Engineering polyzwitterion with acylsulfonamide-based betaine structure for protonated switch of surface chemistry at tumoral pH and reductive responsive drug release of polymeric micelles

The surface chemistry of stimulus-responsive nanoparticles plays an important role in mediating nano-bio interactions in cancer nanomedicine by targeting the unique features of the tumor microenvironment, such as low extracellular pH. To develop therapeutic nanoparticles with high sensitivity and instant response to slight pH differences in the systemic circulation, we produced a novel polyzwitterion with acylsulfonamide-based betaine structure by one-step modification of polycarboxybetaine (PCB) with benzene sulfonamide. The zwitterionic micellar shells show high antifouling in the blood circulation and acutely convert into positive charge via acylsulfonamide protonation, thereby improving cell affinity at tumor sites. Moreover, a disulfide bond between the shell and poly-ε-caprolactone (PCL) core allows for reductive-responsive release of doxorubicin (DOX) after internalization of the polymeric micelles. Finally, in vitro and in vivo competition assays demonstrated that dual responsive drug-loaded micelles have better anticancer efficiency than free DOX or micelles without zwitterionic pH-responsive properties. Thus, we have developed a simple and valuable strategy to enhance pH sensitivity of micellar carriers for cancer treatment.     

Separating nanoparticles by surface charge group using pH-controlled passivated gel electrophoresis

Because ionically stabilized colloids in aqueous dispersions have net surface charges that depend on pH, it is potentially possible to separate mixtures of nanospheres having identical radii, yet different types of stabilizing surface charge groups, efficiently using passivated gel electrophoresis (gel-EP). To demonstrate this, we separate a binary dispersion of polystyrene nanospheres that have nearly identical radii and surface group densities, yet different types of anionic stabilizing surface charge groups: sulfate and carboxylate. We achieve an efficient separation by adjusting the pH of the running buffer to lie between the pK_a values of these charge groups, resulting in significantly different protonation and, consequently, different electrophoretic propagation velocities of the nanospheres. The measured steady-state propagation velocities of both types of anionic nanoparticles as a function of pH can be fit well by an equilibrium model of pH-dependent protonation of anionic surface charge groups. Thus, pH-controlled passivated gel-EP opens a route for separating similarly sized charged colloidal objects that are stabilized by a variety of different surface charge groups.     

Effects of system net charge and electrostatic truncation on all‐atom constant pH molecular dynamics

Constant pH molecular dynamics offers a means to rigorously study the effects of solution pH on dynamical processes. Here, we address two critical questions arising from the most recent developments of the all‐atom continuous constant pH molecular dynamics (CpHMD) method: (1) What is the effect of spatial electrostatic truncation on the sampling of protonation states? (2) Is the enforcement of electrical neutrality necessary for constant pH simulations? We first examined how the generalized reaction field and force‐shifting schemes modify the electrostatic forces on the titration coordinates. Free energy simulations of model compounds were then carried out to delineate the errors in the deprotonation free energy and salt‐bridge stability due to electrostatic truncation and system net charge. Finally, CpHMD titration of a mini‐protein HP36 was used to understand the manifestation of the two types of errors in the calculated pK_a values. The major finding is that enforcing charge neutrality under all pH conditions and at all time via cotitrating ions significantly improves the accuracy of protonation‐state sampling. We suggest that such finding is also relevant for simulations with particle mesh Ewald, considering the known artifacts due to charge‐compensating background plasma. © 2014 Wiley Periodicals, Inc.     

Potentiometry, Stability and Thermodynamics of Diethyltin(IV) Dichloride with Some Selected Biomolecules

The interaction of diethyltin(IV), DET, with selected bioligands having a variety of model functional groups was investigated at 25 °C and ionic strength 0.1 mol·dm^?3 NaCl using the potentiometric technique. The hydrolysis constants of the DET cation and the formation constants of the complexes formed in solution were calculated using the MINIQUAD-75 program. The stoichiometry and stability constants for the complexes formed are reported. The results show the formation of 1:1 and 1:2 complexes with amino acids and DNA constituents. The dicarboxylic acids form 1:1 complexes. The peptides form both 110 complexes and the corresponding deprotonated amide species [Et₂Sn(LH_?1)] (11-1). The participation of different ligand functional groups in binding to organotin is discussed. The concentration distributions of the various complex species were evaluated as a function of pH. The standard thermodynamic parameters ΔH° and ΔS°, calculated from the temperature dependence of the equilibrium constants, were investigated for the interaction of DET with thymine as a representative example of DNA constituents. The effect of ionic strength and solvent on hydrolysis constants of DET, protonation equilibria of thymine and its complex formation with DET were investigated and discussed.     

The effect of pH and surfactant on the aggregation behavior of chlorin p6: a fluorescence spectroscopic study

Steady state and time-resolved fluorescence properties of chlorin P6, a potential drug for photodynamic therapy, have been investigated as functions of pH. A decrease in pH of the medium has been shown to cause protonation of the ionizable carboxylic acid side chain, leading to an increase in hydrophobicity and consequent aggregation. The aggregates dissociate on further protonation. The dissociation is explained in terms of formation of cations and their mutual repulsion. A synchronous fluorescence spectroscopic study revealed the presence of two anionic forms in equilibrium at physiological pH, with a shift in the equilibrium on slight decrease in the pH. The anionic nature of chlorin P6 in aqueous solutions at physiological pH has been confirmed by complexation with surfactants. The nature of the charge on the headgroups of the surfactants has been found to govern the formation of chlorin-surfactant complexes.     

A pH‐responsive cyclopolymer having phospho‐ and sulfopropyl pendents in the same repeating unit: Synthesis,characterization, and its application as an antiscalant

A new zwitterionic monomer 3‐[diallyl{3‐(diethoxyphosphoryl)propyl}ammonio]propane‐1‐sulfonate has been synthesized and cyclopolymerized to give the corresponding polyzwitterion (±) (PZ) bearing both phosphonate and sulfonate functionalities on each repeating unit. phosphonate ester hydrolysis in PZ gave a pH‐responsive dibasic polyzwitterionic acid (±) (PZA) bearing ? PO₃H₂ units. The PZA under pH‐induced transformation was converted into polyzwitterion/anion (± ?) (PZAN) and polyzwitterion/dianion (± =) (PZDAN) having respective ? PO₃H^? and ? PO₃^2? units. The polymers′ interesting solubility and viscosity behaviors have been investigated in detail. The apparent protonation constants in salt‐free water and 0.1 M NaCl of the ? PO₃^2? in (± =) (PZDAN) and ? PO₃H^– in (± ?) (PZAN) as well as in their corresponding monomeric units have been determined. Evaluation of antiscaling properties of the PZA using supersaturated solution of CaSO₄ revealed ≈100% scale inhibition efficiency at a meager concentration of 20 ppm for a duration of 45 h at 40 °C. The PZA has the potential to be used effectively as an antiscalant in reverse osmosis plant. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5130–5142     

Charge selective encapsulation by polymeric micelles with cationic,anionic, or zwitterionic cores

Polymeric micelles showing charge selective and pH‐reversible encapsulation are reported. It is found that for a guest mixture of organic cationic–anionic dyes, a unimolecular micelle (PEI@PS) with a polystyrene (PS) as shell and a hyperbranched polyethylenimine (PEI) as core can exclusively entrap the anionic one; and a physical micelle consisting of brush‐like macromolecule (mPS‐PAA) with multi PS‐b‐polyacrylic acid (PAA) as grafts can exclusively entrap the cationic one. A covalent micelle (PEI‐COOH@PS) bearing a zwitterionic core, that is, PEI covalently derived with dense carboxylic acids, can undergo highly pH‐switchable charge selective and pH‐reversible encapsulation. Both PEI@PS and mPS‐PAA can be used for highly charge‐selective separation of ionic dyes but the pH‐reversibility of the encapsulation is relatively limited. In contrast, PEI‐COOH@PS is less effective to differentiate the anionic–cationic dyes but is well recyclable. A physical micelle obtained from the self‐assembly of PEI and mPS‐PAA shows similar property to PEI‐COOH@PS. The combination of these micelles in mixture separation can enhance the recyclability of the micelle and widen the spectrum of mixtures that can be well separated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

pH‐responsive ampholytic terpolymers of acrylamide,sodium 3‐acrylamido‐3‐methylbutanoate,and (3‐acrylamidopropyl)trimethylammonium chloride. II. Solution properties

The solution properties of low‐charge‐density ampholytic terpolymers of acrylamide, sodium 3‐acrylamido‐3‐methylbutanoate, and (3‐acrylamidopropyl)trimethylammonium chloride were studied as functions of the solution pH, ionic strength, and polymer concentration. Terpolymers with low charge densities, large charge asymmetries, or both exhibited excellent solubility in deionized (DI) water, and higher charge density terpolymers were readily dispersible in DI water; however, the higher charge density terpolymer solutions separated into polymer‐rich and polymer‐poor phases upon standing over time. Charge‐balanced terpolymers exhibited antipolyelectrolyte behavior at pH values greater than or equal to the ambient pH (6.5 ± 0.2); the same terpolymers behaved increasingly as cationic polyelectrolytes with decreasing solution pH because of the protonation of the 3‐acrylamido‐3‐methylbutanoate (AMB) repeat units. Unbalanced terpolymers generally exhibited polyelectrolyte behavior, although the effects of intramolecular electrostatic attractions (i.e., polyampholyte effects) on the hydrodynamic volume of the unbalanced terpolymer coils were evident at certain values of the solution pH and salt concentration. The dilute‐solution behavior of the terpolymers correlated well with the behavior predicted by several polyampholyte solution theories. In the semidilute regime, solution viscosities increased with increasing terpolymer charge density, and this indicated a significant enhancement of the solution viscosity by intermolecular electrostatic associations. Upon the addition of NaCl, semidilute‐solution viscosities tended to decrease because of the disruption of the intermolecular electrostatic associations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3252–3270, 2004     

Polyampholyte terpolymers of amphoteric,amino acid‐based monomers with acrylamide and (3‐acrylamidopropyl)trimethyl ammonium chloride

Low‐charge‐density amphoteric copolymers and terpolymers composed of acrylamide, (3‐acrylamidopropyl)trimethyl ammonium chloride, and the amino acid derived monomers (e.g., N‐acryloyl valine, N‐acryloyl alanine, and N‐acryloyl aspartate) were prepared via free‐radical polymerization in aqueous media to yield terpolymers with random charge distributions and homogeneous compositions. Sodium formate (NaOOCH) was employed as a chain transfer agent during the polymerization to suppress gel effects and broadening of the molecular weight distribution. Terpolymer compositions were determined by ¹³C and ¹H NMR spectroscopy. Terpolymer molecular weights and polydispersity indices were obtained via size exclusion chromatography/multi‐angle laser light scattering, and hydrodynamic diameter values were obtained via dynamic light scattering. The solution properties of low‐charge‐density amphoteric copolymers and terpolymers have been studied as a function of solution pH, ionic strength, and polymer concentration. The low‐charge‐density terpolymers display excellent solubility in deionized (DI) water with no phase separation. The charge‐balanced terpolymers exhibit antipolyelectrolyte behavior at pH values ≥(6.5 ± 0.2). As solution pH is decreased, these charge‐balanced terpolymers become increasingly cationic because of the protonation of the anionic repeat units. Charge‐imbalanced terpolymers generally demonstrate polyelectrolyte behavior, although the effects of intramolecular electrostatic interactions (e.g., polyampholyte effects) on the hydrodynamic volume are evident at certain values of solution pH and salt concentration. The aqueous solution behavior (i.e., globule‐to‐coil transition at the isoelectric point in the presence of salt and globule elongation with increasing charge asymmetry) of the terpolymers in the dilute regime correlates well with that predicted by the polyampholyte solution theories of Dobrynin and Rubinstein as well as Kantor and Kardar. Examination of comonomer charge density, hydrogen‐bonding ability, and spacer group (e.g., the moiety separating the ionic group from the polymer chain) indicates that conformational restrictions of the amino acid comonomers result in increased chain stiffness and higher solution viscosities in DI water and brine solutions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4479–4493, 2006     

Thermodynamic study of transthyretin association (wild‐type and senile forms) with heparan sulfate proteoglycan: pH effect and implication of the reactive histidine residue

The tetramer destabilization of transthyretin into monomers and its fibrillation are phenomena leading to amyloid deposition. Heparan sulfate proteoglycan (HSPG) has been found in all amyloid deposits. A chromatographic approach was developed to compare binding parameters between wild‐type transthyretin (wtTTR) and an amyloidogenic transthyretin (sTTR). Results showed a greater affinity of sTTR for HSPG at pH 7.4 compared with wtTTR owing to the monomeric form of sTTR. Analysis of the thermodynamic parameters showed that van der Waals interactions were involved at the complex interface for both transthyretin forms. For sTTR, results from the plot representing the number of protons exchanged vs pH showed that the binding mechanism was pH‐dependent with a critical value at a pH 6.5. This observation was due to the protonation of a histidine residue as an imidazolium cation, which was not accessible when TTR was in its tetrameric structure. At pH >6.5, dehydration at the binding interface and several contacts between nonpolar groups of sTTR and HSPG were also coupled to binding for an optimal hydrogen‐bond network. At pH <6.5, the protonation of the His residue from sTTR monomer when pH decreased broke the hydrogen‐bond network, leading to its destabilization and thus producing slight conformational changes in the sTTR monomer structure. Copyright © 2014 John Wiley & Sons, Ltd.     

Chiral separation of anionic and neutral compounds using a hepta-substituted cationic beta-cyclodextrin as a chiral selector in capillary electrophoresis

Enantiomeric separations of six anionic and two neutral racemates were achieved using a fully substituted heptakis(6-hydroxyethylamino-6-deoxy)-beta-cyclodextrin (beta-CD-EA) as a chiral selector. As beta-CD-EA provides a dynamic coating on the capillary wall, reverse-polarity capillary electrophoresis (CE) configuration is applied for separations of anionic and neutral chiral compounds. Chiral separations of various classes of anionic and neutral enantiomers were found to be highly dependent on pH because the degree of protonation of beta-CD-EA can alter the shape of the CD cavity by charge repulsion, altering complexation, aiding selectivity, and leading to better enantiomeric separation. In general, the chiral resolution of anionic enantiomers was enhanced at higher pH. This suggests that carboxylate or phosphate groups on the analyte may interact with the protonated amine groups of cationic CD. The successful enantioseparation was achieved in a pH range of 6.6-7.8 for all six anionic analytes, in the presence of 10 mM beta-CD-EA.     

Unexpected differences in the behavior of ovotransferrin at the air-water interface at pH 6.5 and 8.0

Adsorption of purified apo-ovotransferrin at the air-water interface was studied by ellipsometry, surface tension, polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and shear elastic constant measurements. No significant difference was observed between pH 6.5 and 8.0 as regards the final value of surface concentration and surface pressure. However at low concentration, a weak barrier to adsorption is evidenced at pH 6.5 and confirmed by PM-IRRAS measurements. At a pH where the protein net charge is negative (pH 8.0), the behavior of ovotransferrin at the air-water interface is more influenced by charge effects rather than bulk concentration effects. At this pH, the interface exhibits a low shear elastic constant and a spectral signature not usual for globular proteins.     

Computer-assisted choice of discrete spacers for anionic isotachophoresis separations

In isotachophoresis (ITP), the sample constituents migrate, depending on their concentrations in the loaded sample, either in fully developed zones or in the boundary layers between the zones of constituents of the corresponding effective mobilities. The latter (spike) migration mode is analytically beneficial in selective detections of trace analytes, especially, when appropriately chosen discrete spacers minimize detection interferences due to matrix constituents. To facilitate a search for suitable mixtures of discrete spacers, a two-step calculation procedure was developed in this work. Using a pool of discrete spacers consisting of 42 anionic and zwitterionic constituents, this procedure was shown effective in the anionic ITP separations performed at pH = 6.5-10.0. Besides the predictions of the migration orders, it was helpful in identifying the spacing constituents that could cause resolution problems due to an uncertainty with which pH of the leading electrolyte solution is known. The ionic mobility and pKa data, taken for the spacing constituents from the literature and the ones obtained from the ITP experiments carried out in this work, were used in the calculations performed in a context with the choice of spacers. Although the data obtained from the ITP experiments provided better results, small uncertainties with which they were acquired (attributable to fluctuations in the experimental conditions) set practical limits in the calculation based choice of multi-component mixtures of the spacing constituents.     

Determination of Point of Zero Charge of Tunisian Kaolinites by Potentiometric and Mass Titration Methods

This paper deals with determining points of zero charge of natural and Na⁺‐saturated mineral kaolinites using two methods: (1) acid‐base potentiometric titration was employed to obtain the adsorption of H⁺ and OH^? on amphoteric surfaces in solutions of varying ionic strengths in order to determinate graphically the point of zero net proton charge (PZNPC) defined equally as point of zero salt effect (PZSE); (2) mass titration curve at different electrolyte concentrations in order to estimate PZNPCs by interpolation and to compare with those determined by potentiometric titrations. The two methods involved points of zero charge approximately similar for the two kaolinites between 6.5‐7.8, comparable to those reported previously and were in the range expected for these clay minerals. The comparison of potentiometric surface titration curves obtained at 25 °C and those published in the literature reveals significant discrepancies both in the shape and in the pH of PZNPCs values.     

Surface protonation data of kaolinite-reevaluation based on dissolution experiments

The aim of the present study is to compare available surface titration curves of kaolinite, to explain the differences between them, and to constrain their interpretation based on predictions of surface protonation that emerged from dissolution experiments. Comparison of six surface titration curves obtained at 25 degrees C reveals significant discrepancies, both in the shape of the curves and in the pH of the point of zero net proton charge (pH(PZNPC)). Based on an analysis of the different sites available for adsorption on kaolinite surfaces we conclude that different kaolinite samples are expected to have similar pH(PZNPC). Therefore, the major reason for the differences in the observed surface protonation is related to the different ways in which the pH(PZNPC) was determined. To compare the titration curves, some of the curves were recalculated so that the proton surface concentrations of all the titration curves would be zero around pH 5. As a result, we obtained a good agreement between the titration curves. A prediction of the molar fraction of protonated sites was retrieved from modeling of kaolinite dissolution reaction and was compared to the protonation data obtained from surface titration. The model successfully predicts the surface protonation data of most of the surface titrations.     

Direct Electron Transfer Reaction of Ascorbate Oxidase Immobilized by a Self‐Assembled Monolayer and Polymer Membrane Combined System

This paper reports a novel enzyme‐immobilization method for the direct electron transfer (DET) reaction of ascorbate oxidase from Acremonium sp. HI‐25 (ASOM). ASOM was adsorbed onto a gold electrode modified with a self‐assembled monolayer (SAM) of alkanethiol derivatives and immobilized by a cationic polymer membrane and anionic ω‐carboxyalkanethiol combined system. The redox responses of the immobilized ASOM were investigated by cyclic voltammetry. We found that the DET reaction of ASOM was facilitated by this novel immobilization. On the other hand, the redox responses of poly(ethylene oxide) (PEO)‐modified ASOMs were also investigated. ASOM was modified with two types of PEO which possess straight chain‐shaped (PEO₂₀₀₀) or comb‐shaped conformation (PM₆₇). As a result, the DET reactions of PEO‐modified ASOMs were also facilitated by this immobilization method. We concluded that this immobilization method is effective for promoting the DET reaction of ASOMs.     

Photochemical Properties of the Red‐shifted Channelrhodopsin Chrimson

Color‐tuned variants of channelrhodopsins allow for selective optogenetic manipulation of different host cell populations. Chrimson is the channelrhodopsin with the longest wavelength absorbance maximum. We characterize its photochemical properties at different pH values corresponding to two protonation states of the counterion for the protonated Schiff base. Both states will lead to a functional channel opening, but the route is different as reflected in the photochemical states observed spectroscopically. The light‐induced isomerization kinetics change with the local electrostatic environment, becoming faster with the presence of an anionic counterion. The spectral effect is stronger on the ground‐state energy surface. From the excited state, a bifurcated pathway leads to the electronic ground state resulting in a pronounced excitation wavelength dependence. The subsequent steps in the photocycles at pH 6 and pH 9.5 differ in the accumulation of states with a protonated and deprotonated Schiff base, respectively, that can be correlated with the open channel. Therefore, different protonation states are preserved in the open and the initial states. Chrimson's photocycle at alkaline pH shows features observed in other rhodopsins without an internal proton donor to the Schiff base, but it accumulates an intermediate with an even longer lifetime reflecting slow recovery of the initial state.     

Disparity between solution-phase equilibria and charge state distributions in positive-ion electrospray mass spectrometry

Two peptides, bradykinin and gramicidin S, were used to investigate the relationship between protonation in the solution phase and charge state distribution observed in electrospray ionization (ES) mass spectra. The degree of protonation in solution was estimated using acid-base equilibrium calculations where possible. Protonation in solution was varied by adjusting pH, solvent composition and peptide concentration. Major disparities were observed between calculated solution-phase peptide protonation and the charge state distributions observed in ES mass spectra. The [(M + 2H)²⁺]/[(M + H)⁺] ratio calculated in solution was larger than the abundance ratio (M + 2H)²⁺ /(M + H)⁺ in the ES mass spectra of all acidic aqueous (pH < 6.5) and non-aqueous solutions; in basic aqueous solutions (pH > 9.5) the opposite was true. At high pH, electrophoretic droplet charging may reduce the activity of OH^? in positively charged droplets. The results at low pH imply the existence of supplementary factors in the ES ionization process which largely attenuate the degree of charging in the gas phase as compared with solution. Factors such as the increasing intra- and intermolecular coulombic repulsion between charge carriers (protons) and increasing attractive forces between protonated sites and counterions at progressively later stages of charged droplet evaporation were hypothesized to be chiefly responsible for this effect. Non-aqueous solvents of high basicity compete with analytes to some extent for available protons, forming protonated solvent molecules while decreasing the sensitivity and the degree of multiple charging of peptides.     

Synthesis and Characterization of pH‐Sensitive Positive‐charge Silica Nanoparticles for Oral Anionic Drug Delivery

The objective of this study is to utilize the pH sensitivity of modified mesoporous silica nanoparticles (MSN) for oral drug delivery. In the first time, a pH‐sensitive ionic liquid was synthesized through the quaternization of 3‐aminopropyltrimethoxysilane (3‐ATMS) with sodium monochloroacetate (SMCA). Then, silica nanoparticle was modified by this pH‐sensitive ionic liquid and converted to a pH‐sensitive positive‐charge silica nanoparticle (PCSN). The nanoparticle was characterized by FTIR and SEM. Naproxen as anionic drug molecules was entrapped in this pH‐sensitive positive‐charge silica nanoparticles (PCSN) and the in vitro release profiles were established separately in both (SGF, pH 1) and (SIF, pH 7.4).     

Acid‐base properties of poly(amidoamine)s

Polyamidoamines (PAAs) represent a family of degradable polymers carrying tert‐amine groups in the polymer backbone, which behave as polyelectrolytes in aqueous solutions. Many relevant properties of PAAs, including the ability to interact with components of the biological environments, such as nucleic acids, proteins, and living cells, are strongly dependent on their acid‐base properties, hence on their ionization state in different biological districts. In this article, the protonation constants of a series of PAAs have been precisely determined by electrochemical techniques in order to build up a homogeneous library containing both the protonation constants and the average distribution of the charged species, hence the net average charge as a function of pH. Moreover, correlations between chemical and cytotoxicity, have been attempted. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009