While obviously not the natural environment of biological molecules, the gas phase provides the ultimate degree of isolation. It is a reductionist’s paradise, where the subject under study can be investigated in its purest form. Under these conditions, inter- and intramolecular interactions can be scrutinized in the highest possible detail, suspending any inhomogeneities induced by perturbations from the surroundings, and enabling a true comparison with results from quantum-chemical calculations at the highest levels of sophistication. At the same time, the influence of (aqueous) solution can be accurately tracked by non-covalent attachment of individual water molecules.
Spectroscopy, in the various frequency ranges of the electromagnetic spectrum, offers the most direct experimental probe into the quantum-mechanical nature, and hence into the molecular structure, of these dilute isolated biomolecules. Laserbased spectroscopy of jet-cooled gaseous biomolecules has a long and rich history, but has particularly seen impressive developments over the past decade, e.g. with the introduction of laser desorption methods, new infrared laser sources, and sophisticated multi-resonance excitation and detection schemes. The conformation selectivity provided by many of these methods is perhaps one of their foremost assets in the study of biological molecules. The fine interplay between many (noncovalent) interactions, ultimately determining the folding structure of the molecule and hence its biological functioning, can thus be unraveled.
Studies on the fundamental properties of biological molecules have also brought the fields of ion chemistry and spectroscopy closer together over the past decade. With electrospray ionization tandem mass spectrometry, ion chemists have been able to manipulate and characterize biological molecules in the gas phase since the late 1980s. The past decade has seen particularly rapid developments in the application of laser-based spectroscopy to mass-selected molecular ions, with the aim of determining the structure of charged biomolecules. The use of widely tunable infrared free electron lasers and cryogenic ion trapping devices, as well as the combination of ion-mobility conformer separation with ion spectroscopy, have led to rapid progress in this field.
In this book, we have tried to capture some of the excitement of these recent developments in the spectroscopy of gas-phase biological molecules, admittedly without having the slightest illusion of our coverage being anywhere near complete.
IR Spectroscopic Techniques to Study Isolated Biomolecules
Anouk M. Rijs and Jos Oomens
Cryogenic Methods for the Spectroscopy of Large, Biomolecular Ions
Thomas R. Rizzo and Oleg V. Boyarkin
Theoretical Methods for Vibrational Spectroscopy and Collision Induced Dissociation in the Gas Phase
Marie-Pierre Gaigeot and Riccardo Spezia
Peptide Fragmentation Products in Mass Spectrometry Probed by Infrared Spectroscopy
Amanda L. Patrick and Nicolas C. Polfer
Spectroscopy of Metal-Ion Complexes with Peptide-Related Ligands
Robert C. Dunbar
Isolated Neutral Peptides
Eric Gloaguen and Michel Mons
Gas-Phase IR Spectroscopy of Nucleobases
Mattanjah S. de Vries
Emilio J. Cocinero and Pierre C¸ arc¸abal
Microwave Spectroscopy of Biomolecular Building Blocks
Jose´ L. Alonso and Juan C. Lopez