Depicting molecular dissimilarity in complex materials.

Abstract

Natural organic matter (NOM) occurs in soils, freshwater and marine environments, in the atmosphere and in the form of prebiotic organic matter and represents an exceedingly complex mixture of organic compounds that collectively exhibits a nearly continuous range of properties (size-reactivity continuum).   The fate NOM in the bio- and geosphere is governed according to the rather fundamental restraints of thermodynamics and kinetics. In these intricate materials, the “classical” signatures of the (geogenic or ultimately biogenic) precursor molecules, like lipids, glycans, proteins and natural products have been attenuated, often beyond recognition, during a succession of biotic and abiotic (e.g. photo- and redox chemistry) reactions. Because of this loss of biochemical signature, these materials can be designated non-repetitive complex systems.   The most informative, “bottom-up” approach to molecularly characterize these complex materials necessarily relies upon spectroscopic methods which translate high-precision frequency measurements into very significant molecular-level information. Frequencies can be measured with an accuracy of 15 digits. This extent of accuracy in frequency measurements translates directly into high resolution, itself a very useful and even indispensable feature to produce information-rich data with sufficient resolution to overcome the otherwise common and detrimental effects of intrinsic averaging, which deteriorate spectral resolution to the degree of a bulk-type characterization rather than to a molecular resolution analysis.   High-precision frequency measurements, which can be translated into isotope-specific molecular resolution detail of unprecedented significance and richness, define the core of the two most influential methods of organic structural spectroscopy for the investigation of complex materials, namely NMR spectroscopy (provide unsurpassed insight into close-range molecular order to assess the structural space) and FTICR mass spectrometry (provide unsurpassed resolution to explore the compositional space).   The quality of this stand-alone de novo molecular-level resolution data is of unparalleled mechanistic relevance and sufficient to fundamentally advance our understanding of structure and function of NOM, which at present are poorly amenable to meaningful target analysis. The currently available discrete analytical volumetric pixel space to describe complex systems (which is defined by NMR, FT mass spectrometry and separation technology) is in the range of 108-14 volumetric pixels and therefore capable to provide the necessary detail for a meaningful molecular level analysis of any complex mixture of organic molecules.   This presentation will provide an evaluation of state-of-the-art concepts and applications of molecular level structure elucidation to NOM materials of various origin. According to these findings, NOM is a rather active participant of the global carbon cycle, and the current perception of NOM being considered refractory can be regarded as a consequence of insufficient resolution of methods commonly used in its characterization