This study reports for the first time the use of β-carotene
as a natural photosensitizer for both the cationic photopolymerization
and thiol-ene click reactions under visible-light irradiation. In
an all-green synthesis approach, this performing dye-based system
leads to the cationic and thiol-ene polymerization of bio-based monomers,
mono- and di-epoxy limonene, with very high final conversions, and
appears as efficient as the common visible-light photosensitizers
used in free-radical or cationic photopolymerization, that is, thioxanthone
derivatives or camphorquinone. Effective antibacterial and tack-free
coatings have been synthesized through the incorporation of a natural
antibacterial agent (eugenol) in the limonene-derived polymer network.
The antibacterial assays have demonstrated a tremendous effect of
the eugenol-containing coatings against the adhesion of Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive).
Adsorption of (S)-histidine on Cu(110), and Cu(110) modified by adsorbed oxygen, has been studied by reflection absorption infrared spectroscopy (RAIRS). The molecular form and the orientation of the histidine molecule were deduced from experimental RAIRS data; moreover, vibrational spectra were simulated with a molecular mechanics force field (MMFF) calculation to address vibrational modes and the geometry of the adsorbate. The molecule preferentially binds to the surface in its HHis -molecular form. On the metallic Cu(110) surface, the adsorption occurs via the carboxylate group (COO -), with the two oxygen atoms equidistant from the surface, and via the dehydrogenated nitrogen of the imidazole group; the latter adopts an upright position with respect to the copper surface. The amino group (NH 2 ) is likely to be maintained close to the surface, thus facilitating the interaction with the metal. Preadsorption of oxygen (θ ≈ 0.3) on the copper surface induces minor changes in the molecular orientation: the ring tends to be less upright than in the absence of oxygen; the ring now interacts via its NH group as deduced from RAIRS and MMFF calculations. The molecule does not reorient with increasing oxygen coverage (θ ≈ 0.6), and no surface blocking was observed upon oxygen adsorption; both the orientation and the amount of histidine only slightly vary when the oxygen coverage is increased.
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