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1. Light‐responsive and Protic Ruthenium Compounds Bearing Bathophenanthroline and Dihydroxybipyridine Ligands Achieve Nanomolar Toxicity towards Breast Cancer Cells †

   https://doi.org/10.1111/php.13508  

   Oladipupo, Olaitan E. ; Brown, Spenser R. ; Lamb, Robert W. ; Gray, Jessica L. ; Cameron, Colin G. ; DeRegnaucourt, Alexa R. ; Ward, Nicholas A. ; Hall, James Fletcher ; Xu, Yifei ; Petersen, Courtney M. ; et al ( November 2021 , Photochemistry and Photobiology)

   We report new ruthenium complexes bearing the lipophilic bathophenanthroline (BPhen) ligand and dihydroxybipyridine (dhbp) ligands which differ in the placement of the OH groups ([(BPhen)₂Ru(n,n′‐dhbp)]Cl₂withn = 6 and 4 in 1_Aand 2_A, respectively). Full characterization data are reported for 1_Aand 2_Aand single crystal X‐ray diffraction for 1_A. Both 1_Aand 2_Aare diprotic acids. We have studied 1_A, 1_B, 2_A, and 2_B(B = deprotonated forms) by UV‐vis spectroscopy and 1 photodissociates, but 2 is light stable. Luminescence studies reveal that the basic forms have lower energy³MLCT states relative to the acidic forms. Complexes 1_Aand 2_Aproduce singlet oxygen with quantum yields of 0.05 and 0.68, respectively, in acetonitrile. Complexes 1 and 2 are both photocytotoxic toward breast cancer cells, with complex 2 showing EC₅₀light values as low as 0.50 μM with PI values as high as >200vs. MCF7. Computational studies were used to predict the energies of the³MLCT and³MC states. An inaccessible³MC state for 2_Bsuggests a rationale for why photodissociation does not occur with the 4,4′‐dhbp ligand. Low dark toxicity combined with an accessible³MLCT state for¹O₂generation explains the excellent photocytotoxicity of 2.

    

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2. Unlocking the Potential of Ru(II) Dual‐action Compounds with the Power of the Heavy‐atom Effect †

   https://doi.org/10.1111/php.13573  

   Toupin, Nicholas P. ; Steinke, Sean J. ; Herroon, Mackenzie K. ; Podgorski, Izabela ; Turro, Claudia ; Kodanko, Jeremy J. ( December 2021 , Photochemistry and Photobiology)

   We report the synthesis, photochemical and biological characterization of two new Ru(II) photoactivated complexes based on [Ru(tpy)(Me₂bpy)(L)]²⁺(tpy = 2,2':6',2''‐terpyridine, Me₂bpy = 6,6'‐dimethyl‐2,2'‐bipyridine), where L = pyridyl‐BODIPY (pyBOD). Two pyBOD ligands were prepared bearing flanking hydrogen or iodine atoms. Ru(II)‐bound BODIPY dyes show a red‐shift of absorption maxima relative to the free dyes and undergo photodissociation of BODIPY ligands with green light irradiation. Addition of iodine into the BODIPY ligand facilitates intersystem crossing, which leads to efficient singlet oxygen production in the free dye, but also enhances quantum yield of release of the BODIPY ligand from Ru(II). This represents the first report of a strategy to enhance photodissociation quantum yields through the heavy‐atom effect in Ru(II) complexes. Furthermore, Ru(II)‐bound BODIPY dyes display fluorescence turn‐on once released, with a lead analog showing nanomolar EC₅₀values against triple negative breast cancer cells, >100‐fold phototherapeutic indexes under green light irradiation, and higher selectivity toward cancer cells as compared to normal cells than the corresponding free BODIPY photosensitizer. Conventional Ru(II) photoactivated complexes require nonbiorthogonal blue light for activation and rarely show submicromolar potency to achieve cell death. Our study represents an avenue for the improved photochemistry and potency of future Ru(II) complexes.

    

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3. Predicting ligand removal energetics in thiolate-protected nanoclusters from molecular complexes

   https://doi.org/10.1039/d0nr07839e  

   McKay, Julia ; Cowan, Michael J. ; Morales-Rivera, Cristian A. ; Mpourmpakis, Giannis ( January 2021 , Nanoscale)

   null (Ed.)

   Thiolate-protected metal nanoclusters (TPNCs) have attracted great interest in the last few decades due to their high stability, atomically precise structure, and compelling physicochemical properties. Among their various applications, TPNCs exhibit excellent catalytic activity for numerous reactions; however, recent work revealed that these systems must undergo partial ligand removal in order to generate active sites. Despite the importance of ligand removal in both catalysis and stability of TPNCs, the role of ligands and metal type in the process is not well understood. Herein, we utilize Density Functional Theory to understand the energetic interplay between metal–sulfur and sulfur–ligand bond dissociation in metal–thiolate systems. We first probe 66 metal–thiolate molecular complexes across combinations of M = Ag, Au, and Cu with twenty-two different ligands (R). Our results reveal that the energetics to break the metal–sulfur and sulfur–ligand bonds are strongly correlated and can be connected across all complexes through metal atomic ionization potentials. We then extend our work to the experimentally relevant [M 25 (SR) 18 ] − TPNC, revealing the same correlations at the nanocluster level. Importantly, we unify our work by introducing a simple methodology to predict TPNC ligand removal energetics solely from calculations performed on metal–ligand molecular complexes. Finally, a computational mechanistic study was performed to investigate the hydrogenation pathways for SCH 3 -based complexes. The energy barriers for these systems revealed, in addition to thermodynamics, that kinetics favor the break of S–R over the M–S bond in the case of the Au complex. Our computational results rationalize several experimental observations pertinent to ligand effects on TPNCs. Overall, our introduced model provides an accelerated path to predict TPNC ligand removal energies, thus aiding towards targeted design of TPNC catalysts. 

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4. Singlet Oxygen Generation in Peripherally Modified Platinum and Palladium Porphyrins: Effect of Triplet Excited State Lifetimes and meso ‐Substituents on 1 O 2 Quantum Yields

   https://doi.org/10.1002/cplu.202200010  

   Subedi, Dili R. ; Reid, Ryan ; D'Souza, Patrick F. ; Nesterov, Vladimir N. ; D'Souza, Francis ( March 2022 , ChemPlusChem)

   A series ofmeso‐substituted with aromatic (=tolyl, pyrenyl, fluorenyl, naphthyl, and triphenylamine) substituents, platinum (Pt), and palladium (Pd) porphyrins have been synthesized and characterized by spectroscopic and single‐crystal X‐ray diffraction studies to probe structure‐reactivity aspects on the electrochemical redox potentials, and phosphorescence quantum yields and lifetimes. In the X‐ray structures, the aromaticmeso‐substituents were rotated to some extent from the planarity of the porphyrin ring to minimize steric hindrance. Both Pt and Pd porphyrins revealed higher electrochemical redox gaps as compared to their free‐base porphyrin analogs as a result of the harder oxidation and reduction processes. The ability of both Pt and Pd porphyrins to generate singlet oxygen was probed by monitoring the photoluminescence of¹O₂at 1270 nm. Higher quantum yields for both triplet sensitizers compared to their free‐base analogs were witnessed. Singlet oxygen quantum yields close to unity were possible to achieve in the case of Pt and Pd porphyrins bearing triphenylamine substituents at themeso‐position. The present study brings out the importance of differentmeso‐substituents on the triplet porphyrin sensitizers in governing singlet oxygen quantum yields; a key property of photosensitizers needed for photodynamic therapy, chemical synthesis, and other pertinent applications.

    

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5. Redox-active ligand controlled selectivity of vanadium oxidation on Au(100)

   https://doi.org/10.1039/C7SC04752E  

   Tempas, Christopher D. ; Morris, Tobias W. ; Wisman, David L. ; Le, Duy ; Din, Naseem U. ; Williams, Christopher G. ; Wang, Miao ; Polezhaev, Alexander V. ; Rahman, Talat S. ; Caulton, Kenneth G. ; et al ( January 2018 , Chemical Science)

   Metal–organic coordination networks at surfaces, formed by on-surface redox assembly, are of interest for designing specific and selective chemical function at surfaces for heterogeneous catalysts and other applications. The chemical reactivity of single-site transition metals in on-surface coordination networks, which is essential to these applications, has not previously been fully characterized. Here, we demonstrate with a surface-supported, single-site V system that not only are these sites active toward dioxygen activation, but the products of that reaction show much higher selectivity than traditional vanadium nanoparticles, leading to only one V-oxo product. We have studied the chemical reactivity of one-dimensional metal–organic vanadium – 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (DPTZ) chains with O 2 . The electron-rich chains self-assemble through an on-surface redox process on the Au(100) surface and are characterized by X-ray photoelectron spectroscopy, scanning tunneling microscopy, high-resolution electron energy loss spectroscopy, and density functional theory. Reaction of V-DPTZ chains with O 2 causes an increase in V oxidation state from V II to V IV , resulting in a single strongly bonded (DPTZ 2− )V IV O product and spillover of O to the Au surface. DFT calculations confirm these products and also suggest new candidate intermediate states, providing mechanistic insight into this on-surface reaction. In contrast, the oxidation of ligand-free V is less complete and results in multiple oxygen-bound products. This demonstrates the high chemical selectivity of single-site metal centers in metal–ligand complexes at surfaces compared to metal nanoislands. 

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