Hasil untuk "Physical and theoretical chemistry"

Rafael Corrêa Ramos, Lizandra G. Magalhães, Rodrigo C. S. Veneziani et al.

Neglected diseases significantly impact the world, and there is a lack of effective treatments, requiring therapeutic alternatives. Thus, the study of the phytochemical and schistosomicidal activity evaluation of <i>Copaifera oblongifolia</i> leaves’ crude extract was conducted. The quercitrin (<b>1</b>) and afzelin (<b>2</b>) were isolated from the crude extract. In the in vitro schistosomicidal activity test, the isolated compounds demonstrated promising results, with 75% mortality at a concentration of 12.5 µM after 72 h. Molecular docking calculations indicated that compounds <b>1</b> and <b>2</b> could potentially interact with the amino acids of the FAD binding site in the TGR enzyme, a crucial enzyme for the survival of <i>Schistosoma mansoni</i>. These interactions could have binding energies comparable to praziquantel, a preferred drug for treating schistosomiasis. Therefore, in silico and in vitro investigations are crucial for developing new studies that can reveal the antiparasitic potential of compounds of plant origin.

Lu Yu, Aokun Liu, Jian Kuang et al.

Bacterial small laccases (SLAC) are promising industrial biocatalysts due to their ability to oxidize a broad range of substrates with exceptional thermostability and tolerance for alkaline pH. Electron transfer between substrate, copper centers, and O2 is one of the key steps in the catalytic turnover of SLAC. However, limited research has been conducted on the electron transfer pathway of SLAC and SLAC-catalyzed reactions, hindering further engineering of SLAC to produce tunable biocatalysts for novel applications. Herein, the combinational use of electron paramagnetic resonance (EPR) and ultraviolet–visible (UV–vis) spectroscopic methods coupled with redox titration were employed to monitor the electron transfer processes and obtain further insights into the electron transfer pathway in SLAC. The reduction potentials for type 1 copper (T1Cu), type 2 copper (T2Cu) and type 3 copper (T3Cu) were determined to be 367 ± 2 mV, 378 ± 5 mV and 403 ± 2 mV, respectively. Moreover, the reduction potential of a selected substrate of SLAC, hydroquinone (HQ), was determined to be 288 mV using cyclic voltammetry (CV). In this way, an electron transfer pathway was identified based on the reduction potentials. Specifically, electrons are transferred from HQ to T1Cu, then to T2Cu and T3Cu, and finally to O2. Furthermore, superhyperfine splitting observed via EPR during redox titration indicated a modification in the covalency of T2Cu upon electron uptake, suggesting a conformational alteration in the protein environment surrounding the copper sites, which could potentially influence the reduction potential of the copper sites during catalytic processes. The results presented here not only provide a comprehensive method for analyzing the electron transfer pathway in metalloenzymes through reduction potential measurements, but also offer valuable insights for further engineering and directed evolution studies of SLAC in the aim for biotechnological and industrial applications.

V.M. Yurov, K.N. Zhangozin

A theoretical model is proposed that allows one to determine the thickness of the surface layer of liquid R(I). For water and ethanol it turned out to be 1,1 nm. As a result, ethanol is unlimitedly soluble in water. Methyl acetate, benzene and toluene (R(I) of above 1,4 nm) form azeotropic mixtures with water. Glycerol, nitrobenzene and mercury (R(I) greater than 3 nm) are practically insoluble in water. From the proposed model, we can conclude that the surface layer of the liquid is a nanostructure with size effects. It is of interest that the thickness of the surface layer of water coincides with the thickness of the surface layer of iron, cobalt and nickel. The work of adhesion and elastic constants for water and ethanol, including Young’s modulus, were also found. It was established that the elasticity of water is only 100 times less than the elasticity of steel, i.e. water can be considered as an incompressible substance, and the internal friction in water is three times greater than in ethanol. It is also shown that the universal element of the geometry of spaces of liquid systems is the tetrahedron, which corresponds to sp3 hybridization of interatomic or intermolecular bonds.

Ellyse Oktaviani, Natalita M. Nursam, Shobih et al.

A counter electrode is one of the crucial components in dye-sensitized solar cell (DSSC), where platinum, carbon composite, and poly(3,4-dioxythiophene)-poly(styrene sulfonate) or PEDOT:PSS are among the most widely used materials. In terms of configuration, DSSC is typically constructed in two ways: sandwich and monolithic. However, the DSSC performance associated with the selection of both counter electrodes and configuration has received little attention to date. This study aims to study the effect of counter electrode materials on DSSC performance by analyzing their electrical and electrochemical properties from their configuration standpoint. First, the physical properties of the counter electrodes materials were analyzed using scanning electron microscopy (SEM), followed by four-point probes, electrochemical impedance spectroscopy (EIS), incident photon-to-current conversion efficiency (IPCE), and current density-voltage (J-V) characterization. Among all variations, our results show that the sandwich-type DSSC with PEDOT: PSS counter electrode generated the best performance with a power conversion efficiency of 5.40%, which was primarily attributed to the high conductivity (3210 S/cm) and low charge transfer resistance (RCE 53 Ω). It was also found that the electron transfer pathways that are determined by the cell configuration also had a significant impact on the cell performance.

Bouderlique, Elise, Tang, Ellie, Perez, Joëlle et al.

Adenine phosphoribosyltransferase (APRT) deficiency is a genetic disease characterized by an increased production of 2,8 dihydroxyadenine (2,8-DHA) precipitating in urine, leading to a crystalline nephropathy and end-stage renal disease. Here, we describe the high prevalence of granuloma (88%) in biopsies from patients with APRT deficiency. A murine model of 2,8-DHA nephropathy was generated, showing that anakinra or dexamethasone, combined with allopurinol, improved renal function to a larger extent than allopurinol alone, the standard therapy. Inflammation plays a critical role in the development of 2,8-DHA nephropathy, and therapy based upon drugs targeting innate immunity could improve renal function recovery.

Jiabing Chen, Youluan Lu, Leshu Huang et al.

Electrode fouling and passivation are the main reasons for attenuated the electrochemistry signals. In this work, a renewable electrode for determination of 4-nitrophenol (4-NP) which not only has excellent detection signals but also can be photo-catalytically refreshed to remain the selectivity and sensitivity was been created. The GO/TiO2-CuTCPP composite material was characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FT-IR). The electrochemical behavior of 4-NP on GO/TiO2-CuTCPP/GCE was investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV) in 0.2 mol/L acetic acid buffer at pH 5.5. The result showed that the GO/TiO2-CuTCPP/GCE exhibits the higher peak current and photo-catalytic activity to prone the self-cleaning ability. Under the optimal conditions, the oxidation current peak values linearly with the concentration of 4-NP ranging from 0.5 to 100 μmol/L, and the detection limit was 0.16 μmol/L (S/N = 3). Moreover, the sensors showed excellent renewable ability under visible light without damaging the electrode microstructure and attenuating electrochemical signals.

HaoTian Shi, Shunli Wang, Carlos Fernandez et al.

This paper explores the state estimation method of lithium-ion battery pack through theoretical analysis and experimental research. Combining the advantages of the empirical models of various electrochemical models, a new type of composite electrochemistry-dual circuit polarization (E-DCP) model is proposed to better reflect the dynamic performance of the power lithium-ion battery under the conditions of meeting its safe and reliable energy supply requirements. Using the multi-innovation least squares (MILS) algorithm to identify the parameters in the E-DCP model online, so that it has the characteristics of high data utilization efficiency and high parameter identification accuracy. The battery charge and discharge efficiency function is introduced to dynamically modify the battery capacity, and the dynamic function is used to improve the Kalman gain in the extended Kalman filter (EKF), a new type of based on dynamic function improvement and combined with actual capacity correction (FC-DEKF) algorithm is applied to the estimation of battery pack operating characteristics, which solves the problem that the traditional EKF algorithm is difficult to estimate errors when the system input change rate is large. The experimental results of urban dynamometer driving schedule (UDDS) and complex charge-discharge cycle test show that the maximum error of terminal voltage does not exceed 0.04V, the accuracy is 99.05%, and the errors of MILS algorithm combined with FC-DEKF algorithm for SOC estimation are all within 1%. The proposed equivalent circuit modeling method and state estimation correction strategy provide a theoretical basis for the reliable application of high-power lithium-ion battery packs.

Kh. Bazzal, N.A. Alekseenko, E.S. Voropay et al.

A study of the Al2O3 and AlN nanopowder formation under the influence of twin laser pulses with an energy of 52 mJ and between the pulse interval of 10 microseconds on an aluminum target placed in a closed glass rectangular box, depending on the number of pulses. It was found that the highest intensity of the bands of AlO suboxide and AlN molecules is observed at 40 - 50 consecutive double pulses in a series. The size of the primary particles estimated using the high-resolution electron microscopy was mainly 30 - 40 nm, the particles were collected in agglomerates. The possibility of obtaining active forms of aluminum oxides and products of their interaction with oxygen and air nitrogen in a laser plasma deposited on a glass surface is shown by RAMAN methods.

Jia Du, Xu Peng, Yuting Xu et al.

Odorant substances have been detected in the drinking water of several countries and regions. Although the specific harm of these substances to the human body is not yet clear, they can lead to the decline of drinking-water sensory indicators. In addition, odorants also affect the development of the waterdependent beverage industry and aquaculture industry. Dimethyl isoborneol (2-MIB) is the most common odorant substance that causes soil mildew in drinking water. In this work, for the first time, we first report the electrochemical determination of 2-MIB based on an Au electrode. The electrochemical oxidation of 2-MIB can be achieved due to the excellent conductivity and electrocatalytic property of the Au electrode. The proposed electrochemical sensing method is simple, quick and reliable for 2-MIB determination.

G. Gallegos Ortega, V.E. Reyes Cruz, G. Urbano Reyes et al.

This work studied the surface characterisation and the electrochemical evaluation of titanium (Ti) and anodised titanium (A-Ti) electrodes modified with a bacterial biofilm of a novel consortium composed of Enterobacter cloacae complex, Enterococcus gallinarum, Escherichia coli, Klebsiella pneumoniae, and Enterococcus faecium - the biological support media consisted of peptone casein nutrient broth (PCNB), and acid whey (AW) - with the purpose of evaluating the electrochemical response of non- carbonaceous materials with low interferences. This is useful for bio-electrodes, mainly biocathodes intended to operate in bioelectrochemical systems of substrates at neutral pH and acid pH. For this, scanning electron microscopy (SEM) and electrochemical techniques of chronopotentiometry and voltammetry were used, following the biofilm growth after the inoculation of the bacterial consortium on the Ti and A-Ti materials, at times of 24 h and 168 h. The results showed that it was possible to obtain biofilms of bacteria with a high efficiency in a period of 24 hours, noting that the A-Ti material favours the biofilm growth in terms of quantity, chemical stability and a biocathodic response. The biofilms demonstrated specific behaviours depending on the inoculation time and the biological support medium, with evidence of bacterial bodies coated by extracellular polymeric substances (EPS) in the AW media. These results allow the possibility of using Ti and A-Ti materials in bioelectrochemical systems whose purpose is to treat whey solutions with an acidic pH.

Leonardo Salgado, Carolina Blas Pozos, Teresa Zayas et al.

SnO2-Sb electrodes on a Ti substrate, prepared without (Ti/SnO2-Sb) or with a Pt interlayer (Ti/Pt/SnO2-Sb), were prepared using the polymeric precursor method followed by thermal decomposition. The platinum film on titanium (Ti/Pt) was prepared by thermal decomposition of an alcoholic solution of Pt. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and elemental mapping were used to characterize the surfaces of Ti/Pt, Ti/SnO2-Sb, and Ti/Pt/SnO2-Sb. The electrochemical characterization of the electrodes was performed using cyclic voltammetry in a 0.5 M H2SO4 solution. The electroactive area of the electrodes was determined using measurements of the electrosorption hydrogen charge for Ti/Pt and the capacitance of the electric double layer for Ti/SnO2-Sb and Ti/Pt/SnO2-Sb. Tafel slopes for the oxygen evolution reaction (OER) were estimated from polarization curves. The SEM and EDS results obtained from the electrodes prepared with or without a platinum interlayer displayed distinct behaviors. In the absence of Pt, the SnO2-Sb coating on titanium formed a compact layer with a good distribution of Sn, Sb, O, and a low Ti content. In the presence of the Pt coating, SnO2-Sb was heterogeneously distributed. The heterogeneous character of the Ti/Pt/SnO2-Sb film resulted from surface segregation during the calcination process. The voltammetric behaviors of the SnO2-Sb electrodes prepared with or without a Pt interlayer displayed similar trends, although the presence of Pt produced a greater electroactive area and shifted the oxygen evolution potential toward less positive values; therefore, the electrocatalytic activity toward the OER was higher compared to the Ti/SnO2-Sb electrode. The Tafel slope estimated for Ti/Pt/SnO2-Sb is consistent with a mechanism in which OH- generation is the rate controlling step.

Fan Liu, Xu Chen, Yuekun Gu et al.

Magnesium alloys have been widely used in many fields owing to its light weight. However, their poor corrosion resistance has prevented their further applications. In this study, vacuum evaporation deposition coupled with the pretreatment of the AZ91D magnesium alloy substrates were employed to successfully prepare an aluminum coating on AZ91D magnesium alloy in an attempt to enhance its corrosion resistance. The surface morphology, corrosion resistance and adhesive strength of the coatings prepared from different pretreatments were systemically investigated. The effect of deposition time and annealing treatment on the surface morphology, corrosion resistance and adhesive strength was also examined. The results showed that the best corrosion resistance and highest adhesive strength of the aluminum coating were obtained for the specimen pretreated by H3PO4 etching. As the deposition time increases, a continuous and dense aluminum coating gradually forms on the surface of magnesium alloy following the typical island growth (Volmer-Weber) mode. The increase of deposition time enhances the corrosion resistance of magnesium alloy but has no effect on the adhesive strength between the coating and the substrate. With the increase of the annealing temperature, the coating of the sample becomes more uniform with better crystallinity of aluminum compared with unannealed sample.

Zhen Zhang, Qi-Hua Jiang, Yi-Long Liu et al.

1, 1”-((5-(3-(acetylthio)propoxy)-1, 3-phenylene)bis(methylene))bis((4, 4’-bipyridin)-1-ium) has been successfully synthesized by a straightforward reaction and its electrochemical properties of self-assembled monolayers (SAMs) on Au electrode are measured by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The barrier property of the SAMs-modified surface is evaluated by using potassium ferro/ferri cyanide. The results suggest that its SAMs can reduce the charge transfer resistance (Rct) and accelerate the electron transfer rate. CV results showed that SAMs-modified Au electrode rapidly recognized Ag+ and had excellent cycle stability. The structural and morphological information has also been obtained by field emission scanning electron microscope (FE-SEM), the Ag composition of SAMs was 15.53% which is much higher than other compounds we have ever got.

S. Atkins, R.Jimenez- Perez, J.M. Sevilla et al.

The electrochemical reduction of carbamazepine in ethanol and water using a glassy carbon electrode has been studied. In all experimental conditions of scan rate and concentration of carbamazepine an irreversible cathodic wave was observed by cyclic voltammetry (CV). Electrochemical parameters and a plausible EqC mechanism have been reported from the electrochemical measurements and digital simulation. The values of thermodynamic E1/2 were correlated with solvent polarity parameters that it can be interesting for biological, pharmaceutical and forensic purposes. Limits of Detection (LOD) for DPV are 1.1 and 9.0 μg/mL (4.65x10-6 and 3.81x10-5 M) in ethanol and water, respectively. The precision and recoveries obtained for tablets and plasma samples showed that the method could be successfully used for analysis.

H. Faghihian, F. Ghanbari Adivi

A new ion-imprinted polymer (IIP) was prepared by the copolymerization of vinylpyridine as the monomer, ethylene glycol dimethacrylate as the cross-linker and benzoyl peroxide as the initiator in the presence of a Cu(II)–salen complex. The synthesized polymers were characterized by FT-IR, TGA and XRD techniques. To study the adsorption behaviour of the adsorbent, the Cu(II) ion which acts as the template in the salen-functionalized polymer was eluted with 0.1 M HNO 3 . The effect of different experimental conditions on the adsorption capacity was studied. At Cu(II) ion concentrations of 30 ppm and at a pH value of 6.2, an adsorption capacity of 26 mg/g was obtained. Such an adsorption capacity at low Cu(II) ion concentrations is very significant and much higher than that obtained for Zn(II), Ni(II) and Co(II) ions. The relative selectivity coefficient of IIP for Cu(II)/Zn(II), Cu(II)/Ni(II) and Cu(II)/Co(II) was calculated, when it was demonstrated that the polymer is highly selective towards Cu(II) ions. The method was also used for a real sample. The results showed that the new adsorbent can be used for the pre-concentration of Cu(II) ions at low concentration and in the presence of Zn(II), Ni(II) and Co(II) ions.

Shuangkou Chen, Tapas Kar

The relationships between corrosion inhibition performance of four kinds of Schiff base inhibitors and their molecular electronic properties have been studied by quantum chemistry method at the level of DFT/B3LYP with the 6-31+G (d, p) base sets. The relationships between the corrosion inhibitor efficiency (IE) and the result of calculation are discussed using linear regression analysis to determine the most effective parameter on inhibition efficiency, and the regression equations find that the corrosion inhibition performances of these inhibitors have a good linear relationship to total charge of -CH=N- group. In the mean time, the study of the interaction between inhibitors and Al(100) surface shows there are some electrons transferred from inhibitors to the surface, so after adsorption the inhibitor cannot capture electronics from Al and lead corrosion, and it could play a protective effect on the metal surface. Finally, this research might provide a theoretical inhibition performance prediction approach for new homologous inhibitors.

Ljiljana Rajić, Božo Dalmacija, Svetlana Ugarčina Perović et al.

In this work we present the results of a laboratory study to assess the possibility of Fe/C and Fe/Cu galvanic cell utilization for Cu removal from a kaolin model matrix as an electrokinetic treatment without electricity consumption. In addition, we examine improving the desorption of Cu ions from kaolin particles by acidification. Several experiments were conducted: conventional (ECC), Fe/C galvanic cell (GC1), Fe/Cu galvanic cell (GC2), Fe/C galvanic cell with kaolin acidification (GC3) and Fe/Cu galvanic cell with kaolin acidification (GC4). The following removal efficacies were achieved: 44% for ECC, 20% for GC1, 37% for GC2, 46% for GC3 and 45% for GC4. The Fe/Cu galvanic cell resulted in better removal efficacy as metallic Cu was deposited at the cathode. Acidification of kaolin prior to treatment contributed to Cu2+ desorption and thus improved removal efficacy, especially during GC3. This work demonstrates that an Fe/Cu galvanic cell can be used for electrokinetic treatment of Cu contaminated soil with no waste produced after treatment as the Cu is deposited at the cathode.

Greta Radeva, Eva Valcheva, Stefka Veleva

Chemisorption processes taking place on uniformly inhomogeneous surfaces in the presence of entropic inhomogeneity are examined. A new form of linearity relationship connecting the current rate and the equilibrium constant at definite degrees of surface coverage is derived. The relationship can be applied to complex chemisorption processes when determination of the rate constant is impossible. Linear correlations between the activation energy and the adsorption enthalpy, as well as between the entropy characteristics and pre-exponential factors, are obtained. The complex effect of the energy and entropy factors on the kinetics and the equilibrium is discussed theoretically and verified experimentally. These factors operate through a thermodynamic and a kinetic compensation effect. The present paper illustrates the correlation methods employing experimental results derived from the study of the chemisorption of the optical brighteners Leucophor AP and Tinopal UP onto pulp, of Fe 3+ and Cu 2+ ions onto fibrous polyampholyte and of hydrolysis-modified polyacrylonitrile (HMP) onto pulp.

Z.Q. Fang, H.J. Huang

The adsorption of di-n-butyl phthalate (DBP) from aqueous solution was studied in a batch adsorption system. Activated carbons from coals, coconut shell and nutshell were evaluated to determine the most effective adsorbent. Kinetic and equilibrium studies were investigated at various initial DBP concentration (3–6 mg/ℓ), adsorbent dosage (40–140 mg/ℓ), suspension pH (3–9) and temperature (25–55 °C). Equilibrium adsorption isotherms were analyzed using the Langmuir, Freundlich and Temkin models. The experimental isotherms were S-type, with the Freundlich isotherm giving a good description of the data obtained at lower DBP concentration. The pseudo-first-order, pseudo-second-order and intra-particle diffusion models were used to fit the kinetic adsorption data. It was found that the adsorption of DBP followed pseudo-first-order kinetics, with the adsorption rate being controlled by both film and pore diffusion. The enthalpy, entropy and Gibbs' free energy constants were calculated. It was found that the adsorption was spontaneous and endothermic, with favourable adsorption capacities being observed at higher temperatures.

H.J. Wang, C.M. Zhou, F. Peng et al.

Highly dispersed Pt nanoparticles supported on sulfonated multiwalled carbon nanotubes (Pt/sulfonated-MWCNTs) were used to modify glassy carbon (GC) electrode and then glucose oxidase was immobilized on the Pt/sulfonated-MWCNTs/GC electrode to construct a GOD/Pt/sulfonated-MWCNTs/GC glucose biosensor. The electrochemical and detection performance were evaluated by cyclic voltammogram and chronoamperometry. The optimum detection conditions were determined and the stability was studied. The results show that the GOD/Pt/sulfonated-MWCNTs/GC glucose biosensor has much higher detection sensitivity of 0.56 μA/mM and much larger linear range up to 6.4 mM at rather lower working potential of 0.5 V. It can keep more than 85% of its initial activity after continuously using one hour. The results show that the resultant GOD/Pt/sulfonated-MWCNTs/GC glucose biosensor has high electrocatalytic activity and excellent detecting performance for glucose.