Investigation of copper–saccharide complexation reactions using potentiometry and electrospray mass spectrometry

Abstract

The associations between cupric ions and oligosaccharides of cellulose, chitin and chitosan were investigated using potentiometry and electrospray mass spectrometry. The goal of these studies was to understand the degree to which electrospray mass spectra reÑect the solution chemistry of copper-oligosaccharide complexes. To this end, electrospray mass spectrometric data were compared with potentiometric studies. The potentiometric data revealed no copper binding for mono-and tetrasaccharides of cellulose and chitin, while the mass spectrometric data suggested the presence of distinct copper complexes, these attributed to charge attachment during desorption from the highly charged electrospray droplets. Di †erence in the distribution of tetrasaccharide-copper complexes for cellulose and chitin was attributed to possible di †erences in droplet solution conformations of these saccharides. For mono-, diand tetrasaccharides of chitosan the potentiometric data showed strong copper complexation. For the tetrasaccharide the major species expected at pH 7 is a neutral copper complex. This neutral copper-tetrasaccharide complex was observed in the protonated form at relatively low abundances under high-voltage conditions in the electrospray interface. In this complex, Cu(II) is co-ordinated to the C(1)-alkoxide, the four amine nitrogens of chitosan tetrasaccharide and an anion. The ability of electrospray mass spectrometry to probe the immediate environment of the complex provides a clearer picture of the complex as it exists in solution, the associated counter-ions and possible di †erences in conformation. However, electrospray mass spectrometric data best reÑect chemistries in highly charged droplets rather than systems at equilibrium, highlighting the signiÐcance of supporting techniques to fully understand a chemical system.

Application of Spectroscopic Methods for Structural Analysis of Chitin and Chitosan

“…After MALDI, ESI (electrospray ionization) is the second most important ionization technique for chitin/chitosan analysis [ 219 , 232 – 238 ]. The ESI ion source is usually coupled to an ion trap analyser [ 235 ], but a quadrupole type of analyser can also be used [ 237 ].…”

Interactions of metal ions with chitosan-based sorbents: a review

“…In the "bridge model", metal ions are bound with several amine groups from the same chain or from different chains, via inter-or intramolecular complexation [54,[149][150][151], as opposed to the "pendant model", in which the metal ion is bound to an amine group in a pendant fashion [40,[152][153][154]. Several techniques have been used to investigate these interaction mechanisms including circular dichroism [153], UV spectrophotometry [150], infra-red spectrometry [8], Mossbauer spectrometry [155], electrospray mass spectrometry [156], potentiometry [150,151,153,157] and calorimetric titration [32].…”

Copper‐biomolecule complexes in the gas phase. The ternary way

“…Complex saccharides derived from chitin, chitosan, and cellulose form [Cu (II) (saccharide)] 2þ , [Cu (II) (saccharide) 2 ] 2þ , and [Cu (II) (saccharide-H)] þ complexes on electrospray ionization. The structures of the complexes formed have not been elucidated (Shahgholi et al, 1997). Cu (I) complexes with uracil and thiouracil have been reported and studied (Lamsabhi et al, 2004(Lamsabhi et al, , 2006.…”