Thermodynamic analysis of enzyme catalysed reactions: new insights into the Michaelis–Menten equation

A simple thermodynamic analysis of the well-known Michaelis-Menten equation (MME) of enzyme catalysis is proposed that employs the chemical potential to follow the Gibbs free energy changes attending the formation of the enzyme-substrate complex and its turnover to the product. The main conclusion from the above analysis is that low values of the Michaelis constant K _M and high values of the turnover number k _cat are advantageous: this supports a simple algebraic analysis of the MME, although at variance with current thinking. Available data apparently support the above findings. It is argued that transition state stabilisation—rather than substrate distortion or proximity—is the key to enzyme catalysis.     

用IR/TPD法测定氢型丝光沸石上氨的脱附活化能

通过IR/TPD的改进方法, 测定了氨在氢型丝光沸石(HM)上的Bronsted酸位上的脱附活化能和相应的集居数。结果表明, 在HM上有三种不同强度的Bronsted酸位, 分别对应脱附活化能为63.6、49.8和35.4kJ/mol。     

Four-Dimensional Dilatonic Black Holes in Gauss-Bonnet Extended String Gravity

An internal singularity of a string four-dimensional black hole with second order curvature corrections is investigated. A restriction to a minimal size of a neutral black hole is obtained in the frame of the model considered. Vacuum polarization of the surrounding space-time caused by this minimal-size black hole is also discussed.     

离子从水向20wt%和40wt%乙醇-水混合溶剂中迁移的标准自由能的测定

本文论证了由于Cl^-是硬碱而I^-是软碱根据电解质迁移自由能△Gt^o(MCl)、△Gt^o(MBr)和△Gt^o(MI)作图外推计算单独离子标准迁移自由能△Gt^o(i)的方法是不正确的。提出了根据△Gt^o(MF)和△Gt^o(MCl)的作图外推法, 对于20wt%和40wt%乙醇-水混合溶剂, 所计算的△Gt^o(i)与碱金属氯化物的△Gt^o(MCl)作图歪推法所计算的值比较一致。用离子选择电极电位法系统地测定了△Gt^o(NaX)(X=F^-、Cl^-、Br^-、I^-)、△Gt^o(LiCl)和△Gt^o(HCl)。     

Effect of compatibilizers on the crystallization kinetics of cellulose-filled high density polyethylene

High density polyethylene (HDPE) is a ubiquitous material with versatile properties. It is produced and used in greater volume than any other thermoplastic. HDPE is often filled with a variety of materials for various applications. Glass fiber and wood flour are two common fillers for HDPE. This study investigated microcrystalline cellulose (MCC) as a filler in HDPE. The use of compatibilizers, or coupling agents, was investigated as a means of improving the dispersion of the cellulose filler in the HDPE matrix and the mechanical properties of the resulting composites. One compatibilizer was shown to improve the strength of the resulting composite. The stiffness was unaffected, as expected. Thermal properties were measured by means of differential scanning calorimetry. Analysis of the crystallization kinetics indicated that the Avrami coefficient was altered by the filler and was also modified by the presence of the compatibilizer. The presence of cellulose and/or compatibilizer increased the matrix degree of crystallinity. The two compatibilizers studied did not behave similarly and may have different mechanisms of compatibilization.     

Preparation of nano-sized silica with solar energy conversion and storage function by immobilization of norbornadiene moieties to hyperbranched poly(amido amine)-grafted nano-sized silica

The immobilization of norbornadiene (NBD) moieties onto nano-sized silica surface by the direct condensation of the surface terminal amino groups of hyperbranched poly(amido amine) (PAMAM)-grafted silica with 3-phenyl-2,5-norbornadiene-2-carboxylic acid is examined. It is found that the immobilization of NBD moieties onto the silica successfully proceeds in the presence of N,N′-dicyclohexylcarbodiimide (DCC) as a condensing agent. The immobilized NBD moieties onto the silica surface increases with increasing amount of amino groups of hyperbranched PAMAM-grafted silica, but the percentage of amino groups used for the immobilization of NBD moieties is decreased. The immobilized NBD moieties on the silica surface are readily isomerized to quadricyclane (QD) by photo-irradiation in n-hexane. Stored thermal energy by QD-immobilized silica is released as thermal energy by heating. The stored thermal energy of QD-immobilized silica increases with progress of the photo-irradiation time and became constant, about 30 J/g-silica, after 2 h.     

Synthesis of Novel Double Network Hydrogels via Atom Transfer Radical Polymerization

Novel double network (DN) hydrogels were prepared via atom transfer radical polymerization (ATRP) of the first network using two different initiators, and followed by ultraviolet (UV) photo-initiated polymerization for the second network. The first networks of DN hydrogels were prepared by using two different initiators; one is a one-side initiator, and the other is a double-side initiator. The mechanical properties of various DN gels, such as water content and compressive strength, were studied. The network structure of the DN hydrogels was also characterized by dynamic light scattering. Thus, we demonstrated that the ATRP method is useful to control the network structure of the first network for DN gels. Extensive inhomogeneous structure of the first network was obtained by ATRP method and increased both the swelling degree and softness of DN gels.     

Preparation of poly(vinyl alcohol)–silicone based hybrid membranes for the pervaporation separation of water–acetic acid mixtures

Hybrid membranes were prepared using poly(vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS) via hydrolysis followed by condensation. The obtained membranes were characterized by Fourier transform infrared spectroscopy, wide-angle x-ray diffraction and differential scanning calorimetry. A remarkable decrease in degree of swelling was observed with increasing TEOS content in membranes and is attributed to the formation of hydrogen bonding and covalent bonds in the membrane matrix. The pervaporation performance of these membranes for the separation of water–acetic acid mixtures was investigated in terms of feed concentration and the content of TEOS used as cross-linking agent. The membrane containing 1 : 2 mass ratio of PVA and TEOS gave the highest separation selectivity of 1116 with a flux of 3.33 × 10^?2kg/m²h at 30°C for 10 mass% of water in the feed. Except for membrane M-1, the observed values of water flux are close to the values of total flux in the investigated composition range, signifying that the developed membranes are highly water selective. From the temperature dependence of diffusion and permeation values, the Arrhenius apparent activation parameters have been estimated. The resulting activation energy values obtained, showing that water permeation is lower than that of acetic acid, suggest that the membranes have higher separation efficiency. The activation energy values calculated for total permeation and water permeation are close to each other for all the membranes except membrane M-1, signifying that coupled-transport is minimal because of the higher selective nature of membranes. The negative heat of sorption values (ΔH _s) for water in all the membranes suggests a Langmuir mode of sorption.     

On group orders of rational points of elliptic curves

We consider elliptic curves without complex multiplication defined over the rationals or with complex multiplication defined over the Hilbert class field of the endomorphism ring. We examine the distribution of almost prime group orders of these curves when reduced modulo a prime ideal.     

液体的粘度与内压

本文以液体粘性流动的Eyring模型为基础, 由热力学方法建立了一个液体粘度与内压间的关系式, 式中v是活化分子落入空穴的频率; α是一个与液体中形成空穴时所吸收的热与所需能量之比有关的参数, 两者都是液体的特性常数。在引入了某些近似式后, 由这个关系式能够推导出Eyring粘度公式, 与其不同的是推导中假定了空穴的大小等于一个分子所占液体的体积。本文还讨论了液体粘性流动的机理和活化能。