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Results for “Spectroscopy, Fourier Transform Infrared”

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PubMed2004

Preservation of dried liposomes in the presence of sugar and phosphate.

It has been well established that sugars can be used to stabilize liposomes during drying by a mechanism that involves the formation of a glassy state by the sugars as well as by a direct interaction between the sugar and the phospholipid head groups. We have investigated the protective effect of phosphate on solute retention and storage stability of egg phosphatidylcholine (egg PC) liposomes that were dried (air-dried and freeze-dried) in the presence of sugars and phosphate. The protective effect of phosphate was tested using both glucose (low T(g)) and sucrose (high T(g)) by measuring leakage of carboxyfluorescein (CF), which was incorporated inside the vesicles. Liposomes that were dried with glucose or phosphate alone showed complete leakage after rehydration. However, approximately 30% CF-retention was obtained using mixtures of phosphate and glucose. Approximately 75% CF-retention was observed with liposomes that were dried with sucrose. The solute retention further increased to 85% using mixtures of phosphate and sucrose. The pH of the phosphate buffer prior to drying was found to have a strong effect on the solute retention. Fourier transform infrared spectroscopy studies showed that phosphate and sugars form a strong hydrogen bonding network, which dramatically increased the T(g). The HPO(4)(2-) form of phosphate was found to interact stronger with sugars than the H(2)PO(4)(-) form. The increased solute retention of liposomes dried in the sugar phosphate mixtures did not coincide with improved storage stability. At temperatures below 60 degrees C the rate of solute-leakage was found to be strikingly higher in the presence of phosphate, indicating that phosphate impairs storage stability of dried liposomes.

Carbohydrates↗

PubMed2001

Lateral organization and domain formation in a two-component lipid membrane system.

The thermodynamic phase behavior and lateral lipid membrane organization of unilamellar vesicles made from mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2 distearoyl-sn-glycero-3-phosphocholine (DSPC) were investigated by fluorescence resonance energy transfer (FRET) as a function of temperature and composition. This was done by incorporating a headgroup-labeled lipid donor (NBD-DPPE) and acceptor (N-Rh-DPPE) in low concentrations into the binary mixtures. Two instances of increased energy transfer efficiency were observed close to the phase lines in the DMPC/DSPC phase diagram. The increase in energy transfer efficiency was attributed to a differential preference of the probes for dynamic and fluctuating gel/fluid coexisting phases. This differential preference causes the probes to segregate (S. Pedersen, K. Jørgensen, T. R. Baekmark, and O. G. Mouritsen, 1996, Biophys. J. 71:554-560). The observed increases in energy transfer match with the boundaries of the DMPC/DSPC phase diagram, as measured by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). We propose that the two instances of probe segregation are due to the presence of DMPC-rich and DSPC-rich domains, which form a dynamic structure of gel/fluid coexisting phases at two different temperatures. Monitoring the melting profile of each lipid component independently by FTIR shows that the domain structure is formed by DMPC-rich and DSPC-rich domains rather than by pure DMPC and DSPC domains.

Calorimetry, Differential Scanning↗

PubMed2000

Animal models for studies on cold-induced platelet activation in human beings.

When human platelets are chilled below about 20 degrees C, they spontaneously activate, a phenomenon that limits their storage lifetime. We have previously shown that this activation in chilled human platelets is associated with passage through a lipid phase transition. Because animal models are necessary for Investigating methods for cold storage of platelets, it is essential to determine whether such phase transitions and chilling-induced activation are found in these models. In this study we examined platelets from some commonly used animal models-pigs, rhesus monkeys, mice, dogs, and rabbits. Using Fourier transform infrared spectroscopy (FTIR), we detected the thermotropic membrane phase transition in Intact platelets and assessed the morphologic response of the platelets to chilling. Statistical analysis of both FTIR and shape change show that of the animal models tested, pig platelets are most similar to human platelets. These studies suggest that pigs and pig platelets are the models of choice for the study of cold-induced platelet activation in human beings.

Animals↗

PubMed1996

Overview of polyethylene as a bearing material: comparison of sterilization methods.

Polyethylene has been used for more than 30 years as an orthopaedic bearing material; however, there has been recent concern regarding the early failure of a small percentage of the polyethylene bearings. The damage seen in some retrieved polyethylene components has been linked to gamma radiation sterilization in air, which was widely used by the industry for years. Gamma radiation in air has been documented to cause an increase in oxidation and degradation of mechanical properties with time. The degradation of polyethylene initiated by gamma sterilization in air has led the orthopaedic industry toward alternative sterilization methods, including gamma radiation in an inert gas or vacuum environment, ethylene oxide gas sterilization, and gas plasma sterilization. For many of these alternative techniques, little clinical performance data exist. This study is a comparative evaluation of sterilization methods using the same analytic techniques that have been used to document the effects of gamma sterilization in air on polyethylene. Fourier transform infrared spectroscopy, electron spin resonance, and uniaxial tensile testing are used to compare, respectively, the oxidation levels, free radical concentration, and mechanical properties of material sterilized by each method. The polyethylene is evaluated before sterilization, poststerilization, and postartificial aging. All examined alternative sterilization methods, when compared with gamma sterilization in air, caused less material degradation during a component's preimplantation shelf life.

Electron Spin Resonance Spectroscopy↗

PubMed1999

Analysis of bovine serum albumin adsorption on calcium phosphate and titanium surfaces.

The protein adsorption behavior of thin films of calcium phosphate (CaP) bioceramic and titanium (Ti) was studied in this research. The thin films were produced with an ion beam sputter deposition technique using targets of hydroxyapatite (HA), fluorapatite (FA) and titanium (Ti). Fourier transform infrared spectroscopy (FTIR) with attenuated total internal reflectance (ATR) was used to evaluate protein adsorption on these surfaces. This study showed that surface composition and structure influenced the kinetics of protein adsorption and the structure of adsorbed protein. CaP surfaces adsorbed greater amount of protein than the Ti surface, and caused more alteration of the structure of adsorbed BSA than did the Ti surface. The differences in protein adsorption behavior could result in very different initial cellular behavior on CaP and Ti implant surfaces.

Adsorption↗

PubMed1997

Determining mineral content variations in bone using backscattered electron imaging.

The mechanical properties of bones are greatly influenced by the ratio of organic constituents to mineral. Determination of bone mineral content on a macroscopic scale is straightforward, but microscopic variations, which can yield new insights into remodelling activities, mechanical strength, and integrity, are profoundly more difficult to measure. Measurement of microscopic mineral content variations in bone material has traditionally been performed using microradiography. Backscattered electron (BSE) imaging is a technique with significantly better resolution than microradiography with demonstrated consistency, and it does not suffer from projection-effect errors. We report results demonstrating the applicability of quantitative BSE imaging as a tool for measuring microscopic mineral content variations in bones representing a broad range of mineralization. Bones from ten species were analyzed with Fourier-transformed infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectrometry, ash measurements, and BSE imaging. BSE image intensity (graylevel) had a very strong positive correlation to mineral (ash) content. Compositional and crystallographic variations among bones had negligible influence on backscattered electron graylevels. The present study confirms the use of BSE imaging as a tool to measure the microscopic mineral variability in a broad range of mineralized tissues.

Animals↗

PubMed2007

Synthesis and structural characterization of glucopyranosylamide films on gold.

Self-assembled monolayers (SAMs) of glucose derivatives on gold have been prepared from alpha- and beta-glucopyranosylamide derivatives. The glucosyl conjugates were synthesized stereoselectively via the in situ generation of glucosyl isoxazolines followed by treatment with thiopyridyl esters. The resulting film structures were characterized by atomic force microscopy, reflection Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The experimental data indicated that alpha- or beta-linked glucopyranosylamide derivatives with free hydroxyl groups attach to gold via the thiol linker. Both derivatives form monolayer films with high packing densities--comparable to those typically observed for alkanethiol monolayers on gold. Acetate analogues of these conjugates do not form SAMs on gold; they form multilayered films under identical deposition conditions.

Adsorption↗

PubMed1995

Isolation of predominantly submicron-sized UHMWPE wear particles from periprosthetic tissues.

A method of tissue digestion using sodium hydroxide was applied to the isolation and recovery of ultra-high-molecular-weight polyethylene (UHMWPE) particles from tissues around failed total hip replacements. Density gradient ultracentrifugation of the digested tissues was performed to separate the UHMWPE from cell debris and other particulates. Fourier transform infrared spectroscopy and differential scanning calorimetry (DSC) verified that the recovered particles were UHMWPE. When viewed by scanning electron microscopy, individual particles were clearly observed and were either rounded or elongated. The majority were submicron in size. The application of this method to the study of particles from periprosthetic tissues may elucidate aspects of biomaterial particle size and shape that are important to the biologic response to, and clinical outcome of, total joint replacement.

Calorimetry, Differential Scanning↗

PubMed2005

Analysis and evaluation of a biomedical polycarbonate urethane tested in an in vitro study and an ovine arthroplasty model. Part I: materials selection and evaluation.

The polyurethane elastomer (PU) Corethane 80A (Corvita) is being considered as the acetabular bearing material in a novel total replacement hip joint. The biostability of Corethane 80A was investigated in vitro (this work) and in vivo (reported separately) in a fully functioning ovine total hip arthroplasty (THA) model, with the PU as the bearing layer in a prototype compliant layer acetabular cup. The in vitro studies assessed the resistance of Corethane 80A to the main degradation mechanisms observed in PUs: hydrolysis, environmental stress cracking (ESC), metal ion oxidation (MIO) and calcification. The performance of the polycarbonate PU Corethane 80A was assessed alongside three other commercially available biomedical PUs: polyether PUs Pellethane 2363-80A (DOW Chemical) and PHMO-PU (CSIRO, not supplied as a commercial material) as well as polycarbonate PU ChronoFlex AL-80A (CardioTech). Chemical and structural variables that affect the properties of the materials were analysed with particular attention to the nature of the material's hard and soft segments. PU degradation was probed using a range of analytical tools and physical-testing methods, including mechanical testing, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and environmental scanning microscopy (ESEM). Corethane 80A displayed the best overall resistance to hydrolysis, ESC, MIO and calcification, followed by ChronoFlex 80A and PHMO-PU. Pellethane 80A was the least stable. This study provides compelling evidence for the biostability and effectiveness of Corethane 80A and points to its suitability for use as a compliant bearing layer in hip arthroplasty, and possibly also other joints.

Arthroplasty, Replacement, Hip↗

PubMed2004

Specific interactions of tryptophan with phosphatidylcholine and digalactosyldiacylglycerol in pure and mixed bilayers in the dry and hydrated state.

Amphiphilic solutes play an important role in the desiccation tolerance of plant cells, because they can reversibly partition into cellular membranes during dehydration. Their effects on membrane stability depend on their chemical structure, but also on the lipid composition of the host membrane. We have shown recently that tryptophan destabilizes liposomes during freezing. The degree of destabilization depends on the presence of glycolipids in the membranes, but not on the phase preference (bilayer or non-bilayer) of the lipids in mixtures with the bilayer lipid phosphatidylcholine. Here, we have investigated the influence of tryptophan on the phase behavior and intermolecular interactions in dry and hydrated bilayers made from the phospholipid egg phosphatidylcholine and the plant chloroplast glycolipid digalactosyldiacylglycerol, or from a mixture (1:1) of these lipids, using Fourier-transform infrared spectroscopy. To distinguish effects of the hydrophobic ring structure of tryptophan from those of the amino acid moiety, we also performed experiments with the hydrophilic amino acid glycine. Our data show that there are specific interactions between tryptophan and either phospholipid or glycolipid in the dry state, as well as H-bonding interactions between the lipids and both solutes. In the rehydrated state, the H-bonding interactions between amino acids and lipids are mostly replaced by interactions between water and lipids, while the hydrophobic interactions between lipids and tryptophan mostly persist.

Egg Yolk↗

PubMed2000

Assembly of tau protein into Alzheimer paired helical filaments depends on a local sequence motif ((306)VQIVYK(311)) forming beta structure.

We have searched for a minimal interaction motif in tau protein that supports the aggregation into Alzheimer-like paired helical filaments. Digestion of the repeat domain with different proteases yields a GluC-induced fragment comprising 43 residues (termed PHF43), which represents the third repeat of tau plus some flanking residues. This fragment self assembles readily into thin filaments without a paired helical appearance, but these filaments are highly competent to nucleate bona fide PHFs from full-length tau. Probing the interactions of PHF43 with overlapping peptides derived from the full tau sequence yields a minimal hexapeptide interaction motif of (306)VQIVYK(311) at the beginning of the third internal repeat. This motif coincides with the highest predicted beta-structure potential in tau. CD and Fourier transform infrared spectroscopy shows that PHF43 acquires pronounced beta structure in conditions of self assembly. Point mutations in the hexapeptide region by proline-scanning mutagenesis prevent the aggregation. The data indicate that PHF assembly is initiated by a short fragment containing the minimal interaction motif forming a local beta structure embedded in a largely random-coil protein.

Alzheimer Disease↗

PubMed2000

Degree of cure of orthodontic adhesives with various polymerization initiation modes.

The purpose of this study was to estimate the degree of cure (DC) of a light-cured, and a two- and a one-phase (no-mix) chemically-cured, as well as a dual-cured commercially available orthodontic adhesive resin. Forty stainless steel brackets were divided into four groups of 10 brackets each, and the bracket bases were covered with a standardized volume of adhesive. They were then pressed firmly onto a yellowish background surface of 75 per cent reflectance covered with cellulose film to facilitate detachment of the system and recovery of the set material. The visible light- and dual-cured adhesives were photopolymerized by irradiation from the incisal and cervical edges of the bracket for 10 seconds each, while another group of ceramic brackets was used to assess the differential interference of transparent relative to opaque material in the DC. Micro-multiple internal reflectance Fourier transform infrared spectroscopy was employed for the estimation of the DC of the adhesives (alpha = 0.05, n = 10), utilizing a method proposed previously. The dual-cured product demonstrated the highest DC followed by the light-cured combined with the ceramic bracket, and the no-mix and the chemically-cured adhesives. The combination of the metallic bracket with the light-cured product resulted in a DC comparable with that of the chemically-cured material.

Analysis of Variance↗

PubMed2001

[Chemical assessment of mutagenicity of halohydrocarbons: FTIR, UV spectrum characteristics of guanine-halohydrocarbon adducts].

Determination and identification of guanine-halohydrocarbon adduct isomers were carried out by high performance liquid chromatography (HPLC) and Fourier transform infrared spectroscopy (FTIR). The experimental results showed that the UV spectral overlay of O6-guanine adducts retrieved after HPLC at 260-270 nm. The UV spectra of N-side adducts are similarly between 240-250 nm. After thin layer chromatographic separation (silica gel-GF254), the all IR spectra of the N-side adducts of guanine with different halohydrocarbons showed a absorption near 1700 cm-1 assigned the characteristic peak of C=O. The IR spectra among the adducts of O6-guanine with different halohydrocarbons are quite similar.

Chromatography, High Pressure Liquid↗

PubMed2003

[Direct identification of Perilla frutescens seeds from its confusable varieties by FTIR].

The IR of kernel and boil. cortex of perilla frutescens seeds and its confusable varieties were obtained directly, quickly and accurately by Fourier transform infrared spectroscopy. The results show that IR characteristics of different peaks and intensities of kernel and boil. cortex of Perilla frutescens(L). Britt. seeds and its confusable varieties, such as Mosla scabra (Thunb.) C. Y. Wu et H. W. Li, and M. Soochouensis Matsuda, and Mosla dianthera (Buch. Ham.) Maxim., are different. Obvious characteristics for its identification with different chemical compounds in FTIR were revealed, which can be used to identify Perilla frutescens(L.) Britt. seeds and its confusable varieties. Furthermore, the approach can be achieved quickly and accurately without extraction and separation of samples.

Drug Contamination↗

PubMed1999

Fourier-transform infrared studies on azide-binding to the binuclear center of the Escherichia coli bo-type ubiquinol oxidase.

Azide-binding to the heme-copper binuclear center of bo-type ubiquinol oxidase from Escherichia coli was investigated with Fourier-transform infrared spectroscopy. Deconvolution analyses of infrared spectra of the azide (14N3)-inhibited air-oxidized form showed a major infrared azide antisymmetric stretching band at 2041 cm(-1). An additional band developed at 2062.5 cm(-1) during a longer incubation. Isotope substitutions with terminally 15N-labelled azides did not show a splitting of the major band, indicating that the geometry of the bound azide is mainly in a bridging configuration between high-spin heme o and CuB. The band at 2062.5 cm(-1) showed clear splittings upon substitution with the terminally 15N-labelled azides, indicating the Cu(2+)B-N=N=N structure. Partial reduction of the oxidase with beta-NADH in the presence of azide caused an appearance of new infrared bands at 2038.5 (major) and 2009 (minor) cm(-1). The former band also showed clear splittings in the presence of the terminally 15N-labelled azides, indicating that reduction of low-spin heme b alters the structure of the binuclear center leading to the Fe(3+)o-N=N=N configuration.

Azides↗

PubMed2004

Structural characterization and enantioseparation of the chiral compound praziquantel.

In this study, we aimed to characterize the chiral compound type of a leading antischistosomal drug, praziquantel. The optically pure praziquantel enantiomers were recovered from the racemic mixture by enantiomeric separation, which was performed on preparative scale chromatography by using a novel beta-cyclodextrin type chiral column. The thermodynamic properties of praziquantel were determined from differential scanning calorimetry and the physical properties were studied by examining Fourier transform infrared spectroscopy and X-ray powder diffraction. Based on the differential scanning calorimetry data, a melting point binary phase diagram was constructed. A ternary solubility phase diagram of praziquantel in methanol was also determined at the temperature of 0 degrees C. All the experimental results support the conclusion that praziquantel is a racemic compound. The characterization of physical properties of praziquantel and the phase diagram are crucial for understanding the rationality for the successful resolution of praziquantel and also provide the basis for designing the strategy of separation and recovery of pure enantiomer.

Molecular Structure↗

PubMed2005

Analysis and evaluation of a biomedical polycarbonate urethane tested in an in vitro study and an ovine arthroplasty model. Part II: in vivo investigation.

The polyurethane (PU) elastomer Corethane 80A (Corvita) is being considered as the acetabular bearing material in a novel total replacement hip joint. Its biostability was investigated in vitro (Analysis and evaluation of a biomedical polycarbonate urethane tested in an in vitro study and an ovine arthroplasty model. Part I: material selection and evaluation, Biomaterials, in press) together with three other commercially available biomedical PUs: Pellethane 2363-80A (DOW Chemical), a polyhexamethylene oxide based PU, PHMO-PU (CSIRO, not supplied as a commercial product) and ChronoFlex AL-80A (CardioTech). From the in vitro studies, Corethane 80A displayed the best overall resistance to hydrolysis, ESC, MIO and calcification, followed by ChronoFlex 80A and PHMO-PU, with Pellethane 80A being the least stable. Building on the in vitro investigation, the follow-up in vivo study (reported here) assessed Corethane 80A as the bearing layer in a prototype compliant layer acetabular cup, in a fully functioning ovine total hip arthoplasty (THA) model. PU degradation in the retrieved cups was analysed using a range of analytical and physical-testing methods including mechanical testing, differential scanning calorimetry, Fourier transform infrared spectroscopy and environmental scanning electron microscopy. The Corethane 80A functioned well in the THA model, with the bearing surfaces of the retrieved hip cups showing no significant evidence of biodegradation or wear damage after 3 years in vivo. The findings in this study provide compelling evidence for the biostability and effectiveness of acetabular cups incorporating a Corethane 80A compliant bearing layer.

Absorptiometry, Photon↗

PubMed2004

Systematic evolution of a porous hydroxyapatite-poly(vinylalcohol)-gelatin composite.

Hydroxyapatite (HAp)-poly(vinylalcohol) (PVA)-gelatin nanocomposite was biomimetically synthesized and characterized. Fourier transform infrared spectroscopy (FT-IR) analysis of hydroxyapatite, hydroxyapatite-poly(vinylalcohol) and hydroxyapatite-poly(vinylalcohol)-gelatin composites show modification of hydroxyl, amide and phosphate bands as a result of chemical interaction of hydroxyapatite with the above composite matrices. Transmission electron microscopy (TEM) confirmed the time-dependent development of a porous structure of hydroxyapatite-poly(vinylalcohol)-gelatin as a consequence of nucleation at the HAp aggregate-matrix interface. A literature survey holds great promise for the above as scaffolds in terms of increased mechanical properties and bioactivity.

Biocompatible Materials↗