Heavy atom-free BODIPY-anthracene dyads (BADs) generate locally excited triplet states by way of photoinduced electron transfer (PeT), followed by recombination of the resulting charge-separated ...states (CSS). Subsequent quenching of the triplet states by molecular oxygen produces singlet oxygen (1O2), which reacts with the anthracene moiety yielding highly fluorescent species. The steric demand of the alkyl substituents in the BODIPY subunit defines the site of 1O2 addition. Novel bis- and tetraepoxides and bicyclic acetal products, arising from rearrangements of anthracene endoperoxides were isolated and characterized. 1O2 generation by BADs in living cells enables visualization of the dyads distribution, promising new imaging applications.
The selectivity and functional variability of porphyrin cofactors are typically based on substrate binding of metalloporphyrins wherein the pyrrole nitrogen units only serve to chelate the metal ...ions. Yet, using the porphyrin inner core system for other functions is possible through conformational engineering. As a first step towards porphyrin “enzyme‐like” active centers, a structural and spectroscopic study of substrate binding to the inner core porphyrin system shows that a highly saddle‐distorted porphyrin with peripheral amino receptor groups (1, 2,3,7,8,12,13,17,18‐octaethyl‐5,10,15,20‐tetrakis(2‐aminophenyl)porphyrin) coordinates analytes in a switchable manner dependent on the acidity of the solution. The supramolecular ensemble exhibits exceptionally high affinity to and selectivity for the pyrophosphate anion (2.26±0.021)×109 m−1. 1H NMR spectroscopic studies provided insight into the likely mode of binding and the characterization of atropisomers, all four of which were also studied by X‐ray crystallography.
An acid‐activated porphyrin probe for small‐molecule detection is demonstrated, highlighting the colorimetric change of the binding event. The key feature is substrate coordination to the inner core system assisted via peripheral interactions.
N‐substitution of porphyrins has been a neglected route towards nonplanar porphyrins for the past decades. Previously, they featured in a host of potential medicinal and biochemical applications. ...However, tailored syntheses of N‐methylated porphyrins, improvements of synthetic methodology, or full conformational analyses were lacking since the initial studies. Here we investigated and optimized synthetic pathways to generate specific N‐methylated porphyrins exclusively and in good yields. Full characterizations of the spectroscopy and structural properties associated with the insertion of different numbers of methyl into the porphyrin core of 5,10,15,20‐tetrasubstituted A4‐ and 5,15‐disubstituted A2‐type porphyrins was carried out by using UV/Vis, NMR, and X‐ray crystallographic techniques. The latter, in conjunction with detailed normal structural decomposition analyses, identified the structural consequences of number and isomeric pattern of N‐methylation in terms of macrocycle nonplanarity and the underlying out‐of‐plane and in‐plane distortion modes.
Optimized alkylation conditions allow the facile synthesis of porphyrins with various degrees of N‐methylation and investigation of their unique structural characteristics reveals means to control the N‐substitution pattern depending on peripheral substitution macrocycle type.
Previous studies by Desiraju and co‐workers have implicated the acidic hydrogen atoms of cubane as a support network for hydrogen bonding groups. Herein we report a detailed structural analysis of ...all currently available 1,4‐disubstituted cubane structures with an emphasis on how the cubane scaffold interacts in its solid‐state environment. In this regard, the interactions between the cubane hydrogen atoms and acids, ester, halogens, ethynyl, nitrogenous groups, and other cubane scaffolds were cataloged. The goal of this study was to investigate the potential of cubane as a substitute for phenyl. This could be achieved by analyzing all contacts that are directed by the cubane hydrogen atoms in the X‐ray crystal structures. As a result, we have established several new cubane interaction profiles, such as the catemer formation seen in esters, the preferences of halogen–hydrogen contacts over direct halogen bonding, and the stabilizing effects caused by the cubane hydrogen atoms interacting with ethynyl groups. These interaction profiles can then be used as a guide for designing cubane bioisosteres of known materials and drugs containing phenyl moieties.
How the dice rolls: Cubanes have been successfully used as bioisosteres for benzene rings, but most of these studies rely on the fact that the 1,4‐axis of both these compounds are of similar length. However, with its 3D geometry, cubane has a significant difference in the types of interactions that occur in comparison to benzene. Here, we highlight the differences by an in‐depth study on cubane–hydrogen interaction profiles with multiple functional groups.
Herein we report the synthesis of 5,10,15,20-tetraaryl-(X)-substituted-2,3,7,8,12,13,17,18-octaethylporphyrins (OETArXPs) and a structural investigation of their solid-state properties via small ...molecule X-ray diffraction. A series of halogen (fluorine to iodine), nitrogenous (azido, cyano), alkyl (TMS-acetylene and acetylene), and chained (benzyloxy) porphyrins were chosen as the initial target molecules. Following this, a selection of tetravalent metal complexes Cu(II), Ni(II), and Pd(II) based on these porphyrins were synthesized to allow for an investigation of the effects of metal complexes on the structural properties of these highly substituted porphyrins. The size of the halogen atom affects the potential of intermolecular interactions and the resulting crystal packing in these 4-halo-OETArXP complexes. The fluorine series have an equal preference for alkyl or aryl groups (ortho-hydrogen), the chlorine series favor interactions between the alkyl groups, and the bromine appears to favor the aryl (ortho- and meta-hydrogens). This results in an extensive cupping pattern in the unit cell. For the 2,6-halo-OETArXP it was established that the change in position alters the types of the intermolecular contacts toward face-to-edge or face-to-face interactions and alters the packing patterns observed. Within the 4-benzyloxy-OETArXP series the meso-substituent favors interacting with the core of the porphyrin macrocycle. The 4-cyano-OETArXP is a suitable hydrogen-bond acceptor and results in an interesting Z-shape network. Additionally, it was highlighted that solvent effects play a much larger role in crystal packing than intermolecular/intramolecular interaction or metal(II) center substitution. This is accompanied by a study using both the azide- and acetylene-OETArXPs as a base molecule to allow for a quick one-step reaction for the generation of a variety of functionalized compounds. Using a copper(I)-catalyzed azide–alkyne cycloaddition reaction, we were able to append hydrogen bonding functionalities to the OETArXPs framework in high yields. The crystal packing images included in this work shows the potential to create selective and functional receptor sites based on free base porphyrins. However, insofar as analytical measurements indicate, the design of such a free base porphyrin through crystal engineering has not yet been realized. The variety of porphyrin packing arrangements herein indicates the need for further studies.
The generation of bio‐targetable photosensitizers is of utmost importance to the emerging field of photodynamic therapy and antimicrobial (photo‐)therapy. A synthetic strategy is presented in which ...chelating dipyrrin moieties are used to enhance the known photoactivity of iridium(III) metal complexes. Formed complexes can thus be functionalized in a facile manner with a range of targeting groups at their chemically active reaction sites. Dipyrrins with N‐ and O‐substituents afforded (dipy)iridium(III) complexes via complexation with the respective Cp*‐iridium(III) and ppy‐iridium(III) precursors (dipy=dipyrrinato, Cp*=pentamethyl‐η5‐cyclopentadienyl, ppy=2‐phenylpyridyl). Similarly, electron‐deficient IrIII(dipy)(ppy)2 complexes could be used for post‐functionalization, forming alkenyl, alkynyl and glyco‐appended iridium(III) complexes. The phototoxic activity of these complexes has been assessed in cellular and bacterial assays with and without light; the IrIII(Cl)(Cp*)(dipy) complexes and the glyco‐substituted iridium(III) complexes showing particular promise as photomedicine candidates. Representative crystal structures of the complexes are also presented.
Heteroleptic dipyrrinato iridium complexes were synthesized and evaluated for their phototoxic activity against tumor cells and bacteria, the Gram‐positive germ S. aureus and the Gram‐negative Germ P. aeruginosa. Specifically, glycosylated phenylpyridyl‐dipyrrinato complexes showed a high phototoxic effect against cells and S. aureus. Certain cyclopentadienyl‐dipyrrinato complexes exerted a high phototoxic effect on S. aureus and P. aeruginosa.
A targeted synthesis of dodecasubstituted type I porphyrins that utilizes the reaction of unsymmetrical 3,4-difunctionalized pyrroles and sterically demanding aldehydes was developed. This way, type ...I porphyrins could be obtained as the only type isomers, likely due to a minimization of the steric strain arising from peri-interactions. Uniquely, this method does not depend on lengthy precursor syntheses, the separation of isomers, or impractical limitations of the scale. In addition, single-crystal X-ray analysis was used to elucidate the structural features of the macrocycles.
Cubane Cross‐Coupling and Cubane–Porphyrin Arrays Bernhard, Stefan S. R.; Locke, Gemma M.; Plunkett, Shane ...
Chemistry : a European journal,
January 24, 2018, Letnik:
24, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Herein, an improved methodology for aryl‐cubane cross‐coupling is reported. The peculiarities of the cubane core and its behavior during cross‐coupling conditions were analyzed, while the versatility ...of this adapted Baran cross‐coupling methodology was demonstrated by the synthesis of various aryl‐cubane systems, including coupling products of cubanes and porphyrins. Furthermore, arm extension of alkynyl‐cubanes by Sonogashira reactions is demonstrated, showcasing the first proof of the stability of the cubane core in the presence of palladium catalysts.
Alea Iacta Est: The compatibility of cubanes and transition metals (Ni, Pd) was explored, and a direct arylation of cubanes via a Baran‐type nickel‐catalyzed radical cross‐coupling and arm‐extended Sonogashira coupling of alkynyl‐cubanes is reported. Furthermore, the first series of cubane–porphyrins was prepared (see figure).
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