Excitation, Ionization, and Fragmentation of Chiral Molecules in Asymmetric Microenvironments:  A Mass-Resolved R2PI Spectroscopic Study

Abstract

One- and two-color, mass selected R2PI spectra of the S(1) <-- S(0) transitions in the bare (R)-(+)-1-phenyl-1-propanol and its complexes with bidentate solvent molecules, like the (R)-(-)- and (S)-(+)-3-hydroxytetrahydrofuran enantiomers, have been recorded after a supersonic molecular beam expansion. The one-color R2PI excitation spectra of the diastereomeric complexes are characterized by three main peaks, one red-shifted and the other two blue-shifted relative to the band origin of the most stable anti conformer of the bare chromophore. The opposite direction of these spectral shifts is ascribed to the occurrence of three different hydrogen bonded isomeric structures for each individual complex, while their different magnitude depends on the configuration of the bidentate solvent molecule as well as its specific hydrogen bond interaction center, whether the ethereal oxygen atom or the hydroxyl group. The same factors play a major role in determining the magnitude of the phenomenological activation barriers for the loss of an ethyl radical from the ionized diastereomeric complexes.

Molecular and supramolecular chirality: R2PI spectroscopy as a tool for the gas‐phase recognition of chiral systems of biological interest

“…The formation of the adducts with the three P R rotamers has been excluded by comparisons with the excitation spectra of the complexes of P R with analogues monodentate solvents (ciclopentanol, tetrahydrofuran, and secondary alcohols. 120 Therefore, the a2g bands of Figure 16 have been attributed to the three dominant isomeric forms I, II, and III reported in Figure 15a.…”

“…More recently, we focused our attention on the study of chiral molecules of biological or pharmaceutical interest, or tailor-made complexes containing components which mimic the building blocks of large biomolecules. More specifically, we investigated the effects of inter-and intramolecular interactions in the structure and spectral properties of complexes containing chiral fluoroaromatics, 118 furanose rings analogues, 119,120 esters, 121 and neurotransmitters. 80 The Effect of Fluorine Substitution on Chiral Recognition R-1-Phenylethanol (E R ) and R-1-Phenyl-2,2,2-trifluoroethanol (FE R ) of R-and S-2-Aminobutane…”

“…Like many other five-membered rings, Th R and Th S may assume in the isolated state several ring-puckering conformations. 120 In the most stable one, the hydrogen atom of the alcoholic function ( R-(þ)-1-Phenyl-1-propanol (P R ) was chosen as the model chiral receptor for Th R and Th S . We have often used this chromophore as a probe of the noncovalent interactions in diastereomeric complexes.…”

“…These structures exhibit also a weak O structures were found for the [P R Th R/S ] clusters involving the gauche rotamers of the chromophore. 120 Figures 16a and 16b show the 1cR2PI excitation spectrum of the homochiral [P R…”

Structural relationships in small molecule interactions governing gas-phase enantioselectivity and zwitterionic formation

“…The quantification was done by measuring the relative peak intensity of the complexes in mass spectrometer [40 -47]. Speranza applied ESI-MS n CID and REMPI-TOF methodologies to measure the fragmentation thresholds of diastereomeric clusters [19,23,25,32,48,49]. They found that the chiral recognition was very sensitive to cavity size and hydrophilic/hydrophobic properties of the chiral receptor [24,50].…”