Sowrirajan Chandrasekaran

The role of encapsulation by β-cyclodextrin in the interaction of raloxifene with macromolecular targets: a study by spectroscopy and molecular modeling

We report the binding of the drug raloxifene with Calf thymus DNA (ctDNA) and bovine serum albumin (BSA) in the presence and absence of β-cyclodextrin (β-CD) and explain the influence of β-cyclodextrin on the binding of the drug to macromolecules. UV-Vis absorption, fluorescence, proton nuclear magnetic resonance and two-dimensional rotating-frame nuclear overhauser effect spectroscopic techniques are used to study the stoichiometry and the binding strength of the complexes. Molecular modeling is used in combination with other techniques to propose the structure of the inclusion complex and the interaction with ctDNA. The Stern–Volmer quenching constants of the interaction of raloxifene with ctDNA in aqueous and in β-CD solution are compared. The competition for binding of ctDNA with raloxifene and Methylene Blue is studied. The apparent binding constant and the number of binding sites for the binding of raloxifene with BSA in aqueous solution are significantly different from those in the presence of β-CD. The influence of β-CD on the binding of the small molecules with biological macromolecules is discussed. We infer that the binding strengths between raloxifene and macromolecules, viz., ctDNA and BSA are influenced by the β-CD encapsulation. These results may suggest new ways to tune the drug binding to biomacromolecules by encapsulating specific moieties of drugs.

Binding of a chromen-4-one Schiff’s base with bovine serum albumin: capping with β-cyclodextrin influences the binding

This work deals with the synthesis of 6-methyl-3-[(4′-methylphenyl)imino]methyl-4H-chromen-4-one (MMPIMC), its binding to β-cyclodextrin, and the influence of the cyclodextrin complexation on the compound’s binding to bovine serum albumin (BSA). The 1:2 stoichiometry for the complexation of MMPIMC with β-cyclodextrin is determined with the binding constant of 1.90 × 104 M−2. The structure of host–guest complex plays a role in protein binding of MMPIMC. One- and two-dimensional NMR spectra are used to determine the mode of binding of the guest to β-cyclodextrin cavity and the structure of the inclusion complex is proposed. The binding of MMPIMC with BSA in the absence and the presence of β-cyclodextrin is studied. The binding strengths of MMPIMC–BSA (1.73 × 105 M−1) and β-cyclodextrin-complexed MMPIMC–BSA (9.0 × 104 M−1) show difference in magnitude. The Förster Resonance Energy Transfer efficiency and the proximity of the donor and acceptor molecules, are modulated by β-cyclodextrin. Molecular modeling is used to optimize the sites and mode of binding of MMPIMC with bovine serum albumin.

Tuning the binding of coumarin 6 with DNA by molecular encapsulators: effect of β-cyclodextrin and C-hexylpyrogallol[4]arene

We report in this paper that the binding of coumarin 6 (C6) to DNA can be tuned by complexing it with host structures, viz. β‐cyclodextrin (β‐CD) and C‐hexylpyrogallol‐4‐arene (C‐HPA). Because host molecules are used as carriers of small molecules onto target sites, the exposed part of the guest molecule needs to be found out, and the relationship between the host : guest ratio and the mode of binding with the target macromolecule, that is, the DNA needs to be analyzed, in order to comprehend the preferred binding moiety and tune the binding. In this paper, the formation of the inclusion complex of C6 with β‐CD and with C‐HPA is studied by UV‐visible, fluorescence, 2D rotating‐frame nuclear Overhauser effect correlation spectroscopy and diffusion‐ordered spectroscopy nuclear magnetic resonance spectra and molecular modeling. C6 forms a 1:1 complex with β‐CD and a 1:2 complex with C‐HPA. The studies on the protonation of C6 in the presence and the absence of the host molecules suggest that the chromone part of C6 is outside the β‐CD molecule, whereas it is fully covered by C‐HPA. The binding of C6 with calf thymus DNA (ctDNA) occurs through intercalation and hydrogen bonding, and the host–guest structures remain intact on binding with ctDNA. The oxygens of the C6 molecules are exposed when inside the host molecules and aid in the hydrogen bonding with DNA. Copyright

Alteration of the Binding Strength of Dronedarone with Bovine Serum Albumin by β-Cyclodextrin: A Spectroscopic Study

We report the influence of β-cyclodextrin on the binding of the drug dronedarone with bovine serum albumin. The stoichiometry, the binding constant, and the mode of binding of the derivative with β-cyclodextrin are studied by UV–Visible absorption, fluorescence, and 2 Dimensional Rotating Frame Overhauser Effect Spectroscopy (2D ROESY NMR) spectroscopic techniques. The structure of the 1:1 inclusion complex is proposed. The binding of free dronedarone with bovine serum albumin and β-cyclodextrin-bound dronedarone are studied by fluorescence quenching and Förster resonance transfer. The decreased magnitude of the Stern–Volmer constant and the binding constant for the interaction of dronedarone with bovine serum albumin in the presence of β-cyclodextrin are articulated. The donor-to-acceptor distances in the presence and the absence of β-cyclodextrin are compared. The binding sites of the dronedarone with bovine serum albumin are reported by molecular modeling. Dronedarone binds to the sub-domain III of bovine serum albumin. The 3-(dibutylaminopropoxy)benzoyl moiety of dronedarone binds with bovine serum albumin. Encapsulation with β-cyclodextrin decreases the binding strength of dronedarone with bovine serum albumin.

C-hexylpyrogallol[4]arene and β-cyclodextrin as directors of the mode of binding of Coumarin 153 with DNA

The supramolecular interaction between calf thymus DNA (ctDNA) and Coumarin 153 in the presence of β-cyclodextrin (β-CD) or C-hexylpyrogallol[4]arene (C-HPA) was studied. Inclusion complexes of Coumarin 153 with β-CD and C-HPA were characterised by infrared spectroscopy, proton nuclear magnetic resonance spectroscopy and two-dimensional rotating-frame nuclear overhauser effect spectroscopy. The inclusion complexation was further followed by steady-state and time-resolved fluorescence measurements. The influence of β-CD or C-HPA in the binding strength and binding model of C153 with ctDNA was studied by UV–visible, fluorescence and molecular modelling technique. The possible group of interaction of Coumarin 153 with DNA, β-CD and C-HPA was shown by molecular modelling technique.

Binding of the Host–Guest Complex of 7-Aminoflavone/β-Cyclodextrin with Calf Thymus DNA: A Spectroscopic and Molecular Docking Study

The selective binding of 7-aminoflavone (7-AF) molecules with DNA was investigated in the host–guest complex form with β-cyclodextrin (β-CD). The host–guest association of 7-AF with β-CD was investigated using absorption, steady-state fluorescence, time-resolved fluorescence and NMR spectroscopic techniques. The stoichiometry and the binding constant of the inclusion complex were determined. The possible orientation of the 7-AF molecule to the β-CD was confirmed by the 2D ROESY NMR technique and was further studied by molecular modeling. The ground and the excited state pKa values are reported for the free guest molecule and the β-CD complex. The binding of 7-AF to calf thymus DNA with and without the β-CD are reported. The binding constant of DNA with 7-aminoflavone in the presence and the absence of β-CD were calculated.Graphical Abstract

Inclusion complexation between baicalein and β-cyclodextrin and the influence of β-cyclodextrin on the binding of baicalein with DNA: a spectroscopic approach

This work deals with the commonly studied cyclic oligosaccharide and gains importance as it is entered on a drug delivering carbohydrate and provides insight into the oligosaccharide complex–biomolecular interaction. The binding of a flavone, baicalein, to β-cyclodextrin and calf thymus DNA is studied. The binding of baicalein to calf thymus DNA in the presence of β-cyclodextrin is analysed using the UV–vis absorption and fluorescence spectroscopy. The mode of binding and structure of the baicalein–β-cyclodextrin complex are reported. The role of the structure and the stoichiometry of the inclusion complex of baicalein–β-cyclodextrin in its influence on DNA binding are analysed. Highlights • This paper deals with the binding of a flavone, baicalein to β-cyclodextrin and/or DNA. • The inclusion complexation between baicalein and β-cyclodextrin is analysed. • The stoichiometry and the binding strength of the inclusion complex is reported. • The role of β-cyclodextrin in tuning the binding of baicalein to DNA is emphasized. • Spectroscopic and docking analysis are used to articulate the results. Graphical abstract The influence of β-cyclodextrin on the binding of baicalein with DNA

Host–guest association of coumarin 343 with β-cyclodextrin and C-hexylpyrogallol[4]arene: opposite fluorescent behavior and prototropic characteristics

We report here the stoichiometry and the binding strength of coumarin 343 (C343) with β-cyclodextrin (β-CD) and with C-hexylpyrogallol[4]arene (C-HPA) using absorption, steady state fluorescence, time-resolved fluorescence and 2D ROESY NMR spectroscopic techniques. The effect of pH on C343 in water and in the presence of β-CD or C-HPA is studied. The ground state and the excited state pKa values for the neutral-monocation equilibrium of C343 are reported. The opposite fluorescence behavior of C343 in the presence of β-CD and in C-HPA is discussed.Graphical Abstract

Phenylhydrazones of Piperidin-4-ones as AND, OR, NOR, NAND, and INH Molecular Logic Gates

Phenylhydrazone derivatives of 2,6-diarylpiperidin-4-ones viz., 3-methyl-2,6-diphenylpiperidin-4-one (PMP-PH) and 3-methyl-2,6-di-(9H-fluorenyl)piperidin-4-one (FMP-PH) when illuminated and protonated perform the functions of AND, OR, NOR, NAND Boolean logic gates with all optical outputs. The functions of the AND and the NAND gates rely on changes in absorption and emission of the phenylhydrazone upon isomerization of the photochromic unit. We report novel heterocyclic compounds where setting up of threshold absorption or emission can be made as a logic device.

Interaction of Coumarin 7 and Coumarin 314 with C-hexylpyrogallol[4]arene

We report in this paper the different modes of interaction of coumarin 7 and coumarin 314 with the cavity-containing molecule C-hexylpyrogallol[4]arene. The stoichiometry and the binding constant of coumarin 7 for its binding with C-hexylpyrogallol[4]arene are reported. The analysis is done with UV–Vis absorption, steady-state and time-resolved fluorescence, and 2D ROESY spectroscopy. The fluorescence quenching of the two coumarins is analyzed and the Stern–Volmer constants are reported. The mode of binding of coumarin 7 with the host molecule is optimized with 2D ROESY. Coumarin 314 does not form an inclusion complex and this result is supported by the spectral data. The ground and the excited state pKa values for the coumarins, in the presence of C-hexylpyrogallol[4]arene, are reported.