Electrochemical mechanism of ion-ionophore recognition at plasticized polymer membrane/water interfaces

Here, we report on the first electrochemical study that reveals the kinetics and molecular level mechanism of heterogeneous ion-ionophore recognition at plasticized polymer membrane/water interfaces. The new kinetic data provide greater understanding of this important ion-transfer (IT) process, which determines various dynamic characteristics of the current technologies that enable highly selective ion sensing and separation. The theoretical assessment of the reliable voltammetric data confirms that the dynamics of the ionophore-facilitated IT follows the one-step electrochemical (E) mechanism controlled by ion-ionophore complexation at the very interface in contrast to the thermodynamically equivalent two-step electrochemical-chemical (EC) mechanism based on the simple transfer of an aqueous ion followed by its complexation in the bulk membrane. Specifically, cyclic voltammograms of Ag(+), K(+), Ca(2+), Ba(2+), and Pb(2+) transfers facilitated by highly selective ionophores are measured and analyzed numerically using the E mechanism to obtain standard IT rate constants in the range of 10(-2) to 10(-3) cm/s at both plasticized poly(vinyl chloride) membrane/water and 1,2-dichloroethane/water interfaces. We demonstrate that these strongly facilitated IT processes are too fast to be ascribed to the EC mechanism. Moreover, the little effect of the viscosity of nonaqueous media on the IT kinetics excludes the EC mechanism, where the kinetics of simple IT is viscosity-dependent. Finally, we employ molecular level models for the E mechanism to propose three-dimensional ion-ionophore complexation at the two-dimensional interface as the unique kinetic requirement for the thermodynamically facilitated IT.     

Polymer Architectures Consisting of Rotating Fibers Prepared by Photopolymerization in a Cholesteric Phase

Summary: Hydrogen‐bonded polymer films consisting of fine, extended fibers were prepared by photopolymerization of an acrylate monomer containing a benzoic acid group in the fingerprint or Grandjean textures of a cholesteric liquid‐crystalline mixture. Scanning electron microscopy and circular dichroism spectroscopy revealed that the fibers, measuring about 400 nm in diameter, formed helical superstructures and that their helical axes corresponded to the cholesteric helical axes that existed in the LC mixture before photopolymerization.

SEM image of a polymer film.     

Planarity recognition of cationic dyes by anionic, crystalline bilayer aggregates

Steric selectivity in terms of molecular planarity of cationic dyes was investigated using anionic bilayer aggregates. Planar cationic dye (para-type stilbazolium) could be incorporated into the hydrophobic region of anionic crystalline bilayer aggregates, whereas structurally related, less planar dyes (ortho-type stilbazolium) could not be incorporated in spite of somewhat higher hydrophobicity resulting from lengthening of the N-alkyl group.     

Fabrication of Periodic Waveguides Using Organic Crystals and Fluorinated Polyimides for Quasi-Phase-Matched Second-Harmonic Generation

We have developed a new method to fabricate periodic waveguide structures used for quasi-phase-matched second-harmonic generation, where nonlinear optical organic crystals and fluorinated copolyimides are alternately arranged. Quasi-phase-matched second-harmonic generation from an organic waveguide device has been demonstrated.     

A variational approach to distribution function theory

We present a novel formalism for the generation of integral equations for the distribution functions of fluids. It is based on a cumulant expansion for the free energy. Truncation of the expansion at theKth term and minimization of the resulting approximation leads to equations for the distribution functions up toKth order.The formalism is not limited to systems with two-body interactions and does not require the addition of closure relations to yield a complete set of equations. In fact, it automatically generates superposition approximations, such as the Kirkwood three-body superposition approximation or the Fisher-Kopeliovich four-body one.The conceptual approach is adapted from the cluster variation method of lattice theory.     

A heated-electrode discharge lamp for trace analysis by atomic emission spectroscopy

Graphite electrodes heated by d.c- power alone, or a combination of d.c- and r.f. power, are investigated for generating atomic emission from cadmium with specially designed discharge lamps. Best results are achieved if the plasma produced by both power sources can be concentrated within a cylindrical electrode.     

On the stability of characterizations of the exponential distribution

Summary It is shown that if the distribution of min {X ₁/a₁, X₂/a₂,…, X_N/a_N} is close to that ofX ₁, then the distribution is close to the exponential distribution. The paper was presented at the Conference on Mathematical Statistics and Probability Theory held at the New Delhi Centre of the Indian Statistical Institute, December, 1980. The Institute of Statistical Mathematics     

SCF MO calculations of heteroatomic systems with the variable Β approximation

In order to elucidate the electronic structure of protonated N-heterocycles, we have carried out SCF MO calculations, considering the -bond polarizations which are caused by the large net charge on nitrogen atom. Appropriate parametrizations of the valence state energies associated with the -bond polarization model have been proposed. Our calculations showed that a conventional covalent model for protonated N-heterocycles failed to explain the experimental electronic spectral data and an extremely polarized -core model gave quite good results in the whole. The present theory expected that the nature of electronic spectra of quinoline is considerably changed by the -bond polarization due to the protonation.

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Zusammenfassung Um die Elektronenstruktur von protonisierten N-Heterozyklen zu untersuchen, wurden SCF-MO-Rechnungen durchgeführt, bei denen die Polarisierung der -Bindung durch die Ladung am N-Atom berücksichtigt wird. Eine geeignete Parametrisierung der Valenzzustands-Energien in Verbindung mit dem Modell der Polarisierung der -Bindung wird vorgeschlagen. Die Rechnungen zeigen, da\ ein herkömmliches kovalentes Modell für die genannten Verbindungen bei der ErklÄrung des Elektronenspektrums versagt, wÄhrend ein Modell mit stark polarisierten -Bindungen befriedigende Ergebnisse liefert. Aus der vorliegenden Theorie lÄ\t sich folgern, da\ das Elektronenspektrum des Chinolins betrÄchtlich durch die Polarisierung der -Bindung infolge Protonisierung geÄndert wird.

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Résumé Afin d'éclaircir la structure électronique d'hétérocycles protonisés sur l'azote, nous avons effectué des calcules SCF MO en considérant la polarization des liaisons dûe à la forte charge nette sur l'atome d'azote. Des paramétrisations appropriées à ce modèle polarisé sont proposées pour les énergies des états de valence. Nos calculs ont montré qu'un modèle covalent conventionnel pour les N hétérocycles protonisés ne réussit pas à expliquer le spectre électronique expérimental alors qu'un modèle à forte polarisation du squelette donne des résultats dans l'ensemble satisfaisants. Cette théorie prévoit que la nature du spectre électronique de la quinoléine est considérablement modifiée par la polarisation dûe à la protonisation.

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Presented partly at the 23rd Symposium on Molecular Structure and Spectroscopy, The Ohio State University, Columbus, Ohio, U.S.A., September 1968.