Coordination‐Driven Folding and Assembly of a Short Peptide into a Protein‐like Two‐Nanometer‐Sized Channel

Abstract

Short peptide helices have attracted attention as suitable building blocks for soft functional materials, but they are rarely seen in crystalline materials. A new artificial nanoassembly of short peptide helices in the crystalline state is presented in which peptide helices are arranged three-dimensionally by metal coordination. The folding and assembly processes of a short peptide ligand containing the Gly-Pro-Pro sequence were induced by silver(I) coordination in aqueous alcohol, and gave rise to a single crystal composed of polyproline II helices. Crystallographic studies revealed that this material possesses two types of unique helical nanochannel; the larger channel measures more than 2 nm in diameter. Guest uptake properties were investigated by soaking the crystals in polar solutions of guest molecules; anions, organic chiral molecules, and bio-oligomers are effectively encapsulated by this peptide-folded porous crystal, with moderate to high chiral recognition for chiral molecules.

Biologically derived metal organic frameworks

“…(© 2014 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim, reprinted with permission). [112] the derivatives with similar chain length, but different positions of the -OH group gave significantly different enantioselective sorption values. [174] Increasing the size of the ligand allows for the ability to introduce active sites into the pores.…”

“…[112] Single crystal X-ray analysis clearly reveals that the peptide ligand is fixed in a PII helix conformation with all ligands linked by a py-Ag I -py coordination similar to natural polypeptide chains (N→C direction terminal manner). [112] The linear helical strand of the MOF repeats, affording a unique hexagonal entanglement in the crystal giving a 3-dimensional honeycomb network.…”

“…[112] Single crystal X-ray analysis clearly reveals that the peptide ligand is fixed in a PII helix conformation with all ligands linked by a py-Ag I -py coordination similar to natural polypeptide chains (N→C direction terminal manner). [112] The linear helical strand of the MOF repeats, affording a unique hexagonal entanglement in the crystal giving a 3-dimensional honeycomb network. [112] Recently, Rosseinsky et al reported two isoreticular 3-dimensional peptide-based porous frameworks with Gly-L-His-Lys and Gly-L-His-L-Gly to Cu II ( Table 2, entries 18 and 19, respectively) which displayed higher solvent accessible volumes (47 % and 60.2 %, respectively), than previously reported with shorter dipeptides.…”

“…[112] The linear helical strand of the MOF repeats, affording a unique hexagonal entanglement in the crystal giving a 3-dimensional honeycomb network. [112] Recently, Rosseinsky et al reported two isoreticular 3-dimensional peptide-based porous frameworks with Gly-L-His-Lys and Gly-L-His-L-Gly to Cu II ( Table 2, entries 18 and 19, respectively) which displayed higher solvent accessible volumes (47 % and 60.2 %, respectively), than previously reported with shorter dipeptides. [113] Upon desolvation both undergo structural collapse, however, they exhibit sponge-like amorphous-to-crystalline transformation when exposed to water, recovering their open porous framework.…”

“…[65] The peptide Gly-Pro-Pro reported by Fujita et al was modified by introduction of 3-pyridyl groups with amides bonds at both termini to produce a coordinative tripeptide ligand (structure previously described in section 3.2). [112] Through its slow diffusion into an aqueous solution of AgBF4, bio-MOF [(AgBF4)•GlyProPro] formed with two types of 1-dimensional chiral channels running along the crystallographic c axis (Figure 7). [112] The largest channel is surrounded by the peptide backbone forming a left handed duplexlike framework stabilized by π-stacking of the pyridyl groups, while the smaller second channel is closely packed with solvents and anions.…”