Diastereomeric Drug Glucuronides: Enzymatic Glucuronidation and Analysis by Capillary Electrophoresis and Liquid Chromatography-Mass Spectrometry

Foreign compounds, such as drugs are metabolised in the body in numerous reactions. Metabolic reactions are divided into phase I (functionalisation) and phase II (conjugation) reactions. Uridine diphosphoglucuronosyltransferase enzymes (UGTs) are important catalysts of phase II metabolic system. They catalyse the transfer of glucuronic acid to small lipophilic molecules and convert them to hydrophilic and polar glucuronides that are readily excreted from the body. Liver is the main site of drug metabolism. Many drugs are racemic mixtures of two enantiomers. Glucuronidation of a racemic compound yields a pair of diastereomeric glucuronides. Stereoisomers are interesting substrates in glucuronidation studies since some UGTs display stereoselectivity. Diastereomeric glucuronides of O-desmethyltramadol (M1) and entacapone were selected as model compounds in this work. The investigations of the thesis deal with enzymatic glucuronidation and the development of analytical methods for drug metabolites, particularly diastereomeric glucuronides. The glucuronides were analysed from complex biological matrices, such as urine or from in vitro incubation matrices. Various pretreatment techniques were needed to purify, concentrate and isolate the analytes of interest. Analyses were carried out by liquid chromatography (LC) with ultraviolet (UV) or mass spectrometric (MS) detection or with capillary electromigration techniques. Commercial glucuronide standards were not available for the studies. Enzyme-assisted synthesis with rat liver microsomes was therefore used to produce M1 glucuronides as reference compounds. The glucuronides were isolated by LC/UV and ultra performance liquid chromatography (UPLC)/MS, while tandem mass spectrometry (MS/MS) and nuclear magnetic resonance (NMR) spectroscopy were employed in structural characterisation. The glucuronides were identified as phenolic O-glucuronides of M1. To identify the active UGT enzymes in (±)-M1 glucuronidation recombinant human UGTs and human tissue microsomes were incubated with (±)-M1. The study revealed that several UGTs can catalyse (±)-M1 glucuronidation. Glucuronidation in human liver microsomes like in rat liver microsomes is stereoselective. The results of the studies showed that UGT2B7, most probably, is the main UGT responsible for (±)-M1 glucuronidation in human liver. Large variation in stereoselectivity of UGTs toward (±)-M1 enantiomers was observed. Formation of M1 glucuronides was monitored with a fast and selective UPLC/MS method. Capillary electromigration techniques are known for their high resolution power. A method that relied on capillary electrophoresis (CE) with UV detection was developed for the separation of tramadol and its free and glucuronidated metabolites. The suitability of the method to identify tramadol metabolites in an authentic urine samples was tested. Unaltered tramadol and four of its main metabolites were detected in the electropherogram. A micellar electrokinetic chromatography (MEKC) /UV method was developed for the separation of the glucuronides of entacapone in human urine. The validated method was tested in the analysis of urine samples of patients. The glucuronides of entacapone could be quantified after oral entacapone dosing.

Development of atmospheric pressure ionization ion mobility spectrometry and ion mobility spectrometry mass spectrometry

This study is focused on the development and evaluation of ion mobility instrumentation with various atmospheric pressure ionization techniques and includes the following work. First, a high-resolution drift tube ion mobility spectrometer (IMS), coupled with a commercial triple quadrupole mass spectrometer (MS), was developed. This drift tube IMS is compatible with the front-end of commercial Sciex mass spectrometers (e.g., Sciex API-300, 365, and 3000) and also allows easy (only minor modifications are needed) installation between the original atmospheric pressure ion source and the triple quadrupole mass spectrometer. Performance haracteristics (e.g.,resolving power, detection limit, transmission efficiency of ions) of this IMS-MS instrument were evaluated. Development of the IMS-MS instrument also led to a study where a proposal was made that tetraalkylammonium ions can be used as chemical standards for ESI-IMS. Second, the same drift tube design was also used to build a standalone ion mobility spectrometer equipped with a Faraday plate detector. For this highresolution (resolving power about 100 shown) IMS device, a multi-ion source platform was built, which allows the use of a range of atmospheric pressure ionization methods, such as: corona discharge chemical ionization (CD-APCI), atmospheric pressure photoionization (APPI), and radioactive atmospheric pressure chemical ionization (R-APCI). The multi-ion source platform provides easy switching between ionization methods and both positive and negative ionization modes can be used. Third, a simple desorpion/ionization on silicon (DIOS) ion source set-up for use with the developed IMS and IMS-MS instruments was built and its operation demonstrated. Fourth, a prototype of a commercial aspiration-type ion mobility spectrometer was mounted in front of a commercial triple quadrupole mass spectrometer. The set-up, which is simple, easy to install, and requires no major modifications to the MS, provides the possibility of gathering fundamental information about aspiration mobility spectrometry.

Analysis of heat and mass transfer during bulk hydraircooling of spherical food products

Hydraircooling is a technique used for precooling food products. In this technique chilled water is sprayed over the food products while cold unsaturated air is blown over them. Hydraircooling combines the advantages of both air- and hydrocooling. The present study is concerned with the analysis of bulk hydraircooling as it occurs in a package filled with several layers of spherical food products with chilled water sprayed from the top and cold unsaturated air blown from the bottom. A mathematical model is developed to describe the hydrodynamics and simultaneous heat and mass transfer occurring inside the package. The non-dimensional governing equations are solved using the finite difference numerical methods. The results are presented in the form of time-temperature charts. A correlation is obtained to calculate the process time in terms of the process parameters.

Simultaneous heat and mass transfer under unsteady mixed convection along a vertical slender cylinder embedded in a porous medium

Unsteady laminar mixed convection flow (combined free and forced convection flow) along a vertical slender cylinder embedded in a porous medium under the combined buoyancy effect of thermal and species diffusion has been studied. The effect of the permeability of the medium as well as the magnetic field has been included in the analysis. The partial differential equations with three independent variables governing the flow have been solved numerically using a implicit finite difference scheme in combination with the quasilinearization technique. Computations have been carried out for accelerating, decelerating and oscillatory free stream velocity distributions. The effects of the permeability of the medium, buoyancy forces, transverse curvature and magnetic field on skin friction, heat transfer and mass transfer have been studied. It is found that the effect of free stream velocity distribution is more pronounced on the skin friction than on the heat and mass transfer. The permeability and magnetic parameters increase the skin friction, but reduce the heat and mass transfer. The skin friction, heat transfer and mass transfer are enhanced due to the buoyancy forces and curvature parameter. The heat transfer is strongly dependent on the viscous dissipation parameter and the Prandtl number, and the mass transfer on the Schmidt number. Untersucht wurde die instationäre laminare Mischkonvektion längs eines vertikalen, in einem porösen Medium eingebetteten Zylinders unter kombinierten Auftriebseffekten von thermischer und spezieller Diffusion. Der Einfluß der Permeabilität des Mediums sowie des magnetischen Feldes wurden in die Betrachtung einbezogen. Die partiellen Differentialgleichungen mit drei unabhängigen Variablen, welche die Strömung beschreiben, wurde numerisch anhand des Schemas der endlichen Differenzen in Verbindung mit der Technik der Quasilinearisation gelöst. Berechnungen für die beschleunigte, verzögerte und oszillierende Geschwindigkeitsverteilung der freien Strömung sind durchgeführt worden. Untersucht wurden ebenfalls die Effekte der Permeabilität des Mediums, der Auftriebskräfte, der transversalen Krümmung, des magnetischen Feldes auf die Oberflächenreibung sowie die Wärmeund Stoffübertragung. Es wurde festgestellt, daß die Geschwindigkeit mehr Einfluß auf die Oberflächenreibung als auf die Wärmeund Stoffübertragung hat. Die Oberflächenreibung sowie die Wärme- und Stoffübertragung werden durch die Auftriebskräfte und die Krümmungsparameter verbessert. Die Wärmeübertragung ist stark abhängig von den Parametern der viskosen Dissipation und der Prandtl-Zahl; die Stoffübertragung von der Schmidt-Zahl.

Tuning the electronic effective mass in double-doped SrTiO3

We elucidate the relationship between effective mass and carrier concentration in an oxide semiconductor controlled by a double-doping mechanism. In this model oxide system, Sr1-xLaxTiO3-delta, we can tune the effective mass ranging from 6 to 20m(e) as a function of filling (carrier concentration) and the scattering mechanism, which are dependent on the chosen lanthanum-and oxygen-vacancy concentrations. The effective mass values were calculated from the Boltzmann transport equation using the measured transport properties of thin films of Sr1-xLaxTiO3-delta. We show that the effective mass decreases with carrier concentration in this large-band-gap, low-mobility oxide, and this behavior is contrary to the traditional high-mobility, small-effective-mass semiconductors.

Mass transfer and shear rate in baffled surface aerator

The scale up or scale down of the process variables in a surface aerator requires information about the shear rate prevailing in the system. In fact, the performance of surface aerator depends upon the shear rate. Shear rate affects the mass transfer operation needed by the surface aerator. Theoretical analysis of shear rate suggests a nonlinear behavior with rotational speed of the impeller, which has been shown in the present work. Present work also shows that in a geometrically similar system of baffled surface aerator, shear rate can be used as a governing parameter for scaling up or down the mass transfer phenomena.

Contraceptive vaccines: current status and problems in mass application

Progress in the development of contraceptive vaccines for males and females is reviewed. Based on the criteria which need to be met with, none of the proposed candidate antigens meets the requirements for use as a contraceptive vaccine for human application. One of the major problems is the need for periodic injections to maintain required titre and use of an alternate method until effective titres are obtained. Some of the problems associated with active immunization approach can be overcome by the use of preformed, highly specific, potent antibodies. Some progress has been achieved in this direction by the use of humanized single chain monoclonal antibodies to human chorionic gonadotropin.

Thermal degradation products of poly(styrenesulfides) investigated by direct pyrolysis�mass spectrometry and flash pyrolysis�gas chromatography/mass spectrometry

The thermal degradation products of two sulfur polymers, poly(styrenedisulfide) (PSD) and poly(styrenetetrasulfide) (PST), were investigated in parallel by direct pyrolysis-mass spectrometry (DPMS) and by flash pyrolysis-GC/MS (Py-GC/MS). The time-scale of the two pyrolysis techniques is quite different, and therefore they were able to detect significantly different products in the pyrolysis of PSD and PST because of the thermal lability of sulfur-containing compounds. However, the results obtained are not contradictory, and satisfactory mechanisms for the thermal degradation of PSD and PST have been derived from the overall evidence available. Pyrolysis compounds containing sulfur, styrene, and a number of cyclic styrene sulfides and diphenyldithianes have been observed by DPMS. However, in flash pyrolysis-GC/MS, styrene, sulfur, only one cyclic styrene sulfide, and two isomers of diphenylthiophene have been detected. These thiophene derivatives were indeed absent among the compounds obtained by DPMS because they were the terminal (most thermally stable) species arising from further decomposition of the cyclic styrene sulfides formed in the primary thermal degradation processes of PSD and PST.

The effect of surface mass transfer on buoyancy induced flow in a variable porosity medium adjacent to a vertical heated plate

The effect of surface mass transfer on buoyancy induced flow in a variable porosity medium adjacent to a heated vertical plate is studied for high Rayleigh numbers. Similarity solutions are obtained within the frame work of boundary layer theory for a power law variation in surface temperature,T Wpropx lambda and surface injectionv Wpropx(lambda–1/2). The analysis incorporates the expression connecting porosity and permeability and also the expression connecting porosity and effective thermal diffusivity. The influence of thermal dispersion on the flow and heat transfer characteristics are also analysed in detail. The results of the present analysis document the fact that variable porosity enhances heat transfer rate and the magnitude of velocity near the wall. The governing equations are solved using an implicit finite difference scheme for both the Darcy flow model and Forchheimer flow model, the latter analysis being confined to an isothermal surface and an impermeable vertical plate. The influence of the intertial terms in the Forchheimer model is to decrease the heat transfer and flow rates and the influence of thermal dispersion is to increase the heat transfer rate.

Gas-phase controlled mass transfer in a foam-bed reactor

Gas-phase controlled absorption of ammonia in foams made of solutions of sulphuric acid has been studied experimentally. Effects of gas-phase concentration of ammonia and type of surfactant on the performance of the foam-bed reactor are investigated. Gas-phase controlled absorption from a spherical bubble is anaylzed using the asymptotic value of Sherwood number (Sh = 6.58), for both negligible as well as significant changes in the volume of the bubble. The experimental data are shown to be in good agreement with the single-stage model of the foam-bed reactor using these asymptotic sub-models, as well as the diffusion-in-sphere analysis available in literature. Influence of effective diffusivity on the time dependence of fractional gas absorption has been found to be unimportant for foam columns with large times of contact. The asymptotic sub-models have been compared and use of the rigid-sphere asymptotic sub-model is recommended for foam columns of practical relevence.

Influence of carbide particles on the dynamic recrystallization of as-cast 304 stainless steel: a study using secondary ion mass spectrometric (SIMS) analysis

The domain of dynamic recrystallization (DRX) in as-cast 304 stainless steel material occurs at higher temperatures (1250 degrees C) and lower strain rates (0.001 s(-1)) than in wrought 304 stainless steel (1100 degrees C and 0.01 s(-1)). The above result has been explained earlier on the basis of a simple theoretical DRX model involving the rate of nucleation versus rate of grain boundary migration. The present investigation is aimed at examining experimentally the influence of carbide particles on the DRX of ascast 304 using secondary ion mass spectrometric (SIMS) analysis. Isothermal compression tests at a constant true strain rate have been performed on wrought 304 and as-cast 304 materials in the temperature and strain rate ranges of 1000 to 1250 degrees C and 0.001 to 1 s(-1) respectively. The SIMS analysis carried out on the deformed samples revealed that the large carbides present in the as-cast 304 material strongly influence the DRX process. In as-cast 304 material, the presence of large carbide particles in the microstructure shifts the DRX domain to higher temperature and lower strain rate in comparison with wrought 304 material.