ISMSC 2007 - Università degli Studi di Pavia

New emitters for mass spectrometric observation of supramolecular
complexes: sonic spray and porous polymer monolith electrospray
Nannan Fang, Joseph S. Gardner, Roger G. Harrison, John D. Lamb, David V. Dearden
Department of Chemistry and Biochemistry, C100 Benson Science Building, Brigham Young
University, Provo, Utah 84602-5700 U.S.A.
Supramolecular complexes present special challenges to mass spectrometry (MS).
Supramolecular samples are typically available in small amounts, are often impure, and require
special care to avoid dissociation as they are transferred into the gas phase. Most current
supramolecular MS work uses electrospray ionization (ESI), but even ESI is too energetic for
many supramolecular complexes. We discuss two new approaches to introduce
supramolecular complexes into the gas phase for MS study.
In sonic spray ionization (SSI) [1], dissolved samples (typically mM concentrations) are pumped
through a capillary that is nested inside a second, larger capillary. Gas is pumped through the
larger capillary such that it emerges with sonic velocity. This sheath gas nebulizes the sample
solution into small droplets that evaporate, gently introducing the analyte into the mass
spectrometer interface. We have successfully observed metal-assembled resorcinarene and
triazine complexes using this method, in many cases detecting species we could not observe
using conventional electrospray ionization (ESI).
Typical ESI sources tend to discriminate in favour of
easily ionized species. The result is relative peak
heights that are not representative of solution
concentrations. One answer to this problem is to use
ESI spray emitters with orifices on the order of 1 m ID,
which produce droplets so small that a typical droplet
contains less than one analyte complex. However,
these “nanospray” emitters tend to plug or break, and
produce low absolute signal strength (because the low
nL h –1 flow rates result in fewer ions delivered per unit
time). We have investigated the use of porous polymer
monolith (PPM) emitters [2] as a means of retaining the
advantages of nanospray without incurring the
disadvantages noted above. PPM emitters involve
formation of a porous polymer in the end of a relatively
large (75-150 m ID) capillary, resulting in many small
emission sources (Figure 1). In comparison to
conventional tapered fused silica microelectrospray
emitters, the PPM emitters produce generally stronger
absolute signal with much greater temporal stability,
Figure 1. Electron micrograph of
the end of a PPM emitter.
PSA 41
which we demonstrate through observations of well-characterized 18-crown-6•alkali cation
complexes. Further, the PPM emitter produced relative peak heights for the various complexes
in good agreement with known concentration ratios in solution, in contrast to conventional ESI
emitters. These emitters therefore appear promising for MS studies of supramolecular systems.
This work is supported by the U.S. National Science Foundation (NSF CHE 0615964).
[1] Gardner, J.S.;Harrison,R.G.;Lamb,J.D.;Dearden,D.V. New J. Chem. 2006, 30, 1276-
1282.
[2] Koerner, T.; Turck, K.; Brown, L.; Oleschuk, R. D. Anal. Chem. 2004, 76, 6456-6460.
PSA 42
Dynamic Covalent Chemistry of Formaldehyde Acetals. A Facile Synthesis
of Macrocycles.
Roberta Cacciapaglia, Stefano Di Stefano, Luigi Mandolini
Dipartimento di Chimica and IMC – CNR Sezione Meccanismi di Reazione and Università di
Roma La Sapienza, Box 34 - Roma 62, 00185 Roma, stefano.distefano@uniroma1.it
Dynamic Covalent Chemistry (DCC) is receiving growing interest for its potentialities in the field
of organic synthesis and in the discovery of new receptors.[1] We have recently reported [2] that
the metathesis reaction of formaldehyde acetals (formals), carried out in chloroform in the
presence of catalytic amounts of trifluoromethanesulfonic acid, nicely serves to the purpose of
generating the whole family of interconverting macrocycles Ci. These cyclophanes are fully
interchangeable under the adopted mild conditions. The reversibility of the system can be
exploited in the amplification of the yield of one component of the family by the addition to the
equilibrating mixture of a selective guest of the targeted component.
In this communication we report on the impressive amplification of the dimer C2 by the addition
of silver cation acting as a thermodymanic template. This amplification was carried out using as
feedstock the polymeric material obtained in the batchwise acid catalysed reaction of trioxane
with 1,4 benzenedimethanol.
A significant amplification of the trimer C3 by the template effect of the guanidinium cation, is
also reported.
[1] P. T. Corbett, J. Leclaire, L. Vial, K. R. West, J.-L. Wietor, J. K. M. Sanders, S. Otto Chem.
Rev. 2006, 106, 3652-3711.
[2] a) R. Cacciapaglia, S. Di Stefano, L. Mandolini J. Am. Chem Soc. 2005, 127, 13666-13671;
b) R. Cacciapaglia, S. Di Stefano, L. Mandolini Chem. Eur. J. 2006, 12, 8566-8570.