DOSY NMR question

[jlayarza92]

Hi, I'm looking for help to process a DOSY NMR spectrum. I'd like to know how to transform the gradient decay plot for a given region of the spectrum into a plot showing the diffusion constants (x-axis) vs the intensity (y-axis), sort of a distribution of diffusion constants. I've read about it online, and this website Diffusion NMR suggests applying an inverse laplace transform to a gaussian fitting function for the gradient decay plot, but I'm not sure how to do this. I was hoping someone could show me the steps to obtain this plot.

Thank you for your time.

[Joshkurutz]

Jorge,

As with most NMR data, the transformation is usually accomplished either within the software provided by the spectrometer vendor or by third-party software such as MNova  from Mestrelab. I also think that these vendors use some proprietary routines for getting a good 2D plot (for example, minimizing the "streaking" one encounters when two peaks are close in chemical shift but have different diffusion constants).

Is there a particular reason you want to do this manually? Do you have access to vendor-supplied software?

Thanks. - Josh

[jlayarza92]

Hi,

Thanks for answering. I have access to the Bruker topspin student version. I'm studying polymer behaviour in solution, in this case a polysaccharide in water. I've managed to obtain the DOSY 2D plot relating the chemical shift (i.e. the peaks) and their diffusion coeffcients, but what I want is to plot the diffusion coefficient vs intensity for a specific peak, thus obtaining some sort of distribution of diffusion coeffcients.

Thanks for your time.

Jorge

[Joshkurutz]

Jorge,

Ah. This analysis is fairly sophisticated. The distribution of diffusion coefficients for a given resonance is related to the "linewidth" of its DOSY peak in the indirect/diffusion dimension. (A narrow distribution, i.e. a single species would result in a sharp DOSY peak, but a broad range of MW's would give rise to a broad DOSY peak in the D dimension).

A quick search for "dosy measurement of polydispersity" yields this article, which you may find handy:

https://www.researchgate.net/publication/51520216_Polydispersity_index_of_polymers_revealed_by_DOSY_...

Without trying to go into the nitty gritty detail of your processing, perhaps you should investigate whether the tools you need are part of the DOSY Toolbox, a free DOSY analysis package produced by the Nilsson lab at the University of Manchester:

Software

The description on that page indicates their software handles multi exponential decays, so it may be able to handle what you seek.

I'm a firm believer in using software that other people have written to solve problems that many people face - no sense in rewriting software every time a question needs answering.

Good luck! - Josh