PhD 1.10 | Analysis of trace byproducts in lignocellulose chemistry

Background:

Biomass and products from biomass are rich in complex molecules. Often, the unambiguous structural elucidation is necessary to identify unwanted byproducts (e. g. chromophores), to increase the understanding of a process (e. g. degradation products, unintended byproducts), and to describe newly discovered bioactive compounds. The availability of the compounds of interest is often limited either because the effort to isolate sizeable amounts is prohibitive, or because the compounds occur only in minute amounts. Current methodology – the combination of mass spectroscopy after chromatography, nuclear magnetic resonance spectroscopy, infrared spectroscopy – quickly reaches its limit when the available amount of substance is small (microgram). Crystallography allows to determine the structure of organic compounds directly and without ambiguity. The main requirement and obstacle – the availability of single crystals – can be mitigated by two recent developments: crystalline sponges and electron diffraction. These make even volatile and oily substances accessible for structural analysis by crystallography.

Crystalline sponges evade the need to grow single crystals and are compatible with widely available instrumentation for X-ray diffraction. They are porous crystalline metal-organic frameworks (MOFs) that act as a crystalline template for the compounds of interest. The target compounds are dissolved and allowed to diffuse into the MOF that soaks them up like a sponge. In the MOF, the target compounds are adsorbed in an orderly, practically crystalline fashion, which allows a structure elucidation by crystallography.

The field of Crystalline Sponges offers the option to elucidate compounds that so far have evaded a comprehensive analysis or were not available as crystals (examples see “Research objectives”). The combination with chromatographic techniques has been demonstrated and is especially powerful if an adsorption chromatographic method such as supercritical fluid chromatography or normal-phase chromatography is used. Normal-phase thin-layer chromatography with direct bioautographic detection of bioactive molecules that are then embedded in a crystalline sponge for crystallography could become an extremely rapid approach for bioactivity studies.

Research Objectives:

• Synthesis of established crystalline sponges (apolar, polar, carbohydrate-based) for first tests with model compounds.

• Application of the crystalline sponges to the identification of the target compounds which so far have evaded a comprehensive analysis as they were not available as crystals: a) di- and oligosaccharides of celluloses and hemicelluloses, b) chromophores and byproducts formed during pulp processing, fiber manufacturing and cellulose aging, c) extractives and bioactive compounds form plants (secondary metabolites).

• Establishing the combination with preceding chromatographic techniques: supercritical fluid chromatography and high-performance thin-layer chromatography with direct bioautographic detection of bioactive molecules.

Methods:

• Synthesis of established crystalline sponges (apolar, polar, carbohydrate based) for first tests with model compounds.

• Tests of suitability of different MOFs for different model compounds. Type of MOF and the properties of the solvent for infusion will be screened. Inclusion rate is determined from the supernatant before crystallography. Robustness of the developed methodology is evaluated. If necessary: definition of requirements of MOFs that need to be developed.

• Combination of established chromatographic methods – gas chromatography, thin-layer chromatography, liquid chromatography, supercritical fluid chromatography – for selected use cases, e. g. identification of bioactive compounds after bioautography, identification of unknown peaks in gas chromatography

Where to apply:

https://www.circularbioengineering.at/