Cyclodextrins are natural cyclic oligosaccharides and behave as cage molecules. Since their internal cavity is relatively hydrophobic compared to the highly hydrophilic external face, the cyclodextrins and their derivatives exhibit the capacity to incorporate hydrophobic guests in their internal cavity leading to a wealth of applications. NMR appears as the most efficient approach to investigate and evidence the formation of inclusion complexes in aqueous solution. Dedicated experiments are used to derive thermodynamic properties as well as "molecular model" for the solution structure of inclusion complexes as beta-cyclodextrin/Prostaglandin E-2 complex. Classical "NOESY-type" experiments and especially the ROESY sequence are used to proove interactions in cyclodextrin domain. But, due to intrinsic problems, the basic ROESY sequence can lead to misinterpretations. We investigate in this work alternative 2D 1H-NMR ROESY-type experiments and estimated their relative advantages.
Due to its little sensitivity to motion or flow-induced errors, spiral imaging is an excellent technique for flow imaging or functional imaging. A software allowing to optimize the acquisition and processing parameters has been designed. It makes the implementation of spiral imaging easier and is well-adapted to medical applications.
L'imagerie spirale par sa faible sensibilité aux artefacts de flux et de mouvement est la technique de choix pour l'imagerie de flux et pour l'imagerie fonctionnelle. Un logiciel a été développé, qui gère la modélisation de la forme des gradients, l'acquisition (intégrée au logiciel d'exploitation du système), la reconstruction des images ainsi que les corrections des trajectoires d'échantillonnage et des inhomogénéités du champ magnétique. Sa facilité d'utilisation en fait un outil adapté aux applications médicales.
Impromidine (fig.1) is a potent and selective histamine H2 receptor agonist and its structure comprises a strongly basic guanidine group containing two different imidazole-containing side chains. The present work deals with the study of coordination equilibria between impromidine and Cu(II) and Ni(II) in aqueous solution at 25 degrees C, Potentiometric, W-Visible and EPR studies on Cu(II) complexes with impromidine have shown that this anti-ulcerogenic drug is a very potent chelating agent. This drug is found to be a very effective ligand for Ni(II) ions also. The effective coordination of impromidine to metal ions may have significant biological implications.
The three-way catalytic behaviour (CO, HC and NO, conversions and light-off temperatures) of MN/CeO2/Al9O3 (MN: Pt, Ph, Pt-Ph) catalysts, fresh and aged under severe oxidizing, reducing and cycled environments, has been analyzed. The bimetallic Pt-Pi catalyst resulted the most active among those tested.
Instabilities can develop at the "interface" between two miscibles fluids which exihibit patterns very similar to those observed between immiscible fluids. For example, a layer of colored glycerine hanged-up below a glass plate and placed into a water tank, gives rise to organized patterns. Also, a thin layer of glycerine falling into water is unstable and gives falling columns with a regular distance between each other. These similarities between miscible and immiscible fluids lead to the existance of an "effective surface tension" between miscible fluids. This effective tension has a meaning for short times only, and should tend to zero with time. It can be explained by the strong concentration gradient at the "interface".
We have prepared a series of catalysts combining cobalt and a hydroxyapatite by coprecipitation in a basic medium. These sulfided solids catalyse the hydrodesulfurization of dimethyldisulfide at 360 degrees C and its hydrogenolyzis into CH3SH at 200 degrees C. The coprecipitated solids are found more active than the impregnated catalysts because they exhibit a better dispersion of the active Co-S phase at higher Co content. With the precipitated catalysts, Co ions substitute for Ca ions into the apatite structure, The formation of large sulfide particles is thus more difficult as a result of sulfiding because the Co ions have to move to the surface. The apatite catalysts are intrinsically. as active as their homologous Co/Al2O3.
The purpose of this work consists in following physical property variations in relation with geometrical textural parameters during pharmaceutical component compaction. Models are developed to explain porosity variations of granular media submitted to increasing uniaxial pressure. These models are based on reaction mechanisms analogous to these presented in quasi chemical descriptions. Vacancy annihilation occurring when pressure increases is studied in two cases (with or without internal grain porosity). Reaction mechanisms describing different granular rearrangement phenomena are proposed. The behaviour of pure compounds as well as that of binary mixtures are studied from a theoretical point of view, and the model results proposed in this case are compared with the ones derived from experiments. In particular mixtures of one excipient, lactose, and one active principle, ketoprofen, are analysed in order to estimate porosity evolution of such mixtures, and determine mixture effects on tablet properties. The prediction limits which could be done by mixture models giving an expected behaviour starting from pure components only are discussed.
From measurements of pressure and volume of a gas of spherical particles excited by a vibrating piston and undergoing inelastic collisions, we determine a state equation between pressure, volume, particle number and the vibration amplitude and frequency.
Aspergillus nidulans is a filamentous fungus able to use ethanol as sole energy source. The activation of the ethanol regulon genes expression is mediated by the AlcR protein. Its DNA-binding domain is located in the N-terminus (residues 1 to 60), and its NMR solution structure shows a global zinc binuelear cluster fold, with two helices in addition to the basic binuclear motif.A small number of crystallographic structures of DNA complexes of binuclear cluster proteins is yet known, and points out the major groove and the first helix as the principal sites of interaction on the DNA and the protein respectively. In this article we show evidences that the N-terminus of the protein is involved in binding to the minor groove.
Electron paramagnetic resonance and dynamic nuclear polarisation are two techniques that allow the detection of free radicals, They can also be used for in vivo studies for oximetry in blood or tissues. One of the main problems for the development of these techniques is the need of free radicals that are stable in biological media. We present in this communication a study by EPR and DNP of two free radicals that can be suitable for in vivo applications.
We have observed cobalt. 59 NMR on tetrahedric clusters in solution and in the solid stale. From the relaxation times in solution, we are able to deduce the quadrupolar coupling constants for Ru-99 and to simulate the Co-59 spectrum in the solid state for the basal atoms of Co-4(CO)(12) which has never been observed. This short review shows the interest of high fields applied to quadrupolar nuclei.
The influence of radiation on the permeability properties of human basement membrane was investigated by measuring the diffusion rate of several organic compounds (glycine, proline, glucose, urea and insulin) through human anterior lens capsules. The basement membranes borne an gamma-irradiation treatment change significantly their permeability vis-a-vis studied organic substances. This modification in physico-chemical properties is probably due to the radiation, which alters or degrades the complex structure (or architecture) of basement membranes. Moreover the change in permeability is dependent upon the diffusing compounds. An increase in diffusion has been observed for glucose, glycine and urea. However for insulin and proline, a decrease in diffusion rate was observed.
We report measurements of the temporal fluctuations of the heat-flux in Rayleigh-Benard turbulent convection, Although being a global quantity, i. e. spatially averaged on the flow field, we show that its probability density function (PDF) is non-gaussian and asymmetric. The ratio of the rms fluctuations of the heat flux to their mean display a power law. Ra-gamma with gamma = 0.25, on more than two decades in Rayleigh number (2 10(7) < Ra < 4 10(9)), Thus, the fluctuations are roughly proportional to the temperature difference. We discuss this law and we propose a simple mechanism to explain the non-gaussian character of the PDF.
Monte Carlo codes were used to simulate the transport of photons and their secondary electrons produced on a linear and hydrated DNA model. Between 150 and 550 eV, the variation of photon cross section upon the K-ionisation threshold in C, N, O atoms of DNA is responsible for an increase of the biological effectiveness. We showed that, with the same number of absorbed photons, the distribution of breaks as a function of energy reaches a maximum around 450 eV.
Radical recombination reactions are of central importance in radiation chemistry. In general such reactions are slower than diffusion-controlled because of the radical spins. The rate constant is corrected by a multiplicative spin statistical factor, which represents the probability that the radicals encounter one another in a reactive state. However, this method does not account for the possibility that the reactivity of a pair may recover following an unreactive encounter, for example by spin relaxation or by a coherent evolution of the spin function. In this paper we show how the spin statistical factor can be corrected for the recovery of reactivity. The new theory covers a large range of mechanisms for the recovery of reactivity, and gives simple analytical results. Both steady-state and transient solutions are presented and the former are tested against experiment for the reaction between the hydrated electron and oxygen, and for the magnetic field effect on the rate constant of an elementary reaction.
The formation of coke from propene (Pp = 1.3 kPa and 13 kPa) was investigated on HFAU and HEMT zeolites in a microbalance for temperatures ranging from 120 degrees C to 450 degrees C. For both zeolites, the greater the propene pressure and the lower the temperature the faster the initial coke formation. However for high propene pressure, initial coke formation is faster with HEMT zeolite. This can be related to the stronger acidity of the HEMT sample. For low propene pressure and after 420 minutes of coking, a minimum in coke is observed for T = 350 degrees C, which can be related to the difference between the rate of formation and the rate of retention of coke molecules. At low temperature, due to their low volatility, oligomers are easily formed and retained in the zeolite pores. These molecules can be totally eliminated by an adequate thermal treatment in vacuum. At higher temperature, only aromatic or polyaromatic compounds which present a size larger than the pore apertures can be retained in the cavities of the zeolites. The greater the reaction time, the faster the retention. Whatever the reaction temperature, coke molecules are more homogeneously distributed in the HEMT crystallites than in those of HFAU samples. For this latter zeolite coke molecules are preferentially formed in the cavities located near the outer surface of the crystallites (shell coking).
La modification des smectites par les polycations inorganiques tres fortement charges donne des materiaux appeles argiles a piliers (PILCS). Ces materiaux sont potentiellement interessants comme supports d'adsorption pour des molecules d'interet agronomique ou pour des molecules polluantes dans le cas du traitement des eaux usees. Les PILCS modifies par un tensioactif cationique (BTDDMAC) ou par sa tete polaire, le chlorure de benzyl trimethyl ammonium (BTMAC) ont ete utilises comme supports d'adsorption du phenol et de ses derives chlores. Les resultats d'adsorption de ces petites molecules organiques ont ete compares a leur adsorption sur des argiles a piliers non traitees (non organophiles). Globalement, la nature organophile des organo-PILCS accroit l'adsorption des chlorophenols. Les proprietes d'adsorption du phenol sont tres nettement ameliorees par le traitement des PILCS par le BTMAC.
Both geometrical and analytical steps of the new ASC procedure for the approximate computation of molecular van der Waals and solvent-accessible surface areas, were calibrated. The assigned objective was to determine best fit accurate surface values for a representative set of molecular structures, Molecular surfaces, partial atomic surfaces, as also the gradients describing surface changes as a function of atomic displacements are analytically described.After the validation of the ASC model, an endeavour was made to correlate experimental Gibbs free energies of hydration with partial atomic surfaces. A satisfactory correlation was obtained for a large set of organic compounds, provided that sigma- and pi- surface elements are introduced in addition to the traditional differentiation into polar and non-polar partial atomic surfaces.
Phase diagrams of the Water-Phenol-Salt systems (Kcl, NaCl, LiCl, CaCl2 and MgCl2) have been studied. The influence of the cation concentration and ionic radius on the binodal curves and the maxima critical point coordinates has been shown.
