Photoreaction of rac‐Leucine in Ice by Circularly Polarized Synchrotron Radiation: Temperature‐Induced Mechanism Switching from Norrish Type II to Deamination

The delivery of extraterrestrial organics to primitive Earth is considered to have triggered the origin and subsequent evolution of life. Indeed, enantiomerically enriched amino acids of nonterrestrial origin have been found in carbonaceous meteorites, and enantioselective photodecomposition by circularly polarized light (CPL) in outer space has been proposed to have played some role in the initial enantiomeric bias. To experimentally examine this possibility and elucidate the photoreaction mechanisms, we have studied the photolysis of racemic leucine (rac‐Leu) in acidic and neutral ice/water media at 21–298 K with left‐ and right‐CPL in an attempt to detect enantiomerically enriched D ‐ and L ‐Leu, respectively. Comprehensive product analyses revealed that the CPL‐induced deracemization of Leu proceeds in both acidic and neutral ice matrices even at 21 K, and that the main mechanism switches from Norrish‐type II γ‐hydrogen abstraction to S_Ni deamination on lowering the temperature. The potential role of the CPL‐induced photodecomposition of amino acids as a source of the enantiomer imbalance in meteorites is discussed.     

A Facile One-Pot Synthesis of Vinpocetine

A one-pot synthesis of vinpocetine from vincamine was established. Lewis acids caused transesterification and/or dehydration of vincamine in EtOH. FeCl₃ catalyzed both transesterification and dehydration while Ti(OEt)₄ selectively catalyzed transesterification.     

New Procedure for the Synthesis of 2-Alkylbenzimidazoles

Simple, economical, and environmentally friendly method to synthesize 2-alkylbenzimidazoles was developed by modifying the conventional method between o-phenylenediamine and aldehyde.     

Generalization of the Maxwell equation and relation to the elastic equation

In this paper, we propose a hyperbolic system of first‐order pseudo‐differential equations as generalization of the Maxwell equation. We state basic properties of this system corresponding to the ones of the (usual) Maxwell equation and explain that several known generalized Maxwell equations presented by some researchers can be integrated into the system. Namely, their equations can be regarded as our equation in special cases. Their generalized equations admit not only transversal but also longitudinal waves and are examined from the physical viewpoint. Using the present system, from the mathematical viewpoint, we interpret the meaning for presence of the longitudinal wave (with the transversal one) in their generalized equations. This presence means existence of more than one non‐zero characteristic root for the system (ie, non‐zero eigenvalue of the symbol). We prove also that our system becomes a first‐order expression of (generalized) elastic equations. Furthermore, it is shown that introducing the elastic equations implies expressing the generalized Maxwell equations by the potentials.     

注氢纯铝中间隙型位错环一维迁移现象的原位观察

核聚变堆材料在高能粒子辐照过程中会产生大量点缺陷,导致辐照脆性和辐照肿胀等现象.因而,研究点缺陷在辐照过程中的演变过程至关重要.点缺陷团簇的一维迁移现象是这种演变过程的主要研究内容之一.本文采用普通低压(200 kV)透射电镜,在室温条件下对注氢纯铝中的间隙型位错环在电子辐照下的一维迁移现象进行了观察和分析.在200 keV电子辐照下,注氢纯铝中的位错环可多个、同时发生一维迁移运动,也可单个、独立进行一维迁移运动.位错环沿柏氏矢量1/3<111>的方向可进行微米尺度的一维长程迁移,沿柏氏矢量1/2<110>的方向一维迁移也可达数百纳米.电子束辐照时产生的间隙原子浓度梯度是引起位错环一维迁移并决定其迁移方向的原因.位错环发生快速一维迁移时,其后会留下一条运动轨迹;位错环一维迁移的速率越快,运动的轨迹则越长,在完成迁移过后的几十秒内这些运动轨迹会逐渐消失.     

Preparation of novel fluoroalkyl end-capped oligomers/polyaniline and/<Emphasis Type="Italic">N,N′</Emphasis>-diphenyl-1,4-phenylenediamine nanocomposites

Fluoroalkyl end-capped acrylic acid oligomer [R_F-(ACA)_n-R_F]/, 2-(methacryloyloxy)ethanesulfonic acid oligomer [R_F-(MES)_n-R_F]/, 2-acrylamido-2-methylpropanesulfonic acid oligomer [R_F-(AMPS)_n-R_F]/polyaniline [PAn] nanocomposites were prepared by the polymerization of aniline initiated by ammonium persulfate in the presence of the corresponding oligomers, respectively. These fluorinated oligomers were also applied to the preparation of the corresponding fluorinated oligomers/phenyl-capped aniline dimer (An-dimer: N,N′-diphenyl-1,4-phenylenediamine) nanocomposites by the interaction of the fluorinated oligomers with An-dimer. These fluorinated composites thus obtained were found to afford nanometer size-controlled fine particles possessing a good dispersibility and stability in water and traditional organic media such as methanol. UV–vis spectra of R_F-(MES)_n-R_F/PAn nanocomposites and R_F-(AMPS)_n-R_F/PAn nanocomposites showed the similar absorption peaks around 350, 430, and 780 nm to those of the usual Brønsted acid-doped PAn; however, interestingly, R_F-(ACA)_n-R_F/PAn nanocomposites were found to exhibit only an absorption peak around 430 nm based on the polaron transition.

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Formation mechanism of 2-methyl-2-buten-1,4-diol and 2-methyl-3-buten-1,2-diol from 2-methyl-1,3-butadiene on a head-to-head pivalamidato-bridged cis-diammineplatinum(III) binuclear complex

Reactions of a pivalamidato-bridged head-to-head (HH) platinum(III) binuclear complex with 2-methyl-1,3-butadiene (isoprene) and p-styrenesulfonate and of an α-pyrrolidonato-bridged HH platinum(III) binuclear complex with p-styrenesulfonate were studied kinetically using UV-vis spectrophotometry and (1)H NMR spectroscopy, and detailed reaction mechanisms are proposed. Pt(III) binuclear complexes react with p-styrenesulfonate in four successive steps with mechanisms similar to that for an HH α-pyridonato-bridged Pt(III) binuclear complex with p-styrenesulfonate. In the case of isoprene, four steps were observed on the basis of UV-vis spectrophotometry. However, the reaction kinetics for steps 1 and 2 correspond to those for the previous reaction system, and those for steps 3 and 4 do not correspond to those for the previous system or to those observed by using (1)H NMR spectroscopy for the present isoprene system. By using UV-vis spectrophotometry, it was shown that isoprene preferentially π-coordinates to the Pt(N(2)O(2)) atom via the double bond adjacent to the methyl group in step 1. In step 2, a second isoprene molecule π-coordinates to the Pt(N(4)) atom, which is the rate-determining step, followed by nucleophilic attack of a water molecule on the π-coordinated isoprene on the Pt(N(2)O(2)) atom to form two isomeric σ-complexes. In the same step, π-coordinated isoprene on the Pt(N(4)) atom of the σ-complexes is released. This is different from the reaction of the Pt(III) binuclear complexes with other olefins. In step 3, reductive elimination of the σ-complexes occurs to form two diols and the HH pivalamidato-bridged Pt(II) binuclear complex. Finally, acid decomposition of the Pt(II) binuclear complex occurs to form monomers in step 4. From (1)H NMR spectroscopic observations, fast isomerization between σ-complexes and reductive elimination of the σ-complexes occurs in step 3, and isomerization from a 1,4-diol to a 1,2-diol occurs in step 4.     

Synthetic studies toward 13-oxyingenol: construction of the fully substituted tetracyclic compound

13-Oxyingenol and its derivatives have high levels of anti-HIV activity. A fully substituted tetracyclic skeleton of 13-oxyingenol is constructed by using spiro-cyclization and ring-closing olefin metathesis as key steps.     

Structure-reactivity relationship of piperidine nitroxide: electrochemical, ESR and computational studies

We have synthesized several nitroxides with different substituents which vary the steric and electronic environment around the N-O moiety and have systematically investigated the role of substituents on the stability of the radicals. Our results demonstrated the reactivity toward ascorbate correlates with the redox potential of the derivatives. Furthermore, ab initio calculations also indicated a correlation between the reduction rate and the computed singly occupied molecular orbital-lowest unoccupied molecular orbital energy gap, but not with solvent accessible surface area of the N-O moiety, supporting the experimental results and suggesting that the electronic factors largely determine the radicals' stability. Hence, it is possible to perform virtual screening of nitroxides to optimize their stability, which can help to rationally design novel nitroxides for their potential use in vivo.     

One-pot conversion of aromatic bromides and aromatics into aromatic nitriles via aryllithiums and their DMF adduct

Various aromatic bromides and iodides were smoothly converted into the corresponding aromatic nitriles in good to moderate yields by the treatment with n-butyllithium and subsequently DMF, followed by treatment with molecular iodine in aq NH₃. The same treatment of typical aromatics and heteroaromatics with n-butyllithium and subsequently DMF, followed by treatment with molecular iodine in aq NH₃ also provided the corresponding aromatic nitriles in good yields. Moreover, the same treatment of aromatic bromides and aromatics with half amount of DIH (1,3-diiodo-5,5-dimethylhydantoin) instead of molecular iodine worked effectively to give the corresponding aromatic nitriles, respectively, in good yields. These reactions are novel and environmentally benign one-pot methods for the preparation of aromatic nitriles from aromatic bromides and aromatics, respectively, through the formation of aryllithiums and their DMF adducts.