Publications

Abstract The decomposition reaction of dimethyl-1,2-dioxetanone in dichloromethane was studied by using a DFT approach. The low efficiency of triplet and singlet excited-state formation was rationalised. A charge-transfer process was demonstrated to be involved in the chemiluminescence process. Present and previous results allow us to define an interstate crossing-induced chemiexcitation (ICIC) mechanism for the chemiluminescence of dioxetanones. Charge transfer is needed to reach a transition state, in the vicinity of which direct population of excited states is possible. The chemiexcitation process is then governed by singlet/triplet intersystem crossings. Structural modifications then modify the rate of these crossings and the singlet ground and excited-state interaction, thereby modulating the efficiency of this process and the spin of the resulting products.

Abstract Macromolecules, such as polyethylene glycol (PEG), have been frequently used in the preparation of xerogels, mainly with the purpose of tuning the meso- or macroporosity. However, PEG has never been applied in the context of the preparation of molecularly imprinted xerogels for small molecules. Thus, we decided to conduct a computational and experimental study of the incorporation of PEG into formerly studied sol-gel mixtures for the preparation of damascenone-imprinted xerogels. Computationally, two types of pregelification models were studied, one representing the initial mixture (SI3/SIPA:S:3 models) and the other representing the same mixtures after considerable solvent loss (SI3/SIPA:40:1 models). The latter ones were particularly prolific in providing clear effects of the PEG. In the SI3:40:1 model (containing SI3 units of Si3O3(OH)(6) mimicking the final xerogels backbone), a prohibitive instead of a promoting effect of PEG on the template-SI3 association was observed. PEG was found to interpose the SI3 aggregates, turning them smaller and more disperse. In agreement with that, a much higher porosity and surface area were found for the corresponding xerogel prepared with PEG, while no appreciable improvement of the imprinting efficiency could be observed. In the SIPA:40:1 model (containing both SI3 and SIPA units; SIPA, Si3O3(OH)(5)C3H6NHC6H5, representing the introduction of the organic functional group into the xerogel network), the interactions related to the network structuring were not significantly affected. This was due to the fact that the SIPA units themselves had a dispersive effect on the silica network; the PEG molecules were "pushed" into the aqueous/methanolic continuum, and their presence was somewhat redundant. Accordingly, both prepared SIPA-xerogels (with PEG or not) exhibited higher porosity compared to SI3-xerogels. Although the simulation results were not conclusive about the effect of PEG on the template-functional group association, experimentally it was clear that the imprinting effect was not improved with PEG.

Abstract Firefly oxyluciferin presents a pH-sensitive fluorescence in aqueous solutions. Its fluorescence spectra are composed of two green peaks at different pH values, despite the enolate anion being the only emitter. A computational approach was used to further elucidate the photoprotolytic cycle of oxyluciferin and investigate its pH sensitivity. It was found that oxyluciferin forms - stacking complexes both in the ground and excited states, at basic and acidic/neutral pH. However, at different pH values, these complexes adopt a different conformation, which explains the lower energy of the emission at acidic/neutral pH, in comparison with the emission at basic pH.

Abstract Herein we describe the synthesis of water-soluble platinum nanodendrites in dimethylformamide (DMF), in the presence of polyethyleneimine (PEI) as a stabilizing agent. The average size of the dendrites is in the range of 20-25 nm while their porosity can be tuned by modifying the concentration of the metal precursor. Electron tomography revealed different crystalline orientations of nanocrystallites in the nanodendrites and allowed a better understanding of their peculiar branching and porosity. The high surface area of the dendrites (up to 22 m(2) g(-1)) was confirmed by BET measurements, while X-ray diffraction confirmed the abundance of high-index facets in the face-centered-cubic crystal structure of Pt. The prepared nanodendrites exhibit excellent performance in the electrocatalytic oxidation of ethanol in alkaline solution. Sensing, selectivity, cycleability and great tolerance toward poisoning were demonstrated by cyclic voltammetry measurements.

Abstract To gain deeper insight into the structure of the electrode-ionic liquid interface differential capacitance-potential curves have been acquired through electrochemical impedance measurements at the mercury electrode. Understanding the role of the nature and size of the ionic species in the ionic liquid, namely the influence of different lengths of alkyl side chains of the imidazolium cation on the structure of the double layer, is the aim of the work being carried out. Differential capacitance-potential curves were obtained at the mercury electrode in contact with various mixtures of room-temperature ionic liquids of varying cation chain length (1-alkyl-3-methylimidazolium, [CnMIM](+) where n = 2, 6 and 12) with the same anion (bis(trifluoromethylsulfonyl)imide, [Tf2N](-)). For comparison purposes we have also carried out electrochemical measurements of the pure ionic liquids under the same conditions. Systematic variations in the electrocapillary drop-time curves and capacitance were found with increasing amounts of the cation with longer alkyl chains in the mixture. The electrocapillary curve results may be interpreted as indicating the preferential adsorption of the longer alkyl group on the mercury surface.

Abstract The use of agar-based biomaterials for the development of emerging areas, such as tissue engineering or 'smart materials' production has recently gained great interest. Understanding how these gel-forming polysaccharides self-organise in aqueous media and how these associations can be tuned to meet the specific needs of each application is thus of great relevance. As an extension of previous pioneering research concerning the application of the microwave-assisted extraction (MAE) technique in the recovery of native (NA) and alkali-modified (AA) agars, this article focuses on the different molecular assemblies assumed by these novel NA and AA when using different MAE routes. The molecular architectures in dilute (5, 10, 50 and 100 mg mL(-1)) and concentrated (1.5% (w/w)) aqueous media were imaged by AFM and cryoSEM, respectively. Relevant structural and physicochemical properties were investigated to support the microscopic data. Different extraction routes led to polysaccharides with unique properties, which in turn resulted in different molecular assemblies. Even at 5 mu g mL(-1), AFM images included individual fibers, cyclic segments, aggregates and local networks. At higher polymer concentrations, the structures further aggregated forming multilayer polymeric networks for AA. The more compact and denser 3D networks of AA, imaged by cryoSEM, and their higher resistance to large deformations matched the 2D-shapes observed by AFM. Depending on the nature of the AA chains, homogeneous or heterogeneous growth of assemblies was seen during network formation. The obtained results support well the view of double helix formation followed by intensive double helix association proposed for agar gelation.

Abstract Consumers and industrial activities increasingly require goods and services that suit as much as possible to their needs and tastes. The footwear industry has followed these trends leading to the need to use a variety of materials and components that are presently used from casual shoes to technical products such as safety and protective footwear. Rubber is among these materials and has been strongly used in the production of shoe soles since its discovery in 1837 by Goodyear. Although rubber, more precisely vulcanized rubber, present some drawbacks in comparison with other polymers used in footwear applications (e.g. higher density, longer processing operations and slightly higher costs) it gathers a group of superior physical properties suitable for shoe sole production, namely, durability, abrasion resistance, tensile resistance, tear strength resistance, slip resistance, oil resistance and the ability to be molded in different colors. This chapter focuses on the properties and physical-mechanical guidelines for vulcanized rubber applications in footwear and on the description of recent developments regarding shoe sole applications. In particular the work carried out in shock absorption properties in vulcanized rubber, natural rubber incorporating mercerized natural fibers of sisal, jute, hemp and bamboo will be presented.

Abstract We have performed high level ab initio quantum mechanical calculations for aminoethene and the three isomeric 1,1- (Z)- or (E)-1,2-diaminoethenes as well as their singly and doubly charged cations derived by loss of electrons and/or upon protonation. Gas phase molecular structures were computed at the MP2/6-311+G(3df,2p) level. Standard molar enthalpies of formation in the gas phase, at T=298.15K, were estimated using the G3 composite method and atomization, isodesmic and homodesmotic reactions. Other energetic parameters were also calculated at the G3 level: proton affinities, basicities and adiabatic ionization enthalpies. Theoretical and experimental data are compared. The reported experimental data refer only to aminoethene wherein the standard molar enthalpy of formation has a considerable uncertainty, although the molecular structure is well established. There are no such data, neither structural nor thermochemical, for any of the three isomeric diaminoethenes. Isoelectronic comparisons are made. For example, the diprotonated diaminoethenes are isoelectronic to isobutene and (Z)- and (E)-butene, while the doubly ionized diaminoethenes are likewise related to trimethylenemethane and 1,3-butadiene. Copyright (c) 2013 John Wiley & Sons, Ltd.

Abstract The unimolecular decomposition of 1,2-dioxetanedione, the high-energy intermediate of the chemiluminescence peroxyoxalate reaction, was studied by theoretical means for the first time. Our calculations have provided results in line with the experimental data regarding this compound. 1,2-Dioxetanedione decomposes due to a step-wise biradical mechanism. In the biradical region of the decomposition path, there is a path for singlet chemiexcitation. Interactions between the singlet ground and excited states with triplet states can explain the weak unimolecular chemiluminescence of 1,2-dioxetanedione. Copyright (c) 2013 John Wiley & Sons, Ltd.