The role of the PsbU subunit in the light sensitivity of PSII in the cyanobacterium Synechococcus 7942

In the present study we investigated the role of the PsbU subunit in the electron transport characteristics and light sensitivity of the Photosystem II complex. The experiments were performed by using an earlier characterized PsbU-less mutant of the cyanobacterium Synechococcus PCC 7942, which has enhanced antioxidant capacity (Balint et al. FEBS Lett. 580 (2006) 2117-2122). Flash induced Chl fluorescence measurements in the presence and absence of the electron transport inhibitor DCMU showed that both the S(2)Q(A)(-) and the S(2)Q(B)(-) recombination is slowed down in the PsbU mutant relative to the WT strain. Thermoluminescence measurements confirmed the increased stability of the S(2)Q(A)(-) and S(2)Q(B)(-) charge pairs by showing an increased peak temperature of Q and B bands, which were measured in the presence and absence of DCMU, respectively. In addition, the intensity of the TL bands is also increased in the PsbU mutant (≈1.7 times for the B band), as compared to the WT. The PsbU mutant shows enhanced loss of Photosystem II activity under exposure to high light intensity both in the absence and presence of the protein synthesis inhibitor lincomycin. It is concluded from the data that the lack of the PsbU subunit in Synechococcus PCC 7942 affects the energetic stability of the S(2)Q(A)(-) and S(2)Q(B)(-) charge pairs by modifying both the PSII donor and acceptor side components. This effect is most likely caused by structural changes in the vicinity of the Mn cluster and in the inner part of the PSII complex, which are induced by the lack of the PsbU subunit from the lumenal part of the complex. The light sensitivity of Photosystem II in Synechococcus 7942 in the absence of the PsbU subunit is likely due to reactive oxygen species, which are produced as a consequence of disturbed donor side structure and/or due to the modified energetic properties of the primary radical pair.     

A DFT study of the origins of the stereoselectivity in the aldol reaction of bicyclic amino ketones in the presence of water

Experimental diastereoselectivities of the direct solvent-less (neat) aldol reactions of tropinone (8-methyl-8-azabicyclo[3.2.1]octan-3-one) and granatanone (pseudopelletierine, 9-methyl-9-azabicyclo[3.3.1]nonan-3-one) in the presence of catalytic amounts of water are most accurately reproduced by thermodynamic distributions of isomeric products calculated in the gas phase at the B3LYP/6-31g(d) level of theory. Less than 30% systematic errors, on average, exist in the predicted anti/syn-diastereomeric ratio (dr) for the solvent-less reaction of tropinone with several aromatic aldehydes. The CPCM-B3LYP/6-31g(d) method reproduces the anti/syn-diastereomeric ratio of the aqueous aldol reaction of tropinone with several aromatic aldehydes with reasonable deviation (0-88%), excellent (0-10)% agreement was found for the reactions of tropinone and granatanone with benzaldehyde. Qualitatively satisfactory agreement was also found for dr values in different solvents (DMF, THF, and Et₃N). The density functional theory (DFT) results support the notion of the thermodynamic control of the reaction.     

Revelation of the nature of the reducing species in titanocene halide-promoted reductions

The fundamental nature of Ti(III) complexes generated in tetrahydrofuran by reduction of Cp(2)TiCl(2) has been clarified by means of cyclic voltammetry and kinetic measurements. While the electrochemical reduction of Cp(2)TiCl(2) leads to the formation of Cp(2)TiCl(2)(-), the use of metals such as Zn, Al, or Mn as reductants affords Cp(2)TiCl and (Cp(2)TiCl)(2) in a mixture having a dimerization equilibrium constant of 3 x 10(3) M(-)(1), independent of the metal used. Thus, we find it unlikely that the trinuclear complexes or ionic clusters known from the solid phase should be present in solution as previously suggested. The standard potentials determined for the redox couples Cp(2)TiCl(2)/Cp(2)TiCl(2)(-), (Cp(2)TiCl)(2)(+)/(Cp(2)TiCl)(2), Cp(2)TiCl(+)/Cp(2)TiCl, and Cp(2)Ti(2+)/Cp(2)Ti(+) increase in the order listed. However, the reactivity of the different Ti(III) complexes is assessed as (Cp(2)TiCl)(2) greater, similar Cp(2)TiCl approximately Cp(2)Ti(+) > Cp(2)TiCl(2)(-) in their reactions with benzyl chloride and benzaldehyde. None of the reactions proceed by an outer-sphere electron transfer pathway, and clearly the inner-sphere character is much higher in the case of Cp(2)Ti(+) than for (Cp(2)TiCl)(2), Cp(2)TiCl, and in particular Cp(2)TiCl(2)(-). As to the electron acceptor, the inner-sphere character increases, going from benzyl chloride to benzaldehyde, and it is suggested that the chlorine atom in benzyl chloride and the oxygen atom in benzaldehyde may function as bridges between the reactants in the transition state.     

Miscibility of gramicidin A-ethyl nonadecanoate in langmuir monolayers in the presence of salts dissolved in the subphase

The behavior of binary mixed Langmuir monolayers from gramicidin A (GA) and ethyl nonadecanoate (EN), spread on aqueous subphases containing NaCl and CaCl2, was investigated on the basis of the analysis of surface pressure-average area per molecule (pi-A) isotherms complemented with Brewster angle microscopy (BAM) images. Compression modulus versus surface pressure (C(S-1)-pi) curves indicate the existence of interactions in the GA-EN mixed monolayers at low surface pressures (below 5 mN m(-1)). However, for mixtures in which the ester is the predominant component, both GA and EN are miscible within regions from fully expanded to collapse. To examine the interactions between both components in the studied system, values of the mean molecular area per molecule (A12) were plotted as a function of molar fraction of gramicidin A (X(GA)). A12-X(GA) plots exhibit negative deviations from ideality at high surface pressures, wherein beta-helices of GA are vertically oriented in respect to the interface. However, at surface pressures below the plateau transition, which is due to reorientation of GA, the binary system obeys the additive rule. Brewster angle microscopy (BAM) was applied for a direct visualization of the monolayers morphologies. The obtained images prove that for molar ratios of GA > or = 0.3 and at surface pressures above 5 mN m(-1), both components are immiscible at the interface. The observed negative deviations from the additively rule were attributed to the formation of a three-dimensional phase in the mixed film, which provokes its contraction at the interface.     

Influence of the electronics of the phosphine ligands on the H-H bond elongation in dihydrogen complexes

Five new monocationic dihydrogen complexes of ruthenium of the type trans-[RuCl(eta(2)-H(2))(PP)(2)][BF(4)] (PP = bis-1,2(diarylphosphino)ethane, aryl = p-fluorobenzyl, 1a, benzyl, 2a, m-methylbenzyl, 3a, p-methylbenzyl, 4a, p-isopropylbenzyl, 5a) have been prepared by protonating the precursor hydride complexes trans-[RuCl(H)(PP)(2)] using HBF(4).OEt(2). The dihydrogen complexes are quite stable and have been isolated in the solid state. The intact nature of the H-H bond in these derivatives has been established from the short spin-lattice relaxation times (T1, ms) and observation of substantial H, D couplings in the HD isotopomers. The H-H bond distances (dHH, A) increase systematically from 0.97 to 1.03 A as the electron-donor ability of the substituent on the diphosphine ligand increases from the p-fluorobenzyl to the p-isopropylbenzyl moiety. The d(HH) in trans-[Ru(eta(2)-H(2))(Cl)((C(6)H(5)CH(2))(2)PCH(2)CH(2)P(CH(2)C(6)H(5))(2))(2)][BF(4)], 2a, was found to be 1.08(5) A by X-ray crystallography. In addition, two new 16-electron dicationic dihydrogen complexes of the type [Ru(eta(2)-H(2))(PP)(2)][OTf](2) (PP = (ArCH(2))(2)PCH(2)CH(2)P(CH(2)Ar)(2), Ar = m-CH(3)C(6)H(4-), 6a, p-CH(3)C(6)H(4)-, 7a) have also been prepared and characterized. These derivatives were found to possess elongated dihydrogen ligands.     

Calculation of the fine structure and intensity of the singlet-triplet transitions in the imidogen radical

The singlet-triplet transition moments are calculated for the NH radical by multiconfiguration self-consistent field (MCSCF) method with a quadratic response (QR) technique. The band systems in the visible region (b(1)Sigma(+)-->X(3)Sigma(-) and a(1)Delta-->X(3)Sigma(-)) of the NH radical are analyzed in comparison with previous ab initio treatments and with the recent experimental data in attempt to solve some discrepancies. The b(1)Sigma(+)-->X(3)Sigma(Omega)(-) transition moments ratio for the two spin sublevels Omega = 1 and Omega=0 of the ground state is well reproduced and the radiative lifetime of the b(1)Sigma(+) state (tau(b)=58 ms) is obtained in a good agreement with the experimental value tau(b)=53((-13)(+17)) ms. The A(3)Pi<--a(1)Delta transition probability is calculated for the first time and found to be in an excellent agreement with the recent optical pumping measurements of the NH radical in a molecular beam, where population transfer from the metastable a(1)Delta state to the ground X(3)Sigma(-) state is achieved. For the a(1)Delta-->X(3)Sigma(-) transition some improvement is achieved in comparison with the previous ab initio results, but the calculated radiative lifetime (tau(a)=3.9 s) is still much lower than the recent measurement provides (tau(a)=12.5 s). The zero field splitting and spin-rotation coupling constants are calculated for the ground state by different methods and advantage of the density functional theory is stressed.     

Voltammetric determination of traces of Cr(VI) in the flow system in the presence of bipyridyne

The voltammetric method of Cr(VI) determinations in the flow system, based on the combination of selective accumulation of the product of Cr(VI) reduction on HMDE and a very sensitive method of chromium determination in the presence of bipyridine [Z. Gao K.S. Siow, Electroanalysis 8 (1996) 602] is proposed. The calibration graphs were linear from 3x10(-9) to 3x10(-8) and from 5x10(-10) to 5x10(-9) mol l(-1) for accumulation times 120 and 600 s, respectively. The relative standard deviation (R.S.D.) was 6.5% (n=5) for Cr(VI) concentration 1x10(-8) mol l(-1) and the accumulation time 120 s. The influence of foreign ions commonly present in water samples is presented. Validation of the method was made by comparison of the results of analyses of tap water by another electrochemical method and by recovery test for river and mineral water.     

Monooxygenase stereoselectivity in the biosynthesis of stereoisomeric spiroacetals in the cucumber fly,Bactrocera cucumis

[reaction: see text] The stereoselectivity of hydroxylation of alkyltetrahydropyran-2-ols (or their biological equivalents) in the formation of stereoisomers of 2,8-dimethyl-1,7-dioxaspiro[5.5]undecanes in male Bactrocera cucumis has been investigated. Racemic, (6R)-, and (6S)-6-methyl-2-[5-(2)H(1)]-n-pentyltetrahydropyran-2-ol was administered under an [(18)O(2)]-enriched atmosphere. The stereochemistry and isotopic composition of generated spiroacetals were monitored by combined enantioselective GC-MS. The monooxygenase(s) strongly prefers the (6S)-substrate and furnishes predominantly the (S)-alcohol and then the (2S,6R,8S)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane. The (2S,6S,8R) and (2R,6S,8S) (E,Z)-isomers appear to be derived in vivo predominantly from (R)-hydroxylation of the (6S)-tetrahydropyranol.     

The role of the HOOO(-) anion in the ozonation of alcohols: large differences in the gas-phase and in the solution-phase mechanism

The mechanism of the ozonation of isopropyl alcohol was investigated for the gas and the solution phase using second-order many body perturbation theory and density functional theory (DFT) with the hybrid functional B3LYP and a 6-311++G(3df,3pd) basis set. A careful analysis of calculated energies (considering thermochemical corrections, solvation energies, BSSE corrections, the self-interaction error of DFT, etc.) reveals that the gas-phase mechanism of the reaction is dominated by radical or biradical intermediates while the solution-phase mechanism is characterized by hydride transfer and the formation of an intermediate ion pair that includes the HOOO(-) anion. The product distribution observed for the ozonation in acetone solution can be explained on the basis of the properties of the HOOO(-) anion. General conclusions for the ozonation of alcohols and the toxicity of ozone (inhaled or administered into the blood) can be drawn.     

Three Questionable Cases in the Chemistry of Quinoxalines and Benzodiazepines in the Way of the Syntheses of Benzimidazoles

The reaction of 3‐ethoxycarbonylmethylene‐3,4‐dihydroquinoxalin‐2(1H)‐one 5 with the Vilsmeier reagent, the treatment of 3‐(3,4‐dihydroquinoxalin‐2(1H)‐on‐3‐yl)‐1,2‐dihydro‐1,5‐benzodiazepin‐2(1H)‐one hydrochloride 7 with 10% sodium hydroxide and 3‐benzimidazoylquinoxaline‐2(1H)‐one 3 with both 1,2‐phenylenediamine dihydrochloride, and the reactions of 1,2‐phenylenediamine have been reinvestigated, and the structures of these reaction products have been revised. The aforementioned reactions have been shown to proceed with the formation of 1‐N,N‐dimethylaminomethylene‐2‐oxo‐1,2‐dihydrofuro[2,3‐b]quinoxaline 10 in the first case, the formation of 3‐[2‐(benzimidazol‐2‐on‐1‐yl)vinyl]‐1H‐quinoxalin‐2‐one 12 in the second case, and the formation of 2,3‐bis‐(1H‐benzimidazol‐2‐yl)quinoxaline 17 in the third case and not the formation of 3‐(N,N‐dimethylaminocarbonyl)furo[2,3‐b]quinoxaline hydrochloride 6 , the free base of 3‐(3,4‐dihydroquinoxalin‐2(1H)‐on‐3‐yl)‐1,2‐dihydro‐1,5‐benzodiazepin‐2(1H)‐one 7 , that is, compound 11 and benzodiazepine derivative 4 , as has been described earlier. In the third case, the formation of 2,3‐bis‐(1H‐benzimidazol‐2‐yl)quinoxaline 17 occurs according to the novel quinoxalin‐2(1H)‐one benzimidazole rearrangement discovered by us. The potential mechanisms for the investigated reactions are discussed.     

Refinements in the characterization of the heterogeneous dynamics of Li ions in lithium metasilicate

We have performed the molecular dynamics simulations of ionically conducting lithium metasilicate, Li(2)SiO(3), to get a more in depth understanding of the heterogeneous ion dynamics by separating out the partial contributions from localized and diffusive ions to the mean square displacement (MSD) , the non-Gaussian parameter alpha(2)(t), and the van Hove function G(s)(r,t). Several different cage sizes l(c) have been used for the definition of localized ions. Behaviors of fast ions are obtained by the subtraction of the localized component from the r(2)(t) of all ions, and accelerated dynamics is found in the resultant subensemble. The fractional power law of MSD is explained by the geometrical correlation between successive jumps. The waiting time distribution of jumps also plays a role in determining but does not affect the exponent of its fractional power law time dependence. Partial non-Gaussian parameters are found to be instructive to learn how long length-scale motions contribute to various quantities. As a function of time, the partial non-Gaussian parameter for the localized ions exhibits a maximum at around t(x2), the onset time of the fractional power law regime of . The position of the maximum is slightly dependent on the choice of l(c). The power law increases in the non-Gaussian parameter before the maximum are attributed to the Levy distribution of length scales of successive (long) jumps. The decreases with time, after the maximum has been reached, are due to large back correlation of motions of different length scales. The dynamics of fast ions with superlinear dependence in their MSD also start at time around the maximum. Also investigated are the changes of the characteristic times demarcating different regimes of on increasing temperatures from the glassy state to the liquid state. Relation between the activation energies for short time and long time regimes of is in accord with interpretation of ion dynamics by the coupling model.     

On the application of the Dumas technique for the determination of nitrogen in refractory nitrides

The classical Dumas apparatus has been modified. The generally recommended oxidants CuO and V(2)O(5), were found to give relatively high blank values and were therefore replaced by Cu(2)O. The preparation of the Cu(2)O is described. It is an exceptionally suitable oxidant for the Dumas analysis of the Group Va nitrides as well as manganese nitrides and molybdenum nitrides because it does not release oxygen into the gas phase. The reaction of the Group IVa nitrides as well as of CrN with CuO and Cu(2)O is, however, not completely quantitative at 1000-1150 degrees in reasonable reaction times. The results of the Dumas analysis of a Group IVa nitride should be corrected by measuring the nitrogen content of the residue (e.g., by hot extraction). The relative standard deviations do not exceed 0.38%. The nitrogen contents (% w/w) of the residues range from <0.001% for Mo(2)N + MoN to 0.54% for Cr(2)N + CrN. BN, Si(3)N(4) and AlN could not be decomposed with copper oxides under the conditions used. AlN could be analysed by adding V(2)O(5), but the rsd was 0.55% and the nitrogen content in the residue was 0.52% w/w. Neither BN nor Si(3)N(4) could be analysed by addition of V(2)O(5).     

On the mechanism of the initiation reaction in Grubbs-Hoveyda complexes

Grubbs-Hoveyda-type complexes with variable 4-R (complexes 1: 4-R = NEt(2), OiPr, H, F, NO(2)) and 5-R substituents (complexes 2: 5-R = NEt(2), OiPr, Me, F, NO(2)) at the 2-isopropoxy benzylidene ether ligand and with variable 4-R substituents (complexes 3: 4-R = H, NO(2)) at the 2-methoxy benzylidene ether ligand were synthesized and the respective Ru(II/III) redox potentials (ranging from ΔE = +0.46 to +1.04 V), and UV-vis spectra recorded. The initiation kinetics of complexes 1-3 with the olefins diethyl diallyl malonate (DEDAM), butyl vinyl ether (BuVE), 1-hexene, styrene, and 3,3-dimethylbut-1-ene were investigated using UV-vis spectroscopy. Electron-withdrawing groups at the benzylidene ether ligands were found to increase the initiation rates, while electron-donating groups lead to slower precatalyst activation; accordingly with DEDAM, the complex 1(NO(2)) initiates almost 100 times faster than 1(NEt(2)). The 4-R substituents (para to the benzylidene carbon) were found to have a stronger influence on physical and kinetic properties of complexes 1 and 2 than that of 5-R groups para to the ether oxygen. The DEDAM-induced initiation reactions of complexes 1 and 2 are classified as two-step reactions with an element of reversibility. The hyperbolic fit of the k(obs) vs [DEDAM] plots is interpreted according to a dissociative mechanism (D). Kinetic studies employing BuVE showed that the initiation reactions simultaneously follow two different mechanistic pathways, since the k(obs) vs [olefin] plots are best fitted to k(obs) = k(D)·k(4)/k(-D)·[olefin]/(1 + k(4)/k(-D)·[olefin]) + k(I)·[olefin]. The k(I)·[olefin] term dominates the initiation behavior of the sterically less demanding complexes 3 and was shown to correspond to an interchange mechanism with associative mode of activation (I(a)), leading to very fast precatalyst activation at high olefin concentrations. Equilibrium and rate constants for the reactions of complexes 1-3 with the bulky PCy(3) were determined. In general, sterically demanding olefins (DEDAM, styrene) and Grubbs-Hoveyda type complexes 1 and 2 preferentially initiate according to the dissociative pathway; for the less bulky olefins (BuVE, 1-hexene) and complexes 1 and 2 both D and I(a) are important. Activation parameters for BuVE reactions and complexes 1(NEt(2)), 1(H), and 1(NO(2)) were determined, and ΔS(?) was found to be negative (ΔS(?) = -113 to -167 J·K(-1)·mol(-1)) providing additional support for the I(a) catalyst activation.     

Substitution of the halogen atoms in α-halogenonitro compounds of the aliphatic series. 5. Use of the MNDO method to explain the behavior of the chlorine atom in the substitution reactions of chloronitroacetic acid derivatives

The geometric parameters, bond orders, and charge distributions in the molecules of ethyl nitroacetate (I), ethyl chloronitroacetate (II), chloronitroacetamide (III), ethyl chloroacetate (IV), and the anions of ethyl chloronitroacetate (V) and chloronitroacetamide (VI) were calculated by the MNDO method. On the basis of the calculated data and their comparison with the data from x-ray crystallographic analysis (XCA) it was concluded that the nitro group in (II) and (III) is substituted relatively easily, that the order of the C-N bond in (V) and (VI) is close to first, that the charges in the anions alternate, and that there is no conjugation in the C-Cl bond in the.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2012–2017, September, 1990.     

Increased enantioselectivity in the addition of diethylzinc to benzaldehyde by the use of chiral ligands containing the alpha-phenylethylamino group in combination with achiral ligands

Chiral ligands (S,S)-1, (S,S)-2, (S,S)-3, (S)-4, (S)-5, (S,S)-6, (S,S)-7, and (S,S)-8 turned out to be effective promoters in the enantioselective addition of diethylzinc to benzaldehyde. Interestingly, diamine (S,S)-3 and amino alcohols (S)-5 and (S,S)-7 induce the preferential formation of carbinol (R)-10 (unlike stereoinduction) whereas amido analogues (S,S)-2, (S)-4, and (S,S)-6 favor (S)-10 (like stereoinduction). Molecular modeling at the semiempirical PM3 level provided a reasonable interpretation based on conformational effects in the corresponding transition structures. Combinations of chiral ligands 1-8 with an achiral, flexible ligand (9) gave rise to an activated catalytic system that resulted in faster and higher yielding reactions. Furthermore, substantial increases in the observed enantiomeric excesses of product 10 confirmed the relevant role of achiral bis(sulfonamide) 9 as activator and "chiral environment amplifier".     

Irregularities in the effect of potassium phosphate in ynamide synthesis

The yields of ynamides using Hsung's second generation protocol depend substantially on the quality of K(3)PO(4). Samples of K(3)PO(4) from different suppliers were investigated by various techniques, revealing that the use of pure and anhydrous K(3)PO(4) provides higher ynamide yields in comparison to samples contaminated with hydrates (K(3)PO(4) x 1.5 H(2)O and K(3)PO(4) x 7 H(2)O). With high quality K(3)PO(4), a number of ynamides were synthesized in yields of 52-91%. In addition, we report that ynamides can undergo regioselective hydroamination with carbamates.     

A theoretical analysis of the free-energy profile of the different pathways in the alkaline hydrolysis of methyl formate in aqueous solution

The free-energy profile for the different reaction pathways available to the hydroxide ion and methyl formate in aqueous solution is reported for the first time. The theoretical analysis was carried out by using the cluster-continuum method recently proposed by us for calculating the free energy of solvation of ions. Unlike the gas-phase reaction, our results are consistent with the fact that the reaction occurs mainly by nucleophilic attack of the hydroxide on the carbonyl carbon to yield a tetrahedral intermediate (B(AC)2 mechanism). However, an additional pathway, in which the hydroxide ion acts as a general base and a water molecule coordinated to this ion acts as the nucleophile, is also predicted to be important. The relative importance of these pathways is calculated to be 87 % and 13 %, respectively. The tetrahedral intermediate of the hydrolysis reaction has an estimated lifetime of 10 nanoseconds, and its conjugate acid has a pK(a) of 8.8. This tetrahedral intermediate is predicted to proceed to products by two pathways: elimination of methoxide ion (84 %) and by water catalyzed elimination of methanol (16 %). The less common reaction pathway, which involves attack of the hydroxide ion on the formyl hydrogen (decarbonylation mechanism) and leads to water, carbon monoxide, and methanol, is calculated to be only 3 kcal mol(-1) less favorable than the B(AC)2 mechanism. By comparison, direct attack of the hydroxide ion on the methyl group (B(AL)2 or S(N)2 mechanism) leading to an acyl-oxygen bond cleavage has a very high free energy of activation and is not expected to be important. The theoretically observed activation free energy at 298.15 K is calculated to be 15.5 kcal mol(-1), in excellent agreement with the experimentally measured value of 15.3 kcal mol(-1). This present model allows for a clear distinction between contributions due to solvation and those due to intrinsic (gas-phase) effects and proves to yield results in very good agreement with available experimental data.     

Advances in the gas chromatographic determination of persistent organic pollutants in the aquatic environment

Environmental chemists have been challenged for over 30 years to analyse complex mixtures of halogenated organic pollutants like polychlorinated biphenyls (PCBs), polychlorinated alkanes (PCAs), polybrominated diphenyl ethers (PBDEs) and polychlorinated dibenzo-p-dioxins and polychlorinated furans (PCDD/Fs). Gas chromatography (GC) often proved to be the method of choice because of its high resolution. The recent developments in the field of comprehensive two-dimensional GC (GCxGC) show that this technique can provide much more information than conventional (single-column) GC. Large volume injection (e.g. by programmed temperature vaporiser, or on-column injection) can be employed for the injection of tens of microliters of sample extract, in that way substantially improving the detection limits. Electron-capture detection (ECD) is a sensitive detection method but unambiguous identification is not possible and misidentification easily occurs. Mass spectrometric (MS) detection substantially improves the identification and the better the resolution (as with MS/MS, time-of-flight (TOF) MS and high-resolution (HR)MS), the lower the chances of misidentification are. Unfortunately, this comes only with substantially higher investments and maintenance costs. Co-extracted lipids, sulphur and other interferences can disturb the GC separation and detection leading to unreliable results. Extraction, and more so, sample clean-up and fractionation, are crucial steps prior to the GC analysis of these pollutants. Recent developments in sample extraction and clean-up show that selective pressurised liquid extraction (PLE) is an effective and efficient extraction and clean-up technique that enables processing of multiple samples in less than 1h. Quality assurance tools such as interlaboratory studies and reference materials are very well established for PCDD/Fs and PCBs but the improvement of that infrastructure is needed for brominated flame retardants, PCAs and toxaphene.     

Variation of the isotopic composition of xenon in the solar system

Re-examination of a vast amount of existing xenon isotope data, which have been accumulated in the literature since the 1960's, reveals that the variation of the isotopic composition of xenon in the solar system can be attributed to a combined effect of (a) mass-fractionation, (b) spallation and (c) stellar-temperature neutron-capture reactions plus the addition of (d) the beta-decay product of ¹²⁹I and of (e) the spontaneous fission products of ²⁴⁴Pu. The effect of each of the above-mentioned processes can be extremely large, due, primarily to the fact that these processes occurred in the interior of a supernova, which exploded about 5.1 billion years ago.     

CP/MAS spectroscopy in the determination of the tautomeric forms of gossypol, its Schiff bases and hydrazones in the solid state

New Schiff bases and new hydrazones were synthesized and studied by (13)C and (15)N CP/MAS spectroscopy and by (1)H--(1)H COSY, (1)H--(13)C HMBC, (1)H--(13)C HSQC, (1)H--(15)N HMQC and (1)H--(15)N HSQC correlations. The CP/MAS investigation of gossypol has demonstrated that in the solid state it exists exclusively in the aldehyde-aldehyde tautomeric form. In contrast, CP/MAS studies of hydrazones and Schiff bases reveal that these compounds occur in the solid state in the N-imine-N-imine and enamine-enamine tautomeric forms, respectively. It is shown that the (13)C resonances of C-6, C-7 and C-11 carbon atoms are suitable for distinguishing between the tautomeric forms of aza-derivatives of gossypol in the solid state. Furthermore, we have proved that the (15)N CP/MAS spectra can be used to identify these tautomeric forms.