Vibrational Studies on the Heterobifunctional Cross-linking AgentsN-Succinimidyl 3-(2-Pyridyldithio)propionate andN-Succinimidyl 6-[3′-(2-Pyridyldithio)propionamido]hexanoate and Theoretical Elucidations

Infrared and Raman spectra of the heterobifunctional cross-linking agents N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) and N-succinimidyl 6-[3′-(2-pyridyldithio)propionamido]hexanoate (LC-SPDP) are reported and the observed IR and Raman bands are assigned. A comparison of C–S and S–S stretching modes in these two systems suggests that the geometry in the disulfide region is different and LC-SPDP has less torsion. These findings are also supported by semi-empirical MNDO calculations. This study provides a basis for understanding why the bioefficacy of the conjugates, modified through LC-SPDP, is greater. © 1997 by John Wiley & Sons, Ltd.