Spin echo NMR spectra without J modulation

Aguilar, J. A.; Nilsson, Mathias; Bodenhausen, Geoffrey; Morris, Gareth A.

doi:10.1039/c1cc16699a

Cited by 240 publications

(252 citation statements)

References 23 publications

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“…Spectra were obtained with a simple 90 pulse-observe sequence, or in some cases with solvent presaturation and a 128 ms T 2 filter consisting of a spin echo train with suppressed J evolution [21]. All NMR data was processed using Math-ematica.…”

Section: Methodsmentioning

confidence: 99%

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An optimised detector for in-situ high-resolution NMR in microfluidic devices

Finch

Yılmaz

Utz

2016

Journal of Magnetic Resonance

109

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Integration of high-resolution nuclear magnetic resonance (NMR) spectroscopy with microfluidic lab-on-a-chip devices is challenging due to limited sensitivity and line broadening caused by magnetic susceptibility inhomogeneities. We present a novel double-stripline NMR probe head that accommodates planar microfluidic devices, and obtains the NMR spectrum from a rectangular sample chamber on the chip with a volume of 2 l. Finite element analysis is used to jointly optimise the detector and sample volume geometry for sensitivity and RF homogeneity. A prototype of the optimised design has been built, and its properties have been characterised experimentally. The performance in terms of sensitivity and RF homogeneity closely agrees with the numerical predictions. The system reaches a mass limit of detection of 1.57 nMol p s, comparing very favourably with other micro-NMR systems. The spectral resolution of this chipGprobe system is better than 1.75 Hz at a magnetic field of 7 T, with excellent line shape.

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Section: Methodsmentioning

confidence: 99%

“…8 and Fig. 10 have been recorded using standard pre-saturation water suppression with CW irradiation at 90 Hz amplitude; in the case of the DMEM medium spectrum, a perfect echo sequence [21] was used to reduce signals from compounds with high molecular weight.…”

Section: Performance Characterisationmentioning

confidence: 99%

An optimised detector for in-situ high-resolution NMR in microfluidic devices

Finch

Yılmaz

Utz

2016

Journal of Magnetic Resonance

109

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“…Yet homonuclear decoupling and measurements of transverse relaxation rates in coupled spin systems remain an active field of research in NMR spectroscopy. In the last few years, several approaches were presented to tackle this challenge [2][3][4][5]. We recently reviewed the phenomenon of echo modulations [6,7].…”

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confidence: 99%

“…When equivalent spins are present, as in AX 2 -systems, the oscillations are no longer completely suppressed. It was recently shown [5] that this limitation can be readily overcome by incrementing the number n of pulse cycles and keeping the interval s constant, in the manner of Carr and Purcell's 'Method B' [9], and by setting the s interval so that h J = pJ2s ( 1. This 'locks' the evolution due to J-couplings to further spins.…”

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

Segawa

Bodenhausen

2013

Journal of Magnetic Resonance

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a b s t r a c tHomogeneous line-widths that arise from transverse relaxation tend to be masked by B 0 field inhomogeneity and by multiplets due to homonuclear J-couplings. Besides well-known spin-locking sequences that lead to signals that decay with a rate R 1q 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 (Barrère 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 R 2 (I x ) of an in-phase component. Experiments based on Jrefocusing 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.Ó 2013 Elsevier Inc. All rights reserved.When speaking of ''decoupling'', most NMR practitioners primarily think of collapsing multiplets stemming from J-couplings. In this article however, we shall focus on decoupling in time domain rather than in frequency domain. In other words, we will study methods that can 'smooth out' decays that are normally modulated by J-couplings. Indeed, the effects of couplings can be cancelled either in frequency or in time domain. In a heteronuclear system, e.g., comprising a proton coupled to a carbon-13 nucleus, a simple broadband radiofrequency (rf) irradiation on one of the two nuclei is sufficient to achieve effective decoupling. This becomes challenging in the presence of homonuclear interactions. In such cases, the Larmor frequencies of the two nuclei can be very close and broadband rf irradiation might perturb all spins, instead of affecting only one coupling partner. The same ''homonuclear challenge'' appears when attempting to measure the transverse relaxation rate R 2 = 1/T 2 of such a spin system. If a spin echo is applied to a system of coupled protons, the echo envelope does not decay exponentially, but is modulated by homonuclear J-couplings. The first observation of such 'echo modulations' was made by Erwin Hahn while studying protons in ethanol shortly after the original discovery of spin echoes back in 1950 [1].The spin echo is approaching an age where retirement is mandatory for many. Yet homonuclear decoupling and measurements of transverse relaxation rates in coupled spin systems remain an active field of research in NMR spectroscopy. In the last few years, several approaches were presented to tackle this challenge [2][3][4][5]. We recently reviewed the phenomenon of echo modulations [6,7]. In this paper, we would like to compare different pulse sequences and e...

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