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Bracamonte A.G.,Institute Investigaciones En Fisico Quimica Of Cordoba Infiqc | Veglia A.V.,Institute Investigaciones En Fisico Quimica Of Cordoba Infiqc
Journal of Photochemistry and Photobiology A: Chemistry | Year: 2013

The cyclodextrins effects on the serotonin (5HT) and 5-hydroxy-3-indolyl acetic acid (5HIA) fluorescence emission in acid and alkaline quenching conditions were analyzed. From Stern-Volmer plots, the quenching constants (KQ) were determined in the presence and absence of β-cyclodextrin (βCD) and hydroxypropyl-β-cyclodextrin (HPβCD). In both media a decrease in the values of KQ was observed in the presence of CDs, as compared with their absence. In acid media, the decrease was: 36-39% with βCD and 48-54% with HPβCD for 5HIA and 5HT, respectively. In basic media, with the neutral receptors, these values are 69-29% with βCD and 56-43% with HPβCD for 5HIA and 5HT, respectively. Moreover, a complete quenching inhibition produced by ionized cyclodextrins was determined for both substrates. The results showed a net protective effect due to the guest inclusion into the cyclodextrin nanocavity. This study is particularly important for analytical determinations in such media. © 2013 Elsevier B.V. All rights reserved.

Bracamonte A.G.,Institute Investigaciones En Fisico Quimica Of Cordoba Infiqc | Veglia A.V.,Institute Investigaciones En Fisico Quimica Of Cordoba Infiqc
Talanta | Year: 2011

Alternative and sensitive spectrofluorimetric methods for the determination of hydroxyindoles, such as serotonin (5HT) and 5-hydroxyindoleacetic acid (5HIA), were developed on the basis of supramolecular interaction with cyclodextrin (CD) nanocavities (βCD and hydroxypropyl-βCD, HPCD) at different pH values. Both substrates and receptors have acidic protons, therefore the interactions produced in different systems were considered. The effects of neutral CD at pH 2.00 and 6.994, and of anionic CD at pH 13.00 on the specific acid-base species of the compounds at each pH were determined. In all the conditions studied, the fluorescence of the substrates in the presence of CD increased. The association constants (KA, mol-1 L) between the substrates and CD were determined (30-300) and interpreted. A zero-crossing first-derivative spectrofluorimetric method with and without HPCD was developed for the simultaneous determination of 5HT and 5HIA. The limits of detection (LD, ng mL-1) for the best conditions were 0.37 for 5HT and 0.50 for 5HIA at pH 2.00 with HPCD. These LD proved to be better than others reported. The applicability of the direct and derivative spectrofluorimetric methods to urine samples was demonstrated with good recoveries 92-110% and R.S.D. 1-10%. © 2010 Elsevier B.V.All rights reserved.

Montanez J.P.,Institute Investigaciones En Fisico Quimica Of Cordoba Infiqc | Montanez J.P.,CONICET | Gomez S.,CONICET | Gomez S.,National University of Costa Rica | And 2 more authors.
Journal of the Brazilian Chemical Society | Year: 2015

The photocatalytic decomposition of 2-, 3- and 4-chlorobenzoic acids (2CB, 3CB and 4CB, respectively) with TiO2 loaded on HZSM-11 zeolite was investigated. The optimum decomposition rate of 2CB was obtained with TiO2/HZSM-11(30%) (TiO2 30 wt.%) catalyst at a concentration of 1 mg mL-1. 2CB and 3CB decompose at similar rates, but 4CB remains adsorbed on TiO2/HZSM-11(30%) without further degradation. This absorption is attributed to the relative positions of Cl and COOH groups on 4CB. However, this compound can be partially degraded and/or removed from aqueous solutions by TiO2/HZSM-11(50%) catalyst or HZSM-11 zeolite. TiO2/HZSM-11(30%) is stable; it retains its photocatalytic properties after nine cycles, can be easily removed and immediately reused. These are important advantages of TiO2/HZSM-11(30%) over unsupported TiO2, making it a good photocatalyst for the treatment of polluted water. On the other hand, HZSM-11 could be used to selectively adsorb 4CB, thus becoming an alternative method of environmental remediation. © 2015 Sociedade Brasileira de Química.

Pacioni N.L.,Institute Investigaciones En Fisico Quimica Of Cordoba Infiqc | Pierini A.B.,Institute Investigaciones En Fisico Quimica Of Cordoba Infiqc | Veglia A.V.,Institute Investigaciones En Fisico Quimica Of Cordoba Infiqc
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2013

Detailed insights regarding the inclusion process between β-cyclodextrin and the N-methylcarbamates insecticides like Bendiocarb, Carbaryl, Carbofuran and Promecarb, are proposed in bases of experimental and computational methods. The results from Fourier transform infrared spectroscopy, differential scanning calorimetry, induced circular dichroism and molecular dynamics indicate that only in the case of Promecarb the interaction with the macrocycle is produced by the alkyl rest of the molecule. In all other cases the aromatic moiety is the part of the insecticide that is partially included in the cavity of β-cyclodextrin. © 2012 Elsevier B.V. All rights reserved.

Sueldo Occello V.N.,Institute Investigaciones En Fisico Quimica Of Cordoba Infiqc | De Rossi R.H.,Institute Investigaciones En Fisico Quimica Of Cordoba Infiqc | Veglia A.V.,Institute Investigaciones En Fisico Quimica Of Cordoba Infiqc
Journal of Luminescence | Year: 2015

The influence of the macrocyclic compound cucurbit[6]uril (CB6) on the photophysical properties of the fluorophore pyrene (PYR) has been studied. Guest-host interaction was observed by UV-visible spectroscopy and spectrofluorimetry. The fluorescence of PYR was significantly increased in the presence of CB6. The binding equilibrium constants for the complex with 1:1 stoichiometry were determined in HCOOH 55% w/v. The values of the association constants, KA, and the fluorescence quantum yield ratios between complexed and free substrate, φPYR-CB6/φPYR, at different temperatures were (3.1±0.9)×102 M-1 and (5.1±0.2), (3.6±0.5)×102 M-1 and (5.9±0.1), (4.8±0.7)×102 M-1 and (5.5±0.1) at 15.0 °C, 25.0 °C and 40.0 °C, respectively. The enthalpic and entropic contributions to the complexation process were determined, yielding ΔS=(92±3) J mol-1 K-1 and ΔH=(13±1) kJ mol-1. From these results it can be concluded that the complex formation is mainly driven by the entropic term. The forces involved in the complexation are interpreted from the sign and magnitude of the thermodynamic parameters obtained. The partial inclusion of PYR or the formation of a suspended complex is proposed in base of all the data. The interaction is also demonstrated in the solid state by differential scanning calorimetric (DSC) measurements. ©2014 Elsevier B.V. All rights reserved.

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