Ghost of a Butterfly


Sometimes the butterfly disappears when the picture is scaled down, like into this web page. Click it!

Comments

Post a Comment

Popular posts from this blog

Promotional Sale

Image
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...
Read more

Blindly

Image
In the last few days I have been giving the impression that line-fitting is much more time-consuming, difficult and error-prone than integration. It's true, not because line-fitting is more complicated, but because integration is simpler. There are also notable exceptions. The last tutorial published on www.inmr.net illustrates the case. Here is the spectrum to "integrate": It's the kinetic study of a chemical reaction. Not only the concentrations change, but also the frequencies. That's not at all a problem. If you give a look at the article, you see that it's possible to measure the concentrations of all the diagnostic peaks in all the spectra with a single operations. In other words the whole job, including the formatted table of the estimated areas, can be done by the computer in automatic fashion. In this case, they exploit that fact that line-fitting not only gives the intenisities, but the frequencies too. In this way it's easy for the computer to ...
Read more

Hot and Cool

Image
Dynamic NMR includes chemical exchange and internal rotations. They are the same thing, observed via NMR. If the rate of exchange is low, you can start from a non-equilibrium situation and measure the changes of concentration over a period of hours or days. When the rate is higher, you study the situation at equilibrium, either by saturation transfer or by line-shape analysis. The latter is akin to the simulation of spin systems seen so far. There is one more parameter, the exchange rate constant (assumed to be first-order). If you have an exchange among many sites, you can have several different rates, but it's rare. The visible effect of chemical exchange is the broadening of the lines. The effect is dramatic at the coalescence, when two of the corresponding signals of the exchanging species become one. The temperature of coalescence depends on: the exchange rate the difference in Hz The direct consequence is that: a species with n signals can have up to n different temperatures...
Read more