Bifunctional Complex Research Articles

Initiation of ERAD by the bifunctional complex of Mnl1 mannosidase and protein disulfide isomerase.

Misfolded glycoproteins in the endoplasmic reticulum (ER) lumen are translocated into the cytosol and degraded by the proteasome, a conserved process called ER-associated protein degradation (ERAD). In S. cerevisiae , the glycan of these proteins is trimmed by the luminal mannosidase Mnl1 (Htm1) to generate a signal that triggers degradation. Curiously, Mnl1 is permanently associated with protein disulfide isomerase (Pdi1). Here, we have used cryo- electron microscopy, biochemical, and in vivo experiments to clarify how this complex initiates ERAD. The Mnl1-Pdi1 complex first de-mannosylates misfolded, globular proteins that are recognized through a C-terminal domain (CTD) of Mnl1; Pdi1 causes the CTD to ignore completely unfolded polypeptides. The disulfides of these globular proteins are then reduced by the Pdi1 component of the complex, generating unfolded polypeptides that can be translocated across the membrane. Mnl1 blocks the canonical oxidative function of Pdi1, but allows it to function as the elusive disulfide reductase in ERAD.

Innovative hybrid and bifunctional rare earth complexes as corrosion inhibitors for AA2024 Alloy: Electrochemical and surface analysis enhanced by DFT/MD simulation

The hybrid inorganic–organic compounds, RE-thioglycolates (RE = Ce, Nd, Sm), were analyzed as effective green corrosion inhibitors of AA2024 alloy in 0.1 M NaCl solution. Utilizing Electrochemical Impedance Spectroscopy the protective inhibitory film on the alloy’s surface was affirmed, alongside the persistence of a natural oxide layer over time. These complexes demonstrated notable corrosion inhibition efficiency over immersion from 1 h to 3 days, with Sm-thiog retaining the high inhibition efficiency of over 95 % during 72 h. All RE-thioglycolates are mixed-type inhibitors, imparting resistance against both general and pitting corrosion.The presence of a protective inhibitory film on the AA2024 surface in NaCl solution has been substantiated through various analytical techniques including FTIR, SEM/EDS and XPS. A detailed examination of the differential inhibition exhibited by these bifunctional complexes is elucidated through theoretical calculations. The smallest difference of HOMO and LUMO orbitals for Sm-thiog of 3.21 eV indicates that this inhibitor attains the strongest donor–acceptor interactions with the metal surface. Predictions generated by Density Functional Theory/Molecular Dynamics simulations suggest the potential formation of diverse inhibitory species within the electrolyte. The corrosion inhibition mechanism proposed for RE-thioglycolates is grounded in electrochemical and theoretical insights, and subsequently validated through surface analysis methods.

Coupling CO2 Reduction and Acetyl-CoA Formation: The Role of a CO Capturing Tunnel in Enzymatic Catalysis.

The bifunctional CO-dehydrogenase/acetyl-CoA synthase (CODH/ACS) complex couples the reduction of CO2 to the condensation of CO with a methyl moiety and CoA to acetyl-CoA. Catalysis occurs at two sites connected by a tunnel transporting the CO. In this study, we investigated how the bifunctional complex and its tunnel support catalysis using the CODH/ACS from Carboxydothermus hydrogenoformans as a model. Although CODH/ACS adapted to form a stable bifunctional complex with a secluded substrate tunnel, catalysis and CO transport is even more efficient when two monofunctional enzymes are coupled. Efficient CO channeling appears to be ensured by hydrophobic binding sites for CO, which act in a bucket-brigade fashion rather than as a simple tube. Tunnel remodeling showed that opening the tunnel increased activity but impaired directed transport of CO. Constricting the tunnel impaired activity and CO transport, suggesting that the tunnel evolved to sequester CO rather than to maximize turnover.

Insights into the Enantioselective Au(I)‐Catalyzed Reactions between 2‐Alkynyl Ketones and Naphthols using the TCDC Approach

AbstractThe CPAPhosAuCl bifunctional complexes catalyse the enantioselective tandem cycloisomerization‐nucleophilic addition reactions between 2‐alkynylenones and naphthols, where naphthols behave mainly as O‐nucleophiles. The inherent acidity of the catalysts induces then the isomerization of the O‐addition‐ into the C‐addition products with concomitant decrease of their enantiomeric excesses. In depth mechanistic studies have provided insights into these processes. Subsequently, the undesired racemization pathways could be suppressed by using substituted naphthols as nucleophiles, which delivered a large series of chiral bicyclic furanes in high enantioselectivities.

Unveiling a unique outer-sphere pathway in manganese-catalyzed acceptorless dehydrogenation reaction.

First-row transition metals are widely used in acceptorless dehydrogenative coupling reactions, making the detailed investigation of their catalytic mechanisms crucial for the rational design of efficient catalysts. In this study, density functional theory (DFT) was employed to explore the mechanism of an acceptorless dehydrogenation reaction catalyzed by a bifunctional complex based on a high-spin Mn(II) center. The computational results reveal that the Mn(II) catalyst follows a novel dehydrogenation pathway, where the external base KOH first coordinates to the metal center, and dehydrogenation proceeds via an outer-sphere mechanism. The hydride transfer step is identified as the rate-determining step, with an energy barrier of 26.3 kcal mol-1, consistent with experimental results. To further investigate the selectivity of the mechanism, energy decomposition analysis (EDA) and extended transition state-natural orbitals for chemical valence (ETS-NOCV) analysis were conducted on key transition states. The results show that the small steric hindrance and strong orbital interactions of the external base KOH are the key factors contributing to the selectivity of this mechanism. These findings not only deepen our understanding of the reaction mechanism but also provide valuable theoretical insights for the design and optimization of future acceptorless dehydrogenation catalysts.

Strategic Synthesis of Heptacoordinated FeIII Bifunctional Complexes for Efficient Water Electrolysis.

In this research, highly efficient heterogeneous bifunctional (BF) electrocatalysts (ECs) have been strategically designed by Fe coordination (CR ) complexes, [Fe2 L2 (H2 O)2 Cl2 ] (C1) and [Fe2 L2 (H2 O)2 (SO4 )].2(CH4 O) (C2) where the high seven CR number synergistically modifies the electronic environment of the Fe centre for facilitation of H2 O electrolysis. The electronic status of Fe and its adjacent atomic sites have been further modified by the replacement of -Cl- in C1 by -SO4 2- in C2. Interestingly, compared to C1, the O-S-O bridged C2 reveals superior BF activity with extremely low overpotential (η) at 10 mA cm-2 (140 mVOER , 62 mVHER ) and small Tafel slope (120.9 mV dec-1 OER , 45.8 mV dec-1 HER ). Additionally, C2 also facilitates a high-performance alkaline H2 O electrolyzer with cell voltage of 1.54 V at 10 mA cm-2 and exhibits remarkable long-term stability. Thus, exploration of the intrinsic properties of metal-organic framework (MOF)-based ECs opens up a new approach to the rational design of a wide range of molecular catalysts.

Strategic Synthesis of Heptacoordinated FeIII Bifunctional Complexes for Efficient Water Electrolysis

AbstractIn this research, highly efficient heterogeneous bifunctional (BF) electrocatalysts (ECs) have been strategically designed by Fe coordination (CR) complexes, [Fe2L2(H2O)2Cl2] (C1) and [Fe2L2(H2O)2(SO4)].2(CH4O) (C2) where the high seven CR number synergistically modifies the electronic environment of the Fe centre for facilitation of H2O electrolysis. The electronic status of Fe and its adjacent atomic sites have been further modified by the replacement of −Cl− in C1 by −SO42− in C2. Interestingly, compared to C1, the O−S−O bridged C2 reveals superior BF activity with extremely low overpotential (η) at 10 mA cm−2 (140 mVOER, 62 mVHER) and small Tafel slope (120.9 mV dec−1OER, 45.8 mV dec−1HER). Additionally, C2 also facilitates a high‐performance alkaline H2O electrolyzer with cell voltage of 1.54 V at 10 mA cm−2 and exhibits remarkable long‐term stability. Thus, exploration of the intrinsic properties of metal–organic framework (MOF)‐based ECs opens up a new approach to the rational design of a wide range of molecular catalysts.

Switching between Hydrogenation and Olefin Transposition Catalysis via Silencing NH Cooperativity in Mn(I) Pincer Complexes.

While Mn-catalyzed (de)hydrogenation of carbonyl derivatives has been well established, the reactivity of Mn hydrides with olefins remains very rare. Herein, we report a Mn(I) pincer complex that effectively promotes site-controlled transposition of olefins. This reactivity is shown to emerge once the N–H functionality within the Mn/NH bifunctional complex is suppressed by alkylation. While detrimental for carbonyl (de)hydrogenation, such masking of the cooperative N–H functionality allows for the highly efficient conversion of a wide range of allylarenes to higher-value 1-propenybenzenes in near-quantitative yield with excellent stereoselectivities. The reactivity toward a single positional isomerization was also retained for long-chain alkenes, resulting in the highly regioselective formation of 2-alkenes, which are less thermodynamically stable compared to other possible isomerization products. The detailed mechanistic analysis of the reaction between the activated Mn catalyst and olefins points to catalysis operating via a metal–alkyl mechanism—one of the three conventional transposition mechanisms previously unknown in Mn complexes.

Targeted inhibition of methicillin-resistant Staphylococcus aureus biofilm formation by a graphene oxide-loaded aptamer/berberine bifunctional complex

Biofilm formation is known to promote drug resistance in methicillin-resistant Staphylococcus aureus (MRSA), which is closely related to persistent infections in hospital settings. In this study, a DNA aptamer specific to penicillin-binding protein 2a (PBP2a) with a dissociation constant (K d) of 82.97 ± 8.86 nM was obtained after 14 cycles of systematic evolution of ligands by exponential enrichment (SELEX). Next, a bifunctional complex containing the aptamer intercalated by berberine into the double-strand region was prepared and adsorbed onto the surface of graphene oxide (GO) by π-stacking interactions. The GO-loaded aptamer/berberine bifunctional complex showed significantly higher inhibition of MRSA biofilm formation than the control. Furthermore, this study shows that the complex possesses anti-biofilm activity, which can be attributed to the ability of the aptamer to reduce cell-surface attachment by blocking the function of PBP2a and berberine to attenuate the level of the accessory gene regulator (agr) system, which plays an important role in mediating MRSA biofilm formation. Therefore, the simultaneous delivery of berberine and PBP2a-targted aptamer using GO may have potential for the treatment of chronic infections caused by MRSA biofilms. It also provides a new avenue for multitarget treatment of bacterial biofilms.

M(Me6Tren)X]X complex as efficacious bifunctional catalyst for CO2 cycloaddition: The synergism of the metal and halogen ions

Efficient catalysis for fixation and conversion of CO2 is of significance to carbon neutralization. Here, a series of C3 symmetric bifunctional complex catalysts with different metals (Ni, Co, Cu) have been strategically synthesized and evaluated in the CO2 cycloaddition with epoxides. Among these catalysts, [Ni(Me6Tren)I]I 3c exhibits the best performance affording up to 99.1% yield of chloropropylene carbonate under ambient (60 °C, CO2 balloon), cocatalyst- and solvent-free conditions. TPD and XPS showed 3c possessed excellent acid center. Single crystal X-ray diffraction indicated the facile dissociation of Ni-I based on the bond length information. The synergistic effect of the Ni(II) acidic center, the axial and outer iodine ions was discussed. Based on the structure-activity relationship, plausible reaction pathways were proposed for the bifunctional catalysts. Moreover, a large-scale synthesis of chloropropylene carbonate (350 mmol) and recyclability of 3c catalyst highlight its potential for industrial applications.

Insights into H2 Activation and Styrene Hydrogenation by Nickel–Borane and Nickel–Alane Bifunctional Catalysts

Lewis acid–transition metal bifunctional complexes have recently emerged as a new class of catalysts. The nickel–borane complex, Ni[(Mes)B(o-Ph2PC6H4)2], has been reported as an efficient catalyst for H2 activation and styrene hydrogenation. Here, we performed density functional theory calculations to investigate the cooperation between nickel and a group 13 element (Z = B and Al), including the effect of its substituent (R = Mes, Ph, and C6F5 in Ni[(R)Z(o-Ph2PC6H4)2]), on H2 activation and styrene hydrogenation. We found that H2 activation by the nickel–borane complex is dominated by charge transfer from the σ-bonding orbital of H2 to the p-based vacant orbital of boron, whereas H2 activation by the nickel–alane complex is governed by charge transfer from the d-based orbital of Ni to the σ*-antibonding orbital of H2. The resulting trans-dihydride nickel–alane complex has higher negative charges on both terminal and bridging hydrogen atoms than the corresponding nickel–borane complex. This accounts for the lower energy barriers observed for the nickel–alane complex toward both H2 activation and the subsequent hydrogenation of styrene. While the C6F5 electron-withdrawing substituent on boron of the nickel–borane complex facilitates H2 activation and styrene hydrogenation better than the phenyl or mesityl substituent, the substituent on aluminum does not affect the reactivity of the nickel–alane complex. As H2 activation and styrene hydrogenation by nickel–alane complexes proceed with lower energy barriers than those by nickel–borane complexes, the nickel–alane complex with [(R)Z(o-Ph2PC6H4)2] ligand scaffold should be more reactive than the nickel–borane counterpart. Insights into the role of Lewis acid in this Z-type σ-acceptor ligand scaffold will assist with the development of metal–ligand bifunctional catalysts.

Construction of Magneto‐Fluorescent Bifunctional Spin‐Crossover Fe(II) Complex from Pyrene‐Decorated Pybox Ligand

AbstractThe construction of magneto‐fluorescent bifunctional complexes is a feasible approach toward multifunctional molecular materials. Herein we report the synthesis and properties studies of a mononuclear Fe(II) complex [FeL2](ClO4) (1), where L is a pyridine‐2,6‐bis(oxazoline) (pybox) ligand decorated by the pyrene fluorophore. Magnetic susceptibility measurement of desolvated complex 1‐d shows an incomplete and gradual spin‐crossover in the temperature range 50–300 K, which is further confirmed via 57Fe Mössbauer spectroscopy study. Light‐induced excited spin state trapping (LIESST) is also observed below 70 K when the powder sample is irradiated by a 532 nm laser. The change in absorption during the spin‐crossover (SCO) process is investigated via the temperature‐dependent UV‐vis spectroscopy. As expected, through introducing the chromophore, 1 displays fluorescence in both solution and solid state, achieving the coexistence of spin‐crossover and fluorescence in one compound.

Alkyl Phosphine Free, Metal‐Ligand Cooperative Complex Catalyzed Alcohol Dehydrogenative Coupling Reactions

AbstractIn last two decades alcohol has drawn a special attention as a building blocks due to its abundance, low cost and less toxic nature which can be derived from various sustainable resources. By dehydrogenation of alcohol, aldehyde/ketone can be easily accessed which can be further coupled with several nucleophiles for the construction of complex molecules. Among the various strategies, metal‐ligand cooperation is a powerful and efficient tool for the utilization of alcohol to synthesize variety of value‐added products. Numerous alkyl phosphine based bifunctional complexes are well‐known in the literature for the alcohol dehydrogenative coupling reactions. However, the presence of alkyl phosphine moiety and air and moisture sensitive nature of the metal complexes hinder their broad application in catalysis. In this minireview, we highlighted air and moisture stable, metal‐ligand cooperative 5d, 4d and 3d metal‐based complexes which were effectively utilized to fabricate different value‐added compounds by alcohol dehydrogenative coupling reactions.

Syntheses, Characterization, and Application of Tridentate Phenoxyimino-Phenoxy Aluminum Complexes for the Coupling of Terminal Epoxide with CO2: From Binary System to Single Component Catalyst

A series of binuclear aluminum complexes 1–3 supported by tridentate phenoxyimino-phenoxy ligands was synthesized and used as catalysts for the coupling reaction of terminal epoxide with carbon dioxide. The aluminum complex 1, which is catalytically inactive toward the coupling of epoxide with CO2 by itself, shows moderate activity in the presence of excess nucleophiles or organic bases at high temperature. In sharp contrast to complex 1, bifunctional complexes 2 and 3, which incorporate tertiary amine groups as the built-in nucleophile, are able to efficiently transform terminal epoxide with CO2 to corresponding cyclic carbonates as a sole product by themselves at 100 °C. The number of amine groups on the ligand skeleton and the reaction temperature exert a great influence on the catalytic activity. The bifunctional complexes 2 and 3 are also active at low carbon dioxide pressure such as 2 atm or atmospheric CO2 pressure. Kinetic studies of the coupling reactions of chloropropylene oxide/CO2 and styrene oxide/CO2 using bifunctional catalysts under atmospheric pressure of CO2 demonstrate that the coupling reaction has a first-order dependence on the concentration of the epoxide.

High colloidal stability ZnO nanoparticles independent on solvent polarity and their application in polymer solar cells

Significant aggregation between ZnO nanoparticles (ZnO NPs) dispersed in polar and nonpolar solvents hinders the formation of high quality thin film for the device application and impedes their excellent electron transporting ability. Herein a bifunctional coordination complex, titanium diisopropoxide bis(acetylacetonate) (Ti(acac)2) is employed as efficient stabilizer to improve colloidal stability of ZnO NPs. Acetylacetonate functionalized ZnO exhibited long-term stability and maintained its superior optical and electrical properties for months aging under ambient atmospheric condition. The functionalized ZnO NPs were then incorporated into polymer solar cells with conventional structure as n-type buffer layer. The devices exhibited nearly identical power conversion efficiency regardless of the use of fresh and old (2 months aged) NPs. Our approach provides a simple and efficient route to boost colloidal stability of ZnO NPs in both polar and nonpolar solvents, which could enable structure-independent intense studies for efficient organic and hybrid optoelectronic devices.

Water soluble bifunctional complex of tetrapyridino porphyrazinato zinc(II) as highly efficient catalyst for CO2 insertion into epoxide cycles

Abstract The highly active water soluble bifunctional catalyst of porphyrazinato zinc(II) ([Zn(2,3-tmtppa)](MeSO4)4) in which tmtppa stands for tetramethylated tetrapyridino porphyrazine was applied for cycloaddition reaction of CO2 into epoxides to obtain cyclic carbonates. It seems that our catalyst can act as an efficient phase transfer agent because of the presence of tetra positive groups in its structure which increased catalyst solubility in water. Accordingly, the CO2 fixation reaction was performed in water utilizing cheap, simple and commercially available potassium iodide co-catalyst instead of expensive quaternary onium salts (as co-catalyst) because of having the quaternized parts in the porphyrazine skeleton. The mentioned homogeneous catalytic system was adaptable to CO2 insertion into aliphatic, aromatic and functional epoxides efficiently and selectively under mild reaction conditions. Furthermore, our catalyst system was easily recovered and reused in at least three cycles without any decrease of catalytic activity.

White light emission from a green cyclometalated platinum(ii) terpyridylphenylacetylide upon titration with Zn(ii) and Eu(iii ).

The cyclometalated Pt(ii) acetylide derivative with a 1,3-bis(N-octyl-benzimidazol-2-yl)benzene (N^C^N) ligand and a free terpyridine (TPY) receptor has been successfully synthesized and characterized. X-ray crystallography shows its inefficient conjugation degree between the [(N^C^N)Pt] and TPY planes. This bifunctional complex shows an enhanced 1MLCT/LLCT absorption band (ε = 3.30 × 104 dm3 mol-1 cm-1) centered at λmax = 365 nm, and the well-resolved vibronic-structured 3MLCT/LLCT emission bands (Φ = 0.08, τ = 3.43 μs) in the range of ca. 475-700 nm. Consecutive titrations show that added Zn2+ and Eu(HFA)3 bond to its free TPY receptor with 1 : 2 and 1 : 1 stoichiometry to form the heterotrinuclear Pt-Zn-Pt (Ka = 3.48 × 104 mol-1 dm3) and heterodinuclear Pt-Eu (Ka = 1.73 × 104 mol-1 dm3) complexes, respectively. A sensitizing effect of Zn2+ on the TPY unit, and the incomplete d → f energy transfer from the [(N^C^N)Pt(ii)] antenna donor to the Eu(iii) center with maximum efficiency of 51.8% are observed. Using an in situ mixed titration strategy, the R/G/B emission triads consisted of red [(TPY)Eu(HFA)3] and green [(N^C^N)Pt(ii)] dual phosphorescence and blue [(TPY)Zn(TPY)] fluorescence, which can be well balanced to realize the white-light-emission with CIE coordinates (x = 0.36, y = 0.36) by precisely controlling the molar ratio (9 : 1 : 2) of the parent complexes, Eu(HFA)3 and Zn(ClO4)2.

Mechanism-Inspired Design of Bifunctional Catalysts for the Alternating Ring-Opening Copolymerization of Epoxides and Cyclic Anhydrides.

Advances in catalysis have enabled the ring-opening copolymerization of epoxides and cyclic anhydrides to afford structurally and functionally diverse polyesters with controlled molecular weights and dispersities. However, the most common systems employ binary catalyst/cocatalyst pairs which suffer from slow polymerization rates at low loadings. Inspired by new mechanistic insight into the function of binary metal salen/nucleophilic cocatalyst systems at low concentrations, we report a bifunctional complex in which the salen catalyst and an aminocyclopropenium cocatalyst are covalently tethered. A modular ligand design circumvents the extended linear syntheses typical of bifunctional catalysts, enabling systematic variation to understand and enhance catalytic activity. The optimized bifunctional aluminum salen catalyst maintains excellent activity for the ring-opening copolymerization of epoxides and cyclic anhydrides at low concentrations (≥0.025 mol %), and the aminocyclopropenium cocatalyst suppresses undesirable transesterification and epimerization side reactions, preserving the integrity of the polymer backbone.

Evaluation of Synthesized Catalytic Complex Structure-Forming Ability during Paraffin Base Tar Upgrade

The combination of the synthesized multicomponent bifunctional catalytic complex (MBC) components with heavy oil residues (HOR) of the paraffin-naphthenic (P-N) base leads to the chemical structuring of the hydrocarbon (HC) segments of the raw material molecules, and the specifics of HOR physicochemical structure, which will be the criteria for the selection of modifiers with a certain chemical nature [1,2,3,4]. It has been established that the introduction of catalytic activators in the tar composition promotes both the intensification of the oxidation process and the production of bituminous insulating material (BIM) with high physicomechanical properties [1,2,4].Raw materials for the production of special bituminous materials must be highly resinous with a P-HC content of up to 3% by weight. Based on the works by A.S. Kolbanovskaya [6], this is explained by the fact that the dispersed structure of bitumen is significantly dependent on the content of P-HC, since the dispersed phase in the oils is formed by naphthenic (N-) and PN-A-HC at certain temperatures with the side chains of the paraffinic P-HC series. If their content is more than 3% by weight the crystallization skeleton of P-HC is developed, which provides stiffness and reduces the plasticity interval for the system. Together with this, it is known that in the process of HOR oxidation the amount of low-molecular-weight oil A-HC decreases continuously, and the relative amount of PN-HC increases. Due to this, the affinity of the dispersion medium (DM) decreases to asphaltenes [7,8,9], which, moreover, becomes larger, which leads to THE deterioration of the cohesion and adhesion-strength properties of BIM.

Supported ZnBr2and carbon nitride bifunctional complex catalysts for the efficient cycloaddition of CO2with diglycidyl ethers

Bifunctional catalysts with large surface areas performed well in the cycloaddition of CO2and bisepoxides under solvent and co-catalyst free conditions.