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1. Synthesis, Protonation and Aromatic Characteristics of a Series of 1,10-Phenanthroline-Fused Porphyrinoids

   https://doi.org/10.1021/acs.joc.4c01511  

   Ujah, Victoria C; AbuSalim, Deyaa I; Lash, Timothy D (January 2025, The Journal of Organic Chemistry)

   A series of porphyrin analogues with fused 1,10-phenanthroline units were synthesized. The proton NMR spectra for phenanthroline-fused heteroporphyrins showed significantly upfield shifted meso-proton resonances compared to related porphyrinoid systems and the peaks corresponding to alkyl substituents directly attached to these macrocycles were also observed further upfield. These results indicate that the presence of the phenanthroline unit leads to reduced diatropicity, but the internal NH resonance was also further upfield, a result that is inconsistent with this interpretation. A phenanthrene-fused carbaporphyrin gave an unexpectedly upfield singlet for the internal C−H at nearly −9 ppm, while the NH protons appeared at −6.8 ppm. These unusual chemical shifts again imply enhanced diatropicity but the reduced downfield shifts for the external protons indicates that the aromatic ring current has been significantly reduced. Similar results were obtained for phenanthroline-fused oxybenzi- and oxypyriporphyrins. Detailed analyses of the spectroscopic properties for these systems are reported and protonation studies were conducted. The conjugation pathways and aromatic properties were computationally analyzed using nucleus independent chemical shifts (NICS) and anisotropy of induced current density plots. 

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2. A water-soluble iron-porphyrin complex capable of rescuing CO-poisoned red blood cells

   https://doi.org/10.1039/D1CC05542A  

   Droege, Daniel G.; Johnstone, Timothy C. (February 2022, Chemical Communications)

   We describe herein a small-molecule platform that exhibits key properties needed by an antidote for CO poisoning. The design features an iron-porphyrin complex with bulky substituents above and below the macrocyclic plane to provide a hydrophobic pocket for CO binding and to prevent the formation of inactive oxo-bridged dimers. Peripheral charged groups impart water solubility. We demonstrate that the Fe( ii ) complex of a porphyrin with 2,6-diphenyl-4-sulfophenyl meso substituents can bind CO, stoichiometrically sequester CO from carboxyhemoglobin, and rescue CO-poisoned red blood cells. 

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3. Carbonyl-to-Alkyne Electron Donation Effects in up to 10-nm-Long, Unimolecular Oligo(p-phenylene ethynylenes)

   https://doi.org/10.1055/s-0041-1730899  

   Rajappan, Sinu C.; Vestrheim, Olav; Sharafi, Mona; Li, Jianing; Schneebeli, Severin T. (April 2021, Organic Materials)

   null (Ed.)

   We synthesized some of the longest unimolecular oligo(p-phenylene ethynylenes) (OPEs), which are fully substituted with electron-withdrawing ester groups. An iterative convergent/divergent (a.k.a. iterative exponential growth – IEG) strategy based on Sonogashira couplings was utilized to access these sequence-defined macromolecules with up to 16 repeating units and 32 ester substituents. The carbonyl groups of the ester substituents interact with the triple bonds of the OPEs, leading to (i) unusual, angled triple bonds with increased rotational barrier, (ii) enhanced conformational disorder, and (iii) associated broadening of the UV/Vis absorption spectrum. Our results demonstrate that fully air-stable, unimolecular OPEs with ester groups can readily be accessed with IEG chemistry, providing new macromolecular backbones with unique geometrical, conformational, and photophysical properties. 

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4. Fluoro-2,6-dimethylphenyl mono-hydroxychlorin and porphyrin congeners

   https://doi.org/10.1142/S1088424623501213  

   Brown, Cierra; Campbell, Brandon M; Chen, Tina; Darkwa, Richard K; Kim, Geena; Kranchalk, Danielle J; Lamport, Hannah; Le, Colin M-D; Lu, Jenny; McKnight, Giovan N; et al (December 2023, Journal of Porphyrins and Phthalocyanines)

   Mono-hydroxychlorins are uncommon macrocycles that have only been synthetically realized by modifying porphyrin rings using the harsh oxidizing agent OsO₄. We show here that a more directed delivery of the mono-hydroxychlorin may be concomitantly obtained from the oxidation of porphyrinogen using the mild conditions of the high dilution Lindsey porphyrin forming reaction where water content is minimized by using dry CHCl₃within the environment of a glovebox. We now report the direct synthesis of 17,18-dihydro-18-hydroxy-5,10,15,20-tetrakis-(4-fluoro,2,6-dimethylphenyl)-porphyrin (2H-TFChl-[Formula: see text]OH) together with the corresponding freebase porphyrin TFP. The TFP has been metalated with FeBr₂and MgBr₂•OEt₂resulting in metalloporphyrins Fe(III)TFP(Cl) and Mg(II)-TFP which have been structurally characterized by single-crystal X-ray crystallography. We find that the excited state properties of the mono-hydroxychlorin are similar to that of its parent TFP and Mg(II)TFP porphyrin congeners. Excited state deactivation by vibronic coupling to the high energy O-H oscillator is circumvented with the hydroxyl group remote to the 18[Formula: see text]-electron framework of the chlorin ring. These results reveal that strong H-bonding groups may be introduced on the periphery of the chlorin ring while maintaining the light-gathering properties that lie at the heart of photosynthesis of the chlorin ring. 

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5. Serendipitous Discovery of Conjugated Dipyrromethene-Linked Nitronaphthoporphyrins

   https://doi.org/10.1021/acs.joc.4c00824  

   Lash, Timothy D; Salrin, Jared S (July 2024, The Journal of Organic Chemistry)

   Acid-catalyzed condensation of a nitronaphthalene-fused dipyrrylmethane with dipyrrylmethane dialdehydes afforded unique dipyrromethene-naphthoporphyrin conjugates together with expected nitronaphthoporphyrins. The unusual conjugated system retained aromatic porphyrin-type characteristics but afforded highly modified UV−vis spectra with multiple absorptions throughout the visible region. 

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