Comparison of the orders of gas-phase basicities and ammonium ion affinities of polyethers by the kinetic method and ligand exchange technique

Wu, Hui‐Fen; Brodbelt, Jennifer S.

doi:10.1016/1044-0305(93)80050-9

Cited by 30 publications

(9 citation statements)

References 16 publications

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“…Due to multiple hydrogen bonding, relative ammonium ion affinities are much larger for the larger crown ethers than their proton affinities (Meot-Ner (Mautner), 1983;Liou & Brodbelt, 1992a, Wu & Brodbelt, 1993. Within the series of crowns, the binding energy of NH 4 þ ranks in the order of 12-crown-4 < 15-crown-5 < 18-crown-6 < 21-crown-7.…”

Section: A Ammonium Ion Affinitiesmentioning

confidence: 96%

Molecular recognition and supramolecular chemistry in the gas phase

Schalley

2001

Mass Spectrometry Reviews

289

178

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Supramolecular chemistry, in particular, the fields of molecular recognition and self-assembly, profit much from the development of soft ionization techniques and advanced methods for mass analysis and gas-phase chemistry. Vice versa, weakly bonded architectures and host-guest complexes represent a veritable challenge for the mass spectrometrist, leading to further development of methods and techniques. This review describes the state-of-the-art in this field, and includes topics such as the effects of solvation on meta binding to crown ethers, chiral discrimination of guests by chiral hosts, the elucidation of the secondary structure of self assembled complexes, and the mechanistic pathways of self assembly or the fragmentations of supramolecular complexes in the gas phase.

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Section: A Ammonium Ion Affinitiesmentioning

confidence: 96%

Molecular recognition and supramolecular chemistry in the gas phase

Schalley

2001

Mass Spectrometry Reviews

289

178

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“…Two brief reviews31, 32 have been published in this area. We will refer only tangentially to the excellent work done using other mass spectrometric techniques; for instance, ion trap mass spectrometry, which is less expensive, is more widely available, has the same kinds of ion isolation capability, and is probably more easily interfaced to ion sources such as electrospray than FTICR, has been used in a number of important studies 33–45. Finally, this article will focus primarily on work done in the authors' laboratories, with a few examples also drawn from the work of others.…”

Section: Introductionmentioning

confidence: 99%

Study of gas‐phase molecular recognition using Fourier transform ion cyclotron resonance mass spectrometry (FTICR/MS)

et al. 2001

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The application of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry to the quantitative study of molecular recognition in the gas phase is reviewed. Because most quantitative measurements are dependent on accurate determination of the pressure of a neutral reagent, methods for accurate pressure measurement in FTICR, including gauge calibration using a reaction with known rate constants (the traditional method), exothermic proton transfer rate measurement (often the best method when accurate neutral pressures in the trapping cell are desired), and linewidth measurement (a little-used, but generally applicable method) are discussed. The use of rate constant measurements in molecular recognition is illustrated with examples employing natural abundance isotopic labeling to study self-exchange and 2 : 1 ligand:metal complex formation kinetics in crown ether-alkali cation systems. Self-exchange rates do not correlate with alkali cation/crown cavity size relationships, whereas 2 : 1 complex formation kinetics correlate strongly with size relationships. The use of exchange equilibrium constant measurements to characterize molecular recognition is illustrated by alkali cation exchanges between 18-crown-6 and the isomers of dicyclohexano-18-crown-6. These experiments show that the alkyl-substituted ligand binds alkali cations better than unsubstituted 18-crown-6 in the gas phase, in accordance with expectations based on the higher polarizability of the alkyl-substituted ligand. Further, the metal binding thermochemistry differs for the two dicyclohexano-18-crown-6 isomers, with the bowl-shaped cis-syn-cis isomer binding all the alkali cations more strongly than the cis-anti-cis isomer. The measurement of entropies and enthalpies associated with one of the most subtle forms of molecular recognition, enantiomeric discrimination, is illustrated by studies of the discrimination between enantiomers of chiral amines by dimethyldiketopyridino-18-crown-6. This chiral ligand binds chiral primary ammonium cations that have the opposite absolute configuration at their stereocenter more strongly than the enantiomer with the same absolute configuration. Gas-phase studies show that this enantiomeric discrimination is enthalpic in origin, likely related to more favorable pi-pi stacking for the preferred enantiomer. Entropy disfavors binding of the preferred enantiomer.

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“…[3] In our study, [18]crown-6 serves as the guest, it binds to primary ammonium ions in solution, [4] and in the gas phase. [5] Dendritic crown ether/ammonium complexes are Figure 1. Chemical structure of [18]crown-6 and a fourth generation (G4) POPAM dendrimer.…”

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confidence: 99%