Donald C. Jackman

Crystal structure, physical, and photophysical properties of a ruthenium(II) bipyridine diazafluorenone complex

The complex [Ru(bpy)2(dafo)](PF6)2, where bpy is 2,2′-bipyridine and dafo is diazafluorenone crystallizes in the space group P21/n witha=9.505(3) Å,b=14.002(4) Å andc=25.783(8) Å. The coordination geometry of the Ru atom is that of a distorted octahedron with a RuN6 core. The two Ru-N bond distances to the dafo ligand are 2.13(1) and 2.15(1) Å; the four Ru-N bond distances to the bipyridine ligands are 2.03(1), 2.05(1), 2.06(1), and 2.07(1) Å. The three shortest Ru-N distances aretrans to the three longest Ru-N distances. The complex is oxidized and reduced reversibly at 1.41 and −0.65 V vs. SSCE, respectively. It displays absorptions at 438 nm (1.6×104), 285 nm (6.2×104), and 240 nm (4.1×104) and a broad emission centered at 626 nm in water at room temperature. The emission lifetime is 420 ns and the emission quantum yield is 5.3×10−4.

A comparison between chemically and photochemically driven electron transport reactions in immobilized liquid membranes

Abstract Electron transport in immobilized liquid membranes using a microporous polypropylene film as the support was studied in the reagent concentration independent regime and was kinetically controlled under the conditions employed in this study. The velocities depended on the concentration of the carrier (Vitamin K 3 ) in the membrane and varied exponentially with the reciprocal of the absolute temperature. Neither the membrane thickness, concentration of the oxidant (Fe( o phen) 3 3+ ) nor the concentration of reductant (S 2 O 4 2- or MV + generated photochemically) affect the electron transport rate. Maximum velocities at 25°C (7.8 μmol-cm -2 -hr -1 and 2.5 μmol-cm -2 -hr - for the S 2 O 4 2- and MV + driven reactions, respectively) were obtained in the pH range of 6-7 for the reductant compartment and in the 0 to - 1 pH range in the oxidant compartment. The respective turnover rates were 2.1 hr -1 and 0.65 hr -1 based on 2e - /Vitamin K 3 for the S 2 O 4 2- and MV + driven reactions, respectively. The mechanism of electron transport is best interpreted to involve formation of the hydroquinone in the membrane which then reacts with Fe( o -phen) 3 3+ in the rate-limiting electron transfer step.

Behavior of simple salts on silica and C18 columns : Retention dynamics of cations, anions and ion pairs

Abstract The retention behavior of simple inorganic salts on silica and ODS columns was investigated by high-performance liquid chromatography with methanol-water (80:20, v/v) as the mobile phase. Both a major (dissolved salt) and a minor (ion pair) peak were observed on the ODS columns; only the major peak was present on silica columns. The retention time of the major peak was a function of the number of moles of salt placed on the column and was sigmoidal with respect to the logarithm of the number of moles analyzed. The retention time of the minor peak was dependent upon the composition of the mobile phase. It disappeared in a mobile phase of water and was absent on a silica column. The general behavior was independent of the anion or cation being analyzed. The sigmoidal behavior of salt retention was attributed to both cationic and anionic exchange at the silica surface: the ion pair retention was attributed to solubility in the C 18 phase of the ODS columns. The areas under the major peak and the minor peak were used to calculate ion pair formation constants. For sodium nitrate, K = 15 · 10 −3 M −1 , for sodium nitrite, K = 2.0 · 10 −3 M −1 . The ion pair formation constants were used to calculate the theoretical distance of closest approach between the ions based on Bjerrum theory. For sodium nitrate, the distance calculated between center of Na + and NO − 3 in the ion pair was 6.5 A.

The case of the elusive tm values in HPLC

SummaryNumerous ideas and procedures have been suggested in the literature for the determination of tm, the retention time of a non-retained species, in high-performance liquid chromatography. In some cases chromatograms have been obtained showing sample components eluting prior to the assumed non-retained species. This phenomenon results in apparent negative capacity factors for the species in question. We have proposed a method employing small inorganic anions which results in a limiting value for tm and eliminates apparent negative capacity factors.

A determination of electrode potentials at immobilized liquid membrane interfaces: bipolar effects

Abstract Electrochemical potentials of redox carriers (Vitamin K3 and 2 -tert-butylanthraquinone) were determined at the membrane/solution interface. The hydroquinone was generated in a photoelectrochemical cell and the potentials of the quinone/hydroquinone couples were determined at a platinized membrane surface. The values found for the quinone/hydroquinone couples were comparable to the E 1 2 values determined polarographically and exhibited a Nernstian response to the pH of the solution in contact with the membrane. The potentials were shown to be true interfacial membrane potentials, not those of the solution in contact with the membrane. The bipolar effect of having two solutions of differing pH on each side of the membrane was demonstrated by effecting the reduction of a substrate at a higher pH than thermodynamically possible if both solutions were at the same pH.

Electron transport reactions in immobilized liquid membranes: a comparison of the carriers vitamin K3 and 2-tert-butylanthraquinone

Electron transport in immobilized liquid membranes was studied in the reagent concentration-dependent regime. The velocity dependence of cells utilizing Vitamin K3 (VK3) and 2-tert-butylanthraquinone (TBAQ) as carriers was determined. The velocity for the VK3 cell was proportional to the product [MV+]0.5[VK3]0.9 [Fe(phen33+]0.5 exp 40 kJ/RT; that of the TBAQ cell was proportional to the product [MV+]1.3 [TBAQ]1.5 [Fe(phen)33+]0.9 exp 10 kJ/RT. The velocity of electron transport was kinetically controlled at the oxidant interface as verified by independent rate measurements. The rate constant for the reaction of MV+ with TBAQ was 8.4 x 108 M−1-sec−1 (reductant interface); for the reaction of H2TBAQ with Fe(phen)33+, it was 34 M−1-sec−1(oxidant interface). The velocity dependence reduced to the following in the concentration independent regime: for the TBAQ cell, v ∞ exp 10 kJ/RT ([MV+] >0.6 mM, [TBAQ] >0.2 M, [Fe(phen)33+] > 5 mM, [Ru(bpy)32+] > 0.2 mM); for the VK3 cell, v ∞ [VK3] exp 40 kJ/RT ([MV+] > 0.4 mM, [Fe(phen)33+] > 5 mM, [Ru(bpy)33+] > 0.2 mM). The mechanism of electron transport in the TBAQ cell is best interpreted to involve formation of semiquinone and hydroquinone in the membrane which then react with Fe(phen)33+ in the rate-limiting electron transfer step.

Algorithm for plotting titration curves

de Mouras algorithm for plotting redox titration curves seems to be good for systems that are not dependent on pH or product concentration, but is not applicable to those situations that is student is more likely to encounter.