Search results for "absorption"
showing 10 items of 2701 documents
Bis(pyridylvinyl)diaminobenzenes: synthesis, acidochromism and solvatochromism of the fluorescence
2005
Abstract C2-symmetrical 1,4-distyrylbenzenes with 4-dimethylaminobenzene or pyridine as terminal rings, and propyloxy or dipropylamino groups in the central 2,5-positions were prepared. Solvatochromism of the absorption is small, but more pronounced in the fluorescence spectra. Some compounds exhibit huge Stokes shifts. Acid strongly alters the fluorescence: red shifts and decreasing quantum yields is the general result, but depending on the position and character of the basic sites, a strong recovery of fluorescence efficiency combined with large hypsochromic shifts may result in highly acidic solutions.
Spectroscopic Properties of Mg−Chlorin, Mg−Bacteriochlorin, and Bacteriochlorophylls a, b, c, d, e, f, g, and h Studied by Semiempirical and Ab Initi…
2001
The semiempirical PM3 method has been used to calculate fully optimized structures of bacteriochlorophylls a, b, c, d, e, f, g, and h, magnesium−chlorin, and magnesium−bacteriochlorin. Several configuration interaction (CI) methods, the PM3 (5,5) CIS and CISD, ZINDO/S CIS (n,n) with 2 < n <30, and ab initio CIS (5,5)/6-31G* methods, were tested for their predictive power in estimation of spectroscopic properties of bacteriochlorophylls. The ZINDO/S CIS (15,15) method turned out the best results for overall simulation of absorption spectra. Both the transition energies and relative intensities of the Qy, Qx, and Soret bands were correctly predicted. The effect of solvent coordination on the …
Molecular aggregates of quinuclidine and chlorophyll a
1991
A slightly polar molecule quinuclidine seems to form weakly bound aggregates in concentrated water solutions. Molecular dynamics simulation of a 6 mol water solution indicates clustering of quinuclidine molecules into an almost spherical structure with polar ends of the molecules pointing towards the solvent. Experimental evidence of aggregation was obtained by observing a small but obvious red shift of the o'' a absorption and a dramatic shortening of the fluorescence lifetime of the c n transition of concentrated solutions. The observed self-quenching is interpreted in terms of Frster model for energy transfer in the cluster. It is estimated that excitation may migrate on the cluster surf…
Physical Methods for Enhancing Oral Mucosal Delivery: Sonophoresis, Iontophoresis and Electroporation
2015
The need for more rapid onset of action and improved absorption of medications has resulted in great development of drug delivery technologies. Transmucosal drug delivery offers a convenient route of administration for a variety of clinical indications. Unfortunately, the wide variability in structure of the oral mucosal tissues could constitute a key factor in drug penetration and absorption. To circumvent this obstacle and to increase the drug flux through the mucosal membranes, different approaches to permeation enhancement are used. This chapter describes the most significant aspects of the physical techniques widely used such as sonophoresis, iontophoresis, and electroporation. These p…
Design d'un iprodione-MIP (molecularly imprinted polymer) : application à la pré-concentration des fongicides dans le vin
2014
The aim of this study was the synthesis of a MIP (molecularly imprinted polymer) specific for a fungicide that is found in the majority of the french wine: iprodione. The challenge for extracting iprodione from wine medium was that the hydoralcoholic solution is a dipolar solvent, whereas the interaction between the MIP and iprodione is based on dipolar interactions. The first extraction study of iprodione was made on a MIP synthesized by bulk polymerization using methacrylamide and ethylene glycol dimethacrylate (EGDMA). The MIP was found to be more efficient than the NIP (non-imprinted polymer) in hydroalcoholic solutions which demonstrates that the molecular imprinting was successful. Th…
Model, software and database for line-mixing effects in the nu3 and nu4 bands of CH4 and tests using laboratory and planetary measurements - II : H2 …
2006
International audience; The absorption shapes of the nu(2), nu(3) and nu(4) infrared bands of CH4 perturbed by H-2 in large ranges of pressure and temperature have been measured in the laboratory. In order to model these spectra, the theoretical approach accounting for line-mixing effects proposed for CH4-N-2 and CH4-air and successfully tested in the companion paper (1), is used. As before, state-to-state rotational rates are used together with some empirical parameters that are deduced from a fit of a single room temperature spectrum of the nu(3) band at about 50 atm. The comparisons between measured and calculated spectra in the nu(3) and nu(4) regions under a vast variety of conditions …
Spectral Transmission of the Human Corneal Layers
2021
Este artículo se encuentra disponible en la siguiente URL: https://www.mdpi.com/2077-0383/10/19/4490 Este artículo de investigación pertenece a la sección "Ophthalmology". We have assessed the spectral transmittance of the different layers of the human cornea in the ultraviolet (UV), visible, and near-infrared (IR) spectral ranges. Seventy-four corneal sample donors were included in the study. Firstly, the corneal transmittance was measured using a spectrophotometer. Then, all samples were fixed for histopathological analysis, which allowed us to measure the thickness of each corneal layer. Finally, the absorption coefficients of the corneal layers were computed by a linear model reproducin…
Studies of CoxMg1-xO Solid Solutions Using Laboratory EXAFS-Spectrometer
1993
Studies of the local electronic structure and the short-range order in solid solutions Co x Mg1-x O with x equal from 0.02 to 1.00 have been carried out on the Co K-edge X-ray absorption spectra measured using the laboratory EXAFS-spectrometer. A non-monotonous change of the Co-O distance in the first coordination shell with the bent at x=0.5 has been established. The second coordination shell of cobalt has been formed by cobalt and magnesium atoms with a distribution close to statistical.
Study of the diurnal cycle of stressed vegetation for the improvement of fluorescence remote sensing
2006
Chlorophyll fluorescence (Chf) emission allows estimating the photosynthetic activity of vegetation - a key parameter for the carbon cycle models - in a quite direct way. However, measuring Chf is difficult because it represents a small fraction of the radiance to be measured by the sensor. This paper analyzes the relationship between the solar induced Chf emission and the photosynthetically active radiation (PAR) in plants under water stress condition. The solar induced fluorescence emission is measured at leaf level by means of three different methodologies. Firstly, an active modulated light fluorometer gives the relative fluorescence yield. Secondly, a quantitative measurement of the Ch…
Sensitivity analysis of the fraunhofer line discrimination method for the measurement of chlorophyll fluorescence using a field spectroradiometer
2007
The Fraunhofer Line Discrimination (FLD) principle is established as a good method for remote sensing of solar induced chlorophyll fluorescence. Some improvements to the method are analysed in order to determine and reduce the sources of error in the estimation of the fluorescence emission. A sensitivity analysis has been performed over simulated data generated from real diurnal cycle measurements.