Hemoglobin Dynamics in Solution vis-à-vis Under Confinement: An Electrochemical Perspective

Abstract

Confining heme protein in silico often leads to beneficial functionalities such as an enhanced electrochemical response from the heme center. This can be harnessed to design effective biosensors for medical diagnostics. Proteins under confinement, surface confinement on the electrode to be precise, have more ordered and monodisperse structure compared to the protein in bulk solution. As the electrochemical response of a protein comes from those protein molecules that are confined within the electrical double layer across the electrode− electrolyte interface, it is expected that restriction of conformational fluctuations of the polymeric protein will help in enhancement of the electrochemical response. This is probably the prima facie reason for electrochemical response enhancement under confinement. We examine the dynamic features of hemoglobin under confinement visa-vis that in bulk solution. We use a variety of spectroscopic techniques across a wide time−space window to establish the following facts: (a) hardening of the protein polypeptide backbone, (b) slowing down of protein diffusion, (c) increase in relaxation times in NMR, and (d) slowing down of dielectric relaxation times under confinement. This indicates an overall quenching of protein dynamics when the protein is confined inside silica matrix. Thus, we hypothesize that along with retention of secondary structure, this quenching of dynamics contributes to the enhancement of electrochemical response observed.

Why are Vibrational Lines Narrow in Proteins?

“…44 Likewise, the slower dynamics of a confined protein lead to a stronger dynamical freezing and an enhanced electrochemical response. 45 Overall, breaking the restrictions of the fluctuation−dissipation theorem by insufficient sampling might be a successful strategy, alternative to Pauling's stabilization of the activated state, for achieving the catalytic effect. In this view, not only the structure of the active site and the thermodynamic activation free energy but also the relaxation time of the promoting mode determine the function.…”

“…The same mechanism is also behind the recently discovered surprisingly high conductivity of proteins . Likewise, the slower dynamics of a confined protein lead to a stronger dynamical freezing and an enhanced electrochemical response . Overall, breaking the restrictions of the fluctuation–dissipation theorem by insufficient sampling might be a successful strategy, alternative to Pauling’s stabilization of the activated state, for achieving the catalytic effect.…”