Two monosubstituted and one tetrasubstituted N-confused porphyrins (1-3) were prepared in ca. 3-5% yields using a [2 + 2] synthesis. The monosubstituted porphyrins have carbomethoxy (1) or nitro (2) substituents on one of the meso-phenyl groups, while the meso-phenyl groups of the third NCP (3) are substituted with nitro, bromo, and methyl groups in an AB(2)C pattern. The specific regiochemistry of the aryl rings around the macrocycle in each porphyrin was definitively determined using a combination of 1D ((1)H and (13)C) and 2D (gHMBC, gHSQC and ROESY) NMR spectroscopy. The absorption spectra of 1-3 in CH(2)Cl(2) are similar to those of N-confused tetraphenylporphyrin (NCTPP) but have Soret and Q bands that are shifted to lower energies with smaller extinction coefficients in comparison to those for NCTPP.
Some of us have previously reported the preparation of a dimeric form of the iron storage protein, bacterioferritin (Bfr), in which the native heme b is substituted with the photosensitizer, Zn(II)-protoporphyrin IX (ZnPP-Bfr dimer). We further showed that the ZnPP-Bfr dimer can serve as a photosensitizer for platinum-catalyzed H 2 generation in aqueous solution without the usually added electron relay between photosensitizer and platinum (Clark, E. R., et al. Inorg. Chem. 2017, 56, 4584−4593). We proposed reductive or oxidative quenching pathways involving the ZnPP anion radical (ZnPP •− ) or the ZnPP cation radical, (ZnPP •+ ), respectively. The present report describes structural, photophysical, and photochemical properties of the ZnPP in the ZnPP-Bfr dimer. X-ray absorption spectroscopic studies at 10 K showed a mixture of fiveand six-coordinated Zn centers with axial coordination by one long Zn−SγMet distance of ∼2.8 Å and ∼40% having an additional shorter Zn−S distance of ∼2.4 Å, in addition to the expected 4 nitrogen atom coordination from the porphyrin. The ZnPP in ZnPP-Bfr dimer was prone to photosensitized oxidation to ZnPP •+ . The ZnPP •+ was rapidly reduced by ascorbic acid, which we previously determined was essential for photosensitized H 2 production in this system. These results are consistent with an oxidative quenching pathway involving electron transfer from 3 ZnPP* to platinum, which may be assisted by a flexible ZnPP axial coordination sphere. However, the low quantum yield for H 2 production (∼1%) in this system could make reductive quenching difficult to detect, and can, therefore, not be completely ruled out. The ZnPP-Bfr dimer provides a simple but versatile framework for mechanistic assessment and optimization of porphyrin-photosensitized H 2 generation without an electron relay between porphyrin and the platinum catalyst.
The pyrophosphate anion (PPi) plays
an important role in biochemical
processes. Therefore, a simple but reliable analytical technique is
essential for selective detection of PPi in biochemical systems. Here,
we present a principal component analysis (PCA) method for analytical
determination of PPi concentration using a fluorescent conjugated
polyelectrolyte (CPE) combined with a polyamine modifier. The CPE
has anionic side chains and dissolves molecularly in water, as indicated
by its structured fluorescence emission spectrum. However, addition
of tris(3-aminoethyl)amine (tetraamine or
N4
) quenches
the CPE fluorescence emission. Tetraamine, which is a polycation at
neutral pH, binds multiple anionic CPE chains, leading to aggregate
formation, resulting in aggregation-induced fluorescence quenching.
Addition of PPi to the polymer–amine aggregate reverses the
process, resulting in fluorescence recovery. The relatively higher
concentration of PPi compared to that of the polymer allows it to
effectively compete to bind the amine, thus releasing molecularly
dissolved polymer chains. Fluorescence correlation spectroscopy of
the
P1
/
N4
complex and of
P1
/
N4
/PPi confirms the change in size of the CPE aggregates
that occurs upon reversible aggregation. Application of PCA to the
fluorescence emission data set of standard samples yields two principal
components, which are used to create a predictive model for PPi analysis.
The PCA method is able to directly determine the concentration of
PPi with approximately 95% accuracy within the concentration range
from 100 μM to 3 mM, without the need for a reference state
as is typically needed for ratiometric fluorescence assays.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.