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Results for “Spectroscopy, Near-Infrared”

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PubMed1990

Near-infrared optical responses in feline brain and skeletal muscle tissues during respiratory acid-base imbalance.

The effects of hyper- and hypocapnia on oxidative metabolism were evaluated by near-infrared (NIR) multiwavelength spectroscopy in intact brain and skeletal muscle tissues of the anesthetized cat. A 3-wavelength NIR algorithm was used to monitor cytochrome a,a3 oxidation state, regional blood volume, and tissue oxyhemoglobin and O2 stores simultaneously in brain and muscle in ventilated animals. Incremental hypercapnia was produced in 10 cats by raising arterial pCO2 from 27.0 +/- 1.3 to 95.1 +/- 1.9 mmHg with inspired CO2. Hypercapnia produced progressive increases in cerebral HbO2, blood volume, and cytochrome a,a3 oxidation state (P less than 0.01). In contrast, CO2 simultaneously decreased all 3 NIR parameters in intact hindlimb muscles (P less than 0.01). Blood volume changes during hypercapnia correlated with changes in blood flow measured qualitatively by intravascular injections of indocyanine green dye. Hypocapnia produced by hyperventilation in 8 cats lowered paCO2 from 28.5 +/- 0.4 to 13.5 +/- 0.5 mmHg. Hypocapnia decreased cerebral HbO2, blood volume, and cytochrome a,a3 redox level (P less than 0.05), but NIR changes were not seen in skeletal muscle. These experiments demonstrate preferential distribution of oxygen to brain during hypercapnia and the ability of NIR spectroscopy to assess regional oxygenation in multiple tissues non-invasively.

Acid-Base Imbalance↗

PubMed1990

Determination of physiological levels of glucose in an aqueous matrix with digitally filtered Fourier transform near-infrared spectra.

A procedure is described for the measurement of clinically relevant concentrations of glucose in aqueous solutions with near-infrared (NIR) absorbance spectroscopy. A glucose band centered at 4400 cm-1 is used for this analysis. NIR spectra are collected over the frequency range 5000-4000 cm-1 with a Fourier transform spectrometer. A narrow-band-pass optical interference filter is placed in the optical path of the spectrometer to eliminate light outside this restricted range. This configuration provides a 2.9-fold reduction in spectral noise by utilizing the dynamic range of the detector solely for light transmitted through the filter. In addition, a novel spectral processing scheme is described for extracting glucose concentration information from the resulting absorbance spectra. The key component of this scheme is a digital Fourier filter that removes both high-frequency noise and low-frequency base-line variations from the spectra. Numerical optimization procedures are used to identify the best location and width of a Gaussian-shaped frequency response function for this Fourier filter. A dynamic area calculation, coupled with a simple linear base-line correction, provides an integrated area from the processed spectra that is linearly related to glucose concentrations over the range 1-20 mM. The linear calibration model accurately predicted glucose levels in a series of test solutions with an overall mean percent error of 2.5%. Based on the uncertainty in the parameters defining the calibration model and the variability of the magnitudes of the integrated areas, an overall uncertainty of 7.8% was estimated for predicted glucose concentrations.

Calibration↗

PubMed1992

Noninvasive methods for estimating in vivo oxygenation.

Clinical signs of hypoxia and hyperoxia are nonspecific and unreliable, yet both are potentially injurious. Noninvasive methods of oxygen assessment fill the gap between clinical observation and invasive tests, helping physicians deliver sufficient oxygen with minimum toxicity. Potential sites for oxygen measurement vary between the blood and the mitochondria; each method measures at a different site and detects different types of hypoxia and hyperoxia. Thus, values obtained by two different methods are not equivalent, giving each method unique strengths and weaknesses. We review two clinical methods (pulse oximetry and transcutaneous oximetry), as well as four experimental methods (near-infrared spectrophotometry, magnetic resonance spectroscopy, magnetic resonance saturation imaging, and time-of-flight absorbance spectrophotometry). The principles of each method and the clinical situations in which each succeeds or fails are discussed. A fundamental understanding of each method can help in deciding which methods, if any, are appropriate for a given patient and how best to correct observed oxygenation problems once they are discovered.

Blood Gas Monitoring, Transcutaneous↗

PubMed1991

A spectroscopic analysis of the Pro35----Ala mutant of Rhodobacter capsulatus cytochrome c2. The strictly conserved Pro35 is not structurally essential.

Visible, near-ultraviolet circular dichroic, near-infrared and nuclear magnetic resonance spectroscopies show that the secondary and tertiary structures of the mutant Pro35----Ala Rhodobacter capsulatus ferrocytochrome c2 are similar to the wild-type protein. The near-infrared spectrum shows that the methionine-S--Fe-heme bond is intact; however, a small red shift in the heme M transition of the near-ultraviolet circular dichroic spectrum of the mutant indicates that the heme environment may differ slightly between the two proteins. This difference may be a consequence of changes in the ligand and hydrogen bonds of His17 [Gooley, P. R. & MacKenzie, N. E. (1990) FEBS Lett. 260, 225-228]. 1H and 15N chemical shift differences suggest that the microenvironment of pyrrole rings III and IV of the heme prosthetic group differs between the two proteins. As the rings of the Phe51 and Tyr53 flip faster in the mutant protein than the wild type, these chemical shift differences may reflect changes in the time-average ring-current effects and not structural alterations.

Circular Dichroism↗

PubMed1992

Near-infrared FT-Raman spectra of the rat brain tissues.

Near-infrared Fourier transform (FT) Raman spectroscopy was applied to brain tissues in situ. The spectra were obtained from the cerebral cortex, white matter of the cerebrum, caudate-putamen, thalamus, synaptosomal fraction, and myelin fraction. High-quality Raman spectra in the 400 to 2940 cm-1 range were measured without interference of autofluorescence. Common spectral bands were assigned. The ratios of the intensity at 1664 (amide I), 1442 (CH2 deformation), 2885 (CH2 asymmetric stretching), 2938 cm-1 (CH3 symmetric stretching) could be used for differentiation between the gray and white matters.

Animals↗

PubMed1991

Near-infrared Fourier transform Raman and conventional Raman studies of calf gamma-crystallins in the lyophilized state and in solution.

We present in this report a detailed structural study of calf gamma-crystallins both in the solid state and in solution by the newly developed technique of near-infrared (IR) Fourier transform (FT)-Raman spectroscopy as well as by the conventional Raman method. In comparison with conventional laser Raman spectroscopy, the near-IR FT-Raman approach exhibits several attractive features such as fluorescence rejection capability, frequency accuracy, and the FT's multiplex and throughput advantages. These distinct characteristics combined form the basis for the particular suitability of FT-Raman in crystallin structural analysis and elucidation. We have thus obtained evidence in support of the view that native calf gamma-II crystallin does not contain a disulfide bond either in the lyophilized state or in solution. In addition, conventional Raman spectra are examined for all four gamma-crystallin fractions. gamma-S, gamma-II, gamma-III, and gamma-IV, and the results indicate a high degree of structural similarities among them. It is also found that the sulfhydryl groups in all four gamma-crystallins are highly resistant to air oxidation and are capable of maintaining their reduced state during isolation in the absence of added reductants or such chelating agents as EDTA.

Animals↗

PubMed1991

Quantitation of time- and frequency-resolved optical spectra for the determination of tissue oxygenation.

The recent development of near-infrared time- and frequency-resolved tissue spectroscopy techniques to probe tissue oxygenation and tissue oxygenation kinetics has led to the need for further quantitation of spectroscopic signals. In this paper, we briefly review the theory of light transport in strongly scattering media as monitored in the time and frequency domains, and use this theory to develop algorithms for quantitation of hemoglobin saturation from the photon decay rate (delta log R/delta t) obtained using time-resolved spectroscopy, and from the phase-shift (theta) obtained from frequency-resolved, phase-modulated spectroscopy. To test the relationship of these optical parameters, we studied the behavior of delta log R/delta t and theta as a function of oxygenation in model systems which mimicked the optical properties of tissue. Our results show that deoxygenation at varying hemoglobin concentrations can be monitored with the change in the photon decay kinetics, delta delta log R/delta t in the time-resolved measurements, and with the change in phase-shift, delta theta, in the frequency-resolved technique. Optical spectra of the adult human brain obtained with these two techniques show similar characteristics identified from the model systems.

Algorithms↗

PubMedDate not supplied

[Laser spectroscopy in the newborn infant--initial experiences].

Equipment for near-infrared laserspectroscopy for clinical application is newly available. By this technique noninvasive monitoring of biochemical parameters is achievable. We report on our first experience with a Radiometer prototype for such NIR laserspectroscopy during measurements in 5 neonates. Laserdiodes provide emission at a wavelength of 775, 805, 845 and 904 nm. The registered signals are computerized aiming at a calculation of relative changes of saturated and unsaturated hemoglobine, changes in blood volume and cytochrome aa-3. In this article graphical display of the parameters give insights in the redoxstate and the hemodynamics of the biological sample. The near-infrared laserspectroscopy has the potential of becoming an instrument for the study of biophysical and biochemical alterations in the newborn.

Brain Damage, Chronic↗

PubMed1992

Identification of urinary calculi by Raman laser fiber optics spectroscopy.

Human calculi of various compositions were automatically identified by using near-infrared excitation Fourier-transform Raman spectrometry. After having built a 150-compound Raman library as a first step, we used a commercial software for infrared spectra (program BIRSY, from Brüker) to determine the composition of different calculi. Good results were obtained for both classical Raman laser and Raman laser fiber optics spectroscopies. With the use of a natural biological medium, e.g., urine, to mimic as closely as possible clinical in vivo conditions, the automatic search correctly identified the calculus composition with relatively good test quality; in some mixtures, however, the results can only be considered semi-quantitative at present, even after smoothing of the spectra.

Fiber Optic Technology↗

PubMed1990

[Laser spectroscopy--a new procedure in fetal monitoring].

Monitors for laser spectroscopy are available as an additional tool for foetal surveillance. Using this technique, continuous and non-invasive registration of four biochemical parameters (HbO2, HbR, blood volume and cytochrome aa3) can be performed. The calculation is based on the optical density after irradiation of the biological sample with pulsed laser light in the near-infrared range (755, 805, 845, 904 nm). We evaluated the new technique in a clinical trial of 20 patients. The application of the laser sensor was performed, using a modified amnioscope. During prenatal tracings in cases with suspect CTG patterns, hypoxia was not verified. In cases without late decelerations a decrease of the cytochrome aa3 signal was observed in less than 1%. During intrapartual measurements, near-infrared signals were compared with the result of the PO2 measurement in foetal blood analysis. We found a significant correlation for HbO2 and cytochrome aa3 with a correlation coefficient of r = 0.96 respectively r = 0.94. We conclude, that laser spectroscopy will potentially be of benefit for foetal monitoring as it might provide a basis for differentiation between foetuses at risk and non-hazardous cases.

Cardiotocography↗

PubMed1990

Cytochrome c'' isolated from Methylophilus methylotrophus. An example of bis-histidine-co-ordinated Fe3+ haem, with near-perpendicular orientation of the ligands.

Cytochrome c'' (Methylophilus methylotrophus) is a soluble protein, Mr 15,000, possessing one haem which is high-spin in the reduced state but switches to a low-spin form on oxidation. Low-temperature electron-paramagnetic-resonance spectroscopy of the oxidized state shows a low-spin signal at gz = 3.65 with a folded line-shape typical of a haem of low rhombicity, and the near-infrared magnetic-circular-dichroism (m.c.d.) spectra reveal an unusually intense (delta epsilon = 400 M-1.cm-1 at 5 T, 4.2 K) charge-transfer band at 1560 nm, establishing that the oxidized haem is co-ordinated by two His residues in a near-perpendicular orientation. This conformation is well established for transmembrane b cytochromes, but this appears to be the first example in a water-soluble cytochrome. The low-temperature m.c.d. spectra of the reduced form of the protein confirms that the haem contains a high-spin Fe2+ ligated by one His residue. The redox-linked spin-state change releases a His group. Since this residue is likely to bind a proton at pH values less than 6.5, this cytochrome may provide a useful model of a molecular mechanism of a redox-linked proton uptake and release process.

Bacteria↗

PubMed1991

Fluorescence polarization and low-temperature absorption spectroscopy of a subunit form of light-harvesting complex I from purple photosynthetic bacteria.

Measurements of polarized fluorescence and CD were made on light-harvesting complex 1 and a subunit form of this complex from Rhodospirillum rubrum, Rhodobacter sphaeroides, and Rhodobacter capsulatus. The subunit form of LH1, characterized by a near-infrared absorbance band at approximately 820 nm, was obtained by titration of carotenoid-depleted LH1 complexes with the detergent n-octyl beta-D-glucopyranoside as reported by Miller et al. (1987) [Miller J. F., Hinchigeri, S. B., Parkes-Loach, P. S., Callahan, P. M., Sprinkle, J. R., & Loach, P. A. (1987) Biochemistry 26, 5055-5062]. Fluorescence polarization and CD measurements at 77 K suggest that this subunit form must consist of an interacting bacteriochlorophyll a dimer in all three bacterial species. A small, local decrease in the polarization of the fluorescence is observed upon excitation at the blue side of the absorption band of the B820 subunit. This decrease is ascribed to the presence of a high-energy exciton component, perpendicular to the main low-energy exciton component. From the extent of the depolarization, we estimate the oscillator strength of the high-energy component to be at most 3% of the main absorption band. The optical properties of B820 are best explained by a Bchl a dimer that has a parallel or antiparallel configuration with an angle between the Qy transition dipoles not larger than 33 degrees. The importance of this structure is emphasized by the results showing that core antennas from three different purple bacteria have a similar structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriochlorophylls↗

PubMed1990

O2 and CO reactions with heme proteins: quantum yields and geminate recombination on picosecond time scales.

Picosecond time-resolved absorption spectroscopy and low-temperature studies have been undertaken in order to understand the nature of the intrinsic quantum yields and geminate recombination of carbon monoxide and oxygen to hemoglobin and myoglobin. We find that the photoproduct yields at 40 ps and long times (minutes) after photolysis at 8 K are similar; however, the yield of oxygen photoproducts is 0.4 +/- 0.1 while the yield of carbon monoxide photoproducts is 1.0 +/- 0.1 for both myoglobin and hemoglobin. Measurements in the Soret, near-infrared, and far-IR are used to quantitate the photoproduct yields. These results call into question previous cryogenic kinetic studies of O2 recombination. Significant subnanosecond geminate recombination is observed in oxyhemoglobin down to 150 K, while below 100 K this geminate recombination disappears. The lower photoproduct yields for oxyheme protein complexes can be attributed to both subnanosecond and subpicosecond recombination events which are ligand and protein dynamics dependent.

Animals↗

PubMed1992

Thiobacillus ferrooxidans cytochrome c oxidase: purification, and molecular and enzymatic features.

Cytochrome c oxidase from Thiobacillus ferrooxidans was purified to homogeneity and some of its properties were studied. The oxidase was solubilized with n-octyl-beta-D-thioglucoside (OTG) under acidic conditions (pH 4.0) and purified by one step of ion-exchange chromatography with a CM-Toyopearl column. The absorption spectrum of the oxidase showed peaks at 420 and 595 nm in the oxidized form and at 440 and 595 nm in the reduced form. Its CO compound showed a novel absorption spectrum; a double-peaked gamma band appeared at 429 and 438 nm. The oxidase seemed to have CuA-like copper atom from its ESR and near-infrared spectra. The oxidase molecule consisted of three polypeptides with molecular weights of 53,000, 22,000, and 17,000, respectively, as estimated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The molecular weight of the enzyme in a solution containing detergents was estimated to be 169,000 on the basis of the results obtained by gel filtration, while the molecular weight per heme alpha was estimated to be 83,700. The copper content of the oxidase was 1.01 g atom per mol of heme alpha. Therefore, the cytochrome seemed to contain one molecule of heme alpha and one atom of copper in the minimal structural unit consisting of one molecule each of the three subunits, and to occur as a dimer of the unit in the solution. The oxidase oxidized ferrocytochrome c-552 of the bacterium, and the optimal pH of the reaction was 3.5.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Fractionation↗

PubMed1991

Spectroscopic studies of cobalt and nickel substituted rubredoxin and desulforedoxin.

The single iron site of rubredoxin was replaced by nickel and cobalt. The near-infrared/visible/UV spectra of these metal derivatives show ligand-field transitions and charge-transfer bands which closely resemble those of simple tetrathiolate complexes, indicating a tetrahedral arrangement of the sulfur cysteinyl ligands around the metal core. The 1H NMR spectra of the nickel and cobalt derivatives reveal extremely low-field contact shifted resonances of one proton intensity assigned to beta-CH2 and alpha-CH cysteinyl protons. Other well resolved resonances shifted out of the main protein spectral envelope are also observed and probably arise from contact plus pseudocontact shift mechanisms. Rubredoxins from different sulfate reducers were metal substituted and assignments of aliphatic protons are tentatively proposed, taking advantage of the amino acid sequence homologies. The present data is promising in terms of structural analysis of the coordination sphere of the metal core. It was also shown that replacement of the iron atom of desulforedoxin, a close analogue of rubredoxin, by cobalt and nickel was possible.

Amino Acid Sequence↗

PubMed1989

The axial ligands of heme in cytochromes: a near-infrared magnetic circular dichroism study of yeast cytochromes c, c1, and b and spinach cytochrome f.

Room temperature near-infrared magnetic circular dichroism and low-temperature electron paramagnetic resonance measurements have been used to characterize the ligands of the heme iron in mitochondrial cytochromes c, c1, and b and in cytochrome f of the photosynthetic electron transport chain. The MCD data show that methionine is the sixth ligand of the heme of oxidized yeast cytochrome c1; the identify of this residue is inferred to be the single conserved methionine identified from a partial alignment of the available cytochrome c1 amino acid sequences. A different residue, which is most likely lysine, is the sixth heme ligand in oxidized spinach cytochrome f. The data for oxidized yeast cytochrome b are consistent with bis-histidine coordination of both hemes although the possibility that one of the hemes is ligated by histidine and lysine cannot be rigorously excluded. The neutral and alkaline forms of oxidized yeast cytochrome c have spectroscopic properties very similar to those of the horse heart proteins, and thus, by analogy, the sixth ligands are methionine and lysine, respectively.

Amino Acid Sequence↗

PubMed1985

Chemical modification of the CuA center in cytochrome c oxidase by sodium p-(hydroxymercuri)benzoate.

Cytochrome c oxidase contains a copper ion electron-transfer site, CuA, which has previously been found to be unreactive with externally added reagents under conditions in which the protein remains structurally intact. We have studied the reaction of cytochrome oxidase with sodium p-(hydroxymercuri) benzoate (pHMB) and found that the reaction proceeds, under appropriate conditions, to give an excellent yield of a particular derivative of the CuA center that has electron paramagnetic resonance and near-infrared absorption spectroscopic properties which are distinctly different from those of the unmodified center. Spectroscopic and chemical characterization of the other metal ion sites of the enzyme reveals little or no effect of the pHMB modification on the structures of and reactions at those sites. Of particular interest is the observation that the modified enzyme still displays a substantial fraction of the native steady-state activity of electron transfer from ferrocytochrome c to O2. Although the modified copper center retains the ability to receive electrons from the powerful reductant Na2S2O4 and to transfer electrons to O2, it is not significantly reduced when the enzyme is treated with milder (higher potential) reductants such as NADH/phenazine methosulfate or the physiological substrate ferrocytochrome c. CuA exhibits many spectroscopic and chemical properties which make it highly atypical of cuproprotein active sites; the singular nature of this site has prompted speculation about the importance of the structural peculiarities of this metal ion center in the catalytic cycle of the enzyme. In this work, we demonstrate that the unusual features of this site are not prerequisites for competent catalysis of electron transfer and O2 reduction by the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Rapid verification of identity and content of drug formulations using mid-infrared spectroscopy.

A general method for the rapid verification of both identity and content of complete solid drug formulations has been devised. Infrared spectra for the samples were recorded using the diffuse reflectance technique, and specially written software was employed to identify the type of formulation and level of active ingredient. This software was devised to ensure reliable use when applied by those with minimal operator skills. Three differing drug tablet formulations containing simvastatin, enalapril maleate and lovastatin, as well as a capsule formulation containing finastride were studied. Adequate precision was obtained to reliably verify drug dosage levels. Near-infrared (NIR) and mid-infrared (MIR) spectrometers were evaluated for use with the method. The MIR instrument allowed sufficient resolution and spectral/structural selectivity to reliably verify correctness of either of two near derivative drugs necessarily present in the same clinical study. Drug tablet and capsule dosage levels tested ranged from 0.2 to 40 mg of drug. Approximately 1% (w/w) of the drug in the formulation was the minimum amount determined. Parameters affecting method ruggedness in routine use were optimized. Experimental addition of an extraneous material to a simvastatin formulation was easily detected and flagged by the routine test procedure. Subsequent data retrieval and searching against spectral libraries was used to demonstrate identification of the additive.

Anticholesteremic Agents↗