In Situ Observation of Photoswitching by NMR Spectroscopy: A Photochemical Analogue to the Exchange Spectroscopy Experiment.

We present 1D and 2D NMR experiments that provide in situ insights into photoinduced isomerizations. Irradiation during the mixing period of an exchange spectroscopy (EXSY) experiment leads to characteristic cross peaks in 2D spectra. The phototriggered exchange of magnetization occurring in photoswitchable (Z)- and (E)-isomers of three selected azo compounds provides information on the dynamic E/Z equilibria. We report the dependence of the diagonal-to-cross-peak ratio on concentration, light intensity, and mixing time. In analogy to exchange spectroscopy, this ratio mirrors the efficiency of light induced molecular transformations. Furthermore, we present a time-saving 1D version and a combined light/phase cycle scheme for enhanced detectability of photoinduced changes in the spectrum. This insight into light-induced structural changes is highly suited to study macromolecules, in which photoswitchable units trigger conformational changes.

Solvent-independent determination of heteroatom protonation states from NMR spectra by differential deuterium isotope shifts.

The NMR-spectroscopy based structure elucidation of organic molecules containing heteroatoms is often obstructed by the difficulties in determining the heteroatom protonation states. Here we describe a simple but broadly applicable approach for the determination of the protonation states of heteroatoms. Differential deuterium isotope shifts observed upon the addition of small amounts of H2O or D2O to any solvent can be used to determine the protonation states of heteroatoms.

High Resolution for Chemical Shifts and Scalar Coupling Constants: The 2D Real-Time J-Upscaled PSYCHE-DIAG.

The facile determination of chemical shift and scalar coupling constants in NMR spectra is often prevented by spectral overlap and limited resolution. Here, we present a high-resolution NMR experiment for the simultaneous detection of both resonance frequencies and coupling patterns even with small J-values. A PSYCHE-decoupled DIAG (Pure Shift Yielded by Chirp Excitation- DIAGonal) experiment, which resolves chemical shift in the indirect dimension of a 2D experiment is combined with real-time J-upscaling in order to visualize small coupling constants that would otherwise be hidden in the linewidth of a regular proton or DIAG spectrum.

Oxidative Decarboxylation of Short-Chain Fatty Acids to 1-Alkenes.

The enzymatic oxidative decarboxylation of linear short-chain fatty acids (C4:0-C9:0) employing the P450 monooxygenase OleT, O2 as the oxidant, and NAD(P)H as the electron donor gave the corresponding terminal C3 to C8  alkenes with product titers of up to 0.93 g L(-1) and TTNs of >2000. Key to this process was the construction of an efficient electron-transfer chain employing putidaredoxin CamAB in combination with NAD(P)H recycling at the expense of glucose, formate, or phosphite. This system allows for the biocatalytic production of industrially important 1-alkenes, such as propene and 1-octene, from renewable resources for the first time.

Monitoring fast chemical processes by reaction-interrupted excitation transfer (ExTra) NMR spectroscopy.

NMR spectroscopy is generally used to investigate molecules under equilibrium conditions. Despite recent technological and methodogical developments to study on-going reactions, tracing the fate of individual atoms during an irreversible chemical reaction is still a challenging and elaborate task. Reaction-interrupted excitation transfer (ExTra) NMR provides a selective tracking of resonances from atoms, which undergo chemical conversion. We show that reactions triggered either by rapid mixing or by photo-excitation can be conveniently followed at a sub-second time scale using standard NMR equipment. In ExTra NMR we use the selectively inverted magnetization of a selected atom to follow its conversion in the course of a fast chemical reaction. The chemical reaction has to be started within the relaxation period of an initial inverting 180° pulse. The presented protocol provides a generally applicable NMR method for reaction monitoring.

Synthesis of novel ligands targeting phenazine biosynthesis proteins as a strategy for antibiotic intervention.

ABSTRACT: In this contribution, we report synthetic strategies towards potential ligands for the study of binding differences between PhzE, the first enzyme in the biosynthesis of phenazines, and the related enzyme anthranilate synthase. The ligands were designed with the overriding goal to develop new antibiotics via downregulation of phenazine biosynthesis.