RESUMO
Cucurbit[6]uril forms a doubly charged complex with 1,4-butanediammonium cation that is observed using electrospray ionization Fourier transform mass spectrometry. Such 1:1 complexes are not observed for the smaller cucurbit[5]uril, which forms a 2:1 ammonium:cucurbituril complex instead. The 1:1 complex with cucurbit[6]uril is difficult to fragment via collisional activation; when it does fragment, both breakup of the cucurbituril cage and loss of the amine are observed. Further, the complex reacts with tert-butylamine via slow adduction. In contrast, nonrotaxane analogues (such as doubly charged 2:1 complexes of either protonated 1,4-butanediamine or protonated ethylenediamine with cucurbit[6]uril) fragment via easy loss of the intact amine upon collisional activation and react with tert-butylamine via rapid displacement of the original amine. On the basis of stoichiometry, fragmentation behavior, and reactivity, we conclude that the doubly charged complex of cucurbit[6]uril with 1,4-butanediammonium is a gas-phase pseudorotaxane.
RESUMO
A series of macrocyclic tetraazacrown ethers containing two pyridine, quinoline, 8-hydroxyquinoline, or 8-aminoquinoline sidearms has been prepared. Crab-like cyclization of bis(alpha-chloroacetamide)s and diamines followed by reduction of the cyclic diamides was used to synthesize the selected crown ethers containing two unsubstituted macroring nitrogen atoms. The preparation of the macrocycles with sidearms was accomplished by reductive amination of the proper aldehydes with the crown ethers using sodium triacetoxyborohydride (NaBH(OAc)(3)) as the reducing agent. The 8-hydroxyquinoline- and 8-aminoquinoline-containing macrocycles were synthesized by reductive amination of 8-acetoxyquinoline-2-carboxaldehyde or 8-nitroquinoline-2-carboxaldehyde followed by removing the acetate groups or reducing the nitro groups to amino groups, respectively. Complexation of ligand 22 with Cu(2+), Co(2+), Ni(2+), Zn(2+), Cd(2+), and Pb(2+) was evaluated potentiometrically in aqueous solution (0.10 M Me(4)NCl) at 25 degrees C. Ligand 22 formed very stable complexes with these metal ions. The UV-vis spectra of 22 and its complexes were examined in an aqueous acetic acid buffer solution (pH 5). The 22-Cu(2+) complex provided a new absorption band at 258 nm.
RESUMO
Ten new 8-hydroxyquinoline-containing diaza-18-crown-6 ligands and analogues were synthesized via a one-pot or stepwise Mannich reaction, reductive amination, or by reacting diaza-18-crown-6 with 5,7-dichloro-2-iodomethyl-8-quinolinol in the presence of N,N-diisopropylethylamine. The Mannich reaction of N,N'-bis(methoxymethyl)diaza-18-crown-6 with 4-chloro-2-(1H-pyrazol-3-yl)phenol gave the NCH(2)N-linked bis(3-(5-chloro-2-hydroxy)pyrazol-1-ylmethyl)-substituted diazacrown ether (14) in a 98% yield. The reaction of bis(N,N'-methoxymethyldiaza)-18-crown-6 with 2.2 equiv of 10-hydroxybenzoquinoline gave only the monosubstituted diazacrown ether ligand (8). Interaction of some of the ligands with various metal ions was evaluated by a calorimetric titration technique at 25 degrees C in MeOH. Bis(8-hydroxyquinoline-2-ylmethyl)-substituted ligand 13 forms a very strong complex with Ba(2+) (log K = 11.6 in MeOH) and is highly selective for Ba(2+) over Na(+), K(+), Zn(2+), and Cu(2+) (selectivity factor > 10(6)). The (1)H NMR spectral studies of the Ba(2+) complexes with bis(8-hydroxyquinoline-2-ylmethyl)- and bis(5,7-dichloro-8-hydroxyquinoline-2-ylmethyl)-substituted diaza-18-crown-6 ligands (13 and 10) suggest that these complexes are cryptate-like structures with the two overlapping hydroxyquinoline rings forming a pseudo second macroring. UV-visible spectra of the metal ion complexes with selected ligands suggest that these ligands might be used as chromophoric or fluorophoric sensors.
