XRD, vibrational spectra and quantum chemical studies of an anticancer drug: 6-Mercaptopurine

• Single crystal of the hydrated anticancer drug, 6-Mercaptopurine (6-MP), has been grown by slow evaporation technique.
• The crystal and molecular structure identified by single crystal XRD.
• Hydrogen bonding interactions connect the drug molecules in a ladder-like fashion through lattice water molecule.
• Theoretical calculation was attempted by the HF and DFT method.
• The chemical hardness, electro-negativity and chemical potential of the molecule were carried out by HOMO–LUMO plot.

The single crystal of the hydrated anticancer drug, 6-Mercaptopurine (6-MP), has been grown by slow evaporation technique under room temperature. The structure was determined by single crystal X-ray diffraction. The vibrational spectral analysis was carried out using Laser Raman and FT-IR spectroscopy in the range of 3300–100 and 4000–400 cm−1. The single crystal X-ray studies shows that the crystal packing is dominated by N–H⋯O and O–H⋯N classical hydrogen bonds leading to a hydrogen bonded ensemble. This classical hydrogen bonds were further connected through O–H⋯S hydrogen bond to form two primary ring R44(16) and R44(12) motifs. These two primary ring motifs are interlinked with each other to build a ladder like structure. These ladders are connected through N–H⋯N hydrogen bond along c-axis of the unit cell through chain C(5) motifs. Further, the strength of the hydrogen bonds is studied through vibrational spectral measurements. The shifting of bands due to the intermolecular interactions was also analyzed in the solid crystalline state. Geometrical optimizations of the drug molecule were done by Density Functional Theory (DFT) using the B3LYP function and Hartree–Fock (HF) level with 6-311++G(d,p) basis set. The optimized molecular geometry and computed vibrational spectra are compared with experimental results which show significant agreement. The natural bond orbital (NBO) analysis was carried out to interpret hyperconjugative interaction and intramolecular charge transfer (ICT). The chemical hardness, electro-negativity and chemical potential of the molecule are carried out by HOMO–LUMO plot. In which, the frontier orbitals has lower band gap value indicating the possible pharmaceutical activity of the molecule.

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