Lanthanide(III) Complexes of Diethylenetriaminepentaacetic Acid (DTPA)–Bisamide Derivatives as Potential Agents for Bimodal (Optical/Magnetic Resonance) Imaging

Abstract

Diethylenetriaminepentaacetic acid (DTPA)–bisamide derivatives functionalized with p‐toluidine, 6‐aminocoumarin, 1‐naphthalene methylamine and 4‐ethynylaniline were synthesized and fully characterized by mass spectrometry, NMR spectroscopy, FTIR spectroscopy and elemental analysis. LnIII complexes (Ln = Gd, Eu, Tb, Y) of the ligands DTPA–bis‐p‐toluidineamide (DTPA–BTolA), DTPA–bis‐6‐coumarinamide (DTPA–BCoumA), DTPA–bis‐1‐naphthylmethylamide (DTPA–BNaphA) and DTPA–bis‐4‐ethynylphenylamide (DTPA–BEthA) were prepared and studied for their bimodal magnetic resonance imaging/optical properties. EuIII and TbIII derivatives in aqueous solutions exhibit characteristic red and green emission, respectively, with quantum yields of 0.73 % for EuIII–DTPA–BNaphA and 2.5 % for TbIII–DTPA–BEthA. Ligand‐centred photophysical properties of the GdIII complexes were investigated to gain insight into energy‐transfer processes that take place in these systems. The GdIII complexes were also analyzed by nuclear magnetic relaxation dispersion (NMRD) techniques. The relaxivity (r1) at 20 MHz and 310 K equals 4.1 s–1 mM–1 for Gd–DTPA–BTolA, 5.1 s–1 mM–1 for Gd–DTPA–BCoumA, 6.4 s–1 mM–1 for Gd–DTPA–BNaphA and 5.7 s–1 mM–1 for Gd–DTPA–BEthA. These values are higher than the value of 3.8 s–1 mM–1 for Gd–DTPA (Magnevist). The improved relaxivity is due to the increase in the rotational tumbling time τR with a factor of 1.6 for Gd–DTPA–BTolA, 2.1 for Gd–DTPA–BCoumA, 3.1 for Gd–DTPA–BNaphA and 6.5 for Gd–DTPA–BEthA. In a 4 % human serum albumin solution, the apparent relaxivity at 20 MHz increases to values of 13.9 and 19.1 s–1 mM–1 for Gd–DTPA–BNaphA and Gd–DTPA–BEthA, respectively. All these features assist the search for optimal bimodal optical and magnetic resonance imaging probes.

Structural and photophysical properties of lanthanide complexes with N-(diphenylphosphoryl)-4-methylbenzenesulfonamide

“…The Na[Tb(PMSP) 4 ] complex in solid state shows strong luminescence upon excitation into ligand excited state at room and 77 K temperatures. The bands displayed in Fig.…”

“…4. The absorption spectrum exhibit 4 ], which will be further shown. 4 ] single crystal at 77 K are presented in Table 3.…”

“…In the case of this shifting it is conceivable that the lowering temperature implies a slight change in the bond lengths. Polymeric structure of the complex is conducive to this effect but the question is why this phenomenon is not observed for Na[Tb(PMSP) 4 ].…”

“…Powder X-ray diffraction patterns (XRD) for Na[Tb(PMSP) 4 ] was recorded using a Brucker D8 Advance diffractometer system. The powder was exposed to the Cu Ka radiation (k = 1.54 Å).…”

“…in biology and medicine [1][2][3][4] or as electroluminescent devices for OLED (organic light emitting diodes) [5]. So far, Eu 3+ and Tb 3+ complexes have been used most often as luminescent markers and probes.…”