Complexes formed by the N-pyruvoylamino acid oximes CH 3 C( NOH)CONHCHRCO 2 H, where R = H, Me, CH 2 Ph or (CH 2 ) 2 SMe, and 2-hydroxyiminopropanoic acid [alanine oxime, CH 3 C( NOH)-CO 2 H] and some derivatives with H + and Cu 2+ have been studied in aqueous solution using a combination of pH-metric titrations, UV/VIS and EPR spectroscopy. The oxime group was able to bind to Cu 2+ through both the N and O donors from about pH 5 upwards with extensive formation of binuclear complexes, which dominated the equilibria in equimolar solutions.

Oxime derivatives of amino acids, amides, and peptides are very efficient ligands for Ni II ions forming very stable water-soluble complexes. Oxime of amino acids amides forms octahedral and square-planar complexes with the same 4N coordination mode. The spectroscopic and Xray diffraction studies indicate an unusual role for the hydrogen bond in NiH −1 L 2 species, which stabilizes the cis coordination of two ligands in a planar complex. Oxime analogs of natural amino acid can be much more efficient ligands than the parent molecules.

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The problem of high fluoride in water sources in Africa and the rest of the developing world has exacerbated in the latest past due to increasing shortage of water. More people are being exposed to high water fluoride resulting in elevated levels of fluorosis in the societies. Fluoride (F) adsorption from solutions using a siliceous mineral from Kenya (M1) was studied on batch basis and results verified on high fluoride water using fixed-bed column experiments. About 100% batch F adsorption was achieved at 200 mg/L F concentration, 0.5 g/mL adsorbent dosage, 303-333 K, and pH 3.4 AE 0.2. Based on Giles classifications, F adsorption isotherm was found to be an H3 type isotherm. The equilibrium data was correlated to Freundlich and Langmuir models and the maximum Langmuir adsorption capacity was found to be 12.4 mg/g. Column experiments were conducted for different fluoride concentrations, bed depths, and flow rates. The F breakthrough curves were analyzed using the Thomas model and efficient F adsorption was found to occur at low flow rates and low influent concentrations. The Thomas F adsorption capacity (11.7 mg/g) was consistent with the Langmuir isotherm capacity showing that M1 could be applied as an inexpensive medium for water defluoridation.

The fate of excessive fluoride in water is cause for serious public health concerns worldwide. Water defluoridation using various technologies therefore continues to attract disproportionate research interest from around the world. Defluoridation studies using soil adsorbents, in particular, have remained the focus of intense research efforts since the last few decades. So as to assess the research status in this area, soil adsorbents commonly reported for water defluoridation over the last few decades were reviewed. This paper presents a compilation of defluoridation capacities and a summary of requisite parameters for water defluoridation using soil adsorbents. Comparison of defluoridation efficiencies of soil adsorbents is also presented, and the fluoride adsorption kinetics and adsorption equilibrium characteristics of adsorbents discussed. The results indicate that the soil adsorbents that have attracted highest research interest in this regard include hydroxyapatites, montmorillonites, hydrotalcite, zeolites, pumice and kaolinites. On average, however, the minerals that have shown the highest capacities for water defluoridation are: ferrihydrites, hydrotalcite, palygorskites, boehmite/bauxite, and pumice. Fluoride adsorption for most soil adsorbents is fitted by the Langmuir and Freundlich isotherms. Most of the kinetic data, in contrast, were described by the pseudo-second-order kinetics model. Water pH and temperature were the dominant solution factors that controlled fluoride adsorption onto soil adsorbents.