Rudi van Eldik

Mass Spectrometric Analysis of Nitric Oxide-modified Caspase-3

Caspases are a family of cysteine proteases activated during apoptosis. Modification of caspases by nitric oxide and its relevance during apoptosis is currently a controversial subject. In this study we analyzed the S-nitrosated form of caspase-3 at a molecular level. By using electrospray ionization-mass spectrometry, we detected poly-S-nitrosation of caspase-3 with an average of about 2 molecules of NO bound per enzyme. Although NO treatment completely inhibited enzyme activity,S-nitrosation was not restricted to the active site cysteine. Rather, we detected multiple relative mass increases of 30 ± 1 Da in both the p12 and p17 subunits of caspase-3, corresponding to single to triple S-nitrosation. The stability of these S-nitrosations differed in physiologically relevant concentrations of 5 mmglutathione. Whereas all S-nitroso bonds in the p12 subunit were cleaved with release of NO and partial formation of protein-mixed disulfides with glutathione, a single S-nitrosation in the p17 subunit remained stable. Since this S-nitrosation was not observed in a mutant form of caspase-3 lacking the active site cysteine, we conclude that NO nitrosates the active site cysteine of caspase-3 and that this modification is notably inert to fast trans-nitrosation with glutathione. Furthermore, we provide evidence that treatment of caspase-3 with NO can lead to mixed disulfide formation with glutathione, demonstrating the oxidative character of NO.

Gutmann donor and acceptor numbers for ionic liquids.

We present for the first time Gutmann donor and acceptor numbers for a series of 36 different ionic liquids that include 26 distinct anions. The donor numbers were obtained by (23)Na NMR spectroscopy and show a strong dependence on the anionic component of the ionic liquid. The donor numbers measured vary from -12.3 kcal mol(-1) for the ionic liquid containing the weakest coordinative anion [emim][FAP] (1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate), which is a weaker donor than 1,2-dichloroethane, to 76.7 kcal mol(-1) found for the ionic liquid [emim][Br], which exhibits a coordinative strength in the range of tertiary amines. The acceptor numbers were measured by using (31)P NMR spectroscopy and also vary as a function of the anionic and cationic component of the ionic liquid. The data are presented and correlated with other solvent parameters like the Kamlet-Taft set of parameters, and compared to the donor numbers reported by other groups.

Molecular orbital and DFT studies on water exchange mechanisms of metal ions

Abstract An overview of recent molecular orbital theory and density functional theory studies on water exchange reactions of metal ions and complexes in solution is presented. The different theoretical techniques used are reviewed and representative examples are discussed. The mechanistic insight gained is discussed in reference to available experimental data and the predictive nature of the applied techniques is highlighted.

Tuning the Reversible Binding of NO to Iron(II) Aminocarboxylate and Related Complexes in Aqueous Solution

Chelate complexes of FeII were investigated with respect to their reactivity against nitric oxide and dioxygen. Through a systematic variation of the structure of the polyaminocarboxylate EDTA, a series of 38 potential chelate ligands were selected for FeII. The nitrosyl complexes were prepared from the FeII chelates with NO gas and examined spectroscopically by UV/Vis and ATR-IR techniques, and themodynamically by determining the overall binding constants for NO. In addition, the reversibility of NO binding to these FeII chelates and the rate of the competing oxidation by dioxygen were studied qualitatively. Whereas the studied complexes all form more or less stable nitrosyl complexes with a characteristic band pattern in the UV/Vis spectra and only slightly diverging frequencies for the NO stretching vibration in the IR spectra, they differ considerably in the reversibility of NO binding, the overall NO binding constants and the sensitivity towards dioxygen. It was found that an increasing number of donor groups on the chelate ligand causes a stronger coordination to FeII, and increases the tendency of the FeII chelates to transfer electron density from iron to substrates like dioxygen or nitric oxide. This results in an accelerated oxidation of FeII to FeIII by dioxygen and a more pronounced tendency of the corresponding nitrosyl complexes to slowly decompose to FeIII and N2O. In addition, the overall binding constant for NO (KNO), which spans a range from 1·103 to 2·107M−1, increases in the same direction as a result of the inductive effect of the chelate ligand.

New Mechanistic Aspects of the Fenton Reaction

The kinetics of the Fenton reaction was studied in detail. A second reaction step in the presence of excess H2O2 is attributed to formation of the complex Fe(III)(-O2H)(aq). Therefore, the reaction of Fe(H2O)(6)(2+) with Fe(III)(-O2H)(aq) in the presence of Fe(II) to form Fe(III)(aq) (k=(7.7+/-1.5) x 10(5) M(-1) s(-1)) may contribute to the overall Fenton reaction, and could account for some of the debate in the literature concerning its detailed mechanism. If this is correct for LFe(III)(-O2H)(aq) also, then it might be of significant biological importance. The activation parameters DeltaH(not equal), DeltaS(not equal), and DeltaV(not equal) for the Fenton reaction were measured under various experimental conditions, and are used in the mechanistic interpretation.

To be or not to be NO in coordination chemistry? A mechanistic approach

Abstract In this review, the reactions of nitric oxide with selected metal complexes of biological and environmental importance are reviewed. Fundamental chemical kinetics and mechanisms that lead to the formation and decay of nitrosyl complexes are illustrated and discussed on the basis of work on Fe(II) chelate complexes and selected biomolecules such as metmyoglobin and cobalamin. In the context of common interference of higher nitrogen oxides in the studies on the interactions of nitric oxide with metal centres, the reactions of NO 2 − /HONO (in aqueous media) and NO 2 /N 2 O 3 (in aprotic media) with metal complexes are described on the basis of selected examples. Throughout the review the focus is on the mechanistic details of the binding of NO to and the release of NO from metal complexes, and the nature of the stable metal–NO complexes produced in solution.

Metal ion-catalyzed oxidative degradation of Orange II by H2O2. High catalytic activity of simple manganese salts

In an effort to develop new routes for the clean oxidation of non-biodegradable organic dyes, a detailed study of some environmentally friendly Mn(II) salts that form very efficient in situcatalysts for the activation of H2O2 in the oxidation of substrates such as Orange II under mild reaction conditions, was performed. The studied systems have advantages from the viewpoint of green chemistry in that simple metal salts can be used as very efficient catalyst precursors and H2O2 is used as a green oxygen donor reagent. Oxidations were carried out in a glass reactor over a wide pH range in aqueous solution at room temperature. Under optimized conditions it was possible to degrade Orange II in a carbonate buffer solution in less then 100 s using 0.01 M H2O2 in the presence of only 2 × 10−5 M Mn(II) salt. To gain insight into the manganese catalyzed oxidation mechanism, the formation of the active catalyst was followed spectrophotometrically and appears to be the initiating step in the oxidative degradation of the dye. High valent manganese oxo species are instable in the absence of a stabilizing coordinating ligand and lead to a rapid formation of catalytically inactive MnO2. In this context, the role of the organic dye and HCO3− as potential stabilizing ligands was studied in detail. In situUV-Vis spectrophotometric measurements were performed to study the effect of pH and carbonate concentration of the buffer solution on the formation of the catalytically active species. Electrochemical measurements and DFT (B3LYP/LANL2DZp) calculations were used to study the in situ formation of the catalytic species. The catalytic cycle could be repeated several times and demonstrated an excellent stability of the catalytic species during the oxidation process. A mechanism that accounts for the experimental observations is proposed for the overall catalytic cycle.

Extraction of brominated flame retardants from polymeric waste material using different solvents and supercritical carbon dioxide

Abstract Different procedures were examined to extract pure and high concentrations of a series of brominated flame retardants from various polymer materials. These procedures include supercritical carbon dioxide (sc-CO 2 ), modified sc-CO 2 , solvent and soxhlet extraction. Extraction with sc-CO 2 gave low extraction efficiencies (between 6 and 20%) probably due to the low pressure of sc-CO 2 used. The use of toluene, acetonitrile and THF as modifier in sc-CO 2 raised the extraction efficiencies for many flame retardants. High extraction efficiencies were achieved for tetrabromobisphenol A (TBBPA), TBBPA-bis-(2,3-dibromopropylether) (TBBPA-dbp), TBBPA-carbonatoligomer (TBBPA-co) and decabromodiphenylether (DECA) (between 93 and 100%) by using 1-propanol as solvent during soxhlet extraction. Toluene instead of 1-propanol was used where insufficient extraction of the flame retardant occurred. The materials (before and after extraction) were analysed with energy dispersive X-ray fluorescence analysis (EDXRF), high performance liquid chromatography with ultraviolet detection (HPLC/UV), gas chromatography/mass spectrometry (GC/MS) and infrared spectroscopy (IR) techniques. The properties of the extracted flame retardants such as TBBPA, TBBPA-dbp and 1,2-bis(tribromophenoxy)-ethane (TBPE) are in good agreement with those of standard reference materials.

Identification of brominated flame retardants in polymeric materials by reversed-phase liquid chromatography with ultraviolet detection

Abstract A fast and simple method for the qualitative identification of technical flame retardants in polymeric materials is described. The LC separation was achieved on a reversed-phase C 18 column. The identification of a large variety of flame retardants in a single analytical LC run was achieved using a mixture of aqueous phosphate buffer and methanol with ultraviolet detection in the scanning mode. The method was used for the analysis of flame retardants in a number of polymeric waste materials from TV sets and personal computers, on the basis of a comparison with standards.

Drug Metabolism by Cytochrome P450 Enzymes: What Distinguishes the Pathways Leading to Substrate Hydroxylation Over Desaturation?

Cytochrome P450 enzymes are highly versatile biological catalysts in our body that react with a broad range of substrates. Key functions in the liver include the metabolism of drugs and xenobiotics. One particular metabolic pathway that is poorly understood relates to the P450 activation of aliphatic groups leading to either hydroxylation or desaturation pathways. A DFT and QM/MM study has been carried out on the factors that determine the regioselectivity of aliphatic hydroxylation over desaturation of compounds by P450 isozymes. The calculations establish multistate reactivity patterns, whereby the product distributions differ on each of the spin-state surfaces; hence spin-selective product formation was found. The electronic and thermochemical factors that determine the bifurcation pathways were analysed and a model that predicts the regioselectivity of aliphatic hydroxylation over desaturation pathways was established from valence bond and molecular orbital theories. Thus, the difference in energy of the OH versus the OC bond formed and the π-conjugation energy determines the degree of desaturation products. In addition, environmental effects of the substrate binding pocket that affect the regioselectivities were identified. These studies imply that bioengineering P450 isozymes for desaturation reactions will have to include modifications in the substrate binding pocket to restrict the hydroxylation rebound reaction.