Fluorescence study of Co (II), Ni (II), Cu (II) and Zn (II) Complex of
8-[(e)-{[3-(Dimethylamino)propyl]imino}methyl]-7-hydroxy-4-methyl-2h-chromen-2-one
Bapu. R. Thorat1, Vijaya Pawar1, Mustapha M. 1, R.S. Yamgar1 and R. G. Atram2
1P. G. Dept of Chemistry, Govt. of Maharashtra, Ismail Yusuf College of Arts, Science and Commerce, Jogeshwari (East), Mumbai 400 060.
2P. G. Dept of Physics, Govt. of Maharashtra, Ismail Yusuf College of Arts, Science and Commerce,
Jogeshwari (East), Mumbai 400 060.
*Corresponding Author E-mail: bthorat78@gmail.com
ABSTRACT:
The fluorescence properties of novel transition metal Cu(II), Ni(II), Co(II) and Zn(II) complexes of bidentate Schiff base ligand {8-[(E)-{[3-(dimethylamino)propyl]imino}methyl]-7-hydroxy-4- methyl-2H-chromen-2-one]} [DMAPI MHMC] obtained from 4-Methyl-7-hydroxy 8-formylcoumarin, and dimethylamino propane-1,3-diamine have been prepared and characterized by physical, spectral and analytical data. The Schiff base act as 1,5-bidentate ligand for the complexation reaction with Cu(II), Ni(II), Co(II) and Zn(II) halides. The new compounds, possessing the general formula [ML2.2H2O] where [M= Cu(II), Ni(II), Co(II) and Zn(II)] show octahedral geometry. It is further subjected to fluorescence study. The Schiff base shows strong emmision at 503, 507, 508, 509 513 and 514 nm for the excitaion wavelengths 295, 375, 399, 430, 751, 800 and 847nm but the complexes shows strong emission at 400 nm [ZnL2, at 500 nm], 400 nm [CuL2, at 403 and 465 nm], 401 nm [NiL2, at 404, 445 and 810 nm] and 401 nm [CoL2, at 409, 438, 478, 808 and 854 nm].
KEY WORD: Coumarine, Metal complexes, Fluorescence, Schiff bases, Luminescence.
INTRODUCTION:
Phosphors become technologically and industrially important with the introduction of fluorescent lamps in 1938. Thermometry was suggested in the German patent in 1938. First peer-reviewed article, to our knowledge appeared in 1949. Between 1950 to 1980, it was not widely used. Its most common use was aerodynamic applications. Advances in lasers, microelectronics, and other supporting technologies enable additional commercial as well as scientific use. The physics and chemistry of luminescence materials and their applications become and still is the core area covered by Luminescence symposia. The mechanism of luminescence [e.g. for La(III)] has been explain by following diagram.
Coumarines have been synthesized by several routes including Pechmann(1), Perkin(2), Knoevenagel(3), Reformatsky(4), and Wittig(5) reactions. Coumarines and their derivatives are widely used as Fragrances, Pharmaceuticals and as agrochemicals(6). The coumarines substituted with different heterocycles at 4-position have been synthesized and are showing promising antimicrobial activities(7,8). Schiff bases of 8-formyl-7-hydroxy-4-methylcoumarine(9) with various anilines has been synthesized and biological characterized. The optical and fluorescence properties of coumarines have attracted wide range of researcher(10,11). Coumarine prove their applications in optical brighteners, leser dyes, sensitizers in phototherapies(12). The fluorescence and antimicrobial properties of La (III) complex(13) of Schiff base of 8-formyl-7-hydroxy-4-methyl-coumarin with 3-amino pyridine has been studied. The synthesis and photophysical properties of Zn(II) and Cu(II) Complex of 2-{[(E)-(2-Hydroxyphenyl) Methylidene]Amino} Benzoic Acid(14,15) are also studied.
Scheme 1: Synthesis of 4-Methyl-7-hydroxy coumarin (3)
Scheme 2: Synthesis of 4-methyl-7-hydroxy-8-formyl coumarin (4)
Scheme 3: Synthesis of 8-[(E)-{[3-(dimethylamino)propyl]imino}methyl]-7-hydroxy-4- methyl-2H-chromen-2-one] [DMAPIMHMC] (6)
Scheme 4: Synthesis of [M(DMAPIMHMC)2.2H2O] Complex (8a-d)
{Where M (II) - Co(II), Ni(II), Cu(II), Zn(II)}
In the small molecules organic light emitting diodes, the family of carbazoles(16) could be extended to be suitably fit for red(17-19), green(20-22), and blue light(23-25) triplet emitters and therefore, they can be used in full color displays(26-29, 31-34). More recently studies of Thompson, Forrest and co-workers shows that the use of electron blocking layers (EBLs) consisting of IrIII complexes with picolinate ligands produced improved color purities in the case of blue light emitting device(35). Some of the organic molecules are used as EBLs as- fluorinated phenylenes(30), and oxadiazole as well as triazole containing molecules such as trimer of N-arylbenzimidazoles (TPBi)(36,37), 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD)(38), 3-phenyl-4-(1’-naphthyl)-5-phenyl-1,2,4-triazole (TAZ)(39,40), 1,8-Naphthalimides(41), polyquinolines(42), or carbon nanotubes doped in PPV(43) were also found to be useful as hole blocking layers (HBLs). Metal complexes of the heavy metals such as Gold, Tb(III), Eu(III), Ln(III), Y(III), Gd(III), Pt(II) and Ir(III)(can be used as efficient phosphorescent emitters)(44,45-50,51-53) are used as organic phosphors. Zhao et al developed white light emitting electroluminescent devices using lanthanide binuclear complexes, Tb(1-x)Eux(aca)3(phen)(54). Miyamoto et al has synthesized a Eu(III)- β-diketonate complex, Eu(DBM)3(phen)(55).
Searching for highly efficient fluorescence organic compounds (Schiff bases) is a topic of current interest. The aromatic based ligand having electron donating or withdrawing groups has been increased or decreased the intensity of absorption or shifted absorption wavelength on either side. Luminescence properties of the various Schiff base of 3-formyl-2-hydroxyquinoline and its Zn, Cu, Ni and La metal complexes have been checked by using Spectrofluorometer model number RF5301. A Xe laser lamp was used for excitation and emission spectra were scanned from the range 220 nm to 750 nm. The emission of Schiff bases at each excitation wavelength has been checked.
Going through the literature survey and considering the vital role of the coumarin derivatives in diagnostic parameters with fluorescent activities, the present work was undertaken to synthesis Schiff base of 8-Formyl-7-Hydroxy-4-Methylcoumarin (4) with N,N-dimethylpropane-1,3-diamine (5); Schiff base i.e. the ligand 8-[(E)-{[3-(dimethylamino)propyl]imino}methyl]-7-hydroxy-4- methyl-2H-chromen-2-one] [DMAPIMHMC] (6) and their metal complexes (8a-d) such as Zn, Cu, Ni and La.
MATERIAL AND METHODS:
All chemicals and solvents used were of AR grade. All metal (II) salts were used as chlorides. IR spectra were recorded on a Jasco FT-IR Spectrophotometer. UV-Visible spectra were obtained in DMF on a Shimadzu model UV-Visible Spectrophotometer. The proton magnetic spectra were recorded on a Bruker AMX-5000 Spectrometer.
Synthesis of 4-Methyl-7-hydroxy coumarin (3):
Concentrated H2SO4 (500 ml) was cooled to 00C in ice bath. Mixture of ethylacetoacetate (65 ml) and meta-Cresol (55 ml) was added in concentrated H2SO4 under vigorous stirring at 0-50C over a period of 1-1.5 hrs. Stirring was continued at 50C for 2 hrs. Temperature of reaction mixture was then raised slowly to 300C and allowed to stand for 24 hrs. The solution was then poured in ice bath and water. The product precipitated was filtered. The crude product was dissolved in 5% NaOH solution and the solution was then clarified with activated charcoal and filtered. Filtrate was acidified with conc. HCl to give 4-Methyl-7–hydroxyl coumarin. The yield of the product was around 95%.
Synthesis of 4-methyl-7-hydroxy-8-formyl coumarin (4):
4-Methyl-7-hydroxy coumarin (30 g, 0.170 moles) was dissolved in 300 ml glacial acetic acid. Hexamine (60 g, 0.428 moles) was added and heated to 85-900C for 5 hours. Reaction was monitored for its progress by TLC (30% Ethyl acetate in hexane). After reaction was completed as indicated by TLC, reaction mixture was quenched in 20% HCl and heated to 60-800C for 20 minutes. Reaction mixture was cooled to room temperature and product was extracted in methylene chloride (100 ml x 3 times). Combined MDC extract was washed with distilled water and dried over anhydrous Na2SO4. MDC extract was concentrated and crude product was purified by Silica gel column chromatography to get pure 4-Methyl-7-hydroxy-8-formyl coumarin. The yield of the product was around 20%.
Synthesis of Schiff base (6):
The Schiff base i.e. the ligand 8-[(E)-{[3-(dimethylamino)propyl]imino}methyl]-7-hydroxy-4- methyl-2H-chromen-2-one] [DMAPIMHMC] was synthesized by the condensation of 8-Formyl-7-Hydroxy-4-Methylcoumarin with N,N-dimethylpropane-1,3-diamine in (1:1) molar proportion in ethanol in the presence of traces of concentrated hydrochloric acid. The reaction mixture was refluxed for an hour. On cooling, the product was isolated to obtain yellowish brown oily mass of the Schiff base. As the Schiff base was an oily mass and unstable in nature, it was difficult to characterize the compound. Therefore, its oxalate salt was prepared for spectral characterization.
The Schiff base 8-[(E)-{[3-(dimethylamino)propyl]imino}methyl]-7-hydroxy-4-methyl-2H-chromen-2-one] [DMAPIMHMC] was obtained by the reaction of N,N-dimethylpropane-1,3-diamine with 4-methyl-7-hydroxy 8-formyl coumarin in (1:1) molar proportion in ethanol in the presence of traces of concentrated hydrochloric acid. The reaction mixture was refluxed for an hour. It was then treated with Oxalic acid (1 mole equivalent) and further refluxed for an hour. On cooling, the product was isolated as oxalate salt which was recrystallized from alcohol. The yield of the product was around 70%. It was characterized by UV, IR, 1H NMR, Mass and elemental analysis.
Melting point was 1990C; Colour – Yellow; IR : N-H 3468 cm-1, -C=O (Lacton) 1715 cm-1, -C=N 1609 cm-1, -C-O-C 1076 cm-1, Phenolic -C-O 1313 cm-1; Elemental Analysis (Found) : C (57.02%), H (5.69%), N (27.22%), O (9.48%); UV : λmax 225 nm, 313 nm
Mass [M+H]+ 289.3; 1H NMR [DMSO(d6)] (δ in ppm): 1.59-1.60 (t, 2H), 2.07 (s, 3H), 2.11 (s, 3H), 2.51(s, 3H), 3.02( t, 2H), 5.24 (s, 1H),5.87 (d, 2H, J=9.4Hz), 6.84 (d, J=9.4Hz) 8.15 (s, 1H).
Synthesis of Metal Complexes of Schiff base:
As the Schiff base [DMAPIMHMC] was an oily product, it was freshly prepared in situ by mixing N,Ndimethylpropane- 1,3-diamine with 4-methyl-7-hydroxy 8- formyl coumarin in (1:1) molar proportion in ethanol. Then equimolar quantities of divalent metal chloride were mixed and the reaction mixture was heated on water bath for about five hours. It was then cooled and pH was adjusted to about 8.5 by 25% aq. ammonia when coloured solid separated out which was filtered and washed with ethanol, recrystallized in ethanol and dried in oven at 80-1000C. This is the general method for the synthesis of metal complexes of ligand with divalent metal chlorides MCl2.2H2O Where M = Co(II), Ni(II), Cu(II), Zn(II). Since [Zn(DMAPIMHMC)2.2H2O] Complex was diamagnetic in nature, it was possible to scan for 1H NMR As it was nonionic, it was not possible to detect fragments in Mass spectrometer.
[Co(DMAPIMHMC)2.2H2O], Brown color solid, yield 68%, m.p. 2550C (decomposed), IR : 3314 cm-1, 1717 cm-1, 1620 cm-1, 1398 cm-1, 555 cm-1.
[Ni(DMAPIMHMC)2.2H2O], light green solid, yield 72%, m.p. 2500C (decomposed), IR : 3414 cm-1, 1719 cm-1, 1624 cm-1, 1336 cm-1, 559 cm-1.
[Cu(DMAPIMHMC)2.2H2O], green color solid, yield 62%, m.p. 2300C (decomposed), IR : 3435 cm-1, 1721 cm-1, 1620 cm-1, 1342 cm-1, 552 cm-1.
[Zn(DMAPIMHMC)2.2H2O], yellow color solid, yield 79%, m.p. 2450C (decomposed), IR : 3439 cm-1, 1711 cm-1, 1630 cm-1, 1371 cm-1, 554 cm-1.
1H NMR of [Zn(DMAPIMHMC)2.2H2O] Complex in DMSO-d6 : 1.82 (t, 2H, J=6.5Hz), 2.40 (s, 3H), 2.45 (s, 3H), 2.63 (s, 3H), 2.93 (t, 2H, J=6.4Hz)), 3.84 ( t, 2H, J 7.8Hz), 6.09 (s, 1H), 6.67 ( d, 2H, J=8.8Hz), 7.67 (d, J=9.2Hz), 8.93 (s, 1H).
Absorption spectra of Schiff base ligand {8-[(E)-{[3-(dimethylamino)propyl]imino}methyl]-7-hydroxy-4- methyl-2H-chromen-2-one]} [DMAPIMHMC] (6) obtained from 4-Methyl-7-hydroxy 8-formylcoumarin, and dimethylamino propane-1,3-diamine and its metal complexes (8a-d) are recorded by using SL164 Double beam UV-Visible spectrophotometer by using DMF as reference material. The solutions having concentration 300 ppm are prepared in DMF. The absorption wavelengths with intensities are shown in following table 1.
LUMINESCENCE PROPERTIES:
Luminescence properties of the schiff base ligand {8-[(E)-{[3-(dimethylamino)propyl]imino} methyl]-7-hydroxy-4-methyl-2H-chromen-2-one]} [DMAPIMHMC] (6) obtained from 4-Methyl-7-hydroxy 8-formylcoumarin, and dimethylamino propane-1,3-diamine and its metal complexes (8a-d) have been checked by using Spectrofluorometer model number RF5301. A Xe laser lamp was used for excitation and emission spectra were scanned from the range 220 nm to 900 nm. For fluorescence study of the Schiff bases, dimethylformamide is used as solvent and reference material. The solutions in DMF having concentration 300 ppm are prepared for emission spectral analysis. The excitation of the molecule is occurred due to the n→π* and π→π* electronic transitions.
The fluorescence data can be shown in following data:
Slit width: Excitation and emission is 5 mm; Concentration of solution is 300 ppm; Solvent used is DMF.
Table 1: Absorption spectral study of Schiff base and its metal complexes (λmax) (6 and 8a-d).
|
Name Product |
Absorption wavelength |
Intensity (ε) |
|
{8-[(E)-{[3-(dimethylamino)propyl]imino}methyl]-7-hydroxy-4- methyl-2H-chromen-2-one]} (6) |
295 nm 375 nm 399 nm 430 nm 751 nm 800 nm 847 nm |
11.84 9.03 40.26 5.95 2.12 20.22 0.41 |
|
[Co(DMAPIMHMC)2.2H2O] (8a) |
285 nm 401 nm 635 nm 801 nm |
14.91 > 1015.81 2.16 933.61 |
|
[Ni(DMAPIMHMC)2.2H2O] (8b) |
401 nm 477 nm 624 nm 802 nm |
265.09 4.85 1.24 167.39 |
|
[Cu(DMAPIMHMC)2.2H2O] (8c) |
400 nm 454 nm 566 nm 801 nm |
64.93 0.22 0.44 37.82 |
|
[Zn(DMAPIMHMC)2.2H2O] (8d) |
308 nm 400 nm 456 nm 625 nm 800 nm |
13.87 53.08 5.69 2.65 30.91 |
Table 2: Emission of Schiff base 6 and its metal complexes at its excitation/absorption wavelength with emission intensity.
|
Sample Name |
Excitation wavelength (nm) |
Emission wavelength (nm) (ε) |
|
{8-[(E)-{[3-(dimethylamino)propyl]imino}methyl]-7-hydroxy-4- methyl-2H-chromen-2-one]} (6) |
295 nm 375 nm 399 nm 430 nm 751 nm 800 nm 847 nm |
300 (2.90), 335 (0.03), 508 (30.36) 378 (21.41), 513 (129.91), 666 (0.70), 758 (1.16) 400 (32.40), 513 (153.40) 432 (35.61), 507 (267.54) 376 (13.75), 503 (81.43), 756 (3.14) 401 (17.68), 541 (88.85), 805 (0.85) 426 (10.54), 509 (96.71), 728 (0.38) |
|
[Co(DMAPIMHMC)2.2H2O] (8a) (for 150 ppm solution) |
285 nm
401 nm 635 nm 801 nm |
293 (> 1016.06), 314 (37.88), 425 (80.02), 577 (> 1016.06), 716 (2.68), 864 (29.12) 257 (1.3), 409 (> 1015.64), 438 (301.39), 808 (378.22), 854 (5.53) 322 (> 1016.06), 333 (7.09), 433 (62.8), 642 (> 1016.06) 269 (3.1), 406 (> 1016.06), 430 (197.94), 804 (214.55) |
|
[Ni(DMAPIMHMC)2.2H2O] (8b) |
401 nm 477 nm 624 nm 802 nm |
404 (625.8), 445 (103.2), 810 (20.9) 487 (> 1016.06), 513 (29.17) 449 (15.24), 584 (3.47), 633 (> 1016.06) 403 (247.39), 443 (64.83), 685 (0.39), 808 (9.62) |
|
[Cu(DMAPIMHMC)2.2H2O] (8c) |
400 nm 454 nm 566 nm 801 nm |
403 (89.79), 465 (41.81), 808 (4.7) 461 (> 1016.06), 523 (101.93) 517 (0.86), 574 (> 1016.06) 403 (44.84), 465 (24.53), 803 (1.72) |
|
[Zn(DMAPIMHMC)2.2H2O] (8d) |
308 nm 400 nm 456 nm 625 nm 800 nm |
464 (304.65), 878 (9.61) 500 (> 1015.76) 458 (793.85), 516 (252.45), 741 (0.09) 464 (138.42), 628 (392.33), 753 (0.23) 481 (> 1015.74) |
Fig 1: Excitation spectra of {8-[(E)-{[3-(dimethylamino)propyl]imino}methyl]-7-hydroxy-4- methyl-2H-chromen-2-one]} (6)
a. Emission at 295 nm b. Emission at 375 nm
c. Emission at 399 nm d. Emission at 430 nm
e. Emission at 751 nm f. Emission at 800 nm
g. Emission at 847 nm
Fig 2(a-g) : Emission spectra of {8-[(E)-{[3-(dimethylamino)propyl]imino}methyl]-7-hydroxy-4- methyl-2H-chromen-2-one]} (6)
Fig 3 : Excitation spectra of [Co(DMAPIMHMC)2.2H2O] (8a)
a. Emission at 285 nm b. Emission at 401 nm
c. Emission at 635 nm d. Emission at 801 nm
Fig 4(a-d) : Emission spectra of [Co(DMAPIMHMC)2.2H2O] (8a)
Fig 5 : Excitation spectra of [Ni(DMAPIMHMC)2.2H2O] (8b)
a. Emission at 401nm b. Emission at 477nm
c. Emission at 624 nm d. Emission at 802 nm
Fig 6 (a-d) : Emission spectra of [Ni(DMAPIMHMC)2.2H2O] (8b)
Fig 7 : Excitation spectra of [Cu(DMAPIMHMC)2.2H2O] (8c)
a. Emission at 400 nm b. Emission at 454 nm
c. Emission at 566 nm d. Emission at 801nm
Fig 8 (a-d) : Emission spectra of [Cu(DMAPIMHMC)2.2H2O] (8c)
Fig 9 : Excitation Spectra of [Zn(DMAPIMHMC)2.2H2O] (8d)
a. Emission at 308 nm b. Emission at 400 nm
c. Emission at 456 nm d. Emission at 625 nm
e. Emission at 800 nm
Fig 10 (a-e) : Emission Spectra of [Zn(DMAPIMHMC)2.2H2O] (8d)
RESULTS AND DISCUSSION:
The Schiff base [DMAPIMHMC] was freshly prepared by refluxing N,N dimethylpropane-1,3-diamine with 4-methyl-7-hydroxy 8-formyl coumarin in (1:1) molar proportion in ethanol in the presence of traces of concentrated hydrochloric acid. IR spectra of the Schiff base showed the absence of bands at 1725 and 3300 cm-1 due to carbonyl (C=O) and (NH2) stretching vibrations and, instead, appearance of a strong new band at ~ 1610 cm-1 assigned to the azomethine, (C=N) linkage. It suggested that amino and aldehyde moieties of the starting reagents are absent and have been converted into the azomethine moiety. The band appearing at 1610 cm-1 in complex is due to the azomethine was shifted to lower frequency by ~ 10-15 cm-1 indicating participation of the azomethine nitrogen in the complexation. A band appearing at 3414-3449 cm-1 in metal complexes which have significantly different characteristic of –O-H stretching vibration due to stretching modes of coordinated water molecule.
The proton magnetic resonance spectrum of Schiff base (DMAPIMHMC) in DMSO solution shows a NH=C-H protons of Schiff base (DMAPIMHMC) resonating at d 8.15 and methyl protons of 8-Formyl-7-Hydroxy-4-Methylcoumarin at d 2.63 in metal complex. Due to paramagnetic nature of Complexes with Cu [II], Ni[II] and Co[II], it was not possible to take 1H NMR spectrum and the signals obtained were very broad in nature and could not be interpreted properly. Due to its diamagnetic nature, 1H NMR spectrum was scanned for Zinc complex in DMSO-d6. It was observed that the aldehyde proton at 10.59 ppm in 8-Formyl-7-Hydroxy-4-Methylcoumarin was appearing at 8.15 ppm in schiff’s base. After complexation with Zinc metal it was shifted downfield to 8.93 ppm due to deshielding effect of Metal atom. Aromatic protons of coumarin ring appearing at 5.87 ppm and 6.84 ppm in Schiff base were shifted to 6.67 ppm and 7.67 ppm respectively due to the electron withdrawing mesomeric effect exerted by Zinc metal atom. Olefinic proton of coumarin ring appearing at 5.24 ppm was also shifted down field to 6.09 ppm due to electron withdrawing mesomeric effect operating through the conjugation across the aromatic ring over the unsaturated double bond of coumarin ring.
The fluorescence data (excitation and emission wavelengths with intencities) of Schiff base and its complexes are shown in table 2. The Schiff bases {8-[(E)-{[3-(dimethylamino)propyl]imino} methyl]-7-hydroxy-4-methyl-2H-chromen-2-one]} [DMAPIMHMC] (6) showing absorption (fig. 1, excitation spectra) at ~ 399 nm (λmax) along with other wavelengths are 295, 375, 430, 751, 800 and 847 nm is due to basic skeleton of [DMAPIMHMC] either π → π* or and n → π* electronic transitions. The emission study at each excitation wavelength is studied and shown by fig. 2 (a-g). It shows weak emission at some higher wavelength than excitation. The metal complexes (8a-d) shows strong emission (shown by fig. 3, fig. 5, fig. 7, fig. 9) at 400 nm [ZnL2, emission at 500 nm, fig. 10 (b)], 400 nm [CuL2, emission at 403 and 465 nm, fig. 10 (a)], 401 nm [NiL2, emission at 404, 445 and 810 nm, fig. 10 (a)] and 401 nm [CoL2, emission at 409, 438, 478, 808 and 854 nm, fig. 10 (b)]. The λmax metal complexes is also ~ 400 nm indicates that maximum absorption is due to basic schiff base skeleton not by metal ion. The emission wavelengths of metal complexes are same at same excitation wavelength indicates tranformation of energy from organic molecular orbital to metallic orbitals and then emission occurs.
ACKNOWLEDGMENT:
The authors are grateful to the Principal and Head, Department of Chemistry, Govt. of Maharashtra, Ismail Yusuf Arts, Science and Commerce College, Mumbai-60, India, and Principal and Head, Department of Chemistry, Patkar Varde College, Goregaon (W), Mumbai, India for his constant encouragement. For the spectral analyses and HPLC characterization and for providing facilities and helpful discussions during the synthesis the authors are thankful to Ram Jadhav, Dr Dileep Khandekar, Dr. D. D. Patil, Dr. S. S. Pandit. We also thankful our research groups as Arti Nagarsekar, Swati Lele.
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Received on 17.04.2012 Modified on 24.05.2012
Accepted on 15.06.2012 © AJRC All right reserved
Asian J. Research Chem. 5(8): August, 2012; Page 1000-1010