Values Of Equilibrium Constants Research Articles

Quantifying the reversibility of ATP hydrolysis in rabbit skeletal myosin subfragment 1 using a luciferase assay

BackgroundIt is known that the adenosine triphosphate (ATP) hydrolysis in a number of ATPases is reversible. Radioactive methods are standard in measuring ATPase reversibility. We used myosin as a well-studied model enzyme to develop a luciferase-based assay to quantify the reversibility of ATP hydrolysis. In myosin, ATP bound to the active site is hydrolyzed into adenosine diphosphate (ADP) and inorganic phosphate (Pi) and recombined back into ATP multiple times before products of hydrolysis are released. The reversibility of ATP hydrolysis by skeletal myosin was previously confirmed using radioactively labeled isotopes. Transient kinetics studies indicated that the ATP hydrolysis step is temperature-sensitive, with a dissociation equilibrium constant of 1.6 at 3 °C. Consequently, the association equilibrium constant at this temperature is 0.63. The goal of our work was two-fold, (a) to develop a luciferase-based assay to measure the equilibrium constant of enzymatic ATP hydrolysis, eliminating the need for radioactively labeled Pi, and (b) refine the value of the association equilibrium constant of the myosin ATPase hydrolysis step.MethodsIn this assay, a reaction mixture containing myosin and saturating levels of ADP and Pi was incubated to reach equilibrium, then the reaction was terminated, and the amount of ATP produced by myosin was quantified using the luciferase assay. The equilibrium constant of ATP hydrolysis was defined as the ratio of ATP to ADP bound to myosin.ResultsWe obtained a value of 0.78 ± 0.14 for the association equilibrium constant of ATP hydrolysis at 0 °C. 50 μM ADP bound to myosin is turned into 21.9 ± 3.0 μM ATP. Our result is in excellent agreement with the literature data, supporting the viability of the new methodology.DiscussionThis methodology allows a more accessible and safe option to measure ATP production and reversibility of ATPase enzymes. Standard laboratory equipment is utilized in the assay, and the number of steps in the developed assay is reduced significantly compared to the radioactive method.

Physiology-based pharmacokinetic model with relative transcriptomics to evaluate tissue distribution and receptor occupancy of anifrolumab.

Type I interferons contribute to the pathogenesis of several autoimmune disorders, including systemic lupus erythematosus (SLE), systemic sclerosis, cutaneous lupus erythematosus, and myositis. Anifrolumab is a monoclonal antibody that binds to subunit 1 of the type I interferon receptor (IFNAR1). Results of phase IIb and phase III trials led to the approval of intravenous anifrolumab 300 mg every 4 weeks (Q4W) alongside standard therapy in patients with moderate-to-severe SLE. Here, we built a population physiology-based pharmacokinetic (PBPK) model of anifrolumab by utilizing the physiochemical properties of anifrolumab, binding kinetics to the Fc gamma neonatal receptor, and target-mediated drug disposition properties. A novel relative transcriptomics approach was employed to determine IFNAR1 expression in tissues (blood, skin, gastrointestinal tract, lungs, and muscle) using mRNA abundances from bioinformatic databases. The IFNAR1 expression and PBPK model were validated by testing their ability to predict clinical pharmacokinetics over a large dose range from different clinical scenarios after subcutaneous and intravenous anifrolumab dosing. The validated PBPK model predicted high unbound local concentrations of anifrolumab in blood, skin, gastrointestinal tract, lungs, and muscle, which exceeded its IFNAR1 dissociation equilibrium constant values. The model also predicted high IFNAR1 occupancy with subcutaneous and intravenous anifrolumab dosing. The model predicted more sustained IFNAR1 occupancy ≥90% with subcutaneous anifrolumab 120 mg once-weekly dosing vs. intravenous 300 mg Q4W dosing. The results informed the dosing of phase III studies of anifrolumab in new indications and present a novel approach to PBPK modeling coupled with relative transcriptomics in simulating pharmacokinetics of therapeutic monoclonal antibodies.

Design and mediated hydrogen bonding strength of Poly(styrene-alt- N–(ethyl–4–hydroxyphenyl)maleimide) copolymer to enhance miscibility with hydrogen bonded acceptor homopolymers

In this study, the monomer N–(ethyl–4–hydroxyphenyl)maleimide (TyHPMI) was synthesized from tyramine and maleic anhydride. Subsequently, free radical copolymerization was used to prepare the poly(S–alt–TyHPMI) alternating copolymer by reacting TyHPMI with styrene. We confirmed the chemical structure using Fourier transform infrared (FTIR), 1H and 13C nuclear magnetic resonance (NMR). The sequence distribution of the poly(S–alt–TyHPMI) alternating copolymer was analyzed using mass–analyzed laser desorption ionization/time–of–flight (MALDI–TOF) mass spectrometry. Differential scanning calorimetry (DSC) measurements showed a single glass transition temperature (Tg) across various weight fractions of binary blended systems containing strong hydrogen–bonded acceptors, such as poly(S–alt–TyHPMI)/poly(4–vinyl pyridine) (P4VP) and poly(vinyl pyrrolidone) PVP, implying full miscibility. The Tg values predicted by kwei equation for the poly(S–alt–TyHPMI)/P4VP and poly(S–alt–TyHPMI)/PVP blends show a positive deviation from linearity. This deviation is due to the short alkyl chain reinforcing the addition of acidic TyHPMI units, which enhances intermolecular hydrogen bonding between the pyridyl or C=O groups and the OH units of the TyHPMI segment. As a result, FTIR spectral analyses indicate that the intermolecular hydrogen bonding between pyridyl and C=O groups is stronger in the poly(S–alt–TyHPMI) copolymer compared to the poly(S–alt–HPMI) copolymer. This is supported by the larger ratio of the inter/self-association equilibrium constant (KA/KB) value.

Combined steam and CO2 reforming of methane over Ni-based catalysts with spherical porous structure

Combined steam and dry reforming of methane (CSDRM) is expected to be promising when considered as a new alternative feedstock for F-T synthesis because it can produce high-quality syngas without carbon deposition. In this study, the support particle sizes were varied independently to assess their influence on the performance of the metallic Ni. The catalytic activity is most influenced by nickel particle size and distribution, and it has also been investigated for its significant role in the metal-support interaction. To perform CSDRM, the Ni-based catalyst was prepared by impregnation method on a spherical nano-silica support prepared by sol–gel method. The size of the spherical silica nanoparticles (40–300 nm) was controlled by varying the ethanol molar concentration; the spherical particles showed high performance on a uniform and evenly drawn support. In the 44 nm spherical silica catalyst, it was confirmed that the maximum dispersion increased to 21 % and the reducibility increased to 36 %. For stable synthesis gas production, various feed gas ratios (0.7:1.3:1.7) were established and the respective feed gas components (CH4, CO2 and steam) and reactions were investigated. Also, with the increase in the concentration of steam in the feed gas ratio, there was a significant increase in CO production. This trend was attributed to competing reactions occurring due to the side reactions (WGS↔RWGS; CO+H2O↔CO2 + H2) and was investigated with equilibrium constant values using thermodynamic equilibrium plot data. From the experimental results obtained, the catalyst showed high performance on a stable support and produced a stable H2/CO ratio of 2 for 100 h, without side reactions, at the feed gas ratio (CH4:CO2:H2O = 1:0.6:0.85).

Automated method for designing extractive dividing wall columns used to separate minimum azeotropic mixtures with a heavy entrainer

Despite that the extractive divided wall column (E-DWC), which is one of the best examples of process intensification, has already found an industrial application, its design remains a new area of research. None of the few studies that have been published in the literature present a method for designing an E-DWC. Therefore, the first and fully automated design method, for the separation of minimum boiling azeotropic mixtures with a heavy entrainer (class (1.0–1a)-m1) using an extractive dividing wall column, is developed in this work. The developed method is based on the values of the phase equilibrium constant along the sides of composition simplex, with the help of the composition profile properties in the infinitely sharp splits mode and difference point equations. The efficiency of this new design method was tested on the separation of two ternary azeotropic mixtures that belong to class 1.0–1a-m1. The results show that the column trajectories, along the E-DWC, obtained by the rigorous simulation are in very good agreement with those calculated by the new design method. These results prove the reliability and accuracy of the new method.

Potential of Dimethyl Sulfoxide Modified Kaolin and Cetyl Trimethylammonium Bromide as Amoxycillin Adsorben

The large use of amoxicillin allows this antibiotic to enter the environment in large quantities and cause pollution. The adsorption technique can be used as a method to remove amoxicillin contaminants in wastewater by utilizing kaolin as an adsorbent. This study aims to determine the characteristics of kaolin as an adsorbent and determine the ability of kaolin to adsorb amoxicillin. Kaolin was activated with hydrochloric acid and modified using Dimethyl sulfoxide (DMSO) and cetyl trimethylammonium bromide (CTAB). The results showed that the characteristics of DMSO and CTAB-modified kaolin showed a new peak which was an O-H bending vibration in functional group analysis using FTIR. X-ray diffraction results show that the distance between planes in the kaolin structure is larger. Meanwhile, the results of the SEM analysis showed that the surface morphology of kaolin had a higher level of crystallinity than before which proved an increase in the adsorption capacity of kaolin. The adsorption kinetics follows the Santosa kinetic equation model with an adsorption rate of 0.004 min-1 and an equilibrium constant value of 0.007 L.mol-1 . The adsorption isotherm test follows the Freundlich isotherm equation model with an adsorption constant value of 561.694 L.mg-1 and an empirical constant value of 0.270.

ТЕРМОДИНАМИКА КОМПЛЕКСООБРАЗОВАНИЯ И СТРУКТУРА КОМПЛЕКСОВ ЦИНКА(II) С ГИСТИДИНОМ И 2-МЕТИЛДИПИРИДОХИНОКСАЛИНОМ

The complex formation in the zinc(II) - 2-methyldipyrido-[3,2-f:2',3'-h]-quinoxaline (MeDPQ), zinc(II) - L-histidine (HisH) and zinc(II) - 2-methyldipyrido-[3,2-f:2',3'-h]-quinoxaline - L-histidine systems at 37.0 °C on the 0.15 mol dm-3 NaCl background has been investigated by the pH-potentiometry method. A total of 10 complex forms were characterized. Based on the analysis of the complex formation constants and DFT calculations at the B3LYP/TZVPP level, taking into account the solvent effect within the C-PCM model, the structures of Zn(MeDPQ)(HisH)2+, Zn(MeDPQ)(His)+, and Zn(MeDPQ)(His)(OH) complexes were modeled. The higher stability of the homoligand complexes Zn(His)+, Zn(HisH)(His)+, Zn(His)2 and extra-stabilization in the formation constants of the heteroligand complexes Zn(MeDPQ)(HisH)2+ and Zn(MeDPQ)(His)+ were discovered, which was confirmed by the DFT calculations. Higher values of equilibrium constants of the mentioned homoligand forms are explained by coordination to the central nitrogen atom of the imidazole fragment of histidine. Extra-stabilization of heteroligand forms occurs due to d-π-interaction with electron density transfer from π-donor orbitals of oxygen atoms of the carboxy groups of amino acids through the central ion to π-acceptor orbitals of MeDPQ. It is emphasized that the studied zinc(II) complexes, both in binary and ternary systems, can have high biological activity, in particular, due to the nucleophilic attack of the coordinated hydroxide anion on proteins and other biomaterials. This opens up the prospect of using such zinc(II) complexes in medicine. In particular, the studied complexes may exhibit anticancer activity.

Kinetics, equilibrium, and computational study on the monomerization reaction of {CH3ReVO(pdt)}2 dimer with monodentate ligands

The monomerization reaction of {MeReO(pdt)}2 dimer (the pdt is 1,3-propanedithiolate) with monodentate ligand has been studied experimentally:{MeReO(pdt)} + 2 L ⇌ 2 MeReO(pdt)L and L is a monodentate ligand presented in Figure 1. No monomerization reaction have been observed with the indazole and diphenyl sulfides, and 2-methylpyridne. For the 2-methylpyridne case, the no reaction was observed because of the steric effect of the methyl group at the ortho position prevent the nitrogen from coordination. But the phosphines and pyridines derivatives monomerize the dimer. The rate law is given by ν = (ka[L] + kb [L]2) {MeReO(pdt)2} for ligands 1 to 4 in Table 1 and the rate law is ν = kb [L]2 {MeReO(pdt)2} for ligands 6 to 8 in Table 1. The equilibrium constant of the same reaction has been also evaluated. The rate constant (k) and the equilibrium constant (Keq) values correlate well with the basicity of the ligand. The reaction constant (ρ) is -4.9 and -1.3 for pyridine and phosphine, respectively, obtained from Hammett correlation with σ. The computational study on I1 and I2 intermediates (Scheme 3) shows that these intermediates are not plausible intermediates as previously proposed1, 2. These results are attributed to the high angle strain on the bridging sulfur that prevent the formation of the I1 and I2 intermediates and the reaction proceed through different intermediates (I3 and Ia Scheme 4). Therefore, the proposed mechanism is modified to accommodate the computational results.

N‐(4‐Chloromethylbenzyl)‐N, N‐dimethyldodecan‐1‐aminium Chloride: A Quaternary Ammonium Surfactant as Corrosion Inhibitor

AbstractThis study used a quaternary surfactant, N‐(4‐Chloromethylbenzyl)‐N, N‐dimethyldodecan‐1‐aminium chloride (CMBDAC), as an excellent corrosion inhibitor of C1018 carbon steel (C1018 CS) in harsh 15 % HCl acidizing condition. CMBDAC was synthesized with an excellent yield and characterized by NMR, FTIR, and TGA. Gravimetric weight loss (WL), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) studies were employed to measure the efficacy of CMBDAC. At a relatively low concentration of 15 ppm, CMBDAC surpassed 90 % inhibition efficiency, with a maximum inhibition efficiency of 99.25 % being reached just for 50 ppm of CMBDAC. The inhibitor showed an efficacy of 96.16 % even at a temperature of 60 °C via the WL technique, showing potential to be used as a high‐temperature corrosion inhibitor. The adsorption isotherm study revealed that CMBDAC followed Langmuir adsorption isotherm. The Gibbs free energy of adsorption ( was calculated to be −40.43 kJ mol−1, indicating that CMBDAC was adsorbed via chemisorption. A very high value (1.68×105 L mol−1) of equilibrium constant ( ) suggested very strong adsorption of the inhibitor. PDP study disclosed that CMBDAC acted as a mixed‐type inhibitor. SEM‐EDX study demonstrated the adsorption of CMBDAC on the C1018 surface. Different DFT‐optimized parameters have been discussed in detail to support the superb inhibitory action indicated by CMBDAC.

Modeling, optimization and comparative study on abatement of fluoride from synthetic solution using activated laterite soil and fly ash

The supply of potable water by proper treatment of fluoride laden ground water is a challenging task. Batch experiments were executed with activated laterite soil and fly ash individually for removal of fluoride. The process parameters such as particle size (100–620 μm), dose of adsorbent (10–60 g/L), initial concentration of fluoride (2–12 mg/L), agitation speed (20–120 rpm), contact time (0.5–10 h) and pH (4.5–9.5) were investigated and it was observed that activated laterite soil had better fluoride removal efficiency than fly ash. At pH 4.5, contact time 10 h, particle size 100 μm, adsorbent dose 60 g/L, initial concentration of fluoride 12 mg/L, and agitation speed 120 rpm, maximum removal efficiencies of fluoride using activated laterite soil and fly ash were found as 85.91 ± 0.62% and 77.1 ± 0.39%, respectively. Kinetic study was performed and Pseudo 2nd order kinetic model was found to fit the kinetic data best. The Freundlich isotherm model fit the equilibrium data fairly well. The values of adsorption equilibrium constant as used in Freundlich isotherm model vis-à-vis adsorption capacity (KF) for activated laterite soil and fly ash were obtained as 0.1331 and 0.0772 ((mgg−1)(Lmg−1)1/n). A thermodynamic analysis was conducted to examine the process behaviour. In order to determine whether the adsorbent may be used for further cases, regeneration of the adsorbents was also done. Generally, two types of adsorption mechanisms happen like electrostatic attraction and ion exchange. The electrostatic force of attraction favours the adsorption of negatively charged fluoride ions on positively charged adsorbent surfaces. In ion exchange, fluoride ions are exchanged by hydroxyl and hydronium ion. Based on experimental data, Multi-Gene Genetic Programming (MGGP) model could accurately predict the removal efficiency of fluoride under various operating situations. Finally, using Genetic Algorithm (GA) optimization the maximum output values for both adsorbents were estimated as 99.14% and 99.02%.

A novel role of the fission yeast sulfiredoxin Srx1 in heme acquisition.

The transporter Str3 promotes heme import in Schizosaccharomyces pombe cells that lack the heme receptor Shu1 and are deficient in heme biosynthesis. Under microaerobic conditions, the peroxiredoxin Tpx1 acts as a heme scavenger within the Str3-dependent pathway. Here, we show that Srx1, a sulfiredoxin known to interact with Tpx1, is essential for optimal growth in the presence of hemin. The expression of Srx1 is induced in response to low iron and repressed under iron repletion. Coimmunoprecipitation and bimolecular fluorescence complementation experiments show that Srx1 interacts with Str3. Although the interaction between Srx1 and Str3 is weakened, it is still observed in tpx1Δ mutant cells or when Str3 is coexpressed with a mutant form of Srx1 (mutD) that cannot bind Tpx1. Further analysis by absorbance spectroscopy and hemin-agarose pull-down assays confirms the binding of Srx1 to hemin, with an equilibrium constant value of 2.56 μM. To validate the Srx1-hemin association, we utilize a Srx1 mutant (mutH) that fails to interact with hemin. Notably, when Srx1 binds to hemin, it partially shields hemin from degradation caused by hydrogen peroxide. Collectively, these findings elucidate an additional function of the sulfiredoxin Srx1, beyond its conventional role in oxidative stress defense.

Mechanistic and kinetic aspects of Natamycin interaction with serum albumin using spectroscopic and molecular docking methods

Natamycin (NT) is a polyene natural antimycotic, which has an antimicrobial effect against yeasts and molds and is used as a preservative in the food industry. In the present study, we evaluated NT interaction with bovine serum albumin (BSA) through surface plasmon resonance (SPR) and several spectroscopic techniques, which are accompanied by a molecular docking study. According to the results, the intensity of BSA fluorescence decreased by adding different concentrations of NT. The fluorescence quenching results showed that NT reduces the intensity of BSA fluorescence by forming a complex with BSA through a hybrid quenching. Binding constant decreases from 18.73 to 2.13 (102 M−1) with increasing temperature, which indicates a decrease in complex formation owing to the interaction of NT with BSA. Negative values of ΔH° and ΔS° confirmed that van der Waals forces and hydrogen bonds are the basic forces in the interaction of NT with BSA. Moreover, increasing the equilibrium constants values with increasing temperature indicated that BSA binding to NT decreased. Finally, BSA interaction occurring with NT through Ser 109, Asp 111, Lys 114, Leu 115, Glu 424, and Arg 458 have been verified via molecular docking analysis. Attained results via SPR and fluorimetry showed that the binding constant between BSA and NT decreased when the temperature was raised.

Thermodynamic properties of aqueous lanthanum sulfate solutions taking into account the association

Thermodynamic properties (the mean activity coefficients, γ±, and the relative apparent molar enthalpies, φL) of lanthanum sulfate aqueous solutions, strongly deviating from the Debye-Hückel limiting law even at lowest experimentally accessible concentrations, can easily and quantitatively be reproduced assuming the formation of two sulfate complexes, LaSO4+ and LaSO42-, whose existence was established in numerous complex formation studies. The analysis was carried out using a simple SIT model for the activity coefficients of ions with only the electrostatic Debye-Hückel terms. Excellent agreement between measured values of γ± and φL and the values of equilibrium constants was obtained by using the following values of equilibrium constants and enthalpy changes of reactions of formation of LaSO4+ (La3++SO42-⇄ LaSO4+) and La(SO4)2- (La3++2SO42-⇄ La(SO4)2-): log10K1o = 3.65 ± 0.05; log10K2o = 5.63 ± 0.2, ΔrH1o = 17.6 ± 1.0 kJ mol−1; ΔrH20 = 28.1 ± 4.0 kJ mol−1. The agreement with literature data is excellent for log10K1o and ΔrH1o and satisfactory for log10K2o and ΔrH2o. With these log10K1o, log10K2o, ΔrH1o and ΔrH2o results the experimental γ± and φL values are reproduced quantitatively.

Enthalpy of formation and hydrogen bonded dimerization of furfurylamine: Experimental and computational study

The combustion energy and standard molar enthalpy of formation of liquid furfurylamine were determined using an isoperibol calorimeter with a static bomb. The theoretical calculations were used for the interpretation of experimental calorimetric result. The DLPNO-CCSD(T1)/CBS method in conjunction with isodesmic-type reactions was used to calculate the gas-phase enthalpy of formation of this compound. At the same level of theory, the interconversion of the gauche and anti conformers of furfurylamine and the N–H⋯N hydrogen bonding between them leading to the association into dimeric units were studied. The calculated values of equilibrium and rate constants for reaction gauche → anti and enthalpy of dimerization of two conformers suggest that the gaseous furfurylamine exists predominantly in the dimeric form. An additional support for the strong association of furfurylamine in the vapor phase was obtained from comparison of the enthalpies of formation in liquid and gaseous states: the consistency between these two values was achieved only when a correction for dimerization was applied.

Recommendations for performing measurements of apparent equilibrium constants of enzyme-catalyzed reactions and for reporting the results of these measurements.

The measurement of values of apparent equilibrium constants K' for enzyme-catalyzed reactions involve a substantial number of critical details, neglect of which could lead to systematic errors. Here, interferences, impurities in the substances used, and failure to achieve equilibrium are matters of substantial consequence. Careful reporting of results is of great importance if the results are to have archival value. Thus, attention must be paid to the identification of the substances, specification of the reaction(s), the conditions of reaction, the definition of the equilibrium constant(s) and standard states, the use of standard nomenclature, symbols, and units, and uncertainties. This document contains a general discussion of various aspects of these equilibrium measurements as well as STRENDA (Standards for Reporting Enzymology Data) recommendations regarding the measurements and the reporting of results.

Extent of Inhibition of Malonic Acid on the Fermentation of Soursop Juice: A Thermodynamic Evaluation

The fermentation of soursop juice as substrate by Saccharomyces cerevisiae (yeast) was investigated to obtain certain useful thermodynamic parameters. This was achieved by the determination of the effects of temperature, substrate and inhibitor on the rate of carbon (IV) oxide (CO2) production. The extent of inhibition was examined by the addition of malonic acid inhibitor. The results indicate that the rate of fermentation of soursop juice increased in proportion with temperature (optimum 36oC), substrate (optimum 50%v/v) and malonic acid (optimum 30%v/v) up to a limit and decreased. This suggests that the reaction takes place in two steps (equilibrium and decomposition steps). The thermodynamic parameters determined are: enthalpy, ∆H* 151.14 kJmol-1; entropy of activation, ∆S* 275.359 Jmol-1k-1; Gibb’s free energy of activation, ∆G* -752.21 kJmol-1 and Equilibrium constant Keq, 1.33 respectively. The results show that the enthalpy value is positive indicating that the fermentation process is endothermic while the activation energy is same as the enthalpy. The entropy value is positive corroborating the positive enthalpy value. The fermentation process is spontaneous as shown by the negative change in free energy. These values were subsequently used to obtain by calculation Arrhenius constant A, 1.51x1023; orientation factor P, 1.41x10-34 and the collision frequency, Z, 1.07x1011 respectively. The calculated A and the P values obtained on the basis of collision theory and absolute reaction rate theory (or transition state theory), respectively show that the collision factor is of the order of 1011 min-1, about half that of gaseous molecules that can only be attained by an induced reduction in activation energy by a catalyst. The equilibrium constant value K suggests that the intermediate complex is rather interacting more with the substrate and also showing that only a limited amount of the substrate is converted to product. The equilibrium constant K is observed to be 1.33dm3mol-1 and not significantly far from unity implying that G* can be conveniently equated with the change in free energy at standard conditions. Finally, the type of inhibition was found to be uncompetitive from the extrapolated Lineweaver-Burk plots and did not bring about marked decrease in the rate of fermentation as expected.

Co-Pigmentation Mechanism and Thermal Reaction Kinetics of Mulberry Anthocyanins with Different Phenolic Acids.

Applying the intermolecular co-pigmentation to improve the stability of mulberry anthocyanins is an important co-pigment method. Seven co-pigments, ferulic acid (FA), caffeic acid (CA), p-hydroxybenzoic acid (HBA), protocatechuic acid (PA), gallic acid (GA), vanillic acid (VA) and vanillin (VN) were selected to investigate mulberry anthocyanin co-pigmentation thermal reaction kinetics. The strongest co-pigment reactions were observed for FA at a molar ratio of 1:20, pH 3.5 and 20 °C, with the highest hyperchromic effects (52.94%), equilibrium constant (K) values (3.51) and negative values of Gibbs free energy (ΔG°) (-3.06 KJ/mol). Co-pigments that contained more free hydroxyl groups facilitated the co-pigmentation, and methyl contributed more to color enhancement, with respect to the hydrogen group. Ultra Performance Liquid Chromatography-Quadrupole-Time Of Flight-Mass/Mass Spectrometry (UPLC-Q-TOF-MS/MS) results indicated that FA and CA formed different anthocyanin derivatives with mulberry anthocyanin. The Fourier Transform Infrared Spectroscopy (FTIR) and molecular docking confirmed that hydrogen bonding, π-π stacking and hydrophobic interaction were formed between anthocyanins and three prevalent co-pigments (FA, CA and VA). CA and C3G could form four hydrogen bonds and two π-π stackings; this was the most stable system among three phenolic acid-C3G complexes. Due to the functional effect of phenolic acids, the addition of FA and CA not only enhanced the stability and color intensity of mulberry anthocyanins but also the functionality of the processing product.

Applications of spectroscopic techniques to the study of monomer–dimer equilibria for methylene blue in aqueous solutions containing ionic liquid: Probing the structural interactions involving water and ionic liquids

An understanding of the nature of interaction and bonding in dye aggregation process is important for such diverse problems and applications such as stacking interactions in biomolecules, staining properties, photodynamic therapy for cancer, energy transfer in lasing technology and energy transfer and electron transfer processes. In present communication we report visible absorption spectrums and their analysis for the dye methylene blue (MB) in concentration range of 1∙10–6 – 1∙10–4 M in aqueous solutions containing ionic liquids namely, 1–ethyl–3–methyl–imidazolium bromide, 1–butyl–3–methyl–imidazolium bromide and 1–hexyl–3–methyl–imidazolium bromide at 298 ± 1. In this concentration range of MB only Monomer ⇌ Dimer equilibria for the dye exist and hence the spectral characteristics in the visible range of 550–700 nm have been examined. The spectrums obtained are compared with those obtained in aqueous solutions of NaCl. Using suitable developed method of estimating molar absorption extinction coefficient values, the equilibrium constant values are obtained at various ionic strengths of imidazolium ions. It has been found that monomer and dimer absorption maximum occur at 665 and ≈605/610 nm, respectively, do not get much altered on addition of imidazolium ions. The extent of interaction between the MB and imidazolium cations varies with the concentration of imidazolium cations as well as the nature of imidazolium cations, that is, the chain length of the substituents. The dimer dissociation constant values extrapolated to zero ionic strength of ionic liquids exhibit systematic alteration with respect to alteration of chain length in imidazolium cations. The different interactional phenomena such as the formation of ion–pairs, ion–pair complexes, dimer dissociation, solubilization of monomers and binding of MB with imidazolium cations have been examined. The transfer standard free energy changes have been calculated for the transfer of dimers from aqueous solutions to aqueous solutions containing ionic liquids. The changes in dimer geometry from sandwich type and end–on–end types also have been studied. It is observed that the contribution to the interaction energy is mainly from van der Waals type and dispersion forces, in addition to short range forces involving multipoles. The binding of monomers with imidazolium cations is also examined in terms of formation of micellar type aggregates in solution phase. It is proposed that the water structural interaction and hydrophobic interactions are the major factors in the formation and dissociation of aggregates.

Optimization of Arsenic Removal from Aqueous Solutions Using Amidoxime Resin Hosted by Mesoporous Silica.

The paper reports on the performances of cross-linked amidoxime hosted into mesoporous silica (AMOX) in the removal of As(III) and As(V). The optimum pH for sorption of As(III) and As(V) was pH 8 and pH 5, respectively. The PFO kinetic model and the Sips isotherm fitted the best the experimental data. The thermodynamic parameters were evaluated using the equilibrium constant values given by the Sips isotherm at different temperatures and found that the adsorption process of As(III) and As(V) was spontaneous and endothermic on all AMOX sorbents. The spent AMOX sorbents could be easily regenerated with 0.2 mol/L HCl solution and reused up to five sorption/desorption cycles with an average decrease of the adsorption capacity of 18%. The adverse effect of the co-existing inorganic anions on the adsorption of As(III) and As(V) onto the sorbent with the highest sorption capacity (AMOX3) was arranged in the following order: H2PO4– > HCO3– > NO3– > SO42–.

Probing the Interactions of Lamotrigine and Phenobarbital with Tau Protein: Experimental and Molecular Modeling Studies.

Tau, as a small protein in neurons, plays a main role in stabilizing and assembling the internal microtubules. Here, the effects of antiepileptic drugs, including lamotrigine (LTG) and phenobarbital (PHB), on tau protein structure have been investigated by surface plasmon resonance (SPR), fluorescence spectroscopy along molecular modeling. Fluorescence data analysis revealed that both drugs quench the intrinsic emission intensity of tau protein via a static quenching mechanism. Analysis of SPR data at three different temperatures revealed that binding of LTG and PHB to tau protein leads to a decrease and increase in equilibrium constants (KD) values with increasing temperature, respectively. Therefore, the affinity of LTG decreases and PHB increases with increasing temperature. In addition, molecular docking studies indicated that both LTG and PHB bind to the S1 pocket of tau protein. Our data demonstrated the preventive effect of two important antiepileptic pharmaceuticals on the aggregation of tau protein. Given that any damage to the tau protein possibly leads to neurodegenerative diseases, this study can provide useful and important information and a basis for further research and study to treat tauopathy.