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91.
92.
Vincent Wing‐hei Lau Dr. Leon G. A. van de Water Prof. Anthony F. Masters Prof. Thomas Maschmeyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(10):2923-2930
Synthetic solvent systems for the fine‐tuned preparation of CdS nanocrystallites, active in visible‐light photocatalytic hydrogen production, were studied. To control crystallite size and spectral properties, the CdS crystals were synthesised by using different solvent systems, containing a series of tetrabutylammonium amino carboxylate ionic liquids as the crystal‐growth control agents. Six samples of CdS, all with similar physical and spectral properties, exhibited greatly varying photocatalytic activity, with the most active sample outperforming the least active one by almost 60 %. To rationalise this effect, the intermolecular interactions of the synthesis solvent system with the growing CdS nanocrystallites were characterised by using the Reichart betaine dye and the ${E{{{\rm N}\hfill \atop {\rm T}\hfill}}}$ polarity scale. A correlation was observed between the ${E{{{\rm N}\hfill \atop {\rm T}\hfill}}}$ values of the solvent system and the photocatalytic activity of the CdS nanocrystallite, suggesting that the hydrogen‐bond‐donating ability and/or dipolarity/polarisability interactions of the solvent system led to the preferential formation of active surfaces/surface sites on the CdS crystals. 相似文献
93.
The ruthenium(II) complex cis-[Ru(6, 6'-Cl(2)bpy)(2)(OH(2))(2)](CF(3)SO(3))(2) (1) is a robust catalyst for C-H bond oxidations of hydrocarbons, including linear alkanes, using tert-butyl hydroperoxide (TBHP) as terminal oxidant. Alcohols can be oxidized by the "1 + TBHP" protocol to the corresponding aldehydes/ketones with high product yields at ambient temperature. Oxidation of 1 with Ce(IV) in aqueous solution affords cis-[Ru(VI)(6, 6'-Cl(2)bpy)(2)O(2)](2+), which is isolated as a green/yellow perchlorate salt (2). Complex 2 is a powerful stoichiometric oxidant for cycloalkane oxidations under mild conditions. Oxidation of cis-decalin is highly stereoretentive; cis-decalinol is obtained in high yield, and formation of trans-decalinol is not observed. Mechanistic studies showing a large primary kinetic isotope effect suggest a hydrogen-atom abstraction pathway. The relative reactivities of cycloalkanes toward oxidation by 2 have been examined through competitive experiments, and comparisons with Gif-type processes are presented. 相似文献
94.
Hot water extracts of Ginkgo biloba seeds were analyzed for the presence of ginkgotoxin (4'-O-methylpyridoxine) by reversed-phase liquid chromatography (LC) using methanol-0.05M KH2PO4 (1 + 9, v/v) adjusted to pH 3 as mobile phase. Detection was by fluorescence (excitation 280 nm, emission 370 nm). A straight line calibration curve was obtained for the 10-100 ng injected. After addition of beta-glucosidase (37 degrees C/h), an earlier eluting peak disappeared and the ginkgotoxin peak increased. The identity of the ginkgotoxin was confirmed by LC/MS and LC/MS/MS. LC/MS/MS also confirmed the 5'-glucoside by comparison with the 3-glucoside. This is the first identification of a glucoside of ginkgotoxin in Ginkgo biloba. An unknown compound of MW 267 also observed in the Ginkgo biloba seed extract was shown not to be 3,5'-diacetylginkgotoxin by its different LC retention time. Extraction of ground Ginkgo biloba seeds with boiling water in a Soxhlet for 2 x 2 h yielded a total of 179 microg/g of free ginkgotoxin. The concentration in powder from Ginkgo biloba capsules was several times lower than this (17-64 microg/g) in 3 samples but higher in another (457 microg/g). Canned ginkgo seeds (white nuts) contained no detectable free ginkgotoxin but the glucoside was present. Different extraction times were studied: 0.5 h gave only 52 microg/g free ginkgotoxin in the ginkgo seeds. However, boiling an extract for 4 h showed about 15% loss of ginkgotoxin and its glucoside. 相似文献
95.
Two three-dimensional (3D) malonate bridged networks, [Cu(mal)(DMF)](n) (1) and [[Cu(mal)(0.5pyz)].H(2)O](n) (2), have been synthesized in H(2)O-DMF solution. Compound 1 exhibits ferromagnetic ordering below 2.6 K (T(c)), and 2 displays a metamagnetic behavior below 3.2 K (T(N)). 相似文献
96.
Lam WH Jia G Lin Z Lau CP Eisenstein O 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(12):2775-2782
Theoretical calculations on the metathesis process, [Tp(PH3)MR(eta 2-H[bond]CH3)] --> [Tp(PH3)M(CH3)(eta 2-H[bond]R)] (M=Fe, Ru, and Os; R=H and CH3), have been systematically carried out to study their detailed reaction mechanisms. Other than the one-step mechanism via a four-center transition state and the two-step mechanism through an oxidative addition/reductive elimination pathway, a new one-step mechanism, with a transition state formed under oxidative addition, has been found. Based on the intrinsic reaction coordinate calculations, we found that the trajectories of the transferring hydrogen atom in the metathesis processes studied are similar to each other regardless of the nature of reaction mechanisms. 相似文献
97.
Lau JK Wong CH Ng PS Siu FM Ma NL Tsang CW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(14):3383-3396
The potassium cation affinities (PCAs) of 136 ligands (20 classes) in the gas phase were established by hybrid density functional theory calculations (B3-LYP with the 6-311+G(3df,2p) basis set). For these 136 ligands, 70 experimental values are available for comparison. Except for five specific PCA values-those of phenylalanine, cytosine, guanine, adenine (kinetic-method measurement), and Me(2)SO (by high-pressure mass spectrometric equilibrium measurement)-our theoretical estimates and the experimental affinities are in excellent agreement (mean absolute deviation (MAD) of 4.5 kJ mol(-1)). Comparisons with previously reported theoretical PCAs are also made. The effect of substituents on the modes of binding and the PCAs of unsubstituted parent ligands are discussed. Linear relations between Li+/Na+ and K+ affinities suggest that for the wide range of ligands studied here, the nature of binding between the cations and a given ligand is similar, and this allows the estimation of PCAs from known Li+ and/or Na+ affinities. Furthermore, empirical equations relating the PCAs of ligands with their dipole moments, polarizabilities (or molecular weights), and the number of binding sites were established. Such equations offer a simple method for estimating the PCAs of ligands not included in the present study. 相似文献
98.
To meet the need for a new and validated analytical method for simultaneous determination of inorganic and organic acid anions in beverage drinks, a capillary zone electrophoresis (CZE) procedure had been developed based on a new background electrolyte (BGE) system containing 3 mmol/L 1,3,5-benzenetricarboxylic acid (BTA), 15 mmol/L tris(hydroxymethyl)aminomethane and 1.5 mmol/L tetraethylenepentamine (TEPA) at pH 8.4. Baseline separation of anions commonly found in beverage drinks could be achieved in less than 14 min with indirect UV detection at 240 nm. Comigration problems for hydroxycarboxylic acids could be solved using TEPA as BGE additive. The results indicate excellent repeatability for migration time (RSD, 0.27-0.67%, n = 5) and good precision for both peak height (RSD, 3.2-4.2%, n = 5) and peak area (RSD, 3.1-4.5%, n = 5). Under the optimized conditions and using corrected peak area for quantitation, an excellent linear dynamic range (with correlation coefficient > 0.997 in a concentration range from 0.005 to 2.0 mmol/L) and low detection limit (1-4 micro mol/L) were obtained for all the anions investigated. The applicability and reliability of the CE procedure developed were established by parallel method determination using established ion chromatography procedure for the analysis of inorganic and organic acid anions in orange juice and wine samples. Our CZE procedure provided a sensitive and economic technique for simultaneous determination of inorganic and organic acid anions in orange juice, red and white wine samples. 相似文献
99.
Patrick J. Whitham Dennis P. Strommen Sandra Lundell Lisa D. Lau Rene Rodriguez 《Plasma Chemistry and Plasma Processing》2014,34(4):755-766
The plasma enhanced chemical vapor depositions of germanium chalcogenide thin films from germanium tetrachloride, hydrogen sulfide and alkyl chalcogenides were studied to determine the viability of these reagents for thin film deposition. Hydrogen sulfide is a commonly used reagent for this technique and was used to determine optimal reaction conditions for thin film deposition. Germanium tetrachloride, alkylsulfides and alkylselenides were also employed because of their lower potential toxicities and higher availabilities compared to their more typical congeners: germane, hydrogen sulfide and hydrogen selenide in the formation of germanium chalcogenides. Alkylsulfides were found to be unsuitable for the deposition of germanium sulfides, however alkylselenide precursors were used successfully for the deposition of germanium selenides. The relative mass flow rates, reactor pressure, substrate temperature and plasma power density were studied for their effects on germanium chalcogenide deposition. These parameters affected the composition, deposition rate, film quality, and spectroscopic properties of the deposited films. 相似文献
100.
Zhibo Liu Maral Pourghiasian Mark Alex Radtke Joseph Lau Dr. Jinhe Pan Gemma M. Dias Dr. Donald Yapp Dr. Kuo‐Shyan Lin Prof. Dr. Francois Bénard Prof. Dr. David M. Perrin 《Angewandte Chemie (International ed. in English)》2014,53(44):11876-11880
A new zwitterionic organotrifluoroborate is appended to three radiosynthons that afford undergo facile bioconjugation to several clinically relevant peptides and one enzyme inhibitor. Molecularly complex bioconjugates are 18F‐labeled in a single aqueous step in rapid time (<15 min) without HPLC purification to afford tracers in good yields (>200 mCi, 20–40 %) at high specific activity (≥3 Ci/μmol) and at >98 % purity. PET imaging shows in vivo stability and tumor uptake. 相似文献