Scientific paper
Synthesis and Spectroscopic Studies of Novel Rhodanine Azo Dyes: An Excellent Selective Chemosensor for Naked-eye Detecting of Cu2+ Ion
Abdullah Ceylan,1 Salih Zeki Bas,1 Mevlut Bayrakci,2* SerefErtul1
and Ahmet Uysal3
1	Department of Chemistry, Selcuk University, 42031, Konya, Turkey
2	Department of Chemistry, Nigde University, 51100, Nigde, Turkey
3	Department of Biology, Selcuk University, 42031, Konya, Turkey * Corresponding author: E-mail: mevlutbayrakci@gmail.com
Received: 05-02-2012
Abstract
This study is first report on the synthesis of novel rhodanine based azo dyes and their fluorogenic and chromogenic sensing behaviors with metal ions (Li+, Na+, K+, Rb+, Pb2+, Ni2+, Zn2+, Cu2+) by using UV-vis and fluorescence spectroscopy techniques. The results of spectroscopic experiments for rhodanine based azo dye 1a exhibited excellent selectivity for Cu2+ over the other metal ions. Furthermore, anti-bacterial studies of rhodanine azo dyes were performed towards some selected bacteria via microbroth dilution method. Obtained results showed that rhodanine ionophore 1a showed strong antibacterial activity against S.aureus.
Keywords: Rhodanine, copper(II) ion, chemosensor, azo-dye, antibacterial activity.
1. Introduction
Molecular recognition is the first step in the design and synthesis of molecular sensors for detection of anions, metal cations or neutral species in organic or aqueous media. The molecular sensor is designed to exhibit a physical response which must be easily detected in the presence of these target species. Rhodanine is an important part of heterocyclic azo dyes, which has been mainly used to determine noble metals.1'2 According to the relationship between structures and chemiluminescence performances of organic azo dyes, many active groups have been introduced to rhodanine matrix to obtain satisfactory chemiluminescence properties.3 Azo compounds, based on rhodanine, play a important role as chelating agents for a large number of metal ions.45 The complexation studies of the rhodanine based azo dyes with various metal ions along with uranyl, ruthenium, copper, cobalt and nickel ions are documented in the literature.6-9 Chemical properties of rhodanine and its derivatives are of interest due to coordination capacity and their use as metal extracting
agents.10 Careful examination of the literature reveals that considerable work has been reported on the spectrophotometry studies of the heterocyclic azo compounds, their metal complexes and their analytical applications.11 But little information has appeared in the literature concerning azo compounds derived from rhodanine and their metal complexes. It is also accepted that knowledge of the stability constants of such azorhodanines and their metal complexes may eventually help to throw some light on the deactivation of essential trace metals in biological sys-tems.12 Furthermore, heterocyclic compounds based on thiazolidine are biologically active compounds having five membered rings, with different heteroatoms. A wide range of pharmacological activities has been attributed to these molecules. Among these include antimicrobial,13 anticancer,14,15 antiviral,16 anticonvulsant,17-19 antitubercu-lar,20 antifungal,21,22 anti-inflammatory,23 analgesic24 and antiproliferative25,26 activities.
Up to now, although several works about the effect of the rhodanine based azo dyes on the both metal com-plexation and pharmacological activities has been repor-
ted.819 There is no other reported a chemosensor study between metal cations and rhodanine based azo dyes. Therefore, the aim of the present study was to explore the effect of rhodanine based azo dyes on the selective che-mosensor studies for some selected metal cations such as Li+, Na+, K+, Rb+, Pb2+, Ni2+, Zn2+ and Cu2+.
2. Experimental
2. 1. Materials
All of the reagents used in this study were obtained from Merck or Fluka and used without further purification. All the metal salts were used as perchlorate compounds (MClO4, M : Li+, Na+, K+, Rb+, Pb2+, Ni2+, Cu2+, Zn2+). Thin layer chromatography (TLC) was performed using silica gel on glass TLC plates (silica gel H, type 60, Merck). Column chromatographic separations were performed on Merck Silica gel-60 (230-400 mesh).
2. 2. Instrumentation
1H NMR spectra were obtained using a Varian 400 MHz spectrometer operating at 400 MHz. IR spectra were obtained on a Perkin Elmer spectrum 100 FTIR spectrometer (ATR). UV-vis absorption and fluorescence spectra
OH
Scheme 1. Synthesis of azo dyes based rhodanine 1a and 2a-c. i: HCl, NaNO2, CH3COOH, CH3COONa, 1-Aminonaphthalene, 0 °C. ii: HCl, NaNO2, CH3COOH, CH3COONa, 2-Aminophenol, 0 °C. iii: HCl, NaNO2, CH3COOH, CH3COONa, 3-Aminophenol, 0 °C. iv: HCl, NaNO2, CH3COOH, CH3COONa, 4-Aminophenol, 0 °C.
were recorded on a Shimadzu UV-1700 spectrophotometer and on a Perkin-Elmer LS-55 fluorescence spectrometer, respectively. Elemental analyses were performed using a Leco CHNS-932 analyzer. Melting points were determined on a Gallenkamp apparatus.
2. 3. Synthesis
Rhodanine based azo dyes (1a and 2a-c) were synthesized according to the following modified literature procedure (Scheme 1).27,28 All of the reactions were monitored with thin layer chromatography.
2. 4. Synthesis of Rhodanine Based Azo Dyes 1a and 2a-c
2. 4.1 General Procedure
25 ml of distilled water containing hydrochloric acid (12 M, 32.19 mmol) were added to corresponding amin compounds such as 2-naphthylamine or o-, p-, m-amino phenol (5 mmol) respectively. To the cooled (0 °C) and stirred mixture, a solution of sodium nitrite (5.1 mmol, in 10 mL of water) was added dropwise for 10 min. Then, to the formed diazonium chloride mixture, a solution of 2-thioxo-4-thiazolidinone (5 mmol) in 25 mL of glacial acetic acid was added dropwise for 20 min with cooling so that the mixture was maintained 0-5 °C. The mixture containing both the rhodanine and the diazonium salt was then added with stirring to a cold solution of 15 grams of sodium acetate in 50 mL of water. After addition, the resulting slurry was stirred for 2 hours at 5 °C. The mixture was allowed to stand for overnight. Then the obtained dark red precipitates were filtered, washed several times with water. The crude product was purified by recrystalli-zation from hot ethanol.
5-(naphthalen-2-yldiazenyl)-2-thioxothiazolidin-4-one (1a)
Yield = 65%, dark red; Mp 107 °C; IR (vmax, cm-1): 1721 (C=O), 1665 (C=C), 1450 (N=N), 1325 and 1211 (C=S). 1H NMR (CDCl3): 8 8.53 (bs, 1H, NH), 6.85-6.96 (m, 7H, ArH), 3.51 (bs, 1H, CH). Anal. Calc.: C13H9N3OS2. C, 54.34; H, 3.16; N, 14.62%. Found: C, 54.29; H, 3.12; N, 14.68%.
5-(2-hydroxyphenyl) diazenyl-2-thioxothiazolidin-4-one (2a) Yield = 68%, dark red; Mp 80-82 °C; IR (vmax, cm-1): 1720 (C=O), 1671 (C=C), 1440 (N=N), 1317 and 1195 (C=S). 1H NMR (CDCl3): 8 10.03 (s, 1H, OH), 8.71 (s, 1H, NH), 6.77-6.90 (m, 4H, ArH), 3.33 (s, 1H, CH). Anal. Calc.: C9H7N3O2S2. C, 42.68; H, 2.79; N, 16.59%. Found: C, 42.59; H, 2.77; N, 16.63%.
5-(3-hydroxyphenyl) diazenyl-2-thioxothiazolidin-4-one (2b) Yield = 59%, red; Mp 86-89 °C; IR (vmax, cm-1): 1720 (C=O), 1658 (C=C), 1445 (N=N), 1315 and 1211
(C=S). NMR (CDCl3): 8 8.81 (s, 1H, OH), 8.58 (s, 1H, NH), 7.02 (s, 1H, ArH) 6.87-7.00 (m, 3H, ArH), 3.56 (s, 1H, CH). Anal. Calc.: C9H7N3O2S2. C, 42.68; H, 2.79; N, 16.59%. Found: C, 42.61; H, 2.84; N, 16.66%.
5-(4-hydroxyphenyl) diazenyl-2-thioxothiazolidin-4-one (2c)
Yield = 66%, red; Mp 101-104 °C; IR (vmax, cm-1): 1717 (C=O), 1665 (C=C), 1445 (N=N), 1321 and 1213 (C=S). 1H NMR (CDCl3): 8 8.21 (s, 1H, OH), 8.10 (s, 1H, NH), 7.00-7.13 (m, 4H, ArH), 3.50 (s, 1H, CH). Anal. Calc.: C9H7N3O2S2. C, 42.68; H, 2.79; N, 16.59%. Found: C, 42.66; H, 2.82; N, 16.65%.
2. 5. Absorption and Fluorescence Measurements
Stock solutions of the metal perchlorates and rho-danine based azo dyes 1a or 2a-c were prepared 7.0 x 10-3 M and 7.0 x 10-4 M in DMF, respectively. For UV-vis and fluorescence measurements, sample solutions were obtained by mixing appropriate amount of stock solution of receptors 1a or 2a-c with stock solution containing metal perchlorate, and finally diluted with DMF to make the solution having desired concentrations of chemosensor and metal ions in the solution. For the Job plot analyses, a series of solutions in DMF with varying concentrations of receptors 1a and Cu2+ were prepared, and the measurements were performed under the condition of [1a] + [Cu2+] = 7.0 x 10-5 M in final solution (5 mL). All the measurements were taken at room temperature about 25 °C. UV-vis absorption spectra and fluorescence spectra of the mixed solutions were recorded against DMF at the end of the completed reaction between the metal ions and 1a. For the fluorescence measurements, excitation wavelength was 293 nm, with a slit width of 5 nm.
2. 6. Antibacterial Studies
The minimal inhibition concentration (MIC) values of the chemicals were studied for the microorganisms. The inocula of microorganisms were prepared from 12-h broth cultures and suspensions were adjusted to 0.5 Mc-Farland standard turbidity. Mueller Hinton Broth (100 pL) were placed into each 96 wells of the microplates. Chemical solutions at a concentration of 20 mg mL-1 were added into the first rows of microplates and two fold dilutions of the chemicals were made by dispensing the solutions to the remaining wells. Culture suspensions (100 pL) were inoculated into each wells. Gentamicin solution was used as positive control. The sealed microplates were incubated at 37 °C for 18 h. Microbial growth was determined by adding 20 pL of 2,3,5-triphenyl-tetrazolium chloride (0.5%) after incubation to each well and incubating for 30 minutes at 37 °C.29
3. Results and Discussion
Rhodanine based azo dyes 1a and 2a-c were synthesized according to modified literature procedure27,28 as shown in Scheme 1. The formation of 5-arylidenerhodani-nes and 5-arylazorhodanines can be carried out both in an alkaline medium and in acetic acid in the presence of sodium acetate, while the corresponding 5-substituted derivatives of thiazolidine-2,4-dione and 2-thiohydantoin can be obtained only in an alkaline medium.27 All of the newly synthesized compounds 1a and 2a-c were characterized by IR, 1H NMR and elemental analysis. Spectroscopic data were in full agreement with those expected. In the IR spectra of the compounds 1a and 2a-c, peaks were seen around 1710-1720 cm-1 attributable corresponding C=O bond and 1320 and 1210 cm-1 attributable C=S bond stretching.30-32 Additionally, the occurrence of new bands around 1440-1450 cm-1 region attributable azo N=N bond stretching in the IR spectra of the compounds 1a and 2a-c confirmed the completion of the reactions. In the 1H NMR spectra of newly synthesized rhodanine based azo dyes 1a and 2a-c, new peaks attributable aromatic protons were observed around 6.90-7.10 ppm. Furthermore, it was observed that new signals attributed to the phenolic hydroxyl protons were seen around 10.03 ppm for 2a, 8.81 ppm for 2b and 8.21 ppm for 2c respectively. Although, rhodanine ring existed in three tautomeric forms: ketone, enol and thioenol, due to a significant polarity of the rhodanine N-H bond and to the possibility of the proton migration to the oxygen or sulfur atoms of the C=O and C=S groups, we found that the most stable form of the rhodanine ring in crystalline state was the ketone form for compounds 1a and 2a-c. This is not surprisingly results. Because, it is well known that rhodanine ring exists mainly as the ketone form, which is due to the low probability of keto-enol and keto-thioenol transformations.33 The limiting stage of the tautomeric transformation is the hete-rolytic dissociation of the rhodanine N-H bond.34 Also, this situation is supported by quantum-chemical calculations in literature.33,35
3. 1. UV-Vis Studies
The sensing ability of chemosensor 1a for various alkali and heavy metal ions (Li+, Na+, K+, Rb+, Pb2+, Ni2+, Cu2+, Zn2+) in DMF was investigated by UV-vis measurements. In the absence of the metal ions, rhodanine based azo dye 1a showed an absorption band at 414 nm attributed to the n-n* transitions of the rhodanine moiety. Upon addition of Cu2+, the band at 414 nm decreased and a new red-shifted absorption band at 492 nm appeared as shown in Fig. 1a. Correspondingly, the solution color changed from orange to dark brown. The significant color change indicates that compound 1a is a sensitive naked-eye indicator for Cu2+(Fig. 1b). On the other hand, no significant change at 414 nm was observed upon the addition of the
a) 1.2
b)
Fig. 1. (a) UV-vis absorption spectra of receptor 1a (7.0 X 10 M) with various metal ions (6 eq.) in DMF. (b) Chromogenic changes of receptor 1a (7.0 X 10-5 M) in the presence of various metal ions (6 eq.) in DMF.
other metal ions, indicating that receptor 1a shows high selectivity for Cu2+ over these metal ions. This indicated that Cu2+ binding with chemosensor 1a blocked the electron withdrawing ability of the rigid naphthalene group and resulted in a shorter absorption wavelength.
Fig. 2a shows UV-vis absorption spectra of receptor 1a with various concentrations of Cu2+. The absorption peak at 414 nm gradually decreased with increasing amounts of Cu2+ (0-6 eq.). A well-defined isosbestic point
at 450 nm indicates the formation of a new compound. By plotting the changes of receptor 1a in the absorbance intensity at 492 nm as a function of Cu2+ concentration, sig-moidal curve was obtained and the stoichiometry between receptor 1a and Cu2+ ion was determined as 1:1 complex formation as shown in Fig. 2b. To evaluate the stoichiome-try between 1a and Cu2+, Job's plot analysis was also executed. The maximum point occurred at the molar fraction of [1a] / ([Cu2+] + [1a]) of ~ 0.53, confirming the 1:1
a)
350
400
450
500 550 wavelength / nm
600
650
b)
700
0.35
2 3 4 5
rcu^I/Mal
[1a]/([1a]+[Cu *])
Fig. 2. (a) UV-vis titrations of 7.0 X 10 5 M receptor 1a with increasing amounts of Cu2+ (0-6 eq.) in DMF. (b) The absorbance change at 492 nm as a function of Cu2+ concentration. (c) Job's plot of a 1:1 complex of receptor 1a and Cu2+.
stoichiometry (Fig. 2c). The association constant of the complex of compound 1a and Cu2+ was determined to be 7.2 x 104 M-1 by the Benesi-Hildebrand equation.36
l/AA =	J+1/(4Ö]J
(1)
where [D]0 is the initial concentration of receptor 1a (donor), [A]0 is the initial concentration of Cu2+ (acceptor), is the molar coefficient of the complex, K is the asso-
re40 and a restriction in the photoinduced electron transfer (PET).41'42 Addition of the other metal ions almost did not constitute a change in the fluorescence spectra of receptor 1a, in terms of fluorescence intensity at 360 nm and general peak shape (Fig. 3b).
Fig. 4a shows fluorescence spectra of receptor 1a with various concentrations of Cu2+. The fluorescence titration resulted in a gradual decrease in the fluorescence intensity of receptor 1a with the addition of Cu2+ (0-4
Table 1. UV-vis absorption properties of receptors 2a-c (7.0 x 10 5 M) for Cu2+ ion (6 eq.) in DMF. % is the maximum wavelength of the compound. A0 is the absorbance of receptors 2a-c. A is the absorbance of (2a + Cu2+), (2b + Cu2+) or (2c + Cu2+).
Parameter
2a
2a + Cu2
2b
2b + Cu2
2c
2c + Cu2
X (nm) A/A
300
297 0.804
298
296 0.725
299
296 0.793
ciation constant of the complex, AA is the change in the absorbance of the interaction of receptor 1a and Cu2+ after adding Cu2+ ions.
On the other hand, the absorption behaviors of the other rhodanine derivatives (2a-c) were investigated under the same conditions. The UV-vis spectra of receptors 2a-c showed new absorption bands at 300 nm, 298 nm, 299 nm, respectively. Excess perchlorate salts of 6 eq. Cu2+ were tested to evaluate the metal ion-binding properties of receptors 2a-c. Interestingly, we found that receptors 2a-c do not show any UV and color (light yellow) changes, whereas receptors 1a show a significant selectivity for Cu2+ over the other metal ions. The results obtained are summarized in Table 1. Upon the addition of Cu2+, UV-vis absorption spectra of the Cu-complexes exhibited similar photochemical changes compared to those of receptors 2a-c.
3. 2. Fluorescence Studies
The fluorescence spectra of receptor 1a in the absence and presence of various metal ions (Li+, Na+, K+, Rb+, Pb2+, Ni2+, Cu2+, Zn2+) in DMF were recorded at excitation wavelength of 293 nm, and the emission spectrum of free receptor 1a displays a significant band in fluorescence intensity at 360 nm. As shown in Fig. 3a, upon addition of Cu2+, emission intensity of receptor 1a was quenched. In many chemosensing systems, paramagnetic Cu2+ ions can strongly quench the emission of a fluorophore via a photoinduced metal-to-fluorophore electron or electronic energy transfer.3738 In addition, among the more paramagnetic metal ions, Cu2+ has a particularly high ther-modynamic affinity for ligands with zzN" or zzO" as che-lating element, and fast metal-to-ligand binding kine-tics.38 39 Zn2+ has a little effect on the fluorescence intensity of receptor 1a. This behavior can be explained by some factors like an increased rigidity in complex structu-
wavelength I nm
b) Q				
				
9.0				
H? 6.0				
3.0 0,0			.....Ill	
	Cu*		Zn:+ Ui2+ Na+ K+ Li* Rb* Pb2+ 1a	
Fig. 3. (a) Fluorescence spectra of receptor 1a (5.0 X 10-6 M) in the absence and presence of various metal ions (6 eq.) in DMF. (b) Changes in the fluorescence intensity ratio (I0/I) at 360 nm of receptor 1a (5.0 X 10-6 M) in the presence of various metal ions (6 eq.). I0 is the fluorescence intensity of receptor 1a. I is the fluorescence intensity of (1a + Mn+). Xex : 293 nm.
a)
200
S 150
¡S 100
b)
1.50 -
320 340 360 380 400 wavelength I nm
420
c)
Cu^ In1* Nii+ Na+ K* Li+ Rb* Pb+
Fig. 4. (a) Fluorescence titrations of receptor 1a (5.0 X 10- M) with increasing amounts of Cu + (0-4 eq.) in DMF. (b) Changes in the fluorescence intensity ratio (I0/I) at 360 nm as a function of Cu2+ concentration. (c) The fluorescence change profiles of receptor 1a (5.0 X 10-6 M) in the presence of Cu2+ (6 eq.) and miscellaneous ions including Li+, Na+, K+, Rb+, Pb2+, Ni2+ and Zn2+ (6 eq.). Xex: 293 nm.
eq.). The values of (Iq/I) at 360 nm were plotted against the concentration of Cu2+. I0 and I are the fluorescence intensity of receptor 1a and the fluorescence intensity of (1a + Cu2+), respectively. The curve obtained exhibites a linear range between 0.5 pM and 5 pM Cu2+ with a correlation coefficient of 0.9862 (Fig. 4b). Furthermore, to explore the utility of receptor 1a as a ion-selective fluorege-nic chemosensor, fluorescence spectral changes of receptor 1a in competitive metal ion complexation were investigated in the presence of Cu2+(6 eq.) and miscellaneous cations (6 eq.) including Li+, Na+, K+, Rb+, Pb2+, Ni2+ and Zn2+ in DMF. These miscellaneous competitive cations did not lead to any significant spectral change, in the presence of miscellaneous competitive cations, Cu2+ ions still resulted in the similar changes (Fig. 4c). All these results imply that receptor 1a can be useful as a fluorogenic-sen-sing material for selective detection of Cu2+ in the presence of other competitive metal ions.
3. 3. Antibacterial Activity of Receptors 1a and 2a-c
Antibacterial activities of receptors 1a and 2a-c were investigated by microbroth dilution method according to previously published literature procedure29 towards some selected bacterias such as Escherichia coli ATCC 25922, Staphylococcus aureus (MSSA) ATCC 25923, Pseudomonas aeruginosa ATCC 15442 and Klebsiella pneumoniae ATCC 10031. The obtained results are presented in Table 2. All of the receptors were found to be
moderate antibacterial against all test bacteria at 1.25 mg mL-1 dose level. These chemicals were determined as equally effective against pathogen microorganisms tested. MIC values of receptors 2a and 2b were determined as 1.25 mg mL-1 against E. coli, P. aeruginosa and K.pneu-moniae. Comparing the other bacterias and S. Aureus, receptor 2c more affected the S. Aureus and MIC value was determined as 0.625 mg mL-1 for S. aureus. On the other hand, receptor 1a exhibited very strong antibacterial activity against S. aureus at a concentration of 0.0195 mg m-L-1. It manifested a moderate antibacterial activity against E. coli at 1.25 mg mL1 dose level and against P. aeruginosa and K. pneumoniae at a concentraiton of 2.50 mg m-L-1. While receptor 1a showed similar antibacterial activity against E. coli, it was less effective against P. aerugi-nosa and K. pneumoniae when compared with receptors 2a-c. According to the obtained results, it was determined that compound 1a revealed strong antibacterial activity against S. aureus strain used in this study. S. aureus is the most sensitive strain against receptor 1a.
4. Conclusion
In summary, new rhodanine based azo dye derivatives 1a and 2a-c were prepared and their metal ion-selective chemosensing and antibacterial behaviors were investigated. Receptor 1a exhibited a selective change in UV-vis absorption and fluorescence spectra toward Cu2+. The metal-binding properties of 1a-Cu2+ complex were determi-
Table 2. Results of antibacterial activities of receptors 1a and 2a-c and standard antibiotic
Tested microorganisms	MIC values of chemicals (^g mL x)	MIC values of
1a	2a 2b 2c	Gentamicin (^g mL-1)
Escherichia coli ATCC 25922 1250	1250 1250 1250	976
Pseudomonas aeruginosa ATCC 15442 2500	1250 1250 1250	1.22
Staphylococcus aureus (MSSA) ATCC 25923 19.5	1250 1250 625	2.44
Klebsiella pneumoniae ATCC 10031 2500	1250 1250 1250	4.88
ned by spectrophotometry methods. The stoichiometry between receptor 1a and Cu2+ was 1:1 complex formation, and the association constant was determined to be 7.2 x 104 M-1 by the Benesi-Hildebrand equation. Addition of Cu2+ to receptor 1a solution resulted in an obvious color change from orange to dark brown, which made it possible to detect Cu2+ by the naked-eye. Moreover, receptor 1a exhibited a good selectivity toward Cu2+ in the presence of competitive cations (Li+, Na+, K+, Rb+, Pb2+, Ni2+ and Zn2+). Furthermore, rhodanine based azo dyes 1a showed strong antibacterial activity against S.aureus. As a conclusion, this study can be a good example for designing a variety of optical sensing devices based on metal ion detection.
5. Acknowledgements
The authors are grateful for the financial support by the Scientific Research Projects of Selcuk University.
6. References
1.	J. H. Yu, Q. Y. Ou, T. Li, L. G. Wang, Chinese J. Anal. Chem. 2004, 52, 644-646.
2.	J. H. Yu, S. G. Ge, P. Dai, Y. Tan, B. Li, X. L. Cheng, Chinese J. Anal. Chem. 2008, 36, 549-554.
3.	J. H. Yu, F. W. Wan, P. Dai, J. D. Huang, J. J. Cui, IEEE, 2009, 1-4.
4.	S. B. Savvin, R. F. Gur'eva, Talanta, 1987, 34, 87-101.
5.	A. T. Mubarak, J. So. Chem, 2004, 33, 149-155.
6.	A. Z. El-Sonbati, A. A. El-Bindary, E. M. Mabrouk, R. M. Ahmet, Spectrochim. Acta, 2001, 57, 1751-1757.
7.	N. Zidar, J. Kladnik, D. Kikelj, Acta Chim. Slov. 2009, 56, 635-642.
8.	A. A. El-Bindary, A. Z. El-Sonbati, A. El-Dissouky, A. S. Hi-lali, Spectrochim. Acta, 2002, 58, 1365-1374.
9.	A. A. Al-Sarawya, A. A. El-Bindary, D. N. El-Sonbati, Spectrochim. Acta, 2005, 61, 1847-1851.
10.	A. El-Dissouky, A. A. El-Bindary, A. Z. El-Sonbati, A. S. Hi-lali, Spectrochim. Acta, 2001, 57, 1163-1170.
11.	A. M. Khedra, M. Gaberb, R. M. Issaa, H. Erten, Dyes and Pigments, 2005, 67, 117-126.
12.	F. C. Brown, C. K. Bradsher, B. F. Moser, S. Forrester, J. Org. Chem. 1959, 24, 1056-1060.
13.	R. G. Franzen, J. Comb. Chem. 2000, 2, 195.
14.	R. Lakhan, B. J. Rai, J. Chem. Eng. Data, 1987, 32, 384386.
15.	M. J. Hour, L. J. Huang, S. C. Kuo, Y. Xia, K. Bastow, Y. Na-kanishi, E. Hamel, K. H. Lee, J. Med. Chem. 2000, 43, 44794487.
16.	E. Hamel, C. M. Lin, J. Plowman, H. K. Wang, K. Hsiung Lee, K. D. Paul, Biochem. Pharmacol. 1996, 51, 53-59.
17.	J. W. Corbett, S. S. Ko, J. D. Rodgers, L. A. Gearhart, N. A. Magnus, L. T. Bacheler, S. Diamond, S. Jeffrey, R. M. Klabe, B. C. Cordova, S. Garber, K. Logue, G. J. Trainor, P. S. Anderson, S. K. Erickson-Viitanen, J. Med. Chem. 2000, 43, 2019-2030.
18.	Archana, V. K. Srivastava, A. Kumar, Ind. J. Pharm. Sci. 2003, 63, 358-362.
19.	K. Ramkumar, V. N. Yarovenko, A. S. Nikitina, I. V. Zavar-zin, M. M. Krayushkin, L. V. Kovalenko, A. Esqueda, S. Od-de, N. Neamati, Molecules, 2010, 15, 3958-3992.
20.	K. Gundurao, H. Vinayak, A. K. Imtiyaz, G. Pramod, Bioorg. Med. Chem. 2006, 14, 3069-3080.
21.	B. Samir, K. Wesam, A. F. Ahmed, Eur. J. Med. Chem. 2007, 42, 948-954.
22.	J. Bartroli, E. Turmo, M. Alguero, E. Boncompte, M.L. Veri-cat, L. Conte, J. Ramis, M. Merlos, J. Garcia-Rafanell, J. Forn, J. Med. Chem. 1998, 41, 1869-1882.
23.	B. Goel, T. Ram, R. Tyagi, E. Bansal, A. Kumar, D. Mukher-jee, J. N. Sinha, Eur. J. Med. Chem. 1999, 34, 265-269.
24.	W. L. Smith, D. L. Dewitt, Adv. Immunol. 1996, 62, 167215.
25.	D. Picot, P. J. Loll, R. M. Garavito, Nature, 1994, 367, 243246.
26.	S. Chandrappa, S. B. Benaka Prasad, K. Vinaya, C. S. Anan-da Kumar, N. R. Thimmegowda, K. S. Rangappa, Invest. New Drugs, 2008, 26, 437-444.
27.	T. E. Gorizdra, S. N. Baranov, Khim. Geterotsikl. 1968, 4, 67-72.
28.	I. Benghiat, J. C. Howard, (Stauffer Chemical Co., USA). 5-Arylazorhodanines. US Patent 2,952,673, September 13, 1960.
29.	E. Malta§, A. Uysal, S. Yildiz, Y. Durak, Fresen. Environ. Bull. 2010, 19, 3094-3099.
30.	A. Alizadeh, S. Rostamnia, N. Zohreh, R. Hosseinpour, Tetrahedron Lett. 2009, 50, 1533-1535.
31.	S. Ertul, H. A. Tombak, M. Bayrakci, O. Merter, Acta Chim. Slov. 2009, 56, 878-884.
32.	I. Demir, M. Bayrakci, K. Mutlu, A. I. Pekacar, Acta Chim. Slov. 2008, 55, 120-124.
33.	G. V. Baryshnikov, B. F. Minaev, V. A. Minaeva, Russ. J. Gen. Chem. 2011, 81, 576-585.
34.	G. V. Baryshnikov, B. F. Minaev, V. A. Minaeva, H. Âgren, J. Struct. Chem. 2010, 51, 817-823.
35.	A. G. Al-Sehemi, T. M. EL-Gogary, J. Mol. Struct. Theoc-hem, 2009, 907, 66-73.
36.	H. A. Benesi, J. H. Hildebrand, J. Am. Chem. Soc. 1949, 71, 2703-2707.
37.	M. H. Kim, J. H. Noh, S. Kim, S. Ahn, S. K. Chang, Dyes and Pigments, 2009, 82, 341-346.
38.	H. G. Li, Z. Y. Yang, D. D. Qin, Inorg. Chem. Commun. 2009, 12, 494-497.
39.	R. H. Yang, Y. Zhang, K. Li, F. Liu, W. H. Chan, Anal. Chim. Acta, 2004, 525, 97-103.
40.	M. Prabhakar, P. S. Zacharias, S. K. Das, Inorg. Chem. 2005, 44, 2585-2586.
41.	D. M. Roundhill, J. P. Fackler (Eds.), Photochemistry and Photophysics of Metal Complexes, New York, 1994.
42.	M. M. Mostafa, A. El-Hammid, M. Shallaby, A. A. El-Asmy, Transit. Met. Chem. 1981, 6, 303-305.
Povzetek
Predstavljena študija je prvo poročilo o sintezi novih azo barvil na osnovi rodanina ter o njihovih fluorogenih in kromo-genih lastnostih, uporabnih za zaznavanje kovinskih ionov (Li+, Na+, K+, Rb+, Pb2+, Ni2+, Zn2+, Cu2+) z UV-vis in fluorescenčnimi spektroskopskimi tehnikami. Rezultati spektroskopskih poskusov za rodaninsko azo barvilo 1a so pokazali odlično selektivnost za Cu2+ glede na ostale kovinske ione. Poleg tega smo izvedli protibakterijske študije rodaninskih azo barvil za nekatere izbrane bakterije po metodi razredčitve mikrogojišča. Dobljeni rezultati kažejo, da ima rodanin-ski ionofor 1a močno protibakterijsko aktivnost nasproti S. aureus.