Unusual Catalyst Concentration Effects in the Hydrolysis of Phenyl Phosphate Esters and of DNA:  A Systematic Investigation of the Lanthanide Series¹

Abstract

Saturation kinetics are measured with all lanthanides and bis(nitrophenyl) phosphate BNPP as substrate. They show rather constant K M values; the k cat values, however, increase by up to 66 times for La3+ to Er3+ and decrease again for Yb3+ and Lu3+. With all lanthanides, hydrolysis of the intermediate mononitrophenyl phosphate NPP is 2−30 times faster than that of BNPP. The k cat values measured with BNPP correlate with the ion diameter of the lanthanides, in line with accepted mechanisms but with the notable exception of the higher lanthanides. A similar correlation holds for the cleavage rates with plasmid DNA, with striking differences again observed with the higher lanthanides, however. Thus, a concentration increase from 5 × 10-5 to 1 × 10-2 M leads to 64% and 84% more DNA cleavage with La3+ and Pr3+, respectively, but to up to 68% less DNA cleavage, respectively, but with Yb3+, Tm3+ or Lu3+. In contrast to the BNPP cleavage, saturation kinetics derived k cat values with DNA change little with the used cation, which on the other hand led to larger variations in the K M parameters. Preliminary UV and CD studies with plasmid DNA indicate lanthanide-induced conformational changes with pseudo-first-order rate constants 10−100 times higher than the cleavage rate under the same conditions. Again, Yb3+ shows different effects than Eu3+. The unusual behavior of the higher lanthanides is discussed on the basis of cation clustering, which, in contrast to earlier assumptions by Bamann et al., leads to diminished activities. Addition of salts such as of NaCl or MgCl2 leads to distinct decrease of catalytic effects of for instance Eu3+. The corresponding rates correlate well with Debye−Hückel ionic strength parameters. These as well as the effects of added amines are in line with a simple competition mechanism of the added cations for the anionic substrates.

Lanthanide-Containing Molecular and Supramolecular Polymetallic Functional Assemblies

“…59 The improved efficiency of the catalytic pathway observed for smaller Ln(III) is obviously ascribed to the larger Lewis acidity of the cation which enhances both water deprotonation and phosphoryl activation. The unexpected decrease of k cat for the heaviest Ln(III) (Ln ) Yb, Lu) contrasts with this trend and can be traced back to clustering and aggregation which remove free coordination sites for metallic activation of substrates.…”

Importance of the chromophore orientation to the ligand-to-metal energy transfer in lanthanide complexes with pendant-arm fitted cyclen derivatives

“…More environment consisting of b-diketonates, trioctylphosphine recently, coordination compounds have been used for ® oxide and Triton X-100. The metal-centered luminesdesigning analytical sensors [12], catalysts for specific cence of the resulting assembly displays a large quantum cleavage of DNA and RNA [13] and agents for cancer yield (70%) and time-resolved measurements of this radio- [14,15] and photo-therapy [16]. All these applica-III luminescence, to separate it from the luminescence of the tions have produced unprecedented interest in Ln coordi- and 12 has been evidenced in the solid state (Fig.…”

Synthesis of a novel linear polymer of a macrocyclic polyamine copper (II) complex and its interaction with plasmid DNA

“…The half-life for spontaneous hydrolysis of the phosphodiester has been estimated as about 10 11 years at pH 7 and 308C [2]. Some natural enzymes, such as restrition endonucleases and topoisomerases, can catalyze phosphoryl cleavage efficiently under physiological conditions, but the enzymatic reaction is difficult to be performed in the laboratory [3].…”