10.1021/ac401370t.s001 Liuxi Chen Liuxi Chen Shu-Hua Chen Shu-Hua Chen David H. Russell David H. Russell An Experimental Study of the Solvent-Dependent Self-Assembly/Disassembly and Conformer Preferences of Gramicidin A American Chemical Society 2013 dielectric solutions HDX measurements GA dimeric species dissociation dimer ions conformer preferences helix monomerization kinetics CID Conformer Preferences Experimental Study antiparallel hydrogen bonds equilibrium abundances Gramicidin AThe 2013-08-20 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/An_Experimental_Study_of_the_Solvent_Dependent_Self_Assembly_Disassembly_and_Conformer_Preferences_of_Gramicidin_A/2384863 The solvent dependence of self-assembly/disassembly kinetics and conformer preferences of the gramicidin A (GA) dimer is investigated using a combination of techniques, viz., electrospray ionization–ion mobility–mass spectrometry (IM-MS), collision-induced dissociation (CID), and hydrogen/deuterium exchange (HDX)-MS. IM-MS measurements reveal that there are possibly three distinct GA dimeric species, detected as sodium ion adduct ions [2GA + 2Na]<sup>2+</sup>, and these are assigned as the parallel β-helix, antiparallel β-helix, and head-to-head dimer. The monomerization kinetics and equilibrium abundances of the dimer ions depend upon solvent polarity. The antiparallel β-helix was the thermodynamically preferred species in less polar solvents. HDX measurements and collision-induced dissociation (CID) of the intermediate complex confirm the well-protected dimer geometry with strong intermolecular hydrogen bonds. This combined IM-HDX-CID methodology provides a comprehensive view of GA self-assembly/disassembly in low dielectric solutions, showing its potential utility in solving solution-phase protein self-assembly/disassembly kinetics and providing structural information of the multimers at the same time.