Characterization of the structural changes of human serum albumin upon interaction with single-walled and multi-walled carbon nanotubes: spectroscopic and molecular modeling approaches

Abstract

Through the incorporation of spectorescopic and molecular methods of modeling, the researchers investigated the interaction between Carbon Nanotubes (CNTs) and Human Serum Albumin (HSA). Fluorescence spectroscopy revealed the ability in both single-wall and multi-wall CNTs to quench the spectrum through a static quenching procedure obtained from the Stern–Volmer quenching constant (Ksv) at three different temperatures. The Ksv values of HSA–CNTs complexes were 1.96 × 105 M−1 and 2.44 × 105 M−1 that showed two different behaviors of interaction between HSA and CNTs. The Van’t Hoff equation was used to calculate thermodynamic parameters of Gibbs free energy (ΔG°), entropy (ΔS°) and enthalpy changes (ΔH°). The binding distances (r) between the donor (Trp residue of HSA) and acceptor (CNTs) was measured through the Forster theory of non-radiative energy transfer, and it was found to be less than 7 nm. The conformational changes of protein in the presence of CNTs were revealed through synchronous fluorescence spectra and three-dimensional fluorescence spectra analysis. The experimental results were confirmed through molecular modeling technique. Circular dichroism technique showed the secondary structure changes of HSA upon interaction with CNTs. The complex formation of HSA and CNTs was determined by the measurement of the electric conductivity. The molecular modeling technique determined the binding site of CNTs that were embedded in the subdomain IIIB of HSA. These analyses play a major role in drug delivery and pharmacodynamics studies for better understanding of nanotechnology levels.