title: Analysis of Molecular Interaction of Drugs within β-Cyclodextrin Cavity by Solution-State NMR Relaxation.
abstract: The prime focus of the present study is to employ NMR relaxation measurement to address the intermolecular interactions, as well as motional dynamics, of drugs, viz., paracetamol and aspirin, encapsulated within the β-cyclodextrin (β-CD) cavity. In this report, we have attempted to demonstrate the applicability of nonselective (R1ns), selective (R1se), and bi-selective (R1bs) spin-lattice relaxation rates to infer dynamical parameters, for example, the molecular rotational correlation times (τc) and cross-relaxation rates (σij) of the encapsulated drugs. Molecular rotational correlation times of the free drugs were calculated using the selective relaxation rate in the fast molecular motion time regime (ωH2τc2≪ 1 and R1ns/R1se≈ 1.500), whereas that of the 1:1 complexed drugs were found from the ratio of R1ns/R1sein the intermediate motion time regime (ωH2τc2∼ 1 and R1ns/R1se≈ 1.054), and these values were compared with each other to confirm the formation of inclusion complexes. Furthermore, the cross-relaxation rates were used to evaluate the intermolecular proton distances. Also, density functional theory calculations were performed to determine the minimum energy geometry of the inclusion complexes and the results compared with those from experiments. The report, thus, presents the possibility of utilizing NMR relaxation data, a more cost-effective experiment, to calculate internuclear distances in the case of drug-supramolecule complexes that are generally obtained by extremely time consuming two-dimensional nuclear Overhauser enhancement-based methods. A plausible mode of insertion of the drug molecules into the β-CD cavity has also been described based on experimental NMR relaxation data analysis.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Jodhpur , Old Residency Road, Ratanada, Jodhpur 342011, India.
authors.forename: Deepak
authors.initials: D
authors.lastname: Kumar
authors.affiliation: Department of Chemistry, Indian Institute of Technology Jodhpur , Old Residency Road, Ratanada, Jodhpur 342011, India.
authors.forename: Yogeshwaran
authors.initials: Y
authors.lastname: Krishnan
authors.affiliation: Department of Chemistry, Indian Institute of Technology Jodhpur , Old Residency Road, Ratanada, Jodhpur 342011, India.
authors.forename: Manikandan
authors.initials: M
authors.lastname: Paranjothy
authors.affiliation: Department of Chemistry, Indian Institute of Technology Jodhpur , Old Residency Road, Ratanada, Jodhpur 342011, India.
authors.forename: Samanwita
authors.identifier: 0000-0003-3192-9237
authors.initials: S
authors.lastname: Pal