Towards polysaccharide handles for single molecule experiments: Spectroscopic evidence for the selective covalent coupling of terminal sugar residues to desired substrates

Single molecule force spectroscopy (SMFS) has recently given access to an unprecedented level of information regarding the stress-response of a host of biopolymers at the single chain level. However, the difficulty of designing handles for the specific attachment of the different ends of polysaccharide chains to substrates, such as piezoelectric scanners, cantilevers or microbeads; particularly in contrast to nucleotides and proteins, has meant that progress in more sophisticated single carbohydrate measurements has been relatively slow. Herein, methods for generating specific covalent attachments of the terminal sugar residue at one end of a pectin chain to polystyrene microspheres are demonstrated. Using FT-IR spectroscopy in combination with density functional theory (DFT) calculations the attachment was unequivocally shown to be mediated by the introduction of a C–N bond between the reducing end of the polysaccharide chain and a pre-aminated bead.