Phase and structure transformations in water microclusters

The behavior of 12- and 14-molecule water microclusters with ST2 potential in the range of 50–325 K is studied by the molecular dynamics method. Structure and phase transitions, including evaporation of molecules from the clusters and transition through the percolation threshold via hydrogen bonds, were found. Topological, temporal, and energy characteristics of the bond network are analyzed based on the dynamic criterion of hydrogen bonding. Institute of Thermal Physics, Ural Branch, Russian Academy of Sciences. Translated fromZhurmal Strukturnoi Khimii, Vol. 35, No. 1, pp. 64–70, January–February, 1994. Translated by L. Chernomorskaya     

Matrix method of conformational optimization. Application to cyclic and polyhedral water clusters

A matrix method for conformational optimization of quasi-one-dimensional molecular structures is suggested. The method is used to determine cyclic and polyhedral configurations of water clusters with the maximal number of stable trans-conformations of molecular pairs forming hydrogen bonds. Institute of Earth Cryosphere, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 107–115, January–February, 1996 Translated by L. Smolina     

Properties of the network of the hydrogen bonds of water

Networks of the hydrogen bonds and those consisting of lines connecting nearby molecules were constructed using configurations of water molecules obtained by the Monte-Carlo method. The concentrations of closed cycles of hydrogen bonds were established to be determined only by the probability of hydrogen bond formation. Characteristics of a model ideal water network were determined. Topological properties of the Polk model and those of the network of nearest neighbors substantially differ from the properties of the ideal network. The totality of the hydrogen bonds in pure water was proposed to be considered as a hierarchical system. Three topologically different structures of water associates were determined. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 928–931, May, 1997.     

Water clusters in supramolecular inclusion hydrates. Crystal structure of decaazatricyclo[28.2.2.213.16]tetratriacontane nanohydrate

Inclusion compounds of solvate water molecules in a crystal matrix are investigated by X-ray diffraction analysis of a macrocyclic polyamine decaazatricyclo[28.2.2.2^13.16]tetratriacontane nanohydrate (I). When included in a crystal, water molecules are bonded by water-water (O-H...O) and water—macrocycle (0-H...N and N-H...O) hydrogen bonds, forming a linear cluster. Translated fromZhurnal Strukturnoi Khimii, Vol. 40, No. 5, pp. 993–1001, September–October, 1999.     

Prediction of the vaporization enthalpy based on modified Randi? indices. I. Monohydric alcohols

The vaporization enthalpy of monohydric alcohols with different structures under normal conditions is calculated using a modified Randič method with an error comparable to the experimental one. The energy of hydrogen bonds in alcohols is determined and shown to be constant and independent on the alcohol structure. Original Russian Text Copyright ? 2009 by E. L. Krasnykh __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 3, pp. 577–581, May–June, 2009.     

Investigation of the structure of concentrated aqueous solution of LiCl at low temperatures by the method of integral equations

Peculiarities of the formation of the structure of aqueous LiCl solution (at a salt: water molar ratio of 1:5.3) in the temperature range 298-138 K were studied by the method of integral equations. Analysis of the results obtained suggests that transition of the system into the supercooled and glassy state is accompanied by an increase in the tetrahedral ordering of solvent molecules and a decrease in the number of interactions between the water molecules in unbound solvent. Lowering the temperature leads to an increase in the degree of structurization of water molecules surrounding the cation. Preferable formation of hydrogen bonds with the anion under extreme conditions was established. The glassy state of the solution is characterized by the absence of direct anion-cation correlations and increased (compared to standard conditions) probability of the formation of ion-water chains. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1881–1886, October, 1999.     

Novel type of mixed O–H···N/O–H···π hydrogen bonds: monohydrate of pyridine

Investigation of characteristics of hydrogen bonding between pyridine and water by MP2/aug-cc-pvdz method reveals that these two molecules may form three types of hydrogen bonds depending on nature of proton withdrawal site of pyridine. Change of orientation of water with respect to plane of aromatic ring leads to transformation of the O–H···N bond to O–H···π bond via wide region of the potential energy surface where both lone pair of the nitrogen atom and π-system make significant contribution into hydrogen bonding. Hydrogen bond in this intermediate region may be considered as mixed O–H···N/O–H···π bond representing new type of H bonds.     

Combination of ionic and metal-olefin bonds in crystalline copper(I) π-complexes

The ionic field effect on metal-olefin π-binding is considered for 24 Cu(I) compounds based on X-ray diffraction data. Structural features due to Cu…(C=C)−H…An and N−H…An bridges in cationic and zwitterionic π-complexes, respectively, are discussed. Parity of metal-olefin and hydrogen bonds in formation of these structures is shown. I. Franko Lvov State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 5, pp. 109–119, September–October, 1994. Translated by A. Arbuznikov     

Solvation Properties of Aliphatic Alcohol–Water and Fluorinated Alcohol–Water Solutions for Amide Molecules Studied by IR and NMR Techniques

Solvation properties of aliphatic alcohol–water and fluorinated alcohol–water solutions were probed by amide molecules as solutes using infrared (IR) and ¹H and ¹³C NMR techniques. These include four alcohols: ethanol (EtOH), 2-propanol (2-PrOH), 2,2,2-trifluoroethanol (TFE), and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and three amides: N-methylformamide (NMF), N-methylacetamide (NMA) and N-methylpropionamide (NMP). The hydrogen bonds of the amide carbonyl oxygen with water are gradually weakened as the alcohol content increases. This decreases in the order of HFIP > TFE ≈ 2-PrOH > EtOH. In TFE– and HFIP–water solutions, the hydrogen bond between the amide amino hydrogen and water is also gradually broken with increasing x _A. This trend is more notable in the order of NMP > NMA > NMF. The hydrophobic moieties of the amide methyl and ethyl groups are solvated by the fluoroalkyl groups of fluorinated alcohols due to the hydrophobic interaction among them. Thus, the steric hindrance generated by the solvated alkyl group of amides promotes the breaking of the hydrogen bonds between amide and water.     

Hydrogen bonds involving C-H groups of 1,1,2,2-tetrabromoethane and their effect on the conformation equilibrium

The solvent and polymer matrix effects on the conformation equilibrium in 1,1,2,2-tetrabromoethane (TBE) are investigated by IR spectroscopy. The free energy differences (ΔG₀) of TBE conformations correlate with the dielectric permittivity function of the medium. A pronounced solvent effect on the absolute integrated intensities of the IR bands arising from the C-H stretching vibrations indicates H-bonding between the C-H groups of TBE and the solvent. The enthalpies of specific interactions due to hydrogen bonding were estimated using the intensity rule (1–3 kcal/mole). The absence of correlations between ΔG₀ and the solvent basicity parameter leads us to conclude that the trans- and gosh-conformers of TBE form nearly equally strong hydrogen bonds. Kazan State University. Kazan State Technological University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 478–483, May–June, 1998. This work was supported by RFFR grant No. 96-03-32171a.     

Problems of unusual hydrogen bonds between proton donors and transition metal hydrides and borohydrides

The results of experimental and theoretical studies of intermolecular MH...HX and BH...HX hydrogen bonds with the hydride hydrogen atom acting as a proton accepting site are analyzed. Spectral (IR and NMR) criteria for their formation are presented. The spectral, structural, and thermodynamic characteristics of these unusual hydrogen bonds obey the regularities found for classical hydrogen bonds. It was shown that the MH...HX bonds participate in the proton transfer with the formation of nonclassical cationic hydrides and the |M(η²-H₂|⁺ hydrogen bonds are formed in low-polarity media. Problems arising in this new line of investigations are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 846–851, May, 1998.     

Quantum-chemical investigation of the mechanism of transfer of a hydrogen atom in the phenol(NH2) complex

A quantum-chemical investigation of the mechanism of H atom transfer in the phenol(NH₂) complex was undertaken by the unrestricted Hartree-Fock and CASSCF(7e/7o) methods in the 6-31G(d) basis set. Low-lying structures representing two types of hydrogen bonds (classical and so-called πH bonds) were found. On the basic potential energy surface the transfer of H is realized through the conformational maximum of the isomer with a OH...N hydrogen bond and includes three stages, i.e., approach of the N and O atoms, the actual transfer of H, and relaxation of the O...HN hydrogen bond. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol, 35, No. 6, pp 331–337, November–December, 1999.     

Hydrogen bonds and molecular complexes in solutions of cellulose nitrate

Intermolecular hydrogen bonds in the systems based on cellulose nitrate and a number of low-molecular solvents were studied by IR spectroscopy. The majority of the systems under study are characterized only by redistribution of intensities of the spectral bands corresponding to the pure polymer accompanied by their minor shift. In this case, acceptors of cellulose nitrate become sterically accessible for the redistribution of hydrogen bonds, and only an insignificant portion of them forms hydrogen bonds with a solvent. New spectral bands in the IR spectra were observed only for solutions containing diethyldiphenyl carbamide, suggesting the formation of a molecular complex. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 484–487, March, 1999.     

Structure effects of weak interactions in heterodesmicπ-complexes of copper(I)

Structural effects: disordering, twinning, polymorphism, and morphotropism due to substitution of halide atoms are considered using the results of X-ray diffraction analysis of 18 olefinic π-complexes of Cu(I). These effects are associated with the heterodesmic character of compounds, in particular, with weak interactions such as lengthened coordination bonds and hydrogen contacts. Ukrainian State Wood Technology Institute. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 1, pp. 98–107, January–February, 1998.     

Computational chemistry of the silicon nitride surface. 2. Binary hydroxylamine complexes. Geometry and bond energies

In order to study the silicon nitride surface it is interesting to consider hydrogen-bonded complexes with hydroxyl and amine key groups (OH...O, OH...N, NH...O, and NH...N). To investigate the behavior of the above bonds, we considered the water, ammonia, and hydroxylamine dimers and the binary hydroxylamine complexes with water and ammonia. The results of this work are compared with the data obtained by an ab initio method. Russian University of Peoples' Frienfship. Translated fromZhurnal Strukturnoi Khimii Vol. 37, No. 1, pp. 29–47, January–February, 1996. Translated by I. Izvekova     

Vibrational spectra and stereochemistry of mono-and polysaccharides. II. α-anomers of D-glucose and D-galactose. Glucitol and galactitol

The IR and Raman spectra of D-glucose and D-galactose α-anomers are compared with the corresponding spectra of the related polyatomic alcohols glucitol and galactitol. Experimental data on the frequencies and modes of normal vibrations and on the contributions of normal vibrations involving particular skeletal CiOi and CiC(i+1) bonds to the potential energy distribution (PED) are compared with the results of theoretical calculations. The α-anomers of D-glucose and D-galactose with different configurations of the C4C4 and C4H4 bonds are characterized by substantially different sets of frequencies with prevailing contributions to PED from the CiOi and CiC(i+1) bonds. The similar bonds of glucitol and galactitol are also characterized by specific frequency sets. Particular CiOi and CiC(i+1) bonds have different numbers of “localized” frequencies. B. I. Stepanov Institute of Physics, Belarus Academy of Sciences. V. Tshebyatovski Institute of Low Temperatures and Structural Studies, Polish Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 3, pp. 431–442, May–June, 1995. Translated by I. Izvekova     

Thermal decomposition of ammonium dinitramide and mechanism of anomalous decay of dinitramide salts

Thermal decomposition of ammonium dinitramide proceedsvia homolytic rupture of the N−NO₂ bond and partially by the proton transfer reaction. The monomolecular decay of the anion to N₂O and NO₃ ⁻ in the solid state at 60 °C occurs with higher rates than those in the melt. This is related to a change in the reactivity of the anion due to the violation of its symmetry on going to the solid state. The absence of hydrogen bonds between the anion and cations or water molecules is an additional condition for the fast decay. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 50–54, January, 1999.     

Structure and hydrogen bonding in polyhydrated complexes of guanine

Abstract Molecular structure of complexes of guanine with 12, 13, 16, and 17 water molecules were calculated using B3LYP/6-311G(d,p) level of theory. Interaction with water results in some deformation of geometrical parameters of guanine, which can be described as contribution of zwitter-ionic resonant form into the structure of DNA base. Saturation of water binding sites within guanine creates possibilities for the formation of the N···H–O hydrogen bond where the nitrogen atom of amino group acts as proton acceptor. The NBO analysis of guanine–water interactions reveals that hydrogen bonds involving the N(3) and N(7) atoms of guanine represent a case of mixed N···H–O/π···H–O hydrogen bonds where contribution of π-system into total energy of interaction varies from 3% to 41%. This contribution significantly depends on orientation of the hydrogen atom of water molecule with respect to plane of purine bicycle and influence of neighboring water molecules. Graphical Abstract      

Dehydration-induced changes in the vibrational states of dioptase Cu6Si6O18·6H2O

This paper reports on the results of temperature studies (20–880°C) of the IR absorption spectra of dioptase crystals in the range 50–4000 cm⁻¹. During the dehydration of dioptase the state of water changes as follows: (1) initial state, (2) intermediate state with damped external vibrations of H₂O, (3) isolated water molecules with new hydrogen bonds, (4) formation of hydroxyls. The bands of the external virations of H₂O (1) vanish in state (2) because of the formation of vacancies in the six-membered water rings. The frequencies of the translation vibrations of 6H₂O in initial dioptase are close to those in liquid water: 169–170 and 277–290 cm⁻¹. A factor-group analysis of the dioptase vibrations in the space group C _3i ² is performed. All IR active vibrations 23A_u+23E_u are described. The thirty five bands observed in the IR spectra are assigned. The dehydration-induced deformations of the silicate rings are determined from the shifts of the vibrational bands of Si₆O₁₈. Institute of Mineralogy and Petrography, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 68–74, January–February, 1996. Translated by I. Izvekova     

Conformational combinatorial analysis of polyhedral water clusters

A topological model of polyhedral water clusters that takes into account the conformational type of hydrogen bond is suggested. The polyhedral structures are classified according to the number of transand cis-conformations. The structural features of clusters with the maximal number of more stable trans-conformations are studied. Institute of Earth Cryosphere, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 98–106, January–February, 1996 Translated by L. Smolina