Abstract
Carbohydrates are one of the four main building blocks of life, and are categorized as monosaccharides (sugars), oligosaccharides and polysaccharides. Each sugar can exist in two alternative anomers (in which a hydroxy group at C-1 takes different orientations) and each pair of sugars can form different epimers (isomers around the stereocentres connecting the sugars). This leads to a vast combinatorial complexity, intractable to mass spectrometry and requiring large amounts of sample for NMR characterization. Combining measurements of collision cross section with mass spectrometry (IM–MS) helps, but many isomers are still difficult to separate. Here, we show that recognition tunnelling (RT) can classify many anomers and epimers via the current fluctuations they produce when captured in a tunnel junction functionalized with recognition molecules. Most importantly, RT is a nanoscale technique utilizing sub-picomole quantities of analyte. If integrated into a nanopore, RT would provide a unique approach to sequencing linear polysaccharides.
Highlights
Carbohydrates, those attached to proteins, play a central role as mediators in most biological processes
In Recognition Tunneling (RT) characteristic electron tunnel-current spikes are generated when an individual analyte is trapped by capture molecules tethered to two electrodes separated by a few nanometers
The formation of 1:1 and 2:1 complexes between ICA and these two anomers in aqueous solution was detected by Electrospray ionization mass spectrometry (ESI-MS) (Tables S3 and S4, SI; MS data for the other monosaccharides and disaccharides used in the present work are included)
Summary
Carbohydrates, those attached to proteins (glycans), play a central role as mediators in most biological processes. Theoretical simulations show that each of them can form a hydrogen-bonded triplet with a pair of ICA molecules respectively in a 2.2 nm wide tunnel gap, having a distinguishable hydrogen-bonding pattern and energy
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