Jean-Claude Andre

Kinetics of partly diffusion controlled reactions. I. Transient and apparent transient effect in fluorescence quenching

Abstract Analysis of decay curves of electronically excited molecules A* versus time in presence of quencher B leads to the determination of kinetic data for the reaction (i.e. for diffusion limited reactions, the experimental collisional distance σ′ greater than the true collisional distance σ) and the sum D of diffusion coefficients of both reactants). Experimental fluorescence steady state measurements (Stern-Volmer representation) are inconsistent with calculated curves using classical Smoluchowskis model with σ′and D. The difference between this has been interpreted by complex formation in the ground state between A and B. But, this assumption is unnecessary if we take into account a “static” quenching arising from B molecules located at distances between σ and σ′ from A*. A theoretical model based upon this principle is described; good agreement between the model and experimental results was obtained.

Evolution of fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) during the labelling of living cells☆

Abstract Detailed information on the environment of the fluorescent lipid probe 1,6-diphenyl-1,3,5-hexatriene (DPH) during its interaction with a living cellular system was obtained by following the changes in emission parameters of the probe on the nanosecond time scale. Changes in the steady-state anisotropy r , the anisotropy r ∞ at long time, the rotational relaxation time φ and the lifetime τ were recorded during the early course of DPH uptake in murine-transformed cells. Results are compatible with a model assuming that the plasma membrane and the cytoplasm constitute two compartments, with some DPH translocation from one compartment to another. In short term incubation, fluorescence parameters of DPH characterize the plasma membrane. In long term incubation, most fluorescent signals are due to DHP embedded in intracellular lipids which are in a more fluid state than membranous lipids.

Kinetics of partly diffusion-controlled reactions. XVI: The use of liquid state physics for fluorescence quenching models

Abstract Theories of partly diffusion-controlled reaction kinetics are re-investigated, taking into account the existence of a non-uniform radial distribution function. This allows us to partially explain some discrepancies occurring when molecular emission spectroscopy experiments are carried out using continuous or pulsed excitation.

Lateral diffusion in synthetic membranes: models and experiments on protein influence

Diffusion-influenced theories of the Smoluchowsky type are applied to the case of synthetic membranes in which a fluorescent probe (pyrene) is included. These models make the assumption of a pseudo-two-dimensional medium with some refinements such as the curvature of space or the thickness of the membrane. After having shown that it is possible to measure a diffusion coefficient inside the membranes with photophysical methods and to characterize the effects of the temperature and of the length of the carbon chains on the lateral diffusion, some proteins are added to the membranes in order to observe their influence on the lateral molecular transport.

Structural changes of liver microsomes in rat during neonatal life: Influence on the glucuronidation rates of various substrates

The Vmax of the membrane bound UDP-glucuronosyltransferase (UDP-GT) towards group 1 substrates (4-nitrophenol, 2-naphthol) was particularly higher in young rats than in adults. On the contrary, activity towards group 2 substrates such as borneol or testosterone was not detectable in fetus liver. The developmental pattern of UDP-GT was related to changes in lipid composition of microsomes, namely in the content in lysophosphatidylcholine which rose at birth. The phospholipid-cholesterol molar ratio also increased 2 fold from the 16th day of fetal life to the 4th day after birth. Measurement of the steady state anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) as well as determination of the order parameter S and the rotation cone angle of the fluorescent probe strongly suggested an increase in membrane fluidity in rat liver microsomes during ontogenesis.

Kinetics of partly diffusion controlled reactions. VII — Pyrene excimer formation in erythrocyte membranes

Abstract Intermolecular excimer forming systems such as pyrene have been proposed as probes for the microviscosity measurement of model and biological membranes. However, our experimental study of pyrene excimer formation in erythrocyte membranes and the theoretical calculations show that it is quite difficult to get the diffusion coefficient of pyrene in membranes and therefore the microviscosity of its environment.

Kinetics of partly diffusion controlled reactions

We propose a simple kinetic model in which two types of processes between two reactants occur: diffusional processes for distances greater than σ′, the “reaction” distance, and static quenching for distances smaller than σ′. This model might be useful in the studies of diffusion in membrane systems.AbstractБыла предложена простая кинетическая модель, заключающая в себе два типа процессов, протекающих между двумя реагентми: диффузионные процессы для расстояний, превышающих расстояние “реакции” σ′, и статическое гашение для расстояний, меньших σ′. Эта модель может быть использована при исслеловании диффузии в мембранных системах.

On diffusion in organized assemblies and in biological membranes.

The following paper is a brief presentation of problems related to the concepts of diffusion coefficient D and so-called viscosity eta used to characterize the cohesion of biological membranes. The first approach to this problem is a recall of the definition of D and eta in liquids. It appears that the models developed with exogenous probes to account for the diffusion-viscosity relationship are not verified in membranes. The existence of complex diffusional mechanisms, the influence of the size of the probe are presented. The results of a model calculation suggest that there is no direct correlation other than great simplifications, between the diffusion coefficient and viscosity. The calculations are then extended to actual biological assemblies and the influence of proteins on the motion of the probe considered. The limitations of the methods involving exogenous probes for determining the cohesion of biological membranes are discussed.

Kinetics of partly diffusion controlled reactions, IX. Cage effect in the photolysis of benzyl chloride in the liquid phase. First results

The cage recombination of free benzyl and chloride radicals after their formation via photolysis of benzyl chloride is interpreted using a model for partly diffusion controlled reactions. A new kinetic model is presented which takes into account the noncontact of the interacting species at the moment of their formation. There is good agreement between the results observed and the model presented.AbstractРекомбинация в клетке свободных бензильного и хлоридното радикалов, после образования их фотолизом бензил хлорида, была интерпретирована на основе модели реакции, частично контролируемой диффузией. Предлагается новая кинетическая модель, которая принимает во внимание отсутствие контакта между реагирующими частицами при их образовании. Было получено хорошее согласие между наблюдаемыми результатами и приводимой моделью.

Membrane labelling by fluorescent probes: incorporation of TMA-DPH in erythrocyte membranes.

A study of the labelling of isolated resealed erythrocyte membranes by TMA-DPH has been carried out. A quantitative study shows that saturation appears to take place when increasing the relative quantity of probe bulk concentration to membrane concentration; this is readily interpreted by a simple incorporation model with a limited number of sites in the membrane. A qualitative study shows that an increase in the labelling leads to an evolution of the probe fluorescence properties; the existence of different types of sites is involved in the interpretation but the system is too complex to allow it to be represented by a simple model. As a consequence of this study, care has to be taken in labelling biological material so as to avoid excessive probe incorporation.