Biography:

One of their most recent publications is Inhibitory effects of plant polyphenols on rat liver glutathione S-transferases. Which was published in journal Biochemical Pharmacology.

More information about Kai Zhang research including statistics on their citations can be found on their Copernicus Academic profile page.

Kai Zhang's Articles: (77)

Inhibitory effects of plant polyphenols on rat liver glutathione S-transferases

AbstractSeveral novel naturally occurring flavonoids and other polyphenols exerted varying degrees of concentration-dependent inhibition on uncharacterized rat liver glutathione S-transferase (EC 2.5.1.18, GST) isoforms. The order of inhibitory potencies of the five most potent polyphenols was tannic acid > 2-hydroxyl chalcone > butein > morin > quercetin, and their IC50 values were 1.044, 6.758, 9.033, 13.710 and 18.732 μM, respectively. Their inhibitions were reversible, as indicated by dialysis experiments. The optimum pH for the inhibitions by four of the compounds (tannic acid, butein, 2-hydroxyl chalcone and morin) was in the range of pH 6.0 to 6.5, but for quercetin the optimum pH was 8.0. These potent inhibitors possess one or more of the following chemical structural features: (a) polyhydroxylation substitutions, (b) absence of a sugar moiety, (c) for the chalcones, the presence of an open C-ring and hydroxylation at either the C-2 or C-3 position, (d) for the flavonoids, the attachment of the B-ring to C-2, and (e) a double bond between C-2 and C-3. Butein exhibited a non-competitive inhibition toward both glutathione (GSH) and 1-chloro-2,4-dinitrobenzene (CDNB). Interestingly, tannic acid showed a non-competitive inhibition toward CDNB but a competitive inhibition toward GSH. The inhibitory potency of tannic acid on rat liver GSTs was concentration and substrate dependent. Using CDNB, p-nitrobenzyl chloride, 4-nitropyridine-N-oxide, and ethacrynic acid as substrates, the IC50 values for tannic acid were 1.044, 11.151, 20.206, and 57.664 μM, respectively.

Inhibitory effects of plant polyphenols on rat liver glutathione S-transferases

AbstractSeveral novel naturally occurring flavonoids and other polyphenols exerted varying degrees of concentration-dependent inhibition on uncharacterized rat liver glutathione S-transferase (EC 2.5.1.18, GST) isoforms. The order of inhibitory potencies of the five most potent polyphenols was tannic acid > 2-hydroxyl chalcone > butein > morin > quercetin, and their IC50 values were 1.044, 6.758, 9.033, 13.710 and 18.732 μM, respectively. Their inhibitions were reversible, as indicated by dialysis experiments. The optimum pH for the inhibitions by four of the compounds (tannic acid, butein, 2-hydroxyl chalcone and morin) was in the range of pH 6.0 to 6.5, but for quercetin the optimum pH was 8.0. These potent inhibitors possess one or more of the following chemical structural features: (a) polyhydroxylation substitutions, (b) absence of a sugar moiety, (c) for the chalcones, the presence of an open C-ring and hydroxylation at either the C-2 or C-3 position, (d) for the flavonoids, the attachment of the B-ring to C-2, and (e) a double bond between C-2 and C-3. Butein exhibited a non-competitive inhibition toward both glutathione (GSH) and 1-chloro-2,4-dinitrobenzene (CDNB). Interestingly, tannic acid showed a non-competitive inhibition toward CDNB but a competitive inhibition toward GSH. The inhibitory potency of tannic acid on rat liver GSTs was concentration and substrate dependent. Using CDNB, p-nitrobenzyl chloride, 4-nitropyridine-N-oxide, and ethacrynic acid as substrates, the IC50 values for tannic acid were 1.044, 11.151, 20.206, and 57.664 μM, respectively.

Entropy-driven reactions in living cells for assay let-7a microRNA

Highlights•An enzyme-free amplification strategy for microRNA assay is reported.•This strategy is employed to image miRNA in single cells by using entropy-driven reaction.•The method provides a high sensitivity with a detection limit of 0.27 pM of Let-7a.

Pricing American bond options using a penalty method☆

AbstractWe develop a novel numerical method to price American options on a discount bond under the Cox–Ingrosll–Ross (CIR) model which is governed by a partial differential complementarity problem. We first propose a penalty approach to this complementarity problem, resulting in a nonlinear partial differential equation (PDE). To numerically solve this nonlinear PDE, we develop a novel fitted finite volume method for the spatial discretization, coupled with a fully implicit time-stepping scheme. We show that this full discretization scheme is consistent, stable and monotone, and hence the convergence of the numerical solution to the viscosity solution of the continuous problem is guaranteed. To solve the discretized nonlinear system, we design an iterative method and prove that the method is convergent. Numerical results are presented to demonstrate the accuracy, efficiency and robustness of our methods.

Research paperInhibition of glutathione reductase by plant polyphenols

AbstractThe effects of forty-one plant polyphenols on the activity of glutathione reductase (GSH-RD) were studied. These polyphenols showed varying degrees of concentration-dependent inhibition on the enzyme, with ic50 values that varied from approximately 40 μM to 1 mM. 4′-Hydroxychalcone and tannic acid were among the more potent inhibitors, with ic50 values of 47.3 and 50.4 μM, respectively. Different classes of polyphenols varied in potency in the following order: chalcones > tannic acid > flavonoids > coumarins > catechins. Analysis of structure-activity relationships showed certain chemical structures to be important for the inhibition of GSH-RD: (a) C-5 and C-7 hydroxylations in the A-ring, a carbonyl group at C-4, and the B-ring attached to C-2 in flavonoids; (b) C-2′ and C-4′ hydroxylations in chalcones; and (c) C-6 and C-7 hydroxylations in coumarins. The inhibition of GSH-RD by tannic acid and quercetin was time dependent and irreversible, whereas that by 4′-hydroxychalcone and esculin was reversible but not time dependent. Enhanced inhibition of GSH-RD by the four polyphenols 4′-hydroxychalcone, quercetin, butein, and acacetin was observed in the presence of NADPH. Kinetic studies showed that both tannic acid and 4′-hydroxychalcone exhibited non-competitive inhibition on GSH-RD towards glutathione disulfide.

CFD simulation of flow pattern and jet penetration depth in gas-fluidized beds with single and double jets

AbstractA simple two-fluid model is validated by comparing single-jet fluidization experiments and numerical predictions. Subsequently, flow pattern and jet penetration depth are explored numerically in the bed with double jets under equal and unequal gas velocities. Glass balltoni with a density of 2550 kg/m3 and a diameter of 275 μm is employed as solid phase. The model used in this study considers the effect of the dispersed solid phase on both gas and particle momentum equations of the inviscid model A (Gidaspow, 1994). Numerical simulations are carried out in the platform of CFX 4.4, a commercial CFD code, together with user-defined FORTRAN subroutines. Both jet penetration depth and jet frequency predicted are in good quantitative agreement with measurements in an incipiently fluidized bed with a single jet. By combining solid volume fraction distribution and particle-phase velocity vector profile, three flow patterns (isolated, merged and transitional jets) are identified in the gas-fluidized bed with double jets, which depend more on the nozzle distance than the jet gas velocity. For the equal jet gas velocity, the jet penetration depth decreases with increasing nozzle distance in the merged-jet and transitional-jet regions, then reaches a minimum value in the transitional-jet region, and finally keeps steady in the isolated-jet region. For the unequal jet gas velocity, the merged jet penetration depth increases with increase in the velocity of one jet as the other jet gas velocity is fixed, whilst the jet penetration depths change a little in the transitional-jet region and remain a constant in the isolated-jet region.

Simulation of diblock copolymer melts by Dissipative Particle Dynamics

AbstractDissipative Particle Dynamics (DPD), a recently developed mesoscopic simulation technique, is used to model the morphology and dynamical behavior of short-chain diblock copolymer melts. The two blocks, A and B, of the copolymer chain are represented by particles of different DPD “phases”, and composition is varied by varying the number of beads in each block. As composition is varied from 0–50% A, the predicted morphology changes, progressively, from a disordered system to BCC spherical domains of A, and then to cylindrical domains and lamelae. These predicted phase structures are in agreement with experimental and theoretical results from the literature. Steady shear flow is simulated by means of Lees–Edwards boundary conditions to investigate the effect of shear flow on morphology, and to evaluate viscosity and normal stresses under shearing. The predicted effects of shear flow include flow-induced microstructural transitions, and enhanced rheological properties for systems having the BCC equilibrium microstructure.

What weather variables are important in predicting heat-related mortality? A new application of statistical learning methods

Highlights•Apparent temperature is a robust parameter for activating heat alerts.•Absolute humidity should be included in future heat-health studies.•Random forests can be used to guide the choice of weather variables in health studies.

Assessment of T2- and Q-statistics for detecting additive and multiplicative faults in multivariate statistical process monitoring

AbstractThe pioneering multivariate statistical process monitoring (MSPM) methods use the Q-statistic as an alternative for the T2-statistic to detect faults occurring in the residual subspace spanned by the process variables, since directly using T2 for this subspace can lead to numerical problems. Such use has also spread to current work in MSPM field. However, substantial improvement of computational resource has sufficiently mitigated the numerical problem, which, thus, leads to a need to assess their detectability when using in the same position. This paper seeks to solve this historical issue by examining the two statistics in light of the fault detection rate (FDR) index to assess their performance when detecting both additive and multiplicative faults. Theoretical and simulation results show that the two statistics have different impacts on computing the FDR. Furthermore, it is shown that, the T2-statistic performs, in terms of the FDR, better at detecting most additive and multiplicative faults. Finally, based on the achieved results, a remedy to the interpretation of traditional MSPM methods are given.

Dynamic output feedback sliding mode control for spacecraft hovering without velocity measurements

AbstractIn consideration of target angular velocity uncertainty and external disturbance, a modified dynamic output feedback sliding mode control (DOFSMC) method is proposed for spacecraft autonomous hovering system without velocity measurements. As a stepping-stone, an additional dynamic compensator is introduced into the design of sliding surface, then an augmented system is reconstructed with the system uncertainty and external disturbance. Based on the linear matrix inequality (LMI), a sufficient condition is given, which guarantees the disturbance attenuation performance of sliding mode dynamics. By introducing an auxiliary variable, a modified version of adaptive sliding mode control (ASMC) law is designed, and the finite-time stability of sliding variable is established by the Lyapunov stability theory. Compared with other results, the proposed method is less conservative and can decrease the generated control input force significantly. Finally, two simulation examples are performed to validate the effectiveness of the proposed method.

Research articleUsing the expected detection delay to assess the performance of different multivariate statistical process monitoring methods for multiplicative and drift faults

Highlights•Performance assessment of process monitoring approaches has been emphasized.•Extending the expected detection delay to multiplicative and drift fault cases is realized.•Common multivariate statistics-based process monitoring methods are grouped.•Numerical and Tennessee Eastman simulations are presented to show the theory.

Regular ArticleThermodynamics of aqueous amines: excess molar heat capacities, volumes, and expansibilities of {water +  methyldiethanolamine (MDEA)} and {water  +  2-amino-2-methyl-1-propanol (AMP)}

AbstractThe heat capacities of aqueous solutions of methyldiethanolamine (MDEA) and 2-amino-2-methyl-1-propanol (AMP) were measured in a heat-flux differential scanning calorimeter at temperatures 278.15K⩽T⩽ 368.15 K, to yield excess molar heat capacities Cp,mEover the whole mole fraction range. Densities of aqueous AMP were determined with a vibrating tube densimeter over the temperature range 293.15 K⩽T⩽ 353.15 K, and used to derive excess molar volumesVmE and excess molar thermal expansibilitiesEmE =  (∂VmE / ∂T)p. A modified Redlich–Kister treatment was employed to describe the excess functions. The standard partial molar propertiesCp,2o and V2oatT =  298.15 K for MDEA, as determined by extrapolating the Redlich–Kister expressions to infinite dilution, are consistent with results from a Picker calorimeter and densimeter at mole fractionsx2 (MDEA) ⩽ 0.03. Values ofCp,2o and V2ofor AMP from measurements at low mole fractions { x2(AMP) ⩽ 0.03} differ from the Redlich–Kister extrapolations, suggesting that specific interactions take place in dilute solutions. The results are consistent with Lumry’s model (Faraday Symp. Chem. Soc. 1982, 17, 93–108), with MDEA being less hydrophobic than AMP. The mole-fraction dependence of the reduced excess heat capacities is most pronounced at T <  298.15 K, with clear differences in the behaviour of Cp,mE(water + MDEA) and Cp,mE(water + AMP), while the behaviour ofVmE for the two aqueous alkanolamines is similar.

Asymmetric electrochemical carboxylation of prochiral acetophenone: An efficient route to optically active atrolactic acid via selective fixation of carbon dioxide

AbstractA novel method of selective fixation of carbon dioxide was developed in this work. In an undivided cell the pharmaceutically active intermediate 2-hydroxy-2-phenylpropionic acid (atrolactic acid) has been produced from prochiral acetophenone in the presence of two kinds of chiral alkaloids, cinchonidine and cinchonine, acting as the inductors which were inclined to afford R and S products, respectively. Since the alkaloid has a strong tendency to adsorb to the surface of the cathode, three different cathode materials (stainless steel, platinum and copper) were applied in the process of asymmetric electrochemical carboxylation. Eventually, very distinct results were obtained. When the stainless steel was used as the cathode, a highest enantiomeric excess (ee) of 29.8% was achieved with an electrocarboxylation yield of 24.5%. Using cinchonidine and cinchonine as the inductors, the ee value of the aimed 2-hydroxy-2-phenylpropionic acid was also measured as a function of the concentration ratio of the alkaloid to the cocatalyst of butanol, supporting electrolyte, temperature, charge passed, current density and solvent. In particular, the butanol may play a critical role of helping to accomplish the asymmetric electrocarboxylation induction. From further analysis of cyclic voltammograms of acetophenone before and after addition of the alkaloid and butanol, a possible induction mechanism was put forward accordingly.

Convergence analysis of a monotonic penalty method for American option pricing

AbstractThis paper is devoted to study the convergence analysis of a monotonic penalty method for pricing American options. A monotonic penalty method is first proposed to solve the complementarity problem arising from the valuation of American options, which produces a nonlinear degenerated parabolic PDE with Black–Scholes operator. Based on the variational theory, the solvability and convergence properties of this penalty approach are established in a proper infinite dimensional space. Moreover, the convergence rate of the combination of two power penalty functions is obtained.

Symplectic analysis of dynamic properties of hexagonal honeycomb sandwich tubes with plateau borders

AbstractA new type of hexagonal honeycomb sandwich tube with plateau borders are introduced in this work and the Symplectic analysis with its high computational efficiency and high accuracy is applied to obtain the structural dynamic properties. The effects of material distribution (β) and relative density (ρ¯) on the dynamic properties of the structure are also studied. Based on the definition of the elastic constants and the homogenization method, the independent elastic constants are obtained. By introducing dual variables and applying the variational principle, the canonical equations of Hamiltonian system are constructed. The precise integration method and extended Wittrick–Williams algorithm are adopted to solve the canonical equations. The dispersion relations of sandwich tubes are obtained, and the effects of material distribution and relative density on the normalized frequencies of the sandwich tubes are investigated. The proposed homogenization method is verified by comparing with other researchers׳ works. Dispersion relations of the sandwich tubes are obtained. The material distribution parameter and the relative density have significant effects on the dynamic properties of the structures. This work expects to offer new opportunities for the optimal design of metallic honeycomb sandwich tubes and future applications in the engineering sector.

Pharmacology letter Accelerated communicationDecreased expression of the mRNA for somatostatin in the periventricular nucleus of depression-model rats

AbstractExpression of the mRNA for somatostatin (SRIF) in the periventricular nucleus (PeN), the level of SRIF in the stalk-median eminence (SME) and the concentration of growth hormone (GH) in the plasma were examined in depression-model rats in an attempt to confirm the hypothesis that SRIF neurons in the hypothalamus are hypofunctional in this model. We exposed male Wistar rats to intermittent walking stress for two weeks and then we measured their spontaneous running activity for 12 days. We divided the rats into a depression-model group and a partial-recovery group according to the spontaneous running activity of each rat after the termination of exposure to stress. Expression of SRIF mRNA in the PeN of the hypothalamus was monitored by in situ hybridization and relative levels were determined with an image analysis system. The relative level of expression of SRIF mRNA in the PeN was lower in rats in the depression-model group than in the control group and the partial-recovery group. The level of SRIF in the SME was lower and the plasma concentration of GH was higher in the depression-model group than in the other groups. Our findings suggest that reduced expression of mRNA for SRIF in the PeN might be associated with the pathophysiology of rats with this particular model of depression.

Numerical study of flow past a transversely oscillating wavy cylinder at Re=5000

Highlights•The forced vibration of a wavy cylinder is systematically studied.•The concealed Karman vortex shedding resurrect in the forced vibration, and may serve as the mechanism for VIV.•The response curves of the drag and lift coefficients, the vortex shedding patterns of the wavy cylinder resemble that of the normal cylinder.

Original research articlePhotodiode data collection and processing of molten pool of alumina parts produced through selective laser melting

AbstractThough SLM of ceramics is difficult, it is still attracting the attention of many researchers, because it is possible to fabricate high precision complex ceramics parts directly. As the molten pool behavior is the direct impact factor during SLM, monitoring and analysis of the molten pool behavior of ceramic will be beneficial to optimize SLM of ceramic. In this paper, an optimized molten pool data collection method called photodiode multi-detector divisional detection was designed to improve the precision of photodiode data during selective laser melting (SLM). Based on the system, the influence of laser power on the molten pool behavior of Al2O3 in single track was studied and relationships between molten pool data and several defects are analyzed. The experiment results shown that relative distances and incident angles between the molten pool and the photodiode had a great effect on the precision of photodiode data. The new data collection method can overcome this limitation to improve the precision of molten pool. Comparing the photodiode signal values at different laser powers (100 W, 180 W and 260 W), the higher of the laser power was, the bigger fluctuation range of the photodiode signal values was, the less stable of the molten pool became. The data cases shown that the delay of scanner, ‘edge effect’ and the unstable temperature field could be detected by comparing the photodiode data of the molten pool.

The anxiolytic effect of Juniperus virginiana L. essential oil and determination of its active constituents

Highlights•The anxiolytic effect of Juniperus virginiana L. essential oil is confirmed via intraperitoneal administration.•Cedrol is the one of main active constituents.•The mechanism relies on affecting the response to DAnergic activity by modulating the 5-HTnergic system.

Experimental and numerical study of fluid dynamic parameters in a jetting fluidized bed of a binary mixture

AbstractThe solid circulation pattern, the voidage profile, and the jet penetration height have been investigated experimentally and computationally in a cold-flow model of jetting fluidized beds (JFBs) of a binary mixture in this paper. This rectangular two-dimensional bed is 0.30 m wide and 2.05 m high with a central jet and a conical distributor, which roughly stands for the ash-agglomerating fluidized-bed coal gasifier. A video camera and coloured particle tracer method were employed to explore the fluid dynamics in the bed. In terms of the average physical properties of binary mixtures, a hydrodynamic model describing the gas–solid flow characteristics in a jetting bed is resolved by using a modified Semi-Implicit Method for Pressure-Linked Equation (SIMPLE) algorithm. This paper focuses on three features of the fluid dynamics—solid circulation pattern, voidage profile, and jet penetration height. The solid circulation pattern is composed of three regions: the jetting region, the bubble street, and the annular region. Above the central nozzle the time-averaged isoporosity contours are almost elliptic, while near the walls of the bed, the voidage in high solid concentration region is approximately equal to that at the minimum fluidization state. The jet penetration height increases with increasing jet gas velocity and with decreasing average particle diameter. The increase in weight percentage of the lighter component in the binary system reveals that reduction of average density causes the enlargement of jet penetration height. The simulated results show good agreement with the experimental data.

Back | Next (Page 1 of 4)
Advertisement
Join Copernicus Academic and get access to over 12 million papers authored by 7+ million academics.
Join for free!

Contact us