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PubMed2004

Comparison of styrene-divinylbenzene-based monoliths and Vydac nano-liquid chromatography columns for protein analysis.

This report details the fabrication of polystyrene-based nano-LC monolithic columns for the separation of protein molecules. The report focuses on the practical advantages of monolithic columns when compared to conventional packed columns. Capillary columns were made to 100 and 50 microm i.d. and used to analyse a mixture of proteins, these separations were then compared with a conventional protein phase under the same conditions. A second functionalised monolithic polystyrene-based column was also manufactured and compared for the analysis of proteins, under the same analytical conditions, to the standard non-functionalised bare polystyrene monolith. Nano-LC polystyrene monolithic columns were found to be advantageous to conventional phases for the analysis of protein molecules, with a one-step fabrication process, faster analysis times, lower limits of detection hence higher sensitivity.

Chromatography, Liquid↗
PubMed2004

Enantioseparation of amino acid derivatives on an immobilized network polymer derived from L-tartaric acid.

Seven structurally related amino acid derivatives were successfully enantioseparated by HPLC with a commercially available column containing a chiral immobilized network polymer derived from L-tartaric acid. The experiments were carried out under normal-phase conditions. All the solutes could be baseline separated using n-hexane/2-propanol (95/5) as eluent at a flow rate of 1 ml/min at 25 degrees C, with reasonable retention time (<12 min). The effects of the polar alcohol modifier (type and content) in the mobile phase and the column temperature on the enantioseparation were studied. Apparent thermodynamic parameters were also calculated from the plots of ln alpha or ln k' versus 1/T. Some mechanistic aspects of chiral recognition were discussed with respect to the structures of the solutes. It was found that the enantioseparations are all enthalpy driven, and the N-acyl groups of the solutes have significant influence on the chiral recognition.

Alcohols↗
PubMed2005

Highly porous solid-phase microextraction fiber coating based on poly(ethylene glycol)-modified ormosils synthesized by sol-gel technology.

The preparation and characteristics of solid-phase microextraction (SPME) fibers coated with Carbowax 20M ormosil (organically modified silica) are described here. Raw fused silica fibers were coated with Carbowax 20M-modified silica using sol-gel process. Scanning electron micrographs of fibers revealed a highly porous, sponge-like coating with an average thickness of (8 +/- 1) microm. The sol-gel Carbowax fibers were compared to commercial fibers coated with 100 microm polydimethylsiloxane (PDMS) and 65 microm Carbowax-divinylbenzene (DVB). Shorter equilibrium times were possible with the sol-gel Carbowax fiber: for headspace extraction of the test analytes, they ranged from less than 3 min for benzene to 15 min for o-xylene. Extraction efficiencies of the sol-gel Carbowax fiber were superior to those of conventional fibers: for o-xylene, the extracted masses were 230 and 540% of that obtained with 100 microm PDMS and 65 microm Carbowax-DVB fibers, respectively.

Benzene↗
PubMed2005

Solid-phase microextraction for qualitative and quantitative determination of migrated degradation products of antioxidants in an organic aqueous solution.

Low molecular weight aromatic substances may migrate out from plastic packaging to their contents, especially if they consist of organic aqueous solutions or oils. It is, therefore, extremely important to be able to identify and quantify any migrated substances in such solutions, even at very low concentrations. We have in this work investigated and evaluated the use of solid-phase microextraction for the specific task of extraction from an organic aqueous solution such as a simulated pharmaceutical solution consisting of 10 vol.% ethanol in water. The goal was furthermore to investigate the possibility of simultaneously identifying and quantifying the substances in spite of differences in their chemical structures. Methods were developed and evaluated for extraction both with direct sampling and with headspace sampling. Difficulties appeared due to the ethanol in the solution and the minute amounts of substances present. We have shown that a simultaneous quantification of migrated low molecular weight degradation products of antioxidants using only one fibre is possible if the extraction method and temperature are adjusted in relation to the concentration levels of the analytes. Comparions were made with solid-phase extraction.

Antioxidants↗
PubMed2006

Analyte-stationary phase interactions in ion-exclusion chromatography.

The currently accepted analyte-stationary phase interactions occurring in ion-exclusion chromatography are re-examined. In particular, the requirement for the existence of a Donnan membrane separating the flowing, interstitial eluent from the static, occluded, liquid acting as the stationary phase is scrutinized, together with the role of hydrophobic adsorption effects in the retention of aromatic analytes. Plots showing the interconversion of the column between the analyte and eluent forms are used to highlight some shortcomings of the currently accepted mechanism for ion-exclusion chromatography. An alternative retention mechanism for ion-exclusion chromatography is proposed, based on the presence of a potential well at the surface of the fully functionalized styrene-divinylbenzene co-polymer stationary phase. Analytes diffuse into the potential well under the effects of concentration gradients, and undergo repulsion effects from the fixed charges inside the pores. The net contributions of these two opposing processes determine the degree to which an analyte is retained on the stationary phase. Negligible hydrophobic adsorption of the analyte onto the polymeric resin supporting the stationary phase is considered to occur.

Acetic Acid↗
PubMed2006

Monolithic poly(p-methylstyrene-co-1,2-bis(p-vinylphenyl)ethane) capillary columns as novel styrene stationary phases for biopolymer separation.

Novel monolithic capillary supports (200 microm I.D.) were prepared by polymerisation of methylstyrene (MS) and 1,2-bis(p-vinylphenyl)ethane (BVPE) as a crosslinker in the presence of inert diluents (porogens). These polymeric reversed-phases (MS/BVPE) showed excellent mechanical stability and minimised swelling in organic solvents. The chromatographic potential of monolithic MS/BVPE as a stationary phase for micro-high-performance liquid chromatography (mu-HPLC) was investigated by the separation of proteins and peptides applying reversed-phase (RP) and nucleic acids applying ion-pair reversed-phase (IP-RP) conditions. The permeability and chromatographic efficiency of the capillary columns were found to be highly influenced by the total monomer to porogen content as well as by the microporogen nature and its ratio. In the course of these optimisation studies, monoliths covering a broad permeability range were fabricated. The application of volumetric flow rates up to 200 microl/min allowed swift resolution of proteins, while smaller biomolecules were successfully separated at a higher overall porosity. A protein test mixture containing ribonuclease A, cytochrome c, alpha-lactalbumin, beta-lactoglobulin B and ovalbumin was thus baseline separated in 35s, a homologous series of phosphorylated oligothymidylic acids [d(pT)12-18] in less than 2 min.

Biopolymers↗
PubMed2005

Adsorption behaviors of poly(N-p-vinylbenzyl-4-o-beta-d-galactopyranosyl-[1-->4]-d-gluconamide) by quartz-crystal microbalance.

Adsorption behaviors of amphiphilic poly(N-p-vinylbenzyl-4-o-beta-d-galactopyranosyl-[1-->4]-d-gluconamide) (PVLA) on the polystyrene (PS) surface was studied using 27 MHz quartz-crystal microbalance (QCM). The amount of adsorbed PVLA on PS surface was increased with an increase of PVLA concentration as a Langmuir-type in a monolayer. The saturated mass change (DeltaM(max)) and association constant (K(a)) of PVLA on PS surface were 498.6 ng/cm(2) and 1.93 x 10(7)M(-1), respectively. The adsorbed PVLA on PS surface was specifically recognized by Allo A lectin due to specific interaction between galactose moieties in the PVLA and Allo A. The hydrophobic interaction between hydrophobic main chain of PVLA and hydrophobic surface of PS was reduced in the presence of urea and the diameter of PVLA aqueous solution was decreased with an increase of urea concentration.

Adsorption↗
PubMed2005

Influence of hydrophobe on the release behavior of vinyl acetate miniemulsion polymerization.

Poly(vinyl acetate) (PVAc) nanoparticles containing antibiotic have been prepared by miniemulsion polymerization. To compare the effect of hydrophobe types, hexadecane and poly(vinyl acetate) were used as hydrophobe. The particle characteristics as the manufacturing condition were examined by particle size analyzer. As a result, the diameter of PVAc latexes was adjusted between 80 and 260 nm by homogenization conditions and amounts of surfactant. Also, the miniemulsion by using hexadecane showed the more long shelf stability and led to the more small particle size after polymerization, as compared with the case of using poly(vinyl acetate). This indicated that the use of poly(vinyl acetate) as a hydrophobe could not make the stable emulsion, but it could avoid volatile organic chemical problems in the final product. From the release profile of drug through UV spectra, the drug release was very slow and it could be seen that the release of drug encapsulated with PVAc was occurred with the polymer degradation.

Drug Carriers↗
PubMed2004

The effect of a 3-methacryloxypropyltrimethoxysilane and vinyltriisopropoxysilane blend and tris(3-trimethoxysilylpropyl)isocyanurate on the shear bond strength of composite resin to titanium metal.

OBJECTIVES: The aim of this study was to evaluate the reactions of silanes prior to attaching the composite to titanium and evaluate these silanes as coupling agents. Veneered titanium may be used as a prosthetic material. METHODS: Two silane solutions, a mixture of both gamma-methacryloxypropyltrimethoxysilane and vinyltriisopropoxysilane, and tris(3-trimethoxysilylpropyl)isocyanurate were prepared as 2 wt% in two different (95% 2-propanol and 90% acetone) solutions. A control, 2 wt% gamma-methacryloxypropyltrimethoxysilane was prepared in both solutions. These six silane solutions were applied onto flat titanium surfaces. The samples (N = 250) were divided into two main groups: air-dried (room temperature) and heat cured for 1 h at 110 degrees C. Sinfony veneering composite was applied and light-cured on the titanium. The control group was non-silanized. The specimens were assigned to two subgroups: not thermocycled, and thermocycled (5000 cycles, 5-55 degrees C). Shear bond strength of the composite was tested at a crosshead speed of 1.0 mm min(-1). Fresh silane solution hydrolysis, and condensation reaction on titanium surface were monitored by FTIR spectrometry. RESULTS: Dry samples could be successfully tested, while thermocycling after 3700 cycles had gradually de-bonded the composite from the silanized titanium substrate. For dry samples, statistical analysis (ANOVA) showed that solvent and silane significantly affected the shear bond strength. The silane mixture in 2-propanol reacted at room temperature yielded 11.3 MPa (Standard deviation, SD, 3.6 MPa) and on the other hand, tris(3-trimethoxysilylpropyl)isocyanurate in 2-propanol yielded 10.7 MPa (SD 8.0 MPa) and gamma-methacryloxypropyltrimethoxysilane 20.4 MPa (SD 12.2 MPa). Non-silanized samples yielded 4.8 MPa (SD 2.1 MPa). SIGNIFICANCE: In all solvents used, silanes reacted chemically with the titanium surface and covalent Si-O-Ti- and -Si-O-Si- bonds were evident.

Analysis of Variance↗
PubMed2004

A preliminary study of experimental polyacid-modified composite resins ('compomers') containing vinyl phosphonic acid.

OBJECTIVES: The aim of this investigation was to determine the properties of two novel compomers formulated with the monomer vinyl phosphonic acid (VPA). The setting properties, mechanical strength, wear characteristics and fluoride release of two experimental unshaded compomers containing VPA were determined, and compared with the commercial compomer Dyract A (shade C3). METHODS: Two novel compomers were prepared, containing, respectively, 0.24% (A) and 2.31% (B) by mass of VPA, and an appropriate amount of reactive glass filler. Their properties were compared with those of Dyract AP (shade A3). Depth of cure was determined according to the method of ISO 4049. Polymerization of model mixtures of bisGMA, TEGDMA and VPA was studied using FT Raman spectroscopy, by comparing the absorption at 1608cm(-1) (aromatic C-C bond) with that at 1313cm(-1) (CC aliphatic). Compressive and biaxial flexure strengths were determined for sets of 6 specimens stored either wet or dry. Wear was determined using a toothbrushing machine and an abrasive slurry, and fluoride release was determined following up to 6 weeks storage in aqueous media, using a fluoride-selective electrode. RESULTS: Of the model monomer mixtures, the one with the greater quantities of VPA showed lowest degrees of polymerization after irradiation for 40s. Compomer A had an acceptable depth of cure, and similar properties to Dyract AP in terms of compressive and biaxial flexure strength, and also fluoride release. Resistance to toothbrush abrasion of both of the experimental compomers was superior to that of Dyract AP. SIGNIFICANCE: These studies demonstrate that VPA can be used as the active monomer in experimental compomers, and is capable of yielding materials with properties equivalent to a commercial material, but with improved resistance to toothpaste abrasion. The level of VPA in the formulation is critical, because this monomer inhibits addition polymerization, hence must be used only in small amounts.

Analysis of Variance↗
PubMed2005

Volume contraction in photocured dental resins: the shrinkage-conversion relationship revisited.

UNLABELLED: Polymerization shrinkage and degree of conversion (DC) of resin composites are closely related manifestations of the same process. Ideal dental composite would show an optimal degree of conversion and minimal polymerization shrinkage. These seem to be antagonistic goals, as increased monomer conversion invariably leads to high polymerization shrinkage values. OBJECTIVES: This paper aims at accurately determining the polymerization volume contraction of experimental neat resins and to link it to the number of actual vinyl double bonds converted in single ones instead of, as generally done, to the degree of conversion. METHODS: Different mixtures of Bis-GMA/TEGDMA (traditionally used monomers) were analyzed. Contraction of the polymers was determined by pycnometry and the use of a density column. DC was determined by the use of Raman spectrometry. RESULTS: An univocal relationship has been found between the volume contraction and the actual number of vinyl double bonds converted into single ones. A contraction value of 20.39 cm3/mole (of converted C=C) was deduced from 27 measurements. SIGNIFICANCE: This relationship helps in finding solutions to the polymerization shrinkage problem. A reduction of the polymerization shrinkage due to the chemical reaction may obviously be expected from the addition of molecules allowing a decrease in the number of double bonds converted per unit volume of resin matrix, while maintaining the degree of conversion (of Bis-GMA and TEGDMA) and thus the mechanical properties. Further research will be directed at this objective.

Bisphenol A-Glycidyl Methacrylate↗
PubMed2005

Interphase structure-property relationships in thermoset dimethacrylate nanocomposites.

OBJECTIVES: The aim of this research was to better understand the relationships between interphase composition and the resultant mechanical properties of thermoset methacrylate nanocomposites, ultimately for the purpose of improving the properties of dental restorative materials through manipulation of the interphase. METHODS: Silica nanoparticles were silanized with three different silanes and blends of those silanes to generate six different interphase compositions. The silanes varied in their relative polarity, flexibility, and reactivity towards photo-polymerization. Composites containing 60% by mass of the silanized fillers were prepared and analyzed for uncured paste handling characteristics, vinyl conversion, biaxial flexure strength (BFS), modulus, and Knoop hardness. RESULTS: Dual silanization of the fillers improved the handling characteristics of the uncured composite pastes compared to those containing fillers silanized with 3-methacryloxypropyltrimethoxysilane. To obtain high BFS, functional groups reactive in free radical polymerization were needed in the composite interphase, but a high concentration of those groups was not necessary. Moduli were highest for composites with interphases that contained styrylethyltrimethoxysilane, a reactive aromatic silane. The hardness values of the composites with reactive interphases were all comparable. Methacrylate conversion was only modestly influenced by silane interphase composition. SIGNIFICANCE: This study suggests that dual silanization is a practical method for improving the handling characteristics of uncured dental restorative nanocomposites while maintaining or improving the mechanical properties of the cured composites.

Chemical Phenomena↗
PubMed2005

The effect of pressurized carbon dioxide as a temporary plasticizer and foaming agent on the hot stage extrusion process and extrudate properties of solid dispersions of itraconazole with PVP-VA 64.

The aim of the current research project was to explore the possibilities of combining pressurized carbon dioxide with hot stage extrusion during manufacturing of solid dispersions of itraconazole and polyvinylpyrrolidone-co-vinyl acetate 64 (PVP-VA 64) and to evaluate the ability of the pressurized gas to act as a temporary plasticizer as well as to produce a foamed extrudate. Pressurized carbon dioxide was injected into a Leistritz Micro 18 intermeshing co-rotating twin-screw melt extruder using an ISCO 260D syringe pump. The physicochemical characteristics of the extrudates with and without injection of carbon dioxide were evaluated with reference to the morphology of the solid dispersion and dissolution behaviour and particle properties. Carbon dioxide acted as plasticizer for itraconazole/PVP-VA 64, reducing the processing temperature during the hot stage extrusion process. Amorphous dispersions were obtained and the solid dispersion was not influenced by the carbon dioxide. Release of itraconazole from the solid dispersion could be controlled as a function of processing temperature and pressure. The macroscopic morphology changed to a foam-like structure due to expansion of the carbon dioxide at the extrusion die. This resulted in increased specific surface area, porosity, hygroscopicity and improved milling efficiency.

Acrylates↗
PubMed2005

Recent female mouse models displaying advanced reproductive aging.

Reproductive senescence occurs in all female mammals with resultant changes in numerous body functional systems and several important features may be species-specific. Those features that appear to parallel human menopause and aging include general similarity of hormone profiles across the menopausal transition, progression to cycle termination through irregular cycles, declining fertility with age, disturbances in thermogenesis, age-related gains in body weight, fat distribution and disposition towards metabolic syndrome. Structural and hormonal changes in the brain and ovary play a critical role in determining the onset of reproductive senescence. The short life span of rodents such as mice (compared to humans) and the ability to generate specific and timed gene deletions, provide powerful experimental paradigms to understand the molecular and functional changes that precede and follow the loss of reproductive capacity. In theory, any manipulation that compromises ovarian function either partly or totally would impact reproductive events at various levels followed by other dysfunctions. In this article, we provide an overview of three mouse models for the study of female reproductive aging. They are derived from different strategies and their age related phenotypes have been characterized to varying degrees. The follitropin receptor knockout (FORKO) mouse, in its null and haploinsufficient state as well as the dioxin/aryl hydrocarbon receptor (AhR) knockout mouse, serve as two examples of single gene deletions. A third model, using administration of a chemical toxicant such as 4-vinylcyclohexene diepoxide (VCD) in the adult state, produces ovarian deficiencies accompanied by aging changes. These will serve as useful alternatives to previously used radical ovariectomy in young adults. It is anticipated that these new models and more that will be forthcoming will extend opportunities to understand reproductive aging and resolve controversies that abound on issues related to benefits and risks of hormone replacement therapy or other modalities for improving quality of life.

Aging↗
PubMed2005

Inhibition of diethyl ether degradation in Rhodococcus sp. strain DEE5151 by glutaraldehyde and ethyl vinyl ether.

Alkyl ether-degrading Rhodococcus sp. strain DEE5151, isolated from activated sewage sludge, has an activity for the oxidation of a variety of alkyl ethers, aralkyl ethers and dibenzyl ether. The whole cell activity for diethyl ether oxidation was effectively inhibited by 2,3-dihydrofurane, ethyl vinyl ether and glutaraldehyde. Glutaraldehyde of less than 30 microM inhibited the activity by a competitive manner with the inhibition constant, K(I) of 7.07+/-1.36 microM. The inhibition type became mixed at higher glutaraldehyde concentrations >30 microM, probably due to the inactivation of the cell activity by the Schiff-base formation. Structurally analogous ethyl vinyl ether inhibited the diethyl ether oxidation activity in a mixed manner with decreasing the apparent maximum oxidation rate, v(max)(app), and increasing the apparent Michaelis-Menten constant, K(M)(app). The mixed type inhibition by ethyl vinyl ether seemed to be introduced not only by the structure similarity with diethyl ether, but also by the reactivity of the vinyl ether with cellular components in the whole cell system.

Biodegradation, Environmental↗
PubMed2006

Destruction of primordial ovarian follicles in adult cynomolgus macaques after exposure to 4-vinylcyclohexene diepoxide: a nonhuman primate model of the menopausal transition.

OBJECTIVE: To determine whether the 4-vinylcyclohexene diepoxide (VCD)-treated mouse menopause model, which involves accelerated atresia of primordial follicles and induces gradual ovarian failure (while sparing the ovarian stroma), can be adapted to nonhuman primates. DESIGN: Controlled periclinical trial (nonhuman primates). SETTING: Comparative Medicine Clinical Research Center. ANIMAL(S): Four adult female cynomolgus monkeys. INTERVENTION(S): Once-daily i.m. injections for 15 days as follows: vehicle or VCD doses of 80 mg/kg, 160 mg/kg, 250 mg/kg. Ovaries were removed 27 days after treatment, and pathological determinations were made at necropsy. MAIN OUTCOME MEASURE(S): Baseline and interim hematologic and biochemical measures, physical exams, and body weights. Follicle counts and organ evaluation at necropsy. RESULT(S): A nearly complete elimination of primordial, intermediate, primary and secondary follicles was achieved with 250 mg/kg VCD. A 50% reduction in primordial and primary follicles was observed with 160 mg/kg VCD. No effect of 80 mg/kg VCD per day was observed. Clinical health measures remained within normal range except for transient, mild increases in liver enzymes and an inflammatory response at the injection site with 250 mg/kg. Postmortem evaluations (9 months) revealed no gross or histological lesions in the organs studied. CONCLUSION(S): These results demonstrate that the monkey ovary is susceptible to VCD and that as in rodents, primordial and primary follicles are targeted selectively.

Animals↗
PubMed2004

Enhanced transdermal delivery of atenolol from the ethylene-vinyl acetate matrix.

To enhance transdermal delivery of atenolol, ethylene-vinyl acetate (EVA) matrix of drug containing penetration enhancer was fabricated. Effect of penetration enhancer on the permeation of atenolol through the excised rat skin was studied. Penetrating enhancers showed the increased flux probably due to the enhancing effect on the skin barrier, the stratum corneum. Among enhancers used such as glycols, fatty acids and non-ionic surfactants, polyoxyethylene 2-oleyl ether showed the best enhancement. For the controlling transdermal delivery of atenolol, the application of EVA matrix containing permeation enhancer could be useful in the development of transdermal drug delivery system.

Administration, Cutaneous↗
PubMed2004

Release kinetics of bovine serum albumin from pH-sensitive poly(vinyl ether) based hydrogels.

pH-Sensitive amphiphilic hydrogels were synthesized by radiation copolymerization of ethylene glycol vinyl ether (EGVE), butyl vinyl ether (BVE) and acrylic acid (AA) in the presence of crosslinking agent, diethylene glycol divinyl ether (DEGDVE). The results of the swelling experiments indicated that the hydrogel which has 60:40:5 comonomer ratio (mol% of EGVE:BVE:AA in monomeric mixture) is pH-sensitive. While the hydrogel is in a fully hydrated form at pH>6, it extensively dehydrates below pH 6. A two-stage volume phase transition was observed in the range of pH 6.0-7.0 and 7.5-8.0. In addition, the equilibrium water contents of the gels decreased with increasing temperature from 4 to 37 degrees C by following the non-Fickian diffusion mechanism. The utility of pH-sensitive gels in delivery of protein based drugs was investigated. Bovine serum albumin (BSA) loaded gels were prepared and protein release was examined by fluorescence spectroscopy in the range of pH 2-9. While the protein release was very low at pH 2, readily high amount of BSA were released at pH>6. It was concluded that the pH-sensitive EGVE-BVE-AA terpolymers may be suitable for the oral administration of protein based drugs as a carrier through gastrointestinal (GI) tract.

Animals↗