Generation and Dissociation Pathways of Singly and Doubly Protonated Bisguanidines in the Gas Phase

Abstract

Para-bisguanidinyl benzene 1 and its N-permethylated derivative 2 are both sufficiently strong bases to afford not only the monocations [1+H]+ and [2+H]+, but also the doubly protonated ions, [1+2H]2+ and [2+2H]2+, in the gas phase. The title ions generated via electrospray ionization are probed by collision-induced dissociation experiments which inter alia reveal that the dicationic species [1+2H]2+ and [2+2H]2+ can even undergo fragmentation reactions with maintenance of the 2-fold charge. Complementary results from density functional theory predict PAs above 1000 kJ mol(-1) for the neutral compounds, i.e., PA(1) = 1025 kJ mol(-1) and PA(2) = 1067 kJ mol(-1). Due to the stabilization of the positive charge in the guanidinium ions and the para-phenylene spacer separating the basic sites, even the monocations bear sizable proton affinities, i.e., PA([1+H]+) = 740 kJ mol(-1) and PA([2+H]+) = 816 kJ mol(-1).

Clustering of palladium(II) chloride in acetonitrile solution investigated by electrospray mass spectrometry

“…The mass spectrometric measurements were performed with a Finnigan LCQ Classic ion-trap mass spectrometer (IT-MS) [32] by ESI of dilute solutions of PdCl 2 or PdCl 2 (CH 3 CN) 2 in acetonitrile. In brief, the LCQ bears a conventional ESI source (typical flow rate 5 l min −1 , typical spray voltage 5 kV) with nitrogen as a sheath gas, followed by a heated transfer capillary (kept at 200 • C), a first set of lenses which determines the soft-or hardness of ionization by variation of the degree of collisional activation in the medium pressure regime [19][20][21][22], two transfer octopoles, and a Paul iontrap with ca.…”

“…The large amount of clustering in both positive and negative ion mode together with the low total ion currents compared to other metal(II) salts [20,23,25,26,28,31,32,36] or palladium complexes with larger ligands [27,44,45] suggests a significant amount of aggregation of PdCl 2 in acetonitrile solution. Provided these aggregates were comprising larger numbers of palladium atoms, the ESI mass spectra would always sample only the fractional amount of smaller clusters, either present in solution or formed in the ESI process itself, despite the fact that we applied relatively soft ionization conditions.…”

Complexation between the fungicide tebuconazole and copper(II) probed by electrospray ionization mass spectrometry

“…The experiments were performed with a Finnigan LCQ Advantage ion‐trap mass spectrometer (ThermoFinnigan, San Jose, CA, USA) fitted with an electrospray ionization source operated in positive and negative‐ion mode . Dilute solutions of tebuconazole and appropriate copper(II) salts in methanol/water (1:1 v/v) were introduced into the ESI source via a fused‐silica capillary at a flow rate of 1.3 mL·h −1 .…”

Proton Affinities of Organocatalysts Derived from Pyridine N-oxide

“…38,44 It is pertinent to note that MAILD is a new technique in mass spectrometry that complements the standard MALDI technique. Nevertheless, the performance of the pyridine N-oxide matrices would be probably lower than that of the 1,14-diaza [5]helicene, 47 which has been recently shown to be an optimal matrix.…”

“…[1][2][3][4][5] Development of new superbases is usually based on two approaches. One can either conceive molecules with a potential of very efficient delocalization of the positive charge over a large molecular scaffold or alternatively, molecules with more than one highly basic functions cooperating in binding of the proton can be considered.…”