Site-to-site peptide transport on a molecular platform using a small-molecule robotic arm.

Peptides attached to a cysteine hydrazide 'transporter module' are transported selectively in either direction between two chemically similar sites on a molecular platform, enabled by the discovery of new operating methods for a molecular transporter that functions through ratcheting. Substrate repositioning is achieved using a small-molecule robotic arm controlled by a protonation-mediated rotary switch and attachment/release dynamic covalent chemistry. A polar solvent mixtures were found to favour to isomerization of the doubly-protonated switch, transporting cargo in one direction (arbitrarily defined as 'forward') in up to 85% yield, while polar solvent mixtures were unexpectedly found to favour to isomerization enabling transport in the reverse ('backward') direction in >98% yield.

Pick-up, transport and release of a molecular cargo using a small-molecule robotic arm.

Modern-day factory assembly lines often feature robots that pick up, reposition and connect components in a programmed manner. The idea of manipulating molecular fragments in a similar way has to date only been explored using biological building blocks (specifically DNA). Here, we report on a wholly artificial small-molecule robotic arm capable of selectively transporting a molecular cargo in either direction between two spatially distinct, chemically similar, sites on a molecular platform.

Lanthanide Template Synthesis of Trefoil Knots of Single Handedness.

We report on the assembly of 2,6-pyridinedicarboxamide ligands (1) with point chirality about lanthanide metal ion (Ln(3+)) templates, in which the helical chirality of the resulting entwined 3:1 ligand:metal complexes is covalently captured by ring-closing olefin metathesis to form topologically chiral molecular trefoil knots of single handedness. The ligands do not self-sort (racemic ligands form a near-statistical mixture of homoleptic and heteroleptic lanthanide complexes), but the use of only (R,R)-1 leads solely to a trefoil knot of Λ-handedness, whereas (S,S)-1 forms the Δ-trefoil knot with complete stereoselectivity. The knots and their isomeric unknot macrocycles were characterized by NMR spectroscopy, mass spectrometry, and X-ray crystallography and the expression of the chirality that results from the topology of the knots studied by circular dichroism.

Lanthanide template synthesis of a molecular trefoil knot.

We report on a complex featuring three 2,6-pyridinedicarboxamide ligands entwined around a lanthanide (Ln(3+)) ion. The ligand strands can be cyclized by ring-closing olefin metathesis to form a molecular trefoil knot in 58% yield. Demetalation with tetraethylammonium fluoride quantitatively generates the wholly organic 81-atom-loop trefoil knot.

Superelectrophilic amidine dications: dealkylation by triflate anion.

Superelectrophiles: Formamides were designed that when treated with triflic anhydride would be transformed into superelectrophilic amidine dications. These dications were so electrophilic that they underwent in situ dealkylation by the triflate anion (see scheme; Tf = trifluoromethanesulfonyl). DFT calculations were used to determine the mechanistic details of the dealkylation reaction.