Versatile new uranyl(VI) dihalide complexes supported by tunable organic amide ligands

A series of uranyl(VI) dihalide complexes UO2X2L2 (X = Cl, Br) supported by organic amide ligands (L = R'C(O)NR2; R' = i-Pr; R = i-Pr, i-Bu, s-Bu) offers the versatile combination of facile synthesis using benchtop methods, air-stable crystalline solids obtained in high yield, high solubility in common organic solvents and tunable steric/electronic properties.     

Electrospray tandem mass spectrometric analysis of zeaxanthin and its oxidation products

Carotenoids have been implicated in protection of the eye from light-mediated photo-toxicity caused by free radicals. Under conditions of normal oxidative stress the carotenoids serve as protective antioxidants; however, when the oxidative stress exceeds the antioxidant capacity, carotenoids can be oxidized into numerous cleavage products. The determination and identification of oxidized carotenoids in biological samples remains a major challenge due to the small sample size and low stability of these compounds. We investigated the reaction of various zeaxanthin cleavage products with O-ethyl hydroxylamine to evaluate their levels in a biological sample. For this, a sensitive and specific electrospray tandem mass spectrometry (ESI-MS/MS) was developed, avoiding the classical lower sensitive and specific HPLC-UV and fluorescence absorption methods. Protonated molecules [M + H](+) of carotenoids upon collision-induced dissociation produced a number of structurally characteristic product ions. A series of complicated clusters of product ions differing in 14 (CH(2))and 26 (C(2)H(2))Da was characteristic of the polyene chain of intact carotenoids. All carotenoid ethyl oximes of zeaxanthin cleavage products were characterized by the losses of 60 and 61 Da in their MS/MS spectra. Through the application of the LC/MS/MS method, we identified two oxime derivatives of 3-hydroxy-beta-ionone and 3-hydroxy-14'-apocarotenal with protonated molecules at m/z 252 and m/z 370 respectively, in a human eye sample.     

Stopped-flow injection analysis. The influence of diffusion on dispersion of normal and reverse flow injection

A relationship is derived to enable the comparison of the dispersion heights of normal and reverse flow injection analysis (FIA). A single channel flow system is employed in the absence of a chemical reaction. The stopped-flow injection method is used to probe the influence of molecular diffusion on the overall dispersion of normal and reverse FIA, which appeared to demonstrate fundamentally different diffusion behaviors. Small discrepancies are observed between the dispersion heights, which are enhanced by the stopped-flow period, especially when unmatched matrix ionic compositions of the indicator and counter solutions were involved. For these conditions, the diffusion flux rate is enhanced considerably, displaying a peak, in addition to the transient, for both methods. The influence of diffusion on the dispersion characteristics of normal and reverse FIA is discussed theoretically. Diffusion in the proposed model is postulated to oppose dispersion by convection. The latter initiates concentration gradients in the injection zone and propagates it with flow time over the dispersion zone profile. The diffusion flux then reacts in order to confine the indicator dispersion for normal FIA and to enhance it for reverse FIA. This model is consistent with the experimental results and accounts for most of the phenomena encountered. Probably owing to the influence of secondary flow phenomena, the use of coiled tubes has suppressed the effects of diffusion on the overall dispersion behavior.Part of the experimental work was performed at IMI Institute for Research and Development, Haifa, Israel.