Joint density-functional theory for electronic structure of solvated systems

We introduce a new form of density functional theory for the {\em ab initio} description of electronic systems in contact with a molecular liquid environment. This theory rigorously joins an electron density-functional for the electrons of a solute with a classical density-functional theory for the liquid into a single variational principle for the free energy of the combined system. A simple approximate functional predicts, without any fitting of parameters to solvation data, solvation energies as well as state-of-the-art quantum-chemical cavity approaches, which require such fitting.Comment: Fixed typos and minor updates to tex

Molecular dynamics simulations of elementary chemical processes in liquid water using combined density functional and molecular mechanics potentials. II. Charge separation processes

A new approach to carry out molecular dynamics simulations of chemical reactions in solution using combined density functional theory/molecular mechanics potentials is presented. We focus our attention on the analysis of reactive trajectories, dynamic solvent effects and transmission coefficient rather than on the evaluation of free energy which is another important topic that will be examined elsewhere. In a previous paper we have described the generalities of this hybrid molecular dynamics method and it has been employed to investigate low energy barrier proton transfer process in water. The study of processes with activation energies larger than a few kT requires the use of specific techniques adapted to “rare events” simulations. We describe here a method that consists in the simulation of short trajectories starting from an equilibrated transition state in solution, the structure of which has been approximately established. This calculation is particularly efficient when carried out with parallel computers since the study of a reactive process is decomposed in a set of short time trajectories that are completely independent. The procedure is close to that used by other authors in the context of classical molecular dynamics but present the advantage of describing the chemical system with rigorous quantum mechanical calculations. It is illustrated through the study of the first reaction step in electrophilic bromination of ethylene in water. This elementary process is representative of many charge separation reactions for which static and dynamic solvent effects play a fundamental [email protected]

Equilibrium studies of ternary complexes formed by bromide, sulfate, selenite and selenate ions with Zn2+, Mg2+ and 1, 4, 7, 13, 16, 19-hexaaza- 10, 22- dioxacyclotetracosane (obisdien)

Bromide, sulfate, selenite and selenate were found to form bridges in the cavity of mononuclear and binuclear Obisdien:Zn(II) and Obisdien:Mg(II) complexes in aqueous solution at 25.0 °C and m = 0.100 M (KCl). Potentiometric equilibrium measurements were used to determine the formation constants of the species formed in these systems in the pH range 2-12. For the Obisdien: Zn2+:anions complexes, we have established the existence of four species for bromide ion, five species for sulfate ion, six species for selenite ion and four species for selenate ion. We found that the hydroxo binuclear complexes predominate over the others species, and the binding strength decreases in the sequence: SeO4(2-) > SeO3(2-) > SO4(2-) > Br-. The Obisdien:Mg(II) system presents three species in case of binding with bromide ion, four with sulfate ion, five with selenite ion and five with selenate ion. Variation of the binding strength in the Obisdien:Mg(II) complexes is the same as in the Obisdien:Zn(II) complexes: SeO4(2-) > SeO3(2-) > SO4(2-) > Br-. Molecular mechanics calculations show that the dizinc(II)- and dimagnesium(II)-Obisdien complexes adopt several low energy conformations differing in their Zn to Zn and Mg to Mg separations that allow the coordination of SeO4(2-), SeO3(2-), SO4(2-), Br- and OH- anions

Modifying Ligand-Induced and Constitutive Signaling of the Human 5-HT4 Receptor

G protein–coupled receptors (GPCRs) signal through a limited number of G-protein pathways and play crucial roles in many biological processes. Studies of their in vivo functions have been hampered by the molecular and functional diversity of GPCRs and the paucity of ligands with specific signaling effects. To better compare the effects of activating different G-protein signaling pathways through ligand-induced or constitutive signaling, we developed a new series of RASSLs (receptors activated solely by synthetic ligands) that activate different G-protein signaling pathways. These RASSLs are based on the human 5-HT4b receptor, a GPCR with high constitutive Gs signaling and strong ligand-induced G-protein activation of the Gs and Gs/q pathways. The first receptor in this series, 5-HT4-D100A or Rs1 (RASSL serotonin 1), is not activated by its endogenous agonist, serotonin, but is selectively activated by the small synthetic molecules GR113808, GR125487, and RO110-0235. All agonists potently induced Gs signaling, but only a few (e.g., zacopride) also induced signaling via the Gq pathway. Zacopride-induced Gq signaling was enhanced by replacing the C-terminus of Rs1 with the C-terminus of the human 5-HT2C receptor. Additional point mutations (D66A and D66N) blocked constitutive Gs signaling and lowered ligand-induced Gq signaling. Replacing the third intracellular loop of Rs1 with that of human 5-HT1A conferred ligand-mediated Gi signaling. This Gi-coupled RASSL, Rs1.3, exhibited no measurable signaling to the Gs or Gq pathway. These findings show that the signaling repertoire of Rs1 can be expanded and controlled by receptor engineering and drug selection

Application de mesures diélectriques à l’étude de l’adsorption de l’oxygène par l’oxyde de nickel

L’adsorption de l’oxygène par l’oxyde de nickel suivie par des mesures diélectriques en basses fréquences se révèle être un phénomène assez complexe et semble faire intervenir au moins trois formes de l’oxygène adsorbé : 1

Réalisation d'un interféromètre de Michelson en guide surdimensionné mesure de la permittivité complexe des liquides en ondes millimétriques

A Michelson type interferometer in an oversized waveguide is described which is suitable for dielectric measurements on liquids at mm wavelengths. The rectangular oversized waveguide (standard RG 49/U) operating in the TEol mode appears to be more advantageous than the oversized circular waveguide. It is possible to reduce the amount of spurious modes if the machining of the linear tapers and of the other "quasi optical" components is done with a great care. Interferograms, without any liquid in the cell, are not rigorously sinusoidal ; this is probably due to spurious reflections in the dominant mode. Experimental results at 4.35 mm wavelength on some liquids, with dielectric losses, are included to illustrate the accuracy of the method, the precision of which is higher than 2 % for ε' and 4 % for ε".Les auteurs décrivent un interféromètre de type Michelson en guide surdimensionné permettant de mesurer la permittivité complexe des liquides en ondes millimétriques. Le guide surdimensionné rectangulaire (standard RG 49/U), excité dans le mode TEol, présente de réels avantages sur le guide surdimensionné circulaire. Il est possible de réduire le taux de modes parasites en apportant le plus grand soin à la réalisation mécanique de transitions pyramidales et des autres composants « quasi optiques ». Le profil des interférogrammes « à vide » n'est pas rigoureusement sinusoïdal en raison, sans doute, de T.O.S. résiduels dans le mode dominant. Une série de mesures faites à λ = 4,35 mm sur des corps polaires présentant des pertes importantes met en évidence la sensibilité de la méthode dont la précision se révèle supérieure à 2 % pour ε' et 4 % pour ε"

Optimisation de la permittivité complexe d'un liquide à partir de mesures interférométriques en ondes millimétriques

A Michelson interferometer in oversized waveguide is studied, in the assumption of no propagating spurious modes. The influence of disturbing reflections or W.S.V.R. has been analysed and equations for the interferogramms are obtained which allow the authors to propose a numerical method of optimizing the determination of the complex permittivity of liquids in mm. waves. An attempt is also made to evaluate directly the accuracy of the results which is higher than 1 % for ε', 2 % for ε", in the case of some liquids at λ = 4.35 mm.Les auteurs développent l'étude d'un interféromètre de Michelson en G.S.D. dans l'approximation d'une propagation quasi optique non perturbée par des modes supérieurs. Le rôle d'inévitables réflexions ou T.O.S. parasites est précisé et l'équation des interférogrammes est mise sous une forme analytique simple permettant d'optimiser la détermination de la permittivité complexe ε* pour les liquides, en ondes millimétriques. La méthode numérique proposée offre la possibilité d'une estimation directe des barres d'erreur affectant ε' et ε", et pour les liquides étudiés, on donne : [FORMULE]

Modélisation des systèmes complexes. Effets de solvant sur les modes de vibration d'un soluté au sein d'une solution

Le modèle du milieu continu polarisable, dans le formalisme du champ de réaction self consistant, est étendu pour permettre le calcul des vibrations moléculaires au sein d'un liquide au moyen des méthodes de la chimie quantique. Appliqué aux vibrations νC=O d'une série de composés carbonylés en solution dans le cyclohexane et dans l'acétonitrile, le modèle se révèle tout-à-fait apte à permettre le calcul des fréquences de vibrations d'un soluté. L'origine moléculaire de l'effet de solvant est discutée