Determination of transverse relaxation rates in systems with scalar-coupled spins: The role of antiphase coherences

Homogeneous line-widths that arise from transverse relaxation tend to be masked by B-0 field inhomogeneity and by multiplets due to homonuclearf-couplings. Besides well-known spin-locking sequences that lead to signals that decay with a rate R-1p without any modulations, alternative experiments allow one to determine the transverse relaxation rates R-2 in systems with scalar-coupled spins. We evaluate three recent strategies by experiment and simulation: (i) moderate-amplitude SITCOM-CPMG sequences (Dittmer and Bodenhausen, 2006 [2]), (ii) multiple-quantum filtered (MQF) sequences (Barrere et al., 2011 [4]) and (iii) PROJECT sequences (Aguilar et al., 2012 [5]). Experiments where the J-evolution is suppressed by spin-locking measure the pure relaxation rate R2(15) of an in-phase component. Experiments based J-refocusing yield a mixture of in-phase rates R-2(I-x) and antiphase rates R-2(2I(y)S(z)), where the latter are usually faster than the former. Moderate-amplitude SITCOM-CPMG and PROJECT methods can be applied to systems with many coupled spins, but applications of MQF sequences are limited to two-spin systems since modulations in larger systems can only partly be suppressed. (C) 2013 Elsevier Inc. All rights reserved

Apparent transverse relaxation rates in systems with coupled carbon-13 spins

In systems with homonuclear scalar couplings, the envelopes of spin echoes obtained with simple refocusing pulses or trains of such pulses are normally modulated so that it is difficult to extract transverse relaxation rates. It has been shown recently that echo modulations can be quenched by cumulative pulse errors that arise after applying a large number of refocusing pulses with moderate rf amplitudes. The resulting unmodulated decays allow one to extract apparent transverse relaxation rates. Early work on systems comprising only two nitrogen-15 nuclei or two carbon-13 spins has recently been extended to systems with coupled protons. This work focuses on systems with three coupled carbon-13 spins, which in turn are coupled to several neighbouring protons. Unmodulated echo trains can be obtained by optimizing the pulse interval, the carrier frequency and the rf amplitude of the refocusing pulses

Transverse Relaxation of Scalar Coupled Protons in Magnetic Resonance of Non-Deuterated Proteins

The transverse relaxation rates R (2) = 1/T (2) of protons can be determined by spin-echo sequences with multiple refocusing pulses using moderate radio-frequency field strengths and properly chosen inter-pulse delays so as to suppress echo modulations due to homonuclear scalar couplings. Combination with 2D heteronuclear correlation spectroscopy (HSQC) allows one to measure R (2) of arbitrary protons attached to nitrogen-15 or carbon-13 nuclei. Decays of six amide protons in the protein Ubiquitin that is nitrogen-15 enriched (but not deuterated) were measured at different temperatures

Distance measurements between 5 nanometer diamonds – single particle magnetic resonance or optical super-resolution imaging?

5 nanometer sized detonation nanodiamonds (DNDs) are studied as potential single-particle labels for distance measurements in biomolecules

Extending Timescales and Narrowing Linewidths in NMR

Among the different fields of research in nuclear magnetic resonance (NMR) which are currently investigated in the Laboratory of Biomolecular Magnetic Resonance (LRMB), two subjects that are closely related to each other are presented in this article. On the one hand, we show how to populate long-lived states (LLS) that have long lifetimes T_LLS which allow one to go beyond the usual limits imposed by the longitudinal relaxation time T_1. This makes it possible to extend NMR experiments to longer time-scales. As an application, we demonstrate the extension of the timescale of diffusion measurements by NMR spectroscopy. On the other hand, we review our work on long-lived coherences (LLC), a particular type of coherence between two spin states that oscillates with the frequency of the scalar coupling constant J_IS and decays with a time constant T_LLC. Again, this time constant T_LLC can be much longer than the transverse relaxation time T_2. By extending the coherence lifetimes, we can narrow the linewidths to an unprecedented extent. J-couplings and residual dipolar couplings (RDCs) in weakly-oriented phases can be measured with the highest precision

From Chemistry to Consciousness: A Legacy to Hans Primas. Atmanspacher, Harald, Müller-Herold, Ulrich (Eds.)

ISSN:1355-825

Comment on “Sub-5 nm Nanodiamonds Fabricated by Plasma Immersion Ion Implantation as Fluorescent Probes”

ISSN:2574-097

Comment on “Sub-5 nm Nanodiamonds Fabricated by Plasma Immersion Ion Implantation as Fluorescent Probes”

ISSN:2574-097

How to Identify, Attribute, and Quantify Triplet Defects in Ensembles of Small Nanoparticles

Nanodiamonds containing negatively charged triplet (having an electron spin S = 1) nitrogen-vacancy (NV–) centers are an extraordinary room-temperature quantum system, whose electron spins may be polarized and read out optically even in a single nanocrystal. In this Viewpoint we promote a simple but reliable method to identify, attribute, and quantify these triplet defects in a polycrystalline sample using electron paramagnetic resonance (EPR) spectroscopy. The characterization relies on a specific “forbidden” transition (“ΔMS = 2”), which appears at about half the central magnetic field and shows a remarkably small anisotropy. In particular, we emphasize that this method is by far not limited to NV– centers in diamond but could become an important characterization tool for novel triplet defects in various types of nanoparticles.ISSN:1948-718

Apparent Transverse Relaxation Rates in Systems with Scalar-Coupled Protons

The modulation of spin echoes by homonuclear scalar couplings render the determination of transverse relaxation rates of individual spins difficult, in particular for molecules that are isotopically enriched in 13C or 15N, and for all molecules with scalar-coupled protons. To avoid echo modulations, most studies using refocusing pulses have so far been restricted to isolated 1H, 13C, or 15N spins. We report measurements of apparent 1H transverse relaxation rates of backbone and side-chain protons in Cyclosporin A (CsA) determined by quenching the echo modulations that arise from homonuclear scalar couplings between protons