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At least 1,315 records · Page 73Linked to original sources
PubMed2005

A spectroscopic study on applicability of spectral analysis for simultaneous quantification of l-dopa, benserazide and ascorbic acid in batch and flow systems.

The usefulness of derivative spectrophotometry for simultaneous assay of l-dopa, benserazide and ascorbic acid in pharmaceuticals was studied. The parameters of derivatisation depends on composition of solution in which particular compound was determined. For quantification of l-dopa in mixtures with benserazide or ascorbic acid the first derivative was used. Its determination in ternary mixture (l-dopa+benserazide+ascorbic acid) is possible by third derivative spectra. Benserazide was assayed in presence of l-dopa using first derivative while in ternary mixture by third derivative. Direct determination of ascorbic acid is possible applying first derivative only in presence of l-dopa. The elaborated derivative spectrophotometric methods were used for assaying of l-dopa and benserazide in their commercial form "Madopar". The proposed spectrophotometric derivative method of simultaneous determination of l-dopa and benserazide was combined with FIA technique.

Ascorbic Acid↗
PubMed2005

Spectral analysis of Cu(2+): B(2)O(3)--ZnO--PbO glasses.

A new series of heavy metal oxide (PbO) based zinc borate glasses in the chemical composition of (95-x)B(2)O(3)-5ZnO-xPbO (x=10, 15, 20, 25, 30, 35, 40, 45 and 50 mol%) have been prepared to verify their UV filtering performance. Both direct and indirect optical band gaps (E(opt)) have been evaluated for these glasses. For a reference glass of 45B(2)O(3)-5ZnO-50PbO, refractive indices at different wavelengths are measured and found the results satisfactorily correlated with the theoretical data upon the computation of Cauchy's constants of A=1.766029949, B=159531.024 nm(2) and C=-1.078 x 10(10) nm(4). Measurements concerning X-ray diffraction (XRD), FT-IR, differential scanning colorimeter (DSC) profiles have been carried out for this glass. The FT-IR profile has revealed that the glass has both BO(3) and BO(4) units. From DSC thermogram, glass transition temperature (T(g)), crystallization temperature (T(c)) and melting temperature (T(m)) have been located and from them, other related parameters of the glass have also been calculated. Visible absorption spectra of 45B(2)O(3)-5ZnO-(50-x)PbO-xCuO (x=0. 1, 0.2, 0.5 and 1.0 mol%) have revealed two absorption bands at around 400 nm ((2)B(1g)-->(2)E(g)) and 780 nm ((2)B(1g)-->(2)B(2g)) of Cu(2+) ions, respectively. Emission bands at 422 and 512 nm are found for the 1 mol % CuO doped glass with excitations at 306 and 332 nm.

Beryllium↗
PubMed2005

Scaled quantum chemical calculations and FTIR, FT-Raman spectral analysis of 3,4-diamino benzophenone.

The vibrational spectra of 3,4-diamino benzophenone (DABP) have been computed using B3LYP methodology and 6-31G* and 6-31G** basis sets. The solid phase FTIR and FT-Raman spectra were recorded in the region 4000-400 cm-1 and 3500-100 cm-1, respectively. A close agreement was achieved between the observed and calculated frequencies by employing normal coordinate calculations. The observed and simulated spectra were found to be well comparable.

Benzophenones↗
PubMed2005

Reducing-difference infrared spectral analysis of cis- and trans-configurated lactams.

The conventional (non-polarized) and linear-polarized IR-spectra of 2-pyrrolidone and laurolactam as typical representatives of lactams with cis- and trans-amide configuration, respectively, were studied by means of difference IR-spectroscopy. The application of this method to treatment of the non-polarized IR-spectra permits additional conclusions about the likely self-associates of these compounds dissolved in aprotic solvents. By means of the difference linear-dichroic IR-spectroscopy, a more precise assignment of the characteristic bands of the lactam cis- and trans-peptide forms as well as their stereo structures were accomplished. A comparative analysis with the linear-dichroic IR-spectra of epsilon-caprolactam and caprylolactam, as similar compounds, with cis- and trans-conformation, respectively, was also carried out.

Isomerism↗
PubMed2005

Raman spectral analysis of phenoxyacetic acid and some chloro substituted phenoxyacetic acids.

Raman spectra of phenoxyacetic acid and chlorine substituted phenoxyacetic acids viz., o-chlorophenoxyacetic acid, p-chlorophenoxyacetic acid and 2,6-dichlorophenoxyacetic acid have been analysed with the aid of abinitio theoretical calculations. The effect of chlorine substituents on the Raman spectra of phenoxyacetic acid have also been analysed by considering some important vibrational modes.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2006

Polarised Raman and infrared spectral analysis of L-alanine oxalate (C5H9NO6)--a non-linear optical single crystal.

L-alanine oxalate (C5H9NO6), a promising material for effective frequency conversion, was grown by standard slow evaporation technique. Solubility studies were carried out at different temperatures. Unambiguous assignments of fundamental modes of various molecular groups were made from the recorded infrared and polarised Raman spectra. The non-linear optical property has been confirmed from the optical transmission and fluorescence spectra.

Alanine↗
PubMed2006

Vibrational spectral analysis of DL-valine DL-valinium and DL-methionine DL-methioninium picrates.

A comparative study of infrared and Raman spectra of DL-valine DL-valinium picrate (DL-VVP) and DL-methionine DL-methioninium picrate (DL-MMP) at the room temperature in 4000-50 cm(-1) range helps to determine the effect of hydrogen bonds in these crystals. The existence of the zwitterion and the protonated form in both the crystals has been observed. In DL-MMP, the methionine and the methioninium residues form a dimer through a strong hydrogen bond between them in the crystal. The characteristic bands due to gem-methyl group are observed in the case of DL-VVP. Factor group analysis has been made and the numbers of vibrational modes have been calculated. The tentative assignments of the observed bands are given. The picrate group forms the anion in both the crystals and it is unaffected by the presence of the cations.

Hydrogen Bonding↗
PubMed2006

Adaptation of single photon responses in photoreceptors of the housefly, Musca domestica: a novel spectral analysis.

The absorption of a photon by a photoreceptor triggers a small voltage fluctuation termed the 'bump'. Here, in the housefly, I introduce the bispectrum of photoreceptor noise to characterise the bump under dim light. The bispectrum provides explicit phase information and is not contaminated by Gaussian background noise. Over the photon rates examined (<10(4) s(-1)), I show that bumps are minimum-phase, noise spectra are little affected by natural variations in bump shape and bumps adapt such that amplitude is approximately proportional to duration squared. In the dark exists a 'dark event', which I suggest represents spontaneous activation of G-protein.

Adaptation, Ocular↗
PubMed1995

Color Doppler imaging and spectral analysis of the optic nerve vasculature in glaucoma.

PURPOSE: We used color Doppler imaging to study blood flow velocity in the central retinal artery and the short posterior ciliary arteries in patients with glaucoma. METHOD: Fifty-two patients with chronic open-angle glaucoma, 24 patients with normal-tension glaucoma, and 28 normal subjects were studied. The mean of the peak systolic velocity, the end diastolic velocity, and the resistive index were compared in the three groups. RESULTS: Compared with the normal subjects, the patients with chronic open-angle glaucoma showed a statistically significant (P < .05) decrease in the mean end diastolic velocity and an increase in the mean resistive index in all vessels studied. The patients with normal-tension glaucoma showed similar changes, achieving significance most prominently in the central retinal arteries, compared with normal subjects (P < .05). There were no statistically significant differences between the patients with chronic open-angle glaucoma and those with normal-tension glaucoma. CONCLUSIONS: Open-angle glaucoma appears to be associated with a decreased mean flow velocity and an increased mean resistive index in the ocular vasculature. These changes are in keeping with possibly compromised circulation in this region.

Adult↗
PubMed1971

Spectral analysis of laser light scattered from motile microorganisms.

The theoretical basis of laser scattering from motile microorganisms is examined. Spectra of swimming particles are compared with spectra arising from brownian motion. For mixtures of motile and resting organisms, that part of the spectrum related to the motile organisms is enhanced when V(s)/|k|D is large, where V(s) is the mean swimming speed of the motile microorganisms,|k| is the Bragg wave vector, and D is the diffusion coefficient of the nonmotile particles. When the directed motion of swimming microorganisms persists for periods which are much longer than tau = (|k|V(s))(-1), the scattering spectrum is given as S(k, omega) infinity P(| [omega - omega(0)]/k|), where P is the probability distribution obtained by two-dimensional integration over the swimming speed distribution. A computation of scattering from bull spermatozoa, based on published velocity distributions, is investigated in detail.

Animals↗
PubMed1998

An estimate of fetal autonomic state by spectral analysis of human umbilical artery flow velocity waveforms.

OBJECTIVE: Determination of gestational age-related fluctuations in heart rate in the umbilical artery of the early human fetus. METHODS: Doppler velocity recordings from human umbilical artery were obtained, in a cross-sectional study design in 137 singleton pregnancies at 10-20 weeks of gestation. After exclusion criteria were applied, data on 117 normal pregnancies were available and subdivided into group I: 10-12 weeks (n = 49); group II: 13-16 weeks (n = 43); and group III: 17-20 weeks (n = 25). Blood flow velocity waveforms were reconstructed from Doppler audio signals. Variability in heart rate was calculated using Fast Fourier Transforms (FFT). Individual heart rate variability power spectra were subdivided into frequency bands. RESULTS: Fetal heart rate variability decreases at 10-20 weeks and demonstrates a shift to lower frequencies at 17-20 weeks. CONCLUSIONS: Fetal heart rate variability is related to gestational age and shows a shift to lower frequencies which may reflect autonomic functional development.

Adolescent↗
PubMed2001

AR spectral analysis of EEG signals by using maximum likelihood estimation.

In this study, EEG signals were analyzed using autoregressive (AR) method. Parameters in AR method were realized by using maximum likelihood estimation (MLE). Results were compared with fast Fourier transform (FFT) method. It is observed that AR method gives better results in the analysis of EEG signals. On the other hand, the results have also showed that AR method can also be used for some other researches and diagnosis of diseases.

Brain Diseases↗