Monolithic bed structure for capillary liquid chromatography

Monolithic stationary phases show promise for LC as a result of their good permeability, ease of preparation and broad selectivity. Inorganic silica monoliths have been extensively studied and applied for separation of small molecules. The presence of a large number of through pores and small skeletal structure allows the chromatographic efficiencies of silica monoliths to be comparable to columns packed with 5 μm silica particles, at much lower back pressure. In comparison, organic polymeric monoliths have been mostly used for separation of bio-molecules; however, recently, applications are expanding to small molecules as well. Organic monoliths with high surface areas and fused morphology rather than conventional globular morphology have shown good performance for small molecule separations. Factors such as domain size, through-pore size and mesopore size of the monolithic structures have been found to govern the efficiency of monolithic columns. The structure and performance of monolithic columns are reviewed in comparison to particle packed columns. Studying and characterizing the bed structures of organic monolithic columns can provide great insights into their performance, and aid in structure-directed synthesis of new and improved monoliths.     

Methyl 4-toluenesulfonyloxymethylphosphonate, a new and versatile reagent for the convenient synthesis of phosphonate-containing compounds

A straightforward procedure leading to the new phosphonylating reagent, methyl 4-toluenesulfonyloxymethylphosphonate, requiring no chromatographic purification is described. This stable reagent works with the same efficiency as dimethyl and other dialkyl esters for the introduction of an O-phosphonomethyl moiety while, in contrast to dimethyl ester, it does not cause any unwanted methylation of sensitive functionalities. Its utility for the alkylation of protected nucleosides in high yield is exemplified.     

Immobilization in biotechnology and biorecognition: from macro- to nanoscale systems

Biological molecules such as enzymes, cells, antibodies, lectins, peptide aptamers, and cellular components in an immobilized form are extensively used in biotechnology, in biorecognition and in many medicinal applications. This review provides a comprehensive summary of the developments in new immobilization materials, techniques, and their practical applications previously developed by the authors. A detailed overview of several immobilization materials and technologies is given here, including bead cellulose, encapsulation in ionotropic gels and polyelectrolyte complexes, and various immobilization protocols applied onto surfaces. In addition, the review summarises the screening and design of an immobilization protocol, practical applications of immobilized biocatalysts in the industrial production of metabolites, monitoring, and control of fermentation processes, preparation of electrochemical/optical biosensors and biofuel cells.     

Statistical Examination of the <Emphasis Type="Italic">a</Emphasis> and <Emphasis Type="Italic">a</Emphasis> + 1 Fragment Ions from 193 nm Ultraviolet Photodissociation Reveals Local Hydrogen Bonding Interactions

Dissociation of proteins and peptides by 193 nm ultraviolet photodissociation (UVPD) has gained momentum in proteomic studies because of the diversity of backbone fragments that are produced and subsequent unrivaled sequence coverage obtained by the approach. The pathways that form the basis for the production of particular ion types are not completely understood. In this study, a statistical approach is used to probe hydrogen atom elimination from a + 1 radical ions, and different extents of elimination are found to vary as a function of the identity of the C-terminal residue of the a product ions and the presence or absence of hydrogen bonds to the cleaved residue.

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A new controlled release system of chlorhexidine and chlorhexidine:βcd inclusion compounds based on porous silica

The purpose of this study was to prepare and characterize a controlled release system based on porous silica loaded with chlorhexidine (Cx) and its inclusion compounds in β-cyclodextrin (βcd), and to evaluate its antimicrobial activity. Acetate chlorhexidine (CxA), gluconate chlorhexidine (CxG), βcd:chlorhexidine acetate 2:1 (βcd:CxA) and βcd:chlorhexidine gluconate 2:1 (βcd:CxG) were incorporated into porous silica. Drug loading was characterized by FTIR, powder X-ray diffraction, thermal analysis and BET, and was shown to be in an amorphous state and porous matrix. The kinetics release parameter of the drug was established, which showed that the Cx systems release profile followed zero order release until 400 h and Higuchi model release until 750 h, after the burst effect at the first 8 h. Chlorhexidine therapeutic range was reached near first hour for all systems. The chlorhexidine porous silica system was biologically active against Enterococcus faecalis and Candida albicans in vitro. The systems showed an efficient Cx controlled release modulated by the presence of the β-cyclodextrin and by the porous silica matrices, providing effective antimicrobial activity.     

Phenylurethans of pyrazolidinols and piperidazinols as anticonvulsants

The synthesis of 1,2-diethyl-4-hydroxymethylpyrazolidine ( II ) was accomplished in two steps from 1,2-diethyl-4-ethoxycarbonylpyrazolidine ( I ). Also, 1,2-dimethyl-4-hydroxypiperidazine ( VI ) was prepared in three steps from 1,2-diethoxycarbonyl-1,2,3,6-tetrahydropyridazine ( IV ). The two alcohols were added to several aryl isocyanates and afforded fourteen new phenylurethan derivatives which showed moderate anticonvulsant activity in mice.     

Preparation and evaluation of hydrophilic C18 monolithic sorbents for enhanced polar compound retention in liquid chromatography and solid phase extraction

Hydrophilic C18 monolithic polymer sorbents were synthesized for use in solid phase extraction (SPE) and in capillary liquid chromatography (LC). The approach involved incorporating both hydrophobic and hydrophilic monomers into a monolithic material, by copolymerization of stearyl methacrylate (SMA), poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) and ethylene dimethacrylate (EDMA) in the presence of selected porogens, to produce translucent mesoporous monolithic materials in bulk (SPE) or white macroporous monoliths inside fused silica capillary columns (capillary LC). A capillary column containing one of the hydrophilic C18 monoliths (i.e. poly(SMA-co-PEGMEMA-co-EDMA) with 15% (w/w) PEGMEMA) demonstrated nearly 35% reduction in retention of polycyclic aromatic compounds and greater than 40% increase in retention of phenols compared to a hydrophobic C18 monolithic column. In addition, the hydrophilic monolith demonstrated significantly improved resolution of phenols. Similar monolithic materials prepared in bulk were ground and sieved to obtain 45-65 μm particles with desired rigidity for SPE. To achieve optimum extraction performance for phenols, several parameters, including sample pH and volume, and eluent type and volume, were investigated. Under optimized experimental conditions, the method demonstrated good sensitivity (1.6 ng/mL LOD) and linearity (R(2)>0.97 for 10-200 ng/mL). Again, incorporation of 15% (w/w) PEGMEMA in the monolith increased the extraction efficiency of phenols in water from approximately 20% to 67-92% compared to a hydrophobic C18 monolithic material. Increased wettability of the sorbent by the aqueous sample matrix and the presence of hydrogen-bonding interactions are responsible for the improved retention of polar compounds.     

Surfactant addition and alternating current electrophoretic oscillation during size fractionation of nanoparticles in channels with two or three different height segments

An array of parallel planar nanochannels containing two or three segments with varying inner heights was fabricated and used for size fractionation of inorganic and biological nanoparticles. A liquid suspension of the particles was simply drawn through the nanochannels via capillary action. Using fluorescently labeled 30 nm polyacrylonitrile beads, different trapping behaviors were compared using nanochannels with 200-45 nm and 208-54-30 nm height segments. Addition of sodium dodecyl sulfate (SDS) surfactant to the liquid suspension and application of an AC electric field were shown to aid in the prevention of channel clogging. After initial particle trapping at the segment interfaces, significant particle redistribution occurred when applying a sinusoidal 8V peak-to-peak oscillating voltage with a frequency of 150 Hz and DC offset of 4V. Using the 208-54-30 nm channels, 30 nm hepatitis B virus (HBV) capsids were divided into three fractions. When the AC electric field was applied to this trapped sample, all of the virus particles passed through the interfaces and accumulated at the channel ends.     

Effect of colloidal particle size on adsorbed monodisperse and bidisperse monolayers

Coating hydrogel films or microspheres by an adsorbed colloidal shell is one synthesis method for forming colloidosomes. The colloidal shell allows control of the release rate of encapsulated materials, as well as selective transport. Previous studies found that the packing density of self-assembled, adsorbed colloidal monolayers is independent of the colloidal particle size. In this paper we develop an equilibrium model that correlates the packing density of charged colloidal particles in an adsorbed shell to the particle dimensions in monodisperse and bidisperse systems. In systems where the molar concentration in solution is fixed, the increase in adsorption energy with increasing particle size leads to a monotonic increase in the monolayer packing density with particle radius. However, in systems where the mass fraction of the particles in the adsorbing solutions is fixed, increasing particle size also reduces the molar concentration of particles in solution, thereby reducing the probability of adsorption. The result is a nonmonotonic dependence of the packing density in the adsorbed layer on the particle radius. In bidisperse monolayers composed of two particle sizes, the packing density in the layer increases significantly with size asymmetry. These results may be utilized to design the properties of colloidal shells and coatings to achieve specific properties such as transport rate and selectivity.