The structure of 20GaF3–15InF3 –20CdF2–15ZnF2–20PbF2–10SnF2 glass (GICZPS) was studied by EXAFS and XRD. The results indicate that Ga3+ is more stable than In3+ in the GICZPS glass network, and Zn2+ is the glass modifier, the coordination number of which is 6. 相似文献
A novel β-galactosidase of 120 kDa (BgaBM) from Bacillus megaterium 2-37-4-1 was purified, and its gene (bgaBM) was analyzed and expressed. It displayed wide acceptor specificity for transglycosylation with a series of acceptors, including
pentose, hexose, hydroxyl, and alkyl alcohol using o-nitrophenyl-β-d-galactoside (ONPG) as a donor. BgaBM preferentially hydrolyzed ONPG in all tested substrates and showed maximum activity
at pH 7.5–8.0 and 55 °C. It was stable at pH 6.0–9.0 below 40 °C. The Km and Vmax values for ONPG and lactose were 9.5 mM, 16.6 mM/min and 12.6 mM, 54.4 mM/min, respectively. The nucleotide sequence of the
bgaBM gene consists of an ORF of 3,105 bp corresponding to 118 kDa protein, which indicates that BgaBM is a modular enzyme in the
glycosyl hydrolase family 2, including conserved sugar-binding domain, acid–base catalyst, and immunoglobulin-like beta-sandwich
domain. The possible acid/base and nucleophile sites of BgaBM were estimated to be E481 and E547, respectively. Furthermore,
expression of the bgaBM gene in Escherichia coli and purification of the recombinant enzyme were performed. The recombinant enzyme showed similar biochemical characteristics
to natural enzyme. 相似文献
Osmabenzenes can be easily synthesized from two η2‐coordinated olefin osmacycles in the presence of benzonitrile by means of facile hydrogen‐transfer conversions (see graphic). Mechanisms for the formation of osmabenzenes are proposed based on DFT calculations.
Let G be a 4-connected planar graph on n vertices. Malkevitch conjectured that if G contains a cycle of length 4, then G contains a cycle of length k for every k∈{n,n−1,…,3}. This conjecture is true for every k∈{n,n−1,…,n−6} with k≥3. In this paper, we prove that G also has a cycle of length n−7 provided n≥10. 相似文献
A set of integers is called sum-free if it contains no triple (x, y, z) of not necessarily distinct elements with x + y = z. In this paper, we provide a structural characterisation of sum-free subsets of {1, 2,..., n} of density at least 2/5 ? c, where c is an absolute positive constant. As an application, we derive a stability version of Hu’s Theorem [Proc. Amer. Math. Soc. 80 (1980), 711–712] about the maximum size of a union of two sum-free sets in {1, 2,..., n}. We then use this result to show that the number of subsets of {1, 2,..., n} which can be partitioned into two sum-free sets is Θ(24n/5), confirming a conjecture of Hancock, Staden and Treglown [arXiv:1701.04754]. 相似文献