THE FUNDAMENTAL UNIT OF SYNTHETIC MELANIN - A VERIFICATION BY TUNNELING MICROSCOPY OF X-RAY-SCATTERING RESULTS

A characteristic dimension of a melanin protomolecule synthesized from tyrosine has been investigated by scanning tunneling microscopy (STM). Identification of a melanin protomolecule of approximately similar to 20 Angstrom lateral extent and similar to 10 Angstrom height has been established. This size is in good agreement with models constructed to fit wide angle X-ray diffraction experiments on melanin. These protomolecules are believed to consist of Van der Waals interacting stacks of a basic random polymer of 5,6 indolequinone units. There is extensive pi-delocalization within the individual polymeric sheets. Structure minimization and molecular orbital techniques were employed to verify the X-ray and STM results.