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Biomedical subjects

J L Koenig

Publications and source records attributed to J L Koenig.

At least 19 recordsLinked to original sources
PubMed2005

Regions of interest in FTIR imaging applications: diffusion of nicotine into ethylene-co-vinyl acetate films.

Effective image analysis of dynamic processes, such as diffusion and dissolution, requires precise reporting of component locations in space and time. An improved method for analyzing FTIR images is described which employs hypothesis testing in the spatial and temporal domains. Changes in the observed absorbance (over space and time) are revealed by comparison to a reference statistic, which can be tailored by choosing the size of a region of interest. This improved analysis method was used to compare the rates of diffusion of nicotine into poly(ethylene-co-vinyl acetate) film from aqueous solutions containing anionic and nonionic surfactants. Compared to a solution without surfactant, sodium dodecyl sulfate inhibited the uptake of nicotine from aqueous solution whereas Tween 40 enhanced the uptake. The nicotine diffusion rate also showed a dependence on the length of the hydrophobic segment of nonionic surfactants. These results demonstrate the roles of solubilization, wetting, and viscosity on diffusion-controlled drug release.

Diffusion↗
PubMed2001

FTIR images.

Explore the source record for details and available documents.

Journal Article↗
PubMed1997

Determination of water content in bovine lenses using near-infrared spectroscopy.

Near-infrared spectral data of bovine nuclear lens tissue was collected in the 3,500- to 6,500-cm(-1) frequency range. The intensity ratios of the water peak at 5,194 cm(-1) to characteristic protein peaks at 4,862, 4,599, and 4,368 cm(-1) were determined for the nucleus of bovine lens samples. The water and protein mass percentages were determined by using a calibration curve established by spectra obtained from aqueous solutions with various concentrations of bovine serum albumin. The bovine fetal nucleus was found to contain 61.2 +/- 1.6, 61.2 +/- 1.9, and 58.4 +/- 1.9 water using the ratio of the water peak intensity to each of the three characteristic protein peaks within each spectrum. These results are consistent with other analytical techniques, thus showing the accuracy of this technique for obtaining chemical information on lens tissue.

Animals↗
PubMed1995

Structure and regional water content of bovine, porcine, and human lenses examined with proton nuclear magnetic resonance imaging.

A proton nuclear magnetic resonance instrument with a 7-tesla field was used for nuclear magnetic resonance imaging (NMRI) to study bovine, porcine, and human lenses. The NMRI images show detailed changes in the water for normal and diseased tissues. The alterations in the nucleus and the cortex in relation to the health of the tissue are clearly illustrated.

Adult↗
PubMed1993

Cytogenetic evaluation of ova from pubertal and third-estrous gilts.

Cytogenetic characteristics of ova surgically recovered from 19 first-estrous (pubertal) gilts were compared with those from 24 third-estrous gilts. Mean percentage recovery of ova was 82.1 +/- 2.9%. A total of 159 and 203 ova from first- and third-estrous gilts, respectively, were evaluated. Gilts at first and third estrus ovulated more mature ova (metaphase I-II chromosomes visible) than immature ova (germinal vesicle stage through prometaphase stage), but the percentage of immature ova in gilts at first estrus was greater than in those at third estrus (33.1 vs. 24.1%, p < 0.06). Percentage of mature ova with a normal haploid complement of chromosomes was similar in gilts at first and at third estrus (52.7 vs. 47.5%, p > 0.10). Percentage of hyperploid ova did not differ between first- and third-estrous gilts (10.8 vs. 5.9%, respectively); however, estimated frequency of nondisjunction appeared greater for gilts at first than at third estrus (21.6 vs. 11.9%, p < 0.10). These data suggest that ova of first-estrous gilts are inferior in quality compared to those of cyclic gilts.

Animals↗
PubMed1990

1H magnetic resonance imaging study of bovine ocular tissue.

The present study used magnetic resonance imaging (MRI) to study bovine eyes using proton magnetic resonance at a 7-tesla field. The MRI images provide detailed structural information on various sections of the ocular tissues. Detailed images of the lens show several well-defined areas of water content. Relative rankings of various structures of the eye are obtained based on T1, T2 and spin density.

Animals↗
PubMed1986

F.t.-i.r. and laser-Raman spectra of cytosine and cytidine.

Fourier-transform infrared (F.t.-i.r.) and laser-Raman spectra of cytosine and cytidine in the solid state have been recorded and assignments of the frequencies made. Comparison of the observed frequencies for cytosine with those for cytidine permits identification of the bands characteristic of the sugar on the one hand, and of the pyrimidine base on the other.

Cytidine↗
PubMed1986

F.t.-i.r. and laser-Raman spectra of guanine and guanosine.

Fourier-transform infrared (F.t.-i.r.) and laser-Raman spectra have been obtained for solid guanine. The F.t.-i.r. spectrum of guanosine in the solid state was also recorded. Assignments are proposed for the i.r. bands. The molecular basis of the spectral differences between guanine and guanosine are discussed.

Fourier Analysis↗
PubMed1986

Characterization of protein adsorption on soft contact lenses. IV. Comparison of in vivo spoilage with the in vitro adsorption of tear proteins.

Tear protein and gamma-globulin mixtures were adsorbed on soft contact lenses of different chemical composition, surface quality and water content. The adsorption process was followed by Fourier transform infrared-attenuated total reflectance spectroscopy (ATR-FTIR). It was found that gamma-globulin underwent a conformational and orientational change after its adsorption and the extent of structural change appeared to be proportional to the binding strength of the protein with the hydrogel surface. Electrostatic interactions play a major role in the protein adsorption on lenses containing methacrylic acid. Lysozyme is selectively adsorbed on all of the high water content hydrogels and mucin is the major protein component for the pure PHEMA type of lenses. Studies on in vivo spoiled PHEMA and PVP/MMA lenses indicate that lysozyme is the major adsorbed deposit. Papain cleaning of in vivo spoiled lenses shows that although a portion of the deposits is desorbed, the enzyme itself becomes irreversibly adsorbed to the contact lens which may cause harmful effects to the eye.

Adsorption↗
PubMed1986

Protein adsorption on soft contact lenses. III. Mucin.

Adsorption of bovine submaxillary mucin (BSM) on three different soft contact surfaces, lathe cut (LC) and spin cast (SC) crosslinked poly-2-hydroxyethylmethacrylate and spin cast poly(2-hydroxyethylmethacrylate/methacrylic acid) (PHEMA/MAA), was studied. The in vitro process was followed by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). A three-layer structure is envisaged for the adsorbed BSM: a very thin surface layer of strongly bound and conformationally altered mucin constitutes the surface layer. A random to beta-sheet structural transition activated by the hydrogel surface is proposed for this layer. Glycoprotein hydrogen-bonding with the polymer hydroxyls and interaction of charged and hydrophobic groups with hydrogel surfaces are important in stabilizing this layer. Most of the adsorbed BSM (99%) is found in the middle and top layers which are formed by a different degree of associated BSM (their conformation is minimally changed or not changed at all, respectively) and are weakly adsorbed to the lens surfaces. Surface morphology and chemical composition of the lenses are important adsorption parameters only for the reversibly adsorbed BSM.

Adsorption↗
PubMed1985

Protein adsorption on hydrogels. II. Reversible and irreversible interactions between lysozyme and soft contact lens surfaces.

Lysozyme was adsorbed on spin cast and lathe cut soft contact lenses of poly-2-hydroxyethylmethacrylate (PHEMA) and on poly-HEMA-methacrylic acid (PHEMA/MAA). The in vitro adsorption process was followed by ATR-FTIR. Lysozyme adsorbs both, reversibly and irreversibly, on the surfaces. While the reversible bound lysozyme experiences only minor changes in its secondary structure, conformational changes occur for the irreversibly adsorbed protein. The type and extent of structural changes depend on the degree of protein coverage on the lens surface, as well as the chemical structure and surface morphology of the lenses. PHEMA/MAA lenses adsorbed thirty times more lysozyme than either of the PHEMA lenses. Fabrication processes appear to induce different adsorption behaviour, PHEMA lathe cut lenses adsorb twice the amount of protein compared with PHEMA spin cast lenses.

Adsorption↗
PubMed1984

Surface analysis of biomedical polymers by attenuated total reflectance-fourier transform infra-red.

An infra- red approach has been developed to characterize hydrophilic biomaterials, particularly contact lenses. Water was utilized as the optical coupling agent between the sample and the ATR element. This method enables the study of hydrophilic polymers in their natural aqueous environment and simultaneously solves the optical contact problem that usually arises when the ATR technique is used. Some studies were made utilizing this approach: dry and hydrated samples were structurally compared; also, a depth profiling study and a surface comparison were made on soft contact lenses fabricated by different industrial processes. Finally, the three dimensional orientation of one hydrated structure was characterized.

Biocompatible Materials↗
PubMed1984

Characterization of protein adsorption on soft contact lenses. I. Conformational changes of adsorbed human serum albumin.

Adsorption of human serum albumin on three different soft contact lens surfaces (lathe cut and spin cast crosslinked PHEMA and spin cast PHEMA/MAA) was studied. Using ATR--FTIR spectroscopy the spectra of the adsorbed protein were obtained at different times of adsorption. Structural changes were detected, initially characterized by an increase in hydrogen bonding and after that by involvement of the protein hydrophobic side chain residues. At long adsorption times, the protein becomes denatured, its alpha-helix content is drastically reduced and the amounts of random coil and beta-sheet conformations are increased. ATR-FTIR and circular dichroism studies of albumin solutions reveal similar conformational changes to those experienced by the adsorbed protein. Differences in the adsorption behaviour for the hydrogel surface, indicate the importance of the hydrophilicity, surface regularity and the chemical composition of the contact lens surfaces as the controlling parameters in the protein adsorption phenomena.

Adsorption↗
PubMed1977

Analogs of natural lipids. II. Polymorphic behavior of the tris-homoacyl derivatives of cyclopentane-1,2,3-triols.

The polymorphic behavior of three series of tris-homoacyl (C14:0, C16:0 and C18:0) cyclopentane-1,2,3-triol analogs of the natural saturated triglycerides has been studied using differential thermal analysis, Fourier transform infrared spectroscopy, and X-ray diffraction. It was found that the triglyceride analogs derived from the 1,2,3/0 and 1,2/3 cyclopentanetriols exhibit different polymorphic behavior than that of the natural triglycerides. The analogs derived from 1,3/2 cyclopentanetriol, however, were found to parallel the polymorphic behavior of the natural triglycerides quite closely. This polymorphic behavior is discussed in terms of the different configurations which the chains assume in each of the triglyceride analogs.

Cyclopentanes↗