No abstract

Though ammonia–borane (AB) is recognized as an excellent hydrogen storage material, efficient dehydrogenation of AB still remains a challenge. Herein, we report that cyclic (alkyl)­(amino)­carbene iridium complexes are highly efficient for both the thermal dehydrogenation and hydrolysis of AB under mild conditions. At 30 °C, the two processes are completed within 15 and 5 min, releasing 2.1 and 2.8 equiv of H2 per AB, respectively. Moreover, 2.8 equiv of H2 can be released within 10 min by thermal dehydrogenation at 60 °C. Kinetic studies revealed that the activation energies for thermal dehydrogenation and hydrolysis of AB are 10.7 and 8.5 kcal/mol, respectively. The catalyst can be recycled without significant loss of activity at least six times for both processes. The reaction mechanisms were further explored by theoretical calculations, stoichiometric reactions, and kinetic isotope effect experiments.

Nucleosome positioning in promoters is important for gene transcription regulation. In this paper, with a nucleosome prediction model, curvature profile, the characteristics of nucleosome positioning in promoters are analyzed for miRNA genes and protein-coding genes. In the vicinity of transcription start site (TSS), there is a nucleosome-free region (NFR) followed by a positioned nucleosome at ~200 bp downstream of TSS. A similar characteristic is observed in independent intronic promoters and intergenic promoters, namely, both types of promoters have a longer NFR in 0−−400 bp upstream of TSS. Moreover, transcription factor binding sites (TFBSs) locate in the NFR with a high concentration. However, nucleosome pattern in dependent intronic promoters are like that in protein-coding promoters, with two nucleosomes positioned at −200−−400 bp and −400−−600 bp upstream of TSS. The results indicate nucleosome positioning is probably different in independent miRNA promoters and protein-coding promoters; and positioning seems to be an important factor not only in regulation of protein-coding gene, but also in that of miRNA gene. nucleosome positioning, promoter, miRNA gene Citation: Liu H D, Zhang D J, Xie J M, et al. Analysis of nucleosome positioning in promoters of miRNA genes and protein-coding genes.

tert -Butylphenol is widely used as an intermediate in organic synthesis, and the catalyst for the alkylation reaction of phenol and tert -butyl alcohol is the key to synthesizing tert -butylphenol. In our work, a catalyst, 1H-imidazole-1-acetic acid tosilate ([HIMA]OTs), was synthesized and characterized, and an efficient and easily recyclable catalytic system of an ionic liquid was established. In addition, the kinetic and thermodynamic parameters were calculated; the positive value of Δ H * indicated the endothermic nature of the alkylation reaction, and the positive value of Δ S * and negative value of Δ G * implied that the process of alkylation of phenol and tert -butyl alcohol was spontaneous in the current reaction system. The recovery experiments of [HIMA]OTs were performed, and an excellent recycling performance was obtained. This method provides a potential way for the industrial synthesis of tert -butylphenol.