Friday, October 31, 2014

Multi-responsive cellulose nanocrystal-rhodamine conjugates – An advanced structure study by solid-state dynamic nuclear polarization (DNP) NMR


Zhao, L., et al., Multi-responsive cellulose nanocrystal-rhodamine conjugates – An advanced structure study by solid-state dynamic nuclear polarization (DNP) NMR. Phys. Chem. Chem. Phys., 2014.


Multi-stimuli responsive materials based on cellulose nanocrystals (CNC), especially using non-conventional stimuli including light, still need more explorations, to fulfill the requirement of complicated application environments. The structure determination of functional groups on CNC surface constitutes a significant challenge, partially due to their low amounts. In this study, rhodamine spiroamide groups are immobilized onto the surface of CNC leading to a hybrid compound being responsive to pH-value, heating and UV light. After the treatment with external stimuli, the fluorescent and correlated optical color change can be induced, which refers to a ring opening and closing process. Amine and amide groups in rhodamine spiroamide play the critical role during this switching process. Solid-state NMR spectroscopy coupled with sensitivity-enhanced dynamic nuclear polarization (DNP) was used to measure 13C and 15N in natural abundance, allowing the determination of structural changes during the switching process. It is shown that a temporary bond through an electrostatic interaction could be formed within the confined environment on the CNC surface during the heating treatment. The carboxyl groups on CNC surface plays a pivotal role in stabilizing the open status of rhodamine spiroamide groups.

Wednesday, October 29, 2014

Direct enzyme-substrate affinity determination by real-time hyperpolarized (13)C-MRS


Friesen-Waldner, L.J., et al., Direct enzyme-substrate affinity determination by real-time hyperpolarized (13)C-MRS. Chem Commun (Camb), 2014. 50(89): p. 13801-4.


A specialized kinetic analysis of real-time hyperpolarized [1,1,2,2-D4, 1-(13)C]choline (13)C-magnetic resonance spectroscopy enabled the determination of initial rates of metabolic enzyme activity (choline oxidase), enzyme-substrate affinity (Km), and inhibition. In a clinical MRI scanner, metabolite levels lower than 16 muM were detected at a temporal resolution of 1 s.

Monday, October 27, 2014

Primostrato Solid-State NMR Enhanced by Dynamic Nuclear Polarization: Pentacoordinated Al3+ Ions Are Only Located at the Surface of Hydrated γ-Alumina


Lee, D., et al., Primostrato Solid-State NMR Enhanced by Dynamic Nuclear Polarization: Pentacoordinated Al3+ Ions Are Only Located at the Surface of Hydrated γ-Alumina. The Journal of Physical Chemistry C, 2014.


Aluminas (Al2O3) are ubiquitous functional materials. In particular, the ?-alumina form is extensively used in research and industry as a catalyst and catalyst support. Nevertheless, a full structural description, which would aid in comprehension of its properties, is lacking and under large debate. Solid-state NMR has been used previously to study ?-alumina but is limited for certain applications, such as surface studies, due to intrinsic low sensitivity. Here, we detail the implementation of low temperature (?100 K) magic angle spinning combined with dynamic nuclear polarization (MAS-DNP) to significantly enhance the sensitivity of solid-state NMR experiments and gain structural insights into this important material. Notably, we analyze hydrophilic and hydrophobic sample preparation protocols and their implications on the sample and resulting NMR parameters. We show that the choice of preparation does not perturb the spectrum, but it does have a large effect on NMR coherence lifetimes, as does the corresponding required (hyper)polarizing agent. We use this preliminary study to optimize the absolute sensitivity of the following experiments. We then show that there are no detectable hydroxyl groups in the bulk of the material and that DNP-enhanced 1H ? 27Al cross-polarization experiments are selective to only the first surface layer, enabling a very specific study. This primostrato NMR is integrated with multiple-quantum magic angle spinning (MQMAS) and it is demonstrated, interestingly, that pentacoordinated Al3+ ions are only observed in this first surface layer. To highlight that there is no evidence of subsurface pentacoordinated Al3+, a new bulk-filtered experiment is described that can eliminate surface signals.

Friday, October 24, 2014

DNP-enhanced NMR on aligned Lipid Bilayers at ambient Temperature


Jakdetchai, O., et al., DNP-enhanced NMR on aligned Lipid Bilayers at ambient Temperature. J Am Chem Soc, 2014.


DNP-enhanced solid-state NMR has been shown to hold great potential for functional studies of membrane proteins at low temperatures due to its great sensitivity improvement. There are however numerous applications, for which experiments at ambient temperature are desirable and which would also benefit from DNP signal enhancement. Here, we demonstrate as a proof of concept that a significant signal increase for lipid bilayers under room temperature conditions can be achieved by utilizing the Overhauser effect. Experiments were carried out on aligned bilayers at 400 MHz/263 GHz using a stripline structure combined with a Fabry-Perot microwave resonator. A signal enhancement of protons of up to -10 was observed. Our results demonstrate that Overhauser DNP at high field pro-vides efficient polarization transfer within insoluble samples, which is driven by fast local molecular fluc-tuations. Furthermore, our experimental setup offers an attractive option for DNP-enhanced solid-state NMR on ordered membranes and provides a general perspective towards DNP at ambient temperatures.

Wednesday, October 22, 2014

Selective Host-Guest Interaction between Metal Ions and Metal-Organic Frameworks using Dynamic Nuclear Polarization Enhanced Solid-State NMR Spectroscopy


Guo, Z., et al., Selective Host-Guest Interaction between Metal Ions and Metal-Organic Frameworks using Dynamic Nuclear Polarization Enhanced Solid-State NMR Spectroscopy. Chemistry, 2014: p. n/a-n/a.


The host-guest interaction between metal ions (Pt2+ and Cu2+ ) and a zirconium metal-organic framework (UiO-66-NH2 ) was explored using dynamic nuclear polarization-enhanced 15 N{1 H} CPMAS NMR spectroscopy supported by X-ray absorption spectroscopy and density functional calculations. The combined experimental results conclude that each Pt2+ coordinates with two NH2 groups from the MOF and two Cl- from the metal precursor, whereas Cu2+ do not form chemical bonds with the NH2 groups of the MOF framework. Density functional calculations reveal that Pt2+ prefers a square-planar structure with the four ligands and resides in the octahedral cage of the MOF in either cis or trans configurations.

Monday, October 20, 2014

Untangling the Condensation Network of Organosiloxanes on Nanoparticles using 2D (29)Si-(29)Si Solid-State NMR Enhanced by Dynamic Nuclear Polarization


Lee, D., et al., Untangling the Condensation Network of Organosiloxanes on Nanoparticles using 2D (29)Si-(29)Si Solid-State NMR Enhanced by Dynamic Nuclear Polarization. J Am Chem Soc, 2014. 136(39): p. 13781-8.


Silica (SiO2) nanoparticles (NPs) were functionalized by silanization to produce a surface covered with organosiloxanes. Information about the surface coverage and the nature, if any, of organosiloxane polymerization, whether parallel or perpendicular to the surface, is highly desired. To this extent, two-dimensional homonuclear (29)Si solid-state NMR could be employed. However, owing to the sensitivity limitations associated with the low natural abundance (4.7%) of (29)Si and the difficulty and expense of isotopic labeling here, this technique would usually be deemed impracticable. Nevertheless, we show that recent developments in the field of dynamic nuclear polarization under magic angle spinning (MAS-DNP) could be used to dramatically increase the sensitivity of the NMR experiments, resulting in a timesaving factor of approximately 625 compared to conventional solid-state NMR. This allowed the acquisition of previously infeasible data. Using both through-space and through-bond 2D (29)Si-(29)Si correlation experiments, it is shown that the required reaction conditions favor lateral polymerization and domain growth. Moreover, the natural abundance correlation experiments permitted the estimation of (2)J(Si-O-Si)-couplings (13.8 +/- 1.4 Hz for surface silica) and interatomic distances (3.04 +/- 0.08 A for surface silica) since complications associated with many-spin systems and also sensitivity were avoided. The work detailed herein not only demonstrates the possibility of using MAS-DNP to greatly facilitate the acquisition of 2D (29)Si-(29)Si correlation spectra but also shows that this technique can be used in a routine fashion to characterize surface grafting networks and gain structural constraints, which can be related to a system's chemical and physical properties.

Friday, October 17, 2014

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.


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.

Wednesday, October 15, 2014

Long-lived localization in magnetic resonance imaging


Dumez, J.-N., et al., Long-lived localization in magnetic resonance imaging. J. Magn. Reson., 2014. 246(0): p. 27-30.


The longitudinal nuclear relaxation time, T1, sets a stringent limit on the range of information that can be obtained from magnetic resonance imaging (MRI) experiments. Long-lived nuclear spin states provide a possibility to extend the timescale over which information can be encoded in magnetic resonance. We introduce a strategy to localize an ensemble of molecules for a significantly extended duration (∼30 times longer than T1 in this example), using a spatially selective conversion between magnetization and long-lived singlet order. An application to tagging and transport is proposed.

Tuesday, October 14, 2014

Post-doctoral position at CEA-Saclay in NMR hardware development

From the Ampere Magnetic Resonance List


Post-doctoral position at CEA-Saclay in NMR hardware development

We are looking for post-doctoral candidates, to join an exciting project on the development of a new approach to increase sensitivity with NMR spectroscopy. The project aims at developing magic angle coil spinning (MACS) for high-resolution micro-detection of volume-limited biomedical substances, using Dynamic Nuclear Polarization (DNP) and is funded by the French National Science Foundation (ANR). The role of the post-doc associate will be to participate in the development of new hardware on high-field and ultra-high field spectrometers. This project is pursued in close collaboration with the University Pierre and Marie Curie and the group of Prof. Christian Bonhomme.

Post-doctoral candidates should have strong experience in electrical engineering and/or magnetic resonance hardware development (e.g. radio-frequency probes, antennas), or connected areas of experimental physics and engineering.

Funding is available for at least one year, while possibilities for up to 30 months are accessible. Salary will be commensurate with experience.

Our team (http://dsakellariou.free.fr) is part of the laboratory of structure and dynamics by magnetic resonance lab (http://iramis.cea.fr/sis2m/lsdrm/), at the Department of Material Science division of CEA (http://www.cea.fr/english-portal). The group offers a unique environment where the research activity on magnetic resonance methodology and instrumentation encompasses pulse sequence development for solid-state NMR and MRI. The CEA is located 20 km from the heart of Paris, at the center of an extremely dynamic scientific cluster (http://www.epps.fr/en/a-global-cluster/).

Interested candidates should send their full CV to Dimitrios Sakellariou (Dimitrios.Sakellariou@cea.fr) and provide three references in a cover letter.

D. Sakellariou

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Monday, October 13, 2014

Coherent Polarization Transfer Effects Are Crucial for Interpreting Low-Field CIDNP Data


Panov, M., et al., Coherent Polarization Transfer Effects Are Crucial for Interpreting Low-Field CIDNP Data. Appl. Magn. Reson., 2014. 45(9): p. 893-900.


In this work we demonstrate that low-field chemically induced dynamic nuclear polarization (CIDNP) is strongly affected by re-distribution of polarization, which is formed in the course of spin evolution in transient radical pairs, in diamagnetic reaction products. This phenomenon is of importance when the spins of the reaction product are coupled strongly meaning that spin–spin interactions between them are comparable to the differences in their Zeeman interactions with the external magnetic field. In this case, polarization transfer relies on a coherent mechanism; as a consequence, spins can acquire significant polarization even when they have no hyperfine coupling to the electron spins in the radical pairs, i.e., cannot be polarized directly by CIDNP. This is demonstrated by taking CIDNP of n-butylamine as an example: in this case only the α-CH2 protons are polarized directly, which is confirmed by high-field CIDNP, whereas the β-CH2, γ-CH2 and δ-CH3 protons get polarized only indirectly due to the transfer of polarization from the α-CH2 protons. These results show that low-field CIDNP data should be interpreted with care to discriminate between the effects of spin evolution in transient radical pairs and in diamagnetic reaction products.

Friday, October 10, 2014

Solid State Field-Cycling NMR Relaxometry: Instrumental Improvements and New Applications


Fujara, F., D. Kruk, and A.F. Privalov, Solid State Field-Cycling NMR Relaxometry: Instrumental Improvements and New Applications. Prog. NMR. Spec., (0).


The paper reviews recent progress in field cycling (FC) NMR instrumentation and its application to solid state physics. Special emphasis is put on our own work during the last 15 years on instrumentation, theory and applications. As far as instrumentation is concerned we report on our development of two types of electronical FC relaxometers, a mechanical FC relaxometer and a combination of FC and one-dimensional microimaging. Progress has been achieved with respect to several parameters such as the accessible field and temperature range as well as the incorporation of sample spinning. Since an appropriate analysis of FC data requires a careful consideration of relaxation theory, we include a theory section discussing the most relevant aspects of relaxation in solids which are related to prevailing residual dipolar and quadrupolar interactions. The most important limitations of relaxation theory are also discussed. With improved instrumentation and with the help of relaxation theory we get access to interesting new applications such as ionic motion in solid electrolytes, structure determination in molecular crystals, ultraslow polymer dynamics and rotational resonance phenomena.

Wednesday, October 8, 2014

Cross-polarization for dissolution dynamic nuclear polarization


Batel, M., et al., Cross-polarization for dissolution dynamic nuclear polarization. Phys Chem Chem Phys, 2014. 16(39): p. 21407-16.


Dynamic nuclear polarization (DNP) in combination with subsequent dissolution of the sample allows the detection of low-gamma nuclei in the solution state with a signal gain of up to tens of thousand times compared to experiments starting from Boltzmann conditions. The long polarization build-up times of typically more than one hour are a drawback of this technique. The combination of dissolution DNP with cross-polarization (CP) in the solid state was shown to have the potential to overcome this disadvantage. In this article we discuss the cross-polarization step under dissolution DNP conditions in more detail. We show that adiabatic half-passage pulses allow us to enhance the CP efficiency in power-limited DNP probes. As a low-power alternative to Hartmann-Hahn CP we also demonstrate the applicability of frequency-swept de- and re-magnetization pulses for polarization transfer via dipolar order. We investigate the implications and restrictions of the common solid-state DNP mechanisms to the DNP-CP technique and apply a spin-thermodynamic model based on the thermal-mixing mechanism. The model allows us to investigate the dynamics of the polarization levels in a system with two nuclear Zeeman reservoirs and explains the enhanced DNP efficiency upon solvent deuteration within a spin-thermodynamic picture.

Postdoc Position: Metabolic Imaging using hyperpolarized 13C MR

From the Ampere Magnetic Resonance List



Technische Universität München, Munich, Germany
Postdoc Position: Metabolic Imaging using hyperpolarized 13C MR

We are looking for a postdoc who will join our project within the Collaborative Research Centre 824 Imaging for Selection, Monitoring and Individualization of Cancer Therapies at the Department of Nuclear Medicine at the Technische Universität München (Germany).The initial employment has a duration of 1.5 years (extension is possible) starting December 1st, 2014. The salary is according to TV-L E13.

The Department of Nuclear Medicine at Technische Universität München, Germany, is internationally highly regarded in the field of molecular imaging. Since many years, multimodal imaging (SPECT, PET, MRI, CT) in clinical and preclinical applications is a core focus of our department. Recently a 7 T MRI scanner (GE MR901) for preclinical applications has been installed together with a HyperSense DNP Polarizer for hyperpolarized 13C MR imaging.

We are looking for a postdoc with strong background in metabolic, preclinical imaging, metabolomics and broad experience in animal models to join this preclinical 7T MRI laboratory including the DNP Polarizer. The person is expected to take on the role of the biomedical expert, bringing in the strong expertise on preclinical models of cancer and their establishment in animals (rat, mice). The person will further be responsible for research design, internal and external collaborations for preclinical imaging, and study-execution, working closely together with the team of PhD students and the 7T responsible physicist. In addition, the candidate is expected to develop his/her own research focus within the framework of the department’s scientific goals.

Candidates should have a PhD degree in Biology, (Bio-)Chemistry or a related field. Experience in the field of clinical or preclinical MRI is desirable. We expect proven scientific achievements, very good communication skills, and the ability to work in an interdisciplinary team. Women are especially encouraged to apply. Handicapped applicants with equal qualifications will be given preferential treatment.

Applications should include a cover letter, a CV and a list of own publications together with the names of three references and should be sent to: marion.menzel@tum.de

Dr. Marion I. Menzel
Senior Scientist
Diagnostics, Imaging and Biomedical Technologies Europe
GE Global Research 

T +49 89 55283-730

M +49 173 9441337
F +49 89 55283-180 


Freisinger Landstrasse 50
85748 Garching bei München
Germany

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GE Global Research, Zweigniederlassung der General Electric Deutschland Holding GmbH. Sitz von/Registered Office of General Electric Deutschland Holding GmbH: Frankfurt/Main.
Registergericht/Commercial Register: Amtsgericht/Lower District Court Frankfurt; HRB 98088. Geschäftsführer/Managing Director: Ferdinando Beccalli-Falco, Prof. Dr. Ing. Stephan Reimelt, Dr. Volker Wetekam, Dr. Carlos Härtel, Udo Josef Klaeren, Werner van Wickeren.

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