George S. Wilson

Conformational analysis of mesocyclic polythioethers : Gas phase conformational analysis of five mesocyclic polythioethers using photoelectron spectroscopy

Abstract The helium I photoelectron spectra of the mesocyclic polythioethers 1,4-dithiacycloheptane (1,4-DTCH), 1,5-dithiacyclooctane (1,5-DTCO), 1,5-dithiacyclononane (1,5-DTCN), 1,4,7-trithiacyclononane (1,4,7-TTCN), and 1,6-dithiacyclodecane (1,6-DTCD) are reported. The conformations of these molecules in the gas phase are deduced from correlations of the observed spectra with semi-empirical MO calculations, as well as molecular mechanics analysis.

Electrochemical studies of porphyrin redox reactions as cytochrome models

Abstract A series of Fe(III) derivatives of mesoporphyrin IX have been examined electrochemically. These derivatives contain histidine and methionine which have been covalently attached to the porphyrin ring via the propionic acid side chains. These studies show that the attached ligands are capable of intramolecular coordination with the iron to give distinctive electrochemical properties. The pH-dependence of the formal potentials for the various derivatives is presented in the light of the characteristics of cytochrome c. Various approaches to heme model compounds for electrochemical studies are reviewed.

CYCLIC VOLTAMMETRY OF PORPHYRINS AND METALLOPORPHYRINS

The ubiquitous involvement of metalloporphyrins in electron transport in biological systems has resulted in studies of electrochemical properties of particular interest. The classical potentiometric and spectrophotometric studies of Clark and others-3 indicated the influence and attendant complexity of z-axis ligand interactions. More recently, polarographic and cyclic voltammetric studies of the reduction of iron porphyrin c o m p l e x e ~ ~ * ~ have provided additional details concerning the solution equilibria involved. Other porphyrin and metalloporphyrin6-8 reductions in aqueous solution have also been studied using these techniques. For reasons of limited solubility, the absence of strong nucleophiles and/or electrophiles and increased potential range, several electrochemical studies9- have been carried out in nonaqueous (usually aprotic) media. In general, electron transfer in these systems proceeds in one-electron steps in the absence of complicating chemical reactions. Thus, it is possible by involvement of porphyrin orbitals to form, by successive reversible one-electron steps, monoand di-n-cations as well as the corresponding n-anions. If, however, the pertinent orbitals of the central metal atom are comparable in energy to those of the porphyrin, then both the metal and the porphyrin will be electroactive. Several cases have been cited*lB in which both metal and ligand oxidation are believed to have occurred. There are two major classes of naturally occurring metalloporphyrins-those in which the central metal is formally involved in electron transfer as typified by the cytochromes and those in which the metal apparently is not involved. This latter class, exemplified by chlorophyll, raises the possibility that the purpose of the metal is to modify the properties of porphyrin ring reactions.

Highly diastereoselective oxidations of a thioether appended with a neighboring hydroxyl group

Abstract Highly diastereoselective oxidations of endo -alcohol 1 to the corresponding sulfoxides, the relative stereochemistries of these sulfoxides and that of an intermediary alkoxysulfonium salt determined by X-ray crystallographic analysis is reported.

CONFORMATIONAL ANALYSIS OF MESOCYCLIC POLYTHIOETHERS. CRYSTAL AND MOLECULAR STRUCTURES OF 1,4-DITHIACYCLOHEPTANE, 1,5-DITHIACYCLONONANE, AND 1,6-DITHIACYCLODECANE

Abstract The crystal and molecular structures of 1,4-dithiacycloheptane (1,4-DTCH), 1,5-dithiacyclononane (1,5-DTCN), and 1,6-dithiacyclodecane (1,6-DTCD) have been determined by single crystal X-ray studies. These compounds crystallize in the space groups P212121 (No. 19), P21/c (No. 14), and P21/n, respectively with a = 5.409(1), b = 10.883(2), c = 11.390(2) A, Z = 4; a = 9.600(4), b = 12.378(8), c = 7.904(3) A, /gb = 113.31(3)°, Z = 4; and a = 5.290(1), b = 12.853(3), c = 6.850(2) A, β = 93.39(2)°, Z = 2, respectively. The nonhydrogen atoms were located using direct methods and the hydrogen atoms were found by Fourier difference maps. Full-matrix least-squares refinement led to conventional R factors of 0.0459, 0.0558 and 0.0314, respectively. The conformations adopted by 1,4-DTCH, 1,5-DTCN and 1,6-DTCD, in the crystalline slate, are twist chair (C2 symmetry), twist boat chair (C2 symmetry), and boat chair boat (C2k symmetry), respectively. The transannular S-S distances are 3.583, 4.108 and 4.864 A, respectively.

Bis(trithiacyclononane)metal(II) compounds and Jahn-Teller distortions from octahedral geometry, electrochemistry, spectroscopy, and crystal structures of the copper bis(tetrafluoroborate) bis(acetonitrile) complex at 177 K and the cadmium bis(tetrafluoroborate) and copper bis(tetrafluoroborate) bis(nitromethane) complexes at 300 K

The structures and the EPR spectra are described of compounds with formula M(ttcn) 2 (A) 2 , with Aue5fbBF 4 − ; Mue5fbCu, Cd, Fe and the Cu(II)-doped Cd(II) and Fe(II) compounds. Single crystal structures are described for the copper compound Cu(ttcn) 2 (BF 4 ) 2 (MeCN) 2 ( 1 ) at low temperature, and for the cadmium compound Cd(ttcn) 2 (BF 4 ) 2 (MeNO 2 ) 2 ( 2 ) and copper compound Cu(ttcn) 2 (BF 4 ) 2 (MeNO 2 ) 2 ( 3 ) at room temperature. Compound 1 crystallizes in the space group P 2 1 / c with a =20.695(2), b =14.944(1), c =8.864(1) A, β=90.797(8)° and Z =4. The unit cell contains two crystallographically independent Cu ions, each at a crystallographic inversion center, which are structurally almost identical. The copper ion with the CuS 6 2+ chromophore appears to be nearly octahedral, just as found earlier for the room temperature structure. Relevant Cu-S distances are for Cu(A): 2.407, 2.419 and 2.458 and for Cu(B): 2.407, 2.428 and 2.461 A. Compound 2 also crystallized in the space group P 2 1 / c with a =10.314(2), b =15.138(2), c =9.461(2) A, β=99.39(1)° and Z =2. The Cd(II) ion is octahedrally surrounded by six S atoms at almost equal distances varying from 2.649 to 2.663 A. Compound 3 crystallizes in the space group Pbca with a =19.746(2), b =15.422(2), c =9.227(1) A and Z =4. The copper ion occupies a crystallographic inversion center. The copper ion is significantly distorted from an octahedral arrangement of the six coordinated sulfur atoms with Cu-S distances ranging from 2.343(2) to 2.504(2) A. Cyclic voltammetric studies on Cu(ttcn) 2 2+ in aqueous buffer at pH 3 show a reversible one-electron reduction with E o =0.408(1) V versus AgCl/Ag reference. EPR spectra were recorded of the pure copper compound acetonitrile solvate, as well as of Cu(II) dopes in the isomorphous Fe(II) and Cd(II) compounds. The results indicate that in the case of the undiluted copper compound only a single signal ( g =2.06) is observed even down to 4 K, thereby not providing any evidence of a Jahn-Teller splitting. However, Cu(II) dopes in the isomorphous, diamagnetic Fe(II) compound show anisotropic signals below 100 K, with values for g ∥ and g ⊥ of 2.113 and 2.027, respectively ( A ∥=153 G). At room temperature a complex spectrum of isotropic and anisotropic lines is observed. Dopes in the corresponding Cd compounds show well-resolved spectra, with parameters similar to the Fe(II)-doped species. Heat capacity measurements on compound 3 show no phase transition in the temperature range 1.2–300 K. Such measurements on compound 1 show phase transitions near 90 and 150 K.

Characterization of antigen-enzyme conjugates: Theoretical considerations for rate nephelometric assays of immunological reactivities

Abstract A simple method has been developed to assay the immunological reactivity of antigen-enzyme conjugates by rate nephelometry. Unlike immunodiffusion or immunoelectrophoresis, the procedure is independent of molecular hydrodynamics and is based on precipitin rate curves obtained by light-scattering measurements. To our knowledge, no such methods have yet been described in the literature to characterize these conjugates. Theoretical considerations indicate that the scattering properties of the precipitin particles obey Raleigh-Debye conditions. Thus, the rate of increase in light scatter measured is directly proportional to an increasing number of scattering centers on large, growing precipitin particles. This independence of the rate of change in light scatter from the absolute size of the particles makes rate nephelometry an ideal technique to quantitate immunological reactivity. This paper deals with a special case of the fundamental rate law that reoates the rate of change of light scatter to the antibody-antigen reaction under Rayleigh-Debye conditions. In addition, data for two types of conjugates which illustrate the validity of the technique are presented.

Small-volume coulometric redoxostat

Abstract The apparatus described senses the solution redox potential and compares it to a control value. If the two do not agree, the necessary oxidant or reductant is electrolytically generated until the system is brought under control at the desired value. Using the above procedures, a desired solution potential can be obtained with a precision and accuracy of ±4 mV. This has proved applicable to the determination of biological species such as cytochrome b which attain redox equilibrium slowly.

Electron Transfer from Thioethers

Abstract Oxidation of thioethers is greatly facilitated by neighboring group participation by carboxylate, alcohol, and thioether moieties.

Enzyme immunoassays with electrochemical detection

Abstract Electrochemical enzyme immunoassay (EEIA) is a recent innovation, a result of the advent of sensitive and reliable electrochemical detectors. Both voltammetric and potentiometric detection can be easily adapted to flow-through immunoassay procedures allowing rapid automation.