title: Breaking aggregation and driving the keto-to-gem-diol equilibrium of the N,N'-dimethyl-2,6-diaza-9,10-anthraquinonediium dication to the keto form by intercalation in cucurbit[7]uril.
abstract: (1)H NMR, ESI-MS, and DFT calculations with the M062X/6-31G* method show that, in water, the bistetrafluoroborate salt of N,N'-dimethyl-2,6-diaza-9,10-anthraquinonediium dication (DAAQ·2BF4(-)) exists in equilibrium with both its gem-diol and several aggregates (from dimers to at least octamers). With high concentrations of HCl (e.g., 1.2-1.5 M), all aggregates break up and the keto-to-gem-diol equilibrium is shifted quantitatively toward the quinone form. The same effect is observed with 1.5 mol equiv of cucurbit[7]uril, CB[7], with which all equilibria are shifted toward the quinone form, which undergoes slow exchange with the CB[7] cavity as both the free and the CB[7]-intercalated quinone (DAAQ@CB[7]) are observed simultaneously by (1)H NMR. The affinity of DAAQ for the CB[7] cavity (Keq = 4 × 10(6) M(-1)) is in the range found for tricyclic dyes (0.4-5.4 × 10(6) M(-1)), and among the highest observed to date. A computational comparative study of the corresponding CB[7] complex of the N,N'-dimethyl-4,4'-bipyridinium dication (N,N'-dimethyl viologen, MeV) suggests that the higher binding constant for intercalation of DAAQ may be partially attributed to a lesser distortion of CB[7] (required to maximize favorable nonbonding interactions) as a result of the flat geometry of DAAQ.
authors: Department of Chemistry, Missouri University of Science and Technology, Rolla, Missouri 65409, USA.
authors: Arumugam
authors: A
authors: Thangavel
authors: Ian A
authors: IA
authors: Elder
authors: Chariklia
authors: C
authors: Sotiriou-Leventis
authors: Richard
authors: R
authors: Dawes
authors: Nicholas
authors: N
authors: Leventis
mesh_terms: D000438:Alcohols / Q000737:chemistry*; D001952:Bridged-Ring Compounds / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D018360:Crystallography, X-Ray; D007093:Imidazoles / Q000737:chemistry*; D007546:Isoquinolines / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D011789:Quantum Theory; D011809:Quinones / Q000737:chemistry*; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils
chemical_list: D000438:Alcohols; D001952:Bridged-Ring Compounds; D002412:Cations; D007093:Imidazoles; D007546:Isoquinolines; D007659:Ketones; D011809:Quinones; C456276:cucurbit(7)uril; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils