Kinetic analysis of an efficient DNA-dependent TNA polymerase

alpha-l-Threofuranosyl nucleoside triphosphates (tNTPs) are tetrafuranose nucleoside derivatives and potential progenitors of present-day beta-d-2'-deoxyribofuranosyl nucleoside triphosphates (dNTPs). Therminator DNA polymerase, a variant of the 9 degrees N DNA polymerase, is an efficient DNA-directed threosyl nucleic acid (TNA) polymerase. Here we report a detailed kinetic comparison of Therminator-catalyzed TNA and DNA syntheses. We examined the rate of single-nucleotide incorporation for all four tNTPs and dNTPs from a DNA primer-template complex and carried out parallel experiments with a chimeric DNA-TNA primer-DNA template containing five TNA residues at the primer 3'-terminus. Remarkably, no drop in the rate of TNA incorporation was observed in comparing the DNA-TNA primer to the all-DNA primer, suggesting that few primer-enzyme contacts are lost with a TNA primer. Moreover, comparison of the catalytic efficiency of TNA synthesis relative to DNA synthesis at the downstream positions reveals a difference of no greater than 5-fold in favor of the natural DNA substrate. This disparity becomes negligible when the TNA synthesis reaction mixture is supplemented with 1.25 mM MnCl(2). These results indicate that Therminator DNA polymerase can recognize both a TNA primer and tNTP substrates and is an effective catalyst of TNA polymerization despite changes in the geometry of the reactants.     

Synthetic study of azaspiracid-1: synthesis of the EFGHI-ring fragment

Here, we report a synthesis of the lower half C21-C40 fragment of the shellfish toxin, azaspiracid-1. The C28-C40 fragment was synthesized by a coupling between the C28-C35 epoxide and the C36-C40 dithioacetal anion, followed by the HI-ring spiroaminal formation. An aldehyde corresponding to the C28-C40 fragment was then coupled with the C21-C27 allylic stannane by using InCl3. Finally, the FG-ring was constructed by HF.pyridine to accomplish the synthesis of the suitably protected C21-C40 fragment.     

Synthesis of D- and L-selenomethionine double-labeled with deuterium and selenium-82

The synthesis of D- and L-selenomethionine labeled with ?2Se and three deuteriums at Se-methyl group (D- and L-[2H?, ?2Se]selenomethionine) was described. D- And L-[2H?, ?2Se]selenomethionine were prepared by condensation of (R)- and (S)-2-amino-4-bromobutylic acid with lithium [2H?, ?2Se]methaneselenolate, which was prepared from metal (82)Se and [2H?]methyl iodide. The optical purities of D- and L-[2H?, ?2Se]selenomethionine were determined by HPLC with a chiral stationary phase column and were found more than 99% ee. The chemical ionization mass spectra showed that the molecular related ion for N-isobutyloxycarbonyl ethyl ester derivatives of [2H?, ?2Se]selenomethionine did not overlap with the m/z values known from that of non-labeled selenomethionine.     

Convenient asymmetric synthesis of beta-substituted alpha,alpha-difluoro-beta-amino acids via Reformatsky reaction between Davis' N-sulfinylimines and ethyl bromodifluoroacetate

The enantiopure Davis' N-sulfinylimines were found to be efficient as chiral imine equivalents in the high-temperature Reformatsky-type additions with BrZnCF(2)COOEt affording an efficient approach to the enantiomerically pure alpha,alpha-difluoro-beta-amino acids. High chemical and stereochemical yields (drs > 9:1, and as high as 99:1) render this method immediately useful for preparing the target amino acids.     

Mössbauer study of the thermal decomposition products of BaFeO4

A pure sample of a hexavalent iron compound, BaFeO₄, was decomposed at temperatures below 1200°C at oxygen pressures from 0.2 to 1500 atm. In addition to the already known BaFeO_x (2.5 ≦ x < 3.0) phases with hexagonal and triclinic symmetry, two new phases were obtained as decomposition products at low temperatures. One of the new phases, with composition BaFeO_{2.61 – 2.71}, has tetragonal symmetry; lattice constants are a₀ = 8.54 Å, c₀ = 7.29 Å. The phase is antiferromagnetic with Néel temperature estimated to be 225 ± 10 K. Two internal fields observed on its Mössbauer spectra correspond to Fe³⁺ and Fe⁴⁺. In the other new phase, with composition BaFeO_2.5, all Fe³⁺ ions had the same hyperfine field; it too is antiferromagnetic with a Néel temperature of 893 ± 10 K. Mössbauer data on the hexagonal phase coincided with earlier results of Gallagher, MacChesney, and Buchanan [J. Chem. Phys.43, 516 (1965)]. In the triclinic-I BaFeO_2.50 phase, internal magnetic fields were observed at room temperature, and it was supposed that there were four kinds of Fe³⁺ sites. The phase diagram of BaFeO_x system was determined as functions of temperature and oxygen pressure.     

Preparation and some reactions of 3,5:8,10-di-1,3-benzo[8](3,4)-1,2,5-thiadiazolocyclophane

Titled 1,2,5-thiadiazolometacyclophane 1 was prepared via thia[2.3]cyclophane 5 which was obtained by the reaction of di(bromomethyl) 2 with sodium sulfide under phase-transfer-catalyzed conditions. Cyclophane 1 gave the corresponding pyrene derivatives by the oxidative transannular reaction in the reaction with brominating reagent. Reduction of 1 with lithium aluminum hydride followed by acetylation with acetic anhydride gave a 4:l-mixture of cis- and trans-diamide 11 and 12 with a trace amount of cyclophane-ring-cleaved product 13 . On the other hand, 13 was obtained as a major product in the reduction with metal sodium and diisobutylaluminum hydride.     

Functional monomers and polymers. XCIII. Photochemical reactions on the acrylic and methacrylic copolymers containing thymine bases

Photodimerization of Polyacrylic and polymethacrylic derivatives with different pendant thymine unit content was studied in dimethylformamide solution. The quantum efficiency of thymine base for the photodimerization increased with increasing thymine content in the copolymers. The quenching study, which used isoprene as the quencher, revealed that the photodimerization resulted from excited singlet state increases with increasing thymine content. The photochemical results were discussed in terms of self-association of thymine bases in the polymer chain.     

Reactions of highly branched fluoroolefins with methyllithium and methylmagnesium bromide: formations of unexpected polyfluorocyclobutene and polyfluoropentadiene compounds

Introduction of a methyl group into hexafluoropropene trimers was achieved by reactions with organometallic carbon nucleophiles. Unusual cyclization and defluorination occurred simultaneously with a formation of methylated polyfluoroolefins: excess methyllithium provided a polyfluorocyclobutene compound, while a polyfluoropentadiene derivative was formed by use of excess methyllithium.     

Surface Modification of Al2O3 Fiber with Binary Nanoparticles using a Dry-Mechanical Coating Technique

Integrating materials with different functionalities into a composite material to obtain synergetic properties has generated considerable interest in various scientific and technical fields. In this study, a dry-mechanical coating process was used to fix nanosized Al₂O₃ and CuO particles directly onto the surface of Al₂O₃ fiber substrates by employing high shear and compression forces. The resulting composite materials showed good dispersion and homogeneous distribution of Al₂O₃ and CuO nanoparticles. Important coating parameters, including initial particle loadings and processing times were investigated for their effects on coating characteristics and product properties. The experimental results showed that the product surface area increased with higher nanoparticle loadings. The degree of dispersion and homogenous distribution of Al₂O₃ nanoparticles with CuO nanoparticles increased with the processing time. Additionally, the crystalline phase of raw materials was preserved during the coating process under the conditions studied in this work.