I am using ATR FTIR to study complex formation between protein and ligand (drug). i am using ATR at 2 cm-1 and 4 cm-1 resolution. I record the FTIR spectra of my protein, ligand and protein+ Ligand.

1. FTIR spectra of my ligand gives two peak one at 1356 cm-1 and 1278cm-1.

2. when i record the spectra of Protein + ligand, i got the peak at 1358cm-1 and 1278cm-1, including the amide I and amide II peak of protein.

that means my ligand interact with protein with the functional group that corresponds to 1356 cm-1.

but when i record the ftir specta of ligand and ligand + protein at resolution 4cm-1, i did not get, consistently, shift in the peak at 1356 cm-1. Sometimes peak was shifted by 1cm-1 or 2cm-1 or not at all.

i would like to know is there any relationship between use of resolution and change in the peak shift.