The pink pigment prodigiosin: Vibrational spectroscopy and DFT calculations

• New spectroscopic aspects of the red pigment from Serratia marcescens are presented.
• Raman and infrared spectra are given for pure prodigiosin hydrochloride.
• DFT calculations of possible conformers of prodigiosin and its cation were undertaken.
• Tentative vibrational assignments are based on DFT calculations.
• Advantages of combining the experimental and theoretical approaches are highlighted.

Prodigiosin is a pink colored tripyrrole pigment which occurs naturally as a biosynthetic product of Serratia marcescens. The direct acquisition of Raman spectra of this compound from fresh cultures of S. marcescens was found to be not possible even with a range of different excitation conditions and common instrumental settings. Therefore, IR and Raman spectroscopic data are given here for pure prodigiosin hydrochloride. DFT calculations of possible isomers were undertaken to better understand the spectral differences potentially arising from the different structures. Comparison of experimental and theoretical data shows a good correspondence with the selected molecular structure. The spectroscopic data obtained from prodigiosin identify spectral biomarker signatures which can complement information and databases obtained for other pigments considered as biosignatures in the fields of geobiology and exobiology.

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