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Curcumin (Cur) is a natural polyphenol with a wide spectrum of biological activities and appealing therapeutic potential. Herein, it has been delivered by electrospray ionization as gaseous protonated species, [Cur + H] + , and as a Cu(ii) complex, [Cu(Cur - H)] + , a promising antioxidant and radical scavenger. The gas phase structures were assayed by infrared multiple photon dissociation (IRMPD) spectroscopy in both the fingerprint (800-2000 cm -1 ) and hydrogen stretching (3100-3750 cm -1 ) ranges. Comparison between the experimental features and linear IR spectra of the lowest energy structures computed at the B3LYP/6-311+G(d,p) level reveals that bare [Cu(Cur - H)] + exists in a fully planar and symmetric arrangement, where the metal interacts with the two oxygens of the syn-enolate functionality of deprotonated Cur and both OCH 3 groups are engaged in H-bonding with the ortho OH. The effect of protonation on the energetic and geometric determinants of Cur has been explored as well, revealing that bare [Cur + H] + may exist as a mixture of two close-lying isomers associated with the most stable binding motifs. The additional proton is bound to either the diketo or the keto-enol configuration of Cur, in a bent or nearly planar arrangement, respectively.

Linear ω-phenylalkylamines of increasing alkyl chain length have been investigated employing synchrotron radiation in the photon energy range from 7 to 15 eV. These molecules have received considerable interest because they bear the skeleton of biologically relevant compounds including neurotransmitters and because of the possible interaction between the amino moiety and the phenyl ring. Recently, the contribution of this interaction has been assayed in both neutral and protonated species, pointing to a role of the polymethylene chain length. In this work, the ionization energy (IE) values of benzylamine (BA), 2-phenylethylamine (2-PEA), 3-phenylpropylamine (3-PPA), and 4-phenylbutylamine (4-PBA) were investigated in order to ascertain the impact of the different alkyl chain lengths and to verify an amino radical cation-π interaction. The IEs obtained experimentally, 8.54, 8.37, 8.29, and 8.31 eV for BA, 2-PEA, 3-PPA and 4-PBA, respectively, show a decreasing trend that is discussed employing calculations at the CBS-QB3 level. Moreover, the appearance energy values for major fragments produced by the photofragmentation process are reported.