Synthesis, spectral characterization, and antiproliferative studies of mixed ligand titanium complexes of adamantylamine.
The discovery of cisplatin, a metal (platinum) based anticancer drug by Rosenberg et al. in 1965, has created interest in the development of metal based anticancer drugs [1-3]. The effect of transition metal complexes, other than platinum such as ruthenium [4-8], palladium [9-13], gold [14, 15], and titanium [16-25] has also been studied on several cancer cell lines. In addition to cisplatin, many other platinum based drugs, namely, carboplatin, oxaliplatin, tetraplatin, and satraplatin , and nonplatinum based drugs, namely, budotitane, titanocene dichloride ,NAMI-A, KP1019 , and auranofin  have shown remarkable results. Out of these, the first nonplatinum anticancer drugs were budotitane and titanocene dichloride which are titanium based drugs . These titanium complexes offer an alternative to chemotherapy, although these complexes do not follow a mechanism similar to that of other metal complexes. Previous studies have revealed that titanium compounds are effective against those cell lines which are resistant to platinum based drugs and kill the cancer cells through apoptosis. It has also been confirmed that lability of ligand is not a mandatory condition for a compound to show cytotoxicity , but other ligand properties have been found to be necessary for this activity . It is well established that ligands having electron donating atom(s) show increased cytotoxicity due to enhanced coordination capacity [32, 33]. Since few efforts have been made towards the synthesis and use of titanium complexes as chemotherapeutic agents, this is an important area of research. In the present work, we report the synthesis, structural characterization, and antiproliferative potential of some of titanium complexes.
2. Experimental Section
2.1. Materials and Methods. Ligands and titanium tetrachloride used were obtained from Sigma Aldrich. All the solvents were of AR grade (Merck) and purified by standard procedure before use and stored over 4 [Angstrom] molecular sieves. Purity of ligands was checked by checking their melting points. Elemental analyses were performed by using Perkin-Elmer, Series 2400. The UV-visible spectra of the complexes were recorded on Perkin Elmer Lambda 750 in the range of 200-800 nm and FTIR Spectra were recorded from 4000-200 [cm.sup.-1] on Perkin Elmer 1600. The mass spectrum was recorded by using the electron spray ionization technique on Waters Micromas Q Tof Micro. [sup.1]H NMR Spectra were recorded on Brucker Avance 400 MHz spectrometer. Crystalline nature of the complexes has been confirmed by powder XRD technique on Philips 1710 X-ray diffractometer.
2.2. Synthetic Procedures (A-E)
2.2.1. Synthesis of Bis(adamantylamino)bis-(4,4'-dimethoxy2,2-bipyridyl)titanium(II), Ti[(ada).sub.2][(bpome).sub.2], (A). To a colorless solution of 4,4,-dimethoxy-2,2,-bipyridyl (0.45 g, 2.1 mmol) in 25 mL of toluene, a pale yellow colored solution of titanium tetrachloride (0.2 g, 1.05 mmol) in 25 mL of toluene was added dropwise with continuous stirring under ice cold conditions. The reaction mixture was stirred for 2 h followed by refluxing for 10 h till the evolution of chlorine gas ceased. The evolution of chlorine gas was checked by passing the gas through a potassium iodide solution which results in reddish brown color of potassium iodide due to liberation of iodine. After removing solvent through vacuum distillationcompound was dried under vacuum. A light yellow colored solid compound [Ti[Cl.sub.2][(bpome).sub.2]] was obtained. Yield: 0.5 g (86.2%). Now, to a solution of Ti[Cl.sub.2][(bpome).sub.2] (0.5 g, 0.91 mmol) in 25 mL of toluene, adamantylamine (0.27 g, 1.81 mmol) in 25 mL of toluene was added dropwise with continuous stirring. The reaction mixture was stirred for 2 h and refluxed for 14 h till the evolution of HCl gas ceased. The evolution of HCl gas was confirmed by passing the gas through an ammonia solution which results in white dense fumes of ammonium chloride. The excess solvent was removed by vacuum distillation and the compound was washed with petroleum ether. The compound was dried under vacuum. A cream colored solid powder was obtained which was recrystallised in methanol. Yield: 0.45 g (64.28%). Ti[C.sub.44][H.sub.54][N.sub.6][O.sub.4]: elemental anal. Calcd (%): C 67.67, H 7.17, N 10.76; found (%): C 66.71, H 7.05, N 10.52.FTIR (KBr, [cm.sup.-1]) [bar.v]: 3388 (NH Stretching), 3015 (aromatic CH stretching), 2927 (CH stretching), 1629 (C=C stretching), 1522 (C=N stretching), 1449 (NH bending) 1313, 1229 (CH bending), 906, 809 (CH out of plane deformation), 452 (Ti-N stretching). [sup.1]H NMR (DMSO, 400 MHz): adamantylamine [delta], ppm = 2.1 (s, NH), 1.86 (d, [sup.3]J = 1.96 Hz, C[H.sub.2] protons), 1.66,1.59, (dd, [sup.3]J = 12.36, 29.6 Hz CH protons). 4,4'-Dimethoxy-2,27-bipyridine d, ppm = 8.66 (d, [sup.3]J = 6.16 Hz, 4H, [H.sup.6]), 7.96 (s, 4H, [H.sup.3]), 7.37 (d, [sup.3]J = 8 Hz, 4H, [H.sup.5]), 4.09 (s, 12H, OC[H.sub.3]).
2.2.2. Synthesis of Bis(adamantylamino)bis-(6,6'-dimethyl-2,2' -bipyridyl)titanium(II), Ti[(ada).sub.2][(dpme).sub.2], (B). The complex was synthesized in accordance to the procedure used for complex A. Yield: 0.4 g (84.38%). Ti[C.sub.44][H.sub.54][N.sub.6]: elemental anal. Calcd (%): C 73.70, H 7.81, N 11.72; found (%): C 73.91, H 7.94, N 11.54. FTIR (KBr, [cm.sup.-1])[bar.v]: 3336 (NH stretching), 3071 (aromatic CH stretching), 2925 (CH stretching), 1644 (C=C stretching), 1506 (C=N stretching), 1441 (NH bending) 1271,1117 (CH bending), 906, 801 (CH out of plane deformation), 404 (Ti-N stretching). [sup.1]H NMR (DMSO, 400 MHz): adamantylamine [delta], ppm = 2.12 (s, NH), 1.91 (d, [sup.3]J = 2.12 Hz, C[H.sub.2] protons), 1.69,1.64, (dd, [sup.3]J = 12.6, 22.6 Hz CH protons). 6,6'-Dimethyl-2,2'-bipyridine [delta], ppm = 8.5 (d, [sup.3]J = 7.96 Hz, 4H, [H.sup.5]), 8.23 (t, [sup.3]J = 7.8, 7.8 Hz 4H, [H.sup.4]),7.68 (d, [sup.3]J = 7.8 Hz, 4H, [H.sup.3]), 2.89 (s, 12H, C[H.sub.3]).
2.2.3. Synthesis of Bis(adamantylamino)bis-(1,2-diaminocyclohexane)titanium(II), Ti[(ada).sub.2][(dach).sub.2], (C). The complex C was synthesized similarly to complex A. Yield = 0.48 g (87.2%). Ti[C.sub.32][H.sub.58][N.sub.6]: elemental anal. Calcd (%): C 66.63, H 10.41, N 14.57; found (%): C 65.77, H 10.23, N 14.72. FTIR (KBr, [cm.sup.-1])[bar.v]: 3379 (NH stretching), 2925, 2900 (CH stretching), 1595 (C-N stretching), 1522 (NH bending), 1360, 1311 (CH bending), 1084,1020 (CH out of plane deformation), 444 (TiN stretching). [sup.1]HNMR ([D.sub.2]0,400 MHz): adamantylamine [delta], ppm = 2.09 (s, NH), 1.7, [sup.3]J = 4 (d, C[H.sub.2] protons), 1.63, 1.55, (dd, [sup.3]J = 12.52, 36.76 CH protons). 1,2-Diaminocyclohexane [delta], ppm = 3.63 (t, [sup.3]J = 4.8, 4.64 CH), 3.3(m, N[H.sub.2]), 2.01, 1.76, 1.68,1.3 ([H.sup.3],[H.sup.6],[H.sup.4],[H.sup.5]).
2.2.4. Synthesis of Bis(adamantylamino)bis-(1,10-phenanthro line)titanium(II), Ti[(ada).sub.2][(phen).sub.2], (D). The procedure described above for complex A was followed for the synthesis of complex D. Yield: 0.42 g (87.5%). Ti[C.sub.44][H.sub.46][N.sub.6]: elemental anal. Calcd (%): C 74.55, H 6.77, N 11.85; found (%):' C 74.46, H 6.42, N 11.52. FTIR (KBr, [cm.sup.-1]) [bar.v]: 3412 (NH stretching), 3039 (aromatic CH stretching), 2927 (CH stretching), 1612 (C=C stretching), 1514 (N-H bending), 1449 (C=N stretching), 1368,1319 (CH bending), 1084 (CH out of plane deformation), 411 (Ti-N stretching). [sup.1]H NMR ([D.sub.2]O, 400 MHz): adamantylamine [delta], ppm = 2.04 (s, NH), 1.75 (d, [sup.3]J = 2.52, C[H.sub.2] protons), 1.61, 1.55, (dd, [sup.3]J = 24.8 CH protons). 1,10-Phenanthroline [delta], ppm = 8.56 (d, [sup.3]J = 743, 4H, [H.sup.2] & [H.sup.9]), 7.7 (s, 4H, [H.sup.5] & [H.sup.6]), 7.4 (d, [sup.3]J = 9.28, 4H, [H.sup.4] & [H.sup.7]), 6.8 (dd, [sup.3]J = 28, 40,4H, [H.sup.3] & [H.sup.8]).
2.2.5. Synthesis of Bis(adamantylamino)bis(benzoylacetonato) titanium(IV), Ti[(ada).sub.2][(bzac).sub.2], (E). The procedure for the synthesis of complex A was followed for the preparation of complex E. However, there was evolution of HCl gas in both the steps. Yield: 0.43 g (86%). Ti[C.sub.40][H.sub.48][N.sub.2][O.sub.2]: elemental anal. Calcd (%): C 71.61, H 7.45, N 4.17; found (%): C 71.70, H 7.27, N 4.10. FTIR (KBr, cm-1) [bar.v]: 3379 (NH stretching), 2933,2866 (CH stretching), 1612 (C=O stretching), 1522 (C=C stretching), 1449 (NH bending), 1109, 1004 (C-H bending), 557 (Ti-O stretching), 427 (Ti-N stretching). 1HNMR ([D.sub.2]O, 400 MHz): adamantylamine [delta], ppm = 2 (s, NH), 1.71 (d, [sup.3]J = 2.56, C[H.sub.2] protons), 1.58, 1.49, (dd, [sup.3]J = 12.56, 12.08 CH protons). Benzoylacetone [delta], ppm [C.sub.6][H.sub.5]: [delta] = 8.08 (d, [sup.3]J = 7.52, 4H, [H.sup.2] and [H.sup.6]), 7.96 (t, [sup.3]J = 7.16, 4.28, 4H, [H.sup.3] and [H.sup.5]), 7.6 (t, [sup.3]J = 7.64, 7.28, 2H, [H.sup.4]), 3.92 (s, CH protons), 2.5 (s, C[H.sub.3] protons).
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2.3. Cytotoxicity Studies
2.3.1. Cell Lines and Culture. The cytotoxic studies of synthesized complexes were performed on HeLa (cervical cancer cell line), C6 (glioma), and CHO (Chinese hamster ovarian) cell line. The cells were grown in Dulbecco's Modified Eagle's Medium (DMEM) containing fetal calf serum (FCS) (10%), penicillin (100 units/mL), and streptomycin (100 [micro]g/mL) at 37[degrees]C with 90% humidity and 5% C[O.sub.2]. The complexes were dissolved in dimethyl sulphoxide (DMSO) to prepare the solutions of different concentrations. The selected cell lines were treated with these solutions to calculate the IC50 values by using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide) assay while control cells received only DMSO.
2.3.2. MTT Assay. The growth inhibitory effect of newly synthesized titanium complexes on HeLa, C6, and CHO cells was determined by MTT assay . For this, cells were supplemented in complete growth medium to get 1 x [10.sup.5] cells/mL and 100 [micro]L of cell suspension per well was seeded in tissue culture plate. The assay was carried out in 96 well plates in triplicate in which cells were treated with three different concentrations of complexes and incubated for 12 h in C[O.sub.2] incubator. Thereafter, 20 [micro]L of freshly prepared MTT solution, 5 mgm[L.sup.-1] in PBS (phosphate buffered saline) after sterile filtering, was added to each well. Now, culture plates were stirred at 150 rpm for 5 min to thoroughly mix MTT into the media. The plates were further incubated for 4 h at 37[degrees]C to allow metabolization of MTT. MTT formazan crystals were resuspended in 100 [micro]L of DMSO and plates were stirred for 20 min in order to dissolve formazan crystals and optical densitywas measured at 570 nm. The phase contrast imaging was done by using Nikon Eclipse TS100 inverted microscope.
2.3.3. Cell Cycle Analysis. 1 x [10.sup.6] cells/dish well was plated in 24 well plates which were allowed for adheration for 6 h and then treated with complexes at three different concentrations. After 24 h of treatment, cells were harvested from the plate. The cell suspension having 1 x [10.sup.6] cells was centrifuged and the resultant cell pellet was resuspended in phosphate buffered saline (1 mL) solution. The cells were fixed in ice cold 70% ethanol and stained with propidium iodide followed by analysis on the FL-2 channel by BD Accuri C6 flow cytometer (BD Biosciences Immunocytometry Systems, San Jose, CA). DNA content histograms and cell cycle phase distributions were modeled from at least 15,000 single events.
3. Results and Discussion
Synthesis of titanium complexes was carried out in two steps. In the first step, titanium tetrachloride reacted with respective bidentate ligand, that is, 4,4'-dimethoxy-2,2'-bipyridine, 6,6'-dimethyl-2,2'-bipyridine, 1,2-diaminocyclohexane, 1,10phenanthroline, and benzoylacetone which are coligands in 1 : 2 molar ratio under continuous stirring and refluxing by using toluene as a solvent. There was evolution of chlorine gas during the course of reaction. In the next step, respective titanium complexes reacted with main ligand (adamantylamine) in 1: 2 molar ratio in the same solvent, which results in evolution of HCl gas  as shown in Scheme 1. Elemental analysis, that is, Titanium and chlorine estimation, was performed to check the composition by gravimetric and Volhard's method, respectively, and molecular weight was determined by Rast's camphor method (Table 1). The analytical data and spectroscopic characterization of complexes confirm the proposed structure of complexes. The proposed structure of complexes and their corresponding ligands has been shown in Table 2.
3.1. FTIR Spectra. The bands of FTIR were assigned by comparing the spectra of complexes with those of free ligands and were shown in Table 3. From the spectra of complexes, we have found that wave number of [[bar.v].sub.C-H] band appearing around 2900-3000 [cm.sup.-1] does not change much although the intensity of the band changes and gets weaker upon complexation with titanium metal. The absorption band due to [[bar.v].sub.C=C] stretching at 1595,1578, and 1603 [cm.sup.-1] in the bidentate ligand of complexes A, B, and D gets shifted to 1629,1644, and 1612 [cm.sup.-1] (Table 3). The shift maybe due to reduction in electron density after an increase in conjugation caused by complexation with titanium metal . In previous studies, it has been observed that three factors, namely, field effect, steric effect, and ring strain, can cause shift in vibrational frequencies of complexes. Due to field effect , the value of force constant gets changed and there is change in vibration frequencies, due to steric effect , the conjugation in the complex is not completed which results in a shift in absorption frequencies to higher wave number, and due to ring strain in the molecule, more energy is required for vibration of bonds which results in shift of band towards higher wave number. The ring breathing vibration (around 800900 [cm.sup.-1]) having more intensity gets shifted to higher wave number in complexes (around 1000 [cm.sup.-1]). All these changes can be assigned to the coordinated nature of bidentate ligand through nitrogen atoms [12, 13]. The band formed around 3350-3400 [cm.sup.-1] due to N-H stretching of adamantylamine ring, while the occurrence of a strong band in the region 1600-1580 [cm.sup.-1] in complex E may be assigned to stretching modes of [[bar.v].sub.C=O] in benzoylacetone ligand. In complex E carbonyl groups are involved in bonding with the metal ion which is further supported by the appearance of an intense band at ~557 [cm.sup.-1] assignable to [[bar.v].sub.M-O] vibration. Appearance of new bands at 452,404,444,411, and 427 [cm.sup.-1] in complexes A, B, C, D, and E shows that ligands are coordinated to the metal atom through nitrogen [35, 38] and the absence of bands in the region 385-340 [cm.sup.-1] due to [[bar.v].sub.Ti-Cl] bond in all complexes indicates the complete removal of chloride ions .
3.2. UV-Visible Spectra. The UV-visible spectra of the complexes (Figure 1) and ligands were recorded from a solid sample by using diffuse reflectance technique. The transitions observed in the UV-visible spectrum of complexes were due to intraligand charge transfer. The transition around 320-325 nm can be attributed to n [right arrow] [[pi].sup.*] transition in complexes A, B, D, and E get shifted to lower wavelength after coordination. However bands due to n [right arrow] [[pi].sup.*] around 240-245 nm remain almost at the same position even after coordination. Since in complex C both the ligands are of cyclic nature, so there is no possibility of these transitions.
3.3. [sup.1]H NMR Study. The [sup.1]H NMR spectra of the complexes are consistent with the structures proposed in the reaction scheme. We find that bidentate ligands of synthesized complexes show a considerable downfield shift of protons after complexation with titanium. This shift may be due to transfer of electron density from ligand protons to the metal atom [35, 40]. However, protons of adamantylamine in all complexes appearing around 1.2-2.12 ppm show a marginal chemical shift. The cyclic aliphatic nature of both the ligands in complex C creates complications in the spectrum as the peaks corresponding to these falls almost in the same region. However, the integration of signals in all spectra supports the formation of proposed complexes.
3.4. Mass Spectra. The structure of complexes was further confirmed by recording electron spray mass spectrum. The complex A showed base peak at m/z = 152 due to [C.sub.10][H.sub.17]N fragment ion and 4,4'-dimethoxy-2,2'-bipyridine ligand in the complex showed peak at m/z = 217 with relative intensity of 25%. We find that this complex also shows a peak at m/z = 478 due to Ti[C.sub.24][H.sub.24][N.sub.4][O.sub.4] fragment ion. In case of complex B, one peak at m/z = 185 due to [C.sub.12][H.sub.12][N.sub.2] fragment ion and another peak at m/z = 152 due to [C.sub.10][H.sub.17]N fragment ion were found with a relative intensity of 18%. In complex C, peaks were formed at m/z = 98,115, 230 due to [C.sub.6][H.sub.12]N, [C.sub.6][H.sub.14][N.sub.2], and Ti[C.sub.10][H.sub.19][N.sub.2] fragment ions. The complex D shows peaks at m/z = 304 and 335 due to Ti[C.sub.16][H.sub.22][N.sub.3] and Ti[C.sub.16][H.sub.22][N.sub.3] fragment ions. In addition to these peaks, complex D shows a molecular ion peak at m/z = 708 with very low intensity. In complexes C, D, and E, formation of the base peak takes place due to [C.sub.10][H.sub.17]N fragment ion at m/z = 152. The complex E, in addition to base peak, also shows fragment ion peaks, in which one peak is formed at m/z = 401 due to Ti[C.sub.22][H.sub.32][N.sub.2][O.sub.2] fragment ion. The complexes A, B, C, and E show their molecular ion peaks at m/z = 780,716,577, and 670 indicating the formation of complexes. The existence of these different fragment ion peaks, base peaks, and molecular ion peaks supports the stoichiometric formulation of synthesized complexes .
3.5. Powder XRD Study. The powder X-ray diffraction study was performed to understand the lattice structure of the complexes. Figure 2 shows XRD pattern obtained for all the complexes with well-defined peaks in these patterns which indicate the crystalline nature of complexes. Scherrer's equation D = ([lambda] x 0.9)/([beta] x Cos [theta]) [35,41], with D as the crystallite size of (hkl) planes, [lambda] as the wavelength of incident radiation (CuK[alpha], 1.54 [Angstrom]), and [beta] as full width half maximum (FWHM), was used to calculate the crystallite size of complexes. The calculated crystallite size for complexes A, B, C, D, and E was 69,26.5,19.1,115, and 76.6 nm, respectively, which falls in nanorange. Unit cell parameter of the complexes has been calculated by using Powder X software  and the results are summarized in Table 4. We have also observed that as the crystallite size decreases, peaks become broader as seen in Figure 2. On the basis of these different spectroscopic techniques, that is, UV-visible, FTIR, [sup.1]H NMR, and mass spectrometry, an octahedral geometry may be proposed for the synthesized titanium complexes .
3.6. MTT Assay. The IC50 values were calculated by using best fit regression model and results have been tabulated in Table 5. The change in morphological features was observed at different concentrations of complexes, which indicates that such change in morphology is dose dependent as shown in Figure 3. The phase contrast imaging was done with a Nikon microscope at 40x after harvesting stage which clearly shows the formation of small apoptotic bodies, rounding of cells, shrinkage of cells, and plasma membrane blebbing. From the calculated [IC.sub.50] values, it has been observed that complex E with benzoylacetone ligand shows (4.06 [micro]M) better activity than other complexes against the HeLa cell line, which is even better than known anticancer drug camptothecin as seen in Table 5. But ligands were found not much effective against the tested cancer cell lines.
The [IC.sub.50] values of main ligand, that is, adamantylamine along with its complexes, has been shown in Table 5. Complexes A, C, and D with 4,4'-dimethoxy-2,2'-bipyridine, 1,2-diaminocyclohexane, and 1,10-phenanthroline ligand shows good activity against all the tested cell lines which maybe due to the presence of electron withdrawing nature of methoxy group, cyclic nature of 1,2-diaminocyclohexane, and aromatic nature of 1,10-phenanthroline ligand. However, complex B with 6,6'-dimethyl-2,2'-bipyridine was not found much effective against HeLa and C6 cell lines, which maybe due to the presence of electron donating methyl groups in the ligand. So, it could be summarized that electron withdrawing group present in ligand as well as cyclic and aromatic nature of ligand are responsible for the cytotoxicity of titanium complexes.
3.7. Cell Cycle Analysis Using Propidium Iodide. For cell cycle analysis, CHO cells were treated with the complexes at three concentrations almost near to their IC50 values which caused the decrease in the number of cells with an increase in dose due to induction of apoptosis. It has been observed that all complexes increases cells in hypo-diploid cells of cell cycle and also increased the cell death with increase in concentration. Among all the complexes, complex E having benzoylacetone ligand showed 44.3% cell death at 80 [micro]M, which is the maximum for all the complexes. However, known anticancer drug Camptothecin showed 45.5% cell death at 6 [micro]M. Abundant evidences suggest that mitochondria plays a key role in the initiation of apoptosis by releasing Cytochrome C [44, 45]. In addition to Cytochrome C, other factors such as apoptosis signaling molecules and apoptosis inducing factor (AIF) can be important triggers of apoptosis . It has been confirmed from cell cycle analysis (Figure 4) that cell death occurred through increase in hypo-diploid cells (Sub-Gj population) which indicates apoptosis. Previous studies showed that titanium affects polymerase proteins and transcription factors which inhibits protein synthesis and causes cytotoxicity .
We have reported the synthesis of mixed ligand titanium complexes having nitrogen containing ligands. The structure of the complexes has been confirmed by elemental analysis, FTIR, UV-visible, 1H NMR, and mass spectrometry techniques. Cytotoxic studies were done on different cell lines and it has been found that complex E with benzoylacetone ligand was a more potent cytotoxic agent. The morphological analysis on CHO cells indicates characteristics features of apoptosis and cell cycle analysis indicate increase in hypo-diploid cells. The mechanism of action has been certainly established in vitro; however, the efficacy of these complexes with their action mechanisms should also be demonstrated in vivo.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors would like to thank Director of National Institute of Technology, Hamirpur, India, for providing necessary laboratory facilities to carry out this work. The authors also acknowledge Head of Department of Botanical and Environmental Sciences, Guru Nanak Dev University, Amritsar, Punjab, India, for providing the necessary facilities for in vitro analysis.
 E. Wiltshaw, "Cisplatin in the treatment of cancer," Platinum Metals Review, vol. 23, no. 3, pp. 90-98,1979.
 J. Reedijk, "Why does cisplatin reach guanine-N7 with competing S-donor ligands available in the cell?" Chemical Reviews, vol. 99, no. 9, pp. 2499-2510,1999.
 I. Kostova, "Platinum complexes as anticancer agents," Recent Patents on Anti-Cancer Drug Discovery, vol. 1, no. 1, pp. 1-22, 2006.
 S. Fruhauf and W. J. Zeller, "New platinum, titanium, and ruthenium complexes with different patterns of DNA damage in rat ovarian tumor cells," Cancer Research, vol. 51, no. 11, pp. 29432948, 1991.
 A. Bergamo, A. Masi, M. A. Jakupec, B. K. Keppler, and G. Sava, "Inhibitory effects of the ruthenium complex KP1019 in models of mammary cancer cell migration and invasion," Metal-Based Drugs, vol. 2009, Article ID 681270, 9 pages, 2009.
 M. J. Clarke, "Ruthenium in cancer chemotherapy," Platinum Metals Review, vol. 32, no. 4, pp. 198-199,1988.
 S. S. Anchuri, S. Thota, R. Yerra, and S. Dhulipala, "In vitro antioxidant activity of some novel synthetic mononuclear ruthenium (II) compounds," Letters in Drug Design and Discovery, vol. 9, no. 4, pp. 421-425, 2012.
 M. Auzias, B. Therrien, G. Suss-Fink, P. Stepnicka, H. A. Wee, and P. J. Dyson, "Ferrocenoyl pyridine arene ruthenium complexes with anticancer properties: synthesis, structure, electrochemistry, and cytotoxicity," Inorganic Chemistry, vol. 47, no. 2, pp. 578-583, 2008.
 J. -Y. Kim, "Synthesis of some Palladium(II) complexes of 1,2Diamino cyclohexane and dicarboxylates as cis-platin analogues of palladium series," Archives of Pharmacal Research, vol. 15, no. 4, pp. 336-342, 1992.
 A. S. Abu-Surrah, H. H. Al-Sadoni, and M. Y. Abdalla, "Palladium based chemotherapeutic agents. Routes towards complexes with good antitumor activity," Cancer Therapy, vol. 6, pp. 1-10, 2008.
 M. Islami-Moghaddam, H. Mansouri-Torshizi, A. Divsalar, and A. A. Saboury, "Synthesis, characterization, cytotoxic and DNA binding studies of diimine platinum(II) and palladium(II) complexes of short hydrocarbon chain ethyldithiocarbamate ligand," Journal of the Iranian Chemical Society, vol. 6, no. 3, pp. 552-569, 2009.
 P. Chellan, N. Shunmoogam-Gounden, D. T. Hendricks et al., "Synthesis, structure and in vitro biological screening of palladium(II) complexes of functionalised salicylaldimine thiosemicarbazones as antimalarial and anticancer agents," European Journal of Inorganic Chemistry, no. 22, pp. 3520-3528, 2010.
 A. Srivastava and D. C. Gupta, "Synthesis and structural investigations of coordination compounds of palladium(II) with 5-methyl uracil," International Journal of Applied Engineering Research, Dindigul, vol. 1, no. 2, pp. 222-227, 2010.
 C. Gabbiani, A. Casini, and L. Messori, "Gold(III) compounds as anticancer drugs," Gold Bulletin, vol. 40, no. 1, pp. 73-81, 2007
 A. Casini, M. C. Diawara, R. Scopelliti, S. M. Zakeeruddin, M. Gratzel, and P. J. Dyson, "Synthesis, characterisation and biological properties of gold(iii) compounds with modified bipyridine and bipyridylamine ligands," Dalton Transactions, vol. 39, no. 9, pp. 2239-2245, 2010.
 E. Melendez, "Titanium complexes in cancer treatment," Critical Reviews in Oncology/Hematology, vol. 42, no. 3, pp. 309-315, 2002.
 E. Dubler, R. Buschmann, and H. W. Schmalle, "Isomer abundance of bis([beta]-diketonato) complexes of titanium(IV). Crystal structures of the antitumor compound budotitane [[Ti.sup.IV][(bzac).sub.2][(OEt).sub.2]] and of its dichloro-derivative [[Ti.sup.IV][(bzac).sub.2][Cl.sub.2]] (bzac = 1-phenylbutane-1,3-dionate)," Journal of Inorganic Biochemistry, vol. 95, no. 2-3, pp. 97-104, 2003.
 K. O'Connor, C. Gill, M. Tacke et al., "Novel titanocene anticancer drugs and their effect on apoptosis and the apoptotic pathway in prostate cancer cells," Apoptosis, vol. 11, no. 7, pp. 1205-1214, 2006.
 C. Pampillon, J. Claffey, M. Hogan, and M. Tacke, "Novel achiral titanocene anti-cancer drugs synthesised from bis-N,N-dimethylamino fulvene and lithiated heterocyclic compounds," BioMetals, vol. 21, no. 2, pp. 197-204, 2008.
 S. Eger, T. A. Immel, J. Claffey et al., "Titanocene difluorides with improved cytotoxic activity," Inorganic Chemistry, vol. 49, no. 4, pp. 1292-1294, 2010.
 L. M. Gao and E. Melendez, "Cytotoxic properties of titanocenyl amides on breast cancer cell line MCF-7," Metal-Based Drugs, vol. 2010, Article ID 286298, 6 pages, 2010.
 E. A. Williamson, T. J. Boyle, R. Raymond et al., "Cytotoxic activity of the titanium alkoxide [(OPy).sub.2]Ti[(4AP).sub.2] against cancer colony forming cells," Investigational New Drugs, vol. 30, no. 1, pp. 114-120, 2012.
 M. Tacke, L. T. Allen, L. Cuffe et al., "Novel titanocene anticancer drugs derived from fulvenes and titanium dichloride," Journal of Organometallic Chemistry, vol. 689, no. 13, pp. 2242-2249, 2004.
 M. Hogan, J. Claffey, E. Fitzpatrick, T. Hickey, C. Pampillon, and M. Tacked, "Synthesis and cytotoxicity studies of titanocene C analogues," Metal-Based Drugs, vol. 2008, Article ID 754358, 7 pages, 2008.
 F.-J. K. Rehmann, A. J. Rous, O. Mendoza et al., "A trimethoxyphenyl substituted ansa-titanocene: a possible anticancer drug," Polyhedron, vol. 24, no. 11, pp. 1250-1255, 2005.
 G. Sava and A. Bergamo, "Ruthenium-based compounds and tumour growth control (review)," International Journal of Oncology, vol. 17, no. 2, pp. 353-365, 2000.
 J. M. Rademaker-Lakhai, D. Van Den Bongard, D. Pluim, J. H. Beijnen, and J. H. M. Schellens, "A phase I and pharmacological study with imidazolium-trans-DMSO-imidazoletetrachlororuthenate, a novel ruthenium anticancer agent," Clinical Cancer Research, vol. 10, no. 11, pp. 3717-3727, 2004.
 G. Sava, R. Gagliardi, A. Bergamo, E. Alessio, and G. Mestroni, "Treatment of metastases of solid mouse tumours by NAMIA: comparison with cisplatin, cyclophosphamide and dacarbazine," Anticancer Research, vol. 19, no. 2A, pp. 969-972, 1999.
 A. Bergamo, B. Gava, E. Alessio et al., "Ruthenium-based NAMI-A type complexes with in vivo selective metastasis reduction and in vitro invasion inhibition unrelated to cell cytotoxicity," International Journal of Oncology, vol. 21, no. 6, pp. 1331-1338, 2002.
 M. Shavit, D. Peri, A. Melman, and E. Y. Tshuva, "Antitumor reactivity of non-metallocene titanium complexes of oxygenbased ligands: is ligand lability essential?" Journal of Biological Inorganic Chemistry, vol. 12, no. 6, pp. 825-830, 2007
 A. D. Tinoco, H. R. Thomas, C. D. Incarvito, A. Saghatelian, and A. M. Valentine, "Cytotoxicity of a Ti(IV) compound is independent of serum proteins," Proceedings of the National Academy of Sciences of the United States of America, vol. 109, no. 13, pp. 5016-5021, 2012.
 S. Halder, S.-M. Peng, G.-H. Lee et al., "Synthesis, structure, spectroscopic properties and cytotoxic effect of some thiosemicarbazone complexes of palladium," New Journal of Chemistry, vol. 32, no. 1, pp. 105-114, 2008.
 D. Kovala-Demertzi, M. A. Demertzis, J. R. Miller, C. Papadopoulou, C. Dodorou, and G. Filousis, "Platinum(II) complexes with 2-acetyl pyridine thiosemicarbazone: synthesis, crystal structure, spectral properties, antimicrobial and antitumour activity," Journal of Inorganic Biochemistry, vol. 86, no. 2-3, pp. 555-563, 2001.
 T. Mosmann, "Rapid colorimetric assay for cellular growth and survival: application to proliferation and cytotoxicity assays," Journal of Immunological Methods, vol. 65, no. 1-2, pp. 55-63, 1983.
 R. Kaushal, N. Kumar, P. Awasthi, and K. Nehra, "Syntheses, characterization and antibacterial study of titanium complexes," Turkish Journal of Chemistry, vol. 37, no. 6, pp. 936-945, 2013.
 X.-M. Shi, H.-Y. Wang, Y.-B. Li et al., "Spectroscopic studies on Co(II), Ni(II),Zn(II) complexes with 4,4'-bipyridine," Chemical Research in Chinese Universities, vol. 26, no. 6, pp. 1011-1015, 2010.
 D. M. Czakis-Sulikowska, J. Radwanska-Doczekalska, and G. Sojka, "4,4'-Dipyridyl complexes of rare-earth thiocyanates," Monatshefte fur Chemie Chemical Monthly, vol. 115, no. 8-9, pp. 961-973, 1984.
 M. Gulcan, M. Sonmez, and I. Berber, "Synthesis, characterization, and antimicrobial activity of a new pyrimidine Schiff base and its Cu(II), Ni(II), Co(II), Pt(II), and Pd(II) complexes," Turkish Journal of Chemistry, vol. 36, no. 1, pp. 189-200, 2012.
 S. Xiao, H. Lu, and M. Zhang, "Studies on Ti[Cl.sub.4]/Mg [(OEt).sub.2]/EB supported catalysts for propylene polymerization," Chinese Journal of Polymer Science, vol. 8, no. 3, pp. 253-260, 1990.
 K. Zamani, A. Mobinikhaledi, N. Foroughifar, K. Faghihi, and V. Mahdavi, "H NMR studies of some imidazole ligands coordinated to Co(IH)," Turkish Journal of Chemistry, vol. 27, no. 1, pp. 71-75, 2003.
 C. J. Dhanaraj and M. S. Nair, "Synthesis and characterization of metal(II) complexes of poly(3-nitrobenzylidene-1-naphthylamine-co-succinic anhydride)," European Polymer Journal, vol. 45, no. 2, pp. 565-572, 2009.
 S. B. Ade, M. N. Deshpande, and D. G. Kolhatkar, "Synthesis, characterization, spectroscopic studies and antimicrobial activity of 2-[(2-Hydroxy-5-nitrobenzylidene)-amino]-4methyl-phenol with complexes of Cd(II) and Hg(II) ions," International Journal of ChemTech Research, vol. 4, no. 2, pp. 474478, 2012.
 N. P. Priya, S. V. Arunachalam, N. Sathya, V. Chinnusamy, and C. Jayabalakrishnan, "Catalytic and antimicrobial studies of binuclear ruthenium(III) complexes containing bis-[beta]-diketones," Transition Metal Chemistry, vol. 34, no. 4, pp. 437445, 2009.
 J. M. Penninger and G. Kroemer, "Mitochondria, AIF and caspases--rivaling for cell death execution," Nature Cell Biology, vol. 5, no. 2, pp. 97-99, 2003.
 L. Ravagnan, T. Roumier, and G. Kroemer, "Mitochondria, the killer organelles and their weapons," Journal of Cellular Physiology, vol. 192, no. 2, pp. 131-137, 2002.
 C. V. Christodoulou, A. G. Eliopoulos, L. S. Young, L. Hodgkins, D. R. Ferry, and D. J. Kerr, "Anti-proliferative activity and mechanism of action of titanocene dichloride," British Journal of Cancer, vol. 77, no. 12, pp. 2088-2097, 1998.
Raj Kaushal, (1) Nitesh Kumar, (1) Ashun Chaudhary, (2) Saroj Arora, (2) Pamita Awasthi (1)
(1) Department of Chemistry, National Institute of Technology, Hamirpur, Himachal Pradesh 177005, India
(2) Department of Botanical and Environmental Sciences, Guru Nanak Dev University, Amritsar, Punjab 143005, India
Correspondence should be addressed to Nitesh Kumar; email@example.com
Received 14 October 2013; Revised 9 January 2014; Accepted 9 January 2014; Published 27 February 2014
Academic Editor: Ian Butler
TABLE 1: Physical and analytical properties of titanium complexes. Complex Color Yield M.P. Experimental (%) ([degrees] (Theortical) % C) Ti MW Ti[(ada).sub.2] Cream 64.2 205-210 6.3 778 [(bpome).sub.2] (A) (6.1) (780) Ti[(ada).sub.2] Cream 87.3 205-210 7.1 713 [(dpme).sub.2] (B) (6.6) (716) Ti[(ada).sub.2] White 87.2 225-230 8.3 574 [(dach).sub.2] (C) (8.1) (577) Ti[(ada).sub.2] Cream 87.5 210-215 6.0 705 [(phen).sub.2] (D) (6.6) (708) Ti[(ada).sub.2] Light 86 240-245 7.8 668 [(bzac).sub.2] (E) Orange (7.1) (670) TABLE 3: Selected FTIR bands for titanium complexes and their corresponding ligands [bar.v] ([cm.sup.-1]). Ligand/Complex [bar.v] [bar.v] [bar.v] .sub.Ti-O] .sub.Ti-N] .sub.C-H] bend Ada -- -- 1132,1108 bpome -- -- 1303,1230 Ti[(ada).sub.2] -- 452 1313,1229 [(bpome).sub.2] dpme -- -- 1247,1158 Ti[(ada).sub.2] -- 404 1271,1117 [(dpme).sub.2] dach -- -- 1373,1072 Ti[(ada).sub.2] -- 444 1360,1311 [(dach).sub.2] phen -- -- 1344,1093 Ti[(ada).sub.2] -- 411 1368,1319 [(phen).sub.2] Bzac 1255 Ti[(ada).sub.2] 557 427 1109,1004 [(bzac).sub.2] Ligand/Complex [[bar.v] [[bar.v] [[bar.v] .sub.C-C/C=C] .sub.N-H] .sub.C-H] stretch bend strecth Ada 1457 1589 2912 bpome 1595 -- 3071,2974 Ti[(ada).sub.2] 1629 1449 3015,2927 [(bpome).sub.2] dpme 1578 -- 3063,2917 Ti[(ada).sub.2] 1644 1441 3071,2925 [(dpme).sub.2] dach 1433 1578 2924 Ti[(ada).sub.2] 1470 1522 2925, 2900 [(dach).sub.2] phen 1603 -- 3055 Ti[(ada).sub.2] 1612 1514 3039,2927 [(phen).sub.2] Bzac 1409 3063,3006 Ti[(ada).sub.2] 1522 1449 2933,2866 [(bzac).sub.2] Ligand/Complex [[bar.v] [[bar.v] .sub.N-H] .sub.C=O] strecth strecth Ada 3345,3372 bpome -- Ti[(ada).sub.2] 3388 [(bpome).sub.2] dpme -- Ti[(ada).sub.2] 3336 [(dpme).sub.2] dach 3357,3285 Ti[(ada).sub.2] 3379 [(dach).sub.2] phen -- Ti[(ada).sub.2] 3412 [(phen).sub.2] Bzac 1603 Ti[(ada).sub.2] 3379 1612 [(bzac).sub.2] TABLE 4: XRD data of titanium complexes. Empirical formula Ti[C.sub.44] Ti[C.sub.44] Ti[C.sub.32] [H.sub.54] [H.sub.54] [H.sub.58] [N.sub.6] [N.sub.6] (B) [N.sub.6] (C) [O.sub.4] (A) Formula weight 780 716 576 Crystal system Monoclinic Monoclinic Monoclinic Lattice type P P P a (A[omicron]) 17 13 16 b (A[omicron]) 13 11 12 c (A[omicron]) 14 20 15 [alpha] ([omicron]) 90 90 90 [beta] ([omicron]) 91 106 113 [gamma] ([omicron]) 90 90 90 Crystallite size (nm) 69 26.5 19.1 V [(A[omicron]).sup.3] 3094 2860 2880 20 start 10 10 10 20 end 60 60 60 Radiation Cu Cu Cu Wavelength 1.54 1.54 1.54 Empirical formula Ti[C.sub.44] Ti[C.sub.40] [H.sub.46] [H.sub.48] [N.sub.6] (D) [N.sub.2] [O.sub.2] (E) Formula weight 708 670 Crystal system Monoclinic Monoclinic Lattice type P P a (A[omicron]) 11 17 b (A[omicron]) 13 11 c (A[omicron]) 14 16 [alpha] ([omicron]) 90 90 [beta] ([omicron]) 106 85 [gamma] ([omicron]) 90 90 Crystallite size (nm) 115 76.6 V [(A[omicron]).sup.3] 2002 2992 20 start 10 10 20 end 60 60 Radiation Cu Cu Wavelength 1.54 1.54 TABLE 5: Cytotoxic studies of titanium complexes on HeLa, C6 and CHO cancer cell lines as determined by MTT assay. Cell line (Source) Complex Hela C6 (Rat glioma) CHO (Ovary) (cervical) [IC.sub.50] ([micro]M) Ti[(ada).sub.2] 13 178 19.9 [(bpome).sub.2] Ti[(ada).sub.2] 74 69.8 16.1 [(dpme).sub.2] Ti[(ada).sub.2] 20.4 21 16.6 [(dach).sub.2] Ti[(ada).sub.2] 11.1 22.1 21.5 [(phen).sub.2] Ti[(ada).sub.2] 4.06 21.8 46.1 [(bzac).sub.2] Adamantylamine 104.5 148 123 Camptothecin 6.2 6.4 6.4
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|Title Annotation:||Research Article|
|Author:||Kaushal, Raj; Kumar, Nitesh; Chaudhary, Ashun; Arora, Saroj; Awasthi, Pamita|
|Publication:||Bioinorganic Chemistry and Applications|
|Date:||Jan 1, 2014|
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