Orientation-selected 15N-HYSCORE detection of weakly coupled nitrogens around the archaeal rieske [2Fe-2S] center

The weakly coupled 15N atoms around a reduced Rieske [2Fe-2S] cluster of the uniformly 15N-labeled, hyperthermostable archaeal Rieske protein appear to produce readily observable cross-peaks in the HYSCORE spectra, with the well-resolved couplings of 0.3-0.4 MHz for the Nepsilon and 1.1 MHz for the peptide backbone nitrogens, in addition to the contributions from the coordinated Ndelta atoms. These features can be used for structure-mechanism studies of the biological redox protein system involving the weakly coupled nitrogens in coupled electron-proton transfer reactions.     

Construction of optically active CF3-containing quaternary carbon centers via stereospecific S(N)2' reaction

[reaction: see text] Phosphates from 3-substituted 4,4,4-trifluorobut-2-en-1-ols were found to be effective for construction of CF3-containing quaternary carbon centers by way of Cu(I)-catalyzed Grignard reactions in the presence of catalytic amounts of CuCN and trimethylsilyl chloride (TMSCl) in an anti S(N)2' manner.     

REACTION OF SULFUR CHLORIDE WITH ACETOPHENONE. II

Abstract

In a previous paper,¹ we reported the formation of a resinous material (1) from the reaction of sulfur chloride with acetophenone which, upon treatment with DMF, yielded phenylglyoxylthiodimethylamide (4). We now report two additional resinous materials (5, 6), resulting from bromination of sodium phenacylthiosulfate (3) and diphenacyl disulfide (7) respectively, both of which not only resemble resinous 1 in appearance, but also yield 4 upon treatment with DMF in aqueous alkali.

Resinous 1, 5, and 6 appear to have the same common basic structure and differ only in the number of sulfur atoms bonded between the common units. Cleavage at the sulfur-sulfur bonds and elimination of hydrogen halide then yields identical oxothioamides from 1, 5, or 6. The latter appears to be a general reaction, and several oxothioamides were prepared by this synthetic method from 1, 5, and 6 and various amides and amines.     

Accurate mass measurement of low molecular weight compounds by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

We report the application of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the accurate measurement of mass of low molecular weight compounds (smaller than 1500 Da), a linear peptide, two types of cyclic depsipeptides, a polyhydroxy-macrocyclic lactone, and two prenylated flavonoids, with delayed extraction in the reflector mode. The performance of the MALDI-TOF instrument was less than those of fast atom bombardment and Fourier-transform ion cyclotron resonance mass spectrometry instruments and insufficient to give acceptable accuracy for literature reporting. Nevertheless, when combined with NMR spectrometry and/or amino acid analysis to give information on the numbers of carbon atoms and index of hydrogen deficiency, MALDI was useful for determination of the elemental composition of the low molecular weight compounds available in small quantities.     

Difference in electrophoretic mobility and plasmic digestion profile between four recombinant fibrinogens, gamma 308K, gamma 308I, gamma 308A, and wild type (gamma 308N)

We have produced recombinant gamma-chain variant fibrinogens, gamma308K, gamma308I, and gamma308A simultaneously with wild-type fibrinogen, gamma-308N, by genetic protein engineering using Chinese hamster ovary cells. Although all three variant fibrinogens are a result of a single amino acid substitution, the aberrant gamma-chains of gamma308K and gamma308I fibrinogens migrated faster than gamma308N. Furthermore, plasmic digestion profiles were examined in the presence of 5 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) or 1 mM CaCl2. In the presence of EGTA, the three variant fibrinogens were digested into D1 and D2 fragments slightly faster than wild type. In addition, the D2 fragment derived from gamma308K was further digested into D3 by plasmin much faster than that from gamma308N. These data suggest that cleavage of gamma356Lys-gamma357Ala bond by plasmin in gamma308K, gamma308I, and gamma308A is slightly accelerated and the gamma302Lys-gamma303Phe bond is cleaved by plasmin rapidly in only the gamma308K variant. Furthermore, the substitution of Lys for gamma308Asn results in the generation of a new plasmin cleavage site between gamma308Lys and gamma309Gly in the presence of EGTA. In conclusion, a substitution at residue gamma308Asn may cause a conformational change in the gammachain of fragment D affecting polymerization and plasmin cleavage.     

Solid state reaction synthesis of filled skutterudite compounds (Ce or Y)yFexCo4-xSb12 and the effect of filling atoms Ce or Y on lattice thermal conductivity

The synthesis of filled skutterudite compounds (Ce or Y)_y(Fe)_x(Co)_(4x)(Sb)_(12), through a solidstate reaction using chloride of Ce or Y,high purity powder of Co, Fe, and Sb as starting materials,was investigated. (Ce or Y)_y(Fe)_x(Co)_(4x)(Sb)_(12) (x=0--1.0, y=0--0.15) compounds were obtained at850--1 123 K. The results of Rietveld analysis demonstrate that (Ce or Y)_y(Fe)_x(Co)_(4x)(Sb)_12synthesized by a solid state reaction possesses a filled skutterudite structure. The filling fraction ofCe or Y obtained by Rietveld analysis agrees well with the composition obtained by chemicalanalysis. The lattice constant of (Ce)_y(Fe)_x(Co)_(4x)(Sb)_(12) increases with increasing substitution of Fe at Cosites, and with an increasing Ce filling fraction in the Sb-dodecahedron voids. The lattice thermalconductivity of (Ce or Y)_y(Fe)_x(Co)_(4x)(Sb)_(12) decreases significantly with an increasing Ce or Y fillingfraction in the voids and with substitution of Fe at Co sites.     

Irradiation effects on hydrases for biomedical applications

To apply an irradiation technique to sterilize “Hybrid” biomedical materials including enzymes, we selected papain, a well-characterized plant endopeptidase as a model to examine durability of enzyme activity under the practical irradiation condition in which limited data were available for irradiation inactivation of enzymes. Dry powder and frozen aqueous solution of papain showed significant durability against ⁶⁰Co-gamma irradiation suggesting that, the commercial irradiation sterilizing method is applicable without modification. Although irradiation of unfrozen aqueous papain solution showed an unusual change of the enzymatic activity with the increasing doses, and was totally inactivated at 15 kGy, we managed to keep the residual activity more than 50% of initial activity after 30-kGy irradiation, taking such optimum conditions as increasing enzyme concentration from 10 to 100 mg/ml and purging with N₂ gas to suppress the formation of free radicals.     

Synthesis of end‐functionalized poly(phenylacetylene)s with well‐characterized palladium catalysts

End‐functionalized poly(phenylacetylene)s were synthesized by the polymerization of phenylacetylene (PA) using the well‐defined palladium catalysts represented as [(dppf)PdBr(R)] {dppf = 1,1′‐bis(diphenylphosphino)ferrocene}. The Pd catalysts having a series of R groups such as o‐tolyl, mesityl, C(Ph)?CPh₂, C₆H₄‐o‐CH₂OH, C₆H₄‐p‐CN, and C₆H₄‐p‐NO₂ in conjunction with silver triflate polymerized PA to give end‐functionalized poly(PA)s bearing the corresponding R groups in high yields. The results of IR and NMR spectroscopies and MALDI‐TOF mass analyses proved the introduction of these R groups at one end of each polymer chain. The poly(PA) bearing a hydroxy end group was applied as a macroinitiator to the synthesis of a block copolymer composed of poly(PA) and poly(β‐propiolactone) moieties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

A new biisoflavonoid from the roots of Erythrina variegata

A new biisoflavonoid, biseryvarin A (1a), together with two known compounds were isolated from the roots of Erythrina variegata. The structure of biseryvarin A was established on the basis of spectroscopic evidence. Biseryvarin A is the first dimeric isoflavonoid possessing isoprenoid groups from the genus Erythrina. Biseryvarin A showed low activity against methicillin-resistant Staphylococcus aureus (MRSA).