High-precision frequency measurements: indispensable tools at the core of the molecular-level analysis of complex systems

Abstract

This perspective article provides an assessment of the state-of-the-art in the molecular-resolution analysis of complex organic materials. These materials can be divided into biomolecules in complex mixtures (which are amenable to successful separation into unambiguously defined molecular fractions) and complex nonrepetitive materials (which cannot be purified in the conventional sense because they are even more intricate). Molecular-level analyses of these complex systems critically depend on the integrated use of high-performance separation, high-resolution organic structural spectroscopy and mathematical data treatment. At present, only high-precision frequency-derived data exhibit sufficient resolution to overcome the otherwise common and detrimental effects of intrinsic averaging, which deteriorate spectral resolution to the degree of bulk-level rather than molecular-resolution analysis. High-precision frequency measurements are integral to the two most influential organic structural spectroscopic methods for the investigation of complex materials-NMR spectroscopy (which provides unsurpassed detail on close-range molecular order) and FTICR mass spectrometry (which provides unrivalled resolution)-and they can be translated into isotope-specific molecular-resolution data of unprecedented significance and richness. The quality of this standalone de novo molecularlevel resolution data is of unparalleled mechanistic relevance and is sufficient to fundamentally advance our understanding of the structures and functions of complex biomolecular mixtures and nonrepetitive complex materials, such as natural organic matter (NOM), aerosols, and soil, plant and microbial extracts, all of which are currently poorly amenable to meaningful target analysis. The discrete analytical volumetric pixel space that is presently available to describe complex systems (defined by NMR, FT mass spectrometry and separation technologies) is in the range of 10 8-14 voxels, and is therefore capable of providing the necessary detail for a meaningful molecular-level analysis of very complex mixtures. Nonrepetitive complex materials exhibit mass spectral signatures in which the signal intensity often follows the number of chemically feasible isomers. This suggests that even the most strongly resolved FTICR mass spectra of complex materials represent simplified (e.g. isomer-filtered) projections of structural space.

Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean

“…IOS compounds represented on average 49.4 ± 3.2% of the total magnitude in all samples and 54.2 ± 0.4% of the total magnitude in the Weddell Sea samples. The intermediate elemental ratios of the IOS suggest that these molecular formulae also comprise the greatest number of structural realizations for any given H/C, O/C and mass (Hertkorn et al, 2007). Any molecule, once it enters the DOM pool, is biologically and/or (photo-)chemically modified until it is either fully remineralized or ends up in the IOS where it is subject to a much slower degradation.…”

Physico-chemical characterization of SOA derived from catechol and guaiacol – a model substance for the aromatic fraction of atmospheric HULIS

“…Hundreds of calculated elementary compositions were transformed into atomic H/C and O/C ratios for a representation on Van Krevelen Diagrams (Hertkorn et al, 2007;Hertkorn et al, 2008). Based on only one molecular precursor the resulting aerosols cover a major part of the possible CHO compositional space.…”

Metabolic evidence for biogeographic isolation of the extremophilic bacterium Salinibacter ruber

“…From these lists, possible elemental formulas were calculated for each peak in batch mode by a software tool written in-house. The generated formulas were validated by setting sensible chemical constraints (nitrogen rule, atomic oxygen to carbon ratio O/Cp1, element counts: hydrogen Hp(2+C2), carbon Cp100, oxygen Op80, nitrogen Np5 and sulfur Sp1) and only the masses in conjunction with their automated generated theoretical isotope pattern (existence of the 13 C isotope) were taken into consideration (Hertkorn et al, 2007). The obtained reduced peak lists were compared in m/z at 5 p.p.m.…”