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Results for “Spectroscopy, Fourier Transform Infrared”

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PubMed2005

Surface modification of poly(ether urethane urea) with modified dehydroepiandrosterone for improved in vivo biostability.

In this study, a fatty acid urethane derivative of dehydroepiandrosterone (DHEA) was synthesized and evaluated as a polyurethane additive to increase long-term biostability. The modification was hypothesized to reduce the water solubility of the DHEA and physically anchor the additive in the polyurethane during implantation. Polyurethane film weight loss in water as a function of time was studied to determine the polymer retention of the modified DHEA. The polyurethane film with unmodified DHEA had significant weight loss in the first day (10%) that was previously correlated to rapid leaching of the additive. The polyurethane film with modified DHEA had significantly less weight loss at all time points indicating improved polymer retention. The effect of the modified DHEA additive on the biostability of a poly(ether urethane urea) was examined after 5 weeks of subcutaneous implantation in Sprague-Dawley rats. Optical micrographs and infrared analysis of the specimens indicated that the modified DHEA bloomed to the surface of the film forming a crystalline surface layer approximately 10-15 microns thick. After explantation, this surface layer was intact without measurable differences in surface chemistry as monitored by attenuated total reflectance-Fourier transform infrared spectroscopy. There was no evidence of degradation of the polyurethane underneath the modified DHEA surface layer as compared with the polyurethane control. We have concluded that the modified DHEA self-assembled into a protective surface coating that inhibited degradation of the polyurethane. The roughness of the modified DHEA surface layer prevented adherent cell analysis to determine if the additive retained the ability to down-regulate macrophage activity. Subsequent studies will investigate the ability of surface-modifying additives to modulate cellular respiratory bursts in addition to the formation of an impermeable barrier. This bimodal approach to improving biostability holds great promise in the field of polyurethane biomaterials.

Animals↗

PubMed2001

Conformations of the active and inactive states of opsin.

The signaling state metarhodopsin II of the visual pigment rhodopsin decays to the apoprotein opsin and all-trans retinal, which are then regenerated to rhodopsin by the visual cycle. Opsin is known to have at neutral pH only a small residual constitutive activity toward its G protein transducin, which is thought to play a considerable role in light adaptation (bleaching desensitization). In this study we show with Fourier-transform infrared spectroscopy that after metarhodopsin II decay, opsin exists in two conformational states that are in a pH-dependent equilibrium at 30 degrees C with a pK of 4.1 in the presence of hydroxylamine scavenging the endogenous all-trans retinal. Despite the lack of the native agonist in its binding pocket, the low pH opsin conformation is very similar to that of metarhodopsin II and is likewise stabilized by peptides derived from rhodopsin's cognate G protein, transducin. The high pH form, on the other hand, has some conformational similarity to the inactive metarhodopsin I state. We therefore conclude that the opsin apoprotein displays intrinsic conformational states that are merely modulated by bound all-trans retinal.

Animals↗

PubMed2005

Early events in the fibrillation of monomeric insulin.

Insulin has a largely alpha-helical structure and exists as a mixture of hexameric, dimeric, and monomeric states in solution, depending on the conditions: the protein is monomeric in 20% acetic acid. Insulin forms amyloid-like fibrils under a variety of conditions, especially at low pH. In this study we investigated the fibrillation of monomeric human insulin by monitoring changes in CD, attenuated total reflectance-Fourier transform infrared spectroscopy, 8-anilinonaphthalenesulfonic acid fluorescence, thioflavin T fluorescence, dynamic light scattering, and H/D exchange during the initial stages of the fibrillation process to provide insight into early events involving the monomer. The results demonstrate the existence of structural changes occurring before the onset of fibril formation, which are detectable by multiple probes. The data indicate at least two major populations of oligomeric intermediates between the native monomer and fibrils. Both have significantly non-native conformations, and indicate that fibrillation occurs from a beta-rich structure significantly distinct from the native fold.

Acetic Acid↗

PubMed1996

The lytic activity of the bee venom peptide melittin is strongly reduced by the presence of negatively charged phospholipids or chloroplast galactolipids in the membranes of phosphatidylcholine large unilamellar vesicles.

We have investigated the dependence of the lytic activity of the bee venom peptide melittin on the lipid composition of its target membrane. The lysis of large unilamellar liposomes, measured as loss of the fluorescent dye carboxyfluorescein, in the presence of melittin was strongly reduced when the negatively charged lipids phosphatidylglycerol (PG) or phosphatidylserine (PS), or the plant chloroplast lipids monogalactosyldiacylglycerol (MGDG) or digalactosyldiacylglycerol (DGDG) were incorporated into egg phosphatidylcholine (EPC) membranes. This reduction was evident at concentrations below 10 wt% of the additional lipids. It was not due to reduced binding of melittin to the vesicles. It was also not related to a reduced insertion depth of the peptide into the bilayer, as shown by quenching of the intrinsic tryptophan fluorescence of the peptide by the aqueous quencher sodium nitrate. Fourier transform infrared spectroscopy (FTIR) revealed specific interactions of the peptide with the headgroups of the inhibitory lipids. The phosphate peak in PG was shifted by two wavenumbers after the addition of melittin. There was no shift in EPC or PS. Instead, in PS the COO- peak was strongly distorted in the presence of melittin. These data indicate ionic interactions between the basic peptide and the negative charges on the membrane surface. The galactolipids are uncharged. Here the evidence points to hydrogen bonding between melittin and OH-groups of the sugar headgroups. Liposomes containing DGDG were the only case where we found evidence for changes in fatty acyl chain motion due to the presence of melittin, from the CH2-scissoring peaks.

Bee Venoms↗

PubMed2006

Solution synthesis of germanium nanowires using a Ge2+ alkoxide precursor.

A simple solution synthesis of germanium (Ge0) nanowires under mild conditions (<400 degrees C and 1 atm) was demonstrated using germanium 2,6-dibutylphenoxide, Ge(DBP)2 (1), as the precursor where DBP = 2,6-OC6H3(C(CH3)3)2. Compound 1, synthesized from Ge(NR2)2 where R = SiMe3 and 2 equiv of DBP-H, was characterized as a mononuclear species by single-crystal X-ray diffraction. Dissolution of 1 in oleylamine, followed by rapid injection into a 1-octadecene solution heated to 300 degrees C under an atmosphere of Ar, led to the formation of Ge0 nanowires. The Ge0 nanowires were characterized by transmission electron microscopy (TEM), X-ray diffraction analysis, and Fourier transform infrared spectroscopy. These characterizations revealed that the nanowires are single crystalline in the cubic phase and coated with oleylamine surfactant. We also observed that the nanowire length (0.1-10 microm) increases with increasing temperature (285-315 degrees C) and time (5-60 min). Two growth mechanisms are proposed based on the TEM images intermittently taken during the growth process as a function of time: (1) self-seeding mechanism where one of two overlapping nanowires serves as a seed, while the other continues to grow as a wire; and (2) self-assembly mechanism where an aggregate of small rods (<50 nm in diameter) recrystallizes on the tip of a longer wire, extending its length.

Germanium↗

PubMed2004

Triamterene-beta-cyclodextrin systems: preparation, characterization and in vivo evaluation.

The purpose of this research was to improve the solubility and therefore dissolution and bioavailability of triamterene, a poorly water soluble diuretic, by complexation with beta-cyclodextrin. Triamterene has been reported to show low bioavailability after oral administration, with wide intersubject variation. This study presents the formulation of solid dispersions of triamterene with beta-cyclodextrin--by cogrinding, kneading, and coevaporation, using low pH conditions--and their characterization, evaluation of improvement in dissolution profiles, and in vivo advantage. Phase solubility studies indicated complex with possible stoichiometry of 1:1 and a stability constant of 167.67 M(-1). The solid dispersions were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, x-ray diffraction, and differential scanning calorimetry studies. The characterization studies confirmed inclusion of the phenyl ring of triamterene within the nonpolar cavity of beta-cyclodextrin in the coevaporate. Remarkable improvement in in vitro drug release profiles in 0.1N HCl and pH 6.8 phosphate buffer was observed with all dispersions, especially the coevaporate. The coevaporate, when administered orally in rats, also exhibited improved in vivo activity, as measured by net sodium ion excretion, as compared with triamterene powder. Thus, coevaporation of the drug and beta-cyclodextrin from acidified alcohol provide the optimum condition for inclusion complexation to give a binary system with remarkable improvement in in vitro drug release profile and in vivo performance.

Animals↗

PubMed2001

Quantitative interpretation of Fourier-transform infrared spectoscopic data from a size--exlusion chromatorgraphy solvent- evaporation interface.

Quantitative evaluation of polymer composition across the SEC chromatogram can provide more accurate characterization of heterogeneous polymer samples for problem solving and for material specification. To this end Fourier-transform infrared spectroscopy (FTIR) with solvent-evaporation interfaces has become a very powerful detector for size-exclusion chromatography (SEC). The solvent-evaporation interface removes the mobile phase at the exit of the chromatograph and deposits the separated molecular sizes as polymer films on infrared transparent substrates. Quantitative interpretation of the FTIR spectra obtained from these films has recently been found to be best accomplished by using partial least squares. In this paper, polystyrene and poly(methylmethacrylate), alone, as blends, and a copolymer were analyzed in a SEC equipped with an evaporative interface. Molecular weight effects, wavelength selection, the effect of averaging spectra on results, and selection of the best data preprocessing method were investigated. General methods of evaluating these variables were developed to arrive at conditions for this particular "model" situation in order to provide a basis for the analysis of more complex polymers.

Chromatography, Gel↗

PubMed1999

Early detection of ozone-induced hydroperoxides in epithelial cells by a novel infrared spectroscopic method.

In the lower atmosphere ozone is a toxic and an unwanted oxidising pollutant causing injury to the airway epithelial cells by lipid peroxidation to yield products such as phospholipid hydroperoxides (PLHP). Measurements of PLHP, which are primary oxidation products, may reflect an early susceptibility of the target cell to oxidative stress. Biphasic cultures of bronchial epithelial cells (BEAS-2B) were exposed to ozone at environmentally relevant concentrations (0.1-1.0 ppm) for 4 and 12 h. Detection of PLHP was made using a novel technique based on fourier transform infrared spectroscopy (FTIR) in combination with high performance thin-layer chromatography (HPTLC). Six phospholipids were identified on the HPTLC plate; lysophosphatidylcholine (LPC), sphingomyelin (SM), phosphatidylcholine (PC), lysophosphatidylethanolamine (LPE), phosphatidylinositol (PI), and phosphatidylethanolamine (PE). From the FTIR spectra, O-O stretching of hydroperoxides was identified in the range 890-820cm(-1). Multivariate data analysis revealed a positive correlation (r = 0.99 for 4 h exposure and r = 0.98 for 12h exposure) between ozone exposure levels and the region of the FTIR-spectrum comprising the main wavelengths for hydroperoxides. These data support this alternative, versatile and novel spectroscopic approach for the early detection of ozone-mediated damage in human airway epithelial cells.

Bronchi↗

PubMed2006

Synthetic consolidants attacked by melanin-producing fungi: case study of the biodeterioration of Milan (Italy) cathedral marble treated with acrylics.

Monuments and artistic stone surfaces are often consolidated and protected with synthetic polymers, in particular, acrylics. Although it is generally thought that acrylic polymers are resistant to biodeterioration, we report for the first time the systematic occurrence of dematiaceous meristematic fungi on many marble samples of the cathedral in Milan (Italy) previously treated with this material. Fourier transform infrared spectroscopy applied to the Milan cathedral stone samples revealed characteristic features of biodeteriorated synthetic resins that differentiated them from the aged but nonbiodeteriorated samples. Samples showing biological colonization were analyzed for the presence of fungi. Cultivation and morphological characterization and methods independent from cultivation, such as denaturing gradient gel electrophoresis coupled with partial 18S rRNA gene sequencing and immunofluorescence staining with melanin-binding antibodies, showed that melanin-producing species are heavily present on stone surfaces protected with acrylic resins. This observation raises the question of the effectiveness of acrylics in protecting stone artworks.

Acrylic Resins↗

PubMed2006

Does the nature of deposited basic calcium phosphate crystals determine clinical course in calcific periarthritis of the shoulder?

OBJECTIVE: Two typical clinical courses of calcific periarthritis in the shoulder are known: acute, with severe inflammation, and chronic, in the form of impingement syndrome with secondary subacromial bursitis. It remains unclear what factors determine these clinical courses. Our objectives were to clarify whether the calcified deposits that occur in both acute and chronic cases are composed of carbonate apatite; and to compare the Ca:P molar ratio in the 2 forms and to determine if there was any correlation in this respect with the intensity of inflammation induced by basic calcium phosphate crystals. METHODS: Ten samples were aspirated from 10 women (ages 42-65 yrs) with acute inflammation. The average time from first attack to aspiration was 2.3 days. A further 10 samples were operatively removed from 10 women (ages 35-58 yrs) with refractory chronic subacromial bursitis, among whom an average of 7.8 months had passed since the onset of symptoms. All samples were analyzed by x-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy, and Ca:P molar ratios were measured by x-ray fluorescence spectrometry. RESULTS: Calcified deposits from both acute and chronic cases were identified as carbonate apatite, and not hydroxyapatite, octacalcium phosphate, tricalcium phosphate, or dicalcium phosphate dihydrate. The average Ca:P molar ratio of calcified deposits was calculated as 1.71 +/- 0.16 in acute cases and 1.71 +/- 0.16 in chronic cases (statistically nonsignificant). CONCLUSION: Deposits around the shoulder in both acute and chronic calcific periarthritis are composed of carbonate apatite, Ca:P molar ratios being almost identical in the 2 forms. The results suggest that some factor other than the composition of the crystalline deposits may determine clinical course in calcific periarthritis of the shoulder.

Acute Disease↗

PubMed2007

Structure and release behavior of PMMA/silica composite drug delivery system.

The preparation, characterization, and in vitro release of aspirin from polymethylmethacrylate (PMMA)/silica composites prepared via a sol-gel route are reported. The in vitro drug release test revealed that the release rate of aspirin in PBS increased with the silica content in the composites; on the contrary, the increase of the content of 3-(trimethoxysilyl) propyl methacrylate (MSMA), a coupling agent, decreased the drug release rate. The drug release rate/composite structure relationship was studied using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and swelling ratio (SR) measurement. The results indicated that the interface between polymer matrix and inorganic fillers has significant influence on the drug release behavior of the composite materials. In addition, models of mass transfer based on Fickian diffusion law at constant temperature and pressure were employed to analyze the results of the in vitro drug release experiments. The drug release behaviors of the composite samples fitted well with the Fickian diffusion model. The values of k, which is in direct proportion to drug release rate, increased with the increasing content of silica while decreased with that of MSMA in the composite samples.

Aspirin↗

PubMed1995

Azo polymeric hydrogels for colon targeted drug delivery.

Azo polymeric hydrogels were developed for colon specific targeting. Methacryloyloxy azobenzene was synthesized and hydrogels were prepared by copolymerizing with hydroxyethyl methacrylate. These hydrogels were characterized by various spectral techniques such as Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. Equilibrium swelling measurements of the hydrogels were carried out in distilled water and also in simulated gastric and intestinal fluids. The in vitro release studies of the incorporated 5-flurouracil were carried out in simulated gastric and intestinal fluids. The in vitro release profiles of the drug were also obtained in the presence of azoreductase in the culture of intestinal flora. The release was faster and almost followed a zero order pattern. This can be attributed to the cleavage of the azo crosslinks in the hydrogel by the azoreductase and the release of the entrapped drug at the site of targeting i.e., colon.

Azo Compounds↗

PubMed1999

Water-soluble beta-sheet models which self-assemble into fibrillar structures.

Self-assembly of beta-sheet domains resulting in the formation of pathogenic, fibrillar protein aggregates (amyloids) is a characteristic feature of various medical disorders. These include neurodegenerative diseases, such as Alzheimer's, Huntington's, and Creutzfeldt-Jacob's. A significant problem in studying such aggregation processes is the poor solubility of these beta-sheet complexes. The present work describes water-soluble de novo beta-sheet peptides which self-assemble into fibrillar structures. The model peptides enable studies of the relationship between beta-sheet stability and association behavior. The peptides [DPKGDPKG-(VT)n-GKGDPKPD-NH2, n = 3-8] are composed of a central beta-sheet-forming domain (VT-sequence), and N- and C-terminal nonstructured octapeptide sequences which promote water solubility. Conformational analyses by circular dichroism and Fourier transform infrared spectroscopy indicate the influence of peptide length, D-amino acid substitution, and concentration on the ability of the peptides to form stable beta-sheet structures. The association behavior investigated by analytical ultracentrifugation and dynamic light scattering was found to correlate strongly with the stability of a beta-sheet conformation. Model peptides with n >/= 6 form stable, water-soluble beta-sheet complexes with molecular masses of more than 2000 kDa, which are organized in fibrillar structures. The fibrils examined by Congo Red staining and electron microscopy show some similarities with naturally occurring amyloid fibrils.

Amino Acid Sequence↗

PubMed2004

Encapsulation of water-insoluble drug by a cross-linking technique: effect of process and formulation variables on encapsulation efficiency, particle size, and in vitro dissolution rate.

Ibuprofen-gelatin micropellets were prepared by the cross-linking technique using formaldehyde. Spherical micropellets having an entrapment efficiency of 65% to 85% were obtained. The effect of core to coat ratio, speed of agitation, temperature, and volume of oil phase was studied with respect to entrapment efficiency, micropellet size, and surface characteristics. Fourier transform infrared spectroscopy and differential scanning calorimetric analysis confirmed the absence of any drug-polymer interaction. X-ray diffraction patterns showed that there is a decrease in crystallinity of the drug. The micromeritic properties of micropellets were found to be slightly changed by changing various processing parameters to give micropellets of good flow property. The in vitro release profile could be altered significantly by changing various processing parameters to give a controlled release of drug from the micropellets. The stability studies of the drug-loaded micropellets showed that the drug was stable at storage conditions of room temperature, 37 degrees C, 25 degrees/60% relative humidity (RH) and 45 degrees/60% RH, for 12 weeks.

Calorimetry, Differential Scanning↗

PubMed2005

Complexes of fulvic acid on the surface of hematite, goethite, and akaganeite: FTIR observation.

The present work extended our knowledge on the binding and complexation of a fulvic acid (FA) derived from leonardite and the iron oxides (hematite, goethite and akaganeite) by Fourier transform infrared spectroscopy (FTIR). As a prerequisite, the iron oxides were firstly prepared and characterized by transmission electron micrograph (TEM). All iron phases were single and well-described crystalloid. The FTIR data obtained by two different sampling preparation methods gave the consisting evidences that under our experimental conditions the interaction mechanism was to the ligand-exchange involving carboxylic functional groups of the FA and the surfaces sites of both hematite and goethite, while no complexation can be evidenced in the case of akaganeite, only surface adsorption. In general, the binding affinities of the iron oxides with the FA was in the order of hematite>goethite>akaganeite. The present method, although associated with some uncertainties, provided an opportunity to increase the knowledge in the field of the humic chemistry.

Benzopyrans↗

PubMedDate not supplied

Effect of time and polymerization cycle on the degree of conversion of a resin composite.

The aim of this investigation was to verify the influence of 3 light curing units on the degree of conversion, using different irradiation conditions: 1) manufacturers' recommended times of photo-activation, 2) standardizing total energy density among the units and 3) standardizing energy density at the 450-490 nm wavelength range among the units and the effect of these irradiation conditions on the post-cure. Three light curing units were used: halogen, light emitting diodes (LED) and xenon plasma. Seven groups were tested (n=6). Twenty-four hours after the photo-activation procedures, half of the composite specimens were submitted to Fourier Transformed Infrared Spectroscopy analysis. The other half was analyzed after 1 month. The results were submitted to 2-way ANOVA and Tukey's test (5%). Twenty-four hour analysis revealed that the second set of irradiation conditions produced a similar degree of conversion among the LCUs. After 1 month, the conversion values were statistically higher for 20 seconds of halogen exposure (increased from 46.78 to 49.66%), 20 seconds of LED exposure (from 46.20 to 51.15%), 30 seconds of LED exposure (from 48.29% to 50.68%) and 3 seconds of PAC exposure (from 42.57 to 51.39%). The initial degree of conversion and post-cure depended on the photo-activation condition applied.

Composite Resins↗

PubMedDate not supplied

[Binding of lactones by polysaccharides of corn and potato starches].

Sorption of gamma- and delta-lactones from aqueous solutions by cryotropic gels of corn and potato starches was studied using capillary gas-liquid chromatography and Fourier transform infrared spectroscopy. The sorption patterns were similar for both types of starch. However, the sorption of lactones by potato starch was 5-10% lower than their sorption by cornstarch. The amount of substances bound by cryotextures of the starches depended linearly on their initial concentrations in gel. Increase in the length of the alkyl substituent improved sorption of lactones. It was shown that six-membered rings play a greater role in total lactone sorption than five-membered rings. The apparent constants and numbers of binding sites were estimated for compounds that reached the stage of saturation. The interaction between lactones and polysaccharides was accompanied by a decrease in their conformational lability and changes in the rheological characteristics of thermotropic and cryotropic starch gels.

Binding Sites↗

PubMed1996

Boar sperm proacrosin infrared investigation: secondary structure analysis after autoactivation and suramin binding.

Fourier transform infrared spectroscopy was used to investigate the secondary structure of boar sperm proacrosin at p2H 5.5, to determine the structural changes following protein autoactivation to beta-acrosin at p2H 8.0 and to study the effect of suramin binding on the protein secondary structure. At p2H 5.5, proacrosin contents of alpha-helix, beta-sheet, turns, and unordered structures were estimated to be 9, 49-51, 16-18, and 24%, respectively. At p2H 8.0, the protein was partially insoluble; spectral analysis of the soluble fraction, which contained beta-acrosin, showed an overall secondary structure quite similar to that of proacrosin at p2H 5.5. However, p2H 8.0 spectra of the soluble protein (beta-acrosin), together with the thermal denaturation experiments, indicated that, compared to proacrosin, beta-acrosin showed an increased content of beta-sheets exposed to the solvent as well as a different tertiary structure. Proacrosin/suramin interaction at p2H 5.5 resulted in the formation of soluble and insoluble complexes and the relevant infrared spectra showed only minor differences with respect to the native proacrosin. However, the thermal denaturation curves revealed that suramin induced a destabilization of proacrosin structure. The data also indicated that suramin could modify the interaction characteristics of proacrosin aspartyl and glutamyl residues, thus suggesting competition of suramin with these two residues for ionic interactions.

Acrosin↗