An ab initio study of electronic spectra and excited-state properties of 7-azaindole in vapour phase and aqueous solution

The geometries of 7-azaindole (7AI), its tautomer (7AT), and 7AI–H₂O and 7AT–H₂O complexes were optimised in the ground state and some low-lying singlet excited states using the 3-21G basis set. Differences of total energies of the optimised ground and excited states and the vertical excitation energies of these systems were used to explain the observed electronic spectra. Effect of solvation of these systems in bulk water was studied using the polarized continuum model (PCM). The mode of binding of a water molecule in the S₂(n–π^*) excited state of 7AI was found to be quite different from those in its ground and π–π^* excited states. It is shown that crossing of the lowest two singlet excited-state potential surfaces S₁(π–π^*) and S₂(n–π^*) of 7AI occurs in the vapour phase under geometry relaxation while on interaction with water, the S₂(n–π^*) excited state is raised up appreciably going even above the S₃(π–π^*) excited state. Ground- and excited-state molecular electrostatic potential mapping was carried out, which led to valuable information regarding the nature of excited states of the above-mentioned systems.     

Structural Peculiarities of Dioxane Media in H/D Isotope Effects of Water Solvation at 288.15K-318.15K

Using the data of precision densimetry measurements for diluted solutions of H₂O and D₂O in 1,4-dioxane (1,4-DX) at 288.15 K-318.15 K we calculated the limiting partial molar volumes of the H/D isotopomers of water in dioxane and the excess molar volumes of the stated systems. The water molecules dispersed in 1,4-DX form complexes H-bonded into associates whose packing coefficient slightly exceeds that of the structural aggregates in liquid H₂O and D₂O. It is concluded that the structure of 1,4-DX is loosened and concomitantly undergoes volume expansion caused by the water microimpurities. The differentiating temperature effect on the volume solvation effects of H₂O and D₂O in 1,4-DX has been found.Original Russian Text Copyright © 2004 by. E. V. Ivanov, E. Yu. Lebedeva, and V. K. Abrosimov__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 852–861, September–October, 2004.     

Enthalpies of alkyl sulfonates in water,heavy water,and water-alcohol mixtures and the interaction of water with methylene groups

The heats of solution of the sodium n-alkyl sulfonates from methyl to octyl have been measured at 25°C in water, D₂O, and three alcohol-rich mixtures with water, all at solute concentrations low enough so that solute-solute interaction is negligible. Methylene-group contributions to the enthalpies of transfer are readily identified. Collation with the results of earlier studies of enthalpies of transfer leads to the conclusion that methylene-group enthalpies of transfer can be identified as follows: 0.87 kcal-mole^–1 for transfers to the gas phase from water and –0.035 kcal-mole^–1 for transfers to D₂O from H₂O, independent of the solute type provided only that methylene-group contributions can be identified in the data. Compared to other solvents, water is about as lipophilic as dimethylsulfoxide or a mixture of 27 moles of water with 73 moles of methanol. However, the range of the interactions between different groups on a given solute molecule seems to be much greater in water than in any of the other solvents studied, making it more difficult to identify group contributions to solvation in water. Another example of the complexity of the solvation of alkyl groups in water is encountered when one compares the solvation enthalpy of hexane in various solvents with some of the above results.     

DFT study on the intermolecular interactions between Aun (n = 2–4) and thymine

Density functional B3LYP method with 6-31++G** basis set is applied to optimize the geometries of the luteolin, water and luteolin–(H₂O)_n complexes. The vibrational frequencies are also studied at the same level to analyze these complexes. We obtained four steady luteolin–H₂O, nine steady luteolin–(H₂O)₂ and ten steady luteolin–(H₂O)₃, respectively. Theories of atoms in molecules (AIM) and natural bond orbital (NBO) are used to investigate the hydrogen bonds involved in all the systems. The interaction energies of all the complexes corrected by basis set superposition error, are within −13.7 to −82.5 kJ/mol. The strong hydrogen bonding mainly contribute to the interaction energies, Natural bond orbital analysis is performed to reveal the origin of the interaction. All calculations also indicate that there are strong hydrogen bonding interactions in luteolin–(H₂O)_n complexes. The OH stretching modes of complexes are red-shifted relative to those of the monomer.     

A molecular dynamics study on Rh3+ hydration: development and application of a first principles hydrated ion–water interaction potential

The Rh³⁺ aquaion exhibits one of the largest residence times of water molecules in the first hydration shell. The extreme stability of this hexahydrated ion in water solutions makes Rh³⁺ an extremely suitable candidate to be studied using the hydrated ion model. According to this approach, the representative cationic entity in aqueous solution is the ion plus its first hydration shell (i.e. the hydrated ion) and not the bare ion. Our group has successfully applied that concept in the framework of classical statistical simulations based on first principles ion–water interaction potentials. The methodology is now applied to the [Rh(H₂O)₆]³⁺ case based on a previous generalization in which some of the contributions were found to be transferable among the cases already studied (Cr³⁺, Al³⁺, Mg²⁺, Be²⁺). In this contribution a flexible hydrate model is presented, in which rigid first-shell water molecules have rotational and translational degrees of freedom, allowing for internal dynamics of the hydrated ion entity. The potential presented is thoroughly tested by means of a set of molecular dynamics simulations. Structural, dynamical, energetic and spectroscopic information is retrieved from the simulations, allowing the estimation of properties such as ion hydration energy, vibrational spectra of the intermolecular modes, cation mobility, rotational dynamics of the hydrated ion and first-shell water molecules and residence times of the second-shell water molecules. Extension of the Ewald sum to terms r^–4, r^–6 and r^–7 is presented and applied to systems of different size ([Rh(H₂O)₆]³⁺+(n–6)H₂O, n=50, 100, 200, 500, 1000 and 2500) and cutoff radii.Contribution to the Jacopo Tomasi Honorary Issue     

A New Predictive Equation for the Surface Tensions of Aqueous Mixed Ionic Solutions Conforming to the Linear Isopiestic Relation

The linear isopiestic relation has been used, together with the fundamental Butler equations, to establish a new simple predictive equation for the surface tensions of the mixed ionic solutions. This newly proposed equation can provide the surface tensions of multicomponent solutions using only the data of the corresponding binary subsystems of equal water activity. No binary interaction parameters are required. The predictive capability of the equation has been tested by comparing with the experimental data of the surface tensions for the systems HCl–LiCl–H₂O, HCl–NaClO₄–H₂O, HCl–CaCl₂–H₂O, HCl–SrCl₂–H₂O, HCl–BaCl₂–H₂O, LiCl–NaCl–H₂O, LiCl–KCl–H₂O, NaCl–KCl–H₂O, KNO₃–NH₄NO₃–H₂O, and LiCl–NaCl–KCl–H₂O at 298.15 K; KNO₃–NH₄Cl–H₂O, KBr–Sr(NO₃)₂–H₂O, NaNO₃–Sr(NO₃)₂–H₂O, NaNO₃ –(NH₄)₂SO₄–H₂O, KNO₃–Sr(NO₃)₂– H₂O, NH₄Cl–Sr(NO₃)₂–H₂O, NH₄Cl– (NH₄)₂SO₄–H₂O, KBr–KCl–H₂O, KBr–KCl–NH₄Cl–H₂O, KBr–KNO₃– Sr(NO₃)₂–H₂O, KBr–NH₄Cl–Sr(NO₃)₂–H₂O, KNO₃–NH₄Cl–Sr(NO₃)₂–H₂O, and NH₄Cl–(NH₄)₂SO₄–NaNO₃–H₂O at 291.15 K; and KBr–NaBr–H₂O at temperatures from 283.15 to 308.15 K. The agreement is generally quite good.     

Applcation of the Pitzer equations to the solubility of ternary aqueous nitrate solutions at 25°C

The solubilities of the ternary systems Cu(NO₃)₂–Ca(NO₃)₂–H₂O and Cu(NO₃)₂–Mg(NO₃)₂–H₂O at 25°C were calculated from the solubility data for the binary systems by using the Pitzer equations. The calculated solubility isotherms were confirmed experimentally. The activity coefficients of the components, the osmotic coefficient, and the activity of water were calculated from the experimental isotherms.     

Direct hydrogen-1, carbon-13, and nitrogen-15 NMR study of magnesium(II)-isothiocyanate complexing

A hydrogen-1, carbon-13, and nitrogen-15 NMR study of magnesium(II)-isothiocyanate complexation in aqueous mixtures has been completed. At temperatures low enough to slow proton and ligand exchange, separate¹H,¹³C, and¹⁵N NMR signals are observed for coordinated and bulk water molecules and anions. The¹H NMR spectra reveal signals for the hexahydrate and the mono-through triisothiocyanato complexes, as well as two small signals attributed to [Mg(H₂O)₅(OH)]¹⁺ and [Mg(H₂O)₄(OH)(NCS)]. Accurate hydration numbers were obtained from signal area integrations at each NCS^– concentration. In the¹⁵N NMR spectra, signals also were observed for the mono-through triisothiocyanato complexes, and a small signal believed to be due to [Mg(H₂O)₄(OH)(NCS)]. Coordination number contributions for NCS^– were measured from these spectra and when combined with the hydration numbers they totalled essentially six at each anion concentration. Signals for [Mg(H₂O)₅(NCS)]¹⁺ through [Mg(H₂O)₃(NCS)₃]^1– also were observed in the¹³C NMR spectra and the area evaluations were comparable to the¹⁵N NMR results. An analysis of the magnitude and sign of the coordinated NCS^– chemical shifts identified the nitrogen atom as the anion binding site. All spectra indicated [Mg(H₂O)₅(NCS)]¹⁺ and [Mg(H₂O)₄(NCS)₂] were the dominat isothiocyanato complexes over the entire range of anion concentrations. The inability to detect evidence for complexes higher than the triisothiocyanato reflects the competitive binding ability of water molecules and perhaps the decreased electrostatic interaction between NCS^– and negatively charged higher complexes.     

Hydrogen-Bonded Aggregates of Scandium(III) Complexes

The influence of the concentration of halide ions and concentration of an organic component (Solv) in solutions on the composition, coordination number, and structure of the scandium(III) complexes in solutions and in crystal is studied. The ⁴⁵Sc NMR data show that the main factor determining Cl^– coordination in the Sc³⁺–Cl^––H₂O–Solv systems is the Solv concentration. According to the X-ray diffraction analysis data, at the molar ratios of X^– : Sc³⁺ < 3 (X^– = Cl, Br), the [Sc(OH)(H₂O)₅]₂X₄ · 2H₂O salts with a coordination number of Sc 7 are isolated from solutions in H₂O and alcohols (coordination core is ScO₇ and X^– ions are not involved in coordination). Supramolecular H-bonded aggregates containing the ScCl₃(H₂O)₃ molecular complex with coordination number of Sc 6 and meridianal arrangement of analogous ligands are isolated from solutions with the Cl^– : Sc³⁺ molar ratios from 3 to 20 (in concentrated HCl) using macrocyclic molecules (1,4,7,10,13,16-hexaoxocyclooctadecane (18C6) and 1,4,10,13-tetraoxo-7,16-diazacyclooctadecane (DA18C6)).     

Untersuchungen an Kristallhydraten anorganischer Salze, 8. Mitt. Interpretation der Schwingungsspektren vonM(BF4)2·6H2O fürM=Fe2+, Co2+, Ni2+

The infrared and Raman spectra were recorded in the range 4000–160 cm^–1 forM(BF₄)₂·6 H₂O whereM=Fe²⁺, Co²⁺, Ni²⁺. The spectroscopic data support the X-ray structural data in showing that in the crystal hydrates studied two kinds of hydrogen bonds are present: H₂O...H₂O and OH₂... F₄B^–. The energies and molecular force constants (f _OH and fH₂O) andr _OH for OH₂...F₄B^– were calculated for the three crystal hydrates. It was found that the bond OH₂... F₄B^– is comparatively weak, with mean energy 3.7–3.3 kcal/mol. Two types of water molecule with different structures are existing as the first are participating in H₂O...H–O–H...F₄B^– and the second in BF₄ ^–...H–O–H...F₄B^–.     

An approach to the structure and spectra of copper barbiturate trihydrate

In the neutral title complex [Cu(C₄N₂H₃)₂(H₂O)₃] or [Cu(BBR)₂(H₂O)₃] (BBR^– = Barbiturate), the Cu^II ion, in the slightly distorted square-pyramidal geometry, is coordinated by two O atoms of the two monodentate barbiturates and three O atoms of three water ligands. The average bond length of Cu—O (BBR^–) is 1.981(5) Å and the average bond length of Cu—O (H₂O) at the basal sites is 1.94(5) Å, i.e. much shorter than that of Cu—O (H₂O) [2.175(11) Å]. The crystal structure is characterized by an extensive network of hydrogen bonds in which each [Cu(BBR)₂(H₂O)₃] entity links to six adjacent [Cu(BBR)₂(H₂O)₃] by O(C=O) ··· H—O(H₂O) bonds. Tautomerism in the coordination process for BBR^– was found from the crystal structure and i.r. spectral analysis. The interaction of Cu^II and BBR^– in aqueous solution was also investigated by electronic spectra and electrochemical method. It was observed that the copper ion could not only form the [Cu(BBR)₂(H₂O)₃] complex in aqueous but also catalyze the decomposition of BBR^– at pH 1.1.     

Thermodynamic properties of aqueous-organic systems with low water contents. 2. Limiting partial molar volumes of D2O and H2O intert-butyl alcohol and 1,4-dioxane at 288.15–318.15 K

The densities of dilute solutions of H₂O and D₂O in 1,4-dioxane and tert-BuOD have been measured in the interval 288.15–318.15 K with an error of 2·10^–6 g/cm³. The limiting partial molar volumes of D₂O and H₂O in 1,4-dioxane andtert-butanol have been determined by using an original procedure; the changes in the partial molar volume of water due to H-D substitution in the water molecules have been calculated. The analysis of the temperature dependence of the partial volumes of the components of the binary mixtures H₂O (D₂O) + 1,4-dioxane and H₂O (D₂O) +tert-BuOH (tert-BuOD) showed on the basis of Maxwell's crossing equations that the addition of small amounts of water significantly alters the structure of the unary organic solvent. In the presence of trace amounts of water the expansibility of 1,4-dioxane increases and that oftert-butanol decreases.For previous communication, see [1].Institute of the Chemistry of Nonaqueous Solutions, Russian Academy of Sciences, Ivanovo 153018. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 568–571, March, 1992.     

Computer Simulation of the Absorption of CO<Subscript>2</Subscript> Molecules by Water Cluster: 3. Dynamic and Dielectric Properties

Autocorrelation functions of translational and angular velocities of H₂O and CO₂ molecules in (CO₂)_i(H₂O)₁₀ clusters that are generated by the molecular dynamics method, as well as their frequency spectra, are calculated. Self-diffusion coefficients of molecules in clusters are determined. The IR spectra thus obtained and frequency-dependent dielectric permittivity of the clusters indicate the enhancement of absorption of Earth’ thermal radiation by these aggregates with an increase in the number of CO₂ molecules in the aggregates. Dielectric losses also increase with the i number.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 322–327.Original Russian Text Copyright © 2005 by Galashev, Rakhmanova, Chukanov.     

Strong interactions through the XAu–Y bridge: the Au bond?

The interaction between AuOH and the lone-pair donors (HF, H₂O) is shown to result in well-bound complexes whose structure resembles that of the corresponding H-bonded systems with the gold atom replacing hydrogen. The dissociation energies are estimated to be 10.7 and 27.4 kcal/mol for HFAu–OH and H₂OAu–OH, respectively. However, the interaction between AuOH and the lone pair donors is found to involve significant charge transfer. Furthermore, the Au–O stretching frequency increases upon the complex formation. It is concluded that, in spite of certain similarity to the H-bonded species, the Au-bonded complexes should be considered as Lewis acid–base pairs.     

Thermodynamic properties of water/organic systems with small contents of water 1. Limiting partial molal volumes of D2O and H2O in methanol and 2-propanol at various temperatures

Limiting partial molal volumes of D₂O and H₂O in methanol and 2-propanol have been measured in the temperature interval 278–318 K. A hypothesis is advanced regarding the formation of water-alcohol aggregates.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 317–320, February, 1991.     

Interrelation between Kinetics of the Hydrogen Ion Reduction on Iron and the Hydrogen Diffusion Flux into Carbon Steel in Acidic Solutions

Kinetic parameters of discharge of hydrogen ions, which depend on the nature of the slow stage in the Volmer–Tafel and Volmer–Heyrovský mechanisms, are obtained theoretically for commensurate rates of successive reactions on energetically-uniform and evenly-nonuniform surfaces. The results are compared with similar experimental parameters for the Armco iron in the system C₂H₄(OH)₂–H₂O + HCl. Upon adding 2–10 wt % H₂O into C₂H₄(OH)₂, the slow discharge stage gives way to the Tafel reaction if the hydrogen ion adsorption obeys the Temkin isotherm. Upon going to purely aqueous solutions, the discharge process becomes the limiting stage again. A change in the hydrogen diffusion flux through a steel membrane from these mixed solvents does not correlate with the nature of the stage that controls the cathodic reduction of hydrogen ions.     

Super-Molecular Interaction between Cl and H2O within the Restricted Space of Layered Double Hydroxides

A periodical interaction model of LDHs-Cl-yH₂O has been proposed. The geometry optimization and energy of the layered double hydroxides (LDHs) were calculated using CASTEP/LDA method at the CA-PZ level. The distribution of H₂O in the interlayer and the super-molecular interaction between host layer and guest anion have been investigated by analyzing the geometric parameters, charge population, energy, and density of state (DOS). The results showed that there was a strong super-molecular interaction between the host layer and the guest anion Cl⁻. In the system of LDHs-Cl-yH₂O, the interlayer distance increased gradually then tended to invariableness. And in the process of hydration of LDHs-Cl, hydrogen bonding was superior to electrostatic interaction, and layer-water type hydrogen bonding was a little stronger than anion-water type hydrogen bonding between H₂O and the rest of the structure. When y was 1 or 2, Cl⁻ and the plane of water were parallel to the layer; while y was 3 or 4, distribution of Cl⁻ and water was random. Moreover, the LDHs-Cl-yH₂O would change from ionic crystal to molecular crystal with the increase of number of water molecule. The hydration of LDHs-Cl would achieve a definite saturation state.     

Effect of temperature on the solubility of carnallite type double salts

A method based on Pitzer's model has been used for calculation of the solubilities of carnallite type double salts crystallizing in the systems MeX–MgX₂–H₂O (Me=Li, NH₄, K, Rb, Cs; X=Cl, Br). The solubility of congruently soluble double salts was also determined experimentally at 25–75°C. The results from studies of the solubility diagrams of ternary carnallite type water-salt systems over a wide temperature range are summarized. It is found that the width of the crystallization region for each of the salts can be explained by the relative differences in the solubilities of the ternary solution components (MeX, MgX₂·6H₂O and MeX·MgX₂·6H₂O) and by a change of temperature, and by the effect of temperature on the solubility. A method is proposed for calculating Pitzer's ternary parameters of interionic interaction (_MN and _MNX) on the basis of experimental data for the solubility in water of the double salts crystallizing in the corresponding ternary water-salt systems.     

Valence-bond studies of AH2 molecules

Minimal Slater basis set calculations are reported for H₂S. The calculations used both natural and hybrid atomic orbitals. The calculations were performed at H-S-H bond angles of 90 °, 92.2 ° and 95 °. The results are compared with similar calculations on H₂O and with calculations using the molecular orbital approximation. The only definite trend found in going from H₂O to H₂S is that the importance of the SH⁺H^– structure decreases. Changes in the relative importance of covalent and ionic structures depend upon which measure of importance is used. Calculations using a set of orthogonal hybrid orbitals again find the hybrid orbitals exhibiting non-perfect following behaviour with the hybrids remaining at about the equilibrium bond angle. Localized molecular orbitals were found to move in the opposite direction to the change in the H-S-H bond angle.     

Copper(II) Complexes of Spirohydantoins. Synthesis,Quantum-Chemical,and Spectroscopic Study

A series of new Cu(II) complexes with important physiologically active cycloalkane-5-spirohydantoines are synthesized reacting as a result of CuCl₂ · 2H₂O interaction with the ligands in alkaline water medium. Their structures were studied using spectroscopic (IR and EPR) methods. For comparison, ab initio calculations of the structure and IR spectra of the corresponding Cu(II) complexes were also performed. It was proven that with cyclopentane-5-spirohydantoins, distorted (flattened) tetrahedral structure is realized Cu(L_–H)₂(H₂O)₂, while with the higher cycloalkane-5-spirohydantoins linear Cu(II) complexes of the type CuL_–H(OH) are formed.