About the native and renatured conformation of xanthan exopolysaccharide

Thermal Denaturation, Renaturation, and Aggregation of a Double-Helical Polysaccharide Xanthan in Aqueous Solution

“…Figure 4 shows molar mass distributions for renatured sample S14 under the different conditions, obtained by SEC-MALS, where wðMÞ is the weight fraction density of the xanthan component with the molar mass M. In the figure, the solid and broken curves, respectively, indicate the distribution of the native sample S14 and that after dissociation to the unimers which obtained by shifting the solid curve along the log M axis by À log 2. Distributions of the renatured sample in the solutions 1 and 2 (c r ¼ 0:1 or 1.0 mg/cm 3 , C s ¼ 0:01 M; unfilled circles and triangles) are close to the broken curve, indicating that the xanthan exists almost as the dissociated unimer in the solutions, as reported by Capron et al 8 For the renatured sample in the solution 3 (c r ¼ 1:0 mg/cm 3 , C s ¼ 0:1 M; filled circles), the distribution shifts to higher M region, demonstrating that dissociated unimer chains aggregate by the addition of salt into the denatured solution. This result of wðMÞ for the solution 3 is consistent with Kawakami et al 7 result that the average molar mass of xanthan renatured at C s ¼ 0:1 M was between those of dimer and unimer.…”

“…Data points for the solutions 1 and 2 (unfilled circles and triangles) obey the solid curve fitted to the native xanthan data, which indicates the recovery of the double-helical conformation in the solutions. However, xanthan in the solutions 1 and 2 exists as the unimer, as demonstrated in Figure 4, so that the double helix must be constructed by the single chain with a hairpin loop, as proposed by Capron et al 8 Okuyama et al 16 reported the possible antiparallel arrangement of xanthan chains in the native double helix, which supports that the single xanthan chain can form the double helical structure in the anti-parallel manner.…”

“…On the other hand, Oviatt and Brant 2 and also Capron et al 8 denatured xanthan in 0.1 M aqueous NaCl upon heating above 110 C and renatured it by quenching at 25 C. The latter research group studied the renatured xanthan mainly by lowangle light scattering and viscometry, and concluded that the xanthan dimer dissociates into two single chains above 110 C and the renatured xanthan unimer takes the double helical structure with a hairpin loop at the renaturation concentration as low as 1 mg/cm 3 . On the other hand, Oviatt and Brant 2 investigated xanthan renatured at higher concentration (10-30 mg/cm 3 ) by viscoelastic measurements, and found viscosity enhancement of xanthan solutions after renaturation, which indicates the formation of large aggregates of xanthan chains.…”

Electrostatic self-assembly of polysaccharides into nanofibers

“…It is know that xanthan assumes an ordered state at specific temperatures and salt concentrations [8,9,[23][24][25]. Optical rotation measurements ([ ]436) conducted on xanthan solutions at different NaCl concentrations (0-100 mM), confirmed that xanthan dissolved in water at 25 °C assumed the non-ordered conformation, while in NaCl 15 mM it appeared in the ordered state (Fig.…”

Single Molecules and Networks of Xanthan Gum Probed by Atomic Force Microscopy

“…Samples were scanned in air at a scan rate of 0.5 − 1 Hz using a beam-shaped silicon cantilever, the nominal spring constant and resonance frequency of which were given as with a single-stranded hairpin loop at one end in dilute conditions (Capron et al, 1997). The presence of an intra-molecularly associated anti-parallel double-stranded helix with a single-stranded loop is evident in Fig.…”