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Biomedical subjects

A Velayudhan

Publications and source records attributed to A Velayudhan.

15 recordsLinked to original sources
PubMed2000

Isolation and preparative purification of microcystin variants.

Preparative reversed-phase liquid chromatography was successfully used to purify two microcystins (microcystin LR and microcystin LA) from a cyanobacterial process waste. The separation protocol involved extraction of lyophilized cells by methanol, isolation and concentration by solid-phase extraction, and purification by reversed-phase HPLC. Milligram-level loading of microcystins was obtained on a solid-phase extraction cartridge packed with 0.5 g of C18 stationary phase. The separations were first carried out on an analytical column and then scaled-up to a preparative column. The microcystins were quantified by HPLC and enzyme-linked immunosorbent assay. A method to remove microcystins rapidly and economically from the cyanobacterial process waste is also described.

Bacterial Toxins↗
PubMed1999

A study of platelet serotonin receptor in mania.

BACKGROUND: Serotonergic (5-HT) dysfunction has been hypothesized in mania; however platelet studies on the 5-HT uptake rate and the 5-HT transporter have revealed inconsistent results. To the best of our knowledge no studies have been conducted on the 5-HT2 receptor status in mania. METHODS: We determined density (Bmax) and dissociation constant (Kd) of 5-HT2 receptors in the platelets of 29 normal control and 29 manic subjects using 125I-ketanserin as the binding radioligand. The manic patients were assessed for the same after 14 days of treatment with lithium (n = 14) and after return to premorbid levels of functioning (n = 5). RESULTS: There were no significant differences in the Bmax (3.51 +/- 3.04 vs. 3.14 +/- 3.44 fmol/mg protein, p = ms) values between normal control and manic subjects. In comparison to the baseline values Bmax at day 14 (3.49 +/- 3.68 vs. 2.18 +/- 1.90 fmol/mg protein, p = ns) and following recovery (1.17 +/- 0.85 vs. 1.29 +/- 1.13 fmol/mg protein, p = ns) did not show any significant difference. CONCLUSIONS: Our findings preliminarily suggest that the platelet 5-HT2 receptor is neither a state marker nor a trait marker in mania; however studies on the 5-HT2 receptor using positron-emission tomography ligands will help in conclusively ruling out the involvement of this receptor in mania.

Adult↗
PubMed1998

Preparative gradient elution chromatography of chemotactic peptides.

Experimental and computational studies are carried out on the separation of a mixture of chemotactic peptides by reversed-phase gradient elution on commercial octadecyl silica supports with acetonitrile as the modulator. The solubility of this mixture is found to be a complex function not only of mobile phase composition, but also of the order in which the various constituents of the mobile phase are mixed together. In certain cases, the feeds seem to reach a metastable state in which they are fully soluble for several hours: this is exploited here for preparative separations. Separations are also carried out by stepwise and nonlinear isocratic elution, and the yields and productivities compared to those from gradient elution. Predictive simulations of all these separations are run using independently measured single component feed isotherms. Good agreement with experiment is found when multicomponent (nonlinear) feed interactions are accounted for, but not when the usual assumption of linear feed isotherms is made. Simultaneous concentration and separation of these feeds is easily achieved by gradient elution. Simulations indicate that the combination of the focusing power of the gradient with the multicomponent feed interactions is likely to give good separations even at high feed loadings.

Chemotactic Factors↗
PubMed1997

An investigation into the psychobiology of social phobia: personality domains and serotonergic function.

The aim of the present study was to explore a psychobiological perspective in the aetiology of social phobia. The emphasis was on serotonergic function and personality. A total of 20 social phobics according to ICD-10 DCR criteria were assessed with the Schedule for Clinical Assessment in Neuropsychiatry and the International Personality Disorder Examination. They were compared with an age-matched normal population with regard to scores on the Fear of Negative Evaluation Scale, the Social Avoidance and Distress Scale, the Temperament and Character Inventory, and platelet 5HT2 receptor function. Other Axis-I disorders and cluster C personality disorders were frequently encountered. The social phobia group was characterized by high levels of harm avoidance, and low levels of novelty seeking, co-operativeness and self-directedness. Platelet 5HT2 receptor density did not differentiate between the groups, but was associated with severity of social phobia. An integrated psychobiological model is presented.

Adult↗
PubMed1996

Enzyme conversion of lignocellulosic plant materials for resource recovery in a Controlled Ecological Life Support System.

A large amount of inedible plant material composed primarily of the carbohydrate materials cellulose, hemicellulose, and lignin is generated as a result of plant growth in a Controlled Ecological Life-Support System (CELSS). Cellulose is a linear homopolymer of glucose, which when properly processed will yield glucose, a valuable sugar because it can be added directly to human diets. Hemicellulose is a heteropolymer of hexoses and pentoses that can be treated to give a sugar mixture that is potentially a valuable fermentable carbon source. Such fermentations yield desirable supplements to the edible products from hydroponically-grown plants such as rapeseed, soybean, cowpea, or rice. Lignin is a three-dimensionally branched aromatic polymer, composed of phenyl propane units, which is susceptible to bioconversion through the growth of the white rot fungus, Pluerotus ostreatus. Processing conditions, that include both a hot water pretreatment and fungal growth and that lead to the facile conversion of plant polysaccharides to glucose, are presented.

Biodegradation, Environmental↗
PubMed1995

Simultaneous concentration and purification through gradient deformation chromatography.

Mobile-phase additives, commonly used to modulate absorbate retention in gradient elution chromatography, are usually assumed to be either linearly retained or unretained. Previous theoretical work from our laboratory has shown that these modulators, such as salts in ion-exchange and hydrophobic interaction chromatography and organic modifiers in reversed-phase chromatography, can absorb nonlinearly, giving rise to gradient deformation. Consequently, adsorbate peaks that elute in the vicinity of the head of the deformed gradient may exhibit unusual shapes, form shoulders, and/or be concentrated. These effects for a reversed-phase sorbent with aqueous acetonitrile (ACN) as the modulator are verified experimentally. Gradient deformation is demonstrated experimentally and agrees with simulations based on ACN isotherm parameters that are independently determined from batch equilibrium studies using the layer model. Unusual absorbate peak shapes were found experimentally for single-component injections of phenylalanine, similar to those calculated by the simulations. A binary mixture of tryptophan and phenylalanine is used to demonstrate simultaneous concentration and separation, again in agreement with simulations. The possibility of gradient deformation in ion-exchange and hydrophobic interaction chromatography is discussed.

Acetonitriles↗
PubMed1995

Electrochromatographic separation of proteins.

We have developed a modified electrochromatography system which minimizes Joule heating at electric field strengths up to 125 V/cm. A non-linear equilibrium model is described which incorporates electrophoretic mobility, hydrodynamic flow velocity, and an electrically induced concentration polarization at the surface of the stationary phase. This model is able to provide useful estimates of protein retention time and velocity in a column packed with Sephadex gel and subjected to an electric field. A correlation of electrophoretic mobility of peptide and proteins with respect to their charge, molecular mass, and asymmetry enables the selection of solute target molecules for electrochromatographic separations. Good separation of protein mixtures have been obtained.

Chromatography, High Pressure Liquid↗
PubMed1995

Analysis of plant harvest indices for bioregenerative life support systems.

Harvest indices, which are measures of the ratio of edible to total plant weight, are redefined to include edible sugars derived from enzymatic hydrolysis of the cellulose content of inedible plant components. Compositional analysis and carbohydrate contents of rapeseed, rice, soybeans, cowpea, wheat, sweet potato, white potato, and lettuce were analyzed to develop such generalized harvest indices. Cellulose conversion is shown to extend considerably the food available from plants otherwise grown for their oil and protein content in a bioregenerative life support system.

Biomass↗
PubMed1995

Effect of modulator sorption on gradient shape in ion-exchange chromatography.

Mobile phase additives, or modulators, are used in gradient elution chromatography to facilitate separation and reduce separation time. The modulators are usually assumed to be linearly adsorbed or unadsorbed. Here, the consequences of nonlinear modulator adsorption are examined for ion-exchange gradient elution through a series of simulations. Even when the buffer salt is identical to the modulator salt, gradient deformation is observed; the extent of deformation increases as the volume of the feed is increased. When the modulator salt is different from the buffer salt, unusual effects are observed, and the chromatograms are quite different from those predicted by classical gradient elution theory. In particular, local increases in the buffer concentration are found between feed bands, and serve to improve the separation. These effects become more pronounced as the feed volume increases, and could therefore prove valuable in preparative applications.

Adsorption↗
PubMed1994

Adsorption and ion-exchange isotherms in preparative chromatography.

A systematic characterization of ion-exchange and adsorption isotherms is presented. This treatment serves to emphasize the singular nature of monovalent ion-exchange and classical Langmuir isotherms, and describes the more general homovalent and heterovalent isotherms that are applicable to both ion-exchange and adsorption. Such formalisms are applied to adsorptive systems for the first time, and could prove to be useful additions to the canon of available isotherms. The shielding effect of macromolecular adsorbates on the binding of other macromolecules is discussed, and its parallel to the characteristic charge of a macromolecule is brought out. The application of the general adsorptive formalism to reversed-phase chromatography yields a relationship between the retention factor and the modifier concentration that, in two limiting cases, reduces to two well-known results. The first, which is characteristic of small molecules, gives a linear relationship between the logarithmic retention factor and a linear or quadratic term in the modifier. The second, which is characteristic of large molecules, gives a linear relationship between the logarithmic retention factor and the logarithm of the modifier concentration. The use of appropriate concentration units is shown to resolve certain apparently non-standard (non-Tiselian) displacement patterns. The measurement of characteristic charges by displacement described above could be an interesting complement to the more common elution method, and could provide further insight into the underlying physico-chemical phenomena.

Adsorption↗
PubMed1988

Preparative chromatography of proteins analysis of the multivalent ion-exchange formalism.

Multivalent ion exchange is proposed as a generally applicable formalism to describe the non-linear chromatographic adsorption of biopolymers. Single- and multi-component isotherms are calculated that explicitly account for the influence of the mobile phase modulator concentration. Three regions of binding (strong, intermediate, and weak) are distinguished on the basis of strength of interaction, and the potential advantages of operating in the strong region for preparative purposes are pointed out. The inapplicability of the Langmuir isotherm in this region is demonstrated, and separation schemes that take advantage of the characteristic features of biopolymeric adsorption are described. The rectangular single-component ion-exchange isotherms are shown to reduce in the presence of competition to reversible concave-down forms.

Chemical Phenomena↗
PubMed1988

Analysis of multiple front formation in the wetting of thin-layer plates.

Multiple fronts were formed when pure liquids such as methanol or heptane and multi-component liquids such as ethanol-toluene mixtures were flowed through initially dry thin-layer chromatography plates, whether the stationary phase was naked silica or octadecyl-silica. A minor modification to a commercially available thin-layer chromatograph allowed the fronts to be clearly seen, and their dynamics to be measured experimentally. A model is proposed to explain their formation and motion.

Alcohols↗
PubMedDate not supplied

Characterization of the swelling of a size-exclusion gel.

The swelling of a dextran gel, Sephadex G-75, was observed in an aqueous environment at room temperature by a noninvasive technique that uses light microscopy coupled to an image analysis system via a video camera. The rate of swelling was found to follow the Tanaka and Fillmore theory, from which the overall gel diffusion coefficient was estimated as 6.3 x 10(-7) cm2/s. In addition to giving a quantitative measure of gel swelling that could be useful in the mechanical design of liquid chromatography columns, this approach provides data on wet particle size and particle size range, which is needed for the modeling of diffusional and mass transfer effects in size-exclusion chromatography. In this context, key observations are that the gel particles are nearly spherical with an elliptical shape factor of 0.98 (perfect sphere = 1) and that there is little difference between sizes of particles obtained in water, 50 mM Tris-glycine buffer (pH 10.2), and buffer containing 1 mg/mL protein. The diameter of the dry material ranged from 20 to 100 microns, while the hydrated particles had diameters of 40-350 microns. The rate of swelling is rapid, with 50% swelling occurring in about 10 s and swelling to 99% of the final wet particle size being obtained in less than 90 s.

Chemical Phenomena↗
PubMedDate not supplied

Simulation of diauxic production of cephalosporin C by Cephalosporium acremonium: lag model for fed-batch fermentation.

We extend a previously reported model (Chu, W.B.; Constantinides, A. Biotechnol. Bioeng. 1988, 32, 277-288) for the batch fermentation of cephalosporin C under the diauxic growth of Cephalosporium acremonium on glucose and sucrose to a fed-batch system. For this purpose, a novel lag model is proposed for diauxie, which has two functional forms, each embodying the dependence of lag on total cell mass and secondary substrate concentration. This lag model is applicable for batch simulations for arbitrary initial glucose and sucrose concentrations. We used the previously reported batch data to perform locally optimized fed-batch simulations. When applied to fed-batch fermentations, multiple lag times were accounted for. These studies showed that fed-batch fermentations (under the restriction that cell mass concentration did not exceed 25 g/L) could be more productive than simple batch runs. A representative result for a glucose-pulse fed-batch run at optimal cephalosporin production is a productivity of 4.22 mg of cephalosporin C/(L.h) and a yield of 9.25 mg of cephalosporin C/g of total sugar used.

Acremonium↗