Acid–Base Interactions in the Dichloroacetic Acid–Ethyl Acetate System according to IR Spectroscopic Data

The method of multiple total internal reflection infrared spectroscopy (MTIRIRS) is used to study ion–molecular interactions in the system dichloroacetic acid–ethyl acetate in the range of concentrations from pure acid to pure base at 30°C. Depending on the ratio of components in the solution, molecular complexes with acid : base ratios of 1 : 1 or 2 : 1 are formed in the solutions. In the case of excess acid, base is not protonated and species with a strong symmetric hydrogen bond are not formed. It is shown that the absorption coefficient near 2000 cm^–1 can be used to judge the type of the complex formed and the strength of a hydrogen bond in molecular complexes.     

Determining theCP-violating phase γ

The weak phase γ is conventionally probed by theB _s→ρ ⁰ mode. The predicted rate is tiny. Even if aB _s→ρ ⁰ K _s rate difference could be established, it would not be clear that sin 2γ had been measured, because amplitudes with other weak phases may contribute significantly. Non-CP eigenstates, such asB _s →D _s ^± K ^?, have a two-fold advantage overB _s→ρ ⁰ K _s. Their rates are orders of magnitude above that forB _s→ρ ⁰ K _s, and they probe theCP-violating phase γ, without any contamination from other weak phases. Detailed time-dependent studies of non-CP eigenstates remove possible final-state phases and extract the weak phase γ.     

Heat capacities of concentrated multicomponent aqueous electrolyte solutions at various temperatures

The specific heat capacities of the aqueous multicomponent system NaCl +KCl+MgCl₂+CaCl₂ with ionic strength between 8.3 and 9.6 (resembling Dead Sea waters) were measured between 15°C and 45°C. The obtained data were fitted to an empirical equation as a function of concentration and temperature. The thermodynamic functions of the studied multicomponent system were found to be strongly influenced by changes in MgCl₂ concentrations. The application of Young's rule to such concentrated systems was checked at 25°C. The calculated (by Young's rule) specific heat capacitiesC _p and apparent molar heat capacities C_p, of these multicomponent electrolyte solutions were in reasonable agreement with the measured values (–0.008 J-g^–1-K^–1 and –2.6 J-mol^–1-K^–1, respectively).     

Proton solvation in methanol solutions of HCl

The MFTIR IR spectra of solutions of HCl in methanol were obtained in the 900–4000 cm^–1 frequency range. It was found that each proton binds two molecules of methanol. The spectra exhibit intense, continuous absorption (CA) with an intensity coefficient at 2000 cm^–1 of 174±10 liter/(mole·cm), which is in agreement with the corresponding coefficient for H₅O ₂ ⁺ . The optical densities of CA are linear functions of the concentration of HCl at 900–1600 cm^–1; there is no linearity at higher frequencies for C_HCl>4 M, and there are less than two molecules of MeOH for each (MeOH)₂H⁺ ion. The results obtained are in agreement with the model in which CA arises in solutions of strong acids because of the interaction of proton vibrations in a strong symmetric H bond with the vibrations of other groups of the proton disolvate.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2261–2268, October, 1992.     

Si-E (E = N, O, F) bonding in a hexacoordinated silicon complex: new facts from experimental and theoretical charge density studies

The concept of hypervalency in molecules, which hold more than eight valence electrons at the central atom, still is a topic of constant debate. There is general interest in silicon compounds with more than four substituents at the central silicon atom. The dispute, whether this silicon is hypervalent or highly coordinated, is enlightened by the first experimental charge density determination and subsequent topological analysis of three different highly polar Si-E (E = N, O, F) bonds in a hexacoordinated compound. The experiment reveals predominantly ionic bonding and much less covalent contribution than commonly anticipated. For comparison gas-phase ab initio calculations were performed on this compound. The results of the theoretical calculations underline the findings of the experiment.     

Density functional calculation of the electronic circular dichroism spectra of the transition metal complexes [M(phen)3]2+ (M = Fe, Ru, Os)

The circular dichroism spectra of the tris-bidentate metal complexes Lambda-[M(phen)3]2+, with M = Fe, Ru, Os and phen = 1,10-tris-phenanthroline, are investigated computationally, employing time-dependent density functional theory. Good agreement with experimental spectra is obtained for Ru and Os. The Lambda-[Os(phen)3]2+ spectrum is analyzed in detail. It is shown how relativistic effects red shift CD bands where the Os 5d-orbital participates to a large extent in the excitations. Further, the participation of the metal in the ligand pi --> pi exciton CD is determined to be of the order of 10%. Though solvent effects can have a noticeable effect on individual transitions and rotatory strengths, they are demonstrated to have only a very small overall effect on the resulting simulated CD spectra. For Lambda-[Fe(phen)3]2+, the results are shown to be rather sensitive to the choice of the applied hybrid and nonhybrid density functionals, and the optimized geometries based thereupon. In particular, the sign pattern of the lower-energy part (up to 33 x 10(3) cm(-1)) of the Lambda-[Fe(phen)3]2+ CD spectrum is difficult to reproduce. Some combinations of functionals and geometries yield good agreement with experiment, but no "best" approach can be devised based on the available results. Possible sources of errors in the spectrum of Lambda-[Fe(phen)3]2+ due to deficiencies in the functionals and the exchange-correlation kernels are investigated.     

Isolation of selenium organic species from antarctic krill after enzymatic hydrolysis

Total selenium content and its distribution in the soluble and insoluble protein-bound fractions obtained after aqueous extraction of antarctic krill samples were determined. About 26% of the total selenium (2.4 g g^–1 dry weight) was found in the supernatant; the rest was in the pellet. Isolation of low molecular selenium-containing fractions was also performed by enzymatic digestion of the protein, followed by size-exclusion chromatography in conjunction with atomic absorption spectrometry. From the applied various proteinases (pronase E, subtilisin Carlsberg, trypsin, chymotrypsin, proteinase and proteinase N from Bacillus subtilis and Novo 0.6 MPX enzyme), the treatment with pronase E led to best recovery of selenium. About 96% of the total Se was found in the hydrolysate, mainly in low molecular weight fractions. Eighty percent of the Se species were in fractions with molecular weights in the range of amino acids and short peptides. High-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC-ICP-MS) allowed the identification of selenomethionine and the assumption that selenocystine or its derivatives were the main species in these fractions.     

Chiffres non nuls dans le développement en base entière des nombres algébriques irrationnels

We give an effective lower bound for the number of non-zero digits among the first N digits of the expansion of an irrational algebraic number in an integer base.