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991.
J. Orbán Sz. Halasi G. Papp Szilvia Barkó Beáta Bugyi 《Journal of Thermal Analysis and Calorimetry》2005,82(1):287-290
Summary The thermodynamic properties of the cardiac and skeletal a-actin isoforms were studied to characterize the molecular bases
of the functional differences between them with the method of differential scanning calorimetry (DSC). The thermal properties
of the actin filaments were described in the presence of calcium and magnesium ions as well. Based on the calculated free
energy changes the α-cardiac actin filaments appeared to be more stable in its physiologically more relevant, magnesium saturated
form. The magnesium saturated form of the α-cardiac actin filaments seemed to be more stable compared to the calcium saturated
form of it. The enthalpy and entropy changes could differentiate between the α-cardiac and α-skeletal actin isoforms and between
the calcium and magnesium saturated cardiac actin isoforms as well. Our results can demonstrate that the few differences between
the amino acid sequences of the α-actin isoforms have an influence on the thermal properties and maybe on the function of
these proteins as well. 相似文献
992.
Zhou YanXia Tan HongWei Yang ZuoYin Jia ZongChao Liu RuoZhuang Chen GuangJu 《中国科学B辑(英文版)》2007,50(2):266-271
The insect spruce budworm(Choristoneura fumiferana) produces antifreeze protein(AFP) to assist in the protection of the over-wintering larval stage and contains multiple isoforms. Structures for two isoforms,known as CfAFP-501 and CfAFP-337,show that both possess similar left-handed β-helical structure,although thermal hysteresis activity of the longer isoform CfAFP-501 is three times that of CfAFP-337. The markedly enhanced activity of CfAFP-501 is not proportional to,and cannot be simply accounted for,by the increased ice-binding site resulting from the two extra coils in CfAFP-501. In or-der to investigate the molecular basis for the activity difference and gain better understanding of AFPs in general,we have employed several different computational methods to systematically study the structural properties and ice interactions of the AFPs and their deletion models. In the context of intact AFPs,a majority of the coils in CfAFP-501 has better ice interaction and causes stronger ice lattice disruption than CfAFP-337,strongly suggesting a cooperative or synergistic effect among β-helical coils. The synergistic effect would play a critical role and make significant contributions to the anti-freeze activity β-helical antifreeze proteins. This is the first time that synergistic effect and its implica-tion for antifreeze activity are reported for β-helical antifreeze proteins. 相似文献
993.
Jue Xiao CAI Zheng Hong ZHOU Kang Ying LI Chi Hung YEUNG Chu Chi TANG* State Key Laboratory of Elemento-Organic Chemistry Institute of Elemento-Organic Chemistry Nankai University Tianjin Open Laboratory of Chirotechnology D 《中国化学快报》2002,13(7)
Optically active 1,1-binaphthalene-2, 2-diol has become a quite important chiral source in different fields of chirotechnology, especially in asymmetric synthesis1. Its synthesis and resolution has been extensively studied and various resolution methods have been reported2. Among the reported resolution methods, the following three, namely, via the formation of phosphoric acid derivatives3, boric acid derivatives4 and inclusion complexes5, are the most important. OHOH+_( )-1(-)-(S)-1(+)-(R)… 相似文献
994.
Małgorzata Olejnik Teresa Szprengier-Juszkiewicz Piotr Jedziniak Jan Żmudzki 《Accreditation and quality assurance》2007,12(12):637-641
In this paper, the case of FAPAS PT 0270 “Doramectin and Oxfendazole in Sheep Liver” is discussed. During evaluation of the
data received from participants (determination of total, oxidised oxfendazole residue and calculation of the sum of oxfendazole
and oxfendazole sulfone residues), significant differences were observed between the results obtained by use of two analytical
approaches. This phenomenon can be explained by the route of oxfendazole metabolism, which results in the presence of fenbendazole
in the sample. This was not predicted by the provider; consequently, not all the necessary tests on the material were conducted.
Due to the high uncertainty of the z-scores in this test, the results of the PT cannot be used for purposes of evaluation, and the benefits of participation in
PT 0270 are questionable. 相似文献
995.
Zhang B Harb JN Davis RC Kim JW Chu SH Choi S Miller T Watt GD 《Inorganic chemistry》2005,44(10):3738-3745
Horse spleen ferritin (HoSF) containing 800-1500 cobalt or 250-1200 manganese atoms as Co(O)OH and Mn(O)OH mineral cores within the HoSF interior (Co-HoSF and Mn-HoSF) was synthesized, and the chemical reactivity, kinetics of reduction, and the reduction potentials were measured. Microcoulometric and chemical reduction of HoSF containing the M(O)OH mineral core (M = Co or Mn) was rapid and quantitative with a reduction stoichiometry of 1.05 +/- 0.10 e/M forming a stable M(OH)(2) mineral core. At pH 9.0, ascorbic acid (AH(2)), a two-electron reductant, effectively reduced the mineral cores; however, the reaction was incomplete and rapidly reached equilibrium. The addition of excess AH(2) shifted the reaction to completion with a M(3+)/AH(2) stoichiometry of 1.9-2.1, consistent with a single electron per metal atom reduction. The rate of reaction between M(O)OH and excess AH(2) was measured by monitoring the decrease in mineral core absorbance with time. The reaction was first order in each reactant with second-order rate constants of 0.53 and 4.74 M(-1) min(-1), respectively, for Co- and Mn-HoSF at pH 9.0. From the variation of absorbance with increasing AH(2) concentration, equilibrium constants at pH 9.0 of 5.0 +/- 1.9 for Co-HoSF and 2.9 +/- 0.9 for Mn-HoSF were calculated for 2M(O)OH + AH(2) = 2M(OH)(2) + D, where AH(2) and D are ascorbic acid and dehydroascorbic acid, respectively. Consistent with these equilibrium constants, the standard potential for the reduction of Co(III)-HoSF is 42 mV more positive than that of the ascorbic acid reaction, while the standard potential of Mn(III)-HoSF is 27 mV positive relative to AH(2). Fe(2+) in solution with Co- and Mn-HoSF under anaerobic conditions was oxidized to form Fe(O)OH within the HoSF interior, resulting in partial displacement of the Co or Mn by iron. 相似文献
996.
Studies of difference spectra have revealed a dynamic interaction of bilirubin and hemoglobin in the alkaline Jendrassik-Grof diazo blank reagent. The similarity obtained for difference spectra with respect to shape and peak maxima and peak minima of various ferriprotoporphyrin-containing biomolecules, such as hemin, methemoglobin, cyanmethemoglobin, and catalase implicated ferriprotoporphyrin in this interactive process. Further time studies of these mixtures seem to suggest an oxidation-reduction type of reaction, resulting in the formation of ferroprotoporphyrin and presumably the concomitant oxidation of bilirubin. 相似文献
997.
YiHU JueCHEN ZhangGaoLE ZhenChuCHEN QinGuoZHENG 《中国化学快报》2005,16(7):903-905
An efficient method is reported for the synthesis of phenacyl esters by reaction of carboxylic acids with a-bromoacetophenone promoted by potassium fluoride in ionic liquid [Bmim]PF6, the yield of the reaction is almost quantitative and the products are essentially pure. 相似文献
998.
用XRD、FT-IR、ESR、H2-TPR和TPO等方法,对Na2WO4-Mn2O3/SiO2催化剂和其经水煮处理的一系列样品进行了表征.实验发现该催化剂中的结晶态Na2WO4易于流失,单层分布的Na2WO4在苛刻的处理条件下也有可能流失.依此,探讨了上述流失现象与Na2WO4-Mn2O3/SiO2催化剂的催化活性及该催化剂在长时间反应中发生的SiO2相变之间的关系,证明了结晶态Na2WO4的流失对该催化剂甲烷氧化偶联反应的催化活性只有轻微的影响,单层分布Na2WO4的流失可造成催化剂中Mn从Mn3+转变为Mn2+,并使催化剂的催化活性明显降低.但在水煮条件下,无论是结晶态的还是单层分布,Na2WO4的流失都没有对SiO2的α-方石英结构产生影响 相似文献
999.
A number of aryl isocyanates were adducted to 1,2-diazabicyclo[2.2.2]octane and afforded 2-phenyl-carbamoyl-1,2-diazabicyclo[2.2.2]octanes. Some of the products displayed anticonvulsant activity. 相似文献
1000.
The use of reduced overlap population (ROP) analysis from EHMO calculations as a means to gauge the presence of metal–metal
bonds in triosmium clusters is examined. A number of triosmium clusters containing bridging ligands have been used as test
cases, including the bis-ethoxy bridged cluster Os3(μ-OEt)2(CO)10, 1b, and some of its group 15 derivatives Os3(μ-OEt)2(CO)9(EPh3), 2. These latter clusters are newly synthesized and have been characterized completely, including by single-crystal X-ray crystallographic
studies.
In honour of Professor Dieter Fenske on his 65th birthday. 相似文献