ACS Organic & Inorganic Au最新文献

Escalating levels of carbon dioxide (CO₂) in the atmosphere have motivated interest in CO₂ capture and concentration from dilute streams. A guanidino-functionalized aromatic 1,4-bis(tetramethylguanidino)benzene (1,4-btmgb) was evaluated both as a redox-active sorbent and as a pH swing mediator for electrochemical CO₂ capture and concentration. Spectroscopic and crystallographic studies demonstrate that 1,4-btmgb reacts with CO₂ in water to form 1,4-btmgbH₂(HCO₃^–)₂. The product suggests that 1,4-btmgb could be used in an aqueous redox pH swing cycle for the capture and concentration of CO₂. The synthesis and characterization of the mono- and diprotonated forms (1,4-btmgbH⁺ and 1,4-btmgbH₂²⁺) and their pK_a values were measured to be 13.5 and 11.0 in water, respectively. Electrochemical pH swing experiments indicate the formation of an intermediate radical species and other degradation pathways, which ultimately inhibited fully reversible redox-induced pH cycling.

The synthesis of selenofunctionalized oxazolines and isoxazolines from N-allyl benzamides and unsaturated oximes with diselenides was studied by utilizing a continuous flow electrochemical approach. At mild reaction conditions and short reaction times of 10 min product yields of up to 90% were achieved including a scale-up reaction. A broad substrate scope was studied and the reaction was shown to have a wide functional group tolerance.

Near-infrared (NIR)-emitting phosphate glasses containing Nd³⁺ ions are attractive for applications in laser materials and solar spectral converters. The composition–structure–property relation in this type of glass system is thus of interest from fundamental and applied perspectives. In this work, Nd³⁺-containing glasses were made by melting with 50P₂O₅-(50 – x)BaO-xNd₂O₃ (x = 0, 0.5, 1.0, 2.0, 3.0, 4.0 mol %) nominal compositions and studied comprehensively by density and related physical properties, X-ray diffraction (XRD), Raman spectroscopy, O 1s X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), dilatometry, ultraviolet–visible (UV–vis)–NIR optical absorption, and photoluminescence (PL) spectroscopy with decay dynamics assessment. The densities and molar volumes of the Nd³⁺-containing glasses generally increased with Nd₂O₃ concentration also resulting in shorter Nd³⁺–Nd³⁺ distances. XRD supported the amorphous nature of the glasses, whereas the Raman spectra evolution was indicative of glass depolymerization being induced by Nd³⁺ ions. Oxygen (1s) and phosphorus (2p) analysis by XPS for the glass with 4.0 mol % Nd₂O₃ agreed with the increase in nonbridging oxygens relative to the undoped host. DSC results showed that the glass transition temperatures increased with Nd³⁺ concentration, with the glasses also displaying a decreased tendency toward crystallization. Dilatometry showed trends of increasing softening temperatures and decreasing thermal expansion coefficients with increasing Nd₂O₃ content. A glass strengthening/tightening effect was then indicated to be induced by Nd³⁺ with higher field strength compared to Ba²⁺ ions. The UV–vis–NIR absorption by Nd³⁺ ions increased consistently with Nd³⁺ concentration. The UV–vis absorption edges of the Nd-containing glasses were also analyzed via Tauc and Urbach plots for comparison with the undoped host. Concerning the PL behavior, the Nd³⁺ NIR emission intensity was highest for 1.0 mol % Nd₂O₃ and decreased thereafter. The decay kinetics of the ⁴F_3/2 emitting state in Nd³⁺ ions analyzed revealed decreasing lifetimes where the decay rate analysis pointed to the prevalence of ion–ion excitation migration leading to PL quenching at high Nd³⁺ concentrations.

In the past 5 years, hexafluoroisopropanol (HFIP) has been used as a unique solvent or additive to enable challenging transformations through substrate activation and stabilization of reactive intermediates. In this Review, we aim at describing difunctionalization processes which were unlocked when HFIP was involved. Specifically, we focus on cyclizations and additions to alkenes, alkynes, epoxides, and carbonyls that introduce a wide range of functional groups of interest.

Molybdenum(III) complexes bearing pincer-type ligands are well-known catalysts for N₂-to-NH₃ reduction. We investigated herein the impact of an anionic PNP pincer-type ligand in a Mo(III) complex on the (electro)chemical N₂ splitting ([LMoCl₃]⁻, 1^–, LH = 2,6-bis((di-tert-butylphosphaneyl)methyl)-pyridin-4-one). The increased electron-donating properties of the anionic ligand should lead to a stronger degree of N₂ activation. The catalyst is indeed active in N₂-to-NH₃ conversion utilizing the proton-coupled electron transfer reagent SmI₂/ethylene glycol. The corresponding Mo(V) nitrido complex 2H exhibits similar catalytic activity as 1H and thus could represent a viable intermediate. The Mo(IV) nitrido complex 3^– is also accessible by electrochemical reduction of 1^– under a N₂ atmosphere. IR- and UV/vis-SEC measurements suggest that N₂ splitting occurs via formation of an “overreduced” but more stable [(L(N₂)₂Mo⁰)₂μ-N₂]^2– dimer. In line with this, the yield in the nitrido complex increases with lower applied potentials.

A recent reinvestigation of the gas-phase photoelectron spectra of Group 6 metal–metal quadruple-bonded complexes with scalar-relativistic DFT calculations showed that common exchange-correlation functionals reproduce the lowest ionization potentials in a semiquantitative manner. The finding encouraged us to undertake a DFT study of metal–metal quintuple bonds in a set of bisamidinato complexes with the formula M^I₂[HC(NR)₂]₂ (M = Cr, Mo, W; R = H, Ph, 2,6-iPr₂C₆H₃) and idealized D_2h symmetry. Scalar-relativistic OLYP/STO-TZ2P calculations indicated significant shifts in valence orbital energies among the three metals, which translate to lower first ionization potentials, higher electron affinities, and lower HOMO–LUMO gaps for the W complexes relative to their Cr and Mo counterparts. These differences are largely attributable to substantially larger relativistic effects in the case of tungsten relative to those of its lighter congeners.

As the SIRTi analogue series (HL1–HL6) show potent antitumor activity in vitro, we synthesized their corresponding zinc(II) complexes (ZnL1–ZnL6) and investigated their potential as anticancer agents. The Zn(II) complexes showed substantially greater cytotoxicity than HL1–HL6 alone in several cancer cell-types. Notably, distinct structure–activity relationships confirmed the significance of tert-butyl (ZnL2) pharmacophore inclusion in their activity. ZnL2 complexes were found to transmetalate with copper ions inside cells, causing the formation of redox-active copper complexes that induced reactive oxygen species (ROS) production, mitochondrial membrane depolarization, ATP decay, and cell death. This is the first study to exhibit Zn(II) complexes that mediate their activity via transmetalation with copper ions to undergo paraptosis cell death pathway. To further confirm if the SIRT1/2 inhibitory property of SIRTi analogues is conserved, a docking simulation study is performed. The binding affinity and specific interactions of the Cu(II) complex obtained after transmetalation with ZnL2 were found to be higher for SIRT2 (K_i = 0.06 μM) compared to SIRT1 (K_i = 0.25 μM). Thus, the concurrent regulation of several biological targets using a single drug has been shown to have synergistic therapeutic effects, which are crucial for the effective treatment of cancer.

Electrochemical water oxidation is known as the anodic reaction of water splitting. Efficient design and earth-abundant electrocatalysts are crucial to this process. Herein, we report a family of catalysts (1–3) bearing bis(benzimidazole)pyrazolide ligands (H₂L1–H₂L3). H₂L3 contains electron-donating substituents and noninnocent components, resulting in catalyst 3 exhibiting unique performance. Kinetic studies show first-order kinetic dependence on [3] and [H₂O] under neutral and alkaline conditions. In contrast to previously reported catalyst 1, catalyst 3 exhibits an insignificant kinetic isotope effect of 1.25 and zero-order dependence on [NaOH]. Based on various spectroscopic methods and computational findings, the L3Co₂^III(μ-OH) species is proposed to be the catalyst resting state and the nucleophilic attack of water on this species is identified as the turnover-limiting step of the catalytic reaction. Computational studies provided insights into how the interplay between the electronic effect and ligand noninnocence results in catalyst 3 acting via a different reaction mechanism. The variation in the turnover-limiting step and catalytic potentials of species 1–3 leads to their catalytic rates being independent of the overpotential, as evidenced by Eyring analysis. Overall, we demonstrate how ligand design may be utilized to retain good water oxidation activity at low overpotentials.

During the last years, the development of more sustainable and straightforward methodologies to minimize the generation of waste organic substances has acquired high importance within synthetic organic chemistry. Therefore, it is not surprising that many efforts are devoted to ameliorating already well-known successful methodologies, that is, the case of the asymmetric allylic allylation reaction of carbonyl compounds. The use of free alcohols as alkylating agents in this transformation represents a step forward in this sense since it minimizes waste production and the substrate manipulation. In this review, we aim to gather the most recent methodologies describing this strategy by paying special attention to the reaction mechanisms, as well as their synthetic applications.