Selective intracomplex reaction of pendant groups in a purine-pyrimidines base pair

Evidence is presented suggesting that hydrogen-bonded base pairing and/or aryl stacking interactions between derivatives of guanine (9-[(4-aminobutyloxy)-methyl]guanine) and cytosine (1-([(2-benzyloxy)ethoxy]methyl)cytosine) lead to enhanced intracomplex chemical reaction between the corresponding amino and ester groups. On the basis of analysis of the kinetic data it is concluded that a chain length of four methylene groups (4-amino- butyloxy as compared to 2-aminoethoxy or 6-aminohexyloxy) on the guanine is necessary to achieve the appropriate geometry for intracomplex reaction. Support for the reaction scheme is provided by the absence of reaction between the guanine derivative and a corresponding ester derivative of thymine, not expected to associate.     

Continuum Percolation with Unreliable and Spread-Out Connections

We derive percolation results in the continuum plane that lead to what appears to be a general tendency of many stochastic network models. Namely, when the selection mechanism according to which nodes are connected to each other, is sufficiently spread out, then a lower density of nodes, or on average fewer connections per node, are sufficient to obtain an unbounded connected component. We look at two different transformations that spread-out connections and decrease the critical percolation density while preserving the average node degree. Our results indicate that real networks can exploit the presence of spread-out and unreliable connections to achieve connectivity more easily, provided they can maintain the average number of functioningconnections per node.     

Crystallographic report: Trimethylaminedibromopropoxycarbonylborane

The conformation around the boron atom is nearly tetrahedral, with Br? B? Br bond angles of 109.14(19)° and slightly wider N? B? C bond angles up to 113.6(3)°. Copyright © 2005 John Wiley & Sons, Ltd.     

2-(4-Carboxyphenyl)-6-N,N-diethylaminobenzofuran: a useful reagent for the sensitive determination of alcohols by high-performance liquid chromatography with fluorimetric detection

A simple and highly sensitive method for the determination of short, medium and long-chain alcohols using high-performance liquid chromatography with fluorimetric detection is described. The alcohols were derivatized to their corresponding esters with (4-carboxyphenyl)-6-N,N-diethylaminobenzofuran. The esterification reaction proceeded rapidly and smoothly in acetonitrile at 60 degrees C with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (a coupling agent) in the presence of 4-dimethylaminopyridine (a base catalyst). The resulting esters of alcohols from methanol to eicosanol (C1-C20-ol) were separated on a reversed-phase column (Ultrasphere C8) with gradient elution (acetonitrile-water) and detected fluorometrically (excitation 387, emission 537 nm). The lower limits of detection (signal-to-noise ratio of 3) for the derivatized alcohols were in the range of 0.2-0.5 pg.     

Crystallographic report: Dimethyl‐2‐phenylethan‐2‐olamine cyanoborane

The structure of the title compound reveals the geometry around the boron atom to be tetrahedral, and the B? C?N moiety has a bent geometry. Copyright © 2005 John Wiley & Sons, Ltd.     

Determination of lipoic acid and dihydrolipoic acid in human plasma and urine by high-performance liquid chromatography with fluorimetric detection

A highly sensitive method for the determination of -lipoic acid (LA) and dihydrolipoic acid (DHLA) in human plasma and urine has been developed. Samples were acidified and extracted with organic solvent, and the free sulfhydryls of DHLA protected as the dicarboxyethylate by treatment with ethylchloroformate. The free carboxylic function of LA and the SH-protected DHLA were converted into their amide derivatives with the strong fluorophore 2-(4-aminophenyl)-6-methylbenzothiazole in the presence of a coupling agent and a base catalyst. The resulting fluorescent amides of both LA and DHLA were separated on a reversed-phase column (Ultrasphere C₈) using simple isocratic elution with acetonitrile–water (80:20) and detected fluorimetrically (excitation 343, emission 423 nm). The method is highly sensitive, reproducible, and is easily applied for the simultaneous determination of LA and DHLA in biological samples.     

Amidothionophosphates: Novel Antioxidant Molecules

Abstract

This work describes the synthesis and characterization of a new family of antioxidants. The molecules have the same active group, but different oil-to-water and octanol-to-water partition coefficients due to different substituents. Three new molecules were synthesized based on the chemical structure of the primary amide attached to a thiophosphate group forming an amidothionophosphate. The amidothionophosphate molecules were exposed to the oxidative stress of hydrogen peroxide and sodium hypochlorite, and the chemical changes following the exposure were monitored by 31P NMR. The reaction constants with reactive oxygen species such as hydroxyl radical and superoxide radical were also calculated and found to be 1.5?109 M-1 and 8.1?102 M-1S-1, respectively. In order to elucidate the ability of amidothionophosphates to act as antioxidants in protecting lipids and proteins, we examined damage prevention in Bovine serum albumin, egg phosphatidyl choline liposomes and lipid emulsions following oxidative smss. Amidothionophosphate showed unique protection properties in these models. In contrast to other antioxidant molecules (ascorbic acid, cystine, and a-tocopherol) the new group did not have any pro-oxidative effects as measured by oxygen consumption from buffer solutions containing amidothionophosphates and cupric sulfate as a redox-active metal. Amidothionophosphates reduced significantly and in a dose-dependent manner the oxidative burst in human neutrophils as measured by luminol-dependent chemiluminescence, and they also markedly depressed the killing of human fibroblasts by mixtures of glucose oxidase and streptolysin S. The toxicity of these molecules was tested by i.p. injection of up to 1000 mg/kg to white Sabra mice. No mortality was observed 30 days after administration of up to 500 mg/kg.