Model calculations of changes of thermodynamic variables for the transfer of nonpolar solutes from water to water-d2

A recently introduced modified hydration shell hydrogen bond model for rationalizing the thermodynamic consequences of hydrophobic hydration is adapted for use with heavy water. The required adjustment of parameters employs the assumption that breaking hydrogen bonds in water-d₂ involves a greater enthalpy change and a larger entropy increase than bond breaking in ordinary water. It also makes some use of information derived from studies of gas solubilities in the two solvents, although a review of the data leads to serious questions about the reliability of results obtained in this way. The model permits calculations of hydrogen bonding contributions to the changes, G _t ^o , H _t ^o , S _t ^o , and C _p,t ^o , for transfer of nonpolar solutes from water to water-d₂ and implies that such data should show regular trends. Although some of the numerical results depend strongly on the values chosen for the parameters, the pattern defined by these trends is nearly independent of parameters. Predicted values of C _p,t ^o are large and positive for all nonpolar solutes, while S _t ^o is expected to be negative near 0°C, becoming progressively less negative on warming and eventually positive. Both of these quantities should be proportional to the molecular surface area of the solute. Analogous predictions regarding G _t ^o and H _t ^o can also be made, but only if it is permissible to neglect possible contributions to these quantities from van der Waals interactions.     

The volumes of mixing of aqueous solutions of CdCl2, CuCl2, MnCl2, and ZnCl2 with HCl at varying ionic strength at 25°C

The densities of mixtures of aqueous solutions of hydrochloric acid with solutions of cadmium chloride, copper chloride, manganese chloride, and zinc chloride have been measured at constant ionic strengths of 1.0 and 3.0 mol-kg^–1 at 25°C. The density data were used to determine the volumes of mixing (V _m ). The volume of mixing equations of Pitzer were then fit to the resulting V _m data to obtain the Pitzer parameters _V ^MN and _V ^MNX , which are the pressure derivatives of the free energy equation parameters.     

Study on the Melting Process of Nitrocellulose by Thermal Analysis Method

The melting process of NC is studied by using modulated differential scanning calorimetry (MDSC) technique, the microscope carrier method for measuring the melting point and the simultaneous device of the solid reaction cell in situ/RSFT-IR. The results show that the endothermic process in the MDSC curve is reversible. It is caused by the phase change from solid to liquid of the mixture of initial NC, decomposition partly into condensed phase products. The values of the melting point, melting enthalpy (H_m), melting entropy (S_m), the enthalpy of decomposition (H_dec) and the heat-temperature quotient (S_dec) obtained by the MDSC curve of NC at a heating rate of 10 K min^–1 are 476.84 K, 205.6 J g^–1, 0.4312 J g^–1 K^–1, –2475.0 J g^–1 and –5.242 Jg^–1K^–1, respectively. The MDSC results of NC with different nitrogen contents show that with increasing the nitrogen content in NC, the absolute values of H_m, S_m, H_dec and S_dec increase.This revised version was published online in November 2005 with corrections to the Cover Date.     

Absorption spectra of 2-styryl-4-phenyl-thiazole ethiodides in organic solvents of varying polarities and determination of the formation constant of the charge transfer complex formed

The electronic absorption spectra of some 2-styryl-4-phenyl-thiazole ethiodides are studied in organic solvents of different polarities. The shorter wavelength band appearing in the visible region is assigned to an intramolecular charge transfer (CT)-transition originating from the phenyl moiety to the positively charged hetero ring, while the longer wavelength one is due to an intermolecular CT-transition from the iodide ion to the 2-styryl-4-phenyl-thiazolinium cation. These assignments are based on the nature of the aldehydic residue and effects of solvent, concentration, and temperature on both the position and absorptivity of the CT complex-band. It is concluded that the CT complex formed will be highly solvated inDMF, DMSO, ethanol and methanol relative to in CHCl₃, dioxane and acetone. The formation constant of the CT complex in solutions of different polarities is determined at different temperatures. Furthermore, the thermodynamic parameters H ^o, G ^o and S ^o for complex formation are calculated and discussed.

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Absorptionsspektren von 2-Styryl-4-phenyl-thiazol-ethiodiden in verschiedenen Lösungsmitteln und Bestimmung der Bildungskonstanten der Charge-Transfer-Komplexe

Zusammenfassung Die Elektronenanregungsspektren einiger substituierter 2-Styryl-4-phenyl-thiazol-ethiodide wurden in einigen Lösungsmitteln unterschiedlicher Polarität untersucht. Die Absorption bei kürzerer Wellenlänge wird einem intramolekularen Charge-Transfer (CT)-Übergang zugeordnet, die langwellige Bande einem intermolekularen CT-Übergang (Jodid—organ. Kation). Die Diskussion erfolgt basierend auf Substitutions-, Lösungsmittel-, Konzentrations-, und Temperatur-Effekten. Die Komplexbildungskonstanten und die thermodynamischen Parameter H ^o, G ^o und S ^o werden angegeben.

     

Infrared spectroscopy of hydrogen bond and substituent effects in electron donor molecules

The frequency shift, , of the O—H stretching mode in the IR spectra of the H-complexes of phenol with electron donor molecules BX_i (B is the n- or -donor center and X_i are substituents; a total of eight series), the change in the Gibbs free energy, G, due to H-complexation, and the parameter (a measure of the ability of BX_i molecules to donate an electron pair; two series) are determined by both the electrostatic interaction and charge transfer in the formation of H-complex. The , G, and values depend not only on the inductive and resonance effects, but also the polarizability of substituents characterized by the parameters.     

The relation between the nonlinear dielectric effect and solvent polarity

The relation between solvent polarity expressed through the Dimroth-Reichardt spectroscopic parameter E _T (30) and the nonlinear dielectric effect (NDE) expressed through the parameter /E² is demonstrated where is a change in the electric permittivity of a solvent in an external strong electric field E. Both E _T (20) and /E², determined in quite different ways, are extremely sensitive to the dielectric properties of a solvent which depend on molecular interactions. Linear correlations between /E² and E _T (30) have been found for n-alkanols representing hydrogenbond donor solvents, and for halogenobenzenes which are dipolar, aprotic, weakly-associated solvents.Part of this work was presented at The 22^nd International Conference on Solution Chemistry in Linz, Austria, July 1991.     

Thermodynamics of the Second Dissociation Constant of N-tris[Hydroxymethyl]-4-amino-butanesulfonic Acid (TABS) from 5 to 55°C

N-tris[Hydroxymethyl]-4-aminobutanesulfonic acid (TABS) has been investigated for the determination of the values of the second dissociation constant, pK ₂, in water at 12 temperatures in the range 5–55°C, including 37°C. This zwitterionic compound is useful as a secondary pH standard in the range of pH (7–9) for physiological applications. The electromotive force (emf) measurements have been carried out using a hydrogen gas electrode and a silver–silver chloride electrode. The values of pK ₂ are fitted as a function of temperature with the following results: pK ₂ = 1671.305/T+14.8737–2.04383 ln T, where T is the thermodynamic temperature in Kelvins. The experimental values of pK ₂ are 8.834 ± 0.0005 and 8.539 ± 0.0004 at 25 and 37°C, respectively. The related thermodynamic quantities, G°, H°, S°, and C _p ° characterizing the dissociation process have been derived from the pK ₂ and its temperature coefficients.     

Kinetics of substitution of aqua ligands fromcis-diaqua-bis(ethylene-diamine) cobalt(III) ion by quinolinic acid in water-ethanol mixtures

Summary The kinetics of aqua ligand substitution fromcis-[Coen₂(H₂O)₂]³⁺ by quinolinic acid have been studied spectrophotometrically in the 40 to 55°C range. At pH 4.05 the quinolinic acid H₂Quin behaves as uninegative and bidentate (O, O) donor. The replacement of water was found to involve two consecutive step processes. The first is the replacement of one water fromcis-[Coen₂(H₂O)₂]³⁺ by unidentate HQuin^–, involving prior establishment of an ion-pairing associative equilibrium, followed by dissociative interchange. The second step is the slower chelation step, where another water molecule is replaced. The rate constants for both the steps and the ion-pair equilibrium constant for the first step have been evaluated. The activation parameters for the two steps are: H ₁ =117.2 kJ mol^–1, H ₂ =100.5 kJ mol^–1 and S ₁ =69.4 JK^–1 mol^–1, S ₂ =12.1 JK^–1 mol^–1. A probable mechanism for the substitution process is suggested.     

Gas chromatography of saturated fluorinated carboxylic acid esters. 3. Temperature effect on gas chromatographic parameters

In six homologous (R_FC(O)O(CH₂)_mCH₃, m=0–5) and six pseudohomologous (CF₃-(CF₂)_nC(O)OR, n=0–5) of saturated, fluorinated carboxylic acid esters the effect of analysis temperature (T_a) in the range 60–160°C on the values of retention indexes (I) and on the differential molar free energy, enthalpy, and entropy of sorption of methylene and difluoromethylene groups when using SE-30 and SKTFT-50Kh as the stationary phase (SP) was studied. For each homolog I decreases linearly as T_a increases, but the values of dI/dT_a are different for different homologs and increase as the length of the fluorinated chain increases. The sorption parameters H_m (CH₂) and S_m(CH₂) are constant when m > 3 and H_n (CF₂) and S_n(CF₂) vary regularly as n varies. The values of H_m (CH₂) and S_m (CH₂) exceed those of the corresponding H_n (CF₂) and S_n (CF₂) for m=n when adsorbed on both SPs. The thermodynamic sorption parameters of the esters for m=1 and n=1 differ sharply from the corresponding parameters for m > 2 and n > 2.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1487–1493, July, 1991.     

Chromium(VI), chromium(V) and chromium(IV) oxidation of 12-tungstocobaltate(II)

The reaction between Cr^VI and 12-tungstocobaltate(II) was carried out in 2.0 mol dm^–3 HCl and followed a simple second order rate law. The reaction was catalysed by hydrogen ion due to the formation of active H₂CrO₄ and was inhibited by chloride ion as, in its presence, conversion of the active species into inactive chlorochromate occurs. Chromium(V) and chromium(IV) were generated in situ by the use of Cr^VI—V^IV or Cr^VI—2-ethyl-2-hydroxybutyric acid and Cr^VI—i-PrOH reactions respectively, and the oxidation of 12-tungstocobaltate(II) by these atypical oxidation states, was also studied. The rate constants for the oxidation of 12-tungstocobaltate(II) by Cr^VI, Cr^V and Cr^IV were found to be in the ratio 1:1.2:5.2 respectively. The ionic strength did not affect the reaction, while decrease in the solvent polarity increased the rate of the reaction. The activation parameters were also determined and the values H , G and S were found to be 52.4 ± 6 kJ mol^–1, 100.8 ± 7 kJ mol^–1, –151.7 ± 10 J K^–1 mol^–1 respectively, supporting the mechanism proposed.     

Synthesis and spectral characteristics of bis- and tris(Δ2-pyrazolinyl) benzenes

The electronic absorption and fluorescence spectra and the relative quantum yields of 1,3-bis(3-aryl-5-phenyl-²-pyrazolin-1-yl)- and bis- and tris(1-phenyl-5-aryl-²-pyrazolin-3-yl) benzenes were measured and are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1394–1397, October, 1974.     

Electronic structure,energy of hydration,and stability of metal aquo ions

The stability of metal aquo ions with respect to redox reactions is determined by the ionization energies of the atoms and the Gibbs energies of hydration for the ions(–_hG⁰). We present critically selected values of –_hG⁰ for 55 metal ions, determined from electrochemical, thermochemical, and spectra data. We consider the factors determining the values of –_hG⁰ (charges, ionic radii, electronic structure, and relativistic effects). For isoelectronic ions, we observe correlations between the ratios of the Gibbs energies of hydration for these ions with different charges and the ratios of their ionic radii. Based on the use of these correlations, we find –_hG⁰ for a number of aquo ions not observed experimentally and we estimate the unknown oxidation-reduction potentials for the pairs of ions M³⁺/M²⁺. We formulate the principles for stabilization of unstable oxidation states of the metals by including the corresponding ions in complexes with certain classes of ligands.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 1, pp. 1–11, January–February, 1994.     

Thermodynamics of the weak interaction between samarium cation and xylitol in water: A chemical model

The thermodynamic characterization of the weakly complexed model system Sm³⁺-xylitol has been carried out. The standard Gibbs energy enthalpy, entropy, volume and heat capacity of complexation of Sm³⁺ by xylitol have been determined in water at 25°. The stability constant and the enthalpy change have been simultaneously determined by using a calorimetric method. The thermodynamic properties characterizing solely the specific interaction between the cation and the complexing sequence of hydroxyl groups of the ligand have been isolated. The stability constant and the volume of complexation have also been estimated from a similar treatment of the apparent molar volumes. It was found that the reaction between Sm³⁺ and the complexing site of xylitol in water is characterized by: K = 8.1, _rG^o = –5.2 kJ-mol^–1, _rH^o = –13.7 kJ-mol^–1, T_rS^o = –8.5 kJ-mol^–1, _rV^o = 8.8 cm³-mol^–1 and _rC _p ^o = 51 J-K^–1-mol^–1.     

Kinetics of the interaction of aquo-ethylenediaminetetraacetatoruthenate(III) with ferricyanide ion in water

Summary The interaction of aquo-ethylenediaminetetraacetatoruthenate(III) with ferricyanide ion was studied spectrophotometrically as a function of ferricyanide ion concentration, pH (1.5–8.5) and temperature (30–45°C) at ionic strength 0.2 M (NaClO₄). Kinetic and activation parameters (H=27.1±1.75 KJ mol^–1, S=–136.7±5.57 J mol^–1 deg^–1) are consistent with the proposed mechanism.     

Preparation of the simplest Δ1-pyrazolines by isomerization of Δ2-pyrazolines

²-Pyrazolines that do not have substituants in the 1- and 3-positions are not capable of isomerization to 3-substituted pyrazolines and can be converted to ¹-pyrazolines by slow distillation in the presence of bases. This method, which is completely analogous to the synthesis of azo compounds from alkylhydrazones, gives good results when applied to 4-alkyl- and 5,5-dialkyl-²-pyrazolines and makes it possible to obtain the corresponding ¹-pyrazolines in yields of 40–70%. 4-Ethyl-, 5-methyl-5-ethyl-, and 5,5-diethyl-¹-pyrazolines are described for the first time.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 956–957, July, 1971.     

Medium effects on the reactions of coordination complexes: Base hydrolysisof(αβS)(p-hydroxybenzoato)(tetraethylenepentamine) cobalt(III) in iso-propanol–water,tert-butanol–water and dimethyl sulfoxide–water media

The base hydrolysis of (S)(p-hydroxybenzoato)-(tetraethylenepentamine)cobalt(III) has been investigated in aqueous–organic solvent media using i-PrOH, t-BuOH and dimethyl sulfoxide (DMSO) as cosolvents at 20.0 T (°C) 40.0 (I=0.02 mol dm ^-3) with 80% (v/v) of cosolvents. Only the base-catalysed path (k_obs=k_OH[OH^-]) is observed. The relative second order rate constant k _OH ^os /k _OH ^ow at I=0 increases nonlinearly with increasing mol fraction (x_O.S.) of the cosolvents, the rate acceleration in alcoholic cosolvents being greater than in DMSO. The destabilization of ^-OH in mixed solvent media alone does not explain the observed rate acceleration. The solvent composition dependence, log k _OH ^os = log k _OH ^ow + a_ix _os ⁱ [i=1,2,k _OH ⁰ denotes k_OH at I=0 in mixed solvent(s) and water (w)] indicates specific solute–solvent interactions. The values of the relative transfer free-energy data [_TG(t.s.) - _TG^o (i.s.)](sw)(25 °C)(G), where t.s. and i.s. denote the transition state and initial state of the substrates respectively, are positive for all substrates at all compositions, indicating a greater destabilizing effect of the mixed solvent on the transition state than on the initial state. The G values also correlate with G^E(G = ax_O.S. + cG^E) for all solvents, supporting the fact that solvent structural effects mediate the rates and energetics of the reaction. However, the solvent effects on the solvation components of H and S are mutually compensating, thus indicating that there is no change in the mechanism.     

Lipid-similar Thermal Transition of Polyethylene Glycol Alkyl Ether Detergents

A narrow, reversible endothermic main transition is found in the aqueous micellar phase of octaethylene glycol tetradecyl ether (C₁₄E₈) by DSC, characterized by a transition temperature of 41°C and a H value of 0.5 kcal mol^–1, which is not observed by light scattering. This transition is assigned to a cooperative conformational rearrangement of the assembled amphiphilic detergent molecules and not to a micelle aggregation process. It is suggested that the detergents polar head group is primarily involved in this rearrangement.This revised version was published online in November 2005 with corrections to the Cover Date.     

Semiempirical studies of core-electron binding energy shifts

The inner-core binding-energy shifts (BEs) of boron and carbon atoms in various chemical environments were studied by the semiempirical Self-Consistent Charge Molecular Orbital (SCC MO) method. The calculations are based on the initial ground state electrostatic potential model. The main feature of our approach is the empirical treatment of the coefficient relating BEs with the orbital populations of the host atom and the Madelung energy term. These adjustable parameters absorb a large portion of relaxation energy. The so obtained results are in good agreement with experimental data. They are better than earlier CNDO/2 results obtained by using either ground state or relaxation potential models. Present results indicate that semiempirical methods like SCC MO are able to account for changes in BE(1s) with a fair accuracy although the inner-shell electrons are not explicitly considered in the actual calculations.     

A Multilayer Model for Gold Nanoparticle Bioconjugates: Application to Study of Gelatin and Human IgG Adsorption Using Extinction and Light Scattering Spectra and the Dynamic Light Scattering Method

A new model of colloidal gold (CG) bioconjugates is proposed. The model consists of a gold core and a primary polymer shell formed during conjugate synthesis. Additionally, the conjugate includes a secondary shell formed during its interaction with target molecules. Each of the inhomogeneous shells is modeled by the arbitrary number of discrete layers. Using Mie theory for multilayered spheres, we calculated the extinction and static light scattering (SLS, at 90°) spectra, as well as differential spectra A(), I() describing the effects of primary and secondary shells. Our calculations are performed for the conjugates with gold particle diameters d = 10–160 nm and two 5-nm shells. The primary shell consists of two 2.5-nm layers with the refractive indices of 1.50 and 1.45; the secondary shell, of two 2- and 3-nm layers with the refractive indices of 1.45 and 1.40. The differential spectra are related to the adsorption of target molecules and possess a characteristic resonance that is shifted to the red region of spectra compared to the usual localized plasmon resonances of gold particles. The maximal values of differential resonances A _max and I _max are observed for gold particles with diameters about 40–60 nm (extinction spectra) or 70–90 nm (the SLS spectra). The adsorption of human gamma-globulin (hIgG) and gelatin onto 15- and 34-nm gold particles was studied using the SLS and extinction spectra in combination with the dynamic light scattering measurements. It is shown that the thickness of adsorbed layer is equal to 5–6 nm for hIgG and to 15–18 nm for gelatin. The experimental extinction and SLS spectra for CG + hIgG conjugates are well explained by a simple model with the gold core and homogeneous polymer coating. For the CG + gelatin conjugates, we used the new model with inhomogeneous polymer coating, which is modeled by 10 discrete layers with the total thickness of 16–18 nm and exponential spatial profile of shell refractive index.     

Thermodynamic parameters for the interaction of adenosine 5′-diphosphate,and adenosine 5′-triphosphate with Mg2+ from 323.15 to 398.15 K

The interaction of adenosine 5-diphosphate (ADP) and adenosine 5-triphosphate (ATP) with Mg²⁺ in water has been studied calorimetrically at 323.15, 348.15, 373.15, and 398.15 K for ATP and at 348.15 and 373.15 K for ADP. The enthalpies of reaction of Mg²⁺ with ADP and ATP were obtained from the heats of mixing of aqueous solutions of tetramethylammonium salts of ADP and ATP with MgCl₂ solutions in an isothermal flow calorimeter. Equilibrium constant (K), enthalpy change (H°), entropy change (S°), and heat capacity change (Cp°) values were calculated for the interaction: Mg²⁺+L^n–=MgL^2–n and Mg²⁺+MgL^2–n=Mg₂L^4–n, where n=4 for L=ATP and n=3 for L=ADP. The results are consistent with those at lower temperatures. For the two nucleotides studied, the above two reactions are endothermic and entropy-driven in the temperature range studied. Large Cp° values for the interaction of Mg²⁺ with ADP with ATP indicate the involvement of phosphate groups of nucleotides in the coordination of Mg²⁺. The coordination of the first and second Mg²⁺ ions involves the phosphate chain in both ADP and ATP. No evidence was found for the involvement of the adenine ring or the ribose moiety in the coordination of Mg²⁺ with these nucleotides. Approximate values of logK, H°, and S°, and Cp° for the self-association of ADP and ATP in the presence of Mg²⁺ are also given.