Manganese Carbonyls Bearing
Tripodal Polypyridine
Ligands as Photoactive Carbon Monoxide-Releasing Molecules
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Abstract
The recently discovered cytoprotective action of CO has
raised
interest in exogenous CO-releasing materials (CORMs) such as metal
carbonyls (CO complexes of transition metals). To achieve control
on CO delivery with metal carbonyls, we synthesized and characterized
three Mn(I) carbonyls, namely, [Mn(tpa)(CO)<sub>3</sub>]ClO<sub>4</sub> [<b>1</b>, where tpa = tris(2-pyridyl)amine], [Mn(dpa)(CO)<sub>3</sub>]Br [<b>2</b>, where dpa = <i>N</i>,<i>N</i>-bis(2-pyridylmethyl)amine], and [Mn(pqa)(CO)<sub>3</sub>]ClO<sub>4</sub> [<b>3</b>, where pqa = (2-pyridylmethyl)(2-quinolylmethyl)amine],
by crystallography and various spectroscopic techniques. All three
carbonyls are sensitive to light and release CO when illuminated with
low-power UV (5–10 mW) and visible (λ > 350 nm, ∼100
mW) light. The sensitivity of <b>1–3</b> to light has
been assessed with respect to the number of pyridine groups in their
ligand frames. When a pyridine ring is replaced with quinoline, extended
conjugation in the ligand frame increases the absorptivity and makes
the resulting carbonyl <b>3</b> more sensitive to visible light.
These photosensitive CORMs (photoCORMs) have been employed to deliver
CO to myoglobin under the control of light. The superior stability
of <b>3</b> in aqueous media makes it a photoCORM suitable for
inducing vasorelaxation in mouse aortic muscle rings
