Publications

Abstract A fundamental understanding of the mechanisms involved in the surfactant-assisted exfoliation and dispersion of carbon nanotubes (CNTs) in water calls for well-controlled experimental methodologies and reliable comparative metrics. We have assessed the ability of several ionic surfactants to disperse single and multiwalled carbon nanotubes, resorting to a stringently controlled sonication-centrifugation method for the preparation of the dispersions. The CNT concentration was accurately measured for a wide range of surfactant concentration, using combined therrnogravimetric analysis and UV-vis spectroscopy. The obtained dispersibility curves yield several quantitative parameters, which in turn allow for the effects of nanotube morphology and surfactant properties (aromatic rings, chain length, headgroup charge, and cmc) to be assessed and rationalized, both in terms of dispersed indicate that the CNT-surfactant association follows patterns that are markedly different from other equilibrium processes governed by hydrophobicity (such as micellization); in particular, the surfactant concentration needed for maximum dispersibility, c(s,max), and the number of surfactant molecules per unit CNT area at cs,max are shown to depend linearly on chain length. The results further suggest that the presence of micelles in the exfoliation process is not a key factor either for starting CNT dispersibility or attaining its saturation value. nanotube mass and surface area. The data also

Abstract Using the Knudsen-effusion method and/or a diaphragm manometer static method, the vapour pressures of the condensed phases (crystalline and liquid) of nicotinamide, N-methylnicotinamide and N, N-dimethylnicotinamide were measured, respectively, over the following temperatures ranges (341.2 to 433.7) K, (329.2 to 426.6) K and (308.2 to 370.5) K. The experimental results enabled the determination of the standard molar enthalpies, entropies and Gibbs free energies of sublimation and of vaporisation, at T = 298.15 K, as well as phase diagram representations of the (p, T) experimental results, including the triple point, for the three compounds studied. The temperatures and molar enthalpies of fusion were determined using differential scanning calorimetry and were compared with the values derived indirectly from the vapour pressure measurements. The enthalpy of the intermolecular hydrogen bonds N -H center dot center dot O present in crystalline N-methylnicotinamide was calculated and the sum of the enthalpies of the intermolecular hydrogen bonds N -H center dot center dot center dot O and N -H center dot center dot center dot N, [DHB(N -H center dot center dot center dot O) H + DHB(N -H center dot center dot center dot N) H], formed in the crystalline phase of nicotinamide was also estimated.

Abstract Halogenated benzenes form a class of pollutants with a huge number of members - 1504 distinct benzene compounds, where one or more hydrogen atoms are replaced by halogens, may exist theoretically. This study presents a user friendly method for accurate prediction of vapor pressures and enthalpies of vaporization, at 298.15 K, of any mono or poly halobenzene compound. The derived equations for the prediction of those vaporization properties depend just on the number of each constituent halogen atom. This is a consequence of the absence of intramolecular interactions between the halogen atoms, revealed after examining vaporization results of ca. 40 halogenated benzenes. In order to rationalize the estimation equations, the contribution of the halogen atoms for the referred to above properties of vaporization was decomposed into two atomic properties - the volume and electron affinity. Extension of the applicability of the estimation method to substituted benzenes containing other substituent groups beyond halogen atoms as well as to some polycyclic aromatic species was tested with success.

Abstract We report a nanocomposite of ZnS:Mn quantum dots and a third generation PAMAM-OH dendrimer (ZnS:Mn@PAMAM-OHG=3) which was rationalized to be used as ratiometric nanosensor for Cd2+ in aqueous solution. The nanoparticles exhibited a bright yellow-orange emission with peaks at 448 and 595 nm. The structure of ZnS:Mn was not changed after coupling with PAMAM-OH, which was evidenced by the analysis of the emission spectra of the compounds. The results confirm that the prepared fluorescence nanoparticles could selectively detect Cd2+ in aqueous solution with a limit of detection of 24.34 mu M and RSD 4.07%, obtained by using the ratio I-448/I-595. The method was applied to different water samples.

Abstract Firefly bioluminescence is a phenomenon that attracts attention from the research community because of complex challenges for fundamental investigation, as well as diverse opportunities for practical application. Here we have studied the potential deprotonation of firefly oxyluciferin by using a theoretical approach in an enzymatic-like microenvironment in chemiexcited proton transfer involving adenosine 5'-monophosphate. We have uncovered a reaction route that links the evidence that the light-emitter is an anionic molecule while it is chemiexcited in its neutral form. Moreover, the results indicated that the anionic bioluminophore is the enolate anion and not the ketonic one. Further calculations supported this identification of the light-emitter: the spectrum of resulting enolate anion covers the entire yellow-green/red bioluminescence range, which is in line with the experimental findings regarding firefly multicolor bioluminescence.

Abstract Pollen of Betula pendula, Ostrya carpinifolia, and Carpinus betulus was exposed in vitro to relatively low levels of the air pollutants, namely carbon monoxide, ozone, and sulfur dioxide. The allergenicity of the exposed pollen was compared with that of non-exposed pollen samples to assess if air pollution exposition affects the allergenicity potential of pollen. The immunodetection assays indicated higher IgE recognition by all sera of allergic patients to the pollen protein extracts in all exposed samples in comparison to the non-exposed samples. These results show that the pollen exposition to low pollutants' levels induces increased allergic reaction to sensitized individuals.

Abstract Magnesium is an essential mineral in human metabolism, and is the second most abundant intracellular cation and the fourth most abundant in the human body. Magnesium has a large variety of biological functions, including being a cofactor for over 300 enzymes, mainly involving phosphorylation of proteins and nucleic acids. Low levels of magnesium in the body can develop during different illnesses, such as diabetes (type 2), metabolic syndrome, cardiac arrhythmias, and muscular constriction. The present review shows the advances in analytical chemistry based on sensor systems to quantify the concentration of magnesium in different biological samples, plasma, serum, or urine, that are relevant to human health.

Abstract In the current work, the complexes formed between triplet vinyl nitrene ((CH2CHN)-C-3) and some Lewis acids YA (LiH, LiF, BeH2, BeF2, BH3, BF3, ClH, ClF, HCl, HF) have been investigated through calculations of the electronic structure. These calculations have been carried out in order to determine the energetic stability of the N center dot center dot center dot Y (with Y = Li, Be, B, Cl, H) interactions and also to understand their chemical nature. Quantum chemical calculations predict that the molecular complexes (CH2CHN)-C-3 center dot center dot center dot Y-A are always more stable than the separated (CH2CHN)-C-3 and Y-A species. The interaction energies range from -0.98 kcal mol(-1) (in CH2=CHN center dot center dot center dot ClH) to -39.03 kcal mol(-1) (in CH2=CHN center dot center dot center dot BH3) at the CCSD(T)/6-311++G(2d,2p) level of theory. Accordingly, some of these complexes may serve to experimentally detect and characterize the elusive triplet vinyl nitrene species. Moreover, AIM theory, in particular the L(r) = -A1/4a double dagger(2) rho(r) function, reveals that the N center dot center dot center dot Y interactions established between the electron lone pair of the nitrogen atom and the charge density depletion region of the Y atom are mainly of electrostatic character.

Abstract Complex self-assembled structures can be built up in aqueous media by making use of non-covalent interactions between small organic molecules and conventional amphiphiles. The macrocycle p-sulfonatocalix[4]arene (SC4) is a known receptor for organic ammonium cations in aqueous solution, showing strong binding ability for those guests and selectivity for several amino acids. Previous studies have shown that this type of water-soluble calixarenes are able to modify the aggregation behavior of surfactants. Here, we explore the interactions and morphologies present in mixtures of SC4 and a cationic serine-based surfactant, resorting to surface tension, light microscopy, cryo-scanning electron microscopy and nuclear magnetic resonance studies. Complexation of the amino acid-based surfactant by the calixarene leads initially to mixed micelle formation and a significant lowering of the critical micelle concentration with respect to the neat surfactant even for very low content of SC4 (up to 1.4 mol%). Interestingly, as the SC4 fraction in the system is gradually increased (about 2-6 mol%), highly flexible tubular structures and vesicles are assembled. The observed self-assembly is rationalized in terms of electrostatic complexation between the two co-solutes and the preferred packing of the supramolecular complexes formed.

Abstract A theoretical analysis of the enol-based photoacidity of oxyluciferin in water is presented. The basis for this phenomenon is found to be the hydrogen-bonding network that involves the conjugated photobase of oxyluciferin. The hydrogen-bonding network involving the enolate thiazole moiety is stronger than that of the benzothiazole phenolate moiety. Therefore, enolate oxyluciferin should be stabilized versus the phenolate anion. This difference in strength is attributed to the fact that the thiazole moiety has more potential hydrogen-bond acceptors near the proton donor atom than the benzothiazole moiety. Moreover, the phenol-based excited-state proton transfer leads to a decrease in the hydrogen-bond acceptor potential of the thiazole atoms. The ground-state enol-based acidity of oxyluciferin is also studied. This phenomenon can be explained by stabilization of the enolate anion through strengthening of a bond between water and the nitrogen atom of the thiazole ring, in an enol-based proton-transfer-dependent way.