Nanomechanical Recognition of N-Methylammonium Salts

Marco Dionisio†, Giulio Oliviero‡, Daniela Menozzi†, Stefania Federici‡, Roger M. Yebeutchou†, Franz P. Schmidtchen§, Enrico Dalcanale*†, and Paolo Bergese*‡

^† Department of Organic and Industrial Chemistry, University of Parma, and INSTM, UdR Parma, Parco Area delle Scienze 17A, 43124 Parma, Italy

^‡ Chemistry for Technologies Laboratory, University of Brescia, Via Branze 38, 25123 Brescia, Italy

^§ Department Chemie, Technische Universität München, D-85747 Garching, Germany

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja210567k

Publication Date (Web): January 9, 2012

Copyright © 2012 American Chemical Society

 

Turning molecular recognition into an effective mechanical response is critical for many applications ranging from molecular motors and responsive materials to sensors. Herein, we demonstrate how the energy of the molecular recognition between a supramolecular host and small alkylammonium salts can be harnessed to perform a nanomechanical task in a univocal way. Nanomechanical Si microcantilevers (MCs) functionalized by a film of tetra-phosphonate cavitands were employed to screen as guests the compounds of the butylammonium chloride series 1–4, which comprises a range of low molecular weight (LMW) molecules (molecular mass < 150 Da) that differ from each other by one or a few N-methyl groups (molecular mass 15 Da). The cavitand surface recognition of each individual guest drove a specific MC bending (from a few to several tens of nanometer), disclosing a direct, label-free, and real-time mean to sort them. The complexation preferences of tetraphosphonate cavitands toward ammonium chloride guests 1–4 were independently assessed by isothermal titration calorimetry. Both direct and displacement binding experiments concurred to define the following binding order in the alkylammonium series: 2 > 3 ≈ 1 4. This trend is consistent with the number of interactions established by each guest with the host. The complementary ITC experiments showed that the host–guest complexation affinity in solution is transferred to the MC bending. These findings were benchmarked by implementing cavitand-functionalized MCs to discriminate sarcosine from glycine in water.