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Spectrofluorometric studies on the interaction between oxacalix[6]arene-locked trizinc(II)porphyrins and crystal violet
Spectrochimica Acta Part A 73 (2009) 353–357
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Spectrofluorometric studies on the interaction between oxacalix[6]arene-locked trizinc(II)porphyrins and crystal violet Lian Wu, Lijuan Jiao, Qin Lu, Erhong Hao, Yunyou Zhou ∗ Anhui Key Laboratory of Chemo-Biosensing, College of Chemistry and Materials Science, Anhui Normal University, Wuhu 241000, China
a r t i c l e
i n f o
Article history: Received 19 September 2008 Received in revised form 17 February 2009 Accepted 22 February 2009 Keywords: Oxacalix[6]arene-locked trizinc(II)porphyrins Crystal violet Inclusion interaction Spectrofluorimetry
a b s t r a c t A new fluorogenic oxacalix[6]arene bearing three zinc(II) porphyrin groups (1) was prepared. When crystal violet (CV) was bound to 1, fluorescence intensity of 1 was quenched regularly. This indicates that 1 and CV formed a 1:1 complex and the association constant was calculated. The inclusion mechanism was also discussed. This new fluorometric method was developed for rapid determination of CV with a good linearity in the concentration range of 1.40–37.4 mol L−1 . The method was applied for the determination of CV in synthetic samples successfully. © 2009 Elsevier B.V. All rights reserved.
1. Introduction The study of calixarene has been of continuing research interest in the areas of host–guest chemistry, analytical chemistry and supramolecular chemistry. They are very attractive components in the construction of inclusion compounds and organic catalysts [1–5]. Among those, heteroatom-bridged calixarenes, such as the oxygen-bridged calix[4]arenes and their analogues, have attracted much more attentions lately due to their versatile chemical and physical properties [6–9]. Nevertheless the efficient access of large amounts of this type of compounds is still very limited, especially those containing large macrocycles, such as oxacalix[6]arene and oxacalix[8]arene, which have not yet been reported in the literatures [10]. Porphyrin, as a heterocyclic macrocycle derived from four pyrroline subunits, often found applications in the design of some artificial acceptor system. It has been a rapidly developing research area in exploring prophyrins as supermolecule binding sites with numerous macrocyclic compounds such as crown ethers [11,12], cyclodextrins [13] and calixarenes [14,15]. Among those porphyrin-calixarene conjugates have shown highly conformational flexibility [16–20]. Especially those oxacalixarene-locked trizinc(II)porphyrin, as a newly developed unique host molecule, has shown good chemiluminescent properties. Meanwhile, as a biological stain and textile dye, crystal violet is a triphenylmethane type of dye and has found wide applica-
∗ Corresponding author. Tel.: +86 553 3869303; fax: +86 553 3869303. E-mail address: [email protected] (Y. Zhou). 1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2009.02.039
tions in human and veterinary medicine areas. The wide usage of these commercial dyestuffs, has contributed to the pollution of aqueous habitats. Unfortunately, wastewater treatment facilities are often failed to completely remove these molecules from contaminated wastewater. Since crystal violet has shown to be a potent clastogen, and several triphenylmethane dyes has shown to be carcinogenic (U.S. Environmental Protection Agency Genetox program, 1986) and potential reason for the promotion of tumor growth in some species of fish [21], the efficient detection of CV became very important. Previously, we have synthesized a new fluorogenic oxacalix [6]arene-porphyrin conjugates (1) [10]. Herein, we reported the application of this molecule in the spectrofluorometric titrations method as the efficient detection agent for crystal violet (CV) in DMSO media (Scheme 1). The strong binding interaction between CV and 1 leads to remarkable fluorescence intensity decrease, and was able to detect micro amount of CV. A 1:1 stoichiometry for the complexation was established and was verified by Job’s plot. The association constant was calculated and the interaction mechanism of the inclusion process was discussed in this paper. 2. Experimental 2.1. Apparatus Fluorescence spectra and relative fluorescence intensities were measured on a model F-4600 fluorescence spectrophotometer (Hitachi, Japan) using a conventional 10 mm × 10 mm × 45 mm quartz cell. The excitation wavelength was set at 436 nm. The slits
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L. Wu et al. / Spectrochimica Acta Part A 73 (2009) 353–357
Scheme 1. Chemical structures of compound 1, CV and ZnP.
for both the excitation and emission monochromators were fixed at 10.0 nm. All measurements were carried out at room temperature (25 ◦ C). 2.2. Chemicals All reagents used were of analytical-reagent grade or the best grade commercially. Guest dye–crystal violet was of analyticalreagent grade and 1 × 10−3 mol L−1 stock solution was prepared through directly dissolved it in water. Oxacalix[6]arene bearing three zinc(II) porphyrin groups (1) was synthesized according to the literature [10] and identified by MALDI-TOF, 1 H NMR and element analysis. Stock solution of 1 was prepared with DMSO as 7 × 10−5 mol L−1 . 2.3. Procedure 2.3.1. Inclusion process A 1.0 mL aliquot of the solution (7.0 × 10−5 mol L−1 ) of compound 1 was transferred into a 10 mL volumetric flask, then an appropriate amount of 1.0 × 10−3 mol L−1 CV solution (0, 14, 28, 42, 56, 70, 84, 98, 112 and 126 L) was added. The resulting solutions were diluted to 10 mL using DMSO and mixed thoroughly. The fluorescence intensities were determined after letting it standing for 15 min at room temperature.
To establish the stoichiometry between 1 and CV, Job’s experiments were also performed by using fluorescence spectroscopy. The continuous variation method [22] was used to study the binding constant of the mole ratio between 1 and CV. The total mole concentration of 1 and CV was held constant (2.5 × 10−4 mol L−1 ), while the mole fraction of 1 varied from 0.0 to 1.0. A Job’s plot of fluorescence emission intensity difference versus the mole fraction of 1 was used to determine the stoichiometry of the inclusion complex. 2.3.2. Analytical procedures Into a 10 mL volumetric flask were placed an appropriate volume of sample or working solution, then 1.0 mL 7 × 10−5 mol L−1 of 1 solution was added. The mixture was diluted to 10 mL with DMSO and mixed thoroughly. After let it standing for 15 min at 25 ◦ C, the fluorescence intensities were measured. 3. Results and discussion 3.1. Fluorescence spectra characteristics Fig. 1 shows the fluorescence excitation and emission spectra of 1 and CV. It can be seen that 1 has two strong fluorescence emission peaks with the stronger one at 411.4 nm and the weaker one at 660.0 nm. At the same condition, CV does not show any peak at
L. Wu et al. / Spectrochimica Acta Part A 73 (2009) 353–357
Fig. 1. Fluorescence excitation (left) and emission (right) spectra of 1 (a, a : 7.0 × 10−6 mol L−1 ) and CV (b, b : 7.0 × 10−6 mol L−1 ).
the same spectral region. However, when an appropriate amount of 1.00 × 10−3 mol L−1 CV solution was added into 1, the fluorescence intensities of 1 decreased obviously without notable emission wavelength shifts (see Fig. 2). The maximum fluorescence intensity quenching was reached when the solution was incubated at 25 ◦ C for 15 min and remained at least 1.5 h. The considerable fluorescence intensity quenching was exploited to develop a sensitive fluorometric assay for the quantitative determination of CV. Fig. 3 demonstrates that a good linear response could be obtained in a wide concentration range. 3.2. Stoichiometry and complex constant Assuming the composition of the complex was 1:1, according to our earlier work [23], the equation of host–guest inclusion complex can be expressed as Eq. (1): 1 1 1 = + F − F0 F1 − F0 K[H](F1 − F0 )
355
Fig. 3. Plot of fluorescence intensity quenching of 1 at 611.4 nm vs. the concentration of CV.
Here F0 and F1 are the fluorescence intensities of 1 in the absence and presence of CV, respectively. F is the observed fluorescence intensity at each concentration of host molecules 1 being tested. [H] is equilibrium concentration of the guest molecule (CV). Thus, based on Fig. 2, a plot of 1/(F − F0 ) versus 1/[CV] is given in Fig. 4. The excellent linear relationship indicates the formation of a 1:1 complex (R = 0.9994) between 1 and CV. The calculated association constant (K) obtained from the ratio of the intercept to the slope is K = 2.16 × 104 L mol−1 , and the large association constant indicates the strong interaction between the host and the guest molecules. The 1:1 complex stoichiometry was also evidenced by Job’s method. The solution of 1 and guests were mixed in different mole ratio while keeping the total concentration of the 1 and guest molecule as a constant. It was found that the maximal and constant relative fluorescence intensity occurred at [1]/([1] + [CV]) = 0.5, means that the stoichiometry of the complex is 1:1. A typical plot for 1–CV complex is shown in Fig. 5.
(1) 3.3. Discussion of interaction mechanism It is well known that calixarenes and their derivatives can form non-covalent inclusion complexes with various guest molecules
Fig. 2. Fluorescence emission spectra of 7 × 10−6 mol L−1 1 in DMSO with different concentrations of CV: from 0 to 9: 0.0; 1.4; 2.8; 4.2; 5.6; 7.0; 8.4; 9.8; 11.2; 12.6 × 10−6 mol L−1 .
Fig. 4. A plot of 1/(F − F0 ) vs. 1/[CV] for 1–CV complex.
356
L. Wu et al. / Spectrochimica Acta Part A 73 (2009) 353–357
Table 1 Results of the determination of CV samples by standard addition method. Number
Sample content (g mL−1 )
CV added (g mL−1 )
CV found (g mL−1 )
Recovery (%) + S.D. (n = 5)
1 2 3 4
1.0 2.0 3.0 4.0
3.0 2.5 2.0 1.5
3.97 4.56 4.96 5.52
99.0 102.4 98.2 101.3
± ± ± ±
2.02 1.00 0.18 0.57
R.S.D. (%) 1.62 1.83 1.01 0.88
Fig. 5. Job’s plot of 1–CV system, [1] = [CV] = 7 × 10−6 mol L−1 .
of suitable size and characteristics with the assistant of electrostatic interaction, cation– interactions, hydrogen bonding, van der Waals, hydrophobic interactions, and so on [24]. Herein, to study the interacting position between 1 and CV, the interaction between ZnP (the monomer of 1) and CV was also studied (Fig. 6). It can be seen that the fluorescence quenching of ZnP was not very distinct compared to compound 1. A plot similar to Fig. 4 (not shown here) was constructed, which supports the formation of a 1:1 complex between ZnP and CV with a dissatisfactory linear relationship (R = 0.8917). The association constant (K ) was calculated to be 8.42 × 105 L mol−1 , larger than that of 1–CV system. Based on these results, we believe that in ZnP–CV system, one of the electron-rich N atoms of CV bound with an electron-deficient Zn atom of ZnP, from which a 1:1 complex was formed. The insufficient linear relationship may be due to the relatively flexible conforma-
Fig. 7. The proposed pattern of the inclusion complex between 1 and CV.
tion of ZnP–CV complex. While in the 1–CV system, each N atom bound with each Zn atom, forming a conformation like a “cover” locked a “cup”. This greatly stabilized the flexible conformation of 1 to form the rigid host–guest complex and giving an excellent double reciprocal plot (see Fig. 7). The main driving force was believed to be the binding, size/shape fitting and van der Waals. Considering it’s in DMSO media, the electrostatic interaction or hydrogen bonding is not the reason in our case. 3.4. Sample determinations In order to check the validity of the proposed methods, the standard addition method was applied by adding CV to the previously analyzed solution. The recovery of each dye was calculated by comparing the concentration obtained from the spiked mixture with those of the pure dyes. Table 1 shows the results of analysis of synthetic samples by the standard addition method. 4. Conclusion Spectrofluorometric titrations have been employed to investigate the inclusion behavior of oxacalix[6]arene bearing three zinc(II) porphyrin groups with crystal violet in DMSO. The stoichiometry and the association constant at room temperature of the complex were evaluated. The interaction mechanism of the host– guest complex was discussed. Binding, size/shape fitting and van der Waals were believed to play important roles in the formation of the host–guest complex. This work may extend the application of porphyrin-calixarenes in molecular recognition and analytical chemistry research area. Further property studies of the oxacalix[6] arene-locked trizinc(II)porphyrin (1) is in process in our lab. Acknowledgment
Fig. 6. Fluorescence emission spectra of 7 × 10−6 mol L−1 ZnP in DMSO with different concentrations of CV: from 0 to 9: 0.0; 1.4; 2.8; 4.2; 5.6; 7.0; 8.4; 9.8; 11.2; 12.6 × 10−6 mol L−1 .
The authors thank the financial supports of the National Natural Science Foundation of P.R. China (20875002).
L. Wu et al. / Spectrochimica Acta Part A 73 (2009) 353–357
References [1] M. Umadevi, P. Vanelle, T. Terme, V. Ramakrishnan, J. Fluoresc. 16 (2006) 569. [2] T. Arimura, H. Kawabata, T. Matsuda, T. Muramatsu, H. Satoh, K. Fugio, P. Manabe, S. Shinkai, J. Org. Chem. 56 (1991) 301. [3] J.W. Atwood, G.A. Koptsantonis, C.L. Raston, Nature 368 (1994) 229. [4] K. Araki, A. Yanagi, S. Shinkai, Tetrahedron 49 (1993) 6763. [5] H. Yamamoto, S. Shinkai, Chem. Lett. (1994) 1115. [6] B. König, M.H. Fonseca, Eur. J. Inorg. Chem. 11 (2000) 2303. [7] P. Lhoták, Eur J. Org. Chem. 8 (2004) 1675. [8] M.X. Wang, H.B. Yang, J. Am. Chem. Soc. 126 (2004) 15412. [9] J.L. Katz, M.B. Feldman, R.R. Conry, Org. Lett. 7 (2005) 91. [10] E. Hao, F.R. Fronczek, M.G.H. Vicente, J. Org. Chem. 71 (2006) 1233. [11] A. Hamilton, J.M. Lehn, J.L. Sessler, J. Am. Chem. Soc. 108 (1986) 5158. [12] Z.W. Lan, X.Q. Yu, J.T. Chen, J. Mol. Catal. (China) 7 (1993) 239.
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Y. Kuroda, Y. Egawa, H. Seshimo, H. Ogoshi, Chem. Lett. 67 (1994) 2361. T. Nagssaki, H. Fujishima, S. Shinkai, Chem. Lett. 23 (1994) 989. A. Asfari, J. Vicens, J. Weiss, Tetrahedron Lett. 34 (1993) 627. R.G. Khoury, L. Jaquinod, K. Aoyagi, M.M. Olmstead, A.J. Fisher, K.M. Smith, Angew. Chem. 36 (1997) 2497. D. Jokic, Z. Asfari, J. Weiss, Org. Lett. 4 (2002) 2129. J.P. Tremblay-Morin, S. Faure, D. Samar, C. Stern, R. Guilard, P.D. Harvey, Inorg. Chem. 44 (2005) 2836. L. Baldini, P. Ballester, A. Casnati, R.M. Gomila, C.A. Hunter, F. Sansone, R. Ungaro, J. Am. Chem. Soc. 125 (2003) 14181. L.D. Costanzo, S. Geremia, L. Randaccio, R. Purrello, R. Lauceri, D. Sciotto, F.G. Gulino, V. Pavone, Angew. Chem. 40 (2001) 4245. J.A. Bumpus, B.J. Brock, Appl. Environ. Microbiol. 54 (1988) 1143. Y. Liu, Y.W. Yang, Y. Chen, F. Ding, Bioorg. Med. Chem. 13 (2005) 963. Y.Y. Zhou, Q. Lu, S.K. She, L. Wang, Anal. Chim. Acta 552 (2005) 152. S. Shinkai, Tetrahedron 49 (1993) 8933.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Spectrofluorometric studies on the interaction between oxacalix[6]arene-locked trizinc(II)porphyrins and crystal violet Lian Wu, Lijuan Jiao, Qin Lu, Erhong Hao, Yunyou Zhou ∗ Anhui Key Laboratory of Chemo-Biosensing, College of Chemistry and Materials Science, Anhui Normal University, Wuhu 241000, China
a r t i c l e
i n f o
Article history: Received 19 September 2008 Received in revised form 17 February 2009 Accepted 22 February 2009 Keywords: Oxacalix[6]arene-locked trizinc(II)porphyrins Crystal violet Inclusion interaction Spectrofluorimetry
a b s t r a c t A new fluorogenic oxacalix[6]arene bearing three zinc(II) porphyrin groups (1) was prepared. When crystal violet (CV) was bound to 1, fluorescence intensity of 1 was quenched regularly. This indicates that 1 and CV formed a 1:1 complex and the association constant was calculated. The inclusion mechanism was also discussed. This new fluorometric method was developed for rapid determination of CV with a good linearity in the concentration range of 1.40–37.4 mol L−1 . The method was applied for the determination of CV in synthetic samples successfully. © 2009 Elsevier B.V. All rights reserved.
1. Introduction The study of calixarene has been of continuing research interest in the areas of host–guest chemistry, analytical chemistry and supramolecular chemistry. They are very attractive components in the construction of inclusion compounds and organic catalysts [1–5]. Among those, heteroatom-bridged calixarenes, such as the oxygen-bridged calix[4]arenes and their analogues, have attracted much more attentions lately due to their versatile chemical and physical properties [6–9]. Nevertheless the efficient access of large amounts of this type of compounds is still very limited, especially those containing large macrocycles, such as oxacalix[6]arene and oxacalix[8]arene, which have not yet been reported in the literatures [10]. Porphyrin, as a heterocyclic macrocycle derived from four pyrroline subunits, often found applications in the design of some artificial acceptor system. It has been a rapidly developing research area in exploring prophyrins as supermolecule binding sites with numerous macrocyclic compounds such as crown ethers [11,12], cyclodextrins [13] and calixarenes [14,15]. Among those porphyrin-calixarene conjugates have shown highly conformational flexibility [16–20]. Especially those oxacalixarene-locked trizinc(II)porphyrin, as a newly developed unique host molecule, has shown good chemiluminescent properties. Meanwhile, as a biological stain and textile dye, crystal violet is a triphenylmethane type of dye and has found wide applica-
∗ Corresponding author. Tel.: +86 553 3869303; fax: +86 553 3869303. E-mail address: [email protected] (Y. Zhou). 1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2009.02.039
tions in human and veterinary medicine areas. The wide usage of these commercial dyestuffs, has contributed to the pollution of aqueous habitats. Unfortunately, wastewater treatment facilities are often failed to completely remove these molecules from contaminated wastewater. Since crystal violet has shown to be a potent clastogen, and several triphenylmethane dyes has shown to be carcinogenic (U.S. Environmental Protection Agency Genetox program, 1986) and potential reason for the promotion of tumor growth in some species of fish [21], the efficient detection of CV became very important. Previously, we have synthesized a new fluorogenic oxacalix [6]arene-porphyrin conjugates (1) [10]. Herein, we reported the application of this molecule in the spectrofluorometric titrations method as the efficient detection agent for crystal violet (CV) in DMSO media (Scheme 1). The strong binding interaction between CV and 1 leads to remarkable fluorescence intensity decrease, and was able to detect micro amount of CV. A 1:1 stoichiometry for the complexation was established and was verified by Job’s plot. The association constant was calculated and the interaction mechanism of the inclusion process was discussed in this paper. 2. Experimental 2.1. Apparatus Fluorescence spectra and relative fluorescence intensities were measured on a model F-4600 fluorescence spectrophotometer (Hitachi, Japan) using a conventional 10 mm × 10 mm × 45 mm quartz cell. The excitation wavelength was set at 436 nm. The slits
354
L. Wu et al. / Spectrochimica Acta Part A 73 (2009) 353–357
Scheme 1. Chemical structures of compound 1, CV and ZnP.
for both the excitation and emission monochromators were fixed at 10.0 nm. All measurements were carried out at room temperature (25 ◦ C). 2.2. Chemicals All reagents used were of analytical-reagent grade or the best grade commercially. Guest dye–crystal violet was of analyticalreagent grade and 1 × 10−3 mol L−1 stock solution was prepared through directly dissolved it in water. Oxacalix[6]arene bearing three zinc(II) porphyrin groups (1) was synthesized according to the literature [10] and identified by MALDI-TOF, 1 H NMR and element analysis. Stock solution of 1 was prepared with DMSO as 7 × 10−5 mol L−1 . 2.3. Procedure 2.3.1. Inclusion process A 1.0 mL aliquot of the solution (7.0 × 10−5 mol L−1 ) of compound 1 was transferred into a 10 mL volumetric flask, then an appropriate amount of 1.0 × 10−3 mol L−1 CV solution (0, 14, 28, 42, 56, 70, 84, 98, 112 and 126 L) was added. The resulting solutions were diluted to 10 mL using DMSO and mixed thoroughly. The fluorescence intensities were determined after letting it standing for 15 min at room temperature.
To establish the stoichiometry between 1 and CV, Job’s experiments were also performed by using fluorescence spectroscopy. The continuous variation method [22] was used to study the binding constant of the mole ratio between 1 and CV. The total mole concentration of 1 and CV was held constant (2.5 × 10−4 mol L−1 ), while the mole fraction of 1 varied from 0.0 to 1.0. A Job’s plot of fluorescence emission intensity difference versus the mole fraction of 1 was used to determine the stoichiometry of the inclusion complex. 2.3.2. Analytical procedures Into a 10 mL volumetric flask were placed an appropriate volume of sample or working solution, then 1.0 mL 7 × 10−5 mol L−1 of 1 solution was added. The mixture was diluted to 10 mL with DMSO and mixed thoroughly. After let it standing for 15 min at 25 ◦ C, the fluorescence intensities were measured. 3. Results and discussion 3.1. Fluorescence spectra characteristics Fig. 1 shows the fluorescence excitation and emission spectra of 1 and CV. It can be seen that 1 has two strong fluorescence emission peaks with the stronger one at 411.4 nm and the weaker one at 660.0 nm. At the same condition, CV does not show any peak at
L. Wu et al. / Spectrochimica Acta Part A 73 (2009) 353–357
Fig. 1. Fluorescence excitation (left) and emission (right) spectra of 1 (a, a : 7.0 × 10−6 mol L−1 ) and CV (b, b : 7.0 × 10−6 mol L−1 ).
the same spectral region. However, when an appropriate amount of 1.00 × 10−3 mol L−1 CV solution was added into 1, the fluorescence intensities of 1 decreased obviously without notable emission wavelength shifts (see Fig. 2). The maximum fluorescence intensity quenching was reached when the solution was incubated at 25 ◦ C for 15 min and remained at least 1.5 h. The considerable fluorescence intensity quenching was exploited to develop a sensitive fluorometric assay for the quantitative determination of CV. Fig. 3 demonstrates that a good linear response could be obtained in a wide concentration range. 3.2. Stoichiometry and complex constant Assuming the composition of the complex was 1:1, according to our earlier work [23], the equation of host–guest inclusion complex can be expressed as Eq. (1): 1 1 1 = + F − F0 F1 − F0 K[H](F1 − F0 )
355
Fig. 3. Plot of fluorescence intensity quenching of 1 at 611.4 nm vs. the concentration of CV.
Here F0 and F1 are the fluorescence intensities of 1 in the absence and presence of CV, respectively. F is the observed fluorescence intensity at each concentration of host molecules 1 being tested. [H] is equilibrium concentration of the guest molecule (CV). Thus, based on Fig. 2, a plot of 1/(F − F0 ) versus 1/[CV] is given in Fig. 4. The excellent linear relationship indicates the formation of a 1:1 complex (R = 0.9994) between 1 and CV. The calculated association constant (K) obtained from the ratio of the intercept to the slope is K = 2.16 × 104 L mol−1 , and the large association constant indicates the strong interaction between the host and the guest molecules. The 1:1 complex stoichiometry was also evidenced by Job’s method. The solution of 1 and guests were mixed in different mole ratio while keeping the total concentration of the 1 and guest molecule as a constant. It was found that the maximal and constant relative fluorescence intensity occurred at [1]/([1] + [CV]) = 0.5, means that the stoichiometry of the complex is 1:1. A typical plot for 1–CV complex is shown in Fig. 5.
(1) 3.3. Discussion of interaction mechanism It is well known that calixarenes and their derivatives can form non-covalent inclusion complexes with various guest molecules
Fig. 2. Fluorescence emission spectra of 7 × 10−6 mol L−1 1 in DMSO with different concentrations of CV: from 0 to 9: 0.0; 1.4; 2.8; 4.2; 5.6; 7.0; 8.4; 9.8; 11.2; 12.6 × 10−6 mol L−1 .
Fig. 4. A plot of 1/(F − F0 ) vs. 1/[CV] for 1–CV complex.
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L. Wu et al. / Spectrochimica Acta Part A 73 (2009) 353–357
Table 1 Results of the determination of CV samples by standard addition method. Number
Sample content (g mL−1 )
CV added (g mL−1 )
CV found (g mL−1 )
Recovery (%) + S.D. (n = 5)
1 2 3 4
1.0 2.0 3.0 4.0
3.0 2.5 2.0 1.5
3.97 4.56 4.96 5.52
99.0 102.4 98.2 101.3
± ± ± ±
2.02 1.00 0.18 0.57
R.S.D. (%) 1.62 1.83 1.01 0.88
Fig. 5. Job’s plot of 1–CV system, [1] = [CV] = 7 × 10−6 mol L−1 .
of suitable size and characteristics with the assistant of electrostatic interaction, cation– interactions, hydrogen bonding, van der Waals, hydrophobic interactions, and so on [24]. Herein, to study the interacting position between 1 and CV, the interaction between ZnP (the monomer of 1) and CV was also studied (Fig. 6). It can be seen that the fluorescence quenching of ZnP was not very distinct compared to compound 1. A plot similar to Fig. 4 (not shown here) was constructed, which supports the formation of a 1:1 complex between ZnP and CV with a dissatisfactory linear relationship (R = 0.8917). The association constant (K ) was calculated to be 8.42 × 105 L mol−1 , larger than that of 1–CV system. Based on these results, we believe that in ZnP–CV system, one of the electron-rich N atoms of CV bound with an electron-deficient Zn atom of ZnP, from which a 1:1 complex was formed. The insufficient linear relationship may be due to the relatively flexible conforma-
Fig. 7. The proposed pattern of the inclusion complex between 1 and CV.
tion of ZnP–CV complex. While in the 1–CV system, each N atom bound with each Zn atom, forming a conformation like a “cover” locked a “cup”. This greatly stabilized the flexible conformation of 1 to form the rigid host–guest complex and giving an excellent double reciprocal plot (see Fig. 7). The main driving force was believed to be the binding, size/shape fitting and van der Waals. Considering it’s in DMSO media, the electrostatic interaction or hydrogen bonding is not the reason in our case. 3.4. Sample determinations In order to check the validity of the proposed methods, the standard addition method was applied by adding CV to the previously analyzed solution. The recovery of each dye was calculated by comparing the concentration obtained from the spiked mixture with those of the pure dyes. Table 1 shows the results of analysis of synthetic samples by the standard addition method. 4. Conclusion Spectrofluorometric titrations have been employed to investigate the inclusion behavior of oxacalix[6]arene bearing three zinc(II) porphyrin groups with crystal violet in DMSO. The stoichiometry and the association constant at room temperature of the complex were evaluated. The interaction mechanism of the host– guest complex was discussed. Binding, size/shape fitting and van der Waals were believed to play important roles in the formation of the host–guest complex. This work may extend the application of porphyrin-calixarenes in molecular recognition and analytical chemistry research area. Further property studies of the oxacalix[6] arene-locked trizinc(II)porphyrin (1) is in process in our lab. Acknowledgment
Fig. 6. Fluorescence emission spectra of 7 × 10−6 mol L−1 ZnP in DMSO with different concentrations of CV: from 0 to 9: 0.0; 1.4; 2.8; 4.2; 5.6; 7.0; 8.4; 9.8; 11.2; 12.6 × 10−6 mol L−1 .
The authors thank the financial supports of the National Natural Science Foundation of P.R. China (20875002).
L. Wu et al. / Spectrochimica Acta Part A 73 (2009) 353–357
References [1] M. Umadevi, P. Vanelle, T. Terme, V. Ramakrishnan, J. Fluoresc. 16 (2006) 569. [2] T. Arimura, H. Kawabata, T. Matsuda, T. Muramatsu, H. Satoh, K. Fugio, P. Manabe, S. Shinkai, J. Org. Chem. 56 (1991) 301. [3] J.W. Atwood, G.A. Koptsantonis, C.L. Raston, Nature 368 (1994) 229. [4] K. Araki, A. Yanagi, S. Shinkai, Tetrahedron 49 (1993) 6763. [5] H. Yamamoto, S. Shinkai, Chem. Lett. (1994) 1115. [6] B. König, M.H. Fonseca, Eur. J. Inorg. Chem. 11 (2000) 2303. [7] P. Lhoták, Eur J. Org. Chem. 8 (2004) 1675. [8] M.X. Wang, H.B. Yang, J. Am. Chem. Soc. 126 (2004) 15412. [9] J.L. Katz, M.B. Feldman, R.R. Conry, Org. Lett. 7 (2005) 91. [10] E. Hao, F.R. Fronczek, M.G.H. Vicente, J. Org. Chem. 71 (2006) 1233. [11] A. Hamilton, J.M. Lehn, J.L. Sessler, J. Am. Chem. Soc. 108 (1986) 5158. [12] Z.W. Lan, X.Q. Yu, J.T. Chen, J. Mol. Catal. (China) 7 (1993) 239.
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