Category Archives: CIDNP

Photo-induced radical polarization and liquid-state dynamic nuclear polarization using fullerene nitroxide derivatives #DNPNMR

Liu, G., et al., Photo-induced radical polarization and liquid-state dynamic nuclear polarization using fullerene nitroxide derivatives. Phys. Chem. Chem. Phys., 2017. 19(47): p. 31823-31829.

https://www.ncbi.nlm.nih.gov/pubmed/29171613

We report on radical polarization and optically-driven liquid DNP using nitroxide radicals functionalized by photoexcitable fullerene derivatives. Pulse laser excitation of the fullerene moiety leads to transient nitroxide radical polarization that is one order of magnitude larger than that at the Boltzmann equilibrium. The life time of the radical polarization increases with the size of the fullerene derivative and is correlated with the electronic spin-lattice relaxation time T1e. Overhauser NMR signal enhancements of toluene solvent protons were observed under steady-state illumination, which replaced microwave irradiation.

Photo-induced radical polarization and liquid-state dynamic nuclear polarization with fullerene nitroxide derivatives

DNP without microwave radiation? A very interesting approach.

Liu, G., et al., Photo-induced radical polarization and liquid-state dynamic nuclear polarization with fullerene nitroxide derivatives. Phys. Chem. Chem. Phys., 2017.

http://dx.doi.org/10.1039/C7CP06073D

We report on radical polarization and optically-driven liquid DNP with nitroxide radicals functionalized by photoexcitable fullerene derivatives. Pulse laser excitation of the fullerene moiety leads to a transient nitroxide radical polarization that is one order of magnitude larger than at Boltzmann equilibrium. Life time of radical polarization increases with size of the fullerene derivative and correlates with the electronic spin lattice relaxation time T1e. Overhauser NMR signal enhancements of toluene solvent protons were observed under steady-state illumination, which replaced microwave irradiation.

[NMR] PhD Position, Biological Solid-state NMR, Univ. Leipzig

From the Ampere Magnetic Resonance List

PhD Position, Biological Solid-state NMR, Univ. Leipzig

In the group of Jörg Matysik (Analytical Chemistry, University of Leipzig) is a PhD position available in the field of light-induced effects in biological NMR/MRI. Candidates should have either background in magnetic resonance or in biological sample preparation. The interdisciplinary team is embedded in an international network. Applications of highly qualified candidates (cover letter, CV, statement of research interests and qualifications, copies of certificates and transcripts) should be sent to Prof. J. Matysik (joerg.matysik@uni-leipzig.de). Further information is available at https://analytik.chemie.uni-leipzig.de/start/ak-prof-matysik. Evaluation of applications will continue until the position is filled. The position will be for three years and payed according to TV-L E 13, 50 %.

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Prof. Dr. Jörg Matysik

joerg.matysik@uni-leipzig.de

skype: joerg.matysik

http://www.cidnp.net

http://analytik.chemie.uni-leipzig.de

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Institut für Analytische Chemie

Universität Leipzig

Linnéstr. 3 (visit)

Johannisallee 29 (mail)

D-04103 Leipzig

Tel: +49-341-9736112 (direct)

Tel: +49-341-9736100 (Secr.)

Fax: +49-341-9736115

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This is the AMPERE MAGNETIC RESONANCE mailing list:

http://www.drorlist.com/nmrlist.html

NMR web database:

http://www.drorlist.com/nmr.html

Photochemically Induced Dynamic Nuclear Polarization Observed by Solid-State NMR in a Uniformly (13)C-Isotope-Labeled Photosynthetic Reaction Center

Paul, S., et al., Photochemically Induced Dynamic Nuclear Polarization Observed by Solid-State NMR in a Uniformly (13)C-Isotope-Labeled Photosynthetic Reaction Center. J Phys Chem B, 2015. 119(43): p. 13897-903.

http://www.ncbi.nlm.nih.gov/pubmed/26110356

A sample of solubilized and quinone-depleted reaction centers from the purple bacterium Rhodobacter (R.) sphaeroides wild type has been prepared entirely (13)C and (15)N isotope labeled at all positions of the protein as well as of the cofactors. In this sample, the occurrence of the solid-state photo-CIDNP (photochemically induced dynamic nuclear polarization) effect has been probed by (13)C solid-state magic-angle spinning NMR under illumination. Under continuous illumination, signal intensities are modified by the three-spin mixing (TSM) mechanism. Time-resolved illumination experiments reveal the occurrence of light-induced nuclear polarization on the time scale of hundreds of microseconds, initially dominated by the transient polarization of the singlet branch of the radical-pair mechanism. A first kinetic analysis shows that the lifetime of the polarization from the singlet branch, indicated by the enhanced absorptive intensities of the signals from aliphatic carbons, is significantly extended. Upon arrival of the polarization from the triplet decay branch, emissive polarization caused by the TSM mechanism is observed. Also, this arrival is significantly delayed. The decay of TSM polarization occurs in two steps, assigned to intra- and intermolecular spin diffusion.

Strategy for Enhancement of (13)C-Photo-CIDNP NMR Spectra by Exploiting Fractional (13)C-Labeling of Tryptophan

Eisenreich, W., et al., Strategy for Enhancement of (13)C-Photo-CIDNP NMR Spectra by Exploiting Fractional (13)C-Labeling of Tryptophan. J Phys Chem B, 2015. 119(43): p. 13934-43.

http://www.ncbi.nlm.nih.gov/pubmed/2624459

The photo-CIDNP effect has proven to be useful to strongly enhance NMR signals of photochemically active proteins simply by irradiation with light. The evolving characteristic patterns of enhanced absorptive and emissive NMR lines can be exploited to elucidate the photochemistry and photophysics of light-driven protein reactions. In particular, by the assignment of (13)C NMR resonances, redox-active amino acids may be identified and thereby electron-transfer pathways unraveled, in favorable cases, even with (13)C at natural abundance. If signal enhancement is weak, uniform (13)C isotope labeling is traditionally applied to increase the signal strength of protein (13)C NMR. However, this typically leads to cross relaxation, which transfers light-induced nuclear-spin polarization to adjacent (13)C nuclei, thereby preventing an unambiguous analysis of the photo-CIDNP effect. In this contribution, two isotope labeling strategies are presented; one leads to specific but ubiquitous (13)C labeling in tryptophan, and the other is based on fractional isotope labeling affording sets of isotopologs with low probability of next-neighbor isotope accumulation within individual tryptophan molecules. Consequently, cross relaxation is largely avoided while the signal enhancement by (13)C enrichment is preserved. This results in significantly simplified polarization patterns that are easier to analyze with respect to the generation of light-generated nuclear-spin polarization.

Low field photo-CIDNP in the intramolecular electron transfer of naproxen-pyrrolidine dyads

Magin, I.M., et al., Low field photo-CIDNP in the intramolecular electron transfer of naproxen-pyrrolidine dyads. Phys Chem Chem Phys, 2016. 18(2): p. 901-7.

http://www.ncbi.nlm.nih.gov/pubmed/26648262

Photoinduced processes with partial (exciplex) and full charge transfer in donor-acceptor systems are of interest because they are frequently used for modeling drug-protein binding. Low field photo-CIDNP (chemically induced dynamic nuclear polarization) for these processes in dyads, including the drug, (S)- and (R)-naproxen and (S)-N-methyl pyrrolidine in solutions with strong and weak permittivity have been measured. The dramatic influence of solvent permittivity on the field dependence of the N-methyl pyrrolidine (1)H CIDNP effects has been found. The field dependences of both (R,S)- and (S,S)-dyads in a polar medium are the curves with a single extremum in the area of the S-T+ terms intersection. Moreover, the CIDNP field dependences of the same protons measured in a low polar medium present curves with several extrema. The shapes of the experimental CIDNP field dependence with two extrema have been described using the Green function approach for the calculation of the CIDNP effects in the system without electron exchange interactions. The article discusses the possible causes of the differences between the CIDNP field dependence detected in a low-permittivity solvent with the strong Coulomb interactions and in a polar solvent.

[NMR] PhD Position – Uni Leipzig – Solid-state NMR on photoreceptor protein

From the Ampere Magnetic Resonance List

PhD Position – Uni Leipzig – Solid-state NMR on photoreceptor protein

The Institute of Analytical Chemistry at the University of Leipzig invites applications for a PhD position in the field of solid-state NMR characterization of photoreceptors. To be appointed from 01.02.16 or later. The position is limited to 3 years.

The NMR research group of Jörg Matysik works on the development of hyperpolarization and optical NMR techniques for studying photo/spin-chemically relevant systems. The successful candidate will work on an interdisciplinary research project combining biochemical work and solid-state NMR spectroscopy. This DFG financed project aims for understanding of the electronic orbital structure of the chromophore in photoreceptors of the phytochrome family.

The candidate should hold a MSc degree and be highly motivated with a strong interest in protein chemistry and biophysics. Previous experience biochemistry of proteins and is desirable. Experience in the field of magnetic resonance spectroscopy is of advantage.

For further information, please contact Jörg Matysik,

joerg.matysik@uni-leipzig.de.

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This is the AMPERE MAGNETIC RESONANCE mailing list:

http://www.drorlist.com/nmrlist.html

NMR web database:

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Photochemically Induced Dynamic Nuclear Polarization Observed by Solid-State NMR in a Uniformly C-Isotope-Labeled Photosynthetic Reaction Center

Paul, S., et al., Photochemically Induced Dynamic Nuclear Polarization Observed by Solid-State NMR in a Uniformly C-Isotope-Labeled Photosynthetic Reaction Center. J Phys Chem B, 2015.

http://www.ncbi.nlm.nih.gov/pubmed/26110356

A sample of solubilized and quinone-depleted reaction centers from the purple bacterium Rhodobacter (R.) sphaeroides wild type has been prepared entirely 13C and 15N isotope labeled at all positions of the protein as well as of the cofactors. In this sample, the occurrence of the solid-state photo-CIDNP (photochemically induced dynamic nuclear polarization) effect has been probed by 13C solid-state magic-angle spinning NMR under illumination. Under continuous illumination, signal intensities are modified by the three-spin mixing (TSM) mechanism. Time-resolved illumination experiments reveal the occurrence of light-induced nuclear polarization on the time scale of hundreds of microseconds, initially dominated by the transient polarization of the singlet branch of the radical-pair mechanism. A first kinetic analysis shows that the lifetime of the polarization from the singlet branch, indicated by the enhanced absorptive intensities of the signals from aliphatic carbons, is significantly extended. Upon arrival of the polarization from the triplet decay branch, emissive polarization caused by the TSM mechanism is observed. Also, this arrival is significantly delayed. The decay of TSM polarization occurs in two steps, assigned to intra- and intermolecular spin diffusion.

Importance of polarization transfer in reaction products for interpreting and analyzing CIDNP at low magnetic fields

Pravdivtsev AN, Yurkovskaya AV, Ivanov KL, Vieth HM. Importance of polarization transfer in reaction products for interpreting and analyzing CIDNP at low magnetic fields. J Magn Reson. 2015;254(0):35-47.

http://www.ncbi.nlm.nih.gov/pubmed/25797825

The magnetic field dependence of Chemically Induced Dynamic Nuclear Polarization (CIDNP) was studied for the amino acids N-acetyl histidine, N-acetyl tryptophan and N-acetyl tyrosine. It is demonstrated that at low field CIDNP is strongly affected by polarization redistribution in the diamagnetic molecules. Such a polarization transfer is of coherent nature and is due to spin coherences formed together with non-equilibrium population of the spin states. These coherences clearly manifest themselves in an oscillatory time dependence of polarization. Polarization transfer effects are most pronounced at nuclear spin Level Anti-Crossings (LACs), which also result in sharp features in the CIDNP field dependence. Thus, polarization transfer is an important factor, which has to be taken into account in order to interpret low-field CIDNP data on both qualitative and quantitative level. Possible applications of polarization transfer phenomena are also discussed in the paper. In particular, the role of LACs in spin order transfer is highlighted: LACs provide a new tool for precise manipulation of spin hyperpolarization and NMR enhancement of selected target spins.

Detecting a New Source for Photochemically Induced Dynamic Nuclear Polarization in the LOV2 Domain of Phototropin by Magnetic-Field Dependent 13C NMR Spectroscopy

Kothe, G., et al., Detecting a New Source for Photochemically Induced Dynamic Nuclear Polarization in the LOV2 Domain of Phototropin by Magnetic-Field Dependent 13C NMR Spectroscopy. The Journal of Physical Chemistry B, 2014. 118(40): p. 11622-11632.

http://dx.doi.org/10.1021/jp507134y

Phototropin is a flavin mononucleotide (FMN) containing blue-light receptor, which regulates, governed by its two LOV domains, the phototropic response of higher plants. Upon photoexcitation, the FMN cofactor triplet state, 3F, reacts with a nearby cysteine to form a covalent adduct. Cysteine-to-alanine mutants of LOV domains instead generate a flavin radical upon illumination. Here, we explore the formation of photochemically induced dynamic nuclear polarization (CIDNP) in LOV2-C450A of Avena sativa phototropin and demonstrate that photo-CIDNP observed in solution 13C NMR spectra can reliably be interpreted in terms of solid-state mechanisms including a novel triplet mechanism. To minimize cross-polarization, which transfers light-induced magnetization to adjacent 13C nuclei, our experiments were performed on proteins reconstituted with specifically 13C-labeled flavins. Two potential sources for photo-CIDNP can be identified: The photogenerated triplet state, 3F, and the triplet radical pair 3(F??W+?), formed by electron abstraction of 3F from tryptophan W491. To separate the two contributions, photo-CIDNP studies were performed at four different magnetic fields ranging from 4.7 to 11.8 T. Analysis revealed that, at fields <9 T, both 3(F??W+?) and 3F contribute to photo-CIDNP, whereas at high magnetic fields, the calculated enhancement factors of 3F agree favorably with their experimental counterparts. Thus, we have for the first time detected that a triplet state is the major source for photo-CIDNP in a photoactive protein. Since triplet states are frequently encountered upon photoexcitation of flavoproteins, the novel triplet mechanism opens up new means of studying electronic structures of the active cofactors in these proteins at atomic resolution.

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