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PubMed1990

Investigation into the fluidity of lipopolysaccharide and free lipid A membrane systems by Fourier-transform infrared spectroscopy and differential scanning calorimetry.

The phase behaviour, particularly the fluidity within each phase state and the transitions between them, of lipopolysaccharides and of their lipid moiety, free lipid A, of various species of Gram-negative bacteria, especially of Salmonella minnesota and Escherichia coli, has been investigated by applying mainly Fourier-transform infrared spectroscopy and differential scanning calorimetry. For enterobacterial strains, the transition temperatures of the gel----liquid crystalline (beta----alpha) phase transition of the hydrocarbon chains in dependence on the length of the sugar moiety are highest for free lipids A (around 45 degrees C) and lowest for deep rough mutant lipopolysaccharides (around 30 degrees C). Evaluating certain infrared active vibration bands of the hydrocarbon moiety, mainly the symmetric stretching vibration of the methylene groups around 2850 cm-1, it was found that, in the gel state, the acyl chains of lipopolysaccharides and free lipid A have a higher fluidity as compared with saturated and the same fluidity as compared with unsaturated phospholipids. This 'partial fluidization' of lipopolysaccharide below the transition temperature correlates with its reduced enthalpy change at that temperature compared to phospholipids with the same chain length. The fluidity depends strongly on ambient conditions, i.e. on the Mg2+ and H+ content: higher Mg2+ concentrations and low pH values make the acyl chains of free lipid A and lipopolysaccharide preparations significantly more rigid and also partially increase the transition temperature. The influence of Mg2+ is highest for free lipid A and decreases with increasing length of the sugar side chain within the lipopolysaccharide molecules, whereas the effect of a low pH is similar for all preparations. At basic pH, a fluidization of the lipopolysaccharide and lipid A acyl chains and a decrease in transition temperature take place. Free lipid A and all investigated rough mutant lipopolysaccharides exhibit an extremely strong lyotropic behaviour in the beta----alpha melting enthalpy but not in the value of the transition temperature. The phase transition is distinctly expressed only at water concentrations higher than 50-60%. A further increase of the water content still leads to an increase in the phase-transition enthalpy, particularly for lipopolysaccharides with a more complete sugar moiety. The fluidity of the hydrocarbon chains is shown to be an important parameter with respect to the expression of biological activities.(ABSTRACT TRUNCATED AT 400 WORDS)

Calorimetry, Differential Scanning↗
PubMed1994

A mutant rhodopsin photoproduct with a protonated Schiff base displays an active-state conformation: a Fourier-transform infrared spectroscopy study.

In the rhodopsin mutant E113A/A117E the position of the protonated Schiff base counterion, Glu113, is moved by one helix turn from position 113 to 117. The photoreaction of this mutant pigment was studied by Fourier-transform infrared (FTIR) difference spectroscopy. At acidic pH, formation of a 474-nm absorbing photoproduct previously characterized biochemically as a species that activates transducin caused infrared absorption changes typical of metarhodopsin II (MII) formation in native rhodopsin. Specific spectral alterations revealed a localized perturbation near the protonated Schiff base in the dark state. In addition, an infrared band assigned to the C = O stretching vibration of Glu113 in MII of rhodopsin was abolished in the mutant. Absorption changes caused by Asp83 and Glu122 C = O stretching vibrations characteristic of rhodopsin MII formation were not affected. At alkaline pH, mutant E113A/A117E formed predominantly a 382-nm absorbing photoproduct. It displayed infrared-difference absorption bands significantly different from those of native MII over a large spectral range. These results support the conclusion that the 474-nm photoproduct of mutant E113A/A117E, despite a protonated Schiff base linkage, displays a predominantly MII-like conformation capable of catalyzing guanine-nucleotide exchange by transducin.

Carboxylic Acids↗
PubMed2002

Time-resolved step-scan Fourier transform infrared spectroscopy of the CO adducts of bovine cytochrome c oxidase and of cytochrome bo(3) from Escherichia coli.

We have used cryogenic difference FTIR and time-resolved step-scan Fourier transform infrared (TR-FTIR) spectroscopies to explore the redox-linked proton-pumping mechanism of heme-copper respiratory oxidases. These techniques are used to probe the structure and dynamics of the heme a(3)-Cu(B) binuclear center and the coupled protein structures in response to the photodissociation of CO from heme Fe and its subsequent binding to and dissociation from Cu(B). Previous cryogenic (80 K) FTIR CO photodissociation difference results were obtained for cytochrome bo(3), the ubiquinol oxidase of Escherichia coli [Puustinen, A., et al. (1997) Biochemistry 36, 13195-13200]. These data revealed a connectivity between Cu(B) and glutamic acid E286, a residue which has been implicated in proton pumping. In the current work, the same phenomenon is observed using the CO adduct of bovine cytochrome aa(3) under cryogenic conditions, showing a perturbation of the equivalent residue (E242) to that in bo(3). Furthermore, using time-resolved (5 micros resolution) step-scan FTIR spectroscopy at room temperature, we observe the same spectroscopic perturbation in both cytochromes aa(3) and bo(3). In addition, we observe evidence for perturbation of a second carboxylic acid side chain, at higher frequency in both enzymes at room temperature. The high-frequency feature does not appear in the cryogenic difference spectra, indicating that the perturbation is an activated process. We postulate that the high-frequency IR feature is due to the perturbation of E62 (E89 in bo(3)), a residue near the opening of the proton K-channel and required for enzyme function. The implications of these results with respect to the proton-pumping mechanism are discussed. Finally, a fast loss of over 60% of the Cu(B)-CO signal in bo(3) is observed and ascribed to one or more additional conformations of the enzyme. This fast conformer is proposed to account for the uninhibited reaction with O(2) in flow-flash experiments.

Animals↗
PubMed2001

Degeneration of solventogenic Clostridium strains monitored by Fourier transform infrared spectroscopy of bacterial cells.

Strain degeneration in solventogenic clostridia is a known problem in the technical acetone-butanol fermentation bioprocess, especially in the continuous process mode. Clostridial strain degeneration was studied by Fourier transform infrared (FT-IR) spectroscopy of the bacterial cells. Degenerative variant formation in two strains, Clostridium beijerinckii NCIMB 8052 and Clostridium species AA332, was detected spectroscopically. Colonies on solid media were sampled, or assayed directly in situ by IR microscopy. It has previously been shown that the distinctive acidogenic and solventogenic physiological phases of Clostridium acetobutylicum in liquid medium can be discriminated by FT-IR spectroscopy. This was confirmed here for C. beijerinckii NCIMB 8052. The proportion of degenerate cells in a mixed population in liquid medium could be quantified, as the spectral features change in different ways during the normal growth cycle of wild type organisms and degenerate variants in batch culture. This opens a new perspective for physiology-based process monitoring and control, especially of the continuous acetone-butanol fermentation.

Acetone↗
PubMed2002

Single-pass attenuated total reflection Fourier transform infrared spectroscopy for the prediction of protein secondary structure.

Principal component regression (PCR) was applied to a spectral library of proteins in H2O solution acquired by single-pass attenuated total reflectance (ATR) Fourier transform infrared (FT-IR) spectroscopy. PCR was used to predict the secondary structure content, principally alpha-helical and the beta-sheet content, of proteins within a spectral library. Quantitation of protein secondary structure content was performed as a proof of principle that use of single-pass ATR-FT-IR is an appropriate method for protein secondary structure analysis. The ATR-FT-IR method permits acquisition of the entire spectral range from 700 to 3900 cm(-1) without significant interference from water bands. An "inside model space" bootstrap and a genetic algorithm (GA) were used to improve prediction results. Specifically, the bootstrap was utilized to increase the number of replicates for adequate training and validation of the PCR model. The GA was used to optimize PCR parameters, particularly wavenumber selection. The use of the bootstrap allowed for adequate representation of variability in the amide A, amide B, and C-H stretching regions due to differing levels of sample hydration. Implementation of the bootstrap improved the robustness of the PCR models significantly; however, the use of a GA only slightly improved prediction results. Two spectral libraries are presented where one was better suited for beta-sheet content prediction and the other for alpha-helix content prediction. The GA-optimized PCR method for alpha-helix content prediction utilized 120 wavenumbers within the amide I, II, A, B, and IV and the C-H stretching regions and 18 factors. For beta-sheet content predictions, 580 wavenumbers within the amide I, II, A, and B and the C-H stretching regions and 18 factors were used. The validation results using these two methods yielded an average absolute error of 1.7% for alpha-helix content prediction and an average absolute error of 2.3% for beta-sheet content prediction. After the PCR models were developed and validated, they were used to predict the alpha-helix and beta-sheet content of two unknowns, casein and immunoglobulin G.

Multivariate Analysis↗
PubMed2001

Membrane molecule reorientation in an electric field recorded by attenuated total reflection Fourier-transform infrared spectroscopy.

Electric fields play an important role in the physiological function of macromolecules. Much is known about the role that electric fields play in biological systems, but membrane molecule structure and orientation induced by electric fields remain essentially unknown. In this paper, we present a polarized attenuated total reflection (ATR) experiment we designed to study the effect of electric fields on membrane molecule structure and orientation by Fourier-transform infrared (FTIR) spectroscopy. Two germanium crystals used as the internal reflection element for ATR-FTIR experiments were coated with a thin layer of polystyrene as insulator and used as electrodes to apply an electric field on an oriented stack of membranes made of dioleylphosphatidylcholine (DOPC) and melittin. This experimental set up allowed us for the first time to show fully reversible orientational changes in the lipid headgroups specifically induced by the electric potential difference.

Biophysical Phenomena↗
PubMed2006

Utilization of fourier transform infrared spectroscopy for measurement of organic phosphorus and bound calcium in cheddar cheese.

The methods available for measuring organic P and bound Ca in cheese are either cumbersome or involve dilution of the cheese. Dilution of the cheese can lead to erroneous results, particularly in the case of bound Ca. Hence, the objective of this study was to evaluate the feasibility of Fourier transform infrared (FTIR) spectroscopy for direct measurement of organic P and bound Ca in Cheddar cheese. Two hundred sixteen samples of cheese were analyzed for protein-bound organic P, bound Ca using a water-extraction based method, and buffering curves. Additionally, the infrared spectra of the cheeses were collected between 4,000 and 650 cm(-1), at a resolution of 4 cm(-1), and 256 scans per sample. The spectral shifts in the infrared region from 1,050 to 900 cm(-1), in addition to the measured concentrations of organic P, bound Ca, and buffering peak area at pH 5.1, were used to develop calibration models using partial least squares (PLS) regression analysis. The spectral region of 956 to 946 cm(-1) correlated with the measured concentrations of organic P and the overall PLS model had a correlation (R2) of 0.76 between the predicted and measured concentrations. The spectral region at approximately 980 cm(-1) was correlated with the measured concentrations of bound Ca, and the overall PLS model had a correlation (R2) of 0.70 between the predicted and measured concentrations. A similar spectral region at approximately 980 cm(-1) was also correlated with the measured buffering peak areas and the overall PLS model had a correlation (R2) of 0.64 between the predicted and measured peak areas. A linear regression analysis between the bound Ca and buffering peak area demonstrated that bound Ca was correlated (R2 = 0.73) with buffering peak area. This study demonstrates that FTIR can be used to measure organic P in cheeses. It also has the potential to be used for measuring bound Ca in undiluted cheeses, and for prediction of the buffering capacity of cheese.

Buffers↗
PubMed1989

Solubilization of DMPC and DPPC vesicles by detergents below their critical micellization concentration: high-sensitivity differential scanning calorimetry, Fourier transform infrared spectroscopy and freeze-fracture electron microscopy reveal two interaction sites of detergents in vesicles.

The interaction of sodium deoxycholate, sodium cholate and octyl glucoside with sonicated vesicles of L alpha-dimyristoyl-phosphatidylcholine (DMPC) and L alpha-dipalmitoylphosphatidylcholine (DPPC) at concentrations below the critical micellization concentration (cmc) of the detergents was studied by high-sensitivity DSC (hs-DSC), Fourier transform infrared spectroscopy (FT-IR) and freeze-fracture electron microscopy. The two phospholipids exhibited a striking different thermotropic behaviour in the presence of these detergents. For DPPC vesicles, the detergents were found to interact exclusively in the aqueous interface region of the bilayer below the membrane saturation concentration Rsat while in DMPC vesicles two coexisting interaction sites below this concentration persist. These are detergents which interact at the aqueous interface region (site 1) and in the acyl chain region (site 2) of the DMPC vesicles. The partition coefficients K of the detergents between DPPC vesicles and the water phase were calculated from the hs-DSC results at two detergent/phospholipid molar ratios Rtot less than or equal to Rsat as 0.35, 0.049 and 0.040 mol-1 for sodium deoxycholate, sodium cholate and octyl glucoside, respectively. In contrast, for DMPC the K values for Rtot less than or equal to Rsat were found to be dependent on Rtot due to the occupation of site 2 by the detergents above a certain Rtot. The model is discussed on the basis of the detergents free energies of transfer from the water phase to site 1 and site 2 of the vesicles, respectively. The solubilization behaviour of DPPC vesicles, dependent on whether the total detergent concentration is above or below the cmc at Rsat, differed significantly as revealed by hs-DSC. This suggests that in the latter case an additional hydrophobic effect could facilitate the formation of disc shaped mixed micelles. Moreover, this different behaviour was employed to measure the cmc values of the detergents studied in the presence of the vesicles by hs-DSC.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2000

Conformational mapping of the N-terminal segment of surfactant protein B in lipid using 13C-enhanced Fourier transform infrared spectroscopy.

Synthetic peptides based on the N-terminal domain of human surfactant protein B (SP-B1-25; 25 amino acid residues; NH2-FPIPLPYCWLCRALIKRIQAMIPKG) retain important lung activities of the full-length, 79-residue protein. Here, we used physical techniques to examine the secondary conformation of SP-B1-25 in aqueous, lipid and structure-promoting environments. Circular dichroism and conventional, 12C-Fourier transform infrared (FTIR) spectroscopy each indicated a predominate alpha-helical conformation for SP-B1-25 in phosphate-buffered saline, liposomes of 1-palmitoyl-2-oleoyl phosphatidylglycerol and the structure-promoting solvent hexafluoroisopropanol; FTIR spectra also showed significant beta- and random conformations for peptide in these three environments. In further experiments designed to map secondary structure to specific residues, isotope-enhanced FTIR spectroscopy was performed with 1-palmitoyl-2-oleoyl phosphatidylglycerol liposomes and a suite of SP-B1-25 peptides labeled with 13C-carbonyl groups at either single or multiple sites. Combining these 13C-enhanced FTIR results with energy minimizations and molecular simulations indicated the following model for SP-B1-25 in 1-palmitoyl-2-oleoyl phosphatidylglycerol: beta-sheet (residues 1-6), alpha-helix (residues 8-22) and random (residues 23-25) conformations. Analogous structural motifs are observed in the corresponding homologous N-terminal regions of several proteins that also share the 'saposin-like' (i.e. 5-helix bundle) folding pattern of full-length, human SP-B. In future studies, 13C-enhanced FTIR spectroscopy and energy minimizations may be of general use in defining backbone conformations at amino acid resolution, particularly for peptides or proteins in membrane environments.

Carbon Radioisotopes↗
PubMed1990

Resolution-enhanced Fourier transform infrared spectroscopy study of the environment of phosphate ions in the early deposits of a solid phase of calcium-phosphate in bone and enamel, and their evolution with age. I: Investigations in the upsilon 4 PO4 domain.

In order to investigate the possible existence in biological and poorly crystalline synthetic apatites of local atomic organizations different from that of apatite, resolution-enhanced, Fourier transform infrared spectroscopy studies were carried out on chicken bone, pig enamel, and poorly crystalline synthetic apatites containing carbonate and HPO4(2-) groups. The spectra obtained were compared to those of synthetic well crystallized apatites (stoichiometric hydroxyapatite, HPO4(2-)-containing apatite, type B carbonate apatite) and nonapatitic calcium phosphates which have been suggested as precursors of the apatitic phase [octacalcium phosphate (OCP), brushite, and beta tricalcium phosphate and whitlockite]. The spectra of bone and enamel, as well as poorly crystalline, synthetic apatite in the upsilon 4 PO4 domain, exhibit, in addition to the three apatitic bands, three absorption bands that were shown to be independent of the organic matrix. Two low-wave number bands at 520-530 and 540-550 cm-1 are assigned to HPO4(2-). Reference to known calcium phosphates shows that bands in this domain also exist in HPO4(2-)-containing apatite, brushite, and OCP. However, the lack of specific absorption bands prevents a clear identification of these HPO4(2-) environments. The third absorption band (610-615 cm-1) is not related to HPO4(2-) or OH- ions. It appears to be due to a labile PO4(3-) environment which could not be identified with any phosphate environment existing in our reference samples, and thus seems specific of poorly crystalline apatites. Correlation of the variations in band intensities show that 610-615 cm-1 band is related to an absorption band at 560 cm-1 superimposed on an apatite band. All the nonapatitic phosphate environments were shown to decrease during aging of enamel, bone, and synthetic apatites. Moreover, EDTA etching show that the labile PO4(3-) environment exhibited a heterogeneous distribution in the insoluble precipitate.

Aging↗
PubMed2005

Effect of stereotactic radiosurgery on lipids and proteins of normal and hypoperfused rat brain homogenates: a Fourier transform infrared spectroscopy study.

PURPOSE: The effect of stereotactic radiosurgery on lipids and proteins of normal and hypoperfused rat brain was investigated to see if hypoxic areas are really more resistant to radiation effects or not. MATERIALS AND METHODS: Rat brain samples from control, stereotactically irradiated and chronically hypoperfused plus stereotactically irradiated groups were homogenized separately with saline phosphate buffer, and centrifuged at 125,000 g for 15 min. Membrane rich parts (pellet) of these homogenates were used for Fourier Transform Infrared (FTIR) spectroscopy studies. Mann-Whitney U tests were performed on the groups, two by two, to test the significance of the differences between the control group and stereotactically irradiated group as well as the control group and chronically hypoperfused plus stereotactically irradiated group. RESULTS: After a single high dose of X-rays to healthy rat brain, the lipid concentration increased slightly, protein content decreased significantly (p < 0.05) and protein-to-lipid ratio decreased slightly. The secondary structure of the proteins was altered in the irradiated brain samples such that the content of a-helical structure decreased significantly (p < 0.01) and random coil increased dramatically (p < 0.05). The effect of radiation on the content of a-helical structure was not found to be significant in the hypoperfused group, but the decrease in the content of random coil was significant (p < 0.01). CONCLUSION: Stereotactic radiosurgery of the brain increased the lipid concentration, decreased the protein concentration and consequently resulted in a decrease in the protein to lipid ratio compared to un-irradiated brain. Radiation also altered the secondary structure of protein. The variations in lipid and protein content and the resulting lipid to protein ratio imply that chronically hypoperfused brain is more vulnerable to radiation than non-hypoperfused brain and suggests chronic hypoperfusion does not prevent cerebral damage caused by irradiation. However, irradiation of hypoperfused brain resulted in less alteration in protein structure than in non-hyperfused brain, suggesting higher resistance to irradiation using this endpoint.

Animals↗
PubMed1989

Lipid phase transitions measured in intact cells with Fourier transform infrared spectroscopy.

Lipid phase transitions in membranes are thought to be a major damaging event during cooling of cells prior to cryopreservation or during warming after freeze-thaw has been completed. Although there is abundant evidence that such transitions occur in isolated phospholipids, the evidence that they are found in membranes in intact cells is less clear, due largely to technical difficulties in detecting such transitions in the complex mixtures of lipids and proteins found in natural membranes. We show here that Fourier transform infrared spectroscopy provides a rapid, convenient method for detecting these transitions in intact cells. We have used intact pollen grains of cattail (Typha latifolia) as a primary experimental subject. Spectra taken of the intact pollen grains show most of the features commonly seen in natural membrane vesicles or pure phospholipids. Shifts in the vibrational frequency and width of the CH2 bands with temperature can be used to detect lipid phase transitions. Biochemical analysis, coupled with the spectroscopy, was used to assign transitions to nonpolar and polar lipids. Finally, although assignment of the melting lipid unambiguously in other cells has not yet been made, we show that the transitions can nevertheless be detected in other intact cells, including those of four plant species and sperm of three animals.

Freezing↗
PubMed2003

Stopped-flow Fourier transform infrared spectroscopy of nitromethane oxidation by the diiron(IV) intermediate of methane monooxygenase.

The hydroxylase component (MMOH) of soluble methane monooxygenase from Methylococcus capsulatus (Bath) was reduced to the diiron(II) form and then allowed to react with dioxygen to generate the diiron(IV) intermediate Q in the first phase of a double-mixing stopped-flow experiment. CD3NO2 was then introduced in the second phase of the experiment, which was carried out in D2O at 25 degrees C. The kinetics of the reaction of the substrate with Q were monitored by stopped-flow Fourier transform infrared spectroscopy, observing the disappearance of the asymmetric NO2 bending vibration at 1548 cm-1. The data were fit to a single-exponential function, which yielded a kobs of 0.45 +/- 0.07 s-1. This result is in quantitative agreement with a kobs of 0.39 +/- 0.01 s-1 obtained by observing the disappearance of Q by double-mixing stopped-flow optical spectroscopy at its absorption maximum of 420 nm. These results provide for the first time direct monitoring of the hydroxylation of a methane-derived substrate in the MMOH reaction pathway and demonstrate that Q decay occurs concomitantly with substrate consumption.

Escherichia coli↗
PubMed1997

Fourier-transform infrared spectroscopy study of an organic-mineral composite for bone and dental substitute materials.

A new injectable biomaterial for bone and dental surgery is a composite consisting of a polymer as a matrix and bioactive calcium phosphate (CaP) ceramics as fillers. The stability of the polymer is essential in the production of a ready-to-use injectable sterilized biomaterial. The purpose of this study was to detect possible polymer degradation which may have been caused by the interaction with the fillers using Fourier transform infrared spectroscopy. Composites containing CaP fillers (biphasic calcium phosphate, hydroxyapatite and peroxidized hydroxyapatite) and polymer (hydroxypropyl methyl cellulose) were prepared. To investigate the properties of the polymer, the inorganic and organic phases of the composite were separated using several extraction methods. The difficulty in separating the organic (polymer) from the mineral (CaP fillers) phases in the composite investigated in this study suggested the presence of strong interactions between the two phases. Spectra of extracted polymers showed new absorption bands of low intensities and indications that some chemical modifications of the original polymers have occurred. Results also indicated that the filler composition has an effect on the integrity of the polymer.

Journal Article↗
PubMed2005

A variable-temperature diffuse reflectance infrared fourier transform spectroscopy study of the binding of water and pyridine to the surface of acid-activated metakaolin.

Four metakaolins were prepared by heating a Spanish kaolin at 600, 700, 800, and 900 degrees C for 10 h. Following preliminary optimization, these metakaolins were acid activated in 6 M hydrochloric acid at 90 degrees C for 6 h; the samples calcined at 600, 700, and 800 degrees C produced the highest surface area solids and were selected for further study. Variable-temperature diffuse reflectance infrared Fourier transform spectroscopy analysis of the resulting acid-activated metakaolins (AAMKs) identified a wide range of hydrogen bond strengths in adsorbed water at room temperature. Above 300 degrees C it was possible to fit the broad hydroxyl stretching band to seven contributing components at 3730, 3700, 3655, 3615, 3583, 3424, and 3325 cm(-1). As the sample temperature was increased, the 3730 cm(-1) band increased in intensity as the water hydrogen bonded to AlOHAl was thermally desorbed. The other six bands decreased in intensity. The spectra of adsorbed pyridine indicated the presence of both Brönsted and Lewis acid sites on the surface of the air-dried AAMKs. Preheating the AAMK at 200 degrees C prior to pyridine sorption reduced the number of Brönsted acid sites and increased the number of thermally stable Lewis acid sites. A reduction in the amount of adsorbed pyridine after pretreating the AAMK at 400 degrees C was tentatively attributed to a reduction in surface area. This was reflected in fewer thermally stable Lewis acid sites in the AAMK pretreated at 400 degrees C compared to the number present in the sample pretreated at 200 degrees C.

Journal Article↗
PubMed2002

Scanning electron microscopy and Fourier transformed infrared spectroscopy analysis of bone removal using Er:YAG and CO2 lasers.

BACKGROUND: A thorough analysis of laser-ablated bone tissue is required before applying the technique to osseous surgery. In this study, we examine the morphological features and chemical composition of the bone surface after Er:YAG and CO2 lasers ablation. METHODS: Six Wistar rats were used. An Er:YAG laser was used for ablation at an output energy of 100 mJ/pulse and a pulse rate of 10 Hz (1 W). Continuous CO2 laser irradiation was performed at an output energy of 1 W. Sites drilled using a conventional micromotor were used as controls. Analysis using scanning electron microscopy (SEM) and Fourier transformed infrared (FTIR) spectroscopy was performed. RESULTS: Er:YAG laser ablation produced a groove with similar dimensions to that produced by bur drilling, whereas the CO2 laser produced only a charred line with minimal tissue removal. SEM observations revealed that the groove produced by the Er:YAG laser had well-defined edges and a smear layer-free surface with a characteristically rough appearance and with entrapped fibrin-like tissue. The melting and carbonization produced by the CO2 laser were not observed on sites irradiated by the Er:YAG laser. FTIR spectroscopy revealed that the chemical composition of the bone surface after Er:YAG laser ablation was much the same as that following bur drilling. The production of toxic substances that occurred after CO2 laser irradiation was not observed following Er:YAG laser irradiation or bur drilling. CONCLUSION: These results suggest that the use of Er:YAG laser ablation may become an alternative method for oral and periodontal osseous surgery.

Animals↗
PubMed2001

Differential scanning calorimetry and (2)H nuclear magnetic resonance and Fourier transform infrared spectroscopy studies of the effects of transmembrane alpha-helical peptides on the organization of phosphatidylcholine bilayers.

We have studied the effects of the incorporation of the alpha-helical transmembrane peptides Ac-K(2)-L(24)-K(2)-amide (L(24)) and Ac-K(2)-(L-A)(12)-K(2)-amide ((LA)(12)) on the thermotropic phase behavior of 1,2-dipalmitoyl-d(62)-sn-glycero-3-phosphocholine (DPPC-d(62)) and 1-palmitoyl-d(31)-2-oleoyl-sn-glycero-3-phosphocholine (POPC-d(31)) lipid bilayer model membranes by differential scanning calorimetry (DSC) and the conformational and orientational order of the phospholipid chains by Fourier transform infrared (FTIR) spectroscopy and (2)H nuclear magnetic resonance ((2)H-NMR) spectroscopy, respectively. Our DSC and FTIR spectroscopic studies indicate that the peptides L(24) and (LA)(12) both decrease the temperature and enthalpy of the gel/liquid-crystalline phase transition of DPPC-d(62) bilayers, with (LA)(12) having the greater effect in this regard. An examination of the frequencies of the CH(2) and CD(2) symmetric stretching bands of the infrared spectra of liquid-crystalline states of the peptide-free and peptide-containing DPPC-d(62) and POPC-d(31) samples, and a comparison with the orientational order as measured by (2)H-NMR spectroscopy as well as with the chain order as measured by electron spin resonance spectroscopy, lead us to conclude that the CH(2) (or CD(2)) stretching frequencies of lipid hydrocarbon chains are not a reliable measure of chain conformational order in lipid bilayers containing significant amounts of peptides or other lipophilic inclusions. In contrast, the results of our (2)H-NMR spectroscopic studies present a consistent picture in which both L(24) and (LA)(12) increased in a similar way the time-averaged orientational order of the lipid chains of their liquid-crystalline lipid bilayer hosts. The comparison of the effects L(24) and (LA)(12) on phosphatidylcholine bilayers indicates that the gel-to-liquid-crystalline phase transition appears to be more sensitive to small changes in transmembrane peptide surface topology than hydrocarbon carbon chain orientational order in the liquid-crystalline state.

Calorimetry, Differential Scanning↗