Category Archives: CIDNP

A Novel Tri-Enzyme System in Combination with Laser-Driven NMR Enables Efficient Nuclear Polarization of Biomolecules in Solution

Lee, J.H. and S. Cavagnero, A Novel Tri-Enzyme System in Combination with Laser-Driven NMR Enables Efficient Nuclear Polarization of Biomolecules in Solution. The Journal of Physical Chemistry B, 2013. 117(20): p. 6069-6081.

http://dx.doi.org/10.1021/jp4010168

NMR is an extremely powerful, yet insensitive technique. Many available nuclear polarization methods that address sensitivity are not directly applicable to low-concentration biomolecules in liquids and are often too invasive. Photochemically induced dynamic nuclear polarization (photo-CIDNP) is no exception. It needs high-power laser irradiation, which often leads to sample degradation, and photosensitizer reduction. Here, we introduce a novel tri-enzyme system that significantly overcomes the above challenges, rendering photo-CIDNP a practically applicable technique for NMR sensitivity enhancement in solution. The specificity of the nitrate reductase (NR) enzyme is exploited to selectively in situ reoxidize the reduced photo-CIDNP dye FMNH2. At the same time, the oxygen-scavenging ability of glucose oxidase (GO) and catalase (CAT) is synergistically employed to prevent sample photodegradation. The resulting tri-enzyme system (NR-GO-CAT) enables prolonged sensitivity-enhanced data collection in 1D and 2D heteronuclear NMR, leading to the highest photo-CIDNP sensitivity enhancement (48-fold relative to SE-HSQC) achieved to date for amino acids and polypeptides in solution. NR-GO-CAT extends the concentration limit of photo-CIDNP NMR down to the low micromolar range. In addition, sensitivity (relative to the reference SE-HSQC) is found to be inversely proportional to sample concentration, paving the way for the future analysis of even more diluted samples.

Bacteriopheophytin a in the active branch of the reaction center of rhodobacter sphaeroides is not disturbed by the protein matrix as shown by 13C photo-CIDNP MAS NMR

Sai Sankar Gupta, K.B., et al., Bacteriopheophytin a in the Active Branch of the Reaction Center of Rhodobacter sphaeroides Is Not Disturbed by the Protein Matrix as Shown by 13C Photo-CIDNP MAS NMR. The Journal of Physical Chemistry B, 2013. 117(12): p. 3287-3297.

http://www.ncbi.nlm.nih.gov/pubmed/23452037

The electronic structure of bacteriopheophytin a (BPhe a), the primary electron acceptor (PhiA) in photosynthetic reaction centers (RCs) of the purple bacterium Rhodobacter sphaeroides, is investigated by photochemically induced dynamic nuclear polarization (photo-CIDNP) magic-angle spinning (MAS) NMR spectroscopy at atomic resolution. By using various isotope labeling systems, introduced by adding different (13)C selectively labeled delta-aminolevulinic acid precursors in the growing medium of R. sphaeroides wild type (WT), we were able to extract light-induced (13)C NMR signals originating from the primary electron acceptor. The assignments are backed by theoretical calculations. By comparison of these chemical shifts to those obtained from monomeric BPhe a in solution, it is demonstrated that PhiA in the active branch appears to be electronically close to free bacteriopheophytin. Hence, there is little effect of the protein surrounding on the cofactor functionally which contributes with its standard redox potential to the electron transfer process that is asymmetric.

Bacteriopheophytin a in the active branch of the reaction center of rhodobacter sphaeroides is not disturbed by the protein matrix as shown by 13C photo-CIDNP MAS NMR

Sai Sankar Gupta, K.B., et al., Bacteriopheophytin a in the Active Branch of the Reaction Center of Rhodobacter sphaeroides Is Not Disturbed by the Protein Matrix as Shown by 13C Photo-CIDNP MAS NMR. The Journal of Physical Chemistry B, 2013. 117(12): p. 3287-3297.

http://www.ncbi.nlm.nih.gov/pubmed/23452037

The electronic structure of bacteriopheophytin a (BPhe a), the primary electron acceptor (PhiA) in photosynthetic reaction centers (RCs) of the purple bacterium Rhodobacter sphaeroides, is investigated by photochemically induced dynamic nuclear polarization (photo-CIDNP) magic-angle spinning (MAS) NMR spectroscopy at atomic resolution. By using various isotope labeling systems, introduced by adding different (13)C selectively labeled delta-aminolevulinic acid precursors in the growing medium of R. sphaeroides wild type (WT), we were able to extract light-induced (13)C NMR signals originating from the primary electron acceptor. The assignments are backed by theoretical calculations. By comparison of these chemical shifts to those obtained from monomeric BPhe a in solution, it is demonstrated that PhiA in the active branch appears to be electronically close to free bacteriopheophytin. Hence, there is little effect of the protein surrounding on the cofactor functionally which contributes with its standard redox potential to the electron transfer process that is asymmetric.

Creating Long-Lived Spin States at Variable Magnetic Field by Means of Photochemically Induced Dynamic Nuclear Polarization

Kiryutin, A.S., et al., Creating Long-Lived Spin States at Variable Magnetic Field by Means of Photochemically Induced Dynamic Nuclear Polarization. The Journal of Physical Chemistry Letters, 2012. 3(13): p. 1814-1819.

http://dx.doi.org/10.1021/jz3005046

We have shown that long-lived spin states (LLS) can be selectively populated by photogenerated chemically induced dynamic nuclear polarization (CIDNP) over a wide range of magnetic fields. Relaxation times of LLS of the beta-CH2 protons in N-acetyl histidine and partially deuterated histidine have been measured. Our experiments demonstrate that CIDNP enables creating LLS in the amino acid in a field range of up to a few Tesla and that their lifetimes can be 45 times longer than T1. The advantage of the method is thus two-fold: it allows one to accumulate high levels of spin hyperpolarization and to preserve them for periods of time far exceeding T1. Therefore, photo-CIDNP is a technique suitable for creating long-lived spin order in biologically relevant molecules.

Creating Long-Lived Spin States at Variable Magnetic Field by Means of Photochemically Induced Dynamic Nuclear Polarization

Kiryutin, A.S., et al., Creating Long-Lived Spin States at Variable Magnetic Field by Means of Photochemically Induced Dynamic Nuclear Polarization. The Journal of Physical Chemistry Letters, 2012. 3(13): p. 1814-1819.

http://dx.doi.org/10.1021/jz3005046

We have shown that long-lived spin states (LLS) can be selectively populated by photogenerated chemically induced dynamic nuclear polarization (CIDNP) over a wide range of magnetic fields. Relaxation times of LLS of the beta-CH2 protons in N-acetyl histidine and partially deuterated histidine have been measured. Our experiments demonstrate that CIDNP enables creating LLS in the amino acid in a field range of up to a few Tesla and that their lifetimes can be 45 times longer than T1. The advantage of the method is thus two-fold: it allows one to accumulate high levels of spin hyperpolarization and to preserve them for periods of time far exceeding T1. Therefore, photo-CIDNP is a technique suitable for creating long-lived spin order in biologically relevant molecules.

COST summer school 2012 on Spin-Hyperpolarization

COST summer school 2012 on Spin-Hyperpolarization 

Lorentz Center, Leiden, The Netherlands, 29 Oct – 2 Nov 2012 

Organizers: Arno Kentgens & Joerg Matysik 

http://www.lorentzcenter.nl/lc/web/2012/526/info.php3?wsid=526&venue=Snellius

To strengthen and link European efforts on hyperpolarization, the COST Network EUROHyperPOL has been set up (www.eurohyperpol.eu). Annual summer schools presenting an overview and common grounds on the field will be organized. 

PhD students & young postdocs are now invited to apply. Maximum number of students is limited to 20. Please provide a short cv and statement of motivation via our Lorentz website. 

Participants of the network are especially encouraged to apply. Costs for workshop & accomodation (and possibly travel) will be covered. 

Deadline for application is June 11, 2012.

COST summer school 2012 on Spin-Hyperpolarization

COST summer school 2012 on Spin-Hyperpolarization 

Lorentz Center, Leiden, The Netherlands, 29 Oct – 2 Nov 2012 

Organizers: Arno Kentgens & Joerg Matysik 

http://www.lorentzcenter.nl/lc/web/2012/526/info.php3?wsid=526&venue=Snellius

To strengthen and link European efforts on hyperpolarization, the COST Network EUROHyperPOL has been set up (www.eurohyperpol.eu). Annual summer schools presenting an overview and common grounds on the field will be organized. 

PhD students & young postdocs are now invited to apply. Maximum number of students is limited to 20. Please provide a short cv and statement of motivation via our Lorentz website. 

Participants of the network are especially encouraged to apply. Costs for workshop & accomodation (and possibly travel) will be covered. 

Deadline for application is June 11, 2012.

Spin filtering neutrons with a proton target dynamically polarized using photo-excited triplet states

Haag, M., et al., Spin filtering neutrons with a proton target dynamically polarized using photo-excited triplet states. Nucl. Instrum. Methods Phys. Res., Sect. A, 2012. 678(0): p. 91-97.

http://dx.doi.org/10.1016/j.nima.2012.03.014

In a test of principle a neutron spin filter has been built, which is based on dynamic nuclear polarization (DNP) using photo-excited triplet states. This DNP method has advantages over classical concepts as the requirements for cryogenic equipment and magnets are much relaxed: the spin filter is operated in a field of 0.3 T at a temperature of about 100 K and has performed reliably over periods of several weeks. The neutron beam was also used to analyze the polarization of the target employed as a spin filter. We obtained an independent measurement of the proton spin polarization of ∼ 0.13 in good agreement with the value determined with NMR. Moreover, the neutron beam was used to measure the proton spin polarization as a function of position in the naphthalene sample. The polarization was found to be homogeneous, even at low laser power, in contradiction to existing models describing the photo-excitation process.

Spin filtering neutrons with a proton target dynamically polarized using photo-excited triplet states

Haag, M., et al., Spin filtering neutrons with a proton target dynamically polarized using photo-excited triplet states. Nucl. Instrum. Methods Phys. Res., Sect. A, 2012. 678(0): p. 91-97.

http://dx.doi.org/10.1016/j.nima.2012.03.014

In a test of principle a neutron spin filter has been built, which is based on dynamic nuclear polarization (DNP) using photo-excited triplet states. This DNP method has advantages over classical concepts as the requirements for cryogenic equipment and magnets are much relaxed: the spin filter is operated in a field of 0.3 T at a temperature of about 100 K and has performed reliably over periods of several weeks. The neutron beam was also used to analyze the polarization of the target employed as a spin filter. We obtained an independent measurement of the proton spin polarization of ∼ 0.13 in good agreement with the value determined with NMR. Moreover, the neutron beam was used to measure the proton spin polarization as a function of position in the naphthalene sample. The polarization was found to be homogeneous, even at low laser power, in contradiction to existing models describing the photo-excitation process.

Electron Spin Density Distribution in the Special Pair Triplet of Rhodobacter sphaeroides R26 Revealed by Magnetic Field Dependence of the Solid-State Photo-CIDNP Effect

Thamarath, S.S., et al., Electron Spin Density Distribution in the Special Pair Triplet of Rhodobacter sphaeroides R26 Revealed by Magnetic Field Dependence of the Solid-State Photo-CIDNP Effect. J. Am. Chem. Soc., 2012. 134(13): p. 5921-5930.

http://dx.doi.org/10.1021/ja2117377

Photo-CIDNP (photochemically induced dynamic nuclear polarization) can be observed in frozen and quinone-blocked photosynthetic reaction centers (RCs) as modification of magic-angle spinning (MAS) NMR signal intensity under illumination. Studying the carotenoidless mutant strain R26 of Rhodobacter sphaeroides, we demonstrate by experiment and theory that contributions to the nuclear spin polarization from the three-spin mixing and differential decay mechanism can be separated from polarization generated by the radical pair mechanism, which is partially maintained due to differential relaxation (DR) in the singlet and triplet branch. At a magnetic field of 1.4 T, the latter contribution leads to dramatic signal enhancement of about 80 000 and dominates over the two other mechanisms. The DR mechanism encodes information on the spin density distribution in the donor triplet state. Relative peak intensities in the photo-CIDNP spectra provide a critical test for triplet spin densities computed for different model chemistries and conformations. The unpaired electrons are distributed almost evenly over the two moieties of the special pair of bacteriochlorophylls, with only slight excess in the L branch.

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