it is a peptide chain with amino acid sequence of arginine- glycine-aspartic acid- tryptophan-proline-cysteine-mercaptopropionic acid linked together with amide linkage and disulphide bridge, i first thought of oxidation of the disulphide bond to sulphoxide, sulphone or even sulphonic acid(unfortunately, i am not an organic chemistry expert, i just came with this problem during my research)but i looked at the IR frequencies table and found that the frequencies of sulphoxide at 1030-1070 cm-1, sulphone 1325 and 1140 cm and even sulphonic acid at 1345 and 1150 cm-1 so i excluded the oxidation of the disulphide bond as it shouldnot transmit at 1587cm-1 as i found in IR frequency tables, also there is a small shoulder at 1251 cm-1, so i thought about oxidation of N-H of amide groups to nitro containing derivatives as i found two strong broad band at 1587 &1399 cm-1 but of course didn't know is it possible under these conditions or not,lso i did LC-MS analysis of my oxidized product by LC-MS ESI, without fragmentation it gave m/z smaller than the m/z of the intact structure which suggeste certain cleavage of bonds but where and how ,i am still searching for the answer in the intact structure there was two bands in this region one at 1656 and another one as a shoulder of the previous band at 1543 cm-1 , one another small band at 1402 cm-1 then in the oxidized product the band at 1656 cm-1 vanished and one broad band evolved at 1587 cm-1 and another less broad one at 1398 cm-1, what could be the cause??
