Jiaxin Hu

Supramolecular Chemistry And Self-assembly Special Feature: Probing alkali metal–π interactions with the side chainresidue of tryptophan

Feeble forces play a significant role in the organization of proteins. These include hydrogen bonding, hydrophobic interactions, salt bridge formation, and steric interactions. The alkali metal cation-π interaction is a force of potentially profound importance but its consideration in biology has been limited by the lack of experimental evidence. Our previous studies of cation–π interactions with Na+ and K+ involved the side arms of tryptophan (indole), tyrosine (phenol), and phenylalanine (benzene) as the arene donors. The receptor system possesses limiting steric constraints. In this report, we show that direct interactions between alkali metals and arenes occur at or within the van der Waals contact distance.

σ-Donor, π-donor, and anion competition in π-complexation of alkali metal cations

Removal of or replacement of one of two phenylethyl sidearms on azalariats leads to clear evidence for cation–π interactions with the remaining sidearm.

Ferrocene derivatives as receptors to explore ammonium cation–π interactions

The potential importance in biology of ammonium–arene cation–π interactions has fostered the development of a model system that uses ferrocene as a scaffold that can rotate groups with respect to each other while maintaining them at a fixed distance. The preparation of 1-benzyl-1′-N,N-dimethylaminomethylferrocene methiodide is reported along with the solid state structure of it and its precursor. Clear evidence is presented for an intermolecular ammonium–arene interaction. The results are analyzed in the context of existing arene–ammonium ion contacts.

Solid state network formation in arene-Sidearmed lariat ether complexes: contrasting behavior of sodium, potassium, and calcium cation complexes

Abstract Studies of lariat ether receptor systems and their complexes are reported. The receptors afford signficantly different complexes with similarly sized divalent calcium and monovalent sodium ions. Certain of the receptor-cation complexes form infinite networks in the solid state.

Sodium cation complexation behavior of the heteroaromatic sidechains of histidine and tryptophan

Three of the four essential amino acids that have aromatic sidechains exhibit cation-pi interactions with Na+ or K+; histidine does not and is shown here to be a sigma donor.

Solid state evidence for π-complexation of sodium cation by carbon–carbon double bonds

Solid state evidence shows that neutral double bonds, attached to flexible sidearms of a lariat ether, serve as intramolecular pi-donors for a ring-bound Na+ cation.

Calcium cation complexation by lariat ether receptors having arene-terminated sidearms

The first reported calcium azalariat complex has an arene terminated sidearm that behaves differently from an otherwise identical indole-sidearmed complex; twin phenolic sidearms on a diaza-18-crown-6 lead to an infinite, H-bonded network.

Solution complexation between potassium iodide and lariat ethers having pi-donor sidearms

Experimental evidence is presented for the interaction of triple bond pi-donors with potassium cation in acetonitrile solution.

Solid state structures of N-2-(3-indolylethyl)aza-9-crown-3, N,N′-bis(2-(3-indolylethyl))-4,13-diaza-18-crown-6, and their protonated forms

Abstract X-Ray crystal structures of N-2-(3-indolylethyl)aza-9-crown-3 and its protonated form are presented. The N-protonated aza-9-crown-3H-bonds to iodide anion. In contrast, the dimer, N,N′-bis(2-(3-indolylethyl))-4,13-diaza-18-crown-6, forms a capsule in which the N+–H bonds turn inward toward the macrorings center and the sidearms adopt positions above and below it. Hexafluorophosphate, the counterion, is excluded from the coordination sphere.

Solid-State Evidence for Alkali Metal to Arene Pi-Complexation

We report a variety of alkali metal cation-π interactions, documented by X-ray crystallography. These include interactions with the neutral arenes benzene, phenol, and indole. We also include structural results for lithium, sodium, potassium, rubidium, and cesium cation-π complexes in which the arene has enhanced electron richness owing to an adjacent or integral charge.