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Molecular crystals of dipeptides containing open channels can selectively absorb CO2 over N2 and CH4, as shown by experimental and simulated isotherms. The efficient CO2 capture enabled separation from methane and allowed the direct observation by 2D MAS NMR of CO2 sequestered in the peptide-based biozeolites. © 2013 The Royal Society of Chemistry

Hydrophobic dipeptide crystals recently emerged as novel “organic zeolites” featuring tailorable pore size. In fact, seven out of nine pairwise combinations of L-isoleucine, L-valine and L-alanine amino acids crystallize according to the same charge-assisted hydrogen bond pattern, generating a family of microporous materials with right-handed 1D channels, having diameters in the sub-nanometer domain (<6Å), aliphatic environment and different degrees of helicity. The relationship between pore size and material properties was investigated with respect to gas separation, exploiting the affinity of carbon dioxide for the hydrophobic nanochannels of L-alanyl-L-valine (AV), L-isoleucyl-L-valine (IV) and L-valyl-L-isoleucine (VI). Reversible CO2 capture from an equimolar mixture of CO2 and methane, at room temperature and 1 atmosphere, was demonstrated with increasing purification performance with decrease in pore size. Dipeptide were also used as nanovessels in radical polymerizations with the aim of controlling otherwise non-specific reactions. Diene monomers (trans-1,3-pentadiene and isoprene) only yield linear 1,4-trans polymer in accordance with 1-dimensional pore geometry, while poly(acrylonitrile) (PAN) could be obtained as a stereoregular isotactic product by acrylonitrile polymerization in AV dipeptide. Finally, taking advantage of the dipeptide lability and unique thermal properties of poly(acrylonitrile), AV-PAN nanocomposites were used as a scaffold to obtain carbon replicas of the starting nanocomposite crystals (carbon micro-fibrils) showing anisotropic arrangement of the graphite domains.

Porous materials which present open nanochannels of cross-sections ranging from 0.3 to 4 nm. were investigated. Particular attention has been given to microporous frilly-org. substances of synthetic or biol. origin. In the latter family, a no. of dipeptides crystallize in hexagonal lattices with permanent porosity and modulated pore sizes. The affinity towards CO2 and relevant gases, such as methane and hydrogen, and their absorption efficiency was proved for the first time, even under mild conditions. Moreover, mixt. sepns. has been tested successfully, due to the pronounced selectivity (e.g. CO2 vs N2 and CH4). Also, porous org. networks of extremely high surface area (>6000m2/g were prepd. and studied.).

Flexible polymer chains and a suitable aromatic host self-assemble in varied ratios to fabricate crystalline and semi-crystalline materials with robust architectures. The high melting macromolecular adducts were successfully prepared by solvent-free mechanochemical or thermal treatment of the crystalline host and few polymers with various molecular weights. This unconventional strategy has been applied for the selective confinement of copolymer blocks into crystalline inclusion compounds, thus creating novel architectures stabilized by cooperative CH•••pi interactions, as revealed by solid state NMR.

Muscle-derived stem-cell (MDSC) transplantation presents a promising method for the treatment of muscle injuries. This study investigated the ability of exercise to enhance MDSC transplantation into the injured muscle. Mice were divided into four groups: contusion+phosphate-buffered saline (C+PBS; n=14 muscles), C+MDSC transplantation (n=12 muscles), C+PBS+treadmill running (C+PBS+TM; n=17 muscles), and C+MDSC+TM (n=13 muscles). One day after injury, the TM groups began running for 1 or 5 weeks. Two days after injury, muscles of C+MDSC and C+MDSC+TM groups were injected with MDSCs. One or 5 weeks later, the number and differentiation of transplanted MDSCs, myofiber regeneration, collagen I formation, and vascularity were assessed histologically. In vitro, MDSCs were subjected to mechanical stimulation, and growth kinetics were quantified. In vitro, mechanical stimulation decreased the MDSC population doubling time (18.6±1.6h) and cell division time (10.9±0.7h), compared with the controls (population doubling time: 23.0±3.4h; cell division time: 13.3±1.1h) (p=0.01 and 0.03, respectively). In vivo, 5 weeks of TM increased the myogenic contribution of transplanted MDSCs, compared with the controls (p=0.02). C+MDSC, C+PBS+TM, and C+MDSC+TM demonstrated decreased fibrosis at 5 weeks, compared with the C+PBS controls (p=0.00, p=0.03, and p=0.02, respectively). Results suggest that the mechanical stimulation favors MDSC proliferation, both in vitro and in vivo, and that exercise enhances MDSC transplantation after injury. © 2010 Mary Ann Liebert, Inc.

Our strategy is the creation of engineered nanochannels of various size and nature in zeolite-like cryst. compds. Dipeptide crystals contg. channels were used for the first time as hydrogen and methane nanocontainers. The unusual application of peptides as absorbitive materials for energetic purposes opens up novel perspectives in the choice of alternative families of substances for gas storage. A variety of combinations of dipeptide sequences can tune the cross-section of the channels and the microenvironment from narrow channels (3.7 Angstroms) that are suitable to hydrogen, to larger channels of about 5 Angstroms that can host favorably methane. In addn., toxic and contaminant gases such as carbon dioxide can be captured selectively resulting in the purifn. of methane in pipe-lines and of hydrogen before entering the fuel-cells. They are completely biodegradable, avoiding the generation of toxic wastes at the end of their life-cycle. Adsorption isotherms, XRD and MAS NMR provided the evidence of permanent porosity of the crystals and the structure stability after the gas has been totally removed. Moreover, the adsorption energy falls within the suggested limits for efficient loading/unloading performances. Much larger channels of more than 40 Angstrom cross-section were realized in hybrid org.-inorg. mesoporous materials with cryst. channel walls. The org. moieties could advantageously be functionalized to modulate the surface interactions. Furthermore, the discovery of fast mol. rotors with correlation times in the nanosecond regime lining the channel walls and exposed towards the diffusing-in gases allowed us to discuss adsorption properties together with host dynamics.

Dipeptide crystalline materials are proposed for the absorption of environmentally and energetically relevant gases such as carbon dioxide, methane and hydrogen. The crystalline scaffolds, held together by a network of hydrogen bonds, of L-alanyl-L-valine (AV), L-valyl-L-alanine (VA), L-isoleucyl-L-valine (IV) and L-valyl-L-isoleucine (VI) form stable nanochannel pores with internal hydrophobic surfaces and suitable cross-section that encapsulates, efficiently and selectively, guest gases. The soft nature of the interactions guarantees reversibility of the process and triggered delivery simply by reducing gas pressure. With L-isoleucyl-L-valine, showing small channel diameter (3.9 Å), at 195K and already at 250 torr CO2 absorption reaches the value of 53 cm3 (STP) g_1 (90% maximum loading). We were able to attain remarkable CO2/CH4 selectivity even at atmospheric pressure, supporting the idea that this crystalline powder can find application in methane purification from carbon dioxide. Hydrogen showed a particular affinity for the IV and VI as shown by the adsorption isotherms run up to 10 atm and 77K. The type I Langmuir profile at 77 K reached maximum loading already at pressures close to 1 atm, and an absorption capacity of 52 cm3 (STP) g-1 for IV that corresponds to 0.5 mol/mol.