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Materials Letters 60 (2006) 317 – 320 www.elsevier.com/locate/matlet Studies on the spectra and antibacterial properties of rare earth dinuclear complexes with L-phenylalanine and o-phenanthroline He Qizhuang ⁎, Yang Jing, Min Hui, Li Hexing Department of Chemistry, Shanghai Normal University, Shanghai 200234, PR China Received 20 May 2005; accepted 20 August 2005 Available online 21 September 2005 Abstract The complexes RE(Phe)3PhenCl3·3H2O (Phe: phenylalanine; Phen: o-phenanthroline; RE: La3+, Y3+ and Eu3+), RE0.2Eu0.8(Phe)3PhenCl3·3H2O (RE: La3+ and Y3+) were synthesized and characterized in detail IR spectra and Raman spectra indicated that the rare earth ions are coordinated by both the oxygen atom from the COO− group and the nitrogen atom from o-phenanthroline The RE0.2Eu0.8(Phe)3PhenCl3·3H2O also displayed co-fluorescence effect The antibacterial activities testing showed that all these complexes exhibited excellent antibacterial ability against Escherichia coli, Staphylococcus aureus and Candida albicans © 2005 Elsevier B.V All rights reserved Keywords: IR spectra; Raman spectra; Fluorescence spectra; Complex; Antibacterial activity Introduction Recently, considerable attention has been paid on the study on a series of mixed rare earth complexes involving organic carboxylic acid as the primary ligand Because there exists co-fluorescence enhancement between rare earth ions [1–4], and this type of complexes also possess excellent antibacterial property However, studies on spectroscopic and antibacterial properties of the mixed rare earth complexes with amino acids and o-phenanthroline in solid state are quite limited Rare earth ions are frequently used as spectroscopic probes in systems of biological importance [5], and also are provided with some antiseptic function Moreover, the luminescent and antibacterial properties of o-phenanthroline is all well known Lphenylalanine is a common luminescent chromophore in protein molecules These advantages encouraged us to synthesize a novel class of dinuclear complexes using rare earth ions (La3+, Y3+ and Eu3+), L-phenylalanine and o-phenanthroline In the present paper, the complexes La(Phe)3PhenCl3·3H2O, Eu(Phe)3PhenCl3·3H2O, Y(Phe)3PhenCl3·3H2O, La0.2Eu0.8(Phe)3PhenCl3·3H2O and Y0.2Eu0.8(Phe)3PhenCl3·3H2O have been synthesized and char- ⁎ Corresponding author Tel.: +86 21 64322513; fax: +86 21 64322511 E-mail address: yangjingchem@126.com (H Qizhuang) 0167-577X/$ - see front matter © 2005 Elsevier B.V All rights reserved doi:10.1016/j.matlet.2005.08.051 acterized by elemental analysis, molar conductivity, spectroscopic and antibacterial activities testing Experimental 2.1 Materials Rare earth oxides, L-phenylalanine (L-phe), o-phenanthroline (Phen) and absolute ethanol were purchased from Yue Long Chemical Plant (Shanghai) All reagents except L-phenylalanine were of analytical grade and used without further purification L-phenylalanine was of biochemical reagent Hydrated rare earth chlorides were prepared from the corresponding oxides Deionized water was used throughout 2.2 General measurements The contents of elements C, H, N were measured by using Elementar Vario EL III elemental analyzer; rare earth ions were titrated by a complexometric method, using EDTA and xylenol orange as indicator FT-IR spectra were measured on a PK60000 FT-IR spectrometer in KBr pellets Raman spectra were recorded with a Dilor confocal Raman system (SuperRamlab II) It comprises an integral Olympus B ×40 microscope with a 318 H Qizhuang et al / Materials Letters 60 (2006) 317–320 Fig IR spectra of the complex La0.2Eu0.8(Phe)3PhenCl3·3H2O 50× long working-length objective (8 mm), which provides a spectral resolution of cm− 1, and a liquid-nitrogen-cooled 1024 × 800 pixel CCD detector The excitation wavelength was 632.8 nm from an air-cooled He–Ne laser with a power of ca mW The fluorescence spectra were taken with Cary-E fluorescence spectrophotometer The antibacterial activity of the ligands and complexes was preliminary tested by disc diffusion method using Mueller– Hinton agar medium Sterile filter paper discs were soaked in ligands and complex solutions prepared in sterile deionized water The antibacterial effects were investigated after 18 h incubation at 37 °C The MIC of the compounds was examined in liquid Mueller–Hinton medium Each test compound was dissolved to different concentrations in nutrient broth Then × 105∼5 × 106 cfu/ml testing microorganism was added into the above nutrient broth The MIC was determined following 18 h incubation at 37 °C 2.3 Preparation of the complexes Accurately weighed L-phenylalanine (15 mmol 2.4779 g) and o-phenanthroline (5 mmol 0.9911 g) with a molar ratio of : Fig Raman spectra of the complex La(Phe)3PhenCl3·3H2O (A) La0.2Eu0.8 (Phe)3PhenCl3·3H2O (B) L-Phe (C) Phen were respectively dissolved in 50 ml ethanol aqueous solution They were mixed in a water bath at 90 °C for 30 min, then mmol lanthanide chloride in x: (1 − x) = 0.00, 0.20, 1.00 (x = LaCl3·6H2O or YCl3·6H2O; − x = EuCl3·6H2O) molar ratio, also dissolved in 50 ml ethanol aqueous solution, were added to the above system The PH of the mixture was adjusted to 6.5∼7 with dilute aqueous NaOH solution, then refluxed on the water bath for h The resulting solution Table IR spectrum data of ligands and complexes Vibration group Vibration type NH+3 υas υs υas υs Δυas − s δC–H COO− Phen H2O υC=C υC=N υO–H υRE-O RE(Phe)3PhenCl3·3H2O Ligand L-Phe Phen H2O 3064 s 2963 s 1559 vs 1303 s 256 854 s 735 s 1644 m 1585 m 3344–3422 s, b La3+ Eu3+ Y3+ 3+ La3+ 0.2Eu0.8 3+ Y3+ 0.2Eu0.8 3067 m 2965 m 1580 vs 1343 s 237 850 733 m 1624 m 1554 m 3315–3387 s, b 460 w 3065 m 2965 m 1590 vs 1352 s 238 853 735 m 1624 m 1553 m 3316–3385 s, b 465 w 3070 m 2965 m 1585 vs 1347 s 238 853 732 m 1624 m 1554 m 3328–3395 s, b 462 w 3067 m 2964 m 1580 vs 1343 s 237 850 733 m 1624 m 1554 m 3320–3386 s, b 461 w 3070 m 2967 m 1581 vs 1345 s 236 849 733 m 1624 m 1554 m 3318–3390 s, b 467 w H Qizhuang et al / Materials Letters 60 (2006) 317–320 319 was vaporized on a water bath until it turned into a solid pink product, then dried under vacuum for h were measured in KBr matrix in the range of 400–4000 cm− and are listed in Table The absence of the COO− group of the L-phenylalanine at 1559 and 1303 cm− suggests the coordinate of the COO− group with the rare earth ions Two bands at 1580 and 1343 cm− can be attributed, respectively, to the asymmetric and symmetric stretching vibrations The separation between the two bands, Δυ − υas(COO−) − υs(COO−) − 237 cm− 1, shows the carboxylate is bidendate chelating coordination [7] The bands at 3064 and 2963 cm− are attributed to the stretching vibrations of the NH+3 of the Lphenylalanine However, they not change or change slightly in comparison to the corresponding absorption band of the complex, which indicate that the NH+3 does not take part in the coordination of the rare earth ions The bands at 1585 and 1644 cm− are the stretching vibrations of the C=N and C=C groups of the ophenanthroline ligand, shifting to lower energy in the complexes Thus the phenomena indicate the lone-pair electrons of the two nitrogens of the o-phenanthroline are bidendate chelating coordination with the metal ions [8] Furthermore the IR spectra shows a strong and wide band at about 3360 cm− 1, which is most likely ascribed to the stretching vibration of the crystal water molecules Results and discussion 3.3 Raman spectra 3.1 Elemental analysis Raman spectra can also provide the information about molecular structure Electromagnetic radiation field and molecular induce dipole moment are the source of Raman spectra And the spectra arise from the symmetric vibration of the symmetric bond IR spectra, however, are attributed to the changes of molecular dipole moment The two spectra complement and support each other [9] The combination of Raman spectra and IR spectra is a powerful method for characterizing the fluorescent rare earth complexes [10] The Raman spectra of the complexes, L-phenylalanine and ophenanthroline is shown in Fig The COO− group stretching vibrations in L-phenylalanine have been assigned to the strong Raman bands at 1584 and1308 cm− 1, respectively In the complex, however, the COO− group stretching vibrations are at 1518 and 1406 cm− The separation between them, Δυ − υas(COO−) − υs(COO−) − 112 cm− 1, is indicative of bidendate chelating coordination This result is complementary to their IR spectra The bands at 1618, 1603, 1592 and 1566 cm− in the Raman spectra of phen have been assigned to the phenyl ring stretching vibration, which shift to higher frequency of 1624, 1617, 1562 and 1588 cm− in the complex These may be owing to the coordination of the two nitrogens of phen with the rare earth ion, as discussed in the IR spectra above Fig Fluorescence spectra of the complex (a) La0.2Eu0.8(Phe)3PhenCl3·3H2O (b) Y0.2Eu0.8(Phe)3PhenCl3·3H2O (c) Eu(Phe)3PhenCl3·3H2O Elemental analysis results are in good agreement with the stoichiometry of RE(Phe)3PhenCl3·3H2O(RE=La3+–Eu3+–Y3+), La0.2Eu0.8 (Phe)3PhenCl3·3H2O and Y0.2Eu0.8(Phe)3PhenCl3·3H2O Results of elemental analyses are: C 47.80%, H 4.67%, N 7.04%; calc C 48.14%, H 4.53%, N 7.20%; C 47.55%, H 4.65%, N 7.01%; calc C 47.50%, H 4.47%, N 7.10%; C 50.80%, H 4.83%, N 7.35%; calc C 50.75%, H 4.77%, N 7.59% for La(Phe)3PhenCl3·3H2O, Eu(Phe)3PhenCl3·3H2O, Y (Phe)3PhenCl3·3H2O, respectively C 47.60%, H 4.62%, N 7.05%; calc C 47.63%, H 4.48%, N 7.12%; C 47.80%, H 4.65%, N 7.08%; calc C 48.12%, H 4.52%, N 7.20% for La0.2Eu0.8(Phe)3PhenCl3·3H2O and Y0.2Eu0.8(Phe)3PhenCl3·3H2O, respectively The complex is soluble in water, but not in ethanol, DMF, ether, acetone and phene Molar conductivity measurement in water would give further support to this idea, with the complex approaching : electrolyte value [6] (Λ = 365.0 S cm2 mol− 1) 3.2 FT-IR spectra Fig shows the IR spectra of La0.2Eu0.8(Phe)3PhenCl3·3H2O The IR spectra of the five complexes, L-phenylalanine and o-phenanthroline Table Antibacterial in vitro activity expressed as diameter of growth inhibition area Compound tested La(Phe)3PhenCl3·3H2O Y(Phe)3PhenCl3·3H2O Eu(Phe)3PhenCl3·3H2O La0.2Eu0.8(Phe)3PhenCl3·3H2O Y0.2Eu0.8(Phe)3PhenCl3·3H2O L-phenylalanine o-phenanthroline RECl3 Concentration (mol/l) 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 Diameter of growth inhibition area (mm) Bacterial strain E coli ATCC11229 S aureus ATCC6358 P C albicans ATCC10231 25 27 25 25 26 16 18 21 22 19 22 13 16 19 18 18 19 13 320 H Qizhuang et al / Materials Letters 60 (2006) 317–320 Table Antibacterial in vitro activity expressed as MIC Compound tested Minimal inhibitory concentration (ppm) Bacterial strain La(Phe)3PhenCl3·3H2O Y(Phe)3PhenCl3·3H2O Eu(Phe)3PhenCl3·3H2O La0.2Eu0.8(Phe)3PhenCl3·3H2O Y0.2Eu0.8(Phe)3PhenCl3·3H2O L-phenylalanine o-phenanthroline RECl3 E coli ATCC11229 S aureus ATCC6358 P C albicans ATCC10231 60 55 60 60 60 N500 80 N500 200 150 150 200 200 N500 350 N500 400 300 350 400 350 N500 500 N500 In the complex, the bands at 282, 263 and 416 cm− 1, 244 cm− can be assigned to the RE-O, RE-N, RE-Cl stretching vibration, respectively All these bands at lower frequency area (below 500 cm− 1) are not observed in the IR spectra 3.4 Fluorescence spectra The fluorescence spectra of the dinuclear complexes were measured at 500–800 nm and are shown in Fig In the emission spectra(λex = 319 nm), the narrow bands at 592.1, 615.0, and 699.0 nm are attributed to the characteristic emissions of Eu3+ (5D0 → 7F1, 7F2 and 7F4) No characteristic emissions of La3+ and Y3+ are detected for La(Phe)3PhenCl3·3H2O and Y(Phe)3PhenCl3·3H2O However, the increase of fluorescence intensity can be obviously observed (Fig 3) for Eu(Phe)3PhenCl3·3H2O, Y0.2Eu0.8(Phe)3-PhenCl3·3H2O, La0.2Eu0.8(Phe)3PhenCl3·3H2O, respectively The addition of La3+ and Y3+ ions enhances the fluorescence intensity of Eu3+ This interesting phenomenon of fluorescence enhancement is named co-fluorescence effect According to the Forster and Dexter's theories, energy can be transferred to molecules in short distance by an intermolecular energy transfer [11] La3+ and Y3+ ions, belonging to f0, have no low-lying energy levels, so the energy absorbed by their complex molecules cannot be dissipated through the energy levels of La3+ and Y3+, but are transferred to the nearby molecules of Eu(Phe)3PhenCl3·3H2O [12] 3.5 Biological evaluation The antibacterial activity of the complexes were evaluated by the agar-diffusion method against strains belonging to the Escherichia coli, Staphylococcus aureus and Candida albicans The results, expressed as the diameter of growth inhibition area in millimeters, are given in Table The MIC was determined in liquid Mueller–Hinton medium The results of the MIC are given in Table Antibacterial results are as follows: (1) Rare earth complexes exhibited in good antimicrobial activities against E coli, S aureus and C albicans, especially against E coli; (2) The antibacterial activity of the complexes are better than that of each ligand; (3) The antimicrobial mechanism is presumably that the compounds affect the functions associated with cell division of fungi such as cell wall, protein, and/or DNA biosyntheses or kill the exponentially growing cells Conclusions The complexes RE(Phe)3PhenCl3·3H2O(RE: La3+, Y3+ and Eu3+), RE0.2Eu0.8(Phe)3PhenCl3·3H2O(RE: La3+ and Y3+) have been synthesized Co-fluorescence effect of RE0.2Eu0.8 (Phe)3PhenCl3·3H2O(RE: La3+ and Y3+) are reported The addition of La3+ and Y3+ can enhance the fluorescence intensity of Eu3+, respectively According to the antibacterial testing results, these complexes are more active antibacterial agents than each ligand or rare earth ions The complexes belong to broadspectrum antibacterial agents Acknowledgments The work was financially supported by Shanghai-Unilever Research and Development Fund (200406) We are also grateful to Professor Wang Zemin of the Department of Chemistry, Shanghai Normal University References [1] J.Z Ni, Bioinorganic Chemistry of Rare Earth Element, Science Press, Beijing, 1995 [2] M.D Taylor, C.P Carter, C.I Wynter, J Inorg Nucl Chem 30 (1968) 1508 [3] X.S Lian, J Rare Earths 20 (5) (1999) [4] Y.T Yang, Spectrochim Acta 55 (1999) 1527–1533 [5] R.M Supkowski, J.P Bolender, W.D Smith, Coord Chem Rev 185/186 (1999) 307 [6] W.J Gear, Coord Chem Rev (1971) 81 [7] K Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, Wiley, New York, 1986, pp 171–172 [8] Z.M Wang, J.R Cao, F.S Zhu, Chin J Appl Chem 10 (4) (1993) 30 [9] Z.Y Zhu, The Applied of Raman Spectra on Chemistry, North East University Press, Shenyang, 1998 [10] Y Jiang, Z.H Xu, G.X Xu, Spectrochim Acta, Part A 52 (1996) 1499–1505 [11] T Forster, Ann Phys (1948) 55 [12] Y.T Yang, S.Y Zhang, J Mol Struct 646 (2003) 103–109  ... strain E coli ATCC1 122 9 S aureus ATCC6358 P C albicans ATCC1 023 1 25 27 25 25 26 16 18 21 22 19 22 13 16 19 18 18 19 13 320 H Qizhuang et al / Materials Letters 60 (20 06) 317– 320 Table Antibacterial... s 23 8 853 7 32 m 1 624 m 1554 m 3 328 –3395 s, b 4 62 w 3067 m 29 64 m 1580 vs 1343 s 23 7 850 733 m 1 624 m 1554 m 3 320 –3386 s, b 461 w 3070 m 29 67 m 1581 vs 1345 s 23 6 849 733 m 1 624 m 1554 m 3318–3390... m 29 65 m 1580 vs 1343 s 23 7 850 733 m 1 624 m 1554 m 3315–3387 s, b 460 w 3065 m 29 65 m 1590 vs 13 52 s 23 8 853 735 m 1 624 m 1553 m 3316–3385 s, b 465 w 3070 m 29 65 m 1585 vs 1347 s 23 8 853 732