The Experts below are selected from a list of 186 Experts worldwide ranked by ideXlab platform
Armi Wanderley Da Nobrega - One of the best experts on this subject based on the ideXlab platform.
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a liquid chromatography tandem mass spectrometry confirmatory assay for the simultaneous determination of several tetracyclines in milk considering keto enol Tautomerism and epimerization phenomena
Analytica Chimica Acta, 2009Co-Authors: Bernardete Ferraz Spisso, Marcus Antonio Goncalves De Araujo, Mychelle Alves Monteiro, Adelia Mara Belem Lima, Mararlene Ulberg Pereira, Robson Alves Luiz, Armi Wanderley Da NobregaAbstract:Abstract A liquid chromatography-electrospray ionization tandem mass spectrometric (LC–ESI-MS/MS) method for the analysis of several tetracyclines residues in bovine milk has been developed. Milk deproteinization/extraction of samples was performed with acidified acetonitrile. After diluting and purification by solid-phase extraction (SPE), the extracts were injected into the instrument operated in Multiple Reaction Monitoring (MRM) acquisition mode. The reversible epimerization at C-4 of oxytetracycline, tetracycline and chlortetracycline and the keto–enol Tautomerism of chlortetracycline between C-11a and C-12 were considered for reliable quantification. Degradation was also taken in account and minimized for the same purpose. A central composite (response surface) design with desirability function was employed for the optimization of extraction and clean-up steps. The optimization improved the extraction efficiency of the more polar analytes reaching 93.9% for 4-epioxytetracycline and 95.8% for oxytetracycline at 100 μg L −1 . The validation was performed following the criteria established by Commission Decision 2002/657/EC.
Nail Saleh - One of the best experts on this subject based on the ideXlab platform.
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spectroscopic studies of keto enol tautomeric equilibrium of azo dyes
RSC Advances, 2015Co-Authors: M A Rauf, Soleiman Hisaindee, Nail SalehAbstract:Azo dyes account for 60–70% of all dyes known to date. Understanding the factors that affect the direction of keto–enol Tautomerism in azo dyes through spectral measurements is crucial to their potential applications. This review encompasses the most important spectroscopic studies of different azo dyes categorized by their structures within the last few years (2010–2014). It is concluded that the stability of the keto and enol forms largely arises from the ability to establish intra-molecular and inter-molecular hydrogen bonding, respectively. There are many factors that affect the keto or enol form, for example, polar solvent, high temperature, neutral pH and electron withdrawing substituents favor the keto form through intramolecular hydrogen bonding, whereas, nonpolar solvent, low temperature, high pH and electron donating groups favor the enol form through intermolecular hydrogen bonding. Encapsulation inside nanocaged microheterogenous systems creates a rigid environment that stabilizes the enol form mostly, while in the solid state, most of the tautomeric equilibrium lies in favor of the keto form. Understanding of keto–enol Tautomerism in azo dyes helps to probe solvation dynamics, to tune the pKa values in chemical sensing, and to explain proton transfer in the excited state.
Indira K Priyadarsini - One of the best experts on this subject based on the ideXlab platform.
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multitargeting by curcumin as revealed by molecular interaction studies
Natural Product Reports, 2011Co-Authors: Subash C Gupta, Sahdeo Prasad, Ji Hye Kim, Sridevi Patchva, Lauren J Webb, Indira K Priyadarsini, Bharat B AggarwalAbstract:Covering: up to early 2011 Curcumin (diferuloylmethane), the active ingredient in turmeric (Curcuma longa), is a highly pleiotropic molecule with anti-inflammatory, anti-oxidant, chemopreventive, chemosensitization, and radiosensitization activities. The pleiotropic activities attributed to curcumin come from its complex molecular structure and chemistry, as well as its ability to influence multiple signaling molecules. Curcumin has been shown to bind by multiple forces directly to numerous signaling molecules, such as inflammatory molecules, cell survival proteins, protein kinases, protein reductases, histone acetyltransferase, histone deacetylase, glyoxalase I, xanthine oxidase, proteasome, HIV1 integrase, HIV1 protease, sarco (endo) plasmic reticulum Ca2+ ATPase, DNA methyltransferases 1, FtsZ protofilaments, carrier proteins, and metal ions. Curcumin can also bind directly to DNA and RNA. Owing to its β-diketone moiety, curcumin undergoes keto–enol Tautomerism that has been reported as a favorable state for direct binding. The functional groups on curcumin found suitable for interaction with other macromolecules include the α, β-unsaturated β-diketone moiety, carbonyl and enolic groups of the β-diketone moiety, methoxy and phenolic hydroxyl groups, and the phenyl rings. Various biophysical tools have been used to monitor direct interaction of curcumin with other proteins, including absorption, fluorescence, Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy, surface plasmon resonance, competitive ligand binding, Forster type fluorescence resonance energy transfer (FRET), radiolabeling, site-directed mutagenesis, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), immunoprecipitation, phage display biopanning, electron microscopy, 1-anilino-8-naphthalene-sulfonate (ANS) displacement, and co-localization. Molecular docking, the most commonly employed computational tool for calculating binding affinities and predicting binding sites, has also been used to further characterize curcumin's binding sites. Furthermore, the ability of curcumin to bind directly to carrier proteins improves its solubility and bioavailability. In this review, we focus on how curcumin directly targets signaling molecules, as well as the different forces that bind the curcumin–protein complex and how this interaction affects the biological properties of proteins. We will also discuss various analogues of curcumin designed to bind selective targets with increased affinity.
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photophysics photochemistry and photobiology of curcumin studies from organic solutions bio mimetics and living cells
Journal of Photochemistry and Photobiology C-photochemistry Reviews, 2009Co-Authors: Indira K PriyadarsiniAbstract:Curcumin, with its recent success as an anti-tumor agent, has been attracting researchers from wide ranging fields of physics, chemistry, biology and medicine. The chemical structure of curcumin has two o-methoxy phenols attached symmetrically through α,β-unsaturated β-diketone linker, which also induces keto–enol Tautomerism. Due to this, curcumin exhibits many interesting photophysical and photochemical properties. The absorption maximum of curcumin is ∼408–430 nm in most of the organic solvents, while the emission maximum is very sensitive to the surrounding solvent medium (460–560 nm) and the Stokes’ shift varied from 2000 to 6000 cm−1. The fluorescence quantum yield in most of the solvents is low and reduced significantly in presence of water. The fluorescence lifetime is short (<1 ns) and displayed multi-exponential decay profile. The singlet excited states of curcumin decay by non-radiative processes contributed mainly by intra- and intermolecular proton transfer with very low intersystem crossing efficiency. Polarity, π-bonding nature, hydrogen bond donating and accepting properties of the solvent influence the excited state photophysics of curcumin in a complex manner. The triplet excited states of curcumin absorb at 720 nm and react with oxygen to produce singlet molecular oxygen. The photodegradation of curcumin produces smaller phenols and the photobiological activity of curcumin is due to the generation of reactive oxygen species. Being lipophilic in nature, the water solubility of curcumin could be enhanced upon the addition of surfactants, polymers, cyclodextrins, lipids and proteins. Changes in the absorption and fluorescence properties of curcumin have been found useful to follow its interaction and site of binding in these systems. Curcumin fluorescence could be employed to follow the unfolding pattern and structural changes in proteins. The intracellular curcumin showed more fluorescence in tumor cells than in normal cells and fluorescence spectroscopy could be used to monitor its preferential localization in the membrane of tumor cells. This review, presents the current status of research on the photophysical, photochemical and photobiological processes of curcumin in homogeneous solutions, bio-mimetics and living cells. Based on these studies, the possibility of developing curcumin, as a bimolecular sensitive fluorescent probe is also discussed.
Bernardete Ferraz Spisso - One of the best experts on this subject based on the ideXlab platform.
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a liquid chromatography tandem mass spectrometry confirmatory assay for the simultaneous determination of several tetracyclines in milk considering keto enol Tautomerism and epimerization phenomena
Analytica Chimica Acta, 2009Co-Authors: Bernardete Ferraz Spisso, Marcus Antonio Goncalves De Araujo, Mychelle Alves Monteiro, Adelia Mara Belem Lima, Mararlene Ulberg Pereira, Robson Alves Luiz, Armi Wanderley Da NobregaAbstract:Abstract A liquid chromatography-electrospray ionization tandem mass spectrometric (LC–ESI-MS/MS) method for the analysis of several tetracyclines residues in bovine milk has been developed. Milk deproteinization/extraction of samples was performed with acidified acetonitrile. After diluting and purification by solid-phase extraction (SPE), the extracts were injected into the instrument operated in Multiple Reaction Monitoring (MRM) acquisition mode. The reversible epimerization at C-4 of oxytetracycline, tetracycline and chlortetracycline and the keto–enol Tautomerism of chlortetracycline between C-11a and C-12 were considered for reliable quantification. Degradation was also taken in account and minimized for the same purpose. A central composite (response surface) design with desirability function was employed for the optimization of extraction and clean-up steps. The optimization improved the extraction efficiency of the more polar analytes reaching 93.9% for 4-epioxytetracycline and 95.8% for oxytetracycline at 100 μg L −1 . The validation was performed following the criteria established by Commission Decision 2002/657/EC.
Andrey G Lvov - One of the best experts on this subject based on the ideXlab platform.
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reversible shifting of a chemical equilibrium by light the case of keto enol Tautomerism of a β ketoester
Organic Letters, 2020Co-Authors: Andrey G Lvov, Anton V Yadykov, Konstantin A Lyssenko, Frank W Heinemann, Valerii Z Shirinian, Marat M KhusniyarovAbstract:Manipulating the equilibrium between a ketone and an enol by light opens up ample opportunities in material chemistry and photopharmacology. By incorporating β-ketoester into the ethene bridge of a photoactive diarylethene, we achieved reversible light-induced tautomerization to give thermally stable enol. In a pristine state, the tautomeric equilibrium is almost completely shifted toward the ketone. Photocyclization of diarylethene results in a new equilibrium containing a significant fraction of the enol tautomer.
