RESUMO
Rate coefficients of the O3-initiated oxidation of allyl methyl sulfide (H2CâCHCH2SCH3, AMS) and allyl ethyl sulfide (H2CâCHCH2SCH2CH3, AES) were determined at atmospheric conditions by "in situ" FTIR. The relative kinetic experiments were performed using methylcyclohexane (McH) and carbon monoxide (CO) as nascent OH radical scavengers and in the absence of any scavenger, to determine the impact that the formation of OH radicals has on the rate coefficients. In the absence of scavengers, values of kAMS+O3 = (5.23 ± 3.57) × 10-18 and kAES+O3 = (5.76 ± 1.80) × 10-18 cm3 molecule-1 s-1 were obtained. In the presence of the scavengers, however, the rates decreased to kAMS+O3+McH = (3.92 ± 1.92) × 10-18 and kAMS+O3+CO = (2.63 ± 0.47) × 10-18 cm3 molecule-1 s-1 for AMS, and kAES+O3+McH = (4.78 ± 1.38) × 10-18 and kAES+O3+CO = (3.50 ± 0.27) × 10-18 cm3 molecule-1 s-1 for AES. On the basis of these results, we have decided to recommend the values obtained using CO as scavenger as those best representing the rate coefficient for the reactions of O3 with AMS and AES. The reaction mechanism was explored using DFT and post-Hartree-Fock computational methods. It is shown that the barrier for the common cyclization to primary ozonide (-3.7 ± 0.1 kcal mol-1) followed by other reactions, as well as that for the reaction with the sulfur atom (-5.1 ± 0.1 kcal mol-1), is small and quite close, meaning that both reaction paths should contribute significantly to the global reaction rate.
RESUMO
Bacterial contamination is a critical problem in medical implants, which are preferential sites for bacterial adhesion, leading to infections which can compromise health and immune system of patients. Commercial titanium alloys are the most commonly used materials for permanent implants in contact with bone, and the prevention of infections on their surface is therefore a crucial challenge for orthopaedic and dental surgeons. Thus, the aim of this work is to develop polysaccharide antibacterial coatings onto modified titanium surfaces with different surface topography, in order to act as reservoirs of antibacterial agents. For this, hyaluronic acid/chitosan polyelectrolyte multilayers were successfully developed after acid hydrolysis of Ti-6Al -4 V alloys. Surface modification could be monitorized by XPS spectroscopy, fluorescence confocal microscopy and contact angle measurements. Furthermore, the effect of surface micropatterning on the stability, hydrophilicity, capability to the loading and release of triclosan and the antibacterial properties of prepared multilayers against Staphylococcus aureus were also analysed.
