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991.
In this paper, the interaction between herbacetin and BSA was investigated by fluorescence and three-dimensional fluorescence spectroscopy under simulated physiological conditions. It was proved that the fluorescence quenching of BSA by herbacetin was mainly the result of the formation of a herbacetin–BSA complex. The modified Stern–Volmer quenching constant and the corresponding thermodynamic parameters ΔH 0, ΔG 0 and ΔS 0 were calculated at different temperatures. The results indicated that electrostatic interactions were the predominant intermolecular forces in stabilizing the complex. The distance r=3.23 nm between the donor (BSA) and acceptor (herbacetin) was obtained according to Förster’s nonradioactive energy transfer theory. The synchronous fluorescence and three-dimensional fluorescence spectra results showed that the hydrophobity of amino acid residues increased in the presence of herbacetin. These results revealed that the microenvironment and conformation of BSA changed during the binding reaction. 相似文献
992.
The self‐assembled (SA) molecular monolayers of a 3‐aminopropyltrimethoxysilane (3‐APTS) on a silicon (111) surface, and the effects of ultraviolet (UV) pre‐treatment for substrates on the assembling process have been studied using XPS and atomic force microscopy (AFM). The results show that the SA 3‐APTS molecules are bonded to the substrate surface in a nearly vertical orientation, with a thickness of the monolayer of about 0.8–1.5 nm. The SA molecular monolayers show a substantial degree of disorder in molecular packing, which are believed to result from the interactions of amine tails in the silane molecules used with surface functionalities of the substrates, and the oxygen‐containing species from the ambient. UV irradiation for silicon substrates prior to the self‐assembly reaction can enhance the assembly process and hence, significantly increase the coverage of the monolayer assembled for the substrates. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
993.
Three hydroxamic acid ligands (HL1 = acetohydroxamic acid; HL2 = benzohydroxamic acid; HL3 = N-phenylbenzohydroxamic acid), have been used to synthesize series of mono- or dialkyltin(IV) complexes, which include (i) the carboxyl acid hybrid five-coordinated dialkyltin complexes (C4H9)2SnL1L4 (1), [(CH3)2SnL2L5]·0.5C6H6 (2), (HL4 = acetic acid; HL5 = benzoic acid); (ii) the six-coordinated mono-n-butyltin complexes (C4H9)SnL1·Cl2·H2O (3), (C4H9)SnL2·Cl2·H2O (4), [(C4H9)SnL3·Cl2·H2O]·H2O (5), [(C4H9Sn)2(L3)2·Cl2·(OCH3)2] (6); and (iii) the alkali metal-mingled seven-coordinated mono-n-butyltin complexes [(C4H9Sn)3L2Na]+·Cl−·(CH3CH2)2O (7), [(C4H9Sn)3L2K]+·Cl−·CH2Cl2 (8). All complexes were characterized by elemental analyses, IR, 1H, 13C, 119Sn NMR and X-ray single crystal diffraction. In these complexes, hydroxamic acids present bidentate coordination modes with the carbonyl O atom and the hydroxyl O atom binding to tin center. In complexes 1-6, each tin atom is coordinated by one hydroxamic acid ligand. However, in complexes 7 and 8, tin atom is surrounded by three hydroxamic acid ligands, and all hydroxyl O atoms of the ligands also bind to the alkali metal center (Na or K). This kind of organotin(IV) framework containing one alkali metal is found for the first time. Furthermore, the supramolecular structures of 1, 3, 4 and 6 have been found to consist of 1D linear molecular chains formed by intermolecular N-H···X or C-H···X (X = O, N or Cl) hydrogen bonds. For complex 2, an interesting macrocyclic tetramer has been built by the intermolecular N-H···O hydrogen bonds. Fascinatingly, two unique symmetric dimeric structures are recognized in complexes 7 and 8, which is individually bridged by intermolecular N-H···Cl and N-H···O hydrogen bonds. In addition, for 8, the dimeric cycles have been further connected into a 1D supramolecular chain. 相似文献
994.
Pengfei Xiao Changli Bao Naizhong Song Cui Li Qiong Jia 《Russian Journal of Inorganic Chemistry》2011,56(7):1157-1161
In the present study, sec-nonylphenoxy acetic acid (CA100) and its mixtures with four neutral organophosphorus extractants, tri-butyl-phosphate (TBP),
2-ethylhexyl phosphonic acid di-2-ethyl ester (DEHEHP), Cyanex923, and Cyanex925 have been applied to the extraction of rare
earths. Results show that all the four mixing systems do not have evident synergistic effects on the extraction of rare earths.
The different extraction effects have been considered to the separation of rare earths. The four mixtures may be applied to
the separation of yttrium from some certain lanthanoids at proper mole fractions of CA100. 相似文献
995.
A series of novel spindle-like terphenyl-type chromophores, based on 2,5-diphenyl-1,4-distyrylbenzene π-conjugating bridge, N,N-dimethyl and triphenyl amino donors, and Tricyanovinyldihydrofuran(TCF), 1,3,3-trimethyl-5-dicyanovinyl-1-cyclohexene (TDC) acceptors, have been synthesized successfully for the first time. And the non-linear optical properties were evaluated by using the finite-field (FF) method. The results show that, the first-order hyperpolarizability of the chromophores increase with the increase of the withdraw ability of the substituent group on the π-conjugating bridge. 相似文献
996.
997.
The acid–base reaction between Y(CH2SiMe3)3(thf)2 and the pyridyl‐functionalized cyclopentadienyl (Cp) ligand C5Me4H? C5H4N (1 equiv) at 0 °C afforded a mixture of two products: (η5:κ‐C5Me4? C5H4N)Y(CH2SiMe3)2(thf) ( 1 a ) and (η5:κ‐C5Me4? C5H4N)2YCH2SiMe3 ( 1 b ), in a 5:2 ratio. Addition of the same ligand (2 equiv) to Y(CH2SiMe3)3(thf)2, however, generated 1 b together with the novel complex 1 c , the first well defined yttrium mono(alkyl) complex (η5:κ‐C5Me4? C5H4N)[C5HMe3(η3‐CH2)‐C5H4N‐κ]Y(CH2SiMe3) containing a rare κ/η3‐allylic coordination mode in which the C? H bond activation occurs unexpectedly with the allylic methyl group rather than conventionally on Cp ring. If the central metal was changed to lutetium, the equimolar reaction between Lu(CH2SiMe3)3(thf)2 and C5Me4H? C5H4N exclusively afforded the bis(alkyl) product (η5:κ‐C5Me4? C5H4N)Lu(CH2SiMe3)2(thf) ( 2 a ). Similarly, the reaction between the ligand (2 equiv) and Lu(CH2SiMe3)3(thf)2 gave the mono(alkyl) complex (η5:κ‐C5Me4? C5H4N)2LuCH2SiMe3 ( 2 b ), in which no ligand redistribution was observed. Strikingly, treatment of Sc(CH2SiMe3)3(thf)2 with C5Me4H? C5H4N in either 1:1 or 1:2 ratio at 0 °C generated the first cyclopentadienide‐based scandium zwitterionic “tuck‐over” complex 3 , (η5:κ‐C5Me4? C5H4N)Sc(thf)[μ‐η5:η1:κ‐C5Me3(CH2)‐C5H4N]Sc(CH2SiMe3)3. In the zwitterion, the dianionic ligand [C5Me3(CH2)‐C5H4N]2? binds both to Sc13+ and to Sc23+, in η5 and η1/κ modes. In addition, the reaction chemistry, the molecular structures, and the mechanism are also discussed in detail. 相似文献
998.
Tossing aldehydes into the ring: The reaction of a silacyclopentadienylidene with aldehydes leads to C=O bond cleavage with the formation of base-stabilized silanones and cyclopropanation of the adjacent C=C bond, followed by silole ring expansion to give silicon analogues of cyclohexadienones. 相似文献
999.
1000.
Complicated and expensive organic ligands are normally essential in fine chemical synthesis at preparative or industrial levels. The synthesis of fine chemicals by using heterogeneous catalyst systems without additive organic ligand is highly desirable but severely limited due to their poor generality and rigorous reaction conditions. Here, we show the results of carbon–nitrogen or carbon–carbon bond formation catalyzed by an Ag/Mo hybrid material with specific Ag6Mo10O33 crystal structure. 48 nitrogen‐ or oxygen‐containing compounds, that is, amines, carboxamides, sulfonamides, and ketones, were successfully synthesized through a borrowing‐hydrogen mechanism. Up to 99 % isolated yields were obtained under relatively mild conditions without additive organic ligand. The catalytic process shows promise for the efficient and economic synthesis of amine, carboxamide, sulfonamide, and ketone derivatives because of the simplicity of the system and ease of operation. 相似文献