Search

Short peptides are versatile molecules for the construction of supramolecular materials. Most reported peptide materials are hydrophobic, stiff, and show limited response to environmental conditions in the solid‐state. Herein, we describe a design strategy for minimalistic supramolecular metallo‐peptide nanofibers that, depending on their sequence, change stiffness, or reversibly assemble in the solid‐state, in response to changes in relative humidity (RH). We tested a series of histidine (H) containing dipeptides with varying hydrophobicity, XH, where X is G, A, L, Y (glycine, alanine, leucine, and tyrosine). The one‐dimensional fiber formation is supported by metal coordination and dynamic H‐bonds. Solvent conditions were identified where GH/Zn and AH/Zn formed gels that upon air‐drying gave rise to nanofibers. Upon exposure of the nanofiber networks to increasing RH, a reduction in stiffness was observed with GH/Zn fibers reversibly (dis‐)assembled at 60–70 % RH driven by a rebalancing of hydrogen bonding interactions between peptides and water. When these metallo‐peptide nanofibers were deposited on the surface of polyimide films and exposed to varying RH, peptide/water‐vapor interactions in the solid‐state mechanically transferred to the polymer film, leading to the rapid and reversible folding‐unfolding of the films, thus demonstrating RH‐responsive actuation. [ABSTRACT FROM AUTHOR]

The accurate determination of the spectral data for strained molecules is challenging, as their geometries in solid state and in solution may differ because the molecules undergo continuous dynamical changes between different conformations. Calix[3]pyrrole, the recently synthesized smallest calixpyrrole, has the Cs point group of symmetry in its crystal structure, despite showing a single chemical shift value for the N–H protons in solution, which suggests that the geometry of calix[3]pyrrole could take a time-averaged, bowl-shaped geometry having a C3v or C3 point group of symmetry in solution. Density functional theory calculations and molecular dynamics simulations showed the most stable geometry of calix[3]pyrrole in the Cs point group of symmetry, and continuous transformation among the equivalent geometries of calix[3]pyrrole. The rapid dynamical change among the conformations of calix[3]pyrrole in the Cs point group of symmetry is the reason behind the observed experimental chemical shift value. The presence of halide (X− = F−, Cl−, Br−, I−) anions can form stable, bowl-shaped calix[3]pyrrole·X− complexes, and the study on calix[3]pyrrole·F− showed that three NH···F hydrogen bonds are responsible for their stability. The chemical shift value for the N–H protons in calix[3]pyrrole·F− is highly deshielded, as the F− anion lowers electron density in the vicinity of these H-atoms. The consideration of dynamics is helpful in understanding the structure of strained molecules and associated spectral data. [ABSTRACT FROM AUTHOR]

The article titled "Cover Feature: In Silico Design and Characterization of a New Molecular Electride: Li@Calix[3]Pyrrole" introduces Li@calix[3]pyrrole as the latest addition to the molecular electride family. The study reveals that the anionic electron of Li@calix[3]pyrrole is located outside the molecular structure, near the pyrrole N-H moieties. This unique charge-separated configuration is achieved through an electron transfer from lithium to a molecular orbital at the back of the calix[3]pyrrole fragment. For more detailed information, readers can refer to the Research Article by R. Saha, B.B. Skjelstad, and S. Pan. [Extracted from the article]

Density functional theory (DFT) based calculations have been carried out for the endohedral encapsulation of magnesium dimer inside fullerene, that is, Mg2@C60. It is observed that the minimum energy structure of the Mg2@C60 system is C2h symmetry. The MgMg bond distance in the Mg2@C60 system is much shorter than that in the free Mg2 and Mg22+ ion. The formation of the endohedral Mg2@C60 system is thermochemically spontaneous in nature. The natural bond orbital (NBO) analysis showed the presence of an Mg22+ fragment with an MgMg bond inside the C60 cage. The electron density descriptors have identified the covalency in the MgMg bond. A non‐nuclear attractor (NNA) is present in the middle of the two Mg‐atoms. The bonding interaction between the Mg2 and C60 fragments is ionic in nature and the [Mg22+] and [C602−] represent the bonding pattern in the Mg2@C60 system. The designed endohedrally encapsulated system behaves as an electride. [ABSTRACT FROM AUTHOR]