Spectroscopic investigations to reveal the nature of interactions between the haem protein myoglobin and the dye rhodamine 6G

Abstract

In the present investigation, steady-state and time-resolved fluorescence with the combination of circular dichroism (CD) spectroscopic techniques were applied to study the interactions of the well-known dye rhodamine 6 G (R6G) with the haem protein human myoglobin (Mb). From the analysis of the results it appears that the static type of fluorescence quenching mechanism is primarily involved, due to ground-state interactions. Although considerable overlapping of fluorescence emission of the dye R6G with the absorption of Mb in the Q-band region exists, the possibility of occurrences of the excitational singlet-singlet non-radiative energy transfer process from R6G to Mb appears to be unlikely, according to time-resolved fluorescence measurements. From the determinations of the thermodynamic parameters, it was apparent that the combined effect of van der Waals' interactions and hydrogen bonding plays a vital role in Mb-R6G interactions. Induced circular dichroism (ICD) studies demonstrate the possibility of interactions between R6G and Mb. The binding constants, number of binding sites and thermodynamic parameters have been computed. From CD measurements it is apparent that the binding of the dye R6G with the haem protein Mb induces negligible conformational changes in the protein and Mb retains its secondary structure and helicity when it interacts with R6G. The present detailed studies on the interactions with Mb should be helpful in further advancement of medical diagnostics and biotechnology.