Exploring the Conformational Landscape of Poly(l-lysine) Dendrimers Using Ion Mobility Mass Spectrometry

Abstract

Ion mobility mass spectrometry (IM-MS) measures the mass, size, and shape of ions in the same experiment, and structural information is provided via collision cross-section (CCS) values. The majority of commercially available IM-MS instrumentation relies on the use of CCS calibrants, and here, we present data from a family of poly(L-lysine) dendrimers and explore their suitability for this purpose. In order to test these compounds, we employed three different IM-MS platforms (Agilent 6560 IM-QToF, Waters Synapt G2, and a home-built variable temperature drift tube IM-MS) and used them to investigate six different generations of dendrimers in two buffer gases (helium and nitrogen). Each molecule gives a highly discrete CCS distribution suggestive of single conformers for each m/z value. The DT CCS Nd 2 values of this series of molecules (molecular weight: 330−16,214 Da) range from 182 to 2941 Å 2 , which spans the CCS range that would be found by many synthetic molecules including supramolecular compounds and many biopolymers. The CCS values for each charge state were highly reproducible in dayto-day analysis on each instrument, although we found small variations in the absolute CCS values between instruments. The rigidity of each dendrimer was probed using collisionally activated and high-temperature IM-MS experiments, where no evidence for a significant CCS change ensued. Taken together, this data indicates that these polymers are candidates for CCS calibration and could also help to reconcile differences found in CCS measurements on different instrument geometries.

Conformational Landscapes and Energetics of Carbon Nanohoops and their Ring-in-Ring Complexes

“…We suggest that the strong structural integrity of the carbon nanohoops and their host–guest complexes would make them interesting candidates for calibrating ion-mobility data of synthetic molecules, 4 , 43 which is a necessity for most modern ion mobility experiments, namely, traveling-wave IM-MS, 44 as used here, and trapped IM-MS. 45 There is a lack of suitable calibrants for synthetic structures, as they should be easy to purchase/synthesize, rigid when exposed to high temperature and collisions, behave chemically similarly to the analyte, and cover similar m / z and CCS ranges. Although the m / z and CCS range of the structures investigated here is small, we believe that these and similar (larger) compounds have the potential to be used as calibrants in IM-MS.…”