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4. Exploring the effect of pore size on the activity of superoxide dismutase mimics immobilized in mesoporous spherical silica particles.

Author

Patriarca, Matías, Lombardelli, Marcelo, Pellegri, Nora, Daier, Verónica, and Signorella, Sandra R.

Subjects
SUPEROXIDE dismutase, HYBRID materials, COPPER, MESOPOROUS silica, TETRAZOLIUM, METALS
Abstract

The imidazolate-bridged diCu(II) complex [Cu2(dien)2(μ-Im)]3+ (Im = imidazolate, dien = diethylenetriamine) was encapsulated in mesoporous spherical silica particles (MSSP) with retention of the morphology and mesostructure of the guest-free silica particles. This hybrid material catalyzes the dismutation of superoxide efficiently, with second-order catalytic rate constant of 8.28 × 107 M−1 s−1, obtained from the nitro blue tetrazolium photoreduction inhibition superoxide dismutase assay, at pH = 7.8. The small silica channels of MSSP (wp = 2.7 nm) enhance the distortion of the Cu(II) local environment compared to mesoporous silicas with wider pores and ensure the two metal moieties of the reduced catalyst remain in close proximity to react with superoxide. These two combined effects increase the SOD activity of the hybrid material ten times over the free catalyst. The small channel size is also relevant for the salpn derived functional SOD mimic [CuZn(salpn)Cl2] (H2salpn = 1,3-bis(salicylideneamino)propane), which upon encapsulation in MSSP doubles its SOD activity. [ABSTRACT FROM AUTHOR]

Published
2023
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7. Manganese and Catalases

Author

Signorella, Sandra, Palopoli, Claudia, Daier, Verónica, Ledesma, Gabriela, Kretsinger, Robert H., editor, Uversky, Vladimir N., editor, and Permyakov, Eugene A., editor

Published
2013
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16. Oxidación de desoxiazucares de interés biológico por acción del Cr(vi) en medio ácido

Author

Daier, Verónica Andrea and Rizzotto, Marcela Adriana

Subjects
Cinética, Desoxiazucares, Cromo
Abstract

La oxidación de las aldosas y desoxialdosas estudiadas por acción del Cr(VI) conduce a la formación del ácido aldónico (o su lactona) correspondiente y Cr3+ como productos finales de reacción, cuando se trabaja en exceso de agente reductor respecto al Cr(VI) (condiciones de pseudo-orden n). La reacción redox se produce simultáneamente a través de dos caminos de reacción: Cr(VI) > Cr(III) y Cr(VI) > Cr(V) > Cr(III) Las leyes de velocidad para las reacciones de oxidación por acción del Cr(VI) se expresan de la siguiente forma: Rib(6) -d[Cr(VI)]/dt = kobs [Cr(VI)]T = kH[H+]^2 [Rib] [Cr(VI)]T 2dRib(13) d[Cr(VI)]/dt = kobs’ [Cr(VI)]T= (k0 + kH’ [H+]2 [2dRib] [Cr(VI)]T 2dGlc(14) v = -d[Cr(VI)]/dt = kobs [Cr(VI)] {c + (d + e[H+] + f[H+]^2) [2dGlu]} [Cr(VI)] v = -d[Cr(V)]/dt = k^V [Cr^V]= (k1 + k2 [H+]) [2dGlu] [Cr^V] Glc(1), Gal(2), 6dGal(9), Alo(11), 26dRib(12) -d[Cr(VI)]/dt = kH [ald] [Cr(VI)] -d[Cr^V]/dt = kb Kb [ald] [Cr^V] / (1 + Kb [ald]) En el estudio comparativo de aldosas, el orden de reactividad, a 33°c, fue el siguiente: 2,6dRib(12) > Gal(2) > Alo(11) > Gluc(1) >> 6dGal(9) El radical aldosa-alcóxido intermediario pudo atraparse con DMPO, detectándose por espectroscopia RPE dando lugar a una señal multilinea a g= 2.003. El intermediario paramagnético: Cr(V) se genera, probablemente, en un paso rápido de reacción por reacción del radical- aldosa con Cr(VI). El sustrato orgánico es oxidado por ambos agentes oxidantes Cr(VI) y Cr(V) con: a) velocidades comparables, especialmente a medida que aumenta la concentración de aldosa, produciéndose la reducción de Cr(VI) simultánea a la de Cr(V). Aldosas Glc(1), Gal(2), 6dGal(9), Alo(11) b) velocidades de oxidación por Cr(V)>> Cr(VI) . Aldosas: Rib(6), 2dRib(13), 26dRib(14) y 2dGlc(14) Las mediciones espectroscópicas de RPE demostraron que se formaban intermediarios penta- y hexa- coordinados de oxocromato(V), con la aldosa y/o el ácido aldónico actuando como ligando bidentado Fil: Daier, Verónica Andrea. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Departamento de Química-física. Área Inorgánica; Argentina.

Published
1993

17. New dimanganese(III) complexes of pentadentate (N2O3) Schiff base ligands with the [Mn2(μ-OAc)(μ-OR)2]3+ core: Synthesis, characterization and mechanistic studies of H2O2 disproportionation

Author

Biava, Hernán, primary, Palopoli, Claudia, additional, Shova, Sergiu, additional, Gaudio, Mónica De, additional, Daier, Verónica, additional, González-Sierra, Manuel, additional, Tuchagues, Jean-Pierre, additional, and Signorella, Sandra, additional

Published
2006
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28. Synthesis, characterization and antioxidant activity of water soluble MnIII complexes of sulphonato-substituted Schiff base ligands

Author

Moreno, Diego, Daier, Verónica, Palopoli, Claudia, Tuchagues, Jean-Pierre, and Signorella, Sandra

Subjects
*INORGANIC synthesis, *ANTIOXIDANTS, *SOLUBILITY, *COMPLEX compounds, *MANGANESE compounds, *SULFONATES, *SCHIFF bases, *LIGANDS (Biochemistry)
Abstract

Abstract: Two new MnIII complexes Na[Mn(5-SO3-salpnOH)(H2O)]⋅5H2O (1) and Na[Mn(5-SO3-salpn)(MeOH)]⋅4H2O (2) (5-SO3-salpnOH=1,3-bis(5-sulphonatosalicylidenamino)propan-2-ol, 5-SO3-salpn=1,3-bis(5-sulphonatosalicylidenamino)propane) have been prepared and characterized. Electrospray ionization-mass spectrometry, UV–visible and 1H NMR spectroscopic studies showed that the two complexes exist in solution as monoanions [Mn(5-SO3-salpn(OH))(solvent)2]−, with the ligand bound to MnIII through the two phenolato-O and two imino-N atoms located in the equatorial plane. The E 1/2 of the MnIII/MnII couple (−47.11 (1) and −77.80mV (2) vs. Ag/AgCl) allows these complexes to efficiently catalyze the dismutation of , with catalytic rate constants 2.4×106 (1) and 3.6×106 (2) M−1 s−1, and IC 50 values of 1.14 (1) and 0.77 (2) μM, obtained through the nitro blue tetrazolium photoreduction inhibition superoxide dismutase assay, in aqueous solution of pH 7.8. The two complexes are also able to disproportionate up to 250 equivalents of H2O2 in aqueous solution of pH 8.0, with initial turnover rates of 178 (1) and 25.2 (2) mM H2O2 min−1 mM−1 catalyst−1. Their dual superoxide dismutase/catalase activity renders these compounds particularly attractive as catalytic antioxidants. [Copyright &y& Elsevier]

Published
2010
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31. Synthesis, structure and catalase-like activity of dimanganese(iii) complexes of 1,5-bis(X-salicylidenamino)pentan-3-ol (X = 3- and 5-methyl). Influence of phenyl-ring substituents on catalytic activityElectronic supplementary information (ESI) available: Fig. S1 and S2. See DOI: 10.1039/b609366c

Author

Moreno, Diego, Palopoli, Claudia, Daier, Verónica, Shova, Sergiu, Vendier, Laure, Sierra, Manuel González, Tuchagues, Jean-Pierre, and Signorella, Sandra

Abstract

The diMnIIIcomplexes [Mn2(5-Me-salpentO)(µ-MeO)(µ-AcO)(H2O)Br] (1) and [Mn2(3-Me-salpentO)(µ-MeO)(µ-AcO)(MeOH)2]Br (2), where salpentOH = 1,5-bis(salicylidenamino)pentan-3-ol, were synthesised and structurally characterized. The two complexes include a bis(µ-alkoxo)(µ-acetato) triply-bridged diMnIIIcore with an MnMn separation of 2.93–2.94 Å, the structure of which is retained upon dissolution. Complexes 1and 2show catalytic activity toward disproportionation of H2O2, with first-order dependence on the catalyst, and saturation kinetics on [H2O2], in methanol and DMF. In DMF, the two complexes are able to disproportionate at least 1500 eq. of H2O2without significant decomposition, while in methanol, they rapidly lose activity with formation of a non-coupled MnIIspecies. Electrospray ionisation mass spectrometry, EPR and UV/vis spectroscopy used to monitor the reaction suggest that the major active form of the catalyst occurs in the Mn2IIIoxidation state during cycling. The correlation between log(kcat) and the redox potentials of 1, 2and analogous complexes of other X-salpentOH derivatives indicates that, in this series, the oxidation of the catalyst is probably the rate-limiting step in the catalytic cycle. It is also noted that formation of the catalyst-peroxide adduct is more sensitive to steric effects in DMF than in methanol. Overall, kinetics and spectroscopic studies of H2O2dismutation by these complexes converge at a catalytic cycle that involves the Mn2IIIand Mn2IVoxidation states.

Published
2006
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32. Redox and complexation chemistry of the CrVI/CrV–d-galacturonic acid system

Author

González, Juan C., Daier, Verónica, García, Silvia, Goodman, Bernard A., Atria, Ana M., Sala, Luis F., and Signorella, Sandra

Abstract

The oxidation of d-galacturonic acid by CrVI yields the aldaric acid and CrIII as final products when a 30-times or higher excess of the uronic acid over CrVI is used. The redox reaction involves the formation of intermediate CrIV and CrV species, with CrVI and the two intermediate species reacting with galacturonic acid at comparable rates. The rate of disappearance of CrVI, CrIV and CrV depends on pH and [substrate], and the slow reaction step of the CrVI to CrIII conversion depends on the reaction conditions. The EPR spectra show that five-coordinate oxo–CrV bischelates are formed at pH ≤ 5 with the uronic acid bound to CrV through the carboxylate and the α-OH group of the furanose form or the ring oxygen of the pyranose form. Six-coordinated oxo–CrV monochelates are observed as minor species in addition to the major five-coordinated oxo–CrV bischelates only for galacturonic acid ∶ CrVI ratio ≤ 10 ∶ 1, in 0.25–0.50 M HClO4. At pH 7.5 the EPR spectra show the formation of a CrV complex where the vic-diol groups of Galur participate in the bonding to CrV. At pH 3–5 the Galur–CrV species grow and decay over short periods in a similar way to that observed for [Cr(O)(α-hydroxy acid)2]−. The lack of chelation at any vic-diolate group of Galur when pH ≤ 5 differentiates its ability to stabilise CrV from that of neutral saccharides that form very stable oxo–CrV(diolato)2 species at pH > 1.

Published
2004

33. Kinetics and Mechanism of the Reduction of Chromium(VI) and Chromium(V) by <SC>D</SC>-Glucitol and <SC>D</SC>-Mannitol

Author

Roldán, Viviana P., Daier, Verónica A., Goodman, Bernard, Santoro, Mabel I., González, Juan Carlos, Calisto, Nancy, Signorella, Sandra R., and Sala, Luis F.

Abstract

The oxidation of D-glucitol and D-mannitol by CrVI yields the aldonic acid (and/or the aldonolactone) and CrIII as final products when an excess of alditol over CrVI is used. The redox reaction occurs through a CrVI→CrV→CrIII path, the CrVI→CrV reduction being the slow redox step. The complete rate laws for the redox reactions are expressed by: a) −d[CrVI]/dt  {kM2 H [H+]2+kMH [H+]}[mannitol][CrVI], where kM2 H  (6.7±0.3)·10 M s−1 and kMH  (9±2)·10 M s−1; b) −d[CrVI]/dt  {kG2 H [H+]2+kGH [H+]}[glucitol][CrVI], where kG2 H  (8.5±0.2)·10 M s−1 and kGH  (1.8±0.1)·10 M s−1, at 33°. The slow redox steps are preceded by the formation of a CrVI oxy ester with λmax 371 nm, at pH 4.5. In acid medium, intermediate CrV reacts with the substrate faster than CrVI does. The EPR spectra show that five- and six-coordinate oxo-CrV intermediates are formed, with the alditol or the aldonic acid acting as bidentate ligands. Pentacoordinate oxo-CrV species are present at any [H+], whereas hexacoordinate ones are observed only at pH&lt;2 and become the dominant species under stronger acidic conditions where rapid decomposition to the redox products occurs. At higher pH, where hexacoordinate oxo-CrV species are not observed, CrV complexes are stable enough to remain in solution for several days to months.

Published
2000
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34. Kinetics and mechanism of the reduction of CrVIto CrIIIby D-ribose and 2-deoxy-D-ribose

Author

Daier, Verónica, Signorella, Sandra, Rizzotto, Marcela, Frascaroli, María Inés, Palopoli, Claudia, Brondino, Carlos, Salas-Peregrin, Juan Manuel, and Sala, Luis F

Abstract

The oxidation of D-ribose and 2-deoxy-D-ribose by CrVIyields the aldonic acid and Cr3+as final products when an excess of sugar over CrVIis used. The redox reaction occurs through CrVI–>CrIIIand CrVI–>CrV–>CrIIIpaths. The complete rate laws for the CrVIoxidation reactions are expressed by -d[CrVI]/dt= kH[H+]2[ribose][CrVI], where kH= (5.9 ± 0.1) × 10-2mol-3dm9s-1, and -d[CrVI]/dt= (k0+ kH'[H+]2) [2-deoxyribose][CrVI], where k0= (1.3 ± 0.5) × 10-3mol-1dm3s-1and kH' = (4.2 ± 0.1) × 10-2mol-3dm9s-1, at 33°C. An intermediate sugar alkoxide radical could be trapped with DMPO and observed by EPR as a multiline signal at g= 2.003. CrVis formed in a rapid step by reaction of the sugar radical with CrVI. CrVreacts with the substrate faster than CrVIdoes. The EPR spectra show that five- and six-coordinate oxochromate(V) intermediates are formed, and the distribution of these CrVspecies in the reaction mixture essentially depends on the solution acidity.Key words: ribose, 2-deoxyribose, chromium, redox, mechanism, kinetics.

Published
1999
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35. New dimanganese(III) complexes of pentadentate (N2O3) Schiff base ligands with the [Mn2(μ-OAc)(μ-OR)2]3+ core: Synthesis, characterization and mechanistic studies of H2O2 disproportionation

Author

Biava, Hernán, Palopoli, Claudia, Shova, Sergiu, Gaudio, Mónica De, Daier, Verónica, González-Sierra, Manuel, Tuchagues, Jean-Pierre, and Signorella, Sandra

Subjects
*MANGANESE, *ACETATES, *METHANOL, *IMINES, *ORGANONITROGEN compounds
Abstract

Abstract: Two new diMnIII complexes [ (1) and [ (2) (L1H3 =1,5-bis(2-hydroxybenzophenylideneamino)pentan-3-ol; L2H3 =1,5-bis(2-hydroxynaphtylideneamino)pentan-3-ol) were synthesized and structurally characterized. Structural studies evidence that these complexes have a bis(μ-alkoxo)(μ-carboxylato) triply bridged diMnIII core in the solid state and in solution, with two substitution-labile sites – one on each Mn ion – in cis-position. The two complexes show catalytic activity toward disproportionation of H2O2, with saturation kinetics on [H2O2], in methanol and dimethyl formamide at 25°C. Spectroscopic monitoring of the H2O2 disproportionation reaction suggests that (i) complexes 1 and 2 dismutate H2O2 by a mechanism involving redox cycling between and , (ii) the complexes retain the dinuclearity during catalysis, (iii) the active form of the catalyst contains bound acetate, and (iv) protons favors the formation of inactive MnII species. Comparison to other dimanganese complexes of the same family shows that the rate of catalase reaction is not critically dependent on the redox potential of the catalyst, that substitution of phenolate by naphtolate in the Schiff base ligand favors formation of the catalyst-substrate adduct, and that, in the non-protic solvent, the bulkier substituent at the imine proton position hampers the binding to the substrate. [Copyright &y& Elsevier]

Published
2006
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36. Attitudes towards chemistry of students of biological careers (Licenciatura en Biodiversidad y Profesorado en Biología) of the Universidad Nacional del Litoral and its influence on learning and academic yield

Author

Reyes, María Silvina, Porro, Silvia, Odetti, Héctor Santiago, Sgroppo, Sonia Cecilia, Daier, Verónica, and Pirovani, María Élida

Subjects
Actitudes, Academic yield, Attitudes, Student university, Rendimiento académico, Diferencial semántico, Chemical, Likert scale, Química, Semantic differential, Estudiantes universitarios, Escala Likert
Abstract

Fil: Reyes, María Silvina. Universidad Nacional del Litoral. Facultad de Humanidades y Ciencias; Argentina. Fil: Reyes, María Silvina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológica; Argentina. Los objetivos de la presente tesis fueron: evaluar la actitud frente a la química de alumnos de las carreras de Licenciatura en Biodiversidad y Profesorado en Biología, utilizando instrumentos cuantitativos: Diferencial Semántico (DS) y Escala Likert (EL) y cualitativos (observaciones y entrevistas); analizar la evolución de dichas actitudes durante el transcurso de la carrera; determinar si los métodos de DS y EL son equiparables y analizar la incidencia de las actitudes hacia la química en el rendimiento académico. Se encuestaron a 40 alumnos en Química General e Inorgánica (QGI) y 30 alumnos en Química Orgánica (QO) y Química Biológica (QB) -cohorte 2013- como así también a estudiantes que cursaban la carrera en tres momentos diferentes: al inicio (1º año, 45 alumnos), durante (3º año, 30 alumnos) y al final (5º año, 20 alumnos). Los alumnos que se encontraban cursando QGI presentaron actitudes hacia la química valoradas como indiferentes y/o negativas. Al avanzar en sus trayectorias estudiantiles, las actitudes evolucionaron favorablemente al cursar QO y QB. Este comportamiento también fue ratificado realizando las entrevistas. Esta modificación actitudinal positiva también se observó en los alumnos de 3º y 5º en comparación a los de 1º año. El análisis de concordancia arrojó un Kappa igual a 0,091. Por lo tanto los cuestionarios (EL y DS) no son equiparables. Con respecto al análisis del rendimiento académico se concluye que existe una fuerte relación entre las variables implicadas (rendimiento y actitud hacia la química) lo cual queda demostrado con coeficientes de Pearson mayores a 0,80. The aims of this thesis were to assess attitudes toward chemistry of students of Licenciatura en Biodiversidad and Profesorado en Biología using instruments quantitative (semantic differential and the Likert scale) and qualitative (observations and interviews); analyze the changes in these attitudes during the career; determine whether the methods of semantic differential and Likert scale are comparable and analyze the impact of attitudes toward chemistry in the academic yield. These attitudes were studied in 40 students at General and Inorganic Chemistry (GIC) and 30 studies at Organic Chemistry (OC) and Biological Chemistry (BC) -cohort 2013- and during three stages: at the beginning (1st year), during (3rd year) and at the end (5th year) of their careers. All the students who attended each of the analyzed years (45, 30 and 20 students respectively). Students who were enrolled GIC presented attitudes toward chemistry valued as indifferent and / or negative. When the student advance in their careers, attitudes evolved favorably to take OC and BC. This behavior was also ratified conducting interviews. This positive attitudinal change was also observed in the students of 3rd and 5th compared to the 1st year a favorable attitude towards this discipline in correlation to the professional preparation, was recorded. The coefficient Kappa obtained in this study was 0.091, indicating that the correlation between the quantitative instruments is practically null. Regarding the analysis of the academic performance, it concluded that there is a strong relationship between the variables involved (performance and attitude towards chemistry) which is demonstrated with Pearson coefficients greater than 0.80. Secretaría de Políticas Universitarias

Published
2015

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