MOLECULAR RESOLUTION OF POLYSACCHARIDES BY SCANNING TUNNELING MICROSCOPY

Scanning tunneling microscopy has been used to obtain images in constant current mode in air at molecular resolution of the polysaccharides: cellulose azure, hydroxypropylcellulose (hpc), and xanthan. The molecules were deposited from solution onto a graphite substrate. The hpc samples were observed to form readily ordered molecular arrays on the substrate. The molecular dimensions of width and repeat distance along the molecule were found to be close to values previously determined by x-ray diffraction. The observed axial periodicity of 2 nm for xanthan is close to that expected for a double-helix molecule.