KSEF RDE: Arsenite Removal from Water with Magnetic Nanoparticles Functionalized with Oxidation-Resistant Sulfhydryls

The proposed research will explore a potential new class of molecular compounds that are chemically and structurally similar to the highly conserved biological metal binding site containing two cysteine groups, Cys-X-X-Cys. The first member of this new compound class is N, N'-bis(2 mercaptoethyl)isophthalamide), known commonly as "B9" and demonstrated to have an exceptionally high affinity for Cd, Hg, and Pb. B9 incorporates two cysteamine groups within a rigid aryl framework and thiols (S-H) for covalent metal bonding. Compared to other synthetic thiols, B9 has unique, critically important properties that make it an ideal system for studying covalent heavy metal bonding and water treatment applications: a) similarity to the ubiquitous biological metal binding unit, Cys-X-X-Cys, b) resistance to oxidation and no disulfide formation, c) absence of smell, d) formation of neutral, non-polar, covalent M-S bonding, e) absolute insolubility in water and organic solvents, f) immediate precipitation of Cd, Hg, Pb products, and g) resistance to metal release or decomposition through a wide pH range. The proposed research would seek to understand the unusual properties of B9 in anticipation that the properties extend to related compounds. Three new targeted compounds will be created by replacing the cysteamine groups within B9 with L-cysteine (to form "AB9") and L-cysteine alkyl esters (to form "MB9" and "EB9"). The four sulfhydryl ligands will have slightly different inductive influences on the CH2CH2SH binding units and different solubility characteristics but each will maintain the strong similarity to the Cys-X-X-Cys biological metal binding unit. The putative compounds, AB9-M and AB9-As(OH), are anticipated to be soluble in some form of aqueous solution, such that characterization information, ideally including crystal structures, will provide unique insight into M-S and As-S covalent bonding under conditions relevant to natural systems. The cysteine ester compounds, "MB9" and "EB9", are expected to have sufficient solubility in one or more common organic solvents so that the Cd, Hg, Pb, and As(III) may be fully characterized to provide new fundamental information about the M-S bonding; this would include crystal structures. The combination of AB9, MB9, and EB9 with Cd, Hg, and Pb, would produce nine new soft metal compounds with varying degrees of inductive effects (e.g., AB9 carboxylate vs MB9 methyl ester) and hydrophilicity.