Effects of hydrodynamic interaction on the equivalent conductivity minimum of electrolyte solutions in solvents of low dielectric constant.

Brownian dynamics simulation on model electrolyte solutions in our previous work [T. Yamaguchi et al., J. Chem. Phys. 134, 244506 (2011)] is extended to include the hydrodynamic interaction between ions, in order to examine its effects on ionic mobility in solvents of low dielectric constant. The effects of the hydrodynamic interaction are rather small as a whole, and the equivalent conductivity minimum is observed in systems with the hydrodynamic interaction. The hydrodynamic interaction increases the self-diffusion coefficient while decreases the equivalent conductivity, thereby increases the deviation from the Nernst-Einstein relationship. Based on the analysis of the time-dependent ionic mobilities, these changes are elucidated in terms of the electrophoretic and relaxation effects. It is also demonstrated that the concentration dependence of the ionic mobilities with the hydrodynamic interaction is reproduced fairly well by a theoretical calculation.

Roles of translational and reorientational modes in translational diffusion of high-pressure water: comparison with soft-core fluids.

The dynamics of two soft-core fluids that show the increase in diffusivity with isothermal compression is studied with the mode-coupling theory (MCT). The anomalous density dependence of the diffusivity of these fluids is reproduced by the theory, and it is ascribed to the decrease in the first peak of the structure factor. The mechanism is quite different from that of high-pressure water revealed by MCT on molecular liquids described by the interaction-site model [T. Yamaguchi, S.-H. Chong, and F. Hirata, J. Chem. Phys., 119, 1021 (2003)]. The structures used in that study, calculated by the reference interaction-site model integral equation theory, showed the increase in the height of the first peak of the structure factor between oxygen atoms, whereas the structure obtained by molecular dynamics (MD) simulations shows the decrease in the peak height. In this work, calculations with MCT are performed on the simple fluids whose structure factor is the same as that between oxygen atoms of water from MD simulation, in order to clarify the role of translational structure on the increase in diffusivity with compression. The conclusion is that both the translational and reorientational modes contribute to the increase in diffusivity, and the effect of the latter is indispensable for the anomaly alone at least above freezing temperature.

Dynamic mechanism of equivalent conductivity minimum of electrolyte solution.

The theory on electric conductivity of electrolyte solutions we have developed [T. Yamaguchi, T. Matsuoka, and S. Koda, J. Chem. Phys. 127, 064508 (2007)] is applied to a model electrolyte solution that shows a minimum of equivalent conductivity as the function of concentration [T. Yamaguchi, T. Akatsuka, and S. Koda, J. Chem. Phys. 134, 244506 (2011)]. The theory succeeds in reproducing the equivalent conductivity minimum, whereas the mode-coupling theory (MCT) underestimates the conductivity in the low-concentration regime. The theory can also reproduce the decrease in the relaxation time of conductivity with increasing the concentration we have demonstrated with a Brownian dynamics simulation. A detailed analysis shows that the relaxation of the conductivity occurs through two processes. The faster one corresponds to the collision between a cation and an anion, and the slower one does to the polarization of the ionic atmosphere. The increase in the equivalent conductivity with concentration is attributed to the decrease in the effect of the ionic atmosphere, which is in turn explained by the fact that the counter ion cannot penetrate into the repulsive core when the Debye screening length is compatible or smaller than the ionic diameter. The same mechanism is also observed in MCT calculation with static structure factor determined by mean-spherical approximation.

Brownian dynamics simulation of a model simple electrolyte in solvents of low dielectric constant.

Brownian dynamics simulations are performed to investigate the ionic transport of model simple electrolytes, in which ions are interacting with each other through the repulsive core and Coulombic interactions. The equivalent conductivity and self-diffusion coefficient show minima as the function of the number density of ions when the dielectric constant of the solvent is low. Although the minimum of the former is in harmony with various experiments, no experiment has ever been reported on that of the latter. The analysis of time-dependent transport coefficients reveals that the presence of the minima is ascribed to the slow dynamics, rather than to static association models. The inclusion of a model function that resembles the short-range part of the potential of mean force induced by solvent affects the transport coefficients qualitatively, which suggests the importance of solvent-induced potential of mean force in the conduction mechanism of electrolytes in solvents of low dielectric constant.

Mode-coupling theoretical analysis of transport and relaxation properties of liquid dimethylimidazolium chloride.

The mode-coupling theory for molecular liquids based on the interaction-site model is applied to a representative molecular ionic liquid, dimethylimidazolium chloride, and dynamic properties such as shear viscosity, self-diffusion coefficients, reorientational relaxation time, electric conductivity, and dielectric relaxation spectrum are analyzed. Molecular dynamics (MD) simulation is also performed on the same system for comparison. The theory captures the characteristics of the dynamics of the ionic liquid qualitatively, although theoretical relaxation times are several times larger than those from the MD simulation. Large relaxations are found in the 100 MHz region in the dispersion of the shear viscosity and the dielectric relaxation, in harmony with various experiments. The relaxations of the self-diffusion coefficients are also found in the same frequency region. The dielectric relaxation spectrum is divided into the contributions of the translational and reorientational modes, and it is demonstrated that the relaxation in the 100 MHz region mainly stems from the translational modes. The zero-frequency electric conductivity is close to the value predicted by the Nernst-Einstein equation in both MD simulation and theoretical calculation. However, the frequency dependence of the electric conductivity is different from those of self-diffusion coefficients in that the former is smaller than the latter in the gigahertz-terahertz region, which is compensated by the smaller dispersion of the former in the 100 MHz region. The analysis of the theoretical calculation shows that the difference in their frequency dependence is due to the different contribution of the short- and long-range liquid structures.

A theoretical study on the frequency-dependent electric conductivity of electrolyte solutions. II. Effect of hydrodynamic interaction.

The theory on the frequency-dependent electric conductivity of electrolyte solutions proposed previously by Yamaguchi et al. [J. Chem. Phys. 127, 234501 (2007)] is extended to include the hydrodynamic interaction between ions. The theory is applied to the aqueous solution of NaCl and the concentration dependence of the conductivity agrees well with that determined by experiments. The effects of the hydrodynamic and relaxation effects are highly nonadditive in the concentrated solution, because the hydrodynamic interaction between ions affects the time-dependent response of the ionic atmosphere. The decrease in the electric conductivity is divided into the contributions of ion pair distribution at various distances. The long-range ionic atmosphere plays a major role at the concentration as low as 0.01 mol/kg, whereas the contribution of the contact ion pair region is important at 1 mol/kg. The magnitude of the contribution of the contact ion pair region is scarcely dependent on the presence of the hydrodynamic interaction. The transport number of cation is calculated to be a decreasing function of concentration as is observed in experiments.

Serum lactate dehydrogenase and its isozymes in lupus nephritis.

The relationship between the renal pathologic activity of systemic lupus erythematosus (SLE) and serum lactate dehydrogenase (LDH) was examined in 28 patients with active SLE involving only the kidney. Serum levels of total LDH, LDH1, and LDH2 were significantly higher in the patients with diffuse proliferative lupus nephritis (World Health Organization class IV) than in those with milder renal disease (classes I through III and V). Total LDH levels showed good correlations with the activity index and the total pathologic score of the renal pathologic scoring system, and with the glomerular hypercellularity and overall deposits. The elevated level of LDH was mainly due to elevated levels of its isozymes LDH1 and LDH2. These results suggest that the elevation of serum LDH levels in patients with SLE reflects the renal pathologic changes due to lupus nephritis.

A solid-phase radioimmunoassay for the detection of nRNP immune complexes.

We developed a solid-phase radioimmunoassay for complement (C)-fixing nuclear ribonucleoprotein (nRNP):anti-nRNP immune complexes (nRNP ICs). The assay was based on the ability of the C-fixing nRNP ICs to bind strongly to immobilized F(ab')2 anti-C3. The extent of binding was quantified by incubating the C-fixing nRNP ICs bound to anti-C3 with 125I-labeled anti-nRNP-specific IgG. The interaction between anti-C3 and C-fixing nRNP ICs was rapid, time- and concentration-dependent and sensitive over a broad range of nRNP IC concentrations in an antigen-antibody ratio of 8 : 1 (9.8-5000 ng of human aggregated IgG equivalent per ml). We found that the assay also detected an immunoreactive U1-RNP antigen in Sm : anti-Sm immune complexes but did not detect SSA : anti-SSA immune complexes. The assay was preliminary applied for serum samples obtained from patients with mixed connective tissue disease (MCTD), and elevated concentrations of nRNP immune complexes were found in 3 out of 5 patients with MCTD. This assay appears to be applicable to the detection and quantification of circulating nRNP ICs in patients with MCTD.

A new nitric oxide (NO) releaser: spontaneous NO release from FK409.

The remarkable vasorelaxant and anti-platelet effects of FK409 have been reported to be due to nitric oxide (NO) release. The purpose of the present study is to investigate the spontaneous NO-releasing pathway of FK409 in aqueous solutions. 1H-NMR spectra of FK409 suggested that the compound underwent a time-dependent elimination of the hydrogen atom at alpha-position of the nitro moiety (at the 5-position) in weakly alkaline solutions. In addition, the degradation of FK409 monitored by HPLC showed a pH-dependency accelerating with an increase of pH. These results revealed that the first step in the degradation of FK409 might be the hydroxyl ion-dependent subtraction of the hydrogen atom at the 5-position. On the other hand, NO release from FK409 also exhibited a pH-dependency, and the velocity of NO liberation was markedly enhanced above pH 6. Furthermore, a linear relationship between the rate of FK409 degradation and that of NO formation was observed, indicating that the rate-limiting step for NO formation is the same as that for degradation. Thus, the rate-limiting process of NO formation from FK409 is due to the deprotonation reaction of the hydrogen atom at the 5-position by hydroxyl ions. The deprotonation process appears to be an essential step for both FK409 degradation and NO release. On the basis of the results, a possible kinetic scheme for NO release from FK409 is proposed.

Studies on the interaction between polyion and counterions by sound velocity (II).

Sound velocities in polyacrylate solutions neutralized by tetraalkylammonium hydroxide were measured at various concentrations of added NACl. From the results, the degree of counterion binding to polyion and the extent of the changes in hydration volume due to ion binding were determined as a function of the degree of neutralization, alpha. The ion binding accompanying the volume changes appeared above about alpha = 0.6 and the ion binding process depended on the charge density of the polyion. The effect of the size of the tetraalkylammonium ion on ion binding was negligibly small.

Raman spectroscopic studies on the interaction between counterion and polyion.

The interaction between alkali metal ions and the polyacrylate ion was investigated by means of Raman spectroscopy. in comparison with the Raman spectra of propionate salts. The Raman bands due to the metal-oxygen bond were not apparent and no significant difference was observed among the Raman spectra of several univalent salts of polyacrylate. except in the case of the lithium salt. The apparent degree of dissociation of lithium polyacrylate, as determined from the relative intensity of a specific band characteristic of the carboxylate ion, was lower than those of the other alkali metal salts. It is concluded from the Raman data that the electrostatic interaction between counterions and a polyion is not specifically modified by forces of a nonionic nature. Moreover, it is pointed out that the local conformation of polyacrylate changes gradually with the degree of neutralization, but that the change is not like a conformational transition between globular and random coil forms.

Studies on the interaction between alkali metal cations and polyion by sound velocity.

The sound velocities in polyelectrolyte solutions were measured at various concentrations of added salts. When aqueous solutions of tetra (n-butyl)ammonium polyacrylate were titrated with concentrated solutions of LiCl, NaCl, KCl or CsCl, the sound velocity, i.e., the adiabatic compressibility of the solution, did not change linearly with added salt concentration, but showed a breaking point. The degrees of counterion binding on polyacrylate ion estimated from the breaking points were 0.25-0.30, independent of cation species. In polystyrenesulfonate, moreover, no Na+ binding was detected from such sound velocity measurements.

Raman spectroscopic studies on the interaction between divalent counterion and polyion.

The nature of the interaction between polyacrylate ion and several divalent cations, such as Cu2+, Mn2+, Zn2+, Ba2+ and Mg2+, was investigated using Raman spectroscopy. A specific Raman band characteristic of a carboxyl group is shifted upon addition of Cu2+, Zn2+ and Mn2+ to partially neutralized poly(acrylic acid). On the other hand, no frequency shift of the specific Raman band is observed on addition of Mg2+ and Ba2+, though the intensity of the specific Raman band decreases with concentration of MgCl2. It is concluded from these Raman data that the interaction between polyacrylate ion and Cu2+, Zn2+ or Mn2+ includes a specific interaction with bond formation, whereas in the case of Mg2+ and Ba2+, the electrostatic interaction is dominant.

X-ray crystallographic characterization of two polymorphs of 8-(2-methoxycarbonylamino-6-methylbenzyloxy)-2-methyl-3-(2- propynyl)-imidazo [1,2-a]pyridine.

Structural characterization of two polymorphs (Forms A and B) of 8-(2-methoxycarbonylamino-6-methylbenzyloxy)-2-methyl-3-(2-p ropynyl)-imidazo [1,2-a]pyridine (1) was accomplished by X-ray crystallographic analysis. Form A crystallized in the monoclinic space group C2/c, with a = 42.936 (14), b = 4.356 (1), c = 21.536 (6) A, beta = 109.92 (4) degrees, z = 8, and dcal = 1.275 g/cm3. Form B crystallized in the monoclinic space group P2(1)/c, with a = 4.367 (1), b = 38.214 (3), c = 11.253 (1) A, beta = 95.47 (2) degrees, z = 4, and dcal = 1.292 g/cm3. Some subtle conformational differences between the polymorphs were observed. Although the Form B crystal has a somewhat more compactly packed structure than Form A, this compactness is thought to be disadvantageous to conformational features and to the crystal structure of Form B. The intramolecular hydrogen bonding force between N(1) and NH(22) atoms of Form B is weaker than that of Form A, and the stacking force between the imidazopyridine rings of Form B may also be weaker than that of Form A. Thus, Form A is considered to be a more stable structure than Form B. In DSC analysis, Form B transformed to Form A. Based on these results, phase transformation from Form B to A occurs during a transient fluid state.

X-ray structural studies and physicochemical characterization of (E)-6-(3,4-dimethoxyphenyl)-1-ethyl-4-mesitylimino-3-methyl- 3,4-dihydro-2(1H)-pyrimidinone polymorphs.

The polymorphism of (E)-6-(3,4-dimethoxyphenyl)-1-ethyl-4-mesitylimino-3-methyl-3,4-di hydro- 2(1 H)-pyrimidinone (FK664; 1) was characterized by using X-ray powder diffractometry, differential scanning calorimetry (DSC), and IR spectroscopy. Structures of two polymorphs (Forms A and B) were determined by X-ray crystallographic analysis. Form A crystallized in the monoclinic space group P2(1)/c, with a = 13.504(2), b = 6.733(1), c = 24.910(8) A, beta = 96.55(4) degrees, z = 4, and dcal = 1.203 g/cm3, while Form B crystallized in the same space group, with a = 8.067(2), b = 15.128(4), c = 18.657(4) A, beta = 102.34(3) degrees, z = 4, and dcal = 1.216 g/cm3. The conformational features of 1 were very similar between the two polymorphs. Compound 1, in both crystal forms, took an energetically reasonable conformation in three rigid planes, such as 2-pyrimidone, trimethylphenyl, and dimethoxyphenyl rings, but the molecules were packed in different ways between the two polymorphs. In the Form B crystal, a short contact was possible, to form pi-pi interactions between two dimethoxyphenyl groups related with the inversion center in the crystal lattice; this interaction seems to contribute to stabilizing the crystal structure of Form B. Both Forms A and B showed only one endothermic peak due to fusion at 115 and 140 degrees C, respectively, on the DSC thermograms; therefore, it is suggested that there are no transition points between the two polymorphs. The heats of fusion obtained from the DSC thermograms were 33.2(2) kJ/mol for Form A and 36.8(1) kJ/mol for Form B.(ABSTRACT TRUNCATED AT 250 WORDS)

Degradation kinetics and mechanisms of a new cephalosporin, cefixime, in aqueous solution.

Hydrolysis of cefixime in buffer solutions (pH 1-9) at 25 degrees C and a constant ionic strength of 0.3 was investigated using ion-pair reversed-phase HPLC. Hydrolysis rates followed pseudo first-order kinetics; the rate of hydrolysis of cefixime was very slow at pH 4-7, slightly faster at lower pH, and quite rapid at higher pH. In the early stages of hydrolysis, six major degradation products were isolated and identified: a beta-lactam ring-opened product and a 7-epimer (basic conditions), three lactones derived from intramolecular cyclization between the 2-carboxyl and 3-vinyl groups (acidic conditions), and an aldehyde derivative involving a 7-acyl moiety (neutral conditions). Principal degradation pathways for cefixime were found to involve initial cleavage of the beta-lactam ring.

Tautomeric phenomenon of a novel potent immunosuppressant (FK506) in solution. I. Isolation and structure determination of tautomeric compounds.

Tautomeric phenomenon was observed in the HPLC chromatogram obtained from a novel potent immunosuppressant, FK506, in ethanol solution. Two tautomeric compounds derived from FK506 were isolated and purified by HPLC. Their structures were elucidated by spectral analyses. The mechanisms for this tautomerization were also established based on the results of structure analysis.

Moisture adsorption-desorption effect on the structure of inclusion complex of 6-chloro-2-pyridylmethyl nitrate and beta-cyclodextrin.

A new anti-anginal drug, 6-chloro-2-pyridylmethyl nitrate (FR46171), was found to form a complex with beta-cyclodextrin (beta-CyD), molecular ratio 1:1. The FR46171/beta-CyD complex thus prepared showed a moisture adsorption-desorption hysteresis characteristic of hydrophilic polymers. The moisture adsorption-desorption isotherm and differential scanning calorimetry indicated that the moisture adsorbed FR46171/beta-CyD complex includes 13-15 mol of water while the moisture desorbed complex includes 5 mol of water. X-ray diffraction patterns of these samples confirmed their different structures. The scanning electron photomicrographs and the surface areas (BET) suggested that the moisture adsorption-desorption hysteresis observed in FR46171/beta-CyD complex can be attributed to reversible hydrogen bonding between water molecules and hydroxyl groups.

Effect of ultrasonic frequency on polymerization of styrene under sonication.

The effect of ultrasonic frequency on polymerization of styrene under sonication at 50 degrees C was studied at the frequencies of 23.4, 45.7, 92, 518 kHz and 1 MHz. Polymerization under sonication was carried out at the ultrasonic intensity that gives the same reaction rate of decomposition of porphyrin. The magnitude of the polymerization rate increases in the order of 92, 45.7 and 23.4 kHz. At the high frequencies of 518 kHz and 1 MHz, no polymerization was observed. These facts mean that there is an optimum frequency in the range from 92 to 518 kHz for effective polymerization. The average-number molecular weights at the sonication time of 3 h are 5.5 x 10(4), 8.0 x 10(4) and 11.5 x 10(4) for the irradiated frequencies of 92, 45.7 and 23.4 kHz, respectively. Sonication for 3 h at 92 kHz gives polystyrene with very high polydispersity, about 5.0, in comparison with the results obtained at 23.4 and 45.7 kHz. These observations indicate that polymerization under sonication is influenced by the irradiated frequency.

Simple quantification of ultrasonic intensity using aqueous solution of phenolphthalein.

Aqueous phenolphthalein solution under sonication was investigated for use as a chemical dosimeter. The fading time of aqueous phenolphthalein solution under sonication depended on the concentration of phenolphthalein and the pH values of solutions. The fading time was correlated to the ultrasonic intensity in a reaction vessel that is estimated on the basis of decomposition of porphyrin. The relation between the fading time and the ultrasonic intensity for different frequencies is expressed by a single curve. From these results, it is indicated that aqueous solutions of phenolphthalein is useful for simple quantification of ultrasonic intensity for practical use, and one can regard it as one of the ultrasonic intensity indicators.