瓜环与哌嗪衍生物主客体配合物的研究(英)

本文采用核磁共振技术研究瓜环与哌嗪衍生物主客体配合物的结构特征。¹H核磁共振谱证实八元瓜环能与一些哌嗪衍生物形成稳定的双客体主客体配合物,六元瓜环与一些哌嗪衍生物形成稳定的1∶1主客体配合物。而五、七元瓜环和哌嗪衍生物则未表现出明显地相互作用。形成的自组装主客体配合物得到质谱的进一步证实。     

Cavity search: An algorithm for the isolation and display of cavity-like binding regions

Summary A set of algorithms designed to enhance the display of protein binding cavities is presented. These algorithms, collectively entitled CAVITY SEARCH, allow the user to isolate and fully define the extent of a particular cavity. Solid modeling techniques are employed to produce a detailed cast of the active site region, which can then be color-coded to show electrostatic and steric interactions between the protein cavity and a bound ligand.     

Measurement of Diffusion in Zeolites—A Never Ending Challenge?

A review is given on the main problems associated with the determination and interpretation of molecular diffusion in zeolites. It is shown that the diffusivities may most decisively depend on the relevant space and time scales of observation, as well as on the physical state under which the measurements are carried out. Special emphasis is given to the microscopic techniques and their most recent evidence on the existence of transport resistances distributed over the intracrystalline space.     

Molecular and nanoscale materials and devices in electronics

Over the past several years, there have been many significant advances toward the realization of electronic computers integrated on the molecular scale and a much greater understanding of the types of materials that will be useful in molecular devices and their properties. It was demonstrated that individual molecules could serve as incomprehensibly tiny switch and wire one million times smaller than those on conventional silicon microchip. This has resulted very recently in the assembly and demonstration of tiny computer logic circuits built from such molecular scale devices. The purpose of this review is to provide a general introduction to molecular and nanoscale materials and devices in electronics.     

Characteristics and production of thermostable α-amylase

Thermostable α-amylases have application in a variety of industrial processes and enzymes from a substantial number of thermophilic bacteria and fungi have been screened and characterized to varying degrees. The characteristics of these enzymes are summarized in this review. The genetics of α-amylase production inBacillus subtilis is reviewed and classical and recombinant DNA approaches to increasing α-amylase production are discussed.     

New approaches in radical carbonylation chemistry: fluorous applications and designed tandem processes by species-hybridization with anions and transition metal species

New approaches in radical carbonylation chemistry are described. We have successfully integrated tin mediated radical carbonylation chemistry into modern fluorous applications and separation techniques. We revealed that radical carbonylation reactions can be performed using fluorous tin mediators, such as fluorous tin hydride and fluorous allyltin reagents. Fine tuning of the reaction conditions resulted in a good efficiency equivalent to conventional tin mediators. The tedious procedure of removing organotin byproducts can be circumvented through the use of fluorous/organic liquid-liquid extraction or fluorous liquid-solid phase extraction with fluorous reverse phase silica (FRPS). Also described are newly developed tandem carbonylation reactions that are based on species hybridization approaches. Using a radical/anionic hybrid system based on zinc-induced one-electron reduction, we achieved a three-component coupling reaction consisting of 4-alkenyl iodides, carbon monoxide, and electron-deficient alkenes. We observed two types of annulations processes, namely [4 + 1](radical)/[3 + 2](anionic) and [5 + 1](radical)/[3 + 2](anionic), which lead to the production of bicyclo[3.3.0]octanols and bicyclo[3.2.1]octanols, respectively. We found a radical/palladium hybrid system to be useful in the construction of new cyclic systems that incorporate two or three molecules of carbon monoxide.     

The use of TG-FTIR technique for the assessment of hydrogen bromide emissions in the combustion of BFRs

The TG-FTIR technique was used in the present study to investigate the thermal degradation behaviour of materials containing brominated flame retardants under fire conditions. Time-temperature profiles and oxygen concentrations typical of selected fire scenarios were reproduced in the thermogravimetric analyzer, while the characterization of the gaseous products generated was performed by the simultaneous FTIR analysis. FTIR analysis combined with the use of specific calibration procedures allowed the quantitative estimation of the gaseous products evolved as a function of experimental conditions. The results obtained allowed the straightforward assessment and the comparison of the quantities of hydrogen bromide formed in the oxidation and thermal degradation of pure brominated flame retardants and of flame retarded materials of industrial interest. Hydrogen bromide yields resulted dependent on the experimental conditions used, such as oxygen concentration and heating rate. Although TG-FTIR experiments only provide a representation of the actual heterogeneous combustion products in real fire conditions, the coupled TG-FTIR technique proved to be a straightforward experimental methodology allowing one to obtain reference data on the nature and quantities of the macropollutants generated in a fire. This revised version was published online in July 2006 with corrections to the Cover Date.     

Trends in Preconcentration Procedures for Metal Determination Using Atomic Spectrometry Techniques

 Methods for metal preconcentration are often described in the literature. However, purposes are often different, depending on whether the methods are applied in environmental, clinical or technological fields. The respective method needs to be efficient, give high sensitivity, and ideally also is selective which is useful when used in combination with atomic spectroscopy. This review presents the actual tendencies in metal preconcentration using techniques such as Flame Atomic Absorption Spectrometry (FAAS), Electrothermal Atomic Absorption Spectrometry (ETAAS), Hydride Generation Atomic Absorption Spectrometry (HGAAS), Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Procedures based on related to electrochemical, coprecipitation/precipitation, liquid–liquid and solid–liquid extraction and atom trapping mechanisms are presented. Correspondence: Department of Analytical Chemistry, Universidade Estadual de Campinas – UNICAMP, P.O. Box 6154, 13083-970 Campinas, Brazil. e-mail: zezzi@iqm.unicamp.br Received December 20, 2001; accepted October 11, 2002     

Chemometric analysis of groundwater quality data of alluvial aquifer of Gangetic plain, North India

Water quality data set from the alluvial region in the Gangetic plain in northern India, which is known for high fluoride levels in soil and groundwater, has been analysed by chemometric techniques, such as principal component analysis (PCA), discriminant analysis (DA) and partial least squares (PLS) in order to investigate the compositional differences between surface and groundwater samples, spatial variations in groundwater composition and influence of natural and anthropogenic factors. Trilinear plots of major ions showed that the groundwater in this region is mainly of Na/K-bicarbonate type. PCA performed on complete data matrix yielded six significant PCs explaining 65% of the data variance. Although, PCA rendered considerable data reduction, it could not clearly group and distinguish the sample types (dug well, hand-pump and surface water). However, a visible differentiation between the water samples pertaining to two watersheds (Khar and Loni) was obtained. DA identified six discriminating variables between surface and groundwater and also between different types of samples (dug well, hand pump and surface water). Distinct grouping of the surface and groundwater samples was achieved using the PLS technique. It further showed that the groundwater samples are dominated by variables having origin both in natural and anthropogenic sources in the region, whereas, variables of industrial origin dominate the surface water samples. It also suggested that the groundwater sources are contaminated with various industrial contaminants in the region.