Weak Acidic pH Research Articles

Manganese accumulation and solid-phase speciation in a 3.5 m thick mud sequence from the estuary of an acidic and Mn-rich creek, northern Baltic Sea

In sediments, manganese (Mn) is typically enriched in the form of authigenic Mn hydroxides at the water-sediment interface where intensive redox cycling of Mn occurs. Here we show, based on existing hydrochemical and geochemical (sediment core) data and new detailed chemical and mineralogical characterization of a 3.5m long sediment core from a Boreal estuary, that the behavior of Mn can be profoundly different and more complex in estuarine settings receiving an abundance of terrestrial Mn. The most notable feature in the 3.5m long sediment core is two depth intervals (60–155cm and 181–230cm) where there are strong fine-scale variations in Mn concentrations with peaks episodically reaching up to 10–25gkg−1 and 6.7–12gkg−1, respectively. X-ray absorption spectroscopy and sequential chemical extraction show that Mn occurs mainly as authigenic rhodochrosite at these two depth intervals and is mainly surface-sorbed in other sections with relatively low and stable Mn concentrations. The data suggests that the strong fine-scale variations in Mn concentrations are a reflection of the extent of formation and settling of Mn hydroxides, the precursors of the authigenic rhodochrosite (and also of the surface-sorbed Mn), rather than Mn input to the estuary or redox-related Mn translocation within the sediment. There was agreement between the results of linear combination fitting of extended X-ray absorption fine structure data and a 7-step sequential chemical extraction (SCE) in terms of quantification of surface-sorbed Mn species, whereas the SCE experiment failed to fractionate a majority of rhodochrosite into SCE step-2 (1M NH4-acetate at pH6), which is frequently employed to dissolve carbonate. We ascribe this discrepancy to only partial dissolution of rhodochrosite in the weakly acidic (pH=6) NH4-acetate leach.

DEGRADATION OF 4-NITROPHENOL FROM INDUSTERIAL WASTEWATER BY NANO CATALYTIC OZONATION

In this project, a nano catalyst (TiO 2 ) and ozone combined with each other and they were used for the removal of 4-nitrophenol (4NP) in industerial wastewater. The effect of some operational parameters such as initial pH (3-9), the concentration of pollutant (20-80 mg/L), and amount of TiO 2 were investigated. In O 3 /TiO 2 process, the anion radical formed before the production of hydroxyl radical. These results were different from the Ozonation process alone, in which high pH had a positive effect on the degradation of 4NP, because hydroxyl radicals was formed. In ozonation and O 3 /TiO 2 processes, about 89 and 97% of 4NP were degraded respectively, at optimum pH and 60 min of reaction. In catalytic ozonation the degradation rate of 4NP was higher at weak acidic pH conditions (pH=5). The removal of chemical oxygen demand (COD) was increased from 49% (only ozonation) to 74% (O 3 /TiO 2 ) at 90 min of reaction. The kinetic of degradation was pseudo-first-order and degradation and mineralization of 4NP were estimated by HPLC and COD tests, respectively. Ke ywords: Chemical Oxygen demand (COD); Degradation; Iindusterial wastewater; TiO 2 nano catalyst; 4-Nitrophenol (4NP)

A novel platform designed by Au core/inorganic shell structure conjugated onto MTX/LDH for chemo-photothermal therapy

A novel platform making up of methotrexate intercalated layered double hydroxide (MTX/LDH) hybrid doped with gold nanoparticles (NPs) may have great potential both in chemo-photothermal therapy and the simultaneous drug delivery. In this paper, a promising platform of Au@PDDA-MTX/LDH was developed for anti-tumor drug delivery and synergistic therapy. Firstly, Au NPs were coated using Layer-by-Layer (LbL) technology by alternate deposition of poly (diallyldimethylammonium chloride) (PDDA) and MTX molecules, and then the resulting core-shell structures (named as Au@PDDA-MTX) were directly conjugated onto the surface of MTX/LDH hybrid by electrostatic attraction to afford Au@PDDA-MTX/LDH NPs. Here MTX was used as both the agent for surface modification and the anti-tumor drug for chemotherapy. The platform of Au@PDDA-MTX/LDH NPs not only had a high drug-loading capacity, but also showed excellent colloidal stability and interesting pH-responsive release profile. In vitro drug release studies demonstrated that MTX released from Au@PDDA-MTX/LDH was relatively slow under normal physiological pH, but it was enhanced significantly at a weak acidic pH value. Furthermore, the combined treatment of cancer cells by using Au@PDDA-MTX/LDH for synergistic hyperthermia ablation and chemotherapy was demonstrated to exhibit higher therapeutic efficacy than either single treatment alone, underscoring the great potential of the platform for cancer therapy.

Anti-Cancer Efficacy of Paclitaxel Loaded in pH Triggered Liposomes.

Smart liposomes that are responsive to the microenvironment of tumor tissue have been utilized to enhance chemotherapeutic efficiency. Here, we reported a novel liposome called Trojan horse liposome, which has a pH response, to enhance drug accumulation in tumor sites and intercellular uptake. L-lysine was used as a linker to connect 2,3-dimethylmaleic anhydride (DMA) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE) to yield a DSPE-Lys-DMA (DLD) lipid. The pH-responsive DLD was mixed with other commercially available lipids to form liposomes. The size, morphology and zeta potential of the DLD liposomes (DLD-Lip) were measured. Paclitaxel (PTX) was loaded in the liposomes. The release profile, cellular uptake, in vitro and in vivo anticancer activity of the PTX-loaded liposomes were investigated. The results showed that the mean diameter of the liposomes was less than 200 nm. The zeta potential of the liposomes was negative at pH 7.4. However, it was transferred to positive at weak acidic pH values with the cleavage of DMA amide. The charge reversion of DMA in acidic environments facilitated the cellular internalization and endosome escape of DLD-Lip, which inhibited the proliferation of 4T1 cancer cells in vitro. The pH-responsive "Trojan horse"-like liposomes also exhibited efficient anticancer activity in the xenograft breast cancer model in vivo.

Biodegradation and Toxicity of Protease/Redox/pH Stimuli-Responsive PEGlated PMAA Nanohydrogels for Targeting Drug delivery

The application of nanomaterials in intelligent drug delivery is developing rapidly for treatment of cancers. In this paper, we fabricated a new kind of protease/redox/pH stimuli-responsive biodegradable nanohydrogels with methacrylic acid (MAA) as the monomer and N,N-bis(acryloyl)cystamine (BACy) as the cross-linker through a facile reflux-precipitation polymerization. After that, the polyethylene glycol (PEG) and folic acid (FA) were covalently grafted onto the surface of the nanohydrogels for enhancement of their long in vivo circulation lifetime and active targeting ability to the tumor cells and tissues. This kind of nanohydrogels could be disassembled into short polymer chains (Mn<1140; PDI<1.35) both in response to glutathione (GSH) through reduction of the sensitive disulfide bonds and protease by breakage of the amido bonds in the cross-linked networks. The nanohydrogels were utilized to simultaneously load both hydrophilic drug doxorubicin (DOX) and hydrophobic drug paclitaxel (PTX) with high drug loading efficiency. The cumulative release profile showed that the drug release from the drug-loaded nanohydrogels was significantly expedited by weak acidic (pH 5.0) and reducing environment (GSH), which exhibited an distinct redox/pH dual stimuli-responsive drug release to reduce the leakage of drugs before they reach tumor site. In addition, the in vitro experiment results indicated that the multidrug-loaded system had synergistic effect on cancer therapy. Meanwhile, the acute toxicity and intravital fluorescence imaging studies were adopted to evaluate the biocompatibility and biotoxicity of the nanohydrogels, the experimental results showed that the PEG modification could greatly enhance the long in vivo circulation lifetime and reduce the acute toxicity (LD50: from 138.4 mg/kg to 499.7 mg/kg) of the nanohydrogels.

Physicochemical profile of microbial-assisted composting on empty fruit bunches of oil palm trees.

This study was carried out to investigate the physicochemical properties of compost from oil palm empty fruit bunches (EFB) inoculated with effective microorganisms (EM∙1™). The duration of microbial-assisted composting was shorter (∼7 days) than control samples (2 months) in a laboratory scale (2 kg) experiment. The temperature profile of EFB compost fluctuated between 26 and 52 °C without the presence of consistent thermophilic phase. The pH of compost changed from weak acidic (pH ∼5) to mild alkaline (pH ∼8) because of the formation of nitrogenous ions such as ammonium (NH4 (+)), nitrite (NO2 (-)), and nitrate (NO3 (-)) from organic substances during mineralization. The pH of the microbial-treated compost was less than 8.5 which is important to prevent the loss of nitrogen as ammonia gas in a strong alkaline condition. Similarly, carbon mineralization could be determined by measuring CO2 emission. The microbial-treated compost could maintain longer period (∼13 days) of high CO2 emission resulted from high microbial activity and reached the threshold value (120 mg CO2-C kg(-1) day(-1)) for compost maturity earlier (7 days). Microbial-treated compost slightly improved the content of minerals such as Mg, K, Ca, and B, as well as key metabolite, 5-aminolevulinic acid for plant growth at the maturity stage of compost. Graphical Abstract Microbial-assisted composting on empty fruit bunches.

Purification and simultaneous immobilization of Arabidopsis thaliana hydroxynitrile lyase using a family 2 carbohydrate-binding module.

Tedious, time- and labor-intensive protein purification and immobilization procedures still represent a major bottleneck limiting the widespread application of enzymes in synthetic chemistry and industry. We here exemplify a simple strategy for the direct site-specific immobilization of proteins from crude cell extracts by fusion of a family 2 carbohydrate-binding module (CBM) derived from the exoglucanase/xylanase Cex from Cellulomonas fimi to a target enzyme. By employing a tripartite fusion protein consisting of the CBM, a flavin-based fluorescent protein (FbFP), and the Arabidopsis thaliana hydroxynitrile lyase (AtHNL), binding to cellulosic carrier materials can easily be monitored via FbFP fluorescence. Adsorption properties (kinetics and quantities) were studied for commercially available Avicel PH-101 and regenerated amorphous cellulose (RAC) derived from Avicel. The resulting immobilizates showed similar activities as the wild-type enzyme but displayed increased stability in the weakly acidic pH range. Finally, Avicel, RAC and cellulose acetate (CA) preparations were used for the synthesis of (R)-mandelonitrile in micro-aqueous methyl tert-butyl ether (MTBE) demonstrating the applicability and stability of the immobilizates for biotransformations in both aqueous and organic reaction systems.

A hierarchical porous bowl-like PLA@MSNs-COOH composite for pH-dominated long-term controlled release of doxorubicin and integrated nanoparticle for potential second treatment.

We chemically integrated mesoporous silica nanoparticles (MSNs) and macroporous bowl-like polylactic acid (pBPLA) matrix, for noninvasive electrostatic loading and long-term controlled doxorubicin (DOX) release, to prepare a hierarchical porous bowl-like pBPLA@MSNs-COOH composite with a nonspherical and hierarchical porous structure. Strong electrostatic interaction with DOX rendered excellent encapsulation efficiency (up to 90.14%) to the composite. DOX release showed pH-dominated drug release kinetics; thus, maintaining a weak acidic pH (e.g., 5.0) triggered sustained release, suggesting the composite's great potential for long-term therapeutic approaches. In-vitro cell viability assays further confirmed that the composite was biocompatible and that the loaded drugs were pharmacologically active, exhibiting dosage-dependent cytotoxicity. Additionally, a wound-healing assay revealed the composite's intrinsic ability to inhibit cell migration. Moreover, pH- and time-dependent leaching of the integrated MSNs due to pBPLA matrix degradation allow us to infer that the leached (and drug loaded) MSNs may be engulfed by cancer cells contributing to a second wave of DOX-mediated cytotoxicity following pH-triggered DOX release.

Fe3O4@carbon@zeolitic imidazolate framework-8 nanoparticles as multifunctional pH-responsive drug delivery vehicles for tumor therapy in vivo.

Controlled drug release is a promising approach for cancer therapy due to its merits of reduced systemic toxicity and enhanced antitumor efficacy. Here, multifunctional Fe3O4@carbon@zeolitic imidazolate framework-8 (FCZ) hybrid nanoparticles (NPs) were successfully constructed. Owing to the porosity and acid-sensitivity of zeolitic imidazolate framework-8 (ZIF-8), FCZ NPs not only displayed an improved drug loading capacity compared to most of the polymeric nanocarriers, but also exhibited excellent pH-triggered release of doxorubicin (DOX) in vitro. Moreover, carbon dots (CDs) embedded in the porous carbon shell and superparamagnetic iron oxide nanocrystals could simultaneously function as intracellular fluorescence imaging and T2*-weighted magnetic resonance imaging (MRI) contrast agents, respectively. The results obtained from the MTT assay demonstrated good biocompatibility of FCZ NPs. DOX release experiments showed pH regulation-dominated drug release kinetics: a weak acidic pH in tumor areas could trigger sustained drug release, suggesting that FCZ NPs are ideal drug delivery systems. Moreover, the remarkable inhibition of tumor growth without side effects was confirmed in vivo. These results provide convincing evidence establishing the multifunctional FCZ NPs as promising candidates for tumor therapy.

Simultaneous removal of arsenic and fluoride by freshly-prepared aluminum hydroxide

The coexistence of arsenic (As) and fluoride (F) in some underground waters creates challenges in the simultaneous removal of these two toxic elements. This study investigates the effect of fluoride at different molar ratios of fluoride to arsenic (As) (RF:As) on the removal of arsenic [i.e., arsenite (As(III), arsenate (As(V)] by freshly-prepared aluminum hydroxide (AlOxHy), and that of arsenic at different molar ratios of arsenic to fluoride (RAs:F) on fluoride removal. In single pollutant solutions, the removal of neutral As(III) is independent on pH at RAs(III):Al ≤ 0.70:1 and is much lower than that of As(V). The optimum As(V) removal is at weak acidic pH of 5 and 6 whereas that of fluoride is at pH 7 and 8. Fluoride at RF:As(V) > 35:1 significantly impairs the removal of As(V) with more significant inhibition at elevated pH. The negatively-charged As(V) inhibits fluoride removal to a larger extent than the neutral As(III) does. The adverse effect of fluoride on As(V) removal is mainly attributed to the lowered ζ-potential, which is controlled by the combined effects of pH and RF:As(V). In relative terms, the removal of fluoride is highly pH dependent, although RAs(V):F does show some effects. The oxidation of As(III) to As(V) and the adjustment of pH to weak acidic range is well preferred to achieve the simultaneous removal of As and F by AlOxHy adsorption.

Study of the role of anaerobic metabolism in succinate production by Enterobacter aerogenes.

Succinate is a core biochemical building block; optimizing succinate production from biomass by microbial fermentation is a focus of basic and applied biotechnology research. Lowering pH in anaerobic succinate fermentation culture is a cost-effective and environmentally friendly approach to reducing the use of sub-raw materials such as alkali, which are needed for neutralization. To evaluate the potential of bacteria-based succinate fermentation under weak acidic (pH <6.2) and anaerobic conditions, we characterized the anaerobic metabolism of Enterobacter aerogenes AJ110637, which rapidly assimilates glucose at pH 5.0. Based on the profile of anaerobic products, we constructed single-gene knockout mutants to eliminate the main anaerobic metabolic pathways involved in NADH re-oxidation. These single-gene knockout studies showed that the ethanol synthesis pathway serves as the dominant NADH re-oxidation pathway in this organism. To generate a metabolically engineered strain for succinate production, we eliminated ethanol formation and introduced a heterogeneous carboxylation enzyme, yielding E. aerogenes strain ΔadhE/PCK. The strain produced succinate from glucose with a 60.5% yield (grams of succinate produced per gram of glucose consumed) at pH <6.2 and anaerobic conditions. Thus, we showed the potential of bacteria-based succinate fermentation under weak acidic conditions.

PEGylated PAMAM dendrimer–doxorubicin conjugate-hybridized gold nanorod for combined photothermal-chemotherapy

We prepared pH-sensitive drug–dendrimer conjugate-hybridized gold nanorod as a promising platform for combined cancer photothermal-chemotherapy under in vitro and in vivo conditions. Poly(ethylene glycol)-attached PAMAM G4 dendrimers (PEG–PAMAM) were first covalently linked on the surface of mercaptohexadecanoic acid-functionalized gold nanorod (MHA-AuNR), with subsequent conjugation of anti-cancer drug doxorubicin (DOX) to dendrimer layer using an acid-labile-hydrazone linkage to afford PEG–DOX–PAMAM–AuNR particles. The particles with a high PEG–PAMAM dendrimer coverage density (0.28 per nm2 AuNR) showed uniform sizes and excellent colloidal stability. In vitro drug release studies demonstrated that DOX released from PEG–DOX–PAMAM–AuNR was negligible under normal physiological pH, but it was enhanced significantly at a weak acidic pH value. The efficient intracellular acid-triggered DOX release inside of lysosomes was confirmed using confocal laser scanning microscopy analysis. Furthermore, the combined photothermal-chemo treatment of cancer cells using PEG–DOX–PAMAM–AuNR for synergistic hyperthermia ablation and chemotherapy was demonstrated both in vitro and in vivo to exhibit higher therapeutic efficacy than either single treatment alone, underscoring the great potential of PEG–DOX–PAMAM–AuNR particles for cancer therapy.

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.

Mechanism of Peripheral Substituent Effects on Adsorption–Aggregation Behaviors of Cationic Porphyrin Dyes on Tungsten(VI) Oxide Nanocolloid Particles

The adsorption and aggregation behaviors of the cationic porphyrin derivatives such as 5,10,15,20-tetrakis(4-pyridyl)porphyrin [TPyP], 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin [TMPyP], 5,10,15,20-tetrakis(N-ethyl-4-pyridyl)porphyrin [TEPyP], and 5,10,15,20-tetrakis(N-n-propyl-4-pyridyl)porphyrin [TPPyP] (hereafter called "TPyP derivatives") in the tungsten(VI) oxide (WO3) colloid aqueous solution at weak acidic pH were studied by UV-vis spectroscopy. The TPyP derivatives were strongly adsorbed as monolayer onto the WO3 surface via the electrostatic interaction between their peripheral cationic substituents and negatively surface-charged WO3 colloid particles, and most of the ones adsorbed eventually formed J-type dimers aligned in the head-to-tail fashion. These different dimerization states were effectively analyzed by the change of ratios among the intensities of exciton split Soret bands (H- and J-bands). Judging from the exciton coupling theory and adsorption measurements, we concluded that the J-dimer geometry of the TPyP derivatives adsorbed on the WO3 colloid particle surface is strongly dependent on the presence and difference of peripheral substituents. The results described here indicate a new and promising way of designing surface supramolecular structures combination of two principles, the self-association of organic dyes, and the steric repulsive interaction between the peripheral substituents and the inorganic semiconductor surfaces.

Fusion of a Flavin-Based Fluorescent Protein to Hydroxynitrile Lyase from Arabidopsis thaliana Improves Enzyme Stability

Hydroxynitrile lyase from Arabidopsis thaliana (AtHNL) was fused to different fluorescent reporter proteins. Whereas all fusion constructs retained enzymatic activity and fluorescence in vivo and in vitro, significant differences in activity and pH stability were observed. In particular, flavin-based fluorescent reporter (FbFP) fusions showed almost 2 orders of magnitude-increased half-lives in the weakly acidic pH range compared to findings for the wild-type enzyme. Analysis of the quaternary structure of the respective FbFP-AtHNL fusion proteins suggested that this increased stability is apparently caused by oligomerization mediated via the FbFP tag. Moreover, the increased stability of the fusion proteins enabled the efficient synthesis of (R)-mandelonitrile in an aqueous-organic two-phase system at a pH of <5. Remarkably, (R)-mandelonitrile synthesis is not possible using wild-type AtHNL under the same conditions due to the inherent instability of this enzyme below pH 5. The fusion strategy presented here reveals a surprising means for the stabilization of enzymes and stresses the importance of a thorough in vitro characterization of in vivo-employed fluorescent fusion proteins.

Adsorption of α-Chymotrypsin on Plant Biomass Charcoal

The adsorption of α-chymotrypsin onto plant biomass charcoal (PBC), which was prepared from plant biomass wastes such as bagasse and dumped adzuki beans by pyrolysis, has been examined. The PBC was characterized by SEM, specific surface area, and pore size distribution. The adsorption isotherms were successfully correlated by the Freundlich equation. The amount of α-chymotrypsin adsorbed on PBC was dramatically dependent upon the solution pH and temperature. Maximum adsorptions of α-chymotrypsin on adzuki bean charcoal and bagasse charcoal were observed at weak acidic and near neutral pH, respectively. The amount of α-chymotrypsin adsorbed on PBC decreased with an increase in the concentration of salts. Plots of the amount of α-chymotrypsin adsorbed on PBC versus temperature exhibited an optimum temperature.

Co-localization of kallikrein5 and profilaggrin in keratohyalin granules and reduction of filaggrin monomers by kallikrein5 downmodulation

Kallikrein-related peptidases (KLKs) and the lymphoepitherial azal-type inhibitor (LEKTI) play important roles in corneocyte esquamation. It is suggested that KLKs such as KLK5 and 7 are eleased from LEKTI because of acidic pH at the skin surface and egrades corneodesmosomes, resulting in the removal of surface orneocytes. It is still obscure whether the KLK-LEKTI interacion is easily broke in such a weak acidic pH(5.5-6.5). Recently e reported cloning of a new PRSS3 gene product, keratinocytepecificmesotrypsin from the cDNA library. The aim of this study is o elucidate involvementof PRSS3 in thedesquamationprocess.We onstructed various recombinant LEKTI proteins, D2, D2-5, D2-6, 2-7, D5, D6, D6-9, D7, D7-9 andD10-15. All of these recombinants nhibited KLK5 with different extent. However, they did not show ny inhibitory effect on PRSS3. Interestingly we found that single omain LEKTI, D5 and D6were degraded by PRSS3. We then invesigated pH susceptibility between KLK5 and each LEKTI domain. LK5 was incubated with D5, or D6 in different pH buffers ranging rom pH 3.5 to pH 9.0 and residual activities were measured using ln-Ala-Arg-MCA. KLK5 was active between pH 5.5 to pH 9 and hat D5 as well as D6 completely suppressed KLK5 activity in the amepH range. Other LEKTI domain constructs gave similar results. n order to elucidate whether PRSS3 could participate in desquaation process, localization in human skin was examined with mmunoelectronmicroscopy. PRSS3was localized in the cytoplasm f granular cells and intercellular spaces of the cornified layer. Colectively our results suggest that PRSS3 is actively involved in the esquamation process via degradation of the intrinsic inhibitor, EKTI.

수산화칼슘/인산 현탁제가 스타이렌 기반 현탁중합토너의 특성에 미치는 영향

고품질의 현탁중합토너를 제조하기 위해서는 수상 현탁계의 최적화가 매우 중요하다. 따라서 본 연구에서는 무기현탁제로 사용한 수산화칼슘(<TEX>$CaOH_2$</TEX>)/인산(<TEX>$H_3PO_4$</TEX>)(Ca/P)의 몰비 및 수상의 pH가 스타이렌 기반 현탁중합토너의 특성에 미치는 영향을 중점적으로 조사하였다. 먼저 수상을 중성조건(pH=7.5)으로 고정하고 Ca/P의 몰비를 1.5:1부터 1.76:1까지 변화시켰다. 그 결과 Ca/P의 몰비를 1.73:1로 하였을 때 이상적인 인산칼슘염(하이드록시아파타이트)이 만들어졌으며 이 조건에서 제조된 중합토너는 입도분포, 원형화도 및 대전특성이 우수하였다. 이 결과를 바탕으로 Ca/P의 몰비를 1.73:1로 고정하고 수상을 약산성(pH=5.5) 및 약염기성(pH=9.5) 조건으로 변화시켰다. 그 결과 약산성 조건에서 제조된 중합토너는 더욱 더 우수한 입도분포, 원형화도 및 대전특성을 나타냈으며 인쇄품질도 매우 우수하였다. Ca/P의 몰비와 수상의 pH 조건을 최적화하여 고품질의 현탁중합토너를 제조할 수 있었다. Optimizing a water-phase suspending system is very important to manufacture high-quality suspension polymerized toners. Therefore, in this study, the effects of the molar ratio of calcium hydroxide (<TEX>$CaOH_2$</TEX>)/phosphoric acid (<TEX>$H_3PO_4$</TEX>)(Ca/P), which were used as inorganic suspending agents, and pH of the water-phase on the characteristics of styrene-based suspension polymerized toners were mainly investigated. At first, the water-phase was fixed to neutral condition (pH=7.5) and Ca/P molar ratio was changed from 1.5:1 to 1.76:1. As a result, an ideal calcium phosphate (hydroxyapatite) was prepared at the Ca/P molar ratio of 1.73:1 and polymerized toners prepared at this condition showed good particle size distribution, circularity and charging characteristic. Based on this result, Ca/P molar ratio was fixed to 1.73:1 and pH of the water-phase was changed to weak acidic (pH=5.5) and weak basic (pH=9.5) conditions. As a result, polymerized toners prepared under the weak acidic condition showed very good particle size distribution, circularity and charging characteristic along with excellent printing quality. High-quality suspension polymerized toners could be prepared via optimizing Ca/P molar ratio and pH of the water-phase.

Characterization of flocs generated by preformed and in situ formed Al13 polymer

During coagulation process, preformed and in situ formed Al13 polymer are the predominant aluminum hydrolysis species at the optimal pH condition for polyaluminum chloride (PACl) containing high content of Al13 and AlCl3 (AC), respectively. The structure and morphology of the flocs generated by preformed and in situ formed Al13 polymer were investigated from the viewpoint of the relationship between Al speciation and flocs surface structure. The results showed that at pH 6 the predominant composition of PACl and AC flocs were Al13 polymer aggregate and amorphous Al hydroxide, respectively. The flocs generated by preformed Al13 polymer had a better crystalline structure than those from in situ formed one, while they had smaller size and smoother surface structure than those formed by in situ formed Al13 polymer. During weak acidic pH condition and at high dosage of Al coagulant adsorption onto precipitated Al hydroxides was the main pathway for kaolin particle removal. Preformed Al13 polymer showed a stronger charge neutralization ability, while the flocs generated from in situ formed Al13 polymer exhibited a higher adsorption capacity for kaolin particles. Al species distribution during coagulation process governs the floc character and coagulation efficiency of Al coagulant. The present study further conduces to the understanding of coagulation mechanism and puts forward a basis for coagulant selection during water treatment process.

Low Molecular-Weight Chitosan as a pH-Sensitive Stealth Coating for Tumor-Specific Drug Delivery

When a nanoparticle is developed for systemic application, its surface is typically protected by poly(ethylene glycol) (PEG) to help prolonged circulation and evasion of immune clearance. On the other hand, PEG can interfere with interactions between nanocarriers and target cells and negatively influence the therapeutic outcomes. To overcome this challenge, we propose low molecular-weight chitosan (LMWC) as an alternative surface coating, which can protect the nanomedicine in neutral pH but allow cellular interactions in the weakly acidic pH of tumors. LMWCs with a molecular weight of 2-4 kDa, 4-6.5 kDa, and 11-22 kDa were produced by hydrogen peroxide digestion and covalently conjugated with poly(lactic-co-glycolic acid) (PLGA). Nanoparticles created with PLGA-LMWC conjugates showed pH-sensitive cell interactions, which enabled specific drug delivery to cells in a weakly acidic environment. The hydrophilic LMWC layer reduced opsonization and phagocytic uptake. These properties qualify LMWCs as a promising biomaterial for pH-sensitive stealth coating.