Radical-based destruction of nitramines in water: kinetics and efficiencies of hydroxyl radical and hydrated electron reactions

In support of the potential use of advanced oxidation and reduction process technologies for the removal of carcinogenic nitro-containing compounds in water reaction rate constants for the hydroxyl radical and hydrated electron with a series of low molecular weight nitramines (R(1)R(2)-NNO(2)) have been determined using a combination of electron pulse radiolysis and transient absorption spectroscopy. The hydroxyl radical reaction rate constant was fast, ranging from 0.54-4.35 × 10(9) M(-1) s(-1), and seen to increase with increasing complexity of the nitramine alkyl substituents suggesting that oxidation primarily occurs by hydrogen atom abstraction from the alkyl chains. In contrast, the rate constant for hydrated electron reaction was effectively independent of compound structure, (k(av) = (1.87 ± 0.25) × 10(10) M(-1) s(-1)) indicating that the reduction predominately occurred at the common nitramine moiety. Concomitant steady-state irradiation and product measurements under aerated conditions also showed a radical reaction efficiency dependence on compound structure, with the overall radical-based degradation becoming constant for nitramines containing more than four methylene groups. The quantitative evaluation of these efficiency data suggest that some (～40%) hydrated electron reduction also results in quantitative nitramine destruction, in contrast to previously reported electron paramagnetic measurements on these compounds that proposed that this reduction only produced a transient anion adduct that would transfer its excess electron to regenerate the parent molecule.     

Stereoselective synthesis of N-alkylaziridines from N-chloroamines

We report the first racemic and stereoselective synthesis of cis- and trans-N-alkylaziridines viaN-chloroamines; using this methodology an N-3,4,5-trimethoxybenzylaziridine was synthesised and efficiently cleaved, affording the corresponding NH aziridine in high yield.     

Expedient synthesis of substituted (S)-N-(alpha-methylbenzyl)aziridines

We report for the first time that after O-acylation the conjugate addition products of (S)-N-(alpha-methylbenzyl)hydroxylamine undergo an efficient diastereoselective 3-exo-tet ring-closure reaction affording 2- and 2,3-disubstituted-N-alkylaziridines in good to excellent yields.     

Carbamoylation Applied for Structure Determination of Cellulose Derivatives

Carbamoylation of cellulose esters (CE) and investigation of the mixed derivatives obtained with NMR spectroscopy represents a useful analytical tool for the determination of the degree of substitution (DS) and analysis of the distribution of substituents on the level of the anhydroglucose unit (AGU). Especially the carbethoxymethylcarbamoylation and the ethylcarbamoylation of CE combined with ¹H NMR spectroscopy are efficient and inexpensive ways to gain information on the over-all DS and partial DS values in position 2, 3, and 6 of the AGU. Complete subsequent phenylcarbamoylation can be achieved even for CE with bulky substituents, e.g., adamantanecarboxylic acid esters. In addition to NMR experiments the carbamoylated CE were studied by HPLC after complete chain degradation. Carbethoxymethylcarbamoylation has turned out to be the most useful tool for this path. Chromatograms comparable to carboxymethylated cellulose (CMC) were obtained, which can be exploited to calculate the mole fractions of the basic building units (un-, mono-, di- and tri-substituted glucoses) of the polymer. Comparison with statistic calculations gave a first hint on the distribution of substituents along the polymer chain. For a commercial cellulose diacetate a statistic pattern of substitution was determined.     

Design, synthesis and evaluation of a fluorescent peptidyl sensor for the selective recognition of arsenite

A series of fluorescently labelled phytochelatin-like peptide sequences has been designed and synthesised as molecules with the ability both to bind to arsenite and to report this binding event. The peptides have been evaluated against a panel of biologically significant ions. The results of these initial studies are reported herein, and a structure which displays selectivity for As(III) over As(V) and other anions has been identified.