Thursday, 18 September 2008

BayDOSY: What’s under the Hood

I have already posted about our efforts towards the evaluation of diffusion NMR experiments by means of a new Bayesian-based approach, the so-called bayDOSY.
Recently Stan Sykora has given a talk at GIDRM conference covering some background of this technique for NMR DOSY analysis, including its basic math principles and advantages over other techniques. Also, the limitations of this new data evaluation scheme are noted, as well as potential extensions designed to address some of these limitations.
This talk is available in PDF format from the web page below:

As I have already offered, should you be interested in testing bayDOSY, just drop me a line and I will give you a special version of Mnova

Friday, 5 September 2008

2D Phase Correction

Understanding NMR Spectroscopy’ by James Keeler is one of my favorites NMR books which I highly recommend to anyone seriously interested in NMR spectroscopy. All NMR concepts, ranging from quantum mechanics to product operator formalism and data processing are very elegantly and clearly exposed.
These days I’m working on several points regarding 2D phase correction and while consulting this book, I found a phrase which immediately caught my attention. In page 240, you can read this:

(…) However, phasing a two-dimensional spectrum is not quite so straightforward as phasing in one dimension, as it is not feasible to recompute the whole spectrum after each trial phase correction is applied – to do so would simply be too time consuming. (…)

Indeed this is true, to the best of my knowledge, with most existing NMR software packages but not with Mnova or iNMR, in which the recommended way to iteratively adjust the phase of a 2D spectrum is by real time operations (drag & drop) on the full 2D hypercomplex matrix, in just the same way as you do it with 1D spectra. In fact, I believe that this way is much more convenient than the traditional, old fashioned way of extracting some selected traces (cross-sections) parallel to one of the dimensions, calculating the phase on them, and then applying the correction to the full 2D spectrum.
Obviously, real time 2D phase correction was not possible at early times of 2D NMR development (eighties), when computers were not fast enough to make this task possible, so that the 1D cross-sections approach was the only feasible way. However, since the late nineties, advances in computer technology made real time processing of 2D NMR possible, not only regarding phase correction but any other iterative process such as weighting. For example, it is now possible to iteratively adjust the weighting functions in a 2D spectrum and see, in real time, the results in the processed full 2D spectrum.