Konstantinos Kavallieratos

Speciation, formation, stability and analytical challenges of human arsenic metabolites

Human arsenic metabolism produces a number of species with varying toxicities; the presence of some has been identified while the existence of others has been postulated through indirect evidence. Speciation methods for the analysis of arsenite (AsIII), monomethylarsonous acid (MMAIII), dimethylarsinous acid (DMAIII), arsenate (AsV), monomethylarsonic acid (MMAV), dimethylarsinic acid (DMAV), arsino-glutathione (As(GS)3), monomethylarsino-glutathione (MMA(GS)2) and dimethylarsino-glutathione (DMA(GS)) were developed in this study through the use of cation exchange and reverse phase chromatography in a complementary manner. Electrospray ionization mass spectrometry (ESI-MS) was used for molecular identification of the arsenicals while inductively coupled plasma mass spectrometry (ICP-MS) was employed for quantitation purposes. Validation of the developed methods against each other for the quantitation of trivalent and pentavalent arsenicals was performed. The effect of reduced glutathione (GSH) concentration on the formation of arsenic-glutathione (As-GSH) complexes was studied. In the presence of glutathione, the occurrence of chromatographic artifacts on the cation exchange column was observed. The stability of trivalent arsenicals and As-GSH complexes was studied at various pH conditions. The results shed light on the importance of sample preparation, storage and proper choice of analytical column for the accurate identification of the As species. Reinvestigation of some of the previously reported As speciation studies of glutathione-rich biological samples needs to be performed for the verification of occurrence of As-GSH complexes and DMAIII.

Intermolecular Re–H···H–N and Re–H···base hydrogen bonding estimated in solution by a UV-VIS spectroscopic method

Hydrogen bonding (Re–H···H–N) is estimated in solution between ReH5(PPh3)2L (L=pyridine, 4-picoline, 4-dimethylaminopyridine, and 4-carbomethoxypyridine), as hydrogen bond acceptor, and indole, as hydrogen bond donor. Re–H···base hydrogen bonding between [Re(PPh3)2(MeCN)4H][BF4]2 as hydrogen bond donor and various amines as hydrogen bond acceptors is much weaker. The binding strengths are estimated by UV-VIS spectroscopy.

Glutathiyl radical as an intermediate in glutathione nitrosation.

Nitrosation of thiols is thought to be mediated by dinitrogen trioxide (N(2)O(3)) or by nitrogen dioxide radical (()NO(2)). A kinetic study of glutathione (GSH) nitrosation by NO donors in aerated buffered solutions was undertaken. S-nitrosoglutathione (GSNO) formation was assessed spectrophotometrically and by chemiluminescence. The results suggest an increase in the rate of GSNO formation with an increase in GSH with a half-maximum constant EC(50) that depends on NO concentration. Our observed increase in EC(50) with NO concentration suggests a significant contribution of ()NO(2)-mediated nitrosation with the glutathiyl radical as an intermediate in the production of GSNO.

Dual-Host Combinations: Using Tripodal Amides to Enhance Cesium Nitrate Extraction by Crown Ethers

Extraction of alkali metal salts by designed cation hosts, such as crown ethers 1 and calixarenes,2 has been widely investigated in recent years, as driven, to an extent, by the importance of separations of certain cationic contaminants such as Cs+ and Sr2+ in nuclear-fuel reprocessing and waste remediation. 3 New cation hosts used as extractants for these and other metals have reached impressive levels of selectivity for such demanding “needle-in-the-haystack” applications. The success of neutral cation hosts used in ion-pair extraction systems stems in part from the practical advantage of stripping extracted salts with water, resulting in processes that yield a pure salt product stream with little secondary waste. Examples of such practical ion-pair extraction applications include processes for nuclear-waste treatment that produce aqueous streams of relatively pure cesium nitrate2h or sodium pertechnetate,4 suitable for vitrification and geologic disposal. These processes employ calix-crown and crown ether extractants, such as those shown in Figure 1 for cesium. Although ion-pair extraction involves anion co-extraction, ligand design has focused primarily on the design of the cation host, typically with little or no attention to accommodating the anion.

Remarkably selective NH4+ binding and fluorescence sensing by tripodal tris(pyrazolyl) receptors derived from 1,3,5-triethylbenzene: structural and theoretical insights on the role of ion pairing

A fluorescent sensor for NH4+ based on 1,3,5-triethylbenzene shows remarkable binding and sensing selectivity for NH4+vs. K+. Fluorescence and NMR titrations reveal surprising differences in the sensing properties and binding constants of tris-(3,5-dimethyl)pyrazole 1vs. tris(3,5-diphenyl)pyrazole 2. The roles of ion pairing and solvation are revealed by X-ray and DFT studies.

1,3,5-Tris-(4-(iso-propyl)-phenylsulfamoylmethyl)benzene as a potential Am(III) extractant: experimental and theoretical study of Sm(III) complexation and extraction and theoretical correlation with Am(III)

ABSTRACT The problem of legacy alkaline high-level waste (HLW) both in the US and Russia, as a result of weapons production, has prompted studies of ligands for extraction of actinides, that could be possibly used in the future together with Cs extractants for combined HLW extraction processes. The tripodal trisulphonamide ligand 1,3,5-tris-(4-(iso-propyl)-phenylsulfamoylmethyl)benzene (4-iPr-tsa), which has pre-organised functional groups for An(III) binding was synthesised and studied for potential Sm(III) and Am(III) binding and extraction by theoretical (DFT) and experimental (extraction) methods (for Sm(III) only). Both theory and experiments suggest that even though this family of ligands shows promise for Ln(III) and An(III) binding with minima for complex formation, complexation is competing with hydrolysis, and extraction is only feasible in alkaline solutions, in the presence of high concentrations of nitrate ions. Nevertheless, up to 51.8% of Sm(III) was removed under optimal conditions (NaOH = 2 × 10−4 M, NaNO3 = 0.1 M, [Sm]init = 5 × 10−5 M). Quantum chemical calculations demonstrate that the extraction of Sm(III) and Am(III) from the aqueous phase in the form of [M·(H2O)4·(OH)2·(NO3)] to the organic phase in the form of [M·4-iPr-tsa·(H2O)3] is thermodynamically favourable. Theory also shows that Sm(III) is a reasonably good surrogate for Am(III), as the optimised structures of the Sm and Am complexes show remarkable similarities. Even though the ligand was designed with the goal of introducing favourable cation–arene interactions, along with the expected N-binding mode of the ligand in its deprotonated form, it was found that these cation–arene interactions are rather weak in this case, and coordination with O atoms of the sulphonamide, and external water molecules, is favoured instead. GRAPHICAL ABSTRACT

N,N′-(o-Phenyl­ene)dibenzene­sulfonamide

The N atoms of the title compound, C18H16N2O4S2, are not preorganized for metal cation binding. The N—H groups form hydrogen bonds with symmetry-equivalent sulfonamide groups.