title: Conformational analysis of an acyclic tetrapeptide: ab-initio structure determination from X-ray powder diffraction, Hirshfeld surface analysis and electronic structure.
abstract: A terminally protected acyclic tetrapeptide has been synthesized, and the crystal structure of its hydrated form, Boc-Tyr-Aib-Tyr-Ile-OMe·2H2O (1), has been determined directly from powder X-ray diffraction data. The backbone conformation of tetrapeptide (1) exhibiting two consecutive β-turns is stabilized by two 4 → 1 intramolecular N-H · · · O hydrogen bonds. In the crystalline state, the tetrapeptide molecules are assembled through water-mediated O-H · · · O hydrogen bonds to form two-dimensional molecular sheets, which are further linked by intermolecular C-H · · · O hydrogen bonds into a three-dimensional supramolecular framework. The molecular electrostatic potential (MEP) surface of (1) has been used to supplement the crystallographic observations. The nature of intermolecular interactions in (1) has been analyzed quantitatively through the Hirshfeld surface and two-dimensional fingerprint plot. The DFT optimized molecular geometry of (1) agrees closely with that obtained from the X-ray structure analysis. The present structure analysis of Boc-Tyr-Aib-Tyr-Ile-OMe·2H2 O (1) represents a case where ab-initio crystal structure of an acyclic tetrapeptide with considerable molecular flexibility has been accomplished from laboratory X-ray powder diffraction data.
authors.affiliation: Department of Physics, Haldia Government College, Debhog, Purba Medinipur, 721657, India.|Department of Physics, Jadavpur University, Jadavpur, Kolkata, 700032, India.
authors.forename: Uday
authors.initials: U
authors.lastname: Das
authors.affiliation: Department of Bio-chemistry and Bio-physics, University of Kalyani, Nadia, Kalyani, West Bengal, 741235, India.
authors.forename: Jishu
authors.initials: J
authors.lastname: Naskar
authors.affiliation: Department of Physics, Jadavpur University, Jadavpur, Kolkata, 700032, India.
authors.forename: Alok Kumar
authors.initials: AK
authors.lastname: Mukherjee
mesh_terms: D018360:Crystallography, X-Ray / Q000379:methods*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry*; D033362:Powder Diffraction; D055672:Static Electricity; D014867:Water / Q000737:chemistry
chemical_list: D009842:Oligopeptides; D014867:Water
keywords: Hirshfeld surface analysis; Rietveld refinement; X-ray powder diffraction; ab-initio structure determination; acyclic tetrapeptide