Formation of free radicals during the oxidation of N-methylhydroxyurea with dioxovanadium(V) ions

Unlike the oxidation of hydroxyurea with dioxovanadium(V) ions, which proceeds through the formation of a single free radical, oxidation of N-methylhydroxyurea is characterized by consecutive formation of two oxygen-based free radicals, as recorded by EPR spectroscopy. Although the consumption of overall five V(V) ions per N-methylhydroxyurea molecule has been determined, the formation of NO, or was not observed. These results are in accordance with a previous suggestion that nitric oxide transfer requires an unsubstituted acylhydroxylamine group.     

添加Ru的Mo/HZSM-5催化体系上的甲烷无氧脱氢芳构化

研究了在Ｍｏ／ＨＺＳＭ５催化剂中添加过渡金属阳离子以改变催化剂的反应性能，提高甲烷无氧脱氢芳构化的反应活性和稳定性．在添加第二组分的催化剂中，ＭｏＲｕ／ＨＺＳＭ５具有最佳的反应活性和稳定性．Ｒｕ的加入使甲烷的转化率由原来的６％～７％提高到９８％．采用比表面积及孔分布测定，Ｘ射线衍射，程序升温还原，程序升温氨脱附和差热分析等表征方法研究了ＭｏＲｕ／ＨＺＳＭ５催化剂的物理化学性质．结果表明，Ｒｕ的加入引起Ｍｏ／ＨＺＳＭ５催化剂强酸酸量的下降，并促进了Ｍｏ物种的还原．     

Reactions of Ethyne with Some Ruthenium Cluster Complexes Containing dppm

Reactions of ethyne with [Ru₃(μ‐dppm)(CO)₁₀] have given isomeric complexes [Ru₃(μ₃‐C₆H₆)(CO)₆(dppm)], one of which, 2 , contains the dppm chelating an Ru‐atom, together with a hexatrienetriyl ligand attached to the Ru₃ cluster to form a methylideneruthenacyclohexadiene system. The second isomer 3 contains the dppm bridging an Ru−Ru bond, with the C₆H₆ ligand forming a vinylruthenacyclopentadiene system. Also isolated was the open‐chain Ru₃ complex 4 containing a ruthenacyclopentadiene attached to the central Ru‐atom; the other Ru−Ru vector is bridged by a PPh₂CHPPh₂C₄H₅ ligand, formed by a novel insertion of two ethyne molecules into an Ru−P bond. The reaction of ethyne with [Ru₃(μ‐H)(μ₃‐C₂H₂)(CO)₉] proceeded by attack at the coordinated alkyne and at the cluster to give a cluster‐bonded PPh₂CH₂PPh₂CCH system in 7 . Thermolysis of [Ru₃(μ‐H)(μ₃‐C₂SiMe₃)(μ‐dppm)(CO)₇] ( 8 ; refluxing MeOH) in the presence of KF gave [Ru₆(μ‐CCH₂)₂(μ‐dppm)₂(CO)₁₂] ( 9 ; 80%); similar reactions carried out with [RuClCp(PPh₃)₂] also present gave 9 (67%) together with [Ru₃(μ‐H)(μ₃‐C₂H)(μ‐dppm)(CO)₆(PPh₃)] ( 11 ; 23%). The molecular structures of 2 , 3 , 4 , 7 , 9 , and 11 , some as differently solvated forms, have been determined by single‐crystal X‐ray studies.     

Evaluation and optimization of synthetic routes from dihydroartemisinin to the alkylamino-artemisinins artemiside and artemisone: A test of N-glycosylation methodologies on a lipophilic peroxide

10-Alkylamino-artemisinins including artemiside and artemisone display enhanced activities against malaria. Earlier, dihydroartemisinin (DHA) TMS ether was converted by trimethylsilyl bromide into the 10-β-bromide that with amine nucleophiles provided the amino-artemisinins. In an attempt to develop more economic approaches, direct N-glycosylation of DHA was examined but 2-deoxyartemisinin was invariably obtained. However, hydroxyl group activation by conversion into the 10β-halide in non-polar solvents with anhydrous HCl and Group I and II metal halides, oxalyl chloride or thionyl chloride with catalytic DMSO, and oxalyl bromide did succeed. The β-halides were converted in situ by thiomorpholine into artemiside, and by thiomorpholine-1,1-dioxide into artemisone respectively in scalable reactions. Hydrogen peroxide-acetonitrile or the urea-hydrogen peroxide complex efficiently oxidized the sulfide artemiside to the sulfone artemisone. Overall, a generalized approach to 10-alkylamino-artemisinins is now available.     

On the question of self-trapping of positrons in indium

The Doppler-broadening of the positron annihilation line in 5N indium has been studied over the temperature range 77 K to 427 K. No evidence for self-trapping has been discovered; rather, the prevacancy rise in the F-parameter appears linear. The best value for E_V is 0.59±0.03 eV.     

Entropy-based evaluation function in a multi-objective approach for the investigation of the genetic code robustness

The genetic code is the interface between the genetic information stored in DNA molecules and the proteins. Considering the hypothesis that the genetic code evolved to its current structure, some researches use optimization algorithms to find hypothetical codes to be compared to the canonical genetic code. For this purpose, a function with only one objective is employed to evaluate the codes, generally a function based on the robustness of the code against mutations. Very few random codes are better than the canonical genetic code when the evaluation function based on robustness is considered. However, most codons are associated with a few amino acids in the best hypothetical codes when only robustness is employed to evaluate the codes, what makes hard to believe that the genetic code evolved based on only one objective, i.e., the robustness against mutations. In this way, we propose here to use entropy as a second objective for the evaluation of the codes. We propose a Pareto approach to deal with both objectives. The results indicate that the Pareto approach generates codes closer to the canonical genetic code when compared to the codes generated by the approach with only one objective employed in the literature.     

New solvers for higher dimensional poisson equations by reduced B‐splines

We use higher dimensional B‐splines as basis functions to find the approximations for the Dirichlet problem of the Poisson equation in dimension two and three. We utilize the boundary data to remove unnecessary bases. Our method is applicable to more general linear partial differential equations. We provide new basis functions which do not require as many B‐splines. The number of new bases coincides with that of the necessary knots. The reducing process uses the boundary conditions to redefine a basis without extra artificial assumptions on knots which are outside the domain. Therefore, more accuracy would be expected from our method. The approximation solutions satisfy the Poisson equation at each mesh point and are solved explicitly using tensor product of matrices. © 2013 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 30: 393–405, 2014