Study of solvation processes on cholesterol bonded phases

Four cholesterol bonded phases with different structures were investigated. The columns studied were packed with stationary phase containing cholesterol attached to the silica surface using different types of linkage molecules. The presence of the polar amino and carboxyl groups in the structure of the bonded ligand strongly influence on the solvation process. The possibility of hydrogen bonding, dipole-dipole and π-π electron interactions lead to preferential solvation of bonded ligands. The coverage density of bonded ligands and length of the linkage strongly influence the adsorption of solvent from the mobile phase. The removal of residual silanols during the hydrosilation procedure significantly influences solvation of the bonded phase. Excess isotherms of the commonly used solvents in RP HPLC (methanol and acetonitrile) were obtained using the minor disturbance method. For comparison of the stationary phases prepared on different silica gels the excess adsorbed amounts were calculated per volume of the stationary phase in the column. The hydrosilated UDC Cholesterol bonded phase is preferentially solvated by methanol whereas the highest coverage Cosmosil Cholester phase exhibit high adsorption of acetonitrile. Polar groups in the Amino-cholesterol type bonded phase are solvated with both solvent but the mechanisms of these processes are different.     

New alkyl-phosphate bonded stationary phases for liquid chromatographic separation of biologically active compounds

A new type of bonded stationary phase for liquid chromatography, with the properties of immobilized artificial membranes, has been synthesized. Alkyl-phosphate adsorbents were obtained by modification of aminopropyl silica gel. The structures of the synthesized materials were confirmed by use of instrumental techniques--elemental analysis, infrared spectroscopy (FTIR), and (13)C and (29)Si CP/MAS NMR. Analysis revealed that the adsorbents mimic the phospholipids present in natural cell membranes. The new synthesized alkyl-phosphate stationary phases may be used for liquid chromatographic separation of biologically active compounds of different polarity.     

Influence of temperature on mass transfer in an incomplete trapping supported liquid membrane extraction of triazole fungicides

The influence of temperature in a supported liquid membrane (SLM) extraction of triazole fungicides was investigated. The mass transfer parameters such as diffusion coefficient, flux and apparent viscosity were determined at temperatures ranging from 5 to 40°C. Increase in temperature led to an increase in diffusion coefficient and flux with a flowing acceptor solution. The apparent viscosity also decreased with an increase in temperature. However, the increase in mass transfer parameters did not result in an overall increase in extraction efficiency with a stagnant or circulation acceptor phase. Stripping of the analytes from the membrane into the acceptor phase as well as the configuration of the extraction unit could have limited the influence of temperature on mass transfer. The partition coefficient of analytes from the acceptor solution to the membrane, K_A, was found to be much higher than that from the donor solution to the membrane K_D, thus triazole compounds preferred to remain in the membrane even with an increased extraction temperature.     

On log-Sobolev inequalities for infinite lattice systems

For a system on an infinite lattice, we show that a Gibbs measure for a smooth local specification ={E } satisfying the Dobrushin uniqueness theorem also satisfies log-Sobolev inequality, provided it is satisfied for one-dimensional measures E _l .     

The effect of stationary phase on lipophilicity determination of beta-blockers using reverse-phase chromatographic systems

Evaluation of lipophilicity parameters for basic compounds using different chromatographic stationary phases is presented. An HPLC method for determination of lipophilic molecule-stationary phase interactions was based on gradient analysis. Differences in correlation between the lipophilicity of compounds and experimental chromatographic results obtained in pseudo-membrane systems showed a strong influence of stationary phase structure and physico-chemical properties. beta-Blocker drugs with varying lipophilicity and bio-activity were chosen as test compounds. The stationary phases used for the study were monolithic rod-structure C18 and silica gel octadecyl phase SG-C18 as reference material. The second group was silica gel-based polar-embedded alkylamide and cholesterolic phases. The mobile phase was composed of acetonitrile or methanol with ammonium acetate, and a linear gradient of methanol and acetonitrile in mobile phase was performed. A linear correlation of plots of log k(g) = f(log P) was observed, especially for polar-embedded phases, and this allowed log P(HPLC) to be calculated. The behavior of stationary phases in methanol and acetonitrile buffer showed differences between obtained log P(HPLC) values.     

Tissue sample preparations for preclinical research determined by molecular imaging mass spectrometry using matrix-assisted laser desorption/ionization

Matrix-assisted laser desorption/ionization - imaging mass spectrometry is an alternative tool, which can be implemented in order to obtain and visualize the “omic” signature of tissue samples. Its application to clinical study enables simultaneous imaging-based morphological observations and mass spectrometry analysis. Application of fully informative material like tissue allows obtaining the complex and unique profile of analyzed samples. This knowledge leads to diagnosing disease, studying the mechanism of cancer development, selecting the potential biomarkers as well as correlating obtained images with prognosis. Nevertheless, it is worth noticing that this method is found to be objective but the result of the analysis is mainly influenced by the sample preparation protocol, including the collection of biological material, its preservation, and processing. However, the application of this approach requires a special sample preparation procedure. The main goal of the study is to present the current knowledge on the clinical application of matrix-assisted laser desorption/ionization with imaging mass spectrometry in cancer research, with particular emphasis on the sample preparation step. For this purpose, several protocols based on cryosections and formalin-fixed paraffin-embedded tissue were compiled and compared, taking into account the measured metabolites of potential diagnostic importance for a given type of cancer.     

A.c. impedance behaviour of processes involving adsorption and reactivity of guanidonium-type cations at Pt(1 0 0) surface

The present paper reports a.c. impedance spectroscopic studies on adsorption of guanidonium (G⁺) and N,N-dimethylguanidonium (DMG⁺) resonant cations at Pt(1 0 0) single-crystal surface. The resulted information provided confirmation of the role of electrosorption of the above-mentioned molecule–ions through evaluation of the associated charge-transfer resistances and capacitances for the Pt(1 0 0) plane in 0.5 M H₂SO₄. These results also provided support for the interfacial ion-pairing mechanism that had been based on the voltammetric and in situ FTIR spectroscopic results published earlier.     

Simultaneous Enzymatic Cellulose Hydrolysis and Product Separation in a Radial-Flow Membrane Bioreactor

Hydrolysis is the heart of the lignocellulose-to-bioethanol conversion process. Using enzymes to catalyze the hydrolysis represents a more environmentally friendly pathway compared to other techniques. However, for the process to be economically feasible, solving the product inhibition problem and enhancing enzyme reusability are essential. Prior research demonstrated that a flat-sheet membrane bioreactor (MBR), using an inverted dead-end filtration system, could achieve 86.7% glucose yield from purified cellulose in 6 h. In this study, the effectiveness of flat-sheet versus radial-flow MBR designs was assessed using real, complex lignocellulose biomass, namely date seeds (DSs). The tubular radial-flow MBR used here had more than a 10-fold higher membrane surface area than the flat-sheet MBR design. With simultaneous product separation using the flat-sheet inverted dead-end filtration MBR, a glucose yield of 10.8% from pretreated DSs was achieved within 8 h of reaction, which was three times higher than the yield without product separation, which was only 3.5% within the same time and under the same conditions. The superiority of the tubular radial-flow MBR to hydrolyze pretreated DSs was confirmed with a glucose yield of 60% within 8 h. The promising results obtained by the novel tubular MBR could pave the way for an economic lignocellulose-to-bioethanol process.