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991.
Si‐Ping Tang Ying‐Hua Zhou Huo‐Yan Chen Cun‐Yuan Zhao Zong‐Wan Mao Liang‐Nian Ji 《化学:亚洲杂志》2009,4(8):1354-1360
A new β‐cyclodextrin dimer, 2,6‐dimethylpyridine‐bridged‐bis(6‐monoammonio‐β‐cyclodextrin) (pyridyl BisCD, L), is synthesized. Its zinc complex (ZnL) is prepared, characterized, and applied as a catalyst for diester hydrolysis. The formation constant (log KML=7.31±0.04) of the complex and deprotonation constant (pKa1=8.14±0.03, pKa2=9.24±0.01) of the coordinated water molecule were determined by a potentiometric pH titration at (25±0.1)°C, indicating a tridentate N,N′,N′′‐zinc coordination. Hydrolysis kinetics of carboxylic acid esters were determined with bis(4‐nitrophenyl)carbonate (BNPC) and 4‐nitrophenyl acetate (NA) as the substrates. The resulting hydrolysis rate constants show that ZnL has a very high rate of catalysis for BNPC hydrolysis, yielding an 8.98×103‐fold rate enhancement over uncatalyzed hydrolysis at pH 7.00, compared to only a 71.76‐fold rate enhancement for NA hydrolysis. Hydrolysis kinetics of phosphate esters catalyzed by ZnL are also investigated using bis(4‐nitrophenyl)phosphate (BNPP) and disodium 4‐nitrophenyl phosphate (NPP) as the substrates. The initial first‐order rate constant of catalytic hydrolysis for BNPP was 1.29×10?7 s?1 at pH 8.5, 35 °C and 0.1 mM catalyst concentration, about 1600‐fold acceleration over uncatalyzed hydrolysis. The pH dependence of the BNPP cleavage in aqueous buffer was shown as a sigmoidal curve with an inflection point around pH 8.25, which is nearly identical to the pKa value of the catalyst from the potentiometric titration. The kBNPP of BNPP hydrolysis promoted by ZnL is found to be 1.68×10?3 M ?1 s?1, higher than that of NPP, and comparatively higher than those promoted by its other tridentate N,N′,N′′‐zinc analogues. 相似文献
992.
依据单元非成像型光谱辐射计的特点,提出了一种单元非成像型红外光谱辐射计的成像光谱数据获取系统.该系统采用在光谱辐射计前端加装扣描装置.结合同步控制器,实现光谱辐射计的空间扫描.利用光谱辐射计提供的接口,完成了采集获得的成像光谱数据的批量定标.该系统可达到500×500像素的空间分解能力,光谱范围667~5 000 cm-1,光谱分辨率为1 cm-1,空间视场角为150°,瞬时视场角为0.3°.将该系统应用于实际的场景光谱数据获取,通过对得到的实验数据分析和比较,说明本文给出的基于非成像光谱辐射计的成像数据获取系统,能够实现实际场景的成像光谱数据获取,能够满足实时性要求不太高的成像光谱数据获取. 相似文献
993.
994.
Bao‐Zong Li Yan‐Fen Peng Yu‐Ping Zhang Bao‐Long Li Yong Zhang 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(11):m560-m562
In the crystal structure of the title complex, poly[[diazidocobalt(II)]‐di‐μ‐1,4‐bis(1,2,4‐triazol‐1‐ylmethyl)benzene‐κ4N4:N4′], [Co(N3)2(bbtz)2]n, where bbtz is 1,4‐bis(1,2,4‐triazol‐1‐ylmethyl)benzene (C12H12N6), the CoII atom, which lies on an inversion centre, is six‐coordinated by four N atoms from four bbtz ligands and by two N atoms from two azide ligands, in a distorted octahedral coordination environment. The CoII atoms are bridged by four bbtz ligands to form a two‐dimensional [4,4]‐network. 相似文献
995.
We consider the properties on solutions of some q-difference equations of the form ∑ n j=0 aj(z)f(qj z)=an+1(z), where a0(z),..., an+1(z) are meromorphic functions, a0(z)an(z) ≠ 0 and q ∈ C such that 0 〈 |q| ≤ 1. We give estimates on the upper bound for the length of the gap in the power series of entire solutions of (*) when the coefficients a0(z),..., an+1(z) are polynomials and 0 〈 |q| 〈 1. For some special cases, we give estimates of growth of f(z). And we also show that the case 0 〈 |q| 〈 1 is different from the case |q|=1. 相似文献
996.
997.
本文得到了Calderón--Zygmund型算子及其与BMO函数或Lipschitz函数生成的交换子在Herz 型 Hardy空间上的一些有界性结果. 相似文献
998.
Let X be a Banach space and Φ be an Orlicz function.Denote by LΦ(I,X)the space of X-valued Φ-integrable functions on the unit interval I equipped with the Luxemburg norm.For f1,f2,...,fm ∈ LΦ(I,X),a distance formula disΦ(f1,f2,...,fm,LΦ(I,G))is presented,where G is a close subspace of X.Moreover,some existence and characterization results concerning the best simultaneous approximation of LΦ(I,G)in LΦ(I,X)are given. 相似文献
999.
Zhang‐Gao Le Yue Lu Guo‐Fang Jiang Yi‐Shuai Liu Jia Liu Zong‐Bo Xie 《Journal of heterocyclic chemistry》2019,56(11):3135-3144
α‐Chymotrypsin from the bovine pancreas has been shown for the first time to display catalytic nonnatural catalytic ability toward the C (sp3)–H functionalization reaction of 2‐methylquinoline and aromatic aldehydes in water. α‐Chymotrypsin exhibited favorable catalytic activity with good adaptability to different substrates. The activity of the enzyme could be improved by adjusting the solvent, temperature, molar ratio of substrates, and protein loading. The products were obtained in moderate to excellent yields (51%‐93%) in 24 samples. This process afforded a potential biocatalytic approach as an alternative to chemical synthesis for azaarene derivatives. 相似文献
1000.
本文利用NA序列的弱收敛定理及概率不等式,证明了其完全矩收敛精确渐近性的一般结果,改进并推广了已有的结果. 相似文献