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Not everybody remembers how easy it is and how effective it can be to add (or correct) a few points at the beginning of the FID. Two years ago I explained how Linear Prediction works and how we can extrapolate the FID in both directions. This time I will show a simple practical application. I have observed that, in recent years, C-13 spectra acquired on Varian instruments require a much-larger-then-it-used-to-be phase correction. When I say correction, I mean first-order phase correction, because the zero-order correction is merely a different way of representing the same thing (a different perspective). A large first-order phase correction can be substituted with linear prediction. I will show the advantage with a F-19 example, yet the concept is general. The spectrum, after FT and before phase correction, looks well acquired. Now we apply the needed correction, which amounts to no less than 1073 degrees. Have you noticed what happened to the baseline? It's all predictable. When y...

There are three possible reasons why you can be tempted by iNMR. First reason: it's for research. It happens that they are not using iNMR in the industry, not because they don't like it, but because they don't buy Macs anymore in the industry. So, the majority of iNMR users are not doing repetitive activities. They don't ask to process 20 spectra in 20 seconds. Maybe they want to estimate the concentrations by time-consuming line-fitting or they want to monitor the phosphorylation of a protein by a series of thirty H-N HSQC, or they want to simulate the effect of a slow rotation, as they used to do with DNMR in the '70s. iNMR users asked for such things years ago and now you find them already into the program. Second reason: students learn the program by themselves. Nowadays few research groups are pure-NMR-groups. When a new PhD students joins the lab, he has many techniques to learn, not just NMR processing. Luckily, iNMR has many things in common with the other a...

I have good news! With a minimal simplification of my INADEQUATE filter I have been able to rescue the last cross-peak of cholesterol. It had been rejected because too near to the diagonal. I changed the code saying: "if it's on the diagonal, it is bad; if it's just near, let's accept it". So it is possible to have the perfect INADEQUATE of cholesterol, with all the expected cross-peaks IN and everything else OUT. Yesterday I received another INADEQUATE spectrum, this time of sucrose. The S/N is still high enough to make my filter unnecessary. If I play with the contour plot all the noise disappears while the 12 carbon atoms and their 10 bonds remain. Only a spurious peak remains at the coordinates 103.7;-22.9. I have not received the 1-D external projection, so I created it artificially. The spectral width is the same in both dimension (instead of being doubled for the DQF axis). The consequence is that two cross-peaks fall just on the boundary and are partially ...

One of the most ancient 2-D experiments has always been more talked about than practiced. The INADEQUATE was invented 30 years ago (an era in which many chemists were still using CW-NMR) and has always been regarded as a the future thing, like travels to the Moon. Everybody agrees it is useful, but the experimental difficulties are discouraging. The information that can be extracted by this experiment is a formidable aid to unveil the structure of unknown natural compounds. For a long time, however, the experiment has been nearly impossible. You needed a powerful transmitter, because the nominal 180� pulse must be a true 180� pulse over a large spectral width. You also needed a sensitive probe. A cryo-probe is the best. Today we can have both things. I am not mentioning here the many attempts to increase the actual sensitivity with experimental tricks, because this is a blog about software. 19 years ago the S/N limit was overcome by a pure numerical method, see this paper , commerciali...

It was 40 days ago when I mentioned the student license of TopSpin and other products, once pricey, that are now free for academic users. Knowing that many students prefer the MacBook and would like to run authentic Mac applications on it, I am going to write about the student promotion of iNMR . It is not free, but it is as cheap as it can possibly be. It's 39 euro (equivalent to 49 USD or 32 British pounds or 4200 Yens). What's so special about this license is that it is... perfectly normal! I mean: it INCLUDES direct customer support and this is quite valuable for a student that is learning NMR and a new software at the same time. Is this program difficult to learn? As for every NMR program, it CAN be hard if you are so familiar with TopSpin (or VNMR, or Jeol Delta) that you can't adapt yourself to anything else. The learning curve of iNMR is actually incredibly smooth if you start processing easy examples (1-D spectra or well acquired 2-D like TOCSY, HSQC...) before mo...

I want to show you a proton spectrum that has puzzled me during the last weeks. It contains something that's quite typical and something that I can't explain. I have processed the spectrum in two different ways, with zero-filling and without it. The spectrum without zero-filling is black, the spectrum with zero-filling is green (the number of points is doubled). This detail is the bottom part of the TMS signal (magnified to show the ringing effect). Where does the ringing come from? TMS is a small symmetric molecule and its protons have a long relaxation time. Their signal persists at the end of the FID. When we add the zeroes after the signal, a step is created. The FT of the step is the ringing that we see. The spectrum without zero-filling doesn't contain the step, so there is no ringing. The period of the ringing is exactly 1 point. In simpler words: odd points are positive, even points are negative. Things are not so simple, actually, because the rule is reversed on t...