Experimental Insights into the Electronic Nature, Spectral Features, and Role of Entropy in Short CH3···CH3 Hydrophobic Interactions

Sounak Sarkar, Sajesh P. Thomas, Lokeswara Rao Potnuru, Alison J. Edwards, Arnaud Grosjean, Krishna Venkatachala Ramanathan, T. N. Guru Row

Research output: Contribution to journalArticle

3 Citations (Scopus)


Hydrophobic interactions are often explored in solution-state aggregation of molecules. However, an experimental electron density description about these interactions is still lacking. Here, we report a systematic study on the electronic nature of methyl···methyl hydrophobic interactions in a series of multicomponent crystals of biologically active molecules. Charge density models based on high-resolution X-ray diffraction allow the visualization of subtle details of electron density features in the interaction region. Our study classifies these interactions as atypical group···group interactions in contrast to σ-hole interactions, which are stabilized by the minimized electrostatic repulsion and maximized dispersion forces. For the first time, we quantified the solid-state entropic contribution from the torsional mode of the methyl groups in stabilizing these interactions by thermal motion analysis based on neutron diffraction as well as variable-temperature crystallography. The carbon atoms in methyl···methyl interactions show a unique upfield chemical shift in the 13C solid-state NMR signal.

Original languageEnglish
Pages (from-to)7224-7229
Number of pages6
JournalJournal of Physical Chemistry Letters
Publication statusE-pub ahead of print - 7 Nov 2019

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