The Antioxidative Activity of Riboflavin in the Presence of Antipyrin. Spectroscopic Studies

Fluorescent Flavin/PVP-Coated Silver Nanoparticles: Design and Biological Performance

A red-emitting fluorescent Riboflavin (RF)/Polyvinylpyrrolidone (PVP)-coated silver nanoparticles system, λ_em = 527 nm, Φ = 0.242, with a diameter of the metallic core of 27.33 nm and a zeta potential of - 25.05 mV was prepared and investigated regarding its biological activity. We found that PVP has a key role in RF adsorption around the SNPs surface leading to an enhancement of antioxidant properties (∼70%), low cytotoxicity (> 90% cell viability, at 50 µL/mL, after 48 h of incubation) as well as to an efficient process of its cellular uptake (∼ 60%, after 24 h of incubation) in L929 cells. The results are relevant concerning the involvement of RF and its coenzymes forms in SNPs - based systems, in cellular respiration as well as for future studies as antioxidant marker system on tumoral cells for viewing and monitoring them, by cellular imaging.

Carbon Nanodots as a Multifunctional Fluorescent Sensing Platform for Ratiometric Determination of Vitamin B2 and "Turn-Off" Detection of pH

In this work, we synthesized carbon nanodots (CNDs) by a one-pot hydrothermal method to carbonize precursors of dry carnation petals and polyethylenimine. The obtained CNDs possess favorable photostability, good biocompatibility, and excellent water solubility, which can serve as a dual-responsive nanosensor for the determination of vitamin B₂ (VB₂) and pH. A unique ratiometric fluorescence resonance energy transfer probe was developed through a strong interaction between VB₂ and surface moieties of CNDs. CNDs emitted at 470 nm; however, in the presence of VB₂, an enhanced emission peak was clearly observed at 532 nm. The value of I₅₃₂/I₄₇₀ exhibits a stable response to the VB₂ concentration from 0.35 to 35.9 μM with a detection limit of 37.2 nM, which has been used for VB₂ detection in food and medicine samples and ratiometric imaging of VB₂ in living cells with satisfying performance. In addition, the proposed CNDs also displayed pH-sensitive behavior and can be a turn-off fluorescent sensor to monitor pH. The fluorescent intensity at 470 nm is a good linear response against pH values from 3.6 to 8, affording the capability as a single-emissive nanoprobe for intracellular pH sensing.

Spectroscopic, molecular dynamics simulation and biological studies of Flavin MonoNucleotide and Flavin Adenine Dinucleotide in biomimetic systems

The present study describes a comprehensive investigation of the spectroscopic characteristics, stability and in vitro antioxidant and cytotoxic properties of the Flavin MonoNucleotide (FMN) and Flavin Adenine Dinucleotide (FAD) in Dextran70 (Dx70) and Dx70/phospatidylcholine (PC) biomimetic systems by means of the UV-Vis absorption, fluorescence spectroscopy, chemiluminescence and Neutral Red assay. The affinity of FMN, FAD and the precursor riboflavin (RF) to an unsaturated phospholipid bilayer model as well as the location of the probes within the lipid bilayer were assessed from united-atom molecular dynamics simulations carried out on an unsaturated phospholipid bilayer model system, and the theoretical and experimental characterization of the two probes within biomembranes was complemented with the light microscopy survey of the cell morphology of L929 fibroblast cells cultivated in the presence of various dosage of FAD/FMN. In lipid bilayers, FMN/FAD resulted in a noticeable improvement of the antioxidant activity (the scavenging of reactive oxygen species up to 40%) and a significant effect on cellular viability in the L929 fibroblast cells. The results are important in the oxidative stress process concerning the redox reactions of flavins in humans as well as in further studies on different systems belonging to the category of flavoenzymes/flavoproteins, required for cellular respiration.

Synthesis and biophysical characteristics of riboflavin/HSA protein system on silver nanoparticles

Novel l‑Arginine‑Dextran70 based-silver nanoparticles (SNPs) (SNPs^Arg), functionalized with Riboflavin (RF) and Human Serum Albumin (HSA) were characterized by UV-Vis absorption, Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), fluorescence and circular dichroism spectroscopy, chemiluminescence and Neutral red assays. TEM analysis showed the formed faceted particles, large clumps/fused aggregates, nano-featured with the mean particle size of 41.60 nm. Chemiluminescence and Neutral red assays for in vitro antioxidant and cytotoxic activities of the SNPs^Arg/RF/HSA systems have been studied. It was pointed out that SNPs^Arg functionalized with RF and HSA resulted in a bio-nanosystem which leads to a high activity against oxygen free radicals, altered viability, morphology, apoptotic bodies and decreased cell density of L929 fibroblast cells. Results are relevant for understanding the redox properties of RF in the case of biological applications and especially for RF containing drugs.

Spectroscopic study of 3-Hydroxyflavone - protein interaction in lipidic bi-layers immobilized on silver nanoparticles

The interaction of 3-Hydroxyflavone with serum proteins (BSA and HSA) in lecithin lipidic bi-layers (PC) immobilized on silver nanoparticles (SNPs), was studied by fluorescence and Raman spectroscopy. BSA secondary structure was quantified with a deconvolution algorithm, showing a decrease in α-helix structure when lipids were added to the solution. The effect of temperature on the rate of the excited-state intra-molecular proton transfer and on the dual fluorescence emission of 3-HF in the HSA/PC/SNPs systems was discussed. Evaluation of the antioxidant activity of 3-HF in HSA/PC/SNPs systems was also studied. The antioxidant activity of 3-HF decreased in the presence of SNPs. The results are discussed with relevance to the secondary structure of proteins and of the 3-HF based nano-systems to a topical formulation useful in the oxidative stress process.

Antioxidant activity of phytoestrogen type isoflavones in biomimetic environments

Oxidation of phytoestrogen type isoflavones in lecithin lipidic bi-layers and in silver nanoparticle complexes by the chemiluminescence method.