In general, these cross-linkers contain a very labile bond that is fragmented very efficiently in gas phase to yield intense signals of reporter ions detected in a silent region of the MS/MS spectra . Cleavable cross-linkers have also been designed with two labile bonds in their structures to yield a signal signatures in the MS/MS spectra that provides information on the molecular masses of the cross-linked peptides . With the same goal, other option has been the development of cross-linkers that introduces an spacer containing peptide bonds that can be easily cleavable in CID conditions such as the cases of Asp-Pro or Gly-Pro .