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

Zhan Huiying, Song Zhigang
(College of Chemical Engineering, Gansu Lianhe University, Lanzhou, 730000, China)

Received on Jun 10, 2006.

Abstract Eight new solid complexes of Indole-3-acetic acid (C8H6N-CH2-COOH, HL) with rare earth metals (M) and 1,10-phenanthroline (phen) have been synthesized. Elemental analysis, IR, molar conductance, TG-DTA, 1HNMR spectra have been used to characterize the complexes. The general formula of the complexes is ML3·phen (M = La, Pr, Nd, Sm, Eu, Gd, Er, Y). The bioactivity of LaL3·phen complex was tested. The results obtained showed that the complexes possess increasing effects on the growth of seedlings.

    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.
    2.1 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 20-30oC for 5 days.
    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 25oC 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

Compound color m.p (oC) experimental values (ге) Molar conductance /s·cm2·mol-1 (DMSO)
La(IAA)3·phen pale yellow 251-254 16.23(16.50) 59.82(59.88) 3.78(3.80) 8.25(8.32) 16.98
Pr(IAA)3·phen pale yellow 240-243 16.49(16.70) 58.29(59.79) 3.69(3.79) 7.96(8.30) 16.41
Nd(IAA)3·phen pale yellow 245-247 17.10(17.02) 58.62(59.50) 3.78(3.78) 8.28(8.26) 18.06
Sm(IAA)3·phen pale yellow 235-237 17.55(17.63) 58.66(59.07) 3.66(3.75) 8.18(8.20) 14.82
Eu(IAA)3·phen pale yellow 234-236 17.92(17.78) 58.59(58.97) 3.69(3.74) 8.10(8.19) 18.52
Gd(IAA)3·phen pale yellow 253-255 18.85(18.53) 58.29(58.50) 3.67(3.72) 8.17(8.14) 16.66
Er(IAA)3·phen pale red 230-232 19.36(19.23) 57.67(57.93) 3.50(3.68) 7.98(8.05) 15.64
Y(IAA)3·phen pale yellow 246-248 11.07(11.23) 63.64(63.66) 4.00(4.04) 8.87(8.84) 18.22

3.2 IR spectrum
The important IR data of ligand and its typical complexes are listed in Table 2. The absorption peaks at 1517 and 840cm-1 of the complexes can be attributed to ring vibration of phen, the original ring vibration of phen at 1558cm-1 and C-H vibration at 852 cm-1 are red shifted[6]. Theses facts indicate the participation of phen in coordination.

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

phen·H2O 1558 852
IAA 3389 1334
Na(IAA) 3390 1565 1416 149 1344
La(IAA)3·phen 3408 1590
1517 1345 841 535
Gd(IAA)3·phen 3408 1604
1517 1347 840 537
Y(IAA)3·phen 3408 1609
1517 1345 840 536

The absence of water molecules in the formula is confirmed by the absence OH vibration in the spectra. The N-atom of HL does not take part in coordination (little change of ). There are two sets of and in the complexes indicating existence of two coordination modes between the coo of HL and the rare earth metal ion[3]. In order to meet the requirement of change number, there are three HL molecules taking part in coordination. Probably two HL molecules are in monodentate mode ( around 166-183cm-1, greater than 149cm-1 of NaL) and one HL molecule in bidentate mode (84-100cm-1, smaller than 149cm-1 of NaL), that is the complexes are 6-coordinate[7].
Further supports for the existence of the M-O bond and the M-N bond are the presence of a new bond at about 536 cm-1 and 526 cm-1, 267-281 cm-1 due to .
3.3 1HNMR spectrum
LaL3·phen and YL3·phen were used for this study. The number of proton and the relational data are shown in Figure 2 and Table 3 separately. The spectra show the participation of phen (7.86-9.40ppm) and deprotonated HL (disappearance of the HL proton peak at 12.22ppm) in coordination. The nitrogen atom on the HL indole ring does not appear to participate in coordination since there is no apparent change of imino proton shift at 11.00ppm[7].

Figure 1 The labelled proton of ligand and the complexes

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

Compound a b c d a b a’ a”
phen·H2O 9.09 8.01 8.46 7.74
IAA 2.53 6.90-7.73 11.03 12.22
La(IAA)3·phen 2.53 6.76-7.73 10.83 9.40 8.10 8.62 7.86

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 100oC. They all have clearly defined melting points (small sharp heat absorption peak) and begin to lose weight at very high temperature (above 300oC) indicating their high thermal stability[8]. On heating to about 800бц, 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

Complex Crystalline transformation temperature (oC) Decomposition

temperature (oC)

Residue at 800oC Residue weight percentage
Theory Experiment
La(IAA)3·phen 251 300 La2O3 19.36 20.00
Gd(IAA)3·phen 253 282 Gd2O3 21.08 21.21
Er(IAA)3·phen 230 293 Er2O3 21.99 23.30

3.5 Electronic spectrum
The fб·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 (b1/2) 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 b1/2 and d. The b1/2 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 fб·f transition absorption peaks of complexes(cm-1)

Complex nc na Designation Reference value



17271 17397 4I9/2б·4G5/2бв2G7/2 = 0.9922
19048 19182 б·4G7/2 d= 0.79
19455 19512 б·4G9/2 b1/2= 0.088
21008 21039 б·4G11/2
21277 21720 б·1P1/2
Er(IAA)3·phen 18416 18470 4I15/2б·4S3/2 = 0.9993
19194 19149 б·2H11/2 ж─= 0.07
20534 20559 б·4F7/2 b1/2= 0.019
22222 22241 б·4F5/2

3.5 Effect on growth
As seen from Table 6, the ligand HL promoted the elongation of first leaf (L1) within the concentration range tested, The effect was increased with the increasing concentration of compound, but the lanthanum complex possesses inhibition slightly. HL inhibited the certain elongation of the second leaf (L2) but the complex promoted the elongation. As for the length of the root (L), there was an optimum complex concentration (1.00ppm) for the promotion while the ligand inhibited the elongation over the whole concentration range tested. The root number (N) was increased by HL ligand and the complex. As a whole, the ternary complex tested seems to give better effect on the growth of wheat seedling.

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

10-6HL concentration 0.0 0.5 1.0 2.0 4.0 8.0 16.0 32.0 64.0
L1/mm 90.5 100.0 92.0 97.0 92.0 92.0 95.0 93.0 93.0
L2/mm 149.5 148.0 141.0 149.0 145.0 131.0 141.0 137.0 120.0
L/mm 112.5 117.0 108.0 110.0 109.0 107.0 110.0 97.0 95.0
N 6.2 6.2 6.9 6.6 6.2 6.5 6.9 7.4 7.6
10-6LaL3·phen concentration 0.00 0.02 0.05 0.10 0.50 1.00 2.00 5.00 10.00
L1/mm 103.5 97.0 108.3 102.5 101.5 102.0 98.8 97.6 96.6
L2/mm 135.9 138.6 137.3 138.4 139.6 140.7 142.9 144.4 145.2
L/mm 166.0 179.0 164.0 170.1 177.4 209.9 169.4 168.2 150.9
N 6.2 6.1 6.2 6.2 6.6 6.7 7.2 7.6 8.2