First-Principles Investigation of the Optical Properties of Eumelanin Protomolecules.

Using first-principles calculations, we investigate the absorption spectra (in the near-infrared, visible, and first UV range) of the two most probable eumelanin tetrameric molecules exhibiting either a linear open-chain or a cyclic porphyrine-like configuration. In order to simulate a realistic molecular system, an implicit solvent model is used in our calculations to mimic the effect of the solvated environment around the eumelanin molecule. Although the presence of solvent is found not to significantly affect the absorption pattern of both molecules, the onset of the spectra are shifted toward higher energies, especially for the linear tetramer.

Junctional complex revisited by high-resolution scanning electron microscopy.

The present study correlates the ultrastructural morphology of junctional complexes as revealed by transmission electron microscopy (TEM) with that observed by high-resolution scanning electron microscopy (HRSEM), thanks to a new modification of the osmium tetroxide maceration technique. The removal of all cytoplasmic organelles by this technique allows the inspection of the inner side of the plasmalemma. With this treatment, a continuous band of tightly packed particles is observed at the most apical portion of lateral membranes.