Surfactant-based self-assembly of proteins

Let us consider the various possible types of biopolymer-surfactant interactions. We first note that, because of the amphiphilic nature of both biopolymers and surfactants, it can be envisaged that the mechanistic interpretation could be based on attractive or repulsive interactions acting between the original biopolymer and surfactant molecules/particles or between biopolymer particles modified by the surfactants. For example, attractive interactions could arise from  

Analysis of recent experimental data has shown that there are various issues that have to be considered when interpreting the complex character of the interactions in mixed protein + surfactant systems (Kelley and McClements, 2003 II in et al., 2004, 2005 Malhotra and Coupland, 2004 Istarova et al., 2005). Below we identify these general issues as factors A, B, C and D. 

Where this factor plays a role, the hydrophobic interaction between the hydrocarbon chains of the surfactant and the non-polar parts of protein functional groups are predominant. An example of this effect is the marked endothermic character of the interactions between the anionic CITREM and sodium caseinate at pH = 7.2 (Semenova et al., 2006), and also between sodium dodecyl sulfate (SDS) and soy protein at pH values of 7.0 and 8.2 (Nakai et al., 1980). It is important here to note that, when the character of the protein-surfactant interactions is endothermic (/. ., involving a positive contribution from the enthalpy to the change in the overall free energy of the system), the main thermodynamic driving force is considered to be an increase in the entropy of the system due to release into bulk solution of a great number of water molecules. This entropy 

The situation is complicated by the fact that the cmc value determined in the pure surfactant solution generally differs from that fomid in the presence of biopolymer. This is mainly because the surfactant-biopolymer interactions can shift the equilibrium between free surfactant molecules and their micelles, leading to a change in the effective cmc of surfactant molecules in the biopolymer system (Kelley and McClements, 2003 McClements, 2000 Thongngam and McClements, 2005). 

To illustrate some of the structural features of the aggregates formed, we can make use of an empirical relationship between Mw and Re, which takes the form of a power-law equation (Burchard, 1994)  

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