Chromophore orientation and the formation of surface reliefs in azobenzene side-chain polymers

The occurrence of surface relief gratings in azobenzene polymers under illumination with two superimposed laser beams is a puzzling effect which was discovered only few years ago. The origin of the large mass transport which occurs far below the glass transition temperature is not yet understood. We have performed experiments with cw holography. Due to low laser fluence, thermal effects can mostly be neglected. We have studied the relation between the light induced orientation of the chromophores in the bulk of the material and the observed surface relief gratings. We have performed a number of studies: Surface relief gratings were characterized under different polarization geometries of the writing beams, furthermore the grating period was varied. We could show that there is a competing behavior between the diffraction efficiencies by the volume grating and the surface relief, respectively. In order to analyze the orientational distribution function of the azobenzene chromophores, we have performed confocal Raman microspectroscopy in different regions of the surface relief grating. Our results are not in agreement with the current theories for the formation of surface reliefs

Hydroxyapatite Growth Inhibition Effect of Pellicle Statherin Peptides

In our recent studies, we have shown that in vivo–acquired enamel pellicle is a sophisticated biological structure containing a significant portion of naturally occurring salivary peptides. From a functional aspect, the identification of peptides in the acquired enamel pellicle is of interest because many salivary proteins exhibit functional domains that maintain the activities of the native protein. Among the in vivo–acquired enamel pellicle peptides that have been newly identified, 5 peptides are derived from statherin. Here, we assessed the ability of these statherin pellicle peptides to inhibit hydroxyapatite crystal growth. In addition, atomistic molecular dynamics (MD) simulations were performed to better understand the underlying physical mechanisms of hydroxyapatite growth inhibition. A microplate colorimetric assay was used to quantify hydroxyapatite growth. Statherin protein, 5 statherin-derived peptides, and a peptide lacking phosphate at residues 2 and 3 were analyzed. Statherin peptide phosphorylated on residues 2 and 3 indicated a significant inhibitory effect when compared with the 5 other peptides (P < 0.05). MD simulations showed a strong affinity and fast adsorption to hydroxyapatite for phosphopeptides, whereas unphosphorylated peptides interacted weakly with the hydroxyapatite. Our data suggest that the presence of a covalently linked phosphate group (at residues 2 and 3) in statherin peptides modulates the effect of hydroxyapatite growth inhibition. This study provides a mechanism to account for the composition and function of acquired enamel pellicle statherin peptides that will contribute as a base for the development of biologically stable and functional synthetic peptides for therapeutic use against dental caries and/or periodontal disease