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2. Non-destructive chromatographic determination of surface area in reverse phase chromatographic columns.

Author

Figus, Margaret and Kazakevich, Yuri V.

Subjects
*SURFACE area, *ADSORPTION isotherms, *PACKINGS (Chromatography), *SUBVERSIVE activities, *UNITS of measurement
Abstract

One of the critical but underutilized parameters that affect chromatographic separation is an adsorbent surface area (S.A.). We introduce a concept of direct determination of the total surface area of chromatographic columns by utilizing a nondestructive measurement of eluent component excess adsorption isotherm measurement and the application of the Standard Excess Adsorption Isotherm from acetonitrile-water and methanol-water binary mixtures for direct determination of the S.A. in chromatographic columns. This nondestructive technique was used to determine the surface area of five commercial columns, including three core-shell particle type columns (Kinetex-C18, Ascentis C18, and Hallo C18) and in-housemade C18 columns. The traditional low-temperature nitrogen adsorption (LTNA) technique was compared to the novel chromatographic method of nondestructive surface area determination for adsorbents modified with octadecylsilanes. The chromatographically determined surface area was in good agreement with the conventional techniques for all columns used. The difference between the three techniques is less than 10%. Columns were characterized in terms of adsorbent geometry (e.g., pore volume, column void volume, interparticle volume), ligands bonding density, and the amount of the packing material in a chromatographic column. [ABSTRACT FROM AUTHOR]

Published
2024
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5. Surface area of reversed-phase HPLC columns

Author

Giaquinto, A., Liu, Zhaoxia, Bach, Andrew, and Kazakevich, Yuri

Subjects
High performance liquid chromatography -- Methods, Adsorbents -- Properties, Surfaces -- Areas and volumes, Surfaces -- Measurement, Chemistry
Abstract

Six reversed-phase columns from different manufacturers were characterized in terms of adsorbent geometry (e.g., pore volume, surface area, column void volume, and interparticle volume). Measurement of the surface area of chemically modified silica-based adsorbents is discussed together with the methods for the determination of the amount of adsorbent in the column. The behavior of nearly ideal chromatographic systems was studied. Retention factors of alkylbenzenes in acetonitrile/water and methanol/water systems were compared with surfacespecific retention factors. The distribution of conventional retention factor values for the same analyte among the six columns using identical chromatographic conditions exceeded 35%, while the relative standard deviation of surface-specific retention factors was on the level of 3%.

Published
2008

17. Wetting in hydrophobic nanochannels: A challenge of classical capillarity

Author

Helmy, Roy, Kazakevich, Yuri, Chaoying Ni, and Fadeev, Alexander Y.

Subjects
Hydrophobic effect -- Analysis, Capillarity -- Research, Water -- Chemical properties, Chemistry
Abstract

An investigation of water--hydrophobic interface in nanochannels is reported and the intrusion of water in hydrophobic nanochannels is studied. The results suggest the presence of ~0.6 nm low-density fluid separating water from the hydrophobic solid.

Published
2005

50. The Investigation of the Active Sites of Monoamine Oxidase (MAO) A and B and the Study of MAO-A Mediated Neurotoxicity Using 4-Substituted Tetrahydropyridines

Author

Palmer, Sonya Lenette Jr., Chemistry, Castagnoli, Neal Jr., Bell, Harold M., Kingston, David G. I., Tanko, James M., Wolfe, James F., Taylor, Larry T., and Kazakevich, Yuri V.

Subjects
Neurotoxicity, Enzymology, Monoamine Oxidase, Active Sites
Abstract

The mitochondrial membrane bound flavoenzymes monoamine oxidase A and B (MAO-A and MAO-B) catalyze the a-carbon oxidation of a variety of amines including neurotransmitters such as dopamine and serotonin. Although the primary structures of these enzymes have been established from the corresponding gene sequences, relatively little is known regarding the structural features of the active sites which lead to the selectivities observed with various substrates and inhibitors. In spite of many efforts, these enzymes have not been crystallized. In the absence of X-ray structures, the design, synthesis, and evaluation of biological activity remain the only way to assess a view of the active sites, through SAR and QSAR studies. The excellent MAO-A and/or B substrate and inhibitor properties of various 1,4-disubstituted-1,2,3,6-tetrahydropyridine derivatives offer an interesting opportunity to probe the active sites of MAO-A and MAO-B. In an effort to explore the spatial features of the active sites, we have synthesized series of substituted tetrahydropyridines, evaluated their biological activity with purified MAO-A and MAO-B, and carried out a topological analysis of the MAO active sites using molecular modeling. In addition, the results described in this thesis provide evidence that the MAO-A and MAO-B active sites differ in shape, regions of activity, and areas that tolerate polar interactions. The role of MAO in neurodegenerative processes such as Parkinson's Disease has been recognized for some time. The structurally unique parkinsonian inducing substrate 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is bioactivated to neurotoxic metabolites. The mechanism of neurotoxicity has been studied extensively and it is known that MAO-B catalyzes the conversion of MPTP to the 2,3-dihydro-1-methyl-4-phenylpyridinium species (MPDP+) which undergoes further oxidation to the neurotoxic metabolite 1-methyl-4-phenyl pyridnium (MPP+). However, the role of MAO-A in mediating a neurotoxic response, has not been fully defined due to the lack of selective MAO-A substrates. In this thesis, we have investigated the neurotoxic potential of several tetrahydropyridines in C57Bl/6 mice and the ability of selective inhibitors to protect against the expression of MAO mediated neurotoxicity. Ph. D.

Published
1998

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