Paper SS1-FrM5
In Situ Characterization of Surfaces Following Soft and Reactive Landing of Complex Ions

Friday, November 13, 2009, 9:40 am, Room M

Soft- and reactive landing (SL/RL) of mass-selected ions enables highly selective preparation of uniform thin films of a variety of complex molecules on surfaces. We have recently demonstrated covalent immobilization of several model peptides on the self-assembled monolayer (SAM) of N-hydroxysuccinimidyl ester terminated alkylthiol on gold (NHS-SAM) using RL. Another remarkable finding is that SL and RL can be utilized for purification of peptide conformations that may not be stable in solution on SAM surfaces. For example, while Ac-Ala₁₅-Lys peptide mainly exist in its β-sheet conformation in solution, SL and RL of this peptide on the surface results in immobilization of a very stable α-helical conformation. This study presents a pathway for preparation of conformationally-selected peptide arrays that cannot be prepared using traditional solution-phase approaches. Here we present SL of singly and doubly protonated peptides (Gramicidin S, Substance P, Ac-Ala₁₅-LysH⁺ and Ac-LysH⁺-Ala₁₅) onto inert SAMs of alkylthiol (HSAM) and fluorinated alkylthiol (FSAM) on gold, and RL of singly protonated diamines and multiply protonated dendrimers onto reactive NHS-SAM and COF-terminated SAM surfaces. The modified SAM surfaces were characterized using in situ real time infrared reflection absorption spectroscopy (IRRAS) and secondary ion mass spectrometry (SIMS). In situ analysis of substrates during and after the SL/RL processes is essential for understanding charge transfer phenomena, reactivity of soft-landed molecules, and modification of the secondary structure of the molecule as a result of interaction with the surface.