Synthesis, characterization and bioactivity of rare earth ternary complexes containing indole-3-acetic acid and 1,10-phenanthroline

1. INTRODUCTION
Rare earths are very suitable for a variety of industrial and biological applications, due mainly to their spectroscopic and magnetic properties. In industry, the applications of rare earths are many, such as in catalysis, phosphors, magnetic materials, glasses and lasers. In biological systems, the use of trivalent rare earth ions has attracted a great deal of interest^[1]. In these systems, they are usually used as luminescent probes in the investigations of binding sites in proteins and other biomolecules, labels in immunoassays and in non-invasive tests^[2]. Auxins represent one of the important classes of signaling molecules transcribed in plants. They regulate several fundamental processes including cell division, elongation and differentiation. Exogenously applied auxins have been reported to stimulate stem elongation in isolated stem segments as well as in intact plants^[3]. Song Z G et al^[4] have studied the coordination of series of plant growth regulators to some transition metals in solution and the effect of introducing N-containing heterocyclic neutral ligand on the coordination ability of these regulators. In this paper, the study of rare earth ternary complexes containing HL and phen is reported.
2. EXPERIMENTAL
2.1 Measurements
Carbon, hydrogen and nitrogen were determined using a Carlo-Erba 1106 elemental analyser and the rare earth metals by EDTA titration. The IR spectra were recorded on a Nicolet-170SX FT-IR spectrophotometer using KBr tablets in the range of 4000-200cm^-1. ¹HNMR spectra were obtained using a Varian FT-80A spectrometer with d₆-acetone as the solvent and TMS as the internal reference. Thermal analyses were performed using a Beijing Analytical Instrument Plant PCT-2 thermal balance. Absorbencies were determined on a Shimadzu UV-240 spectrophotometer at 560nm.
2.2 Reagents
The chemicals used were analytical grade. The hydrated lanthanide (III) chlorides were prepared dissolving the respective 99.99% oxides (Yaolong Chemical Works, Shanghai, China) in concentrated hydrochloric acid.
2.3 Synthesis of the sodium salt of ligand (NaL)
HL was dissolved with equimolar sodium hydroxide (NaOH) methanol solution. The mixture was stirred until clear, then the solution was put on a water bath to evaporate until a crystal film appeared. The product obtained was collected by filtration and dried over molecular sieves under vacuum. The purity of the product was also confirmed by elemental analysis and IR spectra.
2.4 Synthesis of the complexes
3mmol HL and 3mmol NaOH were dissolved in 10cm³ methanol. Under stirring, a solution of MCl₃·nH₂O (1mmol) and 1.5mmol phen·H₂O methanol (10cm³) was added to the mixture and the precipitate appeared immediately. After stirring the mixture at room temperature for 3h, the precipitate was collected by filtration, washed with methanol three times, and dried in a vacuum dissociactor to constant weight. Eight rare earth (III) complexes with HL and phen were prepared by the same method respectively.
2.5 Test for bioactivity of the complex
Uniform grown seedling of Gansu 1116 wheat was used for the test. Five samples averaged for each concentration and different lots of seedling were used for ligand HL and complexes. The seedlings were illuminated (2000-3000lux) at 20-30^oC for 5 days.

3. RESULTS AND DISCUSSIONS
3.1 Composition and properties of the complexes
Elemental composition, molar conductance and molecular formula of the complexes are listed in Table 1. The complexes are stable in air and soluble in DMF, DMSO methanol and ethanol, while insoluble in water. As seen in Table 1, the molar conductances of complexes in DMSO at 25^oC vary from 14.25-18.52s·cm²·mol^-1, indicating that they are nonelectrolytes^[5].

Table 1 Elemental composition and molar conductance of the ternary complexes

Table 2 Characteristic IR frequendies(cm^-1) of ligand and the complexes

Table 3 ¹HNMR data of ligands and La(m) complex (d/ppm)

3.4 Thermal analysis
From Table 4, we realize that the thermal behavior of eight complexes are alike indicating their similarity in coordination structure. They do not contain water molecules since are there no heat absorption peak around 100^oC. They all have clearly defined melting points (small sharp heat absorption peak) and begin to lose weight at very high temperature (above 300^oC) indicating their high thermal stability^[8]. On heating to about 800℃, the residue weights correspond to values calculated for M₂O₃ (M = La, Pr, Nd, Sm, Eu, Gd, Er, Y).

Table 4 The thermal data of RE(IAA)₃·phen

3.5 Electronic spectrum
The f→f transition absorption spectra and designation of Nd(m) and Er(m) complexes are shown in Figure 3 and Table 5. The covalent parameters (d), bonding parameters (b^1/2) and the expansion coefficients of electron cloud () were calculated from the electronic spectra of Nd and Er complexes. The values are smaller than one, indicating the covalent nature of the coordination bond formed in the two complexes. The covalent nature is also confirmed by the positive values of both b^1/2 and d. The b^1/2 values are very small (0.019-0.088), so the contribution of the 4f orbital of the rare earth ion to bond formation can be neglected^[9].

Figure 2 The electron spetra l(nm) of Nd(IAA)₃·phen(a) and Er(IAA)₃·phen(b)

Table 5 The f→f transition absorption peaks of complexes(cm^-1)

Table 6 Effect of HL and LaL₃·phen on the growth of wheat seedlings

REFERENCES
[1] Ivanov R A, Korsakov I E, Formanovskii A A et al. Russian Journal of Coordination Chemistry, 2002, 28(9): 713.
[2] Keskinov V A, Lishchuk V V, Pyartman A K et al. Russian Journal of Applied Chemistry, 2006, 79(3): 360.
[3] Statvir K. Anil K G, Narinder K. Plant Growth Regulation, 2003, 39: 91.
[4] Song Z G. Application Chemistry, 1999, 16(1):21.
[5] Gao E J, Liu Q T. Acta Chimica Sinica, 2005, 63(8):725.
[6] Yang J X, Hu Z J. Chinese Journal of Chemistry, 2005, 23(5): 533.
[7] Pang X A, Yao Y M. Chinese Journal of Chemistry, 2005, 23(9): 1193.
[8] Khatia I H. Bull. Chem. Soc. Jpn., 1982, 55(7):2258.
[9] GAN X, XIE Y. Acta Chimica Sinica, 2005, 63(14):1307.

吲哚－3－乙酸邻菲啰啉稀土（Ⅲ）三元配合物的合成、表征和生物活性
展惠英 宋之刚
(甘肃联合大学 化工学院 甘肃 兰州 730000)
摘要  合成了八种RE(IAA)₃·phen三元配合物(RE:La、Pr、Nd、Sm、Eu、Gd、Er、Y；IAA：吲哚－3－乙酸；phen: 邻菲啰啉).通过元素分析、红外光谱、电子吸收光谱、¹HNMR谱、热重－差热分析等方法对标题化合物的结构和性质进行了研究，并探讨了La(IAA)₃·phen对小麦幼苗的影响。
关键词  稀土三元配合物；吲哚－3－乙酸；合成；生物活性

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