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At least 91 records · Page 5Linked to original sources
PubMed2006

Capillary electrochromatography with monolithic silica columns. V. Study of the electrochromatographic behaviors of polar compounds on monolithic silica having surface bound cyano functionalities.

In this report, a novel polar monolithic capillary column is described for normal phase CEC (NP-CEC) of representative polar compounds including mono- and oligosaccharides, peptides, and basic drugs. The polar monolithic column, which was described in detail in the preceding paper, consisted of silica-based monolith bonded with 1H-imidazole-4,5-dicarbonitrile (IDCN) and is denoted as 2CN-OH-Monolith. Various retention parameters for neutral polar solutes (e.g., mono- and oligosaccharides) and charged polar solutes (e.g., peptides and basic drugs) were evaluated over a wide-range of elution conditions. These retention parameters yielded quantitative assessment for the polar interactions between the model solutes and the stationary phase under investigation as well as the effect of electromigration of charged solutes on their overall migration in NP-CEC. Furthermore, this investigation demonstrated that despite the possibility of achieving isocratic separation in NP-CEC for widely differing polar species, multistep-gradient elution in NP-CEC is preferred to bring about the rapid separation of a large number of polar species in a single run.

Journal Article↗
PubMed1999

Respirable crystalline silica exposure associated with the installation and removal of RCF and conventional silica-containing refractories in industrial furnaces.

Installation and removal of conventional refractories and refractory ceramic fiber (RCF) in industrial furnaces may lead to occupational exposure to respirable crystalline silica (including quartz, cristobalite, and tridymite). Exposure to elevated concentrations of these materials has been linked to adverse respiratory effects, including silicosis and lung cancer. Unlike conventional refractories, RCF does not contain any of these materials as produced. However, depending upon time and temperature during the service life of the insulation, RCF may partially devitrify, creating the potential for exposure upon removal of after-service insulation. For removal of after-service RCF, exposure data collected as part of a 5-year consent agreement with EPA are presented and analyzed. Because of relatively low concentrations of these materials, limitations on the sensitivity of the analytical method, and the relatively short duration of furnace removal activities, many measurements are less than the limits of detection (LODs), creating challenges for data analysis. Several methods of analysis of censored data are illustrated and the theory of maximum likelihood estimates is generalized to cover the case of multiple LODs. Average exposures to these materials associated with removal of after-service RCF are compared to those in various industries.

Administration, Inhalation↗
PubMed1987

Evaluation of advanced silica packings for the separation of biopolymers by high-performance liquid chromatography. IV. Mobile phase and surface-mediated effects on recovery of native proteins in gradient elution on non-porous, monodisperse 1.5-microns reversed-phase silicas.

The reversed-phase chromatography of proteins by gradient elution with acidic, low-ionic-strength aqueous-organic eluents is often associated with losses of the biological activity of the protein. In this study, the enzymatic activities of catalase, horseradish peroxidase and pepsin were examined under static and dynamic column conditions on non-porous, monodisperse 1.5-microns reversed-phase silicas with various n-alkyl ligands. Catalase readily lost its enzymatic activity under the influence of the acidic aqueous-organic eluents in the absence of the reversed-phase packing, whereas peroxidase was partially deactivated as a result of combined mobile phase and stationary phase effects but regained its activity on storage after elution. The enzymatic activity of pepsin was found to be very dependent on the column residence time and on the type of bonded n-alkyl ligand employed.

Catalase↗
PubMed1989

Displacement chromatography on cyclodextrin-silicas. II. Separation of cis-trans isomers in the reversed-phase mode on alpha-cyclodextrin-silica.

The feasibility of preparative separations of cis-trans isomers by displacement chromatography on analytical-scale alpha-cyclodextrin-silica columns operated in the reversed-phase mode is demonstrated by using the isomers of 3-hexen-1-ol as model substrates and n-alkanols as displacers. The importance of matching the size of the cyclodextrin cavity and the solutes is shown. The crucial role of the displacer (both type and concentration) in the success of the displacement chromatographic separation is demonstrated.

Chromatography, Liquid↗
PubMed1989

Evaluation of advanced silica packings for the separation of biopolymers by high-performance liquid chromatography. VI. Design, chromatographic performance and application of non-porous silica-based anion exchangers.

The linear solvent strength model of Snyder was applied to describe fast protein separations on 2.1-micron non-porous, silica-based strong anion exchangers. It was demonstrated on short columns packed with these anion exchangers that (i) a substantially higher resolution of proteins and nucleotides was obtained at gradient times of less than 5 min than on porous anion exchangers; (ii) the low external surface area of the non-porous anion exchanger is not a critical parameter in analytical separations and (iii) microgram-amounts of enzymes of high purity and full biological activity were isolated.

Biopolymers↗
PubMed2000

Near IR spectroscopy to quantify the silica content and difference between silicified microcrystalline cellulose and physical mixtures of microcrystalline cellulose and silica.

Silicified microcrystalline cellulose (SMCC) has been shown to have advantages over conventional microcrystalline cellulose (MCC). These advantages are (i) improved tablet strength compared to that achieved with MCC, (ii) the retention of compressibility after wet granulation, whereas MCC produces weaker tablets after wet granulation, and (iii) superior flow properties than MCC. In this study near IR spectroscopy has been used to study MCC, SMCC (with different loadings of colloidal silicon dioxide, CSD) and physical mixtures of MCC and CSD. It was found that even though SMCC and MCC were very similar, there was a region of the near IR spectra (second derivative peak at 2194 nm) where a distinctive response was seen for SMCC. The size of the peak was proportional to the CSD content for the co-processed SMCC samples. The peak was not present to the same extent for physical mixtures. A combination of near IR and a test for total silica content would make it possible to discern whether microcrystalline cellulose samples were SMCC material or simple physical mixtures.

Cellulose↗
PubMed2005

Graft polymerization from a silica surface initiated by adsorbed peroxide macroinitiators. I. Adsorption and structure of the adsorbed layer of peroxide macroinitiators on a silica surface.

The adsorption features of two peroxide macroinitiators (PMIs) with various functionalities from their semi-dilute solutions on the silica surface were thoroughly investigated in the present work. These investigations include the study of the adsorption kinetics of PMI in diverse solvents and a detailed examination of the adsorbed layer structure with the aid of ellipsometry, scanning force microscopy (SFM), and contact angle measurements. Rearrangements of PMI macromolecules at the solid surface are supposed to be the main reason for the appearance of extremes on the kinetic curves and, besides, have a more pronounceable effect on adsorption rate than their diffusion rate to the surface even at the initial stage of the process. Both island-like and densely packed structures of absorbed layers were revealed by combining contact angle measurements and SFM. Surprisingly, even in the case when saturation of the adsorbed layer is reached, PMI does not completely occupy the substrate surface which is at least particularly reachable for the wetting liquids. PMIs adsorbed at the solid surface are intended for the formation of tethered polymer "brushes" via the initiation of "grafting from" polymerization.

Journal Article↗
PubMed2006

Redox-active silica nanoparticles. Part 1. Electrochemistry and catalytic activity of spherical, nonporous silica particles with nanometric diameters and covalently bound redox-active modifications.

Nonporous spherical silica nanoparticles resulting from a controlled Stöber process are covalently surface modified with redox-active molecules. Ferrocene, a ruthenium(II) complex with an N2P2Cl2 ligand set, and a sterically hindered biphenylamine are used as modifiers. The resulting materials are characterized by physical, spectroscopic, electrochemical, and chemical methods. The cyclic voltammetric behavior is studied in detail and reveals effects of charge transport by electron hopping along the surface of particles adsorbed on a Pt electrode. The ruthenium(II) complex remains catalytically active with respect to hydrogenation upon immobilization on the particles. Thus, the respective material provides a heterogenized homogeneous hydrogenation catalyst on a solid support.

Adsorption↗
PubMed2006

From cluster to bulk: size dependent energetics of silica and silica-water interaction.

We present our computational investigations on the energetics of clusters that consist of H2O and SiO2 using first-principles Born-Oppenheimer molecular dynamics method. Cohesive energy and hydration energy of both pure (or dry) and hydroxylated (or wet) ring-structured clusters have been investigated as functions of system size. We have found clear trends of energy as the cluster size increases. Energetics of a small silica nano-rod that contains 108 atoms is also obtained as a middle reference point for size evolution. Results from cluster and nano-rod calculations are compared with values from bulk quartz calculations using the same level of theoretical treatments.

Journal Article↗
PubMed2001

"Cap-Tag"-Novel Methods for the Rapid Purification of Oligosaccharides Prepared by Automated Solid-Phase Synthesis Financial support from the donors of the Petroleum Research Fund, administered by the ACS (ACS-PRF 34649-G1), Merck (Predoctoral Fellowship for E.R.P.), Boehringer-Ingelheim (Predoctoral Fellowship for E.R.P.), and the NIH (Biotechnology Training Grant for M.C.H.) is gratefully acknowledged. Funding for the MIT-DCIF Inova 501 was provided by the NSF (Award CHE-9808061). Funding for the MIT-DCIF Avance (DPX) 400 was provided by the NIH (Award 1S10RR13886-01). We thank Silicycle (Quebec City, Canada) for the generous gift of fluorous silica gel and isocyanate silica gel scavenger resin. We thank Dr. O. Plante for helpful discussions and help with the automated oligosaccharide synthesizer.

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Journal Article↗