ABSTRACT
Mechanochemical reactions by ball milling are becoming increasingly popular across a wide range of chemical sciences, but understanding and evaluation of temperature during such processes remains a persistent challenge, especially for organic and metal-organic materials. Here, we describe the first methodology for precise real-time measurement of sample temperature during mechanochemical transformations. Using this technique coupled with real-time in situ reaction monitoring by synchrotron X-ray diffraction and numerical simulations of heat flow, we have shown that the temperature profiles of mechanochemical reactions are dominantly determined by the energy dissipated through friction between the sample and the moving milling assembly, while the reaction enthalpy will usually be comparatively insignificant. With the changes in composition during mechanochemical reactions, frictional properties of the milled material change, leading to either better or worse energy absorption upon collisions in the process of milling. This approach explains unexpected and rapid temperature drops during exothermic transformations of ZIF-8 polymorphs. Since reaction kinetics are highly sensitive to changes in temperature, precise temperature profiles provided here will be mandatory to understand kinetics and its changes during milling, and will aid in developing the comprehensive model of mechanochemical reactivity.
ABSTRACT
Gangliosides and sulfated glycosphingolipids, as building and functional components of animal cell membranes, participate in cell-to-cell interactions and signaling, but also in changes of cell architecture due to different pathophysiological events. In order to enable higher throughput and to facilitate structural characterization of gangliosides/sulfo-glycosphingolipids (GSL) and their neutral GSL counterparts by negative ion mass spectrometry (MS) and tandem MS techniques, a database and data analysis application have been developed. In silico developed glycosphingolipid database considers a high diversity of ceramide compositions, several sialic acid types (N-acetylneuraminic acid, N-glycolylneuraminic acid and 2-keto-3-deoxynononic acid) as well as possible additional substitutions/modifications of glycosphingolipids, such as O-acetylation, de-N-acetylation, fucosylation, glucuronosylation, sulfation, attachment of repeating terminal hexose-N-acetylhexosamine- (Hex-HexNAc-)1-6 extension, and possible lactone forms. Data analysis application, named GSL-finder, enables correlation of negative ion MS and/or low-energy tandem MS spectra with the database structures. The GSL-database construction and the GSL-finder application searching rules are explained. Validation conducted on GD1a fraction as well as on complex mixtures of native gangliosides isolated from different mammalian brain tissues (human fetal and adult brain, and calf brain tissue) demonstrated agreement with previous studies. Plain, fast, and automated routine for structural characterization of gangliosides/sulfated glycosphingolipids and their neutral GSL counterparts described here could facilitate and improve mass spectrometric analysis of complex glycosphingolipid mixtures originating from variety of normal and pathological biomaterial, where it is known that distinctive changes in glycosphingolipid composition occur.
