Complexation of halide ions to tyrosine: role of non-covalent interactions evidenced by IRMPD spectroscopy

The binding motifs in the halide adducts with tyrosine ([Tyr + X]-, X = Cl, Br, I) have been investigated and compared with the analogues with 3-nitrotyrosine (nitroTyr), a biomarker of protein nitration, in a solvent-free environment by mass-selected infrared multiple photon dissociation (IRMPD) spectroscopy over two IR frequency ranges, namely 950–1950 and 2800–3700 cm-1. Extensive quantum chemical calculations at B3LYP, B3LYP-D3 and MP2 levels of theory have been performed using the 6-311++G(d,p) basis set to determine the geometry, relative energy and vibrational properties of likely isomers and interpret the measured spectra. A diagnostic carbonyl stretching band at B1720 cm-1 from the intact carboxylic group characterizes the IRMPD spectra of both [Tyr + X]- and [nitroTyr + X]-, revealing that the canonical isomers (maintaining intact amino and carboxylic functions) are the prevalent structures. The spectroscopic evidence reveals the presence of multiple non-covalent forms. The halide complexes of tyrosine conform to a mixture of plane and phenol isomers. The contribution of phenol-bound isomers is sensitive to anion size, increasing from chloride to iodide, consistent with the decreasing basicity of the halide, with relative amounts depending on the relative energies of the respective structures. The stability of the most favorable phenol isomer with respect to the reference plane geometry is in fact 1.3, -2.1, -6.8 kJ mol-1, for X = Cl, Br, I, respectively. The change in p-acidity by ring nitration also stabilizes anion–p interactions yielding ring isomers for [nitroTyr + X]-, where the anion is placed above the face of the aromatic ring

IR ion spectroscopy in a combined approach with MS/MS and IM-MS to discriminate epimeric anthocyanin glycosides (cyanidin 3-O-glucoside and -galactoside)

Anthocyanins are widespread in plants and flowers, being responsible for their different colouring. Two representative members of this family have been selected, cyanidin 3-O-β-glucopyranoside and 3-O-β-galactopyranoside, and probed by mass spectrometry based methods, testing their performance in discriminating between the two epimers. The native anthocyanins, delivered into the gas phase by electrospray ionization, display a comparable drift time in ion mobility mass spectrometry (IM-MS) and a common fragment, corresponding to loss of the sugar moiety, in their collision induced dissociation (CID) pattern. However, the IR multiple photon dissociation (IRMPD) spectra in the fingerprint range show a feature particularly evident in the case of the glucoside. This signature is used to identify the presence of cyanidin 3-O-β-glucopyranoside in a natural extract of pomegranate. In an effort to increase any differentiation between the two epimers, aluminum complexes were prepared and sampled for elemental composition by FT-ICR-MS. CID experiments now display an extensive fragmentation pattern, showing few product ions peculiar to each species. More noteworthy is the IRMPD behavior in the OH stretching range showing significant differences in the spectra of the two epimers. DFT calculations allow to interpret the observed distinct bands due to a varied network of hydrogen bonding and relative conformer stability

Are you approaching me? Motor execution influences perceived action orientation

Human observers are especially sensitive to the actions of conspecifics that match their own actions. This has been proposed to be critical for social interaction, providing the basis for empathy and joint action. However, the precise relation between observed and executed actions is still poorly understood. Do ongoing actions change the way observers perceive others' actions? To pursue this question, we exploited the bistability of depth-ambiguous point-light walkers, which can be perceived as facing towards the viewer or as facing away from the viewer. We demonstrate that point-light walkers are perceived more often as facing the viewer when the observer is walking on a treadmill compared to when the observer is performing an action that does not match the observed behavior (e.g., cycling). These findings suggest that motor processes influence the perceived orientation of observed actions: Acting observers tend to perceive similar actions by conspecifics as oriented towards themselves. We discuss these results in light of the possible mechanisms subtending action-induced modulation of perception