Statistical mechanics of warm and cold unfolding in proteins

We present a statistical mechanics treatment of the stability of globular proteins which takes explicitly into account the coupling between the protein and water degrees of freedom. This allows us to describe both the cold and the warm unfolding, thus qualitatively reproducing the known thermodynamics of proteins. Received: 19 March 1998 / Revised and Accepted: 25 May 1998     

三十烷醇在GA_3影响水稻幼苗生长和生理性状中的增效作用

微量三十烷醇（ＴＲＩＡ）与ＧＡ３配合使用，比ＧＡ３单独使用能明显地促进幼苗生长和增加幼苗干物质积累．同时还增强了ＧＡ３对幼叶中叶绿素含量、可溶性蛋白质含量、呼吸速率、细胞膜透性和过氧化物酶活性的影响．ＧＡ３＋ＴＲＩＡ与ＧＡ３处理相比，促进幼叶内源ＧＡ３水平提高，稳定保持内源ＺＴ于一定水平，ＴＲＩＡ在ＧＡ３低浓度时降低ＩＡＡ水平，在高浓度时则提高ＩＡＡ水平．作者认为ＴＲＩＡ可作为ＧＡ３处理时的增效剂．     

SPE电极上Pt单组分及Pt-Au双组分还原态CO_2阳极剥离电化学氧化行为研究

采用循环伏安法，对ＳＰＥＰｔ电极以及ＳＰＥＡｕ－Ｐｔ电极上还原态ＣＯ２的电化学氧化行为研究表明，此类电极的电化学特性与光滑Ｐｔ电极一致：ＣＯ２在氢原子吸附电位区０～２５０ｍＶ（ｖｓ．ＲＨＥ）处，可与电极上化学吸附的氢反应，生成还原态的ＣＯ２，通过线性扫描，还原态ＣＯ２即发生一不可逆电化学氧化过程（阳极剥离）．在ＳＰＥＰｔ系列及ＳＰＥＡｕ－Ｐｔ系列上ＣＯ２的电化学行为表明，当ＳＰＥＰｔ系列上Ｐｔ的载量为２．５ｍＬ的０．０１ｍｏｌ·Ｌ－１Ｈ２ＰｔＣｌ６的Ｐｔ时，对还原态ＣＯ２的电催化活性最好，当Ｐｔ的载量相同时，在ＳＰＥＡｕ－Ｐｔ上，催化剂对还原态ＣＯ２的电化学氧化行为比ＳＰＥＰｔ电极更强，这是由于预先沉积的Ａｕ对后沉积的Ｐｔ有调制作用．     

Rotational Motion of a Solute Molecule in a Highly Viscous Liquid Studied byC NMR: 1,3-Dibromoadamantane in Polymeric Chlorotrifluoroethene

The viscosity-dependent retarding effect of a polymeric solvent on the rotation of small solute molecules is investigated by¹³C NMR relaxation measurements. It is found that the relaxation data of 1,3-dibromoadamantane in highly viscous polymeric chlorotrifluoroethene can be explained neither by isotropic nor by realistic anisotropic tumbling in a single environment. The experimental data are rationalized in terms of fast exchange between at least two environments with correlation times differing by up to two orders of magnitude. The study shows that a uniform retardation of molecular tumbling by a polymeric solvent, desirable for shifting the NMR observation window in studies of intramolecular mobility, is not always feasible.     

Thickness of a silica-tethered poly(ethylene oxide) layer measured by spin labeling

EPR spectroscopy of labeled poly(ethylene oxide) (PEO) grafted on silica has been used to characterize the conformation and local dynamics of the chains. Grafted molecules of MW 2000 with grafting ratios of 0.045, 0.057, 0.126, and 0.42 molecules/nm² were in contact with benzene. The mobility of the label was compared with that observed for solution of PEO from very diluted to highly concentrated and even bulk PEO. Thus, the concentration inside the grafted layer could be evaluated and also the thickness, which evolves rather linearly with the grafting ratio. © 1995 John Wiley & Sons, Inc.     

Thermal decomposition of transition metal carboxylates

Dynamics of changes in microstresses during thermal decomposition of Cu(HCOO)₂ crystals and their effect on the thermal decomposition kinetics were studied by IR spectroscopy at 105 to 120 °C. The formation of solid intermediate HCOOCu was observed, and the dynamics of its accumulation was followed. Kinetic regularities of transformation of HCOO groups were compared with those for gas evolution.For Communication 1, see Ref. 1.Translated from Izvestiya va Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 350–354, February, 1996.     

Absorption spectra and the nature of complexes in the polyvinyl Alcohol-Nickel (II) chloride system

We have used electronic spectroscopy in the 160–1100 nm range to study the polyvinyl alcohol-nickel(II) chloride system. Based on the results obtained, we hypothesize formation of mixed-ligand complexes of the type [Ni(H₂O)_6-nCl_n]^2-n (n = 0, 1,..., 5) in the polyvinyl alcohol matrix. Transformation of the coordination sphere as the NiCl₂ concentration changes is apparent both in the region of the d-d transition bands (350–1100 nm) and in the region of the charge transfer bands (160–250 nm). We propose assigning the absorption bands separated by mathematical treatment to complexes of specific compositions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 136–138, January–February, 2006.     

Synthesis and characterization of functional gradient copolymers of allyl methacrylate and butyl acrylate

Functional spontaneous gradient copolymers of allyl methacrylate (A) and butyl acrylate (B) were synthesized via atom transfer radical polymerization. The copolymerization reactions were carried out in toluene solutions at 100 °C with methyl 2‐bromopropionate as the initiator and copper bromide with N,N,N′,N″,N″‐pentamethyldiethylenetriamine as the catalyst system. Different aspects of the statistical reaction copolymerizations, such as the kinetic behavior, crosslinking density, and gel fraction, were studied. The gel data were compared with Flory's gelation theory, and the sol fractions of the synthesized copolymers were characterized by size exclusion chromatography and nuclear magnetic resonance spectroscopy. The copolymer composition, demonstrating the gradient character of the copolymers, and the microstructure were analyzed. The experimental data agreed well with data calculated with the Mayo–Lewis terminal model and Bernoullian statistics, with monomer reactivity ratios of 2.58 ± 0.37 and 0.51 ± 0.05 for A and B, respectively, an isotacticity parameter for A of 0.24, and a coisotacticity parameter of 0.33. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5304–5315, 2006     

飞秒激光脉冲在三能级有机分子介质中传播时的频谱分析

通过采用预估校正的时域有限差分法求解麦克斯韦-布洛赫方程,我们研究了飞秒激光脉冲在三能级有机分子(4,4-二甲氨基二苯乙烯分子)介质中传播时脉冲的频谱演化情况.在单光子共振情况下,即入射脉冲频率等于1、2能级之间的共振频率,对大面积入射脉冲,由于强的二次激发的作用,电场频谱中出现了在ω32附近振荡的频率成分,ω32是2、3能级之间的共振频率,说明对大面积入射脉冲二能级模型已经失效,需要采用多能级模型来描述分子介质.在双光子共振情况下,即入射脉冲频率等于1、3能级之间的共振频率的一半,由于介质中放大的自发辐射和四波混频的作用,部分入射脉冲能量转化为高频和低频电场成分的能量,分子介质表现出了很强的光功率限幅特性.     

Unconventional antiferromagnetic correlations of the doped Haldane gapsystem Y 2 BaNi 1 - x Zn x O 5

We make a new proposal to describe the very low temperature susceptibility of the doped Haldane gap compound Y₂BaNi_1-xZn_xO₅. We propose a new mean field model relevant for this compound. The ground state of this mean field model is unconventional because antiferromagnetism coexists with random dimers. We present new susceptibility experiments at very low temperature. We obtain a Curie-Weiss susceptibility χ( T ) ∼ C /(Θ + T ) as expected for antiferromagnetic correlations but we do not obtain a direct signature of antiferromagnetic long range order. We explain how to obtain the “impurity” susceptibility ( T ) by subtracting the Haldane gap contribution to the total susceptibility. In the temperature range [1 K, 300 K] the experimental data are well fitted by T ( T ) = C _imp 1 + T _imp / T . In the temperature range [100 mK, 1 K] the experimental data are well fitted by T ( T ) = A ln( T / T _c ), where T _c increases with x. This fit suggests the existence of a finite Néel temperature which is however too small to be probed directly in our experiments. We also obtain a maximum in the temperature dependence of the ac-susceptibility ( T ) which suggests the existence of antiferromagnetic correlations at very low temperature. Received 17 July 2001