The heat capacity and density of solutions of cadmium and mercury diiodides in methylpyrrolidone at 298.15 K

The heat capacity and density of solutions of cadmium and mercury diiodides in methylpyrrolidone (MP) at 298.15 K were studied by calorimetry and densimetry. The data obtained are discussed in relation to the special features of solvation and complex formation in solutions of the salts. The standard partial molar heat capacities and volumes (

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and

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) of the electrolytes in MP were calculated. The standard heat capacities

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and volumes

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of the Cd²⁺ and Hg²⁺ ions in solutions in MP at 298.15 K were determined.

     

Heat capacity and density of methylpyrrolidone solutions of sodium and potassium perchlorates at different concentrations and 298.15 K

The heat capacity and density of solutions of sodium and potassium perchlorates in N-methylpyrrolidone (MP) at 298.15 K were studied by calorimetry and densimetry. The standard partial molar heat capacities $ \bar C_{p2}^ \circ $ \bar C_{p2}^ \circ and volumes $ \bar V_2^ \circ $ \bar V_2^ \circ of NaClO₄ and KClO₄ in MP were calculated. The standard heat capacities $ \bar C_{pi}^ \circ $ \bar C_{pi}^ \circ and volumes $ \bar V_i^ \circ $ \bar V_i^ \circ of the perchlorate ion in an MP solution at 298.15 K were determined. The results are discussed with allowance for the specifics of solvation in the solutions of the salts under study. The coordination number of the ClO₄⁻ ion in an MP solution at 298.15 K was calculated.     

Calculating the standard values of the heat capacity of alkaline metal ions and iodide ions in a mixed N-methylpyrrolidone-water solvent at 298.15 K

A system of ionic components of [`(C)]<sub>p,i</sub><sup>0</sup>\bar C_{p,i}^0 is proposed for the standard partial molar heat capacities [`(C)]_p2⁰\bar C_{p2}^0 of electrolytes in a mixed N-methylpyrrolidone (MP)-water solvent. The [`(C)]<sub>p,i</sub><sup>0</sup>\bar C_{p,i}^0 values are calculated for Li<sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup>, Rb<sup>+</sup>, Cs<sup>+</sup>, and I<sup>−</sup> ions in a mixed MP-water solvent at 298.15 K. The individual components of [`(C)]_p,i⁰\bar C_{p,i}^0 values and their dependence on the solvent composition and ion size are considered.     

The thermodynamic properties and solvation of ammonium bromide,iodide, and nitrate in methylpyrrolidone at 298.15 K

The heat capacity and density of solutions of ammonium bromide, iodide, and nitrate in methylpyrrolidone (MP) were studied calorimetrically and densimetrically at 298.15 K. The standard partial molar heat capacities and volumes (\(\overline {C_{p_2 }^O } \) and \(\overline {V_2^O } \)) of the electrolytes in MP were calculated. The standard heat capacities \(\overline {C_{p_i }^O } \) and volumes \(\overline {V_i^O } \) of the nitrate and ammonium ions in MP were determined. The mean coordination numbers of the NH ₄ ⁺ and NO ₃ ^? ions in a solution in MP at 298.15 K were calculated.     

The heat capacity and density of solutions of barium and tetrabutylammonium iodides in N-methylpyrrolidone at 298.15 K

The heat capacity and density of solutions of barium and tetrabutylammonium iodides in N-methylpyrrolidone (MP) were studied at 298.15 K by calorimetry and densimetry. The standard partial molar heat capacities and volumes (\(\overline {C_{p^2 }^ \circ } \) and \(\overline {V_2^ \circ } \)) of the electrolytes in MP were calculated. The standard heat capacities \(\overline {C_{pi}^ \circ } \) and volumes \(\overline {V_i^ \circ } \) of the Ba²⁺ and (C₄H₉)₄N⁺ ions in solution in MP at 298.15 K were determined. With the tetrabutylammonium ion, these values were in agreement with those calculated on the basis of the tetraphenylarsonium-tetraphenyl borate and tetraphenylphosphonium-tetraphenyl borate assumptions. The results are discussed in relation to the special features of solvation in solutions of the salts studied.     

The standard partial molar volumes of ions in N-methylpyrrolidone at 298.15 K

The standard partial molar volumes of electrolytes and ions in N-methylpyrrolidone (MP) at 298.15 K are presented. Separate components of ionic volumes in solutions in MP at infinite dilution, \(\overline {V_i^0 } \), are considered. The influence of various volume effects on ion-solvent interactions is analyzed.     

Resolvation thermodynamics of individual ions in water-ethanol mixtures at 298.15 K

The standard real and chemical thermodynamic characteristics of resolvation for magnesium ions in the water-ethanol mixtures of different composition were determined by their Volta potential differences at 298.15 K. Based on our analysis of these characteristics, the regularities and peculiarities of solvation of investigated ions in the mixed solvent were established. It was shown that the energies of ion resolvation in dependence on their crystallographic radii correspond to the series Ba²⁺< Ca²⁺ < Cd²⁺ < Cu²⁺ < Mg²⁺ < Al³⁺.     

Evaporation from water clusters containing singly charged ions

Molecular dynamics simulations were used to study the evaporation from water clusters containing either Cl(-), H(2)PO(4)(-), Na(+) or NH(4)(+) ions. The simulations ranged between 10 and 500 ns, and were performed in vacuum starting at 275 K. A number of different models were used including polarizable models. The clusters contain 216 or 512 molecules, 0, 4 or 8 of which were ions. The ions with hydrogen bonding properties do not affect evaporation, even though the phosphate ions have a pronounced ion-ion structure and tend to be inside the cluster whereas ammonium shows little ion-ion structure and has a distribution within the cluster similar to that of the water molecules. Since the individual ion-water interactions are much stronger in the case of Na(+)-water and Cl(-)-water clusters, evaporation is somewhat slower for clusters containing these ions. It seems therefore that the main determinant of the evaporation rate in ion-water clusters is the strength of the interaction. Fission of droplets that contain more ions than allowed according to the Rayleigh limit seems to occur more rapidly in clusters containing ammonium and sodium ions.     

Concentration dependences of the heat capacity of solutions of alkali metal iodides in N-methylpyrrolidone-water mixed solvent at 298.15 K

Heat capacities of solutions of alkali metal iodides (MeI) in N-methylpyrrolidone (MP)-water mixed solvent were measured over the range of compositions. The influence of the composition of the mixed solvent on the heat capacity of MeI-MP-H₂O ternary systems is discussed. Standard partial molar heat capacities $ \bar C_{p_2 }^o $ \bar C_{p_2 }^o (MeI) in the MP-water mixed solvent at 298.15 K are calculated.     

Integral heat of dissolution of potassium chlorate in water at 298.15 K

The heat of dissolution of potassium chlorate in water at 298.15 K has been measured on an LKB 8700-1 calorimeter in the concentration range 0.063–0.659 m. The concentration dependence of the measured data was fitted by an empirical equation ΔH_m (kJ mole^?1) = 41.353₈ + 1.862₆m^{$\text{1}\text{2}$} ? 6.430₀m which was derived from our and Andauer—Lange data. The heat of crystallization calculated from this dependence was ΔH_cryst. = 34.7 ± 0.5 kJ mole^?1, which agrees with data calculated for potassium chlorate from solubility and activity data.     

Excess heat capacities at T=298.15 K and excess enthalpies at T=293.15 and 298.15 K of aqueous solution of 2-methoxyethanol

Excess isobaric heat capacities of mixture (2-methoxyethanol+water) were measured at T=298.15 K and excess enthalpies at T=293.15 and 298.15 K. Excess enthalpies were extremely exothermic, up to -1290 J mol^-1 atT=293.15 K and -1240 J mol^-1 at T=298.15 K. Excess isobaric heat capacities were positive and very large, approximately 9 J K^-1 mol^-1 at the maximum. In contrast to the data reported by Page and coworkers, the excess heat capacity data were positive in the entire composition range and there was no change in their signs. Consistently, no crossing was found between the curves of excess enthalpies at T=298.15 and 293.15 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Excess isobaric heat capacities for water + alkanol mixtures at 298.15 K

Excess isobaric heat capacities for water + methanol, + ethanol, + 1-propanol and + 1-butanol mixtures were measured at 298.15 K. The apparatus used in this study was a flow microcalorimeter designed and constructed in our laboratory recently, which can determine excess heat capacities directly by a method different from that of a Picker type calorimeter.The results obtained are roughly in agreement with the literature values, except for the water + 1-propanol mixture. This discrepancy from the literature values may arise from the thermodynamic instability of the water + alkanol mixture with the long-chain alkyl group and the difference in the procedure for obtaining the excess heat capacity.     

Methyl group migration during the fragmentation of singly charged ions of trimethyllysine-containing peptides: Precaution of using MS/MS of singly charged ions for interrogating peptide methylation

Core histones are susceptible to a range of post-translational modifications (PTMs), including acetylation, phosphorylation, methylation, and ubiquitination, which play important roles in the epigenetic control of gene expression. Here, we observed an unusual discrepancy between MALDI-MS/MS and ESI-MS/MS on the methylation of trimethyllysine-containing peptides with residues 9–17 from human histone H3 and residues 73–83 from yeast histone H3. It turned out that the discrepancy could be attributed to an unusual methyl group migration from the side chain of trimethyllysine to the C-terminal arginine residue during peptide fragmentation, and this methyl group transfer only occurred for singly charged ions, but not for doubly charged ions. The methyl group transfer argument received its support from the results on the studies of the fragmentation of the ESI- or MALDI-produced singly charged ions of several synthetic trimethyllysine-bearing peptides. The results presented in this study highlighted that caution should be exerted while MS/MS of singly charged ions is employed to interrogate the PTMs of trimethyllysine-containing peptides.     

Structural properties of reciprocal form factor in neutral atoms and singly charged ions

Structural characteristics of the spherically averaged internally folded density or reciprocal form factor Br are studied within the Hartree-Fock framework for 103 neutral atoms, 54 singly charged cations, and 43 anions in their ground state. The function Br is classified throughout the Periodic Table into three types: (i) monotonic decrease from the origin, (ii) maximum at r=0 and a negative minimum at r>0, and (iii) a local maximum at r=0 and a pair maximum-minimum out of the origin. A detailed study of the corresponding properties for individual subshells as well as their relative weight for the total Br is also carried out. For completeness, the analytical Br for hydrogenlike atoms in both ground and excited states is also analyzed.     

Expansion coefficients and moments of electron momentum densities for singly charged ions

Numerical Hartree–Fock calculations of the first three coefficients of the MacLaurin expansion and the leading coefficient of the large-p asymptotic expansion of the electron momentum densities Π(p) are reported for 54 singly charged atomic cations from He⁺ (atomic number Z = 2) to Cs⁺ (Z = 55) and 43 anions from H⁻ (Z = 1) to I⁻ (Z = 53) in their experimental ground states. We also report all the finite moments <p ^k > (−2≤k≤+4) of the momentum densities Π(p) for the above-mentioned 97 ionic species. The results are compared with the previous ones for neutral atoms [Koga and Thakkar (1996) J Phys B 29: 2973], and the dependence of the expansion coefficients and moments on nuclear charge is discussed among isoelectronic species. Received: 20 November 1998 / Accepted: 15 January 1999 / Published online: 7 June 1999     

Heat capacity and density of potassium iodide solutions in mixed N-methylpyrrolidone-water solvent at 298.15 K

The heat capacity and density of potassium iodide solutions in a mixed N-methylpyrrolidone (MP)-water solvent with a low content of the organic component are measured via calorimetry and densimetry at 298.15 K. Standard partial molal heat capacities \(\bar C_{p,2}^ \circ \) and volumes \(\bar V_2^ \circ \) of potassium iodide in MP-water mixtures are calculated. Standard heat capacities \(\bar C_{p,i}^ \circ \) and volumes \(\bar V_i^ \circ \) of potassium and iodide ions are determined. The character of the changes in heat capacity and volume are discussed on the basis of calculating additivity coefficients δ _c and δ _v upon the mixing of isomolal binary solutions KI-MP and KI-water, depending on the composition of the MP-H₂O mixture and the concentration of the electrolyte.     

The partial molar heat capacity, expansion, isentropic, and isothermal compressions of thymidine in aqueous solution at T = 298.15 K

Solution densities have been determined for aqueous solutions of thymidine at T = (288.15, 298.15, 303.15, and 313.15) K. The partial molar volumes at infinite dilution, , obtained from the density data were used to derive the partial molar isobaric expansion at infinite dilution for thymidine at T = 298.15 K, . The partial molar heat capacity at infinite dilution for thymidine, , at T = 298.15 K has also been determined. Sound speeds have been measured for aqueous solutions of thymidine at T = 298.15 K. The partial molar isentropic compression at infinite dilution, , and the partial molar isothermal compression at infinite dilution, , have been derived from the sound speed data. The , , , and results for thymidine are critically compared with those available from the literature.