Effect of Sodium Sulfate on the Gelling Behavior of Agarose and Water Structure Inside the Gel Networks

Abstract

Agarose hydrogels which constitute a special class of soft matter are undoubtedly one of the most studied biopolymer gels. However, certain issues such as why the sulfate salts and sulfate content in the agarose molecules reduce the gel strength are still not very clear. The present work provides a detailed analysis of structural changes with respect to coil-helix transition or aggregation of helices in the aqueous agarose solutions and hydrogels that accompanied the systematic addition of sodium sulfate. A combined approach which includes the differential scanning calorimetry and temperature-dependent vacuum-ultraviolet circular dichroism measurements permitted the accurate estimates of the energy changes for coil-helix transition and helix-helix interactions. The hydration process of agarose molecule investigated from differential scanning calorimetry and concentration-dependent ultrasonic measurements indicated the loss of both the freeze bound and nonfreezable water molecules with the increase of sulfate content in the solution. Temperature-dependent fluorescence measurements using pyrene as a probe indicated polarity changes when the gel network is created in waters of different salt concentration. Changes in the hydrogen bonding of the water molecules confined in the gel network have been monitored from the intensity ratios of ice-like and liquid-like -OH stretching band of water Fourier transform infrared (FTIR) spectra. Analysis of the -OH stretching band showed the strengthening of hydrogen bonding of water molecules in the gel which tend to weaken with the subsequent addition of sodium sulfate.

Multifunctional Medicated Lyophilised Wafer Dressing for Effective Chronic Wound Healing

“…This may be due to the effect of added drug which decreased the porosity (SEM data) as well as the formation of sodium sulphate which decreased the swelling capacity of wafers. Singh et al reported the effect of sodium sulphate on gels of the polysaccharide, agarose. They showed that the hydration capacity of agarose polysaccharide decreased with increasing concentration of sodium sulphate which is associated with strong hydrophobic hydration of the highly osmotropic sodium sulphate .…”

“…Singh et al reported the effect of sodium sulphate on gels of the polysaccharide, agarose. They showed that the hydration capacity of agarose polysaccharide decreased with increasing concentration of sodium sulphate which is associated with strong hydrophobic hydration of the highly osmotropic sodium sulphate . The presence of sodium sulphate formed in the polymeric gels (POL–CAR and POL–SA) appears to be behaving in the same manner to reduce the swelling capacity of the DL wafers compared with the BLK wafers.…”

Specific ion effects in polysaccharide dispersions

“…The increase in the viscosity upon addition of salting-out salts is explained in terms of (i) the modification of the water structure or (ii) by the change in the interactions between the ions and specific sites on the polymer chains (Yin, Zhang, Huang, & , 2008). Finally, Singh investigated the gelling behaviour of agarose with Na 2 SO 4 , and found that the release of water from the gel is due to the water withdrawing action of sulfate ions (Singh, Meena, & Kumar, 2009).…”

Preparation and functional evaluation of agarose derivatives

“…Anionic polymers are widely used to add coagulation, curtailing water production in oil wells, release of chemicals, and water purification . Gelation of Ag depends on several factors such as concentration, thermal hysteresis, presence of heavy metals, ions, and ionic strength of the solution …”