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61.
Ulrich Deschler Peter Kleinschmit Peter Panster 《Angewandte Chemie (International ed. in English)》1986,25(3):236-252
Silicon and carbon may be looked upon as the two fundamental antipodes with respect to the naturally occurring forms of matter and life on earth: Silicon plays the key role in the “petrification” of inanimate matter, while carbon is the representative element for the “incarnation” of living organisms. If a scientist were to search for a highly efficient method of uniting inorganic and organic matter, he would, at a very early stage of attempting to solve this problem, combine these two natural principles of matter and think of “bireactive” molecules containing a silicon functionality for bonding to inorganic material on the one hand and a carbon functionality for anchoring to an organic counterpart on the other. The title compounds and their derivatives epitomize such molecules: they are wanderers between both (chemical) worlds. Owing to their bifunctionality they are capable of binding to inorganic (especially siliceous) systems as well as to organic polymers. Whether their commercial application concerns the strengthening of polyester resins with glass fibers for use in boatbuilding or the incorporation of silica as a filler in rubber mixtures for the manufacture of wear-resistant tires or even the immobilization of enzymes on glass spheres for carrying out reactions in enzyme reactors—in all cases organofunctionalized silanes guarantee a reliable and permanent union between two otherwise “incompatible” material systems. 相似文献
62.
A method is described for the simultaneous quantitative determination of monoamines and related compounds from urine and brain tissue samples in the pg-range, using a GC/MF instrument LKB-2091 provided with a multiple ion detection (MID) system and capillary columns. The simultaneous detection of “fingerprints” with fourteen and more compounds during one single GC run was achieved after the intoduction of “time gates” for the detection of the different characteristic masses. Several modifications to the LKB equipment permitted exact reproducibility of retention times, which is essential for the use of “time gates”. The detection of “fingerprints” with these acidic, basic and alcoholic substances was achieved by the extraction of the dried biological samples with silylating agents. 相似文献
63.
64.
The molecular structure and absorption spectra of monothio- and dithio-naphthalimides were compared to their naphthalimide analogues using AM1, PM3 and ZINDO/S semiempirical quantum chemical methods. The substitution of the 4R-naphthalimide oxygen atoms by sulphur atoms resulted in a red-shift of the absorption spectra by Δλmax60-65 and 100-140 nm, respectively. The thionated naphthalimide derivatives do not show observable fluorescence due to intersystem crossing to the triplet -states localised at the CS groups. The -absorption bands of monothioimides are located at 525-580 nm (ε=60-80) and those for dithioimides at 535-560 nm (ε=140-390) and 628-686 nm (ε=34-68). None of these transitions are solvent sensitive. The -transitions of N-phenylthioimides have also a small contribution from -states due to a partial conjugation between CS group and π-electronic system of the N-phenyl ring. As a result, the bands of aromatic substituted N-phenylthioimides are red-shifted as compared to those of the aliphatic N-methyl-thioimides. 相似文献
65.
Mahmoud M. Al Omari Mohammad B. Zughul J. Eric D. Davies Adnan A. Badwan 《Journal of inclusion phenomena and macrocyclic chemistry》2006,54(3-4):159-164
Ternary complexes exploiting solubility synergism (SSn) between basic drugs and β-cyclodextrin (β-CD) in the presence of an organic hydoxy acid have been reported to provide the pharmaceutical technology with highly soluble ternary complexes, even with the least soluble β-CD. In this work, phase solubility techniques were used to study factors affecting SSn in aqueous solution, which may help in understanding the mechanism involved in ternary complex formation in solution, under equilibrium conditions. The equilibrium solubility of both β-CD and each of 8 structurally unrelated drugs were measured in tandem in the presence of different acid types at low and high pHs, and at different time intervals over a period of 1–40 days. The results indicate that SSn is evident regardless of acid type (organic and inorganic) at low pH, but the extent of SSn is acid type dependant and is limited by the drug salt solubility product constant (pK
sp). Among different drugs, no apparent trend exists between drug salt solubility and the extent of SSn, but lowering drug salt solubility by increasing pH depresses SSn. The results also reveal no apparent trend between the magnitude of the complex formation constant (K
ij) and SSn. For example, drugs of low K
ij values such as astemizole, cisapride and sildenafil do not show any SSn, yet ketotifen and pizotifen, which also have low K
ij values, exhibit substantial SSn. However, the solublizing power of β-CD represented by the slope of phase solubility diagram can be used as a marker for SSn (slopes exceeding 0.4 induce SSn). 相似文献
66.
67.
Dr. Andreas Kafizas Prof. Claire J. Carmalt Prof. Ivan P. Parkin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(41):13048-13058
It has often been suggested that anatase–rutile mixtures/composites synergistically enhance photocatalysis. However, in the case of dense thin‐films containing an intimate mix of both anatase and rutile phases, such an effect has not been observed. In synthesising combinatorial films with graded film thickness and phase, and applying established photocatalytic mapping methods, we were able to assess how dense thin‐films of intimately mixed anatase–rutile mixtures affect photocatalytic performance. We found that no photocatalytic synergy between anatase–rutile composites (29≤rutile %≤83) within such dense thin‐film systems exists. In fact, an increased presence of rutile caused the photocatalytic activity to fall. This was explained by the unfavourable energetics in the multiple electron transfers required between several neighbouring rutile and anatase sites for the photo‐generated electron to reach the material’s surface; encouraging the trapping of electrons within the bulk and increasing the likelihood of charge recombination. The decrease in photocatalytic activity was found to vary linearly with rutile component. 相似文献
68.
对船载特种设备基准点的空间位置进行测量,得到该基准点的运动轨迹并进行测量误差分析,是某项工程数据处理的重要内容.提出了利用三台船载GPS接收机测量船载特种设备基准点的原理和误差分析方法,介绍了该方法的误差源构成,依据测量原理模型,推导出定位精度的估算公式,并叙述了仿真计算与测量实施. 相似文献
69.
Georgia W. Hodges Deborah Tippins J. Steve Oliver 《School science and mathematics》2013,113(6):263-274
Science teacher retention, attrition, and migration continue to perplex educational scholars, political entities, as well as the general public. This study utilized an interpretive methodological design to generate assertions regarding career choice made by highly qualified science teachers in the deep, rural South through analysis of documents, interviews, focus groups, and observation. Generally considered “difficult to staff” because of location, socioeconomics, and demographics, Wilson County High School is an exemplar in science teacher retention and student achievement. Findings presented include how the science department at Wilson County improved student learning outcomes as well as the reasons why two of the highly qualified science teachers at this school were considering leaving the profession they love. 相似文献
70.