Direct current electrical resistivity of zinc borate glasses containing transition metal oxides

The resistivities of zinc borate glasses containing Fe2O3, V2O5, and Fe2O3 + V2O5 have been measured as a function of composition and temperature. The values of resistivity and activation energy decrease as the transition metal oxide content is increased. The conductivities of the glasses containing Fe2O3 + V2O5 are more than the sum of those of the glasses containing only Fe2O3 or V2O5 (i.e. the activation energies are less than the sum of those in the glasses containing only Fe2O3 or V2O5). The results are discussed in terms of existing theories.

Growth and defect characterization of L-arginine phosphate monohydrate

L-arginine phosphate monohydrate (LAP) is a relatively new organic nonlinear optical material. In this paper, the results of our recent investigations on the growth of this crystal are presented. The growth of the undesirable micro-organisms was prevented by protecting the solution surface by placing a thick layer of n-hexane over it. Colouration of the solution could be avoided by keeping the growth temperature low and by protecting it from light. The effect of pH value of the solution on the solubility and habit was analysed. The grown crystals were characterized by means of X-ray topography.

Interactions of methoxyamine with pyridoxal-5'-phosphate-Schiff's base at the active site of sheep liver serine hydroxymethyltransferase

The mechanism of interaction of methoxyamine with sheep liver serine hydroxymethyltransferase (EC 2.1.2.1) (SHMT) was established by measuring changes in enzyme activity, visible absorption spectra, circular dichroism and fluorescence, and by evaluating the rate constant by stopped-flow spectrophotometry. Methoxyamine can be considered as the smallest substituted aminooxy derivative of hydroxylamine. It was a reversible noncompetitive inhibitor (Ki = 25 microM) of SHMT similar to O-amino-D-serine. Like in the interaction of O-amino-D-serine and aminooxyacetic acid, the first step in the reaction was very fast. This was evident by the rapid disappearance of the enzyme-Schiff base absorbance at 425 nm with a rate constant of 1.3 x 10(3) M-1 sec-1 and CD intensity at 430 nm. Concomitantly, there was an increase in absorbance at 388 nm (intermediate I). The next step in the reaction was the unimolecular conversion (1.1 x 10(-3) sec-1) of this intermediate to the final oxime absorbing at 325 nm. The identity of the oxime was established by its characteristic fluorescence emission at 460 nm when excited at 360 nm and by high performance liquid chromatography. These results highlight the specificity in interactions of aminooxy compounds with sheep liver serine hydroxymethyltransferase and that the carboxyl group of the inhibitors enhances the rate of the initial interaction with the enzyme.

Structure of the putative mutarotase YeaD from Salmonella typhimurium in two different forms: in vivo binding of a sugar phosphate

Salmonella typhimurium YeaD (stYeaD), annotated as a putative aldose 1-epimerase, has a very low sequence identity to other well characterized mutarotases. Sequence analysis suggested that the catalytic residues and a few of the substrate-binding residues of galactose mutarotases (GalMs) are conserved in stYeaD. Determination of the crystal structure of stYeaD in an orthorhombic form at 1.9 angstrom resolution and in a monoclinic form at 2.5 angstrom resolution revealed this protein to adopt the beta-sandwich fold similar to GalMs. Structural comparison of stYeaD with GalMs has permitted the identification of residues involved in catalysis and substrate binding. In spite of the similar fold and conservation of catalytic residues, minor but significant differences were observed in the substrate- binding pocket. These analyses pointed out the possible role of Arg74 and Arg99, found only in YeaD-like proteins, in ligand anchoring and suggested that the specificity of stYeaD may be distinct from those of GalMs

New flame retardant polyarylazo phosphate and phosphoramide esters

Two series of flame retardant polymers, viz. polyarylazo phosphate and phosphoramide esters, were synthesized by solution polycondensation of 4,4′-dihydroxyazobenzene with various aryl phosphorodichlorides and aryl phosphoramidic dichlorides. They were characterized by i.r. 1H-, 13C- and 31P-NMR spectroscopy. The molar mass, thermal and flammability studies were carried out by viscometry, thermogravimetry and limiting oxygen index respectively to examine the influence of the phosphate and phosphoramide linkages. The polyphosphoramide esters possess better thermal and flammability characteristics than the polyphosphate esters.

Serine Hydroxymethyltransferase from Mung Bean (Vigna radiata) Is Not a Pyridoxal-5'-Phosphate- Dependent Enzyme

Serine hydroxymethyltransferase from mammalian and bacterial sources is a pyridoxal-5'-phosphate-containing enzyme, but the requirement of pyridoxal-5'-phosphate for the activity of the enzyme from plant sources is not clear. The specific activity of serine hydroxymethyltransferase isolated from mung bean (Vigna radiata) seedlings in the presence and absence of pyridoxal-5'-phosphate was comparable at every step of the purification procedure. The mung bean enzyme did not show the characteristic visible absorbance spectrum of pyridoxal-5'-phosphate protein. Unlike the enzymes from sheep, monkey, and human liver, which were converted to the apoenzyme upon treatment with L-cysteine and dialysis, the mung bean enzyme similarly treated was fully active. Additional evidence in support of the suggestion that pyridoxal-5'-phosphate may not be required for the mung bean enzyme was the observation that pencillamine, a well-known inhibitor of pyridoxal-5'-phosphate enzymes, did not perturb the enzyme spectrum or inhibit the activity of mung bean serine hydroxymethyltransferase. The sheep liver enzyme upon interaction with O-amino-D-serine gave a fluorescence spectrum with an emission maximum at 455 nm when excited at 360 nm. A 100-fold higher concentration of mung bean enzyme-O-amino-D-serine complex did not yield a fluorescence spectrum. The following observations suggest that pyridoxal-5'-phosphate normally present as a coenzyme in serine hydroxymethyltransferase was probably replaced in mung bean serine hydroxymethyltransferase by a covalently bound carbonyl group: (a) inhibiton by phenylhydrazine and hydroxylamine, which could not be reversed by dialysis and or addition of pyridoxal-5'-phosphate; (b) irreversible inactivation by sodium borohydride; (c) a spectrum characteristic of a phenylhydrazone upon interaction with phenylhydrazine; and (d) the covalent labeling of the enzyme with substrate/product serine and glycine upon reduction with sodium borohydride. These results indicate that in mung bean serine hydroxymethyltransferase, a covalently bound carbonyl group has probably replaced the pyridoxal-5'-phosphate that is present in the mammalian and bacterial enzymes.

Synthesis and spectral studies of polyamide-phosphate esters from phosphine-oxide-containing diols with aryl phosphorodichloridates and their thermal and flammability behaviour

Polyamide-phosphate esters were synthesized by interfacial polycondensation of aryl phosphorodichloridates with the diols of phenoxaphosphine and phosphine oxide in the presence of a phase-transfer catalyst. The polymers were characterized by infra-red and 1H, 13C and 31P nuclear magnetic resonance (n.m.r.) spectroscopy. The molecular weights were determined by end-group analysis using 31P n.m.r. spectral data. The phenoxaphosphine-containing polymers showed superior thermostability and flame retardancy over the phosphine-oxide-containing polymers.

Inhibition of rat liver mevalonate pyrophosphate decarboxylase and mevalonate phosphate kinase by phenyl and phenolic compounds.

1. Mevalonate pyrophosphate decarboxylase of rat liver is inhibited by various phenyl and phenolic acids. 2. Some of the phenyl and phenolic acids also inhibited mevalonate phosphate kinase. 3. Compounds with the phenyl-vinyl structure were more effective. 4. Kinetic studies showed that some of the phenolic acids compete with the substrates, mevalonate 5-phosphate and mevalonate 5-pyrophosphate, whereas others inhibit umcompetitively. 5. Dihydroxyphenyl and trihydroxyphenyl compounds and p-chlorophenoxyisobutyrate, a hypocholesterolaemic drug, had no effect on these enzymes. 6. Of the three mevalonate-metabolizing enzymes, mevalonate pyrophosphate decarboxylase has the lowest specific activity and is probably the rate-determining step in this part of the pathway.

Dielectric and Impedance Studies on 0.5Li(2)O-0.5K(2)O-2B(2)O(3) Glasses

Transparent glasses in the system 0.5Li(2)O-0.5K(2)O-2B(2)O(3) (LKBO) were fabricated via the conventional melt quenching technique. Amorphous and glassy nature of the samples was confirmed by X-ray diffraction and differential scanning calorimetry (DSC) respectively. Complex dielectric and impedance studies were conducted on the samples at different temperatures in the 100 Hz-10 MHz frequency range. ac conductivity was calculated from the dielectric data and the conductivity relaxation was found to obey the Jonscher's law. The Nyquist's plots (Z `'(omega) vs. Z'(omega)) showed single suppressed semicircles at all the temperatures under study indicating the non ideal Debye type relaxation process to be active. Activation energies for conduction and relaxation process were calculated using the Arrhenius relation. The UV-visible optical transmission spectra was shown a wide transmission window and calculated optical band gap was found to be 5.67 eV.

Structure of disocium uridine 5'-Phosphate heptahydrate

Na2[CgHllN2OgP].7H20, M r = 494.0,orthorhombic, C222~, a = 22.880 (7), b = 8.877 (3),c = 19.592 (9) A, Z = 8, V = 3979.2 A 3. The Cu Ka intensity data consisted of 1005 unique reflections. Final R -- 14.5%. This nucleotide shows no unusual conformational features. The uracil base has an anti conformation about the glycosidic bond (tpo o = 44.4°). The furanose ring conformation is C(2')-endo,gauchegauche with tpo o = -75.5 ° and ~Poc = 49"6°.