Stability Constants For Binding Research Articles

Encapsulation of hyperoside with acyclic cucurbiturils: Supramolecular binding behavior, water solubility and in vitro antioxidant activity

Hyperoside (Hyp) is a natural flavonol glycoside widely present in plants, which possesses important pharmacological activities including anti-inflammatory, anti-viral, organ-protection, antioxidant, and anti-tumor, etc. However, its poor water solubility and low oral bioavailability severely limit its further development for pharmaceutical uses. In this work, solid inclusion complexes of Hyp with two acyclic cucurbiturils (ACBs, M1 and M2) were prepared by the method of suspension. The formation of inclusion complexes was confirmed by Fourier transform infrared (FT-IR), powder X-ray diffraction (PXRD) and nuclear magnetic resonance (NMR) analyses. Based on Job's plot, proton nuclear magnetic resonance (1H NMR) spectroscopy, two-dimensional diffusion ordered spectroscopy (2D-DOSY), two-dimensional rotating-frame Overhauser enhancement spectroscopy (2D-ROESY) and molecular docking experiments, a 1:1 inclusion mode was rationally proposed. The binding stability constants (Ks) were determined by fluorescence titration, up to 4.22 × 104 and 6.97 × 104 L·mol-1 for Hyp/M1 and Hyp/M2, respectively. After inclusion complexation with ACDs, the water solubility of Hyp was elevated by more than 300-fold, which was much superior to that with cyclodextrins. Furthermore, in vitro antioxidant activity of Hyp was significantly promoted by formation of inclusion complexes. These results would inspire new strategies for further developments of Hyp for pharmaceutical uses.

Binding behavior and in vitro cytotoxicity of inclusion complexes between aminopterin and cucurbit[7]uril

Aminopterin (AMT) is a kind of universal antineoplastic drugs, but it has severe toxic and side effects, leaving it rarely used in clinic. Herein, we found that cucurbit[7]uril (CB[7]) and AMT can form stable inclusion complexes, and the formation of CB[7]-AMT 2:1 supramolecular inclusion complex was confirmed by UV-visible absorption spectra, fluorescence spectra, 1H NMR, and molecular modeling calculations in aqueous solution. Binding stability constants (Ks) were determined by UV-visible and fluorescence spectra method, with 3.88 × 1010 L2 mol–2 and 5.24 × 1010 L2 mol–2, respectively. The binding energy was calculated to be 102.6 kcal mol–1 for the CB[7]-AMT complex. And then, through a series of cell experiments of CCK8 assay, DAPI staining and hoechst33342/PI double staining, we fully proved that the CB[7]-AMT complex can reduce the toxicity of AMT to normal cells such as hepatocyte line LO2, and improve its anticancer effect on cancer cells overexpressing spermine, typically like human colon cancer cell line HCT116. It confirmed that the CB[7]-AMT complex had the effect of reducing toxicity and increasing efficiency. These results indicated that CB[7]-AMT inclusion complex might be a promising novel formulation of AMT for its clinical development.

Binding behavior, water solubility and in vitro cytotoxicity of inclusion complexes between ursolic acid and amino-appended β-cyclodextrins

Ursolic acid (UA) is a pentacyclic triterpenoid of naturally abundance with a broad spectrum of important biological activities and low toxicity. However, potential applications in pharmaceutical industry are severely hampered by its poor water solubility, which leads to low bioavailability. Herein, we harness the unique and superior inclusion capability of a series of amino-appended β-cyclodextrins (ACDs) to prepare solid inclusion complexes of UA/ACDs. These inclusion complexes were characterized in their solid state by scanning electron microscope (SEM), differential scanning calorimetry (DSC), thermogravimetric (TG) and powder X-ray diffraction (XRD) analyses. Furthermore, their supramolecular binding behavior in aqueous solution was investigated by one-dimensional (1D)- and two-dimensional (2D)-nuclear magnetic resonance (NMR) spectroscopic experiments and NMR-based phase solubility analysis. Binding stability constants (Ks) were determined (1799, 1410, 889 and 993 L mol−1 for UA/a0, UA/a1, UA/a2 and UA/a3, respectively), and dynamic bimodal inclusion modes with a 1:1 inclusion stoichiometry for UA/ACDs systems were proposed. Water solubility of UA is dramatically promoted by more than 200-fold after formation of inclusion complexes. In vitro cytotoxicity of UA achieves significant elevation against human cancer cell lines HepG2, HT-29 and HCT116 by inclusion complexation from MTT assay, while these inclusion complexes show no cytotoxicity against human normal cell line LO2, which confirms their safety. These results would benefit to the further development of liquid formulation of UA for pharmaceutical uses.

Inclusion complexes between chrysin and amino-appended β-cyclodextrins (ACDs): Binding behavior, water solubility, in vitro antioxidant activity and cytotoxicity.

Solid inclusion complexes between chrysin and four amino-appended β-cyclodextrins (ACDs) were prepared by suspension method and characterized in solid and solution states by kinds of analytical methods. The scanning electron microscopy (SEM) showed distinct micro-morphologies of them. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis revealed their unique thermal properties, such as decomposition temperatures and endothermic points. Powder X-ray diffractometry (XRD) analysis disclosed their unique crystal patterns. Their nuclear magnetic resonance (NMR) analyses provided the variations of chemical shifts before and after the formation of inclusion complexes. Their binding stability constants (Ks) were 574, 842, 704, and 474 L·mol-1, respectively, as determined by spectral titration. A 1:1 inclusion mode with self-assembly of their amino side chains inside the ACD cavity was proposed based on Job plot and 2D-ROESY experiments. Water solubility of chrysin was promoted up to 4411.98 μg·mL-1 after formation of inclusion complexes with ACDs, better than that of β-CD and its derivatives, i.e., HP- and SBE-β-CD. In vitro antioxidant activity of chrysin was also improved after inclusion complexation by the DPPH scavenging assay. Furthermore, in vitro cytotoxicity of solid inclusion complexes towards three human cancer cell lines, A549, HT-29 and HCT116 were enhanced significantly.

Dialing in on pharmacological features for a therapeutic antioxidant small molecule.

The pyridinophane molecule L2 (3,6,9,15-tetraazabicyclo[9.3.1]penta-deca-1(15),11,13-trien-13-ol) has shown promise as a therapuetic for neurodegenerative diseases involving oxidative stress and metal ion misregulation. Protonation and metal binding stability constants with Mg2+, Ca2+, Cu2+, and Zn2+ ions were determined to further explore the therapeutic and pharmacological potential of this water soluble small molecule. These studies show that incorporation of an -OH group in position 4 of the pyridine ring decreases the pI values compared to cyclen and L1 (3,6,9,15-tetraazabicyclo[9.3.1]penta-deca-1(15),11,13-triene). Furthermore, this approach tunes the basicity of the tetra-aza macrocyclic ligand through the enhanced resonance stabilization of the -OH in position 4 and rigidity of the pyridine ring such that L2 has increased basicity compared to previously reported tetra-aza macrocycles. A metal binding preference for Cu2+, a redox cycling agent known to produce oxidative stress, indicates that this would be the in vivo metal target of L2. However, the binding constant of L2 with Cu2+ is moderated compared to cyclen due to the rigidity of the ligand and shows how ligand design can be used to tune metal selectivity. An IC50 = 298.0 μM in HT-22 neuronal cells was observed. Low metabolic liability was determined in both Phase I and II in vitro models. Throughout these studies other metal binding systems were used for comparison and as appropriate controls. The reactivity reported to date and pharmacological features described herein warrant further studies in vivo and the pursuit of L2 congeners using the knowledge that pyridine substitution in a pyridinophane can be used to tune the structure of the ligand and retain the positive therapeutic outcomes.

Dynamics of trace metal sorption by an ion-exchange chelating resin described by a mixed intraparticle/film diffusion transport model. The Cd/Chelex case

The time-evolution of Cd2+ ion sorption by Chelex 100 resin was studied in batch experiments as a function of time, pH, ionic strength, stirring rate, mass of resin and initial metal ion concentration. In the experimental conditions, the amount of resin sites are in excess with respect to the amount of metal ion, leading to extensive depletion of metal in bulk solution when equilibrium is reached. The data were described using a mixed control mass transport model in finite volume conditions (MCM) that includes explicitly both intraparticle and film diffusion steps. Exact numerical computations and a new approximate analytical expression of this model are reported here. MCM successfully predicts the influence of pH and ionic strength on the experimental Cd(II)/Chelex kinetic profiles (which cannot be justified by a pure film diffusion controlled mechanism) with a minimum number of fitting parameters. The overall diffusion coefficient inside the resin was modelled in terms of the Donnan factor and the resin/cation binding stability constant. The values of the latter coefficient as a function of pH and ionic strength were estimated from the Gibbs-Donnan model. Even though MCM is numerically more involved than models exclusively restricted to film or intraparticle diffusion control, it proves to be accurate in a wider range of values of the mass transfer Biot number and solution/resin metal ratios.

Development and validation of a biotic ligand model for predicting chronic toxicity of lead to Ceriodaphnia dubia

While it is increasingly being recognized that biotic ligand models (BLMs) are valuable in the risk assessment of metals in aquatic systems, the development of chronic BLMs has been less advanced for lead than for other metals. The authors investigated the univariate effects of Ca and pH on the chronic reproductive toxicity of Pb to Ceriodaphnia dubia at 4 levels. Calcium influenced chronic Pb toxicity to C. dubia only to a relatively small extent, whereas a high pH (8.2) provided strong protection against Pb toxicity (compared with lower pH levels). Based on this data set, a chronic Pb BLM for C. dubia was developed. The effect of pH was modeled as a single biotic ligand site competition by H(+) with a log stability constant for binding of H(+) to the biotic ligand (K(HBL)) of 7.6, while no other competitive constants were needed. The developed BLM was shown, in an independent validation with 3 other data sets, to be capable of predicting chronic Pb toxicity to different clones of C. dubia by an error of less than a factor of 2 in most synthetic and natural waters considered. The results add to the growing evidence that BLM-based risk assessment or water-quality criteria for Pb are likely to be more appropriate relative to hardness-based assessments or criteria.

Role of N-Terminal His6-Tags in Binding and Efficient Translocation of Polypeptides into Cells Using Anthrax Protective Antigen (PA)

It is of interest to define bacterial toxin biochemical properties to use them as molecular-syringe devices in order to deliver enzymatic activities into host cells. Binary toxins of the AB7/8-type are among the most potent and specialized bacterial protein toxins. The B subunits oligomerize to form a pore that binds with high affinity host cell receptors and the enzymatic A subunit. This allows the endocytosis of the complex and subsequent injection of the A subunit into the cytosol of the host cells. Here we report that the addition of an N-terminal His6-tag to different proteins increased their binding affinity to the protective antigen (PA) PA63-channels, irrespective if they are related (C2I) or unrelated (gpJ, EDIN) to the AB7/8-family of toxins. His6-EDIN exhibited voltage-dependent increase of the stability constant for binding by a factor of about 25 when the trans-side corresponding to the cell interior was set to −70 mV. Surprisingly, the C. botulinum toxin C2II-channel did not share this feature of PA63. Cell-based experiments demonstrated that addition of an N-terminal His6-tag promoted also intoxication of endothelial cells by C2I or EDIN via PA63. Our results revealed that addition of His6-tags to several factors increase their binding properties to PA63 and enhance the property to intoxicate cells.

생분해에 따른 용존 유기물질 성상 및 중금속 구리와의 결합특성 변화

Microbial changes in the characteristics of dissolved organic matter (DOM) and the subsequent effects on the conditional stability constants of copper were investigated using 14 day-incubations of Pony Lake fulvic acid (PLFA), Suwannee River fulvic acid (SRFA) and the mixtures of the humic substances and glucose. After incubation, dissolved organic carbon (DOC) concentrations were diminished, and specific UV absorbance values and DOC-normalized fluorescence intensities increased. The microbial changes were minimal for the samples contaning humic substances only whereas they were much pronounced for the mixtures with glucose. The extent of the changes increased with a higher content of glucose in the mixtures. The same trend was observed even for glucose solution. Our results suggest that labile organic moieties may be transformed into more chromophoric and humidified components by biodegradation. For the mixture samples, the copper binding stability constants did not change or even decreased after incubation. Therefore, microbially induced enrichment of the fulvic- and humic-like carbon structures in DOM appears to result in little change or the decrease of the copper binding coefficients.

QFPR Analysis for Selectivity of between Na+

We investigated the solvent effects on the relative free energies of binding of <TEX>$Na^+$</TEX> and <TEX>$Li^+$</TEX> ions to 12-crown-4 and <TEX>${\Delta}log\;K_s$</TEX> (the difference of stability constant of binding) by a Monte Carlo simulation of statistical perturbation theory (SPT) in several solvents. Comparing the relative free energies of binding of <TEX>$Na^+$</TEX> and <TEX>$Li^+$</TEX> ions to 12-crown-4, in <TEX>$CH_3OH$</TEX> of this study with experimental works, there is a good agreement among the studies. We have reported the quantitative free energy polarity (of solvent) relationships (QFPR) of the relationship between the relative free energies and solvent polarity studied on the solvent effects on the relative free energies of binding of <TEX>$Na^+$</TEX> and <TEX>$Li^+$</TEX> ions to 12-crown-4.

Role of Gelling Soluble and Colloidal Microbial Products in Membrane Fouling

The mechanism underlying gel layer formation on membrane surfaces from soluble and colloidal microbial products (SCMPs) produced under unfavorable operational conditions for membrane bioreactors (MBRs) has been investigated using supernatants from a bench-scale MBR. SCMPs can be grossly classified into gelling and nongelling SCMPs with the gelling fraction associated mostly with the polysaccharide content. The significant role played by multivalent metals in gel formation through metal-ligand complexation has been confirmed. Functional groups of the gelling SCMPs were determined by pH titration and zeta potential measurement as amine/phenolic sites (pK(a) 9.3 and 8.0), carboxylic sites (pK(a) 6.6, 4.9, and ca. 4.0), and phosphoric sites (pK(a) ca. 2.5). The carboxylic sites were more directly involved with multivalent cation complexation; however, the gelling propensity of the SCMP dispersion was minimally affected by pH change in the circum-neutral pH range, suggesting that the strong carboxylic sites were principally responsible for gel formation. The SCMPs demonstrated a high potential for gel formation given the high density of the strong carboxylic acid groups of about 0.44 mmol/g-TOC and a moderate calcium binding stability constant of about 4.9 x 10(3) M(-1).

Polymeric membrane electrodes with improved fluoride selectivity and lifetime based on Zr(IV)- and Al(III)-tetraphenylporphyrin derivatives

Novel aluminum(III)- and zirconium(IV)-tetraphenylporhyrin (TPP) derivatives are examined as fluoride-selective ionophores for preparing polymer membrane-based ion-selective electrodes (ISEs). The influence of t-butyl- or dichloro-phenyl ring substituents as well as the nature of the metal ion center (Al(III) versus Zr(IV)) on the anion complexation constants of TPP derivative ionophores are reported. The anion binding stability constants of the ionophores are characterized by the so-called “sandwich membrane” method. All of the metalloporphyrins examined form their strongest anion complexes with fluoride. The influence of plasticizer as well as the type of lipophilic ionic site additive and their amounts in the sensing membrane are discussed. It is shown that membrane electrodes formulated with the metalloporphyrin derivatives and appropriate anionic or cationic additives exhibit enhanced potentiometric response toward fluoride over all other anions tested. Since selectivity toward fluoride is enhanced in the presence of both anionic and cationic additives, the metalloporphyrins can function as either charged or neutral carriers within the organic membrane phase. In contrast to previously reported fluoride-selective polymeric membrane electrodes based on metalloporphyrins, nernstian or near-nernstian (−51.2 to −60.1 mV decade −1) as well as rapid ( t < 80 s) and fully reversible potentiometric fluoride responses are observed. Moreover, use of aluminum(III)- t-butyltetraphenylporphyrin as the ionophore provides fluoride sensors with prolonged (7 months) functional lifetime.

Variability of the protective effect of sodium on the acute toxicity of copper to freshwater cladocerans

The acute biotic ligand model (BLM) is proposed by the U.S. Environmental Protection Agency (U.S. EPA) to incorporate bioavailability in calculating aquatic life criteria for Cu in freshwater. This approach currently assumes that the effects of water chemistry on acute Cu toxicity can be described with one single set of identical BLM parameters for all organisms. An important water characteristic is the concentration of Na, which protects aquatic organisms against Cu toxicity. Based on physiological considerations related to the mechanism of Cu toxicity and the possible role of Na therein, we hypothesized that an interspecies variability of the protective effect of sodium on Cu toxicity might exist among freshwater organisms. To test this hypothesis, acute 48-h toxicity assays with Cu were conducted with 16 field-collected cladoceran populations and a laboratory-reared clone of Ceriodaphnia dubia at Na concentrations of between 0.077 and 10 mM. Increased Na protected all but one population. Contrary to what the BLM predicts, however, an upper limit to this protective effect was observed for some populations at Na concentrations of greater than 4 mM. This may suggest that processes other than just Cu-Na competition at a single unidentate biotic ligand site may be involved in Cu toxicity. Between populations, conditional stability constants for binding of Na to the biotic ligand (log K*(NaBL)), which quantify the protective effect of Na, varied between 2.2 and 4.4. Higher log K values generally were associated with more sensitive populations. Although a full mechanistic explanation for our observations is lacking, our data may potentially be used to refine the U.S. EPA procedure to establish site-specific water-quality criteria for Cu.

QSPR Analysis of Solvent Effect on Selectivity of 18-Crown-6 between Nd3+ and Eu3+ Ions: a Monte Carlo Simulation Study

We have investigated the solvent effects on <TEX>$\Delta log\;K_s $</TEX>(the difference of stability constant of binding) and the different free energies of binding of <TEX>$Nd^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions to 18-crown-6, i.e., the selectivity of <TEX>$Nd^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions to 18-crown-6 using a Monte Carlo simulation of statistical perturbation theory (SPT) in diverse solvents. The stability constant (<TEX>$\Delta log\;K_s $</TEX>) of binding of <TEX>$Nd^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions to 18-crown-6, in <TEX>$CH_3OH$</TEX> was calculated in this study as -1.06 agrees well with the different experimental results of -0.44~-0.6, respectively. We have reported here the quantitative solvent-polarity relationships (QSPR) studied on the solvent effects the relative free energies of binding of <TEX>$Nd^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions to 18-crown-6. From the calculated coefficients of QSPR, we have noted that solvent polarity (ET) and Kamlet -Tafts solvatochromic parameters (b ) dominate the differences in relative solvation Gibbs free energies of <TEX>$Nd^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions but basicity (Bj) dominates the negative values in differences in the stability constant (<TEX>$\Delta log\;K_s $</TEX>) as well as the relative free energies of binding of <TEX>$Nd^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions to 18-crown-6 and acidity (Aj) dominates the positive values in differences in the stability constant (<TEX>$\Delta log\;K_s $</TEX>) as well as the relative free energies of binding of <TEX>$Nd^{3+}$</TEX> and <TEX>$Eu^{3+}$</TEX> ions to 18-crown-6.

Selectivity of 12-Crown-4 to Cations in CH3OH: A Monte Carlo Simulation Study

Crown ethers display the ability to selectively bind specific metals cations in the presence of complex aqueous mixtures of chemically similar ions. For example, 15-crown5 binds Na and 18-crown-6 binds K selectively, although the configuration of crown depends on the solvents used. That ability is thought to be dependent on the size of the crown cavity, a balance between cation-ether and cationwater interactions, the polarity of solvent and the nature of the electron donor atoms in the ring. These characteristics have been used in the design of novel materials for such processes as isotope separations, ion transport through membrane, and transport of therapeutic doses of radiations to tumor sites. Theoretical calculations based on molecular mechanics (MM) and molecular orbital (MO) theories give structures in a vacuum, however, those results cannot be directly compared with those of experiments. In the hostguest interaction, factors in the selective extraction of any host species include the relative free energy of desolvation of the guest molecules and the free energy of organizing the host into a suitable conformation having remote substitution for binding. Because of the large number of particles forming these systems and the variety of different interactions established, molecular dynamics (MD) and Monte Carlo (MC) statistical mechanics computer simulations are wellsuited theoretical tools for understanding and predicting the physicochemical properties of those solutions at the microscopic level. Several statistical mechanical procedures have evolved for computing free energy differences. It is known that solvent effects often play an important role in determining equilibrium constants, transition states and rates of reactions, π-facial selectivity, conformations, and other quantities of chemical, chemical physics and biochemical interest. Therefore, computational chemists have focused their interests on the crown ethers as those molecules are the simplest that show enzyme-like specificity. However, few molecular dynamics (MD) and Monte Carlo (MC) statistical mechanics computer simulation studies of both the selectivity of 12-crown-4 (1,4,7,10-tetraoxacyclododecane) to univalent cations and ∆log Ks, are available. This prompted us to study the selectivity of 12-crown-4 to univalent cations and ∆log Ks using Monte Carlo simulations of statistical perturbation theory (SPT) in CH3OH. Experimental studies of the selectivity of 12-crown-4 to univalent cations in methanol and ab initio studies of 12-crown-4 with univalent cations have been reported. In this note, we present the first calculation to computing on the selectivity of 12-crown-4 to entire series of univalent cations and ∆log Ks of 12-crown-4 to entire series of univalent cations in CH3OH using a Monte Carlo simulation of SPT. We found 12-crown-4/cation complexes with the 12-crown-4 of almost Cs symmetry never found in any crystal structure of the cation complexes of 12-crown-4. Those are the reasons why this study is communicated as note. The calculated relative binding Gibbs free energies (selectivity index) of 12-crown-4 complexes and the published data of the relative free energies and Dlog Ks (the difference of stability constant of binding) obtained using by (1) shown in Scheme 1, are listed in Table 1. We have noticed that 12-crown-4 binds K more tightly than the other cation in CH3OH, i.e., the selectivity of 12-crown-4 to K is more favorable than to other cations in CH3OH. A similar trend has been observed in the study of alkali cation complexes of 18-crown-6 and its derivatives in CCl4 solutions and in the study of alkali cation complexes of 18-crown-6 in diverse solutions. Binding selectivity is often associated with the ionic radius of the cation and the size of the crown ether cavity that it will occupy. The larger mismatch is existed between the ionic radius of the cation and the size of the crown ether cavity, the smaller chance that the cation binds favorably to the crown ether cavity. 12-crown-4 has distances between diagonal oxygen atoms of 4.0 A and selectively binds K over the other cations in CH3OH where the cationic radius of K is 1.38 and the others are 0.74, 1.02, 1.49, and 1.7 A, respectively. Selectivity is apparently the result of a delicate balance of the forces that the cation experiences as the crown ether and solvent molecules compete for the cation in solution. In this study, the cations

Site-directed Mutagenesis of the Greasy Slide Aromatic Residues Within the LamB (Maltoporin) Channel of Escherichia coli: Effect on Ion and Maltopentaose Transport

The 3D-structure of the maltooligosaccharide-specific LamB-channel of Escherichia coli (also called maltoporin) is known from X-ray crystallography. The 3D structure suggests that a number of aromatic residues (Y6, Y41, W74, F229, W358 and W420) within the channel lumen are involved in carbohydrate and ion transport. All aromatic residues were replaced by alanine-scanning mutagenesis. Furthermore, LamB mutants were created in which two, three, four, five and all six aromatic residues were replaced to study their effects on ion and maltopentaose transport through LamB. The purified mutant proteins were reconstituted into lipid bilayer membranes and the single-channel conductance of the mutants was studied in conductance experiments. The results suggest that all aromatic residues provide some steric hindrance for ion transport through LamB. Highest impact is provided by Y6 and Y41 that are localized opposite Y118, which form the central constriction of the LamB channel. Stability constants for binding of maltopentaose to the mutant channels were measured using titration experiments with the carbohydrate. The mutation of one or several aromatic residue(s) led to a substantial decrease of the stability constant of binding. The highest effect was observed when all aromatic residues were replaced by alanine because no binding of maltopentaose could be detected in such a case. However, binding was again possible when Y118 was replaced by tryptophan. The carbohydrate-induced block of the channel function could be used also for the study of current noise through the different mutant LamB-channels. The analysis of the power density spectra of some of the mutants allowed the evaluation of the on-rate and off-rate constants (k1 and k(-1)) of carbohydrate binding to the binding site inside the channels. The results suggest that both on-rate and off-rate constants were affected by the mutations. For most mutants, k1 decreased and k(-1) increased. The possible influence of the aromatic residues of the greasy slide on carbohydrate and ion transport through LamB is discussed.

Development of a chronic zinc biotic ligand model for Daphnia magna

The individual effects of the cations Ca 2+, Mg 2+, Na +, and H + on the chronic toxicity of Zn to the waterflea Daphnia magna were investigated in different series of univariate experiments, resulting in the development of a chronic Zn biotic ligand model (BLM) for this species. Using the mathematical approach based on a linear relationship between cation activity and metal activity at the EC x level, the following stability constants for binding of competing cations to the biotic ligand (BL) were derived: log K CaBL=3.22, log K MgBL=2.69, log K NaBL=1.90, and log K HBL=5.77. With the derived constants and a log K ZnBL of 5.31, two different BLMs that predict chronic zinc toxicity (EC 50, no observed effect concentration (NOEC)) for D. magna as a function of water characteristics were developed. Fractions of binding sites occupied by Zn at the considered effect levels EC 50 and NOEC were 0.127 and 0.084, respectively. The NOEC-based model predicts the Zn toxicity within a factor of 2, while the chronic EC 50 could be predicted within a factor of 1.5. In the future, these chronic Zn BLMs for D. magna can improve the ecological relevancy of zinc risk assessments by decreasing the bioavailability-related uncertainty of zinc toxicity.

Monte Carlo simulation study for QSPR of solvent effect on the selectivity of 18-crown-6 between Gd 3+ and Yb 3+ ions

The solvent effects on the relative free energies of binding of Gd 3+ and Yb 3+ ions to 18-crown-6 and Δ log K s (the difference of stability constant of binding) have been investigated by a Monte Carlo simulation of statistical perturbation theory (SPT) in diverse solvents. The relative free energies of binding of Gd 3+ and Yb 3+ ions to 18-crown-6, in CH 3OH of this study agree well with the experimental results and simulation works. We reported here a new the quantitative solvent-polarity relationships (QSPR) as the multi-parameter regression approach study in the solvent effects on the relative free energies of binding of Gd 3+ and Yb 3+ ions to 18-crown-6 and the structural data of those complexes.

Selectivity of 18-Crown-6 between Cs+ and Rb+ Ion: Solvent Effect by a Monte Carlo Simulation Study

We have investigated the solvent effects on Δlog Ks (the difference of stability constant of binding) and the relative free energies of binding of Cs+ and Rb+ ions to 18-crown-6, that is, the selectivity of Cs+ and Rb+ ions to 18-crown-6 using a Monte Carlo simulation of statistical perturbation theory (SPT) in diverse solvents. Comparing the stability constant (Δlog Ks) of binding of Cs+ and Rb+ ions to 18-crown-6 in H2O (TIP3P) and CH3OH in this study with those in the experimental works, those of H2O (TIP3P) and CH3OH in this study are 0.80 and 1.57 and those of H2O and CH3OH in the experimental works are 0.57 and 0.61∼1.24, respectively. There is a good agreement among the studies. We have reported here the quantitative solvent−polarity relationships (QSPR) studied on the solvent effects the relative free energies of binding of Cs+ and Rb+ ions to 18-crown-6. From the calculated coefficients of QSPR, we have noted that DN dominates the differences in relative solvation Gibbs free energies of Cs+ and R...

Monte Carlo Simulation Study of Solvent Effect on Selectivity of 18-Crown-6 to between La3+and Nd3+Ion

We have investigated the solvent effects on Alog K s (the difference of stability constant of binding) and the relative free energies of binding of La 3 + to Nd 3 + ions to 18-crown-6 by a Monte Carlo simulation of statistical perturbation theory (SPT) in diverse solvents. We compared relative binding Gibbs free energies and the differences in stability constant (Δlog K s ) of binding of La 3 + and Nd 3 + ions to 18-crown-6 in CH 3 OH in this study with the experimental. There is a good agreement between our study and the experimental. We noted that Borns function of the solvents, the electron pair donor properties of the solvent, the radii of host and guest and the differences in solvation dominate the differences in the stability constant (Δlog K s ) as well as the relative free energies of binding of La 3 + to Nd 3 + ions to 18-crown-6. The results of this study appear promising for providing the association properties of crown ethers with alkaline earth metals among polar solvents and the less polar or non-polar solvents.