Article

Characterization of host–guest complexes of cucurbit[n]uril (n = 6, 7) by electrospray ionization mass spectrometry

Department of Applied Chemistry, Kansai University, Yamatecho, Suita 564-8680, Japan.
Journal of Mass Spectrometry (Impact Factor: 2.71). 02/2006; 41(2):202-7. DOI: 10.1002/jms.978
Source: PubMed

ABSTRACT When an intramolecular cavity exists in a molecule, it can trap another chemical species to form a host-guest complex. We examine the formation of such an inclusion complex with cucurbit[n]uril (CBn, n = 6, 7) as the host to trap alkali metal or ammonium ions as the guest, by electrospray ionization mass spectrometry (ESI-MS). The results show that the inclusion complexes are formed between the three-dimensional cylinder of CBn hosts and the guest cations. Selectivity of the complex formation is dependent both on (1) ion-dipole interactions between the cylindrical portal of the CBn hosts and the guest cations and (2) the hydrophobic interactions at the inner cavity of CBn.

0 Followers
 · 
102 Views
 · 
0 Downloads
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The [2]pseudorotaxanes of cucurbit[6]uril with guest molecule 1,6-bis(imidazol-1-yl)hexane (BIMH) were synthesized and characterized by ESI-MS spectrometry, (1)H NMR spectra, and X-ray diffraction crystallography. The influence of different anions on self-assembly in solid-state was discussed by X-ray diffraction crystallography. However, more interestingly, and to our amazement, we discovered the CB[6]/BIMH [2]pseudorotaxane exhibiting efficient cleavage of pBR322 DNA in physiological environment. The cleavage mechanism were studied by fluorescence spectra and the hydrolysis of bis(2,4-dinitrophenyl)-phosphate (BDNPP). From DNA-binding mode being electrostatic force and the first-order kinetics equation, we prove indirectly that the mechanism may be hydrolytic cleavage.
    Bioorganic & Medicinal Chemistry Letters 03/2007; 17(4):932-6. DOI:10.1016/j.bmcl.2006.11.054 · 2.33 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Using the isothermal calorimetric titration technique, we determined the stability constants (K), reaction enthalpy (ΔH°), and entropy (ΔS°) for complexation of cucurbit[6]uril (CB[6]) with a series of aliphatic alcohols, mono- and diamines, as well as spermidine and spermine, in aqueous solutions of alkali metal chlorides. The K for spermine reached 5.4 × 10 M in 0.2 M LiCl, which is the largest amongst the values reported for CB[6]. Propylamine forms the strongest 1:1 complex with CB[6] (K = 21000 M) in 0.1 M Na acetate buffer, which is driven exclusively by entropy. A comparison of K for 1,3-propanediamine versus 1,4-butanediamine reveals an extraordinary >60000-fold enhancement in affinity, which is the largest increment/CH2 ever observed in supramolecular chemistry. The present results in combination with our ESI-MS data reported recently unambiguously demonstrate that CB[6] exists in aqueous solution of alkali metal salts exclusively as a dicationic species, e.g. [CB[6]·2Na].
    Supramolecular Chemistry 03/2007; 19(1-2):39-46. DOI:10.1080/10610270600915292 · 2.13 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Electrospray ionization mass spectrometry makes it possible to generate gas-phase bis-ethylenediamine nickel and copper dications, [M(en)(2)](2+) (M = Ni, 1; M = Cu, 2), as well as their {[M(en)(2)]@cuc[8]}(2+) inclusion complexes with the macrocyclic cavitand cucurbit[8]uril (cuc[8]). The unimolecular gas-phase reactivity of these species has been investigated by electrospray ionization tandem mass spectrometry with a quadrupole-time-of-flight configuration. Distinctive fragmentation pathways have been observed for the free and encapsulated [M(en)(2)](2+) (M = Ni, Cu) dications under collision-induced dissociation (CID) conditions. The dications [M(en)(2)](2+) (M = Ni, Cu) dissociate according to several competitive pathways that involve intra-complex hydrogen or electron-transfer processes. Most of these channels are suppressed after encapsulation inside the cucurbit[8]uril macrocycle and, as a consequence, a simplification of the {[M(en)(2)]@cuc[8]}(2+) fragmentation pattern is observed. The results obtained demonstrate that the encapsulation of a coordination complex inside a host molecule can be used to alter the nature of the product ions generated under CID conditions.
    Journal of the American Society for Mass Spectrometry 11/2007; 18(10):1863-72. DOI:10.1016/j.jasms.2007.07.020 · 3.19 Impact Factor
Show more