Conformation and cooperative order‐disorder transition in aqueous solutions of β‐1,3‐d‐glucan with different degree of branching varied by the Smith degradation

Abstract

β‐1,3‐d‐glucan with different degrees of branching were obtained by selectively and gradually removing side chains from schizophyllan, a water‐soluble triple helical polysaccharide, using the Smith degradation. Size exclusion chromatography combined with a multi‐angle light scattering detection was performed in aqueous 0.1 M NaCl. The degree of branching decreased after the Smith degradation, while the molar mass distributions were almost unchanged. The molecular conformation of the Smith‐degraded β‐1,3‐d‐glucan was analyzed on the basis of the molar mass dependency of the radius gyration, and found to be comparable to the original triple helix of schizophyllan. Differential scanning calorimetry in deuterium oxide–hexadeuterodimethylsulfoxide mixtures was performed to investigate the effects of the degree of branching on the cooperative order‐disorder transition. Removal of side chains affects both the transition temperature and transition enthalpy. The ordered structure is formed by the residual side chains in the triplex unit, so that the linear cooperative system of the triplex is maintained after the Smith degradation.

Association with Imidazole in the Cooperative Order–Disorder Transition in Aqueous Solution of Schizophyllan

“…The theoretical T r curves for N = 114 and N = 57 determined from the peak temperatures of theoretical ΔC s curves, as shown in Figure 8A,B, are represented by the dashed curves in Figure 7A. At the lowtemperature side, the DSC data were affected by the tailing, so that the ΔH r data were underestimated especially at low N. 26,27 This underestimation can be estimated with eq 3 by multiplying ΔH r ∞ by f N (280 K), which is the calculated value of f N at 280 K corresponding to the low-temperature limit of the present DSC measurements. The dashed curves in Figure 6A represent the theoretical ΔH r at N = 114 and N = 57 calculated by f N (280 K) × ΔH r ∞ .…”

“…A strong molar mass dependency has been observed for the transition temperature ( T r ), while the transition enthalpy (Δ H r ) is unchanged by the sample molar mass, similar to the helix-coil transition of polypeptides. Solvent effects of the transition on T r and Δ H r have been observed by exchanging the solvent from H 2 O to D 2 O, , aqueous NaOH, and H 2 O–dimethyl sulfoxide (DMSO) mixtures. , The CODT behavior of aqueous schizophyllan solutions has been analyzed by linear cooperative transition (LCT) theory, and it was concluded that the transition transforms the ordered structure (triple helix I) constructed between the side chains and water molecules at lower temperature into the disordered structure (triple helix II) at higher temperature. − The CODT behaviors for the other analogues of β-1,3- d -glucans with different degrees of branching , and chemically modified schizophyllan derivatives − have been investigated. The dependencies on T r and Δ H r were well reproduced in the same manner as schizophyllan by introducing the reduction of the side chains into theory.…”

Order‐Disorder Transition of Triple Helical β‐1,3‐d‐Glucans in Aqueous Mixtures of Dimethyl Sulfoxide and Imidazole: Schizophyllan and its Chemically Modified Derivatives

“…In addition to the solvent effects, it is needed to control the sample molar mass and the dispersity, because these are sensitive to the CODT behavior. Therefore, we determined T r and Δ H r for sclerox in H 2 O‐DMSO mixtures [ 36 ] and Smith degraded derivative and D 2 O‐DMSO‐d 6 mixtures [ 26 ] from the DSC measurements to investigate the effects of carboxylation and removal of the side chain on CODT in water‐DMSO mixtures.…”

“…In addition to the solvent effects, it is needed to control the sample molar mass and the dispersity, because these are sensitive to the CODT behavior. Therefore, we determined T r and ΔH r for sclerox in H 2 O-DMSO mixtures [36] and Smith degraded derivative and D 2 O-DMSO-d 6 mixtures [26] from the DSC measurements to investigate the effects of carboxylation and removal of the side chain on CODT in water-DMSO mixtures. Figures 9 and 10 show the composition dependencies of T r and ΔH r for schizophyllan, sclerox in H 2 O-DMSO mixtures, and Smith-degraded derivative in D 2 O-DMSO-d 6 mixtures as a function of x. T r and ΔH r data for schizophyllan were increased with increasing x, reflecting a strong affinity between the side chains and DMSO.…”

“…Although the trimer of Smithdegraded derivative has comparable stiffness with schizophyllan triple helix, the sclerox trimer becomes more flexible than those of schizophyllan and Smith-degraded derivatives. [25,26] In this paper, we summarized CODT behaviors of schizophyllan and its derivatives in aqueous solutions synthesized with two different chemical modifications. The linear cooperative transition (LCT) theory was extended for chemically modified derivatives to analyze the molar mass dependencies and the solvent effect in their solutions.…”