Cover Feature: Proximity Effects and Aggregation of Hamilton‐Receptor Barbiturate Host–Guest Complexes Probed by Cross‐Metathesis and ESI MS Analysis (Chem. Eur. J. 8/2025)

The Hamilton receptor (H) forms a 1:1 complex (H−B) in solution with barbiturate (B) via sextuple hydrogen bonds. Although such interactions are well characterized in solution, they reorganize in solvent-free environment, further modulated by factors such as temperature and polarity profiles. We have developed a two-step method to characterize hydrogen-bonding association in solvent-free environments by 1) covalent fixation through cross-metathesis and 2) structural analysis by using electrospray ionization mass spectrometry (ESI-MS). Model molecules H, B and their complex H−B were first fixed by cross-metathesis (“red stapler”), then analyzed by ESI-MS to confirm their structures. The ball-and-stick molecular models, with varying transparency, enhance contrast to highlight major molecules, while arrows guide the reader through the interpretation. The red stapler symbolizes covalent fixation, and the ion sprayer, alongside a representative MS spectrum, illustrates the precision of the ESI-MS analysis. More information can be found in the Research Article by W. H. Binder and co-workers (DOI: 10.1002/chem.202403939).