Covalently linked dimers (CLDs) and their structural isomers have attracted much attention as potential materials for improving power conversion efficiencies through singlet fission (SF). Here, we designed and synthesized two covalently ortho-linked pyrene (Py) dimers, anti- and syn-1,2-di(pyrenyl)benzene (Anti-DPyB and Syn-DPyB, respectively), and investigated the effect of molecular configuration on SF dynamics using steady-state and time-resolved spectroscopies. Both Anti-DPyB and Syn-DPyB, which have different Py-stacking configurations, form excimers, which then relax to the correlated triplet pair ((T1T1)) state, indicating the occurrence of SF. Unlike previous studies where the excimer formation inhibited an SF process, the (T1T1)’s of Anti-DPyB and Syn-DPyB are formed through the excimer state. The dissociation of (T1T1)’s to 2T1 in Anti-DPyB is more favorable than in Syn-DPyB. Our results showcase that the molecular configuration of a CLD plays an important role in SF dynamics.
The catalytic redox activity of Cu(II) bound to the amino-terminal copper and nickel (ATCUN) binding motif (Xxx-Zzz-His, XZH) is stimulating the development of catalytic metallodrugs based on reactive oxygen species (ROS)-mediated biomolecule oxidation. However, low Cu(I) availability resulting from the strong Cu(II) binding affinity of the ATCUN motif is regarded as a limitation to efficient ROS generation. To address this, we replaced the imidazole moiety (pK a 7.0) of Gly−Gly− His−NH 2 (GGHa, a canonical ATCUN peptide) with thiazole (pK a 2.7) and oxazole (pK a 0.8), yielding GGThia and GGOxa, respectively. A newly synthesized amino acid, Fmoc-3-(4oxazolyl)-L-alanine, served as a histidine surrogate featuring an azole ring with the lowest pK a among known analogues. Despite similar square-planar Cu(II)−N 4 geometries being observed for the three Cu(II)−ATCUN complexes by electron paramagnetic resonance spectroscopy and X-ray crystallography, the azole modification enabled the Cu(II)−ATCUN complexes to exhibit significant rate enhancement for ROS-mediated DNA cleavage. Further analyses based on Cu(I)/Cu(II) binding affinities, electrochemical measurements, density functional theory calculations, and X-ray absorption spectroscopy indicated that the azole modification enhanced the accessibility of the Cu(I) oxidation state during ROS generation. Our oxazole/thiazole-containing ATCUN motifs provide a new design strategy for peptide ligands with modulated N donor ability, with potential applications in the development of ROS-mediated metallodrugs.
Natural metalloenzymes stabilize metal centers by utilizing multiple imidazole moieties. Inspired by nature's design principles, the introduction of multiple azoles into ligands has been an effective method for constructing transition metal complexes.Herein, we describe a post-synthetic modification of peptoids to incorporate multiple azoles on side chains. A simple substitution reaction between an azole (imidazole, pyrazole, 1,2,3-triazole, and tetrazole) and a chloroalkyl-containing peptoid provided access to a variety of azole-containing peptoids. Ten azole-containing peptoids were synthesized from a single chloroalkyl-containing peptoid, and the efficiency of each azole for the substitution reaction was evaluated. We have identified that several of the azole-containing peptoids are capable of binding with Cu(II) and Fe(III). Our synthetic approach can contribute to the expansion of peptoids' chemical diversity and the development of novel peptoids for metal recognition and catalysis.
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