Search

We report a single‐molecule mechanistic investigation into 2‐cyanobenzothiazole (CBT) chemistry within a protein nanoreactor. When simple thiols reacted reversibly with CBT, the thioimidate monoadduct was approximately 80‐fold longer‐lived than the tetrahedral bisadduct, with important implications for the design of molecular walkers. Irreversible condensation between CBT derivatives and N‐terminal cysteine residues has been established as a biocompatible reaction for site‐selective biomolecular labeling and imaging. During the reaction between CBT and aminothiols, we resolved two transient intermediates, the thioimidate and the cyclic precursor of the thiazoline product, and determined the rate constants associated with the stepwise condensation, thereby providing critical information for a variety of applications, including the covalent inhibition of protein targets and dynamic combinatorial chemistry., Better off alone: A nanoreactor approach was used to investigate the chemistry of2‐cyanobenzothiazole (CBT), an important bioorthogonal reagent, at the single‐molecule level. Reactions with thiols and aminothiols revealed mechanistic and kinetic information with important implications for several essential applications of CBT reagents.

Responsive hydrogels that undergo controlled shape changes in response to a range of stimuli are of interest for microscale soft robotic and biomedical devices. However, these applications require fabrication methods capable of preparing complex, heterogeneous materials. Here we report a new approach for making patterned, multi-material and multi-responsive hydrogels, on a micrometre to millimetre scale. Nanolitre aqueous pre-gel droplets were connected through lipid bilayers in predetermined architectures and photopolymerized to yield continuous hydrogel structures. By using this droplet network technology to pattern domains containing temperature-responsive or non-responsive hydrogels, structures that undergo reversible curling were produced. Through patterning of gold nanoparticle-containing domains into the hydrogels, light-activated shape change was achieved, while domains bearing magnetic particles allowed movement of the structures in a magnetic field. To highlight our technique, we generated a multi-responsive hydrogel that, at one temperature, could be moved through a constriction under a magnetic field and, at a second temperature, could grip and transport a cargo.

Zinc(II), a dimolybdenum(II) paddlewheel tetramine A, and 2-formylpyridine self-assembled to generate a cubic Zn(II)8(L(A))6 assembly. The paddlewheel faces of this assembly exhibited two distinct conformations, whereas the analogous Fe(II)8(L(A))6 framework displayed no such perturbation to its structure. This variation in behavior is attributed to the subtle difference in ligand rotational freedom between the Zn(II)- and Fe(II)-cornered cubes. The incorporation of a fluorinated Mo(II)2 paddlewheel, B, into analogous Zn(II)8(L(B))6 and Fe(II)8(L(B))6 structures resulted in changes to the rotational dynamics of the ligands. These differing dynamics perturbed the energies of the frontier orbitals of these structures, as determined through spectroscopic and electrochemical methods. The result of these perturbations was an inversion of the halide binding preference of the Zn(II)8(L(B))6 host as compared to its Zn(II)8(L(A))6 congener, whereas the Fe(II)8(L(B))6 host maintained a similar binding hierarchy to Fe(II)8(L(A))6.

The development of catalysts benefits from knowledge of the intermediate steps that accelerate the transformations of substrates into products. However, key transient species are often hidden in ensemble measurements. Here, we show that a protein nanoreactor can sample the intermediate steps in a catalytic cycle by the continuous single-molecule observation of a stoichiometric reaction in solution. By monitoring changes in the flow of ionic current through an α-hemolysin protein pore, we observed three intermediate metal–ligand complexes in a gold(I)-catalyzed reaction that converts an acetylenic acid to an enol lactone, revealing a transitional coordination complex that had been previously unobserved. A kinetic isotope effect helped assign the various metal–ligand species. Measurements of the lifetimes of the intermediates allowed a full kinetic analysis of the metal-catalyzed reaction cycle.

Monosaccharides, such as d-glucose and d-fructose, exist in aqueous solution as an equilibrium mixture of cyclic isomers and can be detected with boronic acids by the reversible formation of boronate esters. The engineering of accurate, discriminating and continuous monitoring devices relies on knowledge of which cyclic isomer of a sugar binds to a boronic acid receptor. Herein, by monitoring fluctuations in ionic current, we show that an engineered α-hemolysin (αHL) nanopore modified with a boronic acid reacts reversibly with d-glucose as the pyranose isomer (α-d-glucopyranose) and d-fructose as either the furanose (β-d-fructofuranose) or the pyranose (β-d-fructopyranose). Both of these binding modes contradict current binding models. With this knowledge, we distinguished the individual sugars in a mixture of d-maltose, d-glucose, and d-fructose.

We present a method for the directed self-assembly of interlocked structures and coordination complexes in a set of metal-organic hosts. New homo- and heteroleptic metal complexes-species that cannot be prepared outside-form within the cavities of cuboctahedral coordination cages. When linear bidentate guests and macrocycles are sequentially introduced to the host, a rotaxane is threaded internally; the resulting ternary host-guest complex is a new kind of molecular gyroscope. Tetradentate guests segregate the cavities of these cages into distinct spaces, promoting new stoichiometries and modes of ligand binding to metal ions. The behaviors of bound complexes were observed to alter markedly as a result of confinement: In situ oxidations and spin transitions, neither of which occur ex situ, were both observed to proceed. By providing a tailored space for new modes of coordination-driven self-assembly, the inner phases of cuboctahedral coordination cages provide a new medium for synthetic coordination chemistry.

The subcomponent self-assembly of a bent dialdehyde ligand and different cationic and anionic templates led to the formation of two new metallosupramolecular architectures: a Fe(II) 4 L6 molecular rectangle was isolated following reaction of the ligand with iron(II) tetrafluoroborate, and a M5 L6 trigonal bipyramidal structure was constructed from either zinc(II) tetrafluoroborate or cadmium(II) trifluoromethanesulfonate. The spatially constrained arrangement of the three equatorial metal ions in the M5 L6 structures was found to induce small-molecule transformations. Atmospheric carbon dioxide was fixed as carbonate and bound to the equatorial metal centers in both the Zn5 L6 and Cd5 L6 assemblies, and sulfur dioxide was hydrated and bound as the sulfite dianion in the Zn5 L6 structure. Subsequent in situ oxidation of the sulfite dianion resulted in a sulfate dianion bound within the supramolecular pocket.

Metal-organic self-assembly has proven to be of great use in constructing structures of increasing size and intricacy, but the largest assemblies lack the functions associated with the ability to bind guests. Here we demonstrate the self-assembly of two simple organic molecules with Cd(II) and Pt(II) into a giant heterometallic supramolecular cube which is capable of binding a variety of mono- and dianionic guests within an enclosed cavity greater than 4200 Å(3) . Its structure was established by X-ray crystallography and cryogenic transmission electron microscopy. This cube is the largest discrete abiological assembly that has been observed to bind guests in solution; cavity enclosure and coulombic effects appear to be crucial drivers of host-guest chemistry at this scale. The degree of cavity occupancy, however, appears less important: the largest guest studied, bound the most weakly, occupying only 11 % of the host cavity.

The incorporation of an N-heterocyclic carbene (NHC) moiety into a self-assembled MII4L6 cage framework required the NHC first to be metallated with gold(I). Bimetallic cages could then be constructed using zinc(II) and cadmium(II) templates, showing weak luminescence. The cages were destroyed by the addition of further gold(I) in the form of AuI(2,4,6-trimethoxybenzonitrile)2SbF6, which caused the reversibly-formed cages to disassemble and controllably release the AuI-NHC subcomponent into solution. This release in turn induced the growth of gold nanoparticles. The rate of dianiline release could be tuned by capsule design or through the addition of chemical stimuli, with different release profiles giving rise to different nanoparticle morphologies.