Heterogeneity Of Binding Sites Research Articles

Study of cross-linked poly(methacrylic acid) and polyvinylimidazole as selective adsorbents for on-line preconcentration and redox speciation of chromium with flame atomic absorption spectrometry determination

A redox speciation and preconcentration study of Cr(III) and Cr(VI) using a flow injection system with dual mini-columns prepared from cross-linked polymers-poly(methacrylic acid) and polyvinylimidazole was developed. Characterization of organic polymers was performed by using FTIR, SEM, TG, C:H:N and BET measurements. The equilibrium data obtained from Cr(III) adsorption on poly(methacrylic acid) and Cr(VI) on polyvinylimidazole were fitted very well to the dual site Langmuir–Freundlich model, suggesting the presence homogeneous and heterogeneous binding site and providing maximum adsorption capacities of 1.42 and 3.24mgg−1, respectively. The adsorption kinetics data were described by the pseudo-second-order model for both polymers, thus corroborating to isotherm data. The on-line preconcentration/speciation system was operated by loading 18.0mL of a solution containing Cr(III) and Cr(VI) at pH4.0 through the dual mini-columns at a flow rate of 3.0mLmin−1, where Cr(III) was selectively retained on poly(methacrylic acid), while Cr(VI) was retained on polyvinylimidazole. The limits of detection were found to be 0.84 and 1.58μgL−1 for Cr(III) and Cr(VI), respectively. The preconcentration factor (PF), consumptive index (CI) and concentration efficiency (CE) were found to be 47.3/8.6, 0.38/2.1mL and 7.88/1.43min−1 for Cr(III) and Cr(VI), respectively. The developed method was successfully applied to the speciation of chromium in different kinds of water samples. Satisfactory recovery values ranging from 89.9 to 108.3% were obtained.

Heterogeneity of Vasoactive Intestinal Peptide Binding Sites in Hut‐78 T‐Lymphocytes

Vasoactive Intestinal Peptide (VIP) is a neuropeptide that possesses potent cell cycle arrest activity in primary healthy T‐Lymphocytes. Transformed T‐cells from human cancer patients and over 25 cell lines (human, mouse, and rat) have consistently shown reduced VIP receptor expression, suggesting that cancer cells obtain a growth advance with reduced VIP receptor signaling. Utilizing the human Hut‐78 T‐lymphoblastic T‐cell line that has reduced levels but functional VIP binding sites, we carried out growth curves +/‐ VIP utilizing alamar blue. Surprisingly, these results were inconclusive as they showed opposite effects of growth from exogenous addition of VIP ligand. To better understand the discrepancy in growth rates by VIP we measured the homogeneity of VIP binding sites in Hut‐78s by VIP‐FAM labeling and flow cytometry analysis. Curiously, three definable subpopulations possessing varying levels of VIP binding sites were observed. These three populations were sorted, cultured, and showed a stable homogenous population with intermediate levels of VIP binding sites. Collectively, we conclude that the heterogeneity of VIP binding sites in HUT‐78s may explain the disparate growth results collected above. Future studies will utilize the stable sorted homogenous VIP binding site sorted populations to investigate the cell cycle arresting abilities of VIP.

Enhanced sorption of Mn2+ ions from aqueous medium by inserting protoporphyrin as a pendant group in poly(vinylpyridine) network

The main goal of the present work was to evaluate the effect of protoporphyrin (PP) (as pendant group) incorporated into a poly(vinylpyridine) [poly(VPY)] polymer network on the sorption of Mn2+ ions from an aqueous medium. The sorbent materials – poly(PP-co-VPY) and poly(VPY) – were characterized by SEM, FTIR, elemental analysis and nitrogen adsorption–desorption measurements (BET – Barrett–Joyner–Halenda and BJH – Brunauer–Emmett–Teller). It was observed that the pseudo-second-order kinetic model fitted the experimental data very well (R2=0.9967), confirming that the Mn2+ sorption onto poly(PP-co-VPY) took place via chemical reactions (chemisorption). To describe the equilibrium between the Mn2+ ions and sorbents and estimate the maximum sorption capacity, different models, including Langmuir, Freundlich, Dubinin–Radushkevich and dual-site non-linear Langmuir–Freundlich equations, were applied to the experimental data. The dual-site Langmuir–Freundlich model provided the best fit for poly(PP-co-VPY) and poly(VPY), yielding the maximum sorption capacity of 5.0 and 1.79mgg−1, respectively. These findings suggest the presence of homogeneous and heterogeneous binding sites able to sorb Mn2+ ions. Binary solutions of Mn2+/Zn2+, Mn2+/Pb2+ and Mn2+/Fe3+ were submitted to competitive sorption in the polymers. The results obtained for these systems demonstrated 4.75, 18.24 and 388-fold increases in the rate of the Mn2+ sorption onto poly(PP-co-VPY), when compared with poly(VPY). The protoporphyrin incorporation into poly(VPY) network appears to be an interesting approach to polymer synthesis by the homogeneous solution method focused on the preparation of solid-phase extraction columns.

New synthesis method for 4-MAPBA monomer and using for the recognition of IgM and mannose with MIP-based QCM sensors

Quartz crystal microbalance (QCM) sensors coated with molecularly imprinted polymers (MIP) have been developed for the recognition of immunoglobulin M (IgM) and mannose. In this method, methacryloylamidophenylboronic acid (MAPBA) was used as a monomer and mannose was used as a template. For this purpose, initially, QCM electrodes were modified with 2-propene-1-thiol to form mannose-binding regions on the QCM sensor surface. In the second step, the methacryloylamidophenylboronic acid-mannose [MAPBA-mannose], pre-organized monomer system, was prepared using the MAPBA monomer. Then, a molecularly imprinted film was coated on to the QCM electrode surface under UV light using ethylene glycol dimethacrylate (EDMA), and azobisisobutyronitrile (AIBN) as a cross-linking agent and an initiator, respectively. The mannose can be simultaneously bound to MAPBA and fitted into the shape-selective cavities. The binding affinity of the mannose-imprinted sensors was investigated using the Langmuir isotherm. The mannose-imprinted QCM electrodes have shown homogeneous binding sites for mannose (K(a): 3.3 × 10(4) M(-1)) and heterogeneous binding sites for IgM (K(a1): 1.0 × 10(4) M(-1); K(a2): 3.3 × 10(3) M(-1)).

Microwave-assisted preparation of pumpkin seed hull activated carbon and its application for the adsorptive removal of 2,4-dichlorophenoxyacetic acid

This study explores the feasibility of pumpkin seed hull as a potential raw precursor for preparation of mesoporous activated carbon by microwave induced KOH activation. The pumpkin seed hull activated carbon (PSHAC) was characterized by pore structural analysis, zero-point-of-charge, Fourier transform infra-red spectroscopy and scanning electron microscopy. The adsorptive performance of PSHAC was quantified using pesticide, 2,4-dichlorophenoxyacetic acid (2,4-D) as model adsorbate. The effects of contact time, initial concentration, and solution pH on the adsorption process were evaluated. Results indicated high percent of removal, with the adsorptive removal of 98.28%, 97.57%, 96.03%, 93.40%, 78.11% and 65.07% at the initial concentration 50, 100, 150, 200, 300 and 400mg/L, respectively. Kinetic studies showed that the adsorption process was well described by the pseudo-second-order kinetic model. The adsorption isotherm was analyzed using the nonlinear Langmuir, Freundlich and Temkin isotherm models. The best fit was obtained with the Temkin isotherm model, predicting a uniform distribution of binding energy over the heterogeneous surface binding sites. The maximum monolayer adsorption capacity of 2,4-D for PSHAC was identified to be 260.79mg/g.

Preparation and performance valuation of high selective molecularly imprinted polymers for malachite green

Molecular imprinting is a technology that facilitates the production of artificial receptors toward compounds of interest. In this study, we prepared a series of molecularly imprinted polymers (MIPs) by precipitation polymerization for the purpose of binding specifically to malachite green (MG). The presence of monomer–template solution complexes in non-covalent MIPs systems had been verified by UV-spectrometric detection and molecular dynamics simulations. The synthesized parameters were, respectively, optimized and the optimal conditions for the efficient adsorption property were as follows: template: MG, 1 mmol; functional monomer: methacrylic acid (MAA), 8 mmol; cross-linker: ethylene glycol dimethacryllate, 16 mmol; and porogen: acetonitrile, 30 mL. Fourier transform infrared spectroscopy and nitrogen adsorption experiments were used to characterize the MIPs. Scatchard analysis was used for estimation of the dissociation constants and maximum amounts of binding sites. The polymer based on MAA had two classes of heterogeneous binding sites characterized by two values of KD and Bmax: KD = 14.10 μmol L−1 and Bmax = 1.37 μmol g−1 for the higher affinity binding sites, and KD = 384.62 μmol L−1 and Bmax = 24.77 μmol g−1 for the lower affinity binding sites. The specificity of MIPs on SPE column was evaluated by rebinding the other structurally similar compounds. The results indicated that the imprinted polymers exhibited an excellent stereo-selectivity toward MG.

Synthesis and optimization of molecularly imprinted polymers for quercetin

AbstractMolecularly imprinted polymers (MIPs) were synthesized through solution polymerization using quercetin as the template molecule, N‐vinylpyrrolidone and acrylic acid as functional monomers, N,N′‐methylenebiacrylamide as crosslinker and the redox system L‐ascorbic acid and hydrogen peroxide as initiator in the porogen of ethanol and water. During the optimization process an interference compound, genistein (5,7,4′‐trihydroxy isoflavone), which possesses the same skeleton and functional groups as quercetin, was adopted to optimize the preparation conditions, and the separation degree of the MIP to quercetin and genistein was chosen to optimize each factor. The synthesized MIP under optimal conditions showed a specific recognition of quercetin from a mixture of quercetin and genistein. Thereafter, the structure of the MIP was comparatively characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and Brunauer–Emmett–Teller analysis using non‐imprinted molecular polymers as control. In addition, the kinetics of the adsorption process were also studied, and Scatchard analysis revealed that heterogeneous binding sites were formed in the polymers. Copyright © 2012 Society of Chemical Industry

A Biosorption Isotherm Model for the Removal of Reactive Azo Dyes by Inactivated Mycelia of Cunninghamella elegans UCP542

The biosorption of three reactive azo dyes (red, black and orange II) found in textile effluents by inactive mycelium of Cunninghamella elegans has been investigated. It was found that after 120 hours of contact the adsorption led to 70%, 85%, 93% and 88% removal of reactive orange II, reactive black, reactive red and a mixture of them, respectively. The mycelium surface was found to be selective towards the azo dyes in the following order: reactive red > reactive black > orange II. Dye removal from a mixture solution resulted in 48.4 mg/g retention by mycelium and indicated a competition amongst the dyes for the cellular surface. A Freundlich adsorption isotherm model exhibited a better fit, thus suggesting the presence of heterogeneous binding sites. Electrondense deposits observed on the mycelium ultrastructure suggest that the dyes are mainly retained under the cellular surface of the inactive biomass of C. elegans.

Synthesis and characterization of 3,4-dihydroxyphenylacetic acid imprinted polymers

Eight molecularly imprinted polymers (MIP1–MIP8) were synthesized with different functional monomers and porogens using 3,4-dihydroxyphenylacetic acid (DOPAC) as a template. Thermal, radical bulk polymerization was employed in the presence of ethylene glycol dimethacrylate as a cross-linker. A computational analysis indicated that complexes with four molecules of 4-vinylpyridine, 1-vinylimidazole and acrylonitrile had high positive enthalpies of formation. The polymers synthesized with these monomers showed an imprinting factor below 1. Polymer MIP8 synthesized with allylamine as the functional monomer, with the highest energy of interaction with DOPAC, was characterized by the highest imprinting factor equal to 1.91. Examination of the binding ability of DOPAC and a group of structurally related compounds showed that the strong interactions between amine groups in the polymer and carboxylic groups in the analyte governed the recognition mechanism. The Langmuir adsorption model and the pseudo-second-order mechanism properly evaluated the MIP8 and non-imprinted polymer 8 adsorption characteristics. Scatchard analysis revealed that MIP8 had two classes of heterogeneous binding sites with Kd(1) = 0.12 µmol L−1 and Kd(2) = 1.46 µmol L−1. Finally, the potential application of MIP8 for separation of DOPAC was demonstrated. Copyright © 2011 Society of Chemical Industry

Application of the Temkin Model to the Adsorption of CO on Gold

A treatment of the Temkin model was developed for describing the adsorption of CO on gold. In this presentation, it is made clear that the Temkin thermodynamic model is an extension of the Langmuir model that incorporates a linear variation of the adsorption enthalpy. It is also stressed that the Temkin model can be interpreted in terms of two distinct physical situations: the first assumes equivalent binding sites and an adsorption enthalpy that varies with coverage due adsorbate interactions, while the second assumes a uniform distribution of heterogeneous binding sites and an adsorption enthalpy that varies due to the heterogeneity of sites. In addition, a midrange approximation, where the surface is roughly half covered with adsorbates, is commonly employed. While each of these situations is similar, they are not equivalent and yield slightly different analytical expressions that describe the adsorption coverage as a function of pressure and temperature. Fitting data with the different analytical expressions therefore produces slightly different thermodynamic values for the adsorption enthalpy and entropy. These different cases are explicitly defined and developed. For the adsorption of CO on gold, the adsorbate interaction case is shown to be most consistent with the current body of experimental and theoretical evidence. The various analytical expressions are used to apply the Temkin model to data for CO adsorption on 1% Au/TiO2 real-world catalysts (from the World Gold Council) studied under catalytically relevant isothermal (T = 275–325 K) and isobaric (PCO = 0–10 Torr) experimental conditions. Infrared transmission spectroscopy was the analytical technique used for quantitatively measuring the adsorption coverage. The coverage as a function of pressure (θ,P) and as a function of temperature (θ,T) was fit with the Temkin adsorption models. The models yield the thermodynamic adsorption enthalpy at zero and full coverage as well as the adsorption entropy. The values of these thermodynamic parameters differ slightly depending upon the particular Temkin situation considered (cf. adsorbate interaction, heterogeneous surface, and midrange approximation cases). While all three Temkin cases produced excellent fits to both the isothermal and isobaric data sets, the adsorbate interaction case is most consistent with experimental and theoretical evidence describing the adsorption of CO on gold. The average enthalpy values from fitting the isothermal and isobaric data sets using the adsorbate interaction model are −ΔH0 = 59.2 kJ/mol and −ΔH1 = 54.6 kJ/mol for zero and full coverage, respectively. The adsorption entropy, −ΔS = 142 J/(K mol), was determined by fitting the data sets from multiple isothermal experiments with the adsorbate interaction case. These thermodynamic adsorption values are in excellent agreement with previously reported values. The validity of the Temkin adsorbate interaction model was further supported by fitting isothermal and isobaric data for the adsorption of CO on a well-defined gold surface, as reported previously by Gottfried et al. This new treatment of the Temkin adsorption model is theoretically and experimentally straightforward and applicable to both isothermal and isobaric data sets. It provides meaningful thermodynamic values of adsorption enthalpy and entropy, which can be used to characterize and explain differences between various catalysts. The model should also be applicable to the adsorption of other small molecules on metal surfaces and particles that show coverage-dependent adsorption properties.

Conjugation of hydroxyapatite nanocrystals with human immunoglobulin G for nanomedical applications

Inorganic nanosized drug carriers are a promising field in nanomedicine applied to cancer. Their conjugation with antibodies combines the properties of the nanoparticles themselves with the specific and selective recognition ability of the antibodies to antigens. Biomimetic carbonate–hydroxyapatite (HA) nanoparticles were synthesized and fully characterized; human IgGs, used as model antibodies, were coupled to these nanocrystals. The maximum loading amount, the interaction modelling, the preferential orientation and the secondary structure modifications were evaluated using theoretical models (Langmuir, Freundlich and Langmuir–Freundlich) spectroscopic (UV–Vis, Raman), calorimetric (TGA), and immunochemical techniques (ELISA, Western Blot). HA nanoparticles of about 30 nm adsorbed human IgGs, in a dose-dependent, saturable and stable manner with micromolar affinity and adsorption capability around 2.3 mg/m 2. Adsorption isotherm could be described by Langmuir–Freundlich model, and was due to both energetically homogeneous and heterogeneous binding sites on HA surface, mainly of electrostatic nature. Binding did not induce secondary structure modification of IgGs. A preferential IgG end-on orientation with the involvement of IgG Fc moiety in the adsorption seems most probable due to the steric hindrance of their Fab domains. Biomimetic HA nanocrystals are suitable substrates to produce nanoparticles which can be functionalized with antibodies for efficient targeted drug delivery to tumours.

Surface‐based protein binding pocket similarity

Protein similarity comparisons may be made on a local or global basis and may consider sequence information or differing levels of structural information. We present a local three-dimensional method that compares protein binding site surfaces in full atomic detail. The approach is based on the morphological similarity method which has been widely applied for global comparison of small molecules. We apply the method to all-by-all comparisons two sets of human protein kinases, a very diverse set of ATP-bound proteins from multiple species, and three heterogeneous benchmark protein binding site data sets. Cases of disagreement between sequence-based similarity and binding site similarity yield informative examples. Where sequence similarity is very low, high pocket similarity can reliably identify important binding motifs. Where sequence similarity is very high, significant differences in pocket similarity are related to ligand binding specificity and similarity. Local protein binding pocket similarity provides qualitatively complementary information to other approaches, and it can yield quantitative information in support of functional annotation.

Biosorption of Heavy Metal Ions: Ion-Exchange versus Adsorption and the Heterogeneity of Binding Sites

Surface heterogeneity-related effects have been studied in the context of biosorption systems designed for the removal of bivalent heavy metal ions from aqueous systems. The research was focused on incorporating these effects into the concept of the ion-exchange (IE) constant. Cases of both correlated and uncorrelated values of the affinity constants towards metal ions and protons were considered. When strong correlations were assumed, the dispersion of the IE constant was smaller (or, in the limiting case, the same) in comparison to the dispersions of the affinity constants. In contrast, when no correlation was assumed, the dispersion of the IE constant was greater than those corresponding to any of the affinity constants. The dispersion of the IE constant could be additionally enhanced by the existence of multi-dentate binding modes related to the metal ions.

Detection of heterogeneous drug-protein binding by frontal analysis and high-performance affinity chromatography.

This study examined the use of frontal analysis and high-performance affinity chromatography for detecting heterogeneous binding in biomolecular interactions, using the binding of acetohexamide with human serum albumin (HSA) as a model. It was found through the use of this model system and chromatographic theory that double-reciprocal plots could be used more easily than traditional isotherms for the initial detection of binding site heterogeneity. The deviations from linearity that were seen in double-reciprocal plots as a result of heterogeneity were a function of the analyte concentration, the relative affinities of the binding sites in the system and the amount of each type of site that was present. The size of these deviations was determined and compared under various conditions. Plots were also generated to show what experimental conditions would be needed to observe these deviations for general heterogeneous systems or for cases in which some preliminary information was available on the extent of binding heterogeneity. The methods developed in this work for the detection of binding heterogeneity are not limited to drug interactions with HSA but could be applied to other types of drug-protein binding or to additional biological systems with heterogeneous binding.

Synthesis of homoveratric acid-imprinted polymers and their evaluation as selective separation materials.

A bulk polymerization method was used to easily and efficiently prepare homo-veratric acid (3,4-dimethoxyphenylacetic acid)-imprinted polymers from eight basic monomers: 2-vinylpyridine, 4-vinylpyridine, 1-vinylimidazole, N-allylaniline, N-allyl-piperazine, allylurea, allylthiourea, and allylamine, in the presence of homoveratric acid as a template in N,N-dimethylformamide as a porogen. The imprinted polymer prepared from allylamine had the highest affinity to the template, showing an imprinting factor of 3.43, and allylamine polymers MIP8/NIP8 were selected for further studies. Their binding properties were analyzed using the Scatchard method. The results showed that the imprinted polymers have two classes of heterogeneous binding sites characterized by two pairs of Kd, Bmax values: Kd(1) = 0.060 μmol/mL, Bmax(1) = 0.093 μmol/mg for the higher affinity binding sites, and Kd(2) = 0.455 μmol/mL, Bmax(2) = 0.248 μmol/mg for the lower affinity binding sites. Non-imprinted polymer has only one class of binding site, with Kd = 0.417 μmol/mL and Bmax = 0.184 μmol/mg. A computational analysis of the energies of the prepolymerization complexes was in agreement with the experimental results. It showed that the selective binding interactions arose from cooperative three point interactions between the carboxylic acid and the two methoxy groups in the template and amino groups in the polymer cavities. Those results were confirmed by the recognition studies performed with the set of structurally related compounds. Allylamine polymer MIP8 had no affinity towards biogenic amines. The obtained imprinted polymer could be used for selective separation of homoveratric acid.

Probing bis-ANS Binding Sites of Different Affinity on Aggregated IgG by Steady-State Fluorescence, Time-Resolved Fluorescence and Isothermal Titration Calorimetry

Fluorescent dyes, for example, 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid dipotassium salt (bis-ANS) are extensively used to detect nonnative protein structures in therapeutic protein products, for example, during formulation development by monitoring the greatly enhanced dye fluorescence upon binding to nonnative species. Our aim was to characterize the level of heterogeneity of bis-ANS binding sites in a thermally stressed monoclonal antibody (IgG) formulation by steady-state fluorescence, time-resolved fluorescence and isothermal titration calorimetry (ITC), and to obtain apparent dissociation constants (Kd ) by data fitting. Because the methods differ in their underlying measurement principles, they provide different information on binding properties of bis-ANS to thermally stressed IgG. We found very heterogeneous bis-ANS binding sites on thermally stressed IgG, with apparent Kd values ranging from as low as 50 nM (time-resolved fluorescence) to 63 μM (ITC). Steady-state fluorescence and ITC gave insight into an overall binding affinity of a wide population of dye binding sites with micromolar Kd values. Time-resolved fluorescence was particularly sensitive to high-affinity binding sites with nanomolar Kd s. The heterogeneity of the bis-ANS binding sites reflects the complex, heterogeneous nature of the heat-stressed IgG used in this study. To probe such heterogeneity adequately, one should apply complementary analytical methods under various experimental conditions as presented in this paper. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:1294-1305, 2011.

Characterization of binding site heterogeneity for copper within dissolved organic matter fractions using two-dimensional correlation fluorescence spectroscopy

The heterogeneity of copper binding characteristics for dissolved organic matter (DOM) fractions was investigated based on the fluorescence quenching of the synchronous fluorescence spectra upon the addition of copper and two-dimensional correlation spectroscopy (2D-COS). Hydrophobic acid (HoA) and hydrophilic (Hi) fractions of two different DOM (algal and leaf litter DOM) were used for this study. For both DOM, fluorescence quenching occurred at a wider range of wavelengths for the HoA fractions compared to the Hi fractions. The combined information of the synchronous and asynchronous maps derived from 2D-COS provided a clear picture of the heterogeneous distribution of the copper binding sites within each DOM fraction, which was not readily recognized by a simple comparison of the changes in the synchronous fluorescence spectra upon the addition of copper. For the algal DOM, higher stability constants were exhibited for the HoA versus the Hi fractions. The logarithms of the stability constants ranged from 4.8 to 6.1 and from 4.5 to 5.0 for the HoA and the Hi fractions of the algal DOM, respectively, depending on the associated wavelength and the fitted models. In contrast, no distinctive difference in the binding characteristics was found between the two fractions of the leaf litter DOM. This suggests that influences of the structural and chemical properties of DOM on copper binding may differ for DOM from different sources. The relative difference of the calculated stability constants within the DOM fractions were consistent with the sequential orders interpreted from the asynchronous 2D-COS. It is expected that 2D-COS will be widely applied to other DOM studies requiring detailed information on the heterogeneous nature and subsequent effects under a range of environmental conditions.

Recent advances in molecular imprinting technology: current status, challenges and highlighted applications

Molecular imprinting technology (MIT) concerns formation of selective sites in a polymer matrix with the memory of a template. Recently, molecularly imprinted polymers (MIPs) have aroused extensive attention and been widely applied in many fields, such as solid-phase extraction, chemical sensors and artificial antibodies owing to their desired selectivity, physical robustness, thermal stability, as well as low cost and easy preparation. With the rapid development of MIT as a research hotspot, it faces a number of challenges, involving biological macromolecule imprinting, heterogeneous binding sites, template leakage, incompatibility with aqueous media, low binding capacity and slow mass transfer, which restricts its applications in various aspects. This critical review briefly reviews the current status of MIT, particular emphasis on significant progresses of novel imprinting methods, some challenges and effective strategies for MIT, and highlighted applications of MIPs. Finally, some significant attempts in further developing MIT are also proposed (236 references).

Mechanisms of nociceptive signal coding: Role of slow sodium channels

321 Using whole-cell patch-clamp method, the rat DRG nociceptive neuron membrane was investigated. Extracellular ouabain applications lead to a decrease of the effective charge transfer in the activation gating system of the slow sodium channels (TTX r , Na v 1.8). Ouabain concentration–effective charge transfer (dose– response) dependence has U-like shape after extracellular ouabain application. Left branch of this dependence is monotonous in the range from 100 pM to 1 μ M (K d = 3 nM). Quantum-chemical calculations have shown that the ouabain molecule could effectively form the chelate complex with free calcium ion. As a result, the equilibrium geometry of this complex changes and the probable consequence of this binding is the fact that this complex better fits the transducer site of the Na + ,K + -ATPase. Besides, the chelate complex should specifically activate this transducer site due to the ionionic binding. Less specific free (without calcium) ouabain higher concentration binding takes place at the different Na + ,K + -ATPase site that probably controls its pumping function. Heterogeneity of the ouabain binding sites could explain the U-like shape of the dose– response function under investigation. The inflammatory pain test shows that injections of ouabain at low concentration (i.p., 0.3 mg/kg) lead to pain relief. We hypothesize that physiological role of the endogenous ouabain results in the decrease of nociceptive signals. Mechanisms of Nociceptive Signal Coding: Role of Slow Sodium Channels

Modeling the Effect of Surface Heterogeneity in Equilibrium of Heavy Metal Ion Biosorption by Using the Ion Exchange Model

This paper is focused on the theoretical modeling of the heavy metal ions biosorption process. The origin of the commonly observed, so-called "heterogeneity effects" has been explained. Two popular models were considered for that purpose: the adsorption model and the ion exchange model. The Condensation Approximation method has been used to develop the model describing the influence of surface heterogeneity on biosorption equilibria. As this model has been derived by accepting the ion exchange processes on the biosorbent surface, the obtained expressions are able to also take into account the pH effect. The mentioned "heterogeneity effects" may be treated as the result of (i) the existence of the continuous function expressing the binding site heterogeneity, (ii) the existence of a few different kinds of binding sites, having different values of ion exchange constant; (iii) stoichiometry of the ion exchange reaction occurring on the biosorbent surface. The latter case is responsible for the so-called "apparent" heterogeneity, when the adsorption model and the ion exchange model offer equally good fits of data but the degree of the surface heterogeneity estimated in this way might be different.