• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Zn(Ⅱ)金屬有機(jī)骨架作為基質(zhì)金屬蛋白酶模擬物催化水解微囊藻毒素-LR

    2023-12-21 01:02:10方艷芬賀玉婷牛慧斌陳春城黃應(yīng)平
    無機(jī)化學(xué)學(xué)報 2023年12期
    關(guān)鍵詞:微囊三峽庫區(qū)宜昌

    方艷芬 賀玉婷 趙 麗 ?;郾?陳春城 李 悅*, 黃應(yīng)平*,

    (1三峽大學(xué)材料與化工學(xué)院,宜昌 443002)

    (2三峽大學(xué)三峽庫區(qū)生態(tài)環(huán)境教育部工程研究中心,宜昌 443002)

    (3南開大學(xué)化學(xué)學(xué)院,天津 300071)

    (4中國科學(xué)院化學(xué)研究所,北京 100190)

    0 Introduction

    Microcystins (MCs) are a large type of cyclic heptapeptide toxins in eutrophic waters, which are commonly considered hepatotoxic and carcinogenic because of the strong inhibition of protein phosphatases and interference with cell signaling pathways. In some bodies of water that have become eutrophicated,the levels of MCs have increased to levels as high as dozens of parts per billion, which greatly exceeds the World Health Organization′s water quality standard of 1.0 parts per billion[1-4]. Advanced oxidation processes(AOPs)are capable of efficiently oxidizing MCs by producing reactive oxygen species (ROS). Nevertheless,due to the high presence of natural organic matter(NOM) in natural water bodies, AOPs are not selective to MCs because most ROS are consumed by NOM[5-7].Hydrolysis, on the other hand, is a gentler and safer way of treating pollutants,making it a preferable option over AOPs[8-11].Based on our earlier research,it was discovered that siderite, a mineral that contains iron, can break down microcystin-LR (MC-LR) peptide bonds,even in the presence of humic acid (HA), which is 10 times its amount[12]. Although siderite′s effectiveness is not very high, the results indicate that catalytic hydrolysis is a feasible approach to achieve the desired degradation of MCs when NOM is present.

    Matrix metalloproteinases (MMPs), a group of proteinases dependent on Zn(Ⅱ), play a significant role in breaking down polypeptide bonds in connective tissues[13-14]. This breakdown can potentially aid in the hydrolysis of peptide bonds in MCs. Metal-organic frameworks(MOFs)hold great potential as a foundation for creating enzyme mimics or nanozymes. This is due to their remarkable versatility in composition, which enables the modification of metal ion identity and coordination environment to replicate enzymatic active sites. The functions of a series of metalloenzymes, such as tyrosinase[15], CO-dehydrogenase[16], and phosphotriesterase[17], have been performed by MOF mimics.Therefore, MOFs having functional groups can be organized in a structured manner, resulting in synergistic action, similar to MMPs. However, there are currently no artificial MMP mimics reported for MC hydrolysis,despite the widespread use of MMPs.

    In this work, the physical and chemical properties of the Zn (Ⅱ)-based MOF nanomaterials (Zn-MOF-1-NSs) were meticulously analyzed and successfully used to hydroxylate MC-LR.The Zn-MOF-1-NS nanomaterial, acting as an MMP mimic, showed remarkable efficiency in catalyzing MC-LR hydroxylation with high activity and substrate specificity. Further investigation revealed that both the Zn(Ⅱ)ion and the carboxyl group of the MOF were involved in activating the peptide bond.

    1 Experimental

    1.1 Chemical and materials

    MC-LR (Fig.S1, Supporting information) standard(1 mg solid, purity not less than 95% by HPLC) was purchased from Express Technology Co., Ltd. and stored at -25 ℃. MC-LR stock solution was prepared by adding H2O to dissolve the MC-LR standard and then stored at 4 ℃. The concentration of the MC-LR solution used inin-situATR-FTIR experiments was 250 mg·L-1and that in the degradation experiments was 2 mg·L-1. Deuterium oxide (D2O, 99.9%) was purchased from Cambridge Isotope Laboratories, Inc.Glutamic acid (D-Glu), arginine (L-Arg), alanine (DAla) and leucine (L-Leu) were obtained from Sigma-Aldrich. River humic acid standard (IR105H) was purchased from the International Humic Substances Society (IHSS). Methanol and acetonitrile were HPLC grade, and water was purified by reverse osmosis and deionization. All chemicals were obtained commercially and used as received without further purification.

    1.2 Preparation of Zn-MOF-1-NS

    Zn-MOF-1 precursor was synthesized by the following procedures[18]: a mixture of ZnSO4·6H2O (143.8 mg, 0.5 mmol), 3-amino-1,2,4-triazole-5-carboxylic acid (38.5 mg, 0.3 mmol), and 1,3,5-benzenetricarboxylic acid (42 mg, 0.2 mmol) was dissolved in water(10.0 mL), and placed in a 23 mL Teflon-lined stainless steel vessel.The pH of the solution was adjusted to 6.0 by triethylamine.This mixture was sealed and heated at 150 ℃for 48 h.After cooling to 25 ℃,the precipitate of the crude product was collected, washed with H2O and methanol, and dried in a vacuum at 60 ℃for 6 h. Anal. Calcd. for Zn-MOF-1 (C22H18N8O15Zn4)(%):C, 29.49; H, 2.02; N, 12.51. Found(%): C, 29.17; H,2.08;N,12.65.

    The exfoliation of Zn-MOF-1 was carried out by sonicating the ethanol suspension of its precursor (8 mg in 7 mL)for 3 h.After the centrifugation at 4 000 r·min-1for 10 min to remove unexfoliated particles,Zn-MOF-1-NSs were separated from the ethanol supernatant by rotatory evaporation.

    1.3 Characterization

    Powder X-ray diffraction (PXRD) patterns were recorded on a Rigaku D/max-2500 diffractometer with CuKαradiation (λ=0.154 06 nm) at 40 kV and 100 mA with a scanning range of 5°-50°.Scanning electron microscopy (SEM) images were taken using a JEOL JSM-7500F scanning electron microscope at an accelerating voltage of 30 kV.Elemental analysis (C, H, and N) was performed on a Perkin-Elmer 240C analyzer.Thermogravimetric analysis (TGA) was operated with a Rigaku standard TG-DTA analyzer from ambient temperature to 700 ℃with a heating rate of 10 ℃·min-1in the air, and an empty Al2O3crucible was used as the reference. Atomic force microscopy (AFM) was carried out on a Bruker Icon probe microscope in tapping mode in the air under ambient conditions, and the delaminated MOF samples were deposited on aluminum-coated silicon cantilevers. Theζpotential of the catalyst was measured using a Malvern Zeta Sizer. N2sorption isotherms were measured with a Micromeritics ASAP 2020 analyzer at 77 K. X-ray photoelectron spectroscopy (XPS) was conducted on an AXIS Supra spectrometer equipped with 300 W AlKαradiation.The hydrocarbon C1sline at 284.8 eV from adventitious carbon was used for energy referencing.A Nicolet iS50 Fourier transform infrared spectrometer collected infrared spectra(FTIR).

    1.4 Hydrolysis experiments

    Reactions were carried out in a 10 mL vial placed in a dark box with magnetic stirring at (25±0.1) ℃. In each experiment, 3 mL aqueous solution of MC-LR with the initial concentration of 2 mg·L-1was placed in the vial, and 5 mg catalyst was dispersed to it. The pH of the suspension was not adjusted. At specified reaction times, 400 μL samples of the reaction mixture were collected, centrifuged to remove the catalyst, and analyzed using HPLC.

    The substrate specificity of Zn-MOF-1-NS toward MC-LR in the presence of NOM was tested with the addition of HA with 1, 2, 10, and 20 mg·L-1. Other reaction and analytical conditions were unchanged.

    1.5 Analytical methods

    MC-LR. A Waters 2690 HPLC determined the concentration of MC-LR with a PDA detector and a Kromasil C18 column (4.6 mm×250 mm, 10 μm particle size). The mobile phase was water and methanol(60∶40,V/V) containing 0.05% trifluoroacetic acid(TFA). The flow rate, injection volume, and column temperature were 0.8 mL·min-1, 20 μL, and 35 ℃,respectively. MC-LR was quantified by its absorption at 238 nm. The retention time of MC-LR was 8.3 min.The quantification range was from 0 to 10 μmol·L-1for MC-LR with the correlation coefficient(R2)for the standard of 0.998(Fig.S2a).

    Amino acids. Before measurement, 0.6 mL of 4∶1(V/V) water-ethanol mixture was added to wash the adsorbed amino acids from the MOF catalyst (Fig.S3)[19].The details about desorption experiments are provided in the Supporting information. The hydrolysis products(D-Glu,L-Arg,D-Ala, andL-Leu) of MC-LR were determined by a Waters 2690 HPLC with an FLR detector and a Nova-PakTMC18 column (3.9 mm×150 mm, 4 μm particle size). The retention times ofD-Glu,L-Arg,D-Ala, andL-Leu were 8.3, 14.3, 19.8, 21.3,and 31.8 min, respectively. The hydrolysis products were quantified using fluorescent detection withλex=330 nm andλem=445 nm. These compounds were identified and quantified by the external standard curves of the peak area. The quantification ranges for four amino acids were from 0.5 to 20 μmol·L-1with theR2for the standards above 0.99(Fig.S2b).

    1.6 In-situ ATR-FTIR analysis

    In-situinfrared spectroscopy was used to monitor the surface interaction between Zn-MOF-1-NS film and MC-LR in different solvents (H2O,D2O,and C6H6).The ATR cell was placed in the internal compartment of a Nicolet iS50 FTIR spectrometer (Thermo, USA)equipped with an MCT-A detector.Thin Zn-MOF-1-NS film was prepared by drying Zn-MOF-1-NS suspension(0.4 mL, 10 g·L-1) on a ZnSe crystal strip (80 mm×10 mm×4 mm). After adding 0.8 mL of solvent to the flow cell, ATR-FTIR spectra were collected continuously for 2 or 4 h until the establishment of the sorption equilibrium between solvent and Zn-MOF-1-NS film. After MC-LR (100 μL, 250 mg·L-1) was added, the timeresolved ATR-FTIR spectra were recorded at the interval of 0.283 s.

    1.7 Theoretical calculation

    The geometry optimization, frequency calculation,and natural bond orbital (NBO) analysis were all performed at the M06/def2-TZVP level[20-21]. To make the calculation affordable, besides the central Zn2+ion,only the ligands coordinating directly with it were considered in treating Zn3 and Zn4. For Zn2, because of the possibility of H2O/reactant forming an H bond with nearby carboxyl groups, two additional btc3-ligands were taken into the model. The initial configurations of Zn2+and ligands were picked up from the crystalline structure of Zn-MOF-1. Since the peripheral carboxyl groups of btc3-ligands are far from the reaction center of Zn2+, they were removed with H atoms supplemented to the vacancies. During optimization, the C atoms in the benzene rings and the N atoms coordinating to peripheral Zn2+ions (not included in the model) were fixed to replicate the bulk behavior, while the other atoms were relaxed (Fig.1). An implicit solvent model of SMD (solvation model density) modulated the solvent effects.

    Fig.1 Coordination environments of(a)Zn1,(b)Zn2,(c)Zn3,and(d)Zn4 in Zn-MOF-1-NS

    2 Results and discussion

    2.1 Selection of MOF catalyst

    Due to the large molecular size of MC-LR (2.4 nm), it is difficult to design channels large enough to accommodate MC-LR molecules without affecting the stability of the MOF. The results reported by Tissot et al.[22]and our previous works[23]have shown the inefficiency of internal active sites towards large-molecular reactants. Therefore, we chose 2D nanosheets, which expose the maximum quantity of active sites on the external surface, as the morphology for the MOF catalyst.Combining with the structure and catalytic mechanism of MMP,the selection criteria of the MOF catalyst were: (1) the backbone is constructed by the connection among Zn2+ions and five-membered N-heterocyclic bridging ligands, and carboxyl groups are contained for the activation of peptide bond;(2)in addition to heterocyclic N atoms, Zn2+ion is coordinated with at least one solvent molecule, which would be easily replaced by substrate and does not destroy the integrity of the MOF; (3) the framework is 2D connected, which could be delaminated to nanosheets. After the screening of the 424 MOFs containing Zn2+and N-pentacyclic ligand containing MOFs summarized in the CCDC database, [Zn4(atz)2(btc)2(H2O)3]n(Zn-MOF-1), a MOF assembled by the ligands of 3-amino-1,2,4-triazolate(atz-) and 1,3,5-benzenetricarboxylate (btc3-), was chosen as a potential catalyst for the following investigation (Fig.2)[18]. This MOF contains four crystallographically independent Zn(Ⅱ)centers (Fig.1). The benzene ring and triazole ring projections on the ab plane are staggered, but there isn′t any effective overlap. Therefore,theπ-πstacking doesn′t play a significant role in the crystal stability of this MOF.All of these Zn(Ⅱ)centers are surrounded by triazole N atoms and carboxyl O atoms, and three of them (Zn2, Zn3, and Zn4) are coordinated by one H2O molecule. The interconnection among Zn2+ions and two kinds of ligands form a double-layer structure, which expands into the supramolecular framework of the crystal only by the weak connection of H bonds. The 2D connected structure of Zn-MOF-1 was drawn with Mercury 4.2.0.

    Fig.2 Two-dimensional connected structure of Zn-MOF-1

    2.2 Preparation and characterization of MOF nanosheets

    Zn-MOF-1 was synthesized generally according to the reported procedure with minor modifications to minimize the particle size[18]. PXRD was applied to characterize the obtained sample (Fig. 3a). All the recorded diffraction peaks could be readily indexed to the simulated pattern, showing that our sample presents the same framework structure and has good phase purity. This backbone was further supported by the results of elemental analysis, thermogravimetric (Fig.S4),and FTIR analyses(Fig.S5).Because of its 2D connected framework, the sample of this MOF presented a layer-stacking morphology under SEM observation(Fig.3b). In consistent with its nonporous structure,Zn-MOF-1 presented a small BET surface area of 8 m2·g-1(Fig.S6a and Table S1). This result implied that Zn-MOF-1 has limited contact with the reactants,so its delamination is necessary.

    Fig.3 (a)XRD patterns and(b)SEM image of Zn-MOF-1

    The Zn-MOF-1 precursor was exfoliated simply by the sonication in ethanol (the product is denoted as Zn-MOF-1-NS).After the removal of sediments,a transparent supernatant was obtained. The exfoliation process was evidenced by an apparent Tyndall effect under the irradiation of a laser beam (Fig.4a).The morphology of the exfoliated sample was examined by AFM.As shown in Fig.4b and 4c,this sample was composed of irregularly shaped nanosheets with several hundred nanometers lateral dimensions.The thicknesses of these nanosheets were generally about 4 nm,indicating that each nanosheet comprises only six two-layer structures of Zn-MOF-1. Zn-MOF-1-NS presented a negativeζpotential of -9.2 mV at pH=7.4 (Fig.S7),which ensured its good stability in the aqueous suspension[24].

    Fig.4 (a)Photograph of the Tyndall effect of the ethanol suspension of Zn-MOF-1-NS;(b)AFM image of Zn-MOF-1-NS;(c)Height profile of the corresponding section of figure b

    2.3 Catalytic degradation of MC-LR

    With 5 mg of Zn-MOF-1-NS, 82.6% of MC-LR was degraded in 7.5 h(Fig.5a).MC-LR decay generally followed first-order kinetics withR2=0.94 (Fig. 5b).Within 7.5 h, only 20.9% of MC-LR was degraded by siderite, indicating that the activity of Zn-MOF-1-NS was much higher than those of siderite that showed the highest activity reported for the hydrolysis of MC-LR[12].To further examine the reuse potential of Zn-MOF-1-NS, cyclic degradation experiments were carried out(Fig.5d).It was observed that Zn-MOF-1-NS continued to display high catalytic activity in five successive cycles. However, due to the high dispersity of nanosheets,part of the catalyst was lost during the recycling process, which induced the slowdown of the reaction(by 45% in five cycles).Furthermore,as evidenced by the PXRD pattern (Fig.S8),the Zn-MOF-1-NS catalyst maintained good stability during the reaction.

    Fig.5 (a)Degradation curves and(b)reaction kinetics of MC-LR using various catalysts;(c)Hydrolysis yield production of amino acids using Zn-MOF-1-NS(Inset:MC-LR degradation curve);(d)Recycling of Zn-MOF-1-NS;(e)Michaelis-Menten kinetic curve of the initial reaction rate against MC-LR concentration;(f)Degradation curves of MC-LR(2 mg·L-1)at different concentrations of HA in Zn-MOF-1-NS(Inset:effect of HA concentration on the reaction rate constant of MC-LR hydrolysis)

    To illustrate the reaction mechanism, another 2D Zn(Ⅱ)based MOF,[Zn7(OH)2(Hbta)6(H2O)6]n(H3bta=N,Nbis-(1(2)H-tetrazol-5-yl)-amine) (named Zn-MOF-2)was also tested for comparison[25]. The characterization of Zn-MOF-2 is also shown in Fig.S9-S11. Under Zn-MOF-2-NS catalysis, the degradation efficiency of MC-LR in 7.5 h could only reach 54.0%,obviously lower than the result of Zn-MOF-1-NS. The Zn2+density could not explain the superior activity of Zn-MOF-1-NS because the surficial Zn2+density of Zn-MOF-1-NS(1.67×10-5nm-2)was even lower than that of Zn-MOF-2-NS (2.31×10-5nm-2). Considering that the carboxyl group was only contained in Zn-MOF-1-NS, we speculated that this group participates in the hydrolysis of MC-LR. However, the addition of acetic acid to the Zn-MOF-2-NS catalytic system could not remarkably accelerate MC - LR consumption. This phenomenon indicated that the relative positions of Zn2+and the carboxyl group are crucial.

    The intermediates produced during the reaction were tested with an initial concentration of MC-LR of 10 mg·L-1.D-Glu,L-Arg,D-Ala, andL-Leu were detected during the decomposition of MC-LR (Fig.5c).At 10 h, the concentrations were 0.653, 0.466, 1.20 and 0.0183 μmol·L-1, respectively. The quantity ofD-Ala could account for 50.0% of MC-LR consumption, confirming that the hydrolysis of peptide bonds was the main pathway for MC-LR degradation.

    A steady-state kinetic assay was performed by varying the initial concentration of MC-LR. The relationship between the initial reaction rate and substrate concentration could be well described by the Michaelis-Menten equation withR2=0.97, showing the enzyme mimic feature of Zn-MOF-1-NS (Fig.5e). The fitting gave the Michaelis constant (Km) of 6.2 μmol·L-1and the maximum reaction rate (Vmax) of 0.61 μmol·L-1·min-1. SinceKmis the substrate concentration at which half the enzymes are bound and its values for MMPs range from tenths to tens of millimoles[26-29], this result indicated that the affinity of Zn-MOF-1-NS for MC-LR is comparable with those of MMPs towards proteins.

    Various NOMs are contained in environmental water samples and could potentially inhibit MC-LR degradation. HA was added to the reaction system to test the ability to resist NOM interference of Zn-MOF-1-NS. Even when the HA concentration was increased to 20 mg·L-1, the rate change of MC-LR (2 mg·L-1) was still negligible (Fig.5f), showing that Zn-MOF-1-NS can specifically degrade MC-LR in the presence of NOMs. In contrast, with Zn-MOF-2-NS as a catalyst,the same concentration of HA led to a significant slowdown of the reaction (the percentage of degradation decreased from 46.7% to 29.5%, Fig.S12). Based on the structure of Zn-MOF-1-NS, this catalyst was expected to catalyze the hydroxylation of the peptide bond by the Lewis acidity of Zn2+ions. However, our previous research illustrated that a single Lewis acid site of mineral catalysts did not display specificity for MC-LR[12].Thus, the phenomenon in the Zn-MOF-1-NS catalytic system indicates the existence of multiple binding processes in the reaction.

    2.4 Hydrolysis of MC-LR on Zn-MOF-1-NS surface

    In the ATR-FTIR spectrum of Zn-MOF-1-NS(Fig.S13a),the wide band at 3 260 cm-1includes O—H and N—H stretching vibrations[30]. The 1 615 and 1 431 cm-1peaks belong to the C=O and C—O stretching vibrations of COO-that coordinate with Zn2+, respectively[12,24]. The vibration at 1 554 cm-1is attributed to N—H[31]. The band at 1 369 cm-1belongs to the C—C bonds of the benzene ring[32]. The absorptions at 1 211 and 1 062 cm-1correspond to the C—N bonds on and in the triazole rings, respectively[33]. The stretching vibration of Zn—O appeared at 734 cm-1[34]. The spectrum of MC-LR is given in Fig.S13b. In this spectrum,the absorption bands at 3 260 and 1 515 cm-1refer to the stretching and bending vibrations of N—H[12]. The bands at 2 925 and 2 851 cm-1are assigned to the stretching vibrations of —CH2—[35]. The C=O stretching vibration of COOH was centered at 1 731 cm-1[36].The peak at 1 642 cm-1(Ⅰband) and 1 450 cm-1(Ⅱband)was ascribed to the amide C=O stretching vibration[37]. The peak at 1 642 cm-1is ascribed to the amide C=O stretching vibration (Ⅰband). The vibrations of C—H in-plane bending, C—O—C stretching, and C—N stretching correspond to the peaks at 1 409, 1 178,and 1 082 cm-1,respectively[25].

    Fig.6a and 6b show thein-situATR-FTIR spectra of the Zn-MOF-1-NS/H2O equilibrium process, which were recorded at intervals after MC-LR addition (100 μL, 250 mg·L-1). The positive bands at 3 501, 3 409,1 648, 1 537, 1 487, 1 401, and 1 087 cm-1showed that MC-LR is adsorbed on the surface of Zn-MOF-1-NS.A redshift of the peak of the amide C=O of MC-LR from 1 648 to 1 637 cm-1was observed,which could be explained by its coordination with the Zn2+of Zn-MOF-1-NS. Because Zn2+works as a Lewis acid site, such coordination would reduce the π electron density of the amide group and thus weaken the C=O bond[38-39]. In addition,the negative peak at 1 615 cm-1indicated that the—COOH of Zn-MOF-1-NS is involved in the interaction with MC-LR in addition to Zn2+. Meanwhile, the new band at 3 183 cm-1illustrates the formation of a hydrogen bond between the amide N—H of MC-LR and the carboxyl oxygen of Zn-MOF-1-NS[27]. With the proceeding of the reaction, two new peaks of —COOH positively occurred at 1 601 and 1 664 cm-1[40-41], while two negative bands appeared at 1 216 and 1 065 cm-1,which are assigned to the cleavage of the amide C—N bond of MC-LR. These changes indicated that the peptide bond of MC-LR is broken into—COOH and N—H under the catalysis of Zn-MOF-1-NS.

    To verify the hydrolysis mechanism,analogous experiments in D2O were performed.In the spectra of Zn-MOF-1-NS, the bands of O—H at 3 297 and 1 644 cm-1were red-shifted to 2 470 and 1 201cm-1for the O—D bond (Fig.S14), which conformed to the Hooke′s law[42]. Upon the addition of MC-LR, the same trend as that in the Zn-MOF-1-NS/H2O system was observed(Fig.6c). A crest appeared at 1 664 cm-1, showing the formation of —COOH by the cleavage of amide C—N[43-44]. The peak of N—H bending vibration at 1 330 cm-1and the valley of the break of the C—N bond at 1 047 cm-1confirm the cleavage of the peptide bond of MC-LR (Fig.6d). The redshifts of the —COO-peak of Zn-MOF-1-NS from 1 431 cm-1(in the pure Zn-MOF-1-NS/D2O system, Fig.S13a) to 1 450 cm-1and the N—H peak of MC-LR from 1 554 to 1 330 cm-1confirm the formation of hydrogen bond between them. Together with the results of the H2O system,these changes manifest that both Zn2+and—COO-of Zn-MOF-1-NS participate in the interaction with MC-LR.The former acts as a Lewis acid site to coordinate with amide C=O and the latter binds to N—H through a hydrogen bond.

    Fig.6 In-situ ATR-FTIR spectra of(a,b)MC-LR(100 μL,250 mg·L-1)in H2O system and(c,d)MC-LR(100 μL,250 mg·L-1)in D2O system

    In addition, the infrared spectra of Zn-MOF-1-NS separately immersed in H2O and D2O were recorded for comparison (Fig.S15). Relative to the system of H2O,two new peaks were observed at 2 488 and 1 246 cm-1in D2O, indicating that D2O replaced the coordinating H2O molecule. Therefore, it is necessary to study the fate of MC-LR after binding with Zn2+sites in the D2O system.After the addition of MC-LR to the D2O system,thein-situATR-FTIR spectra presented a valley at 1 205 cm-1(O—D, for D2O desorption) and the crests at 3 400 cm-1(N—H of adsorbed MC-LR) and 1 450 cm-1(C=O of amide Ⅱ) from 0.2 to 119.5 min(Fig.6d), indicating that the D2O coordinating to Zn2+is replaced by MC-LR.

    Similar phenomena were also observed in the benzene system. Zn-MOF-1-NS equilibrated at C6H6for 2 h (Fig.7a). The loss of the coordinating H2O molecule in Zn-MOF-1-NS gave negative bands of H—O stretching at 3 386 and 1 632 cm-1(Fig.7b).At the same time,it was observed that the Zn—O band presented a blue shift from 774 to 804 cm-1. This change confirms the replacement of the H2O molecule by MC-LR on the Zn2+site.

    Fig.7 In-situ ATR-FTIR spectra of(a)Zn-MOF-1-NS equilibrated for 2 h and(b)MC-LR(100 μL,250 mg·L-1)/Zn-MOF-1-NS in C6H6 system(Solvent-Zn-MOF-1-NS spectrum as background);XPS spectra of Zn-MOF-1-NS before and after the reaction with MC-LR for 10 h:(c)O1s;(d)Zn2p

    We further used XPS spectroscopy to investigate the interaction between MC-LR and Zn-MOF-1-NS.For pristine Zn-MOF-1-NS, three peaks of O1swere recorded at 531.44, 532.08, and 532.52 eV, corresponding to Zn—O[45], O—H[46], and H2O groups[47],respectively (Fig.7c). After the addition of MC-LR, the peak of H2O shifted to 533.49 eV and its area decreased(from 36.1% to 16.0%), verifying the replacement of H2O molecule by MC-LR. Because of the formation of hydrogen bonds with MC-LR,the peak of the O atom of Zn—O presented a blue shift to 532.28 eV. Considering that Zn2+works as the Lewis acid site for MC-LR,we also examined the Zn2pspectrum(Fig.7d).The pristine MOF gave two peaks at 1 022.4 and 1 045.5 eV,which could be assigned to the Zn2p3/2and Zn2p1/2spinorbit components of O/N coordinated Zn atom, respectively[48-49]. Since replacing the coordinating aqueous O atom with the amide O atom of MC-LR does not change the first coordination sphere of Zn2+, the addition of MC-LR did not significantly alter the positions of these two peaks.

    The experimental observations indicate: (1) the much higher activity of Zn-MOF-1-NS than that of Zn-MOF-2-NS proved the participation of the carboxyl group; (2) the substrate specificity of Zn-MOF-1-NS towards MC-LR illustrates the formation of multiple bonds between them; (3) FTIR analysis shows that the amide O atom coordinates to Zn2+ion, and N—H is hydrogen bounded; (4)in-situATR-FTIR and XPS spectra indicate the coordination of amide O atom of MC-LR to Zn2+with the replacement of H2O molecule.So, we speculate that the catalytic mechanism of Zn-MOF-1-NS is similar to that of MMP and involves the participation of both Zn2+ions and carboxyl groups.Thus, we resorted to the theoretical calculation to give an atomic insight into the activation mechanism of MC-LR by Zn-MOF-1-NS. Since the reaction occurred mainly around the peptide bond, N-methylacetamide was taken as a simplified model for MC-LR. As introduced above, among the four crystallographically independent Zn(Ⅱ)centers in Zn-MOF-1-NS,three of them,Zn2, Zn3, and Zn4, are coordinated by H2O molecules and can provide coordination sites for amide O atom.Therefore, we first calculated the Gibbs free energy change (ΔG) values for the substitution of H2O molecule byN-methylacetamide on these metal sites, and the results are listed in Table 1. Due to the similar coordination environments of Zn3 and Zn4, they gave close ΔGvalues of -10.4 and -11.6 kJ·mol-1, respectively.The negative values of these free energy changes show that the coordination of amide to these Zn sites is thermodynamically feasible. The scrutinization of the geometries of these complexes shows that besides the coordination of the amide O atom to Zn2+(Zn—O:0.208 nm for Zn3 and 0.204 nm for Zn4), the N—H also forms a strong hydrogen bond with the carboxyl O atom in the ligand (O…H: 0.198 and 0.202 nm for Zn3 and Zn4, respectively, and ∠N—H…O=163.4° and 157.9°,Fig.S16).

    Table 1 Results of the calculation about amide adsorption to Zn sites of Zn-MOF-1-NS

    In contrast, Zn2 provided a positive ΔGfor the binding with amide (28.3 kJ·mol-1), which may result from the position of its coordinating H2O molecule.Unlike the coordinating H2O molecules of Zn3 and Zn4, which point to the outside of the double-layer structure, the coordinating H2O molecule of Zn2 is located on the opposite layer (Fig.1 and 2). This position makes the substituting amide group crowd with nearly btc3-ligands and thus weakens the formed Zn—O bond (0.226 nm). The steric hindrance also hinders the H bond formation with the carboxyl group coordinating directly with Zn2+. The amide N—H can only form a weak H bond with a carboxyl group in the second coordination sphere with longer O…H distance(0.214 nm) and narrower ∠N—H…O (141.8°). Therefore, the main active sites in Zn-MOF-1-NS are the Zn3 and Zn4 on the surface of the nanosheet, and their carboxyl ligands contribute to the binding with the amide.

    Since the first step of amide hydroxylation is the nucleophilic addition of H2O to the amide C atom, the bond order and polarity of C=O[50]and the LUMO level of the amide group[51]would be parameters to predict the reactivity of the substrate. It is observed that the C=O bonds in three amide-Zn complexes are all longer than those in free N-methylacetamide, and their total NBO polarities (Δt, the difference in the NBO charge between C and O atoms)also show a remarkable increase. The LUMO level of theN-methylacetamide presents aca. 0.5 eV decrease upon the coordination with Zn sites.These results prove that,after the adsorption to the catalyst,the amide C=O bond is weakened,its C atom becomes more positive-charged and electrophilic, and the antibonding orbital of this group becomes more feasible to accommodate the lone pair electrons of nucleophilic agent (H2O), and thus the reactivity is enhanced.

    3 Conclusions

    In summary, simulating the structures of MMPs, a Zn (Ⅱ)- based MOF with nanosheet morphology was developed to catalyze MC-LR hydrolysis. This catalyst can rapidly remove MC-LR even in the presence of a high concentration of HA. The comparison with Zn-MOF-2-NS showed that the carboxyl groups in Zn-MOF-1-NS contribute much to the superior activity and substrate specificity.In-situATR-FTIR,XPS,and theoretical calculation proved that multiple binding processes exist between the MC-LR and Zn-MOF-1-NS and contribute to the peptide bond activation. This work demonstrates the potential of mimic enzyme catalysis in environmental treatment and that MOF is an ideal platform to simulate the multi-group synergism in enzymes.

    Supporting information is available at http://www.wjhxxb.cn

    猜你喜歡
    微囊三峽庫區(qū)宜昌
    宜昌“清單之外無事項”等
    放歌宜昌(女聲獨唱)
    湖北宜昌卷
    三峽庫區(qū)萬家壩滑坡變形區(qū)穩(wěn)定性復(fù)核研究
    奇姝雙生 畫滿宜昌
    中華奇石(2016年9期)2016-12-15 14:20:46
    三峽庫區(qū)產(chǎn)業(yè)培育及結(jié)構(gòu)調(diào)整的思考
    微囊懸浮-懸浮劑和微囊懸浮劑不是同種劑型
    微囊藻毒素-LR對秀麗線蟲精子形成的毒性作用
    馬錢子生物堿微囊的制備及評價
    ELISA試劑盒法測定水中LR型微囊藻毒素
    大陆偷拍与自拍| 午夜福利网站1000一区二区三区| 久久久久久久亚洲中文字幕| 成人无遮挡网站| 日产精品乱码卡一卡2卡三| 美女脱内裤让男人舔精品视频| 久久狼人影院| 中文乱码字字幕精品一区二区三区| 日日爽夜夜爽网站| 亚洲一级一片aⅴ在线观看| 26uuu在线亚洲综合色| 又大又黄又爽视频免费| av免费观看日本| 亚洲美女黄色视频免费看| 亚洲精品视频女| 亚洲精品aⅴ在线观看| 欧美最新免费一区二区三区| 日本黄色日本黄色录像| 精品视频人人做人人爽| 久久精品熟女亚洲av麻豆精品| 国产欧美日韩精品一区二区| 人人妻人人看人人澡| 人人妻人人看人人澡| 国产又色又爽无遮挡免| 高清毛片免费看| 久久人人爽人人片av| 热re99久久精品国产66热6| 婷婷色av中文字幕| 99热这里只有是精品在线观看| 免费黄网站久久成人精品| 亚洲国产精品999| 欧美人与善性xxx| 国内少妇人妻偷人精品xxx网站| 国产亚洲5aaaaa淫片| 99热国产这里只有精品6| 最黄视频免费看| 一本—道久久a久久精品蜜桃钙片| 免费久久久久久久精品成人欧美视频 | 国产色爽女视频免费观看| 亚洲无线观看免费| 午夜福利在线观看免费完整高清在| 亚洲精品视频女| 精品久久久久久电影网| 国内揄拍国产精品人妻在线| 成人影院久久| 免费观看性生交大片5| 黄色视频在线播放观看不卡| 丝袜在线中文字幕| 亚洲丝袜综合中文字幕| 亚洲在久久综合| 黄色日韩在线| 91午夜精品亚洲一区二区三区| 欧美日本中文国产一区发布| 欧美日韩一区二区视频在线观看视频在线| 美女大奶头黄色视频| 国产精品成人在线| av在线观看视频网站免费| 26uuu在线亚洲综合色| av又黄又爽大尺度在线免费看| 国国产精品蜜臀av免费| 最近中文字幕高清免费大全6| 好男人视频免费观看在线| 欧美 亚洲 国产 日韩一| 在线观看免费高清a一片| 免费观看的影片在线观看| 精品人妻熟女av久视频| 久久久久久久国产电影| 91成人精品电影| 久久狼人影院| 亚洲久久久国产精品| 成人亚洲精品一区在线观看| 日韩熟女老妇一区二区性免费视频| 高清视频免费观看一区二区| 欧美日韩一区二区视频在线观看视频在线| 高清黄色对白视频在线免费看 | 国产黄色视频一区二区在线观看| 秋霞在线观看毛片| 久久精品国产亚洲网站| 99久久人妻综合| 国产日韩欧美在线精品| 蜜桃在线观看..| 精品少妇黑人巨大在线播放| 国产白丝娇喘喷水9色精品| 亚洲欧美一区二区三区黑人 | 一级片'在线观看视频| 日本av手机在线免费观看| 成人无遮挡网站| 十八禁高潮呻吟视频 | 亚洲欧美一区二区三区国产| 中国美白少妇内射xxxbb| 日产精品乱码卡一卡2卡三| 久久午夜综合久久蜜桃| 国产中年淑女户外野战色| 午夜福利,免费看| 日日啪夜夜撸| 91久久精品国产一区二区成人| 亚洲国产欧美日韩在线播放 | 丝袜喷水一区| 久久久久久久久久久久大奶| 狂野欧美激情性xxxx在线观看| 人妻系列 视频| 中文资源天堂在线| 久久久久精品久久久久真实原创| 国产精品久久久久成人av| 免费人成在线观看视频色| 日韩一本色道免费dvd| 搡老乐熟女国产| 在线观看www视频免费| 国产成人freesex在线| 一区二区av电影网| 国产老妇伦熟女老妇高清| 日韩一区二区视频免费看| 久久久亚洲精品成人影院| 在线观看国产h片| 99热全是精品| 黄色日韩在线| 国产欧美日韩综合在线一区二区 | 一个人免费看片子| 人妻制服诱惑在线中文字幕| 国产伦精品一区二区三区视频9| 一本大道久久a久久精品| 精品久久久噜噜| 日韩av不卡免费在线播放| 搡老乐熟女国产| 丝袜在线中文字幕| 成年美女黄网站色视频大全免费 | 免费黄色在线免费观看| 免费看光身美女| 菩萨蛮人人尽说江南好唐韦庄| 免费观看的影片在线观看| 国产欧美日韩精品一区二区| 日本色播在线视频| 免费观看的影片在线观看| 国产伦精品一区二区三区四那| 一区二区三区精品91| 青青草视频在线视频观看| 下体分泌物呈黄色| 精品99又大又爽又粗少妇毛片| 成人综合一区亚洲| 午夜福利,免费看| 亚洲av国产av综合av卡| 国产国拍精品亚洲av在线观看| 春色校园在线视频观看| 欧美成人午夜免费资源| 国产精品99久久久久久久久| 两个人的视频大全免费| 日韩大片免费观看网站| 夫妻午夜视频| 午夜福利影视在线免费观看| 人妻系列 视频| 亚洲精品乱码久久久v下载方式| 久久狼人影院| 亚洲欧美成人精品一区二区| 国产av码专区亚洲av| 欧美日韩视频精品一区| 久久ye,这里只有精品| 欧美 亚洲 国产 日韩一| 国产欧美日韩一区二区三区在线 | 亚洲无线观看免费| 欧美精品人与动牲交sv欧美| 十分钟在线观看高清视频www | 亚洲av不卡在线观看| 久久毛片免费看一区二区三区| 夜夜看夜夜爽夜夜摸| 美女国产视频在线观看| 亚洲欧美日韩另类电影网站| h日本视频在线播放| 大码成人一级视频| 久久精品久久久久久久性| 欧美激情极品国产一区二区三区 | 99热国产这里只有精品6| 国产精品久久久久成人av| 人妻 亚洲 视频| 寂寞人妻少妇视频99o| 亚洲av成人精品一二三区| av又黄又爽大尺度在线免费看| 亚洲欧洲国产日韩| 偷拍熟女少妇极品色| 色婷婷久久久亚洲欧美| 欧美成人午夜免费资源| 日日摸夜夜添夜夜添av毛片| 久久免费观看电影| 日韩制服骚丝袜av| 亚洲精品久久午夜乱码| 简卡轻食公司| 日本91视频免费播放| 亚洲欧美日韩东京热| 国产精品福利在线免费观看| 亚州av有码| 久久午夜福利片| 免费黄网站久久成人精品| 国产白丝娇喘喷水9色精品| 哪个播放器可以免费观看大片| 久久久久久久精品精品| 亚洲国产欧美日韩在线播放 | 赤兔流量卡办理| 女性生殖器流出的白浆| 日韩强制内射视频| 大话2 男鬼变身卡| av一本久久久久| 国产91av在线免费观看| 日日啪夜夜撸| 午夜老司机福利剧场| 蜜桃在线观看..| www.色视频.com| 亚洲人与动物交配视频| 欧美三级亚洲精品| 热re99久久国产66热| 日韩精品免费视频一区二区三区 | 亚洲国产精品999| 桃花免费在线播放| 欧美成人精品欧美一级黄| 天堂中文最新版在线下载| 国产综合精华液| 精品亚洲成a人片在线观看| 男女边摸边吃奶| 亚洲成人手机| 亚洲精品国产色婷婷电影| 免费在线观看成人毛片| 国产成人精品久久久久久| 最近中文字幕高清免费大全6| 精品久久久噜噜| 69精品国产乱码久久久| 一级黄片播放器| 黑丝袜美女国产一区| 成人18禁高潮啪啪吃奶动态图 | 在线播放无遮挡| 女人精品久久久久毛片| 亚洲国产成人一精品久久久| 亚洲精品,欧美精品| 欧美 亚洲 国产 日韩一| 久久精品国产亚洲av涩爱| 国产欧美另类精品又又久久亚洲欧美| 18禁动态无遮挡网站| 免费av中文字幕在线| 欧美97在线视频| 国产极品粉嫩免费观看在线 | 亚洲内射少妇av| 人人妻人人添人人爽欧美一区卜| 久久久久精品性色| 青春草国产在线视频| 国产日韩欧美亚洲二区| 精品视频人人做人人爽| 一级爰片在线观看| 国产高清不卡午夜福利| 亚洲精品aⅴ在线观看| 大话2 男鬼变身卡| 少妇丰满av| 国产精品福利在线免费观看| 少妇人妻一区二区三区视频| 少妇人妻 视频| 看非洲黑人一级黄片| 久久久久视频综合| 国产免费一区二区三区四区乱码| 三级国产精品片| 精品午夜福利在线看| 精品人妻偷拍中文字幕| 少妇人妻一区二区三区视频| 一级片'在线观看视频| 九色成人免费人妻av| 97在线视频观看| 在线观看美女被高潮喷水网站| 在线观看美女被高潮喷水网站| 久久青草综合色| 精品卡一卡二卡四卡免费| 国产视频首页在线观看| 国产老妇伦熟女老妇高清| 免费黄网站久久成人精品| 麻豆成人av视频| 精品人妻偷拍中文字幕| 亚洲精品乱久久久久久| 9色porny在线观看| 亚洲国产精品一区三区| 一级毛片我不卡| 亚洲av不卡在线观看| 在线观看免费视频网站a站| 一级毛片aaaaaa免费看小| 成人毛片a级毛片在线播放| 精品少妇内射三级| 亚洲,欧美,日韩| 一级片'在线观看视频| 亚洲图色成人| 精华霜和精华液先用哪个| 亚洲国产精品成人久久小说| 女性生殖器流出的白浆| 嫩草影院新地址| 成年女人在线观看亚洲视频| 最近最新中文字幕免费大全7| 啦啦啦啦在线视频资源| 日韩一本色道免费dvd| 插阴视频在线观看视频| 亚洲中文av在线| 亚洲精品国产成人久久av| 精品亚洲成国产av| 婷婷色综合大香蕉| 久久99热6这里只有精品| 亚洲欧美精品自产自拍| 美女内射精品一级片tv| 国产成人精品福利久久| 国产综合精华液| 午夜免费观看性视频| 精品久久久久久电影网| 中文字幕亚洲精品专区| av播播在线观看一区| 国产 精品1| 成人亚洲欧美一区二区av| 成人18禁高潮啪啪吃奶动态图 | 中文字幕亚洲精品专区| 五月伊人婷婷丁香| 男人狂女人下面高潮的视频| 蜜臀久久99精品久久宅男| 中文乱码字字幕精品一区二区三区| 欧美最新免费一区二区三区| 国产成人a∨麻豆精品| 麻豆成人av视频| 91久久精品国产一区二区三区| 一级爰片在线观看| 日韩三级伦理在线观看| 老女人水多毛片| 日韩伦理黄色片| 青春草国产在线视频| 日韩av不卡免费在线播放| 大香蕉97超碰在线| 国产av码专区亚洲av| 久久97久久精品| 中国美白少妇内射xxxbb| 一级a做视频免费观看| av在线老鸭窝| 爱豆传媒免费全集在线观看| 久久久a久久爽久久v久久| 亚洲av成人精品一二三区| 香蕉精品网在线| 制服丝袜香蕉在线| 99久久精品国产国产毛片| 女性生殖器流出的白浆| 男女边吃奶边做爰视频| 韩国av在线不卡| 国产伦精品一区二区三区四那| 国产精品福利在线免费观看| 2022亚洲国产成人精品| 精品久久久久久电影网| 一本久久精品| 亚洲国产毛片av蜜桃av| 九九在线视频观看精品| 亚洲伊人久久精品综合| 午夜福利影视在线免费观看| 亚洲国产毛片av蜜桃av| 久久久久久久久久久久大奶| 成人影院久久| 婷婷色av中文字幕| 国产精品99久久久久久久久| 一区二区av电影网| 中文乱码字字幕精品一区二区三区| 高清视频免费观看一区二区| 菩萨蛮人人尽说江南好唐韦庄| 下体分泌物呈黄色| 国产毛片在线视频| 九色成人免费人妻av| 大又大粗又爽又黄少妇毛片口| 丰满人妻一区二区三区视频av| 又爽又黄a免费视频| 街头女战士在线观看网站| 久久国内精品自在自线图片| 少妇被粗大的猛进出69影院 | 免费不卡的大黄色大毛片视频在线观看| 国产69精品久久久久777片| 国产男女超爽视频在线观看| 日本猛色少妇xxxxx猛交久久| 国产精品伦人一区二区| 寂寞人妻少妇视频99o| 亚洲情色 制服丝袜| 亚洲国产毛片av蜜桃av| 街头女战士在线观看网站| 夜夜骑夜夜射夜夜干| 在线播放无遮挡| 久久久久久久久大av| 国产中年淑女户外野战色| 性高湖久久久久久久久免费观看| 一级片'在线观看视频| 中文字幕制服av| 交换朋友夫妻互换小说| 天美传媒精品一区二区| 欧美97在线视频| 国产 一区精品| 大香蕉97超碰在线| 99re6热这里在线精品视频| 国产成人精品婷婷| 高清在线视频一区二区三区| 国产亚洲5aaaaa淫片| 国产精品熟女久久久久浪| 伦理电影大哥的女人| 午夜免费鲁丝| 国产欧美日韩精品一区二区| 99热网站在线观看| 热re99久久精品国产66热6| 我的老师免费观看完整版| 在线观看免费高清a一片| 丝袜喷水一区| 最新的欧美精品一区二区| 成人无遮挡网站| 蜜桃在线观看..| 国产成人91sexporn| 人妻系列 视频| 肉色欧美久久久久久久蜜桃| 视频中文字幕在线观看| 少妇精品久久久久久久| 国产 一区精品| 成年人午夜在线观看视频| 黄色一级大片看看| √禁漫天堂资源中文www| 亚洲av在线观看美女高潮| 亚洲精品日韩在线中文字幕| 国语对白做爰xxxⅹ性视频网站| 久久久久久久久久成人| 日韩大片免费观看网站| 欧美成人精品欧美一级黄| 亚洲精品久久久久久婷婷小说| 丰满饥渴人妻一区二区三| 亚洲精品,欧美精品| 91精品国产九色| 久久精品国产自在天天线| 中文字幕免费在线视频6| 日本vs欧美在线观看视频 | 三级国产精品欧美在线观看| 国产成人免费无遮挡视频| 伦精品一区二区三区| 国产成人精品婷婷| 在线观看人妻少妇| 欧美日韩精品成人综合77777| 最近2019中文字幕mv第一页| 男女免费视频国产| 插阴视频在线观看视频| 三级经典国产精品| 欧美国产精品一级二级三级 | 久久精品国产自在天天线| 国产精品一区www在线观看| 大陆偷拍与自拍| 日日爽夜夜爽网站| 成年女人在线观看亚洲视频| 久久久久精品久久久久真实原创| 日韩 亚洲 欧美在线| 日本黄色日本黄色录像| 精品一区在线观看国产| 亚洲国产精品国产精品| 桃花免费在线播放| 麻豆乱淫一区二区| 一级,二级,三级黄色视频| 在现免费观看毛片| av天堂中文字幕网| 欧美性感艳星| 成人午夜精彩视频在线观看| 色婷婷av一区二区三区视频| 男人狂女人下面高潮的视频| 这个男人来自地球电影免费观看 | 国产成人aa在线观看| 国产精品偷伦视频观看了| 久热久热在线精品观看| 最近最新中文字幕免费大全7| 一级毛片aaaaaa免费看小| 99九九线精品视频在线观看视频| 看十八女毛片水多多多| 女性被躁到高潮视频| 国产免费福利视频在线观看| 99久久精品国产国产毛片| 人体艺术视频欧美日本| 日本av手机在线免费观看| 久久毛片免费看一区二区三区| 中国三级夫妇交换| 熟妇人妻不卡中文字幕| 国产一区二区三区av在线| 99热全是精品| a级毛片在线看网站| 国产亚洲精品久久久com| 国产精品一区二区在线观看99| 久久99热这里只频精品6学生| 99国产精品免费福利视频| 亚洲国产精品一区三区| 日韩在线高清观看一区二区三区| 国产成人91sexporn| 女的被弄到高潮叫床怎么办| 久久久久久久久久久久大奶| 国产淫片久久久久久久久| 全区人妻精品视频| 久久热精品热| videossex国产| 人人妻人人澡人人爽人人夜夜| 日本爱情动作片www.在线观看| 欧美老熟妇乱子伦牲交| 丰满乱子伦码专区| 亚洲av成人精品一区久久| 亚洲av男天堂| 久久精品国产鲁丝片午夜精品| 日韩不卡一区二区三区视频在线| 男人狂女人下面高潮的视频| 少妇人妻一区二区三区视频| 丝袜在线中文字幕| 如日韩欧美国产精品一区二区三区 | 一级毛片aaaaaa免费看小| 欧美精品国产亚洲| 亚洲第一av免费看| 一本色道久久久久久精品综合| 中文在线观看免费www的网站| 99热网站在线观看| 观看免费一级毛片| 精品国产乱码久久久久久小说| 女的被弄到高潮叫床怎么办| 久久99蜜桃精品久久| 丰满饥渴人妻一区二区三| 国产黄频视频在线观看| 欧美xxxx性猛交bbbb| 国内少妇人妻偷人精品xxx网站| 女性被躁到高潮视频| 久久99一区二区三区| 亚洲国产色片| av网站免费在线观看视频| 久久精品夜色国产| 蜜臀久久99精品久久宅男| 国产精品一二三区在线看| 男女边摸边吃奶| 熟女人妻精品中文字幕| 国产永久视频网站| a 毛片基地| 久久热精品热| 99热6这里只有精品| 成年美女黄网站色视频大全免费 | 国产黄色视频一区二区在线观看| 日韩av在线免费看完整版不卡| 97精品久久久久久久久久精品| 欧美亚洲 丝袜 人妻 在线| 成人二区视频| 视频区图区小说| 嘟嘟电影网在线观看| 亚洲欧洲国产日韩| 91成人精品电影| xxx大片免费视频| 97在线人人人人妻| 国产欧美另类精品又又久久亚洲欧美| 免费人成在线观看视频色| 亚洲欧洲日产国产| 久久毛片免费看一区二区三区| a级毛片免费高清观看在线播放| 秋霞伦理黄片| 草草在线视频免费看| 中文字幕亚洲精品专区| 国产伦精品一区二区三区视频9| 久久久久久久大尺度免费视频| 欧美亚洲 丝袜 人妻 在线| 亚洲精品中文字幕在线视频 | 亚洲婷婷狠狠爱综合网| 国产永久视频网站| 久久精品国产a三级三级三级| 多毛熟女@视频| 伦理电影大哥的女人| 下体分泌物呈黄色| 亚洲美女黄色视频免费看| 国产高清三级在线| 亚洲精品国产色婷婷电影| 欧美日韩综合久久久久久| 亚洲精品第二区| 最新中文字幕久久久久| 两个人免费观看高清视频 | 天天躁夜夜躁狠狠久久av| 狠狠精品人妻久久久久久综合| 男女边吃奶边做爰视频| 老司机影院毛片| 国产精品一二三区在线看| 黑人高潮一二区| 日本黄色日本黄色录像| 熟女人妻精品中文字幕| 亚洲欧洲国产日韩| 另类亚洲欧美激情| 最近手机中文字幕大全| 69精品国产乱码久久久| 免费人成在线观看视频色| 91精品伊人久久大香线蕉| 亚洲精品久久久久久婷婷小说| tube8黄色片| 久久精品久久精品一区二区三区| 我的老师免费观看完整版| 亚洲精品中文字幕在线视频 | 99热这里只有精品一区| 欧美另类一区| 美女脱内裤让男人舔精品视频| 婷婷色av中文字幕| 精品久久久久久久久av| 国产精品一区二区在线观看99| 亚洲精品成人av观看孕妇| 十分钟在线观看高清视频www | 狂野欧美激情性xxxx在线观看| 九九在线视频观看精品| a级毛色黄片| 亚洲av福利一区| 国产伦精品一区二区三区四那| 亚洲国产最新在线播放| 免费人妻精品一区二区三区视频| 久久国产精品男人的天堂亚洲 | 免费大片18禁| 亚洲av日韩在线播放| 久久精品国产亚洲网站| 草草在线视频免费看| 日韩电影二区| 人人澡人人妻人| 亚洲成人av在线免费| 老司机亚洲免费影院| 亚洲精品久久久久久婷婷小说| 亚洲成人一二三区av| 久久精品国产自在天天线| 又黄又爽又刺激的免费视频.| 国产视频首页在线观看| 伦精品一区二区三区| 成人无遮挡网站| 日韩人妻高清精品专区| 99热全是精品| 日韩不卡一区二区三区视频在线| 欧美一级a爱片免费观看看|