Oxygen-reducing electrodes for acid fuel cells

Electrochemical data are reported for oxygen reduction on platinized coconut-shell charcoal electrodes in 2.5M H*SO,, and 7M HsF’04. In both these media the electrodes exhibit good activity and can sustain currents up to 600 mA cm-* at a polarization of about 400 mV from their rest potentials. The overall performance is comparable with the best type of carbonsupported platinum electrodes reported in the literature.

L-Arginine L-aspartate

C6HxsN40 +.C4H6NO~-, monoclinic, P2,,a = 5.511 (3), b = 8.438 (4), c = 15.265 (9) A, fl = 97.9 (I) °, D,, -- 1.467 (8) (flotation), D c = 1.452 Mg m -a, Z = 2. The structure has been refined to a final R value of 0.044 for 1226 independent counter-measured reflections. The conformation of the arginine molecule is different from those previously observed, whereas the conformation of the aspartate ion is similar to that found in L-aspartic acid, DL-aspartic acid and L-lysine L-aspartate. The unlike molecules aggregate into separate alternating layers and the a-amino and acarboxylate groups in the arginine layer are periodically brought into close proximity in a 'headto-tail' arrangement. There exist a specific ion-pair interaction involving electrostatic attraction and two nearly parallel N-H...O hydrogen bonds between the guanidyl group and the a-carboxylate group of the aspartate ion.

Structure of a new crystal form of 2- ([3-(trifluoromethyl)phenyl] amino)benzoic acid (flufenamic acid)

C14Ht0F3NO2, P2.Jc, a = 12.523 (4), b = 7.868(6), c = 12.874 (3)A, fl = 95.2 (2) ° , O,,, = 1.47 (4), D e = 1.47 Mg m -3, Z = 4. Final R = 0.074 for 2255 observed reflections. The carboxyl group and the phenyl ring bearing the carboxyl group are nearly coplanar whereas the two phenyl rings are inclined with respect to each other at 52.8 ° . The difference between the two polymorphs of flufenamic acid lies in the geometrical disposition of the [3-(trifluoromethyl)- phenyl]amino moiety with respect to the benzoic acid moiety. As in other fenamate structures, the carboxyl group and the imino N atom are connected through an intramolecular hydrogen bond; also, pairs of centrosymmetrically related molecules are connected through hydrogen bonds involving carboxyl groups.

Structure of a new crystal form of 2-{[3-(trifluoromethyl)phenyl]amino}benzoic acid (flufenamic acid)

C14Ht0F3NO2, P2.Jc, a = 12.523 (4), b = 7.868(6), c = 12.874 (3)A, fl = 95.2 (2) ° , O,,, = 1.47 (4), D e = 1.47 Mg m -3, Z = 4. Final R = 0.074 for 2255 observed reflections. The carboxyl group and the phenyl ring bearing the carboxyl group are nearly coplanar whereas the two phenyl rings are inclined with respect to each other at 52.8 ° . The difference between the two polymorphs of flufenamic acid lies in the geometrical disposition of the [3-(trifluoromethyl)- phenyl]amino moiety with respect to the benzoic acid moiety. As in other fenamate structures, the carboxyl group and the imino N atom are connected through an intramolecular hydrogen bond; also, pairs of centrosymmetrically related molecules are connected through hydrogen bonds involving carboxyl groups.

Effect of some "strong" excitants of central neurones on the uptake of L-glutamate and L-aspartate by synaptosomes

"Strong" excitants of central neurones such as β N-oxalyl L α,β-diaminopropionic acid (ODAP), N-methyl-D-aspartic acid (NMDA) and kainic acid (KA) were found to inhibit the high affinity uptake of glutamate and aspartate in synaptosomes isolated from young rat brain. The potency of these "strong" excitants as convulsants appear to parallel their ability to inhibit glutamate uptake by synaptosomes. The data suggest the possibility that the convulsive effect of these "strong" excitants could be mediated by glutamate/aspartate.

Oxidase-peroxidase enzymes of Datura innoxia. Oxidation of formylphenylacetic acid ethyl ester

An enzyme system from Datura innoxia roots oxidizing formylphenylacetic acid ethyl ester was purified 38-fold by conventional methods such as (NH4)2SO4 fractionation, negative adsorption on alumina Cy gel and chromatography on DEAE-cellulose. The purified enzyme was shown to catalyse the stoicheiometric oxidation of formylphenylacetic acid ethyl ester to benzoylformic acid ethyl ester and formic acid, utilizing molecular O2. Substrate analogues such as phenylacetaldehyde and phenylpyruvate were oxidized at a very low rate, and formylphenylacetonitrile was an inhilating agents, cyanide, thiol compounds and ascorbic acid. This enzyme was identical with an oxidase-peroxidase isoenzyme. Another oxidase-peroxidase isoenzyme which separated on DEAE-chromatography also showed formylphenylacetic acid ethyl ester oxidase activity, albeit to a lesser extent. The properties of the two isoenzymes of the oxidase were compared and shown to differ in their oxidation and peroxidation properties. The oxidation of formylphenylacetic acid ethyl ester was also catalysed by horseradish peroxidase. The Datura isoenzymes exhibited typical haemoprotein spectra. The oxidation of formylphenylacetic acid ethyl ester was different from other peroxidase-catalysed reactions in not being activated by either Mn2+ or monophenols. The oxidation was inhibited by several mono- and poly-phenols and by catalase. A reaction mechanism for the oxidation is proposed.

The regulation of the biosynthesis of ubiquinone in the rat

The urinary excretion of p-hydroxybenzoate was not altered by ubiquinone feeding, but, although decreased considerably, was not eliminated in protein deficiency. The incorporation of p-hydroxy[U-14C]benzaldehyde into ubiquinone in vivo increased in cold-exposed and p-chlorophenoxyisobutyrate (clofibrate)-fed rats, and these changes were parallel with the changes in the incorporation of [2-14C]mevalonate under these conditions. Starvation, cholesterol feeding and cholic acid feeding resulted in the decreased incorporation of p-hydroxy[U-14C]benzaldehyde into ubiquinone, confirming the decreased ubiquinone synthesis. Feeding exogenous ubiquinone increased the hepatic ubiquinone concentration, but did not cause any decrease in the incorporation of p-hydroxy[U-14C]benzaldehyde into ubiquinone, indicating the absence of a feedback control.

Studies on the relative biopotencies and intestinal absorption of different apo-beta-carotenoids in rats and chickens.

1. The biopotencies relative to beta-carotene of several apocarotenoids, such as 8'-, 10'- and 12'-apo-beta-carotenal and methyl 8'-apo-beta-carotenoate, were investigated in rats, on a molar basis, by both curative-growth assay and liver-storage tests. 2. In the curative-growth assays, on a molar basis the biopotencies of 8'-, 10'- and 12'-apo-beta-carotenal and methyl 8'-apo-beta-carotenoate were 72, 78, 72 and 53% respectively, whereas on a weight basis the corresponding values were 93, 111, 111 and 63%, with respect to beta-carotene taken as 100%. In terms of yield of vitamin A, these values were much lower in the liver-storage tests. 3. When 8'-apo-beta-carotenal was fed, the unchanged aldehyde together with small amounts of the corresponding alcohol and larger proportions of the acid rapidly appeared in the tissues of both rats and chickens. The 8'-apocarotenol, 8'-apocarotenoic acid and its methyl ester were absorbed unchanged. The free acid disappeared most rapidly from the tissues, but its methyl ester persisted in the tissues longest. 4. On the basis of these observations it is suggested that most of an apocarotenal is oxidized to the corresponding acid, which, in turn, is mostly degraded to retinoic acid, with small proportions of it being attacked by the dioxygenase system giving retinal.

Synthetic polypeptide with antifreeze activity

MUCH information has been gathered in recent years on the so-called 'antifreeze' proteins which lower the freezing point of the serum of certain marine fishes living in sub-zero water temperatures1−4. The proteins from the Antarctic fish Trematomus borchgrevinki are glycoproteins with a repeating alanyl-alanyl-threonyl tripeptide sequence, the threonyl residue being linked to a disaccharide1,2. In contrast, the antifreeze protein from the winter flounder Pseudopleuronectus americanus in the North American Atlantic coastal region is made up of eight ammo acids with no apparent repeating sequence of the residues and no sugar moiety (ref. 4 and unpublished work of C. L. Hew, C. C. Yip & G. Fletcher). The antifreeze activity of these proteins is not compatible with the known colligative properties of solutes in solution and the mechanism of their action is not yet fully understood. But a common feature of both types of the antifreeze proteins is the preponderance of alanine which accounts for over 60% of the total amino residues. This fact, together with the absence of the carbohydrate in the protein from the winter flounder, prompted us to attempt the synthesis of polypeptide analogues having comparable proportions of alanine in them along with suitable other amino acids. As a first step, we made use of the lack of any obvious periodicity in the distribution of the alanyl residues in the flounder's protein and attempted the synthesis of a random copolypeptide containing about 65 mol % of alanine and 35 mol % of aspartic acid. The choice of aspartic acid was made on the basis of its being the next major amino acid in the flounder's protein3,4 and on the expectation that its polar character will help the water-solubility of the alanine-rich copolypeptide, as in other studies on alanine-containing random copolymers. In addition, Duman and DeVries4 have earlier indicated the involvement of carboxyl groups on the antifreeze activity by chemical modification studies. We report here the synthesis of this polypeptide and show that it possesses antifreeze activity.

Encapsulation and release of rifampicin using poly(vinyl pyrrolidone)-poly (methacrylic acid) polyelectrolyte capsules

Poly(vinyl pyrrolidone) and poly(methacrylic acid) multilayer capsules based on hydrogen bonding have been prepared by the layer-by-layer approach and used to encapsulate and release rifampicin, an antituberculosis drug. Removal of silica core using a buffer of ammonium fluoride and hydrofluoric acid at about pH 3 was found to produce better capsules than hydrofluoric acid alone. An eight-layered capsule had a wall thickness of 20 rim. Maximum encapsulation was found to be about 86 mu g at 40 degrees C with 1 +/- 0.2 x 10(6) capsules. Release studies showed a burst kind of release and maximum release was obtained above pH 7 where the capsules disintegrate rapidly thereby releasing the drug in a short period. Interactions studies with Mycobacterium smegmatis showed that the capsules were cytocompatible and the released drug functioned with the same efficacy as the free drug.

Visualization of in situ intracellular aggregation of two cataract-associated human gamma-crystallin mutants: Lose a tail, lose transparency

PURPOSE. To understand the molecular features underlying autosomal dominant congenital cataracts caused by the deletion mutations W156X in human gamma D-crystallin and W157X in human gamma C-crystallin. METHODS. Normal and mutant cDNAs (with the enhanced green fluorescent protein [EGFP] tag in the front) were cloned into the pEGFP-C1 vector, transfected into various cell lines, and observed under a confocal microscope for EGFP fluorescence. Normal and W156X gamma D cDNAs were also cloned into the pET21a(+) vector, and the recombinant proteins were overexpressed in the BL-21(DE3) pLysS strain of Escherichia coli, purified, and isolated. The conformational features, structural stability, and solubility in aqueous solution of the mutant protein were compared with those of the wild type using spectroscopic methods. Comparative molecular modeling was performed to provide additional structural information. RESULTS. Transfection of the EGFP-tagged mutant cDNAs into several cell lines led to the visualization of aggregates, whereas that of wild-type cDNAs did not. Turning to the properties of the expressed proteins, the mutant molecules show remarkable reduction in solubility. They also seem to have a greater degree of surface hydrophobicity than the wild-type molecules, most likely accounting for self-aggregation. Molecular modeling studies support these features. CONCLUSIONS. The deletion of C-terminal 18 residues of human gamma C-and gamma D-crystallins exposes the side chains of several hydrophobic residues in the sequence to the solvent, causing the molecule to self-aggregate. This feature appears to be reflected in situ on the introduction of the mutants in human lens epithelial cells.

Stereochemistry of peptides containing 1-aminocycloheptane-1-carboxylic acid (Ac-c)

The crystal structures of four peptides incorporating 1-aminocycloheptane-1-carboxylic acid (Ac7c) are described. Boc-Aib-Ac7c-NHMe and Boc-Pro-Ac7c-Ala-OMe adopt beta-turn conformations stabilized by an intramolecular 4----1 hydrogen bond, the former folding into a type-I/III beta-turn and the latter into a type-II beta-turn. In the dipeptide esters, Boc-Aib-Ac7c-OMe and Boc-Pro-Ac7c-OMe, the Ac7c and Aib residues adopt helical conformations, while the Pro residue remains semi-extended in both the molecules of Boc-Pro-Ac7c-OMe found in the asymmetric unit. The cycloheptane ring of Ac7c residues adopts a twist-chair conformation in all the peptides studied. 1H-NMR studies in CDCl3 and (CD3)2SO and IR studies in CDCl3 suggest that Boc-Aib-Ac7c-NHMe and Boc-Pro-Ac7c-Ala-OMe maintain the beta-turn conformations in solution.

Mass Spectrometry-Based Systems Approach for Identification of Inhibitors of Plasmodium falciparum Fatty Acid Synthase{triangledown}

The emergence of strains of Plasmodium falciparum resistant to the commonly used antimalarials warrants the development of new antimalarial agents. The discovery of type II fatty acid synthase (FAS) in Plasmodium distinct from the FAS in its human host (type I FAS) opened up new avenues for the development of novel antimalarials. The process of fatty acid synthesis takes place by iterative elongation of butyryl-acyl carrier protein (butyryl-ACP) by two carbon units, with the successive action of four enzymes constituting the elongation module of FAS until the desired acyl length is obtained. The study of the fatty acid synthesis machinery of the parasite inside the red blood cell culture has always been a challenging task. Here, we report the in vitro reconstitution of the elongation module of the FAS of malaria parasite involving all four enzymes, FabB/F (β-ketoacyl-ACP synthase), FabG (β-ketoacyl-ACP reductase), FabZ (β-ketoacyl-ACP dehydratase), and FabI (enoyl-ACP reductase), and its analysis by matrix-assisted laser desorption-time of flight mass spectrometry (MALDI-TOF MS). That this in vitro systems approach completely mimics the in vivo machinery is confirmed by the distribution of acyl products. Using known inhibitors of the enzymes of the elongation module, cerulenin, triclosan, NAS-21/91, and (–)-catechin gallate, we demonstrate that accumulation of intermediates resulting from the inhibition of any of the enzymes can be unambiguously followed by MALDI-TOF MS. Thus, this work not only offers a powerful tool for easier and faster throughput screening of inhibitors but also allows for the study of the biochemical properties of the FAS pathway of the malaria parasite.

Mass Spectrometry-Based Systems Approach for Identification of Inhibitors of Plasmodium falciparum Fatty Acid Synthase{triangledown}

The emergence of strains of Plasmodium falciparum resistant to the commonly used antimalarials warrants the development of new antimalarial agents. The discovery of type II fatty acid synthase (FAS) in Plasmodium distinct from the FAS in its human host (type I FAS) opened up new avenues for the development of novel antimalarials. The process of fatty acid synthesis takes place by iterative elongation of butyryl-acyl carrier protein (butyryl-ACP) by two carbon units, with the successive action of four enzymes constituting the elongation module of FAS until the desired acyl length is obtained. The study of the fatty acid synthesis machinery of the parasite inside the red blood cell culture has always been a challenging task. Here, we report the in vitro reconstitution of the elongation module of the FAS of malaria parasite involving all four enzymes, FabB/F (β-ketoacyl-ACP synthase), FabG (β-ketoacyl-ACP reductase), FabZ (β-ketoacyl-ACP dehydratase), and FabI (enoyl-ACP reductase), and its analysis by matrix-assisted laser desorption-time of flight mass spectrometry (MALDI-TOF MS). That this in vitro systems approach completely mimics the in vivo machinery is confirmed by the distribution of acyl products. Using known inhibitors of the enzymes of the elongation module, cerulenin, triclosan, NAS-21/91, and (–)-catechin gallate, we demonstrate that accumulation of intermediates resulting from the inhibition of any of the enzymes can be unambiguously followed by MALDI-TOF MS. Thus, this work not only offers a powerful tool for easier and faster throughput screening of inhibitors but also allows for the study of the biochemical properties of the FAS pathway of the malaria parasite.