Viscoelastic-mapping of cellulose nanofibrils using low-total-force contact resonance force microscopy (LTF-CRFM)

Cellulose - Low-total-force contact resonance force microscopy (LTF-CRFM), an atomic force microscopy method, is introduced as a non-destructive means to quantify the local viscoelastic loss...     

Periodicity of Two-Dimensional Bonding of Main Group Elements

In the periodic table the position of each atom follows the ‘aufbau’ principle of the individual electron shells. The resulting intrinsic periodicity of atomic properties determines the overall behavior of atoms in two-dimensional (2D) bonding and structure formation. Insight into the type and strength of bonding is the key in the discovery of innovative 2D materials. The primary features of 2D bonding and the ensuing monolayer structures of the main-group II–VI elements result from the number of valence electrons and the change of atom size, which determine the type of hybridization. The results reveal the tight connection between strength of bonding and bond length in 2D networks. The predictive power of the periodic table reveals general rules of bonding, the bonding-structure relationship, and allows an assessment of published data of 2D materials.     

A cationic cysteine-hydrazide as an enrichment tool for the mass spectrometric characterization of bacterial free oligosaccharides

In Campylobacterales and related ε-proteobacteria with N-linked glycosylation (NLG) pathways, free oligosaccharides (fOS) are released into the periplasmic space from lipid-linked precursors by the bacterial oligosaccharyltransferase (PglB). This hydrolysis results in the same molecular structure as the oligosaccharide that is transferred to a protein to be glycosylated. This allowed for the general elucidation of the fOS-branched structures and monosaccharides from a number of species using standard enrichment and mass spectrometry methods. To aid characterization of fOS, hydrazide chemistry has often been used for chemical modification of the reducing part of oligosaccharides resulting in better selectivity and sensitivity in mass spectrometry; however, the removal of the unreacted reagents used for the modification often causes the loss of the sample. Here, we develop a more robust method for fOS purification and characterize glycostructures using complementary tandem mass spectrometry (MS/MS) analysis. A cationic cysteine hydrazide derivative was synthesized to selectively isolate fOS from periplasmic fractions of bacteria. The cysteine hydrazide nicotinamide (Cyhn) probe possesses both thiol and cationic moieties. The former enables reversible conjugation to a thiol-activated solid support, while the latter improves the ionization signal during MS analysis. This enrichment was validated on the well-studied Campylobacter jejuni by identifying fOS from the periplasmic extracts. Using complementary MS/MS analysis, we approximated data of a known structure of the fOS from Campylobacter concisus. This versatile enrichment technique allows for the exploration of a diversity of protein glycosylation pathways.     

Polyaromatic Profluorescent Nitroxide Probes with Enhanced Photostability

Novel profluorescent mono‐ and bis‐isoindoline nitroxides linked to napthalimide and perylene diimide structural cores are described. These nitroxide‐fluorophore probes display strongly suppressed fluorescence in comparison to their corresponding non‐radical diamagnetic methoxyamine derivatives. The perylene‐based probe possessing two isoindoline systems tethered through ethynyl linkages was shown to be the most photostable in solution, demonstrating significantly enhanced longevity over the 9,10‐bis(phenylethynyl)anthracene fluorophore used in previous profluorescent nitroxide probes.     

Identification and separation of saxitoxins using hydrophilic interaction liquid chromatography coupled to traveling wave ion mobility‐mass spectrometry

The aim of this work was to develop a reliable and efficient analytical method to characterise and differentiate saxitoxin analogues (STX), including sulphated (gonyautoxins, GTX) and non‐sulphated analogues. For this purpose, hydrophilic interaction liquid chromatography (HILIC) was used to separate sulphated analogues. We also resorted to ion mobility spectrometry to differentiate the STX analogues because this technique adds a new dimension of separation based on ion gas phase conformation. Positive and negative ionisation modes were used for gonyautoxins while positive ionisation mode was used for non‐sulphated analogues. Subsequently, the coupling of these three complementary techniques, HILIC‐IM‐MS, permitted the separation and identification of STX analogues; isomer differentiation was achieved in HILIC dimension while non‐sulphated analogues were separated in the IM‐MS dimension. Additional structural characteristics concerning the conformation of STXs could be obtained using IM‐MS measurements. Thus, the collision cross sections (CCS) of STXs are reported for the first time in the positive ionisation mode. These experimental CCSs correlated well with the calculated CCS values using the trajectory method. Copyright © 2015 John Wiley & Sons, Ltd.     

HPLC–MS Profiling and Structural Identification of [14C]-Diclofenac Metabolites in Mouse Bile

Biliary metabolites present at 6 h post-dose following a single oral dose of [¹⁴C]-diclofenac (10 mg kg^?1) to male bile duct-cannulated C57BL/6 J mice were profiled and identified. Over the 6 h duration of the study ~19.5 % of the administered radioactivity was excreted into the bile as either [¹⁴C]-diclofenac or metabolites. When profiled using HPLC with online radiodetection, the presence of at least 13 radiolabelled components was indicated. These compounds were shown, by consecutive reaction mass spectrometry, to comprise a range of hydroxylated metabolites conjugated to either taurine, glucose and/or glucuronic acid. Both phenolic and acylglucuronide-containing metabolites were observed. The confirmation of the presence of these glucuronide conjugates in mouse bile may have important consequences in the light of emerging theories concerning the role of bacterial glucuronidases for the GI-tract toxicity of NSAIDs such as diclofenac.