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101.
Contribution of individual zinc ligands to metal binding and peptide folding of zinc finger peptides
Little is known about the contribution of individual zinc-ligating amino acid residues for coupling between zinc binding and protein folding in zinc finger domains. To understand such roles of each zinc ligand, four zinc finger mutant peptides corresponding to the second zinc finger domain of Sp1 were synthesized. In the mutant peptides, glycine was substituted for one of four zinc ligands. Their metal binding and folding properties were spectroscopically characterized and compared to those of the native zinc finger peptide. In particular, the electronic charge-transfer and d-d bands of the Co(II)-substituted peptide complexes were used to examine the metal coordination number and geometry. Fluorescence emission studies revealed that the mutant peptides are capable of binding zinc despite removing one ligand. Circular dichroism results clearly showed the induction of an alpha-helix by zinc binding. In addition, the structures of certain mutant zinc finger peptides were simulated by molecular dynamics calculation. The information indicates that His23 and the hydrophobic core formed between the alpha-helix and the beta-sheet play an essential role in alpha-helix induction. This report demonstrates that each ligand does not contribute equally to alpha-helix formation and coordination geometry in the zinc finger peptide. 相似文献
102.
Xu Q Tanaka K Mori M Helaleh MI Hu W Hasebe K Toada H 《Journal of chromatography. A》2003,997(1-2):183-190
A monolithic ODS-silica gel column modified by saturating it with lithium dodecylsulfate (Li-DS) was used to demonstrate the high-speed separation of H+ from other mono- and divalent cations, such as Na+, NH4+, K+, Mg2+ and Ca2+ using ion chromatography (IC). Using a 5 mM EDTA-2K solution containing 0.10 mM Li-DS (pH 4.80) as eluent, H+ was eluted with a sharp and symmetrical peak within 1.0 min before other cations at a flow-rate of 1.5 ml min(-1). The rapid elution of H+ and its conductimetric detection could be attributed to the presence of EDTA (HY2-), which can convert H+ ions as anions. i.e. H(+) + H2Y(2-) --> H3Y(-). The acidity of rainwater and deionized water samples was determined using this IC system with satisfactory results. 相似文献
103.
RajanBabu TV Nomura N Jin J Nandi M Park H Sun X 《The Journal of organic chemistry》2003,68(22):8431-8446
Through a systematic examination of ligand and counterion effects, new protocols for a nearly quantitative and highly selective codimerization of ethylene and various functionalized vinylarenes have been discovered. In a typical reaction, 4-bromostyrene and ethylene undergo codimerization in the presence of 0.0035 equiv each of [(allyl)NiBr]2, triphenylphosphine, and AgOTf in CH2Cl2 at -56 degrees C to give 3-(4-bromophenyl)-1-butene in >98% yield and selectivity. Corresponding reactions with [(allyl)PdX]2 are much less efficient and less selective and may require further optimization before a viable system can be identified. Another useful protocol that gives comparable yield and selectivity involves the use of a single-component catalyst prepared from allyl 2-diphenylphosphinobenzoate, Ni(COD)2, and (C6F5)3B. Recognition of a synergistic relationship between a chiral hemilabile ligand (for example, (R)-2-methoxy-2'-diphenylphosphino-1,1'-binaphthyl, MOP) and a highly dissociated counteranion (BARF or SbF6) in an enantioselective version of the Ni-catalyzed reaction raises the prospects of developing a practical route for the synthesis of 3-arylbutenes. Several pharmaceutically relevant compounds, including widely used 2-arylpropionic acids, can be synthesized from these key intermediates. This reaction appears to be quite general. Synthesis of several new 2-diphenylphosphino-1,1-binaphthyl derivatives, prepared to probe the effect of hemilabile coordination on the efficiency and selectivity of the reaction, are also described. 相似文献
104.
Kiyoshi Endo Hajime Tsujikawa Takayuki Otsu 《Journal of polymer science. Part A, Polymer chemistry》1986,24(7):1633-1642
5-Phenyl-2-pentene (5Ph2P) was found to undergo monomer-isomerization polymerization with TiCl3–R3Al (R = C2H5 or i-C4H9, Al/Ti > 2) catalysts to give a polymer consisting of exclusively 5-phenyl-1-pentene (5Ph1P) unit. The geometric and positional isomerizations of 5Ph2P to its terminal and other internal isomers were observed to occur during polymerization. The catalyst activity of alkylaluminum examined to TiCl3 was in the following order: (C2H5)3Al > (i-C4H9)3Al > (C2H5)2AlCl. The rate of monomer-isomerization polymerization of 5Ph2P with TiCl3–(C2H5)3Al catalyst was influenced by both the Al/Ti molar ratio and the addition of nickel acetylacetonate [Ni(acac)2], and the maximum rate was observed at Al/Ti = 2.0 and Ni/Ti = 0.4 in molar ratios. 相似文献
105.
Hiroshi Taketa Hiroshi Tatewaki Okio Nomura Kimio Ohno 《Theoretical chemistry accounts》1968,11(5):369-376
It is well known that the energy interval separating 3
u
–
and 3
u
+
states of O2, as given by the conventional ASMO method, is too large. In order to resolve this difficulty, removal of the equivalence restrictions usually employed in the orbital theory is proposed. Thus the orbital exponent of one antibonding g MO is allowed to take a different value from the other g's. Variational calculations show that the resulting outermost orbital is much more diffuse than the others. This model of a single diffuse orbital brings about a considerable energy lowering for the 3
u
–
state and thus the agreement of the 3
u
–
- 3
u
+
interval with experiment is improved.
Zusammenfassung Die konventionelle ASMO-Theorie liefert bekanntlich eine viel zu große Differenz der Terme 3 u – und 3 u + von O2, weswegen der Vorschlag gemacht wird, die üblicherweise vorgenommene Äquivalenz-Einschränkung fallen zu lassen. Der Orbital-Exponent eines lockernden MO's kann von dem der übrigen g's abweichen. Rechnungen zeigen, daß das äußerste MO viel diffuser als die anderen ist und daß die Energie des 3 u – -Zustandes beträchtlich erniedrigt wird.
Résumé La séparation entre les états 3 u – 3 u + de O2 donnée par la méthode ASMO conventionnelle est connue pour être trop grande. Afin de résoudre cette difficulté la levée des restrictions d'équivalence ordinairement utilisées est proposée. Ainsi l'exposant orbital d'une des orbitales moléculaires antiliantes g peut prendre une valeur différente de celui de l'autre orbitale antiliante g. Des calculs variationnels montrent que l'orbitale la plus haute ainsi obtenue est beaucoup plus diffuse que les autres. Ceci a pour effet de diminuer considérablement l'énergie de l'état 3 u – , améliorant la séparation entre les états 3 u – et 3 u + .相似文献
106.
Various poly(macromonomer)s containing sugars have been prepared by ROMP of norbornene macromonomers substituted with ROMP block copolymers containing acetal-protected sugars as the side chain, which upon removal of the protecting group affords a novel amphiphilic architecture. 相似文献
107.
Kiyoshi Hasebe Satoshi Hikima Hitoshi Yoshida 《Fresenius' Journal of Analytical Chemistry》1991,339(4):261-263
Summary The covalent bonding of l-lactate oxidase (no E.C.) to cross-linked copolymers of chitosan (Chitopearl) using the glutaraldehyde method is described and applied to the determination of l-lactate in serums of diseased and normal animals. The bioreactor packing of the immobilized enzyme is stable for at least 4 months and can be continuously used for the rapid and simple determination of l-lactate. The reduction current of pyruvate, corresponding to the product of enzymatic reaction, is determined by differential pulse polarography. The reproducibility (RSD) for 10 mol/l l-lactate is 0.78% (n=6) and the detection limit is 0.62 mol/l (k=2, confidence level 97.72%). 相似文献
108.
109.
Li4Ti5O12 thin films for rechargeable lithium batteries were prepared by a sol-gel method with poly(vinylpyrrolidone). Interfacial properties of lithium insertion into Li4Ti5O12 thin film were examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and potentiostatic intermittent titration technique (PITT). Redox peaks in CV were very sharp even at a fast scan rate of 50 mV s−1, indicating that Li4Ti5O12 thin film had a fast electrochemical response, and that an apparent chemical diffusion coefficient of Li+ ion was estimated to be 6.8×10−11 cm2 s−1 from a dependence of peak current on sweep rates. From EIS, it can be seen that Li+ ions become more mobile at 1.55 V vs. Li/Li+, corresponding to a two-phase region, and the chemical diffusion coefficients of Li+ ion ranged from 10−10 to 10−12 cm2 s−1 at various potentials. The chemical diffusion coefficients of Li+ ion in Li4Ti5O12 were also estimated from PITT. They were in a range of 10−11-10−12 cm2 s−1. 相似文献
110.
Four 6-phenyl-5,6,7,8-tetrahydro-4H-1,3,2,6-dioxathiazocine 2-oxides were synthesized by the reaction of the corresponding N,N-bis(2-hydroxyethyl)aniline with thionyl chloride in the presence of triethylamine. 相似文献