Search results for "Spectrophotometry"
showing 10 items of 644 documents
Different relaxations in myoglobin after photolysis
2004
To clarify the interplay of kinetic hole-burning (KHB), structural relaxation, and ligand migration in myoglobin (Mb), we measured time-resolved absorption spectra in the Soret region after photolysis of carbon monoxide Mb (MbCO) in the temperature interval 120-260 K and in the time window 350 ns to 200 ms. The spectral contributions of both photolyzed (Mb * ) and liganded Mb (MbCO) have been analyzed by taking into account homogeneous bandwidth, coupling to vibrational modes, and static conformational heterogeneity. We succeeded in separating the “time-dependent” spectral changes, and this work provides possibilities to identify the events in the process of ligand rebinding. KHB is domina…
Derivatization of amphetamine and methamphetamine with 1,2-naphthoquinone 4-sulfonic acid into solid-phase extraction cartridges. Determination of am…
1997
The derivatization of amphetamine and methamphetamine with 1,2-naphthoquinone-4-sulfonate (NQS) into solid-phase extraction cartridges (C 18 ) is described. Optimum conditions were the use of carbonate–hydrogencarbonate buffer of pH 10, a 10 min reaction time at 25 °C and an NQS concentration of 9.6 × 10 - 3 M. The accuracy and the precision of the method were tested. The results obtained with the proposed liquid–solid procedure were compared with those obtained with a traditional liquid–liquid extraction with hexane–ethyl acetate. The procedure was used to measure amphetamine in pharmaceutical and urine samples
Release of naltrexone on buccal mucosa: Permeation studies, histological aspects and matrix system design
2007
Transbuccal drug delivery has got several well-known advantages especially with respect to peroral way. Since a major limitation in buccal drug delivery could be the low permeability of the epithelium, the aptitude of NLX to penetrate the mucosal barrier was assessed. Ex vivo permeation across porcine buccal mucosa 800 microm thick was investigated using Franz type diffusion cells and compared with in vitro data previously obtained by reconstituted human oral epithelium 100 microm thick. Both fluxes (Js) and permeability coefficients (K(p)) are in accordance, using either buffer solution simulating saliva or natural human saliva. Permeation was evaluated also in presence of chemical enhance…
Mechanism of Reaction of Melatonin with Human Myeloperoxidase
2001
Recently, it was suggested that melatonin (N-acetyl-5-methoxytryptamine) is oxidized by activated neutrophils in a reaction most probably involving myeloperoxidase (Biochem. Biophys. Res. Commun. (2000) 279, 657-662). Myeloperoxidase (MPO) is the most abundant protein of neutrophils and is involved in killing invading pathogens. To clarify if melatonin is a substrate of MPO, we investigated the oxidation of melatonin by its redox intermediates compounds I and II using transient-state spectral and kinetic measurements at 25 degrees C. Spectral and kinetic analysis revealed that both compound I and compound II oxidize melatonin via one-electron processes. The second-order rate constant measur…
Analysis of spatial diffusion of ferric ions in PVA-GTA gel dosimeters through magnetic resonance imaging
2017
Abstract This work focused on the analysis of the temporal diffusion of ferric ions through PVA-GTA gel dosimeters. PVA-GTA gel samples, partly exposed with 6 MV X-rays in order to create an initial steep gradient, were mapped using magnetic resonance imaging on a 7T MRI scanner for small animals. Multiple images of the gels were acquired over several hours after irradiation and were analyzed to quantitatively extract the signal profile. The spatial resolution achieved is 200 μm and this makes this technique particularly suitable for the analysis of steep gradients of ferric ion concentration. The results obtained with PVA-GTA gels were compared with those achieved with agarose gels, which …
Available Lysine in Protein, Assay Using o-Phthalaldehyde/ N-Acetyl-L-cysteine Spectrophotometric Method
1992
An assay was based on reaction of free e-amino groups in proteins with the o-phthalaldehyde/N-acetyl-L-cysteine reagent to form isoindoles, which absorb at 335 nm. The procedure was suitable for proteins or mixtures of proteins with available lysine contents of more than 5 moles lysine/mole protein and required absence of free amino acids and peptides. This method was simpler and more convenient than other methods, since it did not require hydrolysis, amino acid analysis, long heating periods or solvent extraction.
Micellar versus hydro-organic mobile phases for retention-hydrophobicity relationship studies with ionizable diuretics and an anionic surfactant
2004
Abstract Logarithm of retention factors (log k ) of a group of 14 ionizable diuretics were correlated with the molecular (log P o/w ) and apparent (log P app ) octanol–water partition coefficients. The compounds were chromatographed using aqueous–organic (reversed-phase liquid chromatography, RPLC) and micellar–organic mobile phases (micellar liquid chromatography, MLC) with the anionic surfactant sodium dodecyl sulfate (SDS), in the pH range 3–7, and a conventional octadecylsilane column. Acetonitrile was used as the organic modifier in both modes. The quality of the correlations obtained for log P app at varying ionization degree confirms that this correction is required in the aqueou…
Comparison of the Ultraviolet Light Filtering across Different Intraocular Lenses.
2018
SIGNIFICANCE We have analyzed the ultraviolet transmittance of some commercial intraocular lenses (IOLs). The results show differences of wavelength cutoff among them. PURPOSE The purpose of this study was to measure and compare the ultraviolet light transmittance of different IOLs made out of acrylic hydrophobic, hydrophilic, and hydrophilic with hydrophobic surface materials from different manufacturers. METHODS The spectral transmission curves of eight monofocal IOLs with the same dioptric power of +20.0 diopters were measured using a PerkinElmer Lambda 35 ultraviolet/visible spectrometer. Two IOLs of each type were tested three times. The ultraviolet cutoff wavelength at 10% transmissio…
Scene-based spectral calibration assessment of high spectral resolution imaging spectrometers
2009
An accurate knowledge of the spectral calibration of imaging spectrometers is required for optimum data processing and interpretation. The scene-based spectral characterization of imaging spectrometers is frequently necessary to update or replace the pre-flight laboratory-based spectral characterization supplied by the data provider. An automatic method for the estimation of spectral calibration parameters (channel position and bandwidth) at atmospheric absorption regions from high spectral resolution imaging spectrometers (spectral sampling interval below 5 nm) is presented in this contribution. The method has been tested on two commercial instruments with spectral sampling intervals below…
C172S Substitution in the Chloroplast-encoded Large Subunit Affects Stability and Stress-induced Turnover of Ribulose-1,5-bisphosphate Carboxylase/Ox…
1999
Previous work has indicated that the turnover of chloroplast ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1. 39) may be controlled by the redox state of certain cysteine residues. To test this hypothesis, directed mutagenesis and chloroplast transformation were employed to create a C172S substitution in the Rubisco large subunit of the green alga Chlamydomonas reinhardtii. The C172S mutant strain was not substantially different from the wild type with respect to growth rate, and the purified mutant enzyme had a normal circular dichroism spectrum. However, the mutant enzyme was inactivated faster than the wild-type enzyme at 40 and 50 degrees C. In contrast, C172S mutant …