100 (7.5/10). The intense fluorescence was only observed by
the naked-eye at the mole ratio of 7.5 : 10, though its image
was overexposed due to the excess emission (Fig. 3). Thus, the
naked-eye observation offered an approximate estimate of the
Ca2+ ion concentration. This visual sensing system operated
well in the presence of equimolar Li+, Na+, K+, Mg2+ and
Zn2+ cations, though addition of 5 equivalents of Na+ cation
caused significantly disturbance. It provides an effective basis
for the in situ determination of biologically important metal
cations.
Acknowledgements
The authors thank Professor Yasuo Kubo of Shimane University
for his valuable comments on photochemistry. This research
was supported in part by the Hayashi Memorial Foundation for
Female Natural Scientists.
Fig. 2 UV and fluorescence spectral changes of cyclen 1–Na+ complex
upon UV irradiation. Conditions: cyclen 1–Na+ complex, 1.0 × 10−5M;
in 2 mL of CH3CN; irradiated by UV lamp (254 nm). An asterisk (*)
indicates that this fluorescence is assignable to fluorene derivatives.
Notes and references
Table 1 Photoreaction profiles of armed cyclen 1 in the presence and
† The armed cyclen 1–NaCl complex was employed in Figs. 2 and 3,
because the free ligand was oily and unstable. Photo-irradiation was
carried out in a CH3CN solution (1.0 × 10−5 mol L−1) by UV lamp
(model UVGL-25; UVP Inc., 254 nm, 4 W). The reaction mixture was
analyzed by an HPLC method: Mightysil Si 60 (4.6 × 150 mm) (Kanto
Chemical Co. Inc.); ethyl acetate : hexane = 1 : 4. The obtained fluorene,
9-fluorenol and fluorenone were identified by comparison with authentic
samples.
absence of metal ions
Yield (%)a
Fluorenone
Fluorene derivatives
9-Fluorenol
No Metal
1–Na+
7
5
7
35
39
9
< 1
2
1
1–Ca2+
‡ Metal free cyclen ligand 1 was prepared in situ by the addition of four
equivalents of cryptand[2.2.1] to a CH3CN solution of cyclen 1–NaCl
complex (see ref. 17). Its Ca2+ complex was prepared by addition of 1.5
equivalents of Ca(CF3SO3)2 in CH3CN. After removal of solvent, the
CH2Cl2-soluble fraction was separated. The precipitation from CH2Cl2–
hexane gave a white powder of armed cyclen 1–Ca2+ complex (yield,
31%): mp 209–211 ◦C (decomposition); tmax(neat)/cm−1 1683 (CO);
m/z (ESI, CH3CN) 550 (M2+) and 1250 (M + CF3SO3+); dH(400 MHz,
CD3CN) 2.61 (4H, br d), 2.81 (4H, br d), 3.07 (4H, br s), 3.42 (4H, br
s), 3.68 (4H, br d), 4.27 (4H, br d), 6.27 (4H, br s), 7.06 (4H, s), 7.11
(4H, br s), 7.34 (4H, br s), 7.49 (4H, br s), 7.64 (4H, br s), 7.73 (8H, br
s) and 8.05 (4H, br s); dC(100 MHz, CD3CN) 48.86, 54.29, 57.39, 79.37,
121.15 (q, JC–F = 319 Hz), 121.61, 126.75, 129.20, 131.33, 140.06, 141.30
and 181.14; Found: C, 58.15; H, 4.25; N, 3.98. Calc. for C68H60N4O8–
Ca(CF3SO3)2·2.5H2O: C, 58.20; H, 4.54; N, 3.88.
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a Estimated from HPLC peak area and their UV absorption coefficients.
complexation significantly suppressed fluorenone production,
mainly due to a-cleavage, while the Na+ complex showed
reactivity and product distribution similar to those observed
with cyclen 1 itself. Although the two ions have similar ion-sizes
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The photoreaction of fluorenyl ester-armed cyclen 1 was
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NaCl complex and Ca2+ ion were mixed in various mole ratios.
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was typically added to a series of CH3CN solutions containing
the cyclen 1–NaCl complex (1.0, 2.5, 5.0 and 7.5 × 10−6 mol L−1,
10.00 mL), UV irradiation was carried out for 1 min (see
4th column in Fig. 3). The observed fluorescence intensity at
505 nm was modestly recorded in the presence of a large excess
of Ca2+ ion, but significantly increased as the mole ratio of
cyclen 1 to Ca2+ ion approached 1: relative fluorescence intensity
(mole ratio) = 5.1 (1/10) < 11 (2.5/10) < 27 (5.0/10) <<
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Fig. 3 Visual sensing of Ca2+ ion concentration: pictures of photore-
action mixtures. Cyclen 1–NaCl complex and Ca2+ ion were mixed
in various mole ratios and UV-irradiated for 30 s: CH3CN solution
containing cyclen 1–NaCl complex (1.0, 2.5, 5.0, 7.5 × 10−6 mol L−1
,
10.00 mL); aqueous CaCl2 sample solution (0, 0.5, 1.0, 2.0, 3.0, 4.0 ×
10−3 mol L−1, 0.05 mL).
1 6 1 6
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 6 1 5 – 1 6 1 6