Density Functional Theory and Vibrational Spectral Analysis of a Local Anesthetic Drug 2-diethylaminoethyl p-aminobenzoate

Procaine hydrochloride (2-diethylaminoethyl p-aminobenzoate) is a local anesthetic similar in structure to natural compounds actively participating in nerve impulse transmission. The vibrational spectral investigation of procaine hydrochloride (PRC-HCl) has been carried out using FT-IR and FT-Raman spectra along with the DFT computations to analyze the structural and bonding features responsible for drug activity, nature of hydrogen bonding and charge transfer interactions. The considerable lowering and strong splitting of NH2 asymmetric stretching wavenumber from the computed value is mainly due to intramolecular association between protonated tertiary amine groups and the chloride ion and the intermolecular association between p-aminobenzoate group and the chloride ion through N-H…Cl hydrogen bonding network. The strong quinonoid character of the hydrochloride salt of procaine is due to the fact that the protonated tertiary amino nitrogen is hydrogen bonded to a chloride ion which also interacts with two p-amino groups. The blue-shifting of carbonyl stretching mode and red-shifting of C-N stretching mode of the procaine hydrochloride is observed compared to the respective modes of procaine molecules which explains the differing natures of the intermolecular bonds in procaine and procaine hydrochloride and also changes in quinonoid character of the benzene ring.