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1. SPAAC iClick: progress towards a bioorthogonal reaction in-corporating metal ions

   https://doi.org/10.1039/d1dt02626g  

   Shen, Yu-Hsuan ; Esper, Alec M. ; Ghiviriga, Ion ; Abboud, Khalil A. ; Schanze, Kirk S. ; Ehm, Christian ; Veige, Adam S. ( September 2021 , Dalton Transactions)

   Combining strain-promoted azide–alkyne cycloaddition (SPAAC) and inorganic click (iClick) reactivity provides access to metal 1,2,3-triazolates. Experimental and computational insights demonstrate that iClick reactivity of the tested metal azides (LM-N 3 , M = Au, W, Re, Ru and Pt) depends on the accessibility of the azide functionality rather than electronic effects imparted by the metal. SPAAC iClick reactivity with cyclooctyne is observed when the azide functionality is sterically unencumbered, e.g. [Au(N 3 )(PPh 3 )] (Au–N3), [W(η 3 -allyl)(N 3 )(bpy)(CO) 2 ] (W–N3), and [Re(N 3 )(bpy)(CO) 3 ] [bpy = 2,2′-bipyridine] (Re–N3). Increased steric bulk and/or preequilibria with high activation barriers prevent SPAAC iClick reactivity for the complexes [Ru(N 3 )(Tp)(PPh 3 ) 2 ] [Tp = tris(pyrazolyl)borate] (Ru–N3), [Pt(N 3 )(CH 3 )(P i Pr 3 ) 2 ] [ i Pr = isopropyl] (Pt(II)–N3), and [Pt(N 3 )(CH 3 ) 3 ] 4 ((PtN3)4). Based on these computational insights, the SPAAC iClick reactivity of [Pt(N 3 )(CH 3 ) 3 (P(CH 3 ) 3 ) 2 ] (Pt(IV)–N3) was successfully predicted.
2. Structural Insights Into the 5′UG/3′GU Wobble Tandem in Complex With Ba2+ Cation

   https://doi.org/10.3389/fmolb.2021.762786  

   Ruszkowska, Agnieszka ; Zheng, Ya Ying ; Mao, Song ; Ruszkowski, Milosz ; Sheng, Jia ( January 2022 , Frontiers in Molecular Biosciences)

   G•U wobble base pair frequently occurs in RNA structures. The unique chemical, thermodynamic, and structural properties of the G•U pair are widely exploited in RNA biology. In several RNA molecules, the G•U pair plays key roles in folding, ribozyme catalysis, and interactions with proteins. G•U may occur as a single pair or in tandem motifs with different geometries, electrostatics, and thermodynamics, further extending its biological functions. The metal binding affinity, which is essential for RNA folding, catalysis, and other interactions, differs with respect to the tandem motif type due to the different electrostatic potentials of the major grooves. In this work, we present the crystal structure of an RNA 8-mer duplex r[UCGUGCGA] 2 , providing detailed structural insights into the tandem motif I (5′UG/3′GU) complexed with Ba 2+ cation. We compare the electrostatic potential of the presented motif I major groove with previously published structures of tandem motifs I, II (5′GU/3′UG), and III (5′GG/3′UU). A local patch of a strongly negative electrostatic potential in the major groove of the presented structure forms the metal binding site with the contributions of three oxygen atoms from the tandem. These results give us a better understanding of the G•U tandem motif I asmore »a divalent metal binder, a feature essential for RNA functions.« less
3. Structural determination of arginine-linked cisplatin complexes via IRMPD action spectroscopy: arginine binds to platinum via NO ⁻ binding mode

   https://doi.org/10.1039/d1cp03407c  

   He, C. C. ; Hamlow, L. A. ; Kimutai, B. ; Roy, H. A. ; Devereaux, Zachary J. ; Cunningham, N. A. ; Martens, J. ; Berden, G. ; Oomens, J. ; Chow, C. S. ; et al ( October 2021 , Physical Chemistry Chemical Physics)

   Cisplatin, (NH 3 ) 2 PtCl 2 , has been known as a successful metal-based anticancer drug for more than half a century. Its analogue, Argplatin, arginine-linked cisplatin, (Arg)PtCl 2 , is being investigated because it exhibits reactivity towards DNA and RNA that differs from that of cisplatin. In order to understand the basis for its altered reactivity, the deprotonated and sodium cationized forms of Argplatin, [(Arg-H)PtCl 2 ] − and [(Arg)PtCl 2 + Na] + , are examined by infrared multiple photon dissociation (IRMPD) action spectroscopy in the IR fingerprint and hydrogen-stretching regions. Complementary electronic structure calculations are performed using density functional theory approaches to characterize the stable structures of these complexes and to predict their infrared spectra. Comparison of the theoretical IR spectra predicted for various stable conformations of these Argplatin complexes to their measured IRMPD spectra enables determination of the binding mode(s) of Arg to the Pt metal center to be identified. Arginine is found to bind to Pt in a bidentate fashion to the backbone amino nitrogen and carboxylate oxygen atoms in both the [(Arg-H)PtCl 2 ] − and [(Arg)PtCl 2 + Na] + complexes, the NO − binding mode. The neutral side chain of Argmore »also interacts with the Pt center to achieve additional stabilization in the [(Arg-H)PtCl 2 ] − complex. In contrast, Na + binds to both chlorido ligands in the [(Arg)PtCl 2 + Na] + complex and the protonated side chain of Arg is stabilized via hydrogen-bonding interactions with the carboxylate moiety. These findings are consistent with condensed-phase results, indicating that the NO − binding mode of arginine to Pt is preserved in the electrospray ionization process even under variable pH and ionic strength.« less
4. Lanthanum-based double perovskite nanoscale motifs as support media for the methanol oxidation reaction

   https://doi.org/10.1039/d1cy01668g  

   McGuire, Scott C. ; Koenigsmann, Christopher ; Chou, Chun Chieh ; Tong, Xiao ; Wong, Stanislaus S. ( January 2022 , Catalysis Science & Technology)

   We have not only analyzed the performance of perovskite oxides as support media for the methanol oxidation reaction (MOR) but also examined the impact and significance of various reaction parameters on their synthesis. Specifically, we have generated (a) La 2 NiMnO 6 , LaMnO 3 , and LaNiO 3 nanocubes with average sizes of ∼200 nm, in addition to a series of La 2 NiMnO 6 (b) nanocubes possessing average sizes of ∼70 and 400 nm and (c) anisotropic nanorods characterized by average diameters of 40–50 nm. All of these samples, when used as supports for Pt nanoparticles, exhibited activities which were at least twice that measured for Pt/C. We have investigated and correlated the effect of varying perovskite (i) composition, (ii) size, and (iii) morphology upon the measured MOR activity. (i) The Ni-containing perovskites yielded generally higher performance metrics than LaMnO 3 alone, suggesting that the presence of Ni is favorable for MOR, a finding supported by a shift in the Pt d -band in XPS. (ii) MOR activity is enhanced as the perovskite size increases in magnitude, suggesting that a growth in the perovskite particle size enables favorable, synergistic metal–support interactions. (iii) A comparison of the nanorods andmore »nanocubes of a similar diameter implied that the one-dimensional morphology achieved a greater activity, a finding which can be attributed not only to the anisotropic structure but also to a desirable surface structure. Overall, these data yield key insights into the tuning of metal–support interactions via rational control over the composition, size, and morphology of the underlying catalyst support.« less
5. Controlling the optical and catalytic properties of artificial metalloenzyme photocatalysts using chemogenetic engineering

   https://doi.org/10.1039/D1SC05792H  

   Zubi, Yasmine S. ; Liu, Bingqing ; Gu, Yifan ; Sahoo, Dipankar ; Lewis, Jared C. ( February 2022 , Chemical Science)

   Visible light photocatalysis enables a broad range of organic transformations that proceed via single electron or energy transfer. Metal polypyridyl complexes are among the most commonly employed visible light photocatalysts. The photophysical properties of these complexes have been extensively studied and can be tuned by modifying the substituents on the pyridine ligands. On the other hand, ligand modifications that enable substrate binding to control reaction selectivity remain rare. Given the exquisite control that enzymes exert over electron and energy transfer processes in nature, we envisioned that artificial metalloenzymes (ArMs) created by incorporating Ru( ii ) polypyridyl complexes into a suitable protein scaffold could provide a means to control photocatalyst properties. This study describes approaches to create covalent and non-covalent ArMs from a variety of Ru( ii ) polypyridyl cofactors and a prolyl oligopeptidase scaffold. A panel of ArMs with enhanced photophysical properties were engineered, and the nature of the scaffold/cofactor interactions in these systems was investigated. These ArMs provided higher yields and rates than Ru(Bpy) 3 2+ for the reductive cyclization of dienones and the [2 + 2] photocycloaddition between C -cinnamoyl imidazole and 4-methoxystyrene, suggesting that protein scaffolds could provide a means to improve the efficiency of visible lightmore »photocatalysts.« less