title: Structure and spectral characteristics of diquat-cucurbituril complexes from density functional theory.
abstract: Electronic structure, (1)H NMR and infrared spectra of diquat (6,7-dihydrodipyrido[1,2-b:1',2'-e] pyrazine-5,8-diium or DQ(2+)) encapsulated by cucurbit[n]uril (n = 7,8) hosts are obtained using the density functional theory. Theoretical calculations have shown that both CB[7] or CB[8] host possesses strong affinity toward DQ(2+) compared to its reduced cation or neutral species. Calculated (1)H NMR spectra reveal that Hα protons on bi-pyridinium rings of DQ(2+)@CB[8] complex are de-shielded owing to C=O⋯H interactions. On the other hand aromatic (Hβ and Hδ) of DQ(2+) within the CB[8] cavity exhibit significant shielding. The complexation of CB[8] with DQ(2+) splits the carbonyl stretching vibration (1788 cm(-1)) into two distinct vibrations which correspond to 1765 cm(-1) arising from hydrogen bonded carbonyls and the 1792 cm(-1) band from non-interacting ones. Further, the CN stretching vibration in DQ(2+) exhibits a frequency blue-shift of 6 cm(-1) on its encapsulation within the CB[8] cavity. The direction of frequency shift has been explained on the basis of natural bond orbital analyses.
authors.affiliation: Department of Chemistry, University of Pune, Pune, 411 007, India.
authors.forename: Swarada R
authors.initials: SR
authors.lastname: Peerannawar
authors.forename: Shridhar P
authors.initials: SP
authors.lastname: Gejji
mesh_terms: D004178:Diquat / Q000737:chemistry*; D047028:Macrocyclic Compounds / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared; D014732:Vibration; D000099246:Cucurbit(n)urils
chemical_list: D004178:Diquat; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils