Journal of Thermal Analysis and Calorimetry

, Volume 112, Issue 2, pp 671–681

Synthesis, thermal characterization, and antimicrobial activity of lanthanum, cerium, and thorium complexes of amino acid Schiff base ligand

Authors

    • Department of Chemistry, Faculty of SciencePort Said University
  • Hanan F. Abd El-Halim
    • Department of Chemistry, Faculty of Pharmacy-PharmaceuticalMisr International University
  • M. S. Abd El-sadek
    • Physics Department, Faculty of ScienceSouth Valley University
  • I. S. Yahia
    • Physics Department, Faculty of EducationAin Shams University
  • L. A. Wahab
    • Physics DepartmentNational Center for Radiation Research and Technology
Article

DOI: 10.1007/s10973-012-2628-4

Cite this article as:
Alghool, S., Abd El-Halim, H.F., Abd El-sadek, M.S. et al. J Therm Anal Calorim (2013) 112: 671. doi:10.1007/s10973-012-2628-4

Abstract

Metal complexes of La(III), Ce(IV), and Th(IV), with the amino Schiff base ligand, [N-(2-hydroxybenzyl)-l-methionine acid](H3L), were prepared in the presence of triethylamine as a deprotonating agent. All synthesized compounds were identified and confirmed by mass spectra, elemental analyses, molar conductivities, and spectral analyses (UV–Visible, IR, 1H NMR, and 13CNMR). Conductance measurements suggest the non-electrolytic nature and the complexes were isolated in 1:1 ratios. The thermal decomposition of the complexes was discussed in relation to structure. The data from thermogravimetric analysis clearly indicated that the decomposition of the complexes proceeds in four or five steps and the organic part of the complexes decomposed in one or two intermediates. The decomposition of all complexes ended with metal oxide and carbon residue. The Schiff bases and their complexes were screened for their antibacterial (Escherichia coli, Staphylococcus aureus) and antifungal (Aspergillus flavus and Candida Albicans) activities.

Keywords

Amino acidThermal studiesSchiff baseMetal complexesBacterial

Introduction

The chemistry of metal complexes of Schiff base ligands having nitrogen, oxygen, and sulfur at their donor sites has been extensively studied [14].The coordination chemistry of amino acid Schiff base ligands is considered to constitute a new kind of potential antibacterial, anti-inflammation, and anticancer agent [57]. Transition metal complexes of salicylaldehyde–amino acid Schiff bases are non-enzymatic models for pyridoxal–amino acid systems that are of considerable importance as key intermediates in many metabolic reactions of amino acids catalyzed by enzymes that require pyridoxal as a cofactor [810]. Considerable effort has been devoted to the preparation and structural characterization of Schiff base complexes derived from salicylaldehyde and amino acids such as glycine [1113]. Tridentate amino acid Schiff base complexes within which oxygen of a phenolate group and oxygen of amino acid, imine nitrogen, and a solvent are presumably coordinated to the oxovanadium center in the equatorial position [14]. The chemical behavior of Schiff base complexes with lanthanide has become increasingly significant in the last few years due to the wide variety of applications of lanthanide complexes in photochemistry, medicine [15], and supramolecular [16]. Schiff base complexes were prepared in the past decade among some lanthanide complexes showing catalytic activity for polymerization reaction [17]. Recently, a novel amino acid Schiff base heteronuclear complex of Ln(III) was synthesized and results showed that it has a catalytic activity for polymerization [18]. Also, lanthanides(III) show antitumor and antimicrobial activities [19, 20]. In this article, we synthesized and characterized La(III), Ce(IV), and Th(IV) complexes derived from the amino acid Schiff base ligand. The solid complexes were characterized by elemental analysis, mass spectra, thermal analyses, IR, molar conductance measurements, 1HNMR, and 13CNMR. Thermal decomposition of the complexes was also used to infer the structure.

Experimental

Materials and measurements

La(NO3)3·6H2O, Ce(NO3)3·6H2O, and Th(NO3)4·5H2O from Aldrich Chem. Co. and salicylaldehyde, l-methionine acid, and NaBH4 all from Sigma Chem. Co. were used as received. The solvents methanol, ethanol, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) were reagent grade.

Elemental analysis (C, H, and N) was performed using a Perkin-Elmer CHN 2400 elemental analyzer. The content of metal ions was calculated gravimetrically as metal oxides. Molar conductance measurements of the ligand and its complexes with 1.0 × 10−3 mol/l in DMSO were carried out using a Jenway 4010 conductivity meter. 1H NMR and 13CNMR spectra were recorded on a Bruker 300 MHz NMR spectrometer and referenced to the residual solvent peaks. FAB-mass spectra were recorded on a JEOL SX 102/DA-6000 mass spectrometer/data system using argon/xenon (6 kV, 10 A) as the FAB gas. The UV–Visible Spectra were obtained in DMSO solution (1.0 × 10−3 M) for the ligand and its metal complexes with a Jenway 6405 Spectrophotometer using 1 cm quartz cell, in the range 200–800 nm. IR spectra (4,000–400 cm−1) were recorded as KBr pellets on a Bruker FT-IR spectrophotometer. Thermogravimetric analysis (TG/DTG) was carried out in the temperature range from 25 to 800 °C in a stream of nitrogen atmosphere using a Shimadzu TG 50H thermal analysis instrument. The experimental conditions were platinum crucible, nitrogen atmosphere with a 30 mL min−1 flow rate and a heating rate 10 °C min−1. The purity of the complexes was checked by thin layer chromatography using silica gel-G glass plates as the stationary phase and dichloromethylene and petroleum ether (4:1) as the mobile phase.

Microbiological investigations

For these investigations, the filter paper disk method was applied according to Gupta et al. [21]. The investigated isolates of bacteria and fungi were seeded in tubes with nutrient broth (NB). The seeded NB (1 cm3) was homogenized in the tubes with 9 cm3 of melted (45 °C) nutrient agar. The homogeneous suspensions were poured into Petri dishes. The disks of filter paper (diameter 4 mm) were ranged on the cool medium. After cooling on the formed solid medium, 2 × 10−5 dm3 of the investigated compounds were applied using a micropipette. After incubation for 24 h in a thermostat at 25–27 °C, the inhibition (sterile) zone diameters (including the disk) were measured and expressed in mm. An inhibition zone diameter of over 7 mm indicates that the tested compound is active against the bacteria under investigation. The antibacterial activities of the investigated compounds were tested against Escherichia coli as Gram negative and Staphylococcus aureus as Gram positive. The antifungal activities of the investigated compounds were tested against Aspergillus flavus and Candida albicans. The free ligand and its metal complexes were tested as well as the standard (Tetracycline as an antibacterial agent and Amphotericin B as an antifungal agent). The concentration of each solution was 1.0 × 10−3 mol dm3. Commercial DMSO was employed to dissolve the tested samples.

Synthesis of ligand and its metal complexes

Synthesis of N-(2-hydroxybenzyl)-l-methionine acid, (H3L)

The synthesis of the ligand (Fig. 1) was described by Akhtarul Alam et al. [22]. To the clear solution of l-methionine acid (1.4 g, 9.4 mmol) and NaOH (0.36 g, 9.4 mmol) in a solvent mixture of water (25 mL) and methanol (25 mL), salicylaldehyde (1 mL, 9.4 mmol) was added, then the resulting yellow solution was stirred for 45 min. After cooling the mixture in an ice bath for 30 min, a slight excess of NaBH4 (0.38 g, 10.4 mmol) was added to the mixture. The yellow color slowly dispersed after 20–30 min. A white precipitate was formed; the precipitate was removed by filtration, and then the filtrate was acidified using HCl. The pH of the solution was maintained at 5–6; the white product was precipitated, further stirred for 20–30 min, filtered off and washed with a small amount of H2O (2 × 2 mL), methanol (2 × 2 mL), and diethyl ether (2 × 4 mL), and then dried under vacuum. Crystallization performed using methanol, 50.20 % Yield: (1.2 g, 4.7 mmol).
https://static-content.springer.com/image/art%3A10.1007%2Fs10973-012-2628-4/MediaObjects/10973_2012_2628_Fig1_HTML.gif
Fig. 1

Structure of the ligand (H3L)

IR (KBr): ν(OH) 3423; ν( NH) 3170, νas(COO) 1619, νs(COO) 1380, ν(phenolic, CO) 1280, 759.

1H NMR (DMSO-d6): δ = 7.28 (dd, 1H, 3J = 7 Hz, 4J = 1.5 Hz, H-2), 7.25 (dd, 1H, 3J = 7.5 Hz, 4J = 1.5 Hz, H-4), 6.88–6.85 (m, 2H, H-1, H-2), 4.21 (AB System, 2H, JAB = 8 Hz, H-5), 3.60 (t, 1H, 3J = 6.5 Hz, H-6), 2.63 (dddd, 2H, 3J = 6.5 Hz, 3J = 13 Hz, 3J = 20 Hz, 4J = 2 Hz, H-7) [23], 2.13 (m, 2H, H-8), 2.08 (s, 3H, H-9) ppm.

13C NMR (CD3OD): δ = 16.82 (–SCH3), 31.90 (–CH2), 32.54 (–CH2), 45.10 (–CH), 62.32 (benzylic), 115.91, 120.20, 123.74, 131.08, 152.32 and 162.41 (aromatic), 174.00 (–COOH).

Mass spectra

The final peak at 255 amu (C12H17O3NS) (calculated atomic mass 255 amu) and other peaks at 222, 192, 150, 122, 106, 93, 79, and 45 amu.

Synthesis of the complexes

The complexes were synthesized by a general method. The metal salt (1 mmol) in a mixture of 10 mL methanol and 5 mL H2O was added dropwise to a solution of ligand H3L (255 mg, 1 mmol) and triethylamine (0.42 mL, 3 mmol) dissolved in 25 mL methanol. The resulting solutions were stirred at RT for 2 h. The precipitates of the complexes were filtered and washed with ethanol and diethyl ether, and finally dried under vacuum. The purity of the complexes was checked by thin layer chromatography. The complexes were isolated as powdered material. Mass spectra, elemental analysis (C, H, N), IR, UV–Visible, and TG analyses confirm the composition of the complexes.

Results and discussion

La(III), Ce(IV), and Th(IV) complexes are colored, stable, and non-hygroscopic in nature. The complexes are insoluble in common organic solvents, but soluble in DMF and DMSO. Elemental analyses show that the La(III), Ce(IV), and Th(IV) complexes have 1:1 stoichiometry. The molar conductance values are low, indicating that there is no dissociation of the complexes in DMF, indicating the non-electrolytic nature of the complexes (Table 1).The selected physical properties and characteristic data of the synthesized ligand and its metal complexes were measured and are listed in Table 1. Mass spectra and elemental analysis were in good agreement with those required for the purpose of the formula.
Table 1

Elemental analyses and physical data of H3L ligand and its La(III), Ce(IV), and Th(IV) complexes

Compounds' empirical formula

M. wt

Ω−1 cm2 mol−1

Yield %

Elemental analyses

% C Calc./found

% H

% N

% M

H3L

255.33

17

50

56.45/56.21

6.71/7.00

5.49/5.36

 

C12H17O3NS

[La(L)·2H2O]·2H2O

463.28

20

52

31.11/31.42

4.79/4.99

3.02/2.78

29.98/30.67

C12H22O7NSLa

[Ce(L)·2H2O]·2H2O

464.49

18

76

31.03/32.88

4.77/4.36

3.02/3.52

30.17/31.18

C12H22O7NSCe

[Th(L)·NO3·H2O]·3H2O

618.41

24

72

23.31/23.93

3.59/3.16

4.53/4.81

37.52/37.25

C12H22O10N2STh

Molar conductance

Molar conductance values of the complexes in DMSO solvent (10−3 mol dm−3) were in the range of (18–24) Ω−1 cmmol−1 and are presented in Table 1. The values adequately confirmed the non-electrolytic nature of the complexes. This fact elucidated that the nitrate ions are absent from outside the coordination sphere [24].

UV–Visible spectra

UV–Visible spectra of the ligand and its metal complexes were recorded in DMSO solution in the wavelength range 200–800 nm. The UV–Visible spectrum of the ligand shows three bands at 252 and 311 nm, which may be attributed to π–π and n–π* transitions. In the metal complexes, this band was slightly red shifted to 256–260 and 317–320 nm, which can be attributed to the binding of these coordination centers to the central metal ions. There is a weak band in the spectra of the complexes at ~735 nm because of weak f–f transition. A new absorption band at 472 nm appeared in the spectra of Ce(IV) complex and may be related to the metal-ligand charge transfer excitation [25].

Infrared spectra

IR spectral bands of the ligand and its complexes are listed in Table 2. The IR spectrum of the ligand showed υ(C=O) banding in the region at 1,711 cm−1. A strong band at 2,994 and 3,111 cm−1 could be assigned to aliphatic and aromatic C–H, respectively. A comparison between the infrared spectra of the ligand and the respective complexes reveals the disappearance of absorption bands associated with the stretching NH group, indicating the loss of proton on complexation and the formation of metal nitrogen bond [25]. Carboxylic OH group and OH phenolic group were not considered in the spectra of complexes since triethylamine was used to deprotonate OH groups. The broad band at 3,433–3,435 cm−1 could be attributed to OH of the crystal water molecules [24]. This indicates the existence of water of hydration in the spectra of the complexes. Participation of the phenolic group in complex formation was indicated by the shift in υ(C–O) of the phenolic group, from 1,280 cm−1 in the free ligand to 1,262–1,267 cm−1 in the complexes [26]. Also, the OH group was shifted in position of the υ(OH) in-plane bending from 1,378 cm−1 in the H3L ligand to 1,366–1,355 cm−1 in the complexes. The bands at 1,481 cm−1 and 1,283 cm−1 in the infrared spectra of the Th(IV) complex indicate the existence of the nitro group inside the coordination sphere. On the other hand, the absence of the bands at 1,480 cm−1 and 1,285 cm−1 indicates the absence of the nitrate group from the coordination sphere for La(III) and Ce(IV) complexes [27]. Far IR spectra of all metal complexes in the region at 366–381 cm−1 are due to ν(M–N), (M–S), and the band at 487–490 cm−1 is due to ν(M–O) [26].
Table 2

Infrared spectral data of H3L ligand and its La(III), Ce(IV) ,and Th(IV) complexes cm−1

Compounds

ν(OH) hydrated

ν(NH)

ν(C=O)

ν(OH) phenolic

ν(OH) carboxylic

ν(C–O) phenolic

ν(M–O)

ν(M–N)

ν(M–S)

H3L

3210

1,711/s

3,337

3,431

1,280/m

 

[La(L)·2H2O]·2H2O

3,433/br

1,713/s

1,264/m

370/w

488/m

377/w

[Ce(L)·2H2O]·2H2O

3,434/br

1,716/s

1,267/m

381/w

487/w

375/w

[Th(L)·NO3·H2O]·3H2O

3,435/br

1,713/m

1,262/m

377/w

490/w

366/w

br broad, s strong, w week, m medium

Mass spectra studies of La(III), Ce(IV), and Th(IV) complexes

Mass spectra of La(III), Ce(IV), and Th(IV) complexes with H3L were studied. In the spectrum of Ce(IV) complex (Fig. 2), the molecular ion peak was observed at m/z 464, which is equivalent to its molecular weight. This molecular ion undergoes fragmentation with loss of four water molecules to give a species [Ce(L)] at 392 m/z and other peaks at 359, 276, 252, and 146 amu, Scheme 1. Mass spectra of Th(IV) complex showed the molecular ion peak at m/z 618, which is equivalent to its molecular weight and the other peaks at 546, 486, 386, 366, 252, 146, and 106 amu, Scheme 2. Mass spectrum of La(III) complex showed molecular ions peaks at 463 m/z, which are equivalent to their molecular weight of [La(L)·2H2O]·2H2O. All the complexes undergo demetallation to give a fragment ion at 252 m/z.
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Fig. 2

Mass spectra of the H3L ligand and its metal complexes

https://static-content.springer.com/image/art%3A10.1007%2Fs10973-012-2628-4/MediaObjects/10973_2012_2628_Sch1_HTML.gif
Scheme 1

Mass fragmentation of the Ce(IV) complex

https://static-content.springer.com/image/art%3A10.1007%2Fs10973-012-2628-4/MediaObjects/10973_2012_2628_Sch2_HTML.gif
Scheme 2

Mass fragmentation of the Th(IV) complex

1HNMR and 13CNMR for La(III) and Th(IV)

The 1H NMR spectrum of the ligand was recorded in dimethylsulfoxide (DMSO-d6).The 1H NMR spectra of the complexes were examined in comparison with the H3L ligand. Upon examinations, it was found that the aromatic-H signals appeared in the spectrum of H3L ligand in the range of 6.85–7.28 ppm, which moved to higher frequencies in the complexes as a result of coordinating to lanthanide ion. The methylene-H also shifted to the higher frequencies compared to the parent ligand as a result of high electron density of the lanthanide ions.

AB system appeared in the ligand (each proton of the CH2 group at carbon number 5 was coupled with methyl proton and the adjacent two protons), but disappeared in the 1HNMR of the complexes.

The 13CNMR spectra of the ligand and its metal complexes were recorded in CD3OD. Comparing the Carbon chemical shifts of ligand H3L with complexes reveals that the carbon signals that appeared in the complexes moved to lower frequencies compared to H3L ligand.

1HNMR and 13CNMR for La(III)

1H NMR (DMSO-d6): δ = 7.33–722 (m, 2H, H-3, H-4), 6.88–6.85 (m, 2H, H-1, H-2), 3.98 (s, 2H, H-5), 3.44 (t, 1H, 3J = 6.5 Hz, H-6), 2.53 (d, 2H, 3J = 7 Hz, H-7), 2.23 (m, 2H, H-8), 2.03 (s, 3H, H-9) ppm.

13C NMR (CD3OD): d 15.22 (–SCH3), 30.43 (–CH2), 32.00 (–CH2), 44.76 (–CH), 61.54 (benzylic), 117.66, 121.91, 124.38, 133.11, 153.97 and 165.82 (aromatic), 178.42 (–COOH).

1HNMR and 13CNMR for Th(IV)

1H NMR (DMSO-d6): δ = 7.33–7.01 (m, 4H, H-1, H-2, H-3, H-4), 3.66 (s, 2H, H-5), 3.35 (t, 1H, 3J = 6.5 Hz, H-6), 2.52 (d, 2H, 3J = 7 Hz, H-7), 2.12 (m, 2H, H-8), 2.00 (s, 3H, H-9) ppm.

13C NMR (CD3OD): d 14.31 (–SCH3), 29.25 (–CH2), 30.08 (–CH2), 45.81 (–CH), 60.71 (benzylic), 119.21, 120.73, 125.44, 135.41, 155.35 and 167.31 (aromatic), 177.09 (–COOH).

Thermal analysis data

The thermal properties of H3L ligand, La(III), Ce(IV), and Th(IV) complexes were investigated by TG analysis and DTG and are summarized in Table 3; Fig. 3. The data from TG sn of the ligand proceeded in one broad step from 180 to 320 °C without residue and the complexes decomposed in four or five steps. Crystal Water molecules were lost in between 25 and 140 °C and coordinated water molecules were lost in between 140 and 250 °C. The organic part of the complexes decomposed into one or two intermediates. The decomposition of all complexes ended with metal oxide and carbon residue.
Table 3

Thermal data of La(III), Ce(IV), and Th(IV) complexes

Complexes

Temperature range/°C

DTG peak/°C

TG mass loss % calc./found

Assignments

[La(L)·2H2O]·2H2O

25–140

110

7.77/7.43

2H2O

140–230

205

7.77/8.01

2H2O

230–430

315

24.39/23.79

C3H7 NO3/2 S

430–600

560

17.05/16.97

C6H7

600

90

42.93/43.64

½ (La2O3) + 3C

[Ce(L)·2H2O]·2H2O

25–140

230

7.75/7.02

2H2O

140–240

360

7.75/8.11

2H2O

240–450

565

22.60/22.01

C3H7 NOS

450–600

80

17.00/16.53

C6H7

600

220

44.80/45.22

CeO2 + 3C

[Th(L)·NO3·H2O]·3H2O

25–140

365

8.73/8.33

3H2O

140–240

580

2.91/3.41

H2O

240–450

 

33.50/34.08

NO3 + C6H10SN

450–600

 

12.28/11.77

C6H4

600

 

46.57/45.73

ThO2 + 2C

https://static-content.springer.com/image/art%3A10.1007%2Fs10973-012-2628-4/MediaObjects/10973_2012_2628_Fig3_HTML.gif
Fig. 3

TG and DTG curves of H3L ligand and its metal complexes

Thermal properties of [La(L)2H2O]·2H2O complex

The process of decomposition of [La(L)·2H2O]·2H2O complex has been divided into the following four stages. The first stage, within the temperature range of 25–140 °C with an estimated mass loss of 7.43 % (calculated mass loss 7.77 %), represents the loss of two hydration water molecules. The second stage, within the temperature range of 140–230 °C with an estimated mass loss of 8.01 % (calculated mass loss 7.77 %), represents the loss of two coordinated water molecules. The third stage, within the temperature range of 230–430 °C with an estimated mass loss of 23.79 % (calculated mass loss 24.39 %), is corresponding to the loss of organic part (C3H7NO3/2S), Scheme 3. The fourth stage, within the temperature range of 430–600 °C with an estimated mass loss of 16.97 % (calculated mass loss 17.05 %), could be assigned to the successive loss of organic part (C6H7). The final products, formed above 600 °C, consist of ½(La2O3) and three carbon residue with an estimated mass loss of 43.64 % (calculated mass loss 42.93 %).
https://static-content.springer.com/image/art%3A10.1007%2Fs10973-012-2628-4/MediaObjects/10973_2012_2628_Sch3_HTML.gif
Scheme 3

Thermal degradation of the La(III) complex

Thermal properties of [Ce(L)·2H2O]·2H2O complexes

The TG of [Ce(L)·2H2O]·2H2O complex has been divided into the following four stages of decomposition pattern. The first stage, within the temperature range of 25–140 °C with an estimated mass loss of 7.02 % (calculated mass loss 7.75 %), represents the loss of two hydration water molecules. The second stage, within the temperature range of 140–240 °C with an estimated mass loss of 8.11 % (calculated mass loss 7.75 %), represents the loss of two coordinated water molecules. The third stage, within the temperature range of 240–450 °C with an estimated mass loss of 22.01 % (calculated mass loss 22.60 %), is corresponding to the loss of organic part (C3H7NOS). The fourth stage, within the temperature range of 430–600 °C with an estimated mass loss of 16.53 % (calculated mass loss 17.00 %), could be assigned to the successive loss of organic part (C6H7).The final products, formed above 600 °C, consist of CeO2 and three carbon residue with an estimated mass loss of 45.73 % (calculated mass loss 44.80 %).

Thermal properties of [Th(L)·NO3·H2O]·3H2O complex

The thermal decomposition of [Th(L)·NO3·H2O]·3H2O gives four stages of decomposition pattern. The first stage, within the temperature range of 25–140 °C with an estimated mass loss of 8.33 % (calculated mass loss 8.73 %), represents the loss of three hydration water molecules. The second stage, within the temperature range of 140–240 °C with an estimated mass loss of 3.4 % (calculated mass loss 2.91 %), represents the loss of one coordinated water molecule. The third stage, within the temperature range of 230–450 °C with an estimated mass loss of 34.08 % (calculated mass loss 33.50 %), could be assigned to the successive loss of organic part (NO3 + C6H10ONS). The fourth stage, within the temperature range of 450–600 °C with an estimated mass loss of 11.77 % (calculated mass loss 12.28 %), could be assigned to the successive loss of organic part (C6H4).The final products, formed above 600 °C, consist of (ThO2) and five carbon residue with an estimated mass loss of 45.73 % (calculated mass loss 46.57 %).

Microbiological investigation

The biological activity of H3L ligand and its metal complexes was tested against one Gram positive bacteria (S. aureus), one Gram negative bacteria (E. coli), and two fungi (A. flavus and C. albicans). Tetracycline was used as the standard against the respective bacteria and Amphotericin B was used as the standard against the respective fungi. DMSO was used as the control. The concentration used for testing was 1 mg mL−1 of DMSO. The concentration of Tetracycline and Amphotericin B solution was 1.0 × 10−3 mol dm3. The antimicrobial activity was estimated on the basis of size of inhibition. The zone formed around the wells in the plates. The results of the synthesized compounds are reported in Table 4. An influence of the central ion of the complexes in the antibacterial activity against the tested Gram positive and Gram negative organisms shows that the complexes have less activity compared to the ligand itself.
Table 4

Antibacterial activity data of H3L ligand and its La(III), Ce(IV), and Th(IV) complexes' inhibition zone/mm

Compound

Staphylococcus aureus G+

Escherichia coli G

Aspergillus flavus

Candida albicans

Control DMSO

0.0

0.0

0.0

0.0

Tetracycline (standard)

31

34

Amphotericin B (standard)

18

21

H3L

27

25

0.0

12

[La(L)·2H2O]·2H2O

17

15

0.0

11

[Ce(L)·2H2O]·2H2O

15

13

0.0

0.0

[Th(L)·NO3·H2O]·3H2O

13

15

0.0

11

Conclusions

The coordination ability of N -(2-hydroxybenzyl)-l-methionine acid has been proved in complexation reaction with La(III), Ce(IV), and Th(IV) ions. The elemental analysis, mass spectra, 1HNMR, and 13CNMR confirmed the compositions of the compounds. TG, IR, UV–Visible spectra of the ligand and its metal complexes confirmed the suggested coordination of the ligands through nitrogen, phenolic-OH, carboxylic-OH, and sulfur atom of the ligand. Under the experimental conditions employed, only 1:1 (M:L) complexes have been found (Fig. 4). The TG analysis indicated that the complexes decomposed in four or five steps, and the organic part of the complex decomposed in one or two intermediates. All complexes ended with metal oxide and carbon residue.
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Fig. 4

Structure of the suggested metal complexes

Copyright information

© Akadémiai Kiadó, Budapest, Hungary 2012