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

From PubMed via Jisc Publications RouterPublication status: epublishPeptides 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. Transport of the substrates proceeded in a matter of hours (compared to 6 days even for simple cargoes with the original system) without the peptides at any time dissociating from the machine nor exchanging with others in the bulk. Under the new operating conditions, key intermediates of the switch are sufficiently stabilized within the macrocycle formed between switch, arm, substrate and platform that they can be identified and structurally characterized by H NMR. The size of the peptide cargo has no significant effect on the rate or efficiency of transport in either direction. The new operating conditions allow detailed physical organic chemistry of the ratcheted transport mechanism to be uncovered, improve efficiency, and enable the transport of more complex cargoes than was previously possible. [Abstract copyright: This journal is © The Royal Society of Chemistry.

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 (Ln3+) 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

CCDC 1401219: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

CCDC 1401220: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

Lanthanide template synthesis of a molecular trefoil knot

Molecular knots1 and entanglements are featured in cyclic DNA2 and some proteins3 and are thought to play an important role in the chemical and physical properties of both natural and synthetic polymers.4 Sauvage and co-workers prepared the first synthetic molecular trefoil knot by connecting the end-groups of a linear two-metal-ion double helicate.5 However, the earliest published idea for a template synthesis of a trefoil knot is Sokolov’s proposal6 for assembling three ligands around a metal center to generate the three crossings necessary7 in the cyclized product. Several groups have attempted to prepare trefoil knots using this strategy thus far without achieving the ultimate goal,8 although Hunter has succeeded in synthesizing a trefoil knot by folding a single ligand strand around a transition metal ion,9 and Siegel has made a ‘trefoil knotted cyclophane’ 10 using a related triskelion approach featuring a covalently bonded scaffold.1

CCDC 1026538: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures