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Ruscogenin, a kind of steroid saponin, has been shown to have significant anti-oxidant, anti-inflammatory, and anti-thrombotic characteristics. Furthermore, it has the potential to be employed as a medicinal medication to treat a variety of acute and chronic disorders. The interaction of a drug molecule with cell membranes can help to elucidate its system-wide protective and therapeutic effects, and it's also important for its pharmacological activity. The molecular mechanism by which ruscogenin affects membrane architecture is still a mystery. Ruscogenin's interaction with zwitterionic dipalmitoyl phosphatidylcholine (DPPC) and anionic dipalmitoyl phosphatidylglycerol (DPPG) multilamellar vesicles (MLVs) was studied utilizing two non-invasive approaches, including: Fourier Transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry. Ruscogenin caused considerable alterations in the phase transition profile, order, dynamics and hydration state of head groups and glycerol backbone of DPPC and DPPG MLVs at all concentrations. The DSC results indicated that the presence of ruscogenin decreased the main phase transition temperature (Tm) and enthalpy (?H) values of both membranes and increased half height width of the main transition (?T1/2). The FTIR results demonstrated that all concentrations (1, 3, 6, 9, 15, 24 and 30 mol percent) of ruscogenin disordered the DPPC MLVs both in the gel and liquid crystalline phases while it increased the order of DPPG MLVs in the liquid crystalline phase. Moreover, ruscogenin caused an increase in the dynamics of DPPC and DPPG MLVs in both phases. Additionally, it enhanced the hydration of the head groups of lipids and the surrounding water molecules implying ruscogenin to interact strongly with both zwitterionic and charged model membranes. © 2022 Elsevier Inc., Ege Üniversitesi: FGA-2021-22592, This work was supported by Ege University Scientific Research Projects Coordination. (Project number is FGA-2021-22592)., This work was supported by Ege University Scientific Research Projects Coordination . (Project number is FGA-2021-22592 ).

Peptides containing amino acids with ionisable side chains represent a typical example of weak ampholytes, that is, molecules with multiple titratable acid and base groups, which generally exhibit charge regulating properties upon changes in pH. Charged groups on an ampholyte interact electrostatically with each other, and their interaction is coupled to conformation of the (macro)molecule, resulting in a complex feedback loop. Their charge-regulating properties are primarily determined by the pKA of individual ionisable side-chains, modulated by electrostatic interactions between the charged groups. The latter is determined by the amino acid sequence in the peptide chain. In our previous work we introduced a simple coarse-grained model of a flexible peptide. We validated it against experiments, demonstrating its ability to quantitatively predict charge on various peptides in a broad range of pH. In the current work, we investigated two types of peptide sequences: diblock and alternating, each of them consisting of an equal number of amino acids with acid and base side-chains. We showed that changing the sequence while keeping the same overall composition has a profound effect on the conformation, whereas it practically does not affect total charge on the peptide. Nevertheless, the sequence significantly affects the charge state of individual groups, showing that the zero net effect on the total charge is a consequence of unexpected cancellation of effects. Furthermore, we investigated how the difference between the pKA of acid and base side chains affects the charge and conformation of the peptide, showing that it is possible to tune the charge-regulating properties by following simple guiding principles based on the pKA and on the amino acid sequence. Our current results provide a theoretical basis for understanding of the complex coupling between the ionisation and conformation in flexible polyampholytes, including synthetic polymers, biomimetic materials and biological molecules, such as intrinsically disordered proteins, whose function can be regulated by changes in the pH.

Multidimensional characterization of polyelectrolytes and interpolyelectrolyte complexes in aqueous solutions Abstract: This PhD thesis is dedicated to the study of polyelectrolytes and their self-assembly in aqueous solutions. The morphology and ionization state of individual polymer chains were investigated as well as their co-assembly with oppositely charged species. First, the charge regulation of short and long weak polyelectrolytes in aqueous solution was investigated to deeper understand their pH-responsive properties. The changes of ionization degree and charge of oligopeptides composed of 5 amino acids with acid side-chains and 5 with basic side chains were followed upon varying the pH in order to reveal the effect of interactions between the like-charged and oppositely charged groups. It was shown that intra-molecular electrostatic interactions and conformational flexibility caused the suppression of the total charge and enhancement of ionization of the peptides. To get an insight into the distribution of local H+ concentration in the proximity of a polyelectrolyte chain, a modified polyelectrolyte structure was used with a fluorescent pH- indicator, covalently attached at the end of the chain. Ionization of the pH-responsive fluorophore revealed its effective pK which was compared with the local...

Peptides containing amino acids with ionisable side chains represent a typical example of weak ampholytes, that is, molecules with multiple titratable acid and base groups, which generally exhibit charge regulating properties upon changes in pH. Charged groups on an ampholyte interact electrostatically with each other, and their interaction is coupled to conformation of the (macro)molecule, resulting in a complex feedback loop. Their charge-regulating properties are primarily determined by the pKA of individual ionisable side-chains, modulated by electrostatic interactions between the charged groups. The latter is determined by the amino acid sequence in the peptide chain. In our previous work we introduced a simple coarse-grained model of a flexible peptide. We validated it against experiments, demonstrating its ability to quantitatively predict charge on various peptides in a broad range of pH. In the current work, we investigated two types of peptide sequences: diblock and alternating, each of them consisting of an equal number of amino acids with acid and base side-chains. We showed that changing the sequence while keeping the same overall composition has a profound effect on the conformation, whereas it practically does not affect total charge on the peptide. Nevertheless, the sequence significantly affects the charge state of individual groups, showing that the zero net effect on the total charge is a consequence of unexpected cancellation of effects. Furthermore, we investigated how the difference between the pKA of acid and base side chains affects the charge and conformation of the peptide, showing that it is possible to tune the charge-regulating properties by following simple guiding principles based on the pKA and on the amino acid sequence. Our current results provide a theoretical basis for understanding of the complex coupling between the ionisation and conformation in flexible polyampholytes, including synthetic polymers, biomimetic materials and biological molecules, such as intrinsically disordered proteins, whose function can be regulated by changes in the pH.

[EN] The use of EDTA as a complexing agent in electrodialysis has gained increasing attention in several industrial applications. Variations in pH at the membrane surface are known to alter the chemical equilibrium of EDTA species during electrodialysis. In this work, we investigate the simultaneous transport of EDTA species and hydroxyl ions through an anion-exchange membrane under alkaline conditions, and the influence of their relative concentrations on relevant membrane transport properties. Chronopotentiometric and current-voltage curves were obtained using solutions at different pH and electrolyte concentrations. Intense oscillations in membrane potential drop and a reduction in membrane resistance over time were verified for the solution at pH 11, where EDTA(4-) and OH- ions presented similar molar concentrations. While the intense oscillations can be associated with the onset of electroconvection, the reduction in membrane potential drop can be explained based on the alteration of the chemical equilibrium in the system. At an advanced stage of concentration polarization, the increased exclusion of protons in the membrane phase induces an equilibrium shift and the dissociation of HEDTA(3-) into EDTA(4-) and H+ ions. The formed EDTA(4-) ions migrate to the enriched solution, while protons are released back to the diluting diffusion boundary layer, increasing the conductivity in this region. The equilibrium shift in the membrane/electrolyte system and intense electroconvection at the membrane surface were also noted with the solution at pH 12. When the concentrations of OH- and EDTA species are similar, the equilibrium shift and the occurrence of overlimiting phenomena become more prominent., The authors gratefully acknowledge the financial support given by funding agencies CNPq (Process 141346/2016-7) and CAPES (Process 88881.190502/2018-01). This study was financed in part by the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior - Brasil (CAPES) - Finance Code 001.

The aim of this work is the understanding of how the distribution of functional groups (i.e. basic and acid moieties added through copolymerization) within the polymer network of environmentally responsive microgels influences the microgels’ properties. Applications of microgels are manifold and range from encapsulation/controlled release of drugs and genes and chemical sensing and/or filtration in membranes to coating for non-biofouling and protein-repellent surfaces. With regard to each application, the microgel architecture plays a crucial role. Zwitterionic and ampholyte microgels based on poly(N-vinylcaprolactam) (PVCL) and poly(N-isopropylacrylamide) (PNIPAm) with various distributions of basic and acid moieties within the microgel particle are synthesized and characterized in the first part of the work. The functional groups are incorporated either statistically, as core-shell or Janus. The influence of the distribution of ionizable groups as well as their amount in the microgel on the microgels’ properties such as particle size distribution, hydrodynamic radius, temperature- and pH-sensitivity, and softness is looked at. The second part looks closely at the influence of different microgel architecture on the uptake and release of charged species. Cytochrome c is used as a model protein and its release using various triggers such as temperature, the addition of salt and a change in pH is studied. Here, the focus is on how different distributions of ionizable groups lead to different uptake and release mechanisms. Hybrid materials of the above discussed microgels are studied in the third part of the work. First, ionizable microgels are used as nano-containers for biomineralization of CaCO3 and for bone substitution with β-TCP. Furthermore, zwitterionic microgels are deposited on surfaces to study the influence of the betaine amount on the surface’s hydrophilicity, protein-repellency, and self-healing properties.

Five star polymers based on the positively ionizable hydrophilic 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the hydrophobic but hydrolyzable tetrahydropyranyl methacrylate (THPMA) were prepared by group-transfer polymerization (GTP) using ethylene glycol dimethacrylate (EGDMA) as the coupling agent. In particular, four isomeric star copolymers (one heteroarm, two star block, and the statistical star), all with a 3:1 DMAEMA: THPMA molar ratio, plus one star homopolymer of DMAEMA, with degrees of polymerization of the arms equal to 15, were synthesized. After star polymer preparation and preliminary characterization, the THPMA units were hydrolyzed to negatively ionizable hydrophilic methacrylic acid (MAA) untis, thus yielding star polyampholytes. All the star polyampholytes as well as the commercially available transfection reagent SuperFect were evaluated for their ability to transfect human cervical HeLa cancer cells with the modified plasmid pRLSV40 bearing the enhanced green fluorescent protein (EGFP) as the reporter gene. The transfection efficiency was affected by star architecture. The DMAEMA15-star-MAA5 polyampholyte presented the highest transfection efficiency of all the star polymers tested but lower than that of SuperFect at its optimum conditions. All four star copolymers showed decreased toxicity compared to the DMAEMA star homopolymer for the same amounts of star polymer tested and also compared to the SuperFect at its optimum conditions. © 2006 American Chemical Society. 7 12 3505 3512 Manufacturers: Aldrich, Germany Cited By :65

The wide application of organic acids in the food, chemical and pharmaceutical industry is responsible for the increased interest in the development of new technologies for their isolation, separation and concentration from the complex solutions. The electro-membrane processes are promising. The difficulty to understand the transport mechanisms of the amphoteric solution in the electromembrane system is the coupling of chemical reactions: the ionic forms composition can vary depending on the pH of the solution.The main objectives are the study of the behavior of membrane systems containing ampholyte solutions in a steady state (without transfer force or under very low AC) and in a non-equilibrium state such as in electrodialysis regime (applying a current). In both cases, a study includes the experimental and theoretical parts of characterization of the complex solution transport. In the context of modeling a model of the membrane system which can calculate the ampholyte form distribution inside and outside the membrane depending on the external parameters was developed.The comparison of experimental data and results obtained from the simulation of membrane systems containing ampholytes solutions, shows and explains the specific features in the transfer mechanism of ampholyte ions which associated with changes of the solution pH during electrodialysis and, as a consequence, with modification of ampholyte forms.; L'utilisation croissante d'acides organiques dans l'industrie alimentaire, chimique et pharmaceutique entraîne le développement de nouvelles technologies pour leur isolement, séparation et concentration à partir de solutions complexes. Les procédés électro-membranaires constituent une voie prometteuse. Afin d'intensifier ces procédés, il est nécessaire de mieux comprendre les mécanismes de transport de la solution d'ampholytes dans le système électromembranaire souvent couplé à des réactions chimiques. La composition des formes ioniques peut en effet varier en fonction du pH de la solution. Les principaux objectifs de ce travail sont l'étude du comportement des systèmes membranaires contenant des solutions d'ampholytes dans un état d'équilibre (sans force de transfert ou sous très faible courant alternatif), et hors d'équilibre en régime d'électrodialyse (application d'un courant). Dans les deux cas, l'approche comprend une partie expérimentale et une partie théorique de caractérisation de transport de solution complexe. Dans la cadre de la modélisation associée, on a développé un modèle de système membranaire qui permet d'accéder à la distribution des formes d'ampholyte à l'intérieur et à l'extérieur de la membrane en fonction des paramètres externes.Les résultats de la comparaison des données expérimentales et de simulation de systèmes membranaires montre et explique les spécificités des mécanismes de transfert des ions d'ampholyte associés aux changements du pH de la solution au cours de l'électrodialyse.

Cyclic secondary amines and 2-hydroxybenzaldehydes or related ketones react to furnish benzo[e][1,3]oxazine structures in generally good yields. This overall redox-neutral amine α-C-H functionalization features a combined reductive N-alkylation/oxidative α-functionalization and is catalyzed by acetic acid. In contrast to previous reports, no external oxidants or metal catalysts are required. Reactions performed under modified conditions lead to an apparent reductive amination and the formation of o-hydroxybenzylamines in a process that involves the oxidation of a second equivalent of amine. A detailed computational study employing density functional theory compares different mechanistic pathways and is used to explain the observed experimental findings. Furthermore, these results also reveal the origin of the catalytic efficiency of acetic acid in these transformations. © 2014 American Chemical Society.

The increased application of nanoparticles (NPs) is increasing the risk of their release into the environment. Although many toxicity studies have been conducted, the environmental risk is difficult to estimate, because uptake mechanisms are often not determined in toxicity studies. In the present study, the authors review dominant uptake mechanisms of NPs in cells, as well as the effect of NP properties, experimental conditions, and cell type on NP uptake. Knowledge of NP uptake is crucial for risk assessment and is essential to predict the behavior of NPs based on their physical-chemical properties. Important uptake mechanisms for eukaryotic cells are macropinocytosis, receptor-mediated endocytosis, and phagocytosis in specialized mammalian cells. The studies reviewed demonstrate that uptake into nonphagocytic cells depends strongly on NP size, with an uptake optimum at an NP diameter of approximately 50nm. Increasing surface charges, either positive or negative, have been shown to increase particle uptake in comparison with uncharged NPs. Another important factor is the degree of (homo-) aggregation. Results regarding shape have been ambiguous. Difficulties in the production of NPs, with 1 property changed at a time, call for a full characterization of NP properties. Only then will it be possible to draw conclusions as to which property affected the uptake. Environ Toxicol Chem 2014;33:481-492. © 2013 SETAC.

The present paper reports the structures of bis(adeninium) zoledronate tetrahydrate {systematic name: bis(6-amino-7H-purin-1-ium) hydrogen [1-hydroxy-2-(1H-imidazol-3-ium-1-yl)-1-phosphonatoethyl]phosphonate tetrahydrate}, 2C5H6N5+·C5H8N2O7P22−·4H2O, (I), and bis(adeninium) zoledronate hexahydrate {systematic name: a 1:1 cocrystal of bis(6-amino-7H-purin-1-ium) hydrogen [1-hydroxy-2-(1H-imidazol-3-ium-1-yl)-1-phosphonatoethyl]phosphonate hexahydrate and 6-amino-7H-purin-1-ium 6-amino-7H-purine dihydrogen [1-hydroxy-2-(1H-imidazol-3-ium-1-yl)ethane-1,1-diyl]diphosphonate hexahydrate}, 2C5H6N5+·C5H8N2O7P22−·6H2O, (II). One of the adenine molecules and one of the phosphonate groups of the zoledronate anion of (II) are protonated on a 50% basis. The zoledronate group displays its usual zwitterionic character, with a protonated imidazole ring; however, the ionization state of the phosphonate groups of the anion for (I) and (II) are different. In (I), the anion has both singly and doubly deprotonated phosphonate groups, while in (II), it has one singly deprotonated phosphonate group and a partially deprotonated phosphonate group. In (I), the cations form anR22(10) base pair, while in (II), they formR22(8) andR22(10) base pairs. Two water molecules in (I) and five water molecules in (II) are involved in water–water interactions. The presence of an additional two water molecules in the structure of (II) might influence the different ionization state of the anion as well as the different packing mode compared to (I).

The wide application of organic acids in the food, chemical and pharmaceutical industry is responsible for the increased interest in the development of new technologies for their isolation, separation and concentration from the complex solutions. The electro-membrane processes are promising. The difficulty to understand the transport mechanisms of the amphoteric solution in the electromembrane system is the coupling of chemical reactions: the ionic forms composition can vary depending on the pH of the solution.The main objectives are the study of the behavior of membrane systems containing ampholyte solutions in a steady state (without transfer force or under very low AC) and in a non-equilibrium state such as in electrodialysis regime (applying a current). In both cases, a study includes the experimental and theoretical parts of characterization of the complex solution transport. In the context of modeling a model of the membrane system which can calculate the ampholyte form distribution inside and outside the membrane depending on the external parameters was developed.The comparison of experimental data and results obtained from the simulation of membrane systems containing ampholytes solutions, shows and explains the specific features in the transfer mechanism of ampholyte ions which associated with changes of the solution pH during electrodialysis and, as a consequence, with modification of ampholyte forms., L'utilisation croissante d'acides organiques dans l'industrie alimentaire, chimique et pharmaceutique entraîne le développement de nouvelles technologies pour leur isolement, séparation et concentration à partir de solutions complexes. Les procédés électro-membranaires constituent une voie prometteuse. Afin d'intensifier ces procédés, il est nécessaire de mieux comprendre les mécanismes de transport de la solution d'ampholytes dans le système électromembranaire souvent couplé à des réactions chimiques. La composition des formes ioniques peut en effet varier en fonction du pH de la solution. Les principaux objectifs de ce travail sont l'étude du comportement des systèmes membranaires contenant des solutions d'ampholytes dans un état d'équilibre (sans force de transfert ou sous très faible courant alternatif), et hors d'équilibre en régime d'électrodialyse (application d'un courant). Dans les deux cas, l'approche comprend une partie expérimentale et une partie théorique de caractérisation de transport de solution complexe. Dans la cadre de la modélisation associée, on a développé un modèle de système membranaire qui permet d'accéder à la distribution des formes d'ampholyte à l'intérieur et à l'extérieur de la membrane en fonction des paramètres externes.Les résultats de la comparaison des données expérimentales et de simulation de systèmes membranaires montre et explique les spécificités des mécanismes de transfert des ions d'ampholyte associés aux changements du pH de la solution au cours de l'électrodialyse.

"A comparative study of thiamine mononitrate and thiamine hydrochloride potentiometric titrations with a strong base in water was performed. The analysis of resulting curves allowed associating particular reactions to each observed pH break point. The corresponding pKa values were calculated by using the program SUPERQUAD and they were subsequently used to simulate titration curves. The pKa values obtained in the conditions of the present work are: pKa1 = 4.80 ± 0.05, pKa2 ¿ 10.40 ± 0.04, pKa3 ¿ 8.10 ± 0.04. The system behavior mainly depends on parameters such as the time for measuring pH, NaOH concentration and particularly on the stability of one of the two ampholytes. Comparison of calculated and experimental curves revealed the existence of a dismutation reaction which showed that under steady state conditions and the waiting time between two successive pH measurements, the intermediate "pseudobase (B)", called like this by several researchers, practically does not exist. The results led to find the optimal conditions to propose quantitative alkalimetric titrations. The end-points for the assay of thiamine hydrochloride and thiamine nitrate in raw material were detected by potentiometry. This involves the use of reagents and solvents that are environment-friendly."

Five model conetworks based on cross-linked star ampholytic copolymers were synthesized by group transfer polymerization. The ampholytic copolymers were based on two hydrophilic monomers: the positively ionizable 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the negatively ionizable methacrylic acid (MAA). Ethylene glycol dimethacrylate was used as the cross-linker. These five ampholytic model conetworks were isomers based on equimolar DMAEMA-MAA copolymer stars of different architectures: heteroarm (two), star block (two), and statistical. The two networks based on the homopolymer stars were also synthesized. The MAA units were introduced via the polymerization of tetrahydropyranyl methacrylate and the acid hydrolysis of the latter after network formation. All the precursors to the (co)networks were characterized in terms of their molecular weights using gel permeation chromatography (GPC). The mass of the extractables from the (co)networks was measured and characterized in terms of molecular weight and composition using GPC and proton nuclear magnetic resonance (1H NMR) spectroscopy, respectively. The degrees of swelling (DS) of all the ampholytic conetworks were measured as a function of pH and were found to present a minimum at a pH value which was taken as the isoelectric point, pI. The DS and the pI values did not present a dependence on conetwork architecture. Finally, DNA adsorption studies onto the ampholyte conetworks indicated that DNA binding was governed by electrostatics. © 2008 American Chemical Society. 9 2 574 582 Manufacturers: Aldrich, Germany Cited By :43

Aiming to improve understanding of the mechanisms behind specific anion effects in biological systems we have studied the effects of sodium salts of simple monovalent anions belonging to the Hofmeister series on the bilayers of the zwitterionic lipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine using small-angle x-ray scattering and the osmotic stress technique. NaCl, NaBr, NaNO3, NaI, and NaSCN were used in this investigation. The electrolytes were found to swell the bilayers and to increase the area per lipid headgroup at each value of the osmotic pressure, suggesting the association of anions with the bilayer-lipid interfaces. The effects follow the Hofmeister series with SCN- inducing the most pronounced changes. "Ion competition" experiments with mixed NaI/NaCl solutions at total salinity 0.1 and 0.5 M revealed that the effect of ions on the lipid equation-of-state is roughly linear at low concentrations, but strongly nonlinear at high concentrations. The experimental results are fitted in a companion article to provide "binding or "partitioning" constants of anions in the lipid bilayers. © 2007 by the Biophysical Society. 93 5 1580 1590 Cited By :67

This work is a review of the effect of different monovalent anions (belonging to the Hofmeister series) on a single model amphiphile, phosphatidylcholine molecules in contact with water, in three different geometries, Langmuir monolayers, bilayers and micelles, which differ by area per molecule and radius of curvature. The zwitterionic lipids DPPC (1,2-dipalmitoyl-phosphatidylcholine) and DPC (Dodecylphosphocholine) have been used to form the three geometries. The salt solutions used were NaCl, NaBr, NaNO3, NaI, NaBF4, NaClO4 and NaSCN. Various interfacial and bulk experimental techniques were used in order to study the effect of the anions on the amphiphiles in the three geometries. The interfacial techniques used were surface pressure-area isotherms, Brewster angle microscopy (BAM), Grazing incidence X-ray diffraction (GIXD), infrared reflection absorption spectroscopy (IRRAS). The bulk sensitive techniques used were small-angle X-ray scattering (SAXS), osmotic stress (OS) and light scattering. The experimental results obtained from the three model systems indicate that the interfaces become charged through lipid-ion association. The results were fitted with appropriate theoretical models to provide "binding" or "partitioning" constants of anions in the headgroup region of the lipid molecules. The theoretical analysis strongly suggests that the anions do not associate with the lipid molecules through a local chemical reaction, but rather they partition inside the disordered lipid interfaces. © 2007 Elsevier B.V. All rights reserved. 303 1-2 144 158 Cited By :36

A product and time-resolved kinetic study of the one-electron oxidation of ring-methoxylated phenylpropanoic and phenylbutanoic acids (Ar(CH2)nCO2H, n = 2, 3) has been carried out at different pH values. Oxidation leads to the formation of aromatic radical cations (Ar.+(CH2)nCO2H) or radical zwitterions (Ar.+(CH2)nCO2-) depending on pH, and pKa values for the corresponding acid-base equilibria have been measured. In the radical cation, the acidity of the carboxylic proton decreases by increasing the number of methoxy ring substituents and by increasing the distance between the carboxylic group and the aromatic ring. At pH 1.7 or 6.7, the radical cations or radical zwitterions undergo benzylic C-H deprotonation as the exclusive side-chain fragmentation pathway, as clearly shown by product analysis results. At pH 1.7, the first-order deprotonation rate constants measured for the ring-methoxylated arylalkanoic acid radical cations are similar to those measured previously in acidic aqueous solution for the alpha-C-H deprotonation of structurally related ring-methoxylated alkylaromatic radical cations. In basic solution, the second-order rate constants for reaction of the radical zwitterions with (-)OH (k-OH)) have been obtained. These values are similar to those obtained previously for the (-)OH-induced alpha-C-H deprotonation of structurally related ring-methoxylated alkylaromatic radical cations, indicating that under these conditions the radical zwitterions undergo benzylic C-H deprotonation. Very interestingly, with 3,4-dimethoxyphenylethanoic acid radical zwitterion, that was previously observed to undergo exclusive decarboxylation up to pH 10, competition between decarboxylation and benzylic C-H deprotonation is observed above pH 11.

A product and time-resolved kinetic study of the one-electron oxidation of ring-dimethoxylated phenylethanoic acids has been carried out at different pH values. Oxidation leads to the formation of aromatic radical cations or radical zwitterions depending on pH, and pK(a) values for the corresponding acid-base equilibria have been measured. The radical cations undergo decarboxylation with first-order rate constants (k(dec)) ranging from

The dependence of the exchange current density of the ferric/ferrous reaction on electrode surfaces has been investigated using the work functions of metals, surface potentials of the reactants, adsorption characteristics of water dipoles, hydration numbers, etc. The extent of dehydration of the reactant species at the reaction zone, as well as the influence of desorption of water dipoles from the electrode surface on the magnitude of exchange current density, is demonstrated. ? 2004 Elsevier Inc. All rights reserved.

The increased application of nanoparticles (NPs) is increasing the risk of their release into the environment. Although many toxicity studies have been conducted, the environmental risk is difficult to estimate, because uptake mechanisms are often not determined in toxicity studies. In the present study, the authors review dominant uptake mechanisms of NPs in cells, as well as the effect of NP properties, experimental conditions, and cell type on NP uptake. Knowledge of NP uptake is crucial for risk assessment and is essential to predict the behavior of NPs based on their physical-chemical properties. Important uptake mechanisms for eukaryotic cells are macropinocytosis, receptor-mediated endocytosis, and phagocytosis in specialized mammalian cells. The studies reviewed demonstrate that uptake into nonphagocytic cells depends strongly on NP size, with an uptake optimum at an NP diameter of approximately 50nm. Increasing surface charges, either positive or negative, have been shown to increase particle uptake in comparison with uncharged NPs. Another important factor is the degree of (homo-) aggregation. Results regarding shape have been ambiguous. Difficulties in the production of NPs, with 1 property changed at a time, call for a full characterization of NP properties. Only then will it be possible to draw conclusions as to which property affected the uptake. Environ Toxicol Chem 2014;33:481-492. © 2013 SETAC.

In the considered thesis colloidal particles on polystyrene base, synthesized by the way of emulgator-free copolymerization has been matter of investigation. The surfaces of these particles possess amphoteric groups causing a positive or negative charge depending on the pH of the medium. Considering their isoelectric point the particles show reversible coagulation. These charged colloidal particles perform electrophoretic motion when an electric field is applied to the cell containing the dispersion. In combination of electrophoretic measurements with the well known method of laser-doppler-anemometrie it is possible to get information about the electrophoretic mobility of these particles and so one can draw conclusions about the quantity of effective surface charge. In this paper the electrophoretic mobility as an indicator for surface charge were measured under different conditions. Changing the pH, the kind of electrolyte and its ionic strength and the hydrophobicity of the medium demonstrates the strong influence of these parameters. As a result one can see that even in very low concentrations of the electrolytic systems, i.e. 5*10-7 mol/l, the mobility shows a characteristical behaviour under the examined conditions. Further on it is possible to study the behaviour of stability of the dispersion under these conditions. Furthermore adsorption experiments with the spherical protein bsa on the particle surface were made even under different conditions. It seems obviously clear, that bsa adsorbs more effective on hydrophobized particle surfaces. Compared to these model systems colloidal particles from water and waste water were examined. Neither their real configuration nor their matter is known, but only by knowledge about their electrophoretic behaviour it is possible to draw conclusions about their stability. Using salts on the base of iron and chlorine to separate these particles from the medium it is possible to optimize the required dose. It is a very interesting result that a quick measurement of these physicochemical parameter offers a reliable method in the treatment of water and waste water.

Aqueous size exclusion chromatography (SEC) at 1 M KCl and pH 8.5 was employed to probe the aggregation behavior of methacrylic polyampholytes. In agreement with earlier results obtained by light scattering techniques, shorter retention times were measured for the triblocks consistent with larger hydrodynamic size and, therefore, chain aggregation into micellar structures the two random terpolymers and the diblock polyampholyte showed no aggregation behavior as their retention times corresponded closely to the expected single-chain molecular weights. Micellar aggregation numbers were estimated to be within the range from 10 to 40. 182 2 326 329 Cited By :11

This work reports for the first time a straightforward solvent-free chemical procedure to gain access to Δ-1-pyrroline grafted onto multiwalled carbon nanotubes by the 1,3-dipolar cycloaddition of the mesoionic 4-methyl-2-phenyloxazol-5(4H)-one.