Multiplexing NMR experiments by direct detection of multiple free induction decays (FIDs) in a single experiment offers a dramatic increase in the spectral information content and often yields... Show moreMultiplexing NMR experiments by direct detection of multiple free induction decays (FIDs) in a single experiment offers a dramatic increase in the spectral information content and often yields significant improvement in sensitivity per unit time. Experiments with multi-FID detection have been designed with both homonuclear and multinuclear acquisition, and the advent of multiple receivers on commercial spectrometers opens up new possibilities for recording spectra from different nuclear species in parallel. Here we provide an extensive overview of such techniques, designed for applications in liquid-and solidstate NMR as well as in hyperpolarized samples. A brief overview of multinuclear MRI is also provided, to stimulate cross fertilization of ideas between the two areas of research (NMR and MRI). It is shown how such techniques enable the design of experiments that allow structure elucidation of small molecules from a single measurement. Likewise, in biomolecular NMR experiments multi-FID detection allows complete resonance assignment in proteins. Probes with multiple RF microcoils routed to multiple NMR receivers provide an alternative way of increasing the throughput of modern NMR systems, effectively reducing the cost of NMR analysis and increasing the information content at the same time. Solidstate NMR experiments have also benefited immensely from both parallel and sequential multi-FID detection in a variety of multi-dimensional pulse schemes. We are confident that multi-FID detection will become an essential component of future NMR methodologies, effectively increasing the sensitivity and information content of NMR measurements. (c) 2021 Elsevier B.V. All rights reserved. Show less
Photosynthesis in plants, algae and cyanobacteria releases oxygen and is referred to as oxygenic photosynthesis. Among all the photosynthetic reaction centers only PSII provides a redox potential... Show morePhotosynthesis in plants, algae and cyanobacteria releases oxygen and is referred to as oxygenic photosynthesis. Among all the photosynthetic reaction centers only PSII provides a redox potential sufficiently strong for water oxidation. While the electron flow in PSII is strictly asymmetric, in PSI different levels of bidirectionality indicate functional flexibility of this complex. Photo-CIDNP is non-Boltzmann nuclear magnetization caused by photochemical reactions and can be observed by NMR spectroscopy as strongly enhanced absorptive or emissive signals. In this thesis photo-CIDNP solid state NMR with selective isotope labeling is applied to get direct access to the heart of large PSII and PSI photosynthetic complexes in intact and isolated systems of Spirodela oligorrhiza and Synechocyctis. For the first time the direct observation of selective atoms within the heart of the PSII and PSI complexes by experiment s on entire plants and whole cells is reported. In this way the conservation of the electronic structure of the PSII electron donor at various levels of biological preparations have been addressed and the electron spin density (ρi) in the active cofactors of PSI has been constructed. In addition the functional heterogeneity of the PSI electron donor among different plant species was probed. Show less
Photosynthetic reaction centers (RCs) from plants, heliobacteria and green sulphur bacteria has been investigated with photochemically induced dynamic nuclear polarization (photo-CIDNP) MAS NMR. In... Show morePhotosynthetic reaction centers (RCs) from plants, heliobacteria and green sulphur bacteria has been investigated with photochemically induced dynamic nuclear polarization (photo-CIDNP) MAS NMR. In photosystem (PS) I of spinach, all signals appear negative which is proposed by a predominance of the three spin mixing (TSM) over the differential decay (DD) mechanism. There are contrasting magnetic-field dependence of photo-CIDNP of PSI and PSII. For PSII the optimal NMR enhancement factor of ~5000 is observed at 4.7 T, while the strongest light-induced signals of PSI are at 9.4 T. The simulations indicate that difference between bacterial RCs and plant PS I can be due to an increase of the exchange coupling between the donor and acceptor radicals. In the RCs of Chlorobium tepidum the spectra appear negative and can be tentatively assigned to two bacterio chlorophyll a molecules of the donor. The spectral pattern obtained from membrane fragments of Heliobacillus mobilis at 4.7 T, appear to be both positive and negative, which is similar to the pattern observed in the RCs of plant PSII and RCs of Rhodobacter sphaeroides R-26. However, unlike the other RCs, in this system, at 17.6 T, the positive signals undergo a sign change and appear negative. Show less
The G protein coupled receptor rhodopsin was characterised by physical chemical methods like solid-state NMR, FTIR and UV/Vis spectroscopy. Goal of the research was to determine the impact of... Show moreThe G protein coupled receptor rhodopsin was characterised by physical chemical methods like solid-state NMR, FTIR and UV/Vis spectroscopy. Goal of the research was to determine the impact of steric and electronic properties of the retinal ligand on the rate and efficiency of the photochemical reaction of this light activated receptor. First the required 13C labelled and chemically modified retinal derivatives were obtained by chemical synthesis. Subsequently, solid-state 13C NMR was used as a tool to characterise the electronic structure of the native ligand bound to rhodopsin, while FTIR difference spectroscopy was applied to determine the effect retinal ligands that were modified in the isomerisation region. It transpires that the combined approach of synthesis and spectroscopic techniques can reveal fundamental aspects of the interplay of the electronic properties and the spatial arrangement of the ligand that may ultimately allow a more profound understanding of the activation of GPCRs, in addition to knowledge about the ultrafast and efficient isomerisation of the retinylidene chromophore in rhodopsin Show less
