Nickel oxidation states of F(430) cofactor in methyl-coenzyme M reductase

Magnetic circular dichroism (MCD) spectroscopy and variable-temperature variable-field MCD are used in combination with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to characterize the so-called ox1-silent, red1, and ox1 forms of the Ni-containing cofactor F430 in methyl-coenzyme M reductase (MCR). Previous studies concluded that the ox1 state, which is the precursor of the key reactive red1 state of MCR, is a Ni(I) species that derives from one-electron reduction of the Ni(II)-containing ox1-silent state. However, our absorption and MCD data provide compelling evidence that ox1 is actually a Ni(II) species. In support of this proposal, our DFT and TD-DFT calculations indicate that addition of an electron to the ox1-silent state leads to formation of a hydrocorphin anion radical rather than a Ni(I) center. These results and biochemical evidence suggest that ox1 is more oxidized than red1, which prompted us to test a new model for ox1 in which the ox1-silent species is oxidized by one electron to form a thiyl radical derived from coenzyme M that couples antiferromagnetically to the Ni(II) ion. This alternative ox1 model, formally corresponding to a Ni(III)/thiolate resonance form but with predicted S = 1/2 EPR parameters reminiscent of a Ni(I) (3dx2-y2)1 species, rationalizes the requirement for reduction of ox1 to yield the red1 species and the seemingly incongruent EPR and electronic spectra of the ox1 state.     

Quantitative measurement of collagen methylation by capillary electrophoresis

Collagen methylation has been exploited in various applications involving living cells. We have observed correlation between the collagen methylation with the rate of cell proliferation in three-dimensional (3-D) microenvironment. To quantify the degree of collagen methylation, we have developed a capillary zone electrophoresis method. Using a polyvinyl alcohol-coated fused-silica capillary and UV detection at 200 nm, we have optimized pH and separated the native collagen into three major bands in phosphate buffer (50 mM, pH 2.5) with 0.05% hydroxypropylmethylcellulose. Under these conditions, the methylated collagens were separated into four major bands, which changed with different methylation reaction conditions. We propose an index to quantify the degree of collagen methylation that also correlates with their effects on cell proliferation.     

Metal-thiophen derivatives. Organometallic compounds of palladium and platinum

Thienylmercury(II)chloride reacts with [Pd(PPh₃)₂Cl₂], [Pd(PPh₃)₄] and [Pt(PPh₃)₄] to afford new compounds containing a metal-2-thienyl linkage. The compound [Pd(PPh₃)₂(2-C₄H₃S)Cl] probably has trans stereochemistry.2-Bromothiophen undergoes oxidative addition with [Pd(PPh₃)₄] and [Pt(PPh₃)₄], probably via a radical mechanism. With [Pd(CO)(PPh₃)₃], a carbonyl inserted product is obtained. The bromo-metal(II) complexes have trans stereochemistry. The course of the reaction between 3-methyl-2-bromothiophen and Pd(PPh₃)₄ is more complex. Thus, there is evidence of some cis bromopalladium(II) compounds amongst the products, also there is good evidence to support the view that some isomerisation of 3-methyl-2-thienyl to 4-methyl-2-thienyl occurs during the reaction, thus giving greater molar quantities of [Pd(PPh₃)₂(4-CH₃-2-C₄H₂S)Br] than can be accounted for from any initial 4-methyl-2-bromothiophen impurity.The metallation of the thiophen ring, probably in the 4-position, with palladium(II) is described for 3-theylidene-4-methylaniline.     

2,3,7‐Triazabicyclo[3.3.0]octenes Prepared by Tandem Cascade Reaction of Allyl Azides and Olefinic Dipolarophiles

Tandem cascade reactions of allylazides and olefinic dipolarophiles to give cis‐fused 2,3,7‐triazabicyclo [3.3.0]octenes ( 5, 6 or 7 ) are reported. Therein, an intermolecular dipolar cycloaddition of azide and alkene gave a triazoline which was followed by isomerization of the triazoline to a diazoester ( 4 ) and then an intramolecular dipolar cycloaddition from the diazo functional group and the double bond in 4 to give 5 . Compound 5 may further more undergo a Michael addition to give 7‐substituted‐ 2,3,7‐ triazabicyclo [3.3.0]oct‐2‐ene ( 6 ) or a tautomerization to give 2,3,7‐triazabicyclo[3.3.0]oct‐3‐ene ( 7 ). The reaction may be manipulated to stop at a particular stage by adopting a suit able solvent or an appropriate temperature.     

Aqueous two-phase extraction as an effective tool for isolation of geniposide from gardenia fruit

Natural products are normally obtained by organic solvent extraction and many subsequent chromatographic separations. Compounds of interest are often isolated with very low yield and limited purity. An aqueous two-phase extraction process combined with a simple ethanol treatment, for removing excess inorganic salt, has been developed for preparation of geniposide from gardenia. The system was comprised of PE62, a random copolymer composed of 20% ethylene oxide and 80% propylene oxide, KH2PO4 and ethanol. To find optimal conditions, the partition behavior of geniposide under an aqueous two-phase system was investigated. Various factors were considered, including the concentration of salt, the concentration of polymer, the sample loading, and the addition of ethanol. The experimental results demonstrated that increasing salt concentration or decreasing PE62 concentration results in enhancement of the geniposide partition in the salt-rich phase. The addition of ethanol and higher sample loading also promoted the partition efficiency of geniposide. Based on this study, an optimized system containing 5% PE62, 7.5% KH2PO4, and 10% ethanol was tested on a large-scale extraction. A 39.0-g aliquot of final product (in powder form) with 77% purity of geniposide can be effectively extracted from 500 g of gardenia fruit. This process is proved to be useful for industrial application of geniposide preparation.     

Long‐range π‐type hydrogen bond in dimers CH2?HF,CH2O?H2O,and CH2O?NH3

Using four basis bets, (6‐311G(d,p), 6‐31+G(d,p), 6‐31++G(2d,2p), and 6‐311++G(3df,3pd), the optimized structures with all real frequencies were obtained at the MP2 level for the dimers CH₂O? HF, CH₂O? H₂O, CH₂O? NH₃, and CH₂O? CH₄. The structures of CH₂O? HF, CH₂O? H₂O, and CH₂O? NH₃ are cycle‐shaped, which result from the larger bend of σ‐type hydrogen bonds. The bend of σ‐type H‐bond O…H? Y (Y?F, O, N) is illustrated and interpreted by an attractive interaction of a chemically intuitive π‐type hydrogen bond. The π‐type hydrogen bond is the interaction between one of the H atoms of CH₂O and lone pair(s) on the F atom in HF, the O atom in H₂O, or the N atom in NH₃. In contrast with the above three dimers, for CH₂O? CH₄, because there is not a π‐type hydrogen bond to bend its linear hydrogen bond, the structure of CH₂O? CH₄ is noncyclic shaped. The interaction energy of hydrogen bonds and the π‐type H‐bond are calculated and discussed at the CCSD (T)/6‐311++G(3df,3pd) level. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

DNA LESIONS AND DNA DEGRADATION IN MOUSE LYMPHOMA L5178Y CELLS AFTER PHOTODYNAMIC TREATMENT SENSITIZED BY CHLOROALUMINUM PHTHALOCYANINE

Two closely related strains of mouse lymphoma L5178Y cells, LY-R and LY-S, have been found to differ in their sensitivity to the cytotoxic effects of photodynamic treatment (PDT) with chloroaluminum phthalocyanine (CAPC) and red light. Strain LY-R is more sensitive to photodynamic cell killing than strain LY-S. Differences in uptake of CAPC could not account for the differences in cytotoxic effects. There was no marked difference between the two strains in the induction of single-strand breaks (which includes frank single-strand breaks and alkali-labile lesions), but substantially more DNA-protein cross-links were formed in strain LY-R by CAPC and light. Repair of single-strand breaks proceeded with similar kinetics in both strains for the first 30 min post-irradiation, suggesting that these lesions are not responsible for the differential sensitivity of the two strains to the lethal effects of photodynamic treatment. Thereafter, alkaline elution revealed the presence of increasing DNA strand breakage in strain LY-R. DNA degradation, as measured by the conversion of prelabeled [14C] DNA to acid-soluble radioactivity, was more rapid and extensive in strain LY-R.     

Self‐Assembly,Spectroscopic and Electrochemical Studies of Nickel(II)‐4,8‐Diazaundecanediamide Complex

The self‐assembly of NiCl₂·6H₂O with a diaminodiamide ligand 4,8‐diazaundecanediamide (L‐2,3,2) gave a [Ni(C₉H₂₀N₄O₂)(Cl)(H₂O)] Cl·2H₂O ( 1 ). The structure of 1 was characterized by single‐crystal X‐ray diffraction analysis. Structural data for 1 indicate that the Ni(II) is coordinated to two tertiary N atoms, two O atoms, one water and one chloride in a distorted octahedral geometry. Crystal data for 1: orthorhombic, space group P 21nb, a = 9.5796(3) Å, b = 12.3463(4) Å, c = 14.6305(5) Å, Z = 4. Through NH···Cl–Ni (H···Cl 2.42 Å, N···Cl 3.24 Å, NH···Cl 158°) and OH···Cl–Ni contacts (H···Cl 2.36 Å, O···Cl 3.08 Å, OH···Cl 143°), each cationic moiety [Ni(C₉H₂₀N₄O₂) (Cl)(H₂O)]⁺ in 1 is linked to neighboring ones, producing a charged hydrogen‐bonded 1D chainlike structure. Thermogrametric analysis of compound 1 is consistent with the crystallographic observations. The electronic absorption spectrum of Ni(L‐2,3,2)²⁺ in aqueous solution shows four absorption bands, which are assigned to the ³A_2g → ³T_2g, ³T_2g → ¹Eg, ³T_2g → ³T_1g, and ³A_2g → ³T_1g transitions of triplet‐ground state, distorted octahedral nickel(II) complex. The cyclic volammetric measurement shows that Ni²⁺ is more easily reduced than Ni(L‐2,3,2)²⁺ in aqueous solution.     

Determination of sulphonated azo dyes in food by ion-pair liquid chromatography with photodiode array and electrospray mass spectrometry detection

An ion-pair liquid chromatography method with on-line photodiode-array and electrospray mass spectrometry detection was developed to determine 10 commonly used sulphonated azo dyes (Tartrazine, Amaranth, New Coccine, Sunset Yellow FCF, Allura Red AC, Ponceau R, Ponceau 3R, Orange I, Orange II and Metanil Yellow) in food. A reversed phase C(18) column with gradient elution was utilized to separate these compounds. Triethylamine was added in the mobile phase as an ion-pair reagent for chromatographic separation. Photodiode-array detection was employed for quantitative determination and electrospray mass spectrometry was used for identification. Good linearity (0.05-10 ppm, r(2)=0.999) and detection limit (<0.01 ppm) were determined with 5 mul injection. In addition, precision and accuracy associated with this newly developed method will be presented. A liquid extraction method was also developed to extract these dyes from different foodstuffs. The application of this method was demonstrated by analyzing sulphonated azo dyes in soft drinks, fruit jam, and salted vegetables.