The influence of L-amino acid molecular structure on the phase transition temperature of hydroxypropyl methylcellulose

The influence of molecular structure of small ionised molecules on the thermo-reversible sol:gel phase transition of a hydroxyalkyl cellulose ether has been investigated with respect to an L-amino acid series. The concentration dependency of the phase transition temperature of 1% w/w hydroxypropyl methylcellulose solutions in the presence of different amino acids was studied turbidimetrically. The effects of different amino acids ranged from - 33.54 to + 45.52 degrees C M-1. Correlations between the effect on phase transition temperature and amino acid molecular properties showed the strongest relationships with amino acid hydrophobicity. Small hydrophilic amino acids lowered the transition temperature, whereas large hydrophobic aromatic amino acids increased this temperature. The effect of different amino acids was proposed to be a balance between the ability of their hydrophilic regions to dehydrate and disrupt the polymer hydration sheath, and the ability of their hydrophobic regions to associate with and solubilise the methoxyl-dominated regions of the polymer. (c) 2005 Elsevier Ltd. All rights reserved.