Abstract
Circular dichroism (CD) (and synchrotron circular dichroism (SCD)) spectroscopy is a rapid, highly sensitive technique used to investigate structural conformational changes in biomolecules in response to interactions with ligands in solution and in film. It is a chiroptical method and at least one of the interacting molecules must possess optical activity (or chirality). In this review, we compare the capabilities of CD and SCD in the characterisation of celluloses and lignin polymers in archaeological wood. Cellulose produces a range of spectral characteristics dependent on environment and form; many of the reported transitions occur in the vacuum-ultraviolet region (< 180 nm) most conveniently delivered using a synchrotron source. The use of induced CD in which achiral dyes are bound to celluloses to give shifted spectra in the visible region is also discussed, together with its employment to identify the handedness of the chiral twists in nanocrystalline cellulose. Lignin is one target for the design of future consolidants that interact with archaeological wood to preserve it. It is reportedly achiral, but here we review several studies in which CD spectroscopy has successfully revealed lignin interactions with chiral enzymes, highlighting the potential usefulness of the technique in future research to identify new generation consolidants.
Highlights
Despite its widespread use for a wide range of biomolecules, to date there have been comparatively few studies employing Circular dichroism (CD) spectroscopy to study polysaccharides found in archaeological wood nor polysaccharide interactions in archaeological wood
[34]; wood can be preserved as a fragile skeleton of mainly lignin-rich middle lamella, with lossofof its chirality and biocompatibility are exploited in industrial applications including immobilisation its chiralityand andhemicellulose-rich biocompatibility are exploited in industrial cellulosewood cell wall structuresapplications within [33]. including immobilisation of proteins, antibodies and heparin, for the separation of enantiomers the inversions formation of cellulose cellulose shows complex superstructures, chirality and andfor chiral
In future investigations of degradation of archaeological wood, induced CD may potentially prove a useful tool because cellulose nanocrystals possess a right-handed twist on their surfaces and a left-handed twist amongst inner chains [43,45]
Summary
Circular dichroism (CD) (and synchrotron circular dichroism (SCD)) spectroscopy is widely used to study chiral molecules, in particular biomolecules in solution and in thin amorphous dry films. Despite its widespread use for a wide range of biomolecules, to date there have been comparatively few studies employing CD spectroscopy to study polysaccharides found in archaeological wood nor polysaccharide interactions in archaeological wood This is presumably due to the considerable insolubility of wood polysaccharides and in some cases their reported lack of chirality [22]. CD is a highly sensitive method that is rapid to perform and is well suited to studies of conformational change in biomolecules in response to changing ligand and solvent conditions and to interaction studies in general, as long as solubility of such biomolecules can be achieved In this regard, the solvent, buffer and additive conditions for carrying out CD studies is paramount.
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