Efficient Lewis acid catalysis of an abiological reaction in a de novo protein scaffold.

New enzyme catalysts are usually engineered by repurposing the active sites of natural proteins. Here we show that design and directed evolution can be used to transform a non-natural, functionally naive zinc-binding protein into a highly active catalyst for an abiological hetero-Diels-Alder reaction. The artificial metalloenzyme achieves >10 turnovers per active site, exerts absolute control over reaction pathway and product stereochemistry, and displays a catalytic proficiency (1/K = 2.

Origins of the Endo and Exo Selectivities in Cyclopropenone, Iminocyclopropene, and Triafulvene Diels-Alder Cycloadditions.

The endo and exo stereoselectivities of Diels-Alder reactions of cyclopropenone, iminocyclopropene, and substituted triafulvenes with butadiene were rationalized using density functional theory calculations. When cyclopropenone is the dienophile, there is a 1.8 kcal/mol preference for the exo cycloaddition with butadiene, while the reaction of 3-difluoromethylene triafulvene with butadiene favors the endo cycloaddition by 2.

Building on Cram's legacy: stimulated gating in hemicarcerands.

CONSPECTUS: Donald Cram's pioneering Nobel Prize-winning work on host-guest molecules led eventually to his creation of the field of container molecules. Cram defined two types of container molecules: carcerands and hemicarcerands. Host-guest complexes of carcerands, called carceplexes, are formed during their synthesis; once a carceplex is formed, the trapped guest cannot exit without breaking covalent bonds.

Reversible photochemically gated transformation of a hemicarcerand to a carcerand.

Guests in a gated community: introduction of two anthracene groups into a linker in a hemicarcerand creates a new type of photochemically controlled gated hemicarcerand. The reversible opening and closing of the "gate" of the host is controlled photochemically. The encapsulation and release of the guest molecules such as 1,4-dimethoxybenzene is controlled by irradiation with light of different wavelengths.

Computational design of catalytic dyads and oxyanion holes for ester hydrolysis.

Nucleophilic catalysis is a general strategy for accelerating ester and amide hydrolysis. In natural active sites, nucleophilic elements such as catalytic dyads and triads are usually paired with oxyanion holes for substrate activation, but it is difficult to parse out the independent contributions of these elements or to understand how they emerged in the course of evolution. Here we explore the minimal requirements for esterase activity by computationally designing artificial catalysts using catalytic dyads and oxyanion holes.

Controlled gating of a hemicarcerand by disulfide-dithiol interchange.

Introduction of a disulfide unit into the linker of a hemicarcerand creates a new way to control the entry and exit of guests. When the disulfide bond is reduced to two thiols, the "gate" opens, and guests can freely enter the hydrophobic core of the hemicarcerand. However, when the gate is closed, the host must be heated in the presense of excess guest in order for complexation to result.

Nonlinear optical stabilization of 1064-nm laser pulses with a two-photon absorbing liquid-dye salt system.

Highly effective optical power-limiting and optical-stabilization performances have been achieved in a new type of two-photon absorbing medium. That is a liquid-dye salt system, trans-4-[p-(N,N-dimethoxyethylamino)styryl]-N-3,6,9-trioxadecylpyridinium tetrafluoroborate (abbreviated as ASDPT), which features an unusually high molar concentration (-1 M) of two-photon absorbing chromophores and the capability of withstanding a higher pulsed laser power and energy. The nonlinear transmission property and output-input characteristics were studied based on a 1-cm-long liquid-dye salt sample by use of nanosecond 1064-nm laser pulses with a repetition rate variable from 1 to 10 Hz.

Superquenching in cyanine pendant poly(L-lysine) dyes: dependence on molecular weight, solvent, and aggregation.

A series of poly(L-lysines) ranging in number of repeat units (N(PRU)) from 6 to 900 has been synthesized and the photophysics of the series and monomer cyanine dye have been studied in solution. In water or aqueous dimethyl sulfoxide, the oligomers and polymers exhibit high sensitivity to fluorescence quenching by oppositely charged electron acceptors; in this study, 9,10-anthraquinone-2,6-disulfonate was used as a quencher for the cationic fluorescent polyelectrolytes. Quenching constants (K(SV)) measured in 50:50 (v/v) dimethyl sulfoxide-water increase monotonically with increase in N(PRU) ranging from 630 M(-1) for monomer to 1.