Jul 31, 2013

Light-Induced Spin Polarization in Porphyrin-Based Donor–Acceptor Dyads and Triads

van der Est, A. and P. Poddutoori, Light-Induced Spin Polarization in Porphyrin-Based Donor–Acceptor Dyads and Triads. Appl. Magn. Reson., 2013. 44(1-2): p. 301-318.

The light-induced spin polarization generated by sequential electron transfer in an axially bound triad based on Al(III) porphyrin (AlPor) is discussed. In the triad, TTF > Ph > py > AlPor > Ph > NDI, the electron acceptor naphthalene diimide (NDI) is attached covalently to the Al(III) center, while the donor tetrathiafulvalene (TTF) coordinates to Al(III) via an appended pyridine (py) on the opposite face of the porphyrin ring. Excitation of the porphyrin at room temperature in solution leads to charge separation between the donor and acceptor. In the liquid crystalline solvent 5CB, a spin-polarized transient electron paramagnetic resonance spectrum of a weakly coupled radical pair is observed and is assigned to the state TTFþNDI. In the absence of the donor, a spectrum of the triplet state of the strongly coupled radical pair AlPorþNDIis obtained. The analysis of the spectra is described using a model developed by Kandrashkin et al. (Appl Magn Reson 15: 417–447, 1998). It is shown that in the triad the spectrum of TTFþNDI shows evidence of the singlet–triplet mixing in the precursor AlPorþNDI. At later time, singlet recombination leads to inversion of the spectrum, from which the singlet back reaction lifetime is estimated as 350 ns. The decay of the inverted spectrum yields a lifetime of 8.3 ls for the triplet back reaction lifetime.

Jul 29, 2013

Molecular-level characterization of the structure and the surface chemistry of periodic mesoporous organosilicates using DNP-surface enhanced NMR spectroscopy

Gruning, W.R., et al., Molecular-level characterization of the structure and the surface chemistry of periodic mesoporous organosilicates using DNP-surface enhanced NMR spectroscopy. Phys Chem Chem Phys, 2013. 15(32): p. 13270-4.

We present the molecular level characterization of a phenylpyridine-based periodic mesoporous organosilicate and its post-functionalized organometallic derivatives through the fast acquisition of high quality natural isotopic abundance 1D (13)C, (15)N, and (29)Si and 2D (1)H-(13)C and (1)H-(29)Si solid-state NMR spectra enhanced with dynamic nuclear polarization.

Jul 26, 2013

DNP enhanced NMR using a high-power 94 GHz microwave source: a study of the TEMPOL radical in toluene

This paper was already published in 2010 but I just came across it recently. Please let me know if there are any papers you would like to see posted here, or that I missed. 

Kryukov, E.V., et al., DNP enhanced NMR using a high-power 94 GHz microwave source: a study of the TEMPOL radical in toluene. Phys Chem Chem Phys, 2010. 12(22): p. 5757-65.

DNP enhanced (1)H NMR at 143 MHz in toluene is investigated using an NMR spectrometer coupled with a modified EPR spectrometer operating at 94 GHz and TEMPOL as the polarisation agent. A 100 W microwave amplifier was incorporated into the output stage of the EPR instrument so that high microwave powers could be delivered to the probe in either CW or pulsed mode. The maximum enhancement for the ring protons increases from approximately -16 for a 5 mM TEMPOL solution to approximately -50 for a 20 mM solution at a microwave power of approximately 480 mW. The temperature dependence of the enhancement, the NMR relaxation rates and the ESR spectrum of TEMPOL were also studied in an effort to obtain information on the dynamics of the system.

Jul 24, 2013

Drastic sensitivity enhancement in 29Si MAS NMR of zeolites and mesoporous silica materials by paramagnetic doping of Cu2+

Inagaki, S., et al., Drastic sensitivity enhancement in Si MAS NMR of zeolites and mesoporous silica materials by paramagnetic doping of Cu. Phys Chem Chem Phys, 2013.

The paramagnetic doping of Cu2+ in both mesoporous silica materials and microporous silicate crystals (zeolites) can be used effectively to enhance the signal intensity of 29Si solid state magic angle spinning NMR, as a result of shortening of the spin-lattice relaxation time, T1, by the paramagnetic effect, because of the Cu2+ electronic relaxation time in the range of 10-8 s. This leads to drastically reduced data-collection times, typically 80-fold shorter than that in mesoporous silica. We found that the estimated range of the paramagnetic effect of Cu2+ doping in porous silicates was at least 1 nm.

Jul 23, 2013

Open Position at Bridge12: Scientist – Microwave and Terahertz Systems

Bridge12 is happy to announce a job opening. You can find the original posting at http://www.bridge12.com/careers

Open Position: Scientist – Microwave and Terahertz Systems

Bridge12 is a privately-held startup company focusing on the development of cutting-edge, high-power microwave and terahertz sources and systems for use in scientific research such as magnetic resonance spectroscopy, communication systems and industrial applications. The company has a worldwide customer base and conducts groundbreaking research on applications of microwaves and terahertz in novel fields and has been successful in launching several innovative products based on Small Business Innovation Research (SBIR) grants from several federal agencies.

Jul 19, 2013

Cryogenic solid state NMR studies of fibrils of the Alzheimer's disease amyloid-beta peptide: perspectives for DNP

Lopez del Amo, J.-M., et al., Cryogenic solid state NMR studies of fibrils of the Alzheimer’s disease amyloid-β peptide: perspectives for DNP. J. Biomol. NMR, 2013: p. 1-5.

Dynamic Nuclear Polarization solid-state NMR holds the potential to enable a dramatic increase in sensitivity by exploiting the large magnetic moment of the electron. However, applications to biological solids are hampered in uniformly isotopically enriched biomacromolecules due to line broadening which yields a limited spectral resolution at cryogenic temperatures. We show here that high magnetic fields allow to overcome the broadening of resonance lines often experienced at liquid nitrogen temperatures. For a fibril sample of the Alzheimer's disease beta-amyloid peptide, we find similar line widths at low temperature and at room temperature. The presented results open new perspectives for structural investigations in the solid-state.

Jul 18, 2013

New SBIR award to Bridge12 - NIH Funds Development of THz resonator for solid-state DNP-NMR Probes

Press Release
NIH Funds Development of THz resonator for solid-state DNP-NMR Probes
SBIR Grant Awarded to Bridge12 for Dynamic Nuclear Polarization

Framingham, Mass. – July 18th, 2013 – Bridge12 Technologies, a leading provider of terahertz (THz) technology for applications in science, medicine, security, and defense, announces it has received a National Institute of Health’s small business innovation research (SBIR) grant for the development of a THz resonator for solid-state DNP-NMR probes. Dynamic Nuclear Polarization (DNP) can increase the sensitivity of a NMR experiment by several orders of magnitude, accelerating experiments that typically require weeks to complete in minutes.

Nuclear magnetic resonance (NMR) spectroscopy is used broadly across many disciplines, such as analytical chemistry, structural biology or drug discovery and scientists that are using NMR are often challenged by the low sensitivity of NMR, which slows down research and increases research costs.
In recent years, Dynamic Nuclear Polarization (DNPhas proven to be vastly successful in increasing sensitivity in solid-

state NMR experiments, achieving enhancement factors of > 180 at 400 MHz (1Larmor Frequency) corresponding to a factor of 32,400 in time savings. In other words, an experiment that would otherwise run for three weeks can be performed in less than a minute. This significantly increased overall sensitivity accelerates experiments for analytical applications of NMR spectroscopy as well as the structural characterization of bio-macromolecules or pharmaceutical drug discovery.

Jul 17, 2013

Dynamic Nuclear Hyperpolarization in Liquids

Günther, U., Dynamic Nuclear Hyperpolarization in Liquids, in Modern NMR Methodology, H. Heise and S. Matthews, Editors. 2013, Springer Berlin Heidelberg. p. 23-69.

Nuclear magnetic resonance (NMR) spectroscopy is a broadly used analytical method with major applications in chemistry, biochemistry and medicine. Key applications include structural analysis of small molecules, metabolites, larger biomolecules such as proteins, RNA and DNA, and applications in material science. Magnetic resonance imaging (MRI), which is based on the same physical principles, is extensively used in medical diagnostics and represents the most widespread application of NMR. However, NMR is fundamentally limited in sensitivity and this has always restricted its applicability. Hyperpolarization techniques such as dynamic nuclear polarization (DNP) have become a major field of research and development because they hold the promise of increasing the sensitivity of NMR by several orders of magnitude. Such sensitivity enhancements could significantly broaden NMR applications, combining its unique structural information with much higher sensitivity. Unfortunately, there is no single implementation of DNP that would be suitable for a broader range of typical NMR applications. Experimental conditions often circumscribe areas of possible applications. Nevertheless, recent developments point towards experimental protocols providing solutions for specific applications of NMR. This review summarizes the concepts behind DNP in the light of recent developments and potential applications.

Jul 15, 2013

Cardiovascular Applications of Hyperpolarized MRI

Tyler, D., Cardiovascular Applications of Hyperpolarized MRI. Curr Cardiovasc Imaging Rep, 2011. 4(2): p. 108-115.

Many applications of MRI are limited by an inherently low sensitivity. Previous attempts to overcome this insensitivity have focused on the use of MRI systems with stronger magnetic fields. However, the gains that can be achieved in this way are relatively small and increasing the magnetic field invariably leads to greater technical challenges. More recently, the development of a range of techniques, which can be gathered under the umbrella term of “hyperpolarization,” has offered potential solutions to the low sensitivity. Hyperpolarization techniques have been demonstrated to temporarily increase the signal available in an MRI experiment by as much as 100,000-fold. This article outlines the main hyperpolarization techniques that have been proposed and explains how they can increase MRI signals. With particular emphasis on the emerging technique of dynamic nuclear polarization, the existing preclinical cardiovascular applications are reviewed and the potential for clinical translation is discussed.

Jul 12, 2013

Solid-State NMR Spectroscopy of Proteins

A nice review about solid-state NMR spectroscopy with some solid-state DNP.

Müller, H., M. Etzkorn, and H. Heise, Solid-State NMR Spectroscopy of Proteins, in Modern NMR Methodology, H. Heise and S. Matthews, Editors. 2013, Springer Berlin Heidelberg. p. 121-156.

Solid-state NMR spectroscopy proved to be a versatile tool for characterization of structure and dynamics of complex biochemical systems. In particular, magic angle spinning (MAS) solid-state NMR came to maturity for application towards structural elucidation of biological macromolecules. Current challenges in applying solid-state NMR as well as progress achieved recently will be discussed in the following chapter focusing on conceptual aspects important for structural elucidation of proteins.

Jul 10, 2013

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.

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.

Jul 8, 2013

Dynamic nuclear polarization methods in solids and solutions to explore membrane proteins and membrane systems

Cheng, C.Y. and S. Han, Dynamic nuclear polarization methods in solids and solutions to explore membrane proteins and membrane systems. Annu Rev Phys Chem, 2013. 64(1): p. 507-32.

Membrane proteins regulate vital cellular processes, including signaling, ion transport, and vesicular trafficking. Obtaining experimental access to their structures, conformational fluctuations, orientations, locations, and hydration in membrane environments, as well as the lipid membrane properties, is critical to understanding their functions. Dynamic nuclear polarization (DNP) of frozen solids can dramatically boost the sensitivity of current solid-state nuclear magnetic resonance tools to enhance access to membrane protein structures in native membrane environments. Overhauser DNP in the solution state can map out the local and site-specific hydration dynamics landscape of membrane proteins and lipid membranes, critically complementing the structural and dynamics information obtained by electron paramagnetic resonance spectroscopy. Here, we provide an overview of how DNP methods in solids and solutions can significantly increase our understanding of membrane protein structures, dynamics, functions, and hydration in complex biological membrane environments.

Jul 1, 2013

Happy 4th of July

This week the US celebrates its Independence Day on Thursday July 4th and I will be out of town. So I will take a short break from scanning the literature and blogging about it.