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

2. 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

3. Spectropotentiometric Fitting Software

4. 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

5. Constants Tab
Report species
Report log β values

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

7. Look at speciation at specific pH

8. 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
Fe H2O FeOH H
Fe H2O Fe(OH) H
Fe H2O Fe(OH) H
Fe H2O Fe(OH) H
2 Fe H2O Fe2(OH) H
H2O OH H
A. Stefansson. Environ. Sci. Technol. 2007, 41,

9. HOW SOLUBLE ARE THESE SPECIES?
Thermodynamic Sink
Fe(OH)3 (s) Ksp ~ M
[Fe3+ (aq)] = M

10. Amino Acids

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

12. 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).

13. 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

14. Watson-Crick Model of DNA

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

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