A high-performance liquid chromatography method for determination of flavonoids in dipalmitoylphosphatidylcholine liposome solutions

A high-performance liquid chromatography (HPLC) method for the determination of four different flavonoids, rutin, morin, quercetin, and 3-hydroxyflavone in dipalmitoylphosphatidylcholine (DPPC) liposome solutions hasbeen developed. The method allows to quantify theirconsumption upon reaction with singlet molecular oxygen.The actual HPLC method uses an isocratic elution and detection. The chromatographic separation of these components is achieved using a C18 analytical column with a water:acetonitrile:acetic acid mixture 74.5:24.5:1 v/v. The peaks for the four flavonoids are well resolved and free from matrix interference and reaction products.The method has been found to be linear (r > 0.999) overa wide concentration range and reliable to perform kineticstudies in which singlet molecular oxygen is involved and the time dependent consumption of flavonoids in a microorganized system composed by lipidic surfactants is monitored

Experimental and theoretical studies of the photophysics of 7-amino-3-phenyl-2H-benzo[b] [1,4]oxazin-2-one in homogeneous solvents and b-cyclodextrin aqueous solutions

The photophysical behavior of 7-amino-3-phenyl-2Hbenzo[b][1,4]oxazin-2-one was studied in organic solvents and in aqueous solutions of b-cyclodextrin using steady-state fluorescence and computational chemistry methods. In homogeneous media, fluorescence spectra show a noteworthy solvatochromic effect leading to large Stokes shifts. Linear solvation energy relationship and Lippert-Mataga equation analysis of the Stokes shifts indicate an increase of the dipolar moment in the singlet excited state and the participation of a partial chargetransfer state in the deactivation process. Incorporation of 7-amino-3-phenyl-2H-benzo[b][1,4]oxazin-2-one into the b-cyclodextrin inner cavity was monitored by observing the increase of fluorescence as a function of the cyclodextrin concentration. Analysis of fluorescence data in terms of Job plots and the Benesi-Hildebrand equation are indicate the formation of a 1:1 complex. The binding constantobtained from Benesi-Hildebrand plots was 597 M-1 at 298K. Also, the values of thermodynamics parameters determinedfrom the dependence of the binding constant on thetemperature show that inclusion is an enthalpy-driven process.Docking studies suggest that the complex stability is due to favorable van der Waals interactions within the cavity and a hydrogen bond interaction between the amino substituent and hydroxyl groups located in the narrow rim of the cavity. The same conclusion was achieved employing the Molecular Mechanics Poisson-Boltzmann Surface Area methodology to determine the energy contributions to the total free energy for the inclusion process

Solvent and compartmentalization effects on the photophysics of 4-(benzothiazol-2-yl)-N,N-diphenylaniline

The photophysical properties of 4-(benzothiazol-2-yl)-N,N-diphenylaniline, were studied in a series of solvents. UV–Vis absorption spectra are insensitive to solvent polarity whereas the fluorescence spectra in the same solvent set show an important solvatochromic effect leading tolarge Stokes shifts. Linear solvation energy relationships were employed to correlate the position of fluorescencespectra maxima with microscopic empirical solvent parameters. This study indicates that important intramolecular charge transfer takes place during the excitation process. In addition, an analysis of the solvatochromic behavior ofthe UV–Vis absorption and fluorescence spectra in terms of the Lippert-Mataga equation, shows a large increase of the excited-state dipole moment, which is also compatible with the formation of an intramolecular charge-transfer excited state. Given the above properties, we explored the potential of this fluorescent probe for the determination of thermodynamic parameters of micellar systems. We found that 4-(benzothiazol-2-yl)-N,N-diphenylaniline can be advantageously employed to determine CMC values of ionic (sodium dodecyl sufate) and non-ionic (Triton X-100 andsucrose monocaprate) surfactants and the partition constantof n-alcanols in SDS micelles

NanoFN10: A High-Contrast Turn-On Fluorescence Nanoprobe for Multiphoton Singlet Oxygen Imaging.

An “off-on” fluorescent nanoprobe for near-infrared multiphoton imaging of singlet oxygen has been developed. The nanoprobe comprises a naphthoxazole fluorescent unit and a singlet-oxygen-sensitive furan derivative attached to the surface of mesoporous silica nanoparticles. In solution, the fluorescence of the nanoprobe increases upon reaction with singlet oxygen both under one- and multiphoton excitation, with fluorescence enhancements up to 180-fold. The nanoprobe can be readily internalized by macrophage cells and is capable of imaging intracellular singlet oxygen under multiphoton excitation.Partial funding for open access charge: Universidad de Málag

Sucrose Monoester Micelles Size Determined by Fluorescence Correlation Spectroscopy (FCS)

One of the several uses of sucrose detergents, as well as other micelle forming detergents, is the solubilization of different membrane proteins. Accurate knowledge of the micelle properties, including size and shape, are needed to optimize the surfactant conditions for protein purification and membrane characterization. We synthesized sucrose esters having different numbers of methylene subunits on the substituent to correlate the number of methylene groups with the size of the corresponding micelles. We used Fluorescence Correlation Spectroscopy (FCS) and two photon excitation to determine the translational D of the micelles and calculate their corresponding hydrodynamic radius, Rh. As a fluorescent probe we used LAURDAN (6-dodecanoyl-2-dimethylaminonaphthalene), a dye highly fluorescent when integrated in the micelle and non-fluorescent in aqueous media. We found a linear correlation between the size of the tail and the hydrodynamic radius of the micelle for the series of detergents measured

Solvent effects on reactions of singlet molecular oxygen, O2(1Δg), with antimalarial drugs

Detection of O2(1Δg) emission, λmax=1270 nm, following laser excitation and steady-state methods were employed to measure total reaction rate constants, k T, for the reaction between singlet oxygen and the antimalarial drugs quinine (QU), quinacrine (QC), chloroquine (CQ) and amodiaquine (AQ) in several solvents. Values for k T range from 0.45±0.03×107 M-1 s-1 for AQ in benzene to 25.1±0.88×107 M-1 s-1 for CQ in N, N -dimethylformamide. Analysis of solvent effect on k T for QU, QC, and CQ by using the LSER formalism indicates that singlet oxygen deactivation by these drugs is accelerated by solvents with large π* values and hydrogen bond acceptor (HBA) properties and is inhibited by hydrogen bond donors (HBD) solvents. This result support the formation of an exciplex intermediate of charge transfer character, as proposed for reactions of tertiary amines with singlet oxygen, process largely governed by physical quenching. AQ behaves in a different manner. The LSER equation for this dru

Determination of chemical rate constants in singlet molecular oxygen reaction by using 1,4-dimethylnaphthalene endoperoxide

Thermal decomposition of 1,4-dimethylnaphthalene endoperoxide (DMNE) as a source of singlet oxygen was used to measure chemical rate constants, k(R), for reactions between singlet oxygen, O-2((1)Delta(g)), and various substrates. Time resolved O-2((1)Delta(g)) IR luminescence detection and steady-state experiments were used to monitor the decomposition of the endoperoxide and the rate of singlet oxygen production. Only 25% of oxygen from thermal decomposition of DMNE, in acetonitrile at 20degreesC, is detected as O-2((1)Delta(g)). Values of k(R) for reactions of O-2((1)Delta(g)) with 1,4-diphenylisobenzofurane (DPBF) and rubrene measured by this method are similar to values obtained by photosensitization. Values of k(R) for the chemical reaction of O-2((1)Delta(g)) with the antiinflammatory drugs piroxicam and tenoxicam, of (6.1 +/- 0.4) x 10(6) and (1.6 +/- 0.2) 10(7) M-1 s(-1), respectively, are close to those for the total singlet oxygen deactivation rate. Thermal decomposition of aromatic endoperoxides is a convenient source of singlet oxygen for measurements of rate constants in reactions of O-2((1)Delta(g)) where photosensitization cannot be employed. However, experimental conditions and approaches involved determine the method's limitations and applicability in a given system

Singlet oxygen reactions with flavonoids. a theoretical - experimental study

Detection of singlet oxygen emission, λmax = 1270 nm, following laser excitation and steady-state methods were employed to measure the total reaction rate constant, kT, and the reactive reaction rate constant, kr, for the reaction between singlet oxygen and several flavonoids. Values of kT determined in deuterated water, ranging from 2.4×107 M-1s-1 to 13.4×107 M-1s-1, for rutin and morin, respectively, and the values measured for kr, ranging from 2.8×105 M-1s-1 to 65.7×105 M-1s-1 for kaempferol and morin, respectively, being epicatechin and catechin chemically unreactive. These results indicate that all the studied flavonoids are good quenchers of singlet oxygen and could be valuable antioxidants in systems under oxidative stress, in particular if a flavonoid-rich diet was previously consumed. Analysis of the dependence of rate constant values with molecular structure in terms of global descriptors and condensed Fukui functions, resulting from electronic structure calculations, suppor

Quantum yields of singlet molecular oxygen, O2( 1Δg), produced by antimalaric drugs in organic solvents

Detection of singlet molecular oxygen, O2(1Δ g), by phosphorescence emission, λ = 1270 nm, following laser excitation was employed to measure the quantum yield of O2( 1δg) generation by the antimalaric drugs quinine, quinacrine, chloroquine and primaquine in several organic solvents. The same method was employed to measure total rate constants, kT, for quenching (physical and chemical) of O2(1Δ g) by the antimalaric drugs. All drugs studied sensitize singlet oxygen formation in organic media. Quinine was the most efficient sensitizer in the four solvents employed. Three of the drugs under study, quinine, quinacrine and chloroquine, produced efficiently singlet molecular oxygen in ethanol. Also, the antimalaric drugs are relatively efficient quenchers of singlet oxygen. Values of kT range from (0.63 ± 0.02) × 107 M-1 s-1 for primaquine in hexane to (17.1 ± 0.30) × 107 M-1 s-1 for primaquine in acetonitrile. Data obtained show that undesirable adverse cutaneous and ocular side effects a