A Pitzer Model for Lead Oxide Solubilities in the Presence of Borate to High Ionic Strength

In this study, a hydrolysis model for lead, applicable to high ionic strength, is developed based on lead oxide solubilities as a function of ionic strength. Solubility measurements on lead oxide, α-PbO (tetragonal, red), mineral name litharge, as a function of ionic strength were conducted in NaClO₄ solutions up to I?=?0.45 mol·kg^?1, in NaCl solutions up to I?=?5.0 mol·kg^?1, and in Na₂SO₄ solutions up to I?=?5.4 mol·kg^?1, at room temperature (22.5?±?0.5 °C). The lead hydroxyl species considered in this work include the following,

$$ {\text{PbO}}\left( {\text{cr}} \right) \, + {\text{ 2H}}^{ + } \rightleftharpoons {\text{Pb}}^{ 2+ } + {\text{ H}}_{ 2} {\text{O}}\left( {\text{l}} \right) $$

(1)

$$ {\text{Pb}}^{ 2+ } + {\text{ H}}_{ 2} {\text{O}}\left( {\text{l}} \right) \rightleftharpoons {\text{PbOH}}^{ + } + {\text{ H}}^{ + } $$

(2)

$$ {\text{Pb}}^{ 2+ } + {\text{ 2H}}_{ 2} {\text{O}}\left( {\text{l}} \right) \rightleftharpoons {\text{Pb}}\left( {\text{OH}} \right)_{ 2} \left( {\text{aq}} \right) \, + {\text{ 2H}}^{ + } $$

(3)

$$ {\text{Pb}}^{ 2+ } + {\text{ 3H}}_{ 2} {\text{O}}\left( {\text{l}} \right) \rightleftharpoons {\text{Pb(OH}})_{3}^{ - } + 3{\text{H}}^{ + } $$

(4)

The equilibrium constants for Reactions (1) and (2) were taken from literature. The equilibrium constants in base 10 logarithmic units for Reactions (3) and (4) are determined in this study as ? 17.05?±?0.10 (2σ) and ? 27.99?±?0.15 (2σ), respectively, with a set of Pitzer parameters describing the interactions with Na⁺, Cl^?, and \( {\text{SO}}_{4}^{2 - } .\) In combination with the parameters from literature including those that have already been published by our group, the solution chemistry of lead in a number of media including NaCl, MgCl₂, NaHCO₃, Na₂CO₃, Na₂SO₄, NaClO₄, and their mixtures, can be accurately described in a wide range of ionic strengths.

     

Triplet state properties and triplet-state-oxygen interactions of some linear and angular furocoumarins

Linear and angular furocoumarins with conjugated external carbonyl substituents show higher triplet and singlet oxygen yields than the corresponding unsubstituted molecules. The efficiency of the oxygen quenching process to yield singlet oxygen is also higher for these substituted molecules. These changes are interpreted in terms of the "proximity effect" associated with two nearly degenerate n pi* and pi pi* excited states, and variations in the excess energy following furocoumarin triplet quenching by ground state triplet oxygen to yield singlet oxygen.     

Electrochromatography in packed tubes using 1.5 to 50 μm silica gels and ODS bonded silica gels

Summary Electrochromatography (that is HPLC where the eluent is driven along the column by electro-osmosis using fields of up to 100 kV m⁻¹) promises plate efficiencies for HPLC which are comparable to those attained in capillary gas chromatography, but this requires that narrow-bore columns can be successfully packed with submicron particles. This paper demonstrates that we have now moved a considerable distance towards this goal. We show (1) that, following theory, there is no evidence of any reduction in electroosmotic velocity in columns packed with particles down to 1.5 μm diameter, (2) that reduced plate heights as low as unity are attainable for unretained solutes using both slurrypacked and drawn-packed columns 30 to 200 μm bore and up to 1 m long when packed with conventional 3 and 5 μm silica gels or with 1.5 μm impermeable silica spheres, (3) that columns driven electrically show higher plate efficiencies than identical columns driven by pressure, and (4) that 100,000 plate HPLC separations can be achieved in relatively short times of 30 minutes using in situ derivatised drawn packed capillaries containing 3 and 5 μm ODS-silica gels.     

The synthesis of 13-hydroxylated ent-kaur-16-ene derivatives using an acyloin-like cyclization of keto esters

The synthesis of steviol (27) and two A-ring modified analogues (9 and 15) is described. The synthetic sequences involve the preparation of suitably constituted 17-nor-13,16-seco-ent-kauranoid keto esters (22, 7 and 13) which are then cyclized to 13,16-dooxygenated-17-nor-ent-kauranes (23, 8 and 14).     

On the relation between absorption and emission spectra of molecules in solution

The universal relation between absorption and fluorescence spectra derived by Stepanov in 1957 is reexamined to assess the relative merits of two of the inferences usually drawn from its use in the analysis of data: elevated excited state temperatures (“warm fluorescence”) and inhomogeneous broadening of the molecular spectra. Of these, only the latter appears to give a satisfactory explanation of the anomalous temperatures derived using the Stepanov method in condensed media, and in particular, a purely “warm fluorescence” interpretation implies that a distinct curvature should appear in plots which experimentally appear to be straight lines.     

The measurement of chemiluminescence,aggregation, and 5-hydroxy-6,8,11,14-eicosatetraenoic acid production of n-formyl-methioninyl-leucyl-phenylalanine-stimulated human polymorphonuclear leukocytes

Polymorphonuclear leukocytes (PMNs) which had been treated with nordihydroguaiaretic acid (NDGA) or indomethacin were stimulated with varying doses of n-formyl-methioninyl-leucyl-phenylalanine (FMLP). Aggregation and chemiluminescence (CL) were simulta-neously measured. Supernatant solutions were obtained and saved from cells stimulated with 10^?6M FMLP. These solutions were assayed for 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) using radioimmunoassay (RIA) techniques and used as a measure of 5-lipoxygenase (LO) activity. It was found that 10^?5M NDGA inhibited CL from PMNs stimulated with FMLP. However, NDGA had much less effect on aggregation of these cells. Indomethacin had little effect on PMN aggregation and less effect on CL than NDGA following FMLP stimulation. Indomethacin (10^?5M) did inhibit CL stimulated with FMLP at FMLP doses of 10^?7 and 10^?6M but had no effect of CL at FMLP doses of 10^?5M. Finally, RIA for 5-HETE showed that the effects of NDGA and indomethacin on 5-HETE production could be correlated with their effects on CL responses of cells stimulated with 10^?6M FMLP. These results support two conclusions. First, PMN-CL and LO activity may be correlated. Second, PMN-CL is not necessarily associated with PMN aggregation. These observations may indicate that LO products are not necessary for PMN aggregation to occur.