Laser Spectroscopic Study of Cold Host–Guest Complexes of Crown Ethers in the Gas Phase

Abstract

A laser spectroscopic study on the structure and dynamics of cold host-guest inclusion complexes of crown ethers (CEs) with various neutral and ionic species in the gas phase is presented. The complexes with neutral guest species are formed by using supersonic free jets, and those with ionic species are generated with electrospray ionization combined with a cold 22-pole ion trap. For CEs, various sizes of 3n-crown-n ethers (n=4, 5, 6, and 8) and their benzene-substituted species are used. For the guest species, water, methanol, ammonia, acetylene, and phenol are employed as neutral guest species, and for charged guest species, alkali metal cations are chosen. The electronic and vibrational spectra of the complexes are measured by using various laser spectroscopic methods; electronic spectra for the neutral complexes are measured by laser-induced fluorescence. Discrimination of different species such as conformers is performed by ultraviolet-ultraviolet hole-burning spectroscopy. The vibrational spectra of selected species are observed by infrared-ultraviolet double-resonance (IR-UV DR) spectroscopy. For the ionic complexes, ultraviolet photodissociation and IR-UV DR spectroscopy are applied. The complex structures are determined by comparing the observed spectra with those of possible structures obtained by density functional theory calculations. How the host CEs change their conformation or which conformer prefers to form unique inclusion complexes are discussed. These results reveal the key interactions for forming special complexes leading to molecular recognition.

Cryogenic Methods for the Spectroscopy of Large, Biomolecular Ions

“…The goal has been to provide an appreciation of the various methods for cooling and spectroscopic detection as well as an idea of how they have been combined in creative ways in different laboratories around the world to measure spectra of cold ions. It should be noted that there is nothing that restricts these techniques to biomolecular ions -in fact, applications to molecules such as cation-crown ether complexes [185][186][187], reaction intermediates [188], and organometallic catalysts [147] have proven to be particularly powerful.…”

Geometric and Electronic Structures of Dibenzo-15-Crown-5 Complexes with Alkali Metal Ions Studied by UV Photodissociation and UV–UV Hole-Burning Spectroscopy

“…From this standpoint, gas-phase spectroscopic studies of CEs will play a vital role in the elucidation for the ion selectivity of CEs in solution. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] Since the structure of CE complexes in the gas phase is not perturbed either by neighboring complexes, counteranions, or solvent molecules, the gas-phase spectroscopy will shed light on intrinsic natures of the conformation.…”

Chirality effects in gas-phase spectroscopy and photophysics of molecular and ionic complexes: contribution of low and room temperature studies

“…All the techniques described above have been recently extended to cryogenic traps which have been applied to chiral systems like peptides and offer a wealth of possibilities in terms of sensitivity and diversity [82][83][84][85]147]. However, none of the studies reported so far tackles stereochemical questions.…”

“…By using thermometer reactions, the temperature of the ions in a quadrupole ion trap has been shown to be close to room temperature [79][80][81]. It has been shown also in the recently developed quadrupolar or multipolar ion traps at cryogenic temperatures that the systems are vibrationally [82][83][84][85][86] and rotationally cold [83]. The question of vibrational cooling is especially important for Infra-Red Multiple Photon Dissociation (IRMPD) experiments as they require that Intramolecular Vibrational energy Redistribution (IVR) within the ion is not hampered by collisional quenching.…”