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The structures of proton-bound complexes of 5,7-dimethoxy-4H-chromen-4-one (1) and basic amino acids (AAs), namely, histidine (His) and lysine (Lys), have been examined by means of mass spectrometry coupled with IR ion spectroscopy and quantum chemical calculations. This selection of systems is based on the fact that 1 represents a portion of glabrescione B, a natural small molecule of promising antitumor activity, while His and Lys are protein residues lining the cavity of the alleged receptor binding site. These species are thus a model of the bioactive adduct, although clearly the isolated state of the present study bears little resemblance to the complex biological environment. A common feature of [1+AA+H] + complexes is the presence of a protonated AA bound to neutral 1, in spite of the fact that the gas-phase basicity of 1 is comparable to those of Lys and His. The carbonyl group of 1 acts as a powerful hydrogen-bond acceptor. Within [1+AA+H] + the side-chain substituents (imidazole group for His and terminal amino group for Lys) present comparable basic properties to those of the α-amino group, taking part to a cooperative hydrogen-bond network. Structural assignment, relying on the comparative analysis of the infrared multiple photon dissociation (IRMPD) spectrum and calculated IR spectra for the candidate geometries, derives from an examination over two frequency ranges: 900-1800 and 2900-3700 cm -1 . Information gained from the latter one proved especially valuable, for example, pointing to the contribution of species characterized by an unperturbed carboxylic OH or imidazole NH stretching mode., (© 2020 Wiley-VCH GmbH.)

The structure, stability, and reactivity of proton-bound diastereomeric [M x H x A]+ complexes between some amino acid derivatives (A) and several chiral tetra-amide macrocycles (M) have been investigated in the gas phase by ESI-FT-ICR and ESI-ITMS-CID mass spectrometry. The displacement of the A guest from the diastereomeric [M x H x A]+ complexes by reaction with the 2-aminobutane enantiomers (B) exhibits a distinct enantioselectivity with regards to the leaving amino acid A and, to a minor extent, to the amine reactant B. The emerging selectivity picture, discussed in the light of molecular mechanics calculations, provides compelling evidence that the most stable conformers of the selected chiral tetra-amide macrocycles M may acquire in the gas phase a different conformation by induced fit on complexation with some representative amino acid derivatives A. This leads to the coexistence in the gas phase of stable diastereomeric [M x H x A]+ eq-eq and ax-ax structures, in proportions depending on the configuration of A and M and characterized by different stability and reactivity toward the 2-aminobutane enantiomers. The enantioselectivity of the gas-phase A-to-B displacement in the diastereomeric [M x H x A]+ complexes essentially reflects the free energy gap between the homo- and heterochiral [M x H x A]+ complexes, except when the tetra-amidic host presents an additional macrocycle generated by a decamethylene chain. In this case, the measured enantioselectivity mostly reflects the stability difference between the relevant diastereomeric transition structures.

Diastereomeric proton-bound [1(L)HA]+ complexes between selected amino acids (A=phenylglycine (Phg), tryptophan (Trp), tyrosine methyl ester (TyrOMe), threonine (Thr), and allothreonine (AThr)) and a chiral amido[4]resorcinarene receptor (1(L)) display a significant enantioselectivity when undergoing loss of the amino acid guest A by way of the enantiomers of 2-aminobutanes (B) in the gas phase. The enantioselectivity of the B-to-A displacement is ascribed to a combination of thermodynamic and kinetic factors related to the structure and the stability of the diastereomeric [1(L)HA]+ complexes and of the reaction transition states. The results of the present and previous studies allow classification of the [1(L)HA]+ complexes in three main categories wherein: i) guest A does not present any additional functionalities besides the amino acid one (alanine (Ala), Phg, and phenylalanine (Phe)); ii) guest A presents an additional alcohol function (serine (Ser), Thr, and AThr); and iii) guest A contains several additional functionalities on its aromatic ring (tyrosine (Tyr), TyrOMe, Trp, and 3,4-dihydroxyphenylalanine (DOPA)). Each category exhibits a specific enantioselectivity depending upon the predominant [1(L)HA]+ structures and the orientation of the 2-aminobutane reactant in the relevant adducts observed. The results may contribute to the understanding of the exceptional selectivity and catalytic properties of enzyme mimics towards unsolvated biomolecules.

The structures of proton‐bound complexes of 5,7‐dimethoxy‐4H‐chromen‐4‐one (1) and basic amino acids (AAs), namely, histidine (His) and lysine (Lys), have been examined by means of mass spectrometry coupled with IR ion spectroscopy and quantum chemical calculations. This selection of systems is based on the fact that 1 represents a portion of glabrescione B, a natural small molecule of promising antitumor activity, while His and Lys are protein residues lining the cavity of the alleged receptor binding site. These species are thus a model of the bioactive adduct, although clearly the isolated state of the present study bears little resemblance to the complex biological environment. A common feature of [1+AA+H]+ complexes is the presence of a protonated AA bound to neutral 1, in spite of the fact that the gas‐phase basicity of 1 is comparable to those of Lys and His. The carbonyl group of 1 acts as a powerful hydrogen‐bond acceptor. Within [1+AA+H]+ the side‐chain substituents (imidazole group for His and terminal amino group for Lys) present comparable basic properties to those of the α‐amino group, taking part to a cooperative hydrogen‐bond network. Structural assignment, relying on the comparative analysis of the infrared multiple photon dissociation (IRMPD) spectrum and calculated IR spectra for the candidate geometries, derives from an examination over two frequency ranges: 900–1800 and 2900–3700 cm−1. Information gained from the latter one proved especially valuable, for example, pointing to the contribution of species characterized by an unperturbed carboxylic OH or imidazole NH stretching mode. [ABSTRACT FROM AUTHOR]

Proton-bound [M ⋅H ⋅G]+ diastereomeric complexes between some chiral aromatic amino acids or dipeptides (G) and a chiral multifunctional macrocyclic receptor (M=Chirabite-A) undergo, in the gas phase, highly selective substitution and addition reactions by amines, such as 2-aminobutane and piperidine. All the [M ⋅H ⋅G]+ complexes follow time-dependent monoexponential decays. In some cases, the kinetic curves exhibit a plateau revealing the presence of unreactive [M ⋅H ⋅G]+ structures. In them, the amino acid is accommodated in the macrocycle cavity in the zwitterionic form by sharing its acidic hydrogen atoms with the pyridine nitrogen atoms of the host. The same interactions are structurally inaccessible to G=dipeptides or monofunctional amines, which then can be readily released from [M ⋅H ⋅G]+. When the amino acid interacts with the amidocarbonyl oxygen atoms pointing outside the macrocycle cavity, it saves the canonical structure and can be readily displaced by the amine. The Chirabite-A may act as an efficient template for aromatic amino acids by releasing them or not depending upon the amino acid configuration and the basicity of the amine. These unique properties confer to the gas-phase diastereomeric [M ⋅H ⋅G]+ complexes the features of multi-input multi-output chemo-'logic gates'. [ABSTRACT FROM AUTHOR]

• "sedano bianco di Sperlonga" PGI celery was investigated by a multi-methodological approach. • A detailed phytochemical profile of the edible part (petioles and blade leaves) was obtained. • Biogenic amine and mycotoxin low contents confirmed celery quality and freshness. • Ethanolic extract of blade leaves showed antimutagenic and radical scavenger power. Celery is a widely used vegetable known for its peculiar sensorial and nutritional properties. Here, the white celery (Apium graveolens L.) "sedano bianco di Sperlonga" PGI ecotype was investigated to obtain the metabolic profile of its edible parts (blade leaves and petioles) also related to quality, freshness and biological properties. A multi-methodological approach, including NMR, MS, HPLC-PDA, GC–MS and spectrophotometric analyses, was proposed to analyse celery extracts. Sugars, polyalcohols, amino acids, organic acids, phenols, sterols, fatty acids, phthalides, chlorophylls, tannins and flavonoids were detected in different concentrations in blade leaf and petiole extracts, indicating celery parts as nutraceutical sources. The presence of some phenols in celery extracts was here reported for the first time. Low contents of biogenic amines and mycotoxins confirmed celery quality and freshness. Regarding the biological properties, ethanolic celery extracts inhibited the oxidative-mediated DNA damage induced by tert -butylhydroperoxide and scavenged DPPH and ABTS radicals. [ABSTRACT FROM AUTHOR]