Fe-N-C Artificial Enzyme: Activation of Oxygen for Dehydrogenation

Subscriber access provided by UNIV OF LOUISIANA

Energy, Environmental, and Catalysis Applications

Fe-N-C Artificial Enzyme: Activation of Oxygen for Dehydrogenation and Monoxygenation of Organic Substrates under Mild Condition and Cancer Therapeutic Application Fei He, Li Mi, Yanfei Shen, Toshiyuki Mori, Songqin Liu, and Yuanjian Zhang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b15540 • Publication Date (Web): 24 Sep 2018 Downloaded from http://pubs.acs.org on September 25, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Fe-N-C Artificial Enzyme: Activation of Oxygen for Dehydrogenation and Monoxygenation of Organic Substrates under Mild Condition and Cancer Therapeutic Application Fei He,a Li Mi,a Yanfei Shen,a Toshiyuki Mori,b Songqin Liua and Yuanjian Zhang*a a

Jiangsu Engineering Laboratory of Smart Carbon-Rich Materials and Device, Jiangsu Province Hi-Tech Key Laboratory for Bio-Medical Research, School of Chemistry and Chemical Engineering, Medical School, Southeast University, Nanjing 211189, China

b

Global Research Center for Environment and Energy Based on Nanomaterials Science (GREEN), National Institute for Materials Sciences (NIMS), 1-1 Namiki, Ibaraki, 305-0044, Japan

(*) Email: [email protected] F.H. and L.M. had equivalent contributions. Keywords: Fe-N-C • artificial enzyme • heterogeneous catalysis • aerobic oxidations • cancer treatment Abstract Developing highly efficient biomimetic catalysts that directly use O2 as terminal oxidant to dehydrogenate and monoxygenate substrates with high selectivity under mild conditions has long been pursued but rarely achieved yet. Herein, we report that heterogeneous Fe-N-C, which is commonly used as electrocatalyst for oxygen reduction reaction, had unusual biomimetic catalytic activity in both dehydrogenation and monoxygenation of a series of organic molecules (~100% selectivity) by direct using O2. The Fe-Nx center was verified to be the active site that reductively activated O2 by spontaneous generating specific reactive oxygen species (1O2, O2•−, and H2O2). Aided by these ROS, under physiological conditions, the Fe-N-C was further successfully exampled to kill proliferative lung cancer cells. Fe-N-C had several striking superior features with respect to natural enzymes, classical heterogeneous nanozymes, and homogeneous artificial enzymes in capable of working in harsh conditions (extreme pH and high temperature), ease of separation and recycling, and direct use of O2. It would open up a new vista of Fe-N-C as an artificial enzyme in biomimetic catalysis ranging from fundamental simulation of oxidase/oxygenase metabolism to industrial oxidation processes, and to disease treatment.

1 ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Introduction The natural enzymes catalyzed oxidation of organic substrates with O2 is crucial for the metabolism of living organisms.1-2 A remarkable example of aerobic oxygenation is mediated by the cytochrome P450, which could reductively activate O2 to dehydrogenate and monoxygenate a variety of exogenous and endogenous substrates under very mild conditions.3 However, problems such as sensitivity of catalytic activity to environmental conditions, and the high costs largely limit applications of natural enzymes.4-5 A solution to this problem may be offered by constructing artificial structures as natural enzyme mimics.4 Recently a great deal of landmark works for biomimetic homogeneous catalysts such as metalloporphyrins,6-8 metal complexes,9-11 and heterogeneous “artificial enzyme” such as Au and Fe3O4 nanoparticles12-16 and graphene oxide17 have been explored to mimic enzyme-like catalytic activity, but most of them cannot directly use O2 and have to use organic/inorganic peroxides18 such as H2O2 as artificial oxygen donors.19 Moreover, natural enzymes and few existing biomimetic catalysts, which can directly use O2, are soluble in a homogeneous system, making them difficult to be separated and regenerated. Thus, exploring heterogeneous biomimetic catalysts with enzyme-like activity that could directly utilize O2 under mild conditions is fascinating but still remains challenging. Platinum group metal-free (PGM-free) metal-nitrogen-carbon catalysts (M-N-C) prepared by pyrolysis of M/N/C-containing precursors recently shows excellent electrocatalytic O2 reduction activities at low overpotential.20-22 Pioneering works in microscopic and spectra investigation such as high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) and synchrotron extended X-ray absorption fine structure spectra (EXAFS) have comprehensively disclosed that the key structural motif of M-N-C responsible for the O2 reduction. They generally contain N-coordinated metal (M-Nx) embedded in basal planes of carbon or bridging two graphene planes at edges,20-21, 23 very similar to the active sites of


Page 2 of 22

Page 3 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


some natural enzymes such as cytochrome P450. These facts hint the great potential of M-NC in O2 activation and their potential as natural enzyme-like biomimetic catalysts. Herein, we demonstrate that the Fe-N-C materials could act as a heterogeneous enzymelike biomimetic catalyst, which dehydrogenate and monoxygenate a number of substrates of high selectivity by the direct reductive activation of O2 at Fe-Nx active sites in aqueous solutions at room temperature. Moreover, the Fe-N-C artificial enzyme had excellent stability, ease of separation and recyclability, and uncompromisingly high catalytic activities in organic media, high temperature, extreme pH, and even physiological conditions. Experimental Section Chemicals. Nano-Fe3O4 (20-30 nm) was purchased from Aladdin Chemistry Co., Ltd., China. 5,10,15,20-tetraphenyl-21H,23H-porphine iron(III) chloride (FeTPPCl) was purchased from Energy Chemical, China. Catalase, peroxidase and superoxide dismutase were purchased from Sigma-Aldrich, USA. All other analytical grade chemicals and solvents were purchased from Aladdin Chemistry Co., Ltd. or Sinopharm Chemical Reagent Co., Ltd., China. The purified water (18.2 MΩ cm) was obtained from a Thermal Smart 2 system (USA). Preparation of precursors. Fe-based Ionic Liquid-1: The mixture of 1-butyl-3-methylimidazolium bromide (9.7 g, 44.3 mmol), iron chloride hexahydrate (12.1 g, 44.7 mmol) and dry EtOH (200 mL) were stirred in a flask at room temperature for 12 h. The crude product was obtained by rotary evaporation of EtOH, and rinsed by diethyl ether. The collected dark brown oil was dried for 10 h at 80 oC under vacuum to yield Fe-based ionic liquid-1 (16.7 g, yield: 98.9%). Raman (cm-1): 221, 242 and 266 (Fe-Br), 328 (Fe-Cl). NB: Using different Fe salts (i.e. FeCl3 hexahydrate and anhydrous FeCl3) to prepare Fe-based ionic liquid had less effect on their structures.24 Fe-based Ionic Liquid-2: The mixture of N-methylimidazole (4.73 g, 57.6 mmol), benzyl bromide (9.83 g, 57.5 mmol), and 1, 4-dioxane (100 mL) were stirred with reflux at 60oC for about 22 h. The crude product was obtained by removal of 1, 4-dioxane, and rinsed by 1, 43 ACS Paragon Plus Environment


dioxane and cold diethyl ether. The top layer was decanted off and this procedure was repeated for three times. The obtained oil-like product was dried at 60oC under vacuum to yield 1-benzyl-3-methylimidazolium bromide (14.0 g, yield: 96%). 1H NMR (DMSO-d6, δ, ppm, TMS): 3.86 (3H, CH3N-), 5.44 (2H, -C6H5CH2N-), 7.35-7.45 (5H, benzene ring proton), 7.72, 7.81 and 9.31 (3H, imidazole proton). The mixture of 1-benzyl-3-methylimidazolium bromide (5.02 g, 19.8 mmol), anhydrous iron chloride (3.22 g, 19.9 mmol) and dry EtOH (85 mL) were stirred at room temperature for about 23.5 h. The solution was filtrated, and the filtrate was evaporated to remove EtOH. The oil-like product was rinsed by diethyl ether and dried at 80oC under vacuum to yield Fe-based ionic liquid-2 (5.88 g, yield: 71%). Raman (cm1

): 221, 242 and 266 (Fe-Br), 328 (Fe-Cl).

Fe-complexed polypyrrole: Pyrrole (5.0 g, 74.5 mmol), anhydrous FeCl3 (1.5 g, 15.9 mmol), EtOH (50 mL) and H2O (200mL) were mixed in a round-bottom flask and stirred at room temperature for 17 h. The crude product was obtained by vacuum filtration, and then rinsed by H2O, acetone and diethyl ether, respectively. The collected dark solid was dried for 10 h at 100oC under vacuum to yield Fe-complexed polypyrrole (323 mg). NB: Fe-complexed polypyrrole prepared using anhydrous FeCl3 had been reported to be an amorphous compound based on the XRD result.25 Preparation of Fe-N-C Catalysts. The obtained precursors were pyrolyzed at 750 oC for 1 h in N2 with a heating rate of 10 °C/min. Thereafter, the grounded samples were ultrasonically dispersed in 25 mL of 37 wt.% HCl and leached at room temperature overnight to remove excessive iron species. Then, the catalyst was isolated by centrifugation and washing with water and dried in vacuum at 80 oC overnight. The catalysts derived by Fe-based ionic liquid1, Fe-based ionic liquid-2 and Fe-complexed polypyrrole were denoted as Fe-N-C, Fe-N-C (Ben) and Fe-N-C (Ppy), respectively. Nevertheless, a loss of activity was observed by an elongated treatment with 37 wt.% HCl. Warning: Owing to the possible open release of ROS


Page 4 of 22

Page 5 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


during Fe-N-C catalyzed O2 activation, it should be extremely cautious of the direct contact of skin when handling with Fe-N-C. Dehydrogenation of 1, 4-dihydropyridine (1,4-DHP). 1, 4-dihydropyridine (50 µM~250 µM) and catalyst (50 µg) were mixed in 1 mL of air-saturated phosphate buffer solution (pH=7.4) and stirred at room temperature in a 2 mL centrifuge tube for 30 min. The reaction mixture was then extracted with CH2Cl2 (1 mL). The organic layer was analyzed by highperformance liquid chromatography (HPLC) at 30 oC. A mixture of n-hexene and isopropyl alcohol (20:1, v/v) was used as mobile phase at a flow rate of 1 ml min−1. It was noted that Fe-N-C had a poor long-term stability due to its micrometer size and insolubility, but could keep fair dispersed in the solution during the catalytic reactions when the solution was stirred. Dehydrogenation of 1, 4-dihydropyridine (1,4-DHP) in different temperatures. 1, 4dihydropyridine (250 µM) and catalyst (50 µg) were mixed in 1 mL of air-saturated phosphate buffer solution (pH=7.4) and stirred at room temperature, 45oC or 70oC for 30 min. The reaction mixture was then extracted with CH2Cl2 (1 mL). The organic layer was analyzed by high performance liquid chromatography (HPLC) at 30oC. A mixture of n-hexene and isopropylalcohol (20:1, v/v) was used as mobile phase at a flow rate of 1 ml min-1. Dehydrogenation of 1, 4-dihydropyridine (1,4-DHP) in different pH. 1, 4-dihydropyridine (250 µM) and catalyst (50 µg) were mixed in 1 mL of air-saturated buffer solution (pH: 2～ 11) and stirred at room temperature for 30 min. The reaction mixture was then extracted with CH2Cl2 (1 mL). The organic layer was analyzed by UV-Vis spectrophotometer at room temperature. Dehydrogenation of 1, 4-dihydropyridine (1,4-DHP) in different organic solvents. 1, 4dihydropyridine (250 µM) and catalyst (1 mg) were mixed in 1 mL of air-saturated CH2Cl2, CH3CN or n-hexane and stirred at room temperature for 30 min. The reaction mixture was then extracted with CH2Cl2 (1 mL). The organic layer was analyzed by high performance 5 ACS Paragon Plus Environment


liquid chromatography (HPLC) at 30oC. A mixture of n-hexene and isopropylalcohol (20:1, v/v) was used as mobile phase at a flow rate of 1 ml min-1. Oxidation of 3,3’,5,5’-Tetramethylbenzidine (TMB) by Fe-N-C. 50 µg Fe-N-C was added into 1 mL of air-saturated HAc/NaAc buffer solution (pH=3.6) containing 336 µM TMB. TMB oxidation was estimated by monitoring the intensity of the absorption peak at around 652 nm using a UV-vis spectrophotometer. For scavenger tests, different concentration of scavengers or poison (ascorbic acid, 167 µM; 9, 10-anthracenediyl-bis(methylene)dimalonic acid, 1.1 mM; mannitol, 336 µM; catalase, 1667 U/mL; superoxide dismutase, 1891 U/mL) were used to identify the reactive oxygen species. Oxidation of 3,3’,5,5’-Tetramethylbenzidine (TMB) by nano-Fe3O4. 500 µg nano-Fe3O4 was added into 1 mL of air-saturated HAc/NaAc buffer solution (pH=3.6) containing 493.5 µM TMB and/without 315 µM H2O2. TMB oxidation was estimated by monitoring the absorption peak at around 652 nm using a UV-vis spectrophotometer. Oxidation of 3,3’,5,5’-Tetramethylbenzidine (TMB) by FeTPPCl. 14.3 µg FeTPPCl was added into 1 mL of air-saturated HAc/NaAc buffer solution (pH=3.6) containing 987 µM TMB and/without 630 µM H2O2. TMB oxidation was estimated by monitoring the absorption peak at around 652 nm using a UV-vis spectrophotometer. Oxidation of other N, P-containing compounds by Fe-N-C. Fe-N-C (50 µg~2 mg) and N or P-containing substrate (100 µM~500 µM) were mixed in 1 mL of air-saturated aqueous solution and stirred at room temperature in a 2 mL centrifuge tube for 0.5 or 1.5 h. The reaction mixture was then extracted with CH2Cl2 (1 mL). The organic layer was analyzed by high-performance liquid chromatography (HPLC) at 30oC. A mixture of n-hexene and isopropyl alcohol (9:1~20:1, v/v) was used as mobile phase at a flow rate of 1 ml min−1. For oxidation of different N, P-containing compounds, catalyst content, substrate concentration and reaction time were adjusted to optimize the catalytic performance, which was generally 6 ACS Paragon Plus Environment

Page 6 of 22

Page 7 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


adopted in previous reports. The selectivity in Table 1 was defined as moles of substrate transformed for the target product divided by moles of substrate reacted.26-27 Poisoning Fe-N-C by SCN−. Fe-N-C (50 µg) and NaSCN (676 µM) were added into 1 mL of air-saturated HAc/NaAc buffer solution (pH=3.6). The solution was shaken for 2 minutes. After that, 336 µM 3,3’,5,5’-tetramethylbenzidine (TMB) was introduced into the above solution and TMB oxidation under SCN− poisoning was estimated by monitoring the intensity of the absorption peak at around 652 nm using a UV-vis spectrophotometer. Michiaelis-Menten equation. The apparent kinetic parameters were calculated based on Eq. 1: (1) where ν is the initial velocity, Vmax is the maximal reaction velocity, [S] is the concentration of substrate and Km is the Michaelis constant.28 The value of Kcat was calculated by the following equation Kcat=Vmax/CFe-N-C,29 and the intrinsic catalyst concentration (CFe-N-C) could be expressed by the Fe concentration, which was quantified to be 6.34 µM. Cell culture and staining. Human lung cancer cell (A549) was obtained from American Type

Culture

Collection.

Cells

were

incubated

in

RPMI-1640

containing

1%

penicillin/streptomycin mixture and 10% fetal bovine serum. A549 was cultured in a homemade device equipped with nanobiochip at 37 °C in a humidified atmosphere containing 5% CO2, and harvested using 0.05% trypsin/EDTA solution (HyClone). A549 was also routinely cultured in 48-well plates (Corning Inc., Corning, N.Y., USA) with the same method for comparison. Cell staining was performed according to the manufacture's protocol by using Cell-Light™ EdU Appollo®567 In Vitro Imaging Kit (RiboBio, China) and Hoechst 33342 (RiboBio, China). 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) analysis. Cell viability was measured by the MTT assay (Amresco, USA), which involved cleavage of the 7 ACS Paragon Plus Environment


tetrazolium ring by mitochondrial dehydrogenase to form a purple precipitate. MTT was added in 1640 medium at a concentration of 0.5 mg/mL. After incubation time of 4 h at 37oC, removing the culture medium, the purple precipitate was dissolved in DMSO solution. The absorbance of the solution was measured with Microplate reader at 570 nm. Results and Discussion

a)

b)

c)

e)

Fe2p

2+

Fe 2p1/2 3+

Nx-Fe

N1s

Pyridinic N Pyrrolic N Graphitic N Oxidized N

2+

Fe 2p3/2

Fe 2p3/2

f)

d)

g)

3+

Fe 2p1/2

Satellite peak

710

720

730

Binding energy (eV)

396

399

402

405

Binding energy (eV)

Figure 1 (a) Typical procedures for synthesizing Fe-N-C from ionic liquid-based precursor. (b) SEM and (c) BF-STEM images. Inset: the HR-TEM image of the edges, showing graphitic carbon structure. (d) HAADF-TEM and C, N, and Fe elemental mapping. (e) Fe2p and (f) N1s XPS spectra. (g) The possible chemical structure. Figure 1a showed the general way to prepare Fe-N-C. Briefly, the as prepared Fecontaining ionic liquid precursor was pyrolyzed in N2 and the product was leached in HCl to remove the inactive iron particles and other iron species from agglomeration during pyrolysis if any. The microstructure of Fe-N-C, evaluated by scanning electron microscope (SEM, Figure 1b) and bright-field scanning transmission electron microscope (BF-STEM, Figure 1c), was sheet-like. The high-angle annular dark-field scanning TEM (HAADF-STEM) images and EDS mapping (Figure 1d) demonstrated a uniform distribution of Fe, N and C in Fe-N-C. 8 ACS Paragon Plus Environment

Page 8 of 22

Page 9 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


X-ray diffraction (XRD, Figure S1) showed the as-prepared Fe-N-C comprised typical graphitic carbon.30 Of note, few Fe-related clusters or nanoparticles were observed in the above high resolution microscopic and diffraction characterization, most presumably suggesting a uniform atomic distribution of Fe in Fe-N-C. To understand the detailed chemical/electronic structures of Fe and N in the surface of FeN-C artificial enzyme, X-ray photoelectron spectroscopy (XPS) was further performed. The Fe2p XPS spectrum (Figure 1e) showed five peaks, corresponding to Fe2+ 2p3/2 (710.8 eV), Fe3+ 2p3/2 (714.3 eV), Fe2+ 2p1/2 (723.3 eV), Fe3+ 2p1/2 (727.9 eV) and the satellite peak (719.8 eV), agreeing with the reported result.31 The Fe content in Fe-N-C was further quantified to be 0.71 wt.% by inductively coupled plasma optical emission spectrometer (ICP-OES). The N1s XPS spectrum (Figure 1f) could be deconvoluted into pyridinic N (398.4 eV), Nx-Fe (399.7 eV), pyrrolic N (400.2 eV), graphitic N (401.2 eV), and oxidized N (403.0 eV) (Figure 1g and Table S1).32 Therefore, the as-prepared Fe-N-C consisted of Fe-/N-dopants, and graphitic carbon, and Fe was most presumably dispersed in the form of single atom by complexing with aromatic N. To evaluate the Fe-N-C catalytic activity in dehydrogenation, Hantzsch 1, 4dihydropyridines (1,4-DHP) was used as model molecule, which was an important class of drug for cardiovascular diseases and could be dehydrogenized into diethyl 2,6-dimethyl-3,5pyridine-dicarboxylate (DDPD) (Figure 2a) by natural enzymes.33-34 The catalytic reactions were carried out in air-saturated phosphate buffer solution (pH=7.4) at room temperature. As a control, the catalytic activity of metalloporphyrins, such as 5,10,15,20-tetraphenyl21H,23H-porphine iron(III) chloride (FeTPPCl), and typical artificial enzymes, such as nanoFe3O4 were also evaluated (Figure 2b). The O2-dependent oxidative dehydrogenation of 1, 4DHP catalyzed by Fe-N-C was firstly evaluated by UV-vis absorption spectroscopy. A new absorption peak at 272 nm, typically ascribing to pyridine-based derives DDPD, was observed (Figure S2) for the product,35 an evident proof of the occurrence of the catalytic oxidative 9 ACS Paragon Plus Environment


dehydrogenation reaction. As a control, Fe-N-C showed poor dehydrogenation activity under hypoxic conditions (Figure S3). High-performance liquid chromatography (HPLC) gave further evidences of the pyridine-based product by referring to a standard (Figure S4). Moreover, by using a dissolved oxygen electrode, the consumption of O2 during catalysis was verified (Figure S5). These results collectively verified that Fe-N-C could dehydrogenate substrates by using O2 under mild conditions. a)

5

-1

ν (µM min )

4

FeTPPCl Blank

e

-6

e

-7

e

-8

e

-9

Ea = 45.4 kJ/mol

-1

3

c)

Fe-N-C Fe-N-C (Ppy) Fe-N-C (Ben) nano-Fe3O4

k (s )

b)

2 1

Fe-N-C

0 0.1

0.2

-3

0.3

-3

3.0x10

S (mM)

3.4x10

-1

)

e)

Relative activity (%)


120

d)100

50

-3

3.2x10

1/T (K

90

60

30

0

0

45

RT

o

3

70

6

f) 100

g) 100 Relative activity (%)

50

0

9

pH

Temperature ( C)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 22

12

50

0 PBS

CH2Cl2

CH3CN n-Hexane

1

Different solvents

2

3

4

Recycling times

5

Figure 2 (a) Chemical reaction of dehydrogenation of 1, 4-DHP by P450 or Fe-N-C to the corresponding DDPD product. (b) The kinetic plot of the 1, 4-DHP dehydrogenation 10 ACS Paragon Plus Environment

Page 11 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


catalyzed by Fe-N-C and controls. (c) Arrhenius plot for the dependence of the rate constant (K) for dehydrogenation of 1, 4-DHP by Fe-N-C on temperature (T). Relative dehydrogenation activity of Fe-N-C in different temperature (d), pH (e) and solvents (f). The recovery and recyclability of Fe-N-C (g). The room temperature (RT) was around 20 oC. To get more kinetic insights, the catalytic activity of Fe-N-C artificial enzyme for dehydrogenation by directly using O2 was studied by enzyme kinetics theory and methods (Figure 2a and S6).6, 29 The typical kinetic parameters such as the catalytic constant (Kcat), Michaelis-Menten constant (Km), maximal velocity (Vmax) and the catalytic efficiency (Kcat/Km) are listed in Table S2. It was found the Km and Kcat/Km of Fe-N-C, were comparable to that of some cytochrome P450 enzymes for dehydrogenation of N-heterocycles (Table S3).36 Furthermore, the oxidase-like activity of Fe-N-C that dehydrogenated substrate by using molecular O2 was 33 times of that of the emerging N-doped carbon nanozymes37 in regarding of Vmax under optimized conditions (Figure S7 and Table S2), highlighting the import role of possible Fe-Nx center in further promoting the catalytic activity. The activation energy (Ea) of Fe-N-C was further calculated to be 45.4 kJ/mol (Figure 2c), comparable to that of some enzymes ranging from 30 to 80 kJ/mol for hydrogen abstraction,38 verifying FeN-C could be developed as a biomimetic dehydrogenation catalyst directly using O2 under mild conditions. As a control, the dehydrogenation activity of FeTPPCl and nano-Fe3O4 were also evaluated (Figure 2b). In contrast, although both FeTPPCl and nano-Fe3O4 could dehydrogenate substrate by employing H2O2 as an oxygen donor (Figure S8),16, 39 they could not directly utilize O2 to dehydrogenate 1, 4-DHP (Figure 2b, S4 and Table S2). Another two Fe-N-C artificial enzymes containing similar Fe-Nx center,40 i.e. Fe-N-C (Ben) and Fe-N-C (Ppy) were also prepared by using other Fe-containing precursors (See Experimental section in SI). As shown in Figure S9, both the Fe2p and N1s XPS spectrum of Fe-N-C (Ben) and Fe-N-C (Ppy) showed five peaks, similar to that of Fe-N-C. Furthermore, based on the N1s XPS result, it was found that the proportion of different N species and the 11 ACS Paragon Plus Environment


Page 12 of 22

amount of Fe-Nx active sites could be well tuned by choosing different precursors (Table S1). Interestingly, both of them demonstrated the apparent dehydrogenation activity (Figure 2b and Table S2), indicating the general catalytic character of Fe-N-C in direct utilizing O2 to dehydrogenate substrate under mild condition. Moreover, the modulated kinetics (Table S2) suggested the dehydrogenation activity could be further boosted in principle by optimizing the electronic structure of Fe-Nx via engineering the “solid ligand” (N-doped carbon). In addition, it should be noted that decreasing the size of Fe-N-C by chemical or physical methods would lead to a larger surface-to-volume, improved dispersibility and more exposed active sites, all of which were theoretically beneficial to improve the catalytic activity of Fe-N-C. Most natural enzymes would be denaturized and become less active in organic media, high temperature and extreme pH.28 As advantages, Fe-N-C exhibited an enhanced catalytic activity in elevated temperature up to 70 oC (Figure 2d), and retained up to 66% of activity at high pH and no deactivation in the different polar organic media (e.g. n-Hexene, CH2Cl2 and CH3CN) (Figure 2e and 2f), indicating its higher catalytic stability, which was essentially ascribed to the robust structure of Fe-N-C. The excellent stability of Fe-N-C in air was also observed for other reported Fe-N-C catalysts.26 Moreover, most natural enzymes were difficult to separate and regenerate as well as other homogeneous artificial enzymes that have been developed recently, such as Mn complex and Cu/TEMPO.8,

41

The separation and

recyclability of Fe-N-C artificial enzyme was thus further examined by a simple centrifugation and washing with CH2Cl2 and diethyl ether to remove the product. As shown in Figure 2g, Fe-N-C exhibited negligible loss of activity after five cycles, indicating the excellent stability and recyclability. In these regards, Fe-N-C was superior to natural enzymes that only work in mild conditions and not easy to be separated, many heterogeneous artificial enzymes that cannot directly use O2, and homogeneous artificial enzymes that are hard to be separated and recycled in biomimetic catalysis (Table S4).


Page 13 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1 Fe-N-C catalyzed dehydrogenation and monoxygenation of different substrates by direct using oxygen in aqueous solution.

Substrate

Product

O P

Selectivity (%)

Yield (%)

100

52.1

100

75.3

100

33.0

100

37.4

100

21.6

The selective oxidation of N, P-containing compounds is one of the most important organic transformations for construction of key intermediates in the fine chemical industry.26 Except for 1, 4-DHP, the Fe-N-C artificial enzyme was also applicable for selective dehydrogenization of a broad scope of N, P-containing substrates by direct using O2 under room temperature in aqueous solutions (Table 1 and Figure S10, S11, S12 and S13). For example, Fe-N-C could dehydrogenize diphenylhydrazine into azobenzene in 75.3% yield. Moreover,

Fe-N-C

can

be extended to monoxygenate42 triphenylphosphine

into

triphenylphosphine oxide in 21.6% yield (Table 1). The selectivity for all of the corresponding products was nearly 100%.These results indicated the potential of Fe-N-C artificial enzyme as low-cost and sustainable heterogeneous catalyst for the selective oxidation in industrial processes. Compared to noble metal based nanozymes, the nonprecious Fe-N-C showed better tunability of structure and catalytic activity, which could be achieved by tuning structures of low-cost precursors, and would be a very promising alternative to noble metal-based nanozymes in driving biomimetic catalytic reactions. 13 ACS Paragon Plus Environment


The intermediate species of O2 activation (1O2, O2•− and H2O2, instead of strongly aggressive OH•− that often leads to non-selective oxidation) during Fe-N-C catalyzed oxidation were then further monitored and verified by trapping methods (Figure S14a and S14b). A kinetic isotope effect was observed obviously by increasing the content of deuterons (Figure S14c), suggesting that protons were transferred at the rate-determining step. Moreover, based on SCN− poisoning experiment, it was confirmed that the active site of O2 activation catalyzed by Fe-N-C should contain Fe (Figure S14d).27 In these regards, these specific intermediate reactive oxygen species (ROS) at Fe-Nx center (Figure S14d) were similar to that of the some natural enzymes,43 providing a platform to mimic enzymes for metabolizing exogenous or endogenous substrates in vitro. However, the Fe-N-C catalyzed O2 activation with formation of 1O2, O2•− and H2O2 was rarely reported by other artificial enzyme mimics, because most of them cannot directly use O2 and have to use artificial oxygen donors such H2O2.6, 17 It was noted that activation of O2 at Fe-N site was supposed to be attributed to strong interactions between catalytic site and N-doped carbon support,21 which changed the electronic structure of Fe-N site. During O2 activation, the Fe-N center probably bound and activated 3O2 to form 1O2,44 and then was converted to HO2•− by obtaining proton and electron from substrates. Subsequently, the generated HO2•− picked up electron to produce HO2−,45 which further performed dehydrogenation or monoxygenation of organic substrates. In this regard, except for biomimetic catalytic reaction for molecules conversion, Fe-N-C is also promising for applications that require specific ROS. Cancer cells were vulnerable to damage by an excessive level of ROS that is incompatible with cellular survival.42 Thus using Fe-N-C as an exogenous ROS-modulating material is likely to increase ROS generation and cause elevation of ROS above a cellular tolerability threshold, leading to cancer cell death. For this, we further investigated the capability of Fe-N-C artificial enzyme in reducing the viability of lung cancer cells.


Page 14 of 22

Page 15 of 22

a)

c)

100

100

Cell viability (%)

b)

Cell proliferative rate(%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


50

50

0

0

Blank

CB

Fe-N-C

Blank

CB

Fe-N-C

Figure 3 (a) Fluorescence microscopic images of lung cancer cells treated with and without CB and Fe-N-C for 24 h. (b) MTT assay of lung cell viability incubated with and without CB and Fe-N-C. (c) Proliferation rate of CB and Fe-N-C incubated lung cancer cells determined by cell counting. Fluorescence microscopic images in Figure 3a disclosed Fe- N-C artificial enzyme could significantly decrease the number of proliferative lung cancer cells compared with that of control carbon black (CB) sample. Moreover, based on the statistical result of cell count (Figure 3b), it was observed that the proliferative lung cancer cells was killed by 88% after adding Fe-N-C, which was remarkably superior to CB. The 3-(4,5- dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide (MTT) arrays result (Figure 3c) further indicated the lung cancer cell survival rate was reduced by approximately 70% under 24 h normal oxygen conditions after subjecting the cells to Fe-N-C, agreeing with the statistical result of cell counting. In 15 ACS Paragon Plus Environment


contrast, the CB only reduced the 22% lung cancer cells (Figure 3c). These results clearly implied the potential of Fe-N-C for cancer therapy via ROS production. The detailed quantification of ROS in the cancer cells and the antitumor activity of Fe-N-C to other cancer46 are very important to explore its biological activity and potentials in medical treatment, which would be undertaken in the future study. It is noted that photodynamic therapy (PDT) is widely utilized clinically to treat tumors by using ROS, which is triggered from photosensitizer and oxygen under light illumination. However, the primary downsides of PDT are low light utilization efficiency and its inability to treat tumors located deep under the skin due to absorption, scattering and the short penetration depth of light in tissues.47-48 Compared to PDT, Fe-N-C could activate the dioxygen and generate ROS without any light illumination. Thus, Fe-N-C artificial enzyme might be developed as an effective ROSmodulating material and constitute a potential therapeutic strategy in a smart system for cancer treatment, even for deeper layers of tumor tissues when recognition unit and reversible on/off switch for regulating ROS release was constructed. Conclusion In summary, we reported the general catalytic character of Fe-N-C artificial enzyme in direct utilizing O2 to oxidize substrates of nearly 100% selectivity under mild condition. The corresponding catalytic activity of Fe-N-C could be tuned by modulating the type of precursors for pyrolysis. Fe-N-C had several striking superior features with respect to classical heterogeneous artificial enzymes, and homogeneous artificial enzymes in durability of working in harsh conditions (extreme pH and high temperature), ease of separation and recycling, and direct use of O2 without sacrificial oxygen donors (e.g. H2O2). This work demonstrated the enzyme-like activity of Fe-N-C could be used in a wide range of new potential applications in biomimetic catalysis, industrial oxidation processes and biomedicine. It should be aware that the yield of catalytic dehydrogenation and monooxygenation was not


Page 16 of 22

Page 17 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


very high. Work focused on the structural modulation of Fe-N-C for higher activity and more challenged reactions26, 41 would be performed in the future. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. The XRD and XPS spectra of catalysts, UV-Vis absorption spectra and HPLC tests for catalytic oxidation reactions, Table for comparison of the reported catalysts, and more discussion. Acknowledgements This work was supported by the National Natural Science Foundation of China (21775018, 21675022),

the

Natural

Science

Foundation

of

Jiangsu

Province

(BK20160028,

BK20170084), the Open Funds of the State Key Laboratory of Electroanalytical Chemistry (SKLEAC201703) and the Fundamental Research Funds for the Central Universities. We thank Prof. Jinwen Shi (Xi'an Jiaotong University, China) and Prof. Shimou Chen (Institute of Process Engineering, Chinese Academy of Sciences) for help in XPS and TEM measurements, respectively.

References 1. Que, L. Jr.; Tolman, W. B., Biologically Inspired Oxidation Catalysis. Nature. 2008, 455, 333-340. 2. Maity, A.; Hyun, S.-M.; Powers, D. C., Oxidase Catalysis via Aerobically Generated Hypervalent Iodine Intermediates. Nat. Chem. 2018, 10, 200-204. 3. Roux, Y.; Ricoux, R.; Avenier, F.; Mahy, J. P., Bio-Inspired Electron-Delivering System for Reductive Activation of Dioxygen at Metal Centres towards Artificial Flavoenzymes. Nat. Commun. 2015, 6, 8509. 4. Tao, Y.; Lin, Y.; Huang, Z.; Ren, J.; Qu, X., Incorporating Graphene Oxide and Gold Nanoclusters: A Synergistic Catalyst with Surprisingly High Peroxidase-Like Activity over A Broad pH Range and Its Application for Cancer Cell Detection. Adv. Mater. 2013, 25, 25942599. 5. Han, L.; Zhang, H.; Chen, D.; Li, F., Protein-Directed Metal Oxide Nanoflakes with 17 ACS Paragon Plus Environment


Tandem Enzyme-Like Characteristics: Colorimetric Glucose Sensing Based on One-Pot Enzyme-Free Cascade Catalysis. Adv. Funct. Mater. 2018, 28, 1800018. 6. Xue, T.; Jiang, S.; Qu, Y.; Su, Q.; Cheng, R.; Dubin, S.; Chiu, C. Y.; Kaner, R.; Huang, Y.; Duan, X., Graphene-Supported Hemin as A Highly Active Biomimetic Oxidation Catalyst. Angew. Chem. Int. Ed. 2012, 51, 3822-3825. 7. Omagari, T.; Suzuki, A.; Akita, M.; Yoshizawa, M., Efficient Catalytic Epoxidation in Water by Axial N-Ligand-Free Mn-Porphyrins within A Micellar Capsule. J. Am. Chem. Soc. 2016, 138, 499-502. 8. Guo, M.; Lee, Y. M.; Gupta, R.; Seo, M. S.; Ohta, T.; Wang, H. H.; Liu, H. Y.; Dhuri, S. N.; Sarangi, R.; Fukuzumi, S.; Nam, W., Dioxygen Activation and O-O Bond Formation Reactions by Manganese Corroles. J. Am. Chem. Soc. 2017, 139, 15858-15867. 9. Meunier, B.; Guilmet, E.; De Carvalho, M. E.; Poilblanc, R., Sodium Hypochlorite: A Convenient Oxygen Source for Olefin Epoxidation Catalyzed by (Porphyrinato)manganese Complexes. J. Am. Chem. Soc. 1984, 106, 6668-6676. 10. Kaizer, J.; Klinker, E. J.; Oh, N. Y.; Rohde, J. U.; Song, W. J.; Stubna, A.; Kim, J.; Münck, E.; Nam, W.; Que, L. J., Nonheme FeIVO Complexes That Can Oxidize the C-H Bonds of Cyclohexane at Room Temperature. J. Am. Chem. Soc. 2004, 126, 472-473. 11. Park, J.; Morimoto, Y.; Lee, Y. M.; Nam, W.; Fukuzumi, S., Metal Ion Effect on the Switch of Mechanism from Direct Oxygen Transfer to Metal Ion-Coupled Electron Transfer in the Sulfoxidation of Thioanisoles by A Non-Heme Iron(IV)-Oxo Complex. J. Am. Chem. Soc. 2011, 133, 5236-5239. 12. Wei, H.; Wang, E., Nanomaterials with Enzyme-Like Characteristics (Nanozymes): NextGeneration Artificial Enzymes. Chem. Soc. Rev. 2013, 42, 6060-6093. 13. Wang, X. Y.; Hua, Y. J.; Wei, H., Nanozymes in Bionanotechnology: From Sensing to Therapeutics and Beyond. Inorg. Chem. Front. 2016, 3, 41-60. 14. Comotti, M.; Pina, C. D.; Matarrese, R.; Rossi, M., The Catalytic Activity of “Naked” Gold Particles. Angew. Chem. 2004, 116, 5936 -5939. 15. Ragg, R.; Natalio, F.; Tahir, M. N.; Janssen, H.; Kashyap, A.; Strand, D.; Strand, S.; Tremel, W., Molybdenum Trioxide Nanoparticles with Intrinsic Sulfite Oxidase Activity. ACS Nano. 2014, 8, 5182-5189. 16. Gao, L.; Zhuang, J.; Nie, L.; Zhang, J.; Zhang, Y.; Gu, N.; Wang, T.; Feng, J.; Yang, D.; Perrett, S.; Yan, X., Intrinsic Peroxidase-Like Activity of Ferromagnetic Nanoparticles. Nat. Nanotechnol. 2007, 2, 577-583. 17. Song, Y.; Qu, K.; Zhao, C.; Ren, J.; Qu, X., Graphene Oxide: Intrinsic Peroxidase 18 ACS Paragon Plus Environment

Page 18 of 22

Page 19 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Catalytic Activity and Its Application to Glucose Detection. Adv. Mater. 2010, 22, 2206-2210. 18. Battioni, P.; Renaud, J. P.; Bartoli, J. F.; Reina-Artiles, M.; Fort, M.; Mansuy, D., Monooxygenase-like Oxidation of Hydrocarbons by H2O2 Catalyzed by Manganese Porphyrins and Imidazole: Selection of the Best Catalytic System and Nature of the Active Oxygen Species. J. Am. Chem. Soc. 1988, 110, 8462-8470. 19. Feiters, M. C.; Rowan, A. E.; Nolte, R. J. M., From Simple to Supramolecular Cytochrome P450 Mimics. Chem. Soc. Rev. 2000, 29, 375-384. 20. Chung, H. T.; Cullen, D. A.; Higgins, D.; Sneed, B. T.; Holby, E. F.; More, K. L.; Zelenay, P., Direct Atomic-Level Insight into the Active Sites of A High-Performance PGM-free ORR Catalyst. Science 2017, 357, 479-484. 21. Zitolo, A.; Goellner, V.; Armel, V.; Sougrati, M. T.; Mineva, T.; Stievano, L.; Fonda, E.; Jaouen, F., Identification of Catalytic Sites for Oxygen Reduction in Iron- and NitrogenDoped Graphene Materials. Nat. Mater. 2015, 14, 937-942. 22. Sahraie, N. R.; Paraknowitsch, J. P.; Gobel, C.; Thomas, A.; Strasser, P., Noble-Metal-Free Electrocatalysts with Enhanced ORR Performance by Task-Specific Functionalization of Carbon using Ionic Liquid Precursor Systems. J. Am. Chem. Soc. 2014, 136, 14486-14497. 23.

Li, W.; Wu, J.; Higgins, D. C.; Choi, J.-Y.; Chen, Z., Determination of Iron Active

Sites in Pyrolyzed Iron-Based Catalysts for the Oxygen Reduction Reaction. ACS Catal. 2012, 2, 2761-2768. 24. Hayashi, S.; Hamaguchi, H. O., Discovery of a Magnetic Ionic Liquid [bmim]FeCl4. Chem. Lett. 2004, 33, 1590-1591. 25. Ayad, M.; Salahuddin, N.; Fayed, A.; Bastakoti, B. P.; Suzuki, N.; Yamauchi, Y., Chemical Design of A Smart Chitosan-Polypyrrole-Magnetite Nanocomposite toward Efficient Water Treatment. Phys. Chem. Chem. Phys. 2014, 16, 21812-21819. 26. Cui, X.; Li, Y.; Bachmann, S.; Scalone, M.; Surkus, A. E.; Junge, K.; Topf, C.; Beller, M., Synthesis and Characterization of Iron-Nitrogen-Doped Graphene/Core-Shell Catalysts: Efficient Oxidative Dehydrogenation of N-Heterocycles. J. Am. Chem. Soc. 2015, 137, 10652-10658. 27. Liu, W.; Zhang, L.; Liu, X.; Liu, X.; Yang, X.; Miao, S.; Wang, W.; Wang, A.; Zhang, T., Discriminating Catalytically Active FeNx Species of Atomically Dispersed Fe-N-C Catalyst for Selective Oxidation of the C-H Bond. J. Am. Chem. Soc. 2017, 139, 10790-10798. 28. Ferrier, D. R., Biochemistry 6th ed, Lippincott Williams and Wilkins. 2013, pp 53-68. 29. Cai, R.; Yang, D.; Peng, S.; Chen, X.; Huang, Y.; Liu, Y.; Hou, W.; Yang, S.; Liu, Z.; Tan, W., Single Nanoparticle to 3D Supercage: Framing for an Artificial Enzyme System. J. Am. 19 ACS Paragon Plus Environment


Chem. Soc. 2015, 137, 13957-13963. 30. He, F.; Chen, X.; Shen, Y.; Li, Y.; Liu, A.; Liu, S.; Mori, T.; Zhang, Y., Ionic LiquidDerived Fe–N/C Catalysts for Highly Efficient Oxygen Reduction Reaction Without Any Supports, Templates, or Multi-Step Pyrolysis. J. Mater. Chem. A. 2016, 4, 6630-6638. 31. Lin, L.; Zhu, Q.; Xu, A. W., Noble-Metal-Free Fe-N/C Catalyst for Highly Efficient Oxygen Reduction Reaction under Both Alkaline and Acidic Conditions. J. Am. Chem. Soc. 2014, 136, 11027-11033. 32. Sa, Y. J.; Park, C.; Jeong, H. Y.; Park, S. H.; Lee, Z.; Kim, K. T.; Park, G. G.; Joo, S. H., Carbon Nanotubes/Heteroatom-Doped Carbon Core-Sheath Nanostructures as Highly Active, Metal-Free Oxygen Reduction Electrocatalysts for Alkaline Fuel Cells. Angew. Chem. Int. Ed. 2014, 53, 4102-4106. 33. Boecker, R. H.; Guengerich, F. P., Oxidation of 4-Aryl- and 4-Alkyl-Substituted 2,6Dimethyl-3,5-Bis(alkoxycarbony1)-1,4-Dihydropyridines by Human Liver Microsomes and Immunochemical Evidence for the Involvement of a Form of Cytochrome P-450. J. Med. Chem. 1986, 29, 1596-1603. 34. Filipan-Litvić, M.; Litvić, M.; Vinković, V., An Efficient, Metal-Free, Room Temperature Aromatization of Hantzsch-1,4-Dihydropyridines with Urea-Hydrogen Peroxide Adduct, Catalyzed by Molecular Iodine. Tetrahedron 2008, 64, 5649-5656. 35. Wu, W.; Zhan, L.; Fan, W.; Song, J.; Li, X.; Li, Z.; Wang, R.; Zhang, J.; Zheng, J.; Wu, M.; Zeng, H., Cu-N Dopants Boost Electron Transfer and Photooxidation Reactions of Carbon dots. Angew. Chem. Int. Ed. 2015, 54, 6540-6544. 36. Sun, H.; Ehlhardt, W. J.; Kulanthaivel, P.; Lanza, D. L.; Reilly, C. A.; Yost, G. S., Dehydrogenation of Indoline by Cytochrome P450 Enzymes: A Novel "Aromatase" Process. J. Pharmacol. Exp. Ther. 2007, 322, 843-851. 37. Fan, K.; Xi, J.; Fan, L.; Wang, P.; Zhu, C.; Tang, Y.; Xu, X.; Liang, M.; Jiang, B.; Yan, X.; Gao, L., In Vivo Guiding Nitrogen-Doped Carbon Nanozyme for Tumor Catalytic Therapy. Nat. Commun. 2018, 9, 1440. 38. Olsen, L.; Rydberg, P.; Rod, T. H.; Ryde, U., Prediction of Activation Energies for Hydrogen Abstraction by Cytochrome P450. J. Med. Chem. 2006, 49, 6489-6499. 39. Zhou, Y.; Huang, X.; Zhang, W.; Ji, Y.; Chen, R.; Xiong, Y., Multi-Branched Gold Nanoflower-Embedded Iron Porphyrin for Colorimetric Immunosensor. Biosens. Bioelectron. 2017, 102, 9-16. 40. Ferrero, G. A.; Preuss, K.; Marinovic, A.; Jorge, A. B.; Mansor, N.; Brett, D. J.; Fuertes, A. B.; Sevilla, M.; Titirici, M. M., Fe-N-Doped Carbon Capsules with Outstanding 20 ACS Paragon Plus Environment

Page 20 of 22

Page 21 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Electrochemical Performance and Stability for the Oxygen Reduction Reaction in Both Acid and Alkaline Conditions. ACS Nano. 2016, 10, 5922-5932. 41. Ryland, B. L.; Stahl, S. S., Practical Aerobic Oxidations of Alcohols and Amines with Homogeneous Copper/TEMPO and Related Catalyst Systems. Angew. Chem. Int. Ed. 2014, 53, 8824-8838. 42. Sono, M.; Roach, M. P.; Coulter, E. D.; Dawson, J. H., Heme-Containing Oxygenases. Chem. Rev. 1996, 96, 2841-2887. 43. Hanukoglu, I., Antioxidant Protective Mechanisms Against Reactive Oxygen Species (ROS) Generated by Mitochondrial P450 Systems in Steroidogenic Cells. Drug. Metab. Rev. 2006, 38, 171-196. 44. Long, R.; Mao, K.; Ye, X.; Yan, W.; Huang, Y.; Wang, J.; Fu, Y.; Wang, X.; Wu, X.; Xie, Y.; Xiong, Y., Surface Facet of Palladium Nanocrystals: A Key Parameter to the Activation of Molecular Oxygen for Organic Catalysis and Cancer Treatment. J. Am. Chem. Soc. 2013, 135, 3200-3207. 45. Nath, I.; Chakraborty, J.; Verpoort, F., Metal Organic Frameworks Mimicking Natural Enzymes: A Structural and Functional Analogy. Chem. Soc. Rev. 2016, 45, 4127-4170. 46. Deng, Y.; Li, E.; Cheng, X.; Zhu, J.; Lu, S.; Ge, C.; Gu, H.; Pan, Y., Facile Preparation of Hybrid Core-Shell Nanorods for Photothermal and Radiation Combined Therapy. Nanoscale 2016, 8, 3895-3899. 47. Chen, H.; Wang, G. D.; Chuang, Y. J.; Zhen, Z.; Chen, X.; Biddinger, P.; Hao, Z.; Liu, F.; Shen, B.; Pan, Z.; Xie, J., Nanoscintillator-Mediated X-ray Inducible Photodynamic Therapy for In Vivo Cancer Treatment. Nano Lett. 2015, 15, 2249-2256. 48. Yuan, H.; Chong, H.; Wang, B.; Zhu, C.; Liu, L.; Yang, Q.; Lv, F.; Wang, S., Chemical Molecule-Induced Light-Activated System for Anticancer and Antifungal Activities. J. Am. Chem. Soc. 2012, 134, 13184-13187.



TOC


Page 22 of 22

Fe-N-C Artificial Enzyme: Activation of Oxygen for Dehydrogenation

Recommend Documents