Molecular self-assembly controlled by acid–base non-covalent interactions: a mass spectrometric study of some organic acids and bases

Molecular clusters generated from vacuum adiabatic expansion of liquid droplets including acid and base molecules provide an insight into molecular self-assembly through non-covalent interactions. The mass spectrometric analysis for the resulting clusters indicates a systematic structure change which is dependent on the acid–base interaction: a multilayer stacking structure for relatively strong acid–base pairs (phenol–pyridine, phenol–N,N-dimethylaniline, etc.), and a monolayer structure for relatively weak acid–base pairs (phenol–pyrazine, cyclohexanol–pyridine, etc.). As another viewpoint, mass spectrometry of the molecular clusters composed of acid and base molecules can be presented as a new method to characterise the acid–base interaction.