Macrocycles lanthanide complexes

COMPARISON WITH THE STRUCTURE OF SOME OTHER MACROCYCLIC LANTHANIDE COMPLEXES... 

Zhao, C., Ren, J Gregolinski, J. et al. (2012) Contrasting enantioselective DNA preference chiral helical macrocyclic lanthanide complex binding to DNA. Nucleic Acids Ties., 40 (16), 8186-96. 

Pietraszkiewicz, M., Karpiuk, J., and Rout, A.K. (1993) Lanthanide complexes of macrocyclic and macro-bicyclic N-oxides light-converting supramolecular devices. Pure Appl. Chem, 65(3), 563-566. 

Matthews, K. D. Kahwa, I. A. Williams, D. J. Preparation, structure, and luminescence of dinuclear lanthanide complexes of a novel imine-amine phenolate macrocycle. Inorg. Chem. 1994, 33,1382-1387. 

Although they are not macrocyclic ligands, polyethyleneglycols behave somewhat similarly to the crown ethers regarding lanthanide complexation, as established by a number of crystal structure determinations. Thus a series of neodymium complexes shows consistent 10-coordination, namely [Nd(N03)3(tri-eg)],458 where tri-eg is triethyleneglycol, [Nd(N03)2(penta-eg)]N03,458 and [Nd(N03)2(N03)(tetra-eg)],459 where N03 is monodentate. The larger La3+ ion shows 11-coordination in [La(N03)3(tetra-eg)].460... 

Numerous macrocyclic and macropolycyclic ligands featuring subheterocyclic rings such as pyridine, furan or thiophene have been investigated [2.70] among which one may, for instance, cite the cyclic hexapyridine torands (see 19) [2.39] and the cryptands containing pyridine, 2,2 -bipyridine (bipy), 9,10-phenanthroline (phen) etc. units [2.56,2.57,2.71-2.73]. The [Na+ c tris-bipy] cryptate 20 [2.71] and especially lanthanide complexes of the same class have been extensively studied [2.74, 2.75] (see also Sect. 8.2). 

Introducing a chiral center in the amide functionality renders all 32 potential isomers diastereomeric and thus discernable (in principle) by NMR spectroscopy. In practice, the lanthanide complexes formed (Eu, Gd and Tb) with macrocyclic monoamide tris(phosphinate) ligands bearing a chiral center on the amide group exist as only two non-interconverting diastereomers in a ratio of 2 1 and 4 1 for the a-phenylethyl and a-l-napthylethyl derivatives, respectively (DOTMP-MPMeA and DOTMP-MNaphMeA) [114]. The configuration at... 

This brief overview has shown that there are many possibilities when choosing ligands for the design of luminescent lanthanide complexes. From the examples shown it is apparent that the most luminescent of the lanthanide complexes are formed when macrocyclic ligands are used that fully or almost fully coordinate the metal centre. It should also be apparent that there are many examples and options available when it comes to choosing possible antenna within the criteria set out above (Sect. 2.3.2). 

Figure 5.3 Synthetic conditions for the mixed-ligand Pc complexes, containing one Pc ligand. Route 1 interaction of o-dicyanobenzene(s) and their analogues with lanthanide salts. Route 2 metallation reaction of the macrocyclic ligand or its dianione by lanthanide compounds. Route 3 reactions of axial substitution in the environment of the central atom in lanthanide complexes ([96] and references cited therein). (From Ref. 96, with permission.)...

Calix[ ]arenes are a family of macrocycles prepared by condensation reactions between n /v/ra-substituted phenols and n formaldehyde molecules under either base or acid catalysis. Different sizes of the macrocycles can be obtained (n = 4-20) (Stewart and Gutsche, 1999) depending on the exact experimental conditions, which were mastered in the 1960 s (Gutsche, 1998), but the most common receptors are those with n =4,6,8 (macrocycles with an odd number of phenol units are more difficult to synthesize). We use here the simplified nomenclature in which the number of phenolic units is indicated between square brackets and para substituents are listed first.4 Calixarenes, which can be easily derivatized both on the para positions of the phenolic units and on the hydroxyl groups, have been primarily developed for catalytic processes and as biomimics, but it was soon realized that they can also easily encapsulate metal ions and the first complexes with d-transition metal ions were isolated in the mid-1980 s (Olmstead et al., 1985). Jack Harrowfield characterized the first lanthanide complex with a calixarene in 1987, a bimetallic europium complex with p-terf-butylcalix[8]arene (Furphy etal., 1987). 

Well-examined complexes include derivatives of macrocyclic polyphenols known as calixarenes [147] (Fig. 29, Table 13). Lanthanide complexes containing up to eight phenolic units (calix[8]arene) were reported. 

The most thermodynamically stable and kinetically inert complexes of the trivalent lanthanides are those of the ligand DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) (42, 43). Our search for lanthanide macrocyclic complexes that would remain intact for longer time periods led us to examine derivatives of DOTA. There are two potential difficulties with the use of DOTA complexes of the trivalent lanthanides for RNA cleavage. First, the overall negative charge on the complex is not conducive to anion binding for example, Gd(DOTA)-does not bind hydroxide well (44). Second, DOTA complexes of the middle lanthanides Eu(III) and Gd(III) have only one available coordination site for catalysis. The previous lanthanide complexes that we used, e.g., Eu(L1)3+, were good catalysts and had at least two available coordination sites. 

Several of the complexes in Figure 2 were examined further for their resistance to dissociation. The europium complexes Eu(THED)3+ and Eu(TCMC)3+ were more difficult to study quantitatively by H NMR because of their broad H resonances. Decomposition was monitored by use of a UV-vis assay. Excess Cu2+ was added to solutions containing the lanthanide macrocycles. The Cu2+ ion served the dual purpose of trapping the free macrocycle and as an indicator to monitor the amount of macrocycle that had dissociated. All Cu(II) macrocyclic complexes gave an absorbance peak in the UV-vis spectrum that was characteristic of the Cu(II) macrocycle complex. For all macrocycles, Cu2+ was an effective trap formation of the Cu(II) macrocyclic complex went to completion in the presence of 0.10 mM La3+ or 0.10 mM Eu3+, 0.10 mM ligand and excess Cu2+ (1.0 mM). The increase in the concentration of Cu(II) macrocycle complex over time is a measure of the inertness of the lanthanide complex to dissociation. For the La(THED)3+ complex, the reaction rate (51) was independent of the concentration of Cu2+, consistent with the following mechanism ... 

PART A LANTHANIDE COMPLEXES PART B MACROCYCLIC COMPLEXES... 

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