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Organic azides are valuable precursors in synthetic chemistry, particularly for nitrogen-based functionalization through photochemical activation. In this study, the photoreactivities of 4-azido-1-phenylbutan-1-one (1a) and 4-azido-(4-methoxy)phenylbutan-1-one (1b) were investigated using visible-light photocatalysts [Ir(dF(CF3)ppy)2(dtbpy)]PF6 and [Ru(bpy)3]Cl2 to elucidate the mechanistic differences between triplet energy transfer and photoreductive electron transfer pathways. Direct irradiation of 1a in methanol favors the formation of a biradical species via intramolecular H atom abstraction to generate its lowest triplet ketone (T1K) with an (n,π*) configuration, which selectively yields 2-phenyl-1-pyrroline derivative 2a. However, 1b reacts through its less reactive T1K, which has a (π,π*) configuration, to form 2-phenyl-1H-pyrrole as the major product. When sensitized by [Ir(dF(CF3)ppy)2(dtbpy)]PF6, selective excitation of the triplet azido moiety (TA) of both 1a and 1b yields the corresponding pyrroline (2a and 2b) via triplet alkylnitrene (31aN and31bN) formation. In contrast, photoactivation of [Ru(bpy)3]Cl2 in the presence of diisopropylethylamine (DIPEA) results in photoreductive electron transfer, forming azido radical anion intermediates, which cyclize to also yield 2a and 2b. Product studies, cyclic voltammetry, laser flash photolysis, and DFT calculations supported these mechanistic assignments. This work demonstrates complementary approaches to control alkyl azide photoreactivity and unlock new strategies for visible-light-induced nitrogen incorporation.
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Is the A-1 Pigment in Photosystem I Part of P700? A (P700+–P700) FTIR Difference Spectroscopy Study of A-1 Mutants
The involvement of the second pair of chlorophylls, termed A-1A and A-1B, in light-induced electron transfer in photosystem I (PSI) is currently debated. Asparagines at PsaA600 and PsaB582 are involved in coordinating the A-1B and A-1A pigments, respectively. Here we have mutated these asparagine residues to methionine in two single mutants and a double mutant in PSI from Synechocystis sp. PCC 6803, which we term NA600M, NB582M, and NA600M/NB582M mutants. (P700+–P700) FTIR difference spectra (DS) at 293 K were obtained for the wild-type and the three mutant PSI samples. The wild-type and mutant FTIR DS differ considerably. This difference indicates that the observed changes in the (P700+–P700) FTIR DS cannot be due to only the PA and PB pigments of P700. Comparison of the wild-type and mutant FTIR DS allows the assignment of different features to both A-1 pigments in the FTIR DS for wild-type PSI and assesses how these features shift upon cation formation and upon mutation. While the exact role the A-1 pigments play in the species we call P700 is unclear, we demonstrate that the vibrational modes of the A-1A and A-1B pigments are modified upon P700+ formation. Previously, we showed that the A-1 pigments contribute to P700 in green algae. In this manuscript, we demonstrate that this is also the case in cyanobacterial PSI. The nature of the mutation-induced changes in algal and cyanobacterial PSI is similar and can be considered within the same framework, suggesting a universality in the nature of P700 in different photosynthetic organisms.
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- Award ID(s):
- 2313482
- PAR ID:
- 10516017
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- International Journal of Molecular Sciences
- Volume:
- 25
- Issue:
- 9
- ISSN:
- 1422-0067
- Page Range / eLocation ID:
- 4839
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/ijms25094839
