Dipeptide Crystals as Excellent Permselective Materials: Sequential Exclusion of Argon, Nitrogen, and Oxygen

Abstract

Gas storage and gas separation using porous solids are important technologies that have attracted great attention because of their environmental and energetic applications. Highly porous materials, such as zeolites, silicate, and carbonbased materials, [1] have long-established specific applications. The key for new applications is the development of new frameworks. Advances in gas sorption capacities were achieved through the synthesis of materials such as metalorganic frameworks (MOFs), organic polymers, and microporous organic crystals.[2] Recently, crystals formed by dipeptides were tested as adsorbents [3] with significant results in hydrogen absorption and methane purification from carbon dioxide.

An Ultrastable and Easily Regenerated Hydrogen‐Bonded Organic Molecular Framework with Permanent Porosity

“…Compared with competitors such as zeolites,m etal-organic frameworks (MOFs) and covalent organic frameworks (COFs), [1] HOFs provide inherent advantages,s uch as solubility,m ild reaction conditions and low cost. [3] Generally, HOFs are constructed by weak non-covalent interactions, such as hydrogen bonding and p···p stacking interactions.As ar esult, most HOFs are less stable than other porous materials,t he building units of which are linked by the relatively strong covalent or coordination bonds.C onsequently,f ew permanently porous HOFs have been reported to date,b ecause most HOFs either collapse after solvent removal or are unstable in heat and/or humidity. [3] Generally, HOFs are constructed by weak non-covalent interactions, such as hydrogen bonding and p···p stacking interactions.As ar esult, most HOFs are less stable than other porous materials,t he building units of which are linked by the relatively strong covalent or coordination bonds.C onsequently,f ew permanently porous HOFs have been reported to date,b ecause most HOFs either collapse after solvent removal or are unstable in heat and/or humidity.…”

Permeation of Light Gases through Hexagonal Ice

“…We have already observed this behavior in the permeation through dipeptide microporous crystals [7]. …”

“…The hexagonal ice void nanochannels are smaller than all the gas molecular dimensions, including helium (see Supplementary Information). However, the unexpected penetration of small molecules through other hydrogen-bonded supramolecular crystals was already observed and was attributed to the flexibility of the crystal framework [7,11]. …”

“…The helium flow rate through the hexagonal ice columns is approximately as fast as the flux through the permanent nanochannels of the L-valyl-L-isoleucine (VI) crystals [7]. The estimated VI nanochannels diameter stands between 3.0 and 3.7 Å depending on the determination method [11].…”

“…Crystalline materials, displaying unidirectional and single-sized pores are promising candidates for membrane synthesis. Metal-organic frameworks (MOFs) [3,4] and peptide supramolecular systems [5,6,7,8] are among the most promising crystal structures, due to the variety of pore sizes and high pore density. Nevertheless, the key challenge in the context of using crystalline materials is to scale up the fabrication techniques of either dense polycrystalline layers [3] or mixed matrix membranes, which embed the selective particles inside the polymeric matrix [4].…”