Dioxygen Activation bya Non-Heme Iron(II) Complex: Theoretical Study toward UnderstandingFerric–Superoxo Complexes

Chen, Hui,Cho, Kyung-Bin,Lai, Wenzhen,Nam, Wonwoo,Shaik, Sason American Chemical Society 2012 Journal of chemical theory and computation Vol.8 No.3

<P>We present a systematic study using density functional theory (DFT) and coupled cluster (CCSD(T)) computations with an aim of characterizing a non-heme ferric-superoxo complex [(TMC)Fe(O-2)(2+) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) that was proposed to perform allylic C-H activation of cyclohexene (Lee, Y.-M. et al. J. Am. Chem, Soc. 2010, 132, 10668). As such, we investigated a series of iron-O-2 species without and with a sixth ligand bound to the iron ion in different O-2 coordination modes (end-on and side-on) and different spin states. Most of the iron-O-2 complexes were found to be iron(III)-superoxo species, Fe(III)(O-2(-)), with high-spin (S = 5/2) or intermediate-spin (S = 3/2) ferric centers coupled ferromagnetically or antiferromagnetically to the superoxide anion radical. One iron(IV)-peroxo state, Fe(IV)(O-2(2-)), was also examined. The preference for ferromagnetic or antiferromagnetic coupling modes between the superoxo and ferric radicals was found to depend on the FeOO angle, where a side-on tilt favors ferromagnetic coupling whereas the end-on tilt favors antiferromagnetic states. Experimental findings, e.g., the effects of solvent, spin state, and redox potential of non-heme Fe(II) complexes on O-2 activation, were corroborated in this work. Solvent effects were found to disfavor O-2 binding, relative to the unbound ferrous ion and O-2. The potential H-abstraction reactivity of the iron(III)-superoxo species was considered in light of the recently proposed exchange-enhanced reactivity principle (Shaik, S.; Chen, H.; Janardanan, D. Nat. Chem. 2011, 3, 19). It is concluded that localization and/or decoupling of an unpaired electron in the d-block of high-spin Fe(III) center in the S = 2 and 3 ferric-superoxo complexes during H abstractions enhances exchange stabilization and may be the root cause of the observed reactivity of [(TMC)Fe(O-2)](2+).</P>

The anti-tumor efficacy of 20(S)-protopanaxadiol, an active metabolite of ginseng, according to fasting on hepatocellular carcinoma

Wenzhen Li,YifanWang,Xinbo Zhou,Xiaohong Pan,Junhong Lu,Hongliu Sun,Zeping Xie,Shayan Chen,Xue Gao 고려인삼학회 2022 Journal of Ginseng Research Vol.46 No.1

Background: 20(S)-protopanaxadiol (20(S)-PPD), one of the main active metabolites of ginseng, performs a broad spectrum of anti-tumor effects. Our aims are to search out new strategies to enhance anti-tumor effects of natural products, including 20(S)-PPD. In recent years, fasting has been shown to be multifunctional on tumor progression. Here, the effects of fasting combined with 20(S)-PPD on hepatocellular carcinoma growth, apoptosis, migration, invasion and cell cycle were explored. Methods: CCK-8 assay, trypan blue dye exclusion test, imagings photographed by HoloMonitorTM M4, transwell assay and flow cytometry assay were performed for functional analyses on cell proliferation, morphology, migration, invasion, apoptosis, necrosis and cell cycle. The expressions of genes on protein levels were tested by western blot. Tumor-bearing mice were used to evaluate the effects of intermittent fasting combined with 20(S)-PPD. Results: We firstly confirmed that fasting-mimicking increased the anti-proliferation effect of 20(S)-PPD in human HepG2 cells in vitro. In fasting-mimicking culturing medium, the apoptosis and necrosis induced by 20(S)-PPD increased and more cells were arrested at G0-G1 phase. Meanwhile, invasion and migration of cells were decreased by down-regulating the expressions of matrix metalloproteinase (MMP)-2 and MMP-9 in fasting-mimicking medium. Furthermore, the in vivo study confirmed that intermittent fasting enhanced the tumor growth inhibition of 20(S)-PPD in H22 tumor-bearing mice without obvious side effects. Conclusion: Fasting significantly sensitized HCC cells to 20(S)-PPD in vivo and in vitro. These data indicated that dietary restriction can be one of the potential strategies of chinese medicine or its active metabolites against hepatocellular carcinoma.

A graphene‑based highly sensitive aptasensor for the detection of lung cancer marker CA125

Junnan Chen,Lingmin Yu,Wenzhen Xu,Tao Lin,Sicong Jiang,Caijin Jin 한국탄소학회 2023 Carbon Letters Vol.33 No.6

Graphene-based sensors have emerged as significant tools for biosensing applications due to their unique electrical, mechanical, and thermal properties. In this study, we have developed an innovative and sensitive aptasensor based on the surfacemodified graphene for the detection of lung cancer biomarker CA125. The sensor leverages the combination of graphene surface and gold nanoparticles (AuNPs) electrodeposition to achieve a high level of sensitivity and selectivity for the biomarker detection. A noticeable decrease in electron transfer resistance was observed upon the AuNPs deposition, demonstrating the enhancement of electrochemical performance. Our experimental findings showed a strong linear relationship between the sensor response and CA125 concentrations, ranging from 0.2 to 15.0 ng/mL, with a detection limit of 0.085 ng/ mL. This study presents a novel approach to lung cancer detection, surpassing the traditional methods in terms of invasiveness, cost, and accuracy. The results from this work could pave the way for the development of graphene-based sensors in various other biosensing applications.

Experimental and numerical investigations on effect of reverse flow on transient from forced circulation to natural circulation

Li, Mingrui,Chen, Wenzhen,Hao, Jianli,Li, Weitong Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.9

In a sudden shutdown of primary pump or coolant loss accident in a marine nuclear power plant, the primary flow decreases rapidly in a transition process from forced circulation (FC) to natural circulation (NC), and the lower flow enters the steam generator (SG) causing reverse flow in the U-tube. This can significantly compromise the safety of nuclear power plants. Based on the marine natural circulation steam generator (NCSG), an experimental loop is constructed to study the characteristics of reverse flow under middle-temperature and middle-pressure conditions. The transition from FC to NC is simulated experimentally, and the characteristics of SG reverse flow are studied. On this basis, the experimental loop is numerically modeled using RELAP5/MOD3.3 code for system analysis, and the accuracy of the model is verified according to the experimental data. The influence of the flow variation rate on the reverse flow phenomenon and flow distribution is investigated. The experimental and numerical results show that in comparison with the case of adjusting the mass flow discontinuously, the number of reverse flow tubes increases significantly during the transition from FC to NC, and the reverse flow has a more severe impact on the operating characteristics of the SG. With the increase of flow variation rate, the reverse flow is less likely to occur. The mass flow in the reverse flow U-tubes increases at first and then decreases. When the system is approximately stable, the reverse flow is slightly lower than obverse flow in the same U-tube, while the flow in the obverse flow U-tube increases.

Identification and Partial Characterization of an Alanine Aminotransferase Gene CsAlaAT2 in Response to Shade in Tea (Camellia sinensis)

Wang Jinhe,Chen Wenzhen,Li Yuanda,Zhao Xiuxiu,Xiang Qinzheng,Li Min 한국식물학회 2021 Journal of Plant Biology Vol.64 No.1

Alanine contributes to the taste and nutritional quality of tea and is an important member of alanine metabolism catalyzed by alanine aminotransferase (AlaAT, EC 2.6.1.2). However, the molecular mechanism underlying alanine metabolism in tea plants has not been fully elucidated. In this study, an increase in enzyme activity of AlaAT2 was detected in vitro, and the alanine aminotransferase activity was higher level in leaves than that in other tissues of tea plant, while the CsAlaAT2 transcription was high in leaves and root. Using phylogenetic analysis, an alanine aminotransferase gene CsAlaAT2 was identified as a member of group C, which was located in the mitochondrion. Additionally, the molecular mass of CsAlaAT2 protein was found to be approximately 53 kDa by SDS-PAGE and western blotting. The CsAlaAT2 expression level and the alanine content in photosynthetic tissues increased in response to the shade treatment. Furthermore, the involvement of CsAlaAT2 in alanine biosynthesis was confirmed based on transient suppression assays in tea leaves, and the alanine content and CsAlaAT2 transcript level decreased when CsAlaAT2 expression was suppressed in tea leaves. Thus, this study suggests that CsAlaAT2 is essential for the alanine metabolism in tea plants grown and its response to shade.

The detection and diagnosis model for small scale MSLB accident

Wang, Meng,Chen, Wenzhen Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.10

The main steam line break accident is an essential initiating event of the pressurized water reactor. In present work, the fuzzy set theory and the signal-based fault detection method has been used to detect the occurrence and diagnosis of the location and break area for the small scale MSLB. The models are validated by the AP1000 accident simulator based on MAAP5. From the test results it can be seen that the proposed approach has a rapid and proper response on accident detection and location diagnosis. The method proposed to evaluate the break area shows good performances for small scale MSLB with the relative deviation within ±3%.

Enhanced Reactivities of Iron(IV)-Oxo Porphyrin π-Cation Radicals in Oxygenation Reactions by Electron-Donating Axial Ligands

Kang, Yaeun,Chen, Hui,Jeong, Yu Jin,Lai, Wenzhen,Bae, Eun Hae,Shaik, Sason,Nam, Wonwoo WILEY-VCH Verlag 2009 Chemistry Vol.15 No.39

<P>The proximal axial ligand in heme iron enzymes plays an important role in tuning the reactivities of iron(IV)-oxo porphyrin π-cation radicals in oxidation reactions. The present study reports the effects of axial ligands in olefin epoxidation, aromatic hydroxylation, alcohol oxidation, and alkane hydroxylation, by [(tmp)<SUP>+.</SUP> Fe<SUP>IV</SUP>(O)(p-Y-PyO)]<SUP>+</SUP> (1-Y) (tmp=meso-tetramesitylporphyrin, p-Y-PyO=para-substituted pyridine N-oxides, and Y=OCH<SUB>3</SUB>, CH<SUB>3</SUB>, H, Cl). In all of the oxidation reactions, the reactivities of 1-Y are found to follow the order 1-OCH<SUB>3</SUB> > 1-CH<SUB>3</SUB> > 1-H > 1-Cl; negative Hammett ρ values of −1.4 to −2.7 were obtained by plotting the reaction rates against the σ<SUB>p</SUB> values of the substituents of p-Y-PyO. These results, as well as previous ones on the effect of anionic nucleophiles, show that iron(IV)-oxo porphyrin π-cation radicals bearing electron-donating axial ligands are more reactive in oxo-transfer and hydrogen-atom abstraction reactions. These results are counterintuitive since iron(IV)-oxo porphyrin π-cation radicals are electrophilic species. Theoretical calculations of anionic and neutral ligands reproduced the counterintuitive experimental findings and elucidated the root cause of the axial ligand effects. Thus, in the case of anionic ligands, as the ligand becomes a better electron donor, it strengthens the FeO&n.bond;H bond and thereby enhances its H-abstraction activity. In addition, it weakens the Fe&n.dbond;O bond and encourages oxo-transfer reactivity. Both are Bell–Evans–Polanyi effects, however, in a series of neutral ligands like p-Y-PyO, there is a relatively weak trend that appears to originate in two-state reactivity (TSR). This combination of experiment and theory enabled us to elucidate the factors that control the reactivity patterns of iron(IV)-oxo porphyrin π-cation radicals in oxidation reactions and to resolve an enigmatic and fundamental problem.</P> <B>Graphic Abstract</B> <P>Enzyme models: Reactivity studies of iron(IV)-oxo porphyrin π-cation radicals such as depicted reveal that, in contrast to the non-heme iron(IV)- and ruthenium(IV)-oxo complexes, iron(IV)-oxo porphyrins bearing electron-donating axial ligands are more reactive in oxo-transfer and H-atom abstraction reactions (see figure). <img src='wiley_img/09476539-2009-15-39-CHEM200901238-content.gif' alt='wiley_img/09476539-2009-15-39-CHEM200901238-content'> </P>

Investigation on reverse flow characteristics in U-tubes under two-phase natural circulation

Chu, Xi,Li, Mingrui,Chen, Wenzhen,Hao, Jianli Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.5

The vertically inverted U-tube steam generator (UTSG) is widely used in the pressurized water reactor (PWR). The reverse flow behavior generally exists in some U-tubes of a steam generator (SG) under both single- and two-phase natural circulations (NCs). The behavior increases the flow resistance in the primary loop and reduces the heat transfer in the SG. As a consequence, the NC ability as well as the inherent safety of nuclear reactors is faced with severe challenges. The theoretical models for calculating single- and two-phase flow pressure drops in U-tubes are developed and validated in this paper. The two-phase reverse flow characteristics in two types of SGs are investigated base on the theoretical models, and the effects of the U-tube height, bending radius, inlet steam quality and primary side pressure on the behavior are analyzed. The conclusions may provide some promising references for SG optimization to reduce the disadvantageous behavior. It is also of significance to improve the NC ability and ensure the PWR safety during some accidents.

Quantitative Analysis of Parotid Gland Secretion Function in Sjögren’s Syndrome Patients with Dynamic Magnetic Resonance Sialography

Simin Liu,Weiwei Chen,Min Wang,Tong Wu,Lingli Dong,Chu Pan,Wenzhen Zhu 대한영상의학회 2019 Korean Journal of Radiology Vol.20 No.3

Objective: To evaluate the secretory function of parotid glands by dynamic magnetic resonance (MR) sialography and determine the clinical performance of this technique in diagnosing and evaluating Sjögren’s syndrome (SS) patients. Materials and Methods: This study enrolled 29 healthy volunteers (25 women and 4 men; mean age, 34.8 ± 6.3 years; age range, 26–47 years) and 25 primary SS (pSS) patients (23 women and 2 men; mean age, 37.7 ± 7.9 years; age range, 25–50 years) with decreased secretory function. The volume of the parotid gland ducts was precisely measured for both groups at single pre- and 6 post-gustatory-stimulated phases. Time-dependent volume change ratio curves were generated, four parameters were derived from the curves: the slope of the increase in the first post-stimulation phase (slope1st), the peak value, the time-to-peak, the total saliva secretion post-stimulation. All values were used to quantitatively evaluate the secretory function of the parotid gland. The repeated measurement analysis, Mann-Whitney U test and receiver operating characteristic curve were applied. Results: Time-dependent volume change ratio curves demonstrated that there is a statistically significant difference between the two groups (F = 8.750; p = 0.005). A quickly increasing curve was shown in the volunteer group, whereas a slowly increasing curve was shown in the pSS patient group. The slope1st, peak value and total saliva secretion post-stimulation of the patient group were significantly lower than those of the volunteer group (p = 0.005, p = 0.003, and p = 0.002, respectively). The timeto-peak between the two groups was not significantly different (p = 0.383). The slope1st can be used as a discriminator to diagnose SS patients (p = 0.015; odds ratio = 4.234; area under the curve = 0.726). Conclusion: Dynamic MR sialography is proven to be an effective method in evaluating salivary gland function and has a great potential in diagnosing and evaluating pSS patients.

The Changes of Absorption and Catalytic Capacity on Reduced Graphene Oxide After Electron Beam Irradiation

Peng Liu,Wei Qi,Wenzhen An,Longlong Tian,Zhan Li,Xiaolei Chen,Wang-Suo Wu 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2015 NANO Vol.10 No.3

As is well-known, porous nanomaterials have attracted increasing attention recently, and graphene-related materials (such as porous graphene) have been studied both experimentally and theoretically. Almost all researches are focused on nanoelectronics, supercapacitors, multifunctional membrances, bio-applications or others. Consequently, in order to understand the differences between porous graphene and normal graphene at adsorption and catalytic property, in this experiment, with the removal of metal ion (152Eu(III)) and organic matter (gallic acid) and reduction of 4-nitrophenol (4-NP) by NaBH4 as model reactions, a systematic investigation into the adsorptive performance as well as catalytic activity of graphene with or without electron beam irradiation exposure had been carried out. As the results showed, compared with the reduction of pristine graphene oxidized (R-GO), the reduction of graphene oxidized with electron beam irradiation exposure (100 MGy, about 2 h, radiation graphene oxide (R-RGO)) had many irregular defects caused by lack of atoms; the adsorptive performance of the R-RGO increased for metals but decreased for organic matter. However, the adsorption rate of the R-RGO was lower for metals, but higher for organic matter than that of the R-GO. In addition, the results also showed that the R-RGO had a better catalytic capacity than the R-GO.