High Concentrations Of LiCl Research Articles

ESR and NMR of Mn(II) Complexes in Methanol

ESR spectra of Mn2+ in methanol solutions of Mn(ClO4)2 containing various amounts of LiCl, NaNCS, LiBr, LiNO3, and LiClO4 were studied. In all solutions, variations in the integrated intensity of the ESR signal upon addition of the electrolyte were observed. This effect was interpreted in terms of the formation of asymmetrically substituted octahedral Mn2+ complexes, in many of which the zero-field splitting interaction causes fast electronic relaxation and therefore an ESR signal too broad to observe. Some of the mixed solvent-anion complexes do however yield resolved ESR signals; in particular, a well-defined spectrum due to [Mn(MeOH)4(NCS)2] could be characterized. From the decrease of the ESR signal the equilibrium constants for the formation of monosubstituted octahedral complexes, [Mn(MeOH)5X]+, were estimated. The equilibrium constants for Cl−, NCS−, Br−, NO3−, and ClO4− are respectively >100, >100, 10, 5, and 1M−1. At high LiCl concentrations tetrahedral [MnCl4]2−, exhibiting resolved ESR lines, is formed. In the ESR spectrum of the system Mn(ClO4)2–LiCl–methanol there is, in addition to the intense sextuplet, also a very broad background signal which is attributed to the monochloro complex. From the over-all width of this signal an estimate of the zero-field splitting energy in this complex was made. Proton magnetic resonance measurements were made in methanol solutions of Mn(ClO4)2 containing various amounts of LiCl. There is a strong dependence of the proton linewidth on temperature and on LiCl concentration. The results were interpreted in terms of exchange of methanol molecules in and out of the solvation shells of [Mn(MeOH)6]2+ and the various mixed chloro complexes, but only for [Mn(MeOH)6]2+could a quantitative analysis be made. The kinetic parameters for the exchange reaction of this complex are 1 / τM(25°C) = 9.5 × 105sec−1 and ΔE‡ = 7.4 kcal mole−1. In the monochloro complex the exchange rate is about twice as high.

Oxidative phosphorylation in Micrococcus denitrificans. II. The properties of pyridine nucleotide transhydrogenase

A pyridine nucleotide transhydrogenase activity, supported by ATP or by succinate oxidation, was demonstrated in phosphorylating membrane fragments from Micrococcus denitrificans. The ATP-supported reaction was inhibited by various energy-transfer inhibitors and uncouplers or by treatment with high concentrations of LiCl. P i and arsenate showed a stimulatory effect on the ATP-supported activity; half-maximal stimulation was attained by about 80 μM phosphate. The transhydrogenase reaction dependent on succinate oxidation was not appreciably inhibited by energy-transfer inhibitors, although oleate and pentachlorophenol were almost equally effective in both reactions. P i did not stimulate the succinate-supported activity. From the effects of thyroxine and its derivatives on the energy-dependent and independent reductions of NAD + by NADPH, the involvement of the same transhydrogenase enzyme in both reactions was suggested. These and other results indicated that the energy-transfer system of M. denitrificans was very similar to, though not identical with, that of mammalian mitochondria.

Oxidative phosphorylation in Micrococcus denitrificans. I. Preparation and properties of phosphorylating membrane fragments

A procedure was described to prepare stable membrane fragments from aerobically grown cells of Micrococcus denitrificans. This preparation contained flavins, cytochromes b, c, a and o, and catalyzed the synthesis of ATP coupled to the oxidation of NADH and succinate. The P:O ratios were about 1.0 for NADH and 0.4 for succinate oxidation. The electron-transfer pathways responsible for these oxidations were similar to, though not identical with, those of mammalian mitochondria in their construction and sensitivity to inhibitors. Oxidative phosphorylation by the membrane fragments was uncoupled by the usual uncouplers and energy-transfer inhibitors, though 2,4-dinitrophenol was much less effective and higher concentrations of oligomycin and tributyltin chloride were required for complete inhibition as compared with the mitochondrial system. Oleate also caused uncoupling, which was relieved by serum albumin. Treatment with high concentrations of LiCl yielded an essentially uncoupled preparation, but this treatment as well as many other procedures failed to yield soluble coupling factors. Unlike the mitochondrial ATPase activity, ATP hydrolysis by the membrane fragments was inhibited to about 50% by uncouplers and energy-transfer inhibitors. It seems that the bacterial preparation possessed two types of ATPase, one of which was sensitive to these reagents as well as to LiCl treatment and probably to high concentrations of ADP. The advantage of this preparation for the study of the mechanism of oxidative phosphorylation is discussed.

The Adsorption of Zinc(II) on Anion-exchange Resins. II. Stoichiometry, Thermodynamics, Loading Studies, Dowex-2 Adsorption and Factors Influencing the Rate of the Adsorption Process

The adsorption of macroscopic amounts of zinc(II) on Dowex 1-XB chloride has been studied at room temperature; the chloride content of the resin doubles with the equivalent adsorption of zinc(II) species. The adsorption of tracer zinc(II) on Dowex 1-X8 chloride from LiCl and HC1 solutions at 0.25 and 49 deg has been studied, and the results indicate the presence of a secondary process resulting in apparent resin adsorption at high LiCl concentrations. Loading studies indicate that the equivalent capacity of Dowex l for zinc(II) chloro- complex ions is the same as for chloride ion, thus rendering unlikely the supposition that the adsorption process is other than ion exchange with the resin functional groups. The adsorption of tracer zinc(II) on Dowex 2 from HCl and LiCl solutions, while somewhat less, is substantially the same as on Dowex 1. The influence of resin mesh and amount, the concentration of various constituentc; in the solution phase, and solvent composition on the rate of the adsorption and desorption processes has been studied together with the rate of exchange of radiozinc(II) between resin and solution phases. (auth)