The structures of proton-bound dimers of glycine with phenylalanine and pentafluorophenylalanine

Side-chain effects on the structures of protonated amino acid dimers: A gas-phase infrared spectroscopy study

“…In the case of Ser 2 H + , the present work can be compared to the previous results on Thr 2 H + 32. For both Ser 2 H + and Thr 2 H + , the theoretically most stable conformer is type A; that is This result is in line with previous results for Trp 2 H + and Gly•PheH + 33,34. We can thus conclude that if the protonated amine can interact with a side chain to gain further stabilization (via H-bonding or cation-π interaction), type A interactions (H2 N•••[H-NH 2 ] + ) are preferred to yield charge-solvated protonated dimer structures.…”

“…[24][25][26] For species such as Gly•PheH + , Thr 2 H + , and Trp 2 H + , on the other hand, IR spectra indicate hydrogen bonding between the protonated amine and the neutral amine group of the partner AA (-[H 2 N-H] + •••NH 2 -). [32][33][34] These results suggests that the pairwise interactions in protonated AA dimers are strongly influenced by the AA side chains. The effects of cation-π interactions in the Gly•PheH + dimers have been investigated by replacing the -CH 2 C 6 H 5 (benzyl-) side chain of Phe with -CH 2 C 6 F 5 .…”

“…[22][23][24][25][26][27][28][29][30][31][32][33][34][35] O-H and N-H stretching vibrations in Gly 2 H + , 22,25 Ser 2 H + , 23 Thr 2 H + , 32 Lys 2 H + , 22,29 Pro 2 H + , 31 and Trp 2 H + 33 were investigated in the 2700-3600 cm -1 range and Gly 2 H + , 24,26 Ala 2 H + , 26 Val 2 H + , 26 Cys 2 H + , 35 and Pro 2 H + 24 were studied in the 1000-2000 cm -1 region, in which C=O stretching and N-H bending vibrations can be monitored. Heterodimers, such as Ser•PheH + , 28,30 Ala•GlyH + , 26 Gly•LysH + , 22,25 and Gly•PheH + , 34 were also investigated in both, the 2700-3700 cm -1 and 800-2000 cm -1 ranges. By combining those spectroscopic results with theoretical calculations, a large amount of structural detail was obtained.…”

“…The effects of cation-π interactions in the Gly•PheH + dimers have been investigated by replacing the -CH 2 C 6 H 5 (benzyl-) side chain of Phe with -CH 2 C 6 F 5 . 34 However, in spite of the progress made to date, a general understanding of the influence of the side chains on the dimer binding interactions is lacking. Here, we present a study on protonated AA dimers having polar uncharged, aliphatic as well as aromatic side chains, namely of the AAs serine, isoleucine, phenylalanine and tyrosine.…”

Spectroscopic Discrimination of Diastereomeric Complexes Involving an Axially Chiral Receptor

“…The IRMPD spectra of ESI-formed diastereomeric[ M aR ·H·D D ] + and [M aR ·H·D L ] + complexes were consistent with the III-type structures, in which protonated D wasa ccommodatedo utside the flat cavity of the macrocycle M aR and hydrogen-bonded to its O 2 center.T he absence of IRMPD signals attributable to the more stable I-a nd II-type structures was not surprising and could be explained as follows. First, as reported in previous studies, [17,[31][32][33][34][35] it might be that, as the mixture of M aR /D was transferredi nt he gas phase, the proton-bound complexd id not have enough time and proper pathways to fully relaxt o the more stable structures, but was kinetically trapped in the originall ocal minimum. Second, even once formed, the more stable I-a nd II-type structures might be spectroscopically inactive, that is, stable enough to resist IR-induced fragmentation.…”