title: The conformational and vibrational behavior of the inhibitory neuropeptide derived from beta-endorphin.
abstract: In this study, conformational behavior, structural, and vibrational characterization of the carboxy terminal dipeptide of β-endorphin (glycy-l-glutamine, glycyl-glutamine, beta-endorphin30-31), which is an inhibitory neuropeptide synthesized from beta-endorphin1-31in brain stem regions, has been investigated. The theoretically possible stable conformers were searched by means of molecular mechanics method to determine their energetically preferred conformations. The 360 different conformations were calculated with the φ, Ψ, χ dihedral angles using the Ramachandran maps. The most stable conformation of the title molecule is characterized by the extended backbone shape (e) in the BR conformational range with -.78 kcal/mol energy. The cis- and trans-dimeric forms of the dipeptide were also formed and energetically preferred conformations of dimers were investigated. The experimental methods (FT-IR, micro-Raman spectroscopies) coupled with quantum chemical calculations based on density functional theory (DFT) have been used to identify the geometrical, energetic, and vibrational characteristics of the dipeptide. The assignment of the vibrational spectra was performed based on the potential energy distribution of the vibrational modes. To investigate the electronic properties, such as nonlinear optical properties, the electric dipole moment, the mean polarizability, the mean first hyperpolarizability, and HOMO-LUMO energy gaps were computed using the DFT with the B3LYP/6-31++G(d,p) basis set combination. The second-order interaction energies were derived from natural bonding orbital analysis. The focus of this study is to determine possible stable conformation on inhibitory neuropeptide and to investigate molecular geometry, molecular vibrations of monomeric and dimeric forms, and hydrogen bonding interactions of glycy-l-glutamine dipeptide.
authors.affiliation: a Science Faculty, Physics Department , Istanbul University , Vezneciler, 34134 Istanbul , Turkey.
authors.forename: Serda
authors.initials: S
authors.lastname: Kecel-Gunduz
authors.affiliation: b Engineering Faculty, Electrical-Electronics Engineering Department , Istanbul University , 34320 Avcilar, Istanbul , Turkey.
authors.forename: Sefa
authors.initials: S
authors.lastname: Celik
authors.affiliation: a Science Faculty, Physics Department , Istanbul University , Vezneciler, 34134 Istanbul , Turkey.
authors.forename: Aysen E
authors.initials: AE
authors.lastname: Ozel
authors.affiliation: c Science and Letters Faculty, Physics Department , Istanbul Kultur University , Atakoy Campus, Bakirkoy 34156 , Istanbul , Turkey.
authors.forename: Sevim
authors.initials: S
authors.lastname: Akyuz
mesh_terms: D006860:Hydrogen Bonding; D008958:Models, Molecular; D009479:Neuropeptides / Q000737:chemistry*; D011487:Protein Conformation; D055503:Protein Multimerization; D013057:Spectrum Analysis; D001615:beta-Endorphin / Q000737:chemistry*
chemical_list: D009479:Neuropeptides; D001615:beta-Endorphin
keywords: beta-endorphin30-31; glycy-l-glutamine; inhibitory neuropeptide; vibrational spectra