Determination of Binding Constants and Gas Phase Stabilities\nof Artificial Carbohydrate Receptor Complexes Using Electrospray Mass\nSpectrometry

In\nrecent years, binding studies to determine complex stabilities\nand selectivities of artificial carbohydrate receptors with glycosides\nhave been mainly performed using <sup>1</sup>H NMR, isothermal titration\ncalorimetry (ITC), and other spectroscopic titration techniques. Native\nelectrospray ionization (ESI) mass spectrometry is used only to verify\nthe complex stoichiometries, although determination of dissociation\nconstants is also possible. Herein, the binding of a 1,3,5-substituted\n2,4,6-triethylbenzene-based receptor (CHR) to four alkyl-β-d-glucosides with varying alkyl side chain lengths (methyl (MGP),\nhexyl (HGP), octyl (OGP), and dodecyl (DGP)-β-d-glucosides),\nwhich was analyzed by ESI Fourier transform ion cyclotron resonance\nmass spectrometry (ESI-FT-ICR-MS) under optimized spray conditions\nin both ion modes, is reported. The complexes of the receptor with\ndifferent sugars could be detected in 1:1 and 2:1 stoichiometries.\nDissociation constants calculated for the 1:1 complexes showed a stability\ntrend depending on the length of the alkyl side chain of the sugar:\nCHR:DGP > CHR:OGP > CHR:HGP > CHR:MGP. Gas phase stabilities\ndetermined\nby CID-MS confirm this relative trend in binding affinities. These\nfindings substantiate the validity and applicability of ESI-MS as\na method for investigating noncovalent complex stabilities and thus\nsupport research in the field of molecular recognition of carbohydrates\nby artificial receptors.