Modulations of a Metal-Ligand Interaction and Photophysical Behaviors by Hückel-Möbius Aromatic Switching

Metalla-Carbaporphyrinoids Consisting of an Acyclic N-Confused Tetrapyrrole Analogue Served as Stable Near-Infrared-II Dyes

We present herein the synthesis of novel pseudo-metalla-carbaporphyrinoid species (1M: M=Pd and Pt) achieved through the inner coordination of palladium(II) and platinum(II) with an acyclic N-confused tetrapyrrin analogue. Despite their tetrapyrrole frameworks being small, akin to well-known porphyrins, these species exhibit an unusually narrow HOMO-LUMO gap, resulting in an unprecedentedly low-energy absorption in the second near-infrared (NIR-II) region. Density functional theory (DFT) calculations revealed unique dπ-pπ-conjugated electronic structures involving the metal dπ-ligand pπ hybridized molecular orbitals of 1M. Magnetic circular dichroism (MCD) spectroscopy confirmed distinct electronic structures. Remarkably, the complexes feature an open-metal coordination site in the peripheral NN dipyrrin site, forming hetero-metal complexes (1Pd-BF2 and 1Pt-BF2) through boron difluoride complexation. The resulting hetero metalla-carbaporphyrinoid species displayed further redshifted NIR-II absorption, highly efficient photothermal conversion efficiencies (η; 62-65 %), and exceptional photostability. Despite the challenges associated with the theoretical and experimental assessment of dπ-pπ-conjugated metalla-aromaticity in relatively larger (more than 18π electrons) polycyclic ring systems, these organometallic planar tetrapyrrole systems could serve as potential molecular platforms for aromaticity-relevant NIR-II dyes.

How to ablate the septo-pulmonary bundle: a case-based review of percutaneous ablation strategies to achieve roof line block

Electrical conduction through cardiac muscle fibres separated from the main myocardial wall by layers of interposed adipose tissue are notoriously difficult to target by endocardial ablation alone. They are a recognised important cause for procedural failure due to the difficulties of delivering sufficient energy via the endocardial radiofrequency catheter to reach the outer epicardial layer without risking adverse events of the otherwise thin walled atria. Left atrial ablations for atrial fibrillation (AF) and tachycardia are commonly affected by the presence of several epicardial structures, with the septo-pulmonary bundle (SPB), Bachmann's bundle, and the ligament of Marshall all posing substantial challenges for endocardial procedures. Delivery of a transmural lesion set is essential for sustained pulmonary vein isolation and for conduction block across linear atrial lines which in turn has been described to translate into a reduced AF/atrial tachycardia recurrence rate. To overcome the limitations of endocardial-only approaches, surgical ablation techniques for epicardial or combined hybrid endo-epicardial ablations have been described to successfully target these connections. Yet, these techniques confer an increase in procedure complexity, duration, cost, and morbidity. Alternatively, coronary venous system ethanol ablation has been successfully employed by sub-selecting the vein of Marshall to facilitate mitral isthmus line block, although this approach is naturally limited to this area by the coronary venous anatomy. Increased awareness of the pathophysiological relevance of these epicardial structures and their intracardiac conduction patterns in the era of high-resolution 3D electro-anatomical mapping technology has allowed greater understanding of their contribution to the persistence of AF as well as failure to achieve transmural block by traditional ablation approaches. This might translate into novel catheter ablation strategies with procedural success rates comparable to surgical 'cut-and-sew' techniques. This review aims to give an overview of percutaneous catheter ablation strategies to target the SPB, an important cause of failed block across the roof line and isolation of the left atrial posterior wall and/or the pulmonary veins. Existing and investigational technologies will be discussed and an outlook of future approaches provided.

Effect of fibrosis regionality on atrial fibrillation recurrence: insights from DECAAF II

AIMS

The amount of fibrosis in the left atrium (LA) predicts atrial fibrillation (AF) recurrence after catheter ablation (CA). We aim to identify whether regional variations in LA fibrosis affect AF recurrence.

METHODS AND RESULTS

This post hoc analysis of the DECAAF II trial includes 734 patients with persistent AF undergoing first-time CA who underwent late gadolinium enhancement magnetic resonance imaging (LGE-MRI) within 1 month prior to ablation and were randomized to MRI-guided fibrosis ablation in addition to standard pulmonary vein isolation (PVI) or standard PVI only. The LA wall was divided into seven regions: anterior, posterior, septal, lateral, right pulmonary vein (PV) antrum, left PV antrum, and left atrial appendage (LAA) ostium. Regional fibrosis percentage was defined as a region's fibrosis prior to ablation divided by total LA fibrosis. Regional surface area percentage was defined as an area's surface area divided by the total LA wall surface area before ablation. Patients were followed up for a year with single-lead electrocardiogram (ECG) devices. The left PV had the highest regional fibrosis percentage (29.30 ± 14.04%), followed by the lateral wall (23.23 ± 13.56%), and the posterior wall (19.80 ± 10.85%). The regional fibrosis percentage of the LAA was a significant predictor of AF recurrence post-ablation (odds ratio = 1.017, P = 0.021), and this finding was only preserved in patients receiving MRI-guided fibrosis ablation. Regional surface area percentages did not significantly affect the primary outcome.

CONCLUSION

We have confirmed that atrial cardiomyopathy and remodelling are not a homogenous process, with variations in different regions of the LA. Atrial fibrosis does not uniformly affect the LA, and the left PV antral region has more fibrosis than the rest of the wall. Furthermore, we identified regional fibrosis of the LAA as a significant predictor of AF recurrence post-ablation in patients receiving MRI-guided fibrosis ablation in addition to standard PVI.

Highly Robust and Antiaromatic Rhenium(I) Rosarin

1ReH•Cl, a highly robust and antiaromatic rhenium(I) complex of triarylrosarin, is synthesized. The ¹H NMR spectrum of 1ReH•Cl shows upfield-shifted pyrrole protons and highly downfield-shifted inner protons that confirm its antiaromatic nature, with density functional theory calculations strongly supporting this interpretation. Antiaromatic 1ReH•Cl absorbs from the UV to near-IR region of the optical spectrum; cyclic voltammetry, thin-layer UV-vis spectroelectrochemistry, and spin-density distributions clearly reveal that the rosarin backbone of 1ReH•Cl undergoes redox chemistry. The X-ray structure of 1ReH•Cl shows a fully coordinated and protonated inner cavity that effectively prevents proton-coupled electron transfer when treated with an acid. A remarkably negative NICS(0) value, clockwise anisotropy of the induced current density ring current, and the aromatic shielded inner cavity in the 2D ICSS(0) map reveal that the T₁ state of 1ReH•Cl is aromatic based on Baird's rule.