In situ investigations of Fe3+ induced complexation of adsorbed Mefp-1 protein film on iron substrate

Abstract

A range of in situ analytical techniques and theoretical calculations were applied to gain insights into the formation and properties of the Mefp-1 film on iron substrate, as well as the protein complexation with Fe(3+) ions. Adsorption kinetics of Mefp-1 and the complexation were investigated using QCM-D. The results suggest an initially fast adsorption, with the molecules oriented preferentially parallel to the surface, followed by a structural change within the film leading to molecules extending toward solution. Exposure to a diluted FeCl3 solution results in enhanced complexation within the adsorbed protein film, leading to water removal and film compaction. In situ Peak Force Tapping AFM was employed for determining morphology and nano-mechanical properties of the surface layer. The results, in agreement with the QCM-D observations, demonstrate that addition of Fe(3+) induces a transition from an extended and soft protein layer to a denser and stiffer one. Further, in situ ATR-FTIR and Confocal Raman Micro-spectroscopy (CRM) techniques were utilized to monitor compositional/structural changes in the surface layer due to addition of Fe(3+) ions. The spectroscopic analyses assisted by DFT calculations provide evidence for formation of tri-Fe(3+)/catechol complexes in the surface film, which is enhanced by Fe(3+) addition.