Characterization of Starch Polymorphic Structures Using Vibrational Sum Frequency Generation Spectroscopy

Abstract

The polymorphic structures of starch were characterized with vibrational sum frequency generation (SFG) spectroscopy. The noncentrosymmetry requirement of SFG spectroscopy allows for the detection of the ordered domains without spectral interferences from the amorphous phase and also the distinction of the symmetric elements among crystalline polymorphs. The V-type amylose was SFG-inactive due to the antiparallel packing of single helices in crystal unit cells, whereas the A- and B-type starches showed strong SFG peaks at 2904 cm(-1) and 2952-2968 cm(-1), which were assigned to CH stretching of the axial methine group in the ring and CH2 stretching of the exocyclic CH2OH side group, respectively. The CH2/CH intensity ratios of the A- and B-type starches are significantly different, indicating that the conformation of hydroxymethyl groups in these two polymorphs may be different. Cyclodextrin inclusion complexes were also analyzed as a comparison to the V-type amylose and showed that the head-to-tail and head-to-head stacking patterns of cyclodextrin molecules govern their SFG signals and peak positions. Although the molecular packing is different between V-type amylose and cyclodextrin inclusion complexes, both crystals show the annihilation of SFG signals when the functional group dipoles are arranged pointing in opposite directions.

Comprehensive analysis of cellulose content, crystallinity, and lateral packing in Gossypium hirsutum and Gossypium barbadense cotton fibers using sum frequency generation, infrared and Raman spectroscopy, and X-ray diffraction

“…The 2,904 cm -1 peak does not match the positions of typical primary cell walls (2,920, 2,964 and 3,320 cm -1 ) or secondary cell walls (2,850, 2,944 and 3,320 cm -1 ) Kafle et al 2014b). However the 2,904 cm -1 peak does coincide with the SFG feature of starch (Kong et al 2014). Starch is the main form of glucose storage in plant cells; SFG detected starch in the primary cells of Arabidopsis aerial tissues ).…”

Recreating the synthesis of starch granules in yeast

“…Wide-angle X-ray scattering (WAXS) of purified and dried glucans resulted in a diffraction pattern typical of many starches, where glucan chains form double helices that align with an inter-helical spacing of ~1.6 nm, indicative of a B-type allomorph (Kong et al, 2014; Figure 6D). Small-angle X-ray scattering (SAXS) indicated that the helices were stacked in a weakly ordered lamellar structure with a periodicity of 13.6 nm (Figure 6E), slightly longer than typically reported for plant starches (Pérez and Bertoft, 2010).…”

Effect of short-chain fatty acids on the formation of amylose microparticles by amylosucrase

“…On the other hand, the band at 2900-2950 cm −1 , also seen in all samples, was assigned to CH stretching of the axial methane group in the ring and CH 2 stretching of the exocyclic CH 2 OH side group of the amylose chain. It is interesting to note that the band at 2900-2950 cm −1 for amylose microparticles prepared in the presence of fatty acids was relatively less intense than that prepared in the absence of fatty acids, suggesting that the order of the amylose double helix crystal array was decreased by the presence of the fatty acids (Kong, Lee, Kim, & Ziegler, 2014;Schuster, Ehmoser, Gapes, & Lendl, 2000). However, the representative fatty acid band expected at 1640-1660 cm −1 for an excitation wavelength of 785 nm (Nimz, Gessler, Usón, Sheldrick, & Saenger, 2004) was not observed for any of the amylose microparticles, including those synthesized with fatty acids (Fig.…”