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PubMed2005

A1 reduction in intact cyanobacterial photosystem I particles studied by time-resolved step-scan Fourier transform infrared difference spectroscopy and isotope labeling.

Time-resolved step-scan Fourier transform infrared (FTIR) difference spectroscopy, with 5 mus time resolution, has been used to produce P700(+)A(1)(-)/P700A(1) FTIR difference spectra in intact photosystem I particles from Synechococcus sp. 7002 and Synechocystis sp. 6803 at 77 K. Corresponding spectra were also obtained for fully deuterated photosystem I particles from Synechococcus sp. 7002 as well as fully (15)N- and (13)C-labeled photosystem I particles from Synechocystis sp. 6803. Static P700(+)/P700 FTIR difference spectra at 77 K were also obtained for all of the unlabeled and labeled photosystem I particles. From the time-resolved and static FTIR difference spectra, A(1)(-)/A(1) FTIR difference spectra were constructed. The A(1)(-)/A(1) FTIR difference spectra obtained for unlabeled trimeric photosystem I particles from both cyanobacterial strains are very similar. There are some mode frequency differences in spectra obtained for monomeric and trimeric PS I particles. However, the spectra can be interpreted in an identical manner, with the proposed band assignments being compatible with all of the data obtained for labeled and unlabeled photosystem I particles. In A(1)(-)/A(1) FTIR difference spectra obtained for unlabeled photosystem I particles, negative bands are observed at 1559 and 1549-1546 cm(-)(1). These bands are assigned to amide II protein vibrations, as they downshift approximately 86 cm(-)(1) upon deuteration and approximately 13 cm(-)(1) upon (15)N labeling. Difference band features at 1674-1677(+) and 1666(-) cm(-)(1) display isotope-induced shifts that are consistent with these bands being due to amide I protein vibrations. The observed amide modes suggest alteration of the protein backbone (possibly in the vicinity of A(1)) upon A(1) reduction. A difference band at 1754(+)/1748(-) cm(-)(1) is observed in unlabeled spectra from both strains. The frequency of this difference band, as well as the observed isotope-induced shifts, indicate that this difference band is due to a 13(3) ester carbonyl group of chlorophyll a species, most likely the A(0) chlorophyll a molecule that is in close proximity to A(1). Thus A(1) reduction perturbs A(0), probably via a long-range electrostatic interaction. A negative band is observed at 1693 cm(-)(1). The isotope shifts associated with this band are consistent with this band being due to the 13(1) keto carbonyl group of chlorophyll a, again, most likely the 13(1) keto carbonyl group of the A(0) chlorophyll a that is close to A(1). Semiquinone anion bands are resolved at approximately 1495(+) and approximately 1414(+) cm(-)(1) in the A(1)(-)/A(1) FTIR difference spectra for photosystem I particles from both cyanobacterial strains. The isotope-induced shifts of these bands could suggest that the 1495(+) and 1414(+) cm(-)(1) bands are due to C-O and C-C modes of A(1)(-), respectively.

Amides↗
PubMed2006

Fourier transform infrared imaging and MR microscopy studies detect compositional and structural changes in cartilage in a rabbit model of osteoarthritis.

Assessment of subtle changes in proteoglycan (PG) and collagen, the primary macromolecular components of cartilage, which is critical for diagnosis of the early stages of osteoarthritis (OA), has so far remained a challenge. In this study we induced osteoarthritic cartilage changes in a rabbit model by ligament transection and medial meniscectomy and monitored disease progression by infrared fiber optic probe (IFOP) spectroscopy, Fourier transform infrared imaging spectroscopy (FT-IRIS), and magnetic resonance imaging (MRI) microscopy. IFOP studies combined with chemometric partial least-squares analysis enabled us to monitor progressive cartilage surface changes from two to twelve weeks post-surgery. FT-IRIS studies of histological sections of femoral condyle cartilage revealed that compared with control cartilage the OA cartilage had significantly reduced PG content 2 and 4 weeks post-surgery, collagen fibril orientation changes 2 and 4 weeks post-surgery, and changes in collagen integrity 2 and 10 weeks post-surgery, but no significant changes in collagen content at any time. MR microscopy studies revealed reduced fixed charge density (FCD), indicative of reduced PG content, in the OA cartilage, compared with controls, 4 weeks post-surgery. A non-significant trend toward higher apparent MT exchange rate, k(m), was also found in the OA cartilage at this time point, suggesting changes in collagen structural features. These two MR findings for FCD and k(m) parallel the FT-IRIS findings of reduced PG content and altered collagen integrity, respectively. MR microscopy studies of the cartilage at the 12-week time point also found a trend toward longer T (2) values and reduced anisotropy in the deep zone of the OA cartilage, consistent with increased hydration and less ordered collagen. These studies reveal that FT-IRIS and MR microscopy provide complementary data on compositional changes in articular cartilage in the early stages of osteoarthritic degradation.

Animals↗
PubMed1999

Vibrational modes of ubiquinone in cytochrome bo(3) from Escherichia coli identified by Fourier transform infrared difference spectroscopy and specific (13)C labeling.

In this study we present the infrared spectroscopic characterization of the bound ubiquinone in cytochrome bo(3) from Escherichia coli. Electrochemically induced Fourier transform infrared (FTIR) difference spectra of DeltaUbiA (an oxidase devoid of bound ubiquinone) and DeltaUbiA reconstituted with ubiquinone 2 and with isotopically labeled ubiquinone 2, where (13)C was introduced either at the 1- or at the 4-position of the ring (C=O groups), have been obtained. The vibrational modes of the quinone bound to the discussed high-affinity binding site (Q(H)) are compared to those from the synthetic quinones in solution, leading to the assignment of the C=O modes to a split signal at 1658/1668 cm(-)(1), with both carbonyls similarly contributing. The FTIR spectra of DeltaUbiA reconstituted with the labeled quinones indicate an essentially symmetrical and weak hydrogen bonding of the two C=O groups from the neutral quinone with the protein and distinct conformations of the 2- and 3-methoxy groups. Perturbations of the vibrational modes of the 5-methyl side groups are discussed for a signal at 1452 cm(-)(1). Only negligible shifts of the aromatic ring modes can be reported for the reduced and the protonated form of the quinone. Alterations of the protein upon quinone binding are reflected in the electrochemically induced FTIR difference spectra. In particular, difference signals at 1640-1633 cm(-)(1) and 1700-1670 cm(-)(1) indicate variations of beta-sheet secondary structure elements and loops, bands at 1706 and 1678 cm(-)(1) are tentatively attributed to individual amino acids, and a difference signal a 1540 cm(-)(1) is discussed to reflect an influence on C=C modes of the porphyrin ring or on deprotonated propionate groups of the hemes. Further tentative assignments are presented and discussed. The (13)C labeling experiments allow the assignment of the vibrational modes of a bound ubiquinone 8 in the electrochemically induced FTIR difference spectra of wild-type bo(3).

Binding Sites↗
PubMed1997

Z,E isomerization of the alpha-84 phycoviolobilin chromophore of phycoerythrocyanin from Mastigocladus laminosus investigated by Fourier-transform infrared difference spectroscopy.

The photoreaction of the phycoviolobilin (PVB) chromophore-containing part of phycoerythrocyanin (PEC) from Mastigocladus laminosus was investigated by Fourier-transform infrared spectroscopy (FT-IR). Difference spectra between the parent states P566 and P507 were obtained in 1H2O and 2H2O for the first time. The spectra are generally characterised by large changes in the range between 1710 and 1590 cm(-1) and by a strong difference band around 1270 cm(-1). In order to study the influence on the PVB chromophore upon aggregation, spectra of the alpha-subunit and the (alphabeta)3 trimer are compared, showing distinct differences which may be of relevance for the chromophore-protein and protein-protein interactions. The difference spectra demonstrate many similarities to the spectra recently obtained for the Pr --> meta-Rc transition of phytochrome [Foerstendorf et al. (1996) Biochemistry 35, 10793-10799]. In particular, a band around 1710 cm(-1), which was tentatively assigned to the C = O stretch of ring D is also observed in the spectra of PEC. It strongly supports this identification and the deduced molecular interpretation on the protonation state of the chromophore.

Cyanobacteria↗
PubMed1993

Three-dimensional structure and molecular modelling of C1- inhibitor.

New data on the structure of C1- inhibitor have become available as the result of the completion of its amino acid and nucleic acid sequences and its carbohydrate content, together with data from neutron scattering, crystal structure determinations, 1H NMR spectroscopy and Fourier transform infrared spectroscopy. C1- inhibitor is a two-domain protein. It is constructed as a heavily glycosylated N-terminal domain with 113 amino acids and 3 N-linked and 7 O-linked oligosaccharides, and a C-terminal domain with 365 amino acids and 3 N-linked oligosaccharides. Its molecular weights is calculated as 71,100, rather than the apparent value of 105,000 commonly reported from SDS-PAGE. Neutron scattering shows that C1- inhibitor possesses a distinct two domain structure in which an extended N-terminal domain with extended carbohydrate structures is attached to the C-terminal SERPIN domain. The length of C1- inhibitor is 18 nm, rather than that of 33 nm originally proposed from electron microscopy. Microcalorimetry supports the concept of two independently-folded domains in the C1- inhibitor structure. Combination of the C1- inhibitor sequence with crystal structure determinations of proteins belonging to the SERPIN superfamily of serine protease inhibitors shows that the protein structure of the C-terminal domain is well-described in terms of this structure. Comparison of the exon structure of C1- inhibitor with its presumed protein crystal structure shows that the 7 exons are distributed throughout the SERPIN fold with no obvious segregation into structural elements. Native C1- inhibitor is cleaved at its reactive centre loop to release a more stable cleaved form that is no longer active. 1H NMR spectroscopy shows that structures involved in hydrophobic interactions within the core of the SERPIN fold are preserved to within 0.05 nm before and after the transition. Fourier transform infrared spectroscopy shows the presence of alpha-helix and beta-sheet in both forms. Large changes are detectable in both the alpha-helix and beta-sheet contents of the SERPIN fold, and these changes are matched by a greater rate of 1H-2H exchange in 2H2O solvents in the native form than in the cleaved form. These data show that changes in the whole secondary structure and not just in the reactive site loop are involved in SERPIN inactivation.

Amino Acid Sequence↗
PubMed1995

Prediction and Fourier-transform infrared-spectroscopy estimation of the secondary structure of a recombinant beta-glucosidase from Streptomyces sp. (ATCC 11238).

The secondary structure of a recombinant beta-glucosidase (EC 3.2.1.21) from Streptomyces sp. (ATCC 11238) has been predicted by computer algorithms and also estimated by Fourier-transform IR spectroscopy. From curve fitting of the deconvoluted IR spectra, the most probable distribution of the secondary-structural classes appears to be about 34% alpha-helix, 30% beta-sheet, 25% reverse turns and 11% non-ordered structures. These data showed a good agreement with data from computer prediction (35% alpha-helix, 23% beta-sheet, 31% reverse turns and 11% non-ordered structures).

Algorithms↗
PubMed1995

Bicarbonate binding to the non-heme iron of photosystem II investigated by Fourier transform infrared difference spectroscopy and 13C-labeled bicarbonate.

The binding site of the non-heme iron of photosystem II (PS II) is investigated by light-induced Fourier tranform infrared (FTIR) difference spectroscopy on Tris-washed membranes. The non-heme iron is oxidized (Fe3+) in the dark with ferricyanide and reduced (Fe2+) after light-induced charge separation by electron transfer from the semiquinone anion QA-. EPR experiments and IR modes of ferri- and ferrocyanide show that the electron donor side of PS II is reduced in less than 2 s after a flash and that ferricyanide reoxidizes the non-heme iron with a half-time of approximately 20 s. Recording FTIR spectra before and 2 s after flash illumination thus results in the Fe2+/Fe3+ difference spectrum. This spectrum shows band shifts and intensity changes of IR modes from ligands and neighboring residues of the non-heme iron. The IR modes of bicarbonate are revealed by comparison of Fe2+/Fe3+ spectra obtained on PS II membranes with 12C or 13C isotope labeled bicarbonate in H2O and in 2H2O. The nu as(CO) and nu s(CO) modes of bicarbonate in the Fe2+ state are assigned at 1530 +/- 10 and 1338 cm-1, respectively. The low frequency of the nu as(CO) mode is taken as experimental evidence that bicarbonate is a ligand of the non-heme iron. Furthermore, the small frequency difference (192 cm-1) between the nu as(CO) and nu s(CO) modes as compared to even hydrogen-bonded ionic bicarbonate strongly indicates that bicarbonate is a bidentate ligand of the non-heme iron in PS II. Upon iron oxidation, the bicarbonate modes are largely affected. The nu s(CO) mode is assigned at 1228 cm-1, while the nu as(CO) mode is tentatively assigned at 1658 +/- 20 cm-1. The strong up- and downshifts of the nu as and nu s(CO) modes of bicarbonate upon iron oxidation results in a frequency difference of 430 +/- 20 cm-1 that is not only explained by the increased charge on the iron but indicates that bicarbonate is a monodentate ligand of the oxidized iron. The sensitivity of the nu s(CO) mode of bicarbonate to 1H/2H exchange in both the Fe2+ and Fe3+ states and the presence in the Fe2+ state of a delta (COH) mode at 1258 cm-1 confirm that bicarbonate and not carbonate is the iron ligand and further exhibits hydrogen bond(s) with the protein. The 13C isotope-sensitive modes of bicarbonate are not affected by 15N labeling of the PS II membranes. 15N sensitive signals at 1111/1102 and 1094 cm-1 are assigned to side chain modes from histidine ligands of the iron. The latter signal is proposed to account for a histidine ligand that deprotonates upon iron oxidation. The involvement of protein peptide groups and side chains in the hydrogen-bond network around the iron is also discussed.

Bicarbonates↗
PubMed1998

Structural dynamics of the Streptomyces lividans K+ channel (SKC1): secondary structure characterization from FTIR spectroscopy.

Fourier transform infrared (FTIR) spectroscopy was used to probe the secondary structure, orientation, and the kinetics of amide hydrogen-deuterium exchange (HX) of the small K+ channel from Streptomyces lividans. Frequency component analysis of the amide I band showed that SKC1 is composed of 44-46% alpha-helix, 21-24% beta-sheet, 10-12% turns and 18-20% unordered structures. The order parameter S of the helical component of SKC1 was between 0.60 and 0.69. Close to 80% of SKC1 amide protons exchange within approximately 3 h of D2O exposure, suggesting that the channel is largely accessible to solvent exchange. These results are consistent with a model of SKC1 in which helices slightly tilted from the membrane normal line the water-filled vestibules that flank the K+ selectivity filter.

Amino Acid Sequence↗
PubMed2005

Continuous monitoring of WBC (biochemistry) in an adult leukemia patient using advanced FTIR-spectroscopy.

Fourier transform infrared (FTIR)-spectroscopy has been found useful for monitoring the effectiveness of drugs during chemotherapy in leukemia patients. In the present work, spectral changes that occurred in the white blood cells (WBC) of an adult acute myeloid leukemia (AML) patient and their possible utilization for monitoring biochemistry of WBC were investigated. The phosphate absorbance from nucleic acids and the lipid-protein ratio in the WBC decreased immediately after treatment and then increased to levels of a control group. Similar observations were recorded in child patients with acute lymphoblastic leukemia (ALL) who were used as test cases. These parameters maybe used as possible markers to indicate successful remission and suggest that FTIR-spectroscopy may provide a rapid optical method for continuous monitoring or evaluation of a WBC population.

Adult↗
PubMed2002

Melt, hydration, and micellization of the PEO-PPO-PEO block copolymer studied by FTIR spectroscopy.

Fourier transform infrared (FTIR) spectroscopy was used to study the conformational changes of the polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) block copolymer, Pluronic P104, in a large concentration range in a polymer-water system as a function of temperature. The melt in which the conformational transition of the PEO blocks occurs gives remarkable changes in the spectral behavior. A small amount of water in Pluronic P104 can induce the PEO block amorphism. The addition of more water only swells the PEO dominant region and gives no significant difference in the conformational structure of the block copolymer in the ordered phases of Pluronic P104-water mixtures. The PPO blocks of Pluronic P104 are hydrated only in a condition of lower temperature and higher water content. The temperature dependent micellization of Pluronic P104 in water was analyzed by a FTIR spectroscopic method. The appearance of the symmetric deformation band of the anhydrous methyl groups at temperature below the CMT indicates the existence of a hydrophobic microenvironment. The appearance of the symmetric deformation band of the hydrated methyl groups at higher temperatures indicates that the micellar core must contain some amount of water. The results of FTIR data show that the proportion of the anhydrous methyl groups increases and water content in the micellar core decreases during the micellization process.

Micelles↗
PubMed1998

Pressure-induced structural rearrangements of bovine pancreatic trypsin inhibitor studied by FTIR spectroscopy.

Fourier transform infrared (FTIR) spectroscopy combined with resolution enhancement techniques, second-derivative and difference spectroscopies, have been used to characterize pressure-induced changes in the structural rearrangements of bovine pancreatic trypsin inhibitor (BPTI) in D2O solution at 25.0 degrees C. According to the observed changes in the amide I' band up to 550 MPa, the secondary structure elements of BPTI, such as the alpha-helix, 3(10)-helix, beta-sheet, and beta-turn, are scarcely rearranged except for the loop structure of residues of 9-17 and 36-43. The polypeptide backbone is not extensively unfolded up to 550 MPa. The minor pressure-induced structural rearrangements are completely reversible. A further increase in pressure above 1000 MPa associated with the precipitation of BPTI in D2O buffer solution induces the partial structural rearrangements of the alpha-helix, beta-turn and/or 3(10)-helix, and beta-sheet. The polypeptide backbone of BPTI is not fully unfolded even above 1000 MPa. Most of the protected backbone amide protons involved in the beta-sheet remain intact in the pressure range where BPTI is not precipitated, while those involved in the alpha-helix and beta-turn and/or 3(10)-helix are exchanged with solvent deuterons. The protected backbone amide protons located near the surface regions are more easily exchanged with solvent deuterons by application of high pressure than those involved in the core.

Animals↗
PubMed2002

Structural dynamics of myoglobin: ligand migration among protein cavities studied by Fourier transform infrared/temperature derivative spectroscopy.

Fourier transform infrared (FTIR) spectroscopy in the CO stretch bands combined with temperature derivative spectroscopy (TDS) was used to characterize intermediate states obtained by photolysis of two sperm whale mutant myoglobins, YQR (L29(B10)Y, H64(E7)Q, T67(E10)R) and YQRF (with an additional I107(G8)F replacement). Both mutants assume two different bound-state conformations, A(0) and A(3), which can be distinguished by their different CO bands near 1965 and 1933 cm(-1). They most likely originate from different conformations of the Gln-64 side chain. Within each A substate, a number of photoproduct states have been characterized on the basis of the temperature dependence of recombination in TDS experiments. Different locations and orientations of the ligand within the protein can be distinguished by the infrared spectra of the photolyzed CO. Recombination from the primary docking site, B, near the heme dominates below 50 K. Above 60 K, ligand rebinding occurs predominantly from a secondary docking site, C', in which the CO is trapped in the Xe4 cavity on the distal side, as shown by crystallography of photolyzed YQR and L29W myoglobin CO. Another kinetic state (C") has been identified from which rebinding occurs around 130 K. Moreover, a population appearing above the solvent glass transition at approximately 180 K (D state) is assigned to rebinding from the Xe1 cavity, as suggested by the photoproduct structure of the L29W sperm whale myoglobin mutant. For both the YQR and YQRF mutants, rebinding from the B sites near the heme differs for the two A substates, supporting the view that the return of the ligand from the C', C", and D states is not governed by the recombination barrier at the heme iron but rather by migration to the active site. Comparison of YQR and YQRF shows that access to the Xe4 site (C') is severely restricted by introduction of the bulky Phe side chain at position 107.

Animals↗
PubMedDate not supplied

Investigation of foreign substances in food.

Scanning electron microscopy (SEM) together with energy-dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) were used to investigate foreign substances from seven categories of foreign substances in food. (1) Naturally occurring foreign substances--Using FTIR, a foreign substance was identified as a natural resin probably from the product. (2) Foreign substances introduced during food processing. Scanning electron microscopy-EDS was used to identify a foreign material found on surf clams as calcium phosphate from a product/ingredient interaction. Using SEM-EDS, a crystalline material in a meat product was identified as calcium salts of chloride and phosphate. Fourier transform infrared spectroscopy was used to identify foreign material that clogged an aerosol valve as chipboard. Using SEM-EDS, the metal in the heel of a glass bottle was identified as copper sulfide-containing metal inclusion. (3) Insects, reptiles, and rodents--Scanning electron microscopy was used to determine that a mouse found in food was not processed with the food, but entered the container after it left the factory. (4) Glass fragments--Glass from various sources can be distinguished from one another using SEM-EDS either by the level of the major elements in glass or by the presence of elements in one glass, but not in another. (5) Glass-like particles--Using SEM-EDS, glass-like particles found on beets were determined to be a fatty acid. (6) Metal foreign objects--Using SEM-EDS, metals from a variety of sources can be easily distinguished. For example, a tin-soldered container can be distinguished from a lead-soldered can. Using SEM-EDS, the metal fiber found on the bottom of a two-piece can likely enter the can during the final stage of the manufacture of the drawn and ironed food can. (7) Drug capsule identification--Fourier transform infrared spectroscopy was used to determine that a pill found in food was ibuprofen.

Animals↗
PubMed2002

Transient binding of CO to Cu(B) in cytochrome c oxidase is dynamically linked to structural changes around a carboxyl group: a time-resolved step-scan Fourier transform infrared investigation.

The redox-driven proton pump cytochrome c oxidase is that enzymatic machinery of the respiratory chain that transfers electrons from cytochrome c to molecular oxygen and thereby splits molecular oxygen to form water. To investigate the reaction mechanism of cytochrome c oxidase on the single vibrational level, we used time-resolved step-scan Fourier transform infrared spectroscopy and studied the dynamics of the reduced enzyme after photodissociation of bound carbon monoxide across the mid-infrared range (2300-950 cm(-1)). Difference spectra of the bovine complex were obtained at -20 degrees C with 5 micros time resolution. The data demonstrate a dynamic link between the transient binding of CO to Cu(B) and changes in hydrogen bonding at the functionally important residue E(I-286). Variation of the pH revealed that the pK(a) of E(I-286) is >9.3 in the fully reduced CO-bound oxidase. Difference spectra of cytochrome c oxidase from beef heart are compared with those of the oxidase isolated from Rhodobacter sphaeroides. The bacterial enzyme does not show the environmental change in the vicinity of E(I-286) upon CO dissociation. The characteristic band shape appears, however, in redox-induced difference spectra of the bacterial enzyme but is absent in redox-induced difference spectra of mammalian enzyme. In conclusion, it is demonstrated that the dynamics of a large protein complex such as cytochrome c oxidase can be resolved on the single vibrational level with microsecond Fourier transform infrared spectroscopy. The applied methodology provides the basis for future investigations of the physiological reaction steps of this important enzyme.

Animals↗
PubMed2006

Time-resolved rapid-scan Fourier transform infrared difference spectroscopy on a noncyclic photosystem: rhodopsin photointermediates from Lumi to Meta II.

The visual pigment rhodopsin has been extensively studied for the kinetics of its photointermediates by various spectroscopic methods. Unlike such archaeal retinal proteins as bacteriorhodopsin, visual rhodopsin does not thermally recover its dark state after photoexcitation, which precludes repeated excitation of a single sample and thereby complicates time-resolved experiments. Kinetic data on the late rhodopsin photointermediates have so far been available mainly from time-resolved ultraviolet (UV)-visible spectroscopy, but not from Fourier transform infrared (FTIR) spectroscopy. The latter has the advantage of being informative of structural changes of both chromophore and protein, but does not allow the highly reproducible, automated sample exchange procedures available to UV-visible spectroscopy. Using rapid-scan FTIR difference spectroscopy, we obtained time-resolved data sets that were analyzed by a maximum entropy inverse Laplace-transform. Covering the time range from 8 ms to 15 s at temperatures of 0 and -7 degrees C, the transitions from the Lumi to the Meta I and from the Meta I to the Meta II photoproduct states could be resolved. In the transition from Meta I to Meta II, our data reveal a partial deprotonation of the retinal Schiff base preceding the conformational change of the receptor protein to Meta II. The technique and the results are discussed in regard to its advantages as well as its limitations.

Animals↗
PubMed2000

Low temperature formation of calcium-deficient hydroxyapatite-PLA/PLGA composites.

Hydroxyapatite-biodegradable polymer composites have been formed by a low temperature chemical route. Precomposite structures were prepared by combining alpha-Ca(3)(PO(4))(2) (alpha-tricalcium phosphate or alpha-TCP) with poly(L-lactic) acid and poly(DL-lactide-co-glycolide) copolymers. The final composite structure was achieved by in situ hydrolysis of alpha-TCP to Ca(9)(HPO(4))(PO(4))(5)OH (calcium deficient hydroxyapatite or CDHAp) either in solvent cast or pressed precomposites. Hydrolysis was performed at 56 degrees C-a temperature slightly above the glass transition of the polymers. The effects of polymer chemistry, composite formation technique, and porosity on hydrolysis kinetics and degree of transformation were examined with isothermal calorimetry, X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and scanning electron microscopy. Calorimetric data and XRD analyses revealed that hydrolysis reactions were inhibited in the presence of the polymers. Isothermal calorimetry indicated the extent of the alpha-TCP to CDHAp transformation in 24 h to be 85% in the solvent cast composites containing PLGA (85:15) copolymer; however, XRD analyses suggested almost complete reaction. The CDHAp formation extent was 26% for the pressed composites containing the same polymer. In the presence of NaCl as a pore generator, 81% transformation was observed for the pressed composites. This transformation occurred without any chemical reaction between the polymer-inorganic components, as determined by Fourier transform infrared spectroscopy. Minimal transformation to CDHAp occurred in composites containing poly(L-lactic) acid.

Biocompatible Materials↗
PubMed2005

On-filter determination of collected wood dust by diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS).

A new analytical technique based on DRIFTS spectroscopy has been developed for the specific and sensitive determination of size-fractionated wood dust from 37 mm glass fiber filter samples collected with the Respicon sampler. A translational diffuse reflectance apparatus was modified to accept filter samples by incorporating a special filter holder in the sample stage and a clockwork motor to drive the translational stage during infrared scanning, thus providing an average analysis across the filter face. Filter samples were pre-treated with ethyl acetate to uniformly redeposit dust onto the filter and extract potential chemical interferences. Two absorbance maxima (1251 and 1291 cm(-1)), corresponding to the cellulose content of the wood, were suitable for quantitation of wood dust. Analysis of seven species of wood at 1291 cm(-1) showed an equivalent quantitative response for all species except maple. The response at 1251 cm(-1) was more variable across species but more sensitive for the softwoods. There was a statistically significant effect of particle size on the analytical response, so that analytical standards should be matched to the samples in terms of particle size distribution. Analytical limit of detection was approximately 0.08 mg of wood dust per sample with overall precision of about 6%. Comparison of DRIFTS and gravimetric analyses of 51 pure wood dust samples ranging from about 0.2 to 2 mg yielded a slope of 1.08 and r2 equal to 0.9. Other particulate contaminants common in the industrial wood processing industry showed little or no interference with the determination of wood dust by this method.

Air Pollutants, Occupational↗