1 research outputs found
Second-Sphere Effects in Dinuclear Fe<sup>III</sup>Zn<sup>II</sup> Hydrolase Biomimetics: Tuning Binding and Reactivity Properties
Herein,
we report the synthesis and characterization of two dinuclear Fe<sup>III</sup>Zn<sup>II</sup> complexes [Fe<sup>III</sup>Zn<sup>II</sup>LP1] (<b>1</b>) and [Fe<sup>III</sup>Zn<sup>II</sup>LP2] (<b>2</b>), in which LP1 and LP2 are conjugated systems containing
one and two pyrene groups, respectively, connected via the diamine
âHNÂ(CH<sub>2</sub>)<sub>4</sub>NHâ spacer to the well-known
N<sub>5</sub>O<sub>2</sub>-donor H<sub>2</sub>L ligand (H<sub>2</sub>L = 2-bisÂ{[(2-pyridylmethyl)Âaminomethyl]-6-[(2-hydroxybenzyl)Â(2-pyridylmethyl)]Âaminomethyl}-4-methylphenol).
The complex [Fe<sup>III</sup>Zn<sup>II</sup>L1] (<b>3</b>),
in which H<sub>2</sub>L was modified to H<sub>2</sub>L1, with a carbonyl
group attached to the terminal phenol group, was included in this
study for comparison purposes.<sup>1</sup> Both complexes <b>1</b> and <b>2</b> were satisfactorily characterized in the solid
state and in solution. Extended X-ray absorption fine structure data
for <b>1</b> and <b>3</b> in an acetonitrile solution
show that the multiply bridged structure seen in the solid state of <b>3</b> is retained in solution. Potentiometric and UVâvis
titration of <b>1</b> and <b>2</b> show that electrostatic
interaction between the protonated amino groups and coordinated water
molecules significantly decreases the p<i>K</i><sub>a</sub> of the ironÂ(III)-bound water compared to those of <b>3</b>. On the other hand, catalytic activity studies using <b>1</b> and <b>2</b> in the hydrolysis of the activated substrate
bisÂ(2,4-dinitrophenyl)Âphosphate (BDNPP) resulted in a significant
increase in the association of the substrate (<i>K</i><sub>ass</sub> â
1/<i>K</i><sub>M</sub>) compared to
that of <b>3</b> because of electrostatic and hydrophobic interactions
between BDNPP and the side-chain diaminopyrene of the ligands H<sub>2</sub>LP1 and H<sub>2</sub>LP2. In addition, the introduction of
the pyrene motifs in <b>1</b> and <b>2</b> enhanced their
activity toward DNA and as effective antitumor drugs, although the
biochemical mechanism of the latter effect is currently under investigation.
These complexes represent interesting examples of how to promote an
increase in the activity of traditional artificial metal nucleases
by introducing second-coordination-sphere effects