Employing novel biomaterials for use in energy and environmental applications is currently of great interest, in particular in the areas of gas separation and carbon capture. The dipeptides are one class of organic molecules that offer an attractive possibility in such areas, because they form open hexagonal crystalline structures (space group P6<sub>1</sub>) with quasi one-dimensional channels of tunable pore diameters in the range 3-6 Å. Previous studies indicate that these molecular crystals exhibit selective adsorption, as well as, water and gas transport properties. The selective permeability and transport properties of these biomaterials are believed to result from collective vibrations of the crystal structure that are coupled to the motions of the guest molecules within the channels. Zeolites with 1D channels of comparable diameter have been employed in methane/carbon dioxide separation and purification even at low pressure. The investigations described here are focused on L-Isoleucyl-L-Valine (IV) and L-Valyl-L-Alanine (VA), which have highly hydrophobic walls as a result of the inward pointing methyl groups that line the channels. High-resolution methane adsorption isotherms carried out for IV and VA at low pressure exhibit remarkable adsorption properties with IV exhibiting an adsorption capacity of 20 cm<sup>3</sup> (STP)/g. Recent results on Metal Organic Frameworks (MOFs) suggest the selective adsorption properties might result from a close match of the gas size and the channel diameter of the dipeptides, due to a sizable van der Waals interaction between the hydrophobic walls and the methane adsorbate. In order to more precisely characterize the dipeptide methane interaction, high-resolution Inelastic Neutron Scattering measurements were performed at the Spallation Neutron Source (BASIS spectrometer). These studies revealed strong evidence of rotational tunneling for the IV-methane system, which can be used to gauge the rotational barrier and details concerning the potential energy surface. Some evidence that the flexibility and dynamical motion within the biomaterials channels play a significant role in the adsorption properties will also be presented. Recent modeling investigations of the dynamics within the channels will also be presented.

Investigation of the adsorption properties of dipeptides: A thermodynamic, inelastic neutron scattering and modeling study

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.