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1.  Melanin-Based Coatings as Lead-Binding Agents 
Interactions between metal ions and different forms of melanin play significant roles in melanin biochemistry. The binding properties of natural melanin and related synthetic materials can be exploited for nonbiological applications, potentially including water purification. A method for investigating metal ion-melanin interactions on solid support is described, with lead as the initial target. 2.5 cm discs of the hydrophobic polymer PVDF were coated with synthetic eumelanin from the tyrosinase-catalyzed polymerization of L-dopa, and with melanin extracted from human hair. Lead (Pb2+) binding was quantified by atomic absorption spectroscopy (flame mode), and the data was well fit by the Langmuir model. Langmuir affinities ranged from 3.4 · 103 to 2.2 · 104 M−1. At the maximum capacity observed, the synthetic eumelanin coating bound ~9% of its mass in lead. Binding of copper (Cu2+), zinc (Zn2+), and cadmium (Cd2+) to the synthetic-eumelanin-coated discs was also investigated. Under the conditions tested, the Langmuir affinities for Zn2+, Cd2+, and Cu2+ were 35%, 53%, and 77%, respectively, of the Langmuir affinity for Pb2+. The synthetic-eumelanin-coated discs have a slightly higher capacity for Cu2+ on a per mole basis than for Pb2+, and lower capacities for Cd2+ and Zn2+. The system described can be used to address biological questions and potentially be applied toward melanin-based water purification.
PMCID: PMC3350951  PMID: 22611345
2.  Multivalent Interactions Between Lectins and Supramolecular Complexes: Galectin-1 and Self-Assembled Pseudopolyrotaxanes 
Chemistry & biology  2007;14(10):1140-1151.
Supramolecular chemistry has been employed to develop flexible and adaptable multivalent neoglycoconjugates for binding galectin-1 (Gal-1). Gal-1, a dimeric lectin with two galactoside-binding sites, regulates cancer progression and immune responses. Self-assembled pseudopolyrotaxanes comprised of lactoside-displaying cyclodextrin (LCD) “beads” threaded onto polyviologen “strings,” display mobile ligands as a result of cyclodextrin rotation about, and limited translation along, the polymer chain. The pseudopolyrotaxanes rapidly and efficiently precipitate Gal-1 and provide valency-corrected enhancements of up to 30-fold over native lactose and 20-fold over free LCD in a T-cell agglutination assay. A supramolecular stastical effect was observed, wherein the efficacy of Gal-1 inhibition correlates with the number of ligands connected to each other solely through mechanical and noncovalent interactions. Such flexible and adaptable self-assembled pseudopolyrotaxanes show promise for the study of multivalent interactions and targeting of therapeutically relevant lectins.
PMCID: PMC2072908  PMID: 17961826
3.  Completion of a Programmable DNA-Binding Small Molecule Library 
Tetrahedron  2007;63(27):6146-6151.
Hairpin pyrrole-imidazole (Py-Im) polyamides are programmable oligomers that bind the DNA minor groove in a sequence-specific manner with affinities comparable to those of natural DNA-binding proteins. These cell-permeable small molecules have been shown to enter the nuclei of live cells and downregulate endogenous gene expression. We complete here a library of 27 hairpin Py-Im polyamides which bind 7-base-pair sequences of the general form 5′-WWGNNNW-3′ (where W = A or T, N = W, G, or C). Their equilibrium association constants (Ka) range from Ka = 1×108 M−1 to 4×1010 M−1 with good sequence specificity. A table of binding affinities and sequence contexts for this completed 27-member library has been assembled for the benefit of the chemical biology community interested in molecular control of transcription.
PMCID: PMC2151752  PMID: 18596841
molecular recognition; gene regulation; polyamide; small molecule-nucleic acid interaction

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