Showing papers by "Collège de France published in 1985"

Wetting: statics and dynamics

Abstract: The wetting of solids by liquids is connected to physical chemistry (wettability), to statistical physics (pinning of the contact line, wetting transitions, etc.), to long-range forces (van der Waals, double layers), and to fluid dynamics. The present review represents an attempt towards a unified picture with special emphasis on certain features of "dry spreading": (a) the final state of a spreading droplet need not be a monomolecular film; (b) the spreading drop is surrounded by a precursor film, where most of the available free energy is spent; and (c) polymer melts may slip on the solid and belong to a separate dynamical class, conceptually related to the spreading of superfluids.

Non-commutative differential geometry

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Supramolecular Chemistry: Receptors, Catalysts, and Carriers

Abstract: Supramolecular chemistry is the study of the structures and functions of the supermolecules that result from binding substrates to molecular receptors. Macropolycyclic receptors and coreceptors have been designed that form cryptate inclusion complexes and display molecular recognition towards spherical, tetrahedral, and linear substrates of various kinds (metal cations, inorganic anions, and organic or biological cations or anions). Anion binding has led to the development of anion coordination chemistry. Metalloreceptors simultaneously bind organic molecules and metal ions; speleands combine polar and nonpolar binding subunits. Receptors bearing reactive functional groups may act as molecular reagents or catalysts, performing a chemical transformation on the bound substrates (by such reactions as hydrogen transfer, ester cleavage, and protoadenosinetriphosphatase and protokinase activities). Receptors fitted with lipophilic groups can operate as molecular carriers, translocating bound species through a membrane; this transport can be coupled to chemical potentials (proton and redox gradients).

[3H]8-hydroxy-2-(di-n-propylamino)tetralin binding to pre- and postsynaptic 5-hydroxytryptamine sites in various regions of the rat brain.

Abstract: The specific binding of [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([ 3H]8-OH-DPAT) to 5-hydroxytryptamine (5-HT)-related sites was investigated in several regions of the rat brain. Marked differences were observed in the characteristics of binding to membranes from hippocampus, striatum, and cerebral cortex. Hippocampal sites exhibited the highest affinity (KD approximately 2 nM) followed by the cerebral cortex (KD approximately 6 nM) and the striatum (KD approximately 10 nM). Ascorbic acid inhibited specific [3H]8-OH-DPAT binding in all three regions but millimolar concentrations of Ca2+, Mg2+, and Mn2+ enhanced specific binding to hippocampal membranes, whereas only Mn2+ increased it in the cerebral cortex and all three cations inhibited specific binding to striatal membranes. Guanine nucleotides (0.1 mM GDP, GTP) inhibited binding to hippocampal and cortical membranes only. As intracerebral 5,7-dihydroxytryptamine markedly decreased [3H]8-OH-DPAT binding sites in the striatum, but not in the hippocampus, the striatal sites appear to be on serotoninergic afferent fibers. In contrast, in the hippocampus the sites appear to be on postsynaptic 5-HT target cells, as local injection of kainic acid decreased their density. Both types of sites appear to be present in the cerebral cortex. The postsynaptic hippocampal [3H]8-OH-DPAT binding sites are probably identical to the 5-HT1A subsites, but the relationship between the presynaptic binding sites and the presynaptic autoreceptors controlling 5-HT release deserves further investigation.

Kinetics of collapse for a flexible coil

Abstract: If a polymer chain is transferred abruptly from θ conditions to bad solvent conditions (e.g. by a shift of temperature ΔT) it collapses with a certain characteristic time τc. We propose a scaling structure for τc, based on an « expanding sausage model », and taking into account the hydrodynamic interactions. We find that τ c ≅ τR ΔT/θ where τR is the Rouse time of the θ chain : the time τc increases with the depth of quench.

Impuretés magnétiques et effet Kondo

Abstract: L'evolution des theories de l'effet Kondo au cours des dernieres annees est brievement resumee. Un accent particulier est mis sur les effets de degenerescence orbitale dans les metaux reels, et sur les effets d'interaction et de saturation dans les alliages de concentration finie.

Phasmids : a new class of liquid crystals

Abstract: Two hexa-alkoxy derivatives (7a and 7b) of terephthal-bis-[4-benzoyloxyaniline] are described. They exhibit two new types of mesophase for which the term phasmidic is proposed: one has an hexagonal 2D lattice and the second an oblique 2D lattice Description de deux derives hexaalcoxy de la terephtal-bis-[benzoyloxy-4-aniline], presentent deux nouveaux types de mesophase. L'une de ces phases possede un reseau bidimensionnel hexagonal, l'autre un reseau bidimensionnel oblique

Vasoactive intestinal polypeptide receptors linked to an adenylate cyclase, and their relationship with biogenic amine- and somatostatin-sensitive adenylate cyclases on central neuronal and glial cells in primary cultures.

Abstract: The presence of vasoactive intestinal polypeptide (VIP) receptors coupled to an adenylate cyclase was demonstrated on membranes of neurons or glial cells grown in primary cultures originating from the cerebral cortex, striatum, and mesencephalon of mouse embryos. A biphasic pattern of activation was observed in all these cell types, involving distinct high- and low-apparent-affinity mechanisms. The absence of additive effects of VIP and 3,4-dihydroxyphenylethylamine (DA, dopamine), isoproterenol (ISO), and 5-hydroxytryptamine (5-HT, serotonin) suggests that the peptide receptors are colocated with each of the corresponding amine receptors on neuronal membranes of the three structures studied. The nonadditivity between the VIP- and ISO-induced responses on cortical and striatal glial membranes reveals as well a colocation of VIP and β-adrenergic-sensitive adenylate cyclases on the same cells. A subpopulation of mesencephalic glia could possess only one of the two types of receptors, as a partial additivity of the VIP and ISO responses was seen. In addition, VIP modified the characteristics of the somatostatin inhibitory effect on adenylate cyclase activity of neuronal membranes from the cerebral cortex and striatum but not from those of the mesencephalon. On striatal and mesencephalic glial membranes the somatostatin inhibitory effect was observed only in the presence of VIP. However, as previously seen with ISO, the presence of VIP did not allow the appearance of a somatostatin inhibitory response on cortical glial membranes. This suggests that cortical glia are devoid of somatostatin receptors.

Fetal lung development in the diabetic pregnancy.

Abstract: It seems quite likely that the normal process of fetal lung biochemical maturation is delayed by maternal diabetes and that abnormalities in the pulmonary surfactant system are involved. The appearance of PG in amniotic fluid and possibly in fetal lung is impaired or at least delayed. The same is possibly true for DSPC, the main constituent of surfactant, but recent discrepant data call for further clarification of this specific point. Careful determination of the fetal lung phospholipid profile by amniotic fluid analysis helps predict and prevent RDS in IDM, along with a careful control of the maternal diabetic condition. A study of alveolar surfactant at birth, if it could be performed in addition to amniotic fluid analysis, would help to better characterize surfactant deficiency in IDM. On the basis of both in vivo and in vitro experimental approaches, it seems clear that hyperglycemia and fetal reactional hyperinsulinism are both involved in the processes delaying fetal lung maturation. Further advances in the understanding of cellular and molecular mechanisms leading to this delay will be conditional on the availability of animal models reproducing the features of the metabolic and hormonal environment of human fetuses in diabetic pregnancies. The appropriateness of in vivo models needs to be defined by two kinds of criteria: 1) presence of simultaneous hyperglycemia and hyperinsulinemia in the fetus; 2) the presence of delayed fetal lung maturation as judged by morphology and morphometry of epithelial lung cells, by physiological assessment of surfactant, and by the phospholipid composition of the lung (and including lung tissue per se, bronchoalveolar lavage fluid, lamellar bodies, and/or isolated surfactant fractions). Therefore, future studies must necessarily be comprehensive in scope and include information indicating that fetal growth, blood glucose, and circulating insulin are all increased. Such models already exist in rats and rabbits. Rat models are possibly not the best because of the high basal level of fetal blood insulin in this species and the relatively rapid rate of lung maturation that is not analogous to the human. Monkey models are of interest, because of their close relationship with the human pregnancy, and need to be studied further. They are particularly attractive also because primary fetal hyperinsulinism can be studied (268), as well as the combination of hyperglycemia and hyperinsulinemia in pregnancies of STZ-treated monkeys (152). An appropriate model of the diabetic pregnancy could provide answers to the following questions. Are the biosynthetic pathways of surfactant phospholipids directly impaired?(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation by monoamines of somatostatin-sensitive adenylate cyclase on neuronal and glial cells from the mouse brain in primary cultures

Abstract: : Primary cultures of mouse embryonic neuronal or glial cells from the cerebral cortex, striatum, and mesencephalon were used to identify and determine the cellular localization of somatostatin receptors coupled to an adenylate cyclase. Somatostatin inhibited basal adenylate cyclase activity on neuronal but not on glial crude membranes in the three structures examined. The somatostatin-inhibitory effect on neuronal crude membranes was still observed in the presence of (—)-isoproterenol, 3,4-dihydroxyphenylethylamine (dopamine, DA), or 5-hydroxytryptamine (5-HT, serotonin) used at a concentration (10−5M) inducing maximal adenylate cyclase activation. In addition, in most cases biogenic amines modified the pattern of the somatostatin-inhibitory effect, triggering either an increase in the peptide apparent affinity for its receptors or an increase in the maximal reduction of adenylate cyclase activity or both. However, 5-HT did not modify the somatostatin-inhibitory response on striatal and cortical neuronal crude membranes. The changes in somatostatin-inhibitory responses were interpreted as a colocalization of the amine and the peptide receptors on subtypes of neuronal cell populations. Finally, somatostatin was shown to inhibit adenylate cyclase activity following its activation by (—)-isoproterenol on glial crude membranes of the striatum and the mesencephalon but not on those of the cerebral cortex.

Sur la lacunarité des puissances de η

Abstract: La fonction η de Dedekind est definie parou , Im(z)>0. C'est une forme modulaire parabolique de poids 1/2. Si r est un entier, la puissance r–ieme de η s'ecrit;ou les coefficients pr(n) sone definis par l'identite.

Partial Filling of a Fractal Structure by a Wetting Fluid

Abstract: Certain rocks have been found to be fractal in a sizeable range of length scales \({\ell _2} >\ell>{\ell _1}\). We consider such a rock in equilibrium with a wetting fluid, under an adverse pressure p = pgh ( = bulk fluid density; g = gravitational acceleration). Two lengths are relevant: a) the diameter r(h) of a capillary inside which the fluid climbs up by an amount h; b) the thickness e(h) of the liquid film induced at higher levels h by long range forces (Van der Waals, or other), which is systematically smaller than r. We analyse two families of fractal structures: “iterative pits” and “iterative floes”, and find similar conclusions for both. The most interesting regime corresponds to \({\ell _2} >r>{\ell _1}\). Here we expect that macroscopic pockets of liquid will dominate over contributions from the film, and give a fluid fraction \({{\phi }_{L}} \cong \phi {{({{\ell }_{2}}/r)}^{{3 - D}}}\), where D is the fractal dimension of the surface and J the total porosity. This is to be contrasted with the non fractal case \(({\ell _2} = {\ell _1} = \ell )\) where we find, \({{\phi }_{L}} \cong \phi {{(\ell /r)}^{2}}(at r < \ell )\) for two distinct models. We also discuss various transport coefficients (conductance E, permeability \(\overline K )\), for these structures, and their qualitative effect on the macroscopic concentration profiles during imbibition.

A new method for contact-angle measurements of sessile drops

Abstract: A new method to measure the contact angle θ of sessile drops deposited onto solid substrates is presented. The crux of the method is to use the drop as a convex mirror for large, collimated, incident laser beams. The reflected light is intercepted on a screen in the far field. It appears as a bright circular spot, the diameter of which is simply related to the beam angular divergence 4θ. Overall measuring accuracies can be made better than 0.1° for θ angles less than 45θ. Reproducibility is also excellent because of the natural averaging over the entire three-phase line boundary of the drop. It is estimated to be ±0.25°. An extension of the method, valid for all angles less than 90°, is to use the drop as a plano-convex lens. This is of course applicable only if the solid substrate is optically clear. The refracted light is then intercepted on a screen and analyzed to yield the contact angle through simple geometrical optics considerations. These two methods are demonstrated on a series of short-chain alkanes (hexane to hexadecane) in contact with hydrophobic glass slides and/or polytetrafluoroethylene plates.

Characteristics of tyrosine hydroxylase activation by K+-induced depolarization and/or forskolin in rat striatal slices.

Abstract: The mechanisms of tyrosine hydroxylase (TH) activation by depolarization or exposure of dopaminergic terminals to cyclic AMP have been compared using rat striatal slices. Tissues were incubated with veratridine or 60 mM K+ (depolarizing conditions), on the one hand, and forskolin or dibutyryl cyclic AMP, on the other. K+ -(or veratridine-)induced depolarization triggered an activation of TH (+ 75%) that persisted in soluble extracts of incubated tissues. This effect disappeared when drugs (EGTA, N-(6-aminohexyl)-5-chloro-l-naphthalenesulfon-amide, Gallopamil) preventing Ca2+- and calmodulin-de-pendent processes were included in the incubating medium. In contrast, prior in vivo reserpine treatment or in vitro addition of benztropine did not affect the depolarization-induced activation of TH. In vitro studies of soluble TH extracted from depolarized tissues indicated that activation was associated with a marked increase in the enzyme Vmax but with no change in its apparent affinity for the pteridin cofactor 6-methyl-5,6,7,8-tetrahydrop-terin (6-MPH4) or tyrosine. Furthermore, the activated enzyme from depolarized tissues exhibited the same optimal pH (5.8) as native TH extracted from control striatalslices. In contrast, TH activation resulting from tissue incubation in the presence of forskolin or dibutyryl cyclic AMP was associated with a selective increase in the apparent affinity for 6-MPH4 and a shift in the optimal pH from 5.8 to 7.0–7.2. Clear distinction between the two activating processes was further confirmed by the facts that heparin- and cyclic AMP-dependent phosphorylation stimulated TH activity from K+-exposed (and control) tissues but not that from striatal slices incubated with forskolin (or dibutyryl cyclic AMP). In contrast, the latter enzyme but not that from depolarized tissues could be activated by Ca2+ -dependent phosphorylation. These data strongly support the concept that Ca2+– but not cyclic AMP-dependent phosphorylation is responsible for TH activation in depolarized dopaminergic terminals.

Evidence for the role of fibronectin in amphibian gastrulation

Abstract: In amphibian embryos, fibronectin (FN) assembles as a fibrillar network on the roof of the blastocoel cavity, preceding mesodermal cell migration. Local inversion of the ectoderm to produce a site where no FN is available prevents mesodermal cell migration. Microinjection of monovalent antibodies to FN arrests gastrulation. A complete inhibition of mesodermal cell migration is obtained after microinjection of a synthetic peptide containing the cell binding site sequence of FN. Prevention of interactions between receptors and FN appears to be the primary cause for blockage of gastrulation.

Concentration profile of polymer solutions near a solid wall.

Abstract: Application of the evanescent-wave-induced fluorescence technique to the study of the interfacial depletion layer between a polymer solution and a solid barrier has yielded the first measurement of the monomer concentration as a function of the distance to the wall. The results have been obtained on a dilute aqueous solution of xanthan, a stiff polysaccharide of high molecular weight. The data are described quantitatively by an empirical model for semiflexible chains. Good agreement is also found with the Auvray model for fully rigid rods, for an equivalent rod length of $L=600\ifmmode\pm\else\textpm\fi{}10$ nm.