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PubMed2003

Low-temperature Fourier transform infrared spectra and hydrogen bonding in polycrystalline L-alanine.

The 400-4000 cm(-1) FTIR spectra of pure NH and isotopically substituted (10 and 90% doped ND/NH) polycrystalline L-alanine were recorded in the temperature range 10-300 K. The observed temperature dependence and isotopic shifts behavior enabled to identify, in the spectra of the doped crystals, three well-separated bands ascribable to either the NH or ND stretching vibrations associated with the three different types of hydrogen bonds existing in the crystal. The observed red shifts of these bands relative to the frequency of a reference "free" NH (or ND) stretching mode were found to correlate well with the H-bond distances found in the crystal and provide an indirect way of estimating the enthalpies associated with each type of H-bond found in the crystal. In the low-frequency deformation and torsional spectral region (below 2000 cm(-1)), several bands, which were found to be affected by isotopic substitution, were identified as belonging to the NH3(+) group. Several bands show splitting at low temperatures, indicating the occurrence of a significant reorganization in the crystal structure, which with all probability results mainly from changes in the proton positions. Finally, the literature assignments of the IR spectra of both crystalline NH3(+) and ND3(+) L-alanine were revised taking into consideration their temperature dependence and behavior upon deuteration.

Alanine↗
PubMed1987

Site-directed mutants of staphylococcal nuclease. Detection and localization by 1H NMR spectroscopy of conformational changes accompanying substitutions for glutamic acid-43.

The high-resolution X-ray crystal structure of staphylococcal nuclease suggests that the gamma-carboxylate group of Glu-43 is directly involved in catalysis as a general base that facilitates the attack of water on the substrate phosphodiester. We have used primer-directed, site-specific mutagenesis to generate aspartate, glutamine, asparagine, alanine, and serine substitutions for this residue. The Vmax/Km for the aspartate mutant is reduced 1400-fold and the values for the charge-neutral mutations are reduced 5000-fold relative to the wild-type enzyme. Although these reductions in catalytic efficiency might appear useful in quantitatively estimating the importance of general basic catalysis in the reaction catalyzed by the wild-type enzyme, the thermal stabilities and 1H NMR spectral properties of the mutants suggest that such interpretations are ambiguous. All five mutants have higher melting temperatures for thermal denaturation than the wild-type enzyme, suggesting that the mutants have enhanced thermal stabilities relative to the wild-type enzyme. Chemical shift changes relative to the wild type are observed in both the aromatic and upfield-shifted methyl group regions of the 1H NMR spectra of the aspartate and serine mutants, suggesting the presence of conformational differences between the wild-type and mutant enzymes. That these conformational differences may be large enough to be mechanistically relevant is suggested by comparisons of the magnitudes of nuclear Overhauser effect (NOE) correlations between the aromatic and upfield-shifted methyl group regions observed via two-dimensional nuclear Overhauser effect correlation spectroscopy.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed2006

Lipid-oxidation-induced carboxymyoglobin oxidation.

We evaluated the usefulness of the ratio A503/A581 as a browning index (BI) for estimating brown color formation in solutions containing oxymyoglobin (OxyMb) and carboxymyoglobin (COMb). In split-chamber cuvette analyses with different proportions of metmyoglobin (MetMb), COMb and OxyMb, BI was highly correlated (r = 0.93-0.94) with direct estimation of MetMb. Moreover, A503/A581 was not influenced by different COMb-OxyMb proportions. Second, we investigated 4-hydroxy-2-nonenal (HNE)-induced spectral changes in OxyMb and COMb solutions. At pH 7.4 and 37 degrees C, BI was greater in HNE-treated OxyMb and COMb samples than in aldehyde-free controls (P < 0.05). However, at pH 5.6 and 4 degrees C, HNE-induced browning was more pronounced in COMb than in OxyMb. These results indicated that COMb is susceptible to lipid-oxidation-induced browning in a pH- and temperature-dependent manner.

Animals↗
PubMed1996

Precipitation of proteins in supercritical carbon dioxide.

Supercritical CO2 was used as an antisolvent to form protein particles that exhibited minimal loss of activity upon reconstitution. Organic protein solutions were sprayed under a variety of operating conditions into the supercritical fluid, causing precipitation of dry, microparticulate (1-5 microns) protein powders. Three proteins were studied: trypsin, lysozyme, and insulin. Amide I band Raman spectra were used to estimate the alpha-helix and beta-sheet structural contents of native and precipitate powders of each protein. Analysis of the Raman spectral revealed minimal (lysozyme), intermediate (trypsin), and appreciable (insulin) changes in secondary structure with respect to the commercial starting materials. The perturbations in secondary structure suggest that the most significant event during supercritical fluid-induced precipitation involved the formation of beta-sheet structures with concomitant decreases of alpha-helix. Amide I band Raman and Fourier-transform infrared (FTIR) spectra indicate that higher operating temperatures and pressures lead to more extensive beta-sheet-mediated intermolecular interactions in the precipitates. Raman and FTIR spectra of redissolved precipitates are similar to those of aqueous commercial proteins, indicating that conformational changes were reversible upon reconstitution. These results suggest that protein precipitation in supercritical fluids can be used to form particles suitable for controlled release, direct aerosol delivery to the lungs, and long-term storage at ambient conditions.

Carbon Dioxide↗
PubMed2006

Infrared spectra and radiation stability of H2O2 ices relevant to Europa.

In this paper we present spectra of H2O2-containing ices in the near- and mid-infrared (IR) regions. Spectral changes on warming are shown, as is a comparison of near-IR bands of H2O and H2O2-containing ices. An estimate of the A-value (absolute intensity) for the largest near- IR feature of H2O2 is given. Radiation-decay half-lives are reported for 19 K and 80 K, and are related to the surface radiation doses on Europa. The radiation data show that H2O2 destruction is slower at 80 K than 19 K, and are consistent with the claim that icy material in the outermost micrometer of Europa's surface has been heavily processed by radiation.

Hydrogen Peroxide↗
PubMed1983

Intramolecular stacking association and conformation properties of a 'cap' structure, m7G5'pppUm, and the related model compounds.

The stacking equilibrium quotient of the m7G5'pppUm unit, which occurs as the 5'-terminal "cap" of certain eukaryotic mRNA's, was determined by temperature-dependent difference spectrophotometry as Kstack = 1.82 at 25 degrees and pH 5. In order to evaluate the contribution of different structural modifications to the net stabilization of the cap structures of mRNA, a variety of compounds related to m7G5'pppUm were synthesized and their stacking properties were studied by the same method and compared. The results are summarized as: (1) Introduction of a methyl group into N-7 of G residue results in an increase in base stacking. (2) Methylation at 2'-OH of U residue also stabilizes the stacked structure of G-containing dimers, but it does not influence stacking interaction in m7G-containing dimers. (3) The effect of different types of internucleotide linkages on the order of stacking tendencies is: N5'ppN' greater than N5'pppN' greater than NpN'. UV hypochromicity and CD spectral measurements of the relevant dimers were also conducted, and the hypochromicity values and CD spectra of dimers in their stacked conformation were estimated by making use of the determined Kstack values. The results indicate that, while 2'-O-methylation exerts very little effect on the stacked conformation of the dimers, methylation at N-7 and the nature of the internucleotide linkage strongly influence the stacked conformation, thereby forming unusual left-handed conformations in m7G5'pppU(m), m7G5'ppU(m), and G5'ppU(m).

Nucleic Acid Conformation↗
PubMed2005

Monte Carlo simulation of neutron backscattering from concrete walls in the dense plasma focus laboratory of Bologna University.

Between 2001 and 2003 a 3.2 kJ dense plasma focus (DPF) device has been built at the Montecuccolino Laboratory of the Department of Energy, Nuclear and Environmental Control Engineering (DIENCA) of the University of Bologna. A DPF is a pulsed device in which deuterium nuclear fusion reactions can be obtained through the pinching effects of electromagnetic fields upon a dense plasma. The empirical scale law that governs the total D-D neutron yield from a single pulse of a DPF predicts for this machine a figure of approximately 10(7) fast neutrons per shot. The aim of the present work is to evaluate the role of backscattering of neutrons from the concrete walls surrounding the Montecuccolino DPF in total neutron yield measurements. The evaluation is performed by MCNP-5 simulations that are aimed at estimating the neutron spectra at a few points of interest in the laboratory, where neutron detectors will be placed during the experimental campaigns. Spectral information from the simulations is essential because the response of detectors is influenced by neutron energy. Comparisons are made with the simple r(-2) law, which holds for a DPF in infinite vacuum. The results from the simulations will ultimately be used both in the design and optimisation of the neutron detectors and in their final calibration and placement inside the laboratory.

Algorithms↗
PubMed2000

Using measured 30-150 kVp polychromatic tungsten x-ray spectra to determine ion chamber calibration factors, Nx (Gy C(-1)).

Two methods for determining ion chamber calibration factors (Nx) are presented for polychromatic tungsten x-ray beams whose spectra differ from beams with known Nx. Both methods take advantage of known x-ray fluence and kerma spectral distributions. In the first method, the x-ray tube potential is unchanged and spectra of differing filtration are measured. A primary standard ion chamber with known Nx for one beam is used to calculate the x-ray fluence spectrum of a second beam. Accurate air energy absorption coefficients are applied to the x-ray fluence spectra of the second beam to calculate actual air kerma and Nx. In the second method, two beams of differing tube potential and filtration with known Nx are used to bracket a beam of unknown Nx. A heuristically derived Nx interpolation scheme based on spectral characteristics of all three beams is described. Both methods are validated. Both methods improve accuracy over the current half value layer Nx estimating technique.

Aluminum↗
PubMed1999

Modeling of surface myoelectric signals--Part II: Model-based signal interpretation.

Experimental electromyogram (EMG) data from the human biceps brachii were simulated using the model described in [10] of this work. A multichannel linear electrode array, spanning the length of the biceps, was used to detect monopolar and bipolar signals, from which double differential signals were computed, during either voluntary or electrically elicited isometric contractions. For relatively low-level voluntary contractions (10%-30% of maximum force) individual firings of three to four-different motor units were identified and their waveforms were closely approximated by the model. Motor unit parameters such as depth, size, fiber orientation and length, location of innervation and tendonous zones, propagation velocity, and source width were estimated using the model. Two applications of the model are described. The first analyzes the effects of electrode rotation with respect to the muscle fiber direction and shows the possibility of conduction velocity (CV) over- and under-estimation. The second focuses on the myoelectric manifestations of fatigue during a sustained electrically elicited contraction and the interrelationship between muscle fiber CV, spectral and amplitude variables, and the length of the depolarization zone. It is concluded that a) surface EMG detection using an electrode array, when combined with a model of signal propagation, provides a useful method for understanding the physiological and anatomical determinants of EMG waveform characteristics and b) the model provides a way for the interpretation of fatigue plots.

Action Potentials↗
PubMed2004

Estimation of nonstationary EEG with Kalman smoother approach: an application to event-related synchronization (ERS).

An adaptive spectrum estimation method for nonstationary electroencephalogram by means of time-varying autoregressive moving average modeling is presented. The time-varying parameter estimation problem is solved by Kalman filtering along with a fixed-interval smoothing procedure. Kalman filter is an optimal filter in the mean square sense and it is a generalization of other adaptive filters such as recursive least squares or least mean square. Furthermore, by using the smoother the unavoidable tracking lag of adaptive filters can be avoided. Due to the properties of Kalman filter and benefits of the smoothing the time-frequency resolution of the presented Kalman smoother spectra is extremely high. The presented approach is applied to estimation of event-related synchronization/desynchronization (ERS/ERD) dynamics of occipital alpha rhythm measured from three healthy subjects. With the Kalman smoother approach detailed spectral information can be extracted from single ERS/ERD samples.

Algorithms↗
PubMed2006

A spectral clustering approach to underdetermined postnonlinear blind source separation of sparse sources.

This letter proposes a clustering-based approach for solving the underdetermined (i.e., fewer mixtures than sources) postnonlinear blind source separation (PNL BSS) problem when the sources are sparse. Although various algorithms exist for the underdetermined BSS problem for sparse sources, as well as for the PNL BSS problem with as many mixtures as sources, the nonlinear problem in an underdetermined scenario has not been satisfactorily solved yet. The method proposed in this letter aims at inverting the different nonlinearities, thus reducing the problem to linear underdetermined BSS. To this end, first a spectral clustering technique is applied that clusters the mixture samples into different sets corresponding to the different sources. Then, the inverse nonlinearities are estimated using a set of multilayer perceptrons (MLPs) that are trained by minimizing a specifically designed cost function. Finally, transforming each mixture by its corresponding inverse nonlinearity results in a linear underdetermined BSS problem, which can be solved using any of the existing methods.

Algorithms↗
PubMed1991

Four forms of cytochrome P-450 in human fetal liver: purification and their capacity to activate promutagens.

Four forms of cytochrome P-450 were separated and purified to electrophoretic homogeneity from human fetal livers. These forms of cytochrome P-450, termed P-450HFLa, P-450HFLb, P-450HFLc and P-450HFLd, were distinguishable from each other in their molecular weights, spectral properties, immunochemical properties and mutagen-producing activities from promutagens. The molecular weights of P-450HFLa, b, c and d were estimated to be 51,500, 49,000, 51,500 and 50,000, respectively. Antibodies to P-450HFLa recognized P-450HFLc but not P-450HFLb or d, and antibodies to rat P-448-H (P-450IA2) cross-reacted with P-450HFLb but not with other forms of cytochrome P-450. The N-terminal amino acid sequence of P-450HFLc was highly homologous, but not identical, to that of P-450HFLa. Each form of cytochrome P-450 catalyzed mutagenic activation of aflatoxin B1 (AFB1), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-6-methyldipyrido-[1,2-a:3',2'-d]imidazole (Glu-P-1) at different rates. P-450 HFLa showed activities to produce mutagen(s) from AFB1, IQ and to a lesser extent from Glu-P-1. P-450 HFLb activated IQ at a faster rate than did the other forms. P-450 HFLc produced a mutagen from AFB1 and Glu-P-1 but not from IQ. P-450 HFLd did not activate these promutagens at significant rates.

Chromatography, DEAE-Cellulose↗
PubMed1974

The density and photosensitivity of human rhodopsin in the living retina.

1. The visual pigment in a 5 degrees circular patch of the living human retina 18 degrees temporal from the fovea was studied with the Rushton retinal densitometer. The measuring light (570 nm) was selected to obviate artifacts from colour photoproducts.2. The action spectrum of a 10% bleach agrees well with the action spectrum at absolute threshold for the same patch of retina. The quantized C.I.E. scotopic spectral sensitivity curve is a good description of both spectra. Therefore, the visual pigment studied must be human rhodopsin.3. Its density has been estimated in five different ways. The results are in reasonable agreement. The optical density of human rhodopsin in vivo is about 0.35 (common logarithmic units) at its gamma(max.)4. The photosensitivity of human rhodopsin in vivo was determined by studying its rate of bleaching in response to steps of monochromatic light exposed to the dark adapted eye, by measuring the amount bleached in the steady state by monochromatic lights as well as the amount bleached by 10 sec flashes of white light.5. The results obtained by the different methods are in good agreement with each other and with previous estimates made by others using white light.6. The photosensitivity of human rhodopsin in vivo [epsilongamma(max) = 62,000 to 120,000 l./cm mole] is much higher than expected from in vitro measurements.

Dark Adaptation↗
PubMed1990

Color and chemistry on Triton.

The surface of Triton is very bright but shows subtle yellow to peach hues which probably arise from the production of colored organic compounds from CH4 + N2 and other simple species. In order to investigate possible relationships between chemical processes and the observed surface distribution of chromophores, we classify the surface units according to color/albedo properties, estimate the rates of production of organic chromophores by the action of ultraviolet light and high-energy charged particles, and compare rates, spectral properties, and expected seasonal redistribution processes to suggest possible origins of the colors seen on Triton's surface.

Atmosphere↗
PubMed2006

Mechanism behind augmentation in baroreflex sensitivity after acute exercise in spontaneously hypertensive rats.

A single bout of dynamic exercise increases baroreflex sensitivity (BRS) in spontaneously hypertensive rats (SHR). We examined whether change in hemodynamics (increases in blood pressure and heart rate) associated with dynamic exercise contribute to the post-exercise modulation of BRS. SHR aged 12 weeks were chronically instrumented with a carotid artery catheter and jugular vein catheter. They were then allocated to three groups submitted to 40 min of 1) running on a treadmill at 12 m/min (Run), 2) concomitant infusion of isoproterenol and a relatively high dose of phenylephrine (Iso+Phe(high)), or 3) concomitant infusion of isoproterenol and a relatively low dose of phenylephrine (Iso+Phe(low)). Arterial pressure and heart rate were continuously recorded throughout the experiments. BRS estimated by heart rate responses to phenylephrine injection and systolic blood pressure-low frequency power amplitude (SBP-LFamp) evaluated by power spectral analysis of SBP, a marker of sympathetic activity, were examined before and after running (Run group), or administration of drugs (Iso+Phe(high) or Iso+Phe(low) groups). BRS increased significantly from 1.4 to 1.9 bpm/mmHg after running, but not after administration of Iso+Phe(high) or Iso+Phe(low). Blood pressure and SBP-LFamp significantly decreased in each of the Run, Iso+Phe(high) and Iso+Phe(low) groups. These results suggest that hemodynamic change alone does not contribute to post-exercise modulation of BRS, while hemodynamic change or sympathetic activation during exercise contributes to post-exercise hypotension associated with a reduction of sympathetic activity.

Animals↗
PubMed2005

Breadboard of a Fourier-transform spectrometer for the radiation explorer in the far infrared atmospheric mission.

In preparation for a possible space mission, a breadboard version named REFIR-BB of the Radiation Explorer in the Far Infrared (REFIR) instrument has been built. The REFIR is a Fourier-transform spectrometer with a new optical layout operating in the spectral range 100-1100 cm(-1) with a resolution of 0.5 cm(-1), a 7-s acquisition time, and a signal-to-noise ratio of better than 100. Its mission is the spectral measurement in the far infrared of the Earth's outgoing emission, with particular attention to the long-wavelength spectral region, which is not covered by either current or planned space missions. This measurement is of great importance for deriving an accurate estimate of the radiation budget in both clear and cloudy conditions. The REFIR-BB permits the trade-off among all instrument parameters to be studied, the optical layout to be tested, and the data-acquisition strategy to be optimized. The breadboard could be used for high-altitude ground-based campaigns or could be flown for test flights on aircraft or balloon stratospheric platforms. The breadboard's design and the experimental results are described, with particular attention to the acquisition strategy and characterization of the interferometer. Tests were performed both in laboratory conditions and in vacuum. Notwithstanding a loss of efficiency above 700 cm(-1) caused by the poor performance of the photolithographic polarizers used as beam splitters, the results demonstrate the feasibility of using the spectrometer for space applications.

Journal Article↗
PubMed2006

On-line concentration measurements in wastewater using nonlinear deconvolution and partial least squares of spectrophotometric data.

A procedure for the on-line measurement of concentrations of toxins in wastewater using spectrophotometric data is proposed. The complete absorbance spectrum of a wastewater sample is used to predict the concentrations of all possible substances within. Two techniques are examined. In nonlinear spectral deconvolution, the spectrum is decomposed as a linear combination of base spectra and the coefficients of this deconvolution are used to nonlinearly estimate the concentrations. Under partial least squares analysis, the concentrations are directly estimated as a linear combination of the measured spectrum data. Both techniques show good results for estimating the kinetics of samples taken during the reaction phase in a laboratory anaerobic/aerobic SBR used for p-nitrophenol biodegradation.

Aerobiosis↗
PubMedDate not supplied

[Use of the electroencephalographic spectral edge frequency 90 to monitor sedation of chronically ill patients].

INTRODUCTION: The depth of sedation required for patients in critical care units varies over time and should be subject to control. The clinical assessment scales used at present are inadequate, and several electroencephalographic variables have been investigated in recent years with the aim of quantifying depth of sedation. One such variable is the spectral edge frequency 90 (SEF90). OBJECTIVES: To establish the correlation between SEF90 and the Ramsay score as indicators of depth of sedation. To estimate the ability of SEF90 to predict sedation and a patient's hemodynamic response during aspiration of secretions through the orotracheal tube. PATIENTS AND METHODS: Patients in a surgical intensive care unit. The ability of SEF90 to predict a certain Ramsay score was assessed by logistic regression. We also calculated the predictive probability (Pk) of SEF90 for the appearance of hemodynamic change and of movement in the event of endotracheal aspiration. RESULTS: When SEF90 was < 16 Hz, the probability of a Ramsay score >= 4 was >= 90% (Pk = 0.91). Neither SEF90 nor the Ramsay score predicted hemodynamic response to orotracheal aspiration. CONCLUSIONS: SEF90 distinguishes superficial from deep sedation but does not differentiate further degrees of depth or the likelihood of hemodynamic instability or movement in response to aspiration.

Anesthesia↗