Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 477 485 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa Monodentate Schiff base ligands: Their structural characterization, photoluminescence, anticancer, electrochemical and sensor properties Muhammet Köse a, Gökhan Ceyhan a, Mehmet Tümer a,, _ Ibrahim Demirtasß b, _ Ilyas Gönül c, Vickie McKee d a Chemistry Department, K.Maras Sütcü Imam University, 46100 K.Maras, Turkey b Chemistry Department, Çankırı Karatekin University, 18100 Çankırı, Turkey c Chemistry Department, Çukurova University, 01100 Adana, Turkey d Chemistry Department, Loughborough University, LE11 3TU Leics, UK highlights graphical abstract Two novel Schiff base ligands were prepared and structurally characterized. Absorption, photoluminescence and electrochemical properties of the Schiff bases were examined. Sensor properties of the compounds were examined. Anticancer activity of the compounds were investigated. The ligands were structurally characterized by single crystal X-ray diffraction study. The molecule L 2 is centrosymmetric whereas the L 1 has no crystallographically imposed molecular symmetry. The antiproliferative activities of compounds L 1 and L 2 aganist C6 cell line (a). P < 0.01 when compared to control groups (one-way ANOVA following the Duncan s multiple comparison test). article info abstract Article history: Received 17 July 2014 Received in revised form 21 August 2014 Accepted 24 August 2014 Available online 3 September 2014 Keywords: Schiff base Colorimetric sensors Electrochemistry Photoluminescence Anticancer Two Schiff base compounds, N,N 0 -bis(2-methoxy phenylidene)-1,5-diamino naphthalene (L 1 ) and N,N 0 - bis(3,4,5-trimethoxy phenylidene)-1,5-diamino naphthalene (L 2 ) were synthesized and characterized by the analytical and spectroscopic methods. The electrochemical and photoluminescence properties of the Schiff bases were investigated in the different conditions. The compounds L 1 and L 2 show the reversible redox processes at some potentials. The sensor properties of the Schiff bases were examined and color changes were observed upon addition of the metal cations, such as Hg(II), Cu(II), Co(II) and Al(III). The Schiff base compounds show the bathochromic shift from 545 to 585 nm. The single crystals of the compounds (L 1 ) and (L 2 ) were obtained from the methanol solution and characterized structurally by the X-ray crystallography technique. The molecule L 2 is centrosymmetric whereas the L 1 has no crystallographically imposed molecular symmetry. However, the molecular structures for these compounds are quite similar, differing principally in the conformation about methoxy groups and the dihedral angle between the two aromatic rings and diamine naphthalene. Ó 2014 Elsevier B.V. All rights reserved. Corresponding author. Tel.: +90 344 280 14 44; fax: +90 344 280 13 52. E-mail address: mtumer@ksu.edu.tr (M. Tümer). http://dx.doi.org/10.1016/j.saa.2014.08.088 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

478 M. Köse et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 477 485 Introduction Schiff base ligands have comprehensive applications in a great deal of, such as biological, inorganic and analytical chemistry [1 5]. Application of many new analytical devices requires the presence of organic reagents as essential compounds of the measuring system. Schiff base ligands are used in optical and electrochemical sensors, and likewise in several chromatographic methods, to make possible detection of enhance selectivity and sensitivity [6 8]. The Schiff base compounds have high biological properties substances [9,10]. As the Schiff base ligands have high coordination capability, they are widely used in analytical applications. Schiff base ligands can be easily synthesized by reactions of condensation of primary amines and carbonyl compounds in which the azomethine bond is formed and they can used as complex formation reactions (determination of amines, carbonyl compounds and metal ions); or utilizing the variation in their spectroscopic characteristics. A great number of metal complexes of the Schiff bases (acyclic or cyclic) have been prepared, and they have provided an enormously rich world of chemistry [11]. Transition metal complexes derived from Schiff bases have occupied a central role in the development of coordination chemistry. The azomethine group >C@N of the Schiff base forming a stable metal complexes by coordinating through nitrogen atom. Schiff base ligands are able to coordinate many different metals, and to stabilise them in various oxidation states, enabling the use of Schiff base metal complexes for a large variety of useful catalytic transformations. As the Schiff base compounds contain the imine (>C@N), hydroxyl and various alkyl or alkoxy groups, they have high bioigical activity. Recently, we synthesized some monodentate Schiff base ligands and characterized structurally. As a continuation of our interest in the coordination behavior of Schiff bases with aromatic and aliphatic amines, the synthesis, structural characterization, luminescence, electrochemical, catalysis and anticancer activities of various metal complexes were reported [12 16]. In this study, two Schiff base compounds, N,N 0 -bis(2-methoxy benzaldiimine)-1,5-diamino naphthalene (L 1 ) and N,N 0 -bis(2,3, 4-trimethoxy benzaldiimine)-1,5-diamino naphthalene (L 2 ) were prepared and characterized by analytical and spectroscopic methods. The compounds were structurally characterized by X-ray diffraction studies. Additionally, electrochemical, thermal, luminescence and anticancer properties of the compounds were investigated. To investigate the sensor properties of the Schiff base ligands (L 1 and L 2 ), the metal cations K(I), Na(I), Ba(II), Cd(II), Co(II), Cu(II), Hg(II), Mg(II), Mn(II), Ni(II), Zn(II) and Al(III) for complexation with ligands were used. Experimental Materials and measurements All reagents and solvents were of reagent-grade quality and obtained from commercial suppliers (Aldrich or Merck). Elemental analyses (C, H, N) were performed using a LECO CHNS 932. Infrared spectra were obtained using KBr disc (4000 400 cm 1 ) on a Perkin Elmer Spectrum 100 FT-IR. The electronic spectra in the 200 900 nm range were obtained on a Perkin Elmer Lambda 45 spectrophotometer. Mass spectra of the ligands were recorded on a LC/MS APCI AGILENT 1100 MSD spectrophotometer. 1 H and 13 C NMR spectra were recorded on a Bruker 400 MHz instrument. TMS was used as internal standard and CDCl 3 as solvent. The thermal analysis studies of the compounds were performed on a Perkin Elmer STA 6000 simultaneous Thermal Analyzer under nitrogen atmosphere at a heating rate of 10 C/min. The single-photon fluorescence spectra of the Schiff base compounds L 1 and L 2 were collected on a Perkin Elmer LS55 luminescence spectrometer. All samples were prepared in spectrophotometric grade solvents and analyzed in a 1 cm optical path quartz cuvette. The solutions of ligands (1.0 10 3 1.0 10 7 mol L 1 ) were prepared in DMF solvent. To investigate the solvent effect on the photoluminescence spectra of the ligands, the DMF, CHCl 3, CH 2 Cl 2, THF and dithylether solutions (1.0 10 3 mol L 1 ) of the compounds were used. A stock solution of a concentration of 1 10 3 M and 1 10 4 M of Schiff base compounds was prepared in DMF for electrochemical studies. Cyclic voltammograms were recorded on a Iviumstat Electrochemical workstation equipped with a low current module (BAS PA-1) recorder. The electrochemical cell was equipped with a BAS glassy carbon working electrode (area 4.6 mm 2 ), a platinum coil auxiliary electrode and a Ag + /AgCl reference electrode filled with tetrabutylammonium tetrafloroborate (0.1 M) in DMF and CH 3 CN solution and adjusted to 0.00 V vs SCE. Cyclic voltammetric measurements were made at room temperature in an undivided cell (BAS model C-3 cell stand) with a platinum counter electrode and an Ag + /AgCl reference electrode (BAS). All potentials are reported with respect to Ag + /AgCl. The solutions were deoxygenated by passing dry nitrogen through the solution for 30 min prior to the experiments, and during the experiments the flow was maintained over the solution. Digital simulations were performed using DigiSim 3.0 for windows (BAS, Inc.). Experimental cyclic voltammograms used for the fitting process had the background subtracted and were corrected electronically for ohmic drop. Mettler Toledo MP 220 ph meters was used for the ph measurements using a combined electrode (glass electrode reference electrode) with an accuracy of ±0.05 ph. Data collection for X-ray crystallography was completed using a Bruker APEX2 CCD diffractometer and data reduction was performed using Bruker SAINT [17]. SHELXTL was used to solve and refine the structures [18]. Synthesis of the Schiff base compounds The benzaldehyde derivatives (2 mmol; 272 mg) 2-methoxy benzaldehyde for L 1 and 392 mg 2,3,4-trimethoxy benzaldehyde for L 2 ) in ethanol (20 ml, absolute) and 1,5-diamino naphthalene (1 mmol, 264 mg) in ethanol (20 ml, absolute) were mixed and refluxed for about 10 h at 80 C. The color of the solution changed to brown. After cooling the solution, the resulting precipitate was filtered and washed with cold ethanol. Single crystals of the Schiff base compounds (L 1 and L 2 ) suitable for X-ray diffraction study were obtained by slow evaporation of the compounds in ethanol. Physical properties and other spectroscopic data are given in the experimental section. L 1 : (C 26 H 22 N 2 O 2 ). Yield: 87%, color: brown, d.p.: 218 C(decompose). Elemental analyses, found (calcd. %): C, 79.13 (79.16); H, 5.66 (5.62); N, 7.07 (7.10). 1 H NMR (DMSO- d6, d (ppm)): 8.63 (s, CH@N, 2H), 7.81 6.24 (m, Ar-H, 14H), 3.88 (s, OCH 3, 6H). 13 C NMR (DMSO- d6, d (ppm)): 164.05 (CH@N), 155.15-110.50 (Ar-C), 58.10 (OCH 3 ). Mass spectrum (LC/MS APCI): m/z 394 [M] + (100%), m/z 393 [M 1] + (13%), m/z 395 [M+1] + (25%), m/z 395 [M+2] + (50%). FT-IR: (KBr, cm 1 ): 3010 m(cah) aromatic, 2975 m(c-h) alph, 1612 m(ch@n). L 2 : (C 30 H 30 N 2 O 6 ). Yield: 88%, color: brown, d.p.: 226 C (decompose). Elemental analyses, found (calcd.%): C, 69.97 (70.02); H, 5.93 (5.88); N, 5.49 (5.45). 1 H NMR (DMSO- d6, d (ppm)): 8.85 (s, CH@N, 2H), 7.85-6.20 (m, Ar-H, 10H), 3.95, 384, 3.80 (s, OCH 3, 18H). 13 C NMR (DMSO- d6, d (ppm)): 163.40 (CH@N), 158.45-111.25 (Ar-C), 59.85, 58.60, 57.75 (OCH 3 ). Mass spectrum (LC/MS APCI): m/z 514 [M] + (100%), m/z 515 [M+1] + (35%), m/z 516 [M+2] + (42%).

M. Köse et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 477 485 479 FT-IR: (KBr, cm 1 ): 3006 m(cah) aromatic, 2942 m(cah) alph, 1614 m(ch@n). X-ray determination X-ray diffraction data for these compounds were collected at 150(2)K on a Bruker Apex II CCD diffractometer using Mo Ka radiation (k = 0.71073 Å). The structures were solved by direct methods and refined on F 2 using all the reflections [18]. All the non-hydrogen atoms were refined using anisotropic atomic displacement parameters and hydrogen atoms bonded to carbon were inserted at calculated positions using a riding model. Anticancer activity studies of the Schiff base compounds Preparation of samples Stock solutions of the samples were prepared in DMSO and diluted with Dulbecco s modified eagle medium (DMEM). DMSO final concentration is below 1% in all tests. Cell lines and cell culture HeLa, Vero and C6 cancer cell lines were grown in Dulbecco s modified eagle medium (DMEM) supplemented with 10% fetal bovine serum (FBS), 2% penicilin streptomycin. The medium was changed twice a week. Cell proliferation assay Antiproliferative effects of the plants were investigated on Vero cells (African green monkey kidney), C6 cells (Rat Brain tumor cells) and HeLa cells (human uterus carcinoma) using proliferation BrdU ELISA assay [19,20]. Cultured cells were grown in 96-well plates (COSTAR, Corning, USA) at a density of 3 10 4 cells/well. In each experimental set, cells were plated in triplicates and replicated twice. The cell lines were exposed to two concentrations of methanolic extracts of different organs (flower, steam and root) of CC, for 24 h at 37 C in a humidified atmosphere of 5% CO 2. 5-Fluorouracil, cisplatin were used as standart compounds. Cells were than incubated for overnight before applying the BrdU Cell Proliferation ELISA assay reagent (Roche, Germany) according to manufacturer s procedure. The amount of cell proliferation was assessed by determining the A450 nm of the culture media after addition of the substrate solution by using a microplate reader (Ryto, China). Results were reported as percentage of the inhibition of cell proliferation, where the optical density measured from vehicle-treated cells was considered to be 100% of proliferation. All assays were repeated at least twice using HeLa and C6 cells. Percentage of inhibition of cell proliferation was calculated as follows: ½1 ða samples =A control ÞŠ 100: Table 1 Crystallographic data for the compounds L 1 and L 2. Identification code L 1 L 2 Empirical formula C 26 H 22 N 2 O 2 C 30 H 30 N 2 O 6 Formula weight 394.46 514.56 Crystal color and size (mm 3 ) Brown, 0.52 0.14 0.10 Brown, 0.41 0.26 0.05 Crystal system Monoclinic Triclinic Space group P2(1)/n P 1 Unit cell a (Å) 7.8106(9) 6.6174(7) b (Å) 21.024(2) 7.0865(8) c (Å) 12.1032(13) 13.6122(15) a ( ) 90. 00 90.470(2) b ( ) 93.173(2) 98.272(2) c ( ) 90.00 97.230(2 Volume (Å 3 ) 1984.5(4) 626.45(12) Z 4 1 Density (calculated) (Mg/m 3 ) 1.320 1.364 Completeness to 100.0% 99.1% theta = 28.30 99.1% Goodness-of-fit on F 2 1.033 1.083 Abs. coeff. (mm 1 ) 0.095 0.095 Refl. collected 17,729 6412 Ind. Refl. [R int ] 4062 [0.0353] 3086 [0.0185] R 1, wr 2 [I >2r(I)] 0.0465, 0.1183 0.0452, 0.1206 R 1, wr 2 (all data) 0.0685, 0.1314 0.0571, 0.1288 CCDC number 789662 951727 Results and discussion In this study, two Schiff base compounds (L 1 and L 2 )(Fig. 1) were synthesized and characterized by the elemental analyses, 1 H( 13 C) NMR spectra, UV vis, FT-IR and mass spectral studies. The compounds have symmetric nature and they are stable thermally. Degradation of the Schiff bases may occur during the purification step. Chromatography of Schiff bases on silica gel can cause some degree of decomposition of the Schiff bases through hydrolysis. In such cases, it is better to purify the Schiff bases by re-crystallization. Single crystals of the Schiff bases suitable for X-ray diffraction study were obtained from re-crystallization of the compounds in ethanol. In order to clarify the structures of the Schiff bases (L 1 and L 2 ), their 1 H( 13 C) NMR spectra were investigated and obtained data are given in the experimental section. In the 1 H-NMR spectra of the Schiff bases, the singlets at 8.63 and 8.85 ppm can be attributed to the protons of the azomethine groups. The aromatic ring protons Statistical analysis The results of investigation in vitro are means ± SD of nine measurement. Differences between groups were tested with ANOVA. p values of <0.01 were considered as significant. X-ray structure solution and refinement for the compounds L 1 and L 2 X-ray diffraction data for all three compounds were collected at 150(2)K on a Bruker Apex II CCD diffractometer using Mo Ka radiation (k = 0.71073 Å). All the non-hydrogen atoms were refined using anisotropic atomic displacement parameters and hydrogen atoms bonded to carbon were inserted at calculated positions using a riding model. The crystal data and details of the structure solution and refinement are given in Table 1. Fig. 1. Proposed structures of the synthesized Schiffbase compounds.

480 M. Köse et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 477 485 are shown in the 7.85 6.20 ppm range as multiplet. The signals of the methoxy groups on the benzene rings are shown in the 3.95 3.80 ppm range as singlet. In their 13 C NMR spectra, the signals at 163.40 and 164.05 ppm may be assigned to the azomethine group carbon atom. Aromatic carbon atoms are shown in the 158.45 110.50 ppm range. The signals in the 59.85 57.75 ppm range can be attributed to the methoxy carbon atoms. In the FT-IR spectra of the Schiff bases (L 1 and L 2 ), the vibration signals at 3010 and 3006 cm 1 can be attributed to the aromatic CAH strechings. The bands at 2975 and 2942 cm-1 may be assigned to the m(cah) alph vibrations. The azomethine group [m(ch@n)] vibrations are shown at 1614 and 1612 cm 1. Molecular structures of the Schiff bases (L 1 and L 2 ) are shown in Fig. 2. The crystal data and details of the structure solution and refinement are given in Table 1, bond lengths and angles for the compounds L 1 and L 2 are given in Tables S1 and S2, respectively. All bond lengths and angles for both compounds are within the normal ranges. All bond lengths and angles in the phenyl rings and naphthalene ring have normal Csp2 Csp2 values. The azomethine linkage distances for both compounds are within the range of normal C@N values. The Schiff base molecule (L 2 ) is centrosymmetric whereas the Schiff base (L 1 ) has no crystallographically imposed molecular symmetry; however the molecular structures for these compounds are quite similar, differing principally the number and positions of methoxy groups and the dihedral angle between the two aromatic rings and diimine naphthalene. The two phenyl rings in the Schiff base (L 2 ) are necessarily coplanar and the dihedral angle between the two identical phenyl rings and naphthalene ring is 39.09(7). In the Schiff base (L 1 ), although there is no crystallographically imposed molecular symmetry, two phenyl rings are close to planar with dihedral angle of 1.81(11). The dihedral angle between the two aromatic rings and naphthalene ring (C1AC5/naphthalene and C20AC25/naphthalene) in Schiff base (L 1 ) are are 60.30(5) and 50.06(5), respectively. In the crystal structure of Schiff base (L 1 ), dimers are formed through strong p p interactions; there are naphthalene naphthalene parallel off-set p interactions and this was supported by two p p edge to edge phenyl phenyl staking interactions (Fig. 3). Additionally, two dimeric units are linked again with p p interactions, C3 and C24 are separated by a distance of 3.485 Å under symmetry operation of ½ x, ½+y, ½ z (Figs. 3 and 4). Packing plot of Schiff base (L 1 ) is shown in Fig. 4. There are no similar interactions observed in Schiff base (L 2 ). Molecules of the ligand (L 2 ) are linked via weak hydrogen type interactions (CHN and CHO). The same hydrogen bond contacts are extended between the other symmetry-related molecules in their respective planes to form hydrogen bonding network (Fig. 5 and Table S3). In order to investigate the solvent effect, the spectra of the compounds were taken in DMF, CH 2 Cl 2,(C 2 H 5 ) 2 O, THF and CHCl 3 solutions. In addition, the concentration effect on the electronic properties of the Schiff bases were studied in the 1 10 4 1 10 7 M range in DMF solution. The obtained data from the electronic absorption studies are given in Tables S4 and S5. The electronic spectra of the compounds in the 1 10 4 1 10 7 M concentration range and in the different solvents are shown in Fig. S1a d. In all solvents, the compounds L 1 and L 2 have only two absorption bands in the 380 265 nm range. While the compounds have the highest absorption bands in THF solution, in the diethylether solution, the absorption band of the ligands is lowest. In the spectra of the compounds, the bands in the 300-265 nm range can be attributed to the p p transitions [21]. The ligands have the n p transitions in the 380 350 nm range. In the different concentrations, the ligands have highest absorption intensities in the 1 10 4 M concentration. As the concentration of the ligands decreases, the intensity of the absorption bands decreases. Fig. 2. Molecular structures of the compounds (A) L 1 and (B) L 2.

M. Köse et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 477 485 481 Fig. 3. p p interactions in the compound L 1, hydrogen atoms are omitted for clarity. Symmetry operations: 1 x, y, 1 z, ½ x, ½+y, ½ z. Naked eye detections of transition metals under different lights In order to investigate receptor properties of the Schiff base ligands (L 1 ) and (L 2 ) (1 mm), the complex formation between the ligands and K(I), Na(I), Ba(II), Cd(II), Co(II), Cu(II), Hg(II), Mg(II), Mn(II), Ni(II), Zn(II) and Al(III) in MeOH:H 2 O (3:7) mixture have been studied. Receptor properties of the ligands were studied under four different conditions. These are day light, TL84 (F18T8), F Lamp (40 w, 280 nm) and Uv region (F20T12 BLB). Color changes for the ligand (L 2 ) in the presence of the metal ion is shown in Fig. 6. In day light, significant color changes were observed upon addition of metal ions due to the complexation (1 mm) (from colorless to yellowish for Hg(II) and colorless to light black for Al(III), Co(II), and Cu(II)). But, the most distinguishable color change was shown in the Hg(II) metal ion. The color change was determined by the naked eye. In these conditions, any color change was not detected for the other metal ions. Under TL84 (F18T8), the color changes for the Co(II) and Cu(II) complexes were shown from colorless to purple and green, respectively. But, to become colorful in the Cu(II) complex is more than the Co(II) complex. In the other complexes, color changing was not observed. In other words, under F lamp (40 w, 280 nm), similar results to TL84 were obtained. While the Co(II) complex was shown as a purple, the Cu(II) complex was observed as dark blue. In these conditions, the ligand (L 2 ) may be accepted as a chemisensor for the Cu(II) ion. Finally, under the ultraviole region (F20T12 BLB), the addition of the Hg(II), Al(III) and Cu(II) changed coluorless to light blue and blue, respectively. In the other metal ions, any significant color changes were not observed. When the spectra of the transition metal complexes investigated, the d d transitions in the 680 550 nm range were observed. In donor acceptor interactions, the dipole moments of the compounds increase. That is, upon the Fig. 4. Packing plot of the compound L 1, hydrogen atoms are omitted for clarity, p p interactions are shown as dash lines.

482 M. Köse et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 477 485 Fig. 5. Packing plot of the compound L 2, hydrogen bonds are shown as dash lines. Fig. 6. Color changes of 0.1 mm concentration of receptor L 2 with different metal ions (0.1 mm) in methanol:h 2 O in 1:1 (v/v, ml) molar ratio. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) metal ion complexation, the excited states are more strongly stabilized than the ground states and a bathochromic shift results. The metal ion causes a significant coordination bond with the azomethine moieties and that induces an absorption spectral change. Similar results were also observed for the ligand L 1. The composition of complex The stoichiometric ratio of the Schiff base to metal ion (II)/(III) in course of the formation of the complexes was determined by Job s method [22]. In order to this study, the total concentration (0.1 mm) and volume (10 ml) of the Schiff base and metal ion were kept constant, and changing the molar ratio of ligand from 0.0 to 1.0. In the course of the complexation, the nitrogen and oxygen atoms of the azomethine and methoxy group in the ortho-position of the Schiff base compounds coordinate to the metal ions, respectively. On the basis of this binding mode, upon addition of the metal ion the bathochromic shift in the absorption spectra can be rationalized by intra-molecular charge transfer (ICT). The nitrogen atom of the imine group (C@N) increases its electronwithdrawing character, due to this a stronger ICT from the electron-withdrawing anionic groups to the metal in complex. That is, the compounds behave as the monodentate ligands. The results show that the ligand metal ion complexes absorbance gets a maximum when the molar ratio of the ligand is about 0.5, indicating that forming a 1:1 (Fig. 7) complex between the ligand molecule and metal ion. In the other complexes, the similar interactions were shown and similar data were obtained. The effect of different solvent on the photoluminescence properties of the Schiff base compounds L 1 and L 2 The photoluminescence properties of the Schiff base compounds were studied in the DMF, THF, (C 2 H 5 ) 2 O, CHCl 3 and CH 2 Cl 2 solvents using 4.0 10 5 M solutions. At room temperature, the Schiff base compounds exhibit similar emission spectra in the UV vis region (Tables S4 and S5). The emission and excitation spectra of the Schiff base compounds L 1 and L 2 in various solvents are shown in Fig. S2a d and the obtained data are given in Tables S4 and S5. The spectra of the compounds L 1 and L 2 show one emission band in the 546 581 nm range longer wavelength (LW) region in the DMF, THF, (C 2 H 5 ) 2 O, CHCl 3 and CH 2 Cl 2 solutions. The emission peaks of the compound L 2 were shifted to the longer wavelengths. The photoluminescence emission peaks of the Schiff bases apparently produce red shift with the introduction of the electron donating groups. The introduction of the electron donating groups by mesomeric and inductive effects causes the fluorescence characteristic emission peaks of the Schiff bases to

M. Köse et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 477 485 483 intraligand charge transfer (ILTC) band with the edge at 500 nm. In the excitation spectra of the compound L 1 in THF, CHCl 3 and DMF solutions, the band around 480 nm shifted to longer wavelength region around 550 nm in the (C 2 H 5 ) 2 O and CH 2 Cl 2 solutions. In the spectra of the compound L 2, while the excitation peak at the shorter wavelength (528 nm) is shown in DMF solution, the peak at the longer wavelength (553 nm) is shown in the CHCl 3 solution. It may be that the extended p-conjugation would induce an excited state resonance contribution of the methoxy groups to the benzene rings in the increased polarity. The effect of different concentrations on the photoluminescence properties of the Schiff base compounds L 1 and L 2 Fig. 7. Job s plot between the compound L 2 and the metal ions (1 10 4 M) in acetonitrile/water (1:19, v/v). The absorbance at 366 nm (Cu 2+ ), 364 nm (Co 2+ ), 361 nm (Ni 2+ ), 360 nm (Zn 2+ ), 360 nm (Cd 2+ ) was used. red shift in the range of 30 35 nm. The reason is that the electron density of the phenyl ring is increased with the d p hyper conjugation effect. The Schiff bases with methoxy substituents possess p p conjugation that can increase their photoluminescence emission intensity. As the Schiff bases have p-methoxy substitute groups, they show a good conjugation and rigid planar structure. The Schiff base compounds have highest emission and excitation bands in the THF and (C 2 H 5 ) 2 O solutions. On the other hand, they have lowest emission and excitation bands in the THF and CHCl 3 solution. The excitation spectra of the compounds L 1 and L 2 were also investigated in DMF, THF, (C 2 H 5 ) 2 O, CHCl 3 and CH 2 Cl 2 solutions and obtained data are given in Table S4. The excitation spectra of the compounds L 1 and L 2 resemble one other. But, the excitation peaks of the compound L 2 were shifted to the longer wavelengths. In the spectra of the compound L 1, the peaks consist of the strong p p band with the long-wavelength edge at 480 nm and a weak In order to investigate the effects of the different concentration on the photoluminescence properties of the Schiff base compounds L 1 and L 2, the solutions in 1.0 10 3 1.0 10 7 M range in CHCl 3 were used. The emission and excitation spectra of the Schiff base compounds L 1 and L 2 in various solvents are shown in Fig. S2a d and the obtained data are given in Table S6. In the spectra of the compounds, the emission peaks were shifted shorter wavelengths (SW) from 1.0 10 3 M to 1.0 10 7 M concentration. In addition to, the intensity of the absorption bands were decreased toward to lower concentrations. This situation occur due to the lesser substance quantity in lower concentrations. Similar properties were also shown for the excitation peaks. The electrochemical properties of the compounds L 1 and L 2 Electrochemical properties of the Schiff base compounds (L 1 and L 2 ) were studied in DMF 0.1 M NBu 4 BF 4 as supporting electrolyte at 293 K. In order to study the effects of the solution concentration and the scan rates, we used the solutions in two different concentrations (1.0 10 3 and 1.0 10 4 M) and the scan rates (100, 150, 200, 250, 500, 750, 1000 mv/s) and against an internal ferrocence-ferrocenium standard. The obtained data are Table 2 The electrochemical data of the Schiff base compounds L 1 and L 2. Comp. Concentration (M) Scan rate (mv/s) E pa (V) E pc (V) E 1/2 (V) DE p (V) L 1 1 10 3 100 0.62, 0.94 0.74, 0.95 0.20 150 0.94 0.72, 0.86 0.18 200 0.98 0.71, 0.87 0.27 250 0.52, 1.17 0.66, 1.21 0.51 500 0.44, 0.04, 1.26 0.67, 0.04, 1.32 0.08 750 0.40, 0.08, 1.23 0.79, 0.04, 1.39 0.12 1000 0.38, 0.15, 1.26 0.78, 0.05, 1.45 0.20 1 10 4 100 0.61, 0.20, 1.06, 0.97 0.21 150 0.50, 0.02 1.05, 0.14, 1.02 0.12 200 0.48, 0.02 1.05, 0.08, 1.07 0.06 250 0.44, 0.04, 1.00 1.04, 0.09, 1.13 1.02 0.04 500 0.37, 0.13, 1.10 1.01, 0.07, 1.25 1.06 0.09 750 0.30, 0.19, 1.22 0.96, 0.09, 1.33 0.10 1000 0.26, 0.28, 1.19 0.95, 1.37 0.25 L 2 1 10 3 100 0.60, 0.95 0.70, 0.17, 0.85 0.25 150 0.60, 0.97 0.09, 0.89 0.27 200 0.59, 0.98 0.65, 0.06, 0.89 0.30 250 0.60, 0.98 0.71, 0.04, 0.91 0.27 500 0.54, 1.04 1.06, 0.68, 0.98 0.20 0.01 750 0.50, 0.02, 1.02 0.74, 0.04, 1.00 0.75 0.06 1000 0.49, 0.13, 0.98 0.87, 0.06, 1.06 0.11 1 10 4 100 0.57 0.99, 0.21, 0.90 0.33 150 0.55 0.99, 0.10, 0.99 0.44 200 0.55, 0.01 1.00, 0.08, 1.07 0.07 250 0.48, 0.03, 1.10 1.04, 0.05, 1.12 0.06 500 042, 0.09, 1.19 1.01, 0.10, 1.29 0.01 750 0.35, 0.16, 1.20 0.98, 1.32 0.22 1000 0.33, 0.17, 1.30 0.92, 1.45 0.38 Supporting electrolyte: [NBu 4 ](BF 4 ) (0.1 M). All the potentials are referenced to Ag + /AgCl; where Epa and Epc are anodic and cathodic potentials, respectively. E 1/2 - = 0.5 (E pa + E pc ), DE p = E pa E pc.

484 M. Köse et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 477 485 Fig. 8. The antiproliferative activities of compounds L 1 and L 2 aganist C6 cell line (a), HeLa cell line (b) and Vero cell line (c). The values represent the mean ± SEM (n = 3). P < 0.01 when compared to control groups (one-way ANOVA following the Duncan s multiple comparison test). given in Table 2. The electrochemical curves of the compounds L 1 and L 2 are shown in Fig. S3a d. The compounds in the 100 1000 mv/s range show one, two or three anodic peak potentials in the 0.62 1.30 V range. On the other hand, the compounds have two or three cathodic peak potentials in the 1.45 1.06 V range. In the 1 10 3 M concentration, the compound L 1 shows the irreversible and quasi reversible redox processes at all scan rates. In the 1 10 4 M concentration solution, the compound L 1 has two reversible redox process at 250 and 500 mv/s scan rates and 1.00 and 1.10 V E pa and 1.04 and 1.01 V E pc redox potentials, respectively. The compound L 1 shows irreversible process at the other scan rates. The compound L 2 has only one reversible redox couple at 500 mv/s scan rate and 1.04 E pa and 1.06 E pc potentials in the 1 10 3 M concentration. In the reversible redox process, the Schiff base compounds have been converted to the keto-amine forms [23]. In this process, the oxygen atoms of the methoxy groups of the organic compounds give the electrons to the benzenoid rings and then to the nitrogen atoms by the resonance. This process occurs as the reversible. While the compound L 1 has only one methoxy group (ortho position on the benzene rings), the other compound L 2 have three methoxy groups (ortho, meta and para positions on the benzene rings, respectively). Although the methoxy groups decrease the electron density of the benzenoid rings by the inductive effect, the electron density increase by the mesomeric effect. Electron donating groups to the benzene rings shift the potentials from the positive to negative regions. This situation were seen in these compounds. The compound L 2 shows irreversible and quasi-reversible processes at other scan rates and concentrations. The antiproliferative activities of compounds L 1 and L 2 The antiproliferative activity of compound L 2 was very weak to compare with cisplatin and 5-FU aganist C6 and Vero cell lines. But, this compound has remarkable effects aganist HeLa cell line at 500 lm (Fig. 8a-c). In addition, the activity of the compound L 2 has increased to depending increase of doses aganist all of the cell lines. The compound L 1 have cell selective effects aganist HeLa and C6 cell lines. There are not this effects aganist Vero cell line. The compound L 1 have shown the higher activitiy than 5-FU at all of concentrations aganist C6 cell line. However, the antiproliferative activities of the compound 2 were more effect than cisplatin at 500 and 250 lm aganist HeLa cell line (Fig. 8a-c). In the light of the results, it can be suggested that, the compound L 1 could be developed as an anticancer drug. Conclusion In this work, we synthesized two Schiff base compounds and characterized by the analytical, spectroscopic and X-ray techniques. We investigated their sensor properties against to the metal ions. As observed, the compound L 2 showed higher selectivity toward the softer cation Hg(II), as compared to the harder

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