Determination of phenol and catechol concentrations with oxygen probes coated with immobilized enzymes or immobilized cells

The enzyme phenol 2-hydroxylase was immobilized on Sepharose and used in conjunction with an O₂ electrode for quantitating phenol. Similarly, catechol 1,2-oxygenase was used for quantitating catechol. A third probe was prepared by immobilization ofTrichosporon cutaneum cells rather than purified phenol 2-hydroxylase for phenol quantitation. The whole cell system gave results comparable to the immobilized enzyme system.     

Theory of reflectance measurements in quantitative evaluation in TLC and HPTLC. 1. Multilayer model of reflectance and transmittance

In the approach described in this paper, the layer of adsorbent is divided into n sublayers. The radiation density in each sublayer is given by the sum of the transmittance and the reflectance of the adjacent sublayers. Absorption of light by the layer or the substance will diminish this radiation density. Depending upon the factors of reflectance and transmittance some light will pass to the adjacent sublayers. Two polynomials are derived from this readily understood formulation to calculate the reflectance or the transmittance of a layer of finite thickness. The algorithms given describe the reflectance and transmittance encountered in practical measurements with large amounts of substance per spot, as well as with small amounts. There are no restrictions with respect to nonideal scattering or reflection by the adsorbent layer support.     

An average fock operator technique of approximate open-shell LCAO-MO-SCF calculation

The exchange part of the usual Hartree-Fock potential in the unrestricted Hartree-Fock (UHF) theory is suitablyaveraged to construct an, average one-electron model Hamiltonian which generates a set of spin-restricted one-electron orbitals in a self-consistent manner. These orbitals are then used to calculate the electronic energy of the open-shell system by using the proper functional form for the energy which handles the exchange terms correctly. The eigenvalues ofF ^av can be used for calculating either the spin-polarised or spin-averaged ionisation potentials of different orbitals at theKoopmans’ theorem level of approximation. Comparison ofE ^ac with the UHF-energy shows thatE _UHF<E ^ac in each case revealing some kind of an upper bound nature ofE ^ac. An approximate variational argument is given. Relationship of our model with the hyper-Hartree-Fock theory of slater is explored and the general problem of eliminating ‘self-interaction’ terms in average Fock-operator based theories is discussed.     

Reduced parabolic model for radical addition reactions

The transition state of addition of free radicals and atoms to multiple bonds is considered as a result of intersecting of two parabolic potential curves. One of them characterizes the stretching vibration of the attacked multiple bond, and another curve characterizes the stretching vibration of the bond formed in the transition state. The force constant of the latter is calculated by an empirical equation that correlates the force constant with the bond dissociation energy. In the framework of this model, the thermally neutral activation energy (E _e0) and the elongation of the attacked and formed bonds (r _e) in the transition state were calculated from the experimental data (activation energy (E _e) and enthalpy of reaction (H _e)) for the addition of an H atom and methyl, alkoxyl, aminyl, triethylsilyl, and peroxyl radicals to the C=C bond and the addition of H and CH₃ to the C=O and CC bonds. Analysis of the data obtained showed that E _e0 depends linearly on the |H _e| + E_e sum, i.e., E_e0/kJ mol^–1 = 14.2 + 0.61 · (E_e – H _e), and the bond elongation in the transition state for addition of the most part of radicals to ethylene and acetylene vary within (0.65–0.87)·10_–10 m. The factors affecting the activation energy of the radical addition reactions are discussed.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1542–August, 2004.     

XPS study of interactions between linear carbon chains and colloidal Au nanoparticles

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Influence of particle diameter distribution on protein recovery in the expanded bed adsorption process

The General Rate model has been developed and solved to describe protein adsorption in an expanded bed. The model takes into account axial and local variation of particle size distribution (PSD), external and intra-particle mass transfer resistances, and dispersion in liquid phase. The influence of PSD on breakthrough profiles has been analysed. The simulation results show that for a significantly high expanded bed the lower part of the breakthrough curve profiles, calculated for local particle size distribution (LPSD) and for axial average particle size distribution (APSD) are very similar. However, the upper part of breakthrough profiles calculated for LPSD approaches inlet concentration much more slowly than those calculated for APSD. The retention times of the lower part of uptake curves calculated with average particle diameter are constantly shorter than those obtained from LPSD. For the calculation of the dynamic capacity (DC), the LPSD can be replaced by APSD for large expanded bed heights. Using breakthrough profiles calculated for average particle size, DC values are constantly underestimated.     

The potential of serially coupled alkyl-bonded silica monolithic columns for high resolution separations of pharmaceutical compounds in biological fluids

Summary In this paper we investigate the potential of alkyl-bonded silica monolithic columns for the isolation and identification of drug-related components in biological fluids. Up to 6 columns have been connected in series to produce a chromatographic system with up to 40,000 plates. This high-resolution chromatography system has been coupled to both MS and NMR to enable efficient detection and characterisation of drug-related components in biological fluids. The use of six coupled columns has been shown to give enhanced resolution over a high quality silica particulate column packed with 3 μm material which exhibits the same back pressure. The effect of volume and mass load on the performance of monolithic columns for semi-preparative chromatography of biological fluids has also been investigated. In these studies it was possible to inject up to 100 mL of neat urine with no loss of chromatographic performance. Furthermore, upon re-testing, the columns showed similar chromatographic performance. Again several columns were serially connected, producing enhanced resolution in the semi-preparative mode.     

Elastic behavior of non-Gaussian polymethylene chains

In this paper, elastic behaviors of non-Gaussian polymethylene (PM) chains with chain length N=100 are investigated by rotational isomeric state model. Here the tetrahedral lattice of PM chain and the non-local interaction of Sutherland potential are adopted. In the metropolis movement of PM chain, a four-bond movement model is used. The average energy and average Helmholtz free energy with various elongation ratios λ are calculated by Monte Carlo simulation method. The average energy increases with elongation ratio λ and the average Helmholtz free energy decreases with elongation ratio λ. The elastic force f and the energy contribution to elastic force f_u can be obtained from f=∂〈A〉/∂r and f=∂〈U〉/∂r. We find that the elastic force f increases with elongation ratio λ and the energy contribution f_u decreases with elongation ratio λ, and f_u is less than zero. The ratio f_u/f is close to −0.21 for λ?1.25, and −0.04 to −0.35 for λ>1.25 at T=364 K. In our calculation, the rubber elasticity may be discussed in terms of the chemical structure of polymer chains.     

Linear scaling local correlation approach for solving the coupled cluster equations of large systems

A linear scaling local correlation approach is proposed for approximately solving the coupled cluster doubles (CCD) equations of large systems in a basis of orthogonal localized molecular orbitals (LMOs). By restricting double excitations from spatially close occupied LMOs into their associated virtual LMOs, the number of significant excitation amplitudes scales only linearly with molecular size in large molecules. Significant amplitudes are obtained to a very good approximation by solving the CCD equations of various subsystems, each of which is made up of a cluster associated with the orbital indices of a subset of significant amplitudes and the local environmental domain of the cluster. The combined effect of these two approximations leads to a linear scaling algorithm for large systems. By using typical thresholds, which are designed to target an energy accuracy, our numerical calculations for a wide range of molecules using the 6-31G or 6-31G* basis set demonstrate that the present local correlation approach recovers more than 98.5% of the conventional CCD correlation energy.     

FTIR and WAXS analysis of periodate oxycellulose: Evidence for a cluster mechanism of oxidation

Cellulose paper (Whatman no.1, chromatographic grade) was oxidised with 0.1 M sodium metaperiodate at different oxidation levels (0–11 days at room temperature), and analysed with FTIR before and after chemical treatments (reduction, further oxidation, alkaline hydrolysis). The deconvolution of infrared data allowed us to verify that periodate oxidises cellulose in isolated domains, leading to the decrease of crystallinity, in agreement with the results of wide angle X-ray scattering (WAXS). In particular, the alkaline hydrolysis (β-alkoxy fragmentation) followed by mild acid treatment removed the oxidised groups and recovered most of the crystallinity of cellulose, as determined by the FTIR crystallinity index.