Diazacoronand linked beta-cyclodextrin dimer complexes of Brilliant Yellow tetraanion and their sodium(I) analogues.

Complexation of the Brilliant Yellow tetraanion, 3(4-), by two new diazacoronand linked beta-cyclodextrin (beta CD) dimers 4,13-bis(2-(6A-deoxy-beta-cyclodextrin-6A-yl)aminooctylamidomethyl- and 4,13-bis(8-(6A-deoxy-beta-cyclodextrin-6A-yl)aminooctylamidomethyl)-4,13- diaza-1,7,10-trioxacyclopentadecane, 1 and 2, respectively, has been studied in aqueous solution. UV-visible spectrophotometric studies at 298.2 K, pH 10.0 and I = 0.10 mol dm-3 (NEt4ClO4) yielded complexation constants for the complexes 1 x 3(4-) and 2 x 3(4-), K1 = (1.08 +/- 0.01) x 10(5) and (6.21 +/- 0.08) x 10(3) dm3 mol-1, respectively. Similar studies at 298.2 K, pH 10.0 and I = 0.10 mol dm-3 (NaClO4) yielded K3 = (4.63 +/- 0.09) x 10(5) and (3.38 +/- 0.05) x 10(4) dm3 mol-1 for the complexation of 3(4-) by Na+ x 1 and Na+ x 2 to give Na+ x 1 x 3(4-) and Na+ x 2 x 3(4-), respectively. Potentiometric studies of the complexation of Na+ by 1 and 2 by the diazacoronand component of the linkers to give Na+ x 1 and Na+ x 2 yielded K2 = (2.00 +/- 0.05) x 10(3) and (1.8 +/- 0.05) x 10(3) dm3 mol-1, respectively, at 298.2 K and I = 0.10 mol dm-3(NEt4ClO4). For complexation of Na+ by 1 x 3(4-) and 2 x 3(4-) to give Na+ x 1 x 3(4-) and Na+ x 2 x 3(4-) K2K3/K1 = K4 = 8.6 x 10(2) and 9.8 x 10(3) dm3 mol-1, respectively. The pKaS of 1H4(4+) are 7.63 +/- 0.01, 6.84 +/- 0.02, 5.51 +/- 0.04 and 4.98 +/- 0.03, and those of 2H4(4+) are 8.67 +/- 0.02, 8.11 +/- 0.02, 6.06 +/- 0.02 and 5.14 +/- 0.05. The larger magnitude of K1 for 1 by comparison with K1 for 2 is attributed to the octamethylene linkers of 2 competing with 3(4-) for occupancy of the annuli of the beta CD entities while the competitive ability of the dimethylene linkers of 1 is less. A similar argument applies to the relative magnitudes of K3 for Na+ x 1 and Na+ x 2. Increased electrostatic attraction probably accounts for K3 > K1 for Na+ x 1 x 3(4-) and 1 x 3(4-) and for Na+ x 2 x 3(4-) and 2 x 3(4-). The lesser magnitudes of K2 and K4 for Na+ x 1 and Na+ x 1 x 3(4-) compared with those for Na+ x 2 and Na+ x 2 x 3(4-) are attributed to the octamethylene linkers of 2 producing a more hydrophobic environment for the diazacoronand than that produced by the dimethylene linkers of 1. 1H NMR spectroscopic studies and the syntheses of 1 and 2 are described.

Coordination and fluorescence of the intracellular Zn2+ probe [2-methyl-8-(4-toluenesulfonamido)-6-quinolyloxy]acetic acid (Zinquin A) in ternary Zn2+ complexes.

A potentiometric study of the coordination of the fluorophore, 2-methyl-8-(4-toluenesulfonamido)-6-quinolyloxyacetic acid, (1)LH(2) (the intracellular Zn(2+) probe, Zinquin A) in its deprotonated form, (1)L(2)(-), in Zn(2+) ternary complexes, [Zn(n)L(1)L](n) (where n is the charge of (n)L) at 298.2 K in 50% aqueous ethanol (v/v) and I = 0.10 (NaClO(4)), shows that the formation of [Zn(n)L(1)L](n) from [Zn(n)L]((2+)(n)(+) is characterized by log(K(5)/dm(3) mol(-1)) = 8.23 +/- 0.05, 4.36 +/- 0.18, 8.45 +/- 0.10, 10.00 +/- 0.06, 11.53 +/- 0.06 and 5.92 +/- 0.15, respectively, where (n)L = (2)L - (6)L and (7)L(3-) are 1,4,7,10-tetraazacyclododecane, 1,4,8,11-tetraazacyclotetradecane, 1,4,7-triazacyclononane, 1,5,9-triazacyclododecane, tris(2-aminoethyl)amine and nitrilotriacetate, respectively, and K(5) is the stepwise complexation constant. Dissociation of a hydroxo proton from triethanolamine, (8)L, occurs in the formation of [Zn(8)LH(-1)](+) that subsequently forms [Zn(8)LH(-1)(1)L](-) for which log(K(5)/dm(3) mol(-1)) = 9.87 +/- 0.08. The variation of K(5) and the 5-fold variation of quantum yield of (1)L(2)(-) as its coordination environment changes in Zn(2+) ternary complexes are discussed with reference to the use of (1)L(2-) in the detection of intracellular Zn(2+).