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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. [ABSTRACT FROM AUTHOR]

The molecular origins of second order nonlinear optical properties in proteins structures identified by sum-frequency vibrational spectroscopy are discussed. Noncentrosymmetry, existing at a molecular level, is translated to a macroscopic scale through non-covalent intermolecular interactions. In an alpha-helix hydrogen bonds align C=O and N--H groups parallel to a main axis. In contrast, in a collagen triple helix hydrogen bonds align C=O and N--H groups almost perpendicular to a main axis. The hydrogen bonds create a helical ladder. The effect of these unipolar and helical alignments on the second order nonlinearity is to produce achiral and chiral contributions, respectively. In the collagen triple helix, there is also an achiral contribution caused by methylene molecular groups. [ABSTRACT FROM AUTHOR]