Isotachophoretic determination of mobility and pKa by means of computer simulation : V. Evaluation of mo and pKa of twenty-eight dipeptides and assessment of separability

Isotachophoretic qualitative indices, R_E, for twenty-eight dipeptides were measured in the range pH 7.4–9.6. The absolute mobility, m_o, and pK_a values were evaluated by the use of the least-squares method, utilizing a simulation of the isotachophoretic steady state. The m_o values were newly evaluated and the pK_a values were in good agreement with literature values. By comparison of the evaluated m_o and pK_a values of the dipeptides with those of the constituent amino acids, simple relationships were found which may be used to estimate the m_o and pK_a values of other dipeptides. The separability of the dipeptides was also evaluated by considering the differences between their simulated effective mobilities. It is concluded that isotachophoresis is very convenient for the separation of dipeptides and their constituent amino acids.     

High-performance liquid chromatographic determination of taurine in biological fluids by post-column fluorescence reaction with thiamine.

A high-performance liquid chromatographic method is described for the selective determination of taurine in biological fluids by post-column fluorescence reaction. Taurine was separated on an adsorption-distribution type Shodex Ionpac KC-811 column. Then it was converted with hypochlorite into the corresponding N-chloramine, which was allowed to react with thiamine to give fluorescent thiochrome. As little as 6 ng per injection of taurine could be determined. The average recoveries of spiked taurine in serum and urine were 99.5 +/- 2.7 and 101.8 +/- 2.9%, respectively. The method could be applied to the assay of taurine in human serum and urine with simple pretreatment.     

Release kinetics of nicotinamide from fatty acid-nicotinamide equimolar complexes. II. Activation thermodynamic quantities.

The rates of release of nicotinamide (NAA) from fatty acid (FA)-NAA complexes, FA-NAA, were determined at various temperatures, and the thermodynamic quantities for the release of NAA were estimated. The results were compared with the previous results obtained for FA-thiamine disulfide (TDS) complexes, (FA)6(TDS). The values of activation enthalpy (delta H ++) and activation entropy (delta S ++) for the release of NAA from FA-NAA were positive and negative, respectively, indicating that the release of NAA is disadvantageous from not only enthalpic but also entropic viewpoints. The plots of delta H++ against the carbon number (n) in the constituent FA showed a zig-zag line with an upward convex at an odd-numbered position and the plots of the absolute values of (-delta S++) showed a zig-zag line with a downward convex at an odd-numbered position, though the positive value of delta H++ increases and the negative value of delta S++ decreases with an increasing n for either even-numbered or odd-numbered FA. It was found that the release of NAA from FA-NAA formed with odd-numbered FA is more disadvantageous enthalpically but more advantageous entropically as compared with that from FA-NAA formed with even-numbered FA. This phenomenon was similar to that observed for (FA)6(TDS). Furthermore, it is suggested that FA-NAA is formed at least by van der Waals forces and hydrophobic interactions and that van der Waals forces are dominant for the formation of FA-NAA formed with odd-numbered FA and that hydrophobic interactions are dominant for the formation of FA-NAA formed with even-numbered FA.     

New synthetic method to 1,2-benzisothiazoline-3-one- 1,1-dioxides and 1,2-benzisothiazoline-3-one-1-oxides from N-alkyl(o-methyl) arenesulfonamides

Various N-alkylsaccharins were easily prepared in moderate to good yields by the reaction of N-alkyl(o-methyl)arenesulfonamides with (diacetoxyiodo)benzene in the presence of iodine under irradiation with a tungsten lamp (W-hν). On the other hand, irradiation of N-alkyl(o- methyl)arenesulfonamide derivatives bearing various subslituents on the aromatic ring with a high- pressure mercury lamp (Hg-hν), in the presence of (diacetoxyiodo)benzene and iodine gave the corresponding N-alkyl-1,2-benzisothiazoline-3-one-1-oxide derivatives in moderate yields, together with N-alkyl-1,2-benzisothiazoline-3-one-1,1-dioxide (saccharin) derivatives.     

Furopyridines. XXX. Synthesis and reaction of difuro[3,2-c:- 3′,2′-e]pyridine,a new tricyclic heterocycle

Difuro[3,2-c:3′,2′-e]pyridine 1 , a new tricyclic heteroaromatic, has been prepared for the first time. Bromination of 1 with molecular bromine gave 3-bromo 7 , 8-bromo 7′ and 3,8-dibromo derivative 8 ; nitration with fuming nitric acid yielded 2-nitro compound 9 , while nitration with a mixture of fuming nitric acid and sulfuric acid gave 2,7-dinitro derivative 10 ; formylation with n-butyllithium and dimethylformamide gave 2-formyl 11 , 7-formyl 11′ , and 2,7-diformyl compound 12. The N-oxide 14 of 1 afforded 4-cyano compound 15 by cyanation with trimethylsilyl cyanide, 4-chloro compound 16 by chlorination with phosphorus oxychloride, and 4-acetoxyl compound 17 by acetoxylation with acetic anhydride.     

Copper(I) Complexes with a Proximal Aromatic Ring: Novel Copper–Indole Bonding

A unique bonding of indole to a metal ion has been established. Two new tridentate N ligands with a pendent indole ring gave Cu^I complexes 1 and 2 , the latter of which exhibits the new form of bonding between the Cu^I ion in a distorted tetrahedral geometry and the indole C(2)−C(3) moiety. The bond is dependent upon the length of the side chain and therefore the accessibility of the ring to the metal center.     

Temperature dependent control of the solubility of gallium nitride in supercritical ammonia using mixed mineralizer

Using a mass-loss method, we investigated the solubility change of gallium nitride (GaN) in supercritical ammonia with mixed mineralizers [ammonium chloride (NH₄Cl)?+?ammonium bromide (NH₄Br) and NH₄Cl?+?ammonium iodide (NH₄I)]. The solubilities were measured over the temperature range 450–550 °C, at 100 MPa. The solubility increased with NH₄Cl mole fraction at 450 °C and 100 MPa. The temperature dependence of the solubility curve was then measured at an equal mole ratio of the two mineralizers. The slope of the solubility–temperature relationship in the mixed mineralizer was between those of the individual mineralizers. These results show that the temperature dependence of the solubility of GaN can be controlled by the mineralizer mixture ratio. The results of the van’t Hoff plot suggest that the solubility species were unchanged over the investigated temperature range. Our approach might pave the way to realizing large, high-quality GaN crystals for future gallium-nitride electronic devices, which are increasingly on demand in the information-based age.