Électrons en excès dans les milieux polaires homogènes et hétérogènes

1996 ◽  
Vol 74 (1) ◽  
pp. 1-23 ◽  
Author(s):  
Annette Bernas ◽  
Christiane Ferradini ◽  
Jean-Paul Jay-Gerin
Keyword(s):  
Physicochemical Characteristics ◽  
Molecular Clusters ◽  
Model Systems ◽  
Micellar Solutions ◽  
Solvated Electron ◽  
Heterogeneous Model ◽  
Polar Media ◽  
Excess Electrons ◽  
Solvation Mechanisms ◽  
Homogeneous Media

A review of our present knowledge concerning the solvation of excess electrons e−exc → e−solv produced by photoionization or radiolysis in polar media has been attempted. Various properties of the solvated electron (proposed solvation mechanisms, structure, physicochemical characteristics) are considered. In spite of some similarities, e−solv does not seem to be a good prototype for solvated halide anions. The behavior of e−exc in heterogeneous model systems, such as micellar solutions and molecular clusters, is described and correlated with that observed in homogeneous media. Key words: excess electrons, homogeneous and heterogeneous polar media, photoionization, radiolysis, solvation, charge transfer to solvent, properties of the solvated electron, micellar solutions, molecular clusters, comparison with the solvation of anions.

Employing Exfoliated Graphite as Novel Support Material for Heterogeneous Model Catalysts

2019 ◽  
Author(s):  
Moritz Wolf ◽  
Nico Fischer ◽  
Michael Claeys
Keyword(s):  
Surface Area ◽  
Graphite Powder ◽  
Model Catalysts ◽  
Model Systems ◽  
Exfoliated Graphite ◽  
Support Material ◽  
Heterogeneous Model ◽  
Support Materials ◽  
Metal Support Interaction ◽  
Catalyst Systems

<p>The inert nature of graphitic samples allows for characterisation of rather isolated supported nanoparticles in model catalysts, as long as sufficiently large inter-particle distances are obtained. However, the low surface area of graphite and the little interaction with nanoparticles result in a challenging application of conventional preparation routes in practice. In the present study, a set of graphitic carbon materials was characterised in order to identify potential support materials for the preparation of model catalyst systems. Various sizes of well-defined Co<sub>3</sub>O<sub>4</sub> nanoparticles were synthesised separately and supported onto exfoliated graphite powder, that is graphite after solvent-assisted exfoliation <i>via</i> ultrasonication resulting in thinner flakes with increased specific surface area. The developed model catalysts are ideally suited for sintering studies of isolated nano-sized cobaltous particles as the graphitic support material does not provide distinct metal-support interaction. Furthermore, the differently sized cobaltous particles in the various model systems render possible studies on structural dependencies of activity, selectivity, and deactivation in cobalt oxide or cobalt catalysed reactions.</p>

scholarly journals Determining calcium concentration in heterogeneous model systems using multiple indicators

Cell Calcium ◽  
2007 ◽  
Vol 42 (6) ◽  
pp. 576-589 ◽  
Author(s):  
Krzysztof L. Hyrc ◽  
Ziemowit Rzeszotnik ◽  
Bryan R. Kennedy ◽  
Mark P. Goldberg
Keyword(s):  
Calcium Concentration ◽  
Model Systems ◽  
Heterogeneous Model ◽  
Multiple Indicators

Spectroscopic measurements on solutions of alkali metals in 1, 4, 7, 10, 13-pentaoxacyclopentadecane (15-crown-5)

1988 ◽  
Vol 415 (1848) ◽  
pp. 121-140 ◽  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Electron Spin Resonance ◽  
Alkali Metals ◽  
Alkali Metal Cation ◽  
Paramagnetic Species ◽  
Spectroscopic Techniques ◽  
Solvated Electron ◽  
Spin Resonance ◽  
Excess Electrons ◽  
Cation Complex

The alkali metals potassium, rubidium and caesium dissolve in the liquid crown ether 15-crown-5 to produce intensely coloured blue solutions. In this work we have employed a variety of spectroscopic techniques (optical spectroscopy, nuclear magnetic resonance (NMR) and electron spin resonance (ESR)) to investigate the nature of both the paramagnetic and diamagnetic solution species coexisting in equilibrium. The major paramagnetic species are the solvated electron, e - s , and the (metal-based) electron-cation complex M + s e - s . The diamagnetic species is the alkalimetal anion, M - . Comparisons in characteristic properties for the two liquid macrocyclic ionophores, 12-crown-4 and 15-crown-5, suggest that these two solvents both complex the alkali-metal cation and solvate excess electrons to quite different extents. For the alkali metals in the title solvent, the various equilibria appear to favour the formation of e - s and M + s e - s at the expense of the alkali anion.

Dielectric loss in heterogeneous model systems

1965 ◽  
Vol 12 (1) ◽  
pp. 57-64 ◽  
Author(s):  
L. K. H. Beek ◽  
J. Booy ◽  
H. Looyenga
Keyword(s):  
Dielectric Loss ◽  
Model Systems ◽  
Heterogeneous Model

scholarly journals Rational Development of Liposomal Hydrogels: A Strategy for Topical Vaginal Antiretroviral Drug Delivery in the Context of HIV Prevention

Pharmaceutics ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 485 ◽  
Author(s):  
Maria J. Faria ◽  
Raul Machado ◽  
Artur Ribeiro ◽  
Hugo Gonçalves ◽  
Maria Elisabete C. D. Real Oliveira ◽  
...  
Keyword(s):  
Weibull Model ◽  
Physicochemical Characteristics ◽  
Model Systems ◽  
Drug Release Profile ◽  
Vaginal Microbicides ◽  
Rational Development ◽  
Antiretroviral Drug ◽  
Best Fitting ◽  
Exposure Prophylaxis

HIV/AIDS stands as a global burden, and vaginal microbicides constitute a promising strategy for topical pre-exposure prophylaxis. Preceding the development of a microbicide containing tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC), in silico and in vitro studies were performed to evaluate the physicochemical characteristics of both drugs, and to study their biophysical impact in lipid model systems. Results from these pre-formulation studies defined hydrogels as adequate vehicles to incorporate TDF-loaded liposomes and FTC. After studying interactions with mucin, zwitterionic liposomes with a mean diameter of 134 ± 13 nm, an encapsulation TDF efficiency of approximately 84%, and a transition temperature of 41 °C were selected. The chosen liposomal formulation was non-cytotoxic to HEC-1-A and CaSki cells, and was able to favor TDF permeation across polysulfone membranes (Jss = 9.9 μg·cm−2·h−1). After the incorporation of TDF-loaded liposomes and FTC in carbomer hydrogels, the drug release profile was sustained over time, reaching around 60% for both drugs within 3–6 h, and best fitting the Weibull model. Moreover, liposomal hydrogels featured pseudoplastic profiles that were deemed suitable for topical application. Overall, the proposed liposomal hydrogels may constitute a promising formulation for the vaginal co-delivery of TDF/FTC.

Dynamics and excitations of a solvated electron in molecular clusters

1988 ◽  
Vol 38 (4) ◽  
pp. 2178-2181 ◽  
Author(s):  
R. N. Barnett ◽  
Uzi Landman ◽  
Abraham Nitzan
Keyword(s):  
Molecular Clusters ◽  
Solvated Electron

Pre-solvated electron capture efficiency in polar media

1984 ◽  
Vol 23 (6) ◽  
pp. 745-747
Author(s):  
Thu-Hoa Tran-Thi ◽  
Anne-Marie Koulkes-Pujo
Keyword(s):  
Electron Capture ◽  
Capture Efficiency ◽  
Solvated Electron ◽  
Polar Media

scholarly journals New insights into atmospherically relevant reaction systems using direct analysis in real-time mass spectrometry (DART-MS)

2017 ◽  
Vol 10 (4) ◽  
pp. 1373-1386 ◽  
Author(s):  
Yue Zhao ◽  
Michelle C. Fairhurst ◽  
Lisa M. Wingen ◽  
Véronique Perraud ◽  
Michael J. Ezell ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Real Time ◽  
Atmospheric Chemistry ◽  
Chemical Reactivity ◽  
Direct Analysis ◽  
Model Systems ◽  
Laboratory Model ◽  
Vapor Pressures ◽  
Heterogeneous Model ◽  
Ionization Region

Abstract. The application of direct analysis in real-time mass spectrometry (DART-MS), which is finding increasing use in atmospheric chemistry, to two different laboratory model systems for airborne particles is investigated: (1) submicron C3–C7 dicarboxylic acid (diacid) particles reacted with gas-phase trimethylamine (TMA) or butylamine (BA) and (2) secondary organic aerosol (SOA) particles from the ozonolysis of α-cedrene. The diacid particles exhibit a clear odd–even pattern in their chemical reactivity toward TMA and BA, with the odd-carbon diacid particles being substantially more reactive than even ones. The ratio of base to diacid in reacted particles, determined using known diacid–base mixtures, was compared to that measured by high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS), which vaporizes the whole particle. Results show that DART-MS probes  ∼  30 nm of the surface layer, consistent with other studies on different systems. For α-cedrene SOA particles, it is shown that varying the temperature of the particle stream as it enters the DART-MS ionization region can distinguish between specific components with the same molecular mass but different vapor pressures. These results demonstrate the utility of DART-MS for (1) examining reactivity of heterogeneous model systems for atmospheric particles and (2) probing components of SOA particles based on volatility.

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