L. H. Sutcliffe

Bio: L. H. Sutcliffe is an academic researcher. The author has contributed to research in topics: Electron nuclear double resonance & Nuclear magnetic resonance spectroscopy. The author has an hindex of 1, co-authored 1 publications receiving 115 citations.

Progress in Nuclear Magnetic Resonance Spectroscopy

Abstract: ING AND INDEXING

NMR Spectroscopy for Metabolomics Research.

Abstract: Over the past two decades, nuclear magnetic resonance (NMR) has emerged as one of the three principal analytical techniques used in metabolomics (the other two being gas chromatography coupled to mass spectrometry (GC-MS) and liquid chromatography coupled with single-stage mass spectrometry (LC-MS)). The relative ease of sample preparation, the ability to quantify metabolite levels, the high level of experimental reproducibility, and the inherently nondestructive nature of NMR spectroscopy have made it the preferred platform for long-term or large-scale clinical metabolomic studies. These advantages, however, are often outweighed by the fact that most other analytical techniques, including both LC-MS and GC-MS, are inherently more sensitive than NMR, with lower limits of detection typically being 10 to 100 times better. This review is intended to introduce readers to the field of NMR-based metabolomics and to highlight both the advantages and disadvantages of NMR spectroscopy for metabolomic studies. It will also explore some of the unique strengths of NMR-based metabolomics, particularly with regard to isotope selection/detection, mixture deconvolution via 2D spectroscopy, automation, and the ability to noninvasively analyze native tissue specimens. Finally, this review will highlight a number of emerging NMR techniques and technologies that are being used to strengthen its utility and overcome its inherent limitations in metabolomic applications.

Aromaticity and ring currents.

Abstract: Accepting a commission to review progress in the subject embodied in our title is, perhaps, to take up something of a ‘poisoned chalice’. One of us, contributing on this same topic more than 20 years ago at the 1979 International Symposium on Aromaticity in Dubrovnik, wrote1 “A cynic would say that there are actually only two difficulties in discussing the subject of ‘aromaticity’ and ‘ring currents’sdeciding what is meant by ‘ring current’, and assigning a meaning to the term ‘aromaticity’!” That comment, though ostensibly facetious, had serious intent: it did encapsulate, with only a modicum of exaggeration, the problems that inherently beset any assessment such as the one attempted at Dubrovnik1 and in the present review. At the heart of the matter lies the undeniable fact that neither ring currents nor aromaticity are physical observables. Nevertheless, the intervening period has seen the ring-current idea, at least, become generally less controversial and more accepted than it once was. At the time of our opening quotation, one of us and Haigh had just published an exhaustive review2 of the ring-current concept covering the period up to about 1980sthe end of what might now be regarded as the era of semiempirical calculations in this field.2 This review2 (1979/1980) concluded that “the ‘ring current’ picture has proved itself ... to have great power in rationalising, at least qualitatively, the magnetic properties of π-electron systems. It is so pictorial that one can almost feel what is happening when a [conjugated] molecule is subjected to a magnetic field. Whatever advances the future may bring, it may be that the favourite habitat of the ‘ring current’ will be that in which it was born and brought up, namely, that of semi-empirical π-electron theory”. In other words, these authors were sanguine that, at the time (ca. 1980), the ring-current idea was gently coming to the end of its natural, useful life. However, as recently as 1997, when reviewing progress concerning the status of the ring-current model during the decade and a half or so after 1980s a period in this field that we have dubbed3 ‘the ab initio era’sthe present authors3 were initially somewhat surprised to find themselves concluding that “the ‘ring-current’ idea has well survived the first 15 years of the ab initio era.” Lazzeretti’s subsequent magnum opus4 on ring currents has more than confirmed this. By contrast, the sheer fact that in 2001sthe very first year of the 21st centurysthe American Chemical Society has seen fit to run this particular issue of Chemical Reviews shows that the concept of Aromaticity is as elusive as it ever was (see section II). There are three reasons for our not feeling obliged or inclined to present, in this review, an exhaustive, systematic, or historical critique of the ring-current concept itself. First, as we have just claimed, the idea of a ring current seems more secure now than it was 20 years ago, and it would appear that less apology or justification is needed for invoking it. Second, we ourselves have, in any case, only recently updated 1349 Chem. Rev. 2001, 101, 1349−1383

The delocalization index as an electronic aromaticity criterion: application to a series of planar polycyclic aromatic hydrocarbons.

Abstract: This work introduces a new local aromaticity measure, defined as the mean of Bader's electron delocalization index (DI) of para-related carbon atoms in six-membered rings. This new electronic criterion of aromaticity is based on the fact that aromaticity is related to the cyclic delocalized distribution of pi-electrons. We have found that this DI and the harmonic oscillator model of aromaticity (HOMA) index are strongly correlated for a series of six-membered rings in eleven planar polycyclic aromatic hydrocarbons. The correlation between the DI and the nucleus-independent chemical shift (NICS) values is less remarkable, although in general six-membered rings with larger DI values also have more negative NICS indices. We have shown that this index can also be applied, with some modifications, to study of the aromaticity in five-membered rings.

Solid-state dynamic nuclear polarization at 263 GHz: spectrometer design and experimental results.

Abstract: Dynamic Nuclear Polarization (DNP) experiments transfer polarization from electron spins to nuclear spins with microwave irradiation of the electron spins for enhanced sensitivity in nuclear magnetic resonance (NMR) spectroscopy. Design and testing of a spectrometer for magic angle spinning (MAS) DNP experiments at 263 GHz microwave frequency, 400 MHz 1H frequency is described. Microwaves are generated by a novel continuous-wave gyrotron, transmitted to the NMR probe via a transmission line, and irradiated on a 3.2 mm rotor for MAS DNP experiments. DNP signal enhancements of up to 80 have been measured at 95 K on urea and proline in water–glycerol with the biradical polarizing agent TOTAPOL. We characterize the experimental parameters affecting the DNP efficiency: the magnetic field dependence, temperature dependence and polarization build-up times, microwave power dependence, sample heating effects, and spinning frequency dependence of the DNP signal enhancement. Stable system operation, including DNP performance, is also demonstrated over a 36 h period.