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Cation complexing of crown ethers using fluorescence spectroscopy, part II
Talanta 53 (2000) 137 – 140 www.elsevier.com/locate/talanta
Cation complexing of crown ethers using fluorescence spectroscopy, part II C ¸ akıl Erk a,*, Ayten Go¨c¸men 1 a
Organic Chemistry Laboratoires, Chemistry Department, I: stanbul Technical Uni6ersity, Maslak, 80626 I: stanbul, Turkey Received 28 September 1999; received in revised form 1 February 2000; accepted 9 March 2000
Abstract The complex formations of benzo[12]crown-4, benzo[15]crown-5 and benzo[18]crown-6 with perchlorate salts of Mg2 + , Li+ and Na+ were investigated using the steady state fluorescence emission spectroscopy in acetonitrile. The complexation enhanced quenched fluorescence spectra, (CEQFS) exhibited the ion complexation role of the macrocyclic ethers and equilibrium constant, Ke of 1:1 stoichiometry were estimated. The Ke were found in the order of Mg+ \Na+ \Li+ for benzo[15]crown-5 whilst Na+ \ Mg+ \ Li+ order was found with benzo[12]crown-4 at 298 K. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Macrocyclic ethers; Cation binding; Fluorescence spectroscopy; Mg2 + ; Li+; Na+
1. Introduction Several macrocyclic ethers possessing oxygen dipoles have been synthesized to investigate their alkali and alkaline-earth cation membrane transport and binding properties by means of optical spectroscopy, potentiometry and NMR spectroscopy methods [1,2]. The ionophores bearing suitable light sensitive moieties may undergo intermolecular changes at the electronic level upon
For Part I, see A. Go¨c¸men, C ¸ Erk, J. Incl. Phenom. 26 (1996) 67. * Corresponding author. Tel.: +90-212-285322; fax: + 90212-2856386. E-mail address: [email protected] (C ¸ . Erk). 1 Present address: Chemistry Department, Balıkesir University, 10100 Balıkesir, Turkey.
cationic interactions of donor oxygen atoms [3]. Essentially, the fluorescence spectroscopy of fluoroionophore macrocycles was found to be reliable to study cationic interactions [4–8]. Introduction of fluorescence spectroscopy into the examination of host–guest interactions of ionophore macrocycles has opened an interesting field, although, the different photophysical effects are involved. The developments in this field for detection and recognition of ions offered several analytical techniques depending on the changes in fluorescence intensity or maximum of the wavelength to estimate the extent of host–guest interactions [9–12]. We have recently reported the cation binding effects of macrocyclic ethers with different fluorophore moieties like coumarins using steady state fluorescence spectroscopy [13–17].
0039-9140/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 3 9 - 9 1 4 0 ( 0 0 ) 0 0 3 7 4 - X
C ¸ . Erk, A. Go¨c¸men / Talanta 53 (2000) 137–140
138
The perchlorate salt complexes of Mg2 + , Li+ and Na+ with benzo[12]crown-4, benzo[15]crown5 and benzo[18]crown-6 were investigated using the fluorescence emission spectroscopy in acetonitrile in the present work. The relative Li+ Na+ and K+ binding powers as well as the role of the counter ion ClO− 4 were quantitatively estimated from the spectral alterations which are due to strong interactions between the fluoroionophore and cations [14].
ing. The peak intensities of uncorrected but smoothed emission spectra of free and complexed macrocycles were used at 306 nm instead of Gaussian peak areas (Table 1). The equilibrium constant, Ke of a 1/1 ratio of cation, M, and ionophore, L, is given by Eqs. (1)–(3). L+Ml ML
(1)
Ke = [ML]/{([M0]− [ML])([L0]− [ML])} simply be expressed as, Ke =
2. Experimental section
could
CML CLCM
(2)
The mole fraction of the complex, PML, calculated primarily was used in Eq. (3) to estimate the equilibrium constants, log Ke (9 0.20), where the equivalent initial concentrations of cation and macrocycle, [M0]= [L0] were used [18,19].
The fluorescence spectra of non-degassed samples were measured with Perkin Elmer Luminescence spectrometer model LS-50 in dry acetonitrile in 10 mm quartz cells at room temperature. Salts and fluorophores dried under vacuum were used immediately. The free fluoroionophore [L0] and cation – fluorophore solutions [L0]= [M0] were prepared with a micro syringe which inserted the aliquot into the dry acetonitrile containing stirred fluorescence cell in the spectrometer compartment. The spectral bandwidth, 10 nm at excitation maxima, of 288 nm was used to optimize the concentrations to give practically no quench-
(1− PML)2 1 = PML [L0]Ke
(3)
The fluorescence emission intensity of the cation–fluorophore macrocycle is given, I0 = 8LjL dC0 and Ic = 8LjL dCL + 8MLjML dCML for the complexed macrocycle ligand intensity and Ilim = 8MLjML dC0 for a completely complexed ligand, where ji are the molar extinction coeffi-
Table 1 The experimental data of 1:1 binding of Na/benzo[15]crown-5 in AN at 25°C La (10−5 M−1)
L0b (10−5 M−1)
1/L0c (105 M)
I0d
Ice
Pf
(1−P)2/P g
(1−P)2/P
1.99 3.47 5.65 7.40 9.25 10.99 11.99 14.90 17.09
2.49 4.98 9.90 14.80 19.61 24.39 29.13 38.46 47.65
0.502 0.288 0.177 0.135 0.108 0.091 0.083 0.067 0.059
97.9 176.2 247.6 308.0 367.6 409.0 448.1 481.2 513.6
51.3 90.8 146.1 189.3 226.5 260.3 292.8 343.1 383.1
0.201 0.303 0.429 0.503 0.528 0.553 0.590 0.613 0.641
3.181 1.601 0.759 0.490 0.421 0.361 0.285 0.245 0.201
3.174 1.591 0.804 0.537 0.410 0.331 0.274 0.212 0.173
a
Noncomplex macrocycle. Complex macrocycle. c Inverse of complex concentration. d Intensity of free ligand. e Intensity of complex mixture. f Mole fraction of complexed ligand. g Experimental mole fraction ratio. h Least square results of mole fraction ratio. b
h
C ¸ . Erk, A. Go¨c¸men / Talanta 53 (2000) 137–140
139
Table 2 The 1:1 cation equilibrium constants in acetonitrile at 298°C, DG in kJ mol−1 Crowns
NaClO4
Benzo[12]crown-4 Benzo[15]crown-5 Benzo[18]crown-6
Mg(ClO4)2
ln Ke
−DG
ln Ke
−DG
ln Ke
−DG
6.56 9.45 9.19
16.19 23.31 22.66
3.45 10.78 –
8.51 26.58 –
1.16 –
2.87 –
cients and 8i are the quantum yields of the thermodynamically distinct species 6 and 7. The mole fraction of the 1/1 complex, PML =CML/(CML + CL)= CML/C0 is used in Eq. (3) to estimate the equilibrium constant, Ke. In fact from the intensities the following relationships could be argued, namely, I0 − Ic = 8LjL dC0 − 8LjL dCL −8MLjML dCML this gives, I0 − Ic = 8LjL d(CL+CML)−8LjL dCL−8MLjML dCML, therefore, I0 −Ic/Ilim =dCML8L(jL − jML)/ 8MLjML dC0 =8L(jL −jML)PML/8MLjML. The mole fraction of the cationic complex, PML = (I0 −Ic)/Ilim8MLjML/(jL −jML) 8L is obtained. However, if 8MLjL 8LjL, in the case of CEFS effects, Eq. (4) could be used. PML =
I − I0 Ilim
(4)
In case CEQFS is observed upon complex formation, 8LjL 8jMLjL then the Eq. (5) is obtained which was used in the present work (see Table 2). PML =
I0 −I Ilim
LiClO4
3. Results and discussion The cation induced changes in the triplet state relative to ground, T1 S0 and excited states, S1 T1 of fluorogenic moieties are involved in appropriate solvents [4–7]. The fluorescences of the complexing ionophores gave no isoemissive points and were just altered depending on the cation and the counter-ion in acetonitrile at room temperature. The complexing powers of cations were estimated from peak intensities of steady state fluorescence emission spectra [7]. We obtained 1:1 ratio of equilibrium constants precisely using Eqs. (1)–(5); Tables 1 and 2. The results exhibited the role of cationic radii and macrocyclic size of such fluoroionophores [18,19]. The role of complete encapsulation of a guest in a host due to conformational ability is quite clear since Na+ is better complexed with benzo[15]crown-5 compared with benzo[18]crown6 (Table 2 and Fig. 1). The smallest ring is, however, better complexed with Na+ compared
(5)
In either cases, PML could be used in Eq. (3) for Ke estimations despite the dichotomous behaviors originated from the photophysical interactions [6–8]. The quantum yield of a free fluoroionophore should not vary for different cation complexes, therefore, the experimental results are excellent to display the selectivity among the cations following above conclusions.
Fig. 1. Plot of inverse concentration versus (1 − P)2/P for benzo[15]crown-5/NaClO4 complex in acetonitrile at 298 K, data from Table 1.
140
C ¸ . Erk, A. Go¨c¸men / Talanta 53 (2000) 137–140
with Li+ since the solvent may have marked effect on a host. The small cations usually showed small effects on large macrocyclic hosts. The results displayed role of perchlorate salts with CEQFS since chloride salts have too small effects on fluorescence spectra of such macrocyclic ethers (Table 2). The solvent polarity of AN, which stabilizes the polar structures suppressed the benzo[18]crown-6 [14]. However, the macrocyclic ether and solvent interactions may also deactivate the nonradiative processes. No quantitative work was tried yet for the alkaline earth salts due to their limited solubility in acetonitrile. The similar reports of some other laboratories with different type of macrocycles in different solvents have also contributed to this field [5–12].
Acknowledgements The kind support of Istanbul Technical University Foundation for DPT project of P-126 is acknowledged by the authors.
References [1] F. Vo¨gtle, Supramolecular Chemistry, Wiley, Chichester, 1991.
.
[2] J.-M. Lehn, Supramolecular Chemistry, Concepts and Perspectives, VCH, Weinheim, 1995. [3] H.-J. Schneider, H. Du¨rr, Frontiers in Supramolecular Organic Chemistry and Photochemistry, VCH, Weinheim, 1991. [4] H. Shizuka, K. Takada, T. Morita, J. Phys. Chem. 84 (1980) 994. [5] J. Bourson, J. Pouget, B. Valeur, J. Phys. Chem. 97 (1993) 4552. [6] A.P. de Silva, H.Q.N. Gunaratne, T. Gunnlaugsson, A.J.M. Huxley, C.P. McCoy, J.T. Rademacher, T.E. Rice, Chem. Rev. 97 (1993) 1515. [7] J.-P. Desvergne, A.W. Czarnik (Eds.), NATO ASI SeriesC, vol. 492, Kluwer-Academic Press, Dordrecht, 1997. [8] L.R. Sausa, J.M. Larson, J. Am. Chem. Soc. 99 (1977) 307. [9] O.S. Wolfbeis, H. Offenbacher, Monatsh. Chem. 115 (1984) 647. [10] A. Minta, R.Y. Tsien, J. Biol. Chem. 264 (1989) 19449. [11] J. Bourson, M.-N. Borrel, B. Valeur, Anal. Chim. Acta. 257 (1992) 189. [12] N. Mateeva, T. Deligeorgiev, M. Miteva, S. Simova, Dyes Pigments 20 (1992) 271. [13] A. Go¨c¸men, M. Bulut, C ¸ . Erk, Pure Appl. Chem. 65 (1993) 447. [14] A. Go¨c¸men, C ¸ . Erk, J. Incl. Phenom. 26 (1996) 67. [15] C ¸ . Erk, A. Go¨c¸men, M. Bulut, J. Incl. Phenom. 31 (1998) 319. [16] C ¸ . Erk, A. Go¨c¸men, M. Bulut, Supramol. Chem. 11 (1999) 49. [17] C ¸ . Erk, A. Go¨c¸men M. Bulut, J. Incl. Phenom. 2000, in press. [18] A. Go¨c¸men, C ¸ . Erk, Fresenius J. Anal. Chem. 347 (1993) 472. [19] C ¸ . Erk, B. C ¸ ic¸ek, U8 . C ¸ akır, Mikrochim. Acta 132 (1999) 79.
Cation complexing of crown ethers using fluorescence spectroscopy, part II C ¸ akıl Erk a,*, Ayten Go¨c¸men 1 a
Organic Chemistry Laboratoires, Chemistry Department, I: stanbul Technical Uni6ersity, Maslak, 80626 I: stanbul, Turkey Received 28 September 1999; received in revised form 1 February 2000; accepted 9 March 2000
Abstract The complex formations of benzo[12]crown-4, benzo[15]crown-5 and benzo[18]crown-6 with perchlorate salts of Mg2 + , Li+ and Na+ were investigated using the steady state fluorescence emission spectroscopy in acetonitrile. The complexation enhanced quenched fluorescence spectra, (CEQFS) exhibited the ion complexation role of the macrocyclic ethers and equilibrium constant, Ke of 1:1 stoichiometry were estimated. The Ke were found in the order of Mg+ \Na+ \Li+ for benzo[15]crown-5 whilst Na+ \ Mg+ \ Li+ order was found with benzo[12]crown-4 at 298 K. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Macrocyclic ethers; Cation binding; Fluorescence spectroscopy; Mg2 + ; Li+; Na+
1. Introduction Several macrocyclic ethers possessing oxygen dipoles have been synthesized to investigate their alkali and alkaline-earth cation membrane transport and binding properties by means of optical spectroscopy, potentiometry and NMR spectroscopy methods [1,2]. The ionophores bearing suitable light sensitive moieties may undergo intermolecular changes at the electronic level upon
For Part I, see A. Go¨c¸men, C ¸ Erk, J. Incl. Phenom. 26 (1996) 67. * Corresponding author. Tel.: +90-212-285322; fax: + 90212-2856386. E-mail address: [email protected] (C ¸ . Erk). 1 Present address: Chemistry Department, Balıkesir University, 10100 Balıkesir, Turkey.
cationic interactions of donor oxygen atoms [3]. Essentially, the fluorescence spectroscopy of fluoroionophore macrocycles was found to be reliable to study cationic interactions [4–8]. Introduction of fluorescence spectroscopy into the examination of host–guest interactions of ionophore macrocycles has opened an interesting field, although, the different photophysical effects are involved. The developments in this field for detection and recognition of ions offered several analytical techniques depending on the changes in fluorescence intensity or maximum of the wavelength to estimate the extent of host–guest interactions [9–12]. We have recently reported the cation binding effects of macrocyclic ethers with different fluorophore moieties like coumarins using steady state fluorescence spectroscopy [13–17].
0039-9140/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 3 9 - 9 1 4 0 ( 0 0 ) 0 0 3 7 4 - X
C ¸ . Erk, A. Go¨c¸men / Talanta 53 (2000) 137–140
138
The perchlorate salt complexes of Mg2 + , Li+ and Na+ with benzo[12]crown-4, benzo[15]crown5 and benzo[18]crown-6 were investigated using the fluorescence emission spectroscopy in acetonitrile in the present work. The relative Li+ Na+ and K+ binding powers as well as the role of the counter ion ClO− 4 were quantitatively estimated from the spectral alterations which are due to strong interactions between the fluoroionophore and cations [14].
ing. The peak intensities of uncorrected but smoothed emission spectra of free and complexed macrocycles were used at 306 nm instead of Gaussian peak areas (Table 1). The equilibrium constant, Ke of a 1/1 ratio of cation, M, and ionophore, L, is given by Eqs. (1)–(3). L+Ml ML
(1)
Ke = [ML]/{([M0]− [ML])([L0]− [ML])} simply be expressed as, Ke =
2. Experimental section
could
CML CLCM
(2)
The mole fraction of the complex, PML, calculated primarily was used in Eq. (3) to estimate the equilibrium constants, log Ke (9 0.20), where the equivalent initial concentrations of cation and macrocycle, [M0]= [L0] were used [18,19].
The fluorescence spectra of non-degassed samples were measured with Perkin Elmer Luminescence spectrometer model LS-50 in dry acetonitrile in 10 mm quartz cells at room temperature. Salts and fluorophores dried under vacuum were used immediately. The free fluoroionophore [L0] and cation – fluorophore solutions [L0]= [M0] were prepared with a micro syringe which inserted the aliquot into the dry acetonitrile containing stirred fluorescence cell in the spectrometer compartment. The spectral bandwidth, 10 nm at excitation maxima, of 288 nm was used to optimize the concentrations to give practically no quench-
(1− PML)2 1 = PML [L0]Ke
(3)
The fluorescence emission intensity of the cation–fluorophore macrocycle is given, I0 = 8LjL dC0 and Ic = 8LjL dCL + 8MLjML dCML for the complexed macrocycle ligand intensity and Ilim = 8MLjML dC0 for a completely complexed ligand, where ji are the molar extinction coeffi-
Table 1 The experimental data of 1:1 binding of Na/benzo[15]crown-5 in AN at 25°C La (10−5 M−1)
L0b (10−5 M−1)
1/L0c (105 M)
I0d
Ice
Pf
(1−P)2/P g
(1−P)2/P
1.99 3.47 5.65 7.40 9.25 10.99 11.99 14.90 17.09
2.49 4.98 9.90 14.80 19.61 24.39 29.13 38.46 47.65
0.502 0.288 0.177 0.135 0.108 0.091 0.083 0.067 0.059
97.9 176.2 247.6 308.0 367.6 409.0 448.1 481.2 513.6
51.3 90.8 146.1 189.3 226.5 260.3 292.8 343.1 383.1
0.201 0.303 0.429 0.503 0.528 0.553 0.590 0.613 0.641
3.181 1.601 0.759 0.490 0.421 0.361 0.285 0.245 0.201
3.174 1.591 0.804 0.537 0.410 0.331 0.274 0.212 0.173
a
Noncomplex macrocycle. Complex macrocycle. c Inverse of complex concentration. d Intensity of free ligand. e Intensity of complex mixture. f Mole fraction of complexed ligand. g Experimental mole fraction ratio. h Least square results of mole fraction ratio. b
h
C ¸ . Erk, A. Go¨c¸men / Talanta 53 (2000) 137–140
139
Table 2 The 1:1 cation equilibrium constants in acetonitrile at 298°C, DG in kJ mol−1 Crowns
NaClO4
Benzo[12]crown-4 Benzo[15]crown-5 Benzo[18]crown-6
Mg(ClO4)2
ln Ke
−DG
ln Ke
−DG
ln Ke
−DG
6.56 9.45 9.19
16.19 23.31 22.66
3.45 10.78 –
8.51 26.58 –
1.16 –
2.87 –
cients and 8i are the quantum yields of the thermodynamically distinct species 6 and 7. The mole fraction of the 1/1 complex, PML =CML/(CML + CL)= CML/C0 is used in Eq. (3) to estimate the equilibrium constant, Ke. In fact from the intensities the following relationships could be argued, namely, I0 − Ic = 8LjL dC0 − 8LjL dCL −8MLjML dCML this gives, I0 − Ic = 8LjL d(CL+CML)−8LjL dCL−8MLjML dCML, therefore, I0 −Ic/Ilim =dCML8L(jL − jML)/ 8MLjML dC0 =8L(jL −jML)PML/8MLjML. The mole fraction of the cationic complex, PML = (I0 −Ic)/Ilim8MLjML/(jL −jML) 8L is obtained. However, if 8MLjL 8LjL, in the case of CEFS effects, Eq. (4) could be used. PML =
I − I0 Ilim
(4)
In case CEQFS is observed upon complex formation, 8LjL 8jMLjL then the Eq. (5) is obtained which was used in the present work (see Table 2). PML =
I0 −I Ilim
LiClO4
3. Results and discussion The cation induced changes in the triplet state relative to ground, T1 S0 and excited states, S1 T1 of fluorogenic moieties are involved in appropriate solvents [4–7]. The fluorescences of the complexing ionophores gave no isoemissive points and were just altered depending on the cation and the counter-ion in acetonitrile at room temperature. The complexing powers of cations were estimated from peak intensities of steady state fluorescence emission spectra [7]. We obtained 1:1 ratio of equilibrium constants precisely using Eqs. (1)–(5); Tables 1 and 2. The results exhibited the role of cationic radii and macrocyclic size of such fluoroionophores [18,19]. The role of complete encapsulation of a guest in a host due to conformational ability is quite clear since Na+ is better complexed with benzo[15]crown-5 compared with benzo[18]crown6 (Table 2 and Fig. 1). The smallest ring is, however, better complexed with Na+ compared
(5)
In either cases, PML could be used in Eq. (3) for Ke estimations despite the dichotomous behaviors originated from the photophysical interactions [6–8]. The quantum yield of a free fluoroionophore should not vary for different cation complexes, therefore, the experimental results are excellent to display the selectivity among the cations following above conclusions.
Fig. 1. Plot of inverse concentration versus (1 − P)2/P for benzo[15]crown-5/NaClO4 complex in acetonitrile at 298 K, data from Table 1.
140
C ¸ . Erk, A. Go¨c¸men / Talanta 53 (2000) 137–140
with Li+ since the solvent may have marked effect on a host. The small cations usually showed small effects on large macrocyclic hosts. The results displayed role of perchlorate salts with CEQFS since chloride salts have too small effects on fluorescence spectra of such macrocyclic ethers (Table 2). The solvent polarity of AN, which stabilizes the polar structures suppressed the benzo[18]crown-6 [14]. However, the macrocyclic ether and solvent interactions may also deactivate the nonradiative processes. No quantitative work was tried yet for the alkaline earth salts due to their limited solubility in acetonitrile. The similar reports of some other laboratories with different type of macrocycles in different solvents have also contributed to this field [5–12].
Acknowledgements The kind support of Istanbul Technical University Foundation for DPT project of P-126 is acknowledged by the authors.
References [1] F. Vo¨gtle, Supramolecular Chemistry, Wiley, Chichester, 1991.
.
[2] J.-M. Lehn, Supramolecular Chemistry, Concepts and Perspectives, VCH, Weinheim, 1995. [3] H.-J. Schneider, H. Du¨rr, Frontiers in Supramolecular Organic Chemistry and Photochemistry, VCH, Weinheim, 1991. [4] H. Shizuka, K. Takada, T. Morita, J. Phys. Chem. 84 (1980) 994. [5] J. Bourson, J. Pouget, B. Valeur, J. Phys. Chem. 97 (1993) 4552. [6] A.P. de Silva, H.Q.N. Gunaratne, T. Gunnlaugsson, A.J.M. Huxley, C.P. McCoy, J.T. Rademacher, T.E. Rice, Chem. Rev. 97 (1993) 1515. [7] J.-P. Desvergne, A.W. Czarnik (Eds.), NATO ASI SeriesC, vol. 492, Kluwer-Academic Press, Dordrecht, 1997. [8] L.R. Sausa, J.M. Larson, J. Am. Chem. Soc. 99 (1977) 307. [9] O.S. Wolfbeis, H. Offenbacher, Monatsh. Chem. 115 (1984) 647. [10] A. Minta, R.Y. Tsien, J. Biol. Chem. 264 (1989) 19449. [11] J. Bourson, M.-N. Borrel, B. Valeur, Anal. Chim. Acta. 257 (1992) 189. [12] N. Mateeva, T. Deligeorgiev, M. Miteva, S. Simova, Dyes Pigments 20 (1992) 271. [13] A. Go¨c¸men, M. Bulut, C ¸ . Erk, Pure Appl. Chem. 65 (1993) 447. [14] A. Go¨c¸men, C ¸ . Erk, J. Incl. Phenom. 26 (1996) 67. [15] C ¸ . Erk, A. Go¨c¸men, M. Bulut, J. Incl. Phenom. 31 (1998) 319. [16] C ¸ . Erk, A. Go¨c¸men, M. Bulut, Supramol. Chem. 11 (1999) 49. [17] C ¸ . Erk, A. Go¨c¸men M. Bulut, J. Incl. Phenom. 2000, in press. [18] A. Go¨c¸men, C ¸ . Erk, Fresenius J. Anal. Chem. 347 (1993) 472. [19] C ¸ . Erk, B. C ¸ ic¸ek, U8 . C ¸ akır, Mikrochim. Acta 132 (1999) 79.