Research in the Simon Group

Our research program currently has two major foci: the structure and function of human pigments, with an emphasis on the melanins present in the human brain, and the application of photoelectron emission microsopy (PEEM) to the study of biological and nanoscale materials.

Melanin refers to a range of biological pigments found in a variety of tissues including the hair, skin, eyes, brain, and inner ear. Melanins are commonly divided into two types: the brown-black eumelanins, and the yellow-reddish pheomelanins. These two melanins are distinguished by differences in their molecular precursors. Eumelanins are composed of indolic units derived from the oxidation of tyrosine. Pheomelanins are composed of benzothiazines derived from the oxidation of cysteinyldopa units. Despite significant research efforts, the current understanding of the molecular structure of melanins, the assembly of the pigment within its organelle, and the structural consequences of the association of melanins with protein and metal cations is limited. Likewise, a detailed understanding of the photochemical and photophysical properties of melanins has remained elusive. Our group has used a variety of optical spectroscpies and imaging microscopies to examine the structure, photochemical behavior, lipid composition and metal binding properties of natural melanosomes.

Our group has pioneered the application of Free-Electron Laser Photoelectron Emission Microscopy (FEL-PEEM) to the study of human pigments. Using the tunable output of the Duke OK-4 FEL, we have been able to quantify the photoionization thesholds of melanosomes isolated from human eyes midbrain. The results from these studies have impacted out understanding of the structural morphology of human neuromelanins and the potential role of different pigments in the epidemiology of skin cancers.