DeLanson R. Crist

Interactions of metals and protons with algae

Proton uptake by intact algal cells was found to consist of two processes: (1) a fast (<4 s) surface reaction and (2) a slow (2h) diffusion of protons into cells. A pH titration technique measured only the rapid surface reaction that forms negative sites at higher pH. Adsorption of alkali, alkaline earth, and transition metal ions on algae was quantitatively represented by the Langmuir adsorption isotherm with its two parameters y/sub m/, the maximum amount of metal adsorbed, and K, the equilibrium constant taken as a measure of bond strength. Variations of these parameters with pH and type of metal indicate that metals adsorb to algal surfaces by electrostatic attraction to negative sites, such as carboxylate anions of poly(galaturonic acid) (pectin), as previously suggested.

Use of a novel formulation of kraft lignin for toxic metal removal from process waters

Abstract Kraft lignin, a by‐product in paper production, was converted to a material with high potential for applications in removing toxic metals from process waters. The acid form of kraft lignin in powder form was first converted to Ca‐loaded material by treatment with various amounts of calcium hydroxide and then to a hard solid by combination with a resin in dimethylformamide (DMF) and heating. Strips of these lignin products (LP) were effective in removing Pb and Cd from solutions, with a Pb capacity of ca. 350 µmol/g. One mole of Ca was released to solution for each mole of Pb sorbed, thereby demonstrating that metal uptake was an ion exchange process and not simple adsorption. Advantages to these LP are that 1) they are reuseable with no loss in Pb uptake after eight cycles of uptake/regeneration, 2) their high structural stability is maintained even after immersion in water for 6 weeks, and 3) the DMF used in their preparation can be recovered and recycled.

Ion-Exchange Aspects of Toxic Metal Uptake by Indian Mustard

ABSTRACT Uptake of lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd) as +2 ions by excised roots of Indian mustard was demonstrated to be an ion-exchange process with existing Ca or protons released to the solution. This initial reaction at the root-aqueous interface is important in the uptake of these toxic metals from contaminated soil. Ethylene diamine tetraacetic acid (EDTA)-amended soil for phytoremediation has Pb in anionic form as [Pb-EDTA]2 −, which was not taken up by excised roots. In nonliving B. juncea, Pb2+ was translocated from a solution through a cut stem to petiole and leaves much more quickly than anionic [Pb-EDTA]2 −. However, in living plants [Pb-EDTA]2 − was more quickly translocated from a solution through roots and petiole to leaves than Pb2+. The final amount of uptake on roots of the living plants was the same for both forms of Pb. The present results are important toward understanding the mechanism of phytoremediation of toxic metal-contaminated soil for two reasons: 1) the initial process, uptake of metal ions by roots, was shown to occur by cation exchange and 2) since [Pb-EDTA]2 − was not sorbed by excised roots, other factors such as transpiration and active transport are important in applications using EDTA-amended soils contaminated by Pb.

Cyclic voltammetry of metal complexes of nitrones and nitroxides

Abstract Increasing interest in radicals bound to metals led to the present study of electron transfer to and from metal nitrone complexes and metal nitroxides. These are species involved in biological spin trapping and materials science applications, respectively. Cyclic voltammetry was used to study the redox behavior of complexes of the bidentate N - tert -butyl-α-(2-pyridyl)nitrone (2-PyBN) and the monodentate nitrone 2,5,5-trimethyl-1-pyrroline- N -oxide (M 3 PO) with metal hexafluoroacetylacetonates M(hfac) 2 in CH 2 Cl 2 . Bidentate complexes M(2-PyBN)(hfac) 2 with M=Mn II and Co II were easier to oxidize in CH 2 Cl 2 (less positive E pa ) than the corresponding M(hfac) 2 and harder to reduce (more negative E pc ). In MeCN, this behavior was also observed for M=Co II and Ni II which indicate more facile oxidation when M 3 PO is present as co-ligand compared with M(hfac) 2 alone. CVs of M(2-PyBN)(hfac) 2 and [M(M 3 PO)(hfac) 2 ] 2 in MeCN gave common reduction peaks due to hfac. Nitroxides (aminoxyls) 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrroline-1-oxyl (CPNO) gave quasi-reversible oxidations to oxoammonium cations, while N - tert -butyl-(2-pyridyl)phenylmethanaminoxyl (2-PyBNO) showed only irreversible oxidations. CV of solutions of CPNO in the presence of M(hfac) 2 , where M is Mn II , Co II , or Ni II , indicated formation of metal–nitroxide complexes for Co II and Ni II . For stable metal nitroxides prepared independently, the CV of Mn(TEMPO) 2 (hfac) 2 showed dissociation to free nitroxide and Mn(hfac) 2 in CH 2 Cl 2 , while M(2-PyBNO)(hfac) 2 gave distinctive CVs for M=Mn II , Co II , and Ni II .