Mathias Nilsson

Pure Shift 1H NMR: A Resolution of the Resolution Problem?

Suppressing multiplet structure in 1H??NMR spectra offers a large improvement in spectral resolution (see picture), equivalent to the use of a spectrometer in the GHz range. Such ldquopure shiftrdquo techniques are readily extended to multidimensional methods, for example DOSY.

Ultrahigh-Resolution NMR Spectroscopy

All psyched up: A flexible and general pure shift experiment (PSYCHE) has been developed that offers superior sensitivity, spectral purity, and tolerance of strong coupling over existing methods for broadband homonuclear decoupling. The partial spectra of estradiol in [D6]DMSO obtained by normal 1H NMR spectroscopy and PSYCHE are shown for comparison.

The DOSY Toolbox: A new tool for processing PFG NMR diffusion data

The DOSY Toolbox is a free programme for processing PFG NMR diffusion data (sometimes loosely referred to as DOSY data), distributed under the GNU General Public License. NMR data from three major manufacturers can be imported and all processing is done in a user-friendly graphical user interface. The Toolbox is completely free-standing in the sense that all necessary basic processing of NMR data (e.g., Fourier transformation and phasing) is catered for within the programme, as well as a number of methods specific to DOSY data (e.g., DOSY and SCORE). The programme is written in MATLAB and as such can be run on any platform, but can also run independent of MATLAB in a free-standing compiled version for Windows, Mac, and Linux.

Simultaneously Enhancing Spectral Resolution and Sensitivity in Heteronuclear Correlation NMR Spectroscopy

BIRDs eye view: Adding periodic BIRD J-refocusing (BIRD=bilinear rotation decoupling) to data acquisition in an HSQC experiment causes broadband homonuclear decoupling, giving a single signal for each proton chemical shift. This pure shift method improves both resolution and signal-to-noise ratio, without the need for special data processing.

Content of nutrients and lignans in roller milled fractions of rye

Rye grain was roller milled into six flour fractions (607 g kg-1), a short (341 g kg-1) and a bran (52 g kg-1) in a B???hler laboratory mill. In the different flours (F1-F6) a progressive increase in ash (4-13 g kg-1), crude protein (39-87 g kg-1) and crude fat (5-17 g kg-1) concentration was found and a corresponding decrease in starch (853-699 g kg-1) concentration. Total dietary fibre (55-109 g kg-1) constituents and the lignans, matairesinol (0???05-0???22 mg kg-1) and secoisolariciresinol (0???21-0???38 mg kg-1), showed a different distribution with a maximal concentration in F5. The short and bran had higher concentrations of ash, crude protein, crude fat, dietary fibre components and lignans but a lower concentration of starch than the flours. Compared to the short, the bran contained more of all constituents analysed except mixed-linked beta-glucan and starch. A very high proportion of total dietary fibre components of the rye, such as arabinoxylan (72%), cellulose (76%) and Klason lignin (79%) as well as of matairesinol (87%) and secoisolariciresinol (73%), was found in the short and bran together. ??? 1997 SCI.

Quantitative Interpretation of Diffusion-Ordered NMR Spectra: Can We Rationalize Small Molecule Diffusion Coefficients?†

Appealingly simple: A new method is described that allows the diffusion coefficient of a small molecule to be estimated given only the molecular weight and the viscosity of the solvent used. This method makes possible the quantitative interpretation of the diffusion domain of diffusion-ordered NMR spectra (see picture).

True Chemical Shift Correlation Maps: A TOCSY Experiment with Pure Shifts in Both Dimensions

Signal resolution in (1)H NMR is limited primarily by multiplet structure. Recent advances in pure shift NMR, in which the effects of homonuclear couplings are suppressed, have allowed this limitation to be circumvented in 1D NMR, gaining almost an order of magnitude in spectral resolution. Here for the first time an experiment is demonstrated that suppresses multiplet structure in both domains of a homonuclear two-dimensional spectrum. The principle is demonstrated for the TOCSY experiment, generating a chemical shift correlation map in which a single peak is seen for each coupled relationship, but the principle is general and readily extensible to other homonuclear correlation experiments. Such spectra greatly simplify manual spectral analysis and should be well-suited to automated methods for structure elucidation.

Decoupling Two‐Dimensional NMR Spectroscopy in Both Dimensions: Pure Shift NOESY and COSY

An increase in the resolving power in 2D NMR spectra is obtained by collapsing 2D signals with multiplet structure into 2D singlets. This resolution gain is achieved by combining 2D experiments with pure shift techniques and covariance processing (see picture). The method should be of value in both manual and automated structure determination.

Improving the accuracy of pulsed field gradient NMR diffusion experiments: Correction for gradient non-uniformity

Pulsed field gradient NMR is a well-established technique for the determination of self-diffusion coefficients. However, a significant source of systematic error exists in the spatial variation of the applied pulsed field gradient. Non-uniform pulsed field gradients cause the decay of peak amplitudes to deviate from the expected exponential dependence on gradient squared. This has two undesirable effects: the apparent diffusion coefficient will deviate from the true value to an extent determined by the choice of experimental parameters, and the error estimated by the nonlinear least squares fitting will contain a significant systematic contribution. In particular, the apparent diffusion coefficient determined by exponential fitting of the diffusional attenuation of NMR signals will depend both on the exact pulse widths used and on the range of gradient amplitudes chosen. These problems can be partially compensated for if experimental attenuation data are fitted to a function corrected for the measured spatial dependence of the gradient and signal strength. This study describes a general alternative to existing methods for the calibration of NMR diffusion measurements. The dominant longitudinal variation of the pulsed field gradient amplitude and the signal strength are mapped by measuring pulsed field gradient echoes in the presence of a weak read gradient. These data are then used to construct a predicted signal decay function for the whole sample, which is parameterised as the exponential of a power series. Results are presented which compare diffusion coefficients obtained using the new calibration method with previous literature values.

Matrix‐assisted diffusion‐ordered spectroscopy: mixture resolution by NMR using SDS micelles

Diffusion‐ordered spectroscopy (DOSY) is a powerful technique for mixture analysis, but in its basic form it cannot separate the component spectra for species with very similar diffusion coefficients. It has been recently demonstrated that the component spectra of a mixture of isomers with nearly identical diffusion coefficients (the three dihydroxybenzenes) can be resolved using matrix‐assisted DOSY (MAD), in which diffusion is perturbed by the addition of a co‐solute such as a surfactant [R. Evans, S. Haiber, M. Nilsson, G. A. Morris, Anal. Chem. 2009, 81, 4548–4550]. However, little is known about the conditions required for such a separation, for example, the concentrations and concentration ratios of surfactant and solutes. The aim of this study was to explore the concentration range over which matrix‐assisted DOSY using the surfactant SDS can achieve diffusion resolution of a simple model set of isomers, the monomethoxyphenols. The results show that the separation is remarkably robust with respect to both the concentrations and the concentration ratios of surfactant and solutes, supporting the idea that MAD may become a valuable tool for mixture analysis. Copyright