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+).

The syntheses of the 4- and 5-methoxy isomers of 4-N-(6-methoxy-2-methyl-8-quinolyl)-4-methylbenzenesulfon-amide and of N-(2-methoxy-8-quinolyl)-4-methylbenzenesulfonamide are described. The 6-methoxy compound is a precursor of Zinquin ester, a specific fluorophore for Zn(II). The 2-methoxy analogue was synthesized by nitration of 2-chloroquinoline and subsequent functional group manipulation. The 4-methoxy isomer was synthesized from a 4-quinolone derivative, and the 5-methoxy isomer was synthesized by a standard Skraup quinoline synthesis. The structures of the 4- and 5-methoxy isomers were determined by single-crystal X-ray analysis. All of these compounds showed a bathochromic shift in their ultraviolet/visible spectra upon addition of Zn(II) to the solution. These compounds are all weakly or non-fluorescent in solution. All form fluorescent complexes with Zn(II) except the 5-methoxy compound. The 4-methoxy compound forms a significantly more fluorescent complex than those of the 6-methoxy compound and Zinquin ester and has a higher quantum yield than the others.

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The formation of fluorescent alkali metal and alkaline earth complexes of 1-(2-{10-[2-piperazinoethyl]-9-anthryl}ethyl)piperazine (1) and alkaline earth complexes by 4-(2-{10-[2-(1,4-thiazinan-4-yl)ethyl]-9-anthryl}ethyl)thiomorpholine (2) in acetonitrile is reported. Both (1) and (2) have ‘fluorophore–spacer–receptor’ structures in the sequences ‘anthracene–dimethylene–piperazine’ and ‘anthracene–dimethylene–thiomorpholine’, respectively. Complexation by alkali metal ions and alkaline earth ions, Mm+, modulate photoinduced electron transfer (PET) to increase the fluorescence of (1) and complexation of alkaline earth ions similarly increases the fluorescence of (2). The two receptors of (1) and (2) may either complex Mm+ singly to form [ML]m+ or cooperatively to form a ‘sandwich’ complex [ML′]m+ characterized together by complexation constant K1 and quantum yield φ1. They may also complex two Mm+ in [M2L]2m+ characterized by K2 and φ2. Typical data are exemplified for (1) and Mm+ = Na+ by K1 = 1.33 × 105 dm3 mol–1 (φ1 = 0.02) and K2 = 4.20 × 102 dm3 mol–1 (φ1 = 0.07), for (1) and Mm+ = Ca2+ by K1 = 3.2 × 106 dm3 mol–1 (φ1 = 0.34) and K2 = 1.32 × 104 dm3 mol–1 (φ2 = 0.54), and for (2) and Mm+ = Ca2+ by K1 = 2.29 × 104 dm3 mol–1 (φ1 = 0.20) and K2 = 8.0 × 102 dm3 mol–1 (φ2 = 0.57) at 298.2 K and I = 0.05 mol dm–3 (NEt4ClO4). These data are compared with those for the alkaline earth complexes of 4-{2-[10-(2-morpholinoethyl)-9-anthryl]ethyl}morpholine. In 40 : 60 (v/v) 1,4-dioxan/water, protonation modulates PET to increase the fluorescence of (1)H44+ and (2)H22+. (The pKa values of (1)H44+ are 9.02, 8.06, 4.32, and 2.96 at 298.2 K and I = 0.05 mol dm–3 (NEt4ClO4).) The syntheses of (1) and (2) are reported.

The formation of fluorescent alkaline earth complexes of 4-{2-[10-(2-morpholinoethyl)9-anthryl]methyl}morpholine and its new -ethyl}morpholine and -propyl}morpholine analogues, L = (1)–(3), in acetonitrile is reported. Each L has a ‘fluorophore–spacer–receptor’ structure in the sequence ‘anthracene–(methylene)n–morpholine’ in which quenching of the anthracene fluorophore becomes less effective as the receptor tertiary nitrogen becomes more distant with an increase in n from 1 to 3. Complexation by the alkaline earths (M2+) modulates photoinduced electron transfer (PET) and enhances the fluorescence of (1)–(3). The two alkyl morpholine receptors of (1)–(3) may either complex M2+ singly to form [ML]2+ and [M2L]4+ or cooperatively to form a [ML′]2+ ‘sandwich’ complex depending on the length of the alkyl spacer. Thus, (1) dominantly forms [ML]2+ and [ML′]2+ while (2) and (3) form all three complexes as exemplified by [Mg(2)]2+ and [Mg(2)′]2+ characterized by the overall complexation constant K1 = 9.19 × 104 dm3 mol−1 and [Mg2(2)]4+ characterized by the stepwise complexation constant K2 = 1.19 × 103 dm3 mol−1 at 298.2 K and I = 0.05 mol dm−3 (NEt4ClO4). The most stable and fluorescent complexes are formed by Mg2+ and Ca2+, consistent with M2+ size being an important factor affecting complex characteristics. Eighteen complexation constants and quantum yields are reported for the (1)–(3) complexes together with those for (1)–(3) alone. In 40 : 60 (v/v) 1,4-dioxan/water, protonation modulates PET to increase the fluorescence of (1)H22+–(3)H22+. (The pKa values for (2)H22+ are 6.38 and 5.62, and for (3)H22+ are 7.00 and 6.25.) The syntheses of (2) and (3) are reported.