Analytical and thermodynamic data, EPR, FTIR, solution 1 H and solid-state 13 C cross polarization magic angle spinning NMR and solid-state extended X-ray absorption fine structure (EXAFS) and X-ray absorption nearedge structure (XANES) spectra have been recorded for purified humic acids (HAs) isolated from a German peat (GHA), an Irish peat (IHA), an unpolluted New Hampshire bog soil (NHA) and their tightly bound copper(), iron() and manganese() forms. Brief water washing of partly or fully metal-loaded HAs leaves 'tightly' bound metal in the isolated freeze-dried solids. Most of this metal is removed by washing with 0.1  HCl, indicating acidic HA functional groups as principal metal binding sites. The number of nearest-neighbour atoms coordinated to tightly bound Cu II (four), Fe III (six, probably with distorted geometry) and Mn II (six, undistorted) in solid GHA, IHA and NHA were determined by XANES and EXAFS spectroscopy with reference standards. Isotherms measured at 20.0 ЊC and pH 2.4-3.2 with [M] total = 0.18-25.8 m for tight, reversible Cu 2ϩ (aq), Fe 3ϩ (aq), and Mn 2ϩ (aq) binding by solid IHA and NHA fit the Langmuir model and give the pH-independent stoichiometric site capacities ν i and equilibrium constants K i for metal binding at specific HA sites i = A, B and C. Tight binding sites A, B and C of IHA are occupied by Cu II , sites A and B by Fe III and site A by Mn II , while only identical metal binding site A in NHA is tight enough to resist metal removal by brief water washing. A new helical HA molecular model based on the empirical formula C 36 H 30 N 2 O 15 ؒxH 2 O visualizes metal binding and the likely roles of HAs in biomineralization. Site A is suggested to be carboxylate, mixed ligands probably constitute site B, and site C is tentatively assigned as the interior of the HA helix. Binding free energies and EPR evidence suggest that Cu 2ϩ (aq), Fe 3ϩ (aq) and Mn 2ϩ (aq) rapidly transfer between specific HA binding sites. This affects rates of metal release and transfer to minerals.

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Aqueous nucleic acid constituents uracil, uridine, and uridine-5‘-monophosphate are selectively adsorbed by a solid German peat-derived humic acid (GHA) and its tightly bound mercury(II) form (MGHA). Adsorption isotherms with GHA and MGHA adsorbents were obtained at 19 solute concentrations from 0 to 1.20 mM and seven fixed temperatures from 5.0 to 35.0 °C. Langmuir data analysis indicates that adsorption occurs in sequential steps A, B, and C, depending on the solute and experimental conditions. MGHA very strongly adsorbs low concentrations of uracil and site capacity vA for uracil adsorption on MGHA in step A increases with increasing temperature. The last steps of adsorption of relatively high concentrations of uridine, and uridine-5‘-monophosphate on MGHA are S-curves ascribed to increasing site capacity with increasing solute concentration. Comparison of the new data for adsorbents GHA and MGHA with data for adsorption of uracil, uridine, and uridine-5‘-monophosphate on compost-derived humic acid (CHA) from part 1 reveals similarities and differences. Nevertheless, linear plots of adsorption enthalpies vs entropies in all detected steps with CHA, GHA, and MGHA as adsorbents indicate that selective adsorption of nucleic acid constituents on different HAs is free energy buffered by similar mechanisms.

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