Hydrophobic dipeptide crystals: a promising Ag-free class of ultramicroporous materials showing argon/oxygen adsorption selectivity

Abstract

The adsorption isotherms of nitrogen, oxygen and argon in four VA-class hydrophobic dipeptides are presented. Isotherms were determined at 5, 20 and 35 ºC, for a pressure range of 0-6 bar. Under these conditions, adsorption is still in the Henry region. For all materials and temperatures, the sequence of preferential adsorption is Ar>O2>N2, a highly abnormal result. At 5 ºC, the dipeptide with the smallest pores, VI, has Ar/O2 adsorption equilibrium selectivities up to 1.30, the highest ever measured in Ag -free adsorbents. Gas uptakes, at 1 bar and 20 ºC, are ~0.05 mol·kg -1 , very low relative values that are partially explained by the low porosity of the solids (< 10 %). The significance of these results for the development of new materials for the process of O2 generation by pressure swing adsorption (PSA) is discussed. The results indicate some of the structural and chemical properties that prospective Ag-free adsorbents should have in order to have Ar/O2 selectivity; hydrophobic pores, less than 0.5 nm-wide, and porosity of, at least, 20 %.

Nitric Oxide Release from Antimicrobial Peptide Hydrogels for Wound Healing

“…Short peptides have been used to produce microporous materials suitable for physical adsorption of small gas molecules [27]. The adsorption of Xe [28], CO 4 and H 2 [29], Ar [30], and O 2 and N 2 [31] have already been investigated. Usually the gas uptake and release from these materials are very fast [32], making them unsuitable for NO delivery applications.…”

Transport Properties of Light Gases in Nanochannels of L–Leu‐L‐Ser Dipeptide Crystals: A Comparative Study by Molecular Dynamics Simulations

“…Consequently, the crystal framework shows some degree of flexibility and is capable of relaxing to facilitate the hosting of small guest species, as it was observed experimentally by He‐pycnometry . They are also excellent candidates for use as permeation‐selective barriers,, with the advantage of being made of metal‐free biomolecules thus, in principle, without a potential negative impact on the environment if used at large industrial scale.…”

“…Some crystalline organic materials have also emerged in the last few decades with some advantages in terms of structure and synthesis, namely metal‐organic frameworks. Recently, some dipeptides have shown the ability to crystallize as microporous materials with a very high density of uniform and well‐defined nanoscale channels,, with very low tortuosity, which makes them very promising materials for storage or selective separation purposes . The LS dipeptides (see Figure ) are able to crystallize into typical tubular structures formed by noncovalent stacking of six‐membered ring units, each of which are held by head‐to‐tail hydrogen bonds between the dipeptides.…”

“…This work is focused on the diffusion and flow of light gases, namely Ar, O 2 , N 2 , CO, CO 2 and CH 4 through nanochannels of L–Leucyl‐L‐Serine (LS) crystals at elevated pressure. Experiments with some of these important constituents of earth atmosphere have already been done,,, but a few specific phenomena still lack clear explanations. Therefore, to unravel the dynamics of these processes at the molecular level, MD simulations were performed in appropriated models of LS structures.…”

Spontaneous transition of a water droplet from the Wenzel state to the Cassie state: a molecular dynamics simulation study

“…Superhydrophobicity of a solid surface has attracted much attention because of its applications in self-cleaning, [1][2][3] antiicing, 4,5 drag reduction, 6,7 and so on. 8,9 It is well known that superhydrophobicity has been linked to unique micro-or nanostructures. Water droplets can typically exist in two prominent states on structured surfaces: the Wenzel state and the Cassie state.…”