Unveiling the Shape of Aspirin in the Gas Phase

Amide carbonyl groups in proteins can engage in C=O···C=O and C–X···C=O interactions, where X is a halogen. The putative involvement of four poles suggests that these interactions are primarily dipolar. Our survey of crystal structures with a C–X···C=O contact that is short (i.e., within the sum of the X and C van der Waals radii) revealed no preferred C–X···C=O dihedral angle. Moreover, we found that structures with a short X−···C=O contact display the signatures of an n→π* interaction. We conclude that intimate interactions with carbonyl groups do not require a dipole.

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“…Our current findings support earlier ones, 1,6–11 and suggest that these intimate interactions involving carbonyl groups do not require a dipole.…”

Section: Resultssupporting

confidence: 92%

Intimate Interactions with Carbonyl Groups: Dipole–Dipole or n→π*?

2012

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“…There are a few reported examples of microwave spectroscopic studies on the conformations of amino acids (β‐alanine and γ‐aminobutyric acid) as well as of the drug aspirin stabilized by n→π* interactions –. Recently, Caminati and co‐workers reported the structure of a complex of chlorotrifluoroacetylene and water stabilized by an n→π* interaction .…”

Section: Figurementioning

confidence: 99%

Direct Spectroscopic Evidence for an n→π* Interaction

et al. 2016

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The n!p*interaction is an extremely weak but very important noncovalent interaction. Although this interaction is widely present in biomolecules and materials,i ts existence is counterintuitive and so has been debated extensively.H erein, we have reported direct spectroscopic evidence for an n!p* interaction for the first time by probing the carbonyl stretching frequency in phenyl formate using isolated gas-phase IR spectroscopy. This result also demonstrates that the conformational preference for the cis conformer of phenyl formate compared to the trans conformer arises due to the presence of the n!p* interaction in the former.The direct proof reported herein for this controversial but important noncovalent interaction should stimulate further experimental and theoretical investigation on this intriguing researchtopic.

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“…A Digital Delay generator (Standford Research Systems, DG645) (3) is used to trigger the arbitrary waveform generator and the valve driver. The microwave pulse is upconverted by mixing with a 18.99 GHz phase-locked dielectric resonator oscillator (PDRO) (4) in a broadband mixer (Miteq TB0440LW1) (5) and subsequently amplified by a 300 W traveling wave tube amplifier (IFI, GT186-300) (7). The power level necessary for the polarization of the molecular systems is adjusted using a variable attenuator (6).…”

Section: Cp-ftmw Spectrometer With Laser Ablation Sourcementioning

confidence: 99%

“…Using ns and ps Nd:YAG lasers as vaporization tool, we have probed the structure of several natural amino acids [2], nucleic acid bases [3], dipeptides [4], neurotransmitters [5] and sugars [6]. The shape of aspirin has been also unveiled [7].…”

Section: Introductionmentioning

confidence: 99%