Advances in structure elucidation of small molecules using mass spectrometry

The structural elucidation of small molecules using mass spectrometry plays an important role in modern life sciences and bioanalytical approaches. This review covers different soft and hard ionization techniques and figures of merit for modern mass spectrometers, such as mass resolving power, mass accuracy, isotopic abundance accuracy, accurate mass multiple-stage MS(n) capability, as well as hybrid mass spectrometric and orthogonal chromatographic approaches. The latter part discusses mass spectral data handling strategies, which includes background and noise subtraction, adduct formation and detection, charge state determination, accurate mass measurements, elemental composition determinations, and complex data-dependent setups with ion maps and ion trees. The importance of mass spectral library search algorithms for tandem mass spectra and multiple-stage MS(n) mass spectra as well as mass spectral tree libraries that combine multiple-stage mass spectra are outlined. The successive chapter discusses mass spectral fragmentation pathways, biotransformation reactions and drug metabolism studies, the mass spectral simulation and generation of in silico mass spectra, expert systems for mass spectral interpretation, and the use of computational chemistry to explain gas-phase phenomena. A single chapter discusses data handling for hyphenated approaches including mass spectral deconvolution for clean mass spectra, cheminformatics approaches and structure retention relationships, and retention index predictions for gas and liquid chromatography. The last section reviews the current state of electronic data sharing of mass spectra and discusses the importance of software development for the advancement of structure elucidation of small molecules

Photoionization Spectroscopy of Nucleobasesand Analogues in the Gas Phase UsingSynchrotron Radiation as Excitation LightSource

International audienceWe review here the photoionization and photoelectron spectroscopy ofthe gas phase nucleic acid bases adenine, thymine, uracil, cytosine, and guanine, aswell as the three base analogues 2-hydroxyisoquinoline, 2-pyridone, andδ-valerolactam in the vacuum ultraviolet (VUV) spectral regime. The chapterfocuses on experimental work performed with VUV synchrotron radiation andrelated ab initio quantum chemical calculations of higher excited states beyondthe ionization energy. After a general part, where experimental and theoreticaltechniques are described in detail, key results are presented by order of growingcomplexity in the spectra of the molecules. Here we concentrate on (1) the accuratedetermination of ionization energies of isolated gas phase NABs and investigationof the vibrational structure of involved ionic states, including their mutual vibroniccouplings, (2) the treatment of tautomerism after photoionization, in competitionwith other intramolecular processes, (3) the study of fragmentation of these molecularsystems at low and high internal energies, and (4) the study of the evolution ofthe covalent character of hydrogen bonding upon substitution, i.e., examination ofelectronic effects (acceptor, donor, etc.)