Neutral pH Region Research Articles

Design of supersaturable formulation of telmisartan with pH modifier: in vitro study on dissolution and precipitation

Telmisartan is a biopharmaceutics drug classification system class II drug having a low solubility at neutral pH region. The purpose of this study is to clarify the process of dissolution and precipitation of telmisartan in the gastrointestinal tract from its oral formulation containing meglumine, a pH modifier (alkalizer). Granules of telmisartan containing different amount of meglumine were prepared, and its dissolution and precipitation profiles were investigated under various pH conditions in vitro. It was demonstrated that meglumine induced a supersaturation of telmisartan both at pH 5.0 and pH 6.8. Dissolved amount of telmisartan fluctuated over time and the pattern of dissolved concentration differed depending on the pH and the amount of meglumine. Powder X-ray diffraction analysis and differential scanning calorimetry analysis on precipitates from supersaturated solutions showed that pH of the dissolution medium profoundly affects the crystalline form of telmisartan. Furthermore, the effect of meglumine on oral absorption of telmisartan was investigated with dissolution/permeation System in vitro. At pH 6.8, permeated amount was significantly higher with the formulation which contains larger amount of meglumine. Therefore, despite the very low solubility of telmisartan at neutral pH, meglumine significantly provided high solubility of telmisartan by induction and maintenance of its supersaturation.

Peptide binding to metal oxide nanoparticles.

Magnetic metal oxide nanoparticles demonstrate great applicability in several fields such as biotechnology, medicine and catalysis. A stable, magnetic and low-cost material, nanoscale magnetite, is an interesting adsorbent for protein purification. Downstream processing can account for up to 80% of the total production costs in biotechnological production. As such, the development of new innovative separation methods can be regarded as highly profitable. While short peptide sequences can be used as specific affinity tags for functionalised adsorber surfaces, they need expensive affinity ligands on the particle surface for adsorption. In order to identify peptide tags for several non-functionalised inorganic surfaces, different binding conditions to iron oxide nanoparticles are evaluated. Therefore, magnetite nanoparticles in a range of 5-20 nm were synthesised with a co-precipitation method. Zeta potential measurements indicated an amphiphilic surface with an isoelectric point in the neutral pH region. Glutamic acid-based homo-peptides were used as affinity peptides for the magnetite nanoparticles. We demonstrate a dependence of the binding affinity of the peptides on pH and buffer ions in two different experimental set-ups. The nature of surface coordination for glutamic acid-based peptides can be demonstrated with different spectroscopic approaches such as infrared spectroscopy (IR), Raman spectroscopy and circular dichroism spectroscopy (CD). We want to emphasise the importance of physicochemical properties such as surface energy, polarity, morphology and charge. These parameters, which are dependent on the environmental conditions, play a crucial role in peptide interactions with iron oxide surfaces. The understanding of the adsorption of simple biomolecules on nanoscale metal oxide surfaces also represents the key to the even more complex interactions of proteins at the bio-nano interface. From the identification of interaction patterns and an understanding of the adsorption of these peptides, the up-scaling to tagged model proteins facilitates the possibility of an industrial magnetic separation process and might therefore reduce time and costs in purification processes.

Thermodynamic model for Zr solubility in the presence of gluconic acid and isosaccharinic acid

ABSTRACTZr solubility in the presence of gluconic acid (GLU) and isosaccharinic acid (ISA) was investigated as a function of hydrogen ion concentration (pHc) and the total concentration of GLU or ISA. The dependence of the increase in Zr solubility on the pHc and GLU concentration suggested the existence of Zr(OH)4(GLU)22− in the neutral pH region and Zr(OH)4(GLU)(GLU-H)3− in the alkaline pH region above pHc 10 as the dominant species in the presence of 10−3–10−1 mol/dm3 (M) GLU. In the presence of ISA, the dominant species Zr(OH)4(ISA)22− and Zr(OH)4(ISA)(ISA-H)3− were proposed to occur in the neutral and alkaline pH regions, similar to those found in the presence of GLU. From X-ray diffraction analysis, the solubility-limiting solid phase in the presence of GLU and ISA was considered to be Zr(OH)4(am). The formation constants of the Zr gluconate and isosaccharinate complexes were determined by least-squares fitting analysis of the solubility data, and the obtained values were discussed in comparison with those of tetravalent actinides.

Efficient removal of 17β-estradiol using hybrid clay materials: Batch and column studies

Hybrid materials were obtained modifying the bentonite (BC) and local clay (LC) using hexadecyltrimethylammonium bromide (HDTMA) or the clay were pillared with aluminum followed by modification with HDTMA. The materials were characterized by the SEM, FT-IR and XRD analytical tools. The batch reactor data implied that the uptake of 17β-estradiol (e₂) by the hybrid materials showed very high uptake at the neutral pH region. However, at higher and lower pH conditions, slightly less uptake of e₂ was occurred. The uptake of e₂ was insignificantly affected changing the sorptive concentration from 1.0 to 10.0 mg/L and the background electrolyte (NaCl) concentrations from 0.0001 to 0.1 mol/L. Moreover, the sorption of e₂ by these hybrid materials was fairly efficient since within 30 mins of contact time, an apparent equilibrium between solid and solution was achieved, and the data was best fitted to the PSO (pseudo-second order) and FL-PSO (Fractal-like-pseudo second order) kinetic models compared to the PFO (pseudo-first order) model. The fixed-bed column results showed that relatively high breakthrough volume was obtained for the attenuation of e₂ using these hybrid materials, and the loading capacity of e₂ was estimated to be 75.984, 63.757, 58.965 and 49.746 mg/g for the solids BCH, BCAH, LCH and LCAH, respectively.

Composition, particle size, charge, and colloidal stability of pH-fractionated humic acids

The purpose of this study was to divide humic acids into several fractions by means of their dissolving in buffers with different pH values and to characterize obtained humic fractions with respect to their composition, structure, particle size, and charge. Relationships between determined characteristics of fractionated humic acids and pH values of used buffer solutions and the method of fractionation was investigated. Humic acids were fractionated by means of two different methods: the subsequent dissolution in buffers adjusted to different pH and the sequential dissolution in buffers with increasing pH values. Composition, structure, and properties of the obtained humic fractions were studied using elemental analysis, FT-IR spectroscopy, UV/VIS spectroscopy, and light scattering methods. As expected, fractions obtained by subsequent dissolution were more heterogeneous than those prepared by sequential extraction. Fractions obtained at lower pH values contained higher amounts of aromatic and carboxylic groups, while those extracted at higher pH values were rich in aliphatic and/or peptide groups. Fractions extracted close to neutral pH region had some specific properties. Functional groups dissociated in a range of pH values depending on the chemical structure of the molecules. Weaker carboxylic groups could dissociate in less acidic solutions, and more aromatic fractions could be dissolved. Conformational changes and deaggregation process differed with the fractionation procedure and concentration of studied solutions. A bimodal distribution of particle sizes and higher values of polydispersity were obtained for some for less concentrated solutions of humic fractions. Obtained humic fractions behave as anionic heterogeneous ligands with many carboxylic and phenolic groups of different strength, and present polyfunctional and polyelectrostatic effects due to different functional sites and net charged groups. Two main processes can affect their properties and behavior in aqueous solutions: dissociation of acidic functional groups and breaking of humic aggregates into smaller molecular associations or humic molecules. An important parameter affecting the spatial arrangement of obtained humic fractions is their concentration.

Effects of Al species on coagulation efficiency, residual Al and floc properties in surface water treatment

Effects of coagulant dosage and solution pH on the coagulation behaviors using three different Al-based coagulants were studied in terms of dissolved organic carbon (DOC) removal efficiency and residual Al. The coagulants used in this study were aluminum chloride (AlCl3), Al13O4(OH)247+ polymer (Al13) and (AlO4)2Al28(OH)5618+ polymer (Al30). Surface water from a typical water treatment plant in the north China was used to conduct the experiments. The results showed that DOC removal efficiency correlated well to the content of medium polymerized species (Alb), while the flocs formed by Alb were not as large as those formed by colloidal or gel species (Alc). Monomeric species (Ala) showed a high ability to react with some unsatisfied coordinate bonds of organic matter to facilitate DOC removal, and it was the most unstable species, which could be easily transformed into in-situ Alb species. Compared to preformed Alb, in-situ Alb could remove DOC more efficiently and the flocs were much larger via the mechanism of further hydrolysis and transfer into Alc during coagulation. Results showed that pH had significant effects on residual Al, the total residual dissolved Al achieved the minimal concentrations in the neutral pH region. The results of molecular weight (MW) distribution of residual Al showed large differences at the given coagulation pH, and monomeric species were the predominant Al species at pH 6.0 and pH 8.0 for all coagulants.

Bacterial Profile of Dentine Caries and the Impact of pH on Bacterial Population Diversity

Dental caries is caused by the release of organic acids from fermentative bacteria, which results in the dissolution of hydroxyapatite matrices of enamel and dentine. While low environmental pH is proposed to cause a shift in the consortium of oral bacteria, favouring the development of caries, the impact of this variable has been overlooked in microbial population studies. This study aimed to detail the zonal composition of the microbiota associated with carious dentine lesions with reference to pH. We used 454 sequencing of the 16S rRNA gene (V3–V4 region) to compare microbial communities in layers ranging in pH from 4.5–7.8 from 25 teeth with advanced dentine caries. Pyrosequencing of the amplicons yielded 449,762 sequences. Nine phyla, 97 genera and 409 species were identified from the quality-filtered, de-noised and chimera-free sequences. Among the microbiota associated with dentinal caries, the most abundant taxa included Lactobacillus sp., Prevotella sp., Atopobium sp., Olsenella sp. and Actinomyces sp. We found a disparity between microbial communities localised at acidic versus neutral pH strata. Acidic conditions were associated with low diversity microbial populations, with Lactobacillus species including L. fermentum, L. rhamnosus and L. crispatus, being prominent. In comparison, the distinctive species of a more diverse flora associated with neutral pH regions of carious lesions included Alloprevotella tanerrae, Leptothrix sp., Sphingomonas sp. and Streptococcus anginosus. While certain bacteria were affected by the pH gradient, we also found that ∼60% of the taxa associated with caries were present across the investigated pH range, representing a substantial core. We demonstrated that some bacterial species implicated in caries progression show selective clustering with respect to pH gradient, providing a basis for specific therapeutic strategies.

Dextran derivative-based pH-sensitive liposomes for cancer immunotherapy

pH-Sensitive dextran derivatives having 3-methylglutarylated residues (MGlu-Dex) were prepared by reacting dextran with 3-methyl-glutaric anhydride. MGlu-Dex changed the protonation state and their characteristics from hydrophilic to hydrophobic in neutral and acidic pH regions. Surface modification of egg yolk phosphatidylcholine liposomes with MGlu-Dex produced highly pH-sensitive liposomes that were stable at neutral pH but which were destabilized strongly in the weakly acidic pH region. MGlu-Dex-modified liposomes were taken up efficiently by dendritic cells and delivered entrapped ovalbumin (OVA) molecules into the cytosol. When MGlu-Dex-modified liposomes loaded with OVA were administered subcutaneously to mice, the antigen-specific humoral and cellular immunity was induced more effectively than the unmodified liposomes loaded with OVA. Furthermore, administration of MGlu-Dex-modified liposomes loaded with OVA to mice bearing E.G7-OVA tumor significantly suppressed tumor growth and extended the mice survival. Results suggest that MGlu-Dex-modified liposomes are promising for the production of safe and potent antigen delivery systems that contribute to the establishment of efficient cancer immunotherapy.

“Schizophrenic” Micellization of Poly(Acrylic Acid)-B-Poly(2-Dimethylamino)Ethyl Methacrylate and Responsive Behavior of the Micelles

The well-defined block polyampholyte poly(acrylic acid)-b-poly(2-dimethylamino)ethyl methacrylate (PAA-b-PDMAEMA) was synthesized by sequential atom transfer radical polymerization (ATRP) using protected group chemisty. The block polyampholyte exhibited so-called “schizophrenic” micellization behavior at different pH values. The PAA-core micelles, PDMAEMA-core micelles, and a kind of polyeletrolyte complex were formed in acidic pH (pH < 4.5), basic pH (pH > 9.0), and neutral pH region (5.5–8.5), respectively. The temperature responsive behaviors of the micelles and the complex formed in neutral environment were studied in detail via dynamic light scattering (DLS) and UV-vis transmittance. Salt effect on the temperature responsive behavior was also discussed.[Supplementary materials are available for this article. Go to the publisher's online edition of Soft Materials or http://pubs.acs.org for the following free supplemental resource(s): Synthesis of PtBA-b-PDMAEMA, 1H NMR spectra of block copolymer and TEM image of block copolymer at aqueous solution with NaCl]”

Efficient detection and extraction of cobalt(II) from lithium ion batteries and wastewater by novel composite adsorbent

This study developed a novel composite adsorbent for highly selective and sensitive detection and extraction of cobalt (Co(II)) from lithium-ion batteries (LIBs) and wastewater. The composite adsorbent was prepared by indirect immobilization of 6-((2-(2-hydroxy-1-naphthoyl)hydrazono)methyl)benzoic acid (HMBA) onto mesoporous silica monoliths. The composite adsorbent enhanced the color formation by stable complexation as [Co(II)–HMBA]n+ complexes during detection and sorption operations. The data evident the one-step detection of wide range Co(II) concentrations into interior pore surface coverage of the composite adsorbent from solutions without using high tech instruments, which was unique feature of this adsorbent. The influence of different sorption parameters, such as: initial Co(II) concentration, equilibration time, solution pH and the presence of competing ions and reuses were studied and discussed systematically. The effective pH range for Co(II) ions detection and sorption was neutral pH region and the maximum sorption capacity of the adsorbent was as high as 189.37mg/g. The adsorbed Co(II) was eluted with stripping agent (0.3M HCl) and simultaneously regenerated into initial form for the next capturing operations after rinsing with water. The data also clarified that the composite adsorbent was selectively extracted Co(II) from LIBs even in the presence of high concentration diverse ions. Importantly, the composite adsorbent was retaining functionality in spite of many chemical treatments during sorption–elution-recovery/regeneration cycles. Therefore, the present study revealed that such a low-cost material could be used as potential adsorbent for the selective detection and recovery of Co(II) ions from LIBs and wastewater streams.

Characterization of new β-galactosidase from acidophilic fungus, Teratosphaeria acidotherma AIU BGA-1

The β-galactosidase exhibiting high activity from an extremely acidic pH region to neutral pH region was efficiently purified from an acidophilic fungus, Teratosphaeria acidotherma AIU BGA-1, using affinity chromatography with Toyopearl resins immobilized 4-aminophenyl-β-d-galactopyranoside. The enzyme was stable in the pH range from 1.5 to 7.0, and exhibited optimal activity at pH 2.5-4.0 and 70°C. 2-Nitrophenyl-β-d-galactopyranoside, 4-nitrophenyl-β-d-galactopyranoside and lactose were rapidly hydrolyzed, and the apparent Km values were estimated to be 0.19mM, 1.2mM and 170mM, respectively. Thus, the enzyme can be used in the wide pH range for hydrolysis of lactose. The molecular mass of the enzyme was estimated to be 140kDa with two hetero subunits of 86kDa and 50kDa. The N-terminal amino acid sequence of the small subunit was found to be NTRMIIFNDK. These enzymatic and physicochemical characteristics are remarkably different from those of the previously known β-galactosidases.

Acidophilic fungus, Teratosphaeria acidotherma AIU BGA-1, produces multiple forms of intracellular β-galactosidase

Teratosphaeria acidotherma AIU BGA-1 isolated from an acidic and high temperature hot spring produced four intracellular β-D-galactosidases with different pH activity profiles, in which three forms were acidophilic and stable from extremely acidic to neutral pH region. The other one was alkalophilic and unstable in the acidic pH region.

Effect of operating conditions on the treatment of brackish groundwater by electrodialysis

Desalination of brackish groundwater by electrodialysis was examined in this study. Groundwater samples were taken from a coastal area in Korea where the intrusion of seawater to groundwater is significant. The ion concentrations of the samples were 1,288 mg/L for Cl–, 107 mg/L for SO42-, 273 mg/L for Na+, 118 mg/L for Mg2+, 201 mg/L for Ca2+, and 4.7 mg/L for K+, and electric conductivity was 3.85mS/m. Operating conditions are as follows: applied voltage (from 5 to 30 V), pH (3, 7, 9), concentration of electrolyte solution (from 0 to 10% as Na2SO4), flow rate of dilute/concentrate/electrolyte (1.08, 2.16, 3.24 L/min)/(1.08, 2.16, 3.24 L/min)/(1.68, 3.36, 5.04 L/min). Cations and anions of water samples were analyzed using ion chromatography (Alltech). The rapid increase in the removal of salt ions was observed until a certain level of removal reached. The higher removal was achieved as the applied voltage increased and linear increase in the removal was found as the voltage increased up to 20 V, while no significant increase in the removal rate appeared beyond 20 V. Although the removal of anions and cations was higher in neutral pH region, the pH condition on at the range of pH from 3 to 9 gave little effect. Drastic increase in the removal of various ions was observed as the electrolyte concentration increased from 0 to 0.5%, while the removal increased gradually at the electrolyte concentration over 1%. Flow rate of concentrate, dilute, and electrolyte compartments showed positive relationship with the removal of the ions. This study suggested that various operating conditions could have effects on the performance of electrodialysis in desalting the brackish groundwater. Because the desalting efficiency depends largely on the input energy, the optimal operating conditions should be considered based on the quality of raw and treated water, and the economic concerns for a practical use of electrodialysis in securing alternative fresh water resources.

Sorption Behavior of Nickel and Palladium in the Presence of NH3(aq)/NH4+

ABSTRACTIt is necessary to assess the impact of nitrate salts and their reduction products (e.g. NH3(aq)/NH4+) contained in low-level radioactive waste generated from nuclear reprocessing process for the safety assessment of geological disposal of the waste. In the present study, sorption behavior of Ni and Pd on pumice tuff was investigated in the presence of NH3(aq)/NH4+. Under various NH3(aq)/NH4+ concentration, pH and ionic strength conditions, distribution coefficient (Kd) of Ni and Pd on pumice tuff was determined by a batch experiment. For Ni system, the Kd values showed no significant dependence on initial NH4+ concentration ([NH4+]ini &lt; 1 M) in neutral pH region, which agreed with the prediction from thermodynamic data. For Pd system, the Kd values decreased with an increase of [NH4+]ini, suggesting the formation of stable ammine complexes (Pd(NH3)m2+ (m: 1 – 4)). The obtained Kd values for Ni and Pd were analyzed using a surface complexation model. By taking complexes predicted by thermodynamic data into account, sorption behavior of Ni and Pd in the presence of NH3(aq)/NH4+ were well explained.

Hyperbranched polyglycerol hydrogels prepared through biomimetic mineralization

Hyperbranched polyglycerols find increasing usage in biomedicine owing to their excellent biocompatibility like polysaccharides. To prepare hydrogels, they are cross-linked mainly by treating with toxic epoxy reagents. Here we suggest a one-stage nontoxic procedure for the jellification of aqueous solutions that was previously developed for nongelable polysaccharides. It was carried out via the biomimicking mineralization. As the silica precursor, tetrakis(2-hydroxyethyl)orthosilicate containing ethylene glycol residues was employed. It could mineralize directly hydroxyl-containing macromolecules passing a stage of the sol formation. Jellification was performed in one stage in the neutral pH region at the ambient conditions. An organic solvent was not needed because of high hydrophilicity of both the precursor and polyglycerols. An as-prepared hydrogel is ready for applications because of the absence of toxic products. Its structure and mechanical properties were characterized by scanning and transmission electron microscopy as well as dynamic rheology. It was demonstrated that hyperbranched polyglycerols were encased into silica matrix that formed three-dimensional mesoporous network. A study of initial solutions of hyperbranched polyglycerols by the dynamic light scattering revealed their aggregation. This important result was confirmed by direct observations of aggregated macromolecules with high resolution scanning electron microscopy. Entrapped aggregates were also found in the silica matrix.

Sorption of selenite onto chlorite considering mineral dissolution

In this study we investigated the sorption of selenite (SeO3 2−) onto chlorite as a function of Se(IV) concentration, pH, and ionic strength. The sorption isotherm of Se(IV) onto chlorite was successfully presented by both the Langmuir isotherm and Tempkin equation although the Langmuir isotherm is somewhat better than the Tempkin equation. The sorption of Se(IV) onto chlorite was maintained to be constant at an acidic pH region, while the sorption decreased with an increasing pH at neutral and alkaline pH regions. However, the Se(IV) sorption onto chlorite was independent of the ionic strength of NaClO4 solution. The amount of Se(IV) sorbed onto chlorite was significantly low compared to those of iron oxides such as apatite, goethite, hematite, and magnetite because of the lower content of Fe. We also investigated the effect of Fe(II) ions dissolved from chlorite on the Se(IV) sorption as a function of contact time. The chemical oxidation states of selenium sorbed onto chlorite surface were identified using X-ray absorption near edge structure (XANES) at the Pohang synchrotron light source. The amount of Fe(II) dissolved was increased by the contact time of 28 days but decreased after 28–56 days although the amount of dissolved Fe(II) ions was significantly small. This decrease of the dissolved Fe(II) may be due to the formation of Fe-oxyhydroxides such as ferrihydrite. The results of XANES measurements also showed that the Se(IV) sorbed onto chlorite was not reduced into Se(0) or Se(-II) even in the presence of Fe(II) ions in the solution because of the low Fe content of the chlorite although the mechanism was not clearly understood.

Activation Energy for the Corrosion of Aluminum Powders in Water

The self passivation of aluminum in water generally prevents the generation of hydrogen from an aluminum-water reaction in conditions preferred for portable systems. However the potential for corroding aluminum to produce quantities of hydrogen at a lower total system mass compared to compressed storage tanks is spurring research into accelerating aluminum corrosion by ball milling and mixing with other powders. This allows commercially useful amounts of hydrogen to be generated at moderate temperatures and neutral pH regions. To further study the mechanism behind the increased rate the activation energies were calculated for hydrogen evolution from pure aluminum, aluminum that had been ball milled, and aluminum mixed with alumina powder. Overall, aluminum that is in contact with higher amounts of aluminum hydroxide, either grown or added, showed a drop in activation energy from approximately 80 kJ/mole down to 24 kJ/mole.

Voltammetric Evaluation on Poly α-Aspartic Acid-Zinc Ion Complex in the Helix-coil Transition pH Region

Helix-coil transitions of poly α-aspartic acid (PASP) were studied by dc polarography in the presence of Zn(2+) as a marker attached to the polymer. The diffusion current (i(d)) of Zn(2+) declined markedly in the pH range of 3.5-7.4 due to a formation of metal ion-PASP macromolecular complexes. The complex formation also reflects on an increase of the magnitude at ca. 222 nm of CD spectrum, suggesting that PASP forms the helix structure by coordination of Zn(2+) in the corresponding pH region. Helix content, determined by the decrease in i(d) of Zn(2+), corresponds favorably to that by CD measurements. In the lower acidic pH region, the coordination mode of Zn(2+) to PASP is different from that at neutral pH region. The decrease in i(d) of Zn(2+) is independent of the further formation of helix structure. Zn(2+) coordinates with sparsely dissociated carboxylate groups of the helical part of PASP, which bring about an aggregation of polypeptide strands. The diffusion current of the ion attached to the polymer, therefore, is a parameter sensitive to conformational changes of PASP from acidic through neutral pH region.

Passivation Rates for Small Particulate Aluminum in Contact with Oxide and Nitride Powders

The self passivation of aluminum in water generally prevents the generation of hydrogen from an aluminum-water reaction in conditions preferred for portable systems. However the corrosion rate of aluminum powders is seen to greatly increase when in contact with alumina powder. This allows commercially useful amounts of hydrogen to be generated at moderate temperatures and neutral pH regions. Scratch tests were run on aluminum disks covered with oxide and nitride powders to look at repassivation rates after the surface film was disturbed and a decrease in the repassivation time observed. Small pellets of aluminum powder mixed with oxide or nitride powders were also studied with scratch events showing far lower current perturbation than seen for pure aluminum.

Arsonic acid-presenting superparamagnetic iron oxide for pH-responsive aggregation under slightly acidic conditions

We report the synthesis and characterization of the arsonic acid-presenting superparamagnetic iron oxide (SPIO). We used arsonoacetic acid as the ligand for SPIOs in aqueous media. The surface modification of the SPIOs was accomplished via the ligand exchange from undecanoic acid to the carboxyl moiety of arsonoacetic acid. Consequently, the well-dispersed arsonic acid-presenting SPIOs in water were obtained. We found that the dispersion state of the arsonic acid-presenting SPIOs can be sharply regulated by pH changes in the biological significant region. The well dispersion state of the arsonic acid-presenting SPIOs can be maintained at the neutral pH region. In contrast, the arsonic acid-presenting SPIOs can sensitively form the aggregation below pH 6.1. Moreover, these dispersion states can be controlled reversibly by the pH alteration in the narrow region.