title: Exploring the interaction of phenothiazinium dyes methylene blue, new methylene blue, azure A and azure B with tRNAPhe: spectroscopic, thermodynamic, voltammetric and molecular modeling approach.
abstract: This study focuses on the understanding of the interaction of phenothiazinium dyes methylene blue (MB), new methylene blue (NMB), azure A (AZA) and azure B (AZB) with tRNAPhewith particular emphasis on deciphering the mode and energetics of the binding. Strong intercalative binding to tRNAPhewas observed for MB, NMB and AZB, bound by a partial intercalative mode. AZA has shown groove binding characteristics. From spectroscopic studies binding affinity values of the order of 105M-1were deduced for these dyes; the trend varied as MB > NMB > AZB > AZA. The binding was characterized by an increase of thermal melting temperatures and perturbation in the circular dichroism spectrum of tRNA. All the dyes acquired optical activity upon binding to tRNA. The binding was predominantly entropy driven with a favorable enthalpy term that increased with temperature in all the cases. Dissection of the Gibbs energy to polyelectrolytic and non-polyelectrolytic terms revealed a major role of the non-electrostatic forces in the binding. The small but significant heat capacity changes and the observed enthalpy-entropy compensation phenomenon confirmed the involvement of multiple weak non-covalent forces driving the interaction. The mode of binding was confirmed from quenching, viscosity and cyclic voltammetric results. Using density functional theory, ground state optimized structures of the dyes were calculated to provide insight into theoretical docking studies to correlate the experimental approaches. The modeling results verified the binding location as well as the binding energy of complexation. The results may provide new insights into the structure-activity relationship useful in the design of effective RNA targeted therapeutic agents.
authors.affiliation: Biophysical Chemistry Laboratory, Organic and Medicinal Chemistry Division, CSIR-Indian Institute of Chemical Biology, 4, Raja S. C. Mullick Road, Kolkata 700 032, India. gskumar@iicb.res.in gsk.iicb@gmail.com and Department of Chemistry, Jadavpur University, Kolkata 700 032, India.
authors.forename: Puja
authors.initials: P
authors.lastname: Paul
authors.affiliation: Government General Degree College, Keshiary, Paschim Medinipur, West Bengal 721135, India.
authors.forename: Soumya Sundar
authors.initials: SS
authors.lastname: Mati
authors.affiliation: Department of Chemistry, Jadavpur University, Kolkata 700 032, India.
authors.forename: Subhash Chandra
authors.initials: SC
authors.lastname: Bhattacharya
authors.affiliation: Biophysical Chemistry Laboratory, Organic and Medicinal Chemistry Division, CSIR-Indian Institute of Chemical Biology, 4, Raja S. C. Mullick Road, Kolkata 700 032, India. gskumar@iicb.res.in gsk.iicb@gmail.com.
authors.forename: Gopinatha Suresh
authors.identifier: http://orcid.org/0000-0002-9847-2393
authors.initials: GS
authors.lastname: Kumar