Antibacterial properties of silver nanoparticles in three different sizes and their nanocomposites with a new waterborne polyurethane

Silver nanoparticles (AgNPs) are strong bactericidal agents but they are also cytotoxic. Embedding them in a polymer matrix may reduce their cytotoxic effect. In the present study, AgNPs in three average sizes were tested for their antibacterial activities and cytotoxicity. Nanocomposites from a new waterborne polyetherurethane (PEU) ionomer and AgNPs were prepared without the use of any crosslinker. It was observed that the antibacterial activity of AgNPs against Escherichia coli started at the effective concentration of 0.1–1 ppm, while that against Staphylococcus aureus started at higher concentrations of 1–10 ppm. Cytotoxicity of AgNPs was observed at the concentration of 10 ppm. AgNPs with smaller average size showed greater antibacterial activity as well as cytotoxicity. The PEU synthesized in this study showed high tensile strength, and the addition of AgNPs at all sizes further increased its thermal stability. The delicate surface features of nanophases, however, were only observed in nanocomposites with either small-or medium-sized AgNPs. PEU-Ag nanocomposites had a strong bacteriostatic effect on the growth of E. coli and S. aureus. The proliferation of endothelial cells on PEU-Ag nanocomposites was enhanced, whereas the platelet adhesion was reduced. The expression of endothelial nitric oxide synthase gene was upregulated on PEU-Ag containing small-sized AgNPs (30 ppm) or medium-sized AgNPs (60 ppm). This effect was not as remarkable in nanocomposites from large-sized AgNPs. Overall, nanocomposites from the PEU and 60 ppm of the medium-sized (5 nm) AgNPs showed the best biocompatibility and antibacterial activity. Addition of smaller or larger AgNPs did not produce as substantial an effect in PEU, especially for the larger AgNPs

Sulfonated reduced graphene oxide catalyzed cyclization of hydrazides and carbon dioxide to 1,3,4-oxadiazoles under sonication

Acid catalysts facilitate many chemical reactions. Sulfonated reduced grapheneoxide (rGOPhSO3H) has shown to be an encouraging solid acid catalyst because of its efficiency, cost-effectiveness and safety of use. In this study, we prepared the rGOPhSO3H nano acid catalyst, with the introduction of aromatic sulfonic acid radicals onto GO by fractional removal of oxygenated functions. It was thoroughly characterized by FT-IR, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, energy dispersive spectroscopy (EDS) and solid state 13C MAS NMR (SSNMR). Here we report the conversion of CO2 (1.0 atm pressure, at = 50 °C, the source of C1 carbon feed stock) with hydrazides and a catalytic amount rGOPhSO3H, which through a cyclization reaction results in a new strategy for the synthesis of 5-substituted-3H-[1,3,4]-oxadiazol-2-ones (SOxdOs) under ultrasonic irradiation. Hence this concept of cyclization opens up for new insights

Sulfonated graphene oxide-catalyzed N-acetylation of amines with acetonitrile under sonication

Sulfonated reduced graphene oxide (rGO-SO3H, SRGO) was synthesized by introducing aryl diazonium salt of sulfanilic acid radicals onto chemically modified reduced graphene oxide (rGO) under sonication. SRGO catalyst was characterized by X-ray diffraction (XRD), Raman spectroscopy, solid state 13C MAS NMR (13C SSNMR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron spectroscopy (TEM), and X-ray photoelectron spectroscopy (XPS). SRGO was efficiently used as a reusable, metal-free, solid acid catalyst for the direct N-acetylation of amines with acetonitrile under sonication into the corresponding amides. Thus, the method could also serve as a novel convenient alternative for the other acetylation reactions under sonication to avoid using toxic substances such as acetic anhydride, acetyl chloride, and acetic acid

Facile synthesis of 2-benzimidazolones via carbonylation of o-phenylenediamines with CO2

An efficient synthesis for the benzimidazolones and various 1,3-disubstituted urea derivatives prepared from several nucleophiles like o-phenylenediamines and o-aminophenols with CO2 (1 MPa) under transition-metal-free or acetate complex free conditions has been developed. A variety of chemicals were synthesized in moderate to good yields promoted by tributylamine (TBA) using the nucleophiles and CO2 as a green and renewable C1 source. The cyclization of CO2 and o-phenylenediamine offered a general and straightforward synthesis of benzimidazolones and cyclic ureas promoted by the inexpensive and environmentally-friendly TBA as the carbonylation catalyst. Thus, various valuable cyclic ureas and their carbonyl homologs were synthesized in good yields through this green carbonylation process

Well-Defined Polyamide Synthesis from Diisocyanates and Diacids Involving Hindered Carbodiimide Intermediates

We have uncovered a novel polycondensation strategy for the synthesis of well-defined polyamides of narrow molecular weight distributions based on modifications of our sequential self-repetitive reaction (SSRR) previously developed for diisocyanatedicarboxylic acid polymerization. In our newly discovered SSRR polyamide formation mechanism, a small amount of hindered carbodiimide, N,N-bis(2,6-diisopropylphenyl)carbodiimide (iPr-CDI) or a hindered isocyanate such as 2,6-diisopropylphenyl isocyanate (iPr-NCO), was introduced to the polymerization as an initiator, followed by simultaneous addition of diisocyanates and diacids monomers. By using this new reaction mode, the SSRR mechanism produces polyamide products of narrow molecular weight distributions with their dispersities reduced to 1.21.4, which is far lower than a range of >2.5 found in regular SSRR reactions. Significantly different from a conventional step-growth or standard SSRR reaction, the formation of a polymer backbone is preferential when the diacid is added to the requisite iPr-CDI in the first step, followed by a rearrangement to form amide and fragmented components for SSRR. The control of molecular weight is mainly attributed to the acid addition favoring the unhindered poly-CDI intermediates in the middle of the growing chains over the hindered-CDI at the chain terminals. It appears that the formation of a hindered isocyanate and the subsequent formation of a new hindered-CDI at the terminal end of growing amide-chains in each SSRR cycle force the acid again toward the preferred unhindered CDI sites dictating the observed outcome. This simple polyamide synthesis methodology is unique and unconventional, and it could significantly facilitate the development of tailored-made polyamides from a variety of diisocyanates and diacids

印刷廢紙脫墨之方法

本發明藉印刷油墨成分之性質分成兩種狀況加以脫墨:其一,在水溶液中加入適當的溶劑使油墨中聚合物成分之接著劑溶解,並藉界面活性劑將其乳化,再以洗滌法移除油墨。其二,在水溶液中加入適當的溶劑使油墨中之接著劑軟化,並藉界面活性劑增進油墨對塑膠材料的附著濕潤性而使油墨粘附於PET、PVC、PS等塑膠材料上,最後以篩選的方式除去此黏附有油墨的PET等塑膠材料。附著在塑膠材料上的油墨可更進一步的加以分離,塑膠材料則可再循環使用

Phosphate-catalyzed epimerization of N-acetyl-d-glucosamine to N-acetyl-d-mannosamine for the synthesis of N-acetylneuraminic acid

Phosphate-catalyzed epimerization of N-acetyl-d-glucosamine to N-acetyl-d-mannosamine is reported in this study. The epimerization of N-acetyl-d-glucosamine was found to be facilitated by proton acceptors via the deprotonation of the amide group. Among the proton acceptors tested in this study phosphate exhibited the highest epimerization activity due to its nucleophilicity and its ability in promoting ring-opening reaction. The standard free energy change and standard enthalpy change for the epimerization of N-acetyl-d-glucosamine to N-acetyl-d-mannosamine are +2.32 kJ/mole and +1.83 kJ/mole, respectively. Based on the Arrhenius equation, the activation energy of the phosphate-catalyzed epimerization was estimated as 56.36 ± 2.89 kJ/mole. At 80 °C, the initial rate of the phosphate-catalyzed epimerization, 19.70 mM/h, was more than 47-fold that of the control. Under the optimal conditions, the phosphate-catalyzed epimerization reached equilibrium with a conversion of 0.316 within 7 h, comparable with a conversion of 0.284 after 70 min for the epimerase-catalyzed reaction. Due to its compatibility with the subsequent enzyme reaction, it is possible to conduct the phosphate-catalyzed epimerization and the lyase-catalyzed biotransformation in one single bioreactor for the quantitative transformation of N-acetyl-d-glucosamine to N-acetylneuraminic acid

100% Atom-Economy Efficiency of Recycling Polycarbonate into Versatile Intermediates

This study demonstrates a simple and convenient two-step one-pot, highly efficient process of recycling poly­(bisphenol A carbonate), i.e., PC, into versatile intermediates for polymers such as polyurethanes (PUs). Via a highly efficient and selective amine carbonylation reaction, PC is depolymerized by aliphatic diamines forming hydroxyl-<i>N</i>,<i>N</i>′-diphenylene-isopropylidenyl biscarbamates (hydroxyl DP-biscarbamates) as major interim prepolymers. Both short- and long-chained prepolymers are prepared with their respective diamines, and the prepolymers are chain-extended with commercially available regents such as diisocyanates to produce a variety of PU polymers. Hence, PC is cleaved into pieces of soluble hydroxyl DP-biscarbamates first and then reassembled into new linear polymers without resorting to a separation process. Different from PC-recycling processes reported in the literature, each carbonate group of PC in this new process is fully utilized for making one carbamate group and one hydroxyl terminated intermediate in the absence of catalyst under mild conditions. Most significantly, this process attains 100% atom-economy efficiency and demonstrates the feasibility of converting one functional polymer into another