FaFrit

Highly selective, narcissistic self-sorting can be achieved in the formation of self-assembled cages of rare earth metals with multianionic salicylhydrazone ligands. The assembly process is highly sensitive to the length of the ligand and the coordination geometry. Most surprisingly, high-fidelity sorting is possible between ligands of identical coordination angle and geometry, differing only in a single functional group on the ligand core, which is not involved in the coordination. Supramolecular effects allow discrimination between pendant functions as similar as carbonyl or methylene groups in a complex assembly process.

Equals among equals: The formation of self-assembled cages of rare earth metals and ligands proceeds through highly selective, narcissistic self-sorting. Pendant functionalities as similar as carbonyl and methylene groups are discriminated in this complex assembly process.

The synthesis and characterization of a new type of very large perylene-based molecules 9 are reported. The extension of the conjugated π system was accomplished by the facile condensation of two bay-functionalized perylene moieties with 1,2,4,5-tetraaminobenzene. The resulting chromophore in 9 consists of 35 conjugated π-electron pairs and, therefore, is comparable to pentarylenes and hexarylenes containing 31 and 36 conjugated π-electron pairs, respectively. The unsubstituted imine N atoms of the benz-bisimidazole bridges in 9 can be readily and reversibly protonated to give the dications 9aH₂²⁺. The twofold protonation of 9 is accompanied by a bathochromic shift of the main absorption band and pronounced fluorescence quenching. The experimental results were corroborated by quantum mechanical calculations.

We present the synthesis and characterization of a new type of perylene chromophore. Two perylene moieties are combined to form an overall conjugated π system. Parts of the molecule could be protonated and, thereby, the absorption and fluorescence emission spectra shifted bathochromically. The electronic band gap was determined to be 1.33–1.35 eV.

A method for determining lipase enantioselectivity in the transacylation of sec-alcohols in organic solvent was developed. The method was applied to a model library of Candida antarctica lipase A (CalA) variants for improved enantioselectivity (E values) in the kinetic resolution of 1-phenylethanol in isooctane. A focused combinatorial gene library simultaneously targeting seven positions in the enzyme active site was designed. Enzyme variants were immobilized on nickel-coated 96-well microtiter plates through a histidine tag (His₆-tag), screened for transacylation of 1-phenylethanol in isooctane, and analyzed by GC. The highest enantioselectivity was shown by the double mutant Y93L/L367I. This enzyme variant gave an E value of 100 (R), which is a dramatic improvement on the wild-type CalA (E=3). This variant also showed high to excellent enantioselectivity for other secondary alcohols tested.

Try the library: A method is reported for screening lipase libraries for the enantioselective transacylation of sec-alcohols in organic solvents. This could be useful for creating enantioselective lipase variants for synthetic applications such as the dynamic kinetic resolution of alcohols and amines. The method could also be applied to other His₆-tagged enzymes and other reactions.

Existing methods for the covalent functionalization of nanoparticles rely on kinetically controlled reactions, and largely lack the sophistication of the preeminent oligonucleotide-based noncovalent strategies. Here we report the application of dynamic covalent chemistry for the reversible modification of nanoparticle (NP) surface functionality, combining the benefits of non-biomolecular covalent chemistry with the favorable features of equilibrium processes. A homogeneous monolayer of nanoparticle-bound hydrazones can undergo quantitative dynamic covalent exchange. The pseudomolecular nature of the NP system allows for the in situ characterization of surface-bound species, and real-time tracking of the exchange reactions. Furthermore, dynamic covalent exchange offers a simple approach for reversibly switching—and subtly tuning—NP properties such as solvophilicity.

Ligand swap shop: Dynamic covalent hydrazone exchange within a homogeneous monolayer bound to the surface of gold nanoparticles is tracked in real time. The introduction of appropriately functionalized aldehyde exchange units allows reversible tuning of nanoparticle solvophilicity and presents a generalizable covalent approach to postsynthetic modification of nanoparticle functionalization and properties.

Allosteric synthetic receptors are difficult to access by design. Herein we report a dynamic combinatorial strategy towards such systems based on the simultaneous use of two different templates. Through a process of simultaneous casting (the assembly of a library member around a template) and molding (the assembly of a library member inside the binding pocket of a template), a Russian-doll-like termolecular complex was obtained with remarkable selectivity. Analysis of the stepwise formation of the complex indicates that binding of the two partners by the central macrocycle exhibits significant positive cooperativity. Such allosteric systems represent hubs that may have considerable potential in systems chemistry.

Mix and match: Using a dynamic combinatorial approach, two templates, γ-cyclodextrin (γ-CD) and an ammonium salt, were employed to simultaneously perform casting and molding of dynamic macrocycles (see picture). Binding of the templates by the macrocycle exhibits positive cooperativity forming a Russian-doll-like termolecular complex.