title: Characterization and intramolecular bonding patterns of busulfan: Experimental and quantum chemical approach.
abstract: The investigations of structural conformers, molecular interactions and vibrational characterization of pharmaceutical drug are helpful to understand their behaviour. In the present work, the 2D potential energy surface (PES) scan has been performed on the dihedral angles C6O4S1C5 and C25S22O19C16 to find the stable conformers of busulfan. In order to show the effects of long range interactions, the structures on the global minima of PES scan have been further optimized by B3LYP/6-311++G(d,p) method with and without empirical dispersion functional in Gaussian 09W package. The presence of n→σ* and σ→σ* interactions which lead to stability of the molecule have been predicted by natural bond orbital analysis. The strong and weak hydrogen bonds between the functional groups of busulfan were analyzed using quantum topological atoms in molecules analysis. In order to study the long-range forces, such as van der Waals interactions, steric effect in busulfan, the reduced density gradient as well as isosurface defining these interactions has been plotted using Multiwfn software. The spectroscopic characterization on the solid phase of busulfan has been studied by experimental FT-IR and FT-Raman spectra. From the13C and1H NMR spectra, the chemical shifts of individual C and H atoms of busulfan have been predicted. The maximum absorption wavelengths corresponding to the electronic transitions between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of busulfan have been found by UV-vis spectrum.
authors.affiliation: Department of Physics, University of Lucknow, 226007 Lucknow, India. Electronic address: karthiphy84@gmail.com.
authors.forename: T
authors.initials: T
authors.lastname: Karthick
authors.affiliation: Department of Physics, University of Lucknow, 226007 Lucknow, India. Electronic address: poonam_tandon@yahoo.co.uk.
authors.forename: Poonam
authors.initials: P
authors.lastname: Tandon
authors.affiliation: Department of Physics, University of Lucknow, 226007 Lucknow, India.
authors.forename: Swapnil
authors.initials: S
authors.lastname: Singh
authors.affiliation: Department of Physics, Invertis University, 243123 Bareilly, Uttar Pradesh, India.
authors.forename: Parag
authors.initials: P
authors.lastname: Agarwal
authors.affiliation: Department of Physics, University of Lucknow, 226007 Lucknow, India.
authors.forename: Anubha
authors.initials: A
authors.lastname: Srivastava
mesh_terms: D002066:Busulfan / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D002066:Busulfan
keywords: Atoms in molecules; Busulfan; Multi-wavefunction analysis; Potential energy surface; UV–Vis spectrum; Vibrational spectra