Mariana Voicescu

A way for improving the stability of the essential oils in an environmental friendly formulation.

The essential oils (EOs) possess amazing properties explaining the interest for their applications in many essential domains. They also present the disadvantage of their chemical instability in the presence of air, light, moisture, and high temperatures. The paper focuses on two of the most known and used EOs, lavender and mint, respectively. The idea of the study was to protect them using the encapsulated systems. The originality of the work consists in the combination between the advantages of the molecular encapsulation of the EOs by cyclodextrins (CD) with the advantages offered by the sol-gel process. Original formulations have been processed by entrapping these essential oils in silica matrices obtained from a colloidal silica sol by the aqueous route of the sol-gel method. Another non-toxic ingredient, β-cyclodextrin, able to form inclusion complexes (ICs) with the essential oils has been used. The characterization methods (chromatography, UV-vis, IR, and NMR spectroscopies) have evidenced the presence of the mentioned inclusion complexes. Due to their formation, which modifies the water solubility of the EOs, the chromatographic analysis was possible using water as solvent, which is a novelty in EOs determinations. Protected from both the cyclodextrin and silica matrix, the essential oils became more resistant versus the effects of the environment factors. Thus, the resulted powders can find applications in domains as agriculture, food industries, cosmetics, pharmaceutical, and medicine.

Steady-State and Time Resolved Fluorescence Analysis on Tyrosine–Histidine Model Compounds

Four model compounds, for a tyrosine–histidine covalent bonding, 2-(5-imidazolyl)-4-methylphenol (C–C bonding in ortho-position at the phenyl group); 2′-(1-imidazolyl)-4-methylphenol (C–N bonding in ortho′-position at the phenyl group); 2-(5-imidazolyl)-4-H-phenol and 2-(5-imidazolyl)-4-H-phenol, at physiological pH have been studied by UV-Vis absorption, steady-state and time resolved fluorescence spectroscopy. Their absorption and emission properties are presented and discussed. The photophysical properties depend on the para-substituted phenyl group as well as on C–C/C–N bonding in the Phenol–Imidazole linkage. The N position, N1–N3/N1–N4, in the imidazole group was found to be relevant. The results are discussed with relevance to the redox processes of tyrosine and to better understand the role of a tyrosine–histidine covalent linkage as found in cytochrome c oxidase.

Energy Transfer from the Aminophthalate Dianion to Fluorescein

Energy transfer from the excited aminophthalate dianion species to fluorescein at pH 8.32 (Tris-HCl buffer) was studied. The excited aminophthalate dianion species was obtained either by excitation with UV radiation (330 nm), with fluorescence emission, or by the well-known chemical reaction luminol-hydrogen peroxide in an alkaline medium, with chemiluminescent emission, both with λmax at 425 nm. The influence of Co2+ and Mg2+ on fluorescence and chemiluminescence (CL) was studied. It was found that at low concentrations (10−7−10−9M), these ions do not modify the fluorescein fluorescence, however, the CL is strong affected. The effect of the concentration of these elements, which exert an influence on CL even at a high dilution (nanomolar concentration), was determined. In the case of Co2+ the prooxidant character is stronger than in the case of Mg2+, and therefore the CL enhancer effect is higher. Compared to the system without catalyst, their presence ensures stronger, prolonged, and stable light emission. The emission spectra, in the presence of fluorescein, show two bands with maxima at 425 and 520 nm, the second one being specific to fluorescein emission. The intensity of aminophthalate dianion luminescence is lower and the duration shorter in the presence of fluorescein. The influence of Co2+ and Mg2+ catalyst and fluorescein concentration on the energy transfer process was studied. The efficiency of the energy transfer process for these two situations (fluorescence and CL) was compared. An attempt was made to replace hydrogen peroxide with superoxide anion (solubilized by means of crown ether) and its effect upon the energy transfer process was observed.

Photophysical Properties of Some Flavones Probes in Homogeneous Media

Photophysical properties of five hydroxyflavones (HF) (some typical models of flavonols), (3 - HF, 6 - HF, 7-HF, 3, 6 - diHF and 3, 7 - diHF) were studied in homogeneous media by means of UV–vis and steady-state and time resolved fluorescence spectroscopies. Their absorption and fluorescence characteristics based on the flavonols structure are presented and discussed. It was found that the fluorescence of the flavonols depends on the nature of the solvent and on their molecular structure, especially on the position and the number of the -OH groups of the substituted phenyl ring. Attention is paid to the number of the -OH groups that influence the excited-state intramolecular proton transfer (ESIPT) process. The fluorescence quantum yield and the lifetime of the flavonols in heterogeneous media have been also determined. The results are discussed with relevance to the flavonols as sensitive fluorescence probe and to their microenvironments in the systems of biological interest and especially in a typical protein environment.

Spectrophotometric Study of Luminol in Dimethyl Sulfoxide–Potassium Hydroxide

The spectrophotometric study of luminol (LH2) in dimethyl sulfoxide (DMSO), DMSO-water solutions, and alkaline DMSO and DMSO-water solutions has been done, focusing on the effect of the KOH additon on LH2 absorption and fluorescence properties. The absorption spectra indicate an acid-base equilibrium, and the luminol dianion (L2−) formation at 3 × 10−4 − 2.4 × 10−3M KOH. The decrease of the fluorescence intensity and the variation of the excitation spectra of LH2-DMSO-KOH solutions with KOH concentration have been similarly explained. The acid-base process is reversible. The addition of HCl to the solution with 3.0 × 10−3 M KOH leads to an increase of the fluorescence intensity to its highest value, observed in pure DMSO. The addition of HCl to the LH2-DMSO solution leads to the decrease of the fluorescence intensity as a result of the LH+3 cation formation. In LH2-DMSO-water, the fluorescence band is shifted from 405 nm to 424 nm and increased in the intensity. In the presence of KOH (in LH2-DMSO-water-KOH solution) a new band appears, with the maximum at 485 nm and the band at 405 nm decreased. The changes in fluorescence lifetimes also evidence the different chemical species formed.

Effect of pH on the fluorescence characteristics of some flavones probes.

The photophysical properties such as electronic absorption, molar extinction coefficient, emission spectra, fluorescence quantum yield and lifetime of three different hydroxyflavones (a typical model of flavonols) such as: 3-HF, 3,6-diHF and 3,7-diHF, have been studied in the pH range from 2.5 to 9.2. Both electronic absorption and fluorescence spectra are sensitive to pH. The fluorescence quantum yield at pH 7.4 of the mentioned flavones probes have been determined. The fluorescence lifetime of different emissive species (Normal, Tautomer and Anion forms) as pH dependence have been also estimated. The effect of pH on the intramolecular excited state proton transfer process (ESIPT) has been discussed. The normal and tautomeric forms change as a function of pH, the normal one being more sensitive. The position of the -OH group on the second aromatic ring in the flavonols structure has been also discussed. The results have relevance to compounds which have photoreactions accompanied by dual fluorescence.

3,6-diHydroxyflavone/bovine serum albumin interaction in cyclodextrin medium: Absorption and emission monitoring

Photophysical properties of a bioactive flavonol which can be used as a model for polyhydroxylated natural flavonols, 3,6-diHydroxyflavone (3,6-diHF) in cyclodextrins (CDs)/bovine serum albumin (BSA) systems have been studied by absorption and fluorescence spectroscopy. The influence of CDs nature and of the different molar ratios BSA/CDs on the fluorescent characteristics of 3,6-diHF, and on the excited - state intramolecular proton transfer (ESIPT) process were studied. Quantitative information on the interaction between 3,6-diHF and BSA in CDs medium, were estimated. The influence of temperature (25-60°C range) on the intrinsic fluorescence of BSA in 3,6-diHF/BSA/CDs systems, was investigated. The results are discussed with relevance to 3,6-diHF as a potential sensitive fluorescence probe in the systems of biological interest.

Characterization of Two Quinone Radicals in the NADH:Ubiquinone Oxidoreductase from Escherichia coli by a Combined Fluorescence Spectroscopic and Electrochemical Approach

The NADH:ubiquinone oxidoreductase (complex I) couples the transfer of electrons from NADH to ubiquinone with the translocation of protons across the membrane. It was proposed that the electron transfer involves quinoid groups localized at the end of the electron transfer chain. To identify these groups, fluorescence excitation and emission spectra of Escherichia coli complex I and its fragments, namely, the NADH dehydrogenase fragment containing the flavin mononucleotide and six iron-sulfur (Fe-S) clusters, and the quinone reductase fragment containing three Fe-S clusters were measured. Signals sensitive to reduction by either NADH or dithionite were detected within the complex and the quinone reductase fragment and attributed to the redox transition of protonated ubiquinone radicals. A fluorescence spectroscopic electrochemical redox titration revealed midpoint potentials of -37 and- 235 mV (vs the standard hydrogen electrode) for the redox transitions of the quinone radicals in complex I at pH 6 with an absorption around 325 nm and a fluorescence emission at 460/475 nm. The role of these cofactor(s) for electron transfer is discussed.

Physicochemical Characterization and In Vitro Cytotoxic Effect of 3-Hydroxyflavone in a Silver Nanoparticles Complex.

The aim of this work was to characterize the physico-chemical properties of 3-hydroxyflavone (3-HF) in a silver nanoparticles complex (SNPs) using UV–vis and Fluorescence spectroscopy, Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) analysis. One also evaluated its effect on the cell viability and morphology of L929 mouse fibroblast cells in vitro. The contribution of the carrier protein, Bovine Serum Albumin (BSA) to 3-HF properties has also been investigated. 3-HF in BSA/SNPs systems presented no cytotoxic effect in L929 mouse fibroblast cells at any of the tested concentrations. The results are discussed with relevance to the oxidative stress process.

Fluorescence Characteristics of some Flavones Probes in Different Micellar Media

The fluorescence characteristics of five hydroxiflavones (HFs) (some typical models of flavonols), (3 - HF, 6 - HF, 7-HF, 3, 6 - diHF and 3, 7-diHF) in the micellar media of non-ionic surfactant (Triton X-100), anionic surfactant (SDS) and the block copolymer Pluronic F127, have been investigated by means of UV–Vis and steady-state and time resolved fluorescence spectroscopies. Attention is paid to both excited-state intra-molecular proton transfer (ESIPT) as well as ground-state intermolecular proton transfer. The influence of the -OH groups as well as the effect of temperature on the dual fluorescence emission, the Normal and Tautomer emissions, are also investigated. The fluorescence quantum yield of the HFs in mentioned micellar media has been also determined. The results are discussed with relevance to the local environment of HFs as sensitive fluorescence probe in biological membrane systems.