Hofmeister Effects of Group II Cations as Seen in the Unfolding of Ribonuclease A

This work studies the effects of alkaline-earth cation addition on the unfolding free energy of a model protein, pancreatic Ribonuclease A (RNase A) by differential scanning calorimetry analysis. RNase A was chosen because: a) it does not specifically bind Mg²⁺, Ca²⁺ and Sr²⁺ cations and b) maintains its structural integrity throughout a large pH range. We have measured and compared the effects of NaCl, MgCl₂, CaCl₂ and SrCl₂ addition on the melting point of RNase A. Our results show that even though the addition of group II cations to aqueous solvent reduces the solubility of nonpolar residues (and enhances the hydrophobic effect), their interactions with the amide moieties are strong enough to “salt-them-in” the solvent, thereby causing an overall protein stability reduction. We demonstrate that the amide-cation interactions are a major contributor to the observed “Hofmeister Effects” of group II cations in protein folding. Our analysis suggests that protein folding “Hofmeister Effects” of group II cations, are mostly the aggregate sum of how cation addition simultaneously salts-out hydrophobic moieties by increasing the cavitation free energy, while promoting the salting-in of amide moieties through contact pair formation.     

DSC study of cold and heat denaturation processes of β-lactoglobulin A with guanidine hydrochloride

The cold and heat denaturations of bovine β-lactoglobuhn A (β-lg A) has been studied in solutions of guanidine hydrochloride (GuHCl) by differential scanning calorimelry (DSC) The experimental results are presented and discussed.It is shown that the number of protons bound by the monomeric molecules of β-lg A was unchanged before and after its heat denaturation below pH 3,and that the activation energy of the heat denaturation was depressed owing to the presence of GuHCl.In the solutions with 2.50 and 3.06 mol/L of GuHCl,both the cold and heat denat-urations of β-lg A were observed.In comparison with the heat denaturation,the activation energy of cold denaturation was far lower and the number of GuHCl molecules bound by the unfolded polypeptide chains after cold denaturation increased a lot.The absolute value of the enthalpy of cold denaturation was larger than that of heat denaturation It was found by the analysis that the contribution to the total denaturational enthalpy of conformational change i     

Effect of Solution pH and Composition on Horse Liver Alcohol Dehydrogenase Thermostability

The influence of solution composition (pH, salts, and chelant) on the thermostability of horse liver alcohol dehydrogenase was studied by differential scanning calorimetry (DSC) in the pH range from7.51 to 9.50 and showing the enzyme catalytic activity. The experiments demonstrated that the effect of increasing pH on the heat denaturation temperature of the enzyme was slight, but the denaturation enthalpy was considerably increased, indicating the enzyme conformation alteration by changing pH and the presence of enthalpy-entropy compensation. The effect of ionic strength on thermostability was not noticeable, i.e., the electrostatic interactions were not a dominant factor for the thermostability. The anions Cl⁻ and SCN⁻ imposed diverse influence upon the enzyme thermostability, and SCN⁻can reduce the thermostability considerably. The chelant 1,10-phenanthroline, which can reversibly bind together with the zinc ions functioning the catalytic action in the enzyme molecules, increases the thermostability considerably. The hydration of the enzyme plays an important role to the thermostability. This revised version was published online in July 2006 with corrections to the Cover Date.     

牛血清IgG热化学变性和热变性的研究

使用差示扫描量热仪(DSC)和荧光光谱法研究了在pH 7.4时牛血清IgG (bIgG)热变性, 热化学变性和等温化学变性过程(变性剂为尿素和盐酸胍), 首次报道了bIgG在热化学变性和等温化学变性过程中的相关热力学参数. DSC和荧光光谱实验结果表明, bIgG的热变性和热化学变性过程都是较复杂的不可逆过程, 这个过程可被看作一个三态变构过程. DSC实验表明在热化学变性过程中bIgG的变性温度和焓变值会随着环境中的变性剂浓度的升高而降低. 使用荧光光谱法对bIgG在尿素或盐酸胍存在下的等温化学变性过程进行了研究, 结果显示bIgG的化学变性过程也是一个较复杂的非二态过程. 实验数据分析表明, 变性剂尿素和盐酸胍与bIgG之间主要是依靠氢键相互作用的, 而热变性过程中bIgG的凝集是由于bIgG热变性时结构改变后暴露出的疏水结构互相作用造成的. 实验结果还表明单纯的热变性只能导致bIgG的不完全变性, 而即使是在高浓度变性剂存在时的bIgG热化学变性, 尿素和盐酸胍分别导致的bIgG热化学变性的去折叠态也是不同的.     

Calorimetric Study of Thermal Denaturation of Superoxide Dismutase

The thermal denaturation of superoxide dismutase (SOD) from bovine erythrocytes was studied at various pH values of different buffers and at various concentrations of solutions of two neutral salts by differential scanning calorimetry. The experiments performed indicate that the PIPES is a buffer non-coordinating with the SOD, and that the binding of the anions studied influences more or less the thermal denaturation of SOD, but the effect on the oxidation form of SOD is more apparent. A new conformer of SOD with lower thermostability was discovered by the experiments performed in different buffers at certain pH values higher than the isoelectric point of SOD, or at higher concentrations of neutral salt solutions. The new conformer may be converted irreversibly into the usual conformer with high thermostability during heating. Based on the thermodynamic parameters obtained in distilled water and by thermodynamic analysis using the Ooi's model, it is revealed that the large enthalpy △Hdc contributed by     

二维相关红外光谱研究再生蚕丝蛋白膜的构象与温度之间的关系

通过二维相关红外光谱,研究了再生蚕丝蛋白膜的构象及其转变与温度之间的关系.实验结果表明,将样品从130℃升温到220℃、或在180℃的恒温过程中,丝素蛋白分子链的构象会发生变化,且不同构象对温度升高过程或180℃恒温过程响应的顺序是无规线团变化先于β-折叠、α-螺旋的形成.     

桑蚕丝素-RGD融合蛋白的固态结构及其细胞粘附性分析

利用基因工程方法把含有短肽RGD的氨基酸序列连接到桑蚕丝素蛋白的结晶序列GAGAGS上, 通过调节DNA的聚合度, 合成了具有[TGRGDSPA(GVPGV)₂GG(GAGAGS)₃AS]_n一级结构、不同分子量大小的桑蚕丝素-RGD融合蛋白, 并且通过在M9培养基中添加[3-¹³C]Ala的方法进行融合蛋白的稳定同位素标记. ¹³C CP/MAS NMR结果显示, 融合蛋白中的GAGAGS部分具有与天然桑蚕丝素结晶部分相同的分子结构, 即Silk I处理后为均一的分子结构, 而Silk II处理后为不均一的分子结构, 它包含了三种不同的结构成分. 另一方面, 通过对小鼠成纤维细胞BALB/3T3在不同蛋白材料载体上的粘附和增殖性能的测定结果显示, 融合蛋白对细胞的增殖性能与天然胶原蛋白相近, 但表现出了比胶原蛋白更好的细胞粘附性能. 该研究结果显示, 如果对该桑蚕丝素-RGD融合蛋白进行适当加工, 可能适合于组织工程支架材料的应用.     

Binding Energetics of Lysozyme to Copolymers of N‐Isopropylacrylamide with Sodium Sulfonated Styrene

Interpolyelectrolyte complexes of lysozyme with thermosensitive N‐isopropylacrylamide–sodium sulfonated styrene copolymers of different charge density were investigated by high‐sensitivity differential scanning calorimetry (HS‐DSC) at pH 4.6–7.2 and low ionic strength. A general property of the complexes for all copolymers investigated was a decrease in the conformational stability of the bound protein. This suggested the preferential binding of the unfolded protein to the polymer matrix. The isotherms of lysozyme binding to the copolymers were derived from the HS‐DSC data. They indicate that the binding is irreversible and charge stoichiometric.

     

DSC study of cold and heat denaturation processes of β-lactoglobulin A with guanidine hydrochloride

The cold and heat denaturations of bovine P-lactoglobulin A ((β-lg A) has been studied in solutions of guanidine hydrochloride (GuHCI) by differential scanning calorimetry (DSC). The experimental results are presented and discussed. It is shown that the number of protons bound by the monomeric molecules of β-lg A was unchanged before and after its heat denaturation below pH 3, and that the activation energy of the heat denaturation was depressed owing to the presence of GuHCI. In the solutions with 2.50 and 3.06 mol/L of GuHCI, both the cold and heat denaturations of P-lg A were observed. In comparison with the heat denaturation, the activation energy of cold denaturation was far lower and the number of GuHCl molecules bound by the unfolded polypeptide chains after culd denaturation increased a lot. The absolute value of the enthalpy of cold denaturation was larger than that of heat denaturation. It was found by the analysis that the contribution to the total denaturational enthalpy of conformational change itself of the monomeric molecules of β-lg A was the lowest among the globulins, according to the average of the number of heavy atoms. Project supported by the National Natural Science Foundation of China, and by the fund for excellent items under Director of the Institute of Chemistry.     

Molecular Functionalization of Cold-Plasma-Treated Bombyx mori Silk

Bombyx mori silk treated by cold SF₆ plasma was found to show higher hydrophobic property than the original silk. In order to clarify the chemical changes occurring in this treatment, the changes of functional groups of silk surface were investigated by attenuated total reflection (ATR) infrared spectroscopy, surface charge determination, and quantum mechanical calculation. Infrared spectra of original and plasma-treated silks do not show any change in the frequency regions of amide I, II, and III bands which locate at around 1627, 1513, and 1228 cm⁻¹, respectively. Slight changes were detected for the peak intensities of the bands locating in the frequency region of 1000–1050 cm⁻¹ after plasma treatment. This suggests the formation of CF groups in the Bombyx mori silk chain. The zeta potential experiment suggested that the electrostatic charges of the silk surface were not affected by the plasma treatment. In order to investigate the surface state of the plasma treated silk, the density functional calculation was performed for the model compounds with similar chemical structure as that of Bombyx mori silk. In this calculation, a fluorine radical was located at the various positions of the model compound, and the energetically most plausible structures were extracted to show the chemical reaction of CH + F⁻ → CF + H⁻.     

不同温度下桑蚕丝的力学性能

在严格控温条件下,利用动态机械热分析仪（DMTA）对大量未脱胶和脱胶桑蚕丝的单丝样品在不同温度下拉伸,同时用SEM,TEM以及拉曼光谱观察蚕丝的断面形貌和内部结构的变化,结果表明,在实验温度范围内,蚕丝初始模量和断裂强度皆随温度的升高而降低,拉伸过程会导致丝素蛋白形成更多的β-结构,同时,丝胶表现出较差的力学性能,其主要作用是以涂层的形式丝素蛋白纤维进行保护。     

Effect of Molecular Crowding on the Temperature–Pressure Stability Diagram of Ribonuclease A

FT‐IR spectroscopic and thermodynamic measurements were designed to explore the effect of a macromolecular crowder, dextran, on the temperature and pressure‐dependent phase diagram of the protein Ribonuclease A (RNase A), and we compare the experimental data with approximate theoretical predictions based on configuration entropy. Exploring the crowding effect on the pressure‐induced unfolding of proteins provides insight in protein stability and folding under cell‐like dense conditions, since pressure is a fundamental thermodynamic variable linked to molecular volume. Moreover, these studies are of relevance for understanding protein stability in deep‐sea organisms, which have to cope with pressures in the kbar range. We found that not only temperature‐induced equilibrium unfolding of RNase A, but also unfolding induced by pressure is markedly prohibited in the crowded dextran solutions, suggesting that crowded environments such as those found intracellularly, will also oppress high‐pressure protein unfolding. The FT‐IR spectroscopic measurements revealed a marked increase in unfolding pressure of 2 kbar in the presence of 30 wt % dextran. Whereas the structural changes upon thermal unfolding of the protein are not significantly influenced in the presence of the crowding agent, through stabilization by dextran the pressure‐unfolded state of the protein retains more ordered secondary structure elements, which seems to be a manifestation of the entropic destabilization of the unfolded state by crowding.     

An investigation of the crystalline structure of the quasi-two-dimensional metamagnet of composition [C6H22N4]4+[CuCl4]Cl2 (I), with [C6H22N4]4+=[1,4,7,10-tetraazadecane]·4HC1

[C₆H₂₂N₄]⁴⁺[CuCl₄ ^2–]Cl₂ (I) crystallizes in the monoclinic space groupP2₁/c with cell constantsa=15.573(2) Å,b=7.281(2),c=7.092(2),=91.496(14)°,V= 803.874 ų, andd(z= 2 mol/cell)=1.762 gm cm^–3. Data were collected in the range 4° 2 50°, for a total of 2662 reflections, of which 2201 were independent and hadI 3(I). These were used in the solution and refinement of the structure. TheF(hkl) _obs were corrected for absorption (=23.558 cm^–1) using Psi scan curves of eight suitable reflections, leading to relative transmission coefficient adjustments ranging from 0.9999 to 0.5722. Structural refinement converged atR(F)= 0.023 and R _W (F)=0.026. The coordination around the metal consists of polymeric, axially elongated, six-bonded, trigonal antiprismatic CuCl₆ species, not the hoped for, discrete, molecular CuCl₆ ^4– species implied by their chemical formulation. The crystalline lattice contains three different types of ions: the (C₆H₂₂N₄)⁴⁺ cation, a pair of Cl^– anions which are hydrogen bonded to the secondary ammonium (-NH₂ ⁺-) hydrogens of the cation, and a CuCl₄ ^2– anion. The latter is polymerized into two-dimensional sheets linked to each other by the agency of the cations, in which the two sets of terminal (-NH₃ ⁺) hydrogen bond to the axial Cl^– ligands. The Cu-Cl distances are 2.279, 2.315, and 2.847 Å. The distance between nearest coppers in adjacent sheets is 15.573(2)Å, the length of thea-axis. The magnetic behavior of the compound is that of a metamagnet, which requires a somewhat unusual set of conditions and is very rare in Cu²⁺ compounds. Comparison of the magnetic behavior of (I) with that of related compounds is made. The thermal behavior of (I) was studied using differential scanning calorimetric measurements in the range of 120 K to its melting(dec) point (463 K). It undergoes a phase transition from green (low temperature phase) to golden yellow (room temperature phase) at 168 K, another phase transition (golden yellow to red) at 340.6 K, and another at 383.2 K during which there is not evident color change. Finally, it melts with decomposition at ca. 463 K.     

Thermoanalytical characterization of polyphenylacetylene: III. Use of modulated differential scanning calorimetry (MDSC)

Four polyphenylacetylene samples, synthesized using different C₆H₅OH/Mo molar ratios, were investigated thermoanalytically by modulated temperature differential scanning calorimetry (MTDSC) in order to clarify a non-reversible exothermic event observed between 473 and 523 K on normal DSC. A stepwise, non-reversible change in heat capacity suggests the presence of internal reactions within the sample, that are followed by decomposition with loss of volatile products.     

Reversibility of the low‐temperature transitions of polytetrafluoroethylene as revealed by temperature‐modulated differential scanning calorimetry

Temperature‐modulated differential scanning calorimetry reveals distinct differences in the kinetics of the low‐temperature phase transitions of polytetrafluoroethylene. The triclinic to trigonal transition at 292 K is partially reversible as long it is not complete. As soon as the total sample is converted, supercooling is required to nucleate the reversal of the helical untwisting involved in the transition. The trigonal phase can be annealed in the early stages after transformation with a relaxtion time of about 5 minutes. The dependence of the reversing heat capacity on the modulation amplitude, after a metastable equilibrium has been reached, is explained by a non‐linear, time‐independent increase of the heat‐flow rate, perhaps caused by an increased true heat capacity. The order‐disorder‐transition at 303 K from the trigonal to a hexagonal condis phase is completely reversible and time‐independent. It extends to temperatures as low as the transition at 292 K or even lower. Qualitatively, the thermal history and crystallization conditions of polytetrafluoroethylene do not affect the transition kinetics, that is, melt‐crystallized film and as‐polymerized powders show similar transition behaviors, despite largely different crystallinities. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 750–756, 2001     

DNA纤维热变性过程的差示扫描量热分析

鲱精ＤＮＡ纤维的差示扫描量热（ＤＳＣ）谱中，除存在一个高温区的变性峰以外，还有３个低温区的吸热峰，类似于蛋白质ＤＳＣ分析中出现的“变性前峰”。经过２５３１５Ｋ（－２０℃）冻结处理的ＤＮＡ纤维，空间结构稳定性提高，变性前峰峰温增加４～８Ｋ。冻结与非冻结两类样品中，变性前峰的焓值分别为－１０２５３和－７７６５ｋＪ·ｍｏｌ－１。作者探讨了ＤＮＡ变性前峰的成因，并认为ＤＮＡ变性过程中的多元性可能与碱基序列特异性有关。     

Thermal Analysis And Powder X-Ray Diffraction Study of Terpin: Evidence of a eutectic ‘hydrate/anhydrous form’

When the DSC analysis of different samples of terpin hydrate is carried out, a non identified small endotherm is observed at about 100°C, just before the melting endotherm. This phenomenon is detected whatever the experimental conditions are.After some trials, this endotherm was identified as an eutectic formed with terpin hydrate and desolvated terpin (17/83).The importance of the experimental conditions is preponderant. In an open pan, the desolvation occurs and the melting endotherm of the anhydrous form can be observed at 105°C. In a closed pan, no desolvation is detected and the melting endotherm at 120°C is that of the terpin hydrate.The eutectic exhibits a good compression ability and a fast dissolution. Its stability is correct. Its use in therapeutic tablets can be envisaged.The eutectic structure could be, more generally, favourable to compression owing to the isotropic texture of this particular solid state.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermoanalytical investigation of blood

The aim of this study is to understand some properties and thermal behavior of blood, giving a possible alternative tool which differs from the traditional blood diagnostic methods, and to improve investigations in hematology and artificial bloods. Wistar rat blood samples (WRBS); SHR rat blood samples (SHRBS) and human blood samples (HBS) were analyzed. TG curves showed two decomposition stages for HBS at around 100 and 230°C (T _onset), while three mass degradation stages for WRBS (70, 110, 270°C) and SHRBS (70, 120, 270°C) could be observed. DSC peaks showed five endotherms for HBS at 65, 82, 194, 201 and 309°C and three endotherms for WRBS at 83, 184 and 313°C.