Interaction of polyvinylpyrrolidone with methyl orange and its homologs in aqueous solution: Thermodynamics of the binding equilibria and their temperature dependences

The interaction of polyvinylpyrrolidone with methyl orange, ethyl orange, propyl orange, and butyl orange has been studied by an equilibrium dialysis method at 5, 15, 25, and 35°C. The first binding constants and the thermodynamic parameters in the course of the binding have been calculated. It was found that the free energy and the enthalpy changes are all negative and the entropy change is largely positive. The longer the alkyl chain of the dyes, the more positive is the enthalpy change (though it is always in the negative direction) and hence the larger is the entropy change. The favorable free energy of the binding of butyl orange observed for the formation of the dye–polymer complex seems to be a result of a favorable entropy change rather than any favorable enthalpy change. Temperature dependences of the thermodynamic functions were apparently observed. That is, ΔF and ΔH become larger in absolute magnitude as the temperature increases. The positive quantity of ΔS tends to decrease with increasing temperture. All these facts obtained can be interpreted satisfactorily by the hydrophobic interaction between hydrocarbon portions of the dyes and nonpolar parts of the macromolecule.     

Temperature dependence on the binding of butyl orange by bovine serum albumin

The binding of 4′-dibutylaminoazobenzene-4-sulfonate anion (butyl orange) by bovine serum albumin has been examined quantitatively by an equilibrium dialysis method at 5, 10, 15, 20, 25, and 35°C. The first binding constants and the thermodynamic parameters for the formation of the first dye anion-protein complex have been calculated. The peculiar temperature dependence of the first binding constant could be observed. That is, the value of the first binding constant increases with increasing temperature until it reaches a maximum value at approximately 18°C and then decreases with raising temperature. Accordingly, this binding process is exothermic above 18°C and is endothermic below 18°C. Near 18°C the process exhibits athermal reaction. From the thermodynamic data obtained, it is evident that the favorable free energy of the binding is accompanied by an entropy gain and that the enthalpies of the binding vary from a positive (unfavorable) value below 18°C to a negative (favorable) one above 18°C. Furthermore an apparent temperature dependence of the thermodynamic functions was observed. That is, ΔF° becomes larger in absolute magnitude as the temperature increases. The positive quantity of ΔS° tends to decrease with increasing temperature. All these facts can be interpreted satisfactorily in terms of hydrophobic interactions between hydrophobic portions of the dye and nonpolar parts of the albumin.     

Comparative study on the liquid chromatographic enantioseparation of cyclic β‐amino acids and the related cyclic β‐aminohydroxamic acids on Cinchona alkaloid‐based zwitterionic chiral stationary phases

The enantiomeric pairs of cis and trans stereoisomers of cyclic β‐aminohydroxamic acids and their related cis and trans cyclic β‐amino acids containing two chiral centers were directly separated on four structurally related chiral stationary phases derived from quinine and quinidine modified with (R,R)‐ and (S,S)‐aminocyclohexanesulfonic acids. Applying these zwitterionic ion‐exchangers as chiral selectors, the effects of the composition of the bulk solvent, the acid and base additives, the structures of the analytes, and temperature on the enantioresolution were investigated. To study the effects of temperature and obtain thermodynamic parameters, experiments were carried out at constant mobile phase compositions in the temperature range 5–50°C. The differences in the changes in standard enthalpy Δ(ΔH°), entropy Δ(ΔS°), and free energy Δ(ΔG°) were calculated from the linear van't Hoff plots derived from the ln α versus 1/T curves in the studied temperature range. Results thus obtained indicated enthalpy‐driven separations in all cases. The sequence of elution of the enantiomers was determined and found to be reversed when ZWIX(–)™ was changed to ZWIX(+)™ or ZWIX(–A) to ZWIX(+A).     

Interaction of crosslinked polyvinylpyrrolidone with a homologous series of methyl orange derivatives in aqueous and nonaqueous solutions: Thermodynamics of the binding equilibria

The extent of binding of methvI orange, ethyl orange, propyl orange, and butyl orange by crosslinked polyvinylpyrrolidone was measured in all aqueous Solution. The first binding constants and the thermodynamic parameters accompanying the binding were evaluated. These values were compared with those of water-soluble polyvinylpyrrolidone. The first binding constant, the absolute magnitude of ΔF°, and the value of ΔS° of the crosslinked polyvinylpyrrolidone are substantially larger than those of the water-soluble product for any particular dye. These behaviors can be accounted for in terms of increased hydrophobic domains in the former and enhanced hydrophobic contribution in the binding process. Also the binding of the dye by the crosslinked polymer in a nonaqueous solvent, ethylene glycol, was measured to assess the contribution of hydrophobic interaction to the dye-polymer complex formation in aqueous medium. It was found that the binding of butyl orange by the crosslinked polymer is suppressed in ethylene glycol and the contribution of entropy term to the free energy change in the aqueous environment is large compared with that in ethylene glycol. The significance of the hydrophobic of the hydrophobic interaction in the dye-polymer association process is described.     

Equilibrium anionic polymerization of 4,7-dioxaoctanal and n-octanal

Equilibrium anionic polymerization of 4,7-dioxaoctanal (DOA) and n-octanal (OA) was carried out in tetrahydrofuran in the temperature range of ?90 to ?68°C, and thermodynamic parameters were evaluated as follows: ΔH_ss = ?4.0 ± 0.1 kcal/mole, ΔS_ss = ?18.4 ± 0.5 cal/mole-deg, and T_c,ss = ?56°C for the DOA system; ΔH_sc = ?3.4 ± 0.1 kcal/mole, ΔS_sc = ?15.7 ± 0.4 cal/mole-deg, and T_c,sc = ?59°C for the OA system. Comparison of these values with those in the cases of β-methoxypropionaldehyde and n-valeraldehyde made it clear that the aliphatic aldehyde having a longer alkyl group polymerizes with smaller changes of enthalpy and entropy and that the polar-substituted aldehydes have higher polymerizability than the corresponding unsubstituted aliphatic aldehydes in the temperature range studied. These effects of substituents are interpreted from the viewpoint of the intermolecular interactions of polar groups in monomers and their polymers.     

Determination of thermodynamic parameters for cloud point extraction of Arsenazo-III and Magdala Red dyes using mixed micelles: An essential requirement for high performance

A simple and low cost method for extraction and preconcentration of Arsenazo-III (ARS-III) and Magdala Red (MR) was developed by an efficient cloud point extraction (CPE) method using mixed micelles of Triton X–114 (TX–114) and cetyltrimethyl ammonium bromide (CTAB). Various parameters, such as pH/concentration of H₂SO₄, surfactant concentrations (TX-114 and CTAB), equilibrium temperature and time have been studied to maximise efficiency. Thermodynamic quantities like change in Gibbs free energy (ΔG⁰), change in enthalpy (ΔH⁰) and change in entropy (ΔS⁰) were calculated. The results show that the CPE of ARS-III and MR dye is feasible, spontaneous, and endothermic in the temperature range of (50–80) °C indicating good recoveries for the developed method. The effect of temperature, surfactant concentration and dye concentration on various thermodynamic quantities was investigated and it was found that ΔG⁰ values increased with temperature but decreased with surfactant and dye concentration. ΔH⁰ and ΔS⁰ values increased as surfactant concentration increased and decreased as dye concentration decreased. The recoveries were found to be the range from 90.02 – 101.03 % for ARS-III and 86.07–99.46 % for MR dyes which proves that the method is highly efficient.     

枯草杆菌α-淀粉酶在一些色谱体系中的热力学和超热力学研究

通过测定不同温度范围的热力学平衡常数、焓变、熵变、自由能变和补偿温度,研究了枯草杆菌α-淀粉酶在几种色谱介质上的热力学和超热力学。结果表明,在RP-C18反相介质、Zn2+螯合的Sepharose fast-flow亲和介质和WCX-1阳离子交换介质上,当温度分别在13-30和30-50℃范围时,它们的lnKSL分别随绝对温度的倒数线性变化;而在PEG-400和修饰的PEG-400疏水色谱介质上,当温度分别在13-40和13-30℃范围时,它们的lnKSL分别随绝对温度的倒数线性减小,但当温度分别高于40℃和30℃时,它们则随绝对温度的倒数剧烈减小。通过研究不同温度范围的焓变、熵变、自由能变和α-淀粉酶构象变化之间的关系,发现在RP-C18反相和Zn2+螯合的Sepharose fast-flow亲和介质上在30- 50 ℃温度范围内,在WCX-1阳离子交换介质上在13-30 ℃温度范围内,α-淀粉酶的吸附过程由焓变和熵变共同所支配,而在Zn2+螯合的Sepharose fast-flow亲和介质上在13- 30 ℃温度范围内,在WCX-1阳离子交换介质上在30-50 ℃温度范围和在PEG-400 和修饰的PEG-400疏水色谱介质上在13-65 ℃温度范围时,α-淀粉酶的吸附过程仅仅由熵变所控制。最后,通过α-淀粉酶在这些色谱体系中的补偿温度进一步发现,它们的焓变仅仅只能通过它们构象变化所引起的熵变所补偿。     

Removal of cationic methylene blue and malachite green dyes from aqueous solution by waste materials of Daucus carota

In present study adsorption capacity of waste materials of Daucus carota plant (carrot stem powder: CSP and carrot leaves powder: CLP) was explored for the removal of methylene blue (MB) malachite green (MG) dye from water. The morphology and functional groups present were investigated by scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. The operating variables studied were pH, adsorbent dose, ionic strength, initial dye concentration, contact time and temperature. Equilibrium data were analysed using Langmuir and Freundlich isotherm models and monolayer adsorption capacity of adsorbents were calculated. Kinetic data were studied using pseudo-first and pseudo-second order kinetic models and the mechanism of adsorption was described by intraparticle diffusion model.Various thermodynamic parameters such as enthalpy of adsorption ΔH°, free energy change ΔG° and entropy ΔS° were estimated. Negative value of ΔH° and negative values of ΔG° showed that the adsorption process was exothermic and spontaneous. Negative value of entropy ΔS° showed the decreased randomness at the solid–liquid interface during the adsorption of MB and MG onto CSP and CLP.     

Adsorption of Methylene Blue from Aqueous Solution on High Lime Fly Ash: Kinetic,Equilibrium, and Thermodynamic Studies

Kinetic, equilibrium, and thermodynamic studies were performed for the batch adsorption of methylene blue (MB) on the high lime fly ash as a low cost adsorbent material. The studied operating variables were adsorbent amount, contact time, dye concentration, and temperature. The kinetic data were analyzed using the pseudo-first order and pseudo-second order kinetic models and the adsorption kinetic was followed well by the pseudo-second order kinetic model. The equilibrium data were fitted with the Freundlich, Langmuir, and Dubinin Radushkevich (D–R) isotherms and the equilibrium data were found to be well represented by the Freundlich and D–R isotherms. Based on these two isotherms MB is taken by chemical ion exchange and active sites on the high lime fly ash have different affinities to MB molecules. Various thermodynamic parameters such as enthalpy of adsorption (ΔH°), free energy change (ΔG°), and entropy change (ΔS°) were investigated. The positive value of ΔH° and negative value of ΔG° indicate that the adsorption is endothermic and spontaneous. The positive value of ΔS° shows the increased randomness at the solid–liquid interface during the adsorption. A single-stage batch adsorber was also designed based on the Freundlich isotherm for the removal of MB by the high lime fly ash.     

High‐performance liquid chromatographic enantioseparation of isoxazoline‐fused 2‐aminocyclopentanecarboxylic acids on a chiral ligand‐exchange stationary phase

The application of a chiral ligand‐exchange column for the direct high‐performance liquid chromatographic enantioseparation of unusual β‐amino acids with a sodium N‐((R)‐2‐hydroxy‐1‐phenylethyl)‐N‐undecylaminoacetate‐Cu(II) complex as chiral selector is reported. The investigated amino acids were isoxazoline‐fused 2‐aminocyclopentanecarboxylic acid analogs. The chromatographic conditions were varied to achieve optimal separation. The effects of temperature were studied at constant mobile phase compositions in the temperature range 5–45°C, and thermodynamic parameters were calculated from plots of lnk or lnα versus 1/T. Δ(ΔH°) ranged from –2.3 to 2.2 kJ/mol, Δ(ΔS°) from –3.0 to 7.8 J mol^?1 K^?1 and –Δ(ΔG°) from 0.1 to 1.7 kJ/mol, and both enthalpy‐ and entropy‐controlled enantioseparations were observed. The latter was advantageous with regard to the shorter retention and greater selectivity at high temperature. Some mechanistic aspects of the chiral recognition process are discussed with respect to the structures of the analytes. The sequence of elution of the enantiomers was determined in all cases.     

Thermodynamics of binding of methyl orange and its homologs by poly(vinylpyrrolidone): The effect of inorganic electrolytes

The extent of binding of methyl orange, ethyl orange, propyl orange, and butyl orange by poly(vinylpyrrolidone) has been measured in aqueous solutions of inorganic electrolytes such as NaCl, LiCl, NaSCN, and NaClO₄ by an equilibrium dialysis method. The effect of the salts on the first binding constants and the thermodynamic functions which are accompanied by the dye—polymer association process was investigated relative to the corresponding values in the absence of such salts. It was found that in aqueous solutions of NaCl and LiCl the enthalpy change accompanying the binding is small and the largest contribution to the free energy of binding is from the positive entropy gain. For NaSCN and NaClO₄, the values of ΔF° and ΔH° were both large and negative and the value of ΔS° was small and negative. Thus, the favorable free energy for the complex formation was due entirely to the negative enthalpy term. These characteristics of the thermodynamic quantities are discussed in terms of changes in structural properties of water in the vicinity of the binding entities and conformational changes of the polymer to which the dye is bound due to the added foreign electrolytes.     

Kinetic of Patent Blue VF Adsorption from Aqueous Solution on Activated Bone Charcoal

The effect of temperature of activation on bone charcoal, used as adsorbent for the removal of Patent Blue VF from water solutions was studied. The adsorbent was characterized by FTIR, XRD, SEM and EDS. The kinetic of adsorption of dye was carried out at 10 °C and 45 °C. Carbonization temperature (600–1000 °C) of the adsorbent has significant effect on the removal of dye from water solutions. The first order kinetic, Elovich, Bangham, parabolic diffusion and power function equations were found to fit the kinetic data. Activation energies of adsorption (Δ≠) have higher values for the charcoal activated at high temperatures and the other thermodynamic parameters like ΔH≠, ΔS≠ and ΔG≠ were also found.     

1H NMR Study of Hindered Internal Rotation of Tetramethylthiuram Disulfide in Binary Dimethyl Sulfoxide‐Chloroform Mixtures

Hindered internal rotation about the C‐N single bonds joining the thiuram disulfide was studied by ¹H NMR complete line‐shaped analysis in different dimethyl sulfoxide‐chloroform (DMSO‐CDCl₃) mixtures. From the temperature dependence of methyls proton spectra, activation parameters (E_a, ΔH^≠, ΔS^≠, and ΔG^≠) were obtained. The Arrhenius plots showed a distinct isokinetic temperature at about 35 °C at which the exchange rate is more or less independent of the solvent composition. The resulting ΔH^≠ against TΔS^≠ plot showed a firmly good linear correlation, indicating the existence of an enthalpy‐entropy composition in an exchange process.     

A study of helix formation in polydimethysiloxane by Raman scattering

Depolarization ratios ρ of the Raman bands due to CH₃ stretching at 2907 cm^?1 and the Si? O skeletal mode at 491 cm^?1 have been measured in polydimethylsiloxane gum as a function of temperature from 100°C to ?45°C. Below 0°C the changes in p have been interpreted in terms of the formation of helical regions in the gum. The enthalpy of helix formation ΔH has been determined as 3200 ± 600 cal/mole. An upper limit on the entropy change, ΔS, of 16 ± 3 e.u./mole and minimum values of helix content at different temperatures have been found. The Raman spectrum of crystalline polydimethylsiloxane is presented.     

Cross-linked polyvinylpyrrolidones with increased affinity and specificity for methyl orange and its homologs

Polyvinylpyrrolidones of various degrees of cross-linkage have been prepared by radical polymerization of N-vinylpyrrolidone with methylenebisacrylamide to regulate the fraction of cross-linkage. The insoluble polymers obtained were examined for their ability to bind methyl orange and its homologs, methyl orange, ethyl orange, propyl orange, and butyl orange at 5, 15, 25, and 35°C, respectively, in an aqueous solution. The first binding constants and the thermodynamic parameters that accompanied the binding were calculated. For any particular dye the extent of binding, the absolute magnitude of ΔF°, and the value of ΔS° increased as the degree of cross-linkage increased, starting with water-soluble polyvinylpyrrolidone (zero cross-linkage) and proceeding to the polymer with high cross-linking density. This behavior can be accounted for in terms of more extensive hydrophobic domains in the cross-linked polymeric matrix that enhances hydrophobic interactions in the binding process. Moreover, the cross-linked macromolecule polymerized in the presence of methyl orange and then stripped of the bound methyl orange shows substantially stronger binding for this small molecule than the polymer cross-linked in the absence of methyl orange. In contrast, the cross-linked polymer prepared similarly in the presence of the larger molecule, butyl orange, exhibits decreased affinity toward the smaller consolute, methyl orange, than either of the other polymers described. It seems, therefore, that the polymeric matrix provides favorable binding sites or pockets that can accommodate a specific small molecule. The preparative procedure, which uses a small-molecule template, molds into the polymer some structural specificity in the binding of small molecules.     

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.     

Variable‐Temperature Infrared Spectroscopy Studies on the Thermodynamics of CO Adsorption on the Zeolite Ca–Y

Variable temperature FT–IR spectroscopy (in the range of 298–380 K) is used to study the thermodynamics of formation of Ca²⁺???CO carbonyl species upon CO adsorption on the faujasite‐type zeolite Ca–Y, and also the (temperature‐dependent) isomerization equilibrium between carbonyl and isocarbonyl (Ca²⁺???OC) species. The standard enthalpy and entropy changes involved in formation of the monocarbonyl species resulted to be ΔH⁰=?50.3 (±0.5) kJ mol^?1 and ΔS⁰=?186 (±5) J mol^?1 K^?1, respectively. Isomerization of the (C‐bonded) Ca²⁺???CO carbonyl to yield the (O‐bonded) Ca²⁺???OC isocarbonyl involves an enthalpy change =+11.4 (±1.0) kJ mol^?1. These results are compared with previously reported data for the CO/Sr–Y system; and also, a brief analysis of enthalpy–entropy correlation for CO adsorption on zeolites and metal oxides is given.     

Equilibrium anionic polymerization of β-methoxypropionaldehyde

Anionic polymerization of β-methoxypropionaldehyde (MPA) was carried out in tetrahydrofuran (THF) by using benzophenone–monolithium complex as an initiator. An equilibrium between polymerization and depolymerization was observed at a temperature range of ?90 to ?70°C. From the temperature dependence of the equilibrium monomer concentration, thermodynamic parameters for the polymerization of MPA in THF were evaluated as follows: ΔH_ss = ?4.8 ± 0.2 kcal/mole, ΔH_SS = ?22.4 ± 1.3 cal/mole-deg, and (T_c)_ss = ?59°C. The thermodynamic change upon the conversion of liquid monomer to condensed polymer was computed from both the partial mixing energy of MPA with THF and the linear relationship between the equilibrium volume fraction of MPA monomer and that of the resulting polymer: ΔH_1c = ?4.7 ± 0.2 kcal/mole, ΔS_1c = ?19.5 ± 1.3 cal/mole-deg, and (T_c)_1c = ?35°C.     

Structure and side-chain interactions in poly(δ-N-carbobenzoxy L-ornithine)

Two crystal modifications are found in α-helical poly(δ-N-carbobenzoxy L -ornithine). In films as cast, the two-dimensional unit cell is pseudohexagonal and contains two chains. This form transforms irreversibly into a pseudotetragonal form at about 140°C. A second-order transition associated with the onset of the side-chain motion is observed at about 30°C for the bulk sample (by dilatometry) and for the crystalline phase (by x-ray diffraction). The dielectric behavior of the side-chain dispersion suggests that the side chains interact with one another. The temperature dependence of the infrared absorbance due to the NH stretching vibration reveals that about half the side chains are associated via hydrogen bonds at room temperature and become dissociated at higher temperature. The enthalpy and the entropy of the hydrogen bond formation is estimated to be ΔH = ?5.0 ± 0.5 kcal mol^?1 and ΔS = ?15 ± 1 e.u. mol^?1.     

Spectroscopic and Isothermal Titration Calorimetry Studies of Binding Interactions Between Carbon Nanodots and Serum Albumins

Carbon nanodots (C-dots) have attracted great attention as a new class of luminescent nanomaterials. In order to better understand the basic behavior of C-dots in biological systems, the binding characteristics of C-dots with bovine serum albumin (BSA) and human serum albumin (HSA) were investigated using spectroscopic approaches and isothermal titration calorimetry at pH 7.4. We found that the intrinsic fluorescence of BSA and HSA was quenched by the C-dots with a dynamic quenching mode. It was proved that the C-dots had little influence on the conformation of BSA and HSA by their UV–vis and circular dichroism spectra. Some important thermodynamic parameters were calculated, and the positive values of ΔH° and ΔS° indicate that the binding process was endothermic, and that the interaction was driven by favorable entropy and unfavorable enthalpy. It also showed that the hydrophobic force played a major role in the binding process.