Selective Redox Research Articles

Total Synthesis of Ryanodane Diterpenoids Garajonone and 3‐epi‐Garajonone

AbstractRyanodane diterpenes are structurally complex natural products that are well‐known for their high degree of oxidation and the challenges associated with synthesizing them within the terpene class. Herein, we present a two‐stage synthetic strategy that draws inspiration from the broad biosynthesis of terpenes, allowing us to achieve the first chemical synthesis of garajonone, a ryanodane diterpenoid that occurs naturally at low abundance, as well as its epimer, 3‐epi‐garajonone. The key to this success lies in the rapid construction of the carbon framework of the target molecule by employing an early‐stage palladium‐catalyzed Heck/carbonylative esterification cascade annulation, followed by successive late‐stage selective redox manipulation to establish the desired oxidation state of the molecule. This research not only showcases the synthesis of garajonone and its epimer but also provides a platform for the chemical synthesis of other members and analogs of this complex diterpenoid family.

Achieving optimum balance between mechanical properties and gloss of acrylonitrile–styrene–acrylate resin through control of rubber particle size distribution

AbstractPreparation of acrylonitrile–styrene–acrylate (ASA) with high gloss and superior impact properties is still challenging. Here, we developed a new strategy for the preparation of ASA resins by a selective redox initiation method based on a semi‐continuous emulsion polymerization technique. A series of ASA core‐shell impact modifiers were firstly obtained by grafting styrene (St) and acrylonitrile (AN) onto poly(n‐butyl acrylate) (PBA) seeded latexes of different sizes. The ASA core‐shell impact modifier was then used to toughen the styrene–acrylonitrile copolymer (SAN). The synergistic effects between the single particle size of the rubber phase and different particle sizes were systematically investigated, and the mechanical properties of SAN‐toughened resins at various particle sizes of the rubber phase were analyzed. The results revealed that toughened SAN with small particle sizes possessed better gloss, and the impact strength of the doped small‐particle toughened SAN was much higher than that of the single particle size toughened SAN. The ASA graft powders synthesized from large particle PBA (particle size 316 nm) and small particle PBA (particle size 99 nm), respectively, were mixed at a 50/50 ratio and blended with SAN resin, a gloss level reaching 95, and an impact performance of 275 J/m values almost twice those of a single particle size toughened SAN.Highlights Acrylonitrile–styrene–acrylate resins with an impact strength of 275 J/m and gloss of 95 were prepared. The balance between mechanical properties and gloss of acrylonitrile–styrene–acrylate resin was obtained. Polymerization was initiated at low temperature.

Total Synthesis of Ryanodane Diterpenoids Garajonone and 3-epi-Garajonone.

Ryanodane diterpenes are structurally complex natural products that are well-known for their high degree of oxidation and the challenges associated with synthesizing them within the terpene class. Herein, we present a two-stage synthetic strategy that draws inspiration from the broad biosynthesis of terpenes, allowing us to successfully achieve the first chemical synthesis of garajonone, a ryanodane diterpenoid that occurs naturally at low abundance, as well as its epimer, 3-epi-garajonone. The key to this success lies in the rapid construction of the carbon framework of target molecule by employing an early-stage palladium-catalyzed Heck/carbonylative esterification cascade annulation, followed by successive late-stage selective redox manipulation to establish the desired oxidation state of the molecule. This research not only showcases the synthesis of garajonone and its epimer but also provides a platform for the chemical synthesis of other members and analogs within this complex diterpenoid family.

Silica Nanoparticles Decorated with Ceria Quantum Dots Modulate Intra- and Extracellular Reactive Oxygen Species Formation and Selectively Reduce Human A375 Melanoma Cell Proliferation.

Nanomaterials show great promise for cancer treatment. Nonetheless, most nanomaterials lack selectivity for cancer cells, damaging healthy ones. Cerium dioxide (ceria, CeO2) nanoparticles have been shown to exert selective toxicity toward cancer cells due to the redox modulating properties they display as their size decreases. However, these particles suffer from poor suspension stability. The efficacy of CeO2 nanoparticles for cancer treatment is hampered by their innate high surface energy, which leads to particle agglomeration and, consequently, reactivity loss. This effect increases as particle size decreases; as such, quantum dots (QDs) suffer most from this phenomenon. In this study, it is proposed that silicon dioxide (silica, SiO2) nanoparticles can provide an inert platform for surface encrusted CeO2 QDs and that the resulting nanocomposite (hereafter QDCeO2/SiO2) not only will exhibit negligible agglomeration compared with CeO2 alone but also will improve the modulation of reactive oxygen species (ROS) leading to selective reduction of human A375 melanoma cell proliferation. The SiO2 nanoparticles had a bimodal size distribution with median particle size of 66 and 168 nm, while the CeO2 quantum dots encrusted on their surface had a size of 3.2 nm. An elevated Ce3+/Ce4+ ratio led to the QDCeO2/SiO2 nanocomposite displaying synergistic superoxide dismutase- and catalase-like activity, favoring the accumulation of ROS at pH 6.5 which translated into QDCeO2/SiO2 exerting selective oxidative stress in, and toward, the melanoma cells. Treatment with 50 μg mL-1 QDCeO2/SiO2 significantly reduced cell proliferation by 27% compared to untreated control cells in the colony formation assay. Treatment with either SiO2 or CeO2 alone did not affect the cell proliferation. These results highlight the benefit of dispersing CeO2 QDs on the surface of core nanoparticles and the resulting enhancement of selective redox reactivity and proliferation arrest when compared to CeO2 nanoparticles alone. Furthermore, the method employed here to encrust CeO2 QDs could lead to the facile synthesis of new nanocomposites with enhanced control of ROS activity, not only for in vitro studies using other cancer cell lines of interest but also in animal models and perhaps leading to clinical trials in melanoma patients.

Material Engineering Solutions toward Selective Redox Catalysts for Chemical-Looping-Based Olefin Production Schemes: A Review.

Chemical looping (CL) has emerged as a promising approach in the oxidative dehydrogenation (ODH) of light alkanes, offering an opportunity for significant reductions in emissions and energy consumption in the ethylene and propylene production industry. While high olefin yields are achievable via CL, the material requirements (e.g., electronic and geometric structures) that prevent the total conversion of alkanes to CO x are not clearly understood. This review aims to give a concise understanding of the nucleophilic oxygen species involved in the selective reaction pathways for olefin production as well as of the electrophilic oxygen species that promote an overoxidation to CO x products. It further introduces advanced characterization techniques such as X-ray photoelectron spectroscopy, Raman spectroscopy, electron paramagnetic resonance spectroscopy, and resonant inelastic X-ray scattering, which have been employed successfully in identifying such reactive oxygen species. To mitigate CO x formation and enhance olefin selectivity, material engineering solutions are discussed. Common techniques include doping of the bulk or surface and the deposition of functional coatings. In the context of energy consumption and CO2 intensity, techno-economic assessments of CL-ODH systems have predicted energy savings of up to 80% compared to established olefin production processes such as steam cracking or dehydrogenation. Finally, although their practical application has been limited to date, the potential advantages of the use of fluidized bed reactors in CL-ODH are presented.

Engineering atomic Rb-N configurations to tune radical pathways for highly selective photocatalytic H2O2 synthesis coupled with biomass valorization

Photocatalytic oxygen reduction for hydrogen peroxide (H₂O₂) synthesis presents a green and cost-effective production method. However, achieving highly selective H₂O₂ synthesis remains challenging, necessitating precise control over free radical reaction pathways and minimizing undesirable oxidative by-products. Herein, we report for the visible light-driven simultaneous co-photocatalytic reduction of O2 to H2O2 and oxidation of biomass using the atomic rubidium-nitride modified carbon nitride (CNRb). The optimized CNRb catalyst demonstrates a record photoreduction rate of 8.01 mM h−1 for H2O2 generation and photooxidation rate of 3.75 mM h−1 for furfuryl alcohol to furoic acid, achieving a remarkable solar-to-chemical conversion (SCC) efficiency of up to 2.27%. Experimental characterizations and DFT calculation disclosed that the introducing atomic Rb–N configurations allows for the high-selective generation of superoxide radicals while suppressing hydroxyl free radical formation. This is because the Rb–N serves as the new alternative site to perceive a stronger connection position for O2 adsorption and reinforce the capability to extract protons, thereby triggering a high selective redox product formation. This study holds great potential in precisely regulating reactive radical processes at the atomic level, thereby paving the way for efficient synthesis of H2O2 coupled with biomass valorization.

Detection of ascorbic acid by persistent luminescent nanoparticles based on CoOOH nanosheets modification.

Persistent luminescent nanomaterials (PLNPs) Zn0.8Ga2O4: Cr3+, Zr3+ with high brightness and good dispersion were prepared by hydrothermal method. The PLNPs were used as luminescent units, and CoOOH nanosheets were used as quenching agents. Based on the fluorescence internal filtering effect, the luminescence of PLNPs were effectively quenched by CoOOH modification on the surface of PLNPs. However, the introduction of ascorbic acid (AA) restored the luminescence of PLNPs and successfully achieved highly sensitive and selective detection of AA. This was due to a selective redox reaction between CoOOH and AA, in which CoOOH was reduced to Co2+. The degree of luminescence recovery of PLNPs showed a good linear relationship with AA concentration in the range 5-250 µM, with a detection limit of 0.72 µM. Therecovery of actualspikedsamples were 97.9-102.2%. This method isexpected to provide reference for the study of other redox substances in biological systems.

Predictive Synthesis of Transition Metal Carbide via Thermochemical Oxocarbon Equilibrium.

Fabricating nanoscale metal carbides is a great challenge due to them having higher Gibbs free energy of formation (ΔG°) values than other metal compounds; additionally, these carbides have harsh calcination conditions, in which metal oxidation is preferred in the atmosphere. Herein, we report oxocarbon-mediated calcination for the predictive synthesis of nanoscale metal carbides. The thermochemical oxocarbon equilibrium of CO-CO2 reactions was utilized to control the selective redox reactions in multiatomic systems of Mo-C-O, contributing to the phase-forming and structuring of Mo compounds. By harnessing the thermodynamically predicted processing window, we controlled a wide range of Mo phases (MoO2, α-MoC1-x, and β-Mo2C) and nanostructures (nanoparticle, spike, stain, and core/shell) in the Mo compounds/C nanofibers. By inducing simultaneous reactions of C-O (selective C combustion) and Mo-C (Mo carbide formation) in the nanofibers, Mo diffusion was controlled in C nanofibers, acting as a template for the nucleation and growth of Mo carbides and resulting in precise control of the phases and structures of Mo compounds. The formation mechanism of nanostructured Mo carbides was elucidated according to the CO fractions of CO-CO2 calcination. Moreover, tungsten (W) and niobium (Nb) carbides/C nanofibers have been successfully synthesized by CO-CO2 calcination. We constructed the thermodynamic map for the predictive synthesis of transition metal carbides to provide universal guideline via thermochemical oxocarbon equilibrium. We revealed that our thermochemical oxocarbon-mediated gas-solid reaction enabled the structure and phase control of nanoscale transition metal compounds to optimize the material-property relationship accordingly.

Enzymatic Galvanic Redox Potentiometry for In Vivo Biosensing.

Redox potentiometry has emerged as a new platform for in vivo sensing, with improved neuronal compatibility and strong tolerance against sensitivity variation caused by protein fouling. Although enzymes show great possibilities in the fabrication of selective redox potentiometry, the fabrication of an enzyme electrode to output open-circuit voltage (EOC) with fast response remains challenging. Herein, we report a concept of novel enzymatic galvanic redox potentiometry (GRP) with improved time response coupling the merits of the high selectivity of enzyme electrodes with the excellent biocompatibility and reliability of GRP sensors. With a glucose biosensor as an illustration, we use flavin adenine dinucleotide-dependent glucose dehydrogenase as the recognition element and carbon black as the potential relay station to improve the response time. We find that the enzymatic GRP biosensor rapidly responds to glucose with a good linear relationship between EOC and the logarithm of glucose concentration within a range from 100 μM to 2.65 mM. The GRP biosensor shows high selectivity over O2 and coexisting neurochemicals, good reversibility, and sensitivity and can in vivo monitor glucose dynamics in rat brain. We believe that this study will pave a new platform for the in vivo potentiometric biosensing of chemical events with high reliability.

Switching and control mechanism between p-type and n-type in SnO2 nanorods using laser with added convex lens to control oxygen concentrations

In a significant advancement, a novel technology has been developed to precisely control the electronic sensitization of SnO2 nanorods. This control is accomplished in a matter of seconds through the external injection of energy via laser and convex lens pairs (LCP). Utilizing LCP, selective redox reactions can be induced on the surface of SnO2 nanorods. The study focused on the contrasting effects of NO2, an oxidizing gas, and H2, a reducing gas. In the presence of NO2, the electronic sensitization caused by LCP outweighs the chemical sensitization due to NO2, thereby resulting in both n-type and p-type behaviors. In contrast, when exposed to H2, the nanorods exhibit only n-type behavior, as the chemical sensitization effect of H2 is more significant than the electronic sensitization effect of LCP. The observed variations in electronic properties can be systematically accounted for by the differential bonding energies between oxidizing and reducing gases.

Water Splitting Reaction Mechanism on Transition Metal (Fe-Cu) Sulphide and Selenide Clusters-А DFT Study.

The tetracarbonyl complexes of transition metal chalcogenides M2X2(CO)4, where M = Fe, Co, Ni, Cu and X = S, Se, are examined by density functional theory (DFT). The M2X2 core is cyclic with either planar or non-planar geometry. As a sulfide, it is present in natural enzymes and has a selective redox capacity. The reduced forms of the selenide and sulfide complexes are relevant to the hydrogen evolution reaction (HER) and they provide different positions of hydride ligand binding: (i) at a chalcogenide site, (ii) at a particular cation site and (iii) in a midway position forming equal bonds to both cation sites. The full pathway of water decomposition to molecular hydrogen and oxygen is traced by transition state theory. The iron and cobalt complexes, cobalt selenide, in particular, provide lower energy barriers in HER as compared to the nickel and copper complexes. In the oxygen evolution reaction (OER), cobalt and iron selenide tetracarbonyls provide a low energy barrier via OOH* intermediate. All of the intermediate species possess favorable excitation transitions in the visible light spectrum, as evidenced by TD-DFT calculations and they allow photoactivation. In conclusion, cobalt and iron selenide tetracarbonyl complexes emerge as promising photocatalysts in water splitting.

Modulating Entropic Driving Forces to Promote Metal Ion Mobility in Ionic Liquids

Ionic liquids and organic ionic plastic crystals promise to provide safer, nonflammable alternatives to the unstable organic electrolytes currently used in commercial batteries. However, the performance of ionic liquids and organic ionic plastic crystals as battery electrolytes has been hindered by poor lithium transport, in large part due to the formation of strong lithium-anion complexes. Similar ion coordination exists in ionic liquids containing dissolved sodium, magnesium, and calcium, suggesting that design of ionic liquids for sodium and multivalent battery chemistries will face similar challenges. In this talk, I will discuss our work on the design and characterization of novel ionic liquid-inspired organic electrolytes that leverage unique self-assembly properties of molecular diamond templates, called “diamondoids,” to promote selective redox ion transport. By leveraging the unique self-assembly properties of diamondoids, we show that metal cation-anion coordination can be reduced, and possibly removed, resulting in enhanced mobility of redox-active cations. Specifically, our investigation of electrolyte phase behavior, vibrational spectra, and magnetic environments demonstrates that metal salt solubility can remain high while metal cation-anion coordination is suppressed. Our results provide a new paradigm for enhancing redox species mobility in ionic liquid-derived electrolytes by engineering cation functional groups to enhance organic cation-anion interactions, suppress metal coordination, and leverage packing mismatches to enhance redox species mobility.

Ammonia Recovery from Manure Wastewater and Simultaneous Electrosynthesis and Wastewater Treatment Using Ion Selective Redox Material

The environmental pressure due to greenhouse gas emissions and water contamination generated by livestock manure motivates the development of new approaches to reduce their environmental impacts and improve sustainability. Effective approaches to recover nutrients, especially ammonia, from manure wastewater to produce fertilizer are needed. Here we develop a new electrochemical strategy to achieve simultaneous ammonium (NH4 +) ion recovery and electrochemical synthesis using potassium nickel hexacyanoferrate as the ammonium ion-selective redox material to mediate the process. Our approach is built on our recent advances in designing modular electrochemical synthesis mediated using redox active materials (which we call redox reservoirs). Specifically, NH4 + (and K+) can be spontaneously uptaken from manure wastewater with a nutrient (NH4 + and K+) selectivity of ~100% driven by the oxidation of organic matter. Subsequently, NH4 +-rich fertilizers are released electrochemically together with the electrosynthesis of value-added chemicals, such as H2O2 as a disinfectant, without expensive ion-exchange membranes. We will also discuss our preliminary results on simultaneous advanced oxidation processes to improve the treatment of PFAS chemicals in wastewater. These results provide a new conceptual strategy for distributed electrochemical resource recovery and on-demand electrochemical manufacturing that can improve the sustainability of agricultural and wastewater treatment processes

Carbon-Neutral Energy Cycle via Highly Selective Electrochemical Reactions Using Biomass Derivable Organic Liquid Energy Carriers

Abstract Efficient storage and transport of electric energy is essential to promote the use of renewable energy based electricity. We demonstrate an energy cycle based on highly selective redox reactions between lactic acid (Lac) and pyruvic acid (Pyr), both of which are liquid under ambient conditions and can be obtained from biomass resources, thus realizing a completely low-emission system. As an energy storage device, an electrosynthesis cell (LAEC) for the production of Lac from Pyr was constructed using a membrane electrode assembly (MEA) consisting of a TiO2 cathode catalyst for the electroreduction of Pyr and an IrOx anode catalyst for water oxidation. Our LAEC achieved highly efficient Lac production from 10 M Pyr aqueous solution with Faradaic efficiency (FE) of approximately 100% in the applied voltage range of 1.4–2.4 V, resulting in an energy conversion efficiency of 50% and a current density of −0.4 A cm−2 at 2.0 V. Direct Lac fuel cell (DLAFC) was also constructed and its FE values for the Pyr production reached approximately 100%, enabling direct electronic energy storage in bio-derivative liquid carriers and efficient energy circulation with minimal CO2 emissions.

Ammonium Recovery from Manure Wastewater and Simultaneous Electrosynthesis Using Ammonium-Ion Selective Redox Material

The environmental pressure due to greenhouse gas emissions and water contamination generated by livestock manure motivates the development of new approaches to reduce their environmental impacts and improve sustainability. Effective approaches to recover nutrients, especially ammonium, from manure wastewater to produce fertilizer are needed. Here we develop a new electrochemical strategy to achieve simultaneous ammonium recovery and electrochemical synthesis using potassium nickel hexacyanoferrate (KNiHCF) as the ammonium ion-selective redox material to mediate the processes. The KNiHCF electrode spontaneously uptakes ammonium (and K+) from manure wastewater with a nutrient (NH4 + and K+) selectivity of ~100% and effective reduction of chemical oxygen demand (COD). The subsequent electrochemical process achieves the co-production of NH4 +-rich fertilizers and value-added chemicals, such as H2 as a green fuel and H2O2 as a disinfectant, without expensive ion-exchange membranes. These results provide a new conceptual strategy and insights for distributed electrochemical resource recovery and on-demand electrochemical manufacturing that can improve agricultural sustainability.

Directing the Selectivity of Oxygen Reduction to Water by Confining a Cu Catalyst in a Metal Organic Framework.

Electrocatalysis is to play a key role in the transition towards a sustainable chemical- and energy industry and active, stable and selective redox catalysts are very much needed. Porous structures such as Metal Organic Frameworks (MOFs) are interesting materials as these may influence selectivity of chemical reactions through confinement effects. In this work, we incorporate the oxygen reduction catalyst Cu-tmpa into the NU1000 MOF. Confinement of the catalyst within Nu1000 steers the selectivity of the oxygen reduction reaction (ORR) towards water rather than peroxide. This is attributed to retention of the obligatory H2O2 intermediate in close proximity to the catalytic center. Moreover the resulting Nu1000/Cu-tmpa MOF shows an excellent activity and stability in prolonged electrochemical studies, illustrating the potential of this approach.

LUMO-Mediated Se and HOMO-Mediated Te Nanozymes for Selective Redox Biocatalysis.

Selenium (Se) and tellurium (Te) nanomaterials with novel chain-like structures have attracted widespread interest owing to their intriguing properties. Unfortunately, the still-unclear catalytic mechanisms have severely limited the development of biocatalytic performance. In this work, we developed chitosan-coated Se nanozymes with a 23-fold higher antioxidative activity than Trolox and bovine serum albumin coated Te nanozymes with stronger prooxidative biocatalytic effects. Based on density functional theory calculations, we first propose that the Se nanozyme with Se/Se2- active centers favored reactive oxygen species (ROS) clearance via a LUMO-mediated mechanism, while the Te nanozyme with Te/Te4+ active centers promoted ROS production through a HOMO-mediated mechanism. Furthermore, biological experiments confirmed that the survival rate of γ-irritated mice treated with the Se nanozyme was maintained at 100% for 30 days by inhibiting oxidation. However, the Te nanozyme had the opposite biological effect via promoting radiation oxidation. The present work provides a new strategy for improving the catalytic activities of Se and Te nanozymes.

Introducing Novel Materials with Diffuse Electrons for Applications in Redox Catalysis and Quantum Computing via Theoretical Calculations

Diamond-like structures, where carbon atoms have been replaced with Li+ and C–C bonds with diamines, have currently been introduced as new materials, which can host diffuse electrons in the periphery of each lithium tetra-amine center. These materials display a diverse range of properties behaving as metals or semiconductors depending on the diamine chain length. Multi-reference wavefunction and density functional theory calculations were employed to study the electronic structure of these materials. Initially, gas phase calculations are performed on isolated (NH3)3LiNH2(CH2)1–10H2NLi(NH3)3 molecular strings. One diffuse electron surrounds the periphery of each −NH2Li(NH3)3 terminus. The two terminal electrons couple into a triplet and open-shell singlet states, which are nearly degenerate for long chains and as closed shell singlets for short. At intermediate lengths, the wavefunction of the ground-state singlet state mixes both open- and closed-shell configurations raising doubts about which configuration should be considered for density functional theory calculations. Observations from gas phase calculations accurately predict properties from the condense phase density functional theory calculations carried out for proposed crystalline Li-diamine materials, offering an avenue for further development and insight. Spin-polarized and unpolarized calculations are performed for the whole range of hydrocarbon sizes reporting geometrical and electronic band structures, spin density contours, and density of states. Diffuse electrons can be used for redox reactions or can serve as qubits for quantum computing. Future work will focus on decorating the hydrocarbon backbone with functional groups and/or bulky units, in order to facilitate or block the association between neighboring electrons for more controlled quantum computing applications and propose materials for selective redox catalysis.

CrOx/Ce1−xZrxO2 for chemical looping propane oxidative dehydrogenation: The redox interaction between CrOx and the support

Propane dehydrogenation is an attractive alternative for propylene production to petroleum-based routes. However, overcoming deactivation and toxicity of catalysts in propane direct dehydrogenation (PDH), and over oxidation in oxidative dehydrogenation (ODHP) remain challenging. Here, a chromium-based catalyst supported on a Ce-Zr solid solution is constructed for chemical looping oxidative propane dehydrogenation (CL-ODHP). A dual modulation of oxygen species by Zr doping was unraveled by characterizations and DFT calculation: the oxygen of surface CrOx was constrained while the oxygen mobility of the Ce-Zr support was promoted. Based on these properties, the interaction between surface CrOx and the support further enables an oxygen “donor–acceptor”, which potentially functions as in situ activation and regeneration of redox CrOx species as well as blockage of non-selective oxygen released from the Ce-Zr support. The optimized material (7.5Cr/Ce0.8Zr0.2O2) achieves propane conversion up to 50% and propylene yield of 31% at 600 °C, and has the lowest Cr content among previously reported Cr-based catalysts that have comparable performance. These results provide insights for the design of highly active and selective redox catalysts for chemical looping as a reaction engineering strategy for the upgrading of propane dehydrogenation processes.

Azo Appended Modified Lawsone Derived Ru-Systems with Multi-Redox Entities. Competitive Electronic Form and the Question of Azo Reduction.

The article dealt with the ruthenium complexes of redox active azo appended modified lawsone L1 - (HL1 : (E)-2-hydroxy-3-(p-tolyldiazenyl)naphthalene-1,4-dione))/L2 - (HL2 :5-hydroxy-6-p-tolylazobenzo[a]phenazine) derived [RuIII (acac)2 (L1 - )]/[RuIII (acac)2 (L2 - )] 1/5, [RuII (bpy)2 (L1 - )]ClO4 /[RuII (bpy)2 (L2 - )]ClO4 [2]ClO4 /[6]ClO4 , ctc-[RuII (pap)2 (L1 - )]ClO4 /ctc-[RuII (pap)2 (L2 - )]ClO4 [3]ClO4 /[7]ClO4 and [RuII (CO)(H)(PPh3 )2 (L1 - )]/[RuII (CO)(Cl)(PPh3 )2 (L2 - )] 4/8 (acac=acetylacetonate, bpy=2,2'-bipyridine, pap=2-phenylazopyridine). The ligands L1 - and L2 - differed with respect to the para-quinone versus phenazine moieties linked to the azo function. Structural analysis of the complexes established unreduced state of the azo (N=N) group of coordinated L1 - /L2 - or pap as well as unprecedented para-quinone form of L1 - . The involvement of selective redox center(s) towards the accessible redox steps of the complexes encompassing multiple redox active entities i. e. Ru, phenolate (L1 - /L2 - ), para-quinone (L1 - ), phenazine (L2 - ), azo (L1 - /L2 - , pap), diimine (bpy) was analyzed by combined experimental and DFT calculations. It revealed that under the prevailing competitive scenario oxidation was mostly dominated by the phenolate group of L1 - /L2 - (phenolate→phenoxide), while successive reductions were taken place either at the para-quinone/phenazine units of L1 - /L2 - or azo/diimine functions of pap/bpy. Though the azo function of pap in 3+ /7+ underwent facile reduction, the same azo function associated with L1 - /L2 - conspicuously remained unreduced in all occasions. The frontier molecular orbital analysis revealed that the propensity of pap for the azo reduction with special reference to that in L1 - /L2 - could be correlated with its relatively lower energy π* orbital (LUMO). Complexes displayed intense LMCT (1/5) and bpy (2+ /6+ ), pap (3+ /7+ ), L (4/8) targeted MLCT transitions in the visible region.