Mr. Mahato,

There is unable to obtain a such shifting from 1543 to 1437 cm-1 due to hydrogen bonding effect. The latter is at about 10-15 cm-1. The shown shifting means a dramatic change of the hybridization. Can you provide spectra?

The basic idea is that infrared spectrum is formed because of the absorption of electromagnetic radiation that matches the frequencies of vibration for specific sets of chemical bonds associated with a molecule. The overall spectra are impacted by various factors associated with a molecule based on the contributions due to; (I) electronic, (II) vibrational, (III) rotational, and (IV) translational (The translational energy being associated with the displacement of molecules in space as a function of the normal thermal motions of matter). Therefore, changes in the local bonding can be due to any type of perturbation in the bond when an element (whether H or and other element) is making an intramolecular bonding within the same molecule or an intermolecular bonding that is formed between neighboring molecules. The following link on “Interpretation of Infrared Spectra, A Practical Approach” may be a good reference to examine: http://www3.uma.pt/jrodrigues/disciplinas/QINO-II/Teorica/IR.pdf

Thank You Dr. Bahram Roughani for your elaborate reply. However, I want more specific answer related to the above FTIR spectra.

At the beginning, I suggest to compare the spectra of the peptides/proteins before adding acetonitrile to the spectra after adding this solvent. If you want to get more detailed information, you can do the procedure of splitting the amide bands into individual bands, using e.g. curve-fitting. I used this for example in previous studies on amide bands (see https://doi.org/10.1016/j.saa.2017.07.001). You should receive changes in the bands of secondary protein structures that are overlapped in the amide bands.

Thank You Sylwia Olsztyńska-Janus for your suggestions. Lets see how much it helps.