Thermal stabilities of homopolymers of amino acids

In order to study the thermal stabilities of the α-helical polyamino acids in the solid state, measurements of the infrared spectra at high temperature, weight loss by thermogravimetry, and the expansion of the α-helix by x-ray diffractometry were carried out on poly(γ-methyl D -glutamate), poly(γ-benzyl L -glutamate), poly-L -alanine, poly(β-benzyl L -aspartate), poly-δ-carbobenzoxy-L -ornithine and poly-ε-carbobenzoxy-L -lysine. The thermal degradation temperatures of these polymers lie between 140°C and 230°C. The α-helical conformation is stable at high temperature in these polyamino acids, except for poly(β-benzyl L -asparatate), unless thermal degradation takes place. As temperature rises, the amide A and the amide I bands of the infrared spectra shift slightly to higher frequencies and the amide II band to lower frequencies. At the same time, the intensities of these amide bands decrease. These changes differ among the different molecules. From the x-ray measurement, it was found that the α-helix expands along the helical axis with temperature. It is expected that the intramolecular hydrogen bonds of the α-helix become weak with increasing temperature and that the state of the hydrogen bonds of the α-helices depends upon the molecules.     

Preparation and examination of calcium ion-selective electrodes for flow analysis

The preparation of calcium ion-selective electrodes based on known alkylphenylphosphate exchangers or on the ETH 1001 ionophore, and their use in a flow-through cell in a flow-injection system for the determination of calcium are described. The response and lifetime of the electrodes and the effects of magnesium and sodium ions on the determination of 10^?3?10^?5 M calcium are examined in detail. The ionophore electrode is shown to be most satisfactory.     

Preparation of Weinreb amides using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM)

Weinreb amides were successfully prepared from the corresponding carboxylic acids using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) in the solvents, methanol, isopropyl alcohol, and acetonitrile, which can solubilize DMT-MM. A variety of carboxylic acids were converted to the corresponding Weinreb amides in excellent yields by simply mixing with DMT-MM and N,O-dimethylhydroxylamine hydrochloride.     

Antioxidant action by gold-PAMAM dendrimer nanocomposites

Gold-dendrimer nanocomposites were prepared in the presence of poly(amidoamine) (PAMAM) dendrimer (generation 3, 3.5, 5, and 5.5) via reduction of HAuCl4 with sodium borohydride. The average particle size of the gold nanoparticles was independent of the dendrimer concentration, ranging between 3.0 and 4.3 nm in diameter. The catalytic activities of the gold-dendrimer nanocomposites upon elimination of hydroxyl radicals formed in an H2O2/FeSO4 system were examined using a spin-trapping method. The gold-dendrimer nanocomposites exhibited high catalytic activities which were hardly affected by the concentration and the generation of the dendrimer except PAMAM dendrimer 3.5. The highest activity for the gold-PAMAM dendrimer 3.5 nanocomposites was 85 times that of ascorbic acid.     

Photochemical reactions of 2-bromotropone and 2,7-dibromotropone with 9,10-dicyanoanthracene

The photochemical reactions of 2-bromotropone and 2,7-dibromotropone with 9,10-dicyanoanthracene gave products with anthracene, anthracenone, and dihydroanthracene skeletons both in polar and non-polar solvents. These products were formed by attack of water contaminated in the solvent, by attack of the troponoid, and by attack of the solvent used in the reactions, respectively, on a reaction intermediate. In a mixed solvent of benzene and methanol, a benzaldehyde derivative with a tribenzo-2-oxabicyclo[3.2.2]nonane system was obtained. This result was informative about the reaction mechanism, and suggested the formation of an [8 + 4]pi cycloadduct with a tribenzo-2-oxabicyclo[3.2.2]nonane system between the troponoid as the 8 pi component and the 9,10-dicyanoanthracene as the 4 pi component. In non-polar benzene, a new tetrabromodihydroanthracene derivative was obtained together with anthracenone and anthracene derivatives. It was proved by the reaction in benzene-d6 that the new product was formed by attack of benzene-d6.     

Reversed-phase ion-pair partition liquid chromatography of chelates with 2-(3,5-dibromo-2-pyridylazo)-5-[N-ethyl-N-(3-sulphopropyl) amino] phenol and analogues

The ion-pair reversed-phase chromatography of some transition metal chelates with 2-(3,5-dibromo-2-pyridylazo)-5-[N-ethyl-N-(3-sulphopropyl)amino]phenol (3,5-diBr-PAESPAP) was studied. 3,5-DiBr-PAESPAP and its V(V), Cr(III), Fe(II), Co(III) and Ni(II) chelates were retained on and the copper (II), zinc(II) and cadmium(II) chelates dissociated in an ODS column using acetonitrile/water (37+63, v/v) (pH 7.0) containing 0.01 M acetate, 0.01 M 3-(N-morpholino)propanesulphonate buffer (pH 7.0) and 0.05 M Na⁺ as mobile phase. The chromatograms of 3,5-diBr-PAESPAP chelates were compared with those of the chelates with 2-(3,5-dibromo- 2-pyridylazo)-5-[N-(3-sulphopropyl)amino]phenol (3,5-diBr-PASPAP),2-(5-bromo-2- pyridylazo)-5-[N-(3-sulphopropyl)amino]phenol and 2-(5-bromo-2-pyridylazo)-5-[N-propyl-N- (3-sulphopropyl)amino] phenol. With 3,5-diBr-PAESPAP the Fe(II) and Ni(II) chelates were not resolved, but resolution was achieved with 3,5-diBr-PASPAP. The calibration graphs were linear over the ranges 2.0–10.0 ng (10-μl injection) of Fe, Ni and Co and for 20–100 ng (10-μl injection) for V with 3,5-diBr-PAESPAP and 3,5-diBr-PASPAP.     

Effects of chemical modifications on the swelling behaviors of poly (4-vinyl phenol) gel

Poly (4-vinyl phenol) (P4VPh) gels were prepared by crosslinking with a hydrophilic crosslinker [ethyleneglycoldiglycidylether (EGDGE)] and a hydrophobic one [diglycidyl 1,2-cyclohexane dicarboxylate (DGCHDC)], and the former gel was further modified by CH₃I or C₂H₅I to partially convert the hydrogen of phenol OH to the corresponding alkyl groups. Swelling behaviors of P4VPh gels, thus modified, were investigated to see how the hydrophobic groups introduced to the crosslinker and the polymer substrate affect the super salt resistivity to inorganic ions and the high water content (>90%) that have been observed for the original P4VPh gel. Water content and salt resistivity were unexpectedly preserved even for the modified gels. Effects of the chemical modifications on the gel swelling were only observed in the presence of hydrophobic solutes, i.e., tetrabutyl ammonium chloride and ionic surfactants. All these results strongly suggest that hydration around the polymer substrate in the gel phase is specifically stabilized, probably because of the coexistence of the hydrophobic hydration and the π-hydrogen-bonding hydration around the phenol ring.     

Ferrimagnetic ordering due to Fe(III) d and donor pi spins in (ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide)2.FeBr4

Magnetization and heat capacity were measured down to 0.4 K in a 2:1 charge-transfer (CT) salt of a new donor molecule, ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide (1) with a magnetic FeBr(4)(-) ion (1(2).FeBr(4)). The Fe(III) d spins of FeBr(4)(-) ions were subject to apparently ferromagnetic interaction with each other through the interaction with the pi spins developed by localization of the conducting pi electrons on the donor columns, eventually giving rise to ferrimagnetic ordering (FI) near 1 K, which provides the first example in a molecular pi-d system.     

Electrophoretic studies on the phosphorylation of stathmin and mitogen-activated protein kinases in neuronal cell death induced by oxidized very-low-density lipoprotein with apolipoprotein E

In the central nervous system, stressful conditions can easily cause the oxidation of lipoprotein particles, followed by the oxidative modification of apolipoproteins such as apolipoprotein E (apoE) and the production of free radicals and aldehydes. We have confirmed that oxidized very-low-density lipoprotein (VLDL) inhibits the proliferation, viability and differentiation of neuronal PC12 cells leading to cell death. The cells internalized intact apoE, but did not internalize oxidized apoE. The phosphorylation of stathmin and various mitogen-activated protein (MAP) kinases including extracellular signal-regulated protein kinase (ERK), p38, and c-Jun N-terminal kinase (JNK) was examined in PC12 cells exposed to native and oxidized VLDL, H(2)O(2) (which generates free radicals), and 4-hydroxy-2-nonenal (HNE) (an aldehyde). Oxidized VLDL and H(2)O(2) reduced stathmin phosphorylation while HNE increased it, suggesting that oxidized VLDL and H(2)O(2) stimulated similar signal transduction pathways. Based on the results, free radicals, but not aldehydes may play a major role in the neuronal cell death induced by lipoprotein oxidation. Furthermore, the phosphorylation status of MAP kinases indicated that the activation of the JNK cascade might be required for neuronal cell death.     

Ab initio molecular orbital study on the G-selectivity of GGG triplet in copper(I)-mediated one-electron oxidation

The G-selectivity for Cu(I)-mediated one-electron oxidation of 5'-TG(1)G(2)G(3)-3' and 5'-CG(1)G(2)G(3)-3' has been examined by ab initio molecular orbital calculations. It was confirmed that G(1) is selectively damaged by Cu(I) ion for both 5'-TG(1)G(2)G(3)-3' and 5'-CG(1)G(2)G(3)-3', being good agreement with experimental results. The Cu(I)-mediated G(1)-selectivity is primarily due to the stability of the Cu(I)-coordinated complex, [-XG(1)G(2)G(3)-,-Cu(I)(H(2)O)(3)](+). The Cu(I) ion coordinates selectively to N7 of G(2) of 5'-G(1)G(2)G(3)-3' rather than N7 of G(1). The G(2)-selective coordination induces the G(1)-selective trap of a hole that is created by one-electron oxidation and migrates to GGG triplet. Therefore, the radical cation of G(1) is selectively created in both 5'-TG(1)G(2)G(3)-3' and 5'-CG(1)G(2)G(3)-3', giving the G(1)-selective damage of 5'-G(1)G(2)G(3)-3'.