Potassium Adsorption Phenomenon in Calcareous Soils of Shahrazur Plain

A laboratory study for adsorption of potassium (K) determination was conducted on six soils located in Sharazur plain from the Kurdistan Region of Iraq in 2021 using the batch technique method. Potassium (K) adsorption isotherms were achieved by equilibrating 5.0 g of soil samples with eight grades of K (0 to 300 mg L-1) as KCl in 50 ml of 0.01M CaCl2 solution. To match the data of adsorption, Freundlich, Langmuir, and Temkin adsorption isotherms were used. The results show that the amount of adsorbed K ranged between (45.78 to 52.49) % added K. The Freundlich model fit the equilibrium K adsorption data better for the Serwan location of soil (silty loam), as demonstrated by a greater coefficient of determination (R2 =0.90). The value of heterogeneity factor 1/n for the Freundlich model ranged from (0.34 to 0.47) kg mg-1, which was less than one. The sorption processes for all of the studied soils were normal adsorption. The constant of the Langmuir isotherm (KL) aligned from (0.107 to o.425) L mg-1. Smaller KL values mean that more adsorbed K would be transformed to a non-exchangeable form, either through the creation of crystalline K or through ion occultation. The RL values indicate the type of isotherm, the values of RL> 1 that means the adsorption nature to be unfavorable. The Temkin equilibrium binding constant (AT) was high for all studied soils except the soils of Bestan Sur and Grdigo locations, the high value of AT indicates high binding energy. The Temkin constant (bT) ranged from (10.46 to 13.47) J mole-1 that was related to the nature of the adsorption energy, a positive value indicates that the adsorption process is exothermic.

Applying support-vector machine learning algorithms toward predicting host–guest interactions with cucurbit[7]uril

We evaluate the ability of support-vector machines to predict the equilibrium binding constant of small molecules to cucurbit[7]uril.

Imprinted CS Membrane Using EGCG as Template

A molecularly imprinted membrane was prepared in aqueous media using CS as functional monomer, EGCG as template molecules. The morphologies of molecularly imprinted membrane before and after modification with porogen (PEG) were observed by SEM. The imprinted membrane showed an excellent performance after several times adsorption and desorption. According to Scatchard analysis, the result showed that the imprinted membrane had a binding site for EGCG, the max adsorption capacity of imprinted membrane and equilibrium binding constant arrived at 49.52 mg/g, 4.046, respectively

Study on the Disaggregation of Photosensitizer Pentalysine β-Carbonyl-Phthalocyanine Zinc In Vitro

A novel photosensitizer, pentalysine β-carbonyl-phthalocyanine zinc [ZnPc-(Lys)5] has tendency to form aggregate in aqueous solution. The observed in vivo Photodynamic therapy (PDT) effect of ZnPc-(Lys)5suggests a disaggregation mechanism. In this study, the equilibrium binding constant Ka, the numbers of binding sites n and the distance of Forster radii r between ZnPc-(Lys)5and human serum albumin (HSA) are measured by Spectroscopy. A molecular model of HSA-ZnPc-(Lys)5complex was generated according to these datum. This molecular model provides rationale that the molecular interaction between HSA and ZnPc-(Lys)5facilitates the dissociation of ZnPc aggregates.

Thermal Management Design of a Nanoscale Biocalorimeter

A nanoscale calorimeter design based on temperature induced changes in a surface plasmon based photonics effect has the potential to decrease the mass of experimental compounds consumed and to increase the throughput of experiments investigating drug development. This calorimeter is based on a demonstrated surface plasmon biosensor in which index of refraction changes as small as 10−5 % caused by biochemical reactions on the sensor surface are detected. To achieve this sensitivity require that the device’s temperature be held constant to within ± 0.001 K. In the biosensor the temperature was held constant to measure the concentration changes. For the calorimeter the concentration is held constant and temperature changes are monitored. In the calorimeter design the nanohole array sensor will be used as a sensitive thermometer that will be used to determine the enthalpy of binding, equilibrium binding constant and entropy changes of biochemical reactions. The numerical analysis described in this work demonstrates that nanoscale calorimetry is possible. The simulations demonstrate that two designs can produce temperature rises of 5.5 and 40 C, respectively well above the (10−3) C resolution of the sensors. These results were obtained using less than three orders of magnitude less reactants than is currently being used in calorimetry studies which is a significant advance of this technology.

Binding of glutathione and an inhibitor to microsomal glutathione transferase

Microsomal glutathione transferase is an abundant liver protein that can be activated by thiol reagents. It is not known whether the activation is associated with changed binding properties of the enzyme. Therefore the binding of GSH and an inhibitor to rat liver microsomal glutathione transferase was studied by use of equilibrium dialysis and equilibrium partition in a two-phase system. The radioactive substrate glutathione and an inhibitor (glutathione sulphonate) give hyperbolic binding isotherms with a stoichiometry of 1 mol per mol of enzyme (i.e. 1 molecule per homotrimer). Glutathione had an equilibrium binding constant of 18 μM. Competition experiments involving glutathione sulphonate showed that it could effectively displace GSH. These and kinetic studies showed that the Kd and Ki for glutathione sulphonic acid are close to 10 μM. No change in these parameters was obtained after N-ethylmaleimide activation of the enzyme. Thus activation does not result from changes in binding affinity to GSH.

The linkage between binding of the C-terminal domain of hirudin and amidase activity in human α-thrombin

A method derived from the analysis of viscosity effects on the hydrolysis of the amide substrates D-phenylalanylpipecolyl-arginine-p-nitroaniline, tosylglycylprolylarginine-p-nitroanaline and cyclohexylglycylalanylarginine-p-nitroalanine by human alpha-thrombin was developed to dissect the Michaelis-Menten parameters Km and kcat into the individual rate constants of the binding, acylation and deacylation reactions. This method was used to analyse the effect of the C-terminal hirudin (residues 54-65) [hir-(54-65)] domain on the binding and hydrolysis of the three substrates. The results showed that the C-terminal hir-(54-65) fragment affects only the acylation rate, which is increased approx. 1.2-fold for all the substrates. Analysis of the dependence of acylation rate constants on hirudin-fragment concentration, allowed the determination of the equilibrium binding constant of C-terminal hir-(54-65) (Kd approximately 0.7 microM). In addition this peptide was found to competitively inhibit thrombin-fibrinogen interaction with a Ki which is in excellent agreement with the equilibrium constant derived from viscosity experiments. These results demonstrate that binding of hir-(54-65) to the fibrinogen recognition site of thrombin does not affect the equilibrium binding of amide substrates, but induces only a small increase in the acylation rate of the hydrolysis reaction.

Photochemical and ligand-exchange properties of the cyanide complex of fully reduced cytochrome c oxidase

Cytochrome oxidase, in its fully reduced state, forms a complex with CN having a Kd of 230 microM with a stoicheiometry of 1 CN molecule per cytochrome oxidase. We do not detect a second CN-binding site as seen by i.r. spectroscopy [Yoshikawa & Caughey (1990) J. Biol. Chem. 265, 7945-7958]. The ferrocytochrome a3-CN complex, like the analogous ferrocytochrome a3-CO complex, is photosensitive but with a 15-fold lower quantum yield for photolysis. Analysis of the recombination kinetics after CN photolysis establishes a simple bimolecular binding constant of 235 M-1.s-1, in agreement with the value obtained from stopped-flow studies [Antonini, Brunori, Greenwood, Malmström & Rotillo (1971) Eur. J. Biochem. 23, 396-400]. A rate of 0.07 s-1 for the first-order dissociation of CN from cytochrome a3 is found by the rate of exchange of CO with ferrocytochrome a3-CN, and is consistent with the value calculated from the equilibrium binding constant and the CN on rate. However, O2 is able to oxidize the fully reduced CN compound at a rate well in excess of the CN off rate. The product of this oxidation reaction is a partially reduced CN complex. This implies that O2 either promotes CN dissociation or is able to oxidize the CN-bound enzyme directly. These results are discussed in the context of the structure and dynamics of the ligand-binding site of cytochrome oxidase.