Interaction Between Ginkgolic Acid and Human Serum Albumin by Spectroscopy and Molecular Modeling Methods

The interaction of ginkgolic acid (15:1, GA) with human serum albumin (HSA) was investigated by FT–IR, CD and fluorescence spectroscopic methods as well as molecular modeling. FT–IR and CD spectroscopic showed that complexation with the drug alters the protein’s conformation by a major reduction of α-helix from 54 % (free HSA) to 46–31 % (drug–complex), inducing a partial protein destabilization. Fluorescence emission spectra demonstrated that the fluorescence quenching of HSA by GA was by a static quenching process with binding constants on the order of 10⁵ L·mol^?1. The thermodynamic parameters (ΔH = ?28.26 kJ·mol^?1, ΔS = 11.55 J·mol^?1·K^?1) indicate that hydrophobic forces play a leading role in the formation of the GA–HSA complex. The ratio of GA and HSA in the complex is 1:1 and the binding distance between them was calculated as 2.2 nm based on the Förster theory, which indicates that the energy transfer from the tryptophan residue in HSA to GA occurs with high probability. On the other hand, molecular docking studies reveal that GA binds to Site II of HSA (sub-domain IIIA), and it also shows that several amino acids participate in drug–protein complexation, which is stabilized by H-bonding.     

Thermodynamic study of indoxylsulfate interaction with human serum albumin and competitive binding with p-cresylsulfate

Indoxylsulfate (IS) and p-cresylsulfate (PCS) are natural compounds endowed with toxicity. These molecules are harmful to the environment and removed by the procedure of dialysis. Knowledge of their interaction with biologic compounds such as proteins and particularly human serum albumin (HSA) is limited. This study was therefore designed to determine the thermodynamic parameters of the interaction of IS with HSA and in competition with PCS. Results showed that IS binding is moderate (K _a = 1,750 ± 39 M^?1). The interaction is mainly electrostatic (?H° = ?36.2 ± 1.7 kJ mol^?1) and yields a modification of conformation upon binding (?_conf S° < 0). The thermodynamic parameters obtained at different temperatures show an enthalpy–entropy compensation process. Competition with PCS reveals that affinity for IS decreased by 36 %, with profound modification of the binding forces involved and a release of PCS from the binding site.     

抗肿瘤药物5-氟尿嘧啶与人血清白蛋白相互作用的热力学研究

在298.15 K下,根据本结合过程的假设和Langmuir结合理论, 用等温滴定微量热和圆二色谱分析法研究了抗肿瘤药物5-氟尿嘧啶(5-FU)与人血清白蛋白(HSA)的相互作用. 研究结果表明, 蛋白质(HSA)与药物配体5-氟尿嘧啶的相互作用存在两类结合位点. 第一类结合, 结合位点数N＝71±0.1, 结合常数 K＝(1.46±0.016)×10⁵ L•mol^－1, 结合焓ΔH＝(39.61±0.220) kJ•mol^－1, 结合熵ΔS＝(231.68±0.025) J•mol^－1•K^－1, 结合自由能ΔG＝(－29.48±0.030) kJ•mol^－1. 结合过程为熵驱动过程, 疏水相互作用是过程的主要推动力;第二类结合, 结合位点数N＝140±0.2, 结合常数 K＝(1.49±0.032)×10⁵ L•mol^－1, 结合焓ΔH＝(－19.31±0.103) kJ•mol^－1, 结合熵ΔS＝(34.30±0.055) J•mol^－1•K^－1, 结合自由能ΔG＝(－29.53±0.041) kJ•mol^－1, 结合过程为焓-熵协同驱动过程, 氢键和静电相互作用是过程的主要推动力. 圆二色谱分析结果表明, 在两类结合过程中, 药物5-氟尿嘧啶(5-FU)的作用致使蛋白质(HSA)二级结构单元的相对含量发生了变化.     

Copper Mediated Affinity of Amyloid β to Chondroitin Sulfates

Aβ is a major component of the senile plaques characteristic of Alzheimer disease (AD) and sulfated GAGs such as chondroitin sulfates (CS) have been found in all types of amyloidosis. In this paper, a biochromatographic approach was developed to measure for the first time changes in enthalpy, heat capacity change and copper effect for the binding of Aβ to CS in a wide temperature range. For this, CS was immobilized on a chromatographic support. It was established that this novel CS column was stable during an extended period of time. The thermodynamic data showed that Aβ–CS binding, for low temperature (<10 °C), is enthalpically unfavourable and being dominated by a positive entropy change. This result suggested that dehydration at the binding interface and charge–charge interactions contribute to the Aβ–CS complex formation and a large heat capacity change, ΔC _p = ?2.32 kJ mol^?1 K^?1, was determined. Above 10 °C, the thermodynamic data ΔH and ΔS became negative due to van der Waals interactions and hydrogen bonding which are engaged at the complex interface confirming strong Aβ–CS hydrogen bond networks. Also, for a copper concentration in the range 20–160 μM, it was shown that an increase of the Cu²⁺ concentration in the medium led an increase of this association classically attributed to salt effect (i.e. hydrophobic bonds) and to ion pair formations between the Cu²⁺ cation and Aβ to bind to chondroitin sulfate and could thus improve the Aβ aggregation by copper.     

Kinetic and thermodynamic parameters of volatilization of biodiesel from babassu, palm oil and mineral diesel by thermogravimetric analysis (TG)

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.     

Some Thermodynamic Properties of Aqueous 2-Mercaptopyridine-N-Oxide (Pyrithione) Solutions

The thermodynamic properties of 2-mercaptopyridine-N-oxide (pyrithione, PT) were studied potentiometrically in NaCl aqueous solutions at different ionic strengths and temperatures. A set of protonation constants is provided, together with distribution (water/2-methyl-1-propanol) and solubility data. The total and the specific solubility (solubility of neutral species) values of pyrithione were determined and, for example, are 0.0561 and 0.0518 mol·dm^?3 at c _NaCl = 0.244 mol·dm^?3 and T = 298.15 K. By fitting the distribution and solubility results against the ionic strength, the Setschenow coefficient and the activity coefficients of the neutral species were determined. In pure water, the specific solubility is log₁₀ \( S_{m 0}^{0} = \, {-} 1. 20 \, \pm \, 0.0 4 \) . To determine the activity coefficient of the charged species and the protonation constant at infinite dilution, the data were analyzed by different models, namely the Debye–Hückel type equation, the SIT (Specific ion Interaction Theory) and the Pitzer approach. The interaction coefficient of the deprotonated pyrithione species was determined [ε(Na⁺, PT^?) = ?0.105 ± 0.002]. The protonation enthalpy was also determined, is slightly positive, and the protonation process is entropic in nature. At infinite dilution and T = 298.15 K, log₁₀ K ^H0 = 4.620 ± 0.002, ΔG ⁰ = –26.4 ± 0.1 kJ·mol^?1, ΔH ⁰ = 2.1 ± 0.5 kJ·mol^?1 and TΔS ⁰ = 28.5 ± 0.5 kJ·mol^?1. The electrochemical behavior of pyrithione was studied in NaCl solutions at T = 298.15 K. It was found that voltammetry can be used to study the binding ability of pyrithione towards metal cations. The results of this work are in agreement with literature findings and improve the knowledge of the chemistry of pyrithione in aqueous solutions.     

Study on thermodynamic properties of glyphosate by oxygen-bomb calorimeter and DSC

The combustion enthalpy of glyphosate was determined by XRY-1C oxygen-bomb calorimeter at a constant volume. The standard mole combustion enthalpy and the standard mole formation enthalpy have been calculated to be ?1702.19 and ?1478.36 kJ mol^?1, respectively. For testing the reliability of instrument, glycine and naphthalene were used as reference materials by comparing the measured values with the literature values, the absolute error and relative error are 2.58 kJ mol^?1 and 0.26 % for glycine, respectively, and these of naphthalene are 4.08 kJ mol^?1 and 0.08 %, respectively. Moreover, the constant-pressure heat capacities c _p of glyphosate were measured by differential scanning calorimetry in the temperature range 303.15–365.15 K, and the relationship between c _p and temperature was established. These related studies can provide a thermodynamic basis for their further application.     

Interaction Between Plumbagin and Human Serum Albumin by Fluorescence Spectroscopy

The interaction of plumbagin (PLU) with human serum albumin (HSA) in physiological buffer (pH=7.4) was studied by fluorescence spectroscopy. Results obtained from analysis of the fluorescence spectra indicated that PLU has a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. Fluorescence quenching data revealed that the quenching constants (K) are 4.43×10⁴, 3.26×10⁴ and 1.69×10⁴ L?mol^?1 at 293, 303 and 313 K, respectively. The thermodynamic parameters ΔH° and ΔS° were calculated to be ?36.63 kJ?mol^?1, and ?35.702 J?mol^?1?K^?1 respectively, which suggested that van der Waals interactions and hydrogen bonds play a major role in the interaction of PLU with HSA. The distance between donor (HSA) and acceptor (PLU) was calculated to be 3.76 nm based on Förster’s non-radiative energy transfer theory. The results of synchronous fluorescence spectra showed that binding of PLU to HSA can induce conformational changes in HSA.     

Calorimetric investigation of Al–Zn alloys using Oelsen method

The results of calorimetric study of binary Al–Zn system done according to the Oelsen thermodynamic method are presented in this paper. Main thermodynamic properties, including activities, activity coefficients, partial/integral molar Gibbs excess, and mixing energies were determined at 1,000 K. Positive deviation from Raoult law was noticed, with minimal values of ΔG ^M about ?3 kJ mol^?1 and maximal values of ΔG ^E about +2 kJ mol^?1. The energetics of mixing in liquid Al–Zn alloys has been analyzed through the study of concentration fluctuation in the long-wavelength limit, and weak affinity between Al and Zn atoms in the system was observed. Differential thermal analysis and light optic microscopy were applied in the frame of characterization of investigated binary alloys and phase diagram examination, and the results obtained were in accordance with available literature data.     

Hydrogen sorption–desorption studies on ZrCo–hydrogen system

The ZrCo–H₂ system was investigated in this study owing to its importance as a suitable candidate material for storage, supply, and recovery of hydrogen isotopes. Desorption hydrogen pressure-composition isotherms were generated at six different temperatures in the range of 524–624 K. A van’t Hoff plot was constructed using the plateau pressure data of each pressure-composition isotherms and the thermodynamic parameters were calculated for the hydrogen desorption reaction of ZrCo hydride. The enthalpy and entropy change for the desorption of hydrogen were found to be 83.7 ± 3.9 kJ mol^?1 H₂ and 122 ± 4 J mol^?1 H₂ K^?1, respectively. Hydrogen absorption kinetics of ZrCo–H₂ system was studied at four different temperatures in the range of 544–603 K and the activation energy for the absorption of hydrogen by ZrCo was found to be 120 ± 5 kJ mol^?1 H₂ by fitting kinetic data into suitable kinetic model equation.     

Synthesis, structure analysis and thermodynamics of [Ni(H2O)4(TO)2](NO3)2·2H2O (TO = 1,2,4-triazole-5-one)

A novel complex [Ni(H₂O)₄(TO)₂](NO₃)₂·2H₂O (TO = 1,2,4-triazole-5-one) was synthesized and structurally characterized by X-ray crystal diffraction analysis. The decomposition reaction kinetic of the complex was studied using TG-DTG. A multiple heating rate method was utilized to determine the apparent activation energy (E _a) and pre-exponential constant (A) of the former two decomposition stages, and the values are 109.2 kJ mol^?1, 10^13.80 s^?1; 108.0 kJ mol^?1, 10^23.23 s^?1, respectively. The critical temperature of thermal explosion, the entropy of activation (ΔS ^≠), enthalpy of activation (ΔH ^≠) and the free energy of activation (ΔG ^≠) of the initial two decomposition stages of the complex were also calculated. The standard enthalpy of formation of the new complex was determined as being ?1464.55 ± 1.70 kJ mol^?1 by a rotating-bomb calorimeter.     

Molecular dynamics and energetic perceptions of substrate recognition by thymidylate kinase

Plasmodium deoxyguanylate pathways are an attractive area of investigation for future metabolic and drug discovery studies due to their unusual substrate specificities. We investigated the energetic contribution to thymidylate kinase substrate binding, and the forces underlying ligand recognition. The binding constant varied from 8 × 10⁴ M^?1 at 290 K to 6 × 10⁴ M^?1 at 310 K for dGMP, and from 16 × 10⁴ M^?1 at 290 K to 4 × 10⁴ M^?1 at 310 K for TMP. ΔC _p was estimated as ?1.75 kJ mol^?1 K^?1 for TMP and +2 kJ mol^?1 K^?1 for dGMP. In comparison with TMP, the binding of dGMP to PfTMK produced less favorable enthalpy change, positive or favorable entropic contribution at lower temperature, positive heat capacity change, negative $ \Updelta S_{\text{HE}}^{^\circ } $ , positive ΔS _other, higher total solvent-exposed surface area and more or less rigid body binding. These changes indicate unfavorable conditions for proper binding and lower conformational changes, and suboptimal structural reordering during dGMP binding.     

Thermal studies and spectral characterization of the chelate of bis-(η5-cyclopentadienyl titanium(IV) with salicylidene-4-methylaniline

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.     

Immobilisation of lead(II) ions from aqueous solutions on natural coal

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.     

Investigation of hydrogen desorption from CaSiH by means of calorimetric method

The present work deals with the study of the reaction of hydrogen desorption from the CaSiH_X hydride by means of the calorimetric method. The dehydrogenation of the CaSiH_X hydride was carried out at 548 K. For a calorimetric study, the installation composed of the differential heat-conducting Tian–Calvet type calorimeter connected with a conventional Sieverts-type apparatus was employed. Such installation permitted us to obtain simultaneously the P-X isotherms (P—equilibrium hydrogen pressure, X = H/CaSi) and variation of the partial molar enthalpies of the reaction of hydrogen desorption from CaSiH_X with the hydrogen concentration in the metallic matrix. It was ascertained that in the CaSi-H₂ system there was one region where values of the partial molar enthalpy of the reaction of hydrogen desorption from the CaSiH_X hydride remained constant. This means that formation of one hydride phase in the CaSi-H₂ system took place. The enthalpy and entropy values for the reaction of hydrogen desorption from the CaSiH_X in the plateau range are ΔH _des = 53.8 ± 1.2 kJ mol^?1 H₂ and ΔS _des = 94.2 ± 2.7 J mol^?1 H₂ K^?1 (ΔH _des and ΔS _des—the differential molar enthalpy and entropy desorption, respectively).     

Thermodynamic activation parameters of hindered rotation of the CF<Subscript>3</Subscript> group in the 4-nitrophenyltrifluoromethylsulfone radical anion in DMF

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.     

Thermodynamic studies on protonation constant of adenosine and guanosine at different temperatures and ionic strengths

Stepwise protonation constants of two purine nucleosides (adenosine and guanosine) were determined at different temperatures (293.15 to 308.15) and various ionic strengths (0.101 to 3.503 mol · kg⁻¹ NaClO₄) using a combination of potentiometric and spectrophotometric method. The thermodynamic parameters (i.e. enthalpy change, ΔH, and entropy change, ΔS) of the protonations were calculated at different temperatures using van’t Hoff and virial equations. The dependence of the protonation constant on ionic strength is modeled by a Debye–Hückel type equation and discussed. Finally, the protonation constants of the nucleosides and the enthalpy change of protonations were determined at zero ionic strength.     

Analysis of binding interaction between vitamin B2 and trypsin

The interaction between vitamin B₂ (VB₂), a type of necessary nutrient for the body’s metabolism and repair, and trypsin, a serine protease found in the digestive system, has been investigated in vitro under a simulated physiological condition by UV–Vis spectrophotometry and fluorescence spectrometry. The intrinsic fluorescence intensity of trypsin was strongly quenched by VB₂. Spectrophotometric observations are rationalized in terms of a static quenching process at lower concentrations of VB₂ and a combined quenching (both dynamic and static) process at higher concentrations of VB₂. The binding parameters, such as the binding constants and the number of binding sites, can be evaluated by fluorescence quenching experiments. The apparent binding constants K between VB₂ and trypsin at different temperatures were 1.406, 1.264, and 0.543 × 10⁶ L mol^?1 and the numbers of binding sites n were 1.386, 1.391, and 1.319, which were all evaluated by the fluoresence quenching experiments. The negative values of ΔG for the formation of the trypsin–VB₂ complex implied that the binding was a spontaneous process. According to the van’t Hoff equation, the standard enthalpy change (ΔH) and standard entropy change (ΔS) for the reaction were calculated to be ?49.817 kJ mol^?1 and ?56.219 J mol^?1 K^?1, respectively, indicating that the hydrophobic interaction played a significant role in VB₂ binding to trypsin. In addition, the binding distance between VB₂ (acceptor) and trypsin (donor) was estimated to be 1.11 nm according to Förster’s resonance energy transfer theory. The results obtained here will be of biological significance in pharmacology and clinical medicine.     

Low-temperature heat capacities, and thermodynamic properties of solid–solid phase change material bis(1-octylammonium) tetrachlorocuprate

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, Δ_trs H _{m, 1} = 16.55 ± 0.41 kJ mol^?1, and Δ_trs S _{m, 1} = 53.49 ± 1.3 J K^?1 mol^?1 for the first peak; T _{trs, 2} = 338.5 ± 0.63 K, Δ_trs H _{m, 2} = 6.500 ± 0.10 kJ mol^?1, and Δ_trs 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.