Dissociation Of Carboxyl Groups Research Articles

Oxidised porous starch carrier for caffeine delivery: preparation, characterisation, and in vitro release

SummaryThis work established an oxidised porous starch carrier system for the administration of caffeine by selectively oxidising the main hydroxyl groups at the C6 positions of porous starch to carboxyl groups using 2,2,6,6‐tetramethylpiperidoxyl (TEMPO) oxidation. The loading capacity and encapsulation efficiency of oxidised porous starch on caffeine rose as the oxidation degree (0%–90%) increased, increasing by 4.66 and 4.95 times, respectively, at 90% oxidation. The crystallinity of porous starch diminished after TEMPO oxidation, while the crystalline caffeine transferred into an amorphous state when loaded onto oxidised porous starch. Following oxidation, the absolute value of porous starch surface potential rose, enabling the granules avoided aggregation. Caffeine formed tighter bonds with oxidised porous starch in acidic conditions due to the dissociation of carboxyl groups, which lead to a peak loading capacity (8.02%) of oxidised porous starch with 90% oxidation at pH 4. Electrostatic interactions and hydrogen bonds were the driving forces. Long‐term gastrointestinal release of caffeine was achieved utilising oxidised porous starch as carriers.

A clean label O/W pickering emulsion stabilized by pectin-containing lignocellulosic nanofibrils isolated from apple pomace

With the increasing demand for clean-label food, LCNF is considered a promising candidate to replace artificial surfactants in O/W emulsion. However, the isolation of LCNF usually requires the use of costly and toxic oxidants or grafting reagents to introduce charged groups for higher fibrillation degree and better emulsifying properties. In this study, a new pectin-containing apple nanofibril (A-NF) with native dissociated carboxyl groups (-COO-) was successfully produced from apple pomace by alkaline demethylation followed by high-pressure homogenization. These “native” charged A-NFs are 10–30 nm in diameter and ∼1 μm in length, and can be well dispersed in water for several months due to the release of up to 1.30 mmol/g nanofibrils of -COO- from the insoluble pectin (ISP) fraction by alkaline demethylation. Among A-NFs, A–NF–24h showed the best emulsifying properties (70.85 m2/g of EAI and 94.71% of ESI) and highest emulsion stability (∼1.00 μm of the oil droplet size during 14-day storage). Emulsion microstructure showed that LCNF not only irreversibly adsorbed at the oil-water interface, providing electrostatic stability, but also offered depletion stability by fabricating an entangled network with the unabsorbed portion. Moreover, molecular dynamics simulations further explained that the A-NF system displayed lower absorption energy of −1659.43 kJ/mol and diffusion cofactor of oil molecules of 16.67 μm2/s than that of CNF system at the interface, thus enhancing the emulsion stability. Altogether, these native A-NFs exhibit good colloidal stability, comparable emulsifying properties and emulsion stability, and have promising applications in clean-label O/W emulsions.

4D-printed needle panel meters coupled with enzymatic derivatization for reading urea and glucose concentrations in biological samples

On-site analytical techniques continue being developed with advances in modern technology. To demonstrate the applicability of four-dimensional printing (4DP) technologies in the direct fabrication of stimuli-responsive analytical devices for on-site determination of urea and glucose, we used digital light processing three-dimensional printing (3DP) and 2-carboxyethyl acrylate (CEA)–incorporated photocurable resins to fabricate all-in-one needle panel meters. When adding a sample having a value of pH above the pKa of CEA (ca. 4.6–5.0) into the fabricated needle panel meter, the [H+]-responsive layer of the needle, printed using the CEA-incorporated photocurable resins, swelled as a result of electrostatic repulsion among the dissociated carboxyl groups of the copolymer, leading to [H+]-dependent bending of the needle. When coupled with a derivatization reaction (urease-mediated hydrolysis of urea to decrease [H+]; glucose oxidase-mediated oxidization of glucose to increase [H+]), the bending of the needle allowed reliable quantification of urea or glucose when referencing pre-calibrated concentration scales. After method optimization, the method's detection limits for urea and glucose were 4.9 and 7.0 μM, respectively, within a working concentration range from 0.1 to 10 mM. We verified the reliability of this analytical method by determining the concentrations of urea and glucose in samples of human urine, fetal bovine serum, and rat plasma with spike analyses and comparing the results with those obtained using commercial assay kits. Our results confirm that 4DP technologies can allow the direct fabrication of stimuli-responsive devices for quantitative chemical analysis, and that they can advance the development and applicability of 3DP-enabling analytical methods.

Hybrid hydroxyapatite/graphene oxide composites materials synthesized from eggshell for adsorption of Cr(VI) in aqueous solution

In this work, hydroxyapatite/graphene oxide hybrid composites (HAP/GO) were prepared from eggshell by solvothermal method, which was mainly used as adsorbents for Cr(VI) removal in wastewater. The effect of graphene oxide (GO) on the structure and removal efficiency of HAP/GO was discussed. The results showed that the Cr(VI) removal of HAP/GO10% can reach more than 90% within 1 h, and the adsorption conforms to the first-order kinetics. It was found that the addition of GO changed the pore size distribution of HAP/GO and improved Cr(VI) removal. It can be concluded that the swelling of GO in aqueous solution leads to an increase in the interaction between the dissociated carboxyl groups and Cr(VI), thereby improving the adsorption efficiency.

On the gelation of Premna microphylla turcz extracts: The effects of supernatant and precipitate of plant ash suspension

In order to elucidate the gelling mechanism of Premna microphylla turcz (PMT) induced by plant ash (PA), PA was fractionated into supernatant (PA-S) and precipitation (PA-P) and added to the PMT suspension, respectively. The effects of different concentrations (1–9%) and fractions (PA, PA-S, PA-P) of PA suspension on the gel properties were studied. Results showed that the electrical conductivity, content of monovalent cations, pH were higher in PA-S than PA-P. Both the PA-S and PA-P fractions induced the gelation of PMT (except for the low concentration at 1% for PA-S), and the PA-P-PMT gels showed much higher gel strength and hardness than PA-S-PMT gels. With increased concentration, the gel strength increased in PA-P-PMT, but decreased in PA-S-PMT. A hypothesis for the gelation of PMT induced by PA was proposed: the divalent cations in PA bind to carboxyl group in pectin and form gels; when higher content of PA is added, a higher pH leads to extensive dissociation of carboxyl groups thereby increases the electrostatic repulsion between pectin chains, which ultimately weakens the gelling forces. This study can provide theoretical support for further optimization of the traditional processing of PMT gels.

A substrate protection approach to applying the calcium ion for improving the proteolysis resistance of the collagen.

Enzymatic dehairing, as a crucial part of cleaner leather processing, has reached processive advancement with potentially replacing the traditional hair removal due to increasing pressure from environmental demand. However, this cleaner technology based on proteases has a problem that the hide grain (collagen-rich structure) is susceptible to be hydrolyzed, decreasing the quality of finished leather. From the perspective of improving the stability of collagen fibers and their resistance to proteolysis, a method for protecting the hide grain during the enzymatic dehairing process was developed. The results showed that calcium ions had a swelling effect on collagen fibers under near-neutral conditions (pH 6.0-10.0), decreasing the thermal stability of collagen and the proteolysis resistance of collagen significantly. The alkaline environment (pH 10.0-12.0) will promote the dissociation of carboxyl groups in hide collagen, promoting the combination of calcium ions and carboxyl groups. This strategy can change the surface charge of collagen fibers and strengthen the connection between collagen fibers, thus improving protease resistance and the thermal stability of collagen. However, collagen fibers could swell violently once the alkalinity of the solution environment was extreme. Despite the above situation, calcium ion was still conducive to maintain the structural stability of collagen fibers. At pH 10.0-12.0, pretreating animal hide with a solution containing calcium ions can improve the protease resistance of hide grain, making the hide grain well-protected. This method provided an effective way to establish a safer enzymatic unhairing technology based on substrate protection. KEY POINTS: • A collagen protection method for hair removal of animal hide was developed. • This method applied calcium ions to collagen at alkaline conditions (pH 10.0-12.0). • Pretreatment results of calcium ions at different pH values on animal hide were compared.

Influence of reduction on the fluorescent units and proton binding of humic acids: Synchronous fluorescence spectrum and NICA-Donnan modeling

The effect of reduction on the fluorescent units and proton binding behaviors of two humic acids (HAs) (PPHA and JGHA) was investigated by synchronous fluorescence spectrum (SFS) combined with NICA-Donnan modeling. With variations in pH and reduction time, the fluorescence quenching of the humic-like fraction was much stronger than that of fulvic-like fraction, indicating a greater variation of chemical structure in humic-like fractions. The NICA-Donnan model could satisfactorily describe proton binding, and the optimal NICA-Donnan model parameters indicated that the site density of phenolic groups on reduced HAs increased by 0.95 and 0.72 mmol/g for PPHA and JGHA, respectively. These results were in good agreement with the transferred electrons capacities during the electrochemical reduction (0.90 and 0.76 mmol/gHA for PPHA and JGHA, respectively). A linear negative correlation was established between the peak area of SFS after the peak fitting and the site density of protonated functional groups obtained from the NICA-Donnan model calculation under acidic and neutral conditions. It was then applied to the estimation of the proton binding properties of HAs during the electrochemical reduction. The results showed that reduction had a relatively weak effect on the proton dissociation of carboxylic groups, while the site density of protonated phenolic groups increased significantly with increasing reduction time.

Water Purification by Potassium Humate–C.I. Basic Blue 3 Adsorption-Based Interactions

Interactions of C.I. Basic Blue 3 with potassium humate in aqueous systems were investigated. Both the humic content and dye removal are of crucial significance in relation to water of a desired quality. Dye retention experiments demonstrated that potassium humate is an exceptionally efficient adsorbent. The effect of both the pH and temperature on the adsorption process was investigated. The temperature proved to only slightly influence the extent of dye sorption; contrarily, under mildly acidic conditions (pH = 4.0), the quantity of dye adsorbed was doubled on standing. At this pH value, interactions between the positively charged dye and the dissociated carboxyl groups of humic substances are encountered. This was also supported by the obedience of the experimental data to the pseudo-second-order kinetic model. Three adsorption models, i.e., Langmuir, Freundlich and BET, were fitted to the experimental data; the equilibrium adsorption conformed to the Langmuir and BET isotherm equations on the basis of electrostatic dye–humics interactions, while the fitting of the Freundlich model referred to the heterogeneities of humic substances attributed to their colloidal behavior. Thermodynamic quantities, i.e., enthalpy, entropy and free energy change in the adsorption, were calculated. The low ΔHadsθ values verify the negligible effect of the temperature on the adsorption; ΔSadsθ denotes a thermodynamically favorable reaction, and ΔGadsθ denotes a spontaneous process.

The role of carboxyl groups upon the precipitation of albumin at low pH

Proteins play a major role in the organization of the living matter. Underlying this fact are their unique properties in aqueous solution, for which the available theories provide only a partial explanation. In order to throw some light into the behaviour of proteins in aqueous solution, experiments on the precipitation of electropositive albumin by means of the sodium salts of sulfate, thiocyanate, nitrate, bromide and chloride upon varying the solution pH were undertaken. Results show that the protein undergoes a transition at approximately pH 3, characterized by a change on its precipitation profile. Its shape, of monotonic profile below pH 3, displays a non-monotonic behaviour with separated peaks at higher pH values, which increase in number and decrease in intensity with increasing pH. To elucidate these observations, additional precipitation experiments with sodium thiocyanate in the presence of a secondary salt were undertaken. It is shown that the secondary salt changes significantly the protein's precipitation profile, despite being present in very low concentration. Its influence on the precipitation depends in a great extent on the cation's valence, which induce effects proportional to x, x2, and x3 for monovalent, divalent, and trivalent cations, respectively. The observations reported can be explained under the assumption that i) the protein dissociates into distinct forms, as result of the dissociation of carboxyl groups, and ii) salt cations establish chemical equilibria with the negative charges of the dissociated carboxyl groups present in the emerging protein forms.

Equilibrium Sorption of Histidine on Clinoptilolite

Sorption of histidine in the cationic and zwitterionic forms on a framework aluminosilicate, clinoptilolite, has been investigated. The contributions of the exchange and nonexchange mechanisms of sorption to the sorption capacity have been determined. It has been shown that monolayer histidine sorption on clinoptilolite by the ion-exchange mechanism proceeds due to the electrostatic interaction between $${\text{NH}}_{3}^{ + }$$ groups of the amino acid and electronegative sites of the sorbent matrix. In the region of equivalent exchange, a smaller value of the ion-exchange component of the sorption of histidine zwitterions is due to the Coulomb repulsion between the dissociated carboxyl groups of the amino acid and the negatively charged aluminum–oxygen clinoptilolite matrix. The isotherm of histidine sorption from dilute solutions has been described using the Langmuir theory. The equilibrium sorption parameters have been found. It has been concluded that polymolecular layers of the amino acid are formed as a result of association via hydrogen bonding, as well as dipole–dipole and hydrophobic interactions.

Effect of quaternary ammonium salts on spectral properties of zinc octacarboxyphthalocyanine

The paper presents results of the research on the influence of quaternary ammonium salts on UV–vis absorption and emission spectra of zinc octacarboxyphthalocyanine (ZnPcOC). Quaternary ammonium salts which show biological activity play a crucial role. In ZnPcOC solutions with a proper concentration of tetrabutylammonium salts (TBAX), a strong bathochromic shift band (λmax = 760 nm – “R” band) showing red fluorescence appears in time. The presence of tetrabutylammonium salt causes pH increase and, consequently, a gradual dissociation of carboxyl groups in ZnPcOC molecule. It seems that –COO— anions present in the ZnPcOC complex can interact with tetraalkylammonium cations, causing a decrease in symmetry in ZnPcOC complex. As a result, the “R”- band appears in the UV–vis spectrum of ZnPcOC.

Биомодификация коллагенсодержащих субпродуктов методом ферментативного гидролиза

Low-value by-products can be processed using biotechnological methods, which seems to be the optimal solution for the problem of rational use of secondary raw materials. The authors introduce a method of biotransformation using whey and enzyme preparation of proteolytic action with subsequent massaging. The method neutralizes the specific smell, reduces the time of heat treatment, increases hydrophilicity, and reduces the mechanical strength of mutton rumen tissue. The experiment proved that the enzymatic effect on the connective tissue of the mutton rumen contributes to the destruction of disulfide and hydrogen bonds of the triple helix of the collagen macromolecule. It significantly reduces the mechanical strength and hydrothermal stability of collagen, which, in its turn, reduces the heat treatment time while increasing the functional and technological properties. The research revealed an increase in collagen digestibility. After 4 hours of fermentation, it was 4.5%, after 6 hours – 5.9%, and after 8 hours – 5.9%. Hence, the optimal period of fermentation was determined as 6 hours, since between 6 and 8 hours the main physical and chemical parameters improved insignificantly. The experiment in the cutting pressure of the raw lamb rumen tissue demonstrated softening of the structure as a result of the effect of the acidic medium on the collagen structure. An excess positive charge formed due to the suppression of dissociation of carboxyl groups of side chains. The loosening of the collagen structure occurred due to the expansion of fibrils in the polar areas, which can be attributed to the repulsion between similarly charged groups. As a result, the brine penetrated into the expanded area and caused swelling. The use of whey and fermentation contributed to an additional increase in moisture-binding and moisture-holding capacity. It loosened the structure of proteins and, thus, increased the degree of penetration and the immobilized moisture in the rumen. As a result, its mass increased by 10–20%, and the heat loss reduced. The composition of the brine contributed to the swelling, increased the diameter of the collagen fibers, and enlarged the surface of interaction in during massaging. Moisture was allowed to enter freely, which increased the water binding capacity by 22.2 ± 0.31%. The increase in the water binding capacity could be explained by the modification of collagen and its destructive changes. The changes occurred due to the additional interaction of whey molecules with the protein and the formation of new intermolecular bonds. Fermentation, combined with the massaging of the tripe, contributed to the development of lactic microflora and hydrolytic decomposition of protein components, thereby reducing the heat treatment process. Such changes are associated not only with the processes of protein hydrolysis under enzyme preparation, but also with the complex activity of lactic acid bacteria, as well as endo- and exoenzymes that hydrolyze proteins. The changes can also be attributed to the fact that low-molecular protein substances can assimilate and contribute to bacterial growth. In addition, lactic acid reduces the pH of the medium, thus activating the enzymatic properties. The proposed method of biotransformation of collagen-containing raw materials makes it possible to create environmentally friendly and low-waste technologies.

Gold Nanoparticle-Protein Conjugate Dually-Responsive to pH and Temperature for Modulation of Enzyme Activity

Regulation of the activity and stability of enzymes is important for their biological and biomedical applications. In this regard, considerable attention has been paid to the regulation of enzyme activity by controlling steric effects in protein-thermoresponsive polymer conjugates via temperature change. However, it is difficult to accomplish on/off regulation of activity via steric effects alone. In this work, pH- and temperature- dually-responsive gold nanoparticles (AuNPs) conjugated to poly (N-isopropylacrylamide) (pNIPAM) and poly(methacrylic acid) (pMAA), designated AuNP-pNIPAM-pMAA, are proposed in this work for the regulation of enzyme activity with high precision. Using these particles adsorbed with inorganic pyrophosphatase (PPase) as a model enzyme (AuNP-PPase-pNIPAM-pMAA), it was shown that, by changes in pH and temperature leading to changes in “steric covering” of the protein active site via interpolymer hydrogen bonding, the activity of PPase could be closely regulated. At 25 °C and pH 5.0, the steric covering of pNIPAM and the interpolymer hydrogen bonding between pNIPAM and pMAA gave a cage-like “locking in” structure in the protein active site as the “hidden” state, with a very low specific activity of only 0.2 Kat/Kg, around 2 % of its normal activity. At 45 °C and pH 8.0, the cage structure did not form due to the lack of coverage by the collapsed pNIPAM chains and the inability of the dissociated carboxyl groups in pMAA to form hydrogen bonds, leaving the protein active center fully exposed as the “available” state, and resulting in a high specific activity of 8.3 Kat/Kg. Thus the activity of the enzyme in the conjugate is almost totally suppressed at 25 °C/pH 5.0 and completely recovered at 45 °C/pH 8.0. The controllable range of activity is thus very wide, i.e., from 2 to 100 %. The AuNP-PPase-pNIPAM-pMAA conjugate also has strong resistance to trypsin digestion. In addition, it was shown that after cycling three times between the “hidden” and “available” states, the conjugate retained more than 85 % of its initial activity, showing that this system can be cycled and used multiple times without significant loss of activity. It is concluded that this dual-responsive gold nanoparticle-protein-polymer conjugate has great potential in applications requiring close control of protein activity under complex environmental conditions.

Microwave carbonized cellulose for trace pharmaceutical adsorption

A promising sustainable strategy to valorize cellulose to high-value adsorbents for trace pharmaceuticals, like diclofenac sodium (DCF), in the water is demonstrated. Carbon nanospheres (CN) as the DCF adsorbent were derived from cellulose through a one-pot microwave-assisted hydrothermal carbonization method. CN exhibited efficient DCF removal (100% removal of 0.001 mg/mL DCF in 30 s and 59% removal of 0.01 mg/mL DCF in 1 h). The adsorption kinetics and isotherm data were well-fitted with the pseudo-second-order kinetic model and Langmuir model, respectively. The adsorption process was endothermic and spontaneous as confirmed by the thermodynamic parameters. Multiple characterization techniques including SEM/EDS, FTIR, FTIR-imaging and zeta potential were applied to qualitatively investigate the adsorption process. π-π stacking and hydrogen bonding were proposed as the dominant adsorption interactions. CN also demonstrated effective adsorption capacity towards three other commonly-detected contaminants in the wastewater including ketoprofen (KP), benzophenone (BZP), and diphenylamine (DPA), each bearing partial structural similarity with DCF. The affinity of the contaminants towards CN followed the order DPA > BZP > DCF > KP, which could be explained by the different configurations and chemical units. It was speculated that for DCF and KP, the steric hindrance and electrostatic repulsion produced by dissociated carboxyl groups can impede the adsorption process as compared to DPA and BZP. This methodology could offer further insights into the drug adsorption on the cellulose-derived carbon adsorbents and the use of bioderived carbons for treatment of wastewaters contaminated with pharmaceuticals.

In English

Weakly acidic cation exchange resin was modified with nanoparticles of zirconium hydrophosphate. The materials were investigated with methods of standard contact porosimetry and transmission electron microscopy. Both non-aggregated nanoparticles (4–15 nm) and larger formations (from 250 nm to several microns) have been found. Single particles in clusters and channels of the polymer depress dissociation of carboxylic groups due to counter-ions (H + ) in electric double layer around the particles. This causes transformation of porous structure of the polymer: the contribution of micropores to total porosity increases. These additional selective sites provide stronger interaction of Brilliant Green molecules with the surface in comparison with the pristine polymer. Removal of the dye from deionized water and Ni(II) ions from water containing also hardness ions was studied under dynamic conditions. The composite shows higher break-through capacity than that of the pristine resin. The modifier also facilitates regeneration of the weakly acidic ion-exchanger.

Aging effects on chemical transformation and metal(loid) removal by entrapped nanoscale zero-valent iron for hydraulic fracturing wastewater treatment

In this study, alginate and polyvinyl alcohol (PVA)-alginate entrapped nanoscale zero-valent iron (nZVI) was tested for structural evolution, chemical transformation, and metals/metalloids removal (Cu(II), Cr(VI), Zn(II), and As(V)) after 1–2month passivation in model saline wastewaters from hydraulic fracturing. X-ray diffraction analysis confirmed successful prevention of Fe0 corrosion by polymeric entrapment. Increasing ionic strength (I) from 0 to 4.10M (deionized water to Day-90 fracturing wastewater (FWW)) with prolonged aging time induced chemical instability of alginate due to dissociation of carboxyl groups and competition for hydrogen bonding with nZVI, which caused high Na (7.17%) and total organic carbon (24.6%) dissolution from PVA-alginate entrapped nZVI after 2-month immersion in Day-90 FWW. Compared to freshly-made beads, 2-month aging of PVA-alginate entrapped nZVI in Day-90 FWW promoted Cu(II) and Cr(VI) uptake in terms of the highest removal efficiency (84.2% and 70.8%), pseudo-second-order surface area-normalized rate coefficient ksa (2.09×10−1Lm−2h−1 and 1.84×10−1Lm−2h−1), and Fe dissolution after 8-h reaction (13.9% and 8.45%). However, the same conditions inhibited Zn(II) and As(V) sequestration in terms of the lowest removal efficiency (31.2% and 39.8%) by PVA-alginate nZVI and ksa (4.74×10−2Lm−2h−1 and 6.15×10−2Lm−2h−1) by alginate nZVI. The X-ray spectroscopic analysis and chemical speciation modelling demonstrated that the difference in metals/metalloids removal by entrapped nZVI after aging was attributed to distinctive removal mechanisms: (i) enhanced Cu(II) and Cr(VI) removal by nZVI reduction with accelerated electron transfer after pronounced dissolution of non-conductive polymeric immobilization matrix; (ii) suppressed Zn(II) and As(V) removal by nZVI adsorption due to restrained mass transfer after blockage of surface-active micropores. Entrapped nZVI was chemically fragile and should be properly stored and regularly replaced for good performance.

Chiral Ceramic Nanoparticles and Peptide Catalysis

The chirality of nanoparticles (NPs) and their assemblies has been investigated predominantly for noble metals and II-VI semiconductors. However, ceramic NPs represent the majority of nanoscale materials in nature. The robustness and other innate properties of ceramics offer technological opportunities in catalysis, biomedical sciences, and optics. Here we report the preparation of chiral ceramic NPs, as represented by tungsten oxide hydrate, WO3-x·H2O, dispersed in ethanol. The chirality of the metal oxide core, with an average size of ca. 1.6 nm, is imparted by proline (Pro) and aspartic acid (Asp) ligands via bio-to-nano chirality transfer. The amino acids are attached to the NP surface through C-O-W linkages formed from dissociated carboxyl groups and through amino groups weakly coordinated to the NP surface. Surprisingly, the dominant circular dichroism bands for NPs coated by Pro and Asp are different despite the similarity in the geometry of the NPs; they are positioned at 400-700 nm and 500-1100 nm for Pro- and Asp-modified NPs, respectively. The differences in the spectral positions of the main chiroptical band for the two types of NPs are associated with the molecular binding of the two amino acids to the NP surface; Asp has one additional C-O-W linkage compared to Pro, resulting in stronger distortion of the inorganic crystal lattice and greater intensity of CD bands associated with the chirality of the inorganic core. The chirality of WO3-x·H2O atomic structure is confirmed by atomistic molecular dynamics simulations. The proximity of the amino acids to the mineral surface is associated with the catalytic abilities of WO3-x·H2O NPs. We found that NPs facilitate formation of peptide bonds, leading to Asp-Asp and Asp-Pro dipeptides. The chiroptical activity, chemical reactivity, and biocompatibility of tungsten oxide create a unique combination of properties relevant to chiral optics, chemical technologies, and biomedicine.

Synthesis of dodecylamine-functionalized graphene quantum dots and their application as stabilizers in an emulsion polymerization of styrene

Pickering emulsions have attracted considerable interest due to their potential applications in many fields, such as the food, pharmaceutical, petroleum and cosmetics industries. The study reports the synthesis of dodecylamine-functionalized graphene quantum dots (d-GQDs) and their implementation as stabilizers in an emulsion polymerization of styrene. First, d-GQDs are prepared by thermal pyrolysis of citric acid and dodecylamine in 0.1M ammonium hydroxide. The resulting d-GQDs consist of small graphene sheets with abundant amino, carboxyl, acylamino, hydroxyl and alkyl chains on the edge. The amphiphilic structure gives the d-GQDs high surface activity. The addition of d-GQDs can reduce the surface tension of water to 30.8mNm−1 and the interfacial tension of paraffin oil/water to 0.0182mNm−1. The surface activity is much better than that of previously reported solid particle surfactants for Pickering emulsions and is close to that of sodium dodecylbenzenesulfonate, which is, a classical organic surfactants. Then, d-GQDs are employed as solid particle surfactants for stabilizing styrene-in-water emulsions. The emulsions exhibit excellent stability at pH 7. However, stability is lost when the pH is more than 9 or less than 4. The pH-switchable behaviour can be attributed to the protonation of amino groups in a weak acid medium and dissociation of carboxyl groups in a weak base medium. Finally, 2,2′-azobis(2-methylpropionitrile) is introduced into the Pickering emulsions to trigger emulsion polymerization of styrene. The as-prepared polystyrene spheres display a uniform morphology with a narrow diameter distribution. The fluorescent d-GQDs coated their surfaces. This study presents an approach for the fabrication of amphiphilic GQDs and GQDs-based functional materials, which have a wide range of potential applications in emulsion polymerization, as well as in sensors, catalysts, and energy storage.

Sorption of Cu by humic acid from the decomposition of rice straw in the absence and presence of clay minerals

The sorption of Cu on humic acid (HA) from the decomposition of rice straw in the absence (Ck-HA) and presence of montmorillonite (M-HA), kaolinite (K-HA), gibbsite (Gi-HA) and goethite (Go-HA) was investigated at pH 5.0 by using batch studies combined with isothermal titration calorimetry (ITC) and atomic force microscopy (AFM). Characterization by elemental analysis and potentiometric titration showed the composition difference among these five HA. The sorption capacity and rate increased in the order: M-HA < K-HA < Gi-HA < Ck-HA < Go-HA. ITC results revealed that the sorption process was spontaneous and endothermic. The aggregation of HA particles after sorption were observed by AFM images. The influence of pH and positive correlations between the sorption capacity and the content of acidic functional groups of HA indicated that the dissociated acidic functional groups, especially the dissociation of carboxylic groups in HA played an important role in Cu sorption. Sequential desorption of sorbed Cu showed that the surface bonded fraction (97.6–99.0%) was significantly higher than the ion exchanged fraction (1.0–2.4%). Markedly positive entropies (ΔS, 94.4–104.3 J mol−1 K−1) further demonstrated that Cu binding to HA by forming inner-sphere complexes. The findings of this study would promote the understanding on the environmental impact of the decomposition of organic waste from agricultural production.

Regularities of extracting humic acids from soils using sodium pyrophosphate solutions

Regularities of extracting humic acids from different soil types (soddy-podzolic soil, gray forest soil, and all chernozem subtypes) with sodium pyrophosphate solutions at different pH values (from 5 to 13) have been studied. It is found that, regardless of soil type, the process occurs in two stages through the dissociation of carboxylic groups and phenolic hydroxyls, each of which can be described by a logistic function. Parameters of the logistic equations approximating the extraction of humic acids from soils at different pH values are independent of the content and composition of humus in soils. Changes in the optical density of humic acids extracted from soils using sodium pyrophosphate solutions with different pH values are described in the first approximation by the Gaussian function. The optically densest humic acids are extracted using sodium pyrophosphate solutions at pH 10. Therefore, it is proposed to use an extract with pH 10 for the characterization of organic matter with the maximum possible degree of humification in the given soil.