Volatile Organic Compounds(VOCs)are highly harmful to human beings and other organisms,and thus the elimination of VOCs is extremely urgent.Here,La-Si co-doped TiO_(2)microsphere photocatalysts,which were prepared by ...Volatile Organic Compounds(VOCs)are highly harmful to human beings and other organisms,and thus the elimination of VOCs is extremely urgent.Here,La-Si co-doped TiO_(2)microsphere photocatalysts,which were prepared by a hydrothermal method,exhibited high photocatalytic activity in the decomposition of formaldehyde compared with TiO_(2).The improved activity can be attributed to the promoted separation efficiency and density of the charge carriers,as verified by the electrochemical results in combination with density functional theory calculations.In addition,the Si dopant changed the microstructure and surface acidity,while the addition of La promoted the separation efficiency of charge carriers.More interestingly,it was found that singlet oxygen was the key species in the activation of molecular dioxygen,and it played a pivotal role in the photocatalytic decomposition of formaldehyde.This work provides a novel strategy for the selective activation of dioxygen for use in the decomposition of formaldehyde.展开更多
The dioxygen affinities and catalytic epoxidation performance of transition-metal hydroxamates were investigated for the first time. The effects of substituents on these properties were also discussed in the paper.
The oxygenation of cobalt (II) hydroxamates (CoL2) and its catalytic performance in oxidation of p-xylene to p-toluic acid (PTA) were examined. The effects of X and Y bonded to hydroxamate group on dioxygen affinitie...The oxygenation of cobalt (II) hydroxamates (CoL2) and its catalytic performance in oxidation of p-xylene to p-toluic acid (PTA) were examined. The effects of X and Y bonded to hydroxamate group on dioxygen affinities and catalytic oxidation performance were also investigated.展开更多
A copper-TiO2 based catalyst（Cu-OH-Cl-TiO2） was prepared through a slurry impregnation approach and the catalyst was found to be active and selective for the epoxidation of propylene by dioxygen. With a feed gas of ...A copper-TiO2 based catalyst（Cu-OH-Cl-TiO2） was prepared through a slurry impregnation approach and the catalyst was found to be active and selective for the epoxidation of propylene by dioxygen. With a feed gas of 10% C3H6, 10% O2 and 80% N2 at a gas hourly space velocity（GHSV） of 4000 h-1, a propylene conversion of 4.8% and a propylene oxide（PO） selectivity of 38.9% were achieved over the obtained Cu-OH-Cl-TiO2 catalyst at a reaction temperature of 500 K. It revealed that Cu2＋ provided by crystalline Cu2（OH）3Cl plays a key role in catalytic conversion of propylene to PO.展开更多
The oxygenation constants of transition-metal complexes with benzoin Schiff bases were measured and these complexes were first employed as models for mimicking monooxygenase in catalytic epoxidation of styrene. The hi...The oxygenation constants of transition-metal complexes with benzoin Schiff bases were measured and these complexes were first employed as models for mimicking monooxygenase in catalytic epoxidation of styrene. The highest conversion and selectivity were up to 39.6% and 100% respectively at ambient temperature and pressure. The effects of structures of the bridge group R in the ligands on the dioxygen affinities and catalytic activities to epoxidize styrene were also investigated.展开更多
The dioxygen affinities and biomimetic catalytic performance of transition-metal complexes with (15-crown-5) salophen and its substituted derivatives Mere examined. The oxygenation constants of Co(II) complexes with c...The dioxygen affinities and biomimetic catalytic performance of transition-metal complexes with (15-crown-5) salophen and its substituted derivatives Mere examined. The oxygenation constants of Co(II) complexes with crowned bis-Schiff bases were measured and their Mn(III) complexes were employed as models to mimic monooxygenase in catalytic epoxidation of styrene. The highest conversion and selectivity were up to 57.2% and 100% respectively at ambient temperature and pressure. The effects of crown ether ring and substituents R on the dioxygen affinities and catalytic activities were also investigated through comparing with the uncrowned analogues.展开更多
AIM: To evaluate whether serum and tumor indoleamine 2,3-dioxygenase activities can predict lymphatic invasion (LI) or lymph node metastasis in colorectal carcinoma.METHODS: The study group consisted of 44 colorectal ...AIM: To evaluate whether serum and tumor indoleamine 2,3-dioxygenase activities can predict lymphatic invasion (LI) or lymph node metastasis in colorectal carcinoma.METHODS: The study group consisted of 44 colorectal carcinoma patients. The patients were re-grouped according to the presence or absence of LI and lymph node metastasis. Forty-three cancer-free subjects without any metabolic disturbances were included into the control group. Serum neopterin was measured by enzyme linked immunosorbent assay. Urinary neopterin and biopterin, serum tryptophan (Trp) and kynurenine (Kyn) concentrations of all patients were determined by high performance liquid chromatography. Kyn/Trp was calculated and its correlation with serum neopterin was determined to estimate the serum indoleamine 2,3-dioxygenase activity. Tissue sections from the studied tumors were re-examined histopathologically and were stained by immunohistochemistry with indoleamine-2,3-dioxygenase antibodies.RESULTS: Neither serum nor urinary neopterin was significantly different between the patient and control groups (both P > 0.05). However, colorectal carcinoma patients showed a significant positive correlation between the serum neopterin levels and Kyn/Trp (r = 0.450, P < 0.01). Urinary biopterin was significantly higher in cancer cases (P < 0.05). Serum Kyn/Trp was significantly higher in colorectal carcinoma patients (P < 0.01). Lymphatic invasion was present in 23 of 44 patients, of which only 12 patients had lymph node metastasis. Eleven patients with LI had no lymph node metastasis. Indoleamine-2,3-dioxygenase intensity score was significantly higher in LI positive cancer group (44.56% ± 6.11%) than negative colorectal cancer patients (24.04% ± 6.90%), (P < 0.05). Indoleamine 2,3-dioxygenase expression correlated both with the presence of LI and lymph node metastasis (P < 0.01 and P < 0.05, respectively). A significant difference between the accuracy of diagnosis by using either total indoleamine-2,3-dioxygenase immunostaining score or of lymph node metastasis was found during the evaluation of cancer patients.CONCLUSION: Indoleamine-2,3-dioxygenase expression may predict the presence of unrecognized LI and lymph node metastasis and may be included in the histopathological evaluation of colorectal carcinoma cases.展开更多
The oxygenation constants （Ko2） of cobalt（Ⅱ） hydroxamates （CoL^1 2-CoL^3 2） with benzo-15-crown-5 （B15C5） pendants were measured over the range of -5 to ＋20 ℃, and the values of thermodynamic parameters （...The oxygenation constants （Ko2） of cobalt（Ⅱ） hydroxamates （CoL^1 2-CoL^3 2） with benzo-15-crown-5 （B15C5） pendants were measured over the range of -5 to ＋20 ℃, and the values of thermodynamic parameters （ΔH^0 and ΔS^0） were calculated based on these （Ko2） values, Meanwhile, these crowned complexes were employed to the oxidation for p-xylene to p-toluic acid with air at 110Δ under normal atmospheric pressure. The effects of B15C5 pendant and the length of chain bonded to B15C5 in these complexes on the O2-binding capabilities and oxidation for p-xylene were investigated with the comparison of crown-free analogues CoL^4 2.展开更多
The oxygenation constants and thermodynamic parameter （△H°, △S°） of a series of novel Co （Ⅱ） complexes with phenol ether bridged dihydroxamic acids CoL^1-CoL^6 were measured, their catalytic performan...The oxygenation constants and thermodynamic parameter （△H°, △S°） of a series of novel Co （Ⅱ） complexes with phenol ether bridged dihydroxamic acids CoL^1-CoL^6 were measured, their catalytic performance in oxidation of p-xylene to p-toluic acid （PTA） were examined. The modulation of O2-binding capabilities and catalytic oxidation activities by X （X = Cl, OCH3） and Y （Y = H, CH3, Cl） groups bonded to the aromatic rings of the Co （Ⅱ） complexes were investigated.展开更多
The oxygenation constants and thermodynamic parameter (ΔHo, ΔSo) of Co (II) complexes with unsymmetrical bis-Schiff baeses were measured and their Mn(III) complexes as models of mimicking monooxygenase were employed...The oxygenation constants and thermodynamic parameter (ΔHo, ΔSo) of Co (II) complexes with unsymmetrical bis-Schiff baeses were measured and their Mn(III) complexes as models of mimicking monooxygenase were employed to catalyze epoxidation of styrene. The effect of substituent R in a salicylidene of ML1~ML4 [ M = Co (II), Mn (III)Cl ] on the dioxygen affinities and biomimetic catalytic oxidation performance were also investigated. Among them, the MnL4Cl containing a pendant benzoaza crown ether ring showed highest conversion and selectiviy up to 54.9% and 96.9% respectively.展开更多
Thermodynamic data were determined for the reversible binding of O 2 to two compounds of dicobalt(II) di(meso tetra phenyl)porphyrin derivatives with different lengths of diamidoaliphatic bridge (abbreviated to Co ...Thermodynamic data were determined for the reversible binding of O 2 to two compounds of dicobalt(II) di(meso tetra phenyl)porphyrin derivatives with different lengths of diamidoaliphatic bridge (abbreviated to Co 2PP 8 and Co 2PP 4) in N,N dimethylformamide at room temperature. The partial pressure of dioxygen necessary for half oxygenation ( P 1/2 ) and Hill coefficient ( n ) at 298 K were determined as follows: P 1/2 =54.2 kPa, n =2.0 for Co 2PP 8 and P 1/2 =6.8 kPa, n =1.8 for Co 2PP 4,respectively. The rate equations of reversible oxygen binding by Co 2PP 8 were determined and the reaction path was proposed. The results of thermodynamic and kinetic studies indicate that there exists strong cooperative effect during oxygenation of the compounds. The ESR observation reveals that the dioxygen complexes formed in the solutions are of superoxo (Co O - 2) type.展开更多
ith an improved EHMO method, three modes (flat-lying, vertical , and in-clined insertion) for adsorption and activation of dioxygen on (100) , (110) and(111) surfaces of Na_2O and of K,O have been exaniinecl, and the ...ith an improved EHMO method, three modes (flat-lying, vertical , and in-clined insertion) for adsorption and activation of dioxygen on (100) , (110) and(111) surfaces of Na_2O and of K,O have been exaniinecl, and the interaction ofthese dioxygen adspecies with CH_4 and with CH_3 · (radical) from gas pliase liasbeen investigated. The results indicate that both oxides tend to forni less cliargedadspecies of dioxygen, with the flat-lying adsorption on (110) surface most favor-able energetically. All these cliemisorbed dioxygen species are capable of interactingeffectively with CH_4 and Abstract ing one hydrogen atom from the CH_4 molecule andtheir tendencies to reassociate with CH_3 · , which would easily lead to deep oxida-tion of the fragments of hydrocarbons, are enhanced with inereasing negativecliarges on them. In comparison with Na_2O, K_2O has a little stronger tendency tostabilize less charged dioxygen adspecies; this has a close relation with the knownexperimental fact that K￣+ showed better promoting effect than Na￣+ in improvingC_2-selectivity in methane oxidative coupling (MOC ).展开更多
An active and recyclable catalyst system, poly(maleic acid-divinyi benzene)-ruthenium complexes selectively catalyze the oxidation of styrene with dioxygen to benzaldehyde (60-70% yield) and phenyl acetaldehyde (10-3...An active and recyclable catalyst system, poly(maleic acid-divinyi benzene)-ruthenium complexes selectively catalyze the oxidation of styrene with dioxygen to benzaldehyde (60-70% yield) and phenyl acetaldehyde (10-30%yield). The polymer supports play an important role in the in-situ generation and stabization of catalytically active ruthenium species, RCOORu(IV).展开更多
A family of exceptionally thermally stable[Ni_(8)]cages is reported,each being templated by a rareη^(3):η^(3):μ_(6)-O_(2)^(2-)species produced by dioxygen activation,where the reducing agent for the O_(2)reduction ...A family of exceptionally thermally stable[Ni_(8)]cages is reported,each being templated by a rareη^(3):η^(3):μ_(6)-O_(2)^(2-)species produced by dioxygen activation,where the reducing agent for the O_(2)reduction appears to be the ligand used in the reaction mixtures,which was found within the nickel cages in its oxidized form.展开更多
The study of cobalt porphyrin interactions with O_(2)is important owing largely to its relevance to biological heme-mediated O_(2)transport and storage.The immobilization of a metalloporphyrin site in a metal-organic ...The study of cobalt porphyrin interactions with O_(2)is important owing largely to its relevance to biological heme-mediated O_(2)transport and storage.The immobilization of a metalloporphyrin site in a metal-organic framework(MOF)enables the study of these interactions without interference from solution effects such as bimolecular reactions,axial ligation,and solvent/solute interactions involving the porphyrin ligand.Here,we investigate the reaction of O_(2)with the four-coordinate cobaltous porphyrin complex in the MOF PCN-224Co.Single-crystal X-ray diffraction and electron paramagnetic resonance(EPR)spectroscopy of the oxygenated form,PCN-224CoO_(2)reveals a five-coordinate low-spin Co^(III)center coordinated to an S=1/2 superoxo(O_(2)^(−)•)ligand.Moreover,O_(2)adsorption measurements on PCN-224Co reveal two distinct binding sites with adsorption enthalpies of h_(ads)=−15.2(6)and−10.2(3)kJ mol^(−1).The former binding event is ascribed to ligation of O_(2)at the open Co site,and the obtained value is considerably lower than those observed for cobalt porphyrin units in substituted proteins and model complexes that feature axial ligands.These results provide the first structurally-characterized five-coordinate Co–O_(2)species,further highlight the importance of axial ligation in biological O_(2)transport and storage,and demonstrate the ability of a MOF to enable isolation and study of a species that is highly unstable in molecular form.展开更多
Anchoring of unimolecular metal oxide onto appropriate supports is a promising and attractive approach for designing efficient metal–oxide-based catalysts from the perspective of economic and environmental sustainabi...Anchoring of unimolecular metal oxide onto appropriate supports is a promising and attractive approach for designing efficient metal–oxide-based catalysts from the perspective of economic and environmental sustainability.In the present paper,anchoring of osmium(Os)oxide onto silanol-functionalized polyoxometalates(POMs)to form a single-site supported Os-POM catalyst,in which the isolated osmium tetroxide was tris-grafted on a silanol-functionalized POM platform,has been studied in detail for catalytic oxidation of propylene with dioxygen by using density functional theory(DFT)calculations with the M06L functional.The results derived from the molecular geometry,electronic structure,and OsvO bonding feature for this Os-POM catalyst show that(i)rotation of the anionic center subunit of the silanolfunctionalized trilacunary POM ligand leads to a coordinated environment conversion from a tetrahedron to a trigonal bipyramid around the transition metal Os center;(ii)a detailed comparison shows that the trigonal bipyramid configuration is the most stable species and provides a large OsvO distance and(iii)possesses a matched orbital level for epoxidation of propylene to epoxypropane.The calculated free energy profiles for the epoxidation of propylene show that the rate-determining step is desorption of the first epoxypropane molecule from the Os center.Electronic structure analysis along the reaction pathway shows that the Os-POM catalyst serves as an electrophile,accepting electrons from the propyleneπbonding orbital to the π*antibonding orbital of the Os-POM catalyst to break the OsvO bond during the oxygen transfer process.Oxygen transfer to the terminal carbon atom of propylene is more favored than the bridging carbon atom because the electron-donating methyl substituent in propylene makes the terminal carbon atom more nucleophilic and accessible for the electrophilic attack by the OsvO bond.Cleavage of dioxygen on the Os-POM catalyst is a barrier free process via a quintet-to-singlet state intersystem crossing.The ability of the POM platform to accept and stabilize excess electrons from the Os center effectively promotes the oxygen transfer process,and thus is favorable for epoxidation of propylene by dioxygen.展开更多
Efficient activation of dioxygen (O₂) under mild and environmentally friendly conditions remains a challenging yet crucial area of research in chemistry.In this study,we present a simple yet effective approach for O₂ ...Efficient activation of dioxygen (O₂) under mild and environmentally friendly conditions remains a challenging yet crucial area of research in chemistry.In this study,we present a simple yet effective approach for O₂ activation under 450 nm light irradiation by rationally modulating the coordination environment of Cu(Ⅰ) ions and incorporating a photoactive Ir(Ⅲ) module into a supramolecular system,leading to efficient C(sp³)−H photo-oxidation of N-aryl tetrahydroisoquinolines.The hexaformyl end-capped fac-Ir(ppy)₃ module (1),the Ir(Ⅲ)-based twin-cavity cage (2),and the supramolecular Cu₂@2 entity—where two Cu(Ⅰ) ions are coordinated within cage 2—were comprehensively characterized using NMR,HR-MS,and X-ray crystallography.The confined cavities of 2 effectively trap Cu(Ⅰ) ions,protecting them from oxidation by O₂.Mechanistic studies reveal that photoinduced singlet oxygen (¹O₂),generated by the fac-Ir(ppy)₃ module,activates Cu(Ⅰ) to generate superoxide radical (O₂•⁻) species.Importantly,the Cu(Ⅰ) redox-active state is regenerated through electron transfer from the photoexcited *Ir(Ⅲ) state to the resulting Cu(Ⅱ) ions.This study introduces a gradual and controlled energy/electron delivery mechanism from Ir(Ⅲ) module to O₂ and the Cu centres,offering an advanced supramolecular strategy for photo-induced O₂ activation in oxidation reactions.展开更多
Here,we report the nitric oxide dioxygenation(NOD)reactions of Ni^(III)-peroxo,[(12-TMC)Ni^(III)(O_(2)^(2-))]^(+)(Ni^(III)-O_(2)^(2-),1),and Co^(III)-peroxo,[(12-TMC)Co^(III)(O_(2)^(2-))]^(+)(Co^(III)-O_(2)^(2-),2),co...Here,we report the nitric oxide dioxygenation(NOD)reactions of Ni^(III)-peroxo,[(12-TMC)Ni^(III)(O_(2)^(2-))]^(+)(Ni^(III)-O_(2)^(2-),1),and Co^(III)-peroxo,[(12-TMC)Co^(III)(O_(2)^(2-))]^(+)(Co^(III)-O_(2)^(2-),2),complexes bearing N-tetramethylated cyclam(TMC)ligands.The reaction of complex 1 with nitric oxide(NO)generates Ni^(II)-nitrato complex[(12-TMC)Ni^(II)(NO_(3)^(-))]^(+)(Ni^(II)-NO_(3)^(-),3).However,in contrast to the NOD reaction of 1,compound 2 produces Co^(II)-nitrito complex,[(12-TMC)Co^(II)(NO_(2)^(-))]^(+)(Co^(II)-NO_(2)^(-),4),with O_(2)gas formation.Results suggested the formation of a presumptive Ni-peroxynitrite([Ni-PN]^(+),[Ni-ONOO^(-)]^(+))intermediate,in the NOD reaction of 1,prior to the generation of Ni^(II)-NO_(3)^(-)(3).Although the end product of the reaction of 2 with NO is different from that of 1,the mechanistic study explored by using 2,4-di-tert-butylphenol(2,4-DTBP)suggested that the reaction of 2 with NO also occurs via a presumed Co-peroxynitrite([Co-PN]^(+),[Co-ONOO^(-)]^(+))intermediate.Furthermore,exploring these NOD reactions and tracking the oxygen atom using 18O-labeled hydrogen peroxide(H_(2)^(18)O_(2))revealed that two oxygen atoms of 3(Ni^(II)-18O_(2)N^(16)O^(-))and one oxygen atom of 4(Co^(II)-18ON^(16)O^(-))are derived from the peroxo(O_(2)^(2-))moieties of 1 and 2,respectively.Furthermore,we have explored the M-peroxo regeneration from NOD products(3 and 4),and for the first time,we have observed the formation of M^(III)-O_(2)^(2-)complexes,1 and 2,upon treatment with H_(2)O_(2)and triethylamine(TEA),respectively.This work is the first-ever report which showed the exact NO dioxygenase(NOD)enzyme catalytic cycle.Furthermore,we have also explored the NO activation of 3 and 4,and surprisingly,we observed the formation of Co-nitrosyl(5)from 4 upon reaction with NO;in contrast,3 was unreactive towards NO.Evidence supporting the formation of[Ni-PN]^(+)and[Co-PN]^(+)intermediates is also presented.展开更多
The selective four-electron reduction of O_(2) to H_(2)O is central for efficient energy conversion.Copper-polypyridyl complexes are attractive Oxygen Reduction Reaction(ORR)catalysts,yet benchmark Cu-tris(2-pyridylme...The selective four-electron reduction of O_(2) to H_(2)O is central for efficient energy conversion.Copper-polypyridyl complexes are attractive Oxygen Reduction Reaction(ORR)catalysts,yet benchmark Cu-tris(2-pyridylmethyl)amine(Cu^(tmpa))systems typically operate through a stepwise mechanism with H_(2)O_(2) as an intermediate,which limits selectivity for water production.In this context,we report a mononuclear copper(Ⅱ)complex,[Cu^(tmpa-NH)]^(2+),supported by the pentadentate polypyridylalkylamine ligand N-(2-methylpyridine)-2,11-diaza[3.3](2,6)pyridinophane(tmpa-NH),that enables selective four-electron reduction of O_(2) to H_(2)O both in homogeneous electrochemical conditions in CH_(3)CN with 2,6-lutidinium tetrafluoroborate as proton source and in aqueous media.Single-crystal X-ray diffraction and low-temperature EPR spectroscopy establish a distorted octahedral Cu^(Ⅱ) center withκ^(5) binding of tmpa-NH,while cyclic voltammetry shows a reversible Cu^(Ⅱ/Ⅰ) couple at E_(1/2)≈−0.47 V vs.Fc^(+)/Fc.Rotating ring-disk voltammetry and bulk electrolysis quantify near-exclusive H_(2)O formation(faradaic efficiency 91.7-97.8%)across−0.4 to−0.9 V,with an overpotentialη≈0.87 V referenced to O_(2)/4H^(+)/2H_(2)O in CH_(3)CN.Kinetic analysis(foot-of-the-wave)reveals a third-order rate law,being first-order in[catalyst],[O_(2)],and[acid],with k_(cat)=(5.99±0.14)×10^(3) M^(−2) s^(−1).In a pH 7 phosphate buffer solution,[Cutmpa-NH]^(2+)retains robust ORR activity with high H_(2)O selectivity.The apparent rate constant(kobs=300 s^(−1))in aqueous medium is significantly higher than in CH_(3)CN but lower than that of benchmark Cutmpa in water.By contrast,the complex with the tetradentate parent ligand,[Cu^(bmpa-NH)]^(2+),is inactive under identical conditions.The data are consistent with a mechanistic proposal for turnover control via proton-coupled electron transfer at an end-on Cu^(Ⅱ)-superoxo intermediate,forming a Cu^(Ⅱ)-hydroperoxo species.The added dimethyleneamine“cap”in tmpa-NH provides a fifth donor that preorganizes the first coordination sphere and directs the pathway toward the four-electron process,to enhance H_(2)O selectivity in copper-polypyridyl ORR catalysts across both organic and aqueous media.展开更多
A simple and convenient copper-catalyzed direct oxyphosphorylation of enamides with P（O）-H compounds and dioxygen has been developed under mild conditions. This methodology can allow the synthesis of a series of val...A simple and convenient copper-catalyzed direct oxyphosphorylation of enamides with P（O）-H compounds and dioxygen has been developed under mild conditions. This methodology can allow the synthesis of a series of valuable β-ketophosphine oxides β-ketophosphonates in moderate to good yields with a broad substrate scope simply by using readily-available starting materials.展开更多
基金supported by the National Natural Science Foundation of China(NSFC)(Nos.22076063,22076098,and 21477047)the Natural Science Foundation of Shandong Province(No.ZR2020MB033)+1 种基金the Key Laboratory of Photochemical Conversion and Optoelectronic Materials,TIPC,CAS(No.PCOM202106)the program for Taishan Scholars of Shandong Province,and the Science and Technology Programof the University of Jinan(No.XKY2111).
文摘Volatile Organic Compounds(VOCs)are highly harmful to human beings and other organisms,and thus the elimination of VOCs is extremely urgent.Here,La-Si co-doped TiO_(2)microsphere photocatalysts,which were prepared by a hydrothermal method,exhibited high photocatalytic activity in the decomposition of formaldehyde compared with TiO_(2).The improved activity can be attributed to the promoted separation efficiency and density of the charge carriers,as verified by the electrochemical results in combination with density functional theory calculations.In addition,the Si dopant changed the microstructure and surface acidity,while the addition of La promoted the separation efficiency of charge carriers.More interestingly,it was found that singlet oxygen was the key species in the activation of molecular dioxygen,and it played a pivotal role in the photocatalytic decomposition of formaldehyde.This work provides a novel strategy for the selective activation of dioxygen for use in the decomposition of formaldehyde.
文摘The dioxygen affinities and catalytic epoxidation performance of transition-metal hydroxamates were investigated for the first time. The effects of substituents on these properties were also discussed in the paper.
基金This work is supported by the National Natural Science Foundation of China(Grant No.2007205).
文摘The oxygenation of cobalt (II) hydroxamates (CoL2) and its catalytic performance in oxidation of p-xylene to p-toluic acid (PTA) were examined. The effects of X and Y bonded to hydroxamate group on dioxygen affinities and catalytic oxidation performance were also investigated.
基金Supported by the National Basic Research Program of China(No.2007CB613303)the National Natural Science Foundation of China(No.20731003)
文摘A copper-TiO2 based catalyst（Cu-OH-Cl-TiO2） was prepared through a slurry impregnation approach and the catalyst was found to be active and selective for the epoxidation of propylene by dioxygen. With a feed gas of 10% C3H6, 10% O2 and 80% N2 at a gas hourly space velocity（GHSV） of 4000 h-1, a propylene conversion of 4.8% and a propylene oxide（PO） selectivity of 38.9% were achieved over the obtained Cu-OH-Cl-TiO2 catalyst at a reaction temperature of 500 K. It revealed that Cu2＋ provided by crystalline Cu2（OH）3Cl plays a key role in catalytic conversion of propylene to PO.
文摘The oxygenation constants of transition-metal complexes with benzoin Schiff bases were measured and these complexes were first employed as models for mimicking monooxygenase in catalytic epoxidation of styrene. The highest conversion and selectivity were up to 39.6% and 100% respectively at ambient temperature and pressure. The effects of structures of the bridge group R in the ligands on the dioxygen affinities and catalytic activities to epoxidize styrene were also investigated.
基金the National Natural Science Foundation of China.
文摘The dioxygen affinities and biomimetic catalytic performance of transition-metal complexes with (15-crown-5) salophen and its substituted derivatives Mere examined. The oxygenation constants of Co(II) complexes with crowned bis-Schiff bases were measured and their Mn(III) complexes were employed as models to mimic monooxygenase in catalytic epoxidation of styrene. The highest conversion and selectivity were up to 57.2% and 100% respectively at ambient temperature and pressure. The effects of crown ether ring and substituents R on the dioxygen affinities and catalytic activities were also investigated through comparing with the uncrowned analogues.
基金Supported by Gazi UniversityScientific Research Projects DivisionNo.01/2007-62
文摘AIM: To evaluate whether serum and tumor indoleamine 2,3-dioxygenase activities can predict lymphatic invasion (LI) or lymph node metastasis in colorectal carcinoma.METHODS: The study group consisted of 44 colorectal carcinoma patients. The patients were re-grouped according to the presence or absence of LI and lymph node metastasis. Forty-three cancer-free subjects without any metabolic disturbances were included into the control group. Serum neopterin was measured by enzyme linked immunosorbent assay. Urinary neopterin and biopterin, serum tryptophan (Trp) and kynurenine (Kyn) concentrations of all patients were determined by high performance liquid chromatography. Kyn/Trp was calculated and its correlation with serum neopterin was determined to estimate the serum indoleamine 2,3-dioxygenase activity. Tissue sections from the studied tumors were re-examined histopathologically and were stained by immunohistochemistry with indoleamine-2,3-dioxygenase antibodies.RESULTS: Neither serum nor urinary neopterin was significantly different between the patient and control groups (both P > 0.05). However, colorectal carcinoma patients showed a significant positive correlation between the serum neopterin levels and Kyn/Trp (r = 0.450, P < 0.01). Urinary biopterin was significantly higher in cancer cases (P < 0.05). Serum Kyn/Trp was significantly higher in colorectal carcinoma patients (P < 0.01). Lymphatic invasion was present in 23 of 44 patients, of which only 12 patients had lymph node metastasis. Eleven patients with LI had no lymph node metastasis. Indoleamine-2,3-dioxygenase intensity score was significantly higher in LI positive cancer group (44.56% ± 6.11%) than negative colorectal cancer patients (24.04% ± 6.90%), (P < 0.05). Indoleamine 2,3-dioxygenase expression correlated both with the presence of LI and lymph node metastasis (P < 0.01 and P < 0.05, respectively). A significant difference between the accuracy of diagnosis by using either total indoleamine-2,3-dioxygenase immunostaining score or of lymph node metastasis was found during the evaluation of cancer patients.CONCLUSION: Indoleamine-2,3-dioxygenase expression may predict the presence of unrecognized LI and lymph node metastasis and may be included in the histopathological evaluation of colorectal carcinoma cases.
基金The authors gratefully acknowledge the grants from the National Natural Science Foundation of China(No.20072025)Education 0ffice Foundation of Sichuan Province(No.2005C012)Sichuan Provincial Department of Science&Technology(No.2006J13-143)in support of this work.
文摘The oxygenation constants （Ko2） of cobalt（Ⅱ） hydroxamates （CoL^1 2-CoL^3 2） with benzo-15-crown-5 （B15C5） pendants were measured over the range of -5 to ＋20 ℃, and the values of thermodynamic parameters （ΔH^0 and ΔS^0） were calculated based on these （Ko2） values, Meanwhile, these crowned complexes were employed to the oxidation for p-xylene to p-toluic acid with air at 110Δ under normal atmospheric pressure. The effects of B15C5 pendant and the length of chain bonded to B15C5 in these complexes on the O2-binding capabilities and oxidation for p-xylene were investigated with the comparison of crown-free analogues CoL^4 2.
基金supported by the National Natural Science Foundation of China(No.2007205).
文摘The oxygenation constants and thermodynamic parameter （△H°, △S°） of a series of novel Co （Ⅱ） complexes with phenol ether bridged dihydroxamic acids CoL^1-CoL^6 were measured, their catalytic performance in oxidation of p-xylene to p-toluic acid （PTA） were examined. The modulation of O2-binding capabilities and catalytic oxidation activities by X （X = Cl, OCH3） and Y （Y = H, CH3, Cl） groups bonded to the aromatic rings of the Co （Ⅱ） complexes were investigated.
文摘The oxygenation constants and thermodynamic parameter (ΔHo, ΔSo) of Co (II) complexes with unsymmetrical bis-Schiff baeses were measured and their Mn(III) complexes as models of mimicking monooxygenase were employed to catalyze epoxidation of styrene. The effect of substituent R in a salicylidene of ML1~ML4 [ M = Co (II), Mn (III)Cl ] on the dioxygen affinities and biomimetic catalytic oxidation performance were also investigated. Among them, the MnL4Cl containing a pendant benzoaza crown ether ring showed highest conversion and selectiviy up to 54.9% and 96.9% respectively.
文摘Thermodynamic data were determined for the reversible binding of O 2 to two compounds of dicobalt(II) di(meso tetra phenyl)porphyrin derivatives with different lengths of diamidoaliphatic bridge (abbreviated to Co 2PP 8 and Co 2PP 4) in N,N dimethylformamide at room temperature. The partial pressure of dioxygen necessary for half oxygenation ( P 1/2 ) and Hill coefficient ( n ) at 298 K were determined as follows: P 1/2 =54.2 kPa, n =2.0 for Co 2PP 8 and P 1/2 =6.8 kPa, n =1.8 for Co 2PP 4,respectively. The rate equations of reversible oxygen binding by Co 2PP 8 were determined and the reaction path was proposed. The results of thermodynamic and kinetic studies indicate that there exists strong cooperative effect during oxygenation of the compounds. The ESR observation reveals that the dioxygen complexes formed in the solutions are of superoxo (Co O - 2) type.
文摘ith an improved EHMO method, three modes (flat-lying, vertical , and in-clined insertion) for adsorption and activation of dioxygen on (100) , (110) and(111) surfaces of Na_2O and of K,O have been exaniinecl, and the interaction ofthese dioxygen adspecies with CH_4 and with CH_3 · (radical) from gas pliase liasbeen investigated. The results indicate that both oxides tend to forni less cliargedadspecies of dioxygen, with the flat-lying adsorption on (110) surface most favor-able energetically. All these cliemisorbed dioxygen species are capable of interactingeffectively with CH_4 and Abstract ing one hydrogen atom from the CH_4 molecule andtheir tendencies to reassociate with CH_3 · , which would easily lead to deep oxida-tion of the fragments of hydrocarbons, are enhanced with inereasing negativecliarges on them. In comparison with Na_2O, K_2O has a little stronger tendency tostabilize less charged dioxygen adspecies; this has a close relation with the knownexperimental fact that K￣+ showed better promoting effect than Na￣+ in improvingC_2-selectivity in methane oxidative coupling (MOC ).
文摘An active and recyclable catalyst system, poly(maleic acid-divinyi benzene)-ruthenium complexes selectively catalyze the oxidation of styrene with dioxygen to benzaldehyde (60-70% yield) and phenyl acetaldehyde (10-30%yield). The polymer supports play an important role in the in-situ generation and stabization of catalytically active ruthenium species, RCOORu(IV).
文摘A family of exceptionally thermally stable[Ni_(8)]cages is reported,each being templated by a rareη^(3):η^(3):μ_(6)-O_(2)^(2-)species produced by dioxygen activation,where the reducing agent for the O_(2)reduction appears to be the ligand used in the reaction mixtures,which was found within the nickel cages in its oxidized form.
基金funded by the U.S.Army Research Office through agreement numbers W911NF-14-1-0168,W911NF-15-1-0119,and W911NF-15-1-0331the U.S.Air Force Office of Scientific Research through agreement number FA9550-14-1-0274+4 种基金the Institute for Sustainability and Energy at Northwestern,and Northwestern Universitysupported primarily by the National Science Foundation through the Graduate Research Fellowship Programsupported primarily by the Chemistry of Life Processes through a Lambert Fellowshipsupported by the Northwestern University International Institute for Nanotechnologysupported primarily by the National Science Foundation under NSF Award Number EEC-1359004.
文摘The study of cobalt porphyrin interactions with O_(2)is important owing largely to its relevance to biological heme-mediated O_(2)transport and storage.The immobilization of a metalloporphyrin site in a metal-organic framework(MOF)enables the study of these interactions without interference from solution effects such as bimolecular reactions,axial ligation,and solvent/solute interactions involving the porphyrin ligand.Here,we investigate the reaction of O_(2)with the four-coordinate cobaltous porphyrin complex in the MOF PCN-224Co.Single-crystal X-ray diffraction and electron paramagnetic resonance(EPR)spectroscopy of the oxygenated form,PCN-224CoO_(2)reveals a five-coordinate low-spin Co^(III)center coordinated to an S=1/2 superoxo(O_(2)^(−)•)ligand.Moreover,O_(2)adsorption measurements on PCN-224Co reveal two distinct binding sites with adsorption enthalpies of h_(ads)=−15.2(6)and−10.2(3)kJ mol^(−1).The former binding event is ascribed to ligation of O_(2)at the open Co site,and the obtained value is considerably lower than those observed for cobalt porphyrin units in substituted proteins and model complexes that feature axial ligands.These results provide the first structurally-characterized five-coordinate Co–O_(2)species,further highlight the importance of axial ligation in biological O_(2)transport and storage,and demonstrate the ability of a MOF to enable isolation and study of a species that is highly unstable in molecular form.
基金the National Natural Science Foundation of China(21373043).
文摘Anchoring of unimolecular metal oxide onto appropriate supports is a promising and attractive approach for designing efficient metal–oxide-based catalysts from the perspective of economic and environmental sustainability.In the present paper,anchoring of osmium(Os)oxide onto silanol-functionalized polyoxometalates(POMs)to form a single-site supported Os-POM catalyst,in which the isolated osmium tetroxide was tris-grafted on a silanol-functionalized POM platform,has been studied in detail for catalytic oxidation of propylene with dioxygen by using density functional theory(DFT)calculations with the M06L functional.The results derived from the molecular geometry,electronic structure,and OsvO bonding feature for this Os-POM catalyst show that(i)rotation of the anionic center subunit of the silanolfunctionalized trilacunary POM ligand leads to a coordinated environment conversion from a tetrahedron to a trigonal bipyramid around the transition metal Os center;(ii)a detailed comparison shows that the trigonal bipyramid configuration is the most stable species and provides a large OsvO distance and(iii)possesses a matched orbital level for epoxidation of propylene to epoxypropane.The calculated free energy profiles for the epoxidation of propylene show that the rate-determining step is desorption of the first epoxypropane molecule from the Os center.Electronic structure analysis along the reaction pathway shows that the Os-POM catalyst serves as an electrophile,accepting electrons from the propyleneπbonding orbital to the π*antibonding orbital of the Os-POM catalyst to break the OsvO bond during the oxygen transfer process.Oxygen transfer to the terminal carbon atom of propylene is more favored than the bridging carbon atom because the electron-donating methyl substituent in propylene makes the terminal carbon atom more nucleophilic and accessible for the electrophilic attack by the OsvO bond.Cleavage of dioxygen on the Os-POM catalyst is a barrier free process via a quintet-to-singlet state intersystem crossing.The ability of the POM platform to accept and stabilize excess electrons from the Os center effectively promotes the oxygen transfer process,and thus is favorable for epoxidation of propylene by dioxygen.
基金support from the National Natural Science Foundation of China(22171033 and 22477014).
文摘Efficient activation of dioxygen (O₂) under mild and environmentally friendly conditions remains a challenging yet crucial area of research in chemistry.In this study,we present a simple yet effective approach for O₂ activation under 450 nm light irradiation by rationally modulating the coordination environment of Cu(Ⅰ) ions and incorporating a photoactive Ir(Ⅲ) module into a supramolecular system,leading to efficient C(sp³)−H photo-oxidation of N-aryl tetrahydroisoquinolines.The hexaformyl end-capped fac-Ir(ppy)₃ module (1),the Ir(Ⅲ)-based twin-cavity cage (2),and the supramolecular Cu₂@2 entity—where two Cu(Ⅰ) ions are coordinated within cage 2—were comprehensively characterized using NMR,HR-MS,and X-ray crystallography.The confined cavities of 2 effectively trap Cu(Ⅰ) ions,protecting them from oxidation by O₂.Mechanistic studies reveal that photoinduced singlet oxygen (¹O₂),generated by the fac-Ir(ppy)₃ module,activates Cu(Ⅰ) to generate superoxide radical (O₂•⁻) species.Importantly,the Cu(Ⅰ) redox-active state is regenerated through electron transfer from the photoexcited *Ir(Ⅲ) state to the resulting Cu(Ⅱ) ions.This study introduces a gradual and controlled energy/electron delivery mechanism from Ir(Ⅲ) module to O₂ and the Cu centres,offering an advanced supramolecular strategy for photo-induced O₂ activation in oxidation reactions.
文摘Here,we report the nitric oxide dioxygenation(NOD)reactions of Ni^(III)-peroxo,[(12-TMC)Ni^(III)(O_(2)^(2-))]^(+)(Ni^(III)-O_(2)^(2-),1),and Co^(III)-peroxo,[(12-TMC)Co^(III)(O_(2)^(2-))]^(+)(Co^(III)-O_(2)^(2-),2),complexes bearing N-tetramethylated cyclam(TMC)ligands.The reaction of complex 1 with nitric oxide(NO)generates Ni^(II)-nitrato complex[(12-TMC)Ni^(II)(NO_(3)^(-))]^(+)(Ni^(II)-NO_(3)^(-),3).However,in contrast to the NOD reaction of 1,compound 2 produces Co^(II)-nitrito complex,[(12-TMC)Co^(II)(NO_(2)^(-))]^(+)(Co^(II)-NO_(2)^(-),4),with O_(2)gas formation.Results suggested the formation of a presumptive Ni-peroxynitrite([Ni-PN]^(+),[Ni-ONOO^(-)]^(+))intermediate,in the NOD reaction of 1,prior to the generation of Ni^(II)-NO_(3)^(-)(3).Although the end product of the reaction of 2 with NO is different from that of 1,the mechanistic study explored by using 2,4-di-tert-butylphenol(2,4-DTBP)suggested that the reaction of 2 with NO also occurs via a presumed Co-peroxynitrite([Co-PN]^(+),[Co-ONOO^(-)]^(+))intermediate.Furthermore,exploring these NOD reactions and tracking the oxygen atom using 18O-labeled hydrogen peroxide(H_(2)^(18)O_(2))revealed that two oxygen atoms of 3(Ni^(II)-18O_(2)N^(16)O^(-))and one oxygen atom of 4(Co^(II)-18ON^(16)O^(-))are derived from the peroxo(O_(2)^(2-))moieties of 1 and 2,respectively.Furthermore,we have explored the M-peroxo regeneration from NOD products(3 and 4),and for the first time,we have observed the formation of M^(III)-O_(2)^(2-)complexes,1 and 2,upon treatment with H_(2)O_(2)and triethylamine(TEA),respectively.This work is the first-ever report which showed the exact NO dioxygenase(NOD)enzyme catalytic cycle.Furthermore,we have also explored the NO activation of 3 and 4,and surprisingly,we observed the formation of Co-nitrosyl(5)from 4 upon reaction with NO;in contrast,3 was unreactive towards NO.Evidence supporting the formation of[Ni-PN]^(+)and[Co-PN]^(+)intermediates is also presented.
基金support from the National Natural Science Foundation of China(22001005).
文摘The selective four-electron reduction of O_(2) to H_(2)O is central for efficient energy conversion.Copper-polypyridyl complexes are attractive Oxygen Reduction Reaction(ORR)catalysts,yet benchmark Cu-tris(2-pyridylmethyl)amine(Cu^(tmpa))systems typically operate through a stepwise mechanism with H_(2)O_(2) as an intermediate,which limits selectivity for water production.In this context,we report a mononuclear copper(Ⅱ)complex,[Cu^(tmpa-NH)]^(2+),supported by the pentadentate polypyridylalkylamine ligand N-(2-methylpyridine)-2,11-diaza[3.3](2,6)pyridinophane(tmpa-NH),that enables selective four-electron reduction of O_(2) to H_(2)O both in homogeneous electrochemical conditions in CH_(3)CN with 2,6-lutidinium tetrafluoroborate as proton source and in aqueous media.Single-crystal X-ray diffraction and low-temperature EPR spectroscopy establish a distorted octahedral Cu^(Ⅱ) center withκ^(5) binding of tmpa-NH,while cyclic voltammetry shows a reversible Cu^(Ⅱ/Ⅰ) couple at E_(1/2)≈−0.47 V vs.Fc^(+)/Fc.Rotating ring-disk voltammetry and bulk electrolysis quantify near-exclusive H_(2)O formation(faradaic efficiency 91.7-97.8%)across−0.4 to−0.9 V,with an overpotentialη≈0.87 V referenced to O_(2)/4H^(+)/2H_(2)O in CH_(3)CN.Kinetic analysis(foot-of-the-wave)reveals a third-order rate law,being first-order in[catalyst],[O_(2)],and[acid],with k_(cat)=(5.99±0.14)×10^(3) M^(−2) s^(−1).In a pH 7 phosphate buffer solution,[Cutmpa-NH]^(2+)retains robust ORR activity with high H_(2)O selectivity.The apparent rate constant(kobs=300 s^(−1))in aqueous medium is significantly higher than in CH_(3)CN but lower than that of benchmark Cutmpa in water.By contrast,the complex with the tetradentate parent ligand,[Cu^(bmpa-NH)]^(2+),is inactive under identical conditions.The data are consistent with a mechanistic proposal for turnover control via proton-coupled electron transfer at an end-on Cu^(Ⅱ)-superoxo intermediate,forming a Cu^(Ⅱ)-hydroperoxo species.The added dimethyleneamine“cap”in tmpa-NH provides a fifth donor that preorganizes the first coordination sphere and directs the pathway toward the four-electron process,to enhance H_(2)O selectivity in copper-polypyridyl ORR catalysts across both organic and aqueous media.
基金We gratefully acknowledge financial support from the National Natural Science Foundation of China （Nos. 21572217, 21402184, 21172213, and 21302109）.
文摘A simple and convenient copper-catalyzed direct oxyphosphorylation of enamides with P（O）-H compounds and dioxygen has been developed under mild conditions. This methodology can allow the synthesis of a series of valuable β-ketophosphine oxides β-ketophosphonates in moderate to good yields with a broad substrate scope simply by using readily-available starting materials.
