Do properties of bovine serum albumin at fluid/electrolyte interface follow the Hofmeister series?--An analysis using Langmuir and Langmuir-Blodgett films.

Folding and solubility of proteins are dependent on their state of hydration. How does a protein-bovine serum albumin (BSA) behave in the presence of Hofmeister electrolytes, especially at interfaces? Langmuir films of bovine serum albumin (BSA) in the presence of different Hofmeister electrolytes at air/solution interface and as Langmuir-Blodgett films (LB films) at solid/solution interface have been studied using the surface pressure-molecular area (pi-A) isotherms and surface energy parameters. Changes in secondary structure have been analyzed using circular dichroism (CD) and fluorescence spectroscopy. Hydrodynamically coupled water fraction of BSA in different environments has been estimated using quartz crystal microbalance (QCM) and related to the secondary structural changes. Molecular modeling of BSA in different environments showed that the protein has a compact structure at the interface compared to vacuum. The contact areas estimated using molecular modeling agreed with the experimental results. The results show that the properties of BSA at the interface follow the Hofmeister series with NaF leading to maximum compaction in the protein. Further, in addition to ion specific solvation and different ion size, water structure alteration and the bound water fractions contribute importantly to the Hofmeister effect.