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1. Bimetallic nickel-lutetium complexes: tuning the properties and catalytic hydrogenation activity of the Ni site by varying the Lu coordination environment

   https://doi.org/10.1039/C8SC04712J  

   Ramirez, Bianca L.; Sharma, Prachi; Eisenhart, Reed J.; Gagliardi, Laura; Lu, Connie C. (March 2019, Chemical Science)

   We present three heterobimetallic complexes containing an isostructural nickel center and a lutetium ion in varying coordination environments. The bidentate iPr2PCH2NHPh and nonadentate (iPr2PCH2NHAr)3tacn ligands were used to prepare the Lu metalloligands, Lu( i Pr 2 PCH 2 NPh) 3 ( 1 ) and Lu{( i Pr 2 PCH 2 NAr) 3 tacn} ( 2 ), respectively. Reaction of Ni(COD) 2 (where COD is 1,5-cyclooctadiene) and 1 afforded NiLu( i Pr 2 PCH 2 NPh) 3 ( 3 ), with a Lu coordination number (CN) of 4 and a Ni–Lu distance, d (Ni–Lu), of 2.4644(2) Å. Complex 3 can further bind THF to form 3-THF , increasing both the Lu CN to 5 and d (Ni–Lu) to 2.5989(4) Å. On the other hand, incorporation of Ni(0) into 2 provides NiLu{( i Pr 2 PCH 2 NAr) 3 tacn} ( 4 ), in which the Lu coordination environment is more saturated (CN = 6), and the d (Ni–Lu) is substantially elongated at 2.9771(5) Å. Cyclic voltammetry of the three Ni–Lu complexes shows an overall ∼410 mV shift in the Ni(0/I) redox couple, suggesting tunability of the Ni electronics across the series. Computational studies reveal polarized bonding interactions between the Ni 3d z2 (major) and the Lu 5d z2 (minor) orbitals, where the percentage of Lu character increases in the order: 4 (6.0% Lu 5d z2 ) < 3-THF (8.5%) < 3 (9.3%). All three Ni–Lu complexes bind H 2 at low temperatures (−30 to −80 °C) and are competent catalysts for styrene hydrogenation. Complex 3 outperforms 4 with a four-fold faster rate. Additionally, adding increasing THF equivalents to 3 , which would favor build-up of 3-THF , decreases the rate. We propose that altering the coordination sphere of the Lu support can influence the resulting properties and catalytic activity of the active Ni(0) metal center. 

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2. Evaluating electrochemical accessibility of 4f ⁿ 5d ¹ and 4f ⁿ⁺¹ Ln( ii ) ions in (C ₅ H ₄ SiMe ₃ ) ₃ Ln and (C ₅ Me ₄ H) ₃ Ln complexes

   https://doi.org/10.1039/D1DT02427B  

   Trinh, Michael T.; Wedal, Justin C.; Evans, William J. (October 2021, Dalton Transactions)

   The reduction potentials (reported vs. Fc + /Fc) for a series of Cp′ 3 Ln complexes (Cp′ = C 5 H 4 SiMe 3 , Ln = lanthanide) were determined via electrochemistry in THF with [ n Bu 4 N][BPh 4 ] as the supporting electrolyte. The Ln( iii )/Ln( ii ) reduction potentials for Ln = Eu, Yb, Sm, and Tm (−1.07 to −2.83 V) follow the expected trend for stability of 4f 7 , 4f 14 , 4f 6 , and 4f 13 Ln( ii ) ions, respectively. The reduction potentials for Ln = Pr, Nd, Gd, Tb, Dy, Ho, Er, and Lu, that form 4f n 5d 1 Ln( ii ) ions ( n = 2–14), fall in a narrow range of −2.95 V to −3.14 V. Only cathodic events were observed for La and Ce at −3.36 V and −3.43 V, respectively. The reduction potentials of the Ln( ii ) compounds [K(2.2.2-cryptand)][Cp′ 3 Ln] (Ln = Pr, Sm, Eu) match those of the Cp′ 3 Ln complexes. The reduction potentials of nine (C 5 Me 4 H) 3 Ln complexes were also studied and found to be 0.05–0.24 V more negative than those of the Cp′ 3 Ln compounds. 

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3. Molecular recognition of methylated amino acids and peptides by Pillar[6]MaxQ

   https://doi.org/10.1039/D2OB01487D  

   King, David; Wilson, Chelsea R.; Herron, Lukas; Deng, Chun-Lin; Mehdi, Shams; Tiwary, Pratyush; Hof, Fraser; Isaacs, Lyle (September 2022, Organic & Biomolecular Chemistry)

   We report the molecular recognition properties of Pillar[ n ]MaxQ (P[ n ]MQ) toward a series of (methylated) amino acids, amino acid amides, and post-translationally modified peptides by a combination of 1 H NMR, isothermal titration calorimetry, indicator displacement assays, and molecular dynamics simulations. We find that P6MQ is a potent receptor for N -methylated amino acid side chains. P6MQ recognized the H3K4Me 3 peptide with K d = 16 nM in phosphate buffered saline. 

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4. The exquisite specificity of human protein arginine methyltransferase 7 (PRMT7) toward Arg-X-Arg sites

   https://doi.org/10.1371/journal.pone.0285812  

   Bondoc, Timothy J.; Lowe, Troy L.; Clarke, Steven G. (May 2023, PLOS ONE)

   Ganesan, A (Ed.)

   Mammalian protein arginine methyltransferase 7 (PRMT7) has been shown to target substrates with motifs containing two arginine residues separated by one other residue (RXR motifs). In particular, the repression domain of human histone H2B (29-RKRSR-33) has been a key substrate in determining PRMT7 activity. We show that incubating human PRMT7 and [³H]-AdoMet with full-lengthXenopus laevishistone H2B, containing the substitutions K30R and R31K (RKRSR to RRKSR), results in greatly reduced methylation activity. Using synthetic peptides, we have now focused on the enzymology behind this specificity. We show for the human and Xenopus peptide sequences 23–37 the difference in activity results from changes in the V_maxrather than the apparent binding affinity of the enzyme for the substrates. We then characterized six additional peptides containing a single arginine or a pair of arginine residues flanked by glycine and lysine residues. We have corroborated previous findings that peptides with an RXR motif have much higher activity than peptides that contain only one Arg residue. We show that these peptides have similar apparent k_mvalues but significant differences in their V_maxvalues. Finally, we have examined the effect of ionic strength on these peptides. We found the inclusion of salt had little effect on the V_maxvalue but a considerable increase in the apparent k_mvalue, suggesting that the inhibitory effect of ionic strength on PRMT7 activity occurs largely by decreasing apparent substrate-enzyme binding affinity. In summary, we find that even subtle substitutions in the RXR recognition motif can dramatically affect PRMT7 catalysis. 

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5. Mononuclear and Dinuclear Copper Complexes of Tridentate Redox‐active Ligands with Tunable H‐bonding Donors: Structure, Spectroscopy and H ⁺ /e ⁻ Reactivity

   https://doi.org/10.1002/asia.202100286  

   Wu, Tong; Musgrove, Justin; Siegler, Maxime_A; Garcia‐Bosch, Isaac (May 2021, Chemistry – An Asian Journal)

   Abstract In this research article, we describe the synthesis and characterization of mononuclear and dinuclear Cu complexes bound by a family of tridentate redox‐active ligands with tunable H‐bonding donors. The mononuclear Cu‐anion complexes were oxidized to the corresponding “high‐valent” intermediates by oxidation of the redox‐active ligand. These species were capable of oxidizing phenols with weak O−H bonds via H‐atom abstraction. Thermodynamic analysis of the H‐atom abstractions, which included reduction potential measurements, pK_adetermination and kinetic studies, revealed that modification of the anion coordinated to the Cu and changes in the H‐bonding donor did not lead to major differences in the reactivity of the “high‐valent” CuY complexes (Y: hydroxide, phenolate and acetate), which indicated that the tridentate ligand scaffold acts as the H⁺and e⁻acceptor. 

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