Synthesis and Crystal Structure of [Co(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>](C<Subscript>19</Subscript>H<Subscript>17</Subscript>O<Subscript>4</Subscript>SO<Subscript>3</Subscript>)<Subscript>2</Subscript>⋅8H<Subscript>2</Subscript>O

The title compound, cobalt 4′,7-diethoxylisoflavone-3′-sulfonate([Co(H₂O)₆](X)₂⋅8H₂O, X = C₁₉H₁₇O₄SO₃) was synthesized and its structure was determined by single-crystal X-ray diffraction analysis. It crystallizes in the triclinic space group P-1 with cell parameters a = 9.026(3) Å, b = 16.431(5) Å, c = 18.195(6) Å, α = 72.289(4)^∘, β = 87.498(4)^∘, γ = 82.775(5)^∘, V = 2550.1(13) Å⁻³, D_c = 1.419 Mg m⁻³, and Z = 2. The results show that the title compound consists of one cobalt cation, six coordinated water molecules, eight lattice water molecules, and two 4′,7-diethoxylisoflavone-3′-sulfonate anions, C₁₉H₁₇O₄SO⁻₃. Two anions have different conformations. Twelve H atoms of six coordinated water molecules, as donors, form hydrogen bonds with four oxygen atoms of sulfo-groups of two anions and eight oxygen atoms of eight lattice water molecules. In addition, π < eqid1 > ⋅ < eqid2 > π stacking interactions exist in the crystal structure, which together with hydrogen bonds lead to supramolecular formation with a three-dimensional network.     

Study of donepezil binding to serum albumin by capillary electrophoresis and circular dichroism

The interaction between human serum albumin (HSA) and the acetylcholinesterase inhibitor donepezil, has been studied by means of capillary electrophoresis frontal analysis (CE/FA) and circular dichroism. CE/FA enabled rapid and direct estimation of the quantity of free donepezil present at equilibrium with a physiological level of serum albumin (600 mol L^–1). Application of Scatchard analysis enabled estimation of the binding parameters of HSA towards donepezil, such as association constant and number of binding sites on one protein molecule. Furthermore, due to enantioseparation ability shown by HSA on donepezil in CE mode, displacement experiments were carried out using ketoprofen and warfarin as coadditives to the HSA based running buffer. The addition of these compounds reduced the enantioresolution of donepezil by HSA only when used at high concentration. These data were confirmed and corroborated by circular dichroism (CD) experiments. Using CD, bilirubin was also applied as a ligand specific to site III of HSA. The observed behaviour suggested that donepezil could be considered a ligand with independent binding to sites I and II; although site III is not the highest affinity site, indirect interaction (i.e. cooperative binding) can be assumed.     

Sodium Borohydride – Ammonium Carbonate: An Effective Reducing System for Aldehydes and Ketones

Summary. Reduction of aldehydes and ketones to the corresponding alcohols was achieved in a simple procedure using the system sodium borohydride and ammonium carbonate. This system needs lower excesses of reducing agent and leads to significantly shortened reaction times.     

Pressurised solvent extraction for organotin speciation in vegetable matrices

Because organotin compounds (OTC) are widely used in many fields of activity, they have become an ubiquitous environmental presence. The presence of organotins in the environment impacts upon food safety, making it important to monitor the levels of organotin pesticides in fruits and vegetables. Nevertheless, only a few studies have been published on organotin speciation in plants. The objective of the present study was to evaluate and optimise a specific procedure based on pressurised solvent extraction (PSE) that is suitable for monitoring organotin content in vegetables. In ASE, solvents are used at elevated temperatures and pressures to increase the rate and efficiency of the extraction process. The results from this procedure were compared to those from the technique usually employed, solid/liquid extraction (SLE) performed in an acidic solvent by mechanical shaking. Three extracting solutions were tested—methanol, ethyl acetate and a mixture of methanol and ethyl acetate—and the mixture was found to give the most quantitative results while preserving the speciation. French bean and lettuce leaves as well as potato tubers were used as the plant materials. These vegetables were considered because they are the vegatables consumed in the most quantities in Europe. The study focuses on trisubstituted OTCs, which are the most toxic tin species. The samples were spiked with four trisubstituted organotins: tributyltin (TBT), triphenyltin (TPhT), tricyclohexyltin (TcHexT) and trioctyltin (TOcT). The influence of the pressure and the temperature of the PSE on the quantitativity of the process and on species preservation was evaluated using the experimental design methodology. The optimised PSE allowed detection limits down to 1–2 ng (Sn) g^–1 to be reached. These are higher than those obtained by SLE (0.1–1 ng (Sn) g^–1). Although the repeatability is similar for both PSE and SLE (2–12% for triorganotin compounds), this appears to be highly time-dependent in the case of SLE. Comparison with SLE confirms that PSE is an interesting tool for vegetable analysis considering the satisfactory OTC preservation and repeatability obtained for a relatively short extraction duration (only 15 min against 2–12 h for SLE).     

Partialsynthese der Grandidone A, 7-Epi-A,B, 7-Epi-B,C, D und 7-Epi-D aus 14-Hydroxytaxodion

Partial Synthesis of Grandidones A, 7-Epi-A, B, 7-Epi-B, C, D and 7-Epi-D, from 14-Hydroxytaxodione Oxydative addition of coleon U ( 6 ) to 14-hydroxytaxodione ( 5 ) in the presence of Fétizon's reagent mainly leads to grandidone A ( 1a ) and 7-epigrandidone A ( 1b ) (ca. 15:1), whereas coleon V ( 7 ) and 5 under the same conditions yield grandidone B ( 2a ) and 7-epigrandidone B ( 2b ) (ca. 3:1). Dimerization of 14-hydroxytaxodione ( 5 ) gives grandidone C ( 3 ; ca. 40%), grandidone D ( 4a ; ca. 50%) and 7-epigrandidone D ( 4b ; ca. 10%). All these compounds obtained by partial synthesis are in every respect identical with the natural products, thus establishing their absolute configurations. The thermal transformation of grandidone C ( 3 ) to grandidone D ( 4a )/7-epigrandidone D ( 4b ) and interconversions of 4a and 4b were achieved. Oxydative addition of coleon U ( 6 ) to 14-hydroxytaxodione ( 5 ) in the presence of Fétizon's reagent mainly leads to grandidone A ( 1a ) and 7-epigrandidone A ( 1b ) (ca. 15:1), whereas coleon V ( 7 ) and 5 under the same conditions yield grandidone B ( 2a ) and 7-epigrandidone B ( 2b ) (ca. 3:1). Dimerization of 14-hydroxytaxodione ( 5 ) gives grandidone C ( 3 ; ca. 40%), grandidone D ( 4a ; ca. 50%) and 7-epigrandidone D ( 4b ; ca. 10%). All these compounds obtained by partial synthesis are in every respect identical with the natural products, thus establishing their absolute configurations. The thermal transformation of grandidone C ( 3 ) to grandidone D ( 4a )/7-epigrandidone D ( 4b ) and interconversions of 4a and 4b were achieved. Oxydative addition of coleon U ( 6 ) to 14-hydroxytaxodione ( 5 ) in the presence of Fétizon's reagent mainly leads to grandidone A ( 1a ) and 7-epigrandidone A ( 1b ) (ca. 15:1), whereas coleon V ( 7 ) and 5 under the same conditions yield grandidone B ( 2a ) and 7-epigrandidone B ( 2b ) (ca. 3:1). Dimerization of 14-hydroxytaxodione ( 5 ) gives grandidone C ( 3 ; ca. 40%), grandidone D ( 4a ; ca. 50%) and 7-epigrandidone D ( 4b ; ca. 10%). All these compounds obtained by partial synthesis are in every respect identical with the natural products, thus establishing their absolute configurations. The thermal transformation of grandidone C ( 3 ) to grandidone D ( 4a )/7-epigrandidone D ( 4b ) and interconversions of 4a and 4b were achieved. Oxydative addition of coleon U ( 6 ) to 14-hydroxytaxodione ( 5 ) in the presence of Fétizon's reagent mainly leads to grandidone A ( 1a ) and 7-epigrandidone A ( 1b ) (ca. 15:1), whereas coleon V ( 7 ) and 5 under the same conditions yield grandidone B ( 2a ) and 7-epigrandidone B ( 2b ) (ca. 3:1). Dimerization of 14-hydroxytaxodione ( 5 ) gives grandidone C ( 3 ; ca. 40%), grandidone D ( 4a ; ca. 50%) and 7-epigrandidone D ( 4b ; ca. 10%). All these compounds obtained by partial synthesis are in every respect identical with the natural products, thus establishing their absolute configurations. The thermal transformation of grandidone C ( 3 ) to grandidone D ( 4a )/7-epigrandidone D ( 4b ) and interconversions of 4a and 4b were achieved.     

A method for calculating <Superscript>16</Superscript>o/<Superscript>18</Superscript>o peptide ion ratios for the relative quantification of proteomes

A method is described for the identification and relative quantification of proteomes using accurate mass tags (AMT) generated by nLC-dual ESI-FT-ICR-MS on a 7T instrument in conjunction with stable isotope labeling using 16O/18O ratios. AMTs were used for putative peptide identification, followed by confirmation of peptide identity by tandem mass spectrometry. For a combined set of 58 tryptic peptides from bovine serum albumin (BSA) and human transferrin, a mean mass measurement accuracy of 1.9 ppm +/-0.94 ppm (CIM99%) was obtained. This subset of tryptic peptides was used to measure 16O/18O ratios of 0.36 +/- 0.09 (CIM99%) for BSA (micro = 0.33) and 1.48 +/- 0.47 (CIM99%) for transferrin (micro = 1.0) using a method for calculating 16O/18O ratios from overlapping isotopic multiplets arising from mixtures of 16O, 18O1, and 18O2 labeled C-termini. The model amino acid averagine was used to calculate a representative molecular formula for estimating and subtracting the contributions of naturally occurring isotopes solely as a function of peptide molecular weight. The method was tested against simulated composite 16O/18O spectra where peptide molecular weight, 16O/18O ratio, 18O1/18O2 ratios, and number of sulfur atoms were varied. Relative errors of 20% or less were incurred when the 16O/18O ratios were less than three, even for peptides where the number of sulfur atoms was over- or under-estimated. These data demonstrate that for biomarker discovery, it is advantageous to label the proteome representing the disease state with 18O; and the method is not sensitive to variations in 18O1/18O2 ratio. This approach allows a comprehensive differentiation of expression levels and tentative identification via AMTs, followed by targeted analysis of over- and under-expressed peptides using tandem mass spectrometry, for applications such as the discovery of disease biomarkers.     

Fundamentals of Silicon Chemistry: Molecular States of Silicon-Containing Compounds

Silicon and its compounds have made possible the design of new materials, which, from computers to space travel, have helped to shape the technology of our 20th century. Conversely, the demands of new technology have stimulated the fast development of silicon chemistry as part of the “renaissance” of inorganic chemistry. This article uses selected examples of predominantly organosilicon compounds to discuss in simplified terms the measurement and assignment of suitable spectroscopic “molecular fingerprints” as well as the resulting benefit for the preparative chemist. The comparison of “equivalent” states of “chemically related” molecules is emphasized, based on perturbation arguments and supporting quantum-chemical models. Special attention is given to the relation between structure and energy, which allows us to understand and to predict the connectivity between and the spatial arrangement of silicon “building blocks”, the energy-dependent electron distribution over the effective nuclear potentials of a molecular framework, and, especially, the partly considerable effects of “silicon substituents” on molecular properties. Future-directed extensions and applications include polysilane band structures, Rydberg states of chromophores containing silicon centers, redox reactions and ion-pair formation of silicon-substituted π systems, and molecular dynamic phenomena in solution or on thermal fragmentation in the gas phase. The main objective is a set of clear and practical rules for interpreting measurements and planning experiments.     

In-capillary micro solid-phase extraction and capillary electrophoresis separation of heterocyclic aromatic amines with nanospray mass spectrometric detection

A miniaturised technique to analyse and detect heterocyclic aromatic amines (HAs) using micro solid-phase extraction (SPE) coupled on-line (in-capillary) to capillary electrophoresis (CE) separation with nanospray (nESI) mass spectrometry (MS) detection has been developed. HAs are mutagenic and carcinogenic compounds formed at low levels in protein-rich food during cooking. Due to the low concentrations of HAs and the high complexity of the matrix in which they exist, sensitive and selective analytical methods are required for quantification. SPE was performed on a packed bed of C₁₈ particles inside the CE capillary, which minimised the dead volume. The on-line coupling of SPE, CE and nESI-MS reduced the time for extraction and identification to less than half an hour, which will allow for screening of several samples per day. The new technique provides short analysis time, low sample and solvent consumption, and HAs in standard solutions were easily detected at 12–17 fmol injections, and in spiked urine samples at 750–810 fmol injections.     

Novel large heteropolymetalate complexes formed from Ni(II) and cryptate [As<Subscript>4</Subscript>W<Subscript>40</Subscript>O<Subscript>140</Subscript><Superscript>28-</Superscript>

The heteropolytungstate (NH4)₂₀[Na2(H₂O)₂Ni(H₂O)₅{Ni(H₂O)}₂As₄W₄₀O₁₄₀] · 61H₂O is obtained by the reaction of Na₂₇[NaAs₄W₄₀O₁₄₀] · 60H₂O with NiCl₂ · 6H₂O and NH₄Cl in pH≈4.0. The structure and chemical composition are determined by X-ray diffraction analysis and element analysis. The crystal data and main structure refinement are: a = 1.33135(18) nm, b = 1.9722(3) nm, c = 3.6430(5) nm, α = 78.010(2)°, β = 82.145(2)δ, γ = 74.385(2)°, V = 8.978(2) nm³, triclinic crystal system, space group: P1, Z = 2, R1 = 0.0512, and wR2 = 0.0684(I >2σ). The four S2 sites of the big cyclic ligand [As₄W₄₀O₁₄₀]^28- are occupied by two Na⁺ and two Ni²⁺ respectively, and each site supplies four O_d coordinating to metal ion. The coordination number of Ni²⁺ is six, and that of two Na⁺ is five and six respectively. The third Ni²⁺ locates outside the cyclic [As₄W₄₀O₁₄₀]^28- and connects with one O_d, and its coordination number is six.     

Study of the mechanism of base induced dehydrobromination of trans-β-bromostyrene

Observation that rates of dehydrobromination of trans-β-bromostyrene (1) and the Hofmann degradation of tetrabutyl ammonium cation depend on strength of base in different ways and that treatment of 1 with base results in fast abstraction of the β-proton imply the possibility that the dehydrobromination of 1 could proceed via α-elimination and Ph migration. In order to clarify this question, β-¹³C-labeled 1 was obtained and subjected to PTC dehydrobromination which proceeds without migration of Ph. The obtained results are consistent with an irreversible E1cB mechanism.