Chirality Effects on the IRMPD Spectra of Basket Resorcinarene/Nucleoside Complexes

• Published in: Chemistry : a European journal 2012-07, Vol.18 (27), p.8320-8328
• Main Authors: Filippi, Antonello, Fraschetti, Caterina, Piccirillo, Susanna, Rondino, Flaminia, Botta, Bruno, D'Acquarica, Ilaria, Calcaterra, Andrea, Speranza, Maurizio
• Format: Article
• Language: English
• Subjects: Aromatic compounds; Assessments; Baskets; Chemistry; Chirality; Cytarabine; Cytarabine - chemistry; Cytidine - chemistry; Cytosine; Cytosine - chemistry; Enantiomers; Holes; IRMPD spectroscopy; Molecular Structure; noncovalent interactions; Nucleosides; Nucleosides - chemistry; Oxygen; Oxygen atoms; Photons; Protons; resorcinarenes; Spectra; Spectrophotometry, Infrared - methods; Stereoisomerism
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201200614

The IRMPD spectra of the ESI‐formed proton‐bound complexes of the R,R,R,R‐ and S,S,S,S‐enantiomers of a bis(diamido)‐bridged basket resorcin[4]arene (R and S) with cytosine (1), cytidine (2), and cytarabine (3) were measured in the region 2800–3600 cm−1. Comparison of the IRMPD spectra with the corresponding ONIOM (B3LYP/6‐31(d):UFF)‐calculated absorption frequencies allowed the assessment of the vibrational modes that are responsible for the observed spectroscopic features. All of the complexes investigated, apart from [R⋅H⋅3]+, showed similar IRMPD spectra, which points to similar structural and conformational landscapes. Their IRMPD spectra agree with the formation of several isomeric structures in the ESI source, wherein the N(3)‐protonated guest establishes noncovalent interactions with the host amidocarbonyl groups that are either oriented inside the host cavity or outside it between one of the bridged side‐chains and the upper aromatic nucleus. The IRMPD spectrum of the [R⋅H⋅3]+ complex was clearly different from the others. This difference is attributed to the effect of intramolecular hydrogen‐bonding interactions between the C(2′)OH group and the aglycone oxygen atom of the nucleosidic guest upon repulsive interactions between the same oxygen atom and the aromatic rings of the host. Basket case: Infrared multiple photon dissociation spectra of proton‐bound complexes of a chiral resorcin[4]arene basket with cytosine, cytidine, and cytarabine were consistent with isomeric structures in which the protonated nucleoside was either inside or outside the host cavity (see figure).