Molecular recognition and conductance in crown ethers

Crown ethers have the remarkable property of recognizing and binding specific metal cations in complex mixtures. We propose to combine molecular recognition with molecular electric conductance. The question we address is: can the event of binding a cation be sensed by a change in conductance? Specifically, we study a short molecular wire (MW) containing a crown-6 molecule connected via sulfur atoms to two gold atomic wires acting as metallic leads. Upon binding a cation, the density of states of the system is only slightly affected. This reflects the fact that the cation binding is largely electrostatic in nature and is accompanied by little electronic reorganization. Yet, the cationic binding does significantly lower conductance. We also identify strong interference affecting the conductance. A striking feature is the insensitivity of conductance to the type of ligand with the exception of the proton.     

Gel Chromatography

Gel chromatography can be regarded as a network-limited partitioning of substances. The theory of this method and the preparation and properties of various gel systems are reviewed. Optimization of the method is illustrated for the separation of oligomers.     

Solution properties of polyoxymethylene

Light scattering and viscosity have been measured at 25°C. for dilute solutions of six unfractionated polyoxymethylene samples in the mixed solvent hexafluoroacetone–water (mole ratio 1/1.7) slightly buffered with triethylamine. Dialysis equilibrium through porous Vycor glass thimbles indicates that the polymer is strongly solvated by the hydrate (CF₃)₂C(OH)₂, and this must be taken into account in evaluating weight-average molecular weights from the light-scattering data. Over the molecular weight range 23,000–185,000, the intrinsic viscosities (in deciliter per gram) follow the relation The corresponding unperturbed dimensions are σ = 2.3 ± 0.2 or r₀²/nl² = 10.5 ± 1.5.     

Hexaphosphapentaprismane: a new gateway to organophosphorus cage compound chemistry

Several independent synthetic routes are described leading to the formation of a novel unsaturated tetracyclic phosphorus carbon cage compound tBu4C4P6 (1), which undergoes a light-induced valence isomerization to produce the first hexaphosphapentaprismane cage tBu4C4P6 (2). A second unsaturated isomer tBu4C4P6 (9) of 1 and the bis-[W(CO)5] complex 13 of 1 are stable towards similar isomerization reactions. Another starting material for the synthesis of the hexaphosphapentaprismane cage tBu4C4P6 (2) is the trimeric mercury complex [(tBu4C4P6)Hg]3 (11), which undergoes elimination of mercury to afford the title compound 2. Single-crystal X-ray structural determinations have been carried out on compounds 1, 2, 9, 11, and 13.     

Interaction of UO2 2+ with sodium dodecyl sulfate micelles: association of phenols to micelles through fluorescence quenching data

Time-resolved laser-induced fluorescence (TRLIF) has been used to study the interaction of uranyl ion with sodium dodecyl sulfate (SDS) micelles in H(3)PO(4) 1 M. The titration curve consists of two curved regions with different slopes, one of them more pronounced at low concentration of SDS and the other, with a less pronounced positive slope at larger [SDS] until a plateau is reached. The fluorescence quenching of uranyl ion by para-substituted phenol compounds was studied by TRLIF and steady-state emission intensity measurements. The results were interpreted in terms of binding of phenolic compounds to the micelle. The binding constant (K(Q)) as well as the entrance and exit rate constants were determined for all the quenchers used.     

Eine neue photometrische bestimmung für nickel mit aethylendiamintetraessigsäure

It is possible to determine very high concentrations of nickel photometrically by means of ethylenediaminetetra-acetic acid, by working at a pH between 4.55 and 6.82. The absorption curves obtained for this complex are very reproducible; for these measurements an Elko II apparatus with filter S57E is used. High concentrations of ammoniacal salts hinder the measurement. The formation of the complex is not influenced by the anion of the compound of nickel used. The Lambert-Beer law is followed for strengths of nickel of 40 — 5000 mg/100 ml. This procedure is convenient for alloys rich in nickel.     

Elution order in gas chromatography

The retention behavior of a heterogeneous group of solutes has been examined on seven different stationary phases under isothermal and temperature-programmed conditions. Both ΔH_v (enthalpy of solute vaporization from the stationary phase) and ΔS_v (entropy of solute vaporization from the stationary phase) values were determined for each solute – stationary phase combination under isothermal conditions. Both program rate and carrier gas velocity were shown to affect solute elution order. Unless these and other experimental factors discussed are controlled, column equivalency studies based on solute elution order have dubious value.     

Ga8Ir4B – ein Gallium-Iridiumborid mit isolierten,annähernd quadratisch planaren Ir4B-Gruppen in einer vom CaF2-Typ abgeleiteten Struktur

Ga₈Ir₄B – a Gallium Iridium Boride with isolated, nearly square planar Ir₄B Groups in a Structure derived from the CaF₂ Type The new compound Ga₈Ir₄B (tetragonal, I4₁/acd, a = 853.69(2) pm, c = 2 105.69(6) pm, Z = 8, 614 reflections, 31 parameters, R = 0.034) was prepared by reaction of the elements at 1 100°C. The structure is derived from the CaF₂ type. It contains isolated Ir₄B groups with boron in an unusual, nearly square planar coordination.     

Quantum field theoretical methods in chemically bonded systems II

Summary Many-body perturbation theory is derived for chemical bonds. Paired quasiparticles represent the bonds. Products of the paired quasiparticles define a model Bardeen-Cooper-Schrieffer function. The pairing force is added as a model interaction to the self-consistent problem. The starting model is based on valency and adiabatic symmetry correlation. Symmetries are enforced by the model Hamiltonian. Perturbative corrections are expressed as ordinary Feynman diagrams. The number of diagrams needed is the same as for particle-hole theory.This work was supported in part by the U.S. Department of the Navy, Space and Naval Warfare Systems Command under Contract N00039-89-C-0001, and in part by NATO Research Grant 1861. It was presented, in part, at the A.C. Wahl Memorial Session, Molecular Spectroscopy Symposium, Columbus, Ohio, 1984; and Midwest Theoretical Chemistry Conference, Milwaukee, Wisconsin, 1985.     

Characterizations of the Kerr metric

For stationary, asymptotically flat solutions of Einstein's equations, covariant functionals of the metric variables are defined which characterize the Kerr metric uniquely. For instance, we obtain a generalization of the Bach tensor to stationary metrics, which vanishes if and only if the solution is Kerr. We also give a new interpretation of the Schwarzschild-to-Kerr-transformation. Our results might be applicable to simplify the proof of the uniqueness theorem for stationary black holes.