Conditional stability constants and binding capacities are important parameters with which to estimate the biological availability of metal ions in aqueous solution in the presence of dissolved natural organic matter (fulvic acid, organic matter in natural waters or in aqueous extracts of forest litter). Determination of these parameters depends on analytical methods that can distinguish between free and organically bound metal ions. This speciation is difficult, mainly because natural organic matter typically is a complex mixture. In this paper, multi-wavelength molecular fluorescence spectrometry is evaluated prototypically as a method for the determination of stability constants and binding capacities for Cu(II) and Al(III) complexation by dissolved organic matter in a juniper leaf litter extract. Equilibrium ion exchange quantitation and electron spin resonance spectroscopy served as quantitative and qualitative reference methods, respectively. Three types of binding site for Cu and Al could be differentiated qualitatively by the reaction patterns of various wavelength regions of the total luminescence spectrum of the leaf litter extract in response to increasing metal ion addition. For both Cu (pH 6) and Al (pH 5), binding parameters for the two types of binding site forming the most stable complexes were deduced self-consistently from reactions evaluated at selected excitation/emission wavelength pairs.

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The adsorption of calcium ions on the surface of precipitated calcium carbonate (calcite, prismatic, 0.7 pm diameter) has been studied in 20 w t 94 aqueous slurries by calcium chloride addition. The adsorption of the calcium ions was found to follow the Langmuir adsorption isotherm, and the adsorbed calcium ions were the {-potential-determining ions. The monolayer coverage was determined to be 1.58 X l V mol of Ca2+/m2 (105 A2/Ca2+). Experimentally, this coverage was closely approached at the Ca2+ concentration of 7.51 mM in the bulk solution after adsorption equilibrium and was about one-fifth of the lattice Ca2+ density. The cpotential, as determined in the high-solids slurries by a Matec ESA-8000 instrument, varied with increasing Ca2+ concentration from +3.8 to +18.7 mV. As the {potential increased and the interparticle repulsion became greater, the sedimentation volume decreased, and the dispersion was slower to flocculate, a typical response to improved dispersion. The standard-state Gibbs free energy change for the adsorption process was calculated to be -28.3 kJ/mol (-6.8 kcal/mol) by using the experimentally determined adsorption equilibrium constant. The heat of adsorption measured by direct solution microcalorimetry was -6.9 kcal/mol of Ca2+, indicating that the adsorption is enthalpically driven.

Increased mammographic density (MD) has been shown beyond doubt to be a marker for increased breast cancer risk, though the underpinning pathobiology is yet to be fully elucidated. Estrogenic activity exerts a strong influence over MD, which consequently has been observed to change predictably in response to tamoxifen anti-estrogen therapy, although results for other selective estrogen receptor modulators and aromatase inhibitors are less consistent. In both primary and secondary prevention settings, tamoxifen-associated MD changes correlate with successful modulation of risk or outcome, particularly among pre-menopausal women; an observation that supports the potential use of MD change as a surrogate marker where short-term MD changes reflect longer-term anti-estrogen efficacy. Here we summarize endocrine therapy-induced MD changes and attendant outcomes and discuss both the need for outcome surrogates in such therapy, as well as make a case for MD as such a monitoring marker. We then discuss the process and steps required to validate and introduce MD into practice as a predictor or surrogate for endocrine therapy efficacy in preventive and adjuvant breast cancer treatment settings.

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