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

Photodegradation of nimodipine and felodipine in microheterogeneous systems

Indexación: Web of Science; ScieloThe photochemical behavior of nimodipine (NIMO) and felodipine (FELO), photolabile drugs widely used as antihypertensive calcium channel blockers, is studied in constrained media. Specifically, we are interested in the kinetic analysis of 4-aryl-1,4-dihydropyridine photodegradation processes when they are incorporated in biological-mimicking systems like micelles or liposomes. In order to establish if the nature of the head of surfactant (ionic or nonionic) could be important modulating the photo-reactivity of these drugs, we studied the photodegradation of NIMO and FELO incorporated in micelles formed with sodium dodecyl sulfate (SDS, anionic), dodecyl-pyridinium chloride (DPC, cationic) and mono lauryl sucrose ester (MLS, nonionic) as surfactants. Additionally, the results of the photodegradation of these compounds in liposomes were also included. The results clearly indicate that both dihydropyridines studied, NIMO and FELO, are located near to the interface, but the surface charge of micelles does not affect neither, the photodegradation rate constant nor the photodegradation products profile. The absence of singlet oxygen generation in micellar media is consistent with the proposition of these 4-aryl-1,4-dihidropyridines located near to the interface of the micelle, where a polar environment is sensed. In addition, the ethanol preferential location on membranes and dihydropyridine enhanced photodegradation by alcohol presence are interesting results to consider in future research.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072012000300025&nrm=is

Development and validation of high performance liquid chromatographic and derivative spectrophotometric methods for the determination of candesartan cilexetil in pharmaceutical forms

In this work, two simple and fast methods for the determination of candesartan cilexetil in pharmaceutical forms, having it as a sole drug, were developed and validated. Candesartan cilexetil is a prodrug hydrolyzed to candesartan during absorption from the gastrointestinal tract. Candesartanis a selective AT1 subtype angiotensin II receptorantagonist used in the management of hypertension. The HPLC method uses a Chromolith RP-18e column. The mobile phase is acetonitrile - 0.1% trifluoroacetic acid aqueoussolution in ratio 50.0: 50.0 (v/v) in an isocratic elutionat a flow rate of 1.5 mL min-1. The diode array detector isoperated at 251 nm, and column temperature is set to 20  o C. The UV-derivative spectrophotometric method is based in the linear relation between drug concentration and first-order derivative spectrophotometric measurement. Alkalineaqueous solutions (0.1 M NaOH) of candesartan cilexetilexhibit a maximum at 246 nm and a minimum at 263 nm (1D 246-263). The sum of these two absolute values is the signalused on the range concentration 6.34 mg L-1 to 25.34mg L-1. The accuracy of the method, as mean recovery percent, is 98.9 % and the relative standard deviation, 0.76 %. Both methods were validated according to parameters established for specificity, linearity, precision, accuracy, stability and limits of quantification and detection. The limits of detection and quantification, chromatographic parameters and selectivity obtained are better than other published methods. These methods were applied for the content uniformity of solid dosage pharmaceutical forms of two commercial brands

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

Using Laurdan and Spectral Phasor Analysis to Study Erythrocytes Membrane Solubilization

Erythrocytes are widely used as a model system for membrane studies due to their relatively simple structure (they lack nuclei and organelles having only the plasma membrane), their convenient experimental manipulation and availability. However, the high hemoglobin content inside the red blood cells may be a problem for the use of fluorescent membrane probes. Hemoglobin content inside erythrocytes is around 20 mM and the molecules near the inner membrane surface would be the responsible for the quenching of fluorescent dyes such as 1,6-diphenyl-l,3,5-hexatriene (DPH) and 12-(9-anthroyl) stearic acid (AS).Instituto de Investigaciones Bioquímicas de La Plat

Carminic Acid Linked to Silica Nanoparticles as Pigment/Antioxidant Bifunctional Excipient for Pharmaceutical Emulsions

The incorporation of pigments and natural polyphenols into inorganic matrices, resulting in a hybrid material that improves the resistance and chemical stability of the pigments and the antioxidant capacity of the materials, has been of great interest to the pharmaceutical, chemical and food industries. The aim of this work was to prepare and characterize a bifunctional pigment–antioxidant nanomaterial-based carminic acid-decorated solid core-mesoporous shell silica nanoparticles, evaluating its properties as a pigment, its antioxidant capacity and its properties as a chemical stabilizer of emulsions. The chemical stability of oil-in-water (O/W) Pickering emulsions was evaluated determining the stability of vitamin E solubilized in the oil phase. Carminic acid was attached through the action of coupling ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) agents, and the resulting spherical and homogeneous nanoparticles showed a diameter close to 175 nm. A notorious change of emulsion color was observed by the addition of the nanomaterial. Emulsions showed an attractive pink color, and when the pH was adjusted to pH 3 and pH 9, a change in color was observed, analogous to carminic acid in solution. The nanomaterial incorporation also improved chemical stability, decreasing vitamin E consumption to 9.26% of the initial value, demonstrating an important antioxidant effect of the developed nanomaterial

The Beaker phenomenon and the genomic transformation of northwest Europe

From around 2750 to 2500 bc, Bell Beaker pottery became widespread across western and central Europe, before it disappeared between 2200 and 1800 bc. The forces that propelled its expansion are a matter of long-standing debate, and there is support for both cultural diffusion and migration having a role in this process. Here we present genome-wide data from 400 Neolithic, Copper Age and Bronze Age Europeans, including 226 individuals associated with Beaker-complex artefacts. We detected limited genetic affinity between Beaker-complex-associated individuals from Iberia and central Europe, and thus exclude migration as an important mechanism of spread between these two regions. However, migration had a key role in the further dissemination of the Beaker complex. We document this phenomenon most clearly in Britain, where the spread of the Beaker complex introduced high levels of steppe-related ancestry and was associated with the replacement of approximately 90% of Britain’s gene pool within a few hundred years, continuing the east-to-west expansion that had brought steppe-related ancestry into central and northern Europe over the previous centuries

In memoriam Professor Jaime Talesnik, MD.

In memoriam Jaime Talesnik. Born in Santiago, Chile, 18 May 1915; deceased Toronto, Canada, 7 April 1996. Medical studies at University of Chile, 1935-1940. MD, University of Chile, 1941. Assistant Professor of Physiology, Faculty of Biology and Medicine, University of Chile, 1940-45. Rockefeller Research Fellow, Banting-Best Institute, Department of Medical Research, University of Toronto, Canada, 1945-46. Associate Professor of Physiology, Faculty of Medicine, University of Chile, 1947-51. British Council Research Scholar in Pharmacology, National Institute for Medical Research, London, England, 1951-52. Associate Professor of Pathophysiology, Faculty of Medicine, University of Chile, 1952-63. Professor and Chairman, Department of Experimental Medicine, Faculty of Medicine, University of Chile, 1963-67. Visiting Professor, Department of Pharmacology, University of Toronto, Canada, 1967-69. Professor, Department of Pharmacology, University of Toronto, Canada, 1969-81. Professor Emeri

Is the determination of the association constant of cyclodextrin inclusion complexes dependent on the technique

Artículo de publicación SciELODifferences in association constants values of cyclodextrin inclusion complexes can be found in the literature. Most of the times, different experimental conditions have been used leading to different results. This paper reports the association constants (Ka) values of two different cyclodextrins (CD), namely native beta-CD (βCD) and hydroxypropyl-βCD (HP-βCD) with bentazon (BTZ, herbicide used in control of broadleaf weeds and sedges in many crops). These constants were determined by spectrophotometric and fluorescence measurements carried out under the same experimental conditions, and they were compared with those previously obtained by electrochemical techniques. The association constant values for the BTZ/HP-βCD inclusion complex obtained by fluorescence measurements were lower than those expected taking into account the values obtained from the other techniques. Differences in the complexation of the guest with CD in the excited and basal state could explain these results.Universidad de Chile, project ENL 003, 2013

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