App: ppmfit
Developer: JPG Malthouse
Genres: Education, Productivity

This program can be used to fit pKa values to pH dependent data where the data titrates from one value to another e.g. ppm data, absorbance data, fluorescence data, Ki and Km data etc. 

The program fits and plots data to the equations:-

If one pKa only
Sobs=S1(1+K1/H)+S2/(1+H/K1)
 
If two pKa values
Sobs=(S1*H^2+S2*KA*H+S3*KA*KB)/(H^2+KA*H+KA*KB)
 
When "Fit " is selected you must input the initial estimates of ppm (S1 and S2 or S1,S2 and S3) and the pKa (PK1 or pK1 and PK2) values.  The experimental data is then fitted using an iterative, non linear least-squares regression program. Note the two pKa fit is a five parameter fit and so it requires good data and good estimates to fit the data.
Results can be printed, saved as a text document or copied and pasted into other applications such as Word.

You can enter your data directly into the program and save it. Alternativelyif your data is in another program such as excel simply save it as a csv file or a Tab delimited text file. If you then go to the File menu item you can select “Open csv file” and you will be able to input data from the csv file. To input data saved as a Tab delimited text file go to the File menu and select “Open Tab file”.

If you want to refresh your knowledge of the practical aspects of 1D NMR you might find the iphone app "NMRQA" on the iTunes app store useful. If you want to estimate the contributions of dipolar relaxation and relaxation by Chemical Shift Anisotropy(CSA) you should find "T1calc" on the Mac app store useful.

Release notes:
The graphics functionality lost when using the Big Sur or higher operating system has been restored.