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In situ Studies of Soft- and Reactive Landing of Mass-Selected Ions Using Infrared Reflection Absorption Spectroscopy Qichi Hu, Peng Wang, Paul L. Gassman, and Julia Laskin* Pacific Northwest National Laboratory, Chemical and Materials Sciences Division, Richland, Washington 99352 Grazing incidence infrared reflection absorption spectroscopy (IRRAS) for in situ and in real time characterization of substrates modified by soft and reactive landing (SL and RL) of complex ions was implemented on a massselected ion deposition instrument. Ions produced by electrospray ionization were mass-selected using a quadrupole mass filter and deposited onto inert and reactive self-assembled monolayer (SAM) surfaces. Surface composition during and after ion deposition was monitored using IRRAS. Physisorption of a cyclic peptide, Gramicidin S (GS), was studied for 8 h during deposition and additional 12 h after the end of deposition. The integrated signal of the characteristic amide bands followed a linear increase during the deposition and stayed unchanged after the deposition was finished. Similar linear increase in IRRAS signal was obtained following reactive deposition of the protonated dodecanediamine onto SAMs of dithiobis (succinimidyl undecanoate) (NHS-SAM) and 16mercaptohexadecanoic acid fluoride (COF-SAM) on gold. IRRAS allowed us to monitor for the first time the formation of the amide bond between reactive SAM surfaces and the projectile molecule. Deposition of mass-selected hyperthermal (1-100 eV) ions onto appropriate substrates is a highly specific approach for surface modification and immobilization of a variety of polyatomic molecules on solid supports.1-5 Capture of intact ions with or without loss of charge on surfaces is commonly called ion softlanding (SL),1-8 whereas reactive landing (RL) refers to the process, in which projectile ions or their fragments undergo * To whom correspondence should be addressed. Phone: (509)-371-6136. Fax: (509)-371-6139. E-mail:
[email protected]. (1) Grill, V.; Shen, J.; Evans, C.; Cooks, R. G. Rev. Sci. Instrum. 2001, 72, 3149–3179. (2) Hanley, L.; Sinnott, S. B. Surf. Sci. 2002, 500, 500–522. (3) Gologan, B.; Green, J. R.; Alvarez, J.; Laskin, J.; Cooks, R. G. PCCP 2005, 7, 1490–1500. (4) Gologan, B.; Wiseman, J. M.; Cooks, R. G. Ion soft landing: Instrumentation, phenomena, and applications. In Principles of Mass Spectrometry Applied to Biomolecules; Laskin, J., Lifshitz, C., Eds.; John Wiley & Sons., Inc.: Hoboken, NJ, 2006. (5) Laskin, J.; Wang, P.; Hadjar, O. PCCP. 2008, 10, 1079–1090. (6) Franchetti, V.; Solka, B. H.; Baitinger, W. E.; Amy, J. W.; Cooks, R. G. Int. J. Mass Spectrom. Ion Processes 1977, 23, 29–35. (7) Miller, S. A.; Luo, H.; Pachuta, S. J.; Cooks, R. G. Science 1997, 275, 1447– 1450. (8) Geiger, R. J.; Melnyk, M. C.; Busch, K. L.; Bartlett, M. G. Int. J. Mass spectrom. 1999, 182-183, 415–422.
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reactions with other deposited species or with functional groups present on the surface.9-17 The ability to select the mass-to-charge ratio of the precursor ion, its kinetic energy and charge state along with precise control of the size, shape and position of the ion beam on the target makes SL an attractive approach for surface modification. SL and RL of complex ions have been used for a variety of applications including purification of compounds from complex mixtures,18-20 deposition of mass-selected cluster ions on substrates,21-29 preparation of protein or peptide arrays,30-34 and preparation of novel synthetic materials,35-39 including nanomaterials.40-42 Physical and chemical characterization of surfaces following deposition of mass-selected ions can be performed using a variety of techniques including laser desorption ionization,32,33 low-energy chemical sputtering, secondary ion mass spectrometry (SIMS),30,31,43,44 surface-enhanced Raman spectroscopy (SERS),45 X-ray photoelectron spectroscopy (XPS),14,46 microscopy,22,27,35,37 infrared reflection absorption spectroscopy (IRRAS),17,4247 and temperature-programmed desorption (TPD).35,37,41,42 Because of the very small amount of material deposited on the surface (typically
