Thermal and solvatochromic effects on the emission properties of a thienyl-based dansyl derivative.

Environmental conditions have a profound effect on the photophysical behavior of highly conjugated compounds, which can be exploited in a large variety of applications. In this context, we use a combination of experimental and computational methods to investigate thermal and solvatochromic effects on the fluorescence properties of a dansyl derivative bearing a thienyl substituent, namely 2-(3-thienyl)ethyl dansylglycinate (TEDG). In particular, we analyze how the solvent polarity and temperature affect the ground and excited state energies of TEDG by using time-resolved and steady-state fluorescence techniques. We determine the changes in dipole moment of the TEDG molecule upon photoexcitation, as well as the solvent polarity effects on the excited state lifetime. Besides, we provide theoretical modeling of the HOMO-LUMO orbitals and the vertical absorption and emission energies using time-dependent density functional theory (TDDFT) as well as the polarizable continuum model (PCM) to include the solvent contribution to the absorption and emission energies. Our results show that the emission mechanism of TEDG involves locally excited states derived from hybrid molecular orbitals, accompanied by a moderate variation of the molecular dipole moment upon light excitation. Our findings demonstrate that TEDG exhibits desirable fluorescence properties that make it a promising candidate for use as a photoactive material in electrochromic, optical thermometry, and thermography applications.

Effects of artepillin C on model membranes displaying liquid immiscibility.

It has been hypothesized that the therapeutic effects of artepillin C, a natural compound derived from Brazilian green propolis, are likely related to its partition in the lipid bilayer component of biological membranes. To test this hypothesis, we investigated the effects of the major compound of green propolis, artepillin C, on model membranes (small and giant unilamelar vesicles) composed of ternary lipid mixtures containing cholesterol, which display liquid-ordered (lo) and liquid-disordered (ld) phase coexistence. Specifically, we explored potential changes in relevant membrane parameters upon addition of artepillin C presenting both neutral and deprotonated states by means of small angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and confocal and multiphoton excitation fluorescence microscopy. Thermotropic analysis obtained from DSC experiments indicated a loss in the lipid cooperativity of lo phase at equilibrium conditions, while at similar conditions spontaneous formation of unilamellar vesicles from SAXS experiments showed that deprotonated artepillin C preferentially located at the surface of the membrane. Time-resolved experiments using fluorescence microscopy showed that at doses above 100 µM, artepillin C in its neutral state interacted with both liquid-ordered and liquid-disordered phases, inducing curvature stress and promoting dehydration at the membrane interface.

Interface-driven Sr-morin complexation at Langmuir monolayers for bioactive coating design.

Flavonoid-metal complexes are widely studied because of their interesting luminescent behavior and biological activity. Despite the extensive exploration of flavonoid-metal coordination processes in solution, the formation of complexes using the flavonoid molecule inserted in a lipid membrane has been little investigated. This effect could provide important insight into the biological activity of flavonoids at lipid membranes and could represent an attractive strategy to design supramolecular structures. Here, we studied the complexation between Sr2+ and morin inserted in an octadecylphosphonic acid (OPA) Langmuir monolayer. This is a relevant system due to the synergism imposed by the association of the Sr2+ ability to control bone formation/resorption with the morin antioxidative effect. Morin incorporation into the OPA monolayers and further Sr2+ complexation were monitored by surface pressure isotherms. Electronic absorption spectroscopy and fluorescence techniques showed Sr-morin complexation both in solution and at the air-liquid interface. Although morin complexation has been described to occur only at basic pH, the specific thermodynamic properties at the air-liquid interface drove metal complexation. LB films were deposited on Ti surfaces, and the resulting OPA/Sr-morin coatings exhibited high surface free energy and increase on its polar component. This optimized surface feature supported further serum protein adsorption and osteoblast growth and differentiation, indicating that these lipid-based coatings are promising for bioactive coating design. This study paves the way for the use of this lipid-based coating in the design of implants for faster osteointegration. Moreover, flavonoid-metal complexation at membranes could also help to shed light on the biological role played by flavonoids.

Effects of artepillin C on model membranes displaying liquid immiscibility

It has been hypothesized that the therapeutic effects of artepillin C, a natural compound derived from Brazilian green propolis, are likely related to its partition in the lipid bilayer component of biological membranes. To test this hypothesis, we investigated the effects of the major compound of green propolis, artepillin C, on model membranes (small and giant unilamelar vesicles) composed of ternary lipid mixtures containing cholesterol, which display liquid-ordered (lo) and liquid-disordered (ld) phase coexistence. Specifically, we explored potential changes in relevant membrane parameters upon addition of artepillin C presenting both neutral and deprotonated states by means of small angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and confocal and multiphoton excitation fluorescence microscopy. Thermotropic analysis obtained from DSC experiments indicated a loss in the lipid cooperativity of lo phase at equilibrium conditions, while at similar conditions spontaneous formation of unilamellar vesicles from SAXS experiments showed that deprotonated artepillin C preferentially located at the surface of the membrane. Time-resolved experiments using fluorescence microscopy showed that at doses above 100 µM, artepillin C in its neutral state interacted with both liquid-ordered and liquid-disordered phases, inducing curvature stress and promoting dehydration at the membrane interface.