Selection of conformational states in self-assembled surface structures formed from an oligo(naphthylene-ethynylene) 3-bit binary switch.

Supra-molecular self-assembly on surfaces often involves molecular conformational flexibility which may act to enrich the variation and complexity of the structures formed. However, systematic and explicit investigations of how molecular conformational states are selected in surface self-assembly processes are relatively scarce. Here, we use a combination of high-resolution scanning tunneling microscopy and Density Functional Theory (DFT) calculations to investigate self-assembly for a custom-designed molecule capable of assuming eight distinct surface conformations (four enantiomeric pairs). The conformations result from binary positions of n = 3 naphtalene units on a linear oligo(naphthylene-ethynylene) backbone. On Au(111), inter-molecular interactions involving carboxyl and bulky tert-butyl-phenyl functional groups induce the molecules to form two ordered phases with brick-wall and lamella structure, respectively. These structures each involve molecules in two conformational states, and there is a clear separation between the conformers involved in the two types of structures. On Cu(111), individual molecules isolated by carboxylate-substrate binding show a distribution involving all possible conformational states. Together these observations imply selection and adaptation of conformational states upon molecular self-assembly. From DFT modeling and statistical analysis of the molecular conformations, the observed selection of conformational states is attributed to steric interaction between the naphthalene units. The present study enhances our understanding of how ordering and selection of molecular conformations is controlled by intermolecular interactions in a complex situation with many distinct conformational states for the participating molecules.

Verruciform xanthoma within carcinoma in situ.

This report describes an unusual case of verruciform xanthoma of the posterior floor of the mouth that occurred within carcinoma in situ. The significance of this case is described in light of current theories on the etiology and management of verruciform xanthoma.

Mycosis fungoides: initial diagnosis via palatal biopsy with discussion of diagnostic advantages of plastic embedding.

The authors present an example of mycosis fungoides which was initially diagnosed from a palatal biopsy. The distinctive nuclear morphology of the tumor cells, with a discussion of their diagnostic importance, is presented. The advantages of plastic-embedded formalin-fixed tissue are delineated.

Palatal erythema: another etiologic factor.

The authors present three cases which created diagnostic problems. The etiology of these is, in the authors' experience, unique and not generally known. It is suggested that this etiology be considered whenever palatal erythema, ecchymoses, or petechiae are seen.