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 (K_q~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.

Substituent effect on ESIPT mechanisms and photophysical properties of HBT derivatives

Substituent effects on excited-state intramolecular proton transfer (ESIPT) and photophysical properties of 2-(2-Hydroxyphenyl) benzothiazole (HBT) derivatives have been theoretically unveiled via the density functional theory (DFT) and time-dependent DFT (TDDFT). The optimized geometrical configurations and normal mode analyses confirm that the proton transfer processes are more reactive in excited state. Through calculating the activation energies and rate constants of ESIPT processes, finding that the processes are increasingly inactive when substituent group changes from -CN, -CO₂Me, -Cl, -Me, -NMe₂ to -NO₂. In addition, the photophysical properties analyses indicate the vertical transition energies are in good agreement with those observed in experiment. Note that all the absorption and emission maxima of enol and keto forms have the significant red-shift. In order to clarify the substituent effect on ESIPT and photophysical properties, we draw the frontier molecular orbitals (FMOs) isosurfaces and calculate the distances of electrons and holes and atomic charges. It follows that the intramolecular charge transfer (ICT) degrees are increasingly enlarged as substituting from -CN, -CO₂Me, -Cl, -Me, -NMe₂ to -NO₂ groups, which not only causes the red-shift of absorption and emission of enol and keto forms, but also affects the charge distribution of proton donor and acceptor, inhibiting the occurrence of ESIPT processes.

In vitro phototoxicity of zinc phthalocyanine (ZnPc) loaded in liposomes against human breast cancer cells

In this study, zinc phthalocyanine (ZnPc) was encapsulated in liposomes (Phosphatidylcholine (PC) from soybean lecithin (95% phosphatidylcholine, 5% lysophosphatidylcholine), and phosphatidic acid) obtained by a reverse-phase evaporation method. Liposomes were characterized and cytotoxicity and phototoxicity assays were performed using mouse embryo fibroblast (NIH3T3) and human breast cancer (MDAMB231), respectively. ZnPc was successfully encapsulated in liposomes ([Formula: see text]80%), presenting single populations with sizes of [Formula: see text]300 nm and negative zeta potential (-35 to -40 mV). The release profile at different pH presented a biphasic release controlled by the Fickian diffusion mechanism. The cytotoxicity assays carried out on NIH3T3 cells showed that the liposomes provided good protection for ZnPc, and did not affect the viability of non-cancerous cells. In contrast, free ZnPc significantly reduced non-cancerous cell viability at higher concentrations. ZnPc loaded in liposomes ensured a higher phototoxic effect on the MDAMB231 cells at all concentrations tested when exposed to low light dose.

Co-encapsulation of sodium diethyldithiocarbamate (DETC) and zinc phthalocyanine (ZnPc) in liposomes promotes increases phototoxic activity against (MDA-MB 231) human breast cancer cells

There has been considerable interest in the development of novel photosensitisers for photodynamic therapy (PDT). The use of liposomes as drug delivery systems containing simultaneously two or more drugs is an attractive idea to create a new platform for PDT application. Therefore, the aim of this study was to evaluate the synergistic effect of diethyldithiocarbamate (DETC) and zinc phthalocyanine (PDT) co-encapsulated in liposomes. The reverse-phase evaporation method resulted in the successful encapsulation of DETC and ZnPc in liposomes, with encapsulation efficiencies above 85 %, mean size of 308 nm, and zeta potential of - 36 mV. The co-encapsulation decreased the cytotoxic effects in mouse embryo fibroblast (NIH3T3) cells and inhibited damage to human erythrocytes compared to free DETC + ZnPc. In addition, both the free drugs and co-encapsulated ones promoted more pronounced phototoxic effects on human breast cancer cells (MDA-MB231) compared to treatment with ZnPc alone. This synergistic effect was determined by DETC-induced decreases in the antioxidant enzyme activity of superoxide dismutase (SOD) and glutathione (GSH).

Evaluation of the acidic strengths on electronic ground and excited states of proton transfer dye using Excitation-Emission fluorescence matrix (EEM) and Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS)

Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) was for the first time successfully used to evaluate an intricate photophysical behavior, where deprotonation on the electronic ground state (S₀), intra and intermolecular proton transfer processes (ESPT and ESIPT) on the electronic excited state (S₁) can simultaneously be presented. In this sense, the organic dye 2-(2'-hydroxyphenyl)benzothiazole (HBT) was used as a proof-of-concept model, where MCR-ALS showed to be a powerful tool for discriminate chemical reactions that occur concomitantly on different potential energy surfaces, which include photochemical reactions. As a result, the chemometric method showed to be a straightforward approach for the determination of the acidic strengths of those equilibria were estimated as 8.61 and 1.11 to hydroxyl deprotonation on electronic ground and excited states, respectively.

Deciphering the Dynamics of Organic Nanoaggregates with AIEE Effect and Excited States: Lipophilic Benzothiadiazole Derivatives as Selective Cell Imaging Probes

An aggregation-induced emission enhancement (AIEE) effect in fluorescent lipophilic 2,1,3-benzothiadiazole (BTD) derivatives and their organic nanoaggregates were studied. A set of techniques such as single-crystal X-ray, dynamic light scattering (DLS), electron paramagnetic resonance (EPR), UV-vis, fluorescence, and density functional theory (DFT) calculations have been used to decipher the formation/break (kinetics), properties, and dynamics of the organic nanoaggregates of three BTD small organic molecules. An in-depth study of the excited-state also revealed the preferential relaxation emissive pathways for the BTD derivatives and the dynamics associated with it. The results described herein, for the first time, explain the formation of fluorescent BTD nanoaggregate derivatives and allow for the understanding of their dynamics in solution as well as the ruling forces of both aggregation and break processes along with the involved equilibrium. One of the developed dyes could be used at a nanomolar concentration to selectively stain lipid droplets emitting an intense and bright fluorescence at the red channel. The other two BTDs could also stain lipid droplets at very low concentrations and were visualized preferentially at the blue channel.