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Results for “Spectroscopy, Fourier Transform Infrared”

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PubMed2005

Physicochemical model of alginate-poly-L-lysine microcapsules defined at the micrometric/nanometric scale using ATR-FTIR, XPS, and ToF-SIMS.

Alginate-poly-L-lysine-alginate (APA) microcapsules are currently being investigated as a means to immuno-isolate transplanted cells, but their biocompatibility is limited. In this study, we verified the hypothesis that poly-L-lysine (PLL), which is immunogenic when unbound, is exposed at the APA microcapsule surface. To do so, we analysed the microcapsule membrane at the micrometric/nanometric scale using attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. The results indicate that PLL and alginate molecules interact within the membrane. PLL exists in considerable amounts near the surface, contributing to the majority of the carbon within the outermost 100 Angstroms of the membrane. PLL was also detected at the true surface (the outermost monolayer) of the microcapsules. The exposure of PLL does not appear to result from defects in the outer alginate coating. This physicochemical model of APA microcapsules could explain their immunogenicity and will play an important role in the optimization of the microcapsule design.

Alginates↗

PubMed2006

Spectroscopic characterization of zinc oxide nanorods synthesized by solid-state reaction.

Well-crystallized zinc oxide nanorods have been fabricated by single step solid-state reaction using zinc acetate and sodium hydroxide, at room temperature. The sodium lauryl sulfate (SLS) stabilized zinc oxide nanorods were characterized by using X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and photoluminescence spectroscopy. The X-ray diffraction revealed the wurtzite structure of zinc oxide. The size estimation by XRD and TEM confirmed that the ZnO nanorods are made of single crystals. The growth of zinc oxide crystals into rod shape was found to be closely related to its hexagonal nature. The mass ratio of SLS:ZnO in the nanorods was found to be 1:10 based on the thermogravimetric analysis. Blue shift of photoluminescence emission was noticed in the ZnO nanorods when compared to that of ZnO bulk. FT-IR analysis confirmed the binding of SLS with ZnO nanorods. Apart from ease of preparation, this method has the advantage of eco-friendliness since the solvent and other harmful chemicals were eliminated in the synthesis protocol.

Materials Testing↗

PubMed1997

A predicted beta-sheet from class S components of staphylococcal gamma-hemolysin is essential for the secondary interaction of the class F component.

Site-directed mutagenesis was performed on genes encoding HlgA and HlgC, two of the three proteins expressed from the staphylococcal y-hemolysin locus, which originate two pore-forming toxins (HlgA + HlgB, HlgC + HlgB). As related proteins, HlgA and HlgC were found to bind first to cell membranes. Amino acid substitutions concerned residues that would predictably disrupt a 13 amino acid conserved beta-sheet of the Chou and Fasman secondary structure prediction. The mutation of a threonin into an aspartic acid residue from HlgA (T28D) and from HlgC (T30D) that would break this predicted N-terminal structure lowered dramatically the biological activities on purely lipidic vesicles, erythrocytes and polymorphonuclear cells. The change in secondary structure was confirmed by Fourier Transformed Infrared spectroscopy. The binding of mutated and native proteins at the same kind of sites onto polymorphonuclear cells was evidenced with flow cytometry and fluorescein-labelled anti-class S antibodies or wild type HlgA or HlgC. However, the subsequent binding of fluorescein-labelled HlgB to membrane-bound mutated HlgA or HlgC complexes was inhibited. In conclusion, the first binding of class S components is essential for the subsequent binding of class F components, and a predicted beta-sheet seems to be at least one of the functional domains involved.

Animals↗

PubMed2000

Structure and dynamics of lipid-associated states of apocytochrome c.

Apocytochrome c (apocyt c), which in aqueous solution is largely unstructured, acquires an alpha-helical conformation upon association with lipid membranes. The extent of alpha-helix induced in apocyt c is lipid-dependent and this folding process is driven by both electrostatic and hydrophobic lipid-protein interactions. The structural and dynamic properties of apocyt c in lipid membranes were investigated by attenuated total reflection Fourier transform infrared spectroscopy combined with amide H-D exchange kinetics. Apocyt c acquires a higher content of alpha-helical structure with negatively charged membranes than with zwitterionic ones. For all membranes studied here, the helices of these partially folded states of apocyt c have a preferential orientation perpendicular to the plane of the lipid membrane. The H-D exchange revealed that a small fraction of amide protons of apocyt c, possibly associated with a stable folded domain protected by the lipid, remained protected from exchange over 20 min. However, a large fraction of amide protons exchanged in less than 20 min, indicating that the helical states of apocyt c in lipid membranes are very dynamic.

Apoproteins↗

PubMed1995

New oral dosage form for elderly patients: preparation and characterization of silk fibroin gel.

The pharmaceutical utility of silk fibroin as a possible material for an oral dosage form for elderly patients was investigated. Silk fibroin gel (SFG) was prepared from its aqueous solution. The gel formation was studied as a function of adjusted pH and concentration of silk fibroin (SF). On the basis of Fourier transform infrared spectroscopy of SFG, the transition from the random coil to the beta-structure was observed. The rate of gelation was sufficiently accelerated by the addition of glycerol to the SF aqueous solution. The glycerol content also affected the rate of gelation of the SF solution. Rheological properties of SFG were evaluated using a creep meter. The SF content and/or glycerol content affected the breaking stress of SFG. Moisture desorption from SFG was retarded with an increase in glycerol content. It was found that SFG was able to be prepared at room temperature (20 +/- 5 degrees C), and the SF content and glycerol content affected the formation and physicochemical properties of SFG.

Administration, Oral↗

PubMed2002

[Reconstruction algorithms of computed tomography of remote sensing FTIR].

Reconstruction algorithms of computed tomography-remote sensing fourier transform infrared spectroscopy plays a key role in fast and cost-effective acquirement of gas concentration distribution. Ideally, a reconstruction algorithm can be used to obtain good reconstruction maps only by limited number of measurements and non-symmetric ray configurations, even in the presence of instrument noise, measurement error, poor beam geometry, and variations in the contaminant spatial distribution. Several conventional reconstruction algorithms used to reconstruct two-dimensional concentration maps of the vapor contaminants by remote sensing FTIR, such as ART, MART, SIRT and SBFM, have been reviewed in this paper. Comparing to ART, MART has the advantages of iterative speed and iterative precision, while SIRT overcomes the problem of illegibility and SBFM can reduce the noise sharply.

Air Pollutants↗

PubMed1999

Lipid uptake in synthetic vascular prostheses explanted from humans.

Previous in vivo studies in humans and dogs have revealed an atherosclerosis-like phenomenon in which lipid penetration within arterial prosthesis wall was observed. The primary goal of the present study was therefore to investigate the occurrence of this lipid retention in ePTFE prostheses implanted in humans and therefore identify potential risk factors related to this phenomenon. Lipid uptake in 367 ePTFE microporous vascular prostheses explanted from humans was studied using Fourier transform infrared spectroscopy. The assignment of the infrared absorption features clearly revealed the presence of strongly bonded unsaturated fatty acids to the microporous structure of the prostheses. A one-way ANOVA statistical analysis showed that the lipid uptake in the synthetic vascular prostheses depended on the duration of implantation of the prosthesis and on the sex of the patient. A two-way ANOVA showed that a relationship existed between the estimated lipid uptake and the internal diameter of the prosthesis. These results confirm that the lipid uptake phenomenon depends on some clinical factors related either to the patients or to the prostheses' morphological parameters.

Aged↗

PubMed2005

Solution behavior of IFN-beta-1a: an empirical phase diagram based approach.

An empirical phase diagram approach has been developed as a practical tool to aid macromolecular preformulation/formulation studies. This method employs an eigenvector based procedure to visualize and interpret complex data sets. Human Inteferon-beta-1a, an important therapeutic protein, was used to further develop the method and test its utility. The protein was characterized in solution as a function of pH (2-8), temperature (10 degrees C-85 degrees C) and ionic strength (I = 0.1 and 1.0) using intrinsic and ANS fluorescence, Far-UV circular dichroism (Far-UV CD), Fourier Transform Infrared spectroscopy (FTIR) and derivative UV absorbance spectroscopies, as well as differential scanning calorimetry (DSC) to supplement spectroscopic thermal stability studies. Derivative UV absorbance data were initially used to construct a pH-temperature phase diagram at each ionic strength. Three distinctive phases at I = 0.1 and two major phases at I = 1.0 were identified corresponding to different conformation/aggregation states of the protein. For the first time, heterogeneous data sets (i.e., data from different techniques) including Far-UV CD, fluorescence and UV absorbance results were used to generate empirical phase diagrams. Results from different data sets are compared; precautions in applying the method and its overall utility are discussed.

Calorimetry, Differential Scanning↗

PubMed2000

Ligand--protein interactions in the glutamate receptor.

Fourier transform infrared spectroscopy was used to investigate ligand-protein interactions in the ligand-binding domain of the GluR4 glutamate receptor subunit. Glutamate binding induces more extensive secondary structural changes in the ligand-binding domain than does kainate binding. Glutamate also alters the hydrogen bonding strength of the single free cysteine side chain in the domain, while kainate does not. On the other hand, the interaction of a binding site arginine residue with kainate appears to be stronger than that with glutamate. These results identify chemical and structural differences that may explain the different functional characteristics of the two agonists acting on ionotropic glutamate receptors. In doing so, they complement and extend recent crystallographic structures of the ligand-binding domain.

Binding Sites↗

PubMed2001

Distinct properties of wild-type and the amyloidogenic human cystatin C variant of hereditary cerebral hemorrhage with amyloidosis, Icelandic type.

Variant human cystatin C (L68Q) is an amyloidogenic protein. It deposits in the cerebral vasculature of Icelandic patients with cerebral amyloid angiopathy, leading to stroke. Wild-type and variant cystatin C are cysteine proteinase inhibitors which form concentration dependent inactive dimers; however, variant cystatin C dimerizes at lower concentrations and has an increased susceptibility to a serine protease. We studied the effect of the L68Q amino acid substitution on cystatin C properties, utilizing full length cystatin C purified in mild conditions from media of cells stably transfected with either the wild-type or variant cystatin C genes. The variant cystatin C forms fibrils in vitro detectable by electron microscopy in conditions in which the wild-type protein forms amorphous aggregates. We also show by circular dichroism, steady-state fluorescence and Fourier-transformed infrared spectroscopy that the amino acid substitution modifies cystatin C structure by destabilizing alpha-helical structures and exposing the tryptophan residue to a more polar environment, yielding a more unfolded molecule. These spectral changes demonstrate that variant cystatin C has a three-dimensional structure different from that of the wild-type protein. The structural differences between variant and wild-type cystatin C account for the susceptibility of the variant protein to unfolding, proteolysis and fibrillogenesis.

Amino Acid Substitution↗

PubMed2003

Time-resolved Fourier transform infrared spectrometry using a microfabricated continuous flow mixer: application to protein conformation study using the example of ubiquitin.

We report on the use of time-resolved Fourier transform infrared spectroscopy (FT-IR) to study chemically induced conformational changes of proteins using the example of ubiquitin. For this purpose a micromachined mixer is coupled to a conventional IR transmission cell with a pathlength of 25 microm and operated in both the continuous and the stopped-flow mode. This experimental set-up allows the elucidation of reaction pathways in the time frame of about 500 milliseconds to seconds with little reagent consumption and low pressure. For continuous flow measurements employed in the time frame from 0.5 to 1.4 s the reaction time is determined by the flow rate used as the connection between the point of confluence in the micromixer and the flow cell was kept constant in all experiments. For stopped-flow experiments (>1.4 s) the time is determined by data acquisition of the rapid scanning infrared spectrometer. Ubiquitin, a small well-known protein with 76 amino acid residues, changes its conformation from native to A-state with the addition of methanol under low pH conditions. We investigated the conformational change in the time frame from 0.5 to 10 s by mixing ubiquitin (20% methanol-d(4)) with an 80% methanol-d(4) solution at pD 2 by evaluating the time dependent changes in the amide I band of the protein.

Amides↗

PubMed2003

Albumin and fibrinogen adsorption on PU-PHEMA surfaces.

Materials that adsorb specific proteins may find a variety of applications in the biomedical field. The aim of this study was the preparation of a hydrophilic surface, with low protein adsorption, to be used in the future as a support for the immobilisation of several species, e.g. Cibacron Blue F3G-A, which has been described to induce specific albumin adsorption. Poly(hydroxyethylmethacrylate) (PHEMA) and poly(hydroxyethylacrylate) (PHEA) were chosen as the hydrophilic surface because they can be easily polymerised and possess hydroxyl groups that can be used for the immobilisation of different compounds. Thin films of PHEMA and PHEA were successfully graft polymerised onto the surface of a commercial poly(etherurethane) (PU) using ceric ion as initiator. Grafting polymerisations were followed by mass gain and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Since stability tests demonstrated that only PU-PHEMA was stable in alkaline solutions, a necessary condition to future immobilisations, the investigation was focused on the coating of PU with PHEMA. PU-PHEMA films were characterised in detail using several techniques as mass gain, ATR-FTIR, contact angle measurements, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Protein adsorption was evaluated using radiolabelled albumin and fibrinogen from pure solutions and from mixtures of both proteins. PU surfaces modified with PHEMA have demonstrated low protein adsorption, showing their potential use as substrates. This opens the possibly of exploring the advantages of selective adsorption by appropriate immobilisation of specific molecules.

Adsorption↗

PubMed1997

ATR-FTIR spectroscopic investigation of imipenem-susceptible and -resistant Pseudomonas aeruginosa isogenic strains.

The primary mechanism of imipenem resistance in Pseudomonas aeruginosa has been ascribed to an outer membrane impermeability owing to a loss of expression of protein D2. Attenuated total reflection-Fourier transform infrared spectroscopy in conjunction with statistical methods has been used as a new approach to rapidly discriminate four isogenic strains of P. aeruginosa--susceptible, less susceptible, and highly resistant to imipenem-- and to follow the structural modifications related to this low permeability. Decomposition of the broad protein and carbohydrate contours into underlying Gaussians and comparison of the susceptible and highly resistant strain provided quantitative and ultrastructural information on these strains. This methodology allows for discrimination not of the mutation itself but of its consequences observed in the protein and carbohydrate absorption regions. Its association with other existing biochemical methods may be envisaged since it may allow for rapid orientation of investigations in the field of bacterial resistance diagnosis.

Bacterial Outer Membrane Proteins↗

PubMed2002

Thermal stability: a means to assure tertiary structure in therapeutic proteins.

To be both safe and effective, a therapeutic product must have the correct chemical structure and be free of harmful contaminants. Structure in protein therapeutic products, however, implies not only the correct sequence of amino acids (primary structure) but also the proper folding of that amino acid chain in three-dimensional space (tertiary structure). This work is part of a general strategy to develop a battery of physico-chemical methods that could give assurances of structure (and hence function) in formulated therapeutic proteins in the absence of in vivo data. It focuses on recombinant human growth hormone (rhGH), a well-characterized therapeutic protein, and examines the utility of thermodynamic parameters in assessing its tertiary structure. Resistance of solutions of formulated rhGH to thermal denaturation was followed using Fourier Transform Infrared Spectroscopy (FTIR) by observing decreases in total helicity and increases in intermolecular beta-sheet formation. Under conditions known to induce changes in the intra-molecular ionic and H-bonding patterns stabilizing the tertiary structure but not affecting the protein's secondary structure or global fold, we have observed upwards of a 12 degrees C shift in the melting temperature of the protein. Furthermore, our results indicated that the T(m) of unfolding of rhGH was sensitive to much more subtle changes in the protein structure. Thus, resistance to thermal denaturation may well be a useful means to measure structure in formulations of well-characterized therapeutic proteins.

Deuterium↗

PubMedDate not supplied

Analysis of a retrieved polyethylene total disc replacement component.

BACKGROUND CONTEXT: Although total disc replacements have been performed in Europe since the 1980s, this type of surgery is still new in the United States. The clinical performance of polyethylene in total disc replacements is still not well understood. PURPOSE: To describe the wear, surface damage, oxidation and mechanical properties in an explanted polyethylene total disc replacement component. STUDY DESIGN/SETTING: Case report, analysis of retrieved implant. PATIENT SAMPLE: Case report. OUTCOME MEASURES: Analysis of wear, oxidation and mechanical properties in the retrieved total disc replacement. METHODS: A 49-year-old female patient was implanted at L5-S1 with an SB Charite total disc prosthesis (DePuy Spine, Raynham, MA). After 1.6 years, the patient underwent a posterior, instrumented fusion because of intractable low back, left buttock and radicular left leg pain. Preoperative diagnostics revealed loosening at the bone implant interface at L5 and S1, anterior migration of the L5 base plate and severe degeneration of the L5-S1 facet joints. The retrieved polyethylene core showed evidence of damage around the periphery or rim. Transverse, subsurface cracks in the polyethylene, which initiated near the rim and penetrated into the interior of the component, were imaged using thin-film optical microscopy and micro-computed-tomography imaging. Analysis using Fourier transform infrared spectroscopy (American Society for Testing and Materials [ASTM] F2102) documented low levels of oxidation within 1 mm of the articulating surface. Miniature specimen mechanical testing (ASTM F2183), conducted near the surface where the oxidation was greatest, demonstrated that the mechanical properties were not substantially degraded. CONCLUSION: In this case, the anterior revision surgery was difficult and potentially life-threatening. The revision strategy of an instrumented posterior fusion to salvage a failed SB Charite disc replacement may be unpredictable and, in this case, ultimately unsuccessful. Despite the small size of the retrieved polyethylene core, ASTM standard test techniques developed for analysis of retrieved hip and knee replacements were readily adapted for the total disc prosthesis.

Arthroplasty, Replacement↗

PubMed2000

Do parallel beta-helix proteins have a unique fourier transform infrared spectrum?

Several polypeptides have been found to adopt an unusual domain structure known as the parallel beta-helix. These domains are characterized by parallel beta-strands, three of which form a single parallel beta-helix coil, and lead to long, extended beta-sheets. We have used ATR-FTIR (attenuated total reflectance-fourier transform infrared spectroscopy) to analyze the secondary structure of representative examples of this class of protein. Because the three-dimensional structures of parallel beta-helix proteins are unique, we initiated this study to determine if there was a corresponding unique FTIR signal associated with the parallel beta-helix conformation. Analysis of the amide I region, emanating from the carbonyl stretch vibration, reveals a strong absorbance band at 1638 cm(-1) in each of the parallel beta-helix proteins. This band is assigned to the parallel beta-sheet structure. However, components at this frequency are also commonly observed for beta-sheets in many classes of globular proteins. Thus we conclude that there is no unique infrared signature for parallel beta-helix structure. Additional contributions in the 1638 cm(-1) region, and at lower frequencies, were ascribed to hydrogen bonding between the coils in the loop/turn regions and amide side-chain interactions, respectively. A 13-residue peptide that forms fibrils and has been proposed to form beta-helical structure was also examined, and its FTIR spectrum was compared to that of the parallel beta-helix proteins.

Acyltransferases↗

PubMed2003

Nanosecond temperature jump relaxation dynamics of cyclic beta-hairpin peptides.

The thermal unfolding of a series of 6-, 10-, and 14-mer cyclic beta-hairpin peptides was studied to gain insight into the mechanism of formation of this important secondary structure. The thermodynamics of the transition were characterized using temperature dependent Fourier transform infrared spectroscopy. Thermodynamic data were analyzed using a two-state model which indicates increasing cooperativity along the series. The relaxation kinetics of the peptides in response to a laser induced temperature jump were probed using time-resolved infrared spectroscopy. Single exponential relaxation kinetics were observed and fit with a two-state model. The folding rate determined for these cyclic peptides is accelerated by some two orders of magnitude over the rate of a linear peptide that forms a beta-hairpin. This observation supports the argument that the rate limiting step in the linear system is either stabilization of compact collapsed structures or rearrangement of collapsed structures over a barrier to achieve the native interstrand registry. Small activation energies for folding of these peptides obtained from an Arrhenius analysis of the rates imply a primarily entropic barrier, hence an organized transition state having specific stabilizing interactions.

Kinetics↗

PubMed2005

Quantitative analysis of monomer vapor release from two-solution bone cement by using a novel FTIR technique.

Methyl methacrylate monomer can evaporate from bone cement to reach cytotoxic levels of concentrations in the implant bed of total joint prosthesis. Therefore, this study was performed by using a novel Fourier transform infrared spectroscopy method to quantify the release of monomer vapor from experimental two-solution bone cement in vitro during polymerization, to examine the effect of surface area versus cement mass, and to explore the effect of initiation chemistry. The results revealed that monomer vapor release is a surface phenomenon. In addition, initiation chemistry plays a major role in controlling the reaction time, and therefore heat concentration and dissipation, which resulted in a higher absorbance peak as initiation chemicals concentration increased. It was concluded that using the FTIR to monitor MMA vapors is an effective technique to obtain quantitative information about monomer vapor release from bone cements during polymerization and provides insight on the polymerization kinetics of two-solution acrylic bone cement.

Biocompatible Materials↗