Molecular recognition and supramolecular chemistry in the gas phase

Abstract I. Introduction 254 II. Benefits of Mass Spectrometry for Supramolecular Chemistry 254 A. Non‐Covalent Bonding in the Condensed‐ and Gas‐Phase 256 B. Promise and Pitfalls of Mass Spectrometry for Supramolecular Chemistry 257 III. Crown Ether–Ammonium Ion Complexes 257 A. Ammonium Ion Affinities 258 B. Chiral Recognition of Ammonium Ions 259 C. Collision‐Activated Dissociation and Ion‐Molecule Reactions 260 IV. Crown Ether–Metal Ion Complexes 260 A. Binding Selectivities in Solution as Determined by ESI‐MS 260 B. Orders of Alkali Ion Affinities by the Kinetic Method 262 C. Gas‐Phase Binding Energies from Threshold Collision‐Induced Dissociation Experiments 262 D. Thermochemistry and Kinetics of Ligand Exchange: Gas‐Phase Equilibria 263 E. Gas‐Phase Conformations 264 V. Non‐Covalent Interactions with Small Biomolecules 264 A. Metal Binding to Simple Peptides 265 B. Chiral Differentiation of Amino Acids and Peptides 267 C. Question of Salt Bridges in the Absence of Solvent 269 D. Metal‐Ion Bonding to DNA Bases and Oligonucleotides 270 E. Is the Watson–Crick Base‐Pairing Conserved in the Gas Phase 272 F. Stereodifferentiation of Small Carbohydrates 274 VI. Inclusion Complexes of Cyclodextrins 276 VII. Host–Guest Chemistry of Calixarene and Resorcinarene Derivatives 279 VIII. Metal‐Directed Self‐Assembly 280 A. (Metallo)dendrimers 281 B. Helicates and Metal‐Templated Catenanes 282 C. Molecular Polygons, Polyhedra, and Cages 284 IX. Self‐Assembly Driven by Hydrogen Bonding 286 A. Rosette‐Type Assemblies from Barbiturate and Melamine Subunits 288 B. Self‐Assembling Capsules 291 X. Conclusions: The Benefits of Supramolecular Chemistry for Mass Spectrometry 296 References 297 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. © 2002 Wiley Periodicals, Inc. Mass Spec Rev 20: 253–309, 2001; Published online in Wiley Interscience ( www.interscience.wiley.com ). DOI 10.1002/mas.10009