The Importance of Metal Aqueous Speciation D.C. Crans et al. Inorg. Chem. 2013, 52, 12262 DOI: 10.1021/ic4007873 Prof. Arthur D. Tinoco University of Puerto Rico, Rio Piedras Campus Chemistry 8990(013)

The Color Wheel The color of most things depends on the interaction of visible light and the electrons of its atoms or molecules. Objects absorb certain wavelengths of white light The color that we see is the wavelength of white light that is reflected. The reflected color is the complementary color. 580 nm 560 nm Reflect here 490 nm 650 nm Absorb here 750 nm 430 nm 400 nm

Spectropotentiometric Fitting Software

Aqueous Speciation Data Viewer Click on Species 2. Speciation Window Opens Reactants Tab Define metal and ligand(s) How to add your species Must specify the concentrations

Constants Tab Report species Report log β values

Click on pH Click on pH range Click on metal or ligand Click on calculate

Look at speciation at specific pH

Fe3+ Hydrolysis Constants Water as an “invisible” ligand. Note: All binding processes and proton losses/gains are relative to strength of water binding. log β M H Fe3+ + H2O FeOH2+ + H+ -2.19 1 -1 Fe3+ + 2 H2O Fe(OH)2+ + 2 H+ -5.76 1 -2 Fe3+ + 3 H2O Fe(OH)3 + 3 H+ -14.30 1 -3 Fe3+ + 4 H2O Fe(OH)4- + 4 H+ -21.71 1 -4 2 Fe3+ + 2 H2O Fe2(OH)24+ + 2 H+ -2.92 2 -2 H2O OH- + H+ -14.00 0 -1 A. Stefansson. Environ. Sci. Technol. 2007, 41, 6117-6123

HOW SOLUBLE ARE THESE SPECIES? Thermodynamic Sink Fe(OH)3 (s) Ksp ~ 10-38 M [Fe3+ (aq)] = 10-17 M

Amino Acids

Typical Amino Acid Coordination Amino acids: Can bind protonated or deprotonated but usually deprotonated Can bridge metals Binding preference based on HSAB theory

Metal-Protein Binding Heme: Porphyrin Ligand Covalent bond with His residue Myoglobin shows an example of metal binding (Fe2+) in two forms: As a complex (the heme group) Covalent bonding to a protein residue (His).

Influencing Metal-Amino Acid Coordination in Proteins Fe Heme group H Bond His175 in cytochrome c peroxidase gains a partial anionic character via a Hydrogen bond interaction with the carboxylate of Asp235

Watson-Crick Model of DNA

Metal-DNA Bonds Binding to DNA phosphates Binding to DNA bases i.e. Cisplatin (anticancer drug) DNA adduct

Metal Complex DNA Intercalation Via hydrophobic ligands, metal complexes can insert into the hydrophobic grooves of DNA.