Photophysical Behavior of Plant Flavonols Galangin, Kaempferol, Quercetin, and Myricetin in Homogeneous Media and the DMPC Model Membrane: Unveiling the Influence of the B-Ring Hydroxylation of Flavonols

Excited-state proton transfer based fluorescence in Kaempferol powder and solutions with different concentrations

Kaempferol (KMP) is one of the most common flavonoids, currently being extensively studied for its numerous beneficial health effects. Here we study the fluorescence (FL) emission of KMP powder and of its solutions prepared using different types of solvents (polar and non-polar). In the spectra of KMP powder and KMP solutions with high concentration, the same FL peak with maximum at 1.9 eV is observed. Another FL peak, at higher energy of 2.45 eV, emerges in solutions, its relative intensity increases with decreasing solution concentration. The FL emission of solutions with lowest concentration displays only that peak. To calculate characteristic energies of absorption and emission of KMP molecule in vacuum and in solutions we use time-dependent density functional theory. Comparing the results of computations with measured FL spectra, we associate the FL band at 1.9 eV with the emission due to excited state intramolecular transfer of the proton of -OH5 hydroxyl group. The FL emission at 2.45 eV is related to the -OH3 proton transfer. We measure the FL spectra of KMP powder using two different excitation energies, 3.06 eV and 2.33 eV, and find that its FL spectrum depends on the excitation energy. To understand that dependence, we compare the FL spectra of KMP and Q monohydrate powders. We consider the excited state intermolecular transfer of the proton from -OH3' hydroxyl group to a neighboring molecule in Q crystal and calculate the energy corresponding to the emission of the resulted anion of Q molecule. The spectral feature at 1.69 eV observed only in the FL spectrum of Q hydrate is attributed to the Q anion FL emission.

Exploring the Physical Properties of Lipid Membranes with Polyhydroxy Oxanorbornane Head Group Using NBD-Conjugated and DPH Fluorescent Probes

The present study focuses on exploring the physical properties of lipid membranes based on the polyhydroxy oxanorbornane (PH-ONB) headgroup, designed as synthetic analogues of naturally occurring archaeal lipid membranes. Specifically, we study two variants of PH-ONB headgroup-based lipids differing in the number of hydroxy groups present in the headgroup, with one having two hydroxy groups (ONB-2OH) and the other having three (ONB-3OH). These lipids form stable bilayer membranes. The study begins with a comprehensive analysis of the fluorescence characteristics of nitrobenzoxadiazole (NBD)-tagged ONB-based lipids in different solvent environments and within a model lipid membrane 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). Subsequently, the physical properties of the ONB-based membranes were examined by using an NBD-tagged ONB-based probe and a commonly used extrinsic 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescent probe. The steady-state and time-resolved fluorescence properties of the NBD-tagged ONB-based probe and DPH were used to compare the physical properties of the ONB-based membranes, including polarity, fluidity, phase transition, order, hydration, location, heterogeneity, and rotational diffusion. The solid gel to liquid crystalline phase transition temperatures of ONB-2OH and ONB-3OH lipid membranes are found to be (68 ± 1) °C and (74 ± 1) °C, respectively. The variation in organization (size), fluidity, and phase transition temperature of ONB-based lipid membranes is explained by the extent of hydrogen bonding interactions between lipid head groups. ONB-based membranes exhibit characteristics similar to those of phospholipid membranes and possess a notably high phase transition temperature. These properties make them a promising and cost-effective synthetic alternative to archaeal lipid membranes with a wide range of potential applications.

Comparative Analysis of Fluorescence Emission in Myricetin, Kaempferol, and Quercetin Powders and Solutions

Myricetin is a flavonol with high antioxidant properties. In this research, the fluorescence emission of myricetin powder and its solutions in different solvents were measured and analyzed by comparing with the results of calculations. Comparison of the calculated and measured characteristic wavelengths allowed the identification of all the spectral features in the fluorescence spectra of myricetin powder and solutions with different concentrations. The computation was based on modeling the process of the excited state intermolecular proton transfer, which predicts the formation of tautomeric forms of the flavonol molecule. Characteristic emission wavelengths were obtained using TDDFT/M06-2X/6-31++G(d,p). To understand the influence of the hydroxyl groups in the B-ring of the flavonol molecule on the emission spectrum, we also compared the fluorescence spectra of myricetin with those of kaempferol and quercetin. Moreover, based on the analysis of the changes in the shape of the FL spectra with the concentration of the solution, a criterion for the complete dissolution of the flavonol powders was established, which is important for bioavailability of flavonoids.

Design of flavonol-loaded cationic gold nanoparticles with enhanced antioxidant and antibacterial activities and their interaction with proteins

In this work, four structurally similar flavonols (galangin, kaempferol, quercetin and myricetin) were coated on the surface of (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide (MUTAB)‑gold nanoparticles (AuNPs) by two-step phase transfer and self-assembly, and the cationic MUTAB- AuNPs coated with flavonols (flavonol-MUTAB-AuNPs) were designed. Free radical scavenging and antibacterial experiments show that flavonol-MUTAB-AuNPs greatly improve the scavenging effect on DPPH, hydroxyl and superoxide anion radicals, and significantly enhance the inhibition effect on Staphylococcus aureus and Escherichia coli compared with flavonols and AuNPs. Then γ-globulin, fibrinogen, trypsin and pepsin were selected as representative proteins and their interaction with flavonol-MUTAB-AuNPs were investigated by various spectroscopic techniques. The fluorescence quenching mechanism of these four proteins by flavonol-MUTAB-AuNPs is static quenching. The binding constants Ka between them are in the range of 103 to 106. The interaction between them is endothermic, entropy-driven spontaneous process, and the main non-covalent force is the hydrophobic interaction. The effect of flavonol-MUTAB-AuNPs on the structure of the four proteins were investigated using UV-vis absorption spectra, synchronous fluorescence spectra and circular dichroism spectra. These results offer important insights into the essence of the interaction between flavonol-MUTAB-AuNPs and γ-globulin/fibrinogen/trypsin/pepsin. They will contribute to the development of safe and effective flavonol-MUTAB-AuNPs in biomedical fields.

Quercetin as a possible complementary therapy in multiple sclerosis: Anti-oxidative, anti-inflammatory and remyelination potential properties

Multiple sclerosis (MS) is a complex autoimmune disorder of the central nervous system (CNS) which causes various symptoms such as fatigue, dyscoordination weakness and visual weakness. The intricacy of the immune system and obscure etiology are the main reasons for the lack of a definite treatment for MS. Oxidative stress is one of the most important key factors in MS pathogenesis. It can enhance inflammation, neurodegeneration and autoimmune-mediated processes, which can lead to excessive demyelination and axonal disruption. Recently, promising effects of Quercetin as a non-pharmacological anti-oxidant therapy have been reported in preclinical studies of MS disease. In this review, we provide a compendium of preclinical and clinical studies that have investigated the effects of Quercetin on MS disease to evaluate its potential utility as a complementary therapy in MS. Quercetin treatment in MS disease not only protects the CNS against oxidative stress and neuroinflammation, but it also declines the demyelination process and promotes remyelination potential. The present study clarifies the reported knowledge on the beneficial effects of Quercetin against MS, with future implication as a neuroprotective complementary therapy.

Comparative study on the interaction between transferrin and flavonols: Experimental and computational modeling approaches

Transferrin is the indispensable component in the body fluids and has been explored as a potential drug carrier for target drugs to cancer cells. Flavonols are widely distributed in plants and shown a wide range of biological activities. In the present study, the interaction between flavonols (including galangin, kaempferol, quercetin, and myricetin) and transferrin under physiological conditions was investigated by using experimental as well as computational approaches. Fluorescence data reveal that the fluorescence quenching mechanism of transferrin by flavonols is static quenching. Transferrin has moderate affinity with flavonols, and the binding constants (K_a) are 10³-10⁴ L/mol. In addition, there are two different binding sites for the interaction between kaempferol and transferrin. Thermodynamic parameter analysis shows that the interaction of flavonols and transferrin is synergistically driven by enthalpy and entropy. Hydrophobic interaction, electrostatic force and hydrogen bonds are the main force types. Synchronous fluorescence spectroscopy shows that flavonols decrease the hydrophobicity of the microenvironment around tryptophan (Trp) and have no effect on the microenvironment around tyrosine (Tyr). UV-vis and CD spectra show that the interaction between transferrin and flavonols leads to the loosening and unfolding of transferrin backbone. The increase of β-sheet is accompanied by the decrease of α-helix and β-turn. The specific binding sites of flavonols to transferrin are confirmed by molecular docking. Molecular dynamic simulation suggests that the transferrin-flavonols docked complex is stable throughout the simulation trajectory.

Exploring Steroidal Surfactants as Potential Drug Carriers for an Anticancer Drug Curcumin: An Insight into the Effect of Surfactants' Structure on the Photophysical Properties, Stability, and Activity of Curcumin

Despite having tremendous medicinal benefits, the practical applications of curcumin are limited, owing to two major challenges: poor aqueous solubility and lack of bioavailability. In this regard, biosurfactant-based micellar systems have surged recently for the development of novel and more effective formulations because of their biological relevance. This study deals with a comprehensive and comparative investigation on the effect of seven structurally different steroidal surfactants on the photophysical properties of curcumin and also evaluates these steroidal surfactants as possible drug delivery media for curcumin. The photophysical properties of curcumin exhibited a strong dependence on the structure of the steroidal surfactant; the extent of excited-state proton transfer between curcumin and the surfactants depends strongly on the type of the side chain in the surfactants, which mostly dictates the photophysics of curcumin in the presence of these structural variants. The solubility of curcumin and its stability at different pHs and temperatures and in the presence of salt are significantly enhanced in the presence of these surfactants. Furthermore, the curcumin-loaded micelles exhibited improved intracellular uptake and cytotoxicity against MCF-7 cancer cells than pristine curcumin. Among these steroidal surfactants, CHAPS, the zwitterionic derivative of cholic acid, was the most efficient one to offer better solubility and stability to curcumin under all conditions, and the death rate of MCF-7 cells by curcumin was found to be the highest in the presence of CHAPS, indicating the enhanced bioavailability of curcumin. Therefore, CHAPS-based colloids are found to be promising candidates as potential drug carriers for curcumin.