Search results for "Absorption"
showing 10 items of 2701 documents
J-aggregates prepared by adsorption at monolayer/water interfaces
1991
By adsorption of anionic cyanine dyes at positivly charged lipid monolayers large J-aggregates are formed. Absorption and fluorescence spectra are measured at the air/water interface during the crystallization process. The influence of the lipid/dye interaction on the aggregate structure is studied for two different systems. It is shown that the aggregate structure can be improved by growing crystals from a seed.
Amphiphilic dyes for NLO in LB-films
1991
The influence of structural variations of phenyl-hydrazones and stilbazium salts on monolayer behaviour and second-harmonic generation in LB-monolayers is discussed. In contrast to the stilbazium salts the variation of the substituents of the phenylhydrazones does not influence the absorption maximum of the dyes in resonance enhancement of the nonlinearity. This allows a direct comparison of the substitution pattern on SHG.
Studies on the structure of coumarin-modified dextran nanoparticles by fluorescence spectroscopy.
2012
The photophysical and photochemical characteristics of nano-scaled particles obtained via solvent displacement from coumarin-modified dextrans were studied by means of absorption- and fluorescence-spectroscopy. The environment-dependent fluorescence emission of the pendant 4-methyl-7-alkoxy coumarin groups was exploited as a probe to gain information about the inner structure of the polysaccharide based nanoparticles. Time-resolved fluorescence measurements showed that the particles had two domains of different polarity and it could be confirmed that the core of the nano-assemblies contained water. Moreover, preliminary experiments were carried out demonstrating the possibility to control t…
L -lysine and EDTA polymer mimics as resins for the quantitative and reversible removal of heavy metal ion water pollutants
2012
Traditional precipitation methods for inorganic micropollutant removal from waters are increasingly being replaced by sorption methods based on both natural and synthetic materials. In this context, two novel effective heavy metal ions absorbers are presented. These resins, LYMA and LMT85, were crosslinked poly(amidoamine)s carrying amine and carboxyl groups in their repeating units. In particular, the LYMA-repeating unit contains one carboxyl and two amine groups and is a mimic of L-lysine, whereas LMT85 contains two amine and five carboxyl groups and is a mimic of EDTA. Both resins were prepared at moderate cost by simple eco-friendly procedures. The heavy metal ion set adopted as benchma…
Pre- and post-modification of mixed cyclodextrin-calixarene co-polymers: A route towards tunability
2017
Various pre-modified and post-modified cyclodextrin-calixarene hyper-reticulated co-polymers were synthesized, fully characterized by different techniques (FT-IR, 13C{1H} CP-MAS and LGFS solid-state NMR, thermogravimetry, porosimetry), and tested to assess their absorption abilities as nanosponges. The construction of the polymer network was accomplished exploiting the well-known CuAAC reaction between two different heptakis-6-azido-β-cyclodextrins and two different propargyloxy-calix[4]arenes. Post-modification was aimed to achieve the presence of ionizable (acidic or basic) groups on the polymer framework. Sequestration tests towards two model pollutant molecules surprisingly showed that …
Concentration dependence of the electro-optical spectra from two-dimensional aggregated chromophore systems
1991
The linear and the quadratic Stark effects have been employed to characterize aggregate formation of an amphiphilic cyanine dye mixed with arachidic acid in various concentrations within Langmuir-Blodgett multilayers. Two different electrode configurations with the electric field directions parallel and normal to the films have been employed to test the responses of the electronic spectra to external fields. The observations have been used to quantify the induced and static dipole moment changes on excitation of the chromophores. A comparison of the results obtained from different multilayer arrangements is suggestive of inter-layer couplings for the case of head-to-head configurations of t…
α-Chymotrypsin-Catalyzed Reaction Confined in Block-Copolymer Vesicles
2010
Herein the reactivity of the enzyme α-chymotrypsin in the confinement of polystyrene-block-poly(acrylic acid) (PS-b-PAA) vesicles was investigated. Enzyme and substrate molecules were encapsulated in PS-b-PAA vesicles with internal diameters ranging from 26 nm to 165 nm during the formation of the vesicles. While the loading efficiencies of enzyme and substrate molecules were practically identical for vesicles of identical size, they were found to increase with decreasing vesicle size. The kinetics of the α-chymotrypsin catalyzed hydrolysis of N-succinyl-Ala-Ala-Phe-7-amido-4-methylcoumarin (AMC) was evaluated following the increase of the absorption of the product 7-amino-4-methylcoumarin …
Sumatriptan Succinate Transdermal Delivery Systems for The Treatment of Migraine
2007
We have successfully obtained sumatriptan transdermal systems with different polymer compositions: methyl cellulose (MC), polyvinyl pyrrolidone (PVP) and a polyvinyl pyrrolidone (PVP)-polyvinyl alcohol (PVA) mixture. The systems contained 1,2-propylenglycol (MC) or sorbitol as a plasticizer (PVP and PVP-PVA), methacrylate copolymer as an adhesive agent, and an occlusive liner. Azone (5%, w/w) was incorporated into all the systems as a percutaneous enhancer. Transdermal systems are thin, transparent and non-adhesive when in a dry state. The permeation of sumatriptan succinate across pig ear skin was studied using the systems prepared. The formulation with MC polymer produced a statistically …
Hygrothermal effect on moisture kinetics and mechanical properties of hemp/polypropylene composite: Experimental and numerical studies
2015
The exposition of thermoplastic composites reinforced with natural fibers to moisture and heat is likely to lower their mechanical properties and restrain their use in the design of parts. The present work is focussed on investigating the effects of hygrothermal aging on the mechanical behaviour of injected polypropylene reinforced with short hemp fibers. Moreover, the kinetic of isothermal moisture absorption has been studied for four immersion temperatures. The experimental results show that the time taken to reach saturation decreases significantly with increase in immersion temperature. These tests also reveal that moisture absorption in this type of materials does not follow Fick's law…
Comparative enhancer effects of Span20 with Tween20 and Azone on the in vitro percutaneous penetration of compounds with different lipophilicities.
2000
Sorbitan monolaurate (Span20) was used in this study to analyze the influence of the polar functional group on the effects that non-ionic surfactants have on skin permeability. Its ethoxylate derivative polysorbate 20 (Tween20) and Azone, both with the same C12 alkyl chain as Span20, were used for comparative purposes. We evaluated the relative potency of the three molecules as enhancers in the permeability of a series of compounds with lipophilicities ranging from log Poct=-0.95 to log Poct=2.33. The influence of the enhancer concentration was also studied. For this purpose the epidermis of Wistar rat was pretreated with ethanolic solutions (1 and 5%, w/v) of each enhancer. Our results ind…