Surveying The Hydrogen Bonding Landscape Of An Achiral, Α-amino Acid: Conformation Specific Ir And Uv Spectroscopy Of 2-aminoisobutyric Acid

2-Aminoisobutyric acid (Aib) is an achiral, $\alpha$-amino acid having two equivalent methyl groups attached to C$_{\alpha}$. Extended Aib oligomers are known to preferentially adopt a 3$_{10}$-helical structure in the condensed phase.\footnote{Toniolo, C.; Bonora, G. M.; Barone, V.; Bavoso, A.; Benedetti, E.; Di Blasio, B.; Grimaldi, P.; Lelj, F.; Pavone, V.; Padone, C., Conformation of Pleionomers of $\alpha$-Aminoisobutyric Acid. $\textit{Macromolecules}$ $\textbf{1985}$, $\textit{18}$, 895-902.} Here, we take a simplifying step and focus on the intrinsic folding propensities of Aib by looking at a single, capped Aib structure and then extending to longer oligomers in the gas phase, free from the influence of solvent molecules and cooled in a supersonic expansion. Resonant two-photon ionization and IR-UV holeburning will be used to record single-conformation UV spectra using the Z-cap as UV chromophore. Resonant ion-dip infrared (RIDIR) spectroscopy provides single-conformation IR spectra in the OH stretch, NH stretch, amide I and amide II regions. Two conformational isomers have been identified for the smallest unit in the study, Z-Aib-OH, and four conformational isomers were seen for Z-Aib-Aib-OH, with widely-varying IR spectral patterns. In addition to investigating the conformational dependence on oligomer length, this work also studies the steric and electrostatic impact of different capping groups, R-X where X = -OH, -OMethyl, and -OtButyl. These cACS are considered here for the case of Z-Aib-Aib-X. Extension to larger Z-(Aib)$_{n}$-X oligomers will shed light on the extent to which the solution phase preference for 3$_{10}$-helix formation is retained in the gas phase, and when its onset first appears. When possible $^{13}$C isotopomers will be used to assist with the assignments and modulate the coupling between amide I fundamentals