MEASURING THE SURFACE CHARGE DENSITY IN DERMATAN SULFATE SUBSTRATES AND OBSERVATIONS OF ITS INFLUENCE IN GROWTH OF CALCITE CRYSTALS

One important problem in biomineralization is the interaction of biological macromolecules with mineral surfaces. The present study investigates the relationship between calcite ionic crystal and the polyanionic oligosaccharide dermatan sulfate (DS), which is present in avian eggshells [1]. To get insight about how DS coordinates on calcite crystal surfaces, template substrates of DS biomolecule were made for calcite nucleation process. First the surface charge density of the substrate is obtained using the microsphere cantilever technique in an atomic force microscope (AFM). Then, the DS substrate surface is activated with CaCl2 0.1M and the crystal growth facilitated by adding a supersaturated salt solution. The most favorable sites for nucleation are those able to adsorbe Ca2+ ions [2]. Thus, the crystal nucleus orientations have a narrow relationship with substrate DS anionic groups. Crystals of macroscopic dimensions are observed by visible light optic microscopy and SEM analysis allows us to measure and recognize the crystal angles to determine their orientations. Experimental Procedures To attach firmly DS molecules to a mica substrate, a 3-aminopropyltrimethoxysilane (APTMS) self-assembled monolayer were made. This molecules binds covalently with silane group to mica surface, and leave their amino groups to the upper end [3]. The amino groups remain positively charged until pH<6, here DS molecules are deposited because of their negative charges at pH>4 To verify the change in the surface of the substrate covered by a molecule (none, APTMS, DS) we faced an amorphous silicon dioxide (glass) microsphere [4] covere