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1.
This study was designed to examine the interaction of histamine H2-receptor antagonist drug ranitidine (RTN) with human serum albumin by multi-spectroscopic methods. The experimental results showed the involvement of dynamic quenching mechanism which was further confirmed by lifetime spectral studies. The binding constants (K a) at three temperatures (288, 298, and 308 K) were 2.058 ± 0.020, 4.160 ± 0.010 and 6.801 ± 0.011 × 104 dm3 mol?1, respectively, and the number of binding sites (m) were 1.169, respectively; thermodynamic parameters ΔH 0 (44.152 ± 0.047 kJ mol?1), ΔG 0 (?26.214 ± 0.040 kJ mol?1), and ΔS 0 (236.130 ± 0.025 J K?1 mol?1) were calculated. The distance r between donor and acceptor was obtained (r = 3.40 nm) according to the Förster theory of non-radiative energy transfer. Synchronous fluorescence, CD, AFM and 3D fluorescence spectral results revealed the changes in secondary structure of the protein upon interaction with RTN. A molecular modeling study further confirmed the binding mode obtained by the experimental studies.  相似文献   

2.
The boiling point and volatility are important properties for fuels, as it is for quality control of the industry of petroleum diesel and biofuels. In addition, through the volatility is possible to predict properties, such as vapor pressure, density, latent heat, heat of vaporization, viscosity, and surface tension of biodiesel. From thermogravimetry analysis it is possible to find the kinetic parameters (activation energy, pre-exponential factor, and reaction order), of thermally simulated processes, like volatilization. With the kinetic parameters, it is possible to obtain the thermodynamic parameters by mathematical formula. For the kinetic parameters, the minor values of activation energy were found for mineral diesel (E = 49.38 kJ mol?1), followed by babassu biodiesel (E = 76.37 kJ mol?1), and palm biodiesel (E = 87.00 kJ mol?1). Between the two biofuels studied, the babassu biodiesel has the higher minor value of activation energy. The thermodynamics parameters of babassu biodiesel are, ΔS = ?129.12 J mol?1 K?1, ΔH = +80.38 kJ mol?1 and ΔG = +142.74 kJ mol?1. For palm biodiesel ΔS = ?119.26 J mol?1 K?1, ΔH = + 90.53 kJ mol?1 and ΔG = +141.21 kJ mol?1, and for diesel ΔS = ?131.3 J mol?1 K?1, ΔH = +53.29 kJ mol?1 and ΔG = +115.13 kJ mol?1. The kinetic thermal analysis shows that all E, ΔH, and ΔG values are positive and ΔS values are negative, consequently, all thermodynamic parameters indicate non-spontaneous processes of volatilization for all the fuels studied.  相似文献   

3.
A new chelate (η5-C5H5)2Ti(SB)2, whereSB=O, N donor Schiff base salicylidene-4-methylaniline, was synthesized. The course of thermal degradation of the chelate was studied by thermogravimetric (TG) and differential thermal analysis (DTA) under dynamic conditions of temperature. The order of the thermal decomposition reaction and energy of activation was calculated from TG curve while from DTA curve the change in enthalpy was calculated. Evaluation of the kinetic parameters was performed by Coats-Redfern as well as Piloyan-Novikova methods which gaven=1, ΔH=1.114 kJ·mol?1, ΔE=27.01 kJ·mol?1, ΔS=?340.12 kJ·mol?1·K?1 andn=1, ΔH=1.114 kJ·mol?1, ΔE=20.01 kJ·mol?1, ΔS=?342.60 kJ·mol?1·K?1, respectively. The chelate was also characterized on the basis of different spectral studies viz. conductance, molecular weight, IR, UV-visible and1H NMR, which enabled to propose an octahedral structure to the chelate.  相似文献   

4.
The research shows theoretical calculations on the thermodynamics of digestion/gasification processes where glucose is used as a surrogate for biomass. The change in Enthalpy (?H) and Gibbs Free Energy (?G) is used to obtain the Attainable Region (AR) that shows the overall thermodynamic limits for digestion/gasification from 1 mol of glucose. Gibbs Free Energy and Enthalpy (GH) plots were calculated for the temperature range 25–1500 °C. The results show the effect of temperature on the AR for the processes when water is in both liquid and gas states using 25 °C, 1 bar as the reference state. The AR results show that the production of CO, H2, CH4 and CO2 are feasible at all temperatures studied. The minimum Gibbs Free Energy becomes more negative from ?418.68 kJ mol?1 at 25 °C to ?3024.34 kJ mol?1 at 1500 °C while the process shifts from exothermic (?141.90 kJ mol?1) to endothermic (1161.80 kJ mol?1) for the respective temperatures. Methane and carbon dioxide are favoured products (minimum Gibbs Free Energy) for temperatures up to about 600 °C, and this therefore includes Anaerobic Digestion. The process is exothermic below 500 °C, and thus Anaerobic Digestion requires heat removal. As the temperature continues to increase, hydrogen production becomes more favourable than methane production. The production of gas is endothermic above 500 °C, and it needs a supply of heat that could be done, either by combustion or by electricity (plasma gasification). The calculations show that glucose conversion at temperatures around 700 °C favours the production of carbon dioxide and hydrogen at minimum G. Generally, the results show that the gas from high-temperature gasification (>~800 °C) typically carries the energy mainly in syngas components CO and H2, whereas at low-temperature gasification (<500 °C) the energy is carried in CH4. The overall analysis for the temperature range (25–1500 °C) also suggests a close relationship between biogas production/digestion and gasification as biogas production can be referred to as a form of low-temperature gasification.  相似文献   

5.
The thermodynamic activation parameters of hindered rotation of the CF3 group in the 4-nitrophenyltrifluoromethylsulfone radical anion in DMF were determined from the temperature dependence of the EPR line widths and spin density distributions calculated by the U-B3LYP method in the 6-31+G* basis set. In the range 293 > T > 199 K, the activation energy of hindered rotation E F depends on the temperature and changes in the range 9.67 < E F < 18.95 kJ·mol?1; the changes in the activation enthalpy and entropy are 7.23 < ΔH < 17.30 kJ·mol?1 and ?53.45 < ΔS < ?11.37 J·(mol·K)?1, respectively. Based on the suggested method for evaluating the inner product of the g tensor and the tensor of anisotropic hfi with the 14N nucleus for nitrobenzene radical anions in the liquid state we calculated the correlation time and determined the activation energy of rotational diffusion of the 4-nitrophenyltrifluoromethylsulfone radical anion in DMF, E r = 20.175±0.54 kJ·mol?1.  相似文献   

6.
Isothermal crystallization of an As2Se3 undercooled melt was studied by differential scanning calorimetry and described using the classical theory of nucleation and crystal growth. The maximum rate of nucleation and crystal growth was observed to occur at approximately 235 and 350 °C, respectively. The activation energies of nucleation and crystal growth were determined to be ΔE D = 311 kJ mol?1 and ΔE* = 104 kJ mol?1, respectively. The temperature dependencies of both the activation free energy of nucleation, ΔG*, and the critical diameter, r*, were also calculated.  相似文献   

7.
Modelling of proton and metal exchange in the alginate biopolymer   总被引:1,自引:0,他引:1  
Acid–base behaviour of a commercial sodium alginate extracted from brown seaweed (Macrocystis pyrifera) has been investigated at different ionic strengths (0.1≤I/mol l?1≤1.0) and in different supporting electrolytes (Et4NI, NaCl, KCl, LiCl, NaCl+MgCl2), with the aim of examining the influence of ionic medium on the proton-binding capacity and of quantifying the strength of interaction with light metal ions in the perspective of speciation studies in natural aqueous systems. Potentiometric ([H+]-glass electrode) and titration calorimetric data were expressed as a function of the dissociation degree (α) using different models (Henderson–Hasselbalch modified, Högfeldt three parameters and linear equations). The dependence on ionic strength of the protonation constants was taken into account by a modified specific interaction theory model. Differences among different media were explained in terms of the interaction between polyanion and metal cations of the supporting electrolytes. Quantitative information on the proton-binding capacity, together with the stabilities of different species formed, is reported. Protonation thermodynamic parameters, at α=0.5, are log K H=3.686±0.005, ΔG 0=?21.04±0.03 kJ mol?1, ΔH 0=4.8±0.2 kJ mol?1 and TΔS 0=35.7±0.3 kJ mol?1, at infinite dilution. Protonation enthalpies indicate that the main contribution to proton binding arises from the entropy term. A strict correlation between ΔG and TΔS was found, TΔS=?9.5–1.73 ΔG. Results are reported in light of building up a chemical complexation model of general validity to explain the binding ability of naturally occurring polycarboxylate polymers and biopolymers. Speciation profiles of alginate in the presence of sodium and magnesium ions, naturally occurring cations in natural waters, are also reported.  相似文献   

8.
The pyrolysis of hydrated bis(pyrazinecarboxylate)copper(II) under an argon atmosphere proceeds via the loss of the water molecules at 84–95°C, ΔH=40.4 kJ (mol H2O)?1 followed by the thermal decomposition of the complex at 284–325°C, ΔH=97.0 kJ·mol?1, yielding 0.72 mole of pyrazine, 0.28 mole of bipyrazine, and 2 mole of CO2 per mole of complex.  相似文献   

9.
A new crystalline complex (C8H17NH3)2CuCl4(s) (abbreviated as C8Cu(s)) was synthesized by liquid phase reaction. Chemical analysis, elemental analysis, and X-ray crystallography were applied to characterize the composition and crystal structure of the complex. Low-temperature heat capacities of the complex were measured by a precision automatic adiabatic calorimeter over the temperatures ranging from 78 to 395 K, and two solid–solid phase changes appeared in the heat capacity curve. The temperatures, molar enthalpies and entropies of the two phase transitions of the complex were determined to be: T trs, 1 = 309.4 ± 0.35 K, Δtrs H m, 1 = 16.55 ± 0.41 kJ mol?1, and Δtrs S m, 1 = 53.49 ± 1.3 J K?1 mol?1 for the first peak; T trs, 2 = 338.5 ± 0.63 K, Δtrs H m, 2 = 6.500 ± 0.10 kJ mol?1, and Δtrs S m, 2 = 19.20 ± 0.28 J K?1 mol?1 for the second peak. Two polynomial equations of the heat capacities as a function of the temperature were fitted by least-square method. Smoothed heat capacities and thermodynamic functions of the complex relative to the standard reference temperature of 298.15 K were calculated based on the fitted polynomial equations.  相似文献   

10.
New energetic materials, [Ca(MCZ)3(H2O)2](ClO4)2 and {[Ba2(MCZ)4(H2O)21-ClO4)22-ClO4)2]0.5}n, are synthesized and tried as alternatives to common primary explosives. Both the crystal structures were determined by single-crystal X-ray diffraction. The crystal of [Ca(MCZ)3(H2O)2](ClO4)2 belongs to the monoclinic, P21/c space group, a = 14.168(3) Å, b = 8.5938(18) Å, c = 18.889(4) Å, β = 111.234(2)°, V = 2143.8(8) Å3, ρ = 1.6893 g cm?3, and {[Ba2(MCZ)4(H2O)21-ClO4)22-ClO4)2]0.5}n belongs to the triclinic, P-1 space group, a = 7.166(2) Å, b = 10.461(2) Å, c = 11.738(4) Å, α = 110.563(5)°, β = 93.799(2)°, γ = 96.864(3)°, V = 812.4(4) Å3, ρ = 2.185 g cm?3. Their thermal stabilities were investigated by differential scanning calorimetry (DSC), and exothermic peak temperatures with a heating rate of 10 °C min?1 are 249.7 and 181.7 °C, respectively. Non-isothermal reaction kinetics parameters were calculated via both Kissinger’s method and Ozawa-Doyle’s method to work out EK = 124.6 kJ mol?1, lgAK = 10.38, EO = 126.7 kJ mol?1 for the calcium complex and EK = 100.3 kJ mol?1, lgAK = 9.50, EO = 102.6 kJ mol?1 for the barium complex. Additionally, the critical temperatures of thermal explosion, ΔS, ΔH, and ΔG were calculated as ?231.2 J K?1 mol?1, 120.417 kJ mol?1, 236.728 kJ mol?1 for the calcium complex and ?230.6 J K?1 mol?1, 96.723 kJ mol?1, 195.938 kJ mol?1 for the barium complex. As for their explosive nature, sensitivities toward impact and friction were tested. Both [Ca(MCZ)3(H2O)2](ClO4)2 and {[Ba2(MCZ)4(H2O)21-ClO4)22-ClO4)2]0.5}n are insensitive to friction (>360 N); their impact sensitivities are acceptable (20 and 13 J). Both compounds are energetic complexes.  相似文献   

11.
Interaction of ammonia with H-MCM-22 zeolite (Si/Al = 24.5) was investigated by temperature-programmed desorption technique in order to obtain information on thermodynamics of the process. Average activation energy for desorption of ammonia from Brønsted acid sites of H-MCM-22 zeolite was estimated from the data obtained under conditions varying in heating rate and also flow rate of carrier gas. It resulted in value of E d = 127 kJ mol?1 for heat rate variation method, whereas flow rate variation led to E d value of 111 kJ mol?1. Obtained E d values are compared with those reported in the literature for other zeolitic materials and discussed in the broader context of zeolite acidity. Comparison of E d values estimated here for H-MCM-22 zeolite with corresponding data for other protonic zeolites shows that H-MCM-22 displays mediocre/lower activation energy for ammonia compared with other high-silica zeolites.  相似文献   

12.
A kinetic analysis of the oxidation of semicarbazide (SEM) by the single-electron oxidant [IrCl6]2? has been carried out by stopped-flow spectrometric techniques. The reaction proved to be first order each in [IrCl6 2?] and [SEM]tot, leading to overall second-order kinetics. The variation in the observed second-order rate constant k′ with pH was explored over the pH range of 0–7.11. Spectrophotometric titration revealed a stoichiometry of Δ[IrCl6 2?]/Δ[SEM]tot = 4:1 for the redox reaction. On the basis of the rate law, the redox stoichiometry, and the rapid scan spectra, a reaction mechanism is proposed which involves parallel attacks of [IrCl6]2? on both H2NCONHNH3 + and H2NCONHNH2 as rate-determining steps, followed by several rapid reactions. The rate expression, derived from the reaction mechanism, was utilized to simulate the k′–pH profile yielding a virtually perfect fit and indicating that the reaction path involving H2NCONHNH3 + does not make a significant contribution to the overall rate. The reaction between [IrCl6]2? and H2NCONHNH2 was further studied as a function of both temperature and ionic strength. From the temperature dependence, activation parameters were obtained as: ?H 2 ?  = 34.9 ± 1.5 kJ mol?1 and ?S 2 ?  = ?78 ± 5 J K?1 mol?1. The observed ionic strength dependence suggests that the rate-determining step is between [IrCl6]2? and a neutral species of SEM. Hence, both the temperature and ionic strength dependency studies are in good agreement with the proposed reaction mechanism, in which the rate-determining step involves an outer sphere electron transfer.  相似文献   

13.
In this work, the interaction of memantine with human serum albumin (HSA) immobilized on porous silica particles was studied using a biochromatographic approach. The determination of the enthalpy change at different pH values suggested that the protonated group in the memantine–HSA complex exhibits a heat protonation with a magnitude around 65 kJ mol?1. This value agrees with the protonation of a guanidinium group, and confirmed that an arginine group may become protonated in the memantine–HSA complex formation. The thermodynamic data showed that memantine–HSA binding, for low temperature (<293 K), is dominated by a positive entropy change. This result suggests that dehydration at the binding interface and charge–charge interactions contribute to the memantine–HSA complex formation. Above 293 K, the thermodynamic data ΔH and ΔS became negative due to van der Waals interactions and hydrogen bonding which are engaged at the complex interface. The temperature dependence of the free energy of binding is weak because of the enthalpy–entropy compensation caused by a large heat capacity change, ΔC p = ? 3.79 kJ mol?1 K?1 at pH = 7. These results were used to determine the potential binding site of this drug on HSA.  相似文献   

14.
A precision rotating-bomb combustion calorimeter (thermistor of which was constructed in the laboratory) was calibrated using benzoic acid with purity of 99.999 %. The combustion energy of phenanthroline monohydrate (phen·H2O) at 298.15 K was determined to be Δc U m θ  = ?(5,757.45 ± 2.53) kJ mol?1. Then, the standard enthalpy of combustion and the standard enthalpy of formation of phen·H2O were calculated to be Δc H m θ  = ?(5,759.93 ± 2.53) kJ mol?1 and Δf H m θ  = ?(391.34 ± 2.98) kJ mo1?1, respectively. Particularly, the effect of phen·H2O on growth and metabolism of Escherichia coli (E. coli) was also determined by a TAM air isothermal calorimeter at 37 °C. The thermokinetic parameters, including maximum heat output power (P max), growth rate constant (κ), generation times (t G), inhibitive rate (I), and half inhibition concentration (C I,50), were obtained. The results showed that phen·H2O possessed the bi-directional biological effect and Hormesis effect, which stimulated the growth of E. coli at lower concentration, but inhibited the growth at higher concentration. The half inhibition concentration C I,50 of phen·H2O was found to be 7.31 mg L?1.  相似文献   

15.
The immobilisation of lead(II) ions from aqueous solutions on natural coal was investigated to compare calculated and measured adsorption enthalpies. For this purpose, adsorption isotherms were measured at temperatures of 303, 333 and 353 K. Adsorption enthalpy ΔH was evaluated from temperature dependence of the equilibrium constant of adsorption using the van‘t Hoff equation. Thus, the value of ΔH = 27 kJ mol?1 was obtained manifesting endothermic effect of lead(II) immobilisation on the coal. However, based on the flow and immersion calorimetric measurements, the exothermic character of lead(II) adsorption on the studied coal was proven with a value of about ?7 kJ mol?1.  相似文献   

16.
邸友莹张剑  谭志诚 《中国化学》2007,25(10):1423-1429
A coordination compound of erbium perchlorate with L-α-glutamic acid, [Er2(Glu)2(H2O)6](ClO4)4·6H2O(s), was synthesized. By chemical analysis, elemental analysis, FTIR, TG/DTG, and comparison with relevant literatures, its chemical composition and structure were established. The mechanism of thermal decomposition of the complex was deduced on the basis of the TG/DTG analysis. Low-temperature heat capacities were measured by a precision automated adiabatic calorimeter from 78 to 318 K. An endothermic peak in the heat capacity curve was observed over the temperature region of 290-318 K, which was ascribed to a solid-to-solid phase transition. The temperature Ttrans, the enthalpy △transHm and the entropy △transSm of the phase transition for the compound were determined to be: (308.73±0.45) K, (10.49±0.05) kJ·mol^-1 and (33.9±0.2) J·K^-1·mol^-1. Polynomial equation of heat capacities as a function of the temperature in the region of 78-290 K was fitted by the least square method. Standard molar enthalpies of dissolution of the mixture [2ErCl3·6H2O(s)+2L-Glu(s)+6NaClO4·H2O(s)] and the mixture {[Er2(Glu)2(H2O)6](ClO4)4·6H2O(s)+6NaCl(s)} in 100 mL of 2 mol·dm^-3 HClO4 as calorimetric solvent, and {2HClO4(1)} in the solution A' at T=298.15 K were measured to be, △dHm,1=(31.552±0.026) kJ·mol^-1, △dHm,2 = (41.302±0.034) kJ·mol^-1, and △dHm,3 = ( 14.986 ± 0.064) kJ·mol^-1, respectively. In accordance with Hess law, the standard molar enthalpy of formation of the complex was determined as △fHm-=-(7551.0±2.4) kJ·mol^-1 by using an isoperibol solution-reaction calorimeter and designing a thermochemical cycle.  相似文献   

17.
A new high-nitrogen complex [Cu(Hbta)2]·4H2O (H2bta = N,N-bis-(1(2)H-tetrazol-5-yl) amine) was synthesized and characterized by elemental analysis, single crystal X-ray diffraction and thermogravimetric analyses. X-ray structural analyses revealed that the crystal was monoclinic, space group P2(1)/c with lattice parameters a = 14.695(3) Å, b = 6.975(2) Å, c = 18.807(3) Å, β = 126.603(1)°, Z = 4, D c = 1.888 g cm?3, and F(000) = 892. The complex exhibits a 3D supermolecular structure which is built up from 1D zigzag chains. The enthalpy change of the reaction of formation for the complex was determined by an RD496–III microcalorimeter at 25 °C with the value of ?47.905 ± 0.021 kJ mol?1. In addition, the thermodynamics of the reaction of formation of the complex was investigated and the fundamental parameters k, E, n, \( \Updelta S_{ \ne }^{{{\uptheta}}} \), \( \Updelta H_{ \ne }^{{{\uptheta}}} \), and \( \Updelta G_{ \ne }^{{{\uptheta}}} \) were obtained. The effects of the complex on the thermal decomposition behaviors of the main component of solid propellant (HMX and RDX) indicated that the complex possessed good performance for HMX and RDX.  相似文献   

18.
19.
The adsorption of the uranyl ions from aqueous solutions on the nanoporous ZnO powders has been investigated under different experimental conditions. The adsorption of uranyl on nanoporous ZnO powders were examined as a function of the contact times, pH of the solution, concentration of uranium(VI) and temperature. The ability of this material to remove U(VI) from aqueous solution was followed by a series of Langmuir and Freunlinch adsorption isotherms. The adsorption percent and distribution coefficient for nanoporous ZnO powders were 98.65 % ± 1.05 and 7,304 mL g?1, respectively. The optimum conditions were found as at pH 5.0, contact time 1 h, at 1/5 Zn2+/urea ratio, 50 ppm U(VI) concentration and 303 K. The monomolecular adsorption capacity of nanoporous ZnO powders for U(VI) was found to be 1,111 mg g?1 at 303 K. Using the thermodynamic equilibrium constants obtained at different temperatures, various thermodynamic parameters, such as ΔG°, ΔH° and ΔS°, have been calculated. Thermodynamic parameters (ΔH° = 28.1 kJ mol ?1, ΔS° = 160.30 J mol?1 K?1, ΔG° = ?48.54 kJ mol?1) showed the endothermic and spontaneous of the process. The results suggested that nanoporous ZnO powders was suitable as sorbent material for recovery and adsorption of U(VI) ions from aqueous solutions.  相似文献   

20.
In this study, a series of binary mixtures of N-butyl stearate (nBS) and methyl palmitate (MP) were used to produce a novel composite phase change material (CPCM) for potential application in the eastern China, and their thermal properties were investigated by differential scanning calorimetry (DSC). The results of DSC indicated that the mixture consisting of 10 mass% nBS and 90 mass% MP is optimum as the CPCM in terms of the phase change temperature ranges (T f = 19.74–5.59 °C; T m = 18.34–33.80 °C) and latent heats (ΔH f = 176.8 J g?1; ΔH m = 189.3 J g?1). On the other hand, the thermal reliability and chemical stability of the CPCM after 120, 180, 240, 300, 360 and 500 accelerated thermal cycling tests were studied by DSC and fourier transform infrared (FTIR) analysis. The results demonstrated that the CPCM had good thermal reliability and chemical stability.  相似文献   

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