Conformations and molecular interactions of poly-?-glutamic acid as a soluble microbial product in aqueous solutions.

ABSTRACT: Soluble microbial products (SMPs) are of significant concern in the natural environment and in engineered systems. In this work, poly-?-glutamic acid (?-PGA), which is predominantly produced by Bacillus sp., was investigated in terms of pH-induced conformational changes and molecular interactions in aqueous solutions; accordingly, its sedimentation coefficient distribution and viscosity were also elucidated. Experimental results indicate that pH has a significant impact on the structure and molecular interactions of ?-PGA. The conformation of the ?-PGA acid form (?-PGA-H) is rod-like while that of the ?-PGA sodium form (?-PGA-Na) is sphere-like. The transformation from ?-helix to random coil in the ?-PGA secondary structure is primarily responsible for this shape variation. The intramolecular hydrogen bonds in the ?-PGA-H structure decrease and intramolecular electrostatic repulsion increases as pH increases; however, the sedimentation coefficient distributions of ?-PGA are dependent on intermolecular interactions rather than intramolecular interactions. Concentration has a more substantial effect on intermolecular electrostatic repulsion and chain entanglement at higher pH values. Consequently, the sedimentation coefficient distributions of ?-PGA shift significantly at pH 8.9 from 0.1 to 1.0?g/L, and the viscosity of ?-PGA (5% w/v) significantly increases as pH increases from 2.3 to 6.0.

SUBMITTER: Wang LL 

PROVIDER: S-EPMC5630630 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature