Parametric Nonlinearity in Plant Polysaccharides: A New Harvest
Karen Reiser and Andre Knoesen
The supramolecular organization of the two major plant polysaccharides, glucose and starch, remains poorly understood, despite decades of investigation. Almost all recent advances in the field have relied on methods requiring crystalline samples; as a consequence, relatively little is known about the so-called amorphous regions of either cellulose or starch, or the relationship between crystalline and noncrystalline regions. Parametric nonlinear optical properties such as second harmonic generation, sum frequency generation vibrational spectroscopy, and third harmonic generation are ideally suited for studying both crystalline and amorphous regions in intact samples. In this paper we review the nonlinear optical properties of cellulose and starch in the context of their molecular and supramolecular structure.We speculate on specific questions that could be addressed with this approach, and how they might contribute to a better understanding of common structural themes in biological macromolecules.
Keywords: Second harmonic generation, nonlinear optics, biopolymers, cellulose, starch