Linear and Non-Linear Middle Infrared Spectra of Penicillin G in the CO Stretching Mode Region

: In this work we report the linear and non-linear IR spectral response characterization of the CO bonds of Penicillin Gsodium salt in D2O and in DMSO−d6 solutions. In order to better characterize the spectral IR features in the CO stretching region, broadband middle infrared pump-probe spectra are recorded. The role of hydrogen bonds in determining the inhomogeneous broadening and in tuning anharmonicity of the different types of oscillators is exploited. Narrow band pump experiments, at the three central frequencies of beta-lactan, amide and carboxylate CO stretching modes, identify the couplings between the different types of CO oscillators opening the possibility to gather structural dynamic information. Our results show that the strongest coupling is between the beta-lactam and the carboxylate CO vibrational modes.