Interactions and crowding in the hydrophilic region have also been suggested to affect the propensity for interdigitation. In the case of phospholipids, substituting PC ester linkages with ether linkages allows the lipids to form interdigitated structures at atmospheric pressure. The tendency of ether-linked PCs for interdigitation has been attributed to decreased attraction in the hydrophilic region, i.e., through a reduction in the extent of hydrogen bonding through water molecules. The headgroup size has also been shown to play a role for interdigitation; more bulky headgroups have been shown to correlate with interdigitation in the case of PC versus PE due to increased headgroup repulsion and crowding, as well as formation of voids in the hydrophobic region. While the MMG molecules did not display clear differences in the intermolecular hydrogen bonding, MMG-1 was seen to have a slightly greater extent of intramolecular hydrogen bonding. This might relate to certain geometric configurations involving the headgroup and the hydroxyl group in the corynomycolic acid. It should be noted, however, that MMG-1 and MMG-6 contain identical glycerol moieties, and the glycerol moiety itself has not been shown to affect the type of structure that MMG molecules self-assemble into. 10