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Acid Base Equilibrium

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Igal Szleifer – One of the best experts on this subject based on the ideXlab platform.

  • Lysozyme adsorption in pH-responsive hydrogel thin-films: the non-trivial role of AcidBase Equilibrium.
    Soft matter, 2015
    Co-Authors: Claudio F. Narambuena, Gabriel S. Longo, Igal Szleifer
    Abstract:

    We develop and apply a molecular theory to study the adsorption of lysozyme on weak polyAcid hydrogel films. The theory explicitly accounts for the conformation of the network, the structure of the proteins, the size and shape of all the molecular species, their interactions as well as the chemical Equilibrium of each titratable unit of both the protein and the polymer network. The driving forces for adsorption are the electrostatic attractions between the negatively charged network and the positively charged protein. The adsorption is a non-monotonic function of the solution pH, with a maximum in the region between pH 8 and 9 depending on the salt concentration of the solution. The non-monotonic adsorption is the result of increasing negative charge of the network with pH, while the positive charge of the protein decreases. At low pH the network is roughly electroneutral, while at sufficiently high pH the protein is negatively charged. Upon adsorption, the AcidBase Equilibrium of the different amino Acids of the protein shifts in a nontrivial fashion that depends critically on the particular kind of residue and solution composition. Thus, the proteins regulate their charge and enhance adsorption under a wide range of conditions. In particular, adsorption is predicted above the protein isoelectric point where both the solution lysozyme and the polymer network are negatively charged. This behavior occurs because the pH in the interior of the gel is significantly lower than that in the bulk solution and it is also regulated by the adsorption of the protein in order to optimize protein–gel interactions. Under high pH conditions we predict that the protein changes its charge from negative in the solution to positive within the gel. The change occurs within a few nanometers at the interface of the hydrogel film. Our predictions show the non-trivial interplay between AcidBase Equilibrium, physical interactions and molecular organization under nanoconfined conditions, which leads to non-trivial adsorption behavior that is qualitatively different from what would be predicted from the state of the proteins in the bulk solution.

  • Born energy, AcidBase Equilibrium, structure and interactions of end-grafted weak polyelectrolyte layers.
    The Journal of chemical physics, 2014
    Co-Authors: Rikkert J. Nap, Mario Tagliazucchi, Igal Szleifer
    Abstract:

    This work addresses the effect of the Born self-energy contribution in the modeling of the structural and thermodynamical properties of weak polyelectrolytes confined to planar and curved surfaces. The theoretical framework is Based on a theory that explicitly includes the conformations, size, shape, and charge distribution of all molecular species and considers the AcidBase Equilibrium of the weak polyelectrolyte. Namely, the degree of charge in the polymers is not imposed but it is a local varying property that results from the minimization of the total free energy. Inclusion of the dielectric properties of the polyelectrolyte is important as the environment of a polymer layer is very different from that in the adjacent aqueous solution. The main effect of the Born energy contribution on the molecular organization of an end-grafted weak polyAcid layer is uncharging the weak Acid (or basic) groups and consequently decreasing the concentration of mobile ions within the layer. The magnitude of the effect increases with polymer density and, in the case of the average degree of charge, it is qualitatively equivalent to a small shift in the Equilibrium constant for the AcidBase Equilibrium of the weak polyelectrolyte monomers. The degree of charge is established by the competition between electrostatic interactions, the polymer conformational entropy, the excluded volume interactions, the translational entropy of the counterions and the AcidBase chemical Equilibrium. Consideration of the Born energy introduces an additional energetic penalty to the presence of charged groups in the polyelectrolyte layer, whose effect is mitigated by down-regulating the amount of charge, i.e., by shifting the local-Acid Base Equilibrium towards its uncharged state. Shifting of the local AcidBase Equilibrium and its effect on the properties of the polyelectrolyte layer, without considering the Born energy, have been theoretically predicted previously. Account of the Born energy leads to systematic, but in general small, corrections to earlier theoretical predictions describing the behavior of weak polyelectrolyte layers. However, polyelectrolyte uncharging results in a decrease in the concentration of counterions and inclusion of the Born Energy can result in a substantial decrease of the counterion concentration. The effect of considering the Born energy contribution is explored for end-grafted weak polyelectrolyte layers by calculating experimental observables which are known to depend on the presence of charges within the polyelectrolyte layer: inclusion of the Born energy contribution leads to a decrease in the capacitance of polyelectrolyte-modified electrodes, a decrease of conductivity of polyelectrolyte-modified nanopores and an increase in the repulsion exerted by a planar polyelectrolyte layer confined by an opposing wall.

  • weak polyelectrolytes tethered to surfaces effect of geometry Acid Base Equilibrium and electrical permittivity
    Journal of Polymer Science Part B, 2006
    Co-Authors: Rikkert J. Nap, Peng Gong, Igal Szleifer
    Abstract:

    The structural and thermodynamical properties of weak polyelectrolytes end-tethered to surfaces of arbitrary geometry are studied using a molecular theory. The theory is Based on writing down the free energy functional of the system including all the basic interactions and the explicit AcidBase Equilibrium for the chargeable groups of the polymer. The theory explicitly includes the size, shape, conformations, and charge distribution of all the molecular species. The electrostatic interactions include a density-dependent dielectric function, modeled with the Maxwell-Garnett mixing formula, to account for the composition-dependent permittivity. The minimization of the free energy leads to the distribution of all molecular species and their dependence on bulk pH and salt concentration. We apply the theory to polymer chains end-tethered to planar, cylindrical, and spherical surfaces. The radius of the curved surfaces is small to enhance the curvature effect. We find that when the grafting surfaces are uncharged, the approximation of a constant dielectric function works very well for both structural and thermodynamic properties. The structure of weak polyelectrolytes tethered on cylindrical and spherical surfaces is different from that of polymers tethered on planar surfaces due to the available volume as a function of the distance from the surface. Specifically, the degree of dissociation increases with increasing curvature of the surface. This is a manifestation of the coupling between the local density of protons, counterions, and polymer segments. The results can be interpreted in terms of the local Le Chatelier principle for the AcidBase Equilibrium, with proper account of the three local contributions: counterions, protons, and chargeable groups. We find that one can achieve local changes of pH between one to two units within 1-2 nm. The thickness of the tethered layers as a function of bulk pH shows a large increase when the pH is equal to the bulk pK. However, the variation with salt concentration is different for the different geometries. The largest swelling is found for cylindrical surfaces. The predictions from scaling theories of a maximum in the thickness of the film as a function of salt concentration is found for planar films, but not for curved surfaces. Finally, the interactions between cylinders with tethered polyelectrolytes is very different from the equivalent planar surfaces. These results are important for the interpretation of force measurements with nanoscale AFM tips. The implications of the results for the rational design of responsive tethered polymer layers is discussed together with the limitations of the theoretical approach.

Giovanni Melillo – One of the best experts on this subject based on the ideXlab platform.

  • the slide rule a new method for the assessment of Acid Base Equilibrium disorders
    Minerva Anestesiologica, 2007
    Co-Authors: Di Iorio C, L Rufolo, E M Melillo, Alessandro Granata, Giovanni Melillo
    Abstract:

    Aim. Maps and nomograms are routinely used to evaluate AcidBase Equilibrium (ABE), but often require previous skilled practice and time to be used in the clinical setting; moreover, some definite alterations may be missed. The aim of this study was to evaluate the new slide rule (patented by Authors) for the rapid, precise and complete assessment and diagnosis of altered blood gas analysis (ABG) parameters and compare it to traditional methods. Methods. Once pH, bicarbonate and PaCO 2 values are known by arterial blood gas analysis (ABG), the slide rule can calculate, show and instantly diagnose the related alteration, including possible mixed partial compensated ones. In this regard, 330 patients coming from 6 (4 national and 2 foreign) clinics were studied; each patient underwent evaluation of ABG alterations using traditional methods and the slide rule immediately thereafter. Results. The results of consecutive evaluations on involved patients made by specialists in all clinics were in agreement; nonetheless, the slide rule was far more user friendly, rapid and complete in the ABE alterations’ diagnostic range, in comparison with traditional methods. Conclusion. All involved specialists confirmed that the new slide rule was able to rapidly diagnose ABE alterations, including mixed or partially compensated ones that may be missed by traditional methods.

  • The slide rule: a new method for the assessment of AcidBase Equilibrium disorders.
    Minerva anestesiologica, 2007
    Co-Authors: C. Di Iorio, E M Melillo, L Rufolo, Alessandro Granata, Giovanni Melillo
    Abstract:

    Maps and nomograms are routinely used to evaluate AcidBase Equilibrium (ABE), but often require previous skilled practice and time to be used in the clinical setting; moreover, some definite alterations may be missed. The aim of this study was to evaluate the new slide rule (patented by Authors) for the rapid, precise and complete assessment and diagnosis of altered blood gas analysis (ABG) parameters and compare it to traditional methods. Once pH, bicarbonate and PaCO(2) values are known by arterial blood gas analysis (ABG), the slide rule can calculate, show and instantly diagnose the related alteration, including possible mixed partial compensated ones. In this regard, 330 patients coming from 6 (4 national and 2 foreign) clinics were studied; each patient underwent evaluation of ABG alterations using traditional methods and the slide rule immediately thereafter. The results of consecutive evaluations on involved patients made by specialists in all clinics were in agreement; nonetheless, the slide rule was far more user friendly, rapid and complete in the ABE alterations’ diagnostic range, in comparison with traditional methods. All involved specialists confirmed that the new slide rule was able to rapidly diagnose ABE alterations, including mixed or partially compensated ones that may be missed by traditional methods.

Tahei Tahara – One of the best experts on this subject based on the ideXlab platform.

  • AcidBase Equilibrium at an Aqueous Interface: pH Spectrometry by Heterodyne-Detected Electronic Sum Frequency Generation
    The Journal of Physical Chemistry C, 2011
    Co-Authors: Shoichi Yamaguchi, Kankan Bhattacharyya, Tahei Tahara
    Abstract:

    We applied interface-selective heterodyne-detected electronic sum frequency generation (HD-ESFG) to the pH spectrometry of an air/cationic surfactant/water interface in order to obtain insight into an AcidBase Equilibrium at the interface. We used an indicator molecule adsorbed at the interface to probe local pH and local effective polarity. We obtained unprecedentedly high quality spectral data of the interfacial pH spectrometry, which clearly indicates that this interface has higher pH than the bulk owing to the positive charge of the head group of the surfactant. In addition, we found that the air/surfactant/water interface and the micelle interface of the same surfactant are essentially equivalent in local pH and local effective polarity.

  • Acid Base Equilibrium at an aqueous interface ph spectrometry by heterodyne detected electronic sum frequency generation
    Journal of Physical Chemistry C, 2011
    Co-Authors: Shoichi Yamaguchi, Kankan Bhattacharyya, Tahei Tahara
    Abstract:

    We applied interface-selective heterodyne-detected electronic sum frequency generation (HD-ESFG) to the pH spectrometry of an air/cationic surfactant/water interface in order to obtain insight into an AcidBase Equilibrium at the interface. We used an indicator molecule adsorbed at the interface to probe local pH and local effective polarity. We obtained unprecedentedly high quality spectral data of the interfacial pH spectrometry, which clearly indicates that this interface has higher pH than the bulk owing to the positive charge of the head group of the surfactant. In addition, we found that the air/surfactant/water interface and the micelle interface of the same surfactant are essentially equivalent in local pH and local effective polarity.