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1.
In this study, methanol extracts (MEs) and essential oil (EO) of Angelica purpurascens (Avé-Lall.) Gill obtained from different parts (root, stem, leaf, and seed) were evaluated in terms of antioxidant activity, total phenolics, compositions of phenolic compound, and essential oil with the methods of 2,2-azino-bis(3ethylbenzo-thiazoline-6-sulfonic acid (ABTS•+), 2,2-diphenyl-1-picrylhydrazil (DPPH•) radical scavenging activities, and ferric reducing/antioxidant power (FRAP), the Folin–Ciocalteu, liquid chromatography−tandem mass spectrometry (LC−MS/MS), and gas chromatography-mass spectrometry (GC−MS), respectively. The root extract of A. purpurascens exhibited the highest ABTS•+, DPPH•, and FRAP activities (IC50: 0.05 ± 0.0001 mg/mL, IC50: 0.06 ± 0.002 mg/mL, 821.04 ± 15.96 µM TEAC (Trolox equivalent antioxidant capacity), respectively). Moreover, EO of A. purpurascens root displayed DPPH• scavenging activity (IC50: 2.95 ± 0.084 mg/mL). The root extract had the highest total phenolic content (438.75 ± 16.39 GAE (gallic acid equivalent), µg/mL)). Twenty compounds were identified by LC−MS/MS. The most abundant phenolics were ferulic acid (244.39 ± 15.64 μg/g extract), benzoic acid (138.18 ± 8.84 μg/g extract), oleuropein (78.04 ± 4.99 μg/g extract), and rutin (31.21 ± 2.00 μg/g extract) in seed, stem, root, and leaf extracts, respectively. According to the GC−MS analysis, the major components were determined as α-bisabolol (22.93%), cubebol (14.39%), α-pinene (11.63%), and α-limonene (9.41%) among 29 compounds. Consequently, the MEs and EO of A. purpurascens can be used as a natural antioxidant source.  相似文献   

2.
Halogen-bonded (XB) complexes between halide anions and a cyclopropenylium-based anionic XB donor were characterized in solution for the first time. Spontaneous formation of such complexes confirms that halogen bonding is sufficiently strong to overcome electrostatic repulsion between two anions. The formation constants of such “anti-electrostatic” associations are comparable to those formed by halides with neutral halogenated electrophiles. However, while the latter usually show charge-transfer absorption bands, the UV-Vis spectra of the anion–anion complexes examined herein are determined by the electronic excitations within the XB donor. The identification of XB anion–anion complexes substantially extends the range of the feasible XB systems, and it provides vital information for the discussion of the nature of this interaction.

Spontaneous formation of “anti-electrostatic” complexes in solution demonstrates that halogen bonding can be sufficiently strong to overcome anion–anion repulsion when the latter is attenuated by the polar medium.

Halogen bonding (XB) is an attractive interaction between a Lewis base (LB) and a halogenated compound, exhibiting an electrophilic region on the halogen atom.1 It is most commonly related to electrostatic interaction between an electron-rich species (XB acceptor) and an area of positive electrostatic potential (σ-holes) on the surface of the halogen substituent in the electrophilic molecule (XB donor).2 Provided that mutual polarization of the interacting species is taken into account, the σ-hole model explains geometric features and the variation of stabilities of XB associations, especially in the series of relatively weak complexes.3 Based on the definition of halogen bonding and its electrostatic interpretation, this interaction is expected to involve either cationic or neutral XB donors. Electrostatic interaction of anionic halogenated species with electron-rich XB acceptors, however, seems to be repulsive, especially if the latter are also anionic. Yet, computational analyses predicted that halogen bonding between ions of like charges, called “anti-electrostatic” halogen bonding (AEXB),4 can possibly be formed5–12 and the first examples of AEXB complexes formed by different anions, i.e. halide anions and the anionic iodinated bis(dicyanomethylene)cyclopropanide derivatives 1 (see Scheme 1) or the anionic tetraiodo-p-benzoquinone radical, were characterized recently in the solid state.13,14 The identification of such complexes substantially extends the range of feasible XB systems, and it provides vital information for the discussion of the nature of this interaction. Computational results, however, significantly depend on the used methods and applied media (gas phase vs. polar environment and solvation models) and the solid state arrangements of the XB species might be affected by crystal forces and/or counterions. Unambiguous confirmation of the stability of the halogen-bonded anion–anion complexes and verification of their thermodynamic characteristics thus requires experimental characterization of the spontaneous formation of such associations in solution. Still, while the solution-phase complexes formed by hydrogen bonding between two anionic species were reported previously,15–17 there is currently no example of “anti-electrostatic” XB in solution.Open in a separate windowScheme 1Structures of the XB donor 1 and its hydrogen-substituted analogue 2.To examine halogen bonding between two anions in solution, we turn to the interaction between halides and 1,2-bis(dicyanomethylene)-3-iodo-cyclopropanide 1 (Scheme 1).‡ Even though this compound features a cationic cyclopropenylium core, it is overall anionic, and calculations have demonstrated that its electrostatic potential is universally negative across its entire surface.13 The solution of 1 (with tris(dimethylamino)cyclopropenium (TDA) as counterion) in acetonitrile is characterized by an absorption band at 288 nm with ε = 2.3 × 104 M−1 cm−1 (Fig. 1). As LB, we first applied iodide anions taken as a salt with n-tetrabutylammonium counter-ion, Bu4NI. This salt does not show absorption bands above 290 nm, but its addition to a solution of 1 led to a rise of absorption in the 290–350 nm range (Fig. 1). Subtraction of the absorption of the individual components from that of their mixture produced a differential spectrum which shows a maximum at about 301 nm (insert in Fig. 1). At constant concentration of the XB donor (1) and constant ionic strength, the intensity of the absorption in the range of 280–300 nm (and hence differential absorbance, ΔAbs) rises with increasing iodide concentration (Fig. S1 in the ESI†). This suggests that the interaction of iodide with 1 results in the formation of the [1, I−]-complex which shows a higher absorptivity in this spectral range (eqn (1)):1 + X− ⇌ [1, X−]1Open in a separate windowFig. 1Spectra of acetonitrile solutions with constant concentration of 1 (0.60 mM) and various concentrations of Bu4NI (6.0, 13, 32, 49, 75, 115 and 250 mM, solid lines from the bottom to the top). The dashed lines show spectra of the individual solutions 1 (c = 0.60 mM, red line) and Bu4NI (c = 250 mM, blue line). The ionic strength was maintained using Bu4NPF6. Insert: Differential spectra of the solutions obtained by subtraction of the absorption of the individual components from the spectra of their corresponding mixtures.To clarify the mode of interaction between 1 and iodide in the complex, we also performed analogous measurements with the hydrogen-substituted compound 2 (see Scheme 1). The addition of iodide to a solution of 2 in acetonitrile did not increase the absorption in the 280–300 nm spectral range. Instead, some decrease of the absorption band intensity of 2 with the increase of concentration of I− anions was observed (Fig. S2 in the ESI†). Such changes are related to a blue shift of this band resulting from the hydrogen bonding between 2 and iodide (formation of hydrogen-bonded [2, I−] complex is corroborated by the observation of the small shift of the NMR signal of the proton of 2 to the higher ppm values in the presence of I− anions, see Fig. S3 in the ESI†).§ Furthermore, since H-compound 2 should be at least as suitable as XB donor 1 to form anion–π complexes with the halide, this finding (as well as solid-state and computational data) rules out that any increase in absorption in this region observed with the I-compound 1 may be due to this alternative interaction.Likewise, the addition of NBu4I to a solution of TDA cations taken as a salt with Cl− anions did not result in an increase in the relevant region. Hence, we could also rule out anion–π interactions with the TDA counter-ions as source of the observed changes, which is in line with previous reports on the electron-rich nature of TDA.18All these observations (supported by the computational analysis, vide infra) indicate that the [1, I−] complex (eqn (1)) is formed via halogen bonding of I− with iodine substituents in 1. The changes in the intensities of the differential absorption ΔAbs as a function of the iodide concentration (with constant concentration of XB donor (1) as well as constant ionic strength) are well-modelled by the 1 : 1 binding isotherm (Fig. S1 in the ESI†). The fit of the absorption data produced a formation constant of K = 15 M−1 for the [1, I−] complex (Table 1).|| The overlap with the absorption of the individual XB donor hindered the accurate evaluation of the position and intensity of the absorption band of the corresponding complex which is formed upon LB-addition to 1. As such, the values of Δλmax shown in Table 1 represent a wavelength of the largest difference in the absorptivity of the [1, I−] complex and individual anion 1, and Δε reflects the difference of their absorptivity at this point (see the ESI† for the details of calculations).Equilibrium constants and spectral characteristics of the complexes of 1 with halide anions X−
Complexa K [M−1]Δλmaxc [nm]10−3Δεd [M−1 cm−1]
1·I−15 ± 23029.0
1·I−b8 ± 23038.0
1·Br−17 ± 23023.7
1·Cl−40 ± 83023.0
Open in a separate windowaAll measurements performed in CH3CN at 22 °C, unless stated otherwise.bIn CH2Cl2.cWavelength of the maximum of the differential spectra.dDifferences in extinction coefficients of XB [1, I−] complex and individual 1 at Δλmax.Since earlier computational studies demonstrated substantial dependence of formation of the AEXB complexes on polarity of the medium,6–12 interaction between 1 and I− anions was also examined in dichloromethane. The spectral changes in this moderately-polar solvent were analogous to that in acetonitrile (Fig. S4 in the ESI†). * The values for the formation constants of the [1, I−] complex and Δε (obtained from the fitting of the ΔAbs vs. [I−] dependence) in CH2Cl2 are lower than those in acetonitrile (Table 1). This finding is in line with the computational studies,6–12 predicting stronger binding in more polar solvents.The addition of bromide or chloride salts to an acetonitrile solution of 1 caused changes in the UV-Vis range which were generally similar to that observed upon addition of iodide. The variations of the magnitude of the differential absorption intensities with the increase in the bromide or chloride concentrations are less pronounced than that observed upon addition of iodide (in agreement with the results of the DFT computations of the UV-Vis spectra of the complexes, vide infra). Yet, they could also be fitted using 1 : 1 binding isotherms (see Fig. S5 and S6 in the ESI†). The formation constants of the corresponding [1, Br−] and [1, Cl−] complexes resulted from the fitting of these dependencies are listed in Table 1. The values of K (which correspond to the free energy changes of complex formation in a range of −6 to −8 kJ mol−1) are comparable to those reported for complexes of neutral monodentate bromo- or iodosubstituted aliphatic or aromatic electrophiles with halides.19–22 Thus, despite the “anti-electrostatic” nature of XB complexes between two anions, the stabilities of such associations are similar to that observed with the most common neutral XB donors.In contrast to the similarity in thermodynamic characteristics, the UV-Vis spectral properties of the complexes of the anionic XB donor 1 with halides are substantially different from that reported for the analogous associations with the neutral XB donors. Specifically, a number of earlier studies revealed that intermolecular (XB or anion–π) complexes of halide anions are characterized by distinct absorption bands, which could be clearly segregated from the absorption of the interacting species.21–23 If the same neutral XB donor was used, the absorption bands of the corresponding complexes with chloride were blue shifted, and absorption bands of the complexes with iodide as LB were red shifted as compared to the bands of complexes with bromide. For example, XB complexes of CFBr3 with Cl−, Br− or I− show absorption band maxima at 247 nm, 269 nm and 312 nm, respectively (individual CFBr3 is characterized by an absorption band at 233 nm).21 Within a framework of the Mulliken charge-transfer theory of molecular complexes,24 such an order is related to a rise in the energy of the corresponding HOMO (and electron-donor strength) from Cl− to Br− and to I− anions. In the complexes with the same electron acceptor, this is accompanied by a decrease of the HOMO–LUMO gap, and thus, a red shift of the absorption band. The data in Table 1 shows, however, that the maxima of differential absorption spectra for these systems are observed at roughly the same wavelength. To clarify the reason for this observation, we carried out computational analysis of the associations between 1 and halide anions.The DFT optimization†† at M06-2X/def2-tzvpp level with acetonitrile as a medium (using PCM solvation model)25 produced thermodynamically stable XB complexes between 1 and I−, Br− or Cl− anions (they were similar to the complexes which were obtained earlier via M06-2X/def2-tzvp computations with SMD solvation model13). The calculated structure of the [1, I−] complex is shown in Fig. 2 and similar structures for the [1, Br−] and [1, Cl−] are shown in Fig. S7 in the ESI.†Open in a separate windowFig. 2Optimized geometries of the [1, I−] complex with (3, −1) bond critical points (yellow spheres) and the bond path (green line) from the QTAIM analysis. The blue–green disc indicates intermolecular attractive interactions resulting from the NCI treatments (s = 0.4 a.u. isosurfaces, color scale: −0.035 (blue) < ρ < 0.02 (red) a.u.).QTAIM analysis26 of these structures revealed the presence of the bond paths (shown as the green line) and (3, −1) bond critical points (BCPs) indicating bonding interaction between iodine substituent of 1 and halide anions. Characteristics of these BCPs (electron density of about 0.015 a.u., Laplacians of electron density of about 0.05 a.u. and energy density of about 0.0004 a.u., see Table S1 in the ESI†) are typical for the moderately strong supramolecular halogen bonds.27 The Non-Covalent Interaction (NCI) Indexes treatment28 produced characteristic green–blue discs at the critical points'' positions, confirming bonding interaction in all these complexes.Binding energies, ΔE, for the [1, X−] complexes are listed in Table 2. They are negative and their variations are consistent with the changes in experimental formation constants measured with three halide anions in Table 1. The ΔE value for [1, I−] calculated in dichloromethane is also negative. Its magnitude is lower than that in acetonitrile, in agreement with the smaller formation constant of [1, I−] in less polar dichloromethane.Calculated characteristics of the [1, X−] complexesa
ComplexΔE, kJ mol−1 λ max,c nm10−4ε,c M−1 cm−1Δλmax,d M−1 cm−110−3Δε,d M−1 cm−1
1·I−−14.22525.7025514
1·I−b−4.72536.07——
1·Br−−14.82525.022537.4
1·Cl−−16.22514.782495.3
Open in a separate windowaIn CH3CN, if not noted otherwise.bIn CH2Cl2.cExtinction coefficient for the lowest-energy absorption band of the complex.dPosition and extinction coefficient of the differential absorption (see Fig. 3).The TD DFT calculations of the individual XB donor 1 and its complexes with halides (which were carried at the same level as the optimizations) produced strong absorption bands in the UV range (Fig. 3). The calculated spectrum of the individual anion 1 (λmax = 252 nm and ε = 4.27 × 104 M−1 cm−1) is characterized by somewhat higher energy and intensity of the absorption band than the experimental one, but the differences of about 0.6 eV in energy and about 0.3 in log ε are common for the TD DFT calculations.Open in a separate windowFig. 3Calculated spectra of 1 and its complexes (as indicated). The dashed lines show differential absorption obtained by subtraction of absorption of 1 from the absorption of the corresponding complex.The TD DFT calculations of the XB complexes with all three anions produced absorption bands at essentially the same wavelength as that of the individual XB donor 1, but their intensities were higher (in contrast, the hydrogen-bonded complex of 2 with iodide showed absorption band with slightly lower intensity than that of individual 2). The differential spectra obtained by subtraction of the spectra of individual anion 1 from the spectra of the complexes are shown in Fig. 3, and their characteristics are listed in Table 2. Similarly to the experimental data in Table 1, the calculated values of Δλmax are very close in complexes with different halides, and values of Δε are increasing in the order 1·Cl− < 1·Br− < 1·I−.An analysis of the calculated spectra of the complexes revealed that the distinction in spectral characteristics of the XB complexes of anionic and neutral XB donors with halides are related to the differences in the molecular orbital energies of the interacting species. Specifically, the energy of the highest occupied molecular orbital (HOMO) of the anionic XB donor 1 is higher than the energies of the HOMOs of I−, Br− and Cl−, and the energy of the lowest unoccupied molecular orbital (LUMO) of 1 is lower than those of the halides (Table S2 in the ESI†). As such, the lowest-energy electron excitations (with the substantial oscillator strength) in the AEXB complexes involve molecular orbitals localized mostly on the XB donor (see Fig. S8 in the ESI†). Accordingly, the energy of the absorption bands is essentially independent on the halide. Still, due to the molecular orbital interactions between the halides and 1, the small segments of the HOMOs of the complexes are localized on the halides, which affected the intensity of the transitions.‡‡ In contrast, in the XB complexes with the neutral halogenated electrophiles, the energies of the HOMOs and LUMOs of the halides are higher than the energies of the corresponding orbitals of the XB donors. As such, the HOMO of such complexes (as well as the other common molecular complexes) is localized mostly on the XB acceptors (electron donor), and the LUMO on the XB donor (electron acceptor). Accordingly, their lowest energy absorption bands represent in essence charge-transfer transition, and its energy vary with the energies of the HOMO of halides (the TD DFT calculations suggest that similar charge-transfer transitions in complexes of halides with 1 occur at higher energies, and they are overshadowed by the absorption of components).In summary, combined experimental (UV-Vis spectral) and computational studies of the interaction between halides and 1 demonstrated spontaneous formation of the anion–anion XB complexes in moderately-polar and polar solvents (which attenuate the electrostatic anion–anion repulsion and facilitate close approach of the interacting species§§). To the best of our knowledge, this constitutes the first experimental observation of AEXBs in solution. Stabilities of such “anti-electrostatic” associations are comparable to that formed by halide anions with the common neutral bromo- and iodo-substituted aliphatic or aromatic XB donors. These findings confirm that halogen bonding between our anionic XB donor 1 and halides is sufficiently strong to overcome electrostatic repulsion between two anions. It also supports earlier conclusions29 that besides electrostatics, molecular-orbital (weakly-covalent interaction) play an important role in the formation of XB complexes. Since the HOMO of 1 is higher in energy than those of the halides, the lowest-energy absorption bands in the anion–anion complexes is related mostly to the transition between the XB-donor localized MOs (in contrast to the charge transfer transition in the analogous complexes with neutral XB donors). Therefore, the energies of these transitions are similar in all complexes and the interaction with halides only slightly increase their intensities.  相似文献   

3.
We developed a method for determination of imidacloprid and its metabolites 5-hydroxy imidacloprid, olefin imidacloprid, imidacloprid urea and 6-chloronicotinic acid in Procambarus clarkii (crayfish) tissues using quick, easy, cheap, effective, rugged, and safe (QuEChERS) and high-performance liquid chromatography-triple quadrupole mass spectrometry. Samples (plasma, cephalothorax, hepatopancrea, gill, intestine, and muscle) were extracted with acetonitrile containing 0.1% acetic acid and cleaned up using a neutral alumina column containing a primary secondary amine. The prepared samples were separated using reverse phase chromatography and scanned in the positive and negative ion multiple reaction-monitoring modes. Under the optimum experimental conditions, spiked recoveries for these compounds in P. clarkii samples ranged from 80.6 to 112.7% with relative standard deviations of 4.2 to 12.6%. The limits of detection were 0.02–0.5 μg·L−1, the limits of quantification were 0.05–2.0 μg·L−1 and the method of quantification was 0.05–2.0 μg·kg−1. The method is rapid, simple, sensitive and suitable for rapid determination and analysis of imidacloprid and its metabolites in P. clarkii tissues.  相似文献   

4.
The objective of this study is to develop a comprehensive and simple method for the simultaneous determination of anthelmintic and antiprotozoal drug residues in fish. For sample preparation, we used the “quick, easy, cheap, effective, rugged, and safe” (QuEChERS) method with a simple modification. The sample was extracted with water and 1% formic acid in acetonitrile/methanol (MeCN/MeOH) (95:5, v/v), followed by phase separation (salting out) with MgSO4 and NaCl (4:1, w/w). After centrifugation, an aliquot of the extract was purified by dispersive solid-phase extraction (d-SPE) prior to liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. The method was validated at three concentration levels for all matrices, in accordance with the Codex guidelines (CAC/GL-71). Quantitative analysis was performed using the method of matrix-matched calibration. The recoveries were between 60.6% and 119.9%, with coefficients of variation (CV) <30% for all matrices. The limit of quantitation (LOQ) of the method ranged from 0.02 μg kg−1 to 4.8 μg kg−1 for all matrices. This comprehensive method can be used for the investigation of both anthelmintic and antiprotozoal drugs belonging to different chemical families in fishery products.  相似文献   

5.
Propolis is a resinous natural product collected by honeybees (Apis mellifera and others) from tree exudates that has been widely used in folk medicine. The present study was carried out to investigate the fatty acid composition, chemical constituents, antioxidant, and xanthine oxidase (XO) inhibitory activity of Jordanian propolis, collected from Al-Ghour, Jordan. The hexane extract of Jordanian propolis contained different fatty acids, which are reported for the first time by using GC-FID. The HPLC was carried out to identify important chemical constituents such as fatty acids, polyphenols and α-tocopherol. The antioxidant and xanthine oxidase inhibitory activities were also monitored. The major fatty acid identified were palmitic acid (44.6%), oleic acid (18:1∆9cis, 24.6%), arachidic acid (7.4%), stearic acid (5.4%), linoleic acid (18:2∆9–12cis, 3.1%), caprylic acid (2.9%), lignoceric acid (2.6%), cis-11,14-eicosaldienoic acid (20:2∆11–14cis, 2.4%), palmitoleic acid (1.5%), cis-11-eicosenoic acid (1.2%), α–linolenic acid (18:3∆9–12–15cis, 1.1%), cis-13,16-docosadienoic acid (22:2∆13–16cis, 1.0%), along with other fatty acids. The major chemical constituents identified using gradient HPLC-PDA analysis were pinocembrin (2.82%), chrysin (1.83%), luteolin-7-O-glucoside (1.23%), caffeic acid (1.12%), caffeic acid phenethyl ester (CAPE, 0.79%), apigenin (0.54%), galangin (0.46%), and luteolin (0.30%); while the minor constituents were hesperidin, quercetin, rutin, and vanillic acid. The percentage of α-tocopherol was 2.01 µg/g of the lipid fraction of propolis. Antioxidant properties of the extracts were determined via DPPH radical scavenging. The DPPH radical scavenging activities (IC50) of different extracts ranged from 6.13 to 60.5 µg/mL compared to ascorbic acid (1.21 µg/mL). The xanthine oxidase inhibition (IC50) ranged from 75.11 to 250.74 µg/mL compared to allopurinol (0.38 µg/mL). The results indicate that the various flavonoids, phenolic compounds, α-tocopherol, and other constituents which are present in propolis are responsible for the antioxidant and xanthine oxidation inhibition activity. To evaluate the safety studies of propolis, the pesticide residues were also monitored by LC-MS-MS 4500 Q-Trap. Trace amounts of pesticide residue (ng/mL) were detected in the samples, which are far below the permissible limit as per international guidelines.  相似文献   

6.
Cucurbita moschata Duchesne (Cucurbitaceae) is a plant food highly appreciated for the content of nutrients and bioactive compounds, including polyphenols and carotenoids, which contribute to its antioxidant and antimicrobial capacities. The purpose of this study was to identify phenolic acids and flavonoids of Cucurbita moschata Duchesne using high-performance liquid chromatography–diode array detection–electrospray ionization tandem mass spectrometry (HPLC–DAD–ESI-MS) at different ripening stages (young, mature, ripened) and determine its antioxidant and antimicrobial activities. According to the results, phenolic acids and flavonoids were dependent on the maturity stage. The mature fruits contain the highest total phenolic and flavonoids contents (97.4 mg GAE. 100 g−1 and 28.6 mg QE. 100 g−1).A total of 33 compounds were identified. Syringic acid was the most abundant compound (37%), followed by cinnamic acid (12%) and protocatechuic acid (11%). Polyphenol extract of the mature fruits showed the highest antioxidant activity when measured by DPPH (0.065 μmol TE/g) and ABTS (0.074 μmol TE/g) assays. In the antimicrobial assay, the second stage of ripening had the highest antibacterial activity. Staphylococcus aureus was the most sensitive strain with an inhibition zone of 12 mm and a MIC of 0.75 mg L−1. The lowest inhibition zone was obtained with Salmonella typhimurium (5 mm), and the MIC value was 10 mg L−1.  相似文献   

7.
The reaction between basic [(PCP)Pd(H)] (PCP = 2,6-(CH2P(t-C4H9)2)2C6H4) and acidic [LWH(CO)3] (L = Cp (1a), Tp (1b); Cp = η5-cyclopentadienyl, Tp = κ3-hydridotris(pyrazolyl)borate) leads to the formation of bimolecular complexes [LW(CO)2(μ-CO)⋯Pd(PCP)] (4a, 4b), which catalyze amine-borane (Me2NHBH3, tBuNH2BH3) dehydrogenation. The combination of variable-temperature (1H, 31P{1H}, 11B NMR and IR) spectroscopies and computational (ωB97XD/def2-TZVP) studies reveal the formation of an η1-borane complex [(PCP)Pd(Me2NHBH3)]+[LW(CO3)]− (5) in the first step, where a BH bond strongly binds palladium and an amine group is hydrogen-bonded to tungsten. The subsequent intracomplex proton transfer is the rate-determining step, followed by an almost barrierless hydride transfer. Bimetallic species 4 are easily regenerated through hydrogen evolution in the reaction between two hydrides.

Bimetallic complexes [LW(CO)2(μ-CO)⋯Pd(PCP)] cooperatively activate amine-boranes for their dehydrogenation via N–H proton tunneling at RDS and H2 evolution from two neutral hydrides.  相似文献   

8.
Vertical translocation/leaching of sulfamethoxazole (SMZ) through manure-amended sandy loam soil and significance of biochar application on SMZ retention were investigated in this study. Soil was filled in columns and amended with manure spiked with 13.75 mg kg−1 (S1), 27.5 mg kg−1 (S2), and 55 mg kg−1 (S3) of SMZ. Jujube (Ziziphus jujube L.) wood waste was transformed into biochar and mixed with S3 at 0.5% (S3-B1), 1.0% (S3-B2), and 2.0% (S3-B3) ratio. Cumulative SMZ leaching was lowest at pH 3.0, which increased by 16% and 34% at pH 5.0 and 7.0, respectively. A quicker release and translocation of SMZ from manure occurred during the initial 40 h, which gradually reduced over time. Intraparticle diffusion and Elovich kinetic models were the best fitted to leaching data. S3 exhibited the highest release and vertical translocation of SMZ, followed by S2, and S1; however, SMZ leaching was reduced by more than twofold in S3-B3. At pH 3.0, 2.0% biochar resulted in 99% reduction in SMZ leaching within 72 h, while 1.0% and 0.5% biochar applications reduced SMZ leaching to 99% within 120 and 144 h, respectively, in S3. The higher SMZ retention onto biochar could be due to electrostatic interactions, H-bonding, and π-π electron donor acceptor interactions.  相似文献   

9.
Due to the lack of phytochemical composition data, the major goals of the present study on Amphiroa rigida J.V. Lamouroux were to: (a) investigate and compare volatilome profiles of fresh and air-dried samples obtained by headspace solid-phase microextraction (HS-SPME) and hydrodistillation (HD) followed by gas chromatography and mass spectrometry (GC/MS) analysis; (b) determine fatty acids profile by gas chromatography with flame ionization detector (GC-FID); (c) obtain the pigment profiles of semipurified extracts by high performance liquid chromatography (HPLC) and (d) evaluate the antioxidant and antimicrobial activities of its less polar fractions. The comparison of headspace of fresh (FrAr) and air-dried (DrAr) samples revealed many similarities regarding the presence and abundance of the major (heptadecane and pentadecane) and minor compounds. The hydrodistillate (HD) of DrAr profile was quite different in comparison to HD-FrAr. The predominant compound in HD-FrAr was (E)-phytol. In HD-DrAr, its percentage was approximately one-half reduced, but the abundance of its degradation product phytone and of unsaturated and oxygenated compounds increased indicating more intense fatty acid decomposition and oxidation during drying. The fatty acid determination revealed that the most dominant was palmitic acid (42.86%) followed by eicosapentaenoic acid (19.14%) and stearic acid (11.65%). Among the pigments, A. rigida contained fucoxanthin (0.63 mg g−1 of dry fraction), lutein (5.83 mg g−1), β-carotene (6.18 mg g−1) and chlorophyll a (13.65 mg g−1). The analyzed less polar fractions of A. rigida exhibited antioxidant scavenging activity with diammonium salt of 2,2′-azino-bis (3-ethylbenzthiazolin-6-yl) sulfonic acid (ABTS) assay up to 3.87 mg g−1 trolox equivalents (TE), and with the oxygen radical absorbance capacity (ORAC) assay up to 825.63 μmol g−1 TE (with carotenoids as the major contributors).  相似文献   

10.
Parkinson’s disease (PD) is characterized by the progressive degeneration of dopaminergic neurons. The cause of PD is still unclear. Oxidative stress and mitochondrial dysfunction have been linked to the development of PD. Luteolin, a non-toxic flavonoid, has become interested in an alternative medicine, according to its effects on anti-oxidative stress and anti-apoptosis, although the underlying mechanism of luteolin on PD has not been fully elucidated. This study aims to investigate whether luteolin prevents neurotoxicity induction by 1-methyl-4-phenylpyridinium iodide (MPP+), a neurotoxin in neuroblastoma SH-SY5Y cells. The results reveal that luteolin significantly improved cell viability and reduced apoptosis in MPP+-treated cells. Increasing lipid peroxidation and superoxide anion (O2−), including mitochondrial membrane potential (Δψm) disruption, is ameliorated by luteolin treatment. In addition, luteolin attenuated MPP+-induced neurite damage via GAP43 and synapsin-1. Furthermore, Cdk5 is found to be overactivated and correlated with elevation of cleaved caspase-3 activity in MPP+-exposed cells, while phosphorylation of Erk1/2, Drp1, Fak, Akt and GSK3β are inhibited. In contrast, luteolin attenuated Cdk5 overactivation and supported phosphorylated level of Erk1/2, Drp1, Fak, Akt and GSK3β with reducing in cleaved caspase-3 activity. Results indicate that luteolin exerts neuroprotective effects via Cdk5-mediated Erk1/2/Drp1 and Fak/Akt/GSK3β pathways, possibly representing a potential preventive agent for neuronal disorder.  相似文献   

11.
A quick, sensitive, and reproducible analytical method for the determination of 77 multiclass pesticides and their metabolites in Capsicum and tomato by gas and liquid chromatography tandem mass spectrometry was standardized and validated. The limit of detection of 0.19 to 10.91 and limit of quantification of 0.63 to 36.34 µg·kg−1 for Capsicum and 0.10 to 9.55 µg·kg−1 (LOD) and 0.35 to 33.43 µg·kg−1 (LOQ) for tomato. The method involves extraction of sample with acetonitrile, purification by dispersive solid phase extraction using primary secondary amine and graphitized carbon black. The recoveries of all pesticides were in the range of 75 to 110% with a relative standard deviation of less than 20%. Similarly, the method precision was evaluated interms of repeatability (RSDr) and reproducibility (RSDwR) by spiking of mixed pesticides standards at 100 µg·kg−1 recorded anRSD of less than 20%. The matrix effect was acceptable and no significant variation was observed in both the matrices except for few pesticides. The estimated measurement uncertainty found acceptable for all the pesticides. This method found suitable for analysis of vegetable samples drawn from market and farm gates.  相似文献   

12.
There are a significant number of analytical methodologies employing different techniques to determine phenolic compounds in beverages. However, these methods employ long sample preparation processes and great time consumption. The aim of this paper was the development of a simple method for evaluating the phenolic compounds’ presence in Brazilian craft beers without a previous extraction step. Catechin, caffeic acid, epicatechin, p-coumaric acid, hydrated rutin, trans-ferulic acid, quercetin, kaempferol, and formononetin were analyzed in fifteen different craft beers. The method showed good linearity (R2 ≥ 0.9966). The limit of detection ranged from 0.08 to 0.83 mg L−1, and limits of quantification were between 0.27 and 2.78 mg L−1. The method showed a satisfactory precision (RSD ≤ 16.2%). A good accuracy was obtained by the proposed method for all phenolic compounds in craft beer (68.6% ˂ accuracy ˂ 112%). Catechin showed higher concentrations (up to 124.8 mg L−1) in the samples, followed by epicatechin (up to 51.1 mg L−1) and caffeic acid (up to 8.13 mg L−1). Rutin and formononetin were observed in all analyzed samples (0.52 mg L−1 to 2.40 mg L−1), and kaempferol was less present in the samples. The presence of plant origin products was determinant for the occurrence of the highest concentrations of phenolic compounds in Brazilian craft beers.  相似文献   

13.
The current study investigates the capacity of a lipolytic Lactobacillus paracasei postbiotic as a possible regulator for lipid metabolism by targeting metabolic syndrome as a possibly safer anti-obesity and Anti-dyslipidemia agent replacing atorvastatin (ATOR) and other drugs with proven or suspected health hazards. The high DPPH (1,1-diphenyl-2-picrylhydrazyl) and ABTS [2,2′-azino-bis (3-ethyl benzothiazoline-6-sulphonic acid)] scavenging activity and high activities of antioxidant enzyme such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-px) of the Lactobacillus paracasei postbiotic (cell-free extract), coupled with considerable lipolytic activity, may support its action against metabolic syndrome. Lactobacillus paracasei isolate was obtained from an Egyptian cheese sample, identified and used for preparing the postbiotic. The postbiotic was characterized and administered to high-fat diet (HFD) albino rats (100 and 200 mg kg−1) for nine weeks, as compared to atorvastatin (ATOR; 10 mg kg−1). The postbiotic could correct the disruption in lipid metabolism and antioxidant enzymes in HFD rats more effectively than ATOR. The two levels of the postbiotic (100 and 200 mg kg−1) reduced total serum lipids by 29% and 34% and serum triglyceride by 32–45% of the positive control level, compared to only 25% and 35% in ATOR’s case, respectively. Both ATOR and the postbiotic (200 mg kg−1) equally decreased total serum cholesterol by about 40% and 39%, while equally raising HDL levels by 28% and 30% of the positive control. The postbiotic counteracted HFD-induced body weight increases more effectively than ATOR without affecting liver and kidney functions or liver histopathology, at the optimal dose of each. The postbiotic is a safer substitute for ATOR in treating metabolic syndrome.  相似文献   

14.
Amazonian fruits are excellent sources of bioactive compounds and can be used in beverages to improve the nutritional and sensorial characteristics. The present study aimed to develop a blend of murici (Byrsonima Crassifolia (L.) Kunth) and taperebá (Spondias Mombin L.) through experimental design and investigating the nutritional and sensorial characteristics of fruits and beverages. The murici was highlighted as higher vitamin C content (58.88 mg · 100 g−1) compared to taperebá (25.93 mg · 100 g−1). The murici and taperebá are good sources of total phenolic compounds (taperebá 1304.15 ± 19.14 mgGAE · 100 g−1 and the murici of 307.52 ± 19.73 mg GAE · 100 g−1) and flavonoids (174.87 ± 1.76 μgQE/g and 129.46 ± 10.68 μgQE/g, murici and taperebá, respectively), when compared to other Brazilian fruits. The antioxidant capacity in different methods revealed that the taperebá had a higher average in the results, only in the ORAC method and did not present a significant difference (p > 0.05) in relation to the murici. The beverage development was performed using experimental design 23, showed through sensory analysis and surface response methodology that murici and high sugar content (between 12.5 and 14.2% of sugar) influenced in sensory acceptance. Our findings indicate that beverages with improved nutrition and a sensory acceptance can be prepared using taperebá and murici fruits.  相似文献   

15.
An ultra-high performance liquid chromatography tandem mass spectrometry method was developed and validated for the sensitive determination and unambiguous confirmation of residues of per and polyfluorinated alkyl substances (PFAS) in breastmilk, retail milk and infant formulas following two sample preparation methods. Sample pre-treatment was carried out by a simplified QuEChERS method without requiring dSPE or any further clean-up. The method was validated in accordance with the requirements of Commission Decision 657/2002/EC with slight modifications. The method displayed good linearity with R2 ranging from 0.9843–0.9998 for all target PFAS. The recovery and within-laboratory reproducibility of the method (n = 63) were in the range 60–121% and 5–28%, respectively. The decision limit, detection capability and limit of quantitation ranged from 30–60 ng kg−1 to 40–100 ng kg−1 and 5–50 ng kg−1, respectively. Acceptable matrix effect values in the range −45–29% were obtained with uncertainty of measurement lower than 25% for all target PFAS. The method displays its suitability for the sensitive and high-throughput confirmatory analysis of C4–C14 PFAS in breastmilk, dairy milk and infant formulas.  相似文献   

16.
α-glucosidase is a major enzyme that is involved in starch digestion and type 2 diabetes mellitus. In this study, the inhibition of hypericin by α-glucosidase and its mechanism were firstly investigated using enzyme kinetics analysis, real-time interaction analysis between hypericin and α-glucosidase by surface plasmon resonance (SPR), and molecular docking simulation. The results showed that hypericin was a high potential reversible and competitive α-glucosidase inhibitor, with a maximum half inhibitory concentration (IC50) of 4.66 ± 0.27 mg/L. The binding affinities of hypericin with α-glucosidase were assessed using an SPR detection system, which indicated that these were strong and fast, with balances dissociation constant (KD) values of 6.56 × 10−5 M and exhibited a slow dissociation reaction. Analysis by molecular docking further revealed that hydrophobic forces are generated by interactions between hypericin and amino acid residues Arg-315 and Tyr-316. In addition, hydrogen bonding occurred between hypericin and α-glucosidase amino acid residues Lys-156, Ser-157, Gly-160, Ser-240, His-280, Asp-242, and Asp-307. The structure and micro-environment of α-glucosidase enzymes were altered, which led to a decrease in α-glucosidase activity. This research identified that hypericin, an anthracene ketone compound, could be a novel α-glucosidase inhibitor and further applied to the development of potential anti-diabetic drugs.  相似文献   

17.
This study investigated the cancer chemopreventive effects of an acidic methanol extract of purple rice husk on chemically induced carcinogenesis in rats. This purple rice husk extract (PRHE) had high polyphenol contents. Vanillic acid was a major phenolic compound in PRHE. Three major anthocyanins found in PRHE were malvidin-3-glucoside, peonidin-3-glucoside and cyanidin-3-glucoside. PRHE was not toxic and clastogenic in rats. The LD50 of PRHE was greater than 2000 mg kg−1 body weight (BW). The oral administration of 300 or 1000 mg kg−1 BW of PRHE for 28 days significantly decreased the number of micronucleated hepatocytes in diethylnitrosamine-initiated rats. The inhibitory mechanisms were associated with the reduction of cytochrome P450 2E1 expression and induction of some detoxifying enzymes in the liver. In addition, treatment with 500 mg kg−1 BW of PRHE for eight weeks did not induce preneoplastic lesions in the liver and colon. It significantly inhibited hepatic glutathione-S-transferase positive foci formation induced by diethylnitrosamine and 1,2-dimethylhydrazine by suppression of hepatocyte proliferation and induction of apoptosis. In conclusion, PRHE did not present toxicity, clastogenicity or carcinogenicity in rats. It exhibited cancer chemopreventive properties against chemically induced early stages rat hepatocarcinogenesis. Anthocyanins and vanillic acid might be candidate anticarcinogenic compounds in purple rice husk.  相似文献   

18.
Co-crystallization of the prominent Fe(ii) spin-crossover (SCO) cation, [Fe(3-bpp)2]2+ (3-bpp = 2,6-bis(pyrazol-3-yl)pyridine), with a fractionally charged TCNQδ− radical anion has afforded a hybrid complex [Fe(3-bpp)2](TCNQ)3·5MeCN (1·5MeCN, where δ = −0.67). The partially desolvated material shows semiconducting behavior, with the room temperature conductivity σRT = 3.1 × 10−3 S cm−1, and weak modulation of conducting properties in the region of the spin transition. The complete desolvation, however, results in the loss of hysteretic behavior and a very gradual SCO that spans the temperature range of 200 K. A related complex with integer-charged TCNQ− anions, [Fe(3-bpp)2](TCNQ)2·3MeCN (2·3MeCN), readily loses the interstitial solvent to afford desolvated complex 2 that undergoes an abrupt and hysteretic spin transition centered at 106 K, with an 11 K thermal hysteresis. Complex 2 also exhibits a temperature-induced excited spin-state trapping (TIESST) effect, upon which a metastable high-spin state is trapped by flash-cooling from room temperature to 10 K. Heating above 85 K restores the ground-state low-spin configuration. An approach to improve the structural stability of such complexes is demonstrated by using a related ligand 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) to obtain [Fe(bzimpy)2](TCNQ)6·2Me2CO (4) and [Fe(bzimpy)2](TCNQ)5·5MeCN (5), both of which exist as LS complexes up to 400 K and exhibit semiconducting behavior, with σRT = 9.1 × 10−2 S cm−1 and 1.8 × 10−3 S cm−1, respectively.

Co-crystallization of the cationic complex [Fe(3-bpp)2]2+ with fractionally charged TCNQδ− anions (0 < δ < 1) affords semiconducting spin-crossover (SCO) materials. The abruptness of SCO is strongly dependent on the interstitial solvent content.  相似文献   

19.
The thermodynamic, kinetic, and structural properties of Ln3+ complexes with the bifunctional DO3A-ACE4− ligand and its amide derivative DO3A-BACE4− (modelling the case where DO3A-ACE4− ligand binds to vector molecules) have been studied in order to confirm the usefulness of the corresponding Gd3+ complexes as relaxation labels of targeted MRI contrast agents. The stability constants of the Mg2+ and Ca2+ complexes of DO3A-ACE4− and DO3A-BACE4− complexes are lower than for DOTA4− and DO3A3−, while the Zn2+ and Cu2+ complexes have similar and higher stability than for DOTA4− and DO3A3− complexes. The stability constants of the Ln(DO3A-BACE)− complexes increase from Ce3+ to Gd3+ but remain practically constant for the late Ln3+ ions (represented by Yb3+). The stability constants of the Ln(DO3A-ACE)4− and Ln(DO3A-BACE)4− complexes are several orders of magnitude lower than those of the corresponding DOTA4− and DO3A3− complexes. The formation rate of Eu(DO3A-ACE)− is one order of magnitude slower than for Eu(DOTA)−, due to the presence of the protonated amine group, which destabilizes the protonated intermediate complex. This protonated group causes the Ln(DO3A-ACE)− complexes to dissociate several orders of magnitude faster than Ln(DOTA)− and its absence in the Ln(DO3A-BACE)− complexes results in inertness similar to Ln(DOTA)− (as judged by the rate constants of acid assisted dissociation). The 1H NMR spectra of the diamagnetic Y(DO3A-ACE)− and Y(DO3A-BACE)− reflect the slow dynamics at low temperatures of the intramolecular isomerization process between the SA pair of enantiomers, R-Λ(λλλλ) and S-Δ(δδδδ). The conformation of the Cα-substituted pendant arm is different in the two complexes, where the bulky substituent is further away from the macrocyclic ring in Y(DO3A-BACE)− than the amino group in Y(DO3A-ACE)− to minimize steric hindrance. The temperature dependence of the spectra reflects slower ring motions than pendant arms rearrangements in both complexes. Although losing some thermodynamic stability relative to Gd(DOTA)−, Gd(DO3A-BACE)− is still quite inert, indicating the usefulness of the bifunctional DO3A-ACE4− in the design of GBCAs and Ln3+-based tags for protein structural NMR analysis.  相似文献   

20.
The chemical composition of three Citrus limon oils: lemon essential oil (LEO), lemon terpenes (LT) and lemon essence (LE), and their influence in the virulence factors production and motility (swarming and swimming) of two Pseudomonas aeruginosa strains (ATCC 27853 and a multidrug-resistant HT5) were investigated. The main compound, limonene, was also tested in biological assays. Eighty-four compounds, accounting for a relative peak area of 99.23%, 98.58% and 99.64%, were identified by GC/MS. Limonene (59–60%), γ-terpinene (10–11%) and β-pinene (7–15%) were the main compounds. All lemon oils inhibited specific biofilm production and bacterial metabolic activities into biofilm in a dose-dependent manner (20–65%, in the range of 0.1–4 mg mL−1) of both strains. Besides, all samples inhibited about 50% of the elastase activity at 0.1 mg mL−1. Pyocyanin biosynthesis decreases until 64% (0.1–4 mg mL−1) for both strains. Swarming motility of P. aeruginosa ATCC 27853 was completely inhibited by 2 mg mL−1 of lemon oils. Furthermore, a decrease (29–55%, 0.1–4 mg mL−1) in the synthesis of Quorum sensing (QS) signals was observed. The oils showed higher biological activities than limonene. Hence, their ability to control the biofilm of P. aeruginosa and reduce the production of virulence factors regulated by QS makes lemon oils good candidates to be applied as preservatives in the food processing industry.  相似文献   

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