Five new Eu(III) macrocyclic complexes have been prepared and their solution and catalytic properties studied. The Eu(III) complexes with septadentate ligands TRED and NB-TRED dissociate rapidly at pH 7.4, 37 degrees C (TRED = 1,4,7-tris(hydroxyethyl)-1,4,7,10-tetraazacyclododecane, NB-TRED = 1-(nitrobenzyl)-4,7,10-tris(hydroxyethyl)-1,4,7,10-tetraazacyclododecane). Dissociation rates as determined in the presence and absence of strongly binding competing ligands suggest that under most conditions the Eu(III) complexes of ATHC, ABHC, and CNPHC are more kinetically inert to dissociation than is the Eu(III) complex containing all hydroxyethyl groups (ATHC = 1-(carbamoylmethyl)-4,7,10-tris(hydroxyethyl)-1,4,7,10-tetraazacyclododecane, ABHC = 1,7-bis(carbamoylmethyl)-4,10-bis(hydroxyethyl)-1,4,7,10-tetraazacyclododecane, CNPHC = 1-(1-carboxamido-3-(4-nitrophenyl)propyl)-4,7,10-tris(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecane). Laser-induced luminescence excitation spectra of Eu(III) complexes of ABHC, ATHC, CNPHC, THED, and S-THP suggest that there is a single major species in solution at pH 6.3 and a second species that appears at more basic pH values (THED = 1,4,7,10-tetrakis(hydroxyethyl)-1,4,7,10-tetraazacyclododecane, S-THP = 1S,4S,7S,10S-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane). The species present at basic pH is proposed to be an alkoxide or hydroxide complex; pK(a) values as determined by potentiometric titrations are 7.5 and 8.1 for Eu(CNPHC)(3+) and Eu(ABHC)(3+), respectively. Eu(CNPHC)(3+), Eu(ATHC)(3+), and Eu(ABHC)(3+) promote transesterification of the hydroxypropyl ester of 4-nitrophenyl phosphate with pseudo-first-order rate constants at pH 7.3, 37 degrees C, and 1.00 mM complex of 1.4 x 10(-)(5), 9.3 x 10(-)(6), and 1.0 x 10(-)(6) s(-)(1), respectively. Both Eu(CNPHC)(3+)and Eu(ABHC)(3+) promote attack of an hydroxyethyl group of the macrocycle on bis(4-nitrophenyl) phosphate with pseudo-first-order rate constants at pH 7.3, 37 degrees C, and 1.00 mM complex of 1.5 x 10(-)(4) and 3.5 x 10(-)(5) s(-)(1), respectively. In general, an increase in the number of amide groups on the macrocycle of the Eu(III) complex decreases the rate of both intramolecular or intermolecular phosphate diester transesterification reactions.

Solution and solid-state properties of the Eu(III) complex of the tetraamide macrocyclic ligand TCMC (TCMC = 1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane) are investigated as part of an effort to develop lanthanide(III) macrocyclic catalysts. [EufTCMCXHjOlKCFrSOrhCCHrOH crystallizes in the centrosymmetric monoclinic space group Pl\!n with a -12.0571(15) Á, b = 13.2196(20) Á, c = 25.4250(40) Á; ß = 91.673-(11)°, V = 4050.8 Á* 123, and Z = 4. The structure was solved and refined to R = 4.02% and Rw = 4.33% for 3510 reflections with F > 6o(F). (R = 7.04%, /?w = 6.48% for all 5322 independent reflections.) Four stereoisomers (two enantiomeric pairs) of the [Eu(TCMC)(H20)]3+ cation appear in the crystal. The structure is disordered, containing two overlapping diastereomers that are interrelated by different conformations of the 1,4,7,10tetraazacyclododecane ring defining the asymmetric unit. Two enantiomers are related to these by operations of the second kind (/, n-glide). The nine-coordinate Eu(III) center has a 4:4:1 coordination geometry formed by the octadentate TCMC ligand and a single bound water molecule. The laser-induced luminescence excitation band of a single crystal of [Eu(TCMC)(H2O)](CF3SO3)3*2CH30H resolves into two peaks, suggesting that each diastereomer gives rise to a separate excitation peak. Similarly, the luminescence excitation spectrum of a solution of [Eu(TCMC)]3+ in water indicates that two species are present in solution. Luminescence lifetime measurements in FLO and in D2O indicate that the europium(III) ion in the TCMC complex has 1.5 ± 0.5 bound water molecules. The 3IP NMR resonance of diethyl phosphate is monitored at 18 ± 2 °C, pH 7.4, upon addition of [Eu(TCMC)]3+ as well as upon addition of several lanthanide(III) complexes that are catalysts for RNA cleavage. No binding of diethyl phosphate to [Eu(TCMC)]3* is observed. The hexadentate Schiff-base complex [La(L')]3+ binds to diethyl phosphate with a binding constant of 47.7 ± 0.5 M™1.

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The europium(III) complex of the octadentate tetraamide ligand is inactive as a catalyst for phosphate diester transesterification or for RNA cleavage. Replacement of one of the amide coordinating groups to form a new heptadentate ligand yields a europium(III) complex ([Eu(NBAC)]3+) that is a very active catalyst for phosphate diester transesterification at 37 °C, pH 7.40. Laser-induced luminescence is used to study the number of bound water molecules and self-association of the [Eu(NBAC)]3+ complex as well as the dissociation of the complex in the presence of competing ligands.