Influence of pH, Ionic Strength, and Temperature on Self-Association and Interactions of Sodium Dodecyl Sulfate in the Absence and Presence of Chitosan

Abstract

Chitosan is a cationic biopolymer that has many potential applications in the food industry because of its unique nutritional and physicochemical properties. Many of these properties depend on its ability to interact with anionic surface-active molecules, such as surfactants, phospholipids, and bile acids. The purpose of this study was to examine the influence of pH (3 and 7), ionic strength (0-200 mM NaCl), and temperature (10-50 degrees C) on the interactions between a model anionic surfactant (sodium dodecyl sulfate, SDS) and chitosan using isothermal titration calorimetry, selective surfactant electrode, and turbidity measurements. At pH 3 and 30 degrees C, SDS bound strongly to chitosan to form an insoluble complex that contained about 4-5 mmol of SDS/1 g of chitosan at saturation. When SDS and chitosan were mixed at pH 7 they did not interact strongly, presumably because the biopolymer had lost most of its positive charge at this pH. However, when SDS and chitosan were mixed at pH 3 and then the solution was adjusted to pH 7, the SDS remained bound to the chitosan. The presence of NaCl (0-200 mM) in the solutions decreased the critical micelle concentration (cmc) of SDS (in both the absence and the presence of chitosan) but had little influence on the amount of SDS bound to chitosan at saturation. The cmc of SDS and the amount of SDS bound to the chitosan at saturation were largely independent of the holding temperature (10-40 degrees C). Nevertheless, the enthalpy changes associated with micelle dissociation were highly temperature-dependent, indicating the importance of hydrophobic interactions, whereas the enthalpy changes associated with SDS-chitosan binding were almost temperature-independent, indicating the dominant contribution of electrostatic interactions. This study provides information that may lead to the rational design of chitosan-based ingredients or products with specific nutritional and functional characteristics, for example, cholesterol lowering.

Novel targeting using nanoparticles: an approach to the development of an effective anti-leishmanial drug-delivery system

“…Cs possesses a pKa of near 6.5, with a maximum of one charge per residue. 26 The apparent dissociation constant of ChS has been estimated to be from 4.4 to 4.5. 51 Therefore, to formulate an effective nanoparticle combining Cs and ChS, it is necessary to create an electrostatic interaction between Cs cations and ChS anions, in which the positively charged amino groups of Cs interact with the negatively charged sulfate groups of ChS.…”

“…25 Cs has an intrinsic pKa near 6.5 with a maximum of one positive charge per residue. 26 "ChS" is a glycosaminoglycan present in the extracellular matrix of cartilage that is used in the treatment of osteoarthritis and demonstrates an anti-inflammatory activity. [27][28][29] ChS is also a component of the dermal layer of the US Food and Drug Administration-approved skin substitute, 30 commonly used to enhance re-epithelialization without causing scarring.…”

Chitosan Enhances the In Vitro Surface Activity of Dilute Lung Surfactant Preparations and Resists Albumin-Induced Inactivation

“…It was also reported that the binding between chitosan and anionic surfactants in acidic conditions is irreversible, i.e. after rising to neutral pH, they remain bound (35). This minimizes the risk that chitosan 128 nonspecifically binds to other surfaces (e.g.…”

New delivery systems for amphotericin B applied to the improvement of leishmaniasis treatment

“…Chitosan has an intrinsic pKa near 6.5, with a maximum net positive charge of one per residue (54) . Chondroitin sulfates are glycosaminoglycans that are present in the extracellular matrix of cartilage, and they are used for the treatment of osteoarthritis and for their anti-infl ammatory activity (55) .…”