The methoxy‐ and fluoro‐derivatives of meta‐nitrophenylacetic acid (mNPA) chromophores undergo photodecarboxylation with comparable quantum yields (Φ) to unsubstituted mNPA, but uncage at red‐shifted excitation wavelengths. This observation prompted us to investigate DPAdeCageOMe (2‐[bis(pyridin‐2‐ylmethyl)amino]‐2‐(4‐methoxy‐3‐nitrophenyl)acetic acid) and DPAdeCageF (2‐[bis(pyridin‐2‐ylmethyl)amino]‐2‐(4‐fluoro‐3‐nitrophenyl)acetic acid) as Zn2+ photocages. DPAdeCageOMe has a high Φ and exhibits other photophysical properties comparable to XDPAdeCage ({bis[(2‐pyridyl)methyl]amino}(9‐oxo‐2‐xanthenyl) acetic acid), the best preforming Zn2+ photocage reported to date. Since the synthesis of DPAdeCageOMe is more straightforward than XDPACage, the new photocage will be a highly competitive tool for biological applications.
CTEA (N,N-bis[2-(carboxylmethyl)thioethyl]amine) is a mixed donor ligand that has been incorporated into multiple fluorescent sensors such as NiSensor-1 that was reported to be selective for Ni 2+ . Other metal ions such as Zn 2+ do not produce an emission response in aqueous solution. To investigate the coordination chemistry and selectivity of this receptor, we prepared NiCast, a photocage containing the CTEA receptor. Cast photocages undergo a photoreaction that decreases electron density on a metal-bound aniline nitrogen atom, which shifts the binding equilibrium toward unbound metal ion. The unique selectivity of CTEA was examined by measuring the binding affinity of NiCast and the CTEA receptor for Ni 2+ , Zn 2+ , Cd 2+ and Cu 2+ under different conditions. In aqueous solution, Ni 2+ binds more strongly to the aniline nitrogen atom than Cd 2+ ; however, in CH 3 CN, the change in affinity virtually disappears. The crystal structure of [Cu(CTEA)], which exhibits a Jahn-Teller-distorted square pyramidal structure, was also analyzed to gain more insight into the underlying coordination chemistry. These studies suggest that the fluorescence selectivity of NiSensor-1 in aqueous solution is due to a stronger interaction between the aniline nitrogen atom and Ni 2+ compared to other divalent metal ions except Cu 2+ .
MorphDeCage (2-(4-methoxy-3-nitrophenyl)-2-morpholinoacetic acid) and PyrDeCage (2-(4-methoxy-3-nitrophenyl)-2-(methyl(pyridin-2-ylmethyl)amino)acetic) are Zn 2 + photocages that utilize photodecarboxylation of the methoxy derivative of metanitrophenylacetic acid as the release mechanism. Isothermal titration calorimetry (ITC) was used an alternative to usual approaches to measure the Zn 2 + binding affinities of these new compounds owing to unsuccessful measurement by competitive titration with 4-(2-pyridylazo)resorcinol (PAR). MorphDe-Cage forms a 1 : 1 ligand-metal complex with a 106 μM K d value.PyrDeCage forms both a 1 : 1 and 1 : 2 metal: ligand complexes with 3.2 and 21.7 μM K d values respectively. To further demonstrate the efficacy of the ITC methodology and provide a comparison to direct UV-vis titrations data, two photocages based on Sanger's reagent (SRPs) were prepared. The K d values of the SRPs measured by UV-vis titration and ITC were internally consistent and support the retraction of the original report (J.
The methoxy- and fluoro-derivatives of meta-nitrophenylacetic acid (mNPA) chromophores undergo photodecarboxylation with comparable quantum yields to unsubstituted mNPA, but uncage at red-shifted excitation wavelengths. This observation prompted us to investigate DPAdeCageOMe (2-[bis(pyridin-2-ylmethyl)amino]-2-(4-methoxy-3-nitrophenyl)acetic acid) and DPAdeCageF (2-[bis(pyridin-2-ylmethyl)amino]-2-(4-fluoro-3-nitrophenyl)acetic acid) as Zn2+ photocages. DPAdeCageOMe has a high quantum yield and exhibits other photophysical properties comparable to XDPAdeCage ({bis[(2-pyridyl)methyl]amino}(9-oxo-2-xanthenyl) acetic acid), the best perforiming Zn2+ photocage reported to date. Since the synthesis of DPAdeCageOMe is more straightforward than XDPACage, the new photocage will be a highly competitive tool for biological applications.
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