Biomedical subjects

V T Remcho

Publications and source records attributed to V T Remcho.

8 recordsLinked to original sources

PubMed2001

Novel monolithic columns with templated porosity.

A new type of monolithic stationary phase was prepared within the confines of fused-silica tubing by in situ polymerization of divinylbenzene or ethylene dimethacrylate either with styrene or butyl methacrylate. The porosity of the monolith was dictated by silica beads packed in the capillary prior to flushing the column with the monomeric solution. Subsequent washing of the polymeric rod with sodium hydroxide rendered a porous monolith that was used for both micro-LC and capillary electrochromatography. The novelty of the approach presented herein lies in preparing the polymer within the confines of a fused-silica capillary. The challenges posed in this new context and their resolution are presented in detail. In addition, this study proposes that in addition to tailoring the pore size, the silica beads, through their surface chemistry, can influence the surface characteristics of the finished polymer monolith. For example, the data suggests that octadecyl modified silica particles interacted with hydrophobic moieties of monomers before initiation of polymerization, thus dictating their orientation in the resulting polymer.

Amino Acid Sequence↗

PubMed2001

Affinity screening by packed capillary high performance liquid chromatography using molecular imprinted sorbents. II. Covalent imprinted polymers.

This study concentrates on the production of covalent molecular imprint polymers (MIPs) as highly selective sorbents for nortriptyline (NOR), a representative tricyclic antidepressant (TCA). The functionalized template contains a polymerizable 4-vinylphenyl carbamate moiety used to bind the template molecule to the polymer matrix. Polymerization with a cross-linker followed by hydrolytic cleavage of the labile carbamate functionality leaves an MIP with selective binding sites capable of binding template through hydrogen bonding interactions. Demonstrated chromatographically through a "selection index", these MIPs showed high selectivity for the template molecule (NOR) among a library of structurally similar compounds. The recognition was found to correlate with structural similarity to the template compound. A direct comparison between covalent and non-covalent molecular imprinting strategies reveals a great deal of improvement in the peak shape of the retained compound resulting from covalent imprinting (evidenced by peak asymmetry factors A.).

Antidepressive Agents, Tricyclic↗

PubMed2000

Affinity screening by packed capillary high-performance liquid chromatography using molecular imprinted sorbents. I. Demonstration of feasibility.

Molecular imprint polymers (MIPs) are synthetic polymers capable of selectively binding a template molecule. In this work, the potential utility of MIP-based chromatographic sorbents for affinity screening of structurally similar compounds was investigated as alternatives to in vitro bioassays and biological targets bound to chromatographic supports. A group of structurally similar tricyclic antidepressant drugs and related compounds were used to simulate a combinatorial library. One of the antidepressants, nortriptyline (NOR), was selected as the template species. Using capillary HPLC columns packed with NOR-imprinted MIP particles, the simulated library was screened and the degree of selective interaction of each compound was determined. This correlated with each compound's affinity for the NOR binding site in the polymer. The results of the study revealed that library species which possess the major structural features of the template, specifically the ring structure and pendant secondary amine, were best "recognized" by the MIP, while the most structurally dissimilar compounds exhibited the least selective interaction. An investigation of the retention mechanism on these MIPs provided evidence that hydrogen bonding between the pendant amine group on the antidepressants and a methacrylic acid moiety on the polymer surface was critical in the molecular recognition process.

Antidepressive Agents, Tricyclic↗

PubMed2000

Highly selective separations by capillary electrochromatography: molecular imprint polymer sorbents.

Molecular imprint polymers (MIPs) are synthesized in the presence of a template, or 'imprint' molecule which results in the formation of specific recognition cavities complementary to the template in shape and chemical functionality. The resultant MIP then acts as a selective binding medium for the template molecule. The utility of MIPs lies in the selectivity of the rebinding process, which is based on molecular recognition. In many cases, the selectivity achieved with MIPs toward a particular molecule is comparable to that observed with antibodies. This has led to the application of MIPs to several areas of analytical chemistry including immunoassays, sensors and separations media. One of the most successful application areas of MIPs has been as chromatographic sorbents, where they have been utilized predominately in chiral separations. The use of MIP sorbents in CEC is attractive in that it combines the selectivity of a molecular recognition process with the enhanced flow dynamics of CEC, which can result in higher efficiency and shorter analysis times. This paper will review the use of molecular imprinted stationary phases in CEC. Following a brief introduction to molecular imprinting, various methodologies for preparation of MIP-CEC capillaries in addition to applications of the technique will be discussed.

Antidepressive Agents, Tricyclic↗

PubMed2000

A simple procedure for the preparation of fritless columns by entrapping conventional high performance liquid chromatography sorbents.

A rapid and direct method for immobilizing conventional high performance liquid chromatography (HPLC) packing material inside fritless capillaries has been developed. Due to the simple composition of the entrapment matrix (tetraethoxysilane, alkyltriethoxysilane, ethanol and water), straightforward manufacturing procedure and modest equipment requirement, the method can readily be transferred to any laboratory and easily automated. The entrapment procedure has minimal influence on the structure and chromatographic properties of the original reverse-phase sorbent. Various immobilization solutions have been tested, and a comparison between columns entrapped with different immobilization mixtures and conventional packed capillaries is presented. High efficiency separations were obtained using tert-butyl-triethoxysilane entrapped columns in both capillary electrochromatography (reduced plate heights of 1.1-1.4 were measured) and microliquid chromatography (reduced plate heights of 2.2-2.6 were observed) formats. Elimination of frits, stabilization of the packed bed and on-the-fly customization of column length render mechanically robust columns that are remarkably stable over time, from which manufacturing imperfections can be removed easily.

Capillary Action↗

PubMed1999

Silicate entrapped columns--new columns designed for capillary electrochromatography.

Designed especially for capillary electrochromatography (CEC), silicate-entrapped columns are made by trapping particles of chromatographic packing material in a network of silica. Once entrapped, the capillary no longer requires frits. This renders a more homogeneous and stable packed bed. Accidental breakage of the fragile frits is not an issue with these robust columns. Columns packed with reverse-phase material subjected to silicate entrapment demonstrated faster separations of retained analytes and increased efficiencies compared with nonentrapped columns. The method was also used to prepare chiral CEC columns by entrapping a molecular imprinted polymeric (MIP) packing having minimal surface charge density, thus being unable alone to support sufficient electroosmotic flow for CEC.

Chromatography, Liquid↗

PubMed1998

Molecular imprint polymers as highly selective stationary phases for open tubular liquid chromatography and capillary electrochromatography.

Chiral separations employing molecular imprint polymer (MIP) stationary phases in both open tubular liquid chromatography (OT-LC) and capillary electrochromatography (OT-CEC) are demonstrated. MIPs are highly crosslinked polymers containing spatial and functionality memory of template molecules which provide a higher degree of selectivity when used as stationary phases for chromatographic separations. Thin films of molecular imprinted polymers bonded to the inner walls of 25 microm ID fused-silica capillaries were prepared using an in situ polymerization technique developed in our laboratory that allows the use of conventional fused-silica capillaries with polyimide outer coatings. The success rate in preparing such open tubular columns was about 70%. Methacrylic acid and 2-vinyl pyridine were chosen as functional monomers, and either ethylene dimethacrylate or trimethylol propane trimethacrylate was used as the crosslinker. Toluene was employed as the porogen. Effects of polymerization conditions on column preparation and chromatographic performance were studied. Enantiomeric separations of D- and L-dansyl phenylalanines were achieved in both OT-LC and OT-CEC modes with good selectivity and efficiencies. Both types of separations may be performed on the same column using a single commercial instrument.

Capillary Action↗

PubMed1997

Capillary zone electrophoresis and ion-exchange capillary electrochromatography: analytical tools for probing the Hanford nuclear site environment.

Ion-exchange capillary electrochromatography (IE-CEC) is a relatively new separation technique based on the combination of ion-exchange chromatographic and electrophoretic separation mechanisms. IE-CEC offers both the efficiency of capillary electrophoresis and the selectivity and sample capacity of ion-exchange chromatography. The utility of the method was examined with I- and IO3-, which are common constituents of nuclear wastes at Hanford, Washington and other U.S. Department of Energy (DoE) sites, and ReO4-, a surrogate for TcO4-. The advantages and limitations of IE-CEC relative to capillary zone electrophoresis (CZE) are explored. The chief advantages are increased loading capacity and an alternative selectivity to that of CZE, in addition to increased efficiency (relative to conventional ion-exchange chromatography). The run-to-run reproducibility of IE-CEC, however, was found to be a limitation of the technique.

Chromatography, Ion Exchange↗