Publications

Abstract Pure 1,10-decanedithiol (C(10)-SH) and mixed (1-decanethiol:1,10-decanedithiol) self-assembled monolayers (SAMs) prepared from ethanolic solution on Au(111) surfaces have been used in order to investigate the effect of the SAM organization and the availability of free -SH groups at the SAM/solution interface on the development of layer-by-layer architectures containing SAMs and gold nanoparticles (Au-NPs). The SAM modified electrodes have been electrochemically characterized by cyclic voltammetry in alkaline medium (reductive desorption) and in the presence of an electroactive species, Fe(CN)(6)(3-), in KNO(3) solution, enabling the evaluation of the stability and organization of the SAMs. Enhanced stability, organization, and hindrance to the electron transfer were found for the mixed SAMs with increasing thiol content, when compared with the pure dithiol SAM. The mixed SAM prepared from solution containing the thiol to dithiol proportion of (50:1) and pure C(10)-SH SAMs have been selected for further modification; the electrochemical quartz crystal microbalance (EQCM) enables the detection of different amount of citrate stabilized Au-NPs attachment to the selected SAMs modified electrodes due to distinct availability of free -SH groups at the SAM/solution interface and the electrochemical characterization of the layer-by-layer assemblies (based on pure C(10)-SH and mixed SAMs) showed that the electron transfer (ET) properties of the such architectures strongly depend on the nature of the base SAM and amount of immobilized Au-NPs. Atomic force microscopy (AFM) morphological characterization of the C(10)-SH SAM upon layer-by-layer modification was performed ex situ in air.

Abstract Gold nanorods (AuNRs) with an aspect ratio of 2.33 or 3.16 were self-assembled onto 1,6-hexanedithiol-modified gold electrodes based on covalent interaction at a solution temperature of 35 degrees C. The formation of the 1,6HDT/AuNR bilayers as a function of the nanorods' adsorption time was studied by atomic force microscopy and quartz crystal microbalance, whereas their physical properties and chemical bonding were studied by contact angle and FT-IRRAS spectroscopy measurements. It was found that both types of nanorods were covalently bonded to the Au-1,6HDT-SAM modified electrodes in an end topography and with a high surface density. The electrochemical properties of the Au-1,6HDT-AuNR modified electrodes, as a function of the nanorods' adsorption time, were studied by cyclic voltammetry, square wave voltammetry, and electrochemical impedance spectroscopy using [Fe(CN)(6)](3-/4-) as the redox probes. The highest enhancement of the electrical current in the cyclic voltammograms was recorded at the Au-1,6HDT-AuNR modified electrodes for 7 h of chemisorption of 2.33 aspect ratio rods or 15 h of chemisorption of 3.16 aspect ratio rods. The high decrease of the apparent charge-transfer resistance upon nanorod self-assembly suggests a charging of the rods by the [Fe(CN)(6)](3-/4-) in solution and electron transfer across them. Moreover, the variation of the tunneling parameter beta suggests that the electron tunneling process through the 1,6HDT molecules is more efficient at the electrodes modified with bilayers containing short rods (beta = 0.78 +/- 0.08 angstrom(-1)/per methylene unit) than at the electrodes modified with bilayers containing long rods (beta = 0.84 +/- 0.10 angstrom(-1)/per methylene unit). The self-assembly of the AuNRs in an end-bonding topography with a high surface coverage restored almost completely the electronic communication that was entirely blocked by the preceding 1,6HDT layer.

Abstract The standard (pA(0)A = 0.1 MPa) molar enthalpies of formation in the condensed state of chromone-3-carboxylic acid and coumarin-3-carboxylic acid were derived from the standard molar energies of combustion in oxygen at T = 298.15 K, measured by combustion calorimetry. The standard molar enthalpies of sublimation were obtained by Calvet microcalorimetry. From these values the standard molar enthalpies in the gaseous phase, at T = 298.15 K, were derived. Additionally estimates of the enthalpies of formation, of all the studied compounds in gas-phase, were performed using DFT and other more accurate correlated calculations (MCCM and G3MP2), together with appropriate isodesmic, homodesmic or atomization reactions. There is a reasonable agreement between computational and experimental results.

Abstract Interfaces between two immiscible electrolyte solutions are recognized as a simplified model for biological systems and they can be of great relevance to the characterization of biomolecules and their role in biological systems. In this work, ion transfer and facilitated ion transfer of protonated catecholamines (dopamine and noradrenaline) by dibenzo-18-crown-6 are investigated at the water/1,6-dichlorohexane interface. The formation constant of the complex between both dopamine and noradrenaline with dibenzo-18-crown-6 was evaluated and the experimental conditions for the analytical determination of those catecholamines are established. These results can improve the understanding of the pharmacodynamics of the catecholamines, and contribute to the study of their interaction with biological membranes. Furthermore it can be used to develop an alternative method for the determination of neural signal transmission catecholamines.

Abstract Free fatty acids were derivatized as amides (DFFA) by reaction with (R)-(+)-1-phenyl-ethylamine, using a simple, fast and robust reaction scheme. A HPLC method with diode array and ESI MS detection was developed for the analysis of the derivatized substances. Six fatty acids were used in the method development: myristic, linoleic, palmitic, oleic, margaric and stearic acids. Under these conditions the elution of the DFFA are well resolved with retention times raging from 6.9 to 16.0 min. Fatty acids were extracted from cemetery soil and from adipocere formation experimental soils using a Soxhlet extraction, using as solvent ether/dichloromethane (1:1). Each DFFA is characterized by three m/z peaks: molecular weight of the substance; molecular weight of a dimer of the substance; the molecular weight of the dimer plus the atomic mass of sodium. The analysis of soil samples detected the six fatty acids used in the method developed plus palmitoleic and pentadecanoic. Beside this set of eight fatty acids other 13 fatty acids were detected in trace quantities or only in some soils and some were tentatively assigned as: 10-hydroxystearic, myristoleic, heptadecenoic and arachidic acids.

Abstract An experimental and computational thermochemical study was performed for oxindole. The standard (p degrees = 0.1 MPa) molar enthalpy of formation of solid oxindole was derived from the standard molar energy of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The respective standard molar enthalpy of sublimation, at T = 298.15 K, was measured by Calvet microcalorimetry. The standard molar enthalpy of formation in the gas phase was derived as -(66.8 +/- 3.2) kJ . mol(-1). Density functional theory calculations with the B3LYP hybrid functional and the 6-31G* and 6-311G** sets have also been performed in order to obtain the most stable conformation of oxindole. A comparison has been made between the structure of oxindole and that of the related two-ring molecules: indoline and 2-indanone and the one-ring molecules: pyrrolidine and 2,3-dihydropyrrole. The G3(MP2)//B3LYP method and appropriate reactions were used to obtain estimates of the standard molar enthalpy of formation of oxindole in the gas phase, at T = 298.15 K. Computationally obtained estimates of the enthalpy of formation of oxindole are in very good agreement with the experimental gas phase value. The aromaticity of oxindole was evaluated through the analysis of the nucleus independent chemical shifts (NICS) obtained from the B3LYP/6-311G** wave functions.

Abstract The synthesis and characterization of cadmium sulphide (CdS) quantum dots, conjugated in a porous phosphate heterostructure functionalized with aminopropyl groups is described. The resulting material has fluorescence properties with maximum emission intensity at 575 nm. The fluorescent materials are not soluble in water and exhibit high stability in aqueous solution in the pH ranges from 2 to 9. Energy dispersive X-ray spectroscopy confirmed the qualitative elemental composition of the synthesized materials and X-ray photoelectron spectra showed a surface S/Cd atomic ratio of 1.09. SEM images show that the materials are amorphous, possessing porous with sizes of several tens nanometres, homogeneous and exhibit a layered morphology. The adsorption-desorption analysis by N(2) at 77 K showed the accessibility of the CdS quantum dots onto the pores of the structure. The CdS quantum dots were stabilized by mercaptopropionic acid and bounded to the host materials by amine groups.

Abstract The energetics of 1-benzosuberone was studied by a combination of calorimetric techniques and computational calculations. The standard (p degrees = 0.1 MPa) molar enthalpy of formation of 1-benzosuberone, in the liquid phase, was derived from the massic energy of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The standard molar enthalpy of vaporization, at T = 298.15 K, was measured by Calvet microcalorimetry. From these two parameters the standard (p = 0.1 MPa) molar enthalpy of formation, in the gaseous phase, at T = 298.15 K, was derived: -(96.1 +/- 3.4) kJ . mol(-1). The G3(MP2)//B3LYP composite method and appropriate reactions were used to computationally calculate the standard molar enthalpy of formation of 1-benzosuberone, in the gaseous phase, at T = 298.15 K. The computational results are in very good agreement with the experimental value.

Abstract This paper reports a combined thermochemical experimental and computational study of the two isomers 3- and 4-hydroxycoumarin. The standard (ir = 0.1 MPa) molar enthalpies of formation in the condensed state of the compounds were derived from the standard molar energies of combustion in oxygen at T= 298.15 K. measured by combustion calorimetry. Calvet microcalorimetry was used to derive the standard molar enthalpies of sublimation. By combining these values, the standard molar enthalpies of formation in the gaseous phase, at T= 298.15K, were derived (367.7 +/- 1.9) kJ mo1-1 for 3-hydroxycoumarin and (351.4 +/- 2.4) kl.mo1-1 for 4-hydroxycoumarin. The temperatures of fusion, Tfus, and fusion enthalpies, at T= T(fus), are also reported. Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets, as well as more sophisticated calculations using Doubly Hybrid Density Functional Theory (DHDFT) and more accurate correlated computational techniques of the MCCM suite have been performed for both compounds. The aromaticity of the hydroxycoumarins has been studied using Nucleus Independent Chemical Shifts (NICS) techniques and compared to that of non-substituted coumarin.

Abstract A fluorescent hybrid cadmium sulphide quantum dots (QDs) dendrimer nanocomposite (DAB-CdS) synthesised in water and stable in aqueous solution is described. The dendrimer, DAB-G5 dendrimer (polypropylenimine tetrahexacontaamine) generation 5, a diaminobutene core with 64 amine terminal primary groups. The maximum of the excitation and emission spectra, Stokes' shift and the emission full width of half maximum of this nanocomposite are, respectively: 351, 535, 204 and 212 nm. The fluorescence time decay was complex and a four component decay time model originated a good fit (chi = 1.20) with the following lifetimes: tau (1) = 657 ps; tau (2) = 10.0 ns; tau (3) = 59.42 ns; and tau (4) = 265 ns. The fluorescence intensity of the nanocomposite is markedly quenched by the presence of nitromethane with a dynamic Stern-Volmer constant of 25 M(-1). The quenching profiles show that about 81% of the CdS QDs are located in the external layer of the dendrimer accessible to the quencher. PARAFAC analysis of the excitation emission matrices (EEM) acquired as function of the nitromethane concentration showed a trilinear data structure with only one linearly independent component describing the quenching which allows robust estimation of the excitation and emission spectra and of the quenching profiles. This water soluble and fluorescent nanocomposite shows a set of favourable properties to its use in sensor applications.