Relationship between the density of supercritical CO<Subscript>2</Subscript> + ethanol binary system and its critical properties

The dependent relation between temperature and pressure of supercritical CO₂+ ethanol binary system under the pressure range from 5 to 10 MPa with the variety of densities and mole fractions of ethanol that range from 0 to 2% was investigated by the static visual method in a constant volume. The critical temperature and pressure were experimentally determined simultaneously. The PTρ figures at different ethanol contents were described based on the determined pressure and temperature data, from which pressure of supercritical CO₂ + ethanol binary system was found to increase linearly with the increasing temperature. P-T lines show certain convergent feature in a specific concentration of ethanol and the convergent points shift to the region of higher temperature and pressure with the increasing ethanol compositions. Furthermore, the effect of density and ethanol concentration on the critical point of CO₂ + ethanol binary system was discussed in details. Critical points increase linearly with the increasing mole fraction of ethanol in specific density and critical points change at different densities. The critical compressibility factors Z_c of supercritical CO₂ + ethanol binary systems at different compositions of ethanol were calculated and Z _c -ρ figure was obtained accordingly. It was found from Z _c -ρ figure that critical compressibility factors of supercritical CO₂ unitary or binary systems decline linearly with the increasing density, by which the critical point can be predicted precisely.     

Factor Xa: Simulation studies with an eye to inhibitor design

Factor Xa is a serine protease which activates thrombin and plays a key regulatory role in the blood-coagulation cascade. Factor Xa is at the crossroads of the extrinsic and intrinsic pathways of coagulation and, hence, has become an important target for the design of anti-thrombotics (inhibitors). It is not known to be involved in other processes than hemostasis and its binding site is different to that of other serine proteases, thus facilitating selective inhibition. The design of high-affinity selective inhibitors of factor Xa requires knowledge of the structural and dynamical characteristics of its active site. The three-dimensional structure of factor Xa was resolved by X-ray crystallography and refined at 2.2 Å resolution by Padmanabhan and collaborators. In this article we present results from molecular dynamics simulations of the catalytic domain of factor Xa in aqueous solution. The simulations were performed to characterise the mobility and flexibility of the residues delimiting the unoccupied binding site of the enzyme, and to determine hydrogen bonding propensities (with protein and with solvent atoms) of those residues in the active site that could interact with a substrate or a potential inhibitor. The simulation data is aimed at facilitating the design of high-affinity selective inhibitors of factor Xa.     

Investigation of the Interactions of β‐Peptides with DNA Duplexes by Circular Dichroism Spectroscopy

The interaction of β‐peptides with the DNA duplexes of dA₂₀dT₂₀ and a GCN4‐binding CRE sequence was examined. To gauge the factors that govern these interactions, two β‐pentadecapeptides, 1 and 2 , a β‐dodecapeptide, 3 , three β‐decapeptides, 4 – 6 , three β‐heptapeptides, 7 – 9 , and β‐octaarginine 10 were designed and synthesized. The β‐peptides were conceived to adopt a β‐peptide 3₁₄ helix, in which the side chains at position i and i + 3 are aligned vertically along one side of the helix. The side chains of Lys, Asn, and Arg were positioned such that potential H‐bonding sites were created for a helical conformation to interact with the base pairs of DNA. CD Analysis showed that β‐peptides 1, 2 , and 10 interacted with dA₂₀dT₂₀. In addition, β‐peptides 1 and 2 showed significant interaction with a DNA‐duplex 20mer containing the ATF/CREB recognition sequence for the regulatory protein GCN4. It is impossible, at this stage of the investigation, to make a safe proposal about the actual nature of the interaction of the structures(s) of the complexes, the formation of which is suggested by the CD spectra reported herein.     

Binary mixtures of cyclohexanone, 2-butanone, 1,4-dioxane and 1,2-dimethoxyethane

Densities and sound velocities of binary mixtures of cyclohexanone, 2-butanone, 1,4-dioxane and 1,2-dimethoxyethane were measured at 298.15 K and also the densities at 303.15 K. Excess volumes were determined from densities. Isentropic compressibilities were determined from densities and sound velocities, and excess thermal expansion factors were determined from excess volumes of two temperatures. Excess isothermal compressibilities and excess isochoric heat capacities were then estimated using excess isobaric heat capacities previously reported. Excess volumes and excess isentropic and isothermal compressibilities were negative except for cyclohexanone+1,4-dioxane system. This revised version was published online in August 2006 with corrections to the Cover Date.     

The use of the isotropic orientation factor in fluorescence resonance energy transfer (FRET) studies of the actin filament

A Dale-Eisinger style analysis (R. E. Daleet al., Biophys. J. 26, 161, 1979) is used to produce three-dimensional plots that display the limits on the average orientation factor k ² that is required to calculate molecular distances in F-actin from fluorescence resonance energy transfer measurements. Maxima and minima plots are generated for the transfer of energy from a donor to a single acceptor and for transfer to multiple acceptors that are related by F-actin helical symmetry. The analysis is performed in terms of dipole cone half-angles rather than depolarization factors, in order to facilitate the modeling of the multiple acceptor problem. Calculations are carried out under the restrictive condition of a single electric dipole moment per fluorophore. In addition, both surface and volume averaging of the donor and acceptor dipoles are considered. Comparisons between the plots show that for the multiple acceptor cases with F-actin symmetry, there is a great reduction in the range for maxima and minima limits on k ². The calculations also suggest guidelines for the choice of fluorescence label that will result in an average orientation factor occurring within acceptable limits, i.e., inside the limits for which k ²=2/3 may be employed. Thus, without having detailed knowledge of the mean donor or acceptor dipole relative orientations, the use of k ²=2/3 in radial coordinate studies of F-actin is more than reasonable and is fairly assured of being correct.     

XPS定量分析及其在CdTe（Ⅲ）面识别化学物种中的应用

我们用谱仪能量传输函数修正的相对原子灵敏度因子获得了ＸＰＳ定量数据。通过将定量结果与结合能的化学位移相结合的方法，分析了ＣｄＴｅ表面的两个氧化过程，结果表明，机械抛光样品表面的构成是：６６％ＣｄＴｅ，２８．９％的Ｃｄ（ＯＨ）２和５．１％ＴｅＯｘ（Ｘ＞２），而经化学抛光的表面构成是∶８４．４％的ＴｄＴｅＯ４和１５．６％ＴｅＯｘ（Ｘ＞１）。     

Clathrate and inclusion compounds. Part 8 [1]. An investigation of the usefulness of the spectral substraction technique in analysing the infrared spectra of clathrates

An investigation has been carried out into the usefulness of the spectral subtraction technique in analyzing the infrared spectra of the clathrates of quinol and of Dianin's compound. Due to the flexibility of the quinol host lattice, it is not advisable to use guest-free -quinol as the reference if the host lattice in the clathrate is considerably distorted, as it is in the CH₃CN clathrate. In this case it is advisable to use another clathrate as the reference provided that the spectrum of the new reference does not contain guest bands in the region of interest. The Dianin's compound host lattice is less flexible than that of quinol, and guest-free Dianin's compound can be used as the reference irrespective of the size of the guest molecule. With both clathrates the spectral subtraction technique has revealed guest molecule bands which were previously obscured by host lattice bands.Dedicated to Professor H. M. Powell.     

DFT and NMR parameterized conformation of valeranone

A Monte Carlo random search using molecular mechanics, followed by geometry optimization of each minimum energy structure employing density functional theory (DFT) calculations at the B3LYP/6-31G* level and a Boltzmann analysis of the total energies, generated accurate molecular models which describe the conformational behavior of the antispasmodic bicyclic sesquiterpene valeranone (1). The theoretical H-C-C-H dihedral angles gave the corresponding 1H, 1H vicinal coupling constants using a generalized Karplus-type equation. In turn, the 3J(H,H) values were used as initial input data for the spectral simulation of 1, which after iteration provided an excellent correlation with the experimental 1H NMR spectrum. The calculated 3J(H,H) values closely predicted the experimental values, excepting the coupling constant between the axial hydrogen alpha to the carbonyl group and the equatorial hydrogen beta to the carbonyl group (J(2beta, 3beta)). The difference is explained in terms of the electron density distribution found in the highest occupied molecular orbital (HOMO) of 1. The simulated spectrum, together with 2D NMR experiments, allowed the total assignment of the 1H and 13C NMR spectra of 1.     

Calorimetric study of cesium hexafluoroarsenate CsAsF<Subscript>6</Subscript> at elevated temperatures

Summary Cobalt(II), nickel(II) and copper(II) complexes of some aroylhydrazone Schiff’s bases derived from isoniazide (hydrazide of isonicotinic acid) with p-hydroxybenzaldehyde; 2,4-dihydroxybenzaldehyde or 2-hydroxy-1-naphthaldehyde are prepared and characterized. The study reveals that the ligands coordinate in the keto form. That transformed to the enol through the loss of HCl upon heating the solid complexes. The copper(II) complexes are thermochromic in the solid-state while the cobalt(II) complex, 3 of 2,4-dihydroxybenzaldehyde moiety is solvatochromic in hot DMF. The chromisms obtained were discussed in terms of change in the ligand field strength and/or coordination geometry.     

Synthesis,characterization, and application of griseofulvin surface molecularly imprinted polymers as the selective solid phase extraction sorbent in rat plasma samples

In present study, an investigation was carried out to develop and validate an analytical method for the selective extraction and determination of griseofulvin (GSF) from plasma samples. For this purpose, a rational approach was made to synthesize and characterize the surface molecularly imprinted polymers (SMIPs). The SMIPs were utilized as solid phase extraction (SPE) sorbents. The SMIPs were prepared by using GSF as template molecule on the surface of modified silica particles through a non-covalent technique. The particles demonstrated high adsorption capacity (119.1 µg/mL), fast adsorption equilibrium time (30 min) and good recognition selectivity for the template drug. The scanning electron microscopy and infrared spectroscopy were used to explain the structural and morphological characteristics of the SMIPs and surface non-imprinted polymers. The SPE method was combined with HPLC for plasma analysis. The method validation results demonstrated that the established method possessed good linearity for GSF ranging from 0.1 to 50 µg/mL (R² = 0.997). The limit of detection for this method was 0.02 µg/mL for rat plasma samples. The recoveries of GSF from spiked plasma samples were (90.7–97.7%) and relative standard deviations were (0.9–4.5%). Moreover, the SMIPs as selective SPE sorbent can be reused more than 8 times which is a clear advantage over commercial SPE sorbents. Finally, the usefulness of the proposed strategy was assessed by extraction and detection of GSF in real rat plasma samples.