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 t o 20 Angstrom lateral extent and similar to 10 Angstrom height has bee n established. This size is in good agreement with models constructed to fit wide angle X-ray diffraction experiments on melanin. These prot omolecules are believed to consist of Van der Waals interacting stacks of a basic random polymer of 5,6 indolequinone units. There is extens ive pi-delocalization within the individual polymeric sheets. Structur e minimization and molecular orbital techniques were employed to verif y the X-ray and STM results.