On the role of the reference system in perturbation theory: An augmented van der Waals theory of simple fluids

In this study, we show that the inclusion of a short-range part of the total attractive interaction into a reference system allows a natural extension of the traditional first-order perturbation theory of simple fluids to practically all thermodynamic states. This theory is applied to the thermodynamic functions and the liquid–vapor coexistence curve of the Lennard-Jones-like medium range Yukawa fluid and to the Sutherland fluid. Comparison with computer simulation data and the second-order Barker–Henderson perturbation theory is discussed.     

Low-temperature luminescence and phase structure of 5CB liquid crystal under different cooling regimes

Abstract

The effects of the 5CB liquid crystal (LC) cooling regimes on its luminescence spectra at the low temperature (T?=?4.2 K) have been found out and investigated. Experiments have been carried out at two cooling rates: 2 and 150?deg/min. Differential scanning calorimetry (DSC) data allow us to establish that the 5CB glass-like state (GLS) is formed during the rapid cooling of the sample. Peculiarities of the LC dimer formation under the different cooling conditions are discussed.     

Study of DyFe12−xMx compounds by57Fe and161Dy Mössbauer spectroscopy

DyFe_12?xM_x (M=Si,Ti,Cr) were studied with⁵⁷Fe and¹⁶¹Dy Mössbauer spectroscopy. The deduced coupling constants J_RFe of these compounds are about equal. It is found that Si is substituting one particular Fe-site, while Cr is substituting Fe randomly. In DyFe₁₀Si₂ two Fe-sites favour a c-axis anisotropy, while the third one favours the basal plane.     

A novel phosphoramidite for the synthesis of α-oxo aldehyde-modified oligodeoxynucleotides

The synthesis and use of a novel phosphoramidite derivatized by a bis[2-(tert-butyldisulfanyl)ethoxycarbonylamino]acetyl moiety for the synthesis of oligodeoxynucleotides modified at the 5′-end by an α-oxo aldehyde functionality is presented. Incorporation of the phosphoramidite reagent was performed after the automated solid-phase oligonucleotide synthesis. Simultaneous cleavage/deprotection of the oligodeoxynucleotides and unmasking of the α-oxo aldehyde group could be achieved using NaOH in aqueous methanol in the presence of dithiothreitol.     

Thermodynamics of dipolar hard sphere mixtures

The thermodynamic properties of mixtures of hard spheres with imbedded point dipoles are investigated by an extension of the perturbation theory used by Rushbrooke et al. for pure fluids. Equations are presented for the general multicomponent mixture in which all the hard spheres have the same diameter. Numerical calculations are presented of the phase behaviour and excess thermodynamic mixing functions for the special case of the binary mixture in which only one species is polar. A brief discussion is given of the relationship of this model to experimental results for real fluid mixtures and of possible extensions of this work.     

Fmoc solid-phase synthesis of peptide thioesters using an intramolecularn,S-acyl shift

[reaction: see text] We describe the Fmoc solid-phase synthesis of peptide thioesters based on the alkylation of the safety-catch sulfonamide linker with a protected 2-mercaptoethanol derivative. The thioester is generated on the solid phase after the peptide chain assembly as a consequence of an intramolecular N,S-acyl shift. Depending on the stability of the spacer separating the sulfonamide linker from the resin toward TFA, treatment of the peptidyl resin with TFA led to a soluble or supported deprotected thioester.     

Synthesis and chemical reactivity of semicarbazide-supported silicas

The synthesis of xerogels possessing a Fmoc-protected semicarbazide group covalently linked to a silica matrix is described. BET and fluorescence analyses showed the homogeneity of the xerogels. The xerogels were deprotected and further reacted with aldehydes to give novel materials.     

Determination of metals in composite diet samples by inductively coupled plasma-mass spectrometry

A study was conducted to evaluate the applicability of inductively coupled plasma-mass spectrometry (ICP-MS) techniques for determination of metals in composite diets. Aluminum, cadmium, chromium, copper, lead, manganese, nickel, vanadium, and zinc were determined by this method. Atmospheric pressure microwave digestion was used to solubilize analytes in homogenized composite diet samples, and this procedure was followed by ICP-MS analysis. Recovery of certified elements from standard reference materials ranged from 92 to 119% with relative standard deviations (RSDs) of 0.4-1.9%. Recovery of elements from fortified composite diet samples ranged from 75 to 129% with RSDs of 0-11.3%. Limits of detection ranged from 1 to 1700 ng/g; high values were due to significant amounts of certain elements naturally present in composite diets. Results of this study demonstrate that low-resolution quadrupole-based ICP-MS provides precise and accurate measurements of the elements tested in composite diet samples.