Detection of Sugars via Chirality Induced in Europium(III) Compounds

Abstract

Detection and resolution of simple monosaccharides are difficult tasks because their structure is quite similar. The present study shows that circularly polarized luminescence (CPL) induced in europium complexes provides very specific spectral patterns for fructose, mannose, glucose, and galactose. Differences were also observed between bare Eu(3+) ion and its complexes, when interacting with these sugars. The CPL spectra were measured on a Raman optical activity (ROA) spectrometer, which ensured high fluorescence intensity owing to the strong 532 nm laser excitation. The induced fluorescence was recorded in the same spectrum as the vibrational Raman bands. On the basis of the ligand field theory, most fluorescence spectral peaks could be assigned to f-shell europium transitions. Additional information on the interaction of the lanthanide with the sugar component was provided by measurement of time-dependent fluorescence, as formation of different complexes led to variations in fluorescence decay times. In nuclear magnetic resonance (NMR), the paramagnetic metal ion interacting with the sugars caused specific changes in (13)C chemical shifts. The spectroscopic data and molecular dynamics modeling showed that the interaction between the monosaccharides and Eu ion is rather weak due to the competition of the OH sugar groups with water molecules. However, multiple binding modes are possible, which contributes to the complexity and specificity of the spectra. The induced chirality and fluorescence spectra thus appear to be convenient means for monosaccharide detection and identification.

Recognition of Oligosaccharides by Chirality Induced in Europium (III) Compounds

“…[14,17] In sucrose, the OH group at C1(a1o rientation) of glucose and the C2 OH group of fructose are missing, and induced CPL is relatively weak, which may indicatet he importance of these moieties forE u III binding. Although all the disaccharides contain at least one glucoseu nit, only maltose exhibits CPL signal induced in EuCl 3 resembling that of monomeric glucose.…”

“…Although all the disaccharides contain at least one glucoseu nit, only maltose exhibits CPL signal induced in EuCl 3 resembling that of monomeric glucose. [14] The 5 D 0 ! [14] The orientation of the OH group at C2 in fructose may also be important for the stereo-selective recognition of the EuEDTAc omplex solution as also the EuEDTAs ignal of monomeric fructose was larger than for sucrose.…”

“…The sensitivity of EuEDTAb inding towardsd ifferent cyclodextrins might thus be useful for various applicationsi ncluding chirals eparations, [19] MRI agents, [20] and asymmetrical catalysis. [14] Conclusions We performed as ensitivem easuring of CPL spectrao nt he ROA spectrometer for as eries of saccharides chelatingw ithE u compounds. The raffinose/EuDEPAp rovided low CIDs values and the signal did not saturatef or experimentally achievable concentrationr atios.…”

“…[12] Vibrational techniques includingv ibrational optical activity (VOA) can be applied more generally,b ut the signal is often weak and spectralb ands broadened by molecular flexibility and interaction of the OH groups with (usually aqueous) environment. [14] This technique enableso ne to explore also weak luminescence bands that may not be visible without the intense laser excitation source, although the spectral window is limited ( % 532-612nm). The signal is reasonably stronga nd the chiral spectroscopy is more sensitive than unpolarized technique, in this case total luminescence (TL).…”

“…[13] Measurement of circularly polarized luminescence (CPL) induced in lanthanide(III) compounds can overcome many of these limitations. [14,15] Utilization of the Eu III ion is particularly convenient,s ince total luminescence (TL) and CPL bands are narrow,w ell-resolved, and easy to recognize in the measured spectrum. Previously,w eo btained highly-specific spectralp atterns for monosaccharides, when CPL of trivalente uropiumc omplexes was acquired on a Raman optical activity (ROA)s pectrometer.…”