title: Experimental and theoretical study of the cation binding properties of macrocyclic dehydrodibenzopyrido[15]annulenes.
abstract: The UV/Vis titration measurements, vibrational and NMR spectroscopy of isomeric dehydrodibenzopyrido[15]annulenes (DBPA) 1 and 2 clearly show that under proper conditions these macrocycles can achieve fast, quantitative and unselective binding of metal ions. The macrocycle 1 is an example of a hindered amine 2,6-bis(R)pyridine and its isomer 2 of a non-hindered amine 3,5-bis(R)pyridine. The protonation stoichiometry for both 1 and 2 was assumed to be DBPA:H(+)=1:1 and the formation constants logK=4.77±0.02 for 1, and logK=6.78±0.08 for 2 were obtained that well agree with those obtained under similar conditions for a macrocycle containing bipyridine units. The protonation of 2 gave the estimated stoichiometry of 2:H(+)=1:1 while the stoichiometric protonation of macrocycle 1 could not be achieved and the lower stability of the ion pair containing 1H(+) is most likely due to the inaccessibility of the nitrogen atom of 1 to the counterions and solvent molecules. The structures and electronic absorption spectra of 1 and 2, as well as the structures and spectra of 1H(+) and 2H(+), i.e. the species formed by protonation of the pyridine nitrogen, were calculated with the time-dependent DFT method with a B3LYP functional and a 6-31+G(d) basis set. The solvent effects were incorporated by means of the polarizable continuum model (PCM). The agreement of the calculated absorption data for the parent and protonated species with the observed spectra is rather satisfactory. Vibrational IR and Raman spectra of 1, 2, 1H(+) and 2H(+) in vacuo were calculated at the B3LYP/cc-pVTZ level of theory. Macrocycles 1 and 2, and their products protonated by trifluoromethanesulfonic acid (1HOTf and 2HOTf) were also characterized by temperature-dependent FTIR technique known as two dimensional IR correlation analysis. Quite large difference in degradation temperature between macrocycle 1 and 2 and their protonated complexes was measured, indicating that inclusion of proton leads to significant thermal stabilization of dehydroannulene ring.
authors.affiliation: Division of Organic Chemistry and Biochemistry, R. Bošković Institute, Bijenička 54, 10001 Zagreb, Croatia.
authors.forename: Boris
authors.initials: B
authors.lastname: Zimmermann
authors.affiliation: Division of Organic Chemistry and Biochemistry, R. Bošković Institute, Bijenička 54, 10001 Zagreb, Croatia. Electronic address: baranovi@irb.hr.
authors.forename: Goran
authors.initials: G
authors.lastname: Baranović
authors.affiliation: Galapagos Research Centre, Prilaz baruna Filipovića 29, 10000 Zagreb, Croatia.
authors.forename: Dubravka
authors.initials: D
authors.lastname: Gembarovski
mesh_terms: D001665:Binding Sites; D002412:Cations / Q000737:chemistry; D007477:Ions; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008698:Mesylates / Q000737:chemistry; D008670:Metals / Q000737:chemistry; D008968:Molecular Conformation; D009584:Nitrogen / Q000737:chemistry; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry*; D011485:Protein Binding; D011522:Protons; D012997:Solvents / Q000737:chemistry; D013053:Spectrophotometry; D013055:Spectrophotometry, Infrared; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013696:Temperature
chemical_list: D002412:Cations; D007477:Ions; D008024:Ligands; D008698:Mesylates; D008670:Metals; D011084:Polycyclic Aromatic Hydrocarbons; D011522:Protons; D012997:Solvents; C012077:trifluoromethanesulfonic acid; D009584:Nitrogen
keywords: Dehydroannulenes; Dehydrodibenzopyrido[15]annulenes; Metal cation binding; Polarizable continuum model; Protonation; Time-dependent DFT