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

Article abstract of DOI:10.1021/ja0033786

A cyclen (=1,4,7,10-tetraazacyclododecane) doubly functionalized with three carbamoylmethyl groups and one dansylaminoethyl (dansyl = 2-(5-(dimethylamino)-1-naphthalenesulfonyl) group (L² = 1-(2-(5-(dimethylamino)-1-naphthalenesulfonylamido)eth

Full text of DOI:10.1021/ja0033786

J. Am. Chem. Soc. 2001, 123, 1123-1132
1123
A Double-Functionalized Cyclen with Carbamoyl and Dansyl Groups
(Cyclen ) 1,4,7,10-Tetraazacyclododecane): A Selective Fluorescent
Probe for Y3+ and La3+
Shin Aoki,† Hiroki Kawatani,† Teruhiro Goto,† Eiichi Kimura,*,† and Motoo Shiro‡
Contribution from the Department of Medicinal Chemistry, Faculty of Medicine,
Hiroshima UniVersity, Kasumi 1-2-3, Minami-ku, Hiroshima, 734-8551, Japan, and Rigaku Corporation
X-ray Research Laboratory, Matsubaracho 3-9-12, Akishima, Tokyo, 196-8666, Japan
ReceiVed September 14, 2000
Abstract: A cyclen ()1,4,7,10-tetraazacyclododecane) doubly functionalized with three carbamoylmethyl groups
and one dansylaminoethyl (dansyl ) 2-(5-(dimethylamino)-1-naphthalenesulfonyl) group (L2 ) 1-(2-(5-
(dimethylamino)-1-naphthalenesulfonylamido)ethyl)-4,7,10-tris(carbamoylmethyl)-cyclen) was synthesized and
characterized. Potentiometrtic pH titration and UV spectrophotometric titration of L2 served to determine
deprotonation of the pendant dansylamide (L2 f H-1L2) with a pKa value of 10.6, while the fluorometric
titration disclosed a pKa value of 8.8 ( 0.2, which was assigned to the dansyl deprotonation in the excited
state. The 1:1 M3+-H-1L2 complexation constants (log Kapp ) 6.0 for Y3+ and 5.2 for La3+, where Kapp(M-
H-1L2) ) [M3+-H-1L2]/[M3+ free[L2]free (M-1) at pH 7.4) were determined by potentiometric pH titration and
]
UV and fluorescence spectrophotometric titrations (excitation at 335 nm and emission at 520 nm) in aqueous
solution (with I ) 0.1 (NaNO3)) and 25 °C. The X-ray structure analysis of the Y3+-H-1L complex showed
nine-coordinated Y3+ with four nitrogens of cyclen, three carbamoyl oxygens, and the deprotonated nitrogen
and a sulfonyl oxygen of the dansylamide. The crystal data are as follow: formula C28H49N11O13.5SY (Y3+
-
H-1L2‚2(NO3-)‚2.5H2O), Mr ) 876.73, monoclinic, space group P21/n (No. 14), a ) 18.912(3) Å, b ) 17.042-
(3) Å, c ) 24.318(4) Å, â ) 95.99(1)°, V ) 7794(2) Å3, Z ) 8, R1 ) 0.099. Upon 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 Ln3+-H-1L2 complexes with similar Kapp values, although all
the dansyl fluorescences were weakly quenched. On the other hand, zinc(II) formed only a 1:1 Zn2+-L2
complex at neutral pH with negligible fluorescence change. The X-ray crystal structure of the Zn2+-L2 complex
confirmed the pendant dansylamide being noncoordinating. The crystal data are as follow: formula
C28H51N11O14SZn (Zn2+-L2‚2(NO3-)‚3H2O), Mr ) 863.22, monoclinic, space group C2/n (No. 15), a ) 35.361-
(1) Å, b ) 13.7298(5) Å, c ) 18.5998(6) Å, â ) 119.073(2)°, V ) 7892.3(5) Å3, Z ) 8, R1 ) 0.084. Other
divalent metal ions did not interact with L2 at all (e.g., Mg2+ and Ca2+) or interacted with L2 with the dansyl
fluorescence quenched (e.g., Cu2+).
Introduction
[Ln-(TCMC)]3+ (e.g., 1 where Ln ) La) efficiently promoted
RNA cleavage6 (TCMC ) 1,4,7,10-tetrakis(carbamoylmethyl)-
cyclen, which is also called DOTAM2,7). Characterization
including an X-ray crystal structure of [Ln-(TCMC)]3+ indi-
cated strong coordination of the carbamoyl groups.6a,c The
Macrocyclic polyamines including cyclen ()1,4,7,10-tet-
raazacyclododecane) with attached acetates or carbamoylmethyls
are useful ligands for lanthanide(III) ions in aqueous solution.1-3
The resulting 1:1 complexes are kinetically and thermodynami-
cally stable and useful for magnetic resonance imaging (e.g.,
Gd),1c radiotherapeutic applications (e.g., Y),4 or catalysis (e.g.,
Y, La, and Yb).5 Morrow found that among cationic Ln3+ (Ln
) La, Eu, Dy) tetrakis(carbamoylmethyl)cyclen complexes,
(4) (a) Anderson, C. J.; Welch, M. J. Chem. ReV. 1999, 99, 2219-2234.
(b) Volkert, W. A.; Hoffman, T. J. Chem. ReV. 1999, 99, 2269-2292. (c)
Takeunouchi, K.; Watanabe, K.; Kato, Y.; Koike, T.; Kimura, E. J. Org.
Chem. 1993, 58, 1955-1958. (d) Takenouchi, K.; Tabe, M.; Watanabe,
K.; Hazato, A.; Kato, Y.; Shionoya, M.; Koike, T.; Kimura, E. J. Org.
Chem. 1993, 58, 6895-6899. (e) Moi, M. K.; DeNardo, S. J.; Meares, C.
F. Cancer Res. 1990, 50 (Suppl), 789s-793s.
(5) (a) Shibasaki, M.; Sasai, H.; Arai, T. Angew. Chem., Int. Ed. Engl.
1997, 36, 1237-1256. (b) Kobayashi, S. In Organic Synthesis in Water;
Grieco, P. A. Ed.; Blackie Academic & Professional: London, 1998; pp
262-305.
(6) (a) Amin, S.; Morrow, J. R.; Lake, C. H.; Churchill, M. R. Angew.
Chem., Int. Ed. Engl. 1994, 33, 773-775. (b) Morrow, J. R.; Amin, S.;
Lake, C. H.; Churchill, M. R. Inorg. Chem. 1993, 32, 4566-4572. (c) Amin,
S.; Voss, D. A.; Horrocks, W. D., Jr.; Lake, C. H.; Churchill, M. R.; Morrow,
J. R. Inorg. Chem. 1994, 33, 3294-3300.
(7) (a) Carlton, L.; Hancock, R. D.; Maumela, H.; Wainwright, K. P. J.
J. Chem. Soc., Chem. Commun. 1994, 1007-1008. (b) Maumela, H.;
Hancock, R. D.; Carlton, L.; Reibenspies, J. H.; Wainwright, K. P. J. Am.
Chem. Soc. 1995, 117, 6698-6707.
* To whom correspondence should be addressed. E-mail: ekimura@
hiroshima-u.ac.jp.
† Hiroshima University.
‡ Rigaku Corp.
(1) (a) Alexander, V. Chem. ReV. 1995, 95, 273-342. (b) Parker, D.;
Williams, J. A. G. J. Chem. Soc., Dalton Trans. 1996, 3613-3628. (c)
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Solutions; Plenum Press: New York, 1996. (b) Hancock, R. D.; Martell,
A. E. Chem. ReV. 1989, 89, 1875-1914.
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10.1021/ja0033786 CCC: $20.00 © 2001 American Chemical Society
Published on Web 01/23/2001

1124 J. Am. Chem. Soc., Vol. 123, No. 6, 2001
Aoki et al.
dramatic difference in the reactivity of [Ln-(TCMC)]3+ in RNA
cleavage was attributed to the larger number of coordination
sites of the larger La3+ complexes compared to other Ln3+
complexes, whereby RNA phosphodiesters interacted with La3+
.
In an effort to design useful fluorescent sensors for La3+ and
other relevant M3+, by using the principle of Zn2+-3a com-
plexation, we now have incorporated three carbamoylmethyl
pendants to 3a to make 4 (L2). The three carbamoyl pendants
might affect the microenvironment surrounding the fluorescent
dansyl pendant. After this work was almost finished, Lowe and
Parker independently reported the pH-dependent luminescence
properties of Eu3+- and Tb3+-cyclens appended with an aryl-
sulfonamide and three acetate groups.13 This paper describes
metal-dependent ligation of the sulfonamide and the resulting
dansyl fluorescence responses. It is of interest that 4 allowed a
direct comparison of characteristic acid and coordinating
properties of lanthanide(III) ions and zinc(II) ion.14
On the other hand, among Ln3+ complexes with tetrakis-
(hydroxyethylcyclen) (THED), [Eu-(THED)]3+ 2 was the most
efficient catalyst in the hydrolysis of phosphate diesters, due to
the higher acidity of the Eu3+ complex. One of the metal-bound
hydroxyls deprotonated to 2b with a pKa of 7.4, which provided
a strong nucleophile to attack phosphate esters.8 It is apparent
that Ln3+ remained as strong Lewis acids in these chelates, as
illustrated by the pKa value of 7.4 for a pendant alcohol in 2.
Zinc(II) ions, biologically the most useful Lewis acid, have
been extensively explored as catalysts for ester hydrolyses.9,10
For instance, a hydroxyethylcyclen10a,b efficiently cleaves phos-
phodiesters such as the Eu3+ complex 2b at neutral pH.
Recently, the acidic properties of Zn2+ were used with a dansyl-
pendant cyclen 3a (L1),11 whereby a nanomolar concentration
of Zn2+ was sensed in the deprotonated amide binding complex
3b (Zn2+-H-1L1) with strong fluorescent emission.12
Results
Synthesis of 1-Dansylamidoethyl-4,7,10-tris(carbamoyl-
methyl)-cyclen L2 (4). The ligand 4 was synthesized as shown
in Scheme 1. The mono-N-Cbz-cyclen 7 was obtained as the
3HCl salt by reaction of 3Boc-cyclen 515 with benzyl chloro-
formate (CbzCl) and successive deprotection of three Boc groups
of 6. The acid-free 7 was alkylated with 2-bromoacetoamide to
give 8, whose Cbz group was removed by a conventional
method (H2, Pd/C) to afford 9. Successive alkylation of 9 with
10 gave 4, which was isolated as the 3HCl salt.
(8) For other examplexes of Ln3+-promoted RNA cleavage, see: Magda,
D.; Miller, R. A.; Sessler, J. L.; Iverson, B. L. J. Am. Chem. Soc. 1994,
116, 7439-7440 and references therein.
(9) For other reviews, see: (a) Kimura, E.; Shionoya, M. In Transition
Metals in Supramolecular Chemistry; Fabbrizzi, L., Poggi, A., Eds.;, Kluwer
Academic Publishers: Dordrecht, 1994; pp 245-259. (b) Kimura, E. In
Progress in Inorganic Chemistry; Karlin, K. D., Ed.; John Wiley & Sons:
New York, 1994; Vol. 41, pp 443-491. (c) Kimura, E.; Shionoya, M. In
Metal Ions in Biological Systems; Sigel, A., Sigel, H., Eds.; Marcel
Dekker: New York, 1996; Vol. 33, pp 29-52. (d) Kimura, E.; Koike, T.;
Aoki, S. J. Synth. Org. Chem., Jpn. 1997, 55, 1052-1061. (e) Kimura, E.;
Koike, T. J. Chem. Soc., Chem. Commun. 1998, 1495-1500. (f) Kimura,
E.; Koike, T. In Bioinorganic Catalysis; Reedijk, J., Bouwman, E., Eds.;
Marcel Dekker: New York, 1999; pp 33-54. (g) Kimura, E. Curr. Opin.
Chem. Biol. 2000, 4, 207-213. (h) Kimura, E.; Kikuta, E. J. Biol. Inorg.
Chem. 2000, 5, 139-155.
(10) (a) Koike, T.; Kajitani, S.; Nakamura, I.; Kimura, E.; Shiro, M. J.
Am. Chem. Soc. 1995, 117, 1210-1219. (b) Kimura, E.; Kodama, Y.; Koike,
T.; Shiro, M. J. Am. Chem. Soc. 1995, 117, 8304-8311. (c) Kimura, E.;
Hashimoto, H.; Koike, T. J. Am. Chem. Soc. 1996, 118, 10963-10970. (d)
Koike, T.; Inoue, M.; Kimura, E.; Shiro, M. J. Am. Chem. Soc. 1996, 118,
3091-3099.
Determination of Protonation Constants for 4 (L2). The
protonation constants (Kn) of 4 (L2) were determined by
potentiometric and spectrophotometric pH titrations of 4‚3HCl‚
2H2O (1 mM) against 0.10 mM NaOH with I ) 0.10 (NaNO3)
at 25 °C. A typical potentiometric pH titration curve is shown
in Figure 1a, which indicates dissociation of four protons at 0
< eq(OH-) < 4. The titration data were analyzed for the acid-
base equilibria 1 and 2, where aH is the activity of H+. The
+
four protonation constants, K1, K2, K3, and K4, were calculated
by using the program BEST,16 as summarized in logarithmic
numbers in Scheme 2.
H-1L2 + H+ a L2:
K1 ) [L2]/[H-1L2]aH
(1)
Kn ) [Hn-1L2]/[Hn-2L2]aH
(11) (a) Koike, T.; Watanabe, T.; Aoki, S.; Kimura, E.; Shiro, M. J.
Am. Chem. Soc. 1996, 118, 12696-12703. (b) Koike, T.; Kimura, E.;
Nakamura, I.; Hashimoto, Y.; Shiro, M. J. Am. Chem. Soc. 1992, 114,
7338-7345. For reviews, see: (c) Kimura, E. S.-Afr. Tydskr. Chem. 1997,
50, 240-248. (d) Kimura, E.; Koike, T. Chem. Soc. ReV. 1998, 27, 179-
184. The ligand 4‚5HCl is commercially available from Dojindo Labora-
tories, Japan.
+
Hn-2L2 + H+ a Hn-1L2:
+
(n ) 2, 3, 4) (2)
(12) For other zinc(II) fluorophores, see: (a) Czarnik, A. W. Acc. Chem.
Res. 1994, 27, 302-308. (b) Zalewski, P. D.; Forbes, I. J.; Seamark, R. F.;
Borlinghaus, R.; Betts, W. H.; Lincoln, S. F.; Ward, A. D. Chem. Biol.
1994, 1, 153-161. (c) Hendrickson, K. M.; Rodopoulos, T.; Pittet, P.-A.;
Mahadevan, I.; Lincoln, S. F.; Ward, A. D.; Kurucsev, T.; Duckworth, P.
A.; Forbes, I. J.; Zalewski, P. D.; Betts, W. H. J. Chem. Soc., Dalton Trans.
1997, 3879-3882. (d) Godwin, H. A.; Berg, J. M. J. Am. Chem. Soc. 1996,
118, 6514-6515. (e) Walkup, G. K.; Imperiali, B. J. Am. Chem. Soc. 1997,
119, 3443-3450. (f) Thompson, R. B.; Maliwal, B. P.; Fierke, C. A. Anal.
Chem. 1998, 70, 1749-1754. (g) Sarwar Nasir, M.; Fahrni, C. J.; Suhy, D.
A.; Kolodsick, K. J.; Singer, C. P.; O’Halloran, T. V. J. Biol. Inorg. Chem.
1999, 4, 775-783. (h) Reany, O.; Gunnlaugsson, T.; Parker, D. J. Chem.
Soc., Chem. Commun. 2000, 473-474. (i) Hirano, T.; Kikuchi, K.; Urano,
Y.; Higuchi, T.; Nagano, T. Angew. Chem., Int. Ed. Engl. 2000, 39, 1052-
1054. (j) Walkup, G. K.; Burdette, S. C.; Lippard, S. J.; Tsien, R. Y. J.
Am. Chem. Soc. 2000, 122, 5644-5645.
(13) Lowe, M. P.; Parker, D. J. Chem. Soc., Chem. Commun. 2000, 707-
708.
(14) For previous examples of luminiscent lanthanide(III) complexes,
see: (a) Alpha, B.; Lehn, J.-M.; Mathis, G. Angew. Chem., Int. Ed. Engl.
1987, 26, 266-267. (b) Alpha, B.; Balzani, V.; Lehn, J.-M.; Perathoner,
S.; Sabbatini, N. Angew. Chem., Int. Ed. Engl. 1987, 26, 1266-1267. (c)
Balzani, V.; Lehn, J.-M.; van de Loosdrecht, J.; Mecati, A.; Sabbatini, N.;
Ziessel, R. Angew. Chem., Int. Ed. Engl. 1991, 30, 190-191. (d) Saha, A.
K.; Kross, K.; Kloszewski, E. D.; Upson, D. A.; Toner, J. L.; Anow, R. A.;
Black, C. D. V.; Desai, V. C. J. Am. Chem. Soc. 1995, 115, 11032-11033.
(e) Gunnlaugsson, T.; Parker, D. J. Chem. Soc., Chem. Commun. 1998,
511-512.
(15) Kimura, E.; Aoki, S.; Koike, T.; Shiro, M. J. Am. Chem. Soc. 1997,
119, 3068-3076.
(16) Martell, A. E.; Motekaitis, R. J. Determination and Use of Stability
Constants, 2nd ed.; VCH: New York, 1992.

A SelectiVe Fluorescent Probe for Y3+ and La3+
J. Am. Chem. Soc., Vol. 123, No. 6, 2001 1125
Table 1. Protonation Constants [log Kn and log K5(M-H-1L)] and
Complexation Constants [log K(M-L), log Kapp(M-H-1L) at pH
7.4] of Cyclen, TCMC, 3a, and 4 at 25 °C with I ) 0.1 (NaNO3)a
cyclenb
TCMC
3ae
4
log K1
log K2
log K3
log K4
log K(Zn-L)
log K5(Zn-H-1L)
log K(Y-L)
log K5(Y-H-1L)
log Kapp(Y-H-1L)
log K(La-L)
log K5(La-H-1L)
log Kapp(La-H-1L)
11.0
9.9
7.5c (7.7)d
6.0c (6.2)d
11.8
10.8
9.4
4.0
20.8
5.0
10.6
8.4
6.1
3.5
11.8
10.7
<2
<2c
<2
<2c
15.3
10.5d
6.0
5.5
negf
6.0g
5.5
Figure 1. Typical pH titration curves of 1 mM 4 (a), 1 mM 4 + 1
mM Y3+ (b), 1 mM 4 + 1 mM La3+ (c), and 1 mM 4 + 1 mM Zn2+
(d) at 25 °C with I ) 0.1 (NaNO3), where eq(OH-) is the number of
equivalents of base added.
10.4d
6.2
negf
5.2g
a For the definitions of Kn, K(M-L), K5(M-H-1L), and Kapp(M-
H-1L), see the text. The same titration was carried out at least twice,
and the experimental errors were (3%. b From ref 10a at 25 °C with
I ) 0.1 (NaNO3). c Reference 17. d From ref 7b at 25 °C in 0.1 M
NaNO3. e From ref 11a at 25 °C with I ) 0.1 (NaNO3). f neg )
negligible. The addition of Y3+ or La3+ to 3a had negligible effects on
UV absorption and fluorescence emission spectra. g At pH 7.4.
Scheme 1
Scheme 2
Figure 2. UV-pH profile for 4 (0.1 mM) at 25 °C with I ) 0.1
(NaNO3), (a) at pH 7.4, λmax ) 330 nm (ꢀ 4.5 × 103); (b) at pH 11.8,
λmax ) 320 nm (ꢀ 4.7 × 103); (c) +2 equiv of Y3+ at pH 7.4; (d) +2
equiv of La3+ at pH 7.4.
NHR (L2)) caused the UV absorption spectral change from curve
(a) at pH 7.4 to curve (b) at pH 11.8, from which the pK1 value
of 10.6 was determined. Figure 3a compares pH-dependent
changes in the ꢀ value at 320 nm for 3a and 4 with I ) 0.1
(NaNO3) at 25 °C.
Curve (a) in Figure 4 shows a fluorescence emission spectrum
of 10 µM 4 (Φ (quantum yield) ) 0.03) at pH 7.4 (10 mM
HEPES with I ) 0.1 (NaNO3)), which is almost the same curve
as that of 3a under the same conditions. A remarkable difference
between 3a and 4 was seen in the pH-dependent fluorescence
titration of the dansyl in 10 mM Good’s buffer solutions (Figure
3b). While the fluorescence emission intensity (I) of 3a at 520
nm (excitation at 335 nm) increased by only ca. 30% with a
pKa of 11.8, that of 4 increased dramatically (I/I0 ) 8.5, where
I0 is the fluorescence intensity of 4 (10 µM) at pH 7.4 and 25
°C) (see curve (b) in Figure 4) with a much smaller pKa of 8.8
( 0.2. A quantum yield of 4 at pH 11.0 (Φ ) 0.18) is 6 times
larger than that at pH 7.4 (0.03) (excitation at 335 nm) (this
latter value is almost the same as that of 3a at pH 7.4 (0.03)11a).
The pH-dependent fluorescence curve for 4 (Figure 3b) fit to
the sum of population of L2 and H-1L2 in the speciation diagram
of 4 (Figure 3c). It is concluded that the break at pH 8.8 in
Figure 3b denotes the pKa for (HL2)+ a L2, and, at the same
time, the strong fluorescence due to unprotonated L2 predomi-
nates in Figure 3b for 4. It is suggested that, upon total removal
of protons from the cyclen moiety, three carbamoyl groups may
somehow work to create a hydrophobic microenvironment
around the dansyl group to increase the fluorescence. Naphthyl
fluorescent probes are well known to dramatically increase the
The assignment of the four protonation mode shown in
Scheme 2 is based on the following facts: (i) diprotonated
TCMC ()DOTAM)2 had two protonation constants of 7.5 and
6.0 (Table 1);7b,17 (ii) the pH-dependent UV spectral change
for 4 at 25 °C with I ) 0.1 (NaNO3) (see below) gave a pK1 of
10.6, assignable to ArSO2N-R (H-1L2) + H+ a ArSO2NHR
(L2); and (iii) the log K4 value of 3.5 was assigned for ArN-
(Me)2 (H2L2) + H+ a ArN+H(Me)2 (H3L2) by analogy with
the log K4 value of 4.0 for 3a11a (and by the UV absorption
spectral change of 4 at pH 2-6).
The UV and Fluorescence Spectral Titration of 4 (L2).
We examined the pH-dependent UV and fluorescence properties
of 4. As shown in Figure 2a, 4 has an absorption maximum at
330 nm (ꢀ ) 4.5 × 103 M-1‚cm-1) at pH 7.4 (50 mM HEPES
with I ) 0.1 (NaNO3) and 25 °C (3a has an absorption
maximum at 330 nm with ꢀ ) 4.95 × 103 M-1‚cm-1 at pH 7.3
with I ) 0.10 (NaNO3)11a). Deprotonation of the sulfonamide
NH of dansyl pendant (ArSO2N-R (H-1L2) + H+ a ArSO2-
(17) Kimura, E.; Hata, Y.; Shiro, M. Unpublished results.

1126 J. Am. Chem. Soc., Vol. 123, No. 6, 2001
Aoki et al.
Figure 5. Relative fluorescence intensity of 4 (10 µM) responding to
2 equiv of metal ions at pH 7.4 (10 mM HEPES) and pH 11.0 (10 mM
CAPS) and 25 °C with I ) 0.1 (NaNO3) based on the fluorescence
intensity height at 520 nm (excitation at 335 nm) and pH 7.4.
fluorescence in pH 11.0 aqueous solution (curve (b) in Figure
4). Similarly strong emissions were observed with uncomplexed
3a and N-dansyl-L-valine in MeCN/10 mM HEPES (pH 7.4 with
I ) 0.1 (NaNO3)) (99/1).18 However, 3a in pH 11 aqueous
solution gave a much weaker emission.
Characteristic Fluorescent Responses of 4 to Metal Ions.
We tested the fluorescent responses of 4 (10 µM) to various
metal ions at pH 7.4 (10 mM HEPES with I ) 0.1 (NaNO3))
and 25 °C (excitation at 335 nm, which is an isosbestic point
determined by UV titrations).20 As summarized in Figure 5, the
fluorescence of 4 at 520 nm was not affected by 1-2 equiv of
Figure 3. pH-dependent UV (a) and fluorescence (b) changes of 3a
(black circles) and 4 (white circles) at 25 °C. [3a or 4] ) 0.1 mM for
UV titration and [3a or 4] ) 10 µM for fluorescence titration. I0 is the
fluorescence intensity of 4 (10 µM) at 520 nm and pH 7.4. (c) Speciation
diagram for 10 µM 4 at 25 °C with I ) 0.1 (NaNO3).
Zn2+, Cd2+, Al3+, Fe3+, Au3+, Sc3+, Li+, Na+, K+, Mg2+, Ca2+
,
or Fe2+. On the other hand, Y3+ and La3+ greaty enhanced the
emission (8.6 and 3.8 times, respectively, with 2 equiv each).
It is of particular interest that 4 did not sense Zn2+, although 4
would complex with Zn2+. The emission of 4 was more or less
quenched by Cu2+, Eu3+, Gd3+, Tb3+, and Yb3+. These results
imply that 4 could be a selective fluorescence probe for Y3+
and La3+ at neutral pH in aqueous solution (vide infra).
Figure 4 compares the fluorescence spectra of 4 at various
conditions. Curves (d)-(f) are emission spectra of 4 in the
presence of 3 equiv of Y3+ (Φ ) 0.13), La3+(Φ ) 0.08), and
Eu3+ (Φ ) 0.01), respectively. As described later, the Y3+
-
H-1L2 complex 12a was isolated, which afforded a much larger
quantum yield of 0.26 in MeCN/10 mM HEPES (pH 7.4 with
I ) 0.1 (NaNO3)) (99/1) or MeCN (curve (g) in Figure 4).
Complexation of 4 with Zn2+, Y3+, and La3+ by Poten-
tiometric pH Titration. Complexation of 4 with zinc(II),
yttrium(III), and lanthanum(III) ions were studied by potentio-
metric pH titration of 4‚3HCl (1 mM) in the presence of an
equimolar amount of the metal ions at 25 °C with I ) 0.1
(NaNO3) (see Figure 1b-d). The titration curves for Y3+ (curve
(b)) and La3+ (curve (c)) revealed the formation of stable 1:1
Figure 4. Fluorescence emission spectra of 10 µM 4 at 25 °C with I
) 0.1 (NaNO3), (a) at pH 7.4 (Φ ) 0.03); (b) at pH 11.0 (Φ ) 0.18);
(c) in MeCN (Φ ) 0.19); (d) +30 µM Y3+ (Φ ) 0.13); (e) +30 µM
La3+ (Φ ) 0.08); (f) +30 µM Eu3+ (Φ ) 0.01); (g) Y3+-H-1L2
complex (12a) in MeCN (Φ ) 0.26).
fluorescence intensities in a hydrophobic environment.18,19
Interestingly, the fluorescence of uncomplexed 4 (10 µM) in
MeCN solution (curve (c) in Figure 4) was as strong as the
M
3+-H-1L2 complexes with deprotonated sulfonamide N-
coordination at 5 < pH < 7, on the basis of the lowered L2
buffer regions (at 1 < eq(OH-) < 4) and the neutralization break
at eq(OH-) ) 4. In contrast, curve (d) indicated that Zn2+
formed a more stable 1:1 Zn2+-L2 complex without deproto-
nation of the sulfonamide under pH 6 and at eq(OH-) < 3.
The complexation pattern is commonly shown as in Scheme
(18) (a) Li, Y.-H.; Chan, L.-M.; Tyer, L.; Moody, R. T.; Himel, C. M.;
Hercules, D. M. J. Am. Chem. Soc. 1975, 97, 3118-3126. (b) Cardona, C.
M.; Alvarez, J.; Kaifer, A. E.; McCarley, T. D.; Pandey, S.; Baker, G. A.;
Bonzagni, N. J.; Bright, F. V. J. Am. Chem. Soc. 2000, 122, 6139-6144.
(19) (a) Ikeda, H.; Nakamura, M.; Ise, N.; Oguma, N.; Nakamura, A.;
Ikeda, T.; Toda, F.; Ueno, A. J. Am. Chem. Soc. 1996, 118, 10980-10988.
(b) Ueno, A.; Ikeka, A.; Ikeda, H.; Ikeda, T.; Toda, F. J. Org. Chem. 1999,
64, 382-387. (c) Bu¨gler, J.; Engbersen, J. F. J.; Reinhoudt, D. N. J. Org.
Chem. 1998, 63, 5339-5344. (d) Matsumura, S.; Sakamoto, S.; Ueno, A.;
Mihara, H. Chem. Eur. J. 2000, 6, 1781-1788.
(20) The complexation of 4 with metal ions in general took more than
30 min at neutral pH. Practically, we allowed 1 h to complete the
complexation.

A SelectiVe Fluorescent Probe for Y3+ and La3+
J. Am. Chem. Soc., Vol. 123, No. 6, 2001 1127
Scheme 3
3.21 The complexation constants (K(M-L2)) with Y3+, La3+
,
and Zn2+ ions defined by Scheme 3 and eq 3 at 25 °C with I )
0.10 (NaNO3) were determined to be 6.0 (Y3+), 5.5 (La3+), and
11.8 (Zn2+) by the program BEST,16 as listed in Table 1. The
protonation constants, K5(M-H-1L2), as defined by eq 4, are
also listed in Table 1.22
M
n+ + L2 a Mn+-L2:
K(M-L2) ) [Mn+-L2]/[Mn+][L2]
Mn+-H-1L2 + H+ a Mn+-L2:
(M-1) (3)
K5(M-H-1L2) ) [Mn+-L2]/[Mn+-H-1L2]aH (4)
+
Kapp(M-H-1L2) ) [Mn+-H-1L2]/[Mn+]free[L2]free
(at designated pH)
(M-1) (5)
[L2]free ) [H3L2]free + [H2L2]free + [HL2]free + [L2]free
+
Figure 6. Speciation diagrams for the 1 mM 4 + 1 mM Y3+ (a), 1
mM 4 + 1 mM La3+ (b), and 1 mM 4 + 1 mM Zn2+ (c) as a function
of pH at 25 °C with I ) 0.1 (NaNO3). Other species which exist at
less than 5% are omitted for clarity.
[H-1L2]free + [Mn+-L2] (6)
For practical understanding, an apparent complex formation
constant, Kapp(M-H-1L2), was defined for the dansylamide-
deprotonated complex, Mn+-H-1L2, by eqs 5 and 6, at the
designated pH. The log Kapp(M-H-1L2) values for the Y3+ and
La3+ complexes were 6.0 and 5.5, respectively, at pH 7.4. These
Cd2+, Al3+, Sc3+, Y3+, La3+, Eu3+, Gd3+, Tb3+, and Yb3+) in
pH 7.4 buffer (50 mM HEPES) with I ) 0.1 (NaNO3) at 25
°C. Among them, Fe2+, Zn2+, Cd2+, Al3+, and Sc3+ (up to 2
equiv) caused little UV change. On the other hand, the UV
absorption of 4 shifted to shorter wavelengths (Figure 2) upon
log K(M-H-1L2) values are smaller than that for La3+
-
(TCMC) (10.4), although the apparent complexation constant,
log K(M-L2), for Zn2+-L2 (11.8) is comparable to that for
Zn2+-(TCMC) (10.5). This may be attributed to the nature of
lanthanide(III) ions, which prefer oxygen donors rather than
nitrogen donors.2
addition of Cu2+, Y3+ (curve (c)), La3+ (curve (d)), Eu3+, Gd3+
,
Tb3+, and Yb3+, indicating their interaction with the deproto-
nated sulfonamide. These facts matched with the results from
the potentiometric pH titrations. From the UV titration curves
in Figure 7a, log Kapp(M-H-1L2) values were estimated to be
5.8, 5.3, and 5.1 for Y3+, La3+, and Eu3+, respectively, which
are in reasonable agreement with the log Kapp(M-H-1L2) values
of 6.0 and 5.2 for Y3+ and La3+, respectively, determined earlier
by the potentiometric pH titration. The log Kapp(M-H-1L2)
values for other lanthanide(III) ions were within the range 5.8-
5.1 under the same conditions.
Figure 6a depicts a speciation diagram for a mixture of 4 (1
mM) and Y3+ (1 mM) as a function of pH at 25 °C with I )
0.1 (NaNO3), demonstrating the main population of the Y3+
-
H-1L2 complex 12a, over 95% at pH > 6.5. Figure 6b shows
that 4 forms La3+-H-1L2 12b (at [4] ) [La3+] ) 1 mM) over
95% at pH > 8. By contrast, Figure 6c shows that, at 5 < pH
< 9, Zn2+-L2 11c is the sole major species, and the deproto-
nation of the dansylamine did not occur, unlike the previous
Zn2+-3a complexation. The concentration of Zn2+-L2 became
equal to that of Zn2+-H-1L2 only at pH 10.7 ()pK5).
From the fluorescence titration of 4 (Figure 7b), the log Kapp
-
(M-H-1L2) values for Y3+, La3+, and Eu3+ were determined
to be 5.9, 5.4, and 5.3, respectively, which agreed reasonably
well with log Kapp(M-H-1L2) values obtained by the UV
titrations.
The UV Spectrophotometric and Fluorometric Titration
of 4 with La3+, Y3+, Eu3+, and Zn2+. The interaction of metal
ions with 4 at the dansylamide (λmax ) 330 nm, ꢀ ) 4.5 × 103
M-1‚cm-1 at pH 7.4) was examined by the UV spectrophoto-
X-ray Crystal Structures of Y3+-H-1L2 (12a) and Zn2+
-
L2 Complex (11c). Finally, the stable metal complexes of 4
isolated as 12a and 11c from pH 8 aqueous solution were
characterized by X-ray crystal structure analysis.
metric titration of 4 (0.1 mM) with metal ions (Fe2+, Cu2+, Zn2+
,
(21) From the potentiometric pH titrations and X-ray crystal structure
analysis of 11c and 12a, we concluded that no water molecule coordinates
to the metal ion in 12. The hydration state in 11 was not determined.
(22) It was reported that the Eu3+ and Tb3+ complexes of cyclens having
three acetate groups and an arylsulfonamide moiety (L) have log K5(M-
H-1L) values of 5.7-6.4 (ref 13).
Figure 8 is an ORTEP drawing of the Y3+-H-1L2 12a. The
dansylamide is certainly deprotonated to coordinate to the Y3+
ion. In total, Y3+ is nine-coordinate, with four nitrogen atoms
of the cyclen ring, carbonyl oxygens of three carbamolymethyl

1128 J. Am. Chem. Soc., Vol. 123, No. 6, 2001
Aoki et al.
Figure 9. ORTEP drawings (50% probability ellipsoides) of Zn2+
-
Figure 7. UV titration curves (a) and fluorescence titration curves (b)
of 4 with Zn2+ (white squares), Y3+ (black squares), La3+(white circles),
and Eu3+ (black circles) at 25 °C and pH 7.4 (50 mM HEPES for UV
titration and 10 mM HEPES for fluorescence titration) with I ) 0.1
(NaNO3) ([4] ) 0.1 mM for UV titration and [4] ) 10 µM for
fluorescence titration). eq(Mn+) is the number of equivalents of metal
added against 4.
L2 complex 11c. All external nitrates and water molecules are omitted
for clarity. Selected bond distances (Å): Zn1-N2 2.321(6), Zn1-N5
2.328(7), Zn1-N8 2.353(7), Zn1-N11 2.221(6), Zn1-O35 2.071(5),
Zn1-O39 2.235(5), Zn1-O43 2.214(5). Selected bond angles (deg):
O35-Zn1-O39 84.5(2), O35-Zn1-O43 79.8(2), O35-Zn1-N2 90.2-
(2), O35-Zn1-N5 76.8(2), O35-Zn1-N8 128.1(2), O35-Zn1-N11
152.5(2), O39-Zn1-O43 75.4(2), O39-Zn1-N2 161.6(2), O39-
Zn1-N5 116.4(2), O39-Zn1-N8 71.2(2), O39-Zn1-N11 98.3(2),
O43-Zn1-N2 86.4(2), O43-Zn1-N5 152.3(2), O43-Zn1-N8 132.4-
(2), O43-Zn1-N11 74.5(2), N2-Zn1-N5 79.2(2), N2-Zn1-N8
124.8(2), N2-Zn1-N11 78.5(2), N5-Zn1-N8 74.6(2), N5-Zn1-
N11 124.5(2), N8-Zn1-N11 77.9(2).
which are comparable to 2.64 Å for Eu3+-N(cyclen) and 2.39
Å for Eu3+-O(carbonyl) in nine-coordinate [Eu-(TCMC)-
(H2O)]3+ 13.6c In an homologous nine-coordinate Tb3+ complex
14, the average Tb3+-N(cyclen) and Tb3+-O(carbonyl) bond
lengths are 2.69 and 2.35 Å, respectively.17 As a result of the
coordination of three carbonyl oxygens (due to the swirl of the
pendant groups) and one of the two sulfonyl oxygens to the
Y
3+ ion (Y3+-O bond is 2.56 Å), 11 is a chiral molecule. In a
unit cell, both enantiomers are included. In Zn2+-H-1L1 3b,
the sulfonyl oxygen did not bind to Zn2+
.
Figure 8. ORTEP drawings (50% probability ellipsoides) of Y3+
-
H-1L2 complex 12a. All external nitrates and water molecules are
omitted for clarity. Selected bond distances (Å): Y1-N2 2.616(8), Y1-
N5 2.633(8), Y1-N8 2.606(8), Y1-N11 2.613(7), Y1-N16 2.342-
(7), Y1-O18 2.589(6), Y1-O35 2.365(7), Y1-O39 2.298(6), Y1-
O43 2.329(8). Selected bond angles (deg): O18-Y1-O35 67.1(2),
O18-Y1-O39 72.9(2), O18-Y1-O43 70.5(2), O18-Y1-N2 121.3-
(2), O18-Y1-N5 121.5(2), O18-Y1-N8 133.7(2), O18-Y1-N11
133.5(2), O18-Y1-N16 56.7(2), N2-Y1-N5 68.5(2), N2-Y1-N8
104.6(2), N2-Y1-N11 68.8(2), N2-Y1-N16 65.8(2), O18-S17-
N16 103.3(4), O19-S17-N16 116.3(4).
Figure 9 shows an ORTEP drawing of the Zn2+-L2 11c. It
is now unequivocally proven that the dansylamide proton is not
bound to Zn2+, and hence it locates off the cyclen ring with the
naphthalene ring almost perpendicular to the cyclen face. Zinc-
(II) is seven-coordinate with four nitrogens of the cyclen ring
(the average Zn2+-N bond is 2.31 Å) and three carbonyl
oxygens of carbamoylmethyls (the average Zn2+-O bond is
2.17 Å). For comparison, in the complex 3b, the average Zn2+
-
parts, one sulfonyl oxygen, and the N- of the sulfonamide,
whereby Y3+ has a square antiprismatic coordination geometry.
The Y3+-N-(dansylamide anion) bond length is 2.34 Å, which
is longer than the Zn2+-N- distance of 1.97 Å in Zn2+-H-1L1
N(cyclen) bond length was 2.13 Å. Four nitrogens of the cyclen
ring and the Zn2+ ion form a tetragonal pyramid, and three
oxygens of carbamoylmethyls and Zn2+ form a trigonal pyramid
in 11c.23 In a reported Zn2+-(TCMC) complex 15, Zn2+ is six-
coordinate with an average Zn2+-N distance of 2.25 Å.2,7b
Although the two orthogonal carbonyl oxygens coordinated to
3b. The average Y3+-N(cyclen) bond lengths and Y3+
-
O(carbonyl) bond lengths are 2.62 and 2.33 Å, respectively,

A SelectiVe Fluorescent Probe for Y3+ and La3+
J. Am. Chem. Soc., Vol. 123, No. 6, 2001 1129
Table 2. Selected X-ray Crystal Data for the Y3+ Complex 12a
and the Zn2+ Complex 11c
12a
11c
formula
Mr
cryst syst
space group
a (Å)
b (Å)
c (Å)
C28H49N11O13.5SY C28H51N11O14SZn
876.73
863.22
monoclinic
P21/c (No. 14)
18.912(3)
17.042(3)
24.318(4)
95.99(1)
7794(2)
8
monoclinic
C2/c (No. 15)
35.361(1)
13.7298(5)
18.5998(6)
119.073(2)
7892.3(5)
8
â (deg)
V (Å3)
Z
Figure 10. pH-dependent change of quantum yield ratios (ΦD/ΦH) of
3a (black circles), 4 (white circles), 11c (white squares), and 12a (black
squares) at 25 °C ([3a] ) [4] ) [11c] ) [12a] ) 10 µM).
D
calc (g‚cm-3
)
1.494
1.453
µ(Mo(Cu) KR) (cm-1
)
µ(Cu KR) ) 32.69 µ(Mo KR) ) 7.52
R1 (∑||Fσ| - |Fc||/∑|Fσ|)
no. of reflectns used for
calculation of R1 (I > 2σ(I))
no. of variables
0.160
7140
0.084
6125
the fluorescence emission in D2O and H2O, respectively), while
that for 1-naphthalenesulfonate containing no proton donor is
ca. 1.24 These results were interpreted as an isotope effect on
the rate of proton transfer during the excited-state lifetime. This
technique was applied to check the postulated polarized structure
16. The ΦD/ΦH values for 3a, 4, 11c, and 12a (all 10 µM) in
D2O and H2O were determined at various pH values, as plotted
in Figure 10. The values for 3a stayed at ca. 2 at pH 5-11, and
those for 11c and 12a were ca. 1.9 and ca. 1.6, respectively. In
contrast, the ΦD/ΦH values for 4 changed from 2.2 at lower
pH to 1.4 at higher pH with a tentative pKa value of ca. 8, a
fact supporting the notion (Scheme 4) that the dansylamide is
a protonated form (ArSO2NHR) at lower pH and a deprotonated
form (ArSO2N-R) at higher pH in the excited state.25
887
438
Scheme 4
Zn2+ (the average Zn2+-O length is 2.10 Å) and the other two
carbonyl oxygens remained uncoordinated (Zn2+-O length is
3.23 Å) in the solid state, it is estimated that the rapid
interconversion from one pair of Zn2+-O bonds long and the
other pair short to the opposite arrangement would proceed
through a more regular structure with all Zn2+-O bonds
equivalent.7b Typical crystal data for 12a and 11c are listed in
Table 2.
The second point is the different fluorescent responses to
metal ions by 3a and 4. The preceding compound 3a sensed
Zn2+ (and Cd2+) by strong fluorescent emission but did not sense
lanthanide(III) ions such as Y3+ and La3+. The large (4.9 times)
fluorescence enhancement of 3a (at 528 nm when excited at
330 nm) with a subnanomolar concentration of zinc(II) ion (at
pH 7.3) was ascribed to the deprotonated dansylamide moiety
coordinating to Zn2+ as a fifth ligand from an apical site. Since
lanthanide(III) ions hardly bound to 3a, 3a did not act as a probe
for Y3+ and La3+. In contrast, the present 4 bound both to Zn2+
(as 11c) and to lanthanide(III) ions (as 12) at pH 7.4. The
apparent 1:1 complexation constant for 11c, log Kapp(Zn-L2),26
at pH 7.4 is 10.9, and log Kapp(M-H-1L2) values at pH 7.4 for
12a and 12b are 6.0 and 5.2 (Table 1), respectively. Therefore,
the Zn2+ complex is more stable than the lanthanide(III)
complexes in neutral pH solution. The Zn2+ is already saturated
with seven donors of 4 (four from cyclen N’s and three from
carbonyl O’s) and no longer bothers with further coordination
with the sulfonamide (see Figure 7a) to stay as Zn2+-L2 11c.
One may also describe that three carbamoyl oxygens bind
simultaneously to Zn2+ to mask the acidity of the Zn2+ ion,
which prevented the coordination of the dansyl unit. Deproto-
nation of the dansylamide in 11c occurred only at pH > 11
with a little enhancement of emission (Figure 5). Since its pKa
of 10.7 is close to the value of 10.6 for the free ligand (Scheme
2), Zn2+ may not bind to it, unlike the tentative description of
Discussion
Our newly designed doubly functionalized cyclen with three
carbamoylmethyl groups and a fluorescent dansylamide pendant
4 has two novel properties of the dansylamide fluorescence by
itself and by metal complexes in comparison with those of the
predecessor lacking the carbamoylmethyls, 3a.
First, as disclosed by Figure 3b, the fluorescence of uncom-
plexed 4 itself was remarkably enhanced above pH 8 in aqueous
solution, while that of 3a increased only a little above pH 11.
For 4, the pH-dependent intensity of the fluorescence gave a
pKa of 8.8 ( 0.2 (Figure 3b), which is closed to the log K2 of
8.4 for L2+ H+ a (HL2)+ in Scheme 2. We were thus led to
conclude that emerging nonprotonated L2 above pH 8 is
responsible for the intensified emission (Figure 4b). We then
postulated that the intensified fluorescence of 4 above pH 8
may be derived from the polarized structure in the excited state
16, as depicted in Scheme 4, where three carbamoylmethyls
become available for the proton abstraction from the dansyla-
mide. The pKa value of 8.8 was thus assigned to the dansylamide
deprotonation in the excited state. For 3a, the fluorescence
titration gave a pKa value of 10.8 (Figure 3b), the same as the
value determined for the ground state by the potentiometric pH
titration. It was earlier reported that the ΦD/ΦH value for
5-amino-1-naphthalenesulfonate containing an amino group as
a proton donor is 3.07 (ΦD andΦH are the quantum yields of
(24) Stryer, L. J. Am. Chem. Soc. 1966, 88, 5708-5712.
(25) Negligible phosphorescence was observed for 4, 11c, and 12a
(excitation at 335 nm) at the employed concentration of 10 µM, pH 7.4,
and 25 °C.
(26) The apparent 1:1 complexation constant of 4 with Zn2+, Kapp(Zn-
L2), is defined by eqs 7 and 8.
K
app(Zn-L2) ) [(Zn2+-H-1L2) + (Kapp(Zn-L2) ) [(Zn2+-H-1L2) +
(Zn2+-L2)]/[Zn2+ free[L2]free (M-1) (7)
(at designated pH)
[L2]free ) [H3L2]free + [H2L2]free + [HL2]free + [L2]free + [H-1L2]fre
(8)
]
(23) In the crystal packing, the naphthyl rings of two dansyl units are
placed face to face in an intermolecular manner (see the Supporting
Information).

1130 J. Am. Chem. Soc., Vol. 123, No. 6, 2001
Aoki et al.
7.4; and MES, pH 6.5, 6.0, 5.5, and 5.0) were used, and the ionic
strengths of all were adjusted to 0.10 with NaNO3. The Good’s buffers
(pKa at 20 °C) were purchased from Dojindo and were used without
further purification: CAPS (3-(cyclohexylamino)propanesulfonic acid,
10.4), CHES (2-(3-cyclohexylamino)-2-hydroxypropanesulfonic acid,
9.0), TAPS (3-[N-tris(hydroxymethyl)methylamino]propanesulfonic
acid, 8.1), EPPS (3-(4-(2-hydroxyethyl)-1-piperazinyl)propanesulfonic
acid, 8.0), HEPES (2-(4-(2-hydroxyethyl)-1-piperazinyl)ethanesulfonic
acid, 7.6), and MES (2-morpholinoethanesulfonic acid, 6.2). Melting
points were measured on a Yanaco melting point apparatus and listed
without correction. IR spectra were recorded on a Shimadzu FTIR-
12c in Scheme 3. As a consequence, 4 could not be a
fluorophore for Zn2+ (Figures 5 and 7b). On the other hand,
more acidic and bigger lanthanide(III) ions extend their acidities
to the remote donor, even in the nine-coordinating com-
plexes.1,2,27 The resulting deprotonated dansylamides in 12a and
12b were responsible for Y3+ and La3+ sensings with 4 (Figure
5 and 7b).28,29 Other lanthanide(III) ions also formed 1:1
complexes with similar complexation constants such as 12a and
12b, as concluded from the UV spectophotometric titrations (for
Eu3+, Figure 7a).30 However, all other lanthanide(III) ions with
unfilled f-orbitals quenched the dansyl fluorescence (Figures 5
and 7b).31 Likewise, the d9 Cu2+ complex quenched the emission
(Figures 5 and 7b).
1
4200 spectrometer. H NMR spectra were recorded on a JEOL Delta
(500 MHz) or Alpha (400 MHz) spectrometer. Tetramethylsilane (TMS)
in CDCl3 and CD3OD and 3-(trimethylsilyl)propionic-2,2,3,3-d4 acid
sodium salt (TSP) in D2O were used as internal or external references
for 1H NMR measurements, respectively. 1,4-Dioxane was used as an
internal or external reference for 13C NMR in D2O. The pD values in
D2O were corrected for a deuterium isotope effect using pD ) [pH-
meter reading] + 0.40. Elemental analysis was performed on a Perkin-
Elmer CHN Analyzer 2400. Thin-layer chromatography (TLC) and
silica gel column chromatography were performed using a Merck Art.
5554 (silica gel) TLC plate and Fuji Silysia Chemical FL-100D (silica
gel), respectively.
1-Benzyloxycarbonyl-1,4,7,10-tetraazacyclododecane Trihydro-
chloride Salt (7‚3HCl‚2H2O). Benzyl chloroformate (2.8 g, 16.0 mmol)
was added to a mixture of 1,4,7-tris(tert-butyloxycarbonyl)-1,4,7,10-
tetraazacyclododecane (5) (6.4 g, 13.5 mmol)15 and triethylamine (1.6
g, 16.0 mmol) in CHCl3 (100 mL) at 0 °C, and the whole was stirred
at room temperature for 8 h. An insoluble material was filtered off,
and the reaction mixture was concentrated under reduced pressure. The
remaining residue was purified by silica gel column chromatography
(eluent: hexane/AcOEt) to yield 6 as a colorless amorphous solid (7.8
g).
Conclusions
The double functionalization of a cyclen with a dansyl group
and three carbamoylmethyl moieties, 4, dramatically expanded
the fluorescence behaviors of a cyclen in comparison with 3a.
The three-carbamoyl functionalization provided the hydrogen-
bonding donors to facilitate the nearby dansyl deprotonation to
accompany strong fluorescent emission in the excited state. The
appended three carbamoyls stabilized yttrium(III)- and lan-
thanum(III)-cyclen complexes to permit selective and efficient
signaling from the deprotonated dansyl group. Cyclen deriva-
tives such as 4 may be a convenient and selective sensor for
qualitative and quantitative assays of micromolar concentrations
of Y3+ and La3+ ions in water solutions. Sensing of Y3+, which
is an important metal ion in radioimmunotherapy (90Y),4 should
be clinically useful.32
A colorless solution of 6 (7.8 g, 12.8 mmol) and concentrated HCl
(10 mL) in MeOH (60 mL) was stirred overnight at room temperature.
The precipitated powders were filtered and recrystallized from THF/
H2O to yield 7‚3HCl‚2H2O as colorless powders (4.4 g, 72% yield):
TLC (CH2Cl2/MeOH/aqueous 28% NH3 ) 10:4:1): Rf ) 0.4. Mp 178-
180 °C. IR (KBr): 3566, 3417, 3008, 2948, 2807, 1709, 1670, 1616.
Experimental Section
General Information. All reagents and solvents used were of the
highest commercial quality and used without further purification. Sc-
(NO3)3‚4H2O, Y(NO3)3‚6H2O, La(NO3)3‚6H2O, Eu(NO3)3‚4H2O, and
Tb(NO3)3‚6H2O were purchased from Soekawa Co. Ltd., and Gd(NO3)3‚
6H2O and Yb(NO3)3‚4H2O were purchased from Wako Pure Chemical
Industries, Co. Ltd. The purity of these metals was checked by EDTA-
Arsenazo III (Dojin Chemical Co. Ltd.) titration. All aqueous solutions
were prepared using deionized and redistilled water. Buffer (50 mM)
solutions (CAPS, pH 12.0, 11.5, 11.0, 10.5, and 10.0; CHES, pH 9.5,
9.3, 9.0, and 8.8; TAPS, pH 8.5; EPPS, pH 8.0; HEPES, pH 7.0 and
1
1475, 1447, 1423, 1250, 1145, 732, 706 cm-1. H NMR (400 MHz,
D2O/TSP): δ 3.18-3.23 (12H, m, NCH2), 3.70-3.73 (4H, m, NCH2),
5.21 (2H, s, PhCH2O), 7.45-7.48 (5H, m, ArH). 13C NMR (100 MHz,
D2O/1,4-dioxane): δ 43.79, 45.57, 46.23, 47.53, 69.54, 129.31, 129.74,
129.84, 136.64, 159.39. Anal. Calcd for C16H33N4O4Cl3: C, 42.53; H,
7.36; N, 12.40. Found: C, 42.54; H, 7.66; N, 12.37.
2-(5-(Dimethylamino)-1-naphthalenesulfonylamido)ethyl Chlo-
ride (10). A CHCl3 (35 mL) solution of dansyl chloride (2-(5-
(dimethylamino)-1-naphthalene)sulfonyl chloride) (11.6 g, 43 mmol)
was added dropwise to a mixture of 2-chloroethylamine (5.0 g, 43
mmol) and triethylamine (8.7 g, 86 mmol) in CHCl3 (100 mL) at room
temperature. After being stirred overnight, the reaction mixture was
washed with saturated aqueous NaHCO3, 10% aqueous citric acid, and
saturated aqueous NaCl. The organic layer was dried with K2CO3,
filtered, and concentrated in vacuo. The remaining powders were
recrystallized from AcOEt to yield 10 (7.2 g, 54%): TLC (hexane/
AcOEt ) 2:1): Rf ) 0.5. Mp 100-102 °C dec. IR (KBr): 3271, 2955,
2832, 2790, 2361, 2337, 1435, 1307, 1136, 1084, 922, 799, 630, 561
(27) Nash, K. L. In Handbook on the Physics and Chemistry of Rare
Earths; Gschneidner, K. A., Jr., Eyring, L., Choppin, G. R., Lander, G. H.,
Eds.; North-Holland: Amsterdam, 1994; Vol. 18, pp 197-238.
(28) The 1H NMR (500 MHz) experiments on 4 and its complexes with
Y
3+ and Zn2+ in D2O at pD 7.0 and 11.0 (at 35 °C) showed good agreement
with their deprotonation behavior (see the Supporting Information). Above
a pKa of 10.8, the dansylamide of 4 is deprotonated and the H2′ signal (for
assignment, see Scheme 3 and ref 19) moved upfield by 0.2 ppm. The H2′
signal of Zn2+-L2 11c moved similarly upfield at pD 12.0. The H2′ signal
of Y3+-H-1L2 12a at pD 7.0 appeared more upfield at δ 7.94. The H2′,
H4′, and H8′ signals of La3+-H-1L2 12b at pD 7.0 were broadened, possibly
due to the presence of somewhat slow equilibration between several
conformers.
(29) The metal complexes 11c, 12a, and 12b were kinetically fairly inert.
Because the Zn2+ complex 11c is thermodynamically more stable than the
lanthanide(III) complexes 12a and 12b, the fluorescence intensity of 12a
decreased by 25% after addition of 5 equiv of Zn2+ in 2 days at 25 °C.
(30) The fluorescence of 4 did not respond to Sc3+ (Figure 4). By the
potentiometric pH titration, the log Kapp(M-L2) and pK5(M-H-1L2) values
for the Sc3+ complex of 4 were determined to be 9.2 and 9.8, implying
that dansylamide is scarcely deprotonated at neutral pH.
1
cm-1. H NMR (500 MHz, CDCl3/TMS): δ 2.87 (6H, s, N(CH3)2),
3.23 (2H, dt, NCH2CCH2Cl, J ) 5.6, 6.4 Hz), 3.47 (2H, t, CCH2Cl, J
) 5.6 Hz), 5.11 (1H, t-like, NH), 7.18 (1H, d, ArH (H6′), J ) 7.6 Hz),
7.51 (1H, dd, ArH (H3′), J ) 6.4, 8.8 Hz), 7.57 (1H, dd, ArH (H7′),
J ) 7.6, 8.4 Hz), 8.23 (2H, d, ArH (H4′), J ) 6.4 Hz), 8.26 (1H, d,
ArH (H8′), J ) 8.4 Hz), 8.56 (1H, d, ArH (H2′), J ) 8.8 Hz). 13C
NMR (100 MHz, CHCl3): δ 43.65, 44.76, 45.39, 115.36, 118.53,
123.12, 128.62, 129.54, 129.58, 129.98, 130.82, 134.52, 152.13. Anal.
Calcd for C14H17N2O2SCl: C, 53.76; H, 5.48; N, 8.96. Found: C, 53.85;
H, 5.45; N, 9.10.
1-(2-(5-(Dimethylamino)-1-naphthalenesulfonylamido)ethyl)-4,7,-
10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane Trihydro-
chloride Salt (4‚3HCl‚2H2O). The acid-free 7 was obtained by
extraction of 7‚3HCl‚2H2O (2.7 g, 5.9 mmol) with CHCl3 from 1 N
(31) As pointed out by reviewers, other rare earth metal ions interfere
with Y3+ and La3+ sensing by 4.
(32) For reviews on Y(III) and La(III) complexes, see: (a) Hart, F. A.
In ComprehensiVe Coordination Chemistry; Wilkinson, G. W., Gillard, R.
D., McCleverty, J. A., Eds; Pergamon Press: Oxford, 1987; Vol. 3, pp
1059-1127. (b) Sessler, J. L.; Mody, T. D.; Hemmi, G. W.; Lynch, V.
Inorg. Chem. 1993, 32, 3175-3187. (c) Sessler, J. L.; Hemmi, G.; Mody,
T. D.; Murai, T.; Murrell, A.; Young, S. W. Acc. Chem. Res. 1994, 27,
43-50.

A SelectiVe Fluorescent Probe for Y3+ and La3+
J. Am. Chem. Soc., Vol. 123, No. 6, 2001 1131
NaOH. The resulting free 7 was dissolved in 30 mL of MeCN and
stirred overnight with 2-bromoacetamide (3.4 g, 25 mmol) in the
presence of anhydrous K2CO3 (3.0 g, 22 mmol) under reflux temper-
ature. An insoluble material was filtered off, and the reaction mixture
was concentrated under reduced pressure. The remaining residue was
purified by silica gel column chromatography (CH2Cl2/MeOH) to yield
8 as a colorless oil (1.5 g). TLC (CH2Cl2/MeOH/aqueous 28% NH3 )
Mp 194-196 °C dec. IR (KBr): 3354, 3154, 2947, 2872, 1698, 1676,
1
1653, 1456, 1384, 1325, 1142, 1095, 1021, 943, 803 cm-1. H NMR
(500 MHz, D2O/TSP): δ 2.25-2.32 (2H, m, CH2), 2.36-2.45 (2H,
m, CH2), 2.51 (2H, t-like, dansyl-NCH2CH2N), 2.58-2.72 (8H, m,
CH2), 2.86-2.97 (2H, m, CH2), 2.90 (6H, brs, N(CH3)2), 2.96-3.08
(2H, m, CH2), 3.11 (2H, t-like, dansyl-NCH2CH2N), 3.29 (2H, d, CH2-
CONH2, J ) 17.2 Hz), 3.41 (2H, s, CH2CONH2), 3.59 (2H, d, CH2-
CONH2, J ) 17.2 Hz), 7.46 (1H, d, ArH(6′), J ) 7.6 Hz), 7.71-7.76
(2H, two d, ArH (3′) & ArH (7′)), 8.27 (1H, d, ArH (8′), J ) 8.8 Hz),
8.30 (1H, d, ArH (2′), J ) 7.6 Hz), 8.55 (1H, d, ArH (4′), J ) 8.8 Hz).
13C NMR (100 MHz, D2O/1,4-dioxane): δ 38.32, 46.43, 49.54, 51.90,
52.67, 52.89, 53.56, 56.09, 57.11, 117.58, 120.27, 125.54, 130.28,
130.42, 130.52, 131.63, 131.99, 134.72, 152.43, 175.39, 176.54. Anal.
Calcd for C28H52N11O14.5SZn: C, 38.56; H, 6.01; N, 17.66. Found: C,
38.54; H, 6.01; N, 17.41.
1
10:4:1): Rf ) 0.5. H NMR (400 MHz, CDCl3/TMS): δ 2.60-2.65
(8H, m, NCH2), 2.85-3.02 (4H, m, NCH2), 3.06-3.15 (6H, m, NCH2),
3.49 (4H, brs, NCH2CONH2), 5.10 (2H, s, PhCH2O), 5.89 (2H, br,
NCH2CONH2), 7.05-7.16 (2H, br, NCH2CONH2), 7.32-7.36 (5H, m,
ArH).
A mixture of 8 (1.5 g) and 10% palladium-on-carbon (0.2 g) in THF/
MeOH (1:1) was stirred vigorously under 1 atm of H2 overnight at
room temperature. The mixture was filtered through Celite (No. 545)
with THF/MeOH to afford 9 as a colorless amorphous solid (1.0 g).
TLC (CH2Cl2/MeOH/aqueous 28% NH3 ) 10:4:1): Rf ) 0.1. 1H NMR
(400 MHz, CD3OD/TMS): δ 2.49 (4H, s, NCH), 2.56 (8H, m, NCH2),
3.04 (2H, s, NCH2CONH2), 3.08 (4H, s, NCH2CONH2). 13C NMR (100
MHz, CD3OD/TMS): δ 44.76, 51.19, 56.29, 56.65, 57.73, 175.16,
175.39.
A mixture of crude 9 (1.0 g), 10 (920 mg, 1.8 mmol), and K2CO3
(1.0 g, 2.6 mmol) in MeOH (70 mL) was stirred overnight under reflux
temperature. After the mixture cooled, an insoluble material was filtered
off, and the reaction mixture was concentrated under reduced pressure.
The remaining residue was purified by silica gel column chromatog-
raphy (CH2Cl2/MeOH) to yield 4 as a colorless amorphous solid (0.92
g).
Crystallographic Study of Y3+-H-1L2‚2(NO3-)‚2.5H2O (12a). A
colorless prismatic crystal of Y3+-H-1L2‚2(NO3-)‚2.5H2O (12a)
(C28H49N11O13.5SY, Mr ) 876.73) having approximate dimensions of
0.25 mm × 0.10 mm × 0.10 mm was mounted in a loop, which was
then flash-cooled in a cold gas stream (0.5 H2O was not observed in
the crystal). All measurements were made on a Rigaku RAXIS-RAPID
imaging plate diffractometer with graphite-monochromated Cu KR
radiation. Indexing was performed from three oscillations, which were
exposed for 1.0 min. The camera radius was 127.40 mm. Readout was
performed in the 0.100 mm pixel mode. Cell constants and an
orientation matrix for data collection corresponded to a primitive
monoclinic cell with dimensions a ) 18.912(3) Å, b ) 17.042(3) Å,
c ) 24.318(4) Å, â ) 95.99(1)°, and V ) 7794(2) Å3. For Z ) 8 and
Mr ) 876.73, the calculated density (Dcalcd) was 1.49 g‚cm-3. On the
basis of the systematic absence of h0l (l * 2n) and 0kl (k * 2n) packing
considerations, a statistical analysis of intensity distribution, and the
successful solution and refinement of the structure, the space group
was determined to be P21/c (No. 14). The data were collected at a
temperature of -170 ( 1 °C to a maximum 2θ value of 120.0°. A
total of 36 images, corresponding to 900.0° oscillation angles, were
collected with nine different goniometer settings. The exposure time
was 1.50 min per degree. Data were processed by using the PROCESS-
AUTO program package. Of the 59 475 reflections which were
collected, 13 857 were unique (Rint ) 0.089); equivalent reflections
were merged. The linear absorption coefficient, µ, for Cu KR radiation
is 32.7 cm-1. A symmetry-related absorption correction using the
program ABSCOR was applied which resulted in transmission factors
ranging from 0.52 to 0.72. The data were corrected for Lorentz and
polarization effects. The structure was solved by direct methods (SIR97)
and expanded by means of Fourier techniques (DIRDIF 94). Nitrate
ions were refined isotropically as rigid groups. Of the four ions, three
are disordered at the two locations represented by the corresponding
unprimed and primed numbers. Hydrogen atoms, excluding those of
water, were included but not refined. The final cycle of full-matrix
least-squares refinement was based on 10 373 observed reflections (I
> 0.00σ(I), 2θ < 120.00) and 887 variable parameters and converged
(largest parameter shift was 0.00 times its esd) with unweighted and
The free 4 (0.92 g) was dissolved in MeOH (30 mL), and
concentrated HCl (5 mL) was added at 0 °C. After being stirred for 10
min, the reaction mixture was evaporated in vacuo, and the remaining
powders were recrystallized from EtOH/MeOH to yield 4‚3HCl‚2H2O
as colorless prisms (0.72 g, 16% from 7‚3HCl‚2H2O). Mp 213-215 °C
dec. IR (KBr): 3523, 1672, 1622, 1469, 1440, 1324, 1143, 1089, 794,
1
670, 347, 586 cm-1. H NMR (500 MHz, D2O/TSP): δ 2.98-3.68
(26H, m, CH2), 2.58-2.85 (16H, m, CH2), 2.91 (6H, s, N(CH3)2), 3.19
(8H, brs, CH2), 7.46 (1H, d, ArH (6′), J ) 7.2 Hz), 7.72-7.77 (2H,
two dd, ArH (3′) & ArH (7′)), 8.31 (2H, two d, ArH (2′) & ArH (8′)),
8.56 (1H, d, ArH (4′), J ) 8.8 Hz). 13C NMR (100 MHz, D2O/1,4-
dioxane): δ 38.41, 47.35, 50.12, 50.26, 50.64, 53.44, 55.20, 55.79,
119.98, 125.94, 127.14, 127.38, 127.70, 129.34, 129.47, 131.40, 135.05,
141.49, 180.37, 180.65. Anal. Calcd for C28H52N9O7SCl3: C, 43.95;
H, 6.85; N, 16.47. Found: C, 43.95; H, 7.05; N, 16.25.
1-(2-(5-(Dimethylamino)-1-naphthalenesulfonylamido)ethyl)-4,7,-
10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane Y3+ Com-
plex (Y3+-H-1L2‚2(NO3-)‚3H2O) (12a). 5‚3Cl‚2H2O (122 mg, 0.16
mmol), Y(NO3)3‚6H2O (74 mg, 0.19 mmol), and NaNO3 (0.85 g, 10
mmol) were dissolved in H2O, and the pH was adjusted to pH 8.0 with
aqueous NaOH. This aqueous solution was concentrated slowly under
a reduced pressure at room temperature for 1 week, and Y3+-H-1L2‚
2(NO3-)‚3H2O (12a) was obtained as colorless prisms (61 mg, 43%).
Mp > 250 °C dec (turns yellow at 160 °C). IR (KBr): 3395, 2873,
1668, 1607, 1474, 1459, 1385, 1339, 1224, 1177, 1082, 918, 810, 669,
629 cm-1. 1H NMR (500 MHz, D2O/TSP): δ 2.2-3.9 (26H, brm, CH2),
2.92 (6H, s, N(CH3)2), 7.45 (1H, d, ArH(6′), J ) 7.6 Hz), 7.62 (1H,
dd, ArH (3′), J ) 7.2, 8.8 Hz), 7.71 (1H, dd, ArH (7′), J ) 7.6, 8.0
Hz), 7.94 (1H, d, ArH (2′), J ) 7.2 Hz), 8.35 (1H, d, ArH (8′), J ) 8.0
Hz), 8.38 (1H, d, ArH (4′), J ) 8.8 Hz). 13C NMR (100 MHz, D2O/
1,4-dioxane): δ 46.45, 117.53, 122.27, 125.54, 126.48, 129.50, 130.10,
130.39, 132.24, 135.27, 141.84, 178.99, 180.12 (13C signals of cyclen
moiety and side chains except the dansyl unit were hardly observed).
Anal. Calcd for C28H50N11O14SY: C, 37.97; H, 5.69; N, 17.40. Found:
C, 37.79; H, 5.65; N, 17.12.
1-(2-(5-(Dimethylamino)-1-naphthalenesulfonylamido)ethyl)-4,7,-
10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane Zn2 Com-
plex (Zn2+-L2‚2(NO3-)‚3.5H2O) (11c). 5‚3HCl‚2H2O (152 mg, 0.20
mmol), ZnSO4‚7H2O (63 mg, 0.22 mmol), and NaNO3 (174 mg, 2.0
mmol) were dissolved in H2O, and the pH was adjusted to pH 8.0 with
aqueous NaOH. This aqueous solution was concentrated slowly under
a reduced pressure at room temperature for 1 week, and Zn2+-L2‚
2(NO3-)‚3.5H2O) (11c) was obtained as yellow prisms (91 mg, 52%).
2
2
weighted agreement factors of R ) ∑(Fo - Fc2)/∑Fo = 0.160. Rw
=
(∑w(Fo - Fc2)/∑w(Fo )2)0.5 = 0.229. The standard deviation of an
observation of unit weight was 1.48. The weighting scheme was based
on counting statistics and included a factor (p ) 0.072) to downweight
the intense reflections. Plots of ∑w(|Fo| - |Fc|)2 versus |Fo|, reflection
order in data collection, sin θ/λ, and various classes of indices showed
no unusual trends. The maximum and minimum peaks on the final
2
2
difference Fourier map corresponded to 2.42 and -1.33 e-‚Å-3
,
respectively. Neutral atom scattering factors were taken from Cromer
and Waber (International Tables for X-ray Crystallography, Vol. IV;
The Kynoch Press: Birmingham, England, 1974; Table 2.2 A). All
calculations were performed with the teXsan crystal structure analysis
package developed by Molecular Structure Corp. (1985, 1999).
Crystallographic Study of Zn2+-L2‚2(NO3)‚3H2O (11c). A yellow
prismatic crystal of Zn2+-L2‚2(NO3-)‚3H2O (11c) (C28H51N11O14SZn,
Mr ) 863.22) having approximate dimensions of 0.40 mm × 0.10 mm
× 0.10 mm was mounted in a loop (0.5 H2O was not observed in the
crystal). All measurements were made on a Rigaku RAXIS-RAPID
imaging plate diffractometer with graphite-monochromated Mo KR

1132 J. Am. Chem. Soc., Vol. 123, No. 6, 2001
Aoki et al.
radiation. Indexing was performed from five oscillations which were
exposed for 20.0 min. The camera radius was 127.40 mm. Readout
was performed in the 0.100 mm pixel mode. Cell constants and an
orientation matrix for data collection corresponded to a C-centered
monoclinic cell with dimensions a ) 35.361(1) Å, b ) 13.7298(5) Å,
c ) 18.5998(6) Å, â ) 119.073(2)°, and V ) 7892.3(5) Å3. For Z )
pH Electrode 8102BN) were described earlier.10,11,15 All the test
solutions (50 mL) were kept under an argon (>99.999% purity)
atmosphere. The potentiometric pH titrations were carried out with I
) 0.10 (NaNO3) at 25.0 ( 0.1 °C, and at least two independent titrations
were performed. Deprotonation constants and intrinsic complexation
constants defined in the text were determined by means of the program
BEST.16 All the σ fit values defined in the program are smaller than
8 and Mr ) 863.22, the calculated density (Dcalcd) was 1.45 g‚cm-3
.
0.05. The KW ()aH aOH ), K′W ()[H+][OH-]), and fH values used at
+
-
+
On the basis of the systematic absence of hkl (h + k * 2n) and h0l (l
* 2n) packing considerations, a statistical analysis of intensity
distribution, and the successful solution and refinement of the structure,
the space group was determined to be C2/c (No. 15). The data were
collected at a temperature of -150 ( 1 °C to a maximum 2θ value of
50.0°. A total of 55 images, corresponding to 220.0° oscillation angles,
were collected with two different goniometer settings. The exposure
time was 5.00 min per degree. Data were processed by using the
PROCESS-AUTO program package. Of the 33 737 reflections which
were collected, 6959 were unique (Rint ) 0.076); equivalent reflections
were merged. The linear absorption coefficient, µ, for Mo KR radiation
is 7.5 cm-1. A symmetry-related absorption correction using the
program ABSCOR was applied which applied which resulted in
transmission factors ranging from 0.65 to 0.93. The data were corrected
for Lorentz and polarization effects. The structure was solved by direct
methods (SHELXS86) and expanded by means of Fourier techniques
(DIRDIF 94). Some non-hydrogen atoms were refined anisotropically,
while the rest were refined isotropically. Hydrogen atoms were included
but not refined. The final cycle of full-matrix least-squares refinement
was based on 6125 observed reflections (I > 0.00σ(I), 2θ < 50.00)
and 438 variable parameters and converged (largest parameter shift
was 0.00 times its esd) with unweighted and weighted agreement factors
25 °C are 10-14.00, 10-13.79, and 0.825. The corresponding mixed
constants, K2 ()[HO--bound species]aH /[H2O-bound species]), are
+
derived using [H+] ) aH /fH . The species distribution values (%)
against pH () -log[H+] + 0.084) were obtained using the program
SPE.16
+
+
UV Titrations and Fluorescence Titrations. UV spectra and
fluorescence emission spectra were recorded on a Hitachi U-3500
spectrophotometer and a Hitachi F-4500 fluorescence spectrophotom-
eter, respectively, at 25.0 ( 0.1 °C. For fluorescence titrations, a sample
solution in a 10 mm quartz cuvette was excited at the isosbestic point,
which was determined by UV titrations. The obtained data from UV
titrations (increases in ꢀ267 values at a given wavelength) and fluores-
cence titrations (increases in fluorescence emission intensity at a given
wavelength) were analyzed for apparent complexation constants, Kapp
,
using the program Bind Works (Calorimetry Sciences Corp). Quantum
yields were determined by comparison of the integrated corrected
emission spectrum of a standard quinine. Excitation at 335 nm was
used for quinine in 0.10 M H4SO4, whose quantum yield was 0.54.11a
Acknowledgment. E.K. is thankful for the Grant-in-Aid for
Priority Project “Biometallics” (No. 08249103) from the
Ministry of Education, Science and Culture in Japan. S.A. is
thankful for the Grant-in-Aid for Young Scientists (No.
10771249 and 12771355) and the grants from Nissan Science
Foundation and Uehara Memorial Foundation. T.G. is thankful
for the Graduate Scholarship from the Japan Society for the
Promotion of Science. We are grateful for being allowed the
use of NMR instruments (JEOL Alpha (400 MHz)) in the
Research Center for Molecular Medicine (RCMM), Hiroshima
University.
2
2
2
of R ) ∑(Fo - Fc2)/∑Fo = 0.155. Rw = (∑w(Fo - Fc2)2/
2
∑w(Fo )2)0.5.The standard deviation of an observation of unit weight
was 1.09. The weighting scheme was based on counting statistics and
included a factor (p ) 0.011) to downweight the intense reflections.
Plots of ∑w(|Fo| - |Fc|)2 versus |Fo|, reflection order in data collection,
sin θ/λ, and various classes of indices showed no unusual trends. The
maximum and minimum peaks on the final difference Fourier map
corresponded to 2.60 and -1.36 e-‚Å-3, respectively. Neutral atom
scattering factors were taken from Cromer and Waber (International
Tables for X-ray Crystallography, Vol. IV; The Kynoch Press:
Birmingham, England, 1974; Table 2.2 A). All calculations were
performed using the teXsan crystal structure analysis package developed
by Molecular Structure Corp. (1985, 1999).
Supporting Information Available: 1H NMR spectra
(dansyl region) of 4, 11c, 12a, and 12b, and CIF data for 11c
and 12a. This material is available free of charge via the Internet
at http://pubs.acs.org.
Potentiometric pH Titrations. The preparation of the test solutions
and the calibration method of the electrode system (Orion Research
Expandable Ion Analyzer EA920 and Orion Research Ross Combination
JA0033786