ESI MS, NMR and PM5 semiempirical studies of oligomycin A and its complexes with Li+ and Na+ cations

Fragmentation Behavior and Gas-Phase Structures of Cationized Glycosphingolipids in Ozone-Induced Dissociation Mass Spectrometry

The role of cationization in the fragmentation behavior of glycoconjugates is amply documented in collisional activation techniques but remains less explored in ozone-induced dissociation mass spectrometry (OzID-MS). OzID-MS has been used to elucidate the location of carbon-carbon double bonds in unsaturated lipids. Previously, we demonstrated the structural analysis of unsaturated glycosphingolipids using OzID-MS by mass-selecting the [M+Na]+ adduct for fragmentation. In this work, we aimed to examine the effect of different adducts, namely [M+Na]+, [M+Li]+, and [M+H]+ on the OzID-MS fragmentation behavior of a representative unsaturated glycosphingolipid, LacCer d18:1/18:1(9Z). Our data show that [M+H]+ primarily undergoes dehydration followed by collision-induced dissociation-like loss of the headgroup, while [M+Li]+ and [M+Na]+ dissociate at the double bonds albeit with slightly different intensities of the resulting fragments. Using molecular mechanics and theoretical calculations at the semiempirical level, we report for the first time the gas-phase structure of cationized glycosphingolipids, which helps rationalize the observed bond cleavage. Our findings highlight that the type of adducts can influence gas-phase ion structure of glycosphingolipids and subsequently affect their fragmentation in OzID-MS. This study contributes to the growing body of knowledge on OzID-MS and gas-phase structures of ionized lipids and the findings have the potential to be extended to other more complex glycoconjugates.

RP-HPLC-DAD-MSn Analysis and Butyrylcholinesterase Inhibitory Activity of Barbacenia blanchetii Extracts

High-performance liquid chromatography (HPLC) coupled to a diode-array detector (DAD) and electrospray ionization mass spectrometry (MS) was applied for the separation and identification of phenolic compounds in the n-hexane, ethyl acetate and methanol crude extract of Barbacenia blanchetii. The MS, MSn and UV data together with chemosystematic evidence allowed the structural characterization of five compounds: tricin, chrysoeriol, epi-gallocatechin, kaempferol 3- O-glucoside and caffeoylquinic acid. At the same time, these extracts were evaluated against butyrylcholinesterase using Ellman's method. All extracts inhibited BuChE in a concentration-dependent form; however, the methanol extract showed a better effect that the other extracts. These compounds have been identified previously in the Velloziaceae family, but for the first time as constituents of B. blanchetii.

A comparative study of the single crystal X-ray determination and molecular modelling of the binding of oligomycin to ATP synthase

Recently published X-ray structures of three common forms, A, B and C, of oligomycin, including absolute configurations, are investigated to examine their binding to ATP Synthase. The X-ray studies reveal regions with differences in three-dimensional structure and hydrogen bonding propensity between the oligomycins, which may be associated with their potential to bind to sites on ATP Synthase. Computational docking studies carried out using MOE with the X-ray structures and an homology model of the F(O) domain of ATP Synthase from Escherichia coli, are used to derive an induced fit pocket. Docking of all oligomycins to this pocket indicate that the B and C forms bind more tightly than the A form. Consideration of the single crystal X-ray data alone indicate the B form may be the best inhibitor and that O(24) is the most important ligating group for binding, this is supported by the docking data. The latter reveals Asn214 and other key proton translocating residues to be the main residues contacted by the inhibitor. These data allow the binding modes of different forms of oligomycin to be deduced from X-ray single crystal data supported by molecular modelling and computational docking studies.