Influence Of Cyclodextrin On The Interaction Of Ionic Surfactants With Bovine Serum Albumin

Proteins and surfactants coexist in physiological systems; in cosmetics, foods, pharmaceuticals, and detergents; and in bioseparation and enzymatic processing applications. As a result, physicochemical interactions between surfactants and proteins have attracted considerable interest from the research community. The ability to control the protein-surfactant interaction would lead to optimization of the design and operation of processing technologies used to manufacture protein-containing materials. It is well-known that cyclodextrin's relatively non-polar cavities are capable of accommodating a variety of surfactant molecules to form inclusion complexes. The cyclodextrin thus offers the potential of modulating the protein-surfactant interaction. Therefore, in our work, the bovine serum albumin (BSA)-surfactants interactions modulated by the cyclodextrin have been deeply studied mainly by isothermal titration calorimetry (ITC) and fluorescence spectra measurements. The results will broaden the application range of the protein-surfactant-cyclodextrin ternary system in practice. The following are some main results from our work:1. The influence of the cyclodextrin on the interaction between BSA and the typical anionic surfactant sodium dodecyl sulfate (SDS) was investigated using mainly fluorescence spectra and isothermal titration calorimetry. Below very low SDS concentration c1, SDS molecules bind to specific high offinity sites on the protein by hydrophobic interaction modulated by electrostatic nature; above c1, SDS binding on BSA is associated to non cooperative interactions; above the critical aggregation concentration (cac), a massive increase in binding due to cooperative ligand interactions through hydrophobic interaction takes place. In the presence ofβ-CD, as the size ofβ-CD non-polar cavity has a poor match with the hydrophobic chain of SDS and with a low binding constant, There's a more strong specific binding between SDS and the BSA molecules and therefore, the high affinity interaction between the BSA and SDS has not been inhibited, only lead a slight increase to c1.However, the interaction between the non-polar cavity ofβ-cyclodextrin with hydrophobic chain of SDS molecular will obviously inhibit the non-specific binding between the BSA and SDS. Under the condition of different pH, the the effect ofβ-cyclodextrin to the interaction between BSA and SDS show that the strong special binding between BSA and SDS is not mainly caused by the electrostatic binding but by the combination of electrostatic and hydrophobic interaction between SDS and the special sites of BSA .However, the addition ofα-cyclodextrin can lead to an obvious increase in both c1 and cac, which indicates that the special and non-special interactions between BSA and SDS have both been hindered effectively. The behavior is caused by the higher association constant betweenα-cyclodextrin and SDS. Thus, it seems that the presence of theα-cyclodextrin can be a stronger tool to modulating the interaction between BSA and SDS surfactant.2. The influence of the cyclodextrin on the interaction between BSA and the typical anionic surfactant sodium dodecyl benzensulfonate (SDBS) was investigated using mainly fluorescence spectra and isothermal titration calorimetry. Below very low SDBS concentration c1, SDBS molecules bind to specific high energy sites on the protein by hydrophobic interaction modulated by electrostatic nature; above c1, SDBS binding on BSA is associated to non cooperative interactions; above the critical aggregation concentration (cac), a massive increase in binding due to cooperative ligand interactions through hydrophobic interaction takes place.In the presence ofβ-CD, on the one hand, the size ofβ-CD non-polar cavity has a good match with the hydrophobic chain of SDBS molecular and with a high binding constant, on the other hand, the specific binding interaction between BSA and SDBS molecular is weak because of the benzene ring in SDBS molecular. thus, the specificial interaction between the BSA and SDBS has been inhibited, lead a more effectively increase to c1.Under the condition of different pH ,the result of modulation whichβ-cyclodextrin to the interaction between BSA and SDS show that the strong special binding between BSA and SDBS comes from the combination of electrostatic and hydrophobic interaction between SDBS and the special sites of BSA .However, the addition ofα-cyclodextrin can not lead to an obvious increase in both c1 , which indicates that the special high affinity interactions between BSA and SDBS have not been hindered effectively. The behavior is caused by the low association constant betweenα-cyclodextrin and SDBS.3 The influence of the cyclodextrin on the interaction between BSA and the typical cationic surfactant cetyltrimethyl ammonium bromide (CTAB) was investigated using mainly fluorescence spectra and isothermal titration calorimetry. There are also special binding and non-special binding interaction between CTAB and BSA. In the presence ofβ-CD, on the one hand, the size ofβ-CD non-polar cavity has a good match with the long hydrophobic chain of CTAB molecular and with a high binding constant, on the other hand, compared with CTAB the specific binding interaction between BSA and CTAB molecular is weak .thus, the special interaction between the BSA and CTAB has been inhibited, leading an obviously increase to c1. However, the addition ofα-cyclodextrin can hinder the special interaction between BSA and CTAB more effectively, which is caused by the low association constant betweenα-cyclodextrin and CTAB.