Artificial Metalloenzymes: Reaction Scope and Optimization Strategies.

The incorporation of a synthetic, catalytically competent metallocofactor into a protein scaffold to generate an artificial metalloenzyme (ArM) has been explored since the late 1970's. Progress in the ensuing years was limited by the tools available for both organometallic synthesis and protein engineering. Advances in both of these areas, combined with increased appreciation of the potential benefits of combining attractive features of both homogeneous catalysis and enzymatic catalysis, led to a resurgence of interest in ArMs starting in the early 2000's.

Directed evolution of artificial metalloenzymes for in vivo metathesis.

The field of biocatalysis has advanced from harnessing natural enzymes to using directed evolution to obtain new biocatalysts with tailor-made functions. Several tools have recently been developed to expand the natural enzymatic repertoire with abiotic reactions. For example, artificial metalloenzymes, which combine the versatile reaction scope of transition metals with the beneficial catalytic features of enzymes, offer an attractive means to engineer new reactions.

Library design and screening protocol for artificial metalloenzymes based on the biotin-streptavidin technology.

Artificial metalloenzymes (ArMs) based on the incorporation of a biotinylated metal cofactor within streptavidin (Sav) combine attractive features of both homogeneous and enzymatic catalysts. To speed up their optimization, we present a streamlined protocol for the design, expression, partial purification and screening of Sav libraries. Twenty-eight positions have been subjected to mutagenesis to yield 335 Sav isoforms, which can be expressed in 24-deep-well plates using autoinduction medium.

Profluorescent substrates for the screening of olefin metathesis catalysts.

Herein we report on a 96-well plate assay based on the fluorescence resulting from the ring-closing metathesis of two profluorophoric substrates. To demonstrate the validity of the approach, four commercially available ruthenium-metathesis catalysts were evaluated in six different solvents. The results from the fluorescent assay agree well with HPLC conversions, validating the usefulness of the approach.

Switchable 3D networks by light controlled π-stacking of azobenzene macrocycles.

Azobenzene macrocycles were designed for switchable π-stacking interaction. After efficient preparation and characterization of azobenzene macrocycles containing electron rich as well as electron poor elements a dimeric analogue was synthesized, which formed reversibly 3D-networks. Gel formation was observed with aromatic solvents representing the first example of this type based on switchable azobenzene macrocycles.

meta-Oligoazobiphenyls - synthesis via site-selective Mills reaction and photochemical properties.

The investigation of multi-photochromic compounds constitutes a great challenge, not only from a synthetic point of view, but also with respect to the analysis of the photochemical properties. In this context we designed a novel strategy to access meta-oligoazobiphenyls via site-selective Mills reaction and Suzuki cross-coupling in a highly efficient iterative way. Photochemical examination of the resulting monomeric and oligomeric azo compounds revealed that the overall degree of switching was independent of the connected azo-units.

Synthesis and photochemical properties of oligo-ortho-azobenzenes.

Azobenzenes have attracted great interest in recent years because of their ability to change conformation upon irradiation. This property has been featured in several applications not only in organic chemistry but also in biology. Even though monoazobenzenes have been extensively studied and documented in the literature, only a few methods are available for the synthesis of oligo-ortho-azobenzenes.

A chiral cyclotrisazobiphenyl: synthesis and photochemical properties.

A chiral cyclotrisazobiphenyl macrocycle was synthesized conveniently in three steps from the literature known 3,3'-diaminobimesityl in 37-38% overall yield. Irradiation with 302 nm, 365 nm or visible light allows access to different photostationary states (PSSs). These PSSs can be conveniently read out by CD-spectroscopy as each of them exhibits a positive, a negative, or no signal, respectively, at 275 nm.

Oligoazobenzenophanes--synthesis, photochemistry and properties.

The possibility to modulate molecules reversibly by light has been fascinating chemists early on. One of the most powerful photochromic classes of compounds are azobenzenes, which have been incorporated in multiple molecular systems to alter their functionality. Recently, the incorporation of azobenzenes into macrocyclic scaffolds, azobenzenophanes, revealed a novel aspect of this interesting photoswitch.

Synthesis and isomerization studies of cyclotrisazobiphenyl.

We report an efficient synthesis of cyclotris[(E)-3'-(biphenyl-3-yldiazenyl)] compounds (CTBs). An unsubstituted CTB molecule is accessible in four steps in 10% yield overall, whereas a hexa(methoxymethyl ether) CTB analogue was prepared in nine steps (26% yield). The final macrocyclization step was accomplished in up to 80% yield by using a metal-template effect.

Oligoazobenzenes--switching in a new dimension.

A new synthesis of cyclotrisazobenzene with different substituents was developed with yields of up to 30%. Solid-state structures of cyclotrisazobenzene as well as the tert-butyl derivative were obtained. Also, the photochromic properties and the complexation behaviour with alkali metal ions of this class of molecules were investigated.