Electrochemical and spectral studies on the reductive nitrosylation of water-soluble iron porphyrin

The reaction of iron(III) (meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (Fe(III)TMPyP) with nitric oxide (NO) was studied by electronic absorption spectroscopy, ESR, and electrochemical and spectroelectrochemical techniques in aqueous solutions with pH from 2.2 to 12.0. Fe(III)TMPyP has been found to undergo a reductive nitrosylation in all pHs, and the product of nitric oxide binding to the porphyrin has been determined as iron(II) porphyrin nitrosyl complex ([Fe(II)(NO)TMPyP]). The rate of the reductive nitrosylation exhibits a tendency to get faster with increase in pH. An intermediate species was observed around neutral pH by spectroelectrochemical technique and was proposed to be the iron(II) nitrosyl complex of the mu-oxo dimeric form of FeTMPyP, which is known to be a predominant in neutral solutions.     

Development of a high-performance liquid chromatographic system with enzyme reactors for the determination of N-acetyl branched-chain amino acids

Immobilized enzymes were used as column reactors in a high-performance liquid chromatographic system for the specific detection of N-acetyl branched-chain amino acids (AcBCAs) such as N- acetyl- l -valine (AcVal), N- acetyl- l -leucine (AcLeu) and N- acetyl- l -isoleucine (AcIle). Aminoacylase and leucine dehydrogenase were immobilized onto poly(vinyl alcohol) beads. The AcBCAs were separated as three peaks on a Capcell C(1) SG120 column with 0.03M phosphate buffer (pH 8.0). Aminoacylase was capable of hydrolysing the AcBCAs to amino acids, which react with beta-nicotinamide adenine dinucleotide (NAD(+)) in the presence of leucine dehydrogenase. The reduced nicotinamide adenine dinucleotide (NADH) produced was monitored fluorimetrically. The calibration graphs were linear from 4 to 200muM for AcVal and AcLeu, and from 5 to 300muM for AcIle; detection limits for AcVal, AcLeu and AcIle were 2, 2 and 3muM, respectively. The immobilized aminoacylase reactor should be renewed every 5 days owing to a poor stability of aminoacylase.     

Mitogenic activity of Tulipa gesneriana lectins on mouse and human lymphocytes.

Tulipa gesneriana lectin-erythrocyte (TGL-E) which agglutinates mouse erythrocytes showed a potent mitogenic activity on mouse spleen cells and human peripheral blood lymphocytes, however, TGL-E had only slight mitogenic activity on mouse thymus cells. Its subunit alpha with a molecular weight (MW) of about 26,000 showed a potent mitogenic activity as did that of native lectin, but subunit beta with a MW of about 14,000 showed no activity, indicating that the mitogenic activity of TGL-E originates from subunit alpha. TGL-E stimulated T cell enriched spleen cells which passed through a nylon column, but not spleen cells from a nude mouse or spleen cells treated with anti-Thy 1.2 antibody and complement. Thus, TGL-E stimulates only mouse T cells but not B cells. The other lectin in tulip bulbs, Tulipa gesneriana lectin-yeast showed no mitogenic activity on mouse spleen, thymus cells or human paripheral blood lymphocytes.     

Oxidation products of 2-arylphenanthro-[9,10-d]imidazoles—II : Structure and photochromism of oxidation products of 2-(4-methoxyphenyl)-phenanthro-[9,10-d]imidazole

By ferricyanide oxidation of 2-(4-methoxyphenyl)phenanthro[9,10-d]imidazole, three new photochromic compounds were obtained. These were 4-ethoxy-4H-, 4-methoxy-4H- and 2-methoxy-2H-phenanthro[9,10-d]imidazoles. These compounds gave the 2-(4-methoxyphenyl)-phenanthro[9,10-d]imidazolyl radical and acetaldehyde or formaldehyde by light irradiation. The imidazolyl radical dimerized gradually in the dark and the dimer dissociated to the imidazolyl radical on heating.     

Novel photopolymerizable biodegradable triblock polymers for tissue engineering scaffolds: synthesis and characterization

For use in micro-patterned scaffolds in tissue engineering, novel diacrylated triblock macromers (PLA-b-PCL-b-PLA, PGA-b-PCL-b-PGA and PCL-b-PEO-b-PCL) were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). All diacrylated polymers were designed as triblock copolymers and involved biodegradable blocks of relatively non-polar epsilon-caprolactone (CL) and polar monomers such as glycolide (GA), lactide (LA) or ethylene oxide (EO). All triblock polymers were prepared in molecular weights of a few kilo daltons via the anionic ring-opening polymerization (ROP) of the corresponding lactide, glycolide or caprolactone using stannous octoate [Sn(Oct)(2)] as catalyst. The polymers had low polydispersity indices, ranging from 1.23 to 1.56. Biodegradable polymeric networks were prepared with conversions of 72-84% via photopolymerization of the triblock diacrylated polymers with 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator. PLA-b-PCL-b-PLA copolymers crumbled easily and were not suitable for micro-patterning. PGA-b-PCL-b-PGA copolymers had higher water contact angles than PCL-b-PEO-b-PCL and were also cytocompatible with Fibroblasts 3T3.     

Reanalysis of Chiral Discrimination of Phenoxypropionic Acid Herbicides on a Teicoplanin Phase Using a Bi-Langmuir Approach

Summary The chiral discrimination of phenoxypropionic acid herbicides by reversed-phase chromatography on a teicoplanin phase has been re-examined using the perturbation method to calculate the solute distribution isotherms. The effects of both temperature and the methanol (organic modifier) content of the mobile phase on the chiral discrimination mechanism were well described by the bi-Langmuir model. The method confirmed a change in the mechanism of enantiomer retention at a critical temperature, T^*, and showed that the mechanism was independent of (i) herbicide molecular structure, i.e. the position of the chloro group on the phenol ring, and (ii) the absolute configuration of the carbon atom. Enantioselectivity was enhanced by increasing the mobile phase methanol content. Use of this approach also revealed that secondary sites on the teicoplanin surface were involved in the processes determining both retention and selectivity. It was clearly demonstrated that these secondary sites of low affinity were not affected by the temperature change and were not involved in the chiral recognition mechanism.     

Synthesis and biological activity of novel epothilone aziridines

[reaction: see text]. A series of 12alpha,13alpha-aziridinyl epothilone derivatives were synthesized in an efficient manner from epothilone A. The final semisynthetic route involves a formal double-inversion of stereochemistry at both the C12 and C13 positions. All aziridine analogues were tested for effects on tubulin binding polymerization and cytotoxicity. The results indicate that the aziridine moiety is a viable isosteric replacement for the epoxide in the case of epothilones.     

Cysteine carboxyl O-methylation of human placental 23 kDa protein

C-Terminal carboxyl methylation of a human placental 23 kDa protein catalyzed by membrane-associated methyltransferase has been investigated. The 23 kDa protein substrate methylated was partially purified by DEAE-Sephacel, hydroxyapatite and Sephadex G-100 gel filtration chromatographies. The substrate protein was eluted on Sephadex G-100 gel filtration chromatography as a protein of about 29 kDa. In the absence of Mg2+, the methylation was stimulated by guanine nucleotides (GTP, GDP and GTPgammaS), but in the presence of Mg2+, only GTPgammaS stimulated the methylation which was similar to the effect on the G25K/rhoGDI complex. AFC, an inhibitor of C-terminal carboxyl methylation, inhibited the methylation of human placental 23 kDa protein. These results suggests that the substrate is a small G protein different from the G25K and is methylated on C-terminal isoprenylated cysteine residue. This was also confirmed by vapor phase analysis. The methylated substrate protein was redistributed to membrane after in vitro methylation, suggesting that the methylation of this protein is important for the redistribution of the 23 kDa small G protein for its putative role in intracellular signaling.