Department of Biological Sciences, University of Huddersfield, Huddersfield HD1 3DH, UK.
School of Applied Sciences, RMIT University, City Campus, Melbourne 3001, VIC, Australia.
Carbohydr Polym. 2015;127:182-8. doi: 10.1016/j.carbpol.2015.03.051. Epub 2015 Mar 30.
The influence of pH on the mechanical relaxation of LM-pectin in the presence of co-solute has been investigated by means of differential scanning calorimetry, ζ-potential measurements and small deformation dynamic oscillation in shear. pH was found to affect the conformational properties of the polyelectrolyte altering its structural behavior. Cooling scans in the vicinity of the glass transition region revealed a remarkable change in the viscoelastic functions as the polyelectrolyte rearranges from extended (neutral pH) to compact conformations (acidic pH). This conformational rearrangement was experimentally observed to result in early vitrification at neutral pH values where dissociation of galacturonic acid residues takes place. Time-temperature superposition of the mechanical shift factors and theoretical modeling utilizing WLF kinetics confirmed the accelerated kinetics of glass transition in the extended pectin conformation at neutral pH. Determination of the relaxation spectra of the samples using spectral analysis of the master curves revealed that the relaxation of macromolecules occurs within ∼ 0.1s regardless of the solvent pH.
通过差示扫描量热法、ζ 电位测量和小变形动态剪切振荡研究了 co-solute 存在下 pH 值对 LM-pectin 机械松弛的影响。发现 pH 值会影响聚电解质的构象特性，从而改变其结构行为。在玻璃化转变区域附近的冷却扫描中，由于聚电解质从伸展（中性 pH）到紧凑构象（酸性 pH）的重新排列，发现粘弹性函数发生了显著变化。实验观察到这种构象重排导致在中性 pH 值下发生早期玻璃化，此时半乳糖醛酸残基发生解离。机械移动因子的时-温叠加和利用 WLF 动力学的理论建模证实了中性 pH 值下伸展果胶构象中玻璃化转变的加速动力学。使用主曲线的谱分析确定样品的弛豫谱表明，无论溶剂 pH 值如何，大分子的弛豫都在 0.1s 内发生。
