effects in TMEM16A when applied intracellularly, and that manipulations thought to deplete membrane phospholipids weaken the effect. In comparison, mM concentrations of divalent cations minimally potentiate the current of TMEM16F but significantly change its cation/anion selectivity. We suggest that divalent cations may increase local concentrations of permeant ions via a change in pore electrostatic potential, possibly acting through phospholipid head groups in or near the pore. Monovalent cations appear to exert a similar effect, although with a much lower affinity. Our findings resolve controversies regarding the ion selectivity of TMEM16 proteins. The physiological role of this mechanism, however, remains elusive because of the nearly constant high cation concentrations in cytosols.

Styles APA, Harvard, Vancouver, ISO, etc.

47

Carotenuto, Gianfranco. « Isothermal Kinetic Investigation of the Water-Cations Interaction in Natural Clinoptilolite ». European Journal of Engineering Research and Science 4, n^o 5 (25 mai 2019) : 119–25. http://dx.doi.org/10.24018/ejers.2019.4.5.1341.

Texte intégral

Résumé :

The kinetics of water adsorption by a natural zeolite (clinoptilolite) sample has been investigated by high-frequency AC current intensity measurements. According to the achieved kinetic results, cations should play a relevant role in the clinoptilolite hydration, in fact most of adsorbed water stay in the cationic sites. The water molecules associate withcation one-by-one. In particular, the forced adsorption of water molecules in a wet atmosphere is a quite slow process, while water desorption in air or dry atmosphere is a spontaneous and fast process. The observed increase of cation mobility could be adequately explained by assuming an arrangement of water molecules between the cation and the negatively charged oxygens contained in the cationic site. Such molecular arrangement could increase the strength of both dipole-cation and hydrogen bond interactions.

Styles APA, Harvard, Vancouver, ISO, etc.

48

Carotenuto, Gianfranco. « Isothermal Kinetic Investigation of the Water-Cations Interaction in Natural Clinoptilolite ». European Journal of Engineering and Technology Research 4, n^o 5 (25 mai 2019) : 119–25. http://dx.doi.org/10.24018/ejeng.2019.4.5.1341.

Texte intégral

Résumé :

The kinetics of water adsorption by a natural zeolite (clinoptilolite) sample has been investigated by high-frequency AC current intensity measurements. According to the achieved kinetic results, cations should play a relevant role in the clinoptilolite hydration, in fact most of adsorbed water stay in the cationic sites. The water molecules associate withcation one-by-one. In particular, the forced adsorption of water molecules in a wet atmosphere is a quite slow process, while water desorption in air or dry atmosphere is a spontaneous and fast process. The observed increase of cation mobility could be adequately explained by assuming an arrangement of water molecules between the cation and the negatively charged oxygens contained in the cationic site. Such molecular arrangement could increase the strength of both dipole-cation and hydrogen bond interactions.

Styles APA, Harvard, Vancouver, ISO, etc.

49

Cebollada, Andrea, Alba Vellé et Pablo J. Sanz Miguel. « Hirshfeld and DFT analysis of the N-heterocyclic carbene proligand methylenebis(N-butylimidazolium) as the acetonitrile-solvated diiodide salt ». Acta Crystallographica Section C Structural Chemistry 72, n^o 6 (5 mai 2016) : 456–59. http://dx.doi.org/10.1107/s2053229616006781.

Texte intégral

Résumé :

N-Heterocyclic carbene (NHC) based systems are usually exploited in the exploration of catalytic mechanisms and processes in organocatalysis, and homo- and heterogeneous catalysis. However, their molecular structures have not received adequate attention. The NHC proligand methylenebis(N-butylimidazolium) has been synthesized as the acetonitrile solvate of the diiodide salt, C15H26N42+·2I−·CH3CN [1,1′-methylenebis(3-butylimidazolium) diiodide acetonitrile monosolvate], and fully characterized. An interesting cation–anion connection pattern has been identified in the crystal lattice, in which three iodide anions interact simultaneously with thecisoid-oriented cation. A Hirshfeld surface analysis reveals the predominance of hydrogen bonding over anion–π interactions. This particular arrangement is observed in different methylene-bridged bis(imidazolium) cations bearing chloride or bromide counter-anions. Density functional theory (DFT) calculations with acetonitrile as solvent reproduce the geometry of the title cation.

Styles APA, Harvard, Vancouver, ISO, etc.

50

Bally, Thomas, Stephan Matzinger, Leo Truttman, Matthew S. Platz, Atnaf Admasu, Fabian Gerson, Anton Arnold et Reto Schmidlin. « Diphenylcarbene cation : electronic and molecular structure ». Journal of the American Chemical Society 115, n^o 15 (juillet 1993) : 7007–8. http://dx.doi.org/10.1021/ja00068a082.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

Articles de revues sur le sujet « Molecular cation »

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres