Two Novel 15(10→1)Abeomuurolane Sesquiterpenes from Cosmos sulphureus

Two novel 15(10→1)abeomuurolane sesquiterpenes, cosmosoic acid ( 1 ) and cosmosaldehyde ( 2 ), were isolated from the whole plant of Cosmos sulfurous. Their structures were established by a combination of 1D‐ and 2D‐NMR spectroscopic techniques. Additionally, a chemical correlation between 1 and 2 was also established.     

A nanoengineering approach to regulate the lateral heterogeneity of self-assembled monolayers

Using a scanning probe lithography method known as nanografting in conjunction with knowledge of self-assembly chemistry, regulation of the heterogeneity of self-assembled monolayers (SAMs) is demonstrated. While nanografting in single-component thiols produces areas of SAMs with designed geometry and size, nanofabrication in mixed thiol solution yields segregated domains. The reaction mechanism in nanografting differs significantly from self-assembly in mix-and-grow methods, as proven in systematic studies reported in this article and a companion paper of theoretical calculations of the nanografting process. Knowledge of the reaction pathways enables development of methods for shifting the interplay between the kinetics and thermodynamics in SAM formation, and thus the heterogeneity of mixed SAMs. By varying fabrication parameters, such as shaving speed, and reaction conditions, such as concentration and ratio of the components, the lateral heterogeneity can be adjusted ranging from near molecular mixing to segregated domains of several to tens of nanometers.     

Angular dependence of tunneling magnetoresistance in La0.7Sr0.3MnO3 step-edge junctions

La_0.7Sr_0.3MnO₃ (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$\theta$, 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 H_p almost coincides with the coercive field H_c for θ<60°$\theta <60°$ but obeys a different form from _Hc(θ)$H_{\mathrm{c}}(\theta )$. The high-field junction resistance shows an intrinsic sin²θ${\sin }^2\theta$ angular dependence, while the low-field resistance shows an extrinsic cos(4θ)$\cos (4\theta )$ angular dependence. The distinctive features are mainly due to the induced magnetization anisotropy in the artificial steps of grain boundaries.     

Computing motif correlations in proteins

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/.     

X-ray absorption and resonance Raman studies of methyl-coenzyme M reductase indicating that ligand exchange and macrocycle reduction accompany reductive activation

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.     

Novel Polyhydroxysteroids from the Formosan Soft Coral Sarcophyton Glaucum

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.     

New Norcembranoids from the Soft Coral Sinularia Lochmodes

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.     

Studies of Thermal Transesterification of Phenylurethane by High Pressure Liquid Chromatograph

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.