Structural and vibrational investigations of a neurotransmitter molecule: Serotonin (5-hydroxy tryptamine)

• The most stable conformer of Serotonin has been vibrationally and structurally investigated. All the 69 modes have been assigned.
• The two NH bonds of the NH2 group are found to be slightly dissimilar.
• HOMO, LUMO, Energy gap, MESP, and NBO investigations have also been carried out.
• HOMO-LUMO study supports pharmacologicaly active property and suggests existence of charge transfer within this molecule.

Structural and vibrational studies have been carried out for the most stable conformer of serotonin (5-HT) at the DFT/B3LYP/6-311++G** level using the Gaussian 09 software. In light of the computed vibrational parameters the observed IR and Raman frequencies have been analyzed. To help assign the vibrational fundamentals the GAR2PED software has been used to compute PEDs. Several of the fundamentals are drastically changed in going from indole to serotonin. The two NH bonds of the NH2 group are slightly different possibly due to bonding of the two H atoms of the NH2 group with different atoms. The rocking and wagging modes of the NH2 groups show mixing with the other modes while the remaining four modes are pure group modes. The Kekule phenyl ring stretching mode is found to remain almost unchanged. The HOMO-LUMO energy gap supports to pharmacological active property of the serotonin molecule. The HOMO and LUMO study suggests the existence of charge transfer within the molecule. The NBO analysis has been carried out to gather information regarding the proper and improper hydrogen bonds.

(a) Contour map (b) Contour map (total density array) (c) Isosurface plot of ESP (d) MEP plot of serotonin.Figure optionsDownload as PowerPoint slide