Evaluation of thermodynamic properties of irreversible protein thermal unfolding measured by DSC

Summary We assessed the applicability of the extrapolation procedure at infinite scanning rate to differential scanning calorimetry (DSC) data related to irreversible protein unfolding. To this aim, an array of DSC curves have been simulated on the basis of the Lumry-Eyring model N↔U→F. The results obtained confirmed that when the apparent equilibrium constant K_{app (T=T1/2)} is lower than 3, the application of the extrapolation procedure provides accurate thermodynamic parameters. Although this procedure applies only to monomeric proteins for which the Lumry-Eyring model is a reasonable approximation, it will hopefully contribute to increase the potential of DSC in obtaining reliable thermodynamic information regarding the folding/unfolding equilibrium.     

Kinetics and mechanisms in carbocationic polymerization: The quest for true rate constants

This article is a critical analysis of kinetic dataavailable on carbocationic polymerizations. A survey of published propagation rate constant (k_p) data revealed several orders of magnitude differences. In this article, an explanation of this apparent discrepancy is offered with a case study involving the carbocationic polymerization of 2,4,6‐trimethylstyrene (TMS). With the polymerization mechanism originally proposed for this system, k_p = 1.35 × 10⁴ L mol^?1 s^?1 was extracted from experimental data with the Predici polyreaction package. The alternative mechanism yielded k_p = 1.01 × 10⁷ L mol^?1 s^?1, close to that predicted by Mayr's Linear Free Energy Relationship (LFER). We propose that true rate constants can only be obtained from direct competition experiments or from kinetic interpretation based on independently proven mechanisms. The second part of this review discusses critical analysis of the temperature and concentration dependence of various living IB systems. Comparison of the temperature dependence in systems initiated with 2‐ chloro‐2,4, 4‐ trimethylpentane (TMPCl)/TiCl₄ from various laboratories yielded of ΔH ～?25 and ?34.5 kJ/mol for high and low TMPCl/TiCl₄ ratios, respectively. Aromatic (cumyl‐type) initiators show ΔH ～ ?40 kJ/mol, whereas H₂O/TiCl₄ in the presence of the strong electron‐ pair donor dimethylacetamide gave ΔH = ?12 kJ/mol. The significant differences indicate different underlying mechanisms with complex elementary reactions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5394–5413, 2005     

C60-地塞米松的激光激发

利用激光光解装置检测了C60-地塞米松(C60-DE)的苯溶液在355 nm激光照射下产生的激发三重态, 3C60-DE*出现四个吸收峰, 分别位于700、440、350 和310 nm. 在330 nm处观察到了它的漂白吸收最大值, 这与其基态吸收最大值相对应. 3C60-DE*能够将能量转移给O2分子而淬灭. 与3C60*相比, 3C60-DE*的三重态鄄三重态(T-T)淬灭速率常数减小(3C60*为(5.03±1.31)×109 L·mol-1·s-1, 3C60-DE*为(3.53±0.87)×109 L·mol-1·s-1), 而寿命增加了(3C60*为(12.0±2.6) μs, 3C60-DE*为(18.0±3.3) μs), 这可能是C60分子上连接了地塞米松分子后减小了C60球之间碰撞的几率所致.     

聚氯乙烯结构缺陷和热不稳定性之间关系的研究 2.各种结构缺陷含量和热脱氯化氢速率之间的关系

本工作采用溴加成法、酚解法、FTIR法及臭氧裂解法分别测定了五种不饱和蒸气压下聚合的PVC样品(u-PVC)和五种商品PVC样品(s-PVC)的总双键、总不稳定氯、孤立双键和内部双键的含量.通过研究结构缺陷和PVC的平均分子量及脱HCl速率的相互关系,揭示了不饱和总双键值,总不稳定氯和孤立双键含量彼此的相关性是建立在它们分别与1/M_n的相关性基础之上,从而得出了这三种定量值测得的主要都是端基烯丙基氯结构.根据三者对脱HCl速率的良好线性相关性,首次提出了端基烯丙基氯结构在HCl催化作用下异构化成内部烯丙基氯从而成为脱HCl速率主要原因的机理.     

表面起伏光栅形成速率的影响规律 Ⅰ.偶氮生色团种类和官能度的影响

设计并合成了含有不同生色团以及不同官能度的环氧树脂基偶氮高分子 ,系统研究了偶氮生色团的种类和官能度对光栅形成速率的影响规律 .实验结果表明 ,偶氮苯对位是羧基的聚合物的光栅形成速率明显快于偶氮苯对位是硝基的聚合物 ,光栅形成速率随偶氮生色团官能度的增加而加快 .这两类聚合物都可以形成规整的可擦式表面起伏光栅     

Test of variational transition state theory with multidimensional tunneling contributions against experimental kinetic isotope effects for the CHnD4−n + OH→P (n=0, 4) reactions

 Variational transition state theory including tunneling corrections (as implemented in Polyrate 8.7) and using multilevel energy calculations at the MCCM-CCSD(T)-1sc level for the CH₄ + OH reaction and at the MCCM-CCSD(T)-2m level for the CD₄ + OH process, reproduces very well the experimental rate constants. However, no single methodology was found that reproduces equally well the experimental rate constants for both title reactions. Received: 24 March 2002 / Accepted: 11 April 2002 / Published online: 4 July 2002     

A novel zirconocene/ultradispersed diamond black powder supported catalytic system for ethylene polymerization

A novel carrier of ultradispersed diamond black powder (UDDBP) was used to support metallocene catalyst. Al₂O₃ was also used as carrier in order to compare with UDDBP. Supported catalysts for ethylene polymerization were synthesized by two different reaction methods. One way was direct immobilization of the metallocene on the support, the other was adsorption of MAO onto the support followed by addition of the metallocene. Four supported catalysts Cp₂ZrCl₂/UDDBP, Cp₂ZrCl₂/Al₂O₃, Cp₂ZrCl₂/MAO/UDDBP and Cp₂ZrCl₂/Al₂O₃/MAO were obtained. The content of the zirconium in the supported catalyst was determined by UV spectroscopy. The activity of the ethylene polymerization catalyzed by supported catalyst was investigated. The influence of Al/Zr molar ratio and polymerization temperature on the activity was discussed. The polymerization rate was also observed.     

Spin-adducts of radicals ·P(O)(OPri)2 and ·CMe3 with pyrrolidino[60]fullerenes studied by ESR spectroscopy

The addition of the ^·Bu^t (R¹) and ^·P(O)(OPrⁱ)₂ (R²) radicals to pyrrolidino[60]fullerenes C₆₀CH₂NMeCHX (X = C₆H₄N(CH₂CH₂Cl)₂, 2,6-(Bu^t)₂C₆H₂OH, PhC₆H₄, and indol-3-yl) was studied by ESR spectroscopy. The rate constants of R¹ radical addition to these compounds and dimerization of spin-adducts of the R¹ radicals with pyrrolidino[60]fullerenes were determined. Pyrrolidino[60]fullerenes manifest considerably higher reactivity toward the R¹ radicals than fullerene C₆₀ and methanofullerenes C₆₀CX¹X² (X¹ = X² = CO₂Et; X¹ = CO₂Me, X² = OP(OMe)₂, X¹ = X² = OP(OEt)₂).     

Theoretical study of thermal decomposition of azomethane

Summary.  Thermal one- and two-bond dissociation processes of cis- and trans-azomethane were studied by ab initio computation with DZP and TZ2P basis sets, using the d(N–C) bond lengths as the reaction coordinates. The geometries were optimized at the MP2 level, and the dissociation energies obtained exploiting a single-point, fourth-order M?ller–Plesset calculations [MP4SDTQ/TZ2P]. At this level of theory including zero-point energies, the trans-isomer is by 9.3 kcal/mol more stable than the cis-isomer. The results show that the energetically more favourable one-bond cleavage proceeds without transition state with the predicted bond dissociation energy D ₀ of 47.8 kcal/mol for trans-azomethane and 38.5 kcal/mol for cis-azomethane. With calculated barrier heights the unimolecular dissociation rate constants have been determined by means of the RRKM theory. The second-order saddle points localized for synchronous decomposition pathways lie 13 (trans)-23(cis) kcal/mol above the one-bond dissociation energies [MP2/DZP]. Received May 28, 1996/Final version received November 1, 1996 / Accepted November 1, 1996     

Performance validation of step-isothermal calorimeters

Isothermal calorimetry is becoming indispensable as a tool for the study of a wide variety of systems. As with all scientific instruments it is essential that robust calibration routines be developed in order to validate the data obtained. Chemical test reactions offer many advantages over (the traditionally used) joule effect heating methods, not least because they have the potential to validate instrument performance (i.e. they can be used to assess all aspects of calorimeter operation). In this work the results of a validation exercise, conducted by Thermal Hazard Technology as part of an installation routine, using the base catalysed hydrolysis of methyl paraben are discussed. In the case described, a systematic misreporting of the reported temperature of a calorimeter was identified, caused by an upgrade to the calorimeter's firmware, a discrepancy which may not have been noted using traditional electrical calibration methods and one which highlights the importance of both manufacturers and end-users adopting chemical test reactions into their test and validation routines.