pKs Values Research Articles

Transformation of chernikovite into meta-uranocircite II, Ba(UO2)2(PO4)2.6H2O and study of its solubility

AbstractChernikovite, (H3O)2(UO2)2(PO4)2, was synthesized and subsequently transformed into metauranocircite II, Ba(UO2)2(PO4)2.6H2O, by ion-exchange experiments. The crystals are lemon-yellow and strongly fluorescent. From solubility data a mean pKs value at 25°C was determined as 51.79 ± 0.21. For a cell volume of 16.31.7 Å3 and Z = 4 the density was calculated as 3.970 g/cm3 whereas the measured density is 3.964 g/cm 3. The X-ray powder pattern shows the following strongest lines: 3.609(60)(114), 3.470(60)(123), 2.9272(90)(132)2.9006(90)(312), 2.6065(80)(116), 2.4581(75)(233), 2.2015(100)(143 ; 143), 2.1869(100) (241 ; 226 ;241).

Molybdenum(VI) and phenol reactions in concentrated aqueous sulphuric acid

Depending on molybdenum, phenol, and acid concentrations, and time and the method of solution preparation, molybdenum and phenol can react in several ways. In 96% sulphuric acid Mo(VI) can be reduced to Mo(V) by adding solid phenol to the solution. In other cases molybdenum and phenol form stable or unstable complexes which can be in equilibrium with each other. For excess phenol the recorded spectra show two bands at around 600 and 423 nm; the first one, decreasing with time, is ascribed to the formation of an unstable complex of phenol and Mo(VI). At approximately equal concentrations of molybdenum and phenol the band at 423 nm does not appear, but two time-dependent absorption maxima are formed at 600 and 470 nm with a well defined isosbestic point at 505 nm. The complex is unstable because of the sulphonation of phenol. In 80% sulphuric acid molybdenum and phenol form a stable 1:1 complex which absorbs at 480 nm; its pKs value is 1.44 ± 0.03 at room temperature.

Dual ligand binding of pyridylalkanamides to microsomal cytochrome P-450

Twelve homologous and regioisomeric pyridylalkanamides were examined spectrally for their binding affinity to cytochrome P-450 in phenobarbital- and 3-methylcholanthrene-induced rat liver microsomes. The pKs values were calcuated by the Lineweaver-Burk method andby non-linear analysis using both a one ligand-one acceptor and a one ligand-two acceptor model. The latter model best fits most of the data, conforming that two pKs values exist for most derivatives in the 3-pyridyl and 4-pyridyl series. Structure-binding relationships are discussed. The two binding constants are hypothesized to arise from a dual mode of binding to the ferric ion. At low ligand concentrations, binding to hexacoordinated cytochrome P-450 occurs and involves displacement of an endogenous 6th ligand; at higher concentrations, the ligands bind to the pentacoordinated P-450, resulting in a high-to-low spin shift.

Studies on the stabilized ubisemiquinone species in the succinate-cytochrome c reductase segment of the intact mitochondrial membrane system.

1. Evidence is presented for the presence of a stable ubisemiquinone pair in the vicinity of iron-sulphur centre S-3, based on its thermodynamic and spin relaxation properties. 2. These semiquinones are coupled by dipolar interaction; quantitative analysis of the signals of the spin-coupled semiquinones (at pH 7.4) gives midpoint redox potentials E1 (oxidized to semiquinone state) and E2 (semiquinone to fully reduced state) of 140 and 80mV, respectively, for individual ubiquinones. 3. Values of pKS (pK of the semiquinone form) below 6.5 and pKR (pK of the fully reduced ubiquinone) of about 8.0 or above were estimated from the pH-dependence of the midpoint potentials of the spin coupled signals. Thus the ubisemiquinone associated with succinate dehydrogenase (designated as SQS) functions mostly in the anionic form of the physiological pH range. 4. Theonyltrifluoroacetone, a specific inhibitor of the succinate-ubiquinone reductase segment of the respiratory chain, destabilized the intermediate redox state; thus it quenches both the g = 2.00 signal and ubisemiquinone (SQS) and split signals from the spin coupled pair. This inhibitor has no significant effect on another bound ubisemiquinone species present in the cytochrome bc1 region (designated as SQC). 5. The possible function and location of these stabilized ubisemiquinone species were discussed in connection with Site-II energy transduction.