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Results for “Spectroscopy, Fourier Transform Infrared”

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PubMed2006

Precipitation of calcium phosphate and calcium carbonate induced over chitosan membranes: a quick method to evaluate the influence of polymeric matrices in heterogeneous calcification.

Precipitation of calcium compounds (phosphate and carbonate) was performed on chitosan porous and dense membranes. In order to observe the influence of acetyl groups on the nature of formed precipitates, some chitosan membranes were acetylated in methanol solution before undergoing calcification. Calcification experiments were performed more quickly than using SBF. In this method, a faster precipitation is induced by soaking the membranes in calcium chloride solutions and, in sequence, immersing the same membranes into sodium phosphate or carbonate solutions. This procedure induced the formation of calcium compound precipitates on membrane surfaces, which were analysed through optical microscopy, X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy with attenuated total reflection apparatus (FTIR-ATR) and small angle X-ray scattering (SAXS). The results indicated the biomimetic influence of the organic matrix on morphology, organization and composition of precipitates. The acetyl group induced the formation of organized calcium carbonate better than phosphate, which may correlate with the fact that these two compounds are commonly found together in nature in structures like shells and nacre.

Calcium Carbonate↗

PubMed2006

Lipoprotein PssN of Rhizobium leguminosarum bv. trifolii: subcellular localization and possible involvement in exopolysaccharide export.

Surface expression of exopolysaccharides (EPS) in gram-negative bacteria depends on the activity of proteins found in the cytoplasmic membrane, the periplasmic space, and the outer membrane. pssTNOP genes identified in Rhizobium leguminosarum bv. trifolii strain TA1 encode proteins that might be components of the EPS polymerization and secretion system. In this study, we have characterized PssN protein. Employing pssN-phoA and pssN-lacZ gene fusions and in vivo acylation with [3H]palmitate, we demonstrated that PssN is a 43-kDa lipoprotein directed to the periplasm by an N-terminal signal sequence. Membrane detergent fractionation followed by sucrose gradient centrifugation showed that PssN is an outer membrane-associated protein. Indirect immunofluorescence with anti-PssN and fluorescein isothiocyanate-conjugated antibodies and protease digestion of spheroplasts and intact cells of TA1 provided evidence that PssN is oriented towards the periplasmic space. Chemical cross-linking of TA1 and E. coli cells overproducing PssN-His6 protein showed that PssN might exist as a homo-oligomer of at least two monomers. Investigation of the secondary structure of purified PssN-His6 protein by Fourier transform infrared spectroscopy revealed the predominant presence of beta-structure; however, alpha-helices were also detected. Influence of an increased amount of PssN protein on the TA1 phenotype was assessed and correlated with a moderate enhancement of EPS production.

Artificial Gene Fusion↗

PubMed2004

Influence of manufacturing parameters on development of contraceptive steroid loaded injectable microspheres.

The main objective of this work was to develop a system consisting of polymeric microspheres loaded with steroid drugs. The drugs were encapsulated using biodegradable poly(lactide-co-glycolide) (PLG) and poly(epsilon-caprolactone) (PCL) by double emulsion solvent evaporation method. The lipophilic drugs, levonorgestrel and ethinylestradiol were made soluble by adding ethanol/water mixture. The effects of parameters like polymer concentration and stabilizer concentration were studied on the size, size distribution, surface properties and loading efficiencies of microspheres. The formulated microspheres were smooth, spherical and uniform in shape and size. Fourier transformed infrared spectroscopy and differential scanning calorimetry studies seemed to confirm the absence of chemical interaction between the drugs and the polymers, while the drugs were dispersed in the polymer. The increase in polymer concentrations increased the size as well as the loading efficiency of microspheres. Data obtained in this study demonstrated that the PLG/PCL microspheres may be a suitable polymeric carrier for long acting injectable drug delivery.

Biodegradation, Environmental↗

PubMed1998

A designed cavity in the hydrophobic core of a four-alpha-helix bundle improves volatile anesthetic binding affinity.

The structural features of protein binding sites for volatile anesthetics are being explored using a defined model system consisting of a four-alpha-helix bundle scaffold with a hydrophobic core. Earlier work has demonstrated that a prototype hydrophobic core is capable of binding the volatile anesthetic halothane. Exploratory work on the design of an improved affinity anesthetic binding site is presented, based upon the introduction of a simple cavity into a prototype (alpha 2)2 four-alpha-helix bundle by replacing six core leucines with smaller alanines. The presence of such a cavity increases the affinity (Kd = 0.71 +/- 0.04 mM) of volatile anesthetic binding to the designed bundle core by a factor of 4.4 as compared to an analogous bundle core lacking such a cavity (Kd = 3.1 +/- 0.4 mM). This suggests that such packing defects present on natural proteins are likely to be occupied by volatile general anesthetics in vivo. Replacing six hydrophobic core leucine residues with alanines results in a destabilization of the folded bundle by 1.7-2.7 kcal/mol alanine, although the alanine-substituted bundle still exhibits a high degree of thermodynamic stability with an overall folded conformational delta GH2O = 14.3 +/- 0.8 kcal/mol. Covalent attachment of the spin label MTSSL to cysteine residues in the alanine-substituted four-alpha-helix bundle indicates that the di-alpha-helical peptides dimerize in an anti orientation. The rotational correlation time of the four-alpha-helix bundle is 8.1 +/- 0.5 ns, in line with earlier work on similar peptides. Fluorescence, far-UV circular dichroism, and Fourier transform infrared spectroscopies verified the hydrophobic core location of the tryptophan and cysteine residues, showing good agreement between experiment and design. These small synthetic proteins may prove useful for the study of the structural features of small molecule binding sites.

Amino Acid Sequence↗

PubMed2005

Interaction of humic substances and hematite: FTIR study.

The present work extended the knowledge on the binding and complexation of humic substances( humic acid or fulvic acid) and hematite by Fourier transform infrared spectroscopy( FTIR) . The FTIR data gained gave the consist evidences by two different sampling preparation methods that the interaction mechanism between humic substances and hematite was mainly conform to the ligand-exchange involving carboxylic functional groups of humic substances and the surfaces sites of hematite. The present method, although associated with some uncertainties, provided an opportunity to increase the knowledge in this field.

Benzopyrans↗

PubMed2005

The uptake of titanium ions by hydroxyapatite particles-structural changes and possible mechanisms.

In order to understand the effect of titanium ions on the molecular structure of hydroxyapatite (HAp), HAp powders were incubated in solutions with different titanium concentrations. After incubation, the powders obtained were analysed using different techniques, namely X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), differential thermal analysis (DTA), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDS). The results suggest that, depending on the concentration of titanium in solution, two different mechanisms of interaction with HAp occur. For concentrations equal to or smaller than 200 ppm, the titanium uptake by the solid seems to be primarily due to incorporation in the lattice. For higher concentrations, a dissolution-precipitation process seems to occur, leading to formation of a titanium phosphate compound.

Biocompatible Materials↗

PubMed2001

Lipid-induced pore formation of the Bacillus thuringiensis Cry1Aa insecticidal toxin.

After activation, Bacillus thuringiensis (Bt) insecticidal toxin forms pores in larval midgut epithelial cell membranes, leading to host death. Although the crystal structure of the soluble form of Cry1Aa has been determined, the conformation of the pores and the mechanism of toxin interaction with and insertion into membranes are still not clear. Here we show that Cry1Aa spontaneously inserts into lipid mono- and bilayer membranes of appropriate compositions. Fourier Transform InfraRed spectroscopy (FTIR) indicates that insertion is accompanied by conformational changes characterized mainly by an unfolding of the beta-sheet domains. Moreover, Atomic Force Microscopy (AFM) imaging strongly suggests that the pores are composed of four subunits surrounding a 1.5 nm diameter central depression.

Bacillus thuringiensis↗

PubMedDate not supplied

Penicillin G acylase-fatty lipid biocomposite films show excellent catalytic activity and long term stability/reusability.

The formation of biocomposite films of the pharmaceutically important enzyme penicillin G acylase (PGA) and fatty lipids under enzyme-friendly conditions is described. The approach involves a simple beaker-based diffusion protocol wherein the enzyme diffuses into the lipid film during immersion in the enzyme solution, thereby leading to the formation of a biocomposite film. The incorporation of the enzyme in both cationic as well as anionic lipids suggests the important role of secondary interactions such as hydrophobic and hydrogen bonding in the enzyme immobilization process. The kinetics of formation of the enzyme-lipid biocomposites has been studied by quartz crystal microgravimentry (QCM) measurements. The stability of the enzyme in the lipid matrix was confirmed by Fourier transform infrared spectroscopy (FTIR) and biocatalytic activity measurements. Whereas the biological activity of the lipid-immobilized enzyme was marginally higher than that of the free enzyme, the biocomposite film exhibited increased thermal/temporal stability. Particularly exciting was the observation that the biocomposite films could be reused in biocatalysis reactions without significant loss in activity, which indicates potentially exciting biomedical/industrial application of these films.

Catalysis↗

PubMed1999

Association of partially-folded intermediates of staphylococcal nuclease induces structure and stability.

Staphylococcal nuclease forms three different partially-folded intermediates at low pH in the presence of low to moderate concentration of anions, differing in the amount of secondary structure, globularity, stability, and compactness. Although these intermediates are monomeric at low protein concentration (< or =0.25 mg/mL), increasing concentrations of protein result in the formation of dimers and soluble oligomers, ultimately leading to larger insoluble aggregates. Unexpectedly, increasing protein concentration not only led to association, but also to increased structure of the intermediates. The secondary structure, stability, and globularity of the two less-ordered partially-folded intermediates (A1 and A2) were substantially increased upon association, suggesting that aggregation induces structure. An excellent correlation was found between degree of association and amount of structure measured by different techniques, including circular dichroism, fluorescence, Fourier transform infrared spectroscopy (FTIR), and small-angle X-ray scattering. The associated states were also substantially more stable toward urea denaturation than the monomeric forms. A mechanism is proposed, in which the observed association of monomeric intermediates involves intermolecular interactions which correspond to those found intramolecularly in normal folding to the native state.

Chromatography, Gel↗

PubMed2006

Conformation of the synaptobrevin transmembrane domain.

The synaptic vesicle protein synaptobrevin (also called VAMP, vesicle-associated membrane protein) forms part of the SNARE (soluble N-ethylmaleimide sensitive factor attachment protein receptor) complex, which is essential for vesicle fusion. Additionally, the synaptobrevin transmembrane domain can promote lipid mixing independently of complex formation. Here, the conformation of the transmembrane domain was studied by using circular dichroism and attenuated total reflection Fourier-transform infrared spectroscopy. The synaptobrevin transmembrane domain has an alpha-helical structure that breaks in the juxtamembrane region, leaving the cytoplasmic domain unstructured. In phospholipid bilayers, infrared dichroism data indicate that the transmembrane domain adopts a 36 degrees angle with respect to the membrane normal, similar to that reported for viral fusion peptides. A conserved aromatic/basic motif in the juxtamembrane region may be causing this relatively high insertion angle.

Amino Acid Sequence↗

PubMed2006

Poly-alpha,beta-(N-(2-hydroxyethyl)-L-aspartamide)-g-poly(1,3trimethylene carbonate) amphiphilic graft co-polymer as a potential drug carrier.

A biodegradable amphiphilic graft polymer was successfully synthesized by grafting hydrophobic poly(1,3-trimethylene carbonate) (PTMC) sequences onto a hydrophilic poly-alpha,beta-(N-(2-hydroxyethyl)-L-aspartamide) (PHEA) backbone. The graft polymer, PHEA-g-PTMC, was synthesized by ring-opening polymerization initiated by the macroinitiator PHEA bearing hydroxyl groups without adding any catalyst. The graft polymer was characterized by Fourier transform infrared spectroscopy, 1H-nuclear magnetic resonance spectroscopy, combined size-exclusion chromatography and multiangle laser light scattering analysis. Two drugs with distinct water solubility, prednisone acetate and tegafur, were encapsulated in the PHEA-g-PTMC nanoparticles. The in vitro release of two drugs from PHEA-g-PTMC nanoparticle drug-delivery systems was investigated.

Biocompatible Materials↗

PubMed1999

Membrane interactions of the synthetic N-terminal peptide of HIV-1 gp41 and its structural analogs.

Structural and functional studies assessed the membrane actions of the N terminus of HIV-1 glycoprotein 41000 (gp41). Earlier site-directed mutagenesis has shown that key amino acid changes in this gp41 domain inhibit viral infection and syncytia formation. Here, a synthetic peptide corresponding to the N terminus of gp41 (FP; 23 residues, 519-541), and also FP analogs (FP520V/E with Val-->Glu at residue 520; FP527L/R with Leu-->Arg at 527; FP529F/Y with Phe-->Tyr at 529; and FPCLP1 with FP truncated at 525) incorporating these modifications were prepared. When added to human erythrocytes at physiologic pH, the lytic and aggregating activities of the FP analogs were much reduced over those with the wild-type FP. With resealed human erythrocyte ghosts, the lipid-mixing activities of the FP analogs were also substantially depressed over that with the wild-type FP. Combined with results from earlier studies, theoretical calculations using hydrophobic moment plot analysis and physical experiments using circular dichroism and Fourier transform infrared spectroscopy indicate that the diminished lysis and fusion noted for FP analogs may be due to altered peptide-membrane lipid interactions. These data confirm that the N-terminal gp41 domain plays critical roles in the cytolysis and fusion underlying HIV-cell infection.

Amino Acid Sequence↗

PubMed1994

Topology of diphtheria toxin B fragment inserted in lipid vesicles.

Diphtheria toxin (DT) is a bacterial protein that crosses the membrane of endosomes of target cells in response to the low endosomal pH. In this paper, we have inserted diphtheria toxin in asolectin vesicles at pH 5.0 and treated the reconstituted system with pronase. The peptides that were protected from digestion were separated by gel electrophoresis, transferred to a membrane and their N-terminal sequences were determined. All peptides belong to the B fragment of DT and cover residues 194-223, 265-375 and 429-528. The secondary structures of the peptides inserted in the membrane, determined by Fourier-transformed infrared spectroscopy, were shown to be mostly alpha-helices and beta-sheets (44% and 53%, respectively). On the basis of these data and the recently published X-ray structure of DT, we are proposing a topology for the DTB fragment in the membrane.

Amino Acid Sequence↗

PubMed2004

Contaminants in drinking water and its mitigation using suitable adsorbents: an overview.

Various options are applicable for the removal of water pollutants included reverse osmosis, ion exchange, coagulation, co-precipitation, catalytic reduction, herbal filtration, electrodialysis and adsorption. This paper deals with the sorption phenomena for the removal of pollutants from drinking water. Attempts have been made to use low cost sorbents developed by pretreatment/activation/impregnation with alkalis, acids, iron oxide, manganese dioxide, ferric chloride, alum, lime, aluminum salts with natural products/indigenous minerals viz. activated alumina, activated carbon, groundnut husk, saw dust, chemically coated sand, fly ash, zeolites, clay minerals and other plant products. Application of Freundich and Langmuir isotherms were used to assess the adsorption capacity. Equilibrium isotherms were determined at optimum temperature and pH to characterize the sorption process. Statistical parameters such as mass transfer coefficients, multiple regression analysis were applied to establish the mechanism. It is suggested that the characterization of suitable, and exhausted sorbent through the application of fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray fluorescence (XRF) is essential to establish its surface bonding. Scope for safety evaluation and risk assessment to human and biosphere may provide the guideline and predication to the regulatory agencies for its sustainable use and safe disposal The ecotoxicological assessment of the leachates and low cost removal technology are discussed in this paper.

Adsorption↗

PubMed2005

[Studies on the crystallization characteristics of the hard segments in ethylene terephthalate-epsilon-caprolactone copolyesters].

The crystallization characteristics of the ethylene terephthalate (ET) hard segments in ethylene terephthalate-epsilon-caprolactone (TCL) copolyesters were studied by wide-angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR). It was found that in TCL copolyesters with high hard segment content, the ET hard segment can crystallize to form the crystals having the similar lattice structure as that of pure poly (ethylene terephthalate) (PET). The lamellar thickness and the crystallinity of the ET crystals depend on the ET segment sequence length. As the segment sequence length decreases, the lamellar thickness and the crystallinity decrease.

Caproates↗

PubMed2003

Lag phase and hydrolysis mechanisms of triacylglycerol film lipolysis.

We here present novel insights into the dynamic changes of a nanosized lipid film during enzymatic degradation. When adding an aqueous solution containing a triacylglycerol lipase to an approximately 100nm thin triolein film, which is supported on a hard surface, the film thickness, elasticity, viscosity, and chemical composition were obtained continuously. Both a mechanical technique (quartz crystal microbalance with dissipation monitoring) and a spectroscopic technique (attenuated total reflection Fourier transform infrared spectroscopy) were utilised for this study. Detailed data revealed the effects of pH, Ca(2+), and catalytic rate on lipolysis, including product release from the film. It was found that under basic conditions and without Ca(2+), the lipolytic activity commence instantaneously upon addition of enzyme, whereas product release from the substrate film awaits conditions that favours release. A model for removal of degradation products from the film is introduced, including a novel interpretation of the lag phase phenomenon.

Elasticity↗

PubMed2001

A protocol for the forensic analysis of condom and personal lubricants found in sexual assault cases.

In sexual assault cases, lubricant trace evidence may supplement biological evidence, or may be the primary physical evidence where biological evidence is unavailable. This study considered a total of 50 lubricants from condoms and personal lubricant products available in Australia. Differentiation of the samples was attempted using fluorescence examination, Fourier transform infrared spectroscopy (DRIFTS), gas chromatography-mass spectrometry, liquid chromatography-tandem mass spectrometry, and pyrolysis gas chromatography-mass spectrometry. Eleven of the samples were uniquely identified by the analysis scheme, while the remainder of the samples were separated into nine groups. As a result of this study, a recommended protocol for the detection and analysis of an "unknown" biological swab was produced.

Australia↗

PubMed2002

Microstructural study of aerosol-gel derived hydroxyapatite coatings.

Highly porous aerosol-gel derived hydroxyapatite (HAP) coatings have been prepared from calcium nitrate and phosphoric acid based sols. Precursor solutions were prepared by filtering the suspension formed during the ultrasonic slurring of the reactants mixture. The coatings deposited on Si wafers were studied after sintering at different temperatures by using Fourier transform infrared spectroscopy, X-ray diffraction, energy disperse microanalysis and scanning electron microscopy. The composition, structure and morphology of the coatings sintered at 650 degrees C were found to fit highly porous HAP. That is considered of great relevance since the deposition parameters are compatible with the processing of bioactive coatings on load bearing metallic substrates.

Aerosols↗