M. V. Encinas

Universidad de Santiago de Chile

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E. A. Lissi

Universidad de Santiago de Chile

J. C. Scaiano

University of Ottawa

Carlos M. Previtali

National University of Río Cuarto

A. M. Rufs

Universidad de Santiago de Chile

Sonia G. Bertolotti

National University of Río Cuarto

Emilio Cardemil

Universidad de Santiago de Chile

Miguel G. Neumann

Universidade Federal de São Carlos

Andrés F. Olea

Universidad Autónoma de Chile

C. Majmud

Universidad de Santiago de Chile

P. K. Das

National Renewable Energy Laboratory

Cooperative Institutions

Universidad de Santiago de Chile

University of Chile

Pontificia Universidad Católica de Chile

Universidad Bernardo O'Higgins

National University of Río Cuarto

Consejo Superior de Investigaciones Científicas

University of Notre Dame

University of Buenos Aires

Universidad de La Frontera

Instituto de Química y Fisicoquímica Biológicas

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Solvent effect on the deactivation of excited naphthalene derivatives by unsaturated compounds

Journal of Photochemistry (1985)

M. V. Encinas E. A. Lissi

Hexane

Excimer

10.1016/0047-2670(85)85010-3

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Citations (7)

A sulfated galactan with antioxidant capacity from the green variant of tetrasporic Gigartina skottsbergii (Gigartinales, Rhodophyta)

Carbohydrate Research (2011)

Tamara Barahona M. V. Encinas Andrés Mansilla Betty Matsuhiro Elisa A. Zúñiga

Galactan

Residue (chemistry)

ABTS

Gigartinales

Carrageenan

10.1016/j.carres.2011.11.014

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Citations (44)

Urea-induced unfolding studies of free- and ligand-bound tetrameric ATP-dependent Saccharomyces cerevisiae phosphoenolpyruvate carboxykinase

The International Journal of Biochemistry & Cell Biology (2002)

M. V. Encinas Fernando D. González‐Nilo José M. Andreu Carlos Alfonso Emilio Cardemil

Protein quaternary structure

Denaturation (fissile materials)

Tetramer

10.1016/s1357-2725(01)00175-3

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Citations (6)

Riboflavin/Triethanolamine as Photoinitiator System of Vinyl Polymerization. A Mechanistic Study by Laser Flash Photolysis

Macromolecules (1999)

Sonia G. Bertolotti Carlos M. Previtali A. M. Rufs M. V. Encinas

The polymerization of 2-hydroxyethyl methacrylate photoinitiated by riboflavin in the presence of triethanolamine was investigated. The polymerization was also studied using as photoinitiator lumichrome, the major product obtained in the anaerobic photoreduction of riboflavin. Photopolymerization rates were measured as a function of amine concentration in the UV (366 nm) and visible (>450 nm) regions. The quenching of the excited states of the dyes by triethanolamine was investigated by fluorescence lifetime and laser flash photolysis experiments. Quenching rate constants were determined in the absence and the presence of monomer. These rate constants and singlet and triplet lifetimes were used to fit the polymerization rate vs amine concentration curves. From the fitting it was concluded that the interaction of both singlet and triplet excited states with the amine led to the 2-hydroxyethyl methacrylate polymerization.

Flash photolysis

Triethanolamine

Bulk polymerization

10.1021/ma981246f

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Citations (123)

Structure and Medium Effects on the Photochemical Behavior of Nonfluorinated Quinolone Antibiotics†

Photochemistry and Photobiology (2007)

Paulina Pávez Bárbara Herrera Alejandro Toro‐Labbé M. V. Encinas

The photophysical behavior of the quinolone antibiotics, oxolinic (OX), cinoxacin (CNX) and pipemidic (PM) acids was studied as a function of pH and solvent properties. The ground state of these compounds exhibits different protonated forms, which also exist in the first excited states. Theoretical calculations of the Fukui indexes allowed to assigning the different protonation equilibria. The pK values indicate that the acidity of the 3-carboxylic and 4-carbonyl groups increases with the N-atom at position 2 in CNX. It has been found that fluorescence properties are strongly affected by pH, the more fluorescent species is that with protonated carboxylic acid, protonated species at the carbonyl group and the totally deprotonated form present very low fluorescence. The fluorescence behavior also depends on the chemical structure of the quinolone and on the solvent properties. The analysis of the solvent effect on the maximum and the width of the fluorescence band of OX, using the linear solvent–energy relation solvatochromic equation, indicates that the polarizability and hydrogen bond donor ability are the parameters that condition the spectral changes. The hydrogen bond acceptor ability of the solvents also contributes to the spectral shifts of CNX. The compound bearing the piperazinyl group at the position 7, PM only is fluorescent in high protic solvents. These results are discussed in terms of the competition between the intra- and intermolecular hydrogen bonds. The irradiation of OX, CNX and PM using 300 nm UV light led to a very low photodecomposition rate. Under the same conditions the nalidixic acid (NA), a structurally related quinolone, photodecomposes two orders of magnitude faster.

Solvatochromism

10.1562/2006-08-21-ra-1009

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Citations (8)

ChemInform Abstract: PHOTOCHEMISTRY OF 1,5‐DIARYL‐1,5‐DIKETONES

Chemischer Informationsdienst (1980)

J. P. Bays M. V. Encinas R. D. Small J. C. Scaiano

10.1002/chin.198017117

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Citations (0)

Free Radical Production upon Photoinduced Electron Transfer Reactions in the Presence of Vinyl Monomers. Effect of Water Addition*

Photochemistry and Photobiology (1998)

M. V. Encinas E. A. Lissi A. M. Rufs Marcela S. Altamirano Juan J. Cosa

Abstract Free radical fragments produced in the photoinduced electron transfer from triethylamine (TEA) to excited pyrenebutyltrimethylammonium (*PyBu + ) lead to 1‐vi‐nyl‐2‐pyrrolidinone (VP) and 2‐hydroxyethyl methacry‐late (HEMA) polymerization. Experiments carried out in water/acetonitrile solvent mixtures showed that the polymerization rate of VP increases upon increasing the water content, whereas the polymerization rate of HEMA follows the opposite trend. These results are interpreted in terms of the strong dependence on the solvent properties of the photochemical behavior of PyBu + in the presence of the amine or monomers. Thus, the *PyBu + quenching by VP is almost negligible in both solvents (water and acetonitrile). Whereas, the *PyBu + quenching rate constant by HEMA in water is 4 times 10 9 M −l s −1 and decreases four orders of magnitude in acetonitrile. The quenching of *PyBu + by TEA in aqueous solutions is controlled by hydrogen‐bonding interactions between water molecules and the amine. Quantum yields of the pyrene radical anion (φ Py ) also strongly depend on the water content, decreasing from 0.28 to 0.015 upon going from acetonitrile to water.

Photoinduced electron transfer

10.1111/j.1751-1097.1998.tb02498.x

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Citations (6)

PHOTOPHYSICAL STUDIES OF INDOLE ALKANOIC ACIDS and TRYPTAMINE IN REVERSE MICELLES OF SODIUM DIOCTYL SULFOSUCCINATE

Photochemistry and Photobiology (1990)

M. V. Encinas E. A. Lissi Sonia G. Bertolotti Juan J. Cosa Carlos M. Previtali

Abstract— The fluorescence spectra and emission lifetimes of several 3‐alkanoic indoles of different chain length and tryptamine (TA) were studied in sodium dioctyl sulfosuccinate (AOT)/heptane reverse micelles over a wide range of water/AOT ratio (R ‐ 5 to 44). Fluorescence quenching experiments were done using carbon tetrachloride and acrylamide as quenchers. Experiments with TA were carried out using water at pH 3 in order to assure its protonation. Under these conditions, the results indicate that the indole moiety of TA remains at the micellar interface over all the range considered. Furthermore, the results can be interpreted assuming for the TA population a single microenvironment whose properties remain almost invariant when R increases from 11 to 44. The studies employing the 3‐alkanoic indoles were carried out at pH 10. Under these conditions, the anions are progressively displaced to the water pool when the R value increases. This displacement is determined by the length of the side alkyl chain of the 3‐indole derivatives. For these compounds, the quenching experiments indicate that, even at low R values, the excited indole moieties are distributed among different microenvironments.

Moiety

10.1111/j.1751-1097.1990.tb01814.x

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Citations (19)

The interaction of aliphatic amines with safranine T in aqueous solution

Journal of Photochemistry and Photobiology A Chemistry (1996)

M. V. Encinas Carlos M. Previtali Marcelo H. Gehlen Miguel G. Neumann

10.1016/1010-6030(95)04218-0

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Citations (23)

Saccharomyces cerevisiae phosphoenolpyruvate carboxykinase: physicochemical characteristics of the nucleotide binding site, as deduced from fluorescent spectroscopy measurements

Biochemistry (1990)

M. V. Encinas Veronica Quinones Emilio Cardemil

Saccharomyces cerevisiae phosphoenolpyruvate carboxykinase [ATP:oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.49] is inactivated by the fluorescent sulfhydryl reagent N-(iodoacetyl-N'-(5-sulfo-1-naphthyl)ethylenediamine (1,5-IAEDANS). The inactivation reaction follows pseudo-first-order kinetics with respect to active enzyme to less than 10% remaining enzyme activity, with a second-order inactivation rate constant of 2.6 min-1 mM-1 at pH 7.5 and 30 degrees C. A stoichiometry of 1.05 mol of reagent incorporated per mole of enzyme subunit was found for the completely inactivated enzyme. Almost complete protection of the enzyme activity and of dansyl label incorporation are afforded by MnADP or MnATP, thus suggesting that 1,5-IAEDANS interacts with an enzyme sulfhydryl group at the nucleotide binding site. The fluorescence decay of the AEDANS attached to the protein shows a single-exponential behavior with a lifetime of 18 ns. A comparison of the fluorescence band position and the fluorescence decay with those of the adduct AEDANS-acetylcysteine indicates a reduced polarity for the microenvironment of the substrate binding site. The quenching of the AEDANS moiety in the protein can be described in terms of a collisional and a static component. The rate constant for the collisional component is much lower than that obtained for the adduct in a medium of reduced polarity. These last results indicate that the AEDANS moiety is considerably shielded from the solvent when it is covalently attached to PEPCK.

Moiety

10.1021/bi00471a007

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Citations (18)