Interaction Study between ESIPT Fluorescent Lipophile-Based Benzazoles and BSA.

In this study, the interactions of ESIPT fluorescent lipophile-based benzazoles with bovine serum albumin (BSA) were studied and their binding affinity was evaluated. In phosphate-buffered saline (PBS) solution these compounds produce absorption maxima in the UV region and a main fluorescence emission with a large Stokes shift in the blue-green regions due to a proton transfer process in the excited state. The interactions of the benzazoles with BSA were studied using UV-Vis absorption and steady-state fluorescence spectroscopy. The observed spectral quenching of BSA indicates that these compounds could bind to BSA through a strong binding affinity afforded by a static quenching mechanism (Kq~1012 L·mol-1·s-1). The docking simulations indicate that compounds 13 and 16 bind closely to Trp134 in domain I, adopting similar binding poses and interactions. On the other hand, compounds 12, 14, 15, and 17 were bound between domains I and III and did not directly interact with Trp134.

Proton transfer in fluorescent secondary amines: synthesis, photophysics, theoretical calculation and preparation of photoactive phosphatidylcholine-based liposomes.

In this article, new fluorescent lipophilic based benzazoles were synthesized from the reaction between photoactive formyl derivatives and aliphatic amines followed by NaBH4 reduction with good yields. The photophysics of the benzazoles was investigated experimentally and theoretically. These compounds present absorption maxima in the UV region (∼339 nm) and fluorescence emission maxima in the cyan to green region with a large Stokes shift (∼175 nm) due to a proton transfer process in the excited state. Two fluorophores were successfully used as a proof of concept to produce stable photoactive liposomes prepared from phosphatidylcholine (PC) and were characterized by zeta potential, small angle X-ray scattering (SAXS), FTIR and UV-Vis experiments (turbidity). The scattering data indicate that the presence of compounds 20 and 23 reduces the overall surface charge of the PC vesicles, possibly due to the partial neutralization of phosphatidic acid and/or phosphatidylinositol phosphate by the amine groups, and they also modify the structural features of the assemblies, leading, in particular, to a reduction in the thickness of the hydrophobic inner segment (tt) of the liposomes. DFT and TD-DFT calculations were performed with the ωB97XD functional. Geometric analyses show that the 2-(2'-hydroxyphenyl)benzazolic planar portion allows an effective ππ* electronic transition. Additionally, the calculations indicate a small energy barrier to proton transfer. The results of the absorption and emission maxima show a slight solvent influence on the wavelengths.

Elucidating Bauhinia variegata lectin/phosphatidylcholine interactions in lectin-containing liposomes.

Investigations focused on the interactions of nanoparticles with lectins are relevant since it is well accepted that such proteins can be recognized by carbohydrates as parts of cell membranes. This can ultimately enhance the cellular uptake of the produced assemblies. In this framework, the physical interactions of phosphatidylcholine (PC) liposomes and the Bauhinia variegate lectin (BVL) are reported here. BVL-liposome interactions were characterized by a variety of techniques to understand the influence of BVL in the structural features, thermodynamic and spectroscopic properties of the hybrid material. The produced system is composed of 56% w/w lectin, and the scattering techniques show the presence of stable vesicular structures with a mean diameter DH ∼ 100 nm. The FTIR and NMR results showed a strong lectin effect on the PC choline region, restricting the rotational motion of the lipid group. The BVL-liposome interaction promoted hardening of the protein as evidenced by circular dichroism spectroscopy. The photophysics results suggest higher rigidity of the system in the presence of BVL. The BVL may be present in the inner or outer polar surface of the liposomes. The system was shown to be relatively stable and therefore potentially useful for carbohydrate recognition of nanoparticles.