Dear Sandipan Maji

In NanoAnalyze you can choose Model Editor, then choose appropriate ITC Model and in the Main Function window you can see all the programming standing behind the fitting. You can edit it as well. You can also fix 'n' value as '1' during fitting (by unchecking 'Vary' box in the 'n' line). However, 'n' value around 1.5 suggests (if you are sure that the interaction is only 1:1) that molecule in the cell has higher than expected concentration, or the concentration of molecule in the titrating syringe is lower than expected by you. Or both cases simultaneously.

Dear Tomasz Fraczyk

Thank you very much for your suggestion. ''You can also fix 'n' value as '1' during fitting (by unchecking 'Vary' box in the 'n' line)'' I do not know actually how to do that fitting. Can you please explain how to do that ?

Dear Sandipan Maji

I put example fitting of one experiment, one with 'Vary' box for 'n' value checked ('n' value not fixed in the fitting), and the other one, the opposite (with 'n' value fixed on 0.5).

For this particular case, I would not recommend fixing 'n' value, because it causes systematic error seen in the 'residuals' plot. However, if your data are not so sharp, and for example heats are close to the noise, or you do not have clear saturation in the course of the titration, such a fixing may be justified.

Can you show us your data? Maybe it will show us some clues about the possible issue.

Regards

Dear Tomasz Fraczyk

Many many thanks for very much kind help. At this moment I can not show the data as there is a large power cut in our institute, when everything will be fine I will definitely show you. One thing is that in my data there is Area vs number of injection (not molar ratio), how can I change this plot?

Thank you again for your suggestion and help. Actually I am learning this technique and and very new in this field.

Kind regards

Sandipan

Dear Sandipan Maji

You can change the way of displaying the data by choosing "Ratio" button at the top menu, as shown in the attached snapshot (by purple arrow).

Kind regards

Thanks a lot Tomasz Fraczyk

Kind regards

Sandipan

Dear Tomasz Fraczyk

I have added my result here. It is a reaction of phenoxy vs phenol (details are in the attachment). This time I got n value around 1.2 (for 1:1 reaction). Everytime I am getting good baseline graph. Can I consider it as good result. The main culprit I think is the phenoxy radical causing the different 'n' values. Do you have any suggestion to improve the result?

I am very thankful to you for your kind suggestion.

Kind regards

Sandipan

Dear Sandipan Maji

Your data looks very nice and sharp. I misunderstood that you measure binding reaction, but in fact you are measuring the chemical reaction. In such case you should use different models, as the reaction yield can be different in each of the injections (higher at the beginning of the 'titration', and lower for the subsequent injections). Try to find a model for a kinetics. I am pretty sure that there is something done on NanoITC, especially for enzyme kinetics.

Best regards

Tomasz

Dear Tomasz Fraczyk

Actually the above said reaction is a reported one, I wanted to reproduce the results. The 'PCET' model was used for this case. I used the same. But for my case all thermodynamic values are almost similar except 'n' value, that was serious problem. But now I think it was due to the phenoxy radical. I am trying to improve it.

Best regards

Sandipan

Dear Sandipan Maji

Good luck!

Kind regards

Tomasz

Dear Tomasz Fraczyk

Good morning! As I mentioned I am doing Calorimetric measurement for chemical reactions (A + B = C + D, not A + B = C, you can see the equation in previous answer) I need a preferred model to fit the data. My reaction is not a binding chemistry rather a bond dissociation and formation is happening here. Do you know any reference that describes this equation for Clorimetric measurement and the models behind it?

Tank you for your cordial support in advance

Best regards

Sandipan