Investigation of photochemical reactions of saccharides during direct ultraviolet absorbance detection in capillary electrophoresis

Capillary zone electrophoresis of lipoarabinomannan by multi-layered concentration

The present paper describes a capillary zone electrophoresis method which relies on a multi-layered water-alkali solvent stacking with on-line ionization to enhance detection of mannose, arabinose, and their oligosaccharides, which are used as the migration profile standards but are also the distinctive structural components of lipoarabinomannan. Lipoarabinomannan is detected in patients having tuberculosis. The CE method with ionization of the whole saccharides without degradation in alkaline solution inside the capillary is based structural deprotonation of the molecules under ultrahigh pH conditions. The validation of the CE parameters revealed that the 15-fold electrolyte - water -injection plug allowed detection of one third lower concentrations than detected without on-line concentration. For the first time, the better detectability was seen especially for highly polymerized, but otherwise poorly ionized, arabino-octaose. The applicability of the method for detecting whole large biological saccharide complexes was confirmed by the glycolipid lipoarabinomannan. For the first time also, the migration of the indestructible lipoarabinomannan was detected together with oligosaccharides used representing the capping units, namely mannose, mannobiose and mannotriose. The myo-inositol-phosphate-lipid unit was seen to migrate separately from the arabinomannan, since it was hydrolyzed from one lipoarabinomannan product under alkaline conditions in CE. This article is protected by copyright. All rights reserved.

Ultrafast Photodynamics of Glucose

We have investigated the photodynamics of β-d-glucose employing our field-induced surface-hopping (FISH) method, which allows us to simulate the coupled electron-nuclear dynamics, explicitly including nonadiabatic effects and light-induced excitation. Our results reveal that from the initially populated S₁ and S₂ states, glucose returns nonradiatively to the ground state within about 200 fs. This takes place mainly via conical intersections (CIs), whose geometries in most cases involve the elongation of a single O-H bond, whereas in some instances, ring-opening due to dissociation of a C-O bond is observed. Experimentally, excitation to a distinct excited electronic state is improbable due to the presence of a dense manifold of states bearing similar oscillator strengths. Our FISH simulations, explicitly including a UV laser pulse of 6.43 eV photon energy, reveal that after initial excitation, the population is almost equally spread over several close-lying electronic states. This is followed by a fast nonradiative decay on the time scale of 100-200 fs, with the final return to the ground state proceeding via the S₁ state through the same types of CIs as observed in the field-free simulations.

Capillary electrophoresis as a method to determine underivatized urinary lipoarabinomannans, a biomarker of active tuberculosis caused by Mycobacterium tuberculosis

Tuberculosis is a devastating contagious disease caused by Mycobacterium tuberculosis. This is the first report describing the development of novel capillary electrophoresis methods to detect lipoarabinomannans shed into the blood circulation by replicating bacteria. The novelty of the methods is the detection without derivatization. The lipoarabinomannan is detected owing to the ionization of the diverse functional groups of the structure, such as the multibranched mannan domain or the phosphatidyl group. Four alkaline solutions were used; normal polarity in three of them and reversed polarity in one. Urinary lipoarabinomannans by saccharide domains were identified with direct absorbance detection. The accuracy and the analytical sensitivity were then validated with cello-, manno- and xylooligosaccharides. Lipoarabinomannan detection was feasible within 20 min (RSD 2.1%). This method worked at the dynamic range of 0.1-10 μg/mL. With reversed polarity, indirect absorbance detection, and pH 9.0 electrolyte were used, the analytes migrated already within 5 min (RSD 0.01%). Inorganic nonabsorbing ions were used for this method optimization. This improvement resulted in the detection limit of 1 pg/mL in water and in the linear dynamic range of 1 pg/mL to 10 ng/mL. In conclusion, the described method has great potential as a point-of-care assay for clinical use.