Inter- and intra-annular proton exchange in gaseous benzylbenzenium ions (protonated diphenylmethane)

Two distinct proton exchange reactions occur in metastable gaseous benzylbenzenium ions, generated by isobutane chemical ionization of diphenylmethane and four deuterium-labelled analogues. Whereas the proton ring-walk at the benzenium moiety is fast giving rise to a completely random intraannular proton exchange, the interannular proton exchange is surprisingly slow and competes with the elimination of benzene. A kinetic isotope effect of k_H/k_D= 5 has been determined for the interannular proton transfer, and a particularly high energy barrier of 50–75 kJ mol^?1 has been estimated. These observations are attributed to steric restrictions of the ring-to-ring proton transfer in benzylbenzenium ions and contrasted to the fast interannular proton exchange in the higher homologues.     

Novel Enantioselective Synthesis of Both Enantiomers of Furan‐2‐yl Amines and Amino Acids

A new enantioselective synthesis of furan‐2‐yl amines and amino acids is described, in which the key step is the oxazaborolidine‐catalyzed enantioselective reduction of O‐benzyl (E)‐ and (Z)‐furan‐2‐yl ketone oximes to the corresponding chiral amines. The chirality of the furan‐2‐yl amines is fully controlled by the appropriate choice of the geometrical isomer of the O‐benzyl oxime. Oxidation of the furan ring furnished amino acids in high yields.     

Mass spectrometric fragmentation of isomeric 2-alkyl-substituted 1,3-indandiones and 3-alkylidenephthalides: a seven-step consecutive isomerization of regular and distonic molecular radical cations

The electron impact-induced fragmentation of 2,2-dimethyl- and 2-ethyl-1,3-indandione, 1 and 2, and their isomers, 3-isopropylidene- and 3-propylidenephthalide, 3 and 4, respectively, was studied in detail by mass-analysed ion kinetic energy (MIKE) and collision-induced dissociation (CID-MIKE) spectrometry, including ²H and ¹³C. labelled analogues of 1 and 2. In all regimes of internal energy, the molecular ions 1^+. ? 4^+. interconvert by up to seven consecutive, reversible isomerization steps prior to the main fragmentation processes, viz. loss of CH₃^. and C₂H₄. 1,3-Indandione and 3-methylenephthalide ions with identical alkylidene moieties (i.e. 1^+.?3^+. and 2^+.?4^+.) equilibrate rapidly and completely prior to fragmentation, whereas these pairs of isomers interconvert only slowly via a five-step rearrangement of the indandione ions 1^+.?2^+.. Distinct from the behaviour of simpler ionized carbonyl species, a 1,2-C shift of a (formally) neutral carbonyl group is found to occur along with that of a protonated one. Also distinct from simpler cases, methyl loss does not take place from the ionized enol intermediates formed within the interconversion 1^+.?2^+. of the diketone ions but rather from the n-propylidenephthalide ions 4^+.. This follows from CID-MIKE spectrometry of the [M ? CH₃]⁺ ions of 1–4 and two reference C₁₀H₇O₂⁺ (m/z 159) ions of authentic structures (protonated 2-methylene-1,3-indandione and protonated 1,4-naphthoquinone). The characteristic CID fragmentation of the C₁₀H₇O₂⁺ ions is rationalized. Finally, the multistep isomerization of ionized 1,3-indandiones apparently also extends to higher homologues [e.g. 5^+. from 2-ethyl-2-methyl-1,3-indandione (5) and 6^+. from 2,2-diethyl-1,3-indandione (6)]: the ionized phthaloyl group of 1,3-indandione radical cations 1^+., 2^+., 5^+. and 6^+., originally attached with its two acyl functionalities to the same carbon of the aliphatic chain, performs, in fact, a ‘multi-step migration’.     

Reaction Engineering Aspects of α-l,4-D-Glucan Phosphorylase Catalysis

Some important process properties of α-l,4-D-ghican phosphorylases isolated from the bacteriumCorynebacterium callunae and potato tubers (Solatium tuberosum) were compared. Apart from minor differences in their stability and specificity (represented by the maximum degree of maltodextrin conversion) and a 10-fold higher affinity of the plant phosphorylase for maltodextrin (K _M of 1.3 g/L at 300 mM of orthophosphate), the performances of both enzymes in a continuous ultrafiltration membrane reactor were almost identical. Product synthesis was carried out over a time course of 300–400 h in the presence or absence of auxiliary pullulanase (increasing the accessibility of the glucan substrate for phosphorolytic attack up to 15–20%). The effect of varied dilution rate and reaction temperature on the resulting productivities was quantitated, and a maximum operational temperature of 40°C was identified.     

高温超导体制备条件的人工神经网络识别

高温超导体的制备条件要求严格,其掺杂量大小、烧结温度控制等都直接影响实验样本的超导性质。近几年高温超导研究已积累大量实验数据,如何应用人工智能方法处理这些数据寻找更好的合成条件颇有意义。人工神经网络方法在许多领域己显示其处理复杂数据和模式识别的优越性,但尚未应用到化合物制备研究方面。本文对此作了初步尝试。