Marcelo Gehlen - Academia.edu (original) (raw)
Papers by Marcelo Gehlen
Molecules, Dec 4, 2017
Quinizarin diester is used as a fluoro-chromogenic substrate of the activity of lipase supported ... more Quinizarin diester is used as a fluoro-chromogenic substrate of the activity of lipase supported in poly(methylmetacrylate) beads (CALB, Novozym® 435) dispersed in organic solvents. The monoester and diester of quinizarin are both non-fluorescent species contrasting with the enzymatic product quinizarin that shows optical absorption in the visible region and strong fluorescence signal. The enzymatic conversion is accomplished by spectroscopic measurements and it follows a sigmoid curve from which the mean reaction time of the enzymatic process can be determined. This parameter indicates the enzyme activity of the immobilized lipase. Its dependency with the amount of lipase allowed the determination of the ratio of the catalytic rate and the Michaelis constant (kc/Km) and the experimental value found was (1.0 ± 0.1) × 10−2 mg−1/min in the case of quinizarin diacetate.
The Journal of Physical Chemistry
Global analysis with the reference convolution method is applied to study the effect of probe mig... more Global analysis with the reference convolution method is applied to study the effect of probe migration between micelles on the fluorescence quenching. Analysis of synthetic single-photon timing data based on a modified Infelta-Tachiya equation including probe ...
The Journal of Physical Chemistry
EPE molecule. For comparison, the micelles first formed in PEO are small with an aggregation numb... more EPE molecule. For comparison, the micelles first formed in PEO are small with an aggregation number around 20 and increase in size to an aggregation number around 50 at saturation, ie, at the concentration where free micelles with an aggregation number of about 60 ...
Phys. Chem. Chem. Phys.
Knoevenagel condensation producing a fluorescent dye is studied at a single molecule level establ... more Knoevenagel condensation producing a fluorescent dye is studied at a single molecule level establishing a new method to investigate the molecular rate of amino catalysis.
Inorganic chemistry, Jan 7, 2017
Ruthenium polypyridine complexes have shown promise as agents for photodynamic therapy (PDT) and ... more Ruthenium polypyridine complexes have shown promise as agents for photodynamic therapy (PDT) and tools for molecular biology (chromophore-assisted light inactivation). To accomplish these tasks, it is important to have at least target selectivity and great reactive oxygen species (ROS) photogeneration: two properties that are not easily found in the same molecule. To prepare such new agents, we synthesized two new ruthenium complexes that combine an efficient DNA binding moiety (dppz ligand) together with naphthyl-modified (1) and anthracenyl-modified (2) bipyridine as a strong ROS generator bound to a ruthenium complex. The compounds were fully characterized and their photophysical and photochemical properties investigated. Compound 2 showed one of the highest quantum yields for singlet oxygen production ever reported (ΦΔ= 0.96), along with very high DNA binding (log Kb = 6.78). Such photochemical behavior could be ascribed to the lower triplet state involving the anthracenyl-modif...
Photochem. Photobiol. Sci., 2016
PbLIM is used to investigate the photostability of thionine in zeolite L. The gradient in the spa... more PbLIM is used to investigate the photostability of thionine in zeolite L. The gradient in the spatial distribution of the photostability is ascribed to a non-homogeneous distribution of active oxygen in the channels after irradiation.
Journal of Molecular Structure: THEOCHEM, 1999
Charge transfer (CT) complexation between pyrene (Py) and benzylviologen (BV+2) dication (1,1′-di... more Charge transfer (CT) complexation between pyrene (Py) and benzylviologen (BV+2) dication (1,1′-dibenzyl-4,4′-bipyridinium (2+)) is studied using AM1 semiempirical molecular orbital calculations and photophysical techniques. The optimized geometry of the single BV+2 dication shows a torsion angle φ of 43° for the central C–C bond of the dication in the ground state. The torsional barrier at φ=0° is of the order
The Journal of Physical Chemistry, 1993
ABSTRACT
Inorganic chemistry, Jan 10, 2003
The photophysical properties of a series of prepared ruthenium tris(bipyridine) complexes, covale... more The photophysical properties of a series of prepared ruthenium tris(bipyridine) complexes, covalently linked to aromatic species, of type [Ru(bpy)(2)-(4-methyl-4'-(arylaminocarbonyl)-2,2'-bipyridine)](2+) ([Ru(bpy)(2)(mbpy-L)](2+), where bpy = 2,2'-bipyridine; mbpy = 4-methyl-4'-carbonyl-2,2'-bipyridine; and L = 2-aminonaphthyl (naph), 9-aminoanthryl (anth), 1-aminopyrenyl (pyr), or 9-aminoacridinyl (acrd)) were studied by electronic absorption spectroscopy and steady state and time resolved luminescence spectroscopies. The absorption spectra of the MLCT electronic transition of the complexes are similar, which is in agreement with a practically constant redox potential of Ru(III/II) close to 1.28 V versus Ag/AgCl. However, the luminescence spectra of the new complexes are red shifted compared to Ru(bpy)(3)(2+), and this effect is ascribed to solvation and inductive effects of the amide group which enhance the symmetry breakdown among the three bipyridyl ligands....
Reviews in Fluorescence, 2011
Fluorescent dyes with photoinduced intramolecular charge-transfer (ICT) process driven by β-enami... more Fluorescent dyes with photoinduced intramolecular charge-transfer (ICT) process driven by β-enaminone group capable to form resonance-assisted hydrogen bond (RAHB) structure were prepared from aromatic and heterocyclic precursor molecules, such as 1-aminopyrene, 9-amino acridine, and adenine. The electronic ground and excited-state spectral properties of these new dyes are modulated by the type of substituent in the β-enaminone group and solvent interaction as well. The excited-state properties and the complex kinetics observed are results of the interplay between charge and proton transfer, together with the presence of possible conformers or tautomers associated with the keto-amine/enol-imine equilibrium. The applications of such dye derivatives as molecular probes in radical copolymerization with acrylic monomers and as reporters in silver nanoparticles dye interaction in solution are also discussed.
The Journal of Physical Chemistry, 1995
Journal of the Chemical Society, Faraday Transactions, 1997
The quenching of singlet and triplet electronic excited states of acridine cation by vinyl monome... more The quenching of singlet and triplet electronic excited states of acridine cation by vinyl monomers is investigated in homogeneous (methanol), aqueous, and reverse micelles of sodium dodecyl sulfate (SDS). The fluorescence quenching of the dye by styrene derivatives in methanol as well as in aqueous SDS micelles is very efficient with quenching rate constants of the order of 10 10 M -1 s -1 and 5×10 7 s -1 , respectively. However, triplet quenching rate constants in methanol are much lower than the diffusion controlled limit, and no dye photoblenching is observed suggesting that a quenching process follows a reversible photoinduced charge-transfer mechanism. The fluorescence quenching of the dye by styrene derivatives in reverse SDS micelles is a pseudo-first-order process with no micellar quenching transient. It is shown that placing the dye inside a reverse micelle substantially reduces the quenching rate by styrene derivatives. The scope of this effect on photoinitiation efficiency for radical polymerization of styrene derivatives via a photoredox process of cationic dyes in reverse micelles is discussed. Association constants of vinyl monomers to SDS micelles, K, as well as partition coefficients in n-octanol/water have been also determined using the fluorescence quenching method. K is correlated with the boiling points of the vinyl monomers.
Journal of the Chemical Society, Faraday Transactions, 1997
... Miguel G. Neumann,a* Marcelo H. Gehlen,a Maria V. Encinas,b Norman S. Allen,c Teresa Corrales... more ... Miguel G. Neumann,a* Marcelo H. Gehlen,a Maria V. Encinas,b Norman S. Allen,c Teresa Corrales,d Carmen Peinadod and Fernando ... TX3 and TX4 were carried out start-ing from the corresponding chloropropoxy derivatives, obtained as described earlier:11 0.3 moles of 1 ...
Journal of Molecular Structure: THEOCHEM, 2004
Electronic and vibrational spectra of 9-aminoacridine and acridine-9-N-methacrylamide are measure... more Electronic and vibrational spectra of 9-aminoacridine and acridine-9-N-methacrylamide are measured and compared with theoretical values obtained by quantum chemical calculations. Geometry, electronic transitions, charge distribution, population analysis, and the IR normal modes of this new dye and of its precursor have been computed by density functional theory (DFT) method with the functional B3LYP and the 6-31G(d) Gaussian basis set. The
Polymer Degradation and Stability, 2003
The thermal stability of poly(N-vinyl-2-pyrrolidone-co-methacrylic acid) copolymers was studied b... more The thermal stability of poly(N-vinyl-2-pyrrolidone-co-methacrylic acid) copolymers was studied by thermogravimetry and infrared spectroscopy in inert atmosphere. The thermogravimetric curves suggested that the effective degradation of both systems occurred in the temperature range 350-500 C with more than 60% mass loss. At this temperature, the activation energy was in the range 160-200 kJ mol À1 (average values), suggesting that the degradation occurred by a random scission of the chain. The FTIR results indicated that the main volatile products of degradation are CO 2 , CO and hydrocarbons (unsaturated structures) with low molecular weight. Pure PVP also showed the formation of NH 3 which was apparently suppressed in the copolymer by the formation of large amounts of CO 2 and CO. The results suggested that the thermal stability of the copolymers was essentially associated with the N-vinyl-2-pyrrolidone monomer, losing stability when the percentage of methacrylic acid in the copolymer system was increased.
Journal of Physical Chemistry, 1995
... In the reference convolution method, the time-resolved fluorescence profile of the sample, d,... more ... In the reference convolution method, the time-resolved fluorescence profile of the sample, d,(Aex,A,,,t), obtained by excitation at wavelength Lex and observed at emission wavelength ,Iem, is represented by30 ds(hexJem~) = dr(hexJem,t) ?(hex Jemtf) (13) ...
Journal of Nanoparticle Research, 2014
The enzymatic hydrolysis of quinizarin diester in silica nanoparticle (NP) of 200 nm diameter is ... more The enzymatic hydrolysis of quinizarin diester in silica nanoparticle (NP) of 200 nm diameter is investigated by confocal fluorescence microscopy. The quinizarin diester substrate and the intermediate quinizarin monoester are non-fluorescent species and only the end product—quinizarin formed by enzymatic hydrolysis produces intense fluorescence of the silica NP. The enzyme activity of lipase adsorbed into silica NP was similar to that observed for lipase chemically bound to silica surface. In both situations, partial aggregation of the silica NP dispersed in thin film of polyvinylpyrrolidone was observed from fluorescence and scanning electron microscopy images. The fluorescence decay of the end product—quinizarin in silica NP was biexponential with decay times of 0.49 and 2.17 ns. These two decay times found are ascribed to quinizarin adsorbed in silica NP and dispersed in the surrounding medium, respectively.
Molecules, Dec 4, 2017
Quinizarin diester is used as a fluoro-chromogenic substrate of the activity of lipase supported ... more Quinizarin diester is used as a fluoro-chromogenic substrate of the activity of lipase supported in poly(methylmetacrylate) beads (CALB, Novozym® 435) dispersed in organic solvents. The monoester and diester of quinizarin are both non-fluorescent species contrasting with the enzymatic product quinizarin that shows optical absorption in the visible region and strong fluorescence signal. The enzymatic conversion is accomplished by spectroscopic measurements and it follows a sigmoid curve from which the mean reaction time of the enzymatic process can be determined. This parameter indicates the enzyme activity of the immobilized lipase. Its dependency with the amount of lipase allowed the determination of the ratio of the catalytic rate and the Michaelis constant (kc/Km) and the experimental value found was (1.0 ± 0.1) × 10−2 mg−1/min in the case of quinizarin diacetate.
The Journal of Physical Chemistry
Global analysis with the reference convolution method is applied to study the effect of probe mig... more Global analysis with the reference convolution method is applied to study the effect of probe migration between micelles on the fluorescence quenching. Analysis of synthetic single-photon timing data based on a modified Infelta-Tachiya equation including probe ...
The Journal of Physical Chemistry
EPE molecule. For comparison, the micelles first formed in PEO are small with an aggregation numb... more EPE molecule. For comparison, the micelles first formed in PEO are small with an aggregation number around 20 and increase in size to an aggregation number around 50 at saturation, ie, at the concentration where free micelles with an aggregation number of about 60 ...
Phys. Chem. Chem. Phys.
Knoevenagel condensation producing a fluorescent dye is studied at a single molecule level establ... more Knoevenagel condensation producing a fluorescent dye is studied at a single molecule level establishing a new method to investigate the molecular rate of amino catalysis.
Inorganic chemistry, Jan 7, 2017
Ruthenium polypyridine complexes have shown promise as agents for photodynamic therapy (PDT) and ... more Ruthenium polypyridine complexes have shown promise as agents for photodynamic therapy (PDT) and tools for molecular biology (chromophore-assisted light inactivation). To accomplish these tasks, it is important to have at least target selectivity and great reactive oxygen species (ROS) photogeneration: two properties that are not easily found in the same molecule. To prepare such new agents, we synthesized two new ruthenium complexes that combine an efficient DNA binding moiety (dppz ligand) together with naphthyl-modified (1) and anthracenyl-modified (2) bipyridine as a strong ROS generator bound to a ruthenium complex. The compounds were fully characterized and their photophysical and photochemical properties investigated. Compound 2 showed one of the highest quantum yields for singlet oxygen production ever reported (ΦΔ= 0.96), along with very high DNA binding (log Kb = 6.78). Such photochemical behavior could be ascribed to the lower triplet state involving the anthracenyl-modif...
Photochem. Photobiol. Sci., 2016
PbLIM is used to investigate the photostability of thionine in zeolite L. The gradient in the spa... more PbLIM is used to investigate the photostability of thionine in zeolite L. The gradient in the spatial distribution of the photostability is ascribed to a non-homogeneous distribution of active oxygen in the channels after irradiation.
Journal of Molecular Structure: THEOCHEM, 1999
Charge transfer (CT) complexation between pyrene (Py) and benzylviologen (BV+2) dication (1,1′-di... more Charge transfer (CT) complexation between pyrene (Py) and benzylviologen (BV+2) dication (1,1′-dibenzyl-4,4′-bipyridinium (2+)) is studied using AM1 semiempirical molecular orbital calculations and photophysical techniques. The optimized geometry of the single BV+2 dication shows a torsion angle φ of 43° for the central C–C bond of the dication in the ground state. The torsional barrier at φ=0° is of the order
The Journal of Physical Chemistry, 1993
ABSTRACT
Inorganic chemistry, Jan 10, 2003
The photophysical properties of a series of prepared ruthenium tris(bipyridine) complexes, covale... more The photophysical properties of a series of prepared ruthenium tris(bipyridine) complexes, covalently linked to aromatic species, of type [Ru(bpy)(2)-(4-methyl-4'-(arylaminocarbonyl)-2,2'-bipyridine)](2+) ([Ru(bpy)(2)(mbpy-L)](2+), where bpy = 2,2'-bipyridine; mbpy = 4-methyl-4'-carbonyl-2,2'-bipyridine; and L = 2-aminonaphthyl (naph), 9-aminoanthryl (anth), 1-aminopyrenyl (pyr), or 9-aminoacridinyl (acrd)) were studied by electronic absorption spectroscopy and steady state and time resolved luminescence spectroscopies. The absorption spectra of the MLCT electronic transition of the complexes are similar, which is in agreement with a practically constant redox potential of Ru(III/II) close to 1.28 V versus Ag/AgCl. However, the luminescence spectra of the new complexes are red shifted compared to Ru(bpy)(3)(2+), and this effect is ascribed to solvation and inductive effects of the amide group which enhance the symmetry breakdown among the three bipyridyl ligands....
Reviews in Fluorescence, 2011
Fluorescent dyes with photoinduced intramolecular charge-transfer (ICT) process driven by β-enami... more Fluorescent dyes with photoinduced intramolecular charge-transfer (ICT) process driven by β-enaminone group capable to form resonance-assisted hydrogen bond (RAHB) structure were prepared from aromatic and heterocyclic precursor molecules, such as 1-aminopyrene, 9-amino acridine, and adenine. The electronic ground and excited-state spectral properties of these new dyes are modulated by the type of substituent in the β-enaminone group and solvent interaction as well. The excited-state properties and the complex kinetics observed are results of the interplay between charge and proton transfer, together with the presence of possible conformers or tautomers associated with the keto-amine/enol-imine equilibrium. The applications of such dye derivatives as molecular probes in radical copolymerization with acrylic monomers and as reporters in silver nanoparticles dye interaction in solution are also discussed.
The Journal of Physical Chemistry, 1995
Journal of the Chemical Society, Faraday Transactions, 1997
The quenching of singlet and triplet electronic excited states of acridine cation by vinyl monome... more The quenching of singlet and triplet electronic excited states of acridine cation by vinyl monomers is investigated in homogeneous (methanol), aqueous, and reverse micelles of sodium dodecyl sulfate (SDS). The fluorescence quenching of the dye by styrene derivatives in methanol as well as in aqueous SDS micelles is very efficient with quenching rate constants of the order of 10 10 M -1 s -1 and 5×10 7 s -1 , respectively. However, triplet quenching rate constants in methanol are much lower than the diffusion controlled limit, and no dye photoblenching is observed suggesting that a quenching process follows a reversible photoinduced charge-transfer mechanism. The fluorescence quenching of the dye by styrene derivatives in reverse SDS micelles is a pseudo-first-order process with no micellar quenching transient. It is shown that placing the dye inside a reverse micelle substantially reduces the quenching rate by styrene derivatives. The scope of this effect on photoinitiation efficiency for radical polymerization of styrene derivatives via a photoredox process of cationic dyes in reverse micelles is discussed. Association constants of vinyl monomers to SDS micelles, K, as well as partition coefficients in n-octanol/water have been also determined using the fluorescence quenching method. K is correlated with the boiling points of the vinyl monomers.
Journal of the Chemical Society, Faraday Transactions, 1997
... Miguel G. Neumann,a* Marcelo H. Gehlen,a Maria V. Encinas,b Norman S. Allen,c Teresa Corrales... more ... Miguel G. Neumann,a* Marcelo H. Gehlen,a Maria V. Encinas,b Norman S. Allen,c Teresa Corrales,d Carmen Peinadod and Fernando ... TX3 and TX4 were carried out start-ing from the corresponding chloropropoxy derivatives, obtained as described earlier:11 0.3 moles of 1 ...
Journal of Molecular Structure: THEOCHEM, 2004
Electronic and vibrational spectra of 9-aminoacridine and acridine-9-N-methacrylamide are measure... more Electronic and vibrational spectra of 9-aminoacridine and acridine-9-N-methacrylamide are measured and compared with theoretical values obtained by quantum chemical calculations. Geometry, electronic transitions, charge distribution, population analysis, and the IR normal modes of this new dye and of its precursor have been computed by density functional theory (DFT) method with the functional B3LYP and the 6-31G(d) Gaussian basis set. The
Polymer Degradation and Stability, 2003
The thermal stability of poly(N-vinyl-2-pyrrolidone-co-methacrylic acid) copolymers was studied b... more The thermal stability of poly(N-vinyl-2-pyrrolidone-co-methacrylic acid) copolymers was studied by thermogravimetry and infrared spectroscopy in inert atmosphere. The thermogravimetric curves suggested that the effective degradation of both systems occurred in the temperature range 350-500 C with more than 60% mass loss. At this temperature, the activation energy was in the range 160-200 kJ mol À1 (average values), suggesting that the degradation occurred by a random scission of the chain. The FTIR results indicated that the main volatile products of degradation are CO 2 , CO and hydrocarbons (unsaturated structures) with low molecular weight. Pure PVP also showed the formation of NH 3 which was apparently suppressed in the copolymer by the formation of large amounts of CO 2 and CO. The results suggested that the thermal stability of the copolymers was essentially associated with the N-vinyl-2-pyrrolidone monomer, losing stability when the percentage of methacrylic acid in the copolymer system was increased.
Journal of Physical Chemistry, 1995
... In the reference convolution method, the time-resolved fluorescence profile of the sample, d,... more ... In the reference convolution method, the time-resolved fluorescence profile of the sample, d,(Aex,A,,,t), obtained by excitation at wavelength Lex and observed at emission wavelength ,Iem, is represented by30 ds(hexJem~) = dr(hexJem,t) ?(hex Jemtf) (13) ...
Journal of Nanoparticle Research, 2014
The enzymatic hydrolysis of quinizarin diester in silica nanoparticle (NP) of 200 nm diameter is ... more The enzymatic hydrolysis of quinizarin diester in silica nanoparticle (NP) of 200 nm diameter is investigated by confocal fluorescence microscopy. The quinizarin diester substrate and the intermediate quinizarin monoester are non-fluorescent species and only the end product—quinizarin formed by enzymatic hydrolysis produces intense fluorescence of the silica NP. The enzyme activity of lipase adsorbed into silica NP was similar to that observed for lipase chemically bound to silica surface. In both situations, partial aggregation of the silica NP dispersed in thin film of polyvinylpyrrolidone was observed from fluorescence and scanning electron microscopy images. The fluorescence decay of the end product—quinizarin in silica NP was biexponential with decay times of 0.49 and 2.17 ns. These two decay times found are ascribed to quinizarin adsorbed in silica NP and dispersed in the surrounding medium, respectively.