Molecular dynamics study of the cations,water molecules,and polymer chains in Nafion type membranes

The structure and dynamics of the hydrated cationic complexes in Nafion type membrane pores has been studied by the molecular dynamics approach. The mechanism of the cationic transport has been examined. The dependence of the cationic transport coefficients on temperature and the number of water molecules has been investigated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1233–1236, July, 1995.The present work was made possible in part by financial support of the International Science Foundation (Grant MPG000) and the Russian Foundation for Basic Research (Grant 93-03-4205).     

New triple-decker complexes prepared by the stacking reactions of cationic metallofragments with sandwich compounds

The results of our recent studies devoted to the synthesis of cationic triple-decker complexes are summarized. The stacking reactions of cationic metallofragments with sand-with compounds can be used as a general method for the synthesis of these complexes. This method was used for the preparation of 30- and 34-electron cationic triple-decker complexes containing cyclopentadienyl and pentaphospholyl ligands in the bridging position and carbocycles C _n H _n (n=4–7) and carboranes as terminal ligands. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1636–1642, September, 1999.     

Synthesis of sulfur-containing cationic lipids of the 1,3-dioxolane type

A series of cationic acetal lipids containing different spacer and cationic groups were synthesized starting from 1,2-O-hexadecylidene-3-thioglycerol. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1590–1592, August, 1998.     

Electrophilic substitution of thetert-butyl-NNO-azoxy group by the bromine atom

The electrophilic substitution of thetert-butyl-NNO-azoxy group by the bromine atom was observed for the first time when 6-bromo-2,4-bis(tert-butyl-NNO-azoxy)-5-chloro-1,3-phenylenediamine was treated with bromine in AcOH. The structural factors promoting this reaction are discussed. The direction of the replacement was confirmed by PM3 calculations of the heats of formation of intermediate cationic σ-adducts. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2131–2134, November, 1999.     

Photoconductive organic materials for the near-IR radiation range

Polymer composition films based on polystyrene and containing electron donors, viz., substituted tetrathiafulvalenes, an electron acceptor, viz., 2,4,5,7-tetranitrofluoren-9-one, and sensitizers, viz., a cationic polymethine dye, 1,3,3-trimethyl-2-[3-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)prop-1-en-1-yl]-3H-indolium tetrafluoroborate, and a neutral merocyanine dye, 5-{3-[(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)ethylidene]-2-phenyl-cyclopent-1-en-1-ylmethylene}-2-thioxodihydropyrimidine-4,6(1H,5H)-dione, were prepared. The internal photo effect upon film irradiation in the near-IR range is provided by low ionization potentials of the donors and the high electron affinity of the acceptor. The photoconductivity increases upon replacement of a cationic dye by a neutral one, mainly because of photogeneration of mobile charge carriers of both signs and a decrease in the activation energy for the photoconduction current. The decrease in the activation energy for the photocurrent is due to the fact that in the case of a neutral dye, the mobile charge carriers move away from each other during their separation, while in the case of a cationic dye, the colorless counterion strongly holds the photo generated charge carrier.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1611–1617, August, 2004.     

Thermodynamics and selectivity of complexation of lithium and sodium thiocyanates with phosphorus-containing podands and compounds modeling the terminal groups of these podands

A series of model compounds and heptadentate neutral phosphorus-containing podands that differ in the conformational rigidity of the terminal groups and in the coordination properties of the phosphoryl groups were synthesized. The thermodynamic parameters of complexation and the cationic selectivity of organophosphorus compounds and podands with respect to LiNCS and NaNCS were studied by calorimetric titration in acetonitrile at 298 K. The reasons for the high selectivity of certain phosphorus-containing podands to the Li⁺ cation are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1581–1587, September, 1994.This work was financially supported by the Russian Foundation for Basic Research (Grant No. 94-03-08848) and the International Science Foundation (Grant No. MTH000).     

Cationic polymerization of hydrocarbon monomers induced by complexes of acyl halides with Lewis acids 6. The effect of 2,6-dimethylpyridine on the polymerization of isobutylene

The effect of 2,6-dimethylpyridine on the cationic polymerization of isobutylene inn-hexane and dichloromethane at -78 °C under the action of complexes of acetyl bromide with AlBr₃ of the compositions 1 : 1 and 1 : 2 was investigated. 2,6-Dimethylpyridine significantly depresses the initiation and chain transfer processes involving free protons and also retards the proton elimination from growing carbocations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1180–1183, May, 1996.     

Structure and Reactivity of the 1,10-Phenanthroline Complex with Nitrenium Cation

According to the X-ray diffraction data, the cationic fragment in 1-amino-1,10-phenanthrolinium mesitylenesulfonate is a unidentate n-complex whose asymmetric structure is retained in solution. Quantum-chemical calculations by the AM1 method and ab initio (6-31G, 6-31G*, MP2/6-31G) give geometric parameters of the cation, which are similar to those determined experimentally. No dynamic processes involving intra- or intermolecular transfer of the NH2 group was observed up to 100°C by NMR spectroscopy. 1-Amino-1,10-phenanthrolinium cation does not react with 4-methylpyridine and 4-methyl-1,10-phenan-throline with transfer of the amino group, and it fails to react with mesitylene and anthracene at elevated temperature.     

The effect of the nature of the head group on the micellar effects of functional/cationic co-micelles in acyl transfer reactions

The reactivity of co-micelles of functional/cationic surfactants [functional surfactants-1-cetyl-3-(2-hydroxyiminopropyl)-, 1-cetyl-3-(2-amino-2-hydroxyiminoethyl)-, and 1-cetyl-3-(2-hydroxyaminoethyl-2-onyl)imidazolium chlorides, cationic surfactants-1-cetyl-3-methylimidazolium and cetyltrimethyl-ammonium chlorides] toward the 4-nitrophenyl esters of diethylphosphoric, diethylphosphonic, and toluenesulfonic acids was investigated. It was shown that the nucleophilicity of the functional groups in the surfactant does not undergo substantial changes with variation in the nature of the head group of the cationic surfactant and the fraction of functional detergent in the co-micelle. This makes it possible to create systems that decompose organophosphorus substrates unusually quickly even with small contents of the functional surfactant. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 1, pp. 30–37, January–February, 2007.     

Nature of the 5-norbornen-2-yl Cation Intermediate in the acetolysis of 2-deuterio-endo-5-norbornen-2-yl brosylate

Mass spectrometrical and ¹H-NMR.-analyses of the exo-5-norbornen-2-yl acetate, formed by acetolysis of endo-5-norbornen-2-yl-2-exo-d brosylate, demonstrate that the deuterium initially on C(2) migrates partially (30%) onto C(1) (mechanism Ia or Ib). No deuterium could be detected on the other positions, which shows that C(1–7) migration is insignificant. ¹³C-NMR.-analysis of the deuteriated nortricyclyl acetate obtained as main product shows that the deuterium is equally and uniquely distributed between positions C(1) and C(6). This indicates that the nortricyclyl derivatives do not arise from nucleophilic attack on C(5) of asymmetrical norbornenyl intermediates, but from the reaction of a symmetrical nortricyclyl cation intermediate with solvent (mechanism Ib). Since the pioneering work of Roberts [1] and Winstein [2] on the solvolysis of exo- and endo-5-norbornen-2-yl derivatives 1-X and 2-X many papers have dealt with the cationic intermediate, the nature of which has still not been established satisfactorily [3]. We discuss briefly the main features of this homoallylic system and present experimental results that allow, for the first time, a clear distinction between five possible mechanisms Ia, Ib, II, III and IV of the degenerate rearrangement of the cationic intermediate formed in the acetolysis of the endo-5-norbornen-2-yl brosylate.     

The catalytic effect of the cationic surfactant-polyethylene imine-water system in the hydrolysis ofO-alkylO-p-nitrophenyl chloromethylphosphonates

The kinetics of the hydrolysis ofO-alkylO-p-nitrophenyl chloromethylphosphonates in the cationic surfactant—polyethylene imine—water system was studied. The catalytic effects of the nature of the surfactant and substrate and the surfactant—polyethylene imine ratio were found. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1510–1514, September, 2000.     

Physicochemical features of the formation of siliceous porous mesophases

The formation of mesoporous mesophase materialsvia precipitation of soluble SiO₂ forms on the surface of cationic cetyltrimethylammonium micelles was studied. The main physicochemical factors determining the formation of siliceous mesoporous materials and providing an explanation of the observed changes in the structural and textural characteristics of the materials were identified and discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1845–1851, October, 1999.     

Synthesis of (±)-4-alkanolides from pent-4-enoic acid

Synthesis of (±)-4-hexanolide, (±)-4-nonanolide, and (±)-4-dodecanolide, racemic forms of the insect signal substances, has been accomplished by cationic cyclization of pent-4-enoic acid and its amide in the key step. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 644–646, March, 2008.     

Asymmetric Hydrogenation of Cationic Intermediates for the Synthesis of Chiral N,O-Acetals

For over half a century, transition-metal-catalyzed homogeneous hydrogenation has been mainly focused on neutral and readily prepared unsaturated substrates. Although the addition of molecular hydrogen to C=C, C=N, and C=O bonds represents a well-studied paradigm, the asymmetric hydrogenation of cationic species remains an underdeveloped area. In this study, we were seeking a breakthrough in asymmetric hydrogenation, with cationic intermediates as targets, and thereby anticipating applying this powerful tool to the construction of challenging chiral molecules. Under acidic conditions, both N- or O-acetylsalicylamides underwent cyclization to generate cationic intermediates, which were subsequently reduced by an iridium or rhodium hydride complex. The resulting N,O-acetals were synthesized with remarkably high enantioselectivity. This catalytic strategy exhibited high efficiency (turnover number of up to 4400) and high chemoselectivity. Mechanistic studies supported the hypothesis that a cationic intermediate was formed in situ and hydrogenated afterwards. A catalytic cycle has been proposed with hydride transfer from the iridium complex to the cationic sp² carbon atom being the rate-determining step. A steric map of the catalyst has been created to illustrate the chiral environment, and a quantitative structure–selectivity relationship analysis showed how enantiomeric induction was achieved in this chemical transformation.     

Cationic amphiphiles of both lipid and nonlipid nature in gene therapy

The synthesis and biological activity of cationic lipids and cationic amphiphiles of different natures are considered. The general factors influencing the transfection efficiency are identified and summarized for various classes of compounds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 385–400, March. 2000.     

Interaction of chromophores in dissimilar associates of cationic and anionic polymethine dyes in water

A strong interaction between chromophores of cationic and anionic components was found based on the analysis of electronic absorption spectra of aqueous solutions of mixtures of cationic indopolycarbocyanines with anionic cyanines. Strong dissimilar 1∶1 associates are formed. Association constants were estimated spectrophotometrically. The main factors determining the degree of interaction of chromophores were revealed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 950–955, May, 1997.     

Interactions of monomeric and dimeric cationic surfactants with anionic polyelectrolytes: a fluorescence study

The interactions of conventional cationic, i.e. dodecyl-(DTAB), tetradecyl-(TTAB), and hexadecyltrimethylammonium bromides (HTAB), and dimeric cationic surfactants, i.e. dimethylene bis decyl-(10-2-10), and dodecyldimethylammonium bromides (12-2-12) with anionic polyelectrolytes, were studied by fluorescence measurements. The variation of I₁/I₃ ratio of the fluorescence of pyrene in aqueous solutions of polyelectrolytes was measured as a function of surfactant concentration. A three-step aggregation process involving the critical aggregation concentration (cac) and critical micelle concentration (cmc) was observed in each case. The cationic surfactants with lower hydrophobicity demonstrated higher degree of binding and vice versa.     

Chemistry of natural compounds and bioorganic chemistry

The racemic form of the metabolite of theDysidea sea sponge, furanoterpenoid pallescensin A, was synthesized by cationic cyclization of the sulfonyl-substituted linear sesquiterpene precursors. Deceased. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2060–2064, November, 1997.     

The characteristic fragment ions and visualization of cationic starches on pulp fiber using ToF‐SIMS

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was used to investigate the distribution of cationic starch on pulp fiber. To identify the characteristic fragment ions of the cationic starches, deuterium‐labeled cationic starches were prepared and analyzed using ToF‐SIMS. The starch 2‐hydroxypropyltrimethylammonium chloride derivative generated characteristic fragments at m/z 58 and 59, which were identified as [H₂C?N(CH₃)₂]⁺ and [N(CH₃)₃]^+·, respectively. The fragmentation patterns were also suggested. From the imaging analysis, the adsorption of the cationic starch on fibers was uneven on individual fibers, as well as between fibers. This may have been on account of fiber morphology and structure. On examining scanning electron microscope (SEM) images, the quaternary ammonium starch derivative (QS) did not penetrate the fiber. No migration of cationic starch was observed under various drying conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

Theoretical study on the structure and property relationship of the cationic conjugated polyelectrolytes

A theoretical study using density functional theory was performed to understand the structure/property relationship of the cationic conjugated polyelectrolytes, poly[9,9-bis-(6′-N,N,N-trimethylammonium) hexyl] fluorene-alt-4,7-(2,1,3-benzothiadiazole)] (PFBT-X, where X = Br). The torsion angle between the fluorene and benzothiadiazole units in the PFBT monomer was found to substantially affect the structural and electronic properties of the cationic PFBT monomer. The changes of geometrical parameter, HOMO and LUMO energy levels, and band gap, as well as the absorption maximum are discussed in terms of the torsion in the PFBT monomer structure. For comparison, its neutral analogue, the monomer of poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) was also studied. The length of conjugation backbone was also examined.