Temperature-induced conformational transition in xanthans with partially hydrolyzed side chains

Area of Science:

• Biopolymer Science
• Carbohydrate Chemistry
• Materials Science

Background:

• Xanthan is a microbial polysaccharide with a complex structure, including side chains with terminal beta-mannose.
• The conformational properties of xanthan are critical for its functionality in various applications.
• Understanding xanthan's structural transitions is key to controlling its rheological behavior.

Purpose of the Study:

• To investigate the conformational properties of xanthan variants with partially hydrolyzed side chains.
• To determine the role of terminal beta-mannose and glucuronic acid in xanthan's order-disorder transition.
• To analyze the cooperativity and thermodynamic parameters of xanthan conformational changes.

Main Methods:

• Optical rotation (OR) measurements to assess conformational changes.
• Circular dichroism (CD) spectroscopy to probe secondary structure.
• Differential scanning calorimetry (DSC) to determine transition temperatures and enthalpies.

Main Results:

• Xanthan variants exhibit a temperature-driven order-disorder transition, largely independent of transition temperature on beta-mannose content.
• Up to 80% of optical rotation and transition enthalpy changes are linked to conformational alterations in side chains, particularly terminal beta-mannose.
• Modified side chains affect CD signals, with glucuronic acid being a major determinant; cooperativity increases with beta-mannose content.

Conclusions:

• Terminal beta-mannose plays a significant role in the conformational changes and thermodynamic stability of xanthan.
• The study provides insights into the structural basis of xanthan's properties, relevant for polysaccharide research.
• Current theories like Manning polyelectrolyte theory do not fully explain the observed thermodynamic behavior of xanthan.