Photochemical reactions of a diamidocarbene: cyclopropanation of bromonaphthalene, addition to pyridine, and activation of sp3 C-H bonds.

We report unprecedented photochemistry for the diamidocarbene 1. Described within are the double cyclopropanation of 1-bromonaphthalene, the double addition to pyridine, and remarkably, the insertion into the unactivated sp3 C-H bonds of cyclohexane, tetramethylsilane, and n-pentane to give compounds 2-6, respectively. All compounds have been fully characterized, and the solid state structure of 4 was obtained using single crystal electron diffraction.

Serial block face scanning electron microscopy reveals region-dependent remodelling of transverse tubules post-myocardial infarction.

The highly organized transverse tubule (t-tubule) network facilitates cardiac excitation-contraction coupling and synchronous cardiac myocyte contraction. In cardiac failure secondary to myocardial infarction (MI), changes in the structure and organization of t-tubules result in impaired cardiac contractility. However, there is still little knowledge on the regional variation of t-tubule remodelling in cardiac failure post-MI. Here, we investigate post-MI t-tubule remodelling in infarct border and remote regions, using serial block face scanning electron microscopy (SBF-SEM) applied to a translationally relevant sheep ischaemia reperfusion MI model and matched controls. We performed minimally invasive coronary angioplasty of the left anterior descending artery, followed by reperfusion after 90 min to establish the MI model. Left ventricular tissues obtained from control and MI hearts eight weeks post-MI were imaged using SBF-SEM. Image analysis generated three-dimensional reconstructions of the t-tubular network in control, MI border and remote regions. Quantitative analysis revealed that the MI border region was characterized by t-tubule depletion and fragmentation, dilation of surviving t-tubules and t-tubule elongation. This study highlights region-dependent remodelling of the tubular network post-MI and may provide novel localized therapeutic targets aimed at preservation or restoration of the t-tubules to manage cardiac contractility post-MI. This article is part of the theme issue 'The cardiomyocyte: new revelations on the interplay between architecture and function in growth, health, and disease'.

Photochemically Switching Diamidocarbene Spin States Leads to Reversible Büchner Ring Expansions.

The discovery of thermal and photochemical control by Woodward and Hoffmann revolutionized how we understand chemical reactivity. Similarly, we now describe the first example of a carbene that exhibits differing thermal and photochemical reactivity. When a singlet ground-state N,N'-diamidocarbene 1 was photolyzed at 380 nm, excitation to a triplet state was observed. The triplet-state electronic structure was characteristic of the expected biradical σ1pπ1 spin configuration according to a combination of spectroscopic and computational methods. Surprisingly, the triplet state of 1 was found to engage a series of arenes in thermally reversible Büchner ring expansion reactions, marking the first examples where both cyclopropanation and ring expansion of arenes were rendered reversible. Not only are these photochemical reactions different from the known thermal chemistry of 1, but the reversibility enabled us to perform the first examples of photochemically induced arene exchange/expansion reactions at a single carbon center.

Photoreduction of Pt(IV) chloro complexes: substrate chlorination by a triplet excited state.

The Pt(IV) complexes trans-Pt(PEt3)2(Cl)3(R) 2 (R = Cl, Ph, 9-phenanthryl, 2-trifluoromethylphenyl, 4-trifluoromethylphenyl, 3-perylenyl) were prepared by chlorination of the Pt(II) complexes trans-Pt(PEt3)2(R)(Cl) 1 with Cl2(g) or PhICl2. Mixed bromo-chloro complexes trans,trans-Pt(PEt3)2(Cl)2(Br)(R) (R = 9-phenanthryl, 4-trifluoromethylphenyl), trans,cis-Pt(PEt3)2(Cl)2(Br)(4-trifluoromethylphenyl), trans,trans-Pt(PEt3)2(Br)2(Cl)(R) (R = 9-phenanthryl), and trans,cis-Pt(PEt3)2(Br)2(Cl)(4-trifluoromethylphenyl) were obtained by halide exchange or by oxidative addition of Br2 to 1 or Cl2 to trans-Pt(PEt3)2(R)(Br). Except for 2 (R = Ph, 4-trifluoromethylphenyl), all of the Pt(IV) complexes are photosensitive to UV light and undergo net halogen reductive elimination to give Pt(II) products, trans-Pt(PEt3)2(R)(X) (X = Cl, Br). Chlorine trapping experiments with alkenes indicate a reductive-elimination mechanism that does not involve molecular chlorine and is sensitive to steric effects at the Pt center. DFT calculations suggest a radical pathway involving (3)LMCT excited states. Emission from a triplet is observed in glassy 2-methyltetrahydrofuran at 77 K where photoreductive elimination is markedly slowed.