Apr 8, 2020

Characterizing oils in oil-water mixtures inside porous media by Overhauser dynamic nuclear polarization #DNPNMR #ODNP

Chen, Junfei, Jiwen Feng, Fang Chen, Zhen Zhang, Li Chen, Zhekai Zhang, Rugang Liao, Maili Liu, and Chaoyang Liu. “Characterizing Oils in Oil-Water Mixtures inside Porous Media by Overhauser Dynamic Nuclear Polarization.” Fuel 257 (December 2019): 116107.

We present a method to identify and sort the oils in oil-water mixtures based on the Overhauser dynamic nuclear polarization (ODNP) enhancement at low field. Through combining two types of radicals, e.g. ODNP enhancer TEMPO and relaxation reagent Mn2+, we can selectively enhance the 1H NMR signal of oil in oil-water mixture infiltrated in porous media. More importantly, we have found that the enhancements of light oils in porous materials are inversely dependent of their viscosities but independent of pore size approximately above 10 μm. This allows us to roughly sort oils according to their ODNP enhancement values. The verification experiments in sandstones saturated with several oil and water mixtures show that the method is useful for oils identification and classification in porous media, especially for reservoir assessment or development.

Apr 7, 2020

Updated Conference Schedule due to COVID-19 #DNPNMR

Many conferences and meetings get postponed or canceled due to COVID-19. As of today, the updated dates for conferences that Bridge12 will attending are:

Apr 6, 2020

[NMR] Junior postdoctoral position in Barcelona: Optically Detected Magnetic Resonance

The Institute of Photonic Sciences (ICFO) in Barcelona, Spain, invites applications for a Junior postdoctoral position in the area of optically detected magnetic resonance.

The successful candidate(s) will join the Atomic Quantum Optics group to carry out research tasks associated with the development of new techniques in atomic physics, magnetometry and magnetic resonance. The candidate will design new magneto-optical sensing approaches that involve atomic and nuclear spin systems. 

Relevant ongoing projects in the group include: 

Development of microfabricated optically pumped atomic magnetometers operating at the femtotesla sensitivity level, for application in biomagnetic field detection. Part of the EU Quantum Flagship program. 
Nuclear magnetic resonance spectroscopy in the ultralow-field regime below earth's magnetic field. Supported by EU Marie Skłodowska Curie Actions.
Techniques for atomic and nuclear spin polarization in the ultralow-field regime. Supported by EU Regional Development Fund.

Requirements and conditions
Applicants should hold an internationally recognized Ph.D. degree in Physics, Chemistry or closely related field to experimental quantum optics or magnetic resonance.

Experience in the design, development and implementation of hardware, as well as a knowledge of spin dynamics is essential. 

The applicant should have a demonstrated ability to work with collaborators.

ICFO is an equal opportunity employer. Candidates are selected exclusively on merit and potential on the basis of submitted application material. No restrictions related to disabilities, citizenship or gender apply to ICFO positions. ICFO abides by the principles of openness, efficiency, transparency, supportiveness, and international comparability as stated in the European Charter for Researchers and the European Code of Conduct for the Recruitment of Researchers.

The contract is offered for periods of one year, renewable on an annual basis.

Application process

For informal inquiries please send a CV to Dr. Michael Tayler (michael.tayler@icfo.eu) and Prof. Morgan Mitchell (morgan.mitchell@icfo.eu)

The formal application should be submitted online via http://jobs.icfo.eu/index.php?detail=485

Suitable candidates are requested to submit:

Presentation letter with a declaration of interest,
Curriculum Vitae, including contact details,
Scanned copies of the complete (Bachelor and Master equivalent) official academic transcripts in English or Spanish,
The contact e-mail of two potential referees.
Candidates may contact jobs@icfo.eu for informal enquiries regarding the application, as well as address scientific enquiries to michael.tayler@icfo.eu

Applications are considered on a continuing basis, until the positions are filled.

For updated information about ICFO, please visit http://www.icfo.eu/
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SABRE: Chemical kinetics and spin dynamics of the formation of hyperpolarization

Barskiy, Danila A., Stephan Knecht, Alexandra V. Yurkovskaya, and Konstantin L. Ivanov. “SABRE: Chemical Kinetics and Spin Dynamics of the Formation of Hyperpolarization.” Progress in Nuclear Magnetic Resonance Spectroscopy 114–115 (October 2019): 33–70.

In this review, we present the physical principles of the SABRE (Signal Amplification By Reversible Exchange) method. SABRE is a promising hyperpolarization technique that enhances NMR signals by transferring spin order from parahydrogen (an isomer of the H2 molecule that is in a singlet nuclear spin state) to a substrate that is to be polarized. Spin order transfer takes place in a transient organometallic complex which binds both parahydrogen and substrate molecules; after dissociation of the SABRE complex, free hyperpolarized substrate molecules are accumulated in solution. An advantage of this method is that the substrate is not modified chemically, and its polarization can be regenerated multiple times by bubbling fresh parahydrogen through the solution. Thus, SABRE requires two key ingredients: (i) polarization transfer and (ii) chemical exchange of both parahydrogen and substrate. While there are several excellent reviews on applications of SABRE, the background of the method is discussed less frequently. In this review we aim to explain in detail how SABRE hyperpolarization is formed, focusing on key aspects of both spin dynamics and chemical kinetics, as well as on the interplay between them. Hence, we first cover the known spin order transfer methods applicable to SABRE — cross-relaxation, coherent spin mixing at avoided level crossings, and coherence transfer — and discuss their practical implementation for obtaining SABRE polarization in the most efficient way. Second, we introduce and explain the principle of SABRE hyperpolarization techniques that operate at ultralow (<1 lT), at low (1lT to 0.1 T) and at high (>0.1 T) magnetic fields. Finally, chemical aspects of SABRE are discussed in detail, including chemical systems that are amenable to SABRE and the exchange processes that are required for polarization formation. A theoretical treatment of the spin dynamics and their interplay with chemical kinetics is also presented. This review outlines known aspects of SABRE and provides guidelines for the design of new SABRE experiments, with the goal of solving practical problems of enhancing weak NMR signals.

Apr 3, 2020

Shim-on-Chip Design for Microfluidic NMR Detectors

Active shims to achieve high-resolution spectra are crucial parts of the NMR instrumentation. Typically, shims are designed to produce a magnetic correction field corresponding to individual spherical harmonics. Other methods have been proposed (e.g. matrix shims) and the approach described in this article simplify uses flat ribbon cables.

Meerten, S. G. J. van, P. J. M. van Bentum, and A. P. M. Kentgens. “Shim-on-Chip Design for Microfluidic NMR Detectors.” Analytical Chemistry 90, no. 17 (September 4, 2018): 10134–38.

In this contribution we present a novel system for shimming capillary samples such as used in microuidic NMR probe heads. Due to the small sample size shimming microliter samples using regular shim coils is complicated. Here we demonstrate the use of a series of parallel wires placed perpendicular to B0 as a Shim-on-Chip shim system. This is achieved by placing a ribbon at cable horizontally over the NMR detector, in our case a stripline. The current through each wire of the ribbon cable can be controlled independently employing a 16 channel DAC. This makes for a simple, cheap and easy to construct alternative to regular shim systems. The Shim-on-Chip is, nevertheless, quite exible in creating a magnetic eld which matches the inhomogeneity of the magnet in 1 dimension. The capillary sample geometry is well suited for this type of shimming since its length (8mm) is much larger than its width (100 µm to 250 µm). With this Shim-on-Chip system we have reached linewidths of 2:2 Hz (at 50%) and 27 Hz (at 0:55%) on a 144MHz NMR spectrometer without any other room temperature shims. Unlike regular shims the Shim-on-Chip is located inside the NMR probe. It is always centered on the NMR sample, because of this the shims have an intuitive eect on the lineshape. Therefore the manual shimming is simpler when compared to a regular shim system, as it is dicult to position a microliter sample in the exact center of the shim coils. We furthermore demonstrate the use of a Shim-on-Chip method in a 400MHz Rapid-Melt DNP system. Decent linewidths were achieved even for a sample which is located o-center inside the NMR magnet.

Apr 1, 2020

The past, present, and future of 1.26 T2

This article is not directly related to DNP-NMR spectroscopy but offers some very valuable insight how to optimize acquisition parameters.

Rovnyak, David. “The Past, Present, and Future of 1.26 T2.” Concepts in Magnetic Resonance Part A 47A, no. 2 (March 2018): e21473.

This mini-­review considers the scientific and historical development of the constant 1.26T2, which represents the acquisition time for which the signal-­to-­noise ratio of a decaying exponential (with time constant T2) is a maximum in the presence of thermal noise. While first reported in 1977, interest in this result greatly increased after about the year 2000, when it began to influence thinking in nonuniform sampling, sensitivity, and pulse sequence design. Overall, 1.26T2 has become a lens through which to view the evolution of NMR data acquisition and processing. An enduring lesson of the 1.26T2 story is the value of describing and analyzing the properties of magnetic resonance signals in the time domain prior to any further spectral analysis and processing, a concept which is at the core of many modern analytic techniques.

Mar 30, 2020

Conformational control of nonplanar free base porphyrins: towards bifunctional catalysts of tunable basicity #DNPNMR

Roucan, M., M. Kielmann, S. J. Connon, S. S. R. Bernhard, and M. O. Senge. “Conformational Control of Nonplanar Free Base Porphyrins: Towards Bifunctional Catalysts of Tunable Basicity.” Chemical Communications 54, no. 1 (2018): 26–29.

For the first time, free base and N-methylated porphyrins have been utilized as bifunctional organocatalysts in Michael additions and it was found that distortion of the macrocycle is a vital prerequisite for their catalytic activity. Conformational design has been used to tailor the properties of nonplanar porphyrins with regards to availability of the N–H units for hydrogen bonding (distortion-dependent hydrogen bonding) and the basicity of the heterocyclic groups. NMR spectroscopic- and catalyst screening studies provided insight into the likely mode of catalyst action. This unprecedented use of free base and N-substituted porphyrins as organocatalysts opens a new functional role for porphyrins.