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71.
Isothiazolidinones are a rare but potentially important chemical moiety in biochemistry. We report the identification of several thiol, phosphinate, and carbon nucleophiles that form covalent adducts by addition to the sulfenamide sulfur. This reduction is selective for isothiazolidinones over similar peptide disulfides. We synthesized a coumarin-based thioacid nucleophile which shows a marked fluorescence increase after addition to an isothiazolidinone sulfenamide bond. [structure: see text] 相似文献
72.
L.M. Wang Jyh-Yi Lee H.C. Yang J.C. Chen Hsiang-Lin Liu Kun-Sheng Lu Lance Horng H.E. Horng 《Journal of magnetism and magnetic materials》2006
La0.7Sr0.3MnO3 (LSMO) tunneling magnetoresistance (TMR) junctions have been fabricated on step-edge (0 0 1) SrTiO3 substrates with a high step-edge angle. In the measurement of magnetoresistance (MR) ratio versus external magnetic field H, butterfly-like MR curves are clearly observed. The MR(H ) curves vary with θ, the angle between the applied magnetic field and the current direction in the substrate plane, showing anisotropic MR properties. A much broader MR(H) response is observed for the configuration of H perpendicular to the substrate plane. Additionally, the maxima-MR field Hp almost coincides with the coercive field Hc for θ<60° but obeys a different form from Hc(θ). The high-field junction resistance shows an intrinsic sin2θ angular dependence, while the low-field resistance shows an extrinsic cos(4θ) angular dependence. The distinctive features are mainly due to the induced magnetization anisotropy in the artificial steps of grain boundaries. 相似文献
73.
Horng JT Huang HD Wang SH Chen MY Huang SL Hwang JK 《Journal of computational chemistry》2003,24(16):2032-2043
Protein motifs, which are specific regions and conserved regions, are found by comparing multiple protein sequences. These conserved regions in general play an important role in protein functions and protein folds, for example, for their binding properties or enzymatic activities. The aim here is to find the existence correlations of protein motifs. The knowledge of protein motif/domain sharing should be important in shedding new light on the biologic functions of proteins and offering a basis in analyzing the evolution in the human genome or other genomes. The protein sequences used here are obtained from the PIR-NREF database and the protein motifs are retrieved from the PROSITE database. We apply data mining approach to discover the occurrence correlations of motif in protein sequences. The correlation of motifs mined can be used in evolution analyses and protein structure prediction. We discuss the latter, i.e., protein structure prediction in this study. The correlations mined are stored and maintained in a database system. The database is now available at http://bioinfo.csie.ncu.edu.tw/ProMotif/. 相似文献
74.
Tang Q Carrington PE Horng YC Maroney MJ Ragsdale SW Bocian DF 《Journal of the American Chemical Society》2002,124(44):13242-13256
Methyl-coenzyme M reductase (MCR) catalyzes methane formation from methyl-coenzyme M (methyl-SCoM) and N-7-mercaptoheptanoylthreonine phosphate (CoBSH). MCR contains a nickel hydrocorphin cofactor at its active site, called cofactor F(430). Here we present evidence that the macrocyclic ligand participates in the redox chemistry involved in catalysis. The active form of MCR, the red1 state, is generated by reducing another spectroscopically distinct form called ox1 with titanium(III) citrate. Previous electron paramagnetic resonance (EPR) and (14)N electron nuclear double resonance (ENDOR) studies indicate that both the ox1 and red1 states are best described as formally Ni(I) species on the basis of the character of the orbital containing the spin in the two EPR-active species. Herein, X-ray absorption spectroscopic (XAS) and resonance Raman (RR) studies are reported for the inactive (EPR-silent) forms and the red1 and ox1 states of MCR. RR spectra are also reported for isolated cofactor F(430) in the reduced, resting, and oxidized states; selected RR data are reported for the (15)N and (64)Ni isotopomers of the cofactor, both in the intact enzyme and in solution. Small Ni K-edge energy shifts indicate that minimal electron density changes occur at the Ni center during redox cycling of the enzyme. Titrations with Ti(III) indicate a 3-electron reduction of free cofactor F(430) to generate a stable Ni(I) state and a 2-electron reduction of Ni(I)-ox1 to Ni(I)-red1. Analyses of the XANES and EXAFS data reveal that both the ox1 and red1 forms are best described as hexacoordinate and that the main difference between ox1 and red1 is the absence of an axial thiolate ligand in the red1 state. The RR data indicate that cofactor F(430) undergoes a significant conformational change when it binds to MCR. Furthermore, the vibrational characteristics of the ox1 state and red1 states are significantly different, especially in hydrocorphin ring modes with appreciable C=N stretching character. It is proposed that these differences arise from a 2-electron reduction of the hydrocorphin ring upon conversion to the red1 form. Presumably, the ring-reduction and ligand-exchange reactions reported herein underlie the enhanced activity of MCR(red1), the only form of MCR that can react productively with the methyl group of methyl-SCoM. 相似文献
75.
Guey‐Horng Wang Jui‐Hsin Su Chien‐Ting Chen Chang‐Yih Duh Chang‐Feng Dai Jyh‐Horng Sheu 《中国化学会会志》2004,51(1):217-220
Two novel polyhydroxysteroids, (24S)‐24‐methylcholestane‐3β,5α,6β,25ξ;,26‐pentol 26‐n‐decanoate ( 1 ), (24S)‐24‐methylcholestane‐3β,5α,6β,25ξ;,26‐pentol 25,26‐diacetate ( 2 ), and three known sterols ( 3‐5 ), have been isolated from a Formosan soft coral Sarcophyton glaucum. The molecular structures of these compounds were determined by spectral methods. The cytotoxicity of these compounds toward various cancer cell lines has also been determined. 相似文献
76.
Yen‐Ju Tseng Atallah F. Ahmed Chi‐Hsin Hsu Jui‐Hsin Su Chang‐Feng Dai Jyh‐Horng Sheu 《中国化学会会志》2007,54(4):1041-1044
Two new C‐4 norcembranoids sinulochmodins D ( 1 ) and E ( 2 ), along with three known norditerpenoids ( 3–5 ), have been isolated from the organic extract of a Taiwanese soft coral Sinularia lochmodes (Kolonko). The structures of 1 and 2 were determined on the basis of extensive spectroscopic analyses and by comparison of their spectral data with those of related metabolites. 相似文献
77.
Thermal transesterification of phenylurethane with n-octanol was carried out in DMSO. It was found that the reaction followed first-order kinetics with an average rate constant of 8.630 × 10?5 sec ?1at 140°C. High pressure liquid chromatograph technique was employed to analyze chemical species in the course of the reaction. The reaction obeyed Arrhenius equation closely between 133°C and 155°C with activation energy of 29.6 kcal/mole and entropy of activation of ?8.2 cal/mole deg at 140°C. An intramolecular cyclic intermediate mechanism was proposed for this reaction. 相似文献
78.
Wen-Feng Liaw Yih-Chern Horng Der-Shiaw On Chin-Yuan Chuang Chen-Kang Lee Gene-Hsiang Lee Shie-Ming Peng 《中国化学会会志》1995,42(1):59-65
The monomeric rhenium(I) complex with bidentate telluroether ligand Re(CO)3Br(PhTe(CH2)3TePh) (1) was accessible via reaction of the PhTe(CH2)3TePh with Re(CO)5Br. This chelate complex crystallized in triclinic space group $ {\rm P}\bar 1 $ with a = 9.390(5) Å, b = 10.961(3) Å, c = 11.849(4) Å a = 63.30(3)°, β = 87.49(4)° γ = 69.31(4)°, V = 1009.5(7) Å3 Z = 2, R = 0.033, and Rw = 0.034. Reaction of Re(CO)5Cl with NaTePh yielded the Re(I) specics PhTeRe(CO)5 (2). This complex crystallized in triclinic space group $ {\rm P}\bar 1 $ with a = 7.085(1) Å, b = 9.203(1) Å, c = 11.341(1) Å, α = 107.24(1)°, β = 100.56(1)°, γ = 96.47(1)°, V = 683.2(2) Å3, Z = 2, R = 0.027, Rw = 0.022. Reaction of PhTeRe(CO)5 and (PhSe)2 in THF at 65 °C yielded a product that was confirmed crystallographically to be the known species Re2(μ-SePh)2(CO)8 (3), in which two phenylselenolate ligands bridge the two Re(I). Compound 3 crystallized in monoclinic space group P21/n with a = 7.210(2) Å, b = 18.862(6) Å, c = 9.083(3) Å, β = 107.48(3)° V = 1178.2(7) Å3, Z = 2, R = 0.046, and Rw = 0.051. Methylation of PhTeRe(CO)5 with [Me3O][BF4] afforded Re(I) product [(PhTeMe)Re(CO)5][BF4] (4). This monodentate telluroether species crystallized in monoclinic space group P21/n with a = 8.405(1) Å, b = 13.438(3) Å, c = 15.560(2) Å, β = 92.59(1)° V = 1755.5(5) Å3, Z = 4, R = 0.035, and Rw = 0.035. 相似文献
79.
Chia-Yang Shiau Ji-Wang Chern Kang-Chien Liu Chao-Han Chan Mou-Hsiung Yen Ming-Chu Cheng Yu Wang 《Journal of heterocyclic chemistry》1990,27(5):1467-1472
To search for novel antihypertensive heterocycles in the condensed quinazoline series, two representative compounds were synthesized via a suitable reaction sequences. Treating anthranilonitrile with allyl isocyanate gave 2-(allylureido)benzonitrile ( 10 ) in a quantitative yield. Compound 10 was cyclized to 3-allylquinazoline-2(1H, 4(3H)-dione ( 11 ). Bromination of 11 in carbon tetrachloride converted it into the corresponding 3-(2,3-dibromopropyl) derivative ( 12 ) in 92% yield. Ring closure of 12 was effected by the action of alkali to afford 2-bromomethyl-2,3-dihydro-5H-oxazolo[2,3-b]quinazolin-5-one ( 13 ). The title compound, 2-(4-benzylpiperazin-1-ylmethyl)-2,3-dihydro-5H-oxazolo[2,3-b]quinazolin-5-one ( 7 ) could be obtained by a reaction of either 12 or 13 with 1-benzylpiperazine respectively. Starting from the readily available 3-allyl-2H-thioxoquinazolin-4(3H)-one ( 16 ) via the analogous reactions gave the 2-bromomethyl-2,3-dihydro-5H-thiazolo[2,3-b]-quinazolin-5-one ( 19 ) in good yield. However, the reaction of 19 with 1-benzylpiperazine provided another target compound, 2-(4-benzylpiperazin-1-ylmethyl)-2,3-dihydro-5H-thiazolo[2,3-b]quinazolin-5-one ( 8 ) only in poor yield (8%). As major product, the dehydrobrominated compound, 2-methylene-2,3-dihydro-5H-thiazolo[2,3-b]quinazolin-5-one ( 22 ) was isolated. A preliminary pharmacological evaluation revealed that both compounds 7 and 8 are devoid of the antihypertensive activity. 相似文献
80.
Four new phenolic compounds containing an oxepine ring, artocarpols B ( 1 ), C ( 2 ), D ( 3 ), and E ( 4 ), were isolated from the root bark of Artocarpus rigida. The structures, including relative configurations, were elucidated by means of spectroscopic data. 相似文献