Solution pH Research Articles

Highly Compressible, Superabsorbent, and Biocompatible Hybrid Cryogel Constructs Comprising Functionalized Chitosan and St. John's Wort Extract.

Biobased porous hydrogels enriched with phytocompounds-rich herbal extracts have aroused great interest in recent years, especially in healthcare. In this study, new macroporous hybrid cryogel constructs comprising thiourea-containing chitosan (CSTU) derivative and a Hypericum perforatum L. extract (HYPE), commonly known as St John's wort, were prepared by a facile one-pot ice-templating strategy. Benefiting from the strong interactions between the functional groups of the CSTU matrix and those of polyphenols in HYPE, the hybrid cryogels possess excellent liquid absorption capacity, mechanical resilience, antioxidant performance, and a broad spectrum of antibacterial activity simultaneously. Thus, owing to their design, the hybrid constructs exhibit an interconnected porous architecture with the ability to absorb over 33 and 136 times their dry weight, respectively, when contacted with a phosphate buffer solution (pH 7.4) and an acidic aqueous solution (pH 2). These cryogel constructs have extremely high compressive strengths ranging from 839 to 1045 kPa and withstand elevated strains of over 70% without developing fractures. Moreover, the water-swollen hybrid cryogels with the highest HYPE content revealed a complete and instant shape recovery after uniaxial compression. The incorporation of HYPE into CSTU cryogels enabled substantial improvement in scavenging reactive oxygen species and an expanded antibacterial spectrum toward multiple pathogens, including Gram-positive bacteria (Staphylococcus aureus and Staphylococcus epidermidis), Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa), and fungi (Candida albicans). Cell viability experiments demonstrated the cytocompatibility of the 3D cryogel constructs, which did not induce changes in the fibroblast morphology. This work showcases a simple and effective strategy to immobilize HYPE extracts on CSTU 3D networks, allowing the development of novel multifunctional platforms with promising potential in hemostasis, wound dressing, and dermal regeneration scaffolds.

Development of an Efficient Process for the Separation of Co(ii), Mn(ii), and Ni(ii) from Chloride Solution by Precipitation

ABSTRACT The demand for nickel, cobalt, and manganese is increasing owing to their critical role in the performance of lithium-ion batteries. Precipitation is simpler to operate than solvent extraction in the separation of metal ions. In this work, precipitation-based procedures were developed to separate Co(II), Mn(II) and Ni(II) from synthetic chloride solutions. Dimethylglyoxime (DMG) was effective in selectively precipitating Ni(II) from the chloride solutions containing Co(II) and Mn(II). Solution pH greatly affected the precipitation of Ni(II) by DMG. In the first procedure, Ni(II) was first precipitated using DMG from solution with initial pH 6 at a DMG/Ni(II) molar ratio of 3, a reaction time of 30 min and then Co(II) was separated from the filtrate by precipitation with Na2S, with optimal conditions being an initial pH of 6, a Na2S/Co(II) molar ratio of 2 and a reaction time of 15 min. In the second procedure, both Ni(II) and Co(II) was simultaneously precipitated with Na2S, leaving Mn(II) in the filtrate. Then the mixed sulfides of Co(II) and Ni(II) were dissolved by using HCl solution containing NaClO as an oxidizing agent. From the leaching solution, Ni(II) was separated by precipitation with DMG. Optimum conditions for the separation conditions were obtained. In both procedures, the separation degree among the three metal ions was higher than 99%. The developed procedures were simple and effective for the separation of the three metal ions compared to solvent extraction.

A Chemically Robust 2D Ni-MOF as an Efficient Heterogeneous Catalyst for One-Pot Synthesis of Therapeutic and Bioactive 2-Amino-3-Cyano-4H-Pyran Derivatives.

Despite possessing numerous catalytic advantages of MOFs, developing 2D frameworks having excellent chemical stability along with new catalytic properties, remains a grand challenge. Herein, by employing a mixed ligand synthetic approach, we have constructed a 2D Ni-MOF, IITKGP-52, which exhibits excellent framework robustness in open air, water, as well as over a wide range of pH solutions (2-12). Benefitting from its robustness and abundant Lewis acidic open metal sites, IITKGP-52 is explored in catalyzing the heterogeneous three-component condensation reaction for the tandem synthesis of bioactive 2-amino-3-cyano-4H-pyran derivatives with low catalytic loading, greater compatibility for a wide range of substrates, excellent recyclability and superior catalytic efficiency than the previously employed homo and heterogeneous systems. IITKGP-52inaugurates the employment of MOF-based catalysts for one-pot synthesis of therapeutic and bioactive 2-amino-3-cyano-4H-pyran derivatives.

Rare Earth Element Binding and Recovery by a Beta Roll-Forming RTX Domain.

The Block V of the RTX domain of the adenylate cyclase protein from Bordetella pertussis is disordered, and upon binding eight calcium ions, it folds into a beta roll domain with a C-terminal capping group. Due to their similar ionic radii and coordination geometries, trivalent lanthanide ions have been used to probe and identify calcium-binding sites in many proteins. Here, we report using a FRET-based assay that the RTX domain can bind rare earth elements (REEs) with higher affinities than calcium. The apparent disassociation constants for lanthanide ions ranged from 20 to 75 μM, which are an order of magnitude higher than the affinity for calcium, with a higher selectivity toward heavy REEs over light REEs. Most proteins release bound ions at mildly acidic conditions (pH 5-6), and the high affinity REE-binding lanmodulin protein can bind 3-4 REE ions at pH as low as ∼2.5. Circular dichroism (CD) spectra of the RTX domain demonstrate pH-induced folding of the beta roll domain in the absence of ions, indicating that protonation of key amino acids enables structure formation in low pH solutions. The beta roll domain coordinates up to four ions in extreme pH conditions (pH < 1), as determined by equilibrium ultrafiltration experiments. Finally, to demonstrate a potential application of the RTX domain, REE ions (Nd3+ and Dy3+) were recovered from other non-REEs (Fe2+ and Co2+) in a NdFeB magnet simulant solution (at pH 6).

A study of bacteria producing carbonic anhydrase enzyme for CaCO3 precipitation and soil biocementation.

We study the carbonic anhydrase (CA) pathway using autochthonous CA-producing bacteria as a means of inducing calcite precipitation, which acts as a biocement to improve the engineering soil properties. Forty different microbial strains producing CA were isolated from the foundation soil of a railway embankment in Prickwillow, UK. Three of the best CA-producing strains were selected and identified by DNA sequencing as Bacillus licheniformis, Bacillus toyonensis and Bacillus pumilus with CA activity values respectively of 1.79 U/ml, 1.42 U/ml and 1.55 U/ml. To optimise the treatments, we investigated the effect of pH, temperature, zinc co-factor and cementation solution molarity on the growth and CA activity and bioprecipitates, with CO2 added in the form of bicarbonate. Scanning electron microscope (SEM) analysis of the bioprecipitates showed that these had characteristic morphologies of calcite and vaterite crystals. The formation of calcite was further corroborated by FT-IR and Raman analysis of bioprecipitates. The precultured bacteria were injected into the fine-grained soil together with cementation solution. Unconfined compressive strength in treated soil increased up to 1MPa, and its calcium carbonate content increased by 2.78%. This, as well as the stability of the treated soil upon water immersion, proved the biocementation of the fine-grained soil. These findings suggest the potential of employing the CA biocementation route for soil stabilisation pending further development of the technique.

Assessment of carbonized himalayan chir pine biomass as an eco-friendly adsorbent for effective removal of industrial dyes.

This study investigates the use of carbonized Himalayan Chir Pine Biomass, known as Chir Pine Activated Carbon (CPAC), as an eco-friendly and cost-effective adsorbent for efficient industrial dye removal, with a focus on environmental sustainability. By applying different additive treatments, four adsorbents (C1, C2, C3, and C4) were formulated. CPAC was synthesized through pyrolysis and characterized using various analytical techniques including FE-SEM, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The adsorption capacity of CPAC was evaluated using Malachite Green (MG) dye as a model contaminant. FE-SEM images revealed high porosity (~ 10µm) and a high surface area (119.886m2/g) as confirmed by BET testing. CPAC effectively removed MG dye within 30min at a solution pH of 7. Langmuir and Freundlich isotherm models indicated both monolayer and multilayer adsorption, while kinetic models suggested chemisorption. The regeneration efficiency was assessed using 0.1 N HCl over five consecutive cycles, with C4 demonstrating a high regeneration tendency of 85% and only a 9% reduction in adsorption ability after the fifth cycle. The developed CPAC shows excellent potential for use in the textile, paper, and leather industries for industrial dye adsorption, contributing to the protection of aquatic ecosystems. Additionally, CPAC can be utilized in other water and air purification applications.

Synergistic enhancement of nitrogenous compounds in bio-oils: Hydrogen peroxide pretreatment and nitrogen-rich pyrolysis

A novel pretreatment method, combining H2O2 and nitrogen-rich pyrolysis for biomass was proposed to address the issue of low nitrogen compounds or levoglucosan content in pyrolysis bio-oil. Bio-oil enriched with high content of levoglucosan and nitrogenous compounds was obtained. In this study, the effects of pretreatment conditions (H2O2 solution concentration, pretreatment time, solution pH) and nitrogen-rich ratio on the pyrolysis characteristics of corn stover were investigated. The difficulty of converting different components into nitrogenous compounds was evaluated for the first time. The results reveal that H2O2 pretreatment effectively removed most lignin and ash, leading to a substantial enrichment of cellulose. Notably, carbohydrate content in bio-oil increased by more than 970 %. However, excessive pyrolysis temperature and pH of H2O2 solution can aggravate the decomposition of carbohydrates. The co-pyrolysis of the pretreated corn stover with urea increased the bio-oil yield (up to 56.32 wt%) and the content of nitrogenous compounds (43.16 wt%). The order of ease in converting certain components into nitrogenous compounds is Ketones > Aldehyde > Furans > Phenols > Esters > Alcohols. This study not only clarified the correlation coupling mechanisms between raw material pretreatment conditions and nitrogen-rich ratio with pyrolysis product characteristics. It can also provide guidance for biorefining. Based on the excellent lignin removal effect of the method proposed in this study, it has broad application prospects in the field of biorefinery of lignocellulosic biomass.

U(VI) mitigation via forward osmosis: elucidation of retention mechanisms and co-ion effects

Uranium (U) is a chemical and radioactive toxic contaminant affecting many groundwater systems. The focus of this study was to evaluate the suitability of forward osmosis (FO) for uranium rejection from contaminated groundwater under field-relevant conditions. Laboratory experiments with aqueous solution containing uranium were performed with FO membrane to understand the uranium rejection mechanism under varied pH, draw solution concentration, and presence of co-ions. Further, experiments were performed with U-contaminated field groundwater. Results of the hydrogeochemcial modelling using PHREEQC indicated that the rejection mechanism of uranium was highly dependent on aqueous speciation. Uranium rejection was maximum at alkaline pH with ca. 99% rejection due to charge-based interactions between membrane and dominant uranyl complexes. The results of the co-ion study indicated that nitrate and phosphate ions decrease uranium rejection. Whereas, bicarbonates, calcium, and magnesium ions concentrated uranium in feed solution. Further, the uranium adsorption onto the membrane surface primarily depended on pH of the aqueous solution with maximum adsorption at pH 5.5. Our results show that the World Health Organization’s drinking water guideline value of 30 μgL−1 for U could be achieved via FO process in field groundwater containing low dissolved solids.

Degradation Behavior of Medical MgZZC-1 in Various Simulated Body Fluids.

Magnesium-based biodegradable metal bone implants exhibit superior mechanical properties compared to biodegradable polymers for orthopedic and cardiovascular stents. In this study, MgZZC-x (x = 1, 1.2) alloys were screened by in vitro biocompatibility tests in three simulated body fluids under nontoxic conditions. The MgZZC-1 alloys with better biocompatibility were selected to predict the days required for complete degradation. The evolution of degradation products was analyzed, and the mechanism of formation of the product film was inferred. A degradation kinetic model was established to investigate the effect of MEM components on the degradation of the alloys. The results demonstrate that the proteins in MEM can greatly retard the degradation progress by attaching to the surface of MgZZC-1 alloys, which are predicted to degrade completely within 341 days. The carbonate and phosphate buffers were adjusted to pH in MEM solution, delaying the degradation of magnesium alloys. This process in MEM more accurately reflects the actual degradation in the body and is superior to that in Hanks and SBF solutions. This study will promote the application of biodegradable materials in clinical medicine.

Response of wheat (Triticum aestivum L. cv.) to the coexistence of micro-/nanoplastics and phthalate esters alter its growth environment

Micro- and nano-plastics (MPs/NPs) have emerged as a global pollutant, yet their impact on the root environment of plants remains scarcely explored. Given the widespread pollution of phthalate esters (PAEs) in the environment due to the application of plastic products, the co-occurrence of MPs/NPs and PAEs could potentially threaten the growth medium of plants. This study examined the combined effects of polystyrene (PS) MPs/NPs and PAEs, specifically dibutyl phthalate and di-(2-ethylhexyl) phthalate, on the chemical properties and microbial communities in a wheat growth medium. It was observed that the co-pollution with MPs/NPs and PAEs significantly increased the levels of oxalic acid, formic acid, and total organic carbon (TOC), enhanced microbial activity, and promoted the indigenous input and humification of dissolved organic matter, while slightly reducing the pH of the medium solution. Although changes in chemical indices were primarily attributed to the addition of PAEs, no interaction between PS MPs/NPs and PAEs was detected. High-throughput sequencing revealed no significant change in microbial diversity within the media containing both PS MPs/NPs and PAEs compared to the media with PS MPs/NPs alone. However, alterations in energy and carbohydrate metabolism were noted. Proteobacteria dominated the bacterial communities in the medium solution across all treatment groups, followed by Bacteroidetes and Verrucomicrobia. The composition and structure of these microbial communities varied with the particle size of the PS in both single and combined treatments. Moreover, variations in TOC, oxalic acid, and formic acid significantly influenced the bacterial community composition in the medium, suggesting they could modulate the abundance of dominant bacteria to counteract the stress from exogenous pollutants. This research provides new insights into the combined effects of different sizes of PS particles and another abiotic stressor in the wheat root environment, providing a critical foundation for understanding plant adaptation in complex environmental conditions.

Modifying Specific Ion Effects: Studies of Monovalent Ion Interactions with Amines.

Specific ion effects in the interactions of monovalent anions with amine groups─one of the hydrophilic moieties found in proteins─were investigated using octadecylamine monolayers floating at air-aqueous solution interfaces. We find that at solution pH 5.7, larger monovalent anions induce a nonzero pressure starting at higher areas/molecules, i.e., a wider "liquid expanded" region in the monolayer isotherms. Using X-ray fluorescence at near total reflection (XFNTR), an element- and surface-specific technique, ion adsorption to the amines at pH 5.7 is confirmed to be ion-specific and to follow the conventional Hofmeister series. However, at pH 4, this ion specificity is no longer observed. We propose that at the higher pH, the amine headgroups are only partially protonated, and large polarizable ions such as iodine are better able to boost amine protonation. At the lower pH, on the other hand, the monolayer is fully protonated, and electrostatic interactions dominate over ion specificity. These results demonstrate that ion specificity can be modified by changing the experimental conditions.

Application of Bimetallic Hydroxide/Graphene Composites in Wastewater Treatment

The increasing discharge of antibiotic wastewater leads to increasing water pollution. Most of these antibiotic wastewaters are persistent, strongly carcinogenic, easy to bioaccumulate, and have other similar characteristics, seriously jeopardizing human health and the ecological environment. As a commonly used wastewater treatment technology, non-homogeneous electro-Fenton technology avoids the hazards of H2O2 storage and transportation as well as the loss of desorption and reabsorption. It also facilitates electron transfer on the electrodes and the reduction of Fe3+ on the catalysts, thereby reducing sludge production. However, the low selectivity and poor activity of electro-synthesized H2O2, along with the low concentration of its products, combined with the insufficient activity of electrically activated H2O2, results in a low ∙OH yield. To address the above problems, composites of layered bimetallic hydroxides and carbon materials were designed and prepared in this paper to enhance the performance of electro-synthesized H2O2 and non-homogeneous electro-Fenton by changing the composite mode of the materials. Three composites, NiFe layered double hydroxides (LDHs)/reduced graphene oxide (rGO), NiMn LDHs/rGO, and NiMnFe LDHs/rGO, were constructed by the electrostatic self-assembly of exfoliated LDHs with few-layer graphene. The LDHs/rGO was loaded on carbon mats to construct the electro-Fenton cathode materials, and the non-homogeneous electro-Fenton oxidative degradation of organic pollutants was realized by the in situ electrocatalytic reduction of O2 to ∙OH. Meanwhile, the effects of solution pH, applied voltage, and initial concentration on the performance of non-homogeneous electro-Fenton were investigated with ceftazidime as the target pollutant, which proved that the cathode materials have an excellent electro-Fenton degradation effect.

Accelerated peroxymonosulfate activation over defective perovskite with anchored cobalt nanoparticles for organic contaminant removal

In this study, a novel perovskite oxide (Co@D-PBSC) for activation peroxymonosulfate (PMS) to degrade organic pollutants in wastewater was developed. Cobalt nanoparticles (Co NPs) and oxygen vacancies (OVs) were introduced to the perovskite oxide lattice via a non-stoichiometric ratio and separate-out strategy. The OVs and Co NPs provided abundant active sites for the activation of PMS and the generation of reactive oxygen species. The Co metal-OVs bridge promote the adsorption of PMS, meanwhile, Co nanoparticles accelerate the Co2+/Co3+ redox cycle, resulting in the production of the main reactive substance, sulfate radicals (SO4•−). The results of catalytic experiments showed that 85 % of ofloxacin (OFX) degradation efficiency was obtained within 1 min at 0.1 g/L Co@D-PBSC, 0.3 g/L PMS, 20 mg/L OFX (150 mL), and solution pH 7.0, which indicated that Co@D-PBSC/PMS system exhibits excellent performance. This work demonstrated an efficient perovskite catalyst for PMS activation in wastewater treatment and provided a useful catalyst design strategy for the advanced oxidation processes (AOPs).

Effect of confined Mn oxides on regulating capability of activated coke for persulfate-based oxidation of a sweetener acesulfame

Mn oxides are confined within the porous structure of activated coke (ACO) via impregnation followed by calcination treatment. The Mn-ACO sample calcined at 600°C (Mn-ACO600) demonstrated superior performance despite containing only a minute atomic ratio of 0.11% Mn on its surface. This treatment led to a slight increase in the specific surface area and pore volume of ACO, with a significant enhancement in the proportion of micropores, rising from 54.2% in ACO to 71.8% in Mn-ACO600. Raman spectroscopy indicated additional defects in Mn-ACO, while XPS analysis confirmed the coexistence of Mn(II), Mn(III), and Mn(IV) oxides. Although ACO adsorption alone was ineffective in removing acesulfame (ACE), Mn-ACO600 achieved a removal rate of 19.0%. The introduction of peroxydisulfate (PDS) further boosted the degradation of Mn-ACO600, with a Kapp value that was 2.28 times of that of the combined Mn-ACO600 adsorption and PDS oxidation process, indicating a remarkable synergistic effect. To optimize the experimental conditions, a response surface methodology design analysis was conducted, revealing that solution pH and the dosage of Mn-ACO600 were crucial factors. Furthermore, the study confirmed non-radical oxidizing species, such as 1O2 and h+ , played a predominant role in the process, with relatively minor contributions from radical oxidizing species.

Mechanism investigation of food waste compost as a source of passivation agents for inhibiting pyrite oxidation

Pyrite oxidation causes the generation of acid mine drainage (AMD), posing significant challenges in the management of sulfide tailings. Passivation agents such as humic acid have been tested to prevent pyrite oxidation. The potential of using humate rich food waste compost as a source of passivation agents to suppress pyrite oxidation was explored in this study. Batch leaching tests were conducted at room temperature, involved oxidatively leaching a pure pyrite and a pyrite-containing coal refuse sample, respectively, with and without adding the compost at acidic pH. The involved passivation mechanisms were investigated by solution leaching tests and spectroscopic (XPS) and microscopic (SEM) analysis of the pure pyrite sample and its leaching residues. Compared to the control, adding the compost led to the increases in solution pH, removal of the Fe2+/Fe3+ ions from the solutions by adsorption, and remarkable decreases (≥58 %) in sulfur concentration in both samples. Both SEM and XPS analysis indicated that a coating layer was successfully established on pyrite surface after being leached in the presence of the compost. The coating layer comprised a mixture of organic species (e.g., O-CO and N-H/C groups) and phosphate, potentially improving the likelihood of providing antioxidant protection over acidic pH. As a low-cost material, food waste compost can benefit the source control of AMD not only in terms of its surface passivation, but also its intrinsic alkalinity, metal immobilization, and low environmental risk.

Application of a Green Deep Eutectic Solvent for Preconcentration and Determination of Copper and Cadmium in Food, Cosmetic, and Water Samples

Background:: Determination of environmental pollutants is important due to their harmful effects on the health of living organisms. However, direct measurement of many of these pollutants is not possible due to their low concentrations, which necessitates the need for sample preparation methods. One of the rapid and simple sample preparation methods is the Air-Agitated Liquid-Liquid Microextraction (AALLME) method, which requires toxic organic solvents that can lead to environmental pollution. Therefore, finding green solvents like Deep Eutectic Solvents (DESs) to replace them can be investigated. Methods:: A novel Deep Eutectic Solvent (DES) was synthesized from a combination of choline chloride and 2-phenylethanol with a molar ratio of 1:4, and it was examined using FT-IR analysis. This solvent was used in an AALLME method for measuring copper and cadmium heavy metal ions in complex real samples with Flame Atomic Absorption Spectroscopy (FAAS). Results:: The influential parameters of this method, such as solution pH (5.4), extraction cycles (12), and extraction solvent volume (440 μL), were optimized utilizing central composite design (CCD). Underneath the optimized circumstances, the detection limits for Cu2+ and Cd2+ were 0.14 and 0.09 ng mL-1, and the linear dynamic range was 0.47-50.0 and 0.32-22.5 ng mL-1, respectively. The preconcentration factors for these cations were 139.7 and 133.4, respectively. Conclusion:: Combining this novel green solvent and rapid sample preparation method for the preconcentration and determination of the studied heavy metal ions has shown promising results in terms of enrichment factors and detection limit values.

Controls on Li partitioning and isotopic fractionation in inorganic calcite

The δ7Li of marine carbonates has been interpreted as an archive of the evolution of seawater δ7Li, and therefore continental weathering, through geological time. However, little is known about the incorporation of Li into calcium carbonate minerals and, consequently, the controls on Li partitioning (DLi) and isotopic fractionation (Δ7Lisolid-fluid) associated with Li incorporation. Crucially, we lack a fundamental understanding of how Li partitioning and Δ7Lisolid-fluid change in response to the chemical and physical conditions of crystal formation. Here, we present DLi and Δ7Lisolid-fluid data from a series of inorganic calcite precipitation experiments where temperature, and solution pH and dissolved inorganic carbon (DIC) were independently varied. We find DLi values in the range 0.8–1.5x10−3, which show no relationship with temperature, a strong positive correlation with pH, and a weak positive correlation with DIC. At face value, these patterns are inconsistent with the results of previous precipitation studies. However, the correlations with pH and DIC are consistent with a strong precipitation rate effect on DLi that aligns well with previous data, with a likely secondary influence from the incorporation of Li-HCO30 ion pairs from solution. We find Δ7Lisolid-fluid values in the range −6 to −2 ‰, which show no relationship with temperature or pH, and a weak positive correlation with DIC and crystal precipitation rate. These results do not agree with previously published data. Considered alongside previously published data, we observe no consistent relationship between Δ7Lisolid-fluid and any reported physical or chemical experimental parameter, highlighting the need for substantial further work to determine whether systematic controls on Li isotopic fractionation exist in carbonate minerals, and whether they may be environmentally significant.

Lithium recovery from Mexican geothermal brine via microwave-synthesized ion sieves

This paper investigates for the first time the feasibility of lithium recovery using lithium ion-sieves from a Mexican geothermal brine from a well of Cerro Prieto power plant. The materials were prepared following the microwave-assisted hydrothermal route to favor their sustainability. Also, the effect of the three manganese-based compounds as precursors was evaluated in which the vacancies were generated by acid treatment, by varying the acid concentration and the contact time. The structural characterizations showed that manganese sulfate was an efficient precursor for synthesizing LiMn2O4 spinel. The results of the uptake experiments, varying the pH of the Li solution showed that the highest sorption capacity is obtained at pH 12. The adsorption kinetics was better described by a pseudo second order equation (R2=0.9392). According to the Weber-Morris model, the process seems to be governed by film diffusion rather by intraparticle diffusion. The maximum adsorption capacity that was achieved was 9.64 mg/g and the thermodynamic equilibrium was best described by the Freundlich isotherm (R2=0.9769). Finally, the material was able to retain a competitive uptake capacity after five adsorption-desorption cycles.

The Principle for Proton Motive Force Generated by Quinones Oxidoreduction

The proton motive force across the inner mitochondrial membrane drives adenosine triphosphate synthesis. Q-cycle is a mechanism of the proton motive force generation. Its essential feature is a bifurcation and forming semiquinone, which remains contentious. Three cathodic waves of benzoquinone appeared in dilute phosphate buffered solution (pH 3.35), which was attributed to dramatic pH change at electrode surface. These waves indicated that at different potential of the electrode, benzoquinone accepted the protons from H3O+, H2PO4 −, and H2O, and produced H2O, HPO4 2−, and OH−, respectively. It revealed that the pKa of hydroquinone was dependent on the potential of the electrode and external oxidant, which was attributed to the nature of proton-coupled electron transfer of quinone oxidoreduction. We proposed a mechanism that the proton motive force was directly produced by the reductant at Qi site and the oxidant at Qo site through quinone oxidoreduction.

Moment Analysis Method for Determination of Rate Constants of Solute Permeation across Interface of Spherical Molecular Aggregates by Means of High-Performance Liquid Chromatography

A moment analysis method was developed for the study of solute permeation at the interface of spherical molecular aggregates. At first, new moment equations were developed for determining the partition equilibrium constant (Kp) and permeation rate constants (kin and kout) of solutes from the first absolute (μ1A) and second central (μ2C) moments of elution peaks measured by using high-performance liquid chromatography (HPLC). Then, the method was applied to the analysis of mass transfer phenomena of three solutes, i.e., hydroquinone, resorcinol, and catechol, at the interface of sodium dodecylsulfate (SDS) micelles. HPLC data were measured by using an ODS column and an aqueous phosphate buffer solution (pH = 7.0) as the mobile phase solvent. Pulse response experiments were conducted while changing SDS concentration (5 - 20 mmol dm−3) in the mobile phase under the conditions that the surface of ODS stationary phase was dynamically coated by SDS monomers. In order to demonstrate the effectiveness of the moment analysis method using HPLC, the values of Kp, kin, and kout were determined for the three solutes as 35 - 69, 2.4 × 10−8 - 1.4 × 10−6 m s−1, and 7.0 × 10−10 - 2.1 × 10−8 m s−1, respectively. Their values increase with an increase in the hydrophobicity of the solutes. The method has some advantages for the study of interfacial solute permeation of molecular aggregates. For example, neither immobilization nor chemical modification of both solute molecules and molecular aggregates is required when elution peaks are measured by using HPLC. Interfacial solute permeation takes place in the mobile phase without any chemical reaction or physical action on molecular aggregates. The values of Kp, kin, and kout were analytically determined from those of μ1A and μ2C by using the moment equations. The results of this study must contribute to the dissemination of an opportunity for studying the interfacial solute permeation of molecular aggregates to many researchers because of extremely high versatility of HPLC.