Interactions between deep eutectic solvents and bovine serum albumin studied by spectroscopic and electrochemical methods

Deep eutectic solvent (DES) has become a potential protein extractant as its good biocompatibility, environmental friendliness and accessibility. In this study, two types of DESs, ferric chloride hexahydrate: oxalic acid (FeCl 3 ·6H 2 O: H 2 C 2 O 4 ) and choline chloride: zinc chloride (ChCl: ZnCl 2 ), were prepared. The interactions between these two types of DESs and bovine serum albumin (BSA) were investigated by utilizing spectroscopic and electrochemical methods. It was found that both FeCl 3 ·6H 2 O: H 2 C 2 O 4 and ChCl: ZnCl 2 are able to form complexes with BSA by a relatively high affinity. During the process, no significant change in BSA conformation was observed. The binding ratios of BSA in the FeCl 3 ·6H 2 O: H 2 C 2 O 4 and ChCl: ZnCl 2 systems are up to 98.59 % and 98.14 %, respectively, indicating that the two DESs are both promising extractants for BSA. The interactions between the DESs and BSA are mainly hydrogen bond and van der Waals force, which are strong enough to extract BSA but not too strong for regeneration, making the DESs more applicable in the industry. Moreover, it was found that the binding ratio of BSA in the FeCl 3 ·6H 2 O: H 2 C 2 O 4 -BSA system remains above 91.7 % in the temperature range of 298–313 K, illustrating the potential of FeCl 3 ·6H 2 O: H 2 C 2 O 4 to be used in BSA extraction under a wider range of temperature. In contrast, ChCl: ZnCl 2 will be better used under lower temperatures.