Laser Desorption Mass Spectrometry of End Group-Protected Linear Polyynes: Evidence of Laser-Induced Cross-Linking

Abstract

End group-protected linear polyynes of composition Tr*−(CC) n −Tr* (with Tr* representing the super trityl group and n = 2, 4, 6, 8, 10) and tBu−(CC) 6 − tBu (with tBu being the tertiary butyl group) have been studied by laser desorption ionization (LDI) time-of-flight (ToF) mass spectrometry. tBu-terminated polyyne molecules show considerably higher stability during laser activation than Tr*-end-capped polyyne molecules. A key feature is the abundant formation of oligomeric species upon laser activation. Tandem mass spectrometry reveals strong bonding within the oligomers which indicates cross-linking of the former polyynes within the oligomers. The process is more abundantly occurring and less energy demanding than the laser-induced coalescence of C 60 . Cross-linking is more efficient with the smaller end group (tBu), and larger oligomers are formed when the chain length of the polyyne increases, both a result of enhanced interaction of the triple bonds in neighboring chains. The presence of the matrix molecules in matrix-assisted (MA)LDI hinders the polyyne interaction, and oligomer formation is markedly reduced.

Direct Covalent Coupling of Porphyrins to Graphene

“…This method employs laser activation for desorption and ionization of the materials and extends the mass range well beyond the intact porphyrins. Related applications of LDI have recently been published. − While the use of graphene-based materials as a matrix for matrix-assisted LDI (MALDI) is under intense investigation, − the analysis of covalently functionalized graphene derivatives by means of LDI is unprecedented.…”

Silver cation tagged on 5,7,12,14-tetraphenyl-6,13-diazapentacene and its dihydro-form

“…For instance, a [1 : 1] complex of a planar PAH and Ag + formed either in solution and/or in the electrospray would -upon travelling through the collision quadrupole -pick up a further H 2 O molecule to result in a [1 : 1 : 1] complex. The attachment of a second, p-electron density providing ligand is often thermochemically attractive 16,17,20,21 and has to be seen as the driving force of this process. H 2 O is an omnipresent residual background gas in the instrument.…”

“…The present study investigates the Ag + complexes of 5,7,12, 14-tetraphenyl-substituted 6,13-diazapentacene and its reduced 6,13-dihydro counterpart. 12,13 The motivation for this work originates from the importance of the silver(I) cation for the ion formation of unsaturated hydrocarbons [14][15][16][17][18][19][20][21][22] and, in particular, polycyclic aromatic hydrocarbons (PAHs) [23][24][25][26][27] which enables the application of electrospray ionization mass spectrometry (ESI-MS) for the analysis of these compounds. [28][29][30][31] ESI is one of the most important mass spectrometry-based methods for the analysis of molecules.…”

Sample preparation free tissue imaging using Laser Desorption – Rapid Evaporative Ionisation Mass spectrometry (LD-REIMS)

“…While the rationale of this application for tissue analysis is straightforward, LDI has never gained true popularity as an organic MS method due to a handful of inherent problems stemming from the fundamentals of biological matter-laser interactions. These problems include (1) thermally induced condensation reactions which turn biological samples into a three-dimensional, highly cross-linked polymer structure (eventually leading to carbonisation) efficiently trapping analyte molecules, (2) formation of a large amount of neutral molecules in the gas phase relative to the formation of ions (3) aerosolization of samples leading to particles containing up to 10 8 -10 9 molecules (4)(5)(6). All these three effects act against ionisation efficiency, deeming the approach insensitive for most bioanalytical applications.…”