Spectroscopic characterization of the inclusion complexes of luteolin with native and derivatized beta-cyclodextrin.

The inclusion complexes of Luteolin (LU) with cyclodextrins (CDs) including beta-cyclodextrin (betaCD), hydroxypropyl-beta-cyclodextrin (HPbetaCD) and dimethyl-beta-cyclodextrin (DMbetaCD), Scheme 1, have been investigated using the method of steady-state fluorescence. The stoichiometric ratio of the three complexes was found to be 1:1 and the stability constants (K) were estimated from spectrofluorometric titrations, as well as the thermodynamic parameters. Maximum inclusion ability was obtained in the case of HPbetaCD followed by DMbetaCD and betaCD. Moreover, 1H NMR and 2D NMR were carried out, revealing that LU has different form of inclusion which is in agreement with molecular modeling studies. These models confirm that when LU-betaCD and LU-DMbetaCD complexes are formed, the B-ring is oriented toward the primary rim; however, for LU-HPbetaCD complex this ring is oriented toward the secondary rim. The ESR results showed that the antioxidant activity of luteolin was the order LU-HPbetaCD>LU-DMbetaCD>LU-betaCD>LU, hence the LU-complexes behave are better antioxidants than luteolin free.

New heteroaryl nitrones with spin trap properties: Identification of a 4-furoxanyl derivative with excellent properties to be used in biological systems.

A new series of heteroaryl nitrones, 1-7, bearing furoxanyl and thiadiazolyl moieties, were evaluated for their free radical-trapping properties. The physicochemical characterization by electron paramagnetic resonance (EPR) demonstrated its capability to trap and stabilize oxygen-, carbon-, sulfur-, and nitrogen-centered free radicals. The 4-furoxanyl nitrone 3 (FxBN), alpha(Z)-(3-methylfuroxan-4-yl)-N-tert-butylnitrone, showed appropriate solubility in aqueous solution and taking into account that this physicochemical property is very important for biological applications, we studied it deeply in terms of its trapping and kinetic behaviors. For this, kinetic studies of the hydroxyl adduct decay gave rate constants k(ST) of 1.22x10(10)dm(3)mol(-1)s(-1) and half-live up to 7200s at physiological pH, without any artifactual signals. The ability of FxBN to directly traps and stabilizes superoxide free radical, with a half-life of 1620s at physiological pH, was also demonstrated. Besides, FxBN-hydroxyl and -superoxide adducts exhibited distinct and characteristic EPR spectral patterns. Finally, we confirmed the ability of FxBN to act as spin trap in a specific biological system, that is, in the free radical production of experimental anti-trypanosomatid drugs using Trypanosoma cruzi microsomes as biological system. Moreover, previous observations of low FxBN toxicity transform it in a good candidate for in vivo spin trapping.

Comparative spectroscopic and electrochemical study of nitroindazoles: 3-alcoxy, 3-hydroxy and 3-oxo derivatives.

Cyclic voltammetry and electron spin resonance techniques were used in the investigation of novel 3-alkoxy- and 3-hydroxy-1-[omega-(dialkylamino)alkyl]-5-nitroindazole derivatives. A self-protonation process involving the protonation of the nitro group was observed. The reactivity of the nitro-anion radical for these derivatives with glutathione, a biological relevant thiol, was also studied by cyclic voltammetry. These studies demonstrated that glutathione could react with radical species from 5-nitroindazole system. Also we demonstrated that nitro-anion radicals show three different patterns of delocalization where the indazole 1-lateral chain does not have major influence.

ESR, electrochemical and reactivity studies of antitrypanosomal palladium thiosemicarbazone complexes.

Cyclic voltammetry (CV) and electron spin resonance (ESR) techniques were used in the investigation of novel palladium complexes with bioactive thiosemicarbazones derived from 5-nitrofurane or 5-nitrofurylacroleine. Sixteen palladium complexes grouped in two series of the formula [PdCl(2)HL] or [PdL(2)] were studied. ESR spectra of the free radicals obtained by electrolytic reduction were characterized and analyzed. The ESR spectra showed two different hyperfine patterns. The stoichiometry of the complexes does not seem to affect significantly the hyperfine constants however we observed great differences between 5-nitrofurane and 5-nitrofurylacroleine derivatives. The scavenger properties of this family of compounds were lower than Trolox.

Redox-active complexes formed during the interaction between glutathione and mercury and/or copper ions.

Prompted by the recently reported capacity of the physiologically occurring Cu(I)-[glutathione](2) complex (Cu(I)-[GSH)](2)) to reduce oxygen, the effect of various GSH-binding metals (Co(2+), Cd(2+), Zn(2+), Pb(2+), Al(3+), Hg(2+) and Ni(2+)) on the superoxide-generating capacity of such complex was investigated. Amongst all tested metals, only Hg(2+) was able to substantially affect the capacity of Cu(I)-[GSH](2) to generate superoxide. When Hg(2+) and Cu(I)-[GSH](2) were mixed equimolarly, the superoxide formation, assessed through the cytochrome c reduction and dihydroethidium oxidation, was increased by over 50%. Such effect was totally inhibitable by SOD. Based on the reportedly higher affinity of Hg(2+) for GSH and the observed ability of Hg(2+) to lower the concentration of Cu(I)-[GSH](2) (spectroscopically assessed), we suggest that Hg(2+) displaces Cu(I) from Cu(I)-[GSH](2), to release Cu(I) ions and form a Hg(II)-[GSH](2) complex. The latter species would account for the Hg(2+)-induced exacerbation of the superoxide production. In fact, the present study provides first time evidence that a preformed Hg(II)-[GSH](2) complex is able to concentration-dependently reduce oxygen. Such redox-activity was evidenced using cytochrome c and confirmed by EPR studies using DMPO (5,5-dimethyl-1-pyrroline N-oxide, a spin-trapping agent). Considering this novel ability of Hg(II)-[GSH](2) to generate superoxide, a further characterization of its redox-activity and its potential to affect superoxide-susceptible biological targets appears warranted.