Electro-optical fluorescence studies on the DNA binding of medically active drugs

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.

Spontaneous formation of fluorescent nanofibers and reticulated solid from berberine palmitate: a new example of aggregation-induced emission enhancement in organic ion pairs

The salt formed between the large aromatic berberine cation and the long-chain palmitate anion was synthesized and used to prepare aqueous suspensions of particles owing to a solvent-exchange method. Under these conditions, elongated particles were readily obtained. They were studied by transmission microscopy with polarized light, as well as by fluorescence and electron microscopy. They were shown to be probably crystallized nanofibers, which were stable in suspension. Unexpectedly, upon filtration and drying, these fibers evolved to give a reticulated solid. The fluorescence properties of the compound were analyzed in solution, in aqueous suspension and in the powder crystalline state. Interestingly, berberine palmitate is virtually not fluorescent in aqueous solution because of the quenching effect of water, but transition to the solid state was accompanied by a strong increase in fluorescence intensity. This phenomenon was explained by the original molecular arrangement in the solid state. Actually, in the crystal, the anions form a distinct layer, which limits parallel-stacking of the fluorescent cations. Moreover, the berberine cations are protected from the access of water molecules, and so no quenching effect can take place. This example confirms that the newly introduced concept of ion-pair aggregation-induced fluorescence enhancement can be extended to a variety of structures. It also shows the interest of ion pairs for preparing fluorescent nanofibers and reticulated solids using a solvent-exchange method that is particularly easy to implement.