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The interaction of melatonin with water containing either sodium bis (2-ethylhexyl) sulfosuccinate (AOT) or soybean phosphatidylcholine (lecithin) reversed micelles has been investigated by UV absorption spectroscopy, at a molar ratio of melatonin:surfactant 1:800 for AOT and 1:400 for lecithin reversed micelles, and by varying the water:surfactant molar ratio (R). Our results suggest that in the presence of domains from apolar organic solvent to surfactant and to water, melatonin positions itself in the micellar phase, with a preferential location in the surfactant polar head group domain, independent of the nature of the surfactant and the amount of water encapsulated into the micellar core. Effects are due to the hydrophilic and lipophilic moieties of melatonin. The effectiveness of melatonin as an electron donor and free radical scavenger has been recently recognized. While supporting the hypothesis that melatonin may provide antioxidant protection without the benefit of receptors, present findings may suggest that the molecule could easily scavenge aqueous as well as lipophilic radicals.

quite difficult. It has been shown that the width of the filter window is inversely proportional to the degrees of freedom allowable in the subsequent 2 34minimization routine. Practically, then, one must perform the minimization on the unfiltered spectrum leading to the undesirable consequence of minimization in many parameters of a maximum likelihood estimator that is large and, hence, relatively insensitive to the small changes in parameters that would differentiate between models. ConclusionsThe surface EXAFS of underpotentially deposited silver on gold (111) films on mica was studied with the electrode under potential control. It was revealed that both gold and oxygen are present as backscatterers in the first coordination shell of silver. It was estimated that the bond lengths to gold and oxygen were 2.75 ± 0.05 and 2.42 ± 0.05 Á, respectively, and the respective coordination numbers were 3 and 1. A model consistent with these findings is one where the silver atoms sit on 3-fold sites on the gold surface and have oxygen from water or electrolyte bound at a well-defined distance. This model is qualitatively the same as that proposed for the Cu UPD layer on gold (111) electrodes.

The interaction of native calf thymus DNA with the Zn(II) and Cu(II) complexes of 5-triethyl ammonium methyl salicylidene ortophenylendiimine (ZnL 2+ and CuL 2+ ), in 1 mM Tris-HCl aqueous solutions at neutral pH, has been monitored as a function of the metal complex-DNA molar ratio by UV absorption spectrophotometry, circular dichroism (CD) and fluorescence spectroscopy. The results support for an intercalative interaction of both ZnL 2+ and CuL 2+ with DNA, showing CuL 2+ an affinity of approximately 10 times higher than ZnL 2+ . In particular, the values of the binding constant, determined by UV spectrophotometric titration, equal to 7.3 · 10 4 and 1.3 · 10 6 M À1 , for ZnL 2+ and CuL 2+ , respectively, indicate the occurrence of a marked interaction with a binding size of about 0.7 in base pairs. The temperature dependence of the absorbance at 258 nm suggests that both complexes strongly increase the DNA melting temperature (Tm) already at metal complex-DNA molar ratios equal to 0.1. As evidenced by the quenching of the fluorescence of ethidium bromide-DNA solutions in the presence of increasing amounts of metal complex, ZnL 2+ and CuL 2+ are able to displace the ethidium cation intercalated into DNA. A tight ZnL 2+ -DNA and CuL 2+ -DNA binding has been also proven by the appearance, in both metal complex-DNA solutions, of a broad induced CD band in the range 350-450 nm. In the case of the CuL 2+ -DNA system, the shape of the CD spectrum, at high CuL 2+ content, is similar to that observed for w-DNA solutions. Such result allowed us to hypothesize that CuL 2+ induces the formation of supramolecular aggregates of DNA in aqueous solutions.

The state of melatonin confined in dry cholesterol/lecithin mixed reversed micelles dispersed in CCl4 was investigated using 1H-NMR and FT-IR spectroscopies as a function of the melatonin to lecithin molar ratio (R(MLT)) and of the cholesterol to lecithin molar ratio (R(CHL)). An analysis of experimental results leads to the hypothesis that, independent of R(MLT) and as a consequence of anisotropic melatonin/lecithin, melatonin/cholesterol and cholesterol/lecithin interactions, melatonin is totally solubilized in reversed micelles. Melatonin is mainly located in and oriented in the nanodomain constituted by the hydrophilic groups of cholesterol and lecithin. A competition of melatonin and cholesterol for the hydrophilic binding sites of the reversed micelles was observed by changing the R(CHL). Some possible biological implications of the specific interactions governing the solubilization process, the preferential location and the peculiar properties of melatonin confined in cholesterol/lecithin mixed reversed micelles are discussed.

The coating effect of alkali metal salt clusters by the surfactant anion bis(2-ethylhexyl)sulfosuccinate has been investigated by electrospray ionization mass spectrometry (MS) and MS/MS. The analysis of the data emphasized the formation and stability in the gas phase of reverse micelle-like surfactant aggregates carrying in their interior ionic clusters. Two main contributions have been postulated to account for the observed stability: intra-aggregate electrostatic interactions and screening of inter-aggregate attractive interactions due to the exclusion volume effect caused by the surfactant alkyl chains. Moreover, the stability and structural arrangement of these supramolecular aggregates result in strong dependency on the alkali metal salt identity.

The self-assembling of sodium bis (2-ethylhexyl) sulfosuccinate (AOT) in gas phase has been investigated by electrospray ionization- and matrix-assisted laser desorption/ionization mass spectrometry. Large surfactant clusters with an aggregation number close to that found in apolar media have been observed either as positive or negative ions. Moreover, the marked predominance of singly charged species as well as preliminary theoretical calculations strongly suggest an aggregate structure characterized by an internal hydrophilic core hosting the extra charge surrounded by an apolar shell constituted by the surfactant alkyl chains. This structure is similar to that of the more familiar reversed micelles formed when an appropriate surfactant is solubilized in apolar solvents. Finally, similar trends are observed independently either on the ionization technique or the polarity of the solvent used. This, together with the large dependence of the aggregation number on the flow rates, strongly indicates that self-assembling of the surfactant molecules occurs during the evaporation step.

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