Calcium-Ion Binding Mediates the Reversible Interconversion of Cis and Trans Peroxido Dicopper Cores

Polysaccharide‑platinum complexes for cancer theranostics

Platinum anticancer drugs have been explored and developed in recent years to reduce systematic toxicities and resist drug resistance. Polysaccharides derived from nature have abundant structures as well as pharmacological activities. The review provides insights on the design, synthesis, characterization and associating therapeutic application of platinum complexes with polysaccharides that are classified by electronic charge. The complexes give birth to multifunctional properties with enhanced drug accumulation, improved tumor selectivity and achieved synergistic antitumor effect in cancer therapy. Several techniques developing polysaccharides-based carriers newly are also discussed. Moreover, the lasted immunoregulatory activities of innate immune reactions triggered by polysaccharides are summarized. Finally, we discuss the current shortcomings and outline potential strategies for improving platinum-based personalized cancer treatment. Using platinum-polysaccharides complexes for improving the immunotherapy efficiency represents a promising framework in future.

Visible Light-ATRP Driven by Tris(2-Pyridylmethyl)Amine (TPMA) Impurities in the Open Air

Atom transfer radical polymerization (ATRP) of oligo(ethylene oxide) monomethyl ether methacrylate (OEOMA500 ) in water is enabled using CuBr2 with tris(2-pyridylmethyl)amine (TPMA) as a ligand under blue or green-light irradiation without requiring any additional reagent, such as a photo-reductant, or the need for prior deoxygenation. Polymers with low dispersity (Đ = 1.18-1.25) are synthesized at high conversion (>95%) using TPMA from three different suppliers, while no polymerization occurred with TPMA is synthesized and purified in the laboratory. Based on spectroscopic studies, it is proposed that TPMA impurities (i.e., imine and nitrone dipyridine), which absorb blue and green light, can act as photosensitive co-catalyst(s) in a light region where neither pure TPMA nor [(TPMA)CuBr]+ absorbs light.

Lewis Acids and Electron-Withdrawing Ligands Accelerate CO Coordination to Dinuclear CuI Compounds

A series of dinuclear molecular copper complexes were prepared and used to model the binding and Lewis acid stabilization of CO in heterogeneous copper CO₂ reduction electrocatalysts. Experimental studies (including measurement of rate and equilibrium constants) and electronic structure calculations suggest that the key kinetic barrier for CO binding may be a σ-interaction between Cu^I and the incoming CO ligand. The rate of CO coordination can be increased upon the addition of Lewis acids or electron-withdrawing substituents on the ligand backbone. Conversely, K_eq for CO coordination can be increased by adding electron density to the metal centers of the compound, consistent with stronger π-backbonding. Finally, the electrochemically measured kinetic results were mapped onto an electrochemical zone diagram to illustrate how these system changes enabled access to each zone.

Peroxide-Selective Reduction of O2 at Redox-Inactive Rare-Earth(III) Triflates Generates an Ambiphilic Peroxide

Metal peroxides are key species involved in a range of critical biological and synthetic processes. Rare-earth (group III and the lanthanides; Sc, Y, La-Lu) peroxides have been implicated as reactive intermediates in catalysis; however, reactivity studies of isolated, structurally characterized rare-earth peroxides have been limited. Herein, we report the peroxide-selective (93-99% O₂^2-) reduction of dioxygen (O₂) at redox-inactive rare-earth triflates in methanol using a mild metallocene reductant, decamethylferrocene (Fc*). The first molecular praseodymium peroxide ([Pr^III₂(O₂^2-)(18C6)₂(EG)₂][OTf]₄; 18C6 = 18-crown-6, EG = ethylene glycol, ^-OTf = ^-O₃SCF₃; 2-Pr) was isolated and characterized by single-crystal X-ray diffraction, Raman spectroscopy, and NMR spectroscopy. 2-Pr displays high thermal stability (120 °C, 50 mTorr), is protonated by mild organic acids [pK_a1(MeOH) = 5.09 ± 0.23], and engages in electrophilic (e.g., oxygen atom transfer) and nucleophilic (e.g., phosphate-ester cleavage) reactivity. Our mechanistic studies reveal that the rate of oxygen reduction is dictated by metal-ion accessibility, rather than Lewis acidity, and suggest new opportunities for differentiated reactivity of redox-inactive metal ions by leveraging weak metal-ligand binding events preceding electron transfer.

Controlling the Direction of S-Nitrosation versus Denitrosation: Reversible Cleavage and Formation of an S-N Bond within a Dicopper Center

Iron and copper enzymes are known to promote reversible S-nitrosation/denitrosation in biology. However, it is unclear how the direction of S-N bond formation/scission is controlled. Herein, we demonstrate the interconversion of metal-S-nitrosothiol adduct M(RSNO) and metal nitrosyl thiolate complex M(NO)(SR), which may regulate the direction of reversible S-(de)nitrosation. Treatment of a dicopper(I,I) complex with RSNO leads to a mixture of two structural isomers: dicopper(I,I) S-nitrosothiol [Cu^ICu^I(RSNO)]²⁺ and dicopper(II,II) nitrosyl thiolate [Cu^IICu^II(NO)(SR)]²⁺. The K_eq between these two structural isomers is sensitive to temperature, the solvent coordination ability, and counterions. Our study illustrates how copper centers can modulate the direction of RS-NO bond formation and cleavage through a minor perturbation of the local environment.

Modulation of a μ-1,2-Peroxo Dicopper(II) Intermediate by Strong Interaction with Alkali Metal Ions

The properties of metal/dioxygen species, which are key intermediates in oxidation catalysis, can be modulated by interaction with redox-inactive Lewis acids, but structural information about these adducts is scarce. Here we demonstrate that even mildly Lewis acidic alkali metal ions, which are typically viewed as innocent "spectators", bind strongly to a reactive cis-peroxo dicopper(II) intermediate. Unprecedented structural insight has now been obtained from X-ray crystallographic characterization of the "bare" Cu^II₂(μ-η¹:η¹-O₂) motif and its Li⁺, Na⁺, and K⁺ complexes. UV-vis, Raman, and electrochemical studies show that the binding persists in MeCN solution, growing stronger in proportion to the cation's Lewis acidity. The affinity for Li⁺ is surprisingly high (∼70 × 10⁴ M^-1), leading to Li⁺ extraction from its crown ether complex. Computational analysis indicates that the alkali ions influence the entire Cu-OO-Cu core, modulating the degree of charge transfer from copper to dioxygen. This induces significant changes in the electronic, magnetic, and electrochemical signatures of the Cu₂O₂ species. These findings have far-reaching implications for analyses of transient metal/dioxygen intermediates, which are often studied in situ, and they may be relevant to many (bio)chemical oxidation processes when considering the widespread presence of alkali cations in synthetic and natural environments.