34 research outputs found

    Morphology, Surface Layer Evolution, and Structure–Dye Adsorption Relationship of Porous Fe<sub>3</sub>O<sub>4</sub> MNPs Prepared by Solvothermal/Gas Generation Process

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    A new system based on dimethylacetamide, ethanolamine, and azobis­(isobutyronitrile) (AIBN) was employed to synthesize porous Fe<sub>3</sub>O<sub>4</sub> magnetic nanoparticles (MNPs) for the first time. The formation mechanism, morphology, and surface layer evolution of MNPs at the different AIBN ratios were revealed. The MNPs prepared without AIBN showed a randomly assembled morphology with a BET surface area of 174 m<sup>2</sup>/g, which is almost the highest reported until now. After AIBN was added, N<sub>2</sub> gas and radical were produced by the thermal decomposition reaction. The high gas pressure enhanced the growth and self-assembly of nanounits, leading to a microsphere morphology. The radical caused a surface modification effect, which led to a decline in both the specific saturation magnetization and surface area of Fe<sub>3</sub>O<sub>4</sub> MNPs. The surface of MNPs was fully modified when prepared at a high AIBN ratio. The methyl orange (MO) adsorption revealed that the modification coverage and surface composition of Fe<sub>3</sub>O<sub>4</sub> MNPs are responsible for its adsorption capacity irrespective of the surface area. The naked Fe<sub>3</sub>O<sub>4</sub> MNPs showed a limited adsorption capacity, which was saturated during the synthesis process. Moreover, the prepared MNPs(3) showed a maximum adsorption capacity of 46.7 mg/g. The surface coverage ratio revealed that its surface was almost fully covered with dye molecules. Moreover, it has shown good acidic stability and can be regenerated for dye adsorption applications

    Surface Modification of Polyacrylonitrile Membrane by Chemical Reaction and Physical Coating: Comparison between Static and Pore-Flowing Procedures

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    The influences of static and pore-flowing procedures on the surface modification of a polyacrylonitrile (PAN) ultrafiltration membrane through chemical reaction and physical coating were investigated in detail. For chemical modification by ethanolamine, a membrane modified by the pore-flowing procedure showed a higher flux and different morphology. The reasons were explained by two effects: the pore-flowing resistance to the random thermal motion of PAN at high temperatures and different reaction kinetics related to the reactant concentration profile on the interface between the membrane and reaction solution and the kinetic property of the fluid (driving force and miscibility) and reaction (time and rate). For physical coating modification, a dense and flat layer via a loose and random layer was formed during the pore-flowing process and static process, which changed the flux and antifouling property of the membrane. The membrane prepared by dead-end filtration showed the best trade-off between the flux and antifouling property. Overall, the procedure kinetics plays an important role in the optimization of membrane modification

    In Situ-Forming Polyamidoamine Dendrimer Hydrogels with Tunable Properties Prepared via Aza-Michael Addition Reaction

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    In this work, we describe synthesis and characterization of novel in situ-forming polyamidoamine (PAMAM) dendrimer hydrogels (DHs) with tunable properties prepared via highly efficient aza-Michael addition reaction. PAMAM dendrimer G5 was chosen as the underlying core and functionalized with various degrees of acetylation using acetic anhydride. The nucleophilic amines on the dendrimer surface reacted with α, β-unsaturated ester in acrylate groups of polyethylene glycol diacrylate (PEG-DA, <i>M</i><sub>n</sub> = 575 g/mol) via aza-Michael addition reaction to form dendrimer hydrogels without the use of any catalyst. The solidification time, rheological behavior, network structure, swelling, and degradation properties of the hydrogel were tuned by adjusting the dendrimer surface acetylation degree and dendrimer concentration. The DHs were shown to be highly cytocompatible and support cell adhesion and proliferation. We also prepared an injectable dendrimer hydrogel formulation to deliver the anticancer drug 5-fluorouracil (5-FU) and demonstrated that the injectable formulation efficiently inhibited tumor growth following intratumoral injection. Taken together, this new class of dendrimer hydrogel prepared by aza-Michael addition reaction can serve as a safe tunable platform for drug delivery and tissue engineering

    DenTimol as A Dendrimeric Timolol Analogue for Glaucoma Therapy: Synthesis and Preliminary Efficacy and Safety Assessment

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    In this work, we report the synthesis and characterization of DenTimol, a dendrimer-based polymeric timolol analog, as a glaucoma medication. A timolol precursor (<i>S</i>)-4-[4-(oxiranylmethoxy)-1,2,5-thiadiazol-3-yl]­morpholine (OTM) was reacted with the heterobifunctional amine polyethylene glycol acetic acid (amine–PEG–acetic acid, <i>M</i><sub>n</sub> = 2000 g/mol) via a ring opening reaction of an epoxide by an amine to form the OTM–PEG conjugate. OTM–PEG was then coupled to an ethylenediamine (EDA) core polyamidoamine (PAMAM) dendrimer G3 to generate DenTimol using the <i>N</i>-(3-(dimethylamino)­propyl)-<i>N</i>′-ethylcarbodiimide hydrochloride (EDC)/<i>N</i>-hydroxysuccinimide (NHS) coupling reaction. MALDI mass spectrometry, <sup>1</sup>H NMR spectroscopy, and HPLC were applied to characterize the intermediate and final products. Ex vivo corneal permeation of DenTimol was assessed using the Franz diffusion cell system mounted with freshly extracted rabbit cornea. The cytotoxicity of DenTimol was assessed using the WST-1 assay. Our results show that DenTimol is nontoxic up to an OTM equivalent concentration of 100 μM. DenTimol is efficient at crossing the cornea. About 8% of the dendrimeric drug permeated through the cornea in 4 h. Its IOP-lowering effect was observed in normotensive adult Brown Norway male rats. Compared to the undosed eye, an IOP reduction by an average of 7.3 mmHg (∼30% reduction from baseline) was observed in the eye topically treated with DenTimol (2 × 5 μL, 0.5% w/v timolol equivalent) in less than 30 min. Daily dosing of DenTimol for a week did not cause any irritation or toxicity as confirmed by the histological examination of ocular tissues, including the cornea, ciliary body, and retina

    Synthesis and Characterization of Clickable Cytocompatible Poly(ethylene glycol)-Grafted Polyoxetane Brush Polymers

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    We report a new family of clickable poly­(ethylene glycol) (PEG)-grafted polyoxetane brush polymers as a potential modular platform for delivery of drugs and imaging agents. 3-Ethyl-3-hydroxymethyloxetane (EHMO) monomer reacted with propargyl benzenesulfonate in the presence of sodium hydride to yield alkyne-substituted monomer (EAMO). Subsequently, cationic ring-opening polymerization using boron trifluoride diethyl etherate catalyst and 1,4-butanediol initiator produced P­(EAMO) homopolymer with a DP of ∼30 (30 alkynes per chain). Methoxypoly­(ethylene glycol) azide (mPEG750-azide) prepared from mPEG750 (750 g mol<sup>–1</sup>) was grafted to P­(EAMO) via copper­(I)-catalyzed alkyne–azide cycloaddition (CuAAC) click chemistry. Water-soluble cytocompatible P­(EAMO)-<i>g</i>-PEG brush polymers with controlled degrees of PEGylation were synthesized by varying the feed molar ratio of mPEG750-azide to alkyne (25:100, 50:100, 75:100, and 100:100). <sup>1</sup>H NMR, GPC, end-group analysis, FTIR, and DSC were applied for polymer characterization. The utility of P­(EAMO)-<i>g</i>-PEG for carrying imaging agents was demonstrated by preparing fluorescently labeled P­(EAMO)-<i>g</i>-PEG. 5-(Aminoacetamido)­fluorescein (AAF) was used as a model compound. Fluorescein-carrying P­(EAMO)-<i>g</i>-PEG was synthesized by click coupling bifunctional spacer 6-azidohexanoic acid (AHA) to P­(EAMO)-<i>g</i>-PEG and subsequently coupling of AAF to AHA with EDC/NHS chemistry

    Temporal dynamics of SPAD readings of labeled rice leaves under six N application rates.

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    <p>Each value is an average of 30 measurements. Bars indicate standard error of means. Numbers underneath bars are coefficients of variation (%) of SPAD readings obtained on the same day under the six N application rates. SPAD readings are not shown for control plants on the 45th day after full expansion (DAFE 45) because some leaves in plots without N application were dead. N1 to N6 are the same as in the legend in Fig. 1.</p

    Photosynthetic photon flux density (PPFD) in relation to canopy position.

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    <p>Data are represented in terms of the percentage of PPFD measured at the uppermost canopy position. Measurements were taken at midday at the flag leaf and the next three leaves (2nd, 3rd, and 4th leaves) on (A) Sept. 1, 2008, and (B) Aug. 26, 2009. N1, N2, N3, N4, N5, and N6 indicate N application rates of 0, 75, 150, 225, 300, and 375 kg N ha<sup>−1</sup>, respectively.</p

    Processing–Structure–Property Correlations of Polyethersulfone/Perfluorosulfonic Acid Nanofibers Fabricated via Electrospinning from Polymer–Nanoparticle Suspensions

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    Polyethersulfone (PES)/perfluorosulfonic acid (PFSA) nanofiber membranes were successfully fabricated via electrospinning method from polymer solutions containing dispersed calcium carbonate (CaCO<sub>3</sub>) nanoparticles. ATR-FTIR spectra indicated that the nanoparticles mainly existed on the external surface of the nanofibers and could be removed completely by acid treatment. Surface roughness of both the nanofibers and the nanofiber membranes increased with the CaCO<sub>3</sub> loading. Although FTIR spectra showed no special interaction between sulfonic acid (−SO<sub>3</sub>) groups and CaCO<sub>3</sub> nanoparticles, XPS measurement demonstrated that the content of −SO<sub>3</sub> groups on external surface of the acid-treated nanofibers was enhanced by increasing CaCO<sub>3</sub> loading in solution. Besides, the acid-treated nanofiber membranes were performed in esterification reactions, and exhibited acceptable catalytic performance due to the activity of −SO<sub>3</sub>H groups on the nanofiber surface. More importantly, this type of membrane was very easy to separate and recover, which made it a potential substitution for traditional liquid acid catalysts
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