Synthesis, spectral characterization and biological ...

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Synthesis, spectral characterization and biological evaluation of some Lanthanide(III) complexes of Schiff bases of carbostyril derivatives a

b

Mohammedshafi A. Phaniband , Prakash Gouda Avaji & Shreedhar D. Dhumwad

a

a

Department of Chemistry, Karnatak University's Karnatak Science College, Dharwad, India b

P.G. Department of Chemistry, Karnatak University, Dharwad, India Available online: 18 Mar 2009

To cite this article: Mohammedshafi A. Phaniband, Prakash Gouda Avaji & Shreedhar D. Dhumwad (2008): Synthesis, spectral characterization and biological evaluation of some Lanthanide(III) complexes of Schiff bases of carbostyril derivatives, Main Group Chemistry, 7:4, 271-283 To link to this article: http://dx.doi.org/10.1080/10241220802688442

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Main Group Chemistry Vol. 7, No. 4, December 2008, 271–283

Synthesis, spectral characterization and biological evaluation of some Lanthanide(III) complexes of Schiff bases of carbostyril derivatives Mohammedshafi A. Phanibanda, Prakash Gouda Avajib and Shreedhar D. Dhumwada* a

Downloaded by [Ewha Womans University] at 23:55 27 October 2011

Department of Chemistry, Karnatak University’s Karnatak Science College, Dharwad, India; b P.G. Department of Chemistry, Karnatak University, Dharwad, India (Received 24 July 2008; final version received 14 December 2008) A series of La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III) and Dy(III) complexes have been synthesized with Schiff bases derived from 4-aminomethylcarbostyril and substituted salicylaldehyde. The characterized involved elemental analyses, molar conductance, magnetic susceptibility, electronic, IR, NMR, mass and thermal studies. Spectral studies show all the Schiff bases behave as bidentate ligands and coordinate through the azomethine nitrogen and phenolic oxygen. The ligands and their metal complexes have been screened for their biological studies. The results indicate that the biological activity increases on complexation. The Lanthanium(III) complexes of the above ligands show greater inhibitory action towards the P388/s tumor cells at lower concentrations. Keywords: synthesis; biological; lanthanides; complexes; carbostyril

1. Introduction Coordination chemistry favors the conversion of stable compounds into yet another set of stable and structurally challenging compounds. The nature of the coordination compounds depends on the nature of metal ion, the donor atoms, the structure of the ligand and metal–ligand interaction [1,2]. The important factors, which contribute to thermodynamic stability of metal complexes, depend considerably on the nature of the ligand and on the metal ion [3–5]. Vast interest has been developed by bioinorganic chemists to devise small molecule models, the properties of which can be compared with different metal complexes [6,7]. Metal complexes have proven their significance by entering into the field of diagnosis of a wide variety of disease states ranging from heart diseases, brain disorders, cancer and diabetics. Metal complexes are also able to determine specific aspects of disease such as tissue hypoxia, as well as to detect molecular phenomena such as multi-drug resistance [8]. The use of metal complexes as diagnostic agents is a relatively new area of medical research and has flourished rapidly from last 4–5 decades [9]. Today, there are a wide variety of radiometals and its complexes which are used in gamma

*Corresponding author. Email: dhumwad_ic@rediffmail.com ISSN 1024-1221 print/ISSN 1745-1167 online Ó 2008 Taylor & Francis DOI: 10.1080/10241220802688442 http://www.informaworld.com


272

M.A. Phaniband et al.

scintigraphy and positron emission tomography. An even more recent development is the use of paramagnetic metal complexes for enhancing contrast of magnetic resonance imaging (MRI) and single photon emission computed tomography. Nowadays even non-radioactive metal complexes are used as MRI contrast agents. Carbostyril, an aromatic compound, is known for its wide range of applications and peculiar characteristics. Carbostyril nucleus has been a part of many alkaloids and antibiotics [10–12]. Two specific characteristics of carbostyrils are the complex molecular structure and the prominent pharmacological activity associated with them. The systematic studies about the fluorescence properties of differently substituted carbostyrils were reported [13–15]. These properties also make carbostyril interesting for use in sensor devices utilizing the new blue laser diodes. Carbostyril offer the advantages of greater chemical and thermal stability. Besides other uses, this makes them possible candidates as wave-shifting flours in highenergy particle detection [16]. Researcher’s interested in luminescent dyes has intensified with the emphases mainly on analytical applications in biological sciences. One of the promising approaches consists in the use of sensitizing chromophors for Lanthanide chelates [17–21]. After publishing our work on transition series of the these novel carbostyrils [22], we take upon the interesting Lanthanide (III) complexes of Schiff bases (Figures 1–3) and their biological evaluation with various physico–chemical methodologies. 2.

Experimental

All the chemicals were of reagent grade and used without further purification. Elemental analyses (C, H and N) were performed on a Perkin–Elmer 2400 CHN elemental Analyzer Model 1106. The IR spectra of the ligands and their Lanthanide complexes were recorded on a HITACHI-270 IR spectrophotometer in the 4000– 400 cm71 region in KBr disks. Molar conductivity measurements were recorded on an ELICO-CM-82 T conductivity bridge with a cell having cell constant 0.51. The electronic spectra of the complexes were recorded in DMF on a VARIAN CARY 50BIO UV-spectrophotometer in the region of 200–1100 nm. The proton PMR spectra of ligands were recorded in CDCl3 on BRUKER 300 MHz spectrometer at room temperature using TMS as an internal reference. FAB mass spectra were recorded on a JEOL SX 102/DA-6000 mass spectrometer/data system using Argon/Xenon (6 KV, 10 Am) as the FAB gas. The accelerating voltage was 10 KV and the spectra were

Figure 1.

Salicylidene 4-aminomethycarbostyril (1).


Main Group Chemistry

Figure 2.

O-vanillin salicylidene 4-aminomethycarbostyril (10).

Figure 3.

50 Chloro salicylidene 4-aminomethycarbostyril (19).

273

recorded at room temperature. m-nitrobenzyl alcohol was used as the matrix. The mass spectrometer was operated in the þve ion mode. Thermogravimetric analysis data were measured from room temperature to 10008C at a heating rate of 108C/min. The data were obtained by using a PERKIN–ELMER DIAMOND TG/DTA instrument. 2.1.

Synthesis of Schiff bases

Equimolar ratio of 4-aminomethylcarbostyril and substituted salicylaldehydes were refluxed about 4–5 h in alcohol maintaining the reaction medium in slightly acidic condition by adding 3 to 4 drops of acetic acid. The Schiff bases so obtained by cooling in ice water were filtered and recrystallised from methanol. 2.2.

Synthesis of Lanthanide(III) complexes

The following general procedure was used to isolate all the Lanthanide(III) complexes. M(III) nitrate (M ¼ La, Ce, Pr, Nd, Sm, Eu, Gd, Dy) (0.001 mol) was dissolved in 10 mL of dry alcohol. The ligand (0.001 mol) in the same solvent (20 mL) was added to the above solution with constant stirring. The mixture was refluxed on a water bath for about 4 h and then pH of the mixture was raised to 6.5 by drop-wise addition of alcoholic ammonia. This mixture was again refluxed for 2 h. The solution was concentrated to a small volume and the solid complex formed was filtered, washed with absolute alcohol and dried under vacuum at room temperature.

274


2.3.

M.A. Phaniband et al. Antitumor studies of lanthanium(III) complexes

The antitumor activities of the ligands and their Lanthanium(III) metal complexes were carried out in vitro against P388 lymphocytic leukemia cells sensitive to adriamycin (P388/s) by MTT [3-(4,5-dimethylthiazole-2-yl)- 2,5 diphenyltetrazolium bromide] assay. Cells were suspended in supplemented Dulbecco’s minimum essential medium at a density of 1 6 106 cells/mL. One hundred microliters of this suspension was dispensed into 96 wells in flat-bottomed microliter plates containing 10 mL of drug dilutions. Wells containing no drug and no cells were taken as blank in the spectrophotometer. After incubation at 378C in 5% CO2 for 42 h, an aliquot of 10 mL of MTT solutions (5 mg/mL) was added to each well and incubated further for 6 h. Formazon crystals were dissolved with 100 mL acidified isopropanol. The optical density of the wells was measured in a micro plate spectrophotometer (Titretek Multiscan MCC) at 540 nm. The % inhibition was calculated as follows. % Inhibition ¼ ðtreated ODÞ100=ðcontrol ODÞ 3.

Results and discussion

3.1. Physico–chemical methods The molar conductance values of Lanthanide(III) complexes in Table 1 show that they are non-electrolytic in nature. The observed magnetic moments of the present Lanthanide(III) complexes show very little deviation from Van-Vleck values suggesting the non participation of the 4f electrons in the bond formation. 3.2. Electronic spectra The important electronic frequencies with their tentative assignments of ligands and their corresponding Lanthanide(III) complexes in solid state (diffused reluctance spectra) and solution state (DMF) have been recorded. The data presented in Table 2 reveals that the Nephelauxetic value being less than unity and all other parameters exhibit positive values suggest some covalent character in metal–ligand band, particularly the value of B1/2 suggests the comparative involvement of 4f orbital metal–ligand band. The covalence decreases from Pr(III) to Sm(III) complexes which is due to lanthanide contraction [23]. 3.3.

Infrared spectra

The infrared spectra of the ligands show a broad weak band at 2900 cm71 [24] due to the phenolic OH group suggesting the intramolecular hydrogen bonding between hydroxyl hydrogen and nitrogen of the azomethine group. The absorption peaks at around 1730, 1620 and 1250 cm71 are due to nC¼¼O (lactone carbonyl), nC¼¼N (azomethine) and nC O (phenolic) respectively [25]. The IR spectra of all complexes show no band in the region 3200–2900 cm71, which suggests the cleavage of intramolecular hydrogen bonded OH with subsequent deprotonation and coordination through phenolic oxygen. The nC O (phenolic) observed at 1250 cm71 in the ligands show a higher shift of 15–30 cm71 in the complexes. This further confirms the involvement of phenolic oxygen in the complexation [26]. The lower shift of

275


Table 1. Analytical, magnetic and conductance data of the carbostyril Schiff bases and their Lanthanide(III) complexes.


Compound code Complex 1

C17H14N2O2

2

[La(1)(NO3)2]4H2O

3

[Ce(1)(NO3)2]4H2O

4

[Pr(1)(NO3)2]2H2O

5

[Nd(1)(NO3)2]2H2O

6

[Sm(1)(NO3)2]5H2O

7

[Eu(1)(NO3)2]2H2O

8

[Gd(1)(NO3)2]4H2O

9

[Dy(1)(NO3)2]4H2O

10

C18H17N2O3

11

[La(10)(NO3)2]4H2O

12

[Ce(10)(NO3)2]4H2O

13

[Pr(10)(NO3)2]2H2O

14

[Nd(10)(NO3)2]2H2O

15

[Sm(10)(NO3)2]5H2O

16

[Eu(10)(NO3)2]2H2O

17

[Gd(10)(NO3)2]4H2O

18

[Dy(10)(NO3)2]4H2O

19

C17H13N2O2Cl

20

[La(19)(NO3)2]4H2O

21

[Ce(19)(NO3)2]4H2O

22

[Pr(19)(NO3)2]2H2O

23

[Nd(19)(NO3)2]2H2O

24

[Sm(19)(NO3)2]5H2O

25

[Eu(19)(NO3)2]4H2O

C

H

N

Cl

M

Molar conductance (Ohm71 cm2 mol71)

72.98 (73.38) 32.97 (33.35) 33.06 (33.27) 35.16 (35.30) 34.88 (35.09) 31.58 (31.81) 32.43 (32.64) 32.03 (32.37) 31.94 (32.10) 69.63 (69.90) 33.23 (33.60) 33.21 (33.53) 35.25 (35.47) 34.98 (35.28) 31.97 (32.13) 34.54 (34.84) 32.38 (32.67) 32.13 (32.41) 65.04 (65.38) 31.29 (31.58) 31.38 (31.52) 31.27 (31.40) 31.03 (31.32) 30.84 (31.03) 30.61

4.89 (5.04) 3.28 (3.43) 3.18 (3.43) 2.73 (2.94) 2.68 (2.92) 3.24 (3.59) 2.51 (2.72) 3.14 (3.33) 3.12 (3.30) 5.39 (5.50) 3.01 (3.27) 3.43 (3.72) 2.96 (3.28) 3.03 (3.27) 3.49 (3.87) 3.03 (3.23) 3.38 (3.63) 3.33 (3.60) 4.05 (4.16) 2.81 (3.10) 2.88 (3.10) 2.86 (3.09) 2.16 (2.45) 3.01 (3.35) 2.19

9.23 (10.07) 9.32 (9.16) 8.96 (9.13) 9.49 (9.69) 9.59 (9.63) 8.61 (8.73) 8.63 (8.96) 8.54 (8.89) 8.63 (8.81) 8.78 (9.06) 8.36 (8.71) 8.41 (8.69) 9.07 (9.20) 8.88 (9.15) 8.13 (8.33) 8.89 (9.03) 8.28 (8.47) 8.21 (8.40) 8.79 (8.97) 8.48 (8.67) 8.44 (8.66) 8.47 (8.64) 8.38 (8.60) 8.31 (8.52) 8.23

–

–

–

–

22.57 (22.71) 22.50 (22.85) 23.98 (24.33) 24.71 (24.81) 23.14 (23.44) 24.07 (24.32) 24.67 (24.95) 25.24 (25.57) –

25.4

– – – – – – – – – – – – – – – – – 5.29 (5.49) 5.33 (5.48) 5.30 (5.48) 5.21 (5.44) 5.04 (5.39) 5.24

21.41 (21.61) 21.12 (21.75) 22.89 (23.14) 23.40 (23.56) 22.04 (22.36) 24.26 (24.51) 23.41 (23.78) 24.09 (24.38) 10.90 (11.20) 21.28 (21.51) 21.36 (21.65) 21.41 (21.75) 21.87 (22.15) 22.48 (22.87) 22.84

26.7 27.3 26.1 30.9 26.4 27.8 30.5 – 24.9 25.6 25.8 24.9 30.5 25.1 25.8 29.8 – 24.2 25.4 26.8 25.4 30.4 25.7 (continued)

276 Table 1.

M.A. Phaniband et al. (Continued).

Compound code Complex 26


27

Table 2.

4

5

6

6

H

N

Cl

(30.96) (2.42) (8.50) 30.46 2.83 8.19 (30.71) (3.01) (8.43) 2.61 8.02 [Dy(19)(NO3)2]4H2O 30.23 (30.47) (2.98) (8.36)

[Gd(19)(NO3)2]4H2O

M

(5.38) (23.06) 5.06 23.34 (5.34) (23.68) 5.03 24.03 (5.29) (24.35)

25.4 29.4

Electronic spectra data of Lanthanide(III) nitrate complex.

Complex code Medium 4

C

Molar conductance (Ohm71 cm2 mol71)

lmax of ligand (cm71)

Solid

DMF

DMF

Solid

DMF

lmax of Ln(III) ion (cm71)

lmax of complex (cm71)

– – 21494 17226 10001 06431

36362 26316 21402 17051 09983 06385

22376 21224 20642 16814

36463 26491 22294 21048 20436 16705

19456 19028 17149 13598 13328 12468 11446

36462 26473 19418 18958 17028 13528 13265 12417 11396

27138 21889

36364 26907 27084 21823

24657 23784 21398 20609

36451 26488 24639 23731 21345 20583

37037 267–38

37037 26738

–

37038 26739

B’

D

B1/2

N

0.9956 0.9901 0.8473 0.0643 0.0041 0.9888 0.9923 B’av ¼ 0.9917

0.9956 0.9918 0.7453 0.0608 0.0038 0.9890 0.9936 B’av ¼ 0.9925

0.9969 0.9968 0.9933 0.5329 0.0514 0.0028 0.9945 0.9943 0.9958 0.9918 B’av ¼ 0.9948

0.9875 0.9963 Bav ¼ 0.9919

0.2458 0.0349 0.0016

0.9987 0.9979 0.2006 0.0317 0.0010 0.9964 0.9952 B’av ¼ 0.9971


277

nC¼¼N to about 25–30 cm71 in all the complexes indicates the participation of azomethine nitrogen in coordination [27,28]. In all the complexes, the unaltered position of band assign to nC¼¼O (lactone carbonyl) confirms its non involvement in coordination. The complexes showed a medium intensity band in the region 550– 430 cm71 assigned to n(M N) and 350–320 cm71 assigned to n(M O) modes. This also suggests that the nitrate group in the complex co-ordinated in bidentate fashion; the data were listed in (Table 3).


3.4.

1

H NMR studies

The formation of Schiff bases is confirmed by the sharp singlet at d 8.70 due to the azomethine proton. A singlet observed at d 12.70 is probably due to phenolic OH group. The sharp multiplet signals of the phenyl protons are found in the region d 6.4–7.6. The N H proton and methylene protons of the ligand are observed as a sharp peak at d 11.3 and d 5.0, respectively. The peak due to phenolic OH appeared at d 12.70 in the ligand is not observed in the complexes, this confirms the involvement of phenolic oxygen in coordination with the metal via deprotonation. The downfield shift of the azomethine proton d 9.3 in the complexes indicates the participation of azomethine nitrogen in the coordination. 3.5. FAB mass spectrum The FAB spectrum of ligand 1 showed a molecular ion peak at m/z 279 which is equivalent to its molecular weight. The fragments in the spectrum lead to the formation of the species [C17H14N2O2]þ. The FAB mass spectrum of La(III) complex 2 of ligand 1 contain molecular ion peak Mþat m/z 613 which is equivalent to its molecular weight of the Lanthanium(III) complex 2. This molecular ion underwent fragmentation with the loss of two water molecules and produced a species, i.e. [La(L)(NO3)2]þ at m/z 541. Further, this fragment ion by the loss of two nitrate molecules gave a fragment ion at m/z 417. Finally, it underwent demetallation to form the species [L þ H]þ which gave a fragment ion at m/z 279. 3.6.

Thermal studies

Thermograms obtained for representative Lanthanium(III) complexes 2, 11 and 20 at room temperature. The percentage weight loss, nature of decomposed chemical change with the temperature range and percentage of metal oxide obtained are given in Table 4. The thermal decomposition of Lanthanium(III) complexes 2, 11 and 20 takes place in two steps as indicated by DTG peak around 120–2408C and 260–7008C with the decomposition of coordinated water molecule and ligand moieties, respectively. The final weight corresponded to that of the metal oxide.

3.7. Biological studies 3.7.1. Antibacterial and antifungal activities The antibacterial activity of ligand 1 and its Lanthanide(III) complexes were assayed against two bacteria namely, E. coli and B. cirroglagellous by cuplate

1730s 1728s 1725s 1729s 1727s 1725s 1726s 1728s 1725s

– 3412b 3386b 3428b 3288b 3391b 3416b 3358b 3451b

s, strong; b, broad; m, medium; w, weak.

1 2 3 4 5 6 7 8 9

nC¼¼O

n(OH) of water 1620s 1652s 1643s 1645s 1645s 1638s 1640s 1650s 1645s

nC¼¼N 1210s 1235s 1240s 1227s 1228s 1225s 1229s 1235s 1232s

nC O (phenolic) – 1528s 1532s 1555s 1543s 1526s 1537s 1541s 1539s

n4 – 1308s 1311s 1328s 1315s 1300s 1304s 1317s 1320s

n1 – 1018m 1022m 1025m 1018m 1020m 1028m 1035m 1030m

n2

Infrared spectral data of representative Schiff base and its Lanthanide(III) complexes in cm71.

Compound code

Table 3.

– 822m 819m 815m 817m 820m 819m 813m 820m

n6


– 738m 741m 740m 742m 740m 738m 737m 737m

n3

– 697m 708m 703w 700m 704m 693w 695w 698w

n5

– 552w 550w 565w 570w 560w 560w 550w 560w

n(M N)

385m

389m

384m

–

n(M O)

278 M.A. Phaniband et al.

279



method. Similar procedure was followed for the antifungal activity of the above said ligand and its metal complexes against two fungi namely, A. niger and Candida albicans. The zone of inhibition for the ligand and its Lanthanide(III) complexes are presented (Figures 4 and 5). The biological data for the ligand and its Lanthanide(III) complexes are presented in Table 5. From the data of metal complexes, it is clear that the metal chelates exhibit higher antimicrobial activity than that of the free ligand molecules. In the present case, when compared with other metal complexes Lanthanide(III) complexes were good antibacterial agents. The activity of any compound is a complex combination of steric, electronic and pharmacokinetic factors. A possible explanation for the toxicity of the complexes has been postulated in the light of chelation theory. It was suggested that the chelation considerably reduces the charge of the metal ion mainly because of partial sharing of its positive charge with the donor groups and possible p-electron delocalization over the whole chelate ring. This increases the lipophilic character of the metal chelate which favors its permeation through lipoid layers of cell membranes. Furthermore, the mode of action of the compounds may involve the formation of a hydrogen bond through the N¼¼C group of the chelate or the ligand with the active centers of the cell constituents resulting in interference with the normal Table 4.

Thermal data of representative Lanthanide(III) complexes.

Complex Temp. code range (8C) 2

140–220 280–725

11

130–234 275–700

20

140–245 265–695

Figure 4.

% weight loss

Nature of DTA peak

5.38 (5.55) Endothermic 80.76 (81.01) Broad endothermic þ strong exothermic 4.89 (5.06) Endothermic 82.82 (83.18) Broad endothermic þ strong exothermic 4.81 (5.02) Endothermic 69.89 (70.93) Broad endothermic þ strong exothermic

Proposed chemical change

% of metal

(2H2O) (2L) þ O2

9.38 (9.72)

(2H2O) (2L) þ O2

8.09 (8.29)

(2H2O) (2L) þ 2O2

7.85 (8.19)

Antibacterial spectrum of Schiff base and its Lathanide(III) complexes.

280

M.A. Phaniband et al.

cell process. The higher bacteriotoxicity experienced by the compounds may be ascribed to the fact that the ligand and metal ions are more susceptible towards the bacterial cells than fungicidal cells. Thus, it can be concluded that although these compounds are not good fungicides yet they may serve as good bactericides [29,30]. 3.7.2.

Antitumor activity


The antitumor activities of the ligands and their Lanthanium(III) metal complexes were carried out in vitro against P388 lymphocytic leukemia cells sensitive to adriamycin (P388/s) by MTT [3-(4,5-dimethylthiazole-2-yl)- 2,5-diphenyltetrazolium bromide] assay (Table 6). The results indicate that the compounds (19) and (20) are active towards the tumor cells.

Figure 5.

Antifungal spectrum of Schiff base (1) and its Lanthanide(III) complexes.

Table 5. Antibacterial and antifungal activity of representative Schiff base and its Lanthanide(III) complexes (zone of inhibition in mm). Antibacterial

Antifungal

Compound code

E. coli

S. aureus

P. aurogenese

B. cirroglagellous

A. niger

C. albicans

1 2 3 4 5 6 8 9 Gentamycine Flucanazole DMF

16 18 14 18 16 16 18 18 20 – 06

16 14 14 14 16 14 14 16 20 – 06

14 18 16 16 14 14 14 16 20 – 06

16 14 12 14 14 12 12 14 20 – 06

11 12 14 16 14 12 14 14 – 24 06

12 18 14 20 20 16 16 19 – 24 06

Key to interpretation: 510 mm ¼ inactive, 510–15 mm ¼ weakly active, 5 15–20 mm ¼ moderately active, 4 20 mm ¼ highly active.


281

Table 6. Effect of Schiff bases and their Lanthanide(III) complexes on P 388/S tumor cells (in vitro). Compound code 1


2

10

11

19

20

Figure 6.

Concentration (mg/ml)

% inhibition

0.1 0.5 1.0 5.0 10.0 0.1 0.5 1.0 5.0 10.0 0.1 0.5 1.0 5.0 10.0 0.1 0.5 1.0 5.0 10.0 0.1 0.5 1.0 5.0 10.0 0.1 0.5 1.0 5.0 10.0

16.63 21.78 26.94 31.03 35.65 48.93 36.15 27.43 21.96 17.02 18.13 26.54 33.65 35.43 40.80 52.30 39.73 30.04 25.68 15.80 20.93 27.06 34.75 41.38 49.53 54.86 41.73 32.58 24.96 16.78

Proposed structure of metal complexes.

282 4.

M.A. Phaniband et al. Conclusions

The Synthesized Schiff bases act as bidentate ligands through the coordination of azomethine nitrogen and phenolic oxygen atom to the metal ion. The bonding of ligands to metal ion is confirmed by the analytical, IR, 1H-NMR, electronic, magnetic, FAB mass and thermal studies. All these observations put together lead us to propose the following structures shown in (Figure 6). In biological studies, some of the compounds have shown promising results. The in vitro antitumor study of the complexes reveals that the activity of Lanthanide(III) complexes increases at lower concentrations.


Acknowledgements Authors are thankful to the University Grant Commission, New Delhi for the financial support for the work under the X Plan. Authors are thankful to Director, University Sophisticated Instrumentation Centre (USIC) for recording the spectral data. Authors are thankful to Prof. S.T. Nandibewoor, Chairman, Department of Chemistry, Karnatak University, Dharwad for providing the instrumental facility. Authors thank Central Drug Research Institute, Lucknow for providing EI and FAB mass spectra. Thanks are to Sophisticated Test and Instrumentation Centre (STIC) Cochin, for providing the thermal and analytical data. Thanks are extended for IIT, Powai, Mumbai for ESR spectra. Authors are also thankful to Dr. S.R. Pattan, Department of Pharmacology, Belgaum for his support in carrying out the biological studies of the compounds.

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