A double-functionalized cyclen with carbamoyl and dansyl groups (cyclen=1,4,7,10-tetraazacyclododecane): A selective fluorescent probe for Y3+ and La3+

A cyclen (=1,4,7,10-tetraazacyclododecane) doubly functionalized with three carbamoylmethyl groups and one dansylaminoethyl (dansyl = 2-(5-(dimethylam ino)-1-naphthalenesulfonyl) group (L-2 = 1-(2-(5-(dimethylamino)-1-naphthal enesulfonylamido)ethyl)-4,7,10-tris(carbamoylmethyl)-cyclen) was synthesize d and characterized. Potentiometrtic pH titration and UV spectrophotometric titration of L2 served to determine deprotonation of the pendant dansylami de (L2 --> H-1L2) With a pK(a) value of 10.6, while the fluorometric titrat ion disclosed a pK(a) value of 8.8 +/- 0.2, which was assigned to the dansy l deprotonation in the excited state. The 1:1 M3+-H-L-1(2) complexation con stants (log K-app = 6.0 for Y3+ and 5.2 for La3+ where K-app(M-H-1L2) = [M3 +-H-1L2]/[M3+](free)[L-2](free) (M-1) at pH 7.4) were determined by potenti ometric pH titration and UV and fluorescence spectrophotometric titrations (excitation at 335 nm and emission at 520 MI) in aqueous solution (with I = 0.1 (NaNO3)) and 25 degreesC. The X-ray structure analysis of the Y3+-H-1L complex showed nine-coordinated Y3+ with four nitrogens of cyclen, three c arbamoyl oxygens, and the deprotonated nitrogen and a sulfonyl oxygen of th e dansylamide. The crystal data are as follow: formula C28H49N11O13.5SY (Y3 +-H-1L2.2(NO3-).2.5H(2)O), M-r = 876.73, monoclinic, space group P2(1)/n (N o. 14), a = 18.912(3) Angstrom, b = 17.042(3) Angstrom, c = 24.318(4) Angst rom, beta = 95.99(1)degrees, V = 7794(2) Angstrom (3), Z = 8, R1 = 0.099. U pon M3+-H-1L2 complexation, the dansyl fluorescence greatly increased (8.6 and 3.8 times for Y3+ and La3+, respectively) in aqueous solution at pH 7.4 . Other lanthanide ions also yielded Ln(3+)-H-1L2 complexes with similar K- app values, although all the dansyl fluorescences were weakly quenched. On the other hand, zinc(II) formed only a 1:1 Zn2+-L-2 complex at neutral pH w ith negligible fluorescence change. The X-ray crystal structure of the Zn2-L-2 complex confirmed the pendant dansylamide being noncoordinating. The c rystal data are as follow: formula C28H51N11O14SZn (Zn2+-L-2.2(NO3-). 3H(2) O), M-r = 863.22, monoclinic, space group C2/n (No. 15), a = 35.361(1) Angs trom, b = 13.7298(5) Angstrom, c = 18.5998(6) Angstrom, beta = 119.073(2)de grees, V = 7892.3(5) Angstrom (3), Z = 8, R1 = 0.084. Other divalent metal ions did not interact with L-2 at all (e.g., Mg2+ and Ca2+) or interacted w ith L-2 With the dansyl fluorescence quenched (e.g., Cu2+).