Ricerc@Sapienza

The effects that an increase of environmental pH has on the triple helix of scleroglucan (Sclg)
and on the Sclg/borax hydrogel are reported. Rheological experiments show that the hydrogel is less
sensitive to pH increase than Sclg alone, while at pH = 14 a dramatic viscosity decrease takes place for
both systems. This effect is evidenced also by the reduced water uptake and anisotropic elongation
detected, at pH = 14, by the swelling behaviour of tablets prepared with the Sclg/borax system.
On the opposite, a different behaviour was observed with guar gum and locust bean gum tablets,
tested as reference polysaccharides. The effect of pH on the structure of Sclg and Sclg/borax was
investigated also by means of spectroscopic approaches based on the interaction between Congo red
(CR) and the Sclg triple helix. Obtained results indicated that the CR absorbance maximum is shifted
as a function of pH and by the presence of borax. Principal component analysis allowed very precise
identification of the pH value at which the Sclg helix collapses. Molecular dynamics simulations of
the Sclg/borax–CR complex indicated that, at physiological pH, only a few ordered configurations
are populated, according to the induced circular dichroism (CD) spectrum evidence.