Theoretical Study of the Interactions between Isolated <Emphasis Type="Italic">DNA</Emphasis> Bases and Various Groups IA and IIA Metal Ions by <Emphasis Type="Italic">Ab Initio</Emphasis> Calculations

Summary. Interactions of the DNA bases adenine (A), guanine (G), cytosine (C), and thymine (T) with various metal ions (M) of groups IA and IIA of the periodic table of the elements were studied at the HF, MP2, and DFT levels of theory. The structures and thermodynamic stabilities of these species were studied at the gas phase. The calculations uphold that there exist two active sites in G and one in A, C, and T. The calculations also show that the O² atom in T is a more active site for metal ion bindings than that in C. The stability energies for G … M complexes are larger than those for A … M complexes and the stability energies for T … M complexes are larger than those for C … M complexes. As z/r ratio for the metal ion increases, the interaction energy for the complex increases systematically. Thermodynamic quantities such as ΔH, ΔG, ΔS, and ln K were determined for each complexation reaction, [Base+M ⁿ⁺ →(Base … M) ⁿ⁺]. A, G, and C complexation reactions except for C … Rb⁺ are exothermic. The situation is quite different for T complexation reactions and all except for T … Be²⁺ and T … Mg²⁺ are endothermic.     

Topological structures of tetrahedral (Td and T) fullerenes with hexagonal and triangular faces and their vibration and NMR spectra

On analyzing the topological structures of the three types of tetrahedral fullerenes (which consist only of triangles and hexagons), (1) C _n (T _d ,n=12h ²; h=1,2,…), (2) C _n (T _d ,n=4h ²;h=1,2,…), and (3) C _n (T,n=4(h ²+hk+k ²);h>k,h,k=1,2,…), we have obtained theoretically the Infrared and Raman active modes by means of the derived formulas for the decomposition of their nuclear motions into irreducible representations, and the ¹³C NMR spectra with natural abundance for ¹³C by using the distribution functions for all of the tetrahedral (T _d and T) fullerenes, respectively. Received: 25 May 1998 / Accepted: 30 July 1998 / Published online: 23 November 1998     

Dependence of the energy of surface-active substances/metal interaction on their ionization potentials. Evaluation of hydrophilicity of metal

The function Δ(ΔG _A ⁰), which is the difference of Gibbs energies characterizing surface-active substance (surfactant, SAS) adsorption at metal/solution and air/solution surfaces, has been introduced. The equation connecting the function Δ(ΔG _A ⁰) with SAS ionization potential has been obtained using the elementary theory of donor-acceptor interactions. Published experimental data on SAS adsorption at mercury, bismuth and gold have been used for Δ(ΔG _A ⁰) calculation. The dependence of Δ(ΔG _A ⁰) on ionization potentials can be described by an equation derived in this work. It has been demonstrated that the value of the hydrophilicity of gold is much higher than the values for mercury and bismuth. The lifetime of SAS molecules at a metal surface has been estimated. The question of the possibility of theoretica l estimation of standard energies ΔG _A ⁰ characterizing SAS adsorption at a metal/solution surface has been discussed. Received: 9 December 1996 / Accepted: 13 January 1997     

A Conductometric Study of Complexation Reactions Between Dibenzo-18-Crown-6 (DB18C6) with Cu2+, Zn2+, Tl+ and Cd2+ Metal Cations in Dimethylsulfoxide–Ethylacetate Binary Mixtures

The complex formation between Cu²⁺, Zn²⁺, Tl⁺ and Cd²⁺ metal cations with macrocyclic ligand, dibenzo- 18-crown-6 (DB18C6) was studied in dimethylsulfoxide (DMSO)–ethylacetate (EtOAc) binary systems at different temperatures using conductometric method. In all cases, DB18C6 forms 1:1 complexes with these metal cations. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program, Genplot. The non-linear behaviour which was observed for variations of log K _f of the complexes versus the composition of the mixed solvent was discussed in terms of changing the chemical and physical properties of the constituent solvents when they mix with one another and, therefore, changing the solvation capacities of the metal cations, crown ether molecules and even the resulting complexes with changing the mixed solvent composition. The results show that the selectivity order of DB18C6 for the metal cations in pure ethylacetate and pure dimethylsulfoxide is: Tl⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺ but the selectivity order is changed with the composition of the mixed solvents. The values of enthalpy changes (ΔH°_C) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in standard enthalpy (ΔS°_C) were calculated from the relationship: ΔG°_C,298.15=ΔH°_C − 298.15 ΔS°_C. The obtained results show that in most cases, the complexes are enthalpy stabilized, but entropy destabilized and the values of ΔH°_C and ΔS°_C depend strongly on the nature of the medium.     

Anion-molecular interaction through CH3 groups: Model ab initio studies

3-21G, 6–31G and 6–31 +G calculations have been performed on Cr…H₃CCl and LiCl…H₃CCl complexes with two different configurations each. Optimized geometries, stabilization energies, CH force constants and harmonic vibrational frequencies for CH₃Cl and its complexes are reported. Comparison of the calculated frequency shifts of CH-stretching bands of CH₃C1, on complexation, with experimental results of related systems indicate that the interaction of Cl^- with CH₃ group takes place in a linear manner with the CH bond. A lower frequency shift for LiCl…H₃CX with reference to the C1^-…H₃CX complexes is explained on the basis of the reduction of the basicity of Cl^- ion in the presence of counter ion in the former complex considered.     

Thermodynamic characteristics of hydrated acrylamide and polyacrylamide complexes of cobalt nitrate at <Emphasis Type="Italic">T</Emphasis> → 0 to 380 K

The temperature dependences of the heat capacities of hydrated acrylamide and poly(acrylamide) complexes of cobalt nitrate are studied via high-precision adiabatic calorimetry at 6 to 300–380 K. The energy of combustion is estimated via isothermic calorimetry. This evidence makes it possible to calculate thermodynamic functions C _p ^ℴ(T), H ^ℴ(T) − H ^ℴ(0), S ^ℴ(T), G ^ℴ(T) − H ^ℴ(0) at 0 to 300–380 K; the standard enthalpy of combustion, ΔcH ^ℴ; and the thermodynamic parameters of formation, Δ _f H ^ℴ, Δ _f S ^ℴ, and Δ _f G ^ℴ, of monomer and polymer complexes composed of simple compounds at 298.15 K. The results are used for the estimation of enthalpy Δ_pol H ^ℴ, entropy Δ_pol S ^ℴ, and Gibbs function Δ_pol G ^ℴ of bulk polymerization for hydrated acrylamide complexes of cobalt nitrate at 0–300 K.     

Discussion on complexation reactions between dicyclohexyl-18-crown-6 (DCH18C6) with Na+, K+, Cs+, Rb+, and Tl+ metal cations in acetonitrile-water binary mixtures

The complex formation between Na⁺, K⁺, Cs⁺, Rb⁺ and Tl⁺ metal cations with macrocyclic ligand, dicyclohexyl-18-crown-6 (DCH18C6) was studied in acetonitrile-water (AN-H₂O) binary systems at different temperatures using conductometric method. DCH18C6 forms 1:1 complexes with these metal cations. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program Genplot. The results show that the selectivity order of DCH18C6 for the metal cations in acetonitrile-water mixtures (AN = 25.3 and 50.4 mol %) is: Tl⁺ > K⁺ > Rb⁺ > Cs⁺ > Na⁺. A non-linear behaviour was observed between the log K _f of the complexes versus the composition of the mixed solvent which it related to changes of acidity, basicity, polarity and also polarizability of AN-H₂O mixtures with the composition of this binary solution. The values of standard enthalpy changes (ΔH _s⁰) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in the standard entropy (ΔS _s⁰) were calculated from the relationship: ΔG _s,298.15⁰ = ΔH _s⁰ − 298.15ΔS _s⁰. The obtained results show that in most cases, the complexes are enthalpy stabilized but entropy destabilized. Original Russian Text ? M.H. Soorgi, G.H. Rounaghi, M.S. Kazemi, 2008, published in Zhurnal Obshchei Khimii, 2008, vol. 78, No. 10, pp. 1627–1632.     

Solubility and Ionic Processes in the Cu X 2? MX ?H2O ( X ?=Cl?, Br?; M +=Li+, Na+, K+, NH4+, Cs+) Systems

 Solubility isotherms in the CuBr₂−MBr−H₂O (M ⁺ = Li⁺, Na⁺, Cs⁺) systems at 298.15 K were measured. The results together with other available literature data for copper chloride and bromide systems were treated by hydration analysis, and comparative discussion of ionic processes taking place in the respective saturated solutions was performed.     

Molecular modeling of hydration properties of hydrophobic ions Li<Superscript>+</Superscript>@C<Subscript>60</Subscript> and K<Superscript>+</Superscript>@C<Subscript>60</Subscript>

The Gibbs free energies of solvation (ΔG _s) and the electronic structures of endohedral metallofullerenes M⁺@C₆₀ (M⁺= Li⁺, K⁺) were calculated within the framework of the density functional theory and the polarizable continuum model. In water environment, the equilibrium position of K⁺ is at the center of the fullerene cavity whereas that of Li⁺ is shifted by 0.14 nm toward the fullerene cage. The Li⁺ cation is stabilized by interactions with both the fullerene and solvent. The equilibrium structures of both endohedral metallofullerenes are characterized by very close ΔG _s values. In particular, the calculated ΔG _s values for K⁺@C₆₀ are in the range from −124 to −149 kJ mol⁻¹ depending on the basis set and on the type of the density functional. Molecular dynamics simulations (TIP3P H₂O, OPLS force field, water sphere of radius 1.9 nm) showed that the radial distribution functions of water density around C₆₀ and M⁺@C₆₀ are very similar, whereas orientations of water dipoles around the endohedral metallofullerenes resemble the hydration pattern of isolated metal ions.     

Solubility and Ionic Processes in the Cu X 2? MX ?H2O ( X ?=Cl?, Br?; M +=Li+, Na+, K+, NH4+, Cs+) Systems

Summary.  Solubility isotherms in the CuBr₂−MBr−H₂O (M ⁺ = Li⁺, Na⁺, Cs⁺) systems at 298.15 K were measured. The results together with other available literature data for copper chloride and bromide systems were treated by hydration analysis, and comparative discussion of ionic processes taking place in the respective saturated solutions was performed. Corresponding author. E-mail: jitka@prfdec.natur.cuni.cz Received August 6, 2002; accepted (revised) November 29, 2002 Published online April 3, 2003     

Excess Molar Volumes,Viscosities and Speeds of Sound of the Ternary Mixture 1-Heptanol (1) + Tetrachloroethylene (2) + Methylcyclohexane (3) at 298.15 K

Densities (ρ), viscosities (η) and speeds of sound (u) of the ternary mixture (1-heptanol + tetrachloroethylene + methylcyclohexane) and the corresponding binary mixtures (1-heptanol + tetrachloroethylene), (1-heptanol + methylcyclohexane) and (tetrachloroethylene + methylcyclohexane) at 298.15 K were measured over the whole composition range. The data obtained are used to calculate the excess molar volumes (V ^E), excess isobaric thermal expansivities (α ^E), viscosity deviations (Δη), excess Gibbs energies of activation of viscous flow (ΔG ^*E) and excess isentropic compressibilities (κ _S ^E) of the binary and ternary mixtures. The data from the binary systems were fitted by the Redlich–Kister equation whereas the best correlation method for the ternary system was found using the Nagata equation. Viscosities, speeds of sound and isentropic compressibilities of the binary and ternary mixtures have been correlated by means of several empirical and semi-empirical equations. The best correlation method for viscosities of binary systems is found using the Iulan et al. equation and for the ternary system using the Heric and McAllister equations. The best correlation method for the speeds of sound and isentropic compressibilities of the binary system (1-heptanol + methylcyclohexane) is found using IMR (Van Deal ideal mixing relation) and for the binary system (tetrachloroethylene + methylcyclohexane) it is found using the NR (Nomoto relation) and for the binary system (1-heptanol + tetrachloroethylene) and the ternary system (1-heptanol + trichloroethylene + methylcyclohexane) it is obtained from the FLT (Jacobson free length theory).     

The effect of CH<Subscript>3</Subscript>, F and NO<Subscript>2</Subscript> substituents on the individual hydrogen bond energies in the adenine–thymine and guanine–cytosine base pairs

The substituent effects on the geometrical parameters and the individual hydrogen bond (HB) energies of base pairs such as X–adenine–thymine (X–A–T), X–thymine–adenine (X–T–A), X–guanine–cytosine (X–G–C), and X–cytosine–guanine (X–C–G) have been studied by the quantum mechanical calculations at the B3LYP and MP2 levels with the 6–311++G(d,p) basis set. The electron withdrawing (EW) substituents (F and NO₂) increase the total binding energy (ΔE) of X–G–C derivatives and the electron donating (ED) substituent (CH₃) decreases it when they are introduced in the 8 and 9 positions of G. The effects of substituents are reversed when they are located in the 1, 5, and 6 positions of C, with exception of CH₃ in the 1 position and F in the 5 position, which in both cases the ΔE value decreases negligibly small. With minor exceptions (X=8–CH₃, 8–F, and 9–NO₂), both ED and EW substituents increase slightly the ΔE values of X–A–T derivatives. The individual HB energies (∆E _HBs) have been estimated using electron densities that calculated at the hydrogen bond critical points (HBCPs) by the atoms in molecules (AIM) method. Most of changes of individual HBs are in consistent with the ED/EW nature of substituents and the role of atoms entered H-bonding. The remarkable change is observed for NO₂ substituted derivative in each case.     

Thermodynamics of phenylated polyphenylene between 0 and 340 K

In an adiabatic vacuum calorimeter, the temperature dependence of the heat capacity C _p of phenylated polyphenylene and initial comonomer 1,4-bis(2,4,5-triphenylcyclopentadienone-3-yl)benzene was studied between 6 and 340 K with an uncertainty of about 0.2%. In a calorimeter with a static bomb and an isothermal shield their energies of combustion DUcomb were measured. From the experimental data, the thermodynamic functions C _p ⁰ (T), H ⁰(T)-H ⁰(0), S ⁰(T)-S⁰(0), G ⁰(T)-H ⁰(0) were calculated from 0 to 340 K, and standard enthalpies of combustion ΔH _comb ⁰ and thermodynamic parameters of formation-enthalpies ΔH _f ⁰, entropies ΔH _f ⁰, Gibbs functions ΔG _f ⁰ - of the substances studied were estimated at T=298.15 K at standard pressure. The results were used to calculate the thermodynamic characteristics (ΔH _f ⁰ ,ΔS _f ⁰, ΔG _f ⁰) of phenylated polyphenylene synthesis in the range from 0 to 340 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solvent Effect on Deprotonation Equilibria of Acids of Various Charge Types in Non-aqueous Isodielectric Mixtures of Protic Ethylene Glycol and Dipolar Aprotic N,N-Dimethylformamide at 298.15 K

Deprotonation constants of phthalic (H₂A) and biphthalic (HA⁻) acids and of mono-protonated (BH⁺) and di-protonated (BH₂²⁺) piperazine acids have been determined at 25 °C by measuring the Emf of galvanic cells comprising H⁺-sensitive glass GE(H⁺) and Ag,AgCl electrodes in non-aqueous isodielectric mixtures of protic ethylene glycol (EG) and dipolar aprotic N,N-dimethylformamide (DMF). Solvent effects on deprotonation of the acids: ∂(ΔG _diss^o)=2.303RT[p(_s K _a)−p(_R K _a)], have been dissected into transfer Gibbs energies, ΔG _t^o _, of the species involved by evaluating ΔG _t^o of the uncharged phthalic acid and base piperazine (B) from the measured solubilities of the acid and base, respectively, and using ΔG _t^o of H⁺ based on the TATB reference electrolyte assumptions, as evaluated earlier. The contributions of the different species involved in the protolytic equilibria i.e., H⁺,H₂A,HA⁻,BH₂²⁺ and BH⁺ and their respective conjugate bases HA⁻,A²⁻,BH⁺ and B have been discussed in terms of their solvation behavior as guided by the ‘acid-base’, dispersion, structural and electronic characteristics of the acid-base species and of the co-solvent molecules and binary mixtures, ignoring the Born-type electrostatic interactions on the ionic species as the solvent system is quasi isodielectric.     

Conductometric and microcalorimetric analysis of the alkaline-earth/alkali-metal ion exchange onto polyacrylic acid

The specificity of the exchange between divalent (Di²⁺ = Ca²⁺ or Ba²⁺) and monovalent (M⁺ = Li⁺, Na⁺ or K⁺) ions onto a polyacrylic chain is examined using conductometric and microcalorimetric techniques. Assuming the formation of a bidentate complex between the Di²⁺ and the carboxylate groups, the conductometric data give the exchange ratio (Di²⁺/M⁺) and the speciation of the acrylic groups. No significant difference is observed between the three alkali-metal ions for a given Di²⁺ ion. Comparisons between Ca²⁺ and Ba²⁺ show a stronger hydrophobicity of the former as it precipitates at a complexation ratio r = 0.33 versus r = 0.45 for the Ba²⁺ salt. Microcalorimetric data show that all Di²⁺/M⁺ exchange energies are positive and depend significantly on the type of cations. The largest displacement energy (the more positive) is found for the binding of Ca²⁺ with sodium polyacrylate (8.13 kJ · mol⁻¹) and the smallest for Ba²⁺ with lithium polyacrylate (1.88 kJ · mol⁻¹). The interpretation of the data leads to the conclusion that specificity of the Di²⁺ binding originates in the dehydration phenomenon and specificity between the three alkali-metal ions is due to the decrease in the electrostatic bond strength with an increase in the ionic radii. The Di²⁺/M⁺ exchange is entropically driven. Received: 28 January 1999 Accepted in revised form: 7 April 1999     

An ab initio Molecular Orbital Study of the Conformational Properties of all-( Z )-Cyclododeca-1,4,7,10-tetraene

 Ab initio HF/6-31G^* and MP2/6-31G^*//HF/6-31G^* methods were used to calculate the structure optimization and conformational interconversion pathways for all-(Z )-cyclododeca-1,4,7,10-tetraene. This compound adopts the symmetrical crown (C _4v) conformation. Ring inversion takes place via symmetrical intermediates, such as boat-chair (BC, C _s) and twist (C _2h) conformers and requires about 22.3 kJ · mol⁻¹. The calculated strain energies for BC and twist conformers are 5.9 and 13.5 kJ · mol⁻¹. The results of semiempirical AM1 calculations for structural parameters and relative energies of the important geometries of the title compound are in good agreement with the results of ab initio methods.     

Study of complexation reactions between alkali and alkaline-earth metal cations with dibenzo-18-crown-6(DB18C6) in mixed nonaqueous solvents using the conductometry method

The complexation reactions between alkali and alkaline-earth metal cations with DB18C6 were studied in acetonitrile-methanol (AN-MeOH) and tetrahydrofuran-threechloromethane (THF-CHCl₃) binary mixtures at different temperatures using the conductometric method. The obtained results show that in most cases, the DB18C6 forms 1:1 complexes with these metal cations and the stability of the complexes is affected by the nature and composition of the mixed solvents. The stability order of complexes in AN-MeOH binary systems was found to be Na⁺ > Li⁺, and in the case of THF-CHCl₃ binary mixtures was Na⁺ > Ba²⁺ > Li⁺. An anomalous and interesting behavior was observed for the case of complexation of a K+ ion with DB18C6 in the AN-MeOH binary mixture and also for complexation of Mg²⁺ and Ca²⁺ cations with this ligand in pure THF and also in THF-CHCl₃ binary systems. The values of the thermodynamic parameters (ΔH _c ^o and ΔS _c ^o ) for complexation reactions obtained from the temperature dependence of the stability constants and the results show that the complexes are both enthalpy-and entropy-stabilized. The text was submitted by the authors in English.     

The thermodynamic properties of 2-ethylhexyl acrylate over the temperature range from <Emphasis Type="Italic">T</Emphasis> → 0 to 350 K

The temperature dependence of the heat capacity C _p ^o= f(T) 2 of 2-ethylhexyl acrylate was studied in an adiabatic vacuum calorimeter over the temperature range 6–350 K. Measurement errors were mainly of 0.2%. Glass formation and vitreous state parameters were determined. An isothermic shell calorimeter with a static bomb was used to measure the energy of combustion of 2-ethylhexyl acrylate. The experimental data were used to calculate the standard thermodynamic functions C _p ^o(T), H ^o(T)-H ^o(0), S ^o(T)-S ^o(0), and G ^o(T)-H ^o(0) of the compound in the vitreous and liquid states over the temperature range from T → 0 to 350 K, the standard enthalpies of combustion Δ_c H ^o, and the thermodynamic characteristics of formation Δ_f H ^o, Δ_f S ^o, and Δ_f G ^o at 298.15 K and p = 0.1 MPa.     

Synthesis,spectroscopic, thermal and biological aspect of mixed ligand copper(II) complexes

Derivative of 8-hydroxyquinoline i.e. Clioquinol is well known for its antibiotic properties, drug design and coordinating ability towards metal ion such as Copper(II). The structure of mixed ligand complexes has been investigated using spectral, elemental and thermal analysis. In vitro anti microbial activity against four bacterial species were performed i.e. Escherichia coli, Pseudomonas aeruginosa, Serratia marcescens, Bacillus substilis and found that synthesized complexes (15–37 mm) were found to be significant potent compared to standard drugs (clioquinol i.e. 10–26 mm), parental ligands and metal salts employed for complexation. The kinetic parameters such as order of reaction (n = 0.96–1.49), and the energy of activation (E _a = 3.065–142.9 kJ mol⁻¹), have been calculated using Freeman–Carroll method. The range found for the pre-exponential factor (A), the activation entropy (S* = −91.03 to−102.6 JK⁻¹ mol⁻¹), the activation enthalpy (H* = 0.380–135.15 kJ mol⁻¹), and the free energy (G* = 33.52–222.4 kJ mol⁻¹) of activation reveals that the complexes are more stable. Order of stability of complexes were found to be [Cu(A⁴)(CQ)OH] · 4H₂O > [Cu(A³)(CQ)OH] · 5H₂O > [Cu(A¹)(CQ)OH] · H₂O > [Cu(A²)(CQ)OH] · 3H₂O     

Quasi-thermodynamics of Viscous Flow of Electrolyte Solutions in Aqueous, Non-aqueous and Mixed Aqueous Solvents

Viscosity B-coefficients for cesium chloride and lithium sulfate in methanol + water mixtures at 25 and 35 °C are reported. A general treatment of the quasi-thermodynamics of viscous flow of electrolyte solutions is described. ΔG ₃ ^Θ (1→1′), the contribution made to the Gibbs energy of activation of the solution by the influence of the solute on the solvent, is a function of solute–solvent interactions only; but, ΔH ₃ ^Θ (1→1′) and ΔS ₃ ^Θ (1→1′) also reflect the solvent–solvent interactions. In aqueous solution all alkali-metal ions except Li⁺ are sterically unsaturated, having solvent co-ordination numbers n<n _max, the maximum allowed sterically. Such complexes exchange molecules with the solvent more readily than saturated ones and have energy–reaction co-ordinate diagrams in forms that explain the negative B or ΔG ₃ ^Θ (1→1′) values found in aqueous solution. Saturated complexes are the norm in non-aqueous solvents, and the ΔG ₃ ^Θ (1→1′) values are determined mainly by the secondary solvation. Behavior in mixed solvents reflects the transition from aqueous to non-aqueous behavior across the range of solvent composition.