Effective extraction and simultaneous determination of Sudan dyes from tomato sauce and chili‐containing foods using magnetite/reduced graphene oxide nanoparticles coupled with high‐performance liquid chromatography

A simple, effective, and robust magnetic solid‐phase extraction method was developed using magnetite/reduced graphene oxide nanoparticles as the adsorbent for the simultaneous determination of Sudan dyes (I, II, III, and IV) in foodstuffs. The magnetite/reduced graphene oxide nanoparticles were characterized by X‐ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. The extraction parameters including extraction time, elution solution, and elution time and volume were investigated in detail. Such magnetite/reduced graphene oxide nanoparticles based magnetic solid‐phase extraction in combination with high‐performance liquid chromatography and variable wavelength detection gave the detection limits of 3–6 μg/kg for Sudan I–IV in chili sauce, tomato sauce, chili powder, and chili flake samples. The recoveries were 79.6–108% at three spiked levels with the intra‐ and inter‐day relative standard deviations of 1.2–8.6 and 4.5–9.6%, respectively. The feasibility was further performed by a comparison with commercial alumina‐N. This method is suitable for the routine analysis of Sudan dyes due to its sensitivity, simplicity, and low cost.     

Preparation and application of magnetic molecularly imprinted nanoparticles for the selective extraction of osthole in Libanotis Buchtomensis herbal extract

In this work, novel magnetic molecularly imprinted polymers were prepared for the selective extraction of osthole from Libanotis Buchtomensis herbal extract. During the synthesis process, double bonds grafted on the surface of Fe₃O₄ nanoparticles could not only drive the temple molecules to locate onto the surface of vinyl‐functionalized magnetic nanoparticles by π–π conjugation, which makes the distribution of binding sites ordered, but also direct the occurrence of imprinting polymerization at the surface of magnetic nanoparticles by the copolymerization of vinyl terminal groups with functional monomers and cross‐linking agent. The characteristics of the resulting polymers were evaluated by transmission electron microscopy, X‐ray diffraction, Fourier‐transform infrared spectroscopy, and vibrating sample magnetometry. Adsorption kinetics, isotherms, selectivity, reproducibility, and reusability were discussed, which suggest that the obtained nanomaterials possess rapid binding kinetics, high adsorption capacity of 17.65 mg/g, and favorable selectivity for the target molecule. Satisfactory reproducibility and reusability were verified as well. Meanwhile, the resultant imprinted nanoparticles were successfully applied to selectively separate osthole from the herbal extract, which show great potential in extracting active ingredients from traditional Chinese medicine.     

“Wet” Versus “Dry” Folding of Polyproline

When the all-cis polyproline-I helix (PPI, favored in 1-propanol) of polyproline-13 is introduced into water, it folds into the all-trans polyproline-II (PPII) helix through at least six intermediates [Shi, L., Holliday, A.E., Shi, H., Zhu, F., Ewing, M.A., Russell, D.H., Clemmer, D.E.: Characterizing intermediates along the transition from PPI to PPII using ion mobility-mass spectrometry. J. Am. Chem. Soc. 136, 12702–12711 (2014)]. Here, we show that the solvent-free intermediates refold into the all-cis PPI helix with high (>90%) efficiency. Moreover, in the absence of solvent, each intermediate appears to utilize the same small set of pathways observed for the solution-phase PPII → PPI transition upon immersion of PPII_aq in 1-propanol. That folding in solution (under conditions where water is displaced by propanol) and folding in vacuo (where energy required for folding is provided by collisional activation) occur along the same pathway is remarkable. Implicit in this statement is that 1-propanol mimics a “dry” environment, similar to the gas phase. We note that intermediates with structures that are similar to PPII_aq can form PPII under the most gentle activation conditions—indicating that some transitions observed in water (i.e., “wet” folding, are accessible (albeit inefficient) in vacuo. Lastly, these “dry” folding experiments show that PPI (all cis) is favored under “dry” conditions, which underscores the role of water as the major factor promoting preference for trans proline.

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Toughening hydrogels by immersing with oppositely charged polymers

A very simple yet novel strategy to significantly enhance the mechanical properties of hydrogels is reported. Poly(acrylic acid) (PAA) hydrogels with aligned macroporous channels are immersed in the aqueous solutions of poly(dimethyl diallyl ammonium chloride) (PDMDAAC). Strong electrostatic interactions are formed between the anionic PAA and cationic PDMDAAC chains. In the resultant PAA/PDMDAAC hybrid hydrogels, the mass ratio of PDMDAAC to PAA is about 0.2 and PDMDAAC is uniformly distributed throughout the gels. The mechanical properties of the formed hybrid hydrogels are largely enhanced in comparison with the original PAA hydrogels. The hybrid hydrogels exhibit high tensile strengths (0.38–1.73 MPa), elastic moduli (0.21–1.59 MPa) and toughness (up to 3.0 MJ/m³), about several to more than 10 times those of the corresponding PAA hydrogels. In addition, the PAA/PDMDAAC hydrogels also show excellent and very rapid shape recovery ability in both air and deionized water. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2432–2441     

Antibacterial poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) fibrous membranes containing quaternary ammonium salts

In this study, antimicrobial membranes based on biodegradable material poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) [P(3HB‐4HB)] and quaternary ammonium salts (QASs) by two methods have been performed. Three QASs with varied alkyl chain lengths have been synthesized successfully and characterized by ¹H nuclear magnetic resonance and Fourier transform infrared. The synthesized QASs were blended with P(3HB‐4HB) and electrospun into composite fibrous membranes or casted into conventional membranes. Electrospun fibrous membranes with large surface areas are a superior type of antimicrobial biomaterials, and they exhibit preferable properties than solution casting membranes. Specifically, electrospun fibrous membranes are tougher and can inactivate both Gram‐positive Staphylococcus aureus and Gram‐negative Escherichia coli O157:H7 in a contact time of 30 min, whereas the solution casting membranes cannot. The length of alkyl chain in the quaternary ammonium groups on the modified P(3HB‐4HB) membranes is able to influence the antimicrobial activity. This type of antimicrobial material may have potential applications in biomaterial field. Copyright © 2016 John Wiley & Sons, Ltd.     

Rheology and crystallization behavior of asymmetric PLLA/PDLA blends based on linear PLLA and PDLA with different structures

In this study, several asymmetric poly(L‐lactide)/poly(D‐lactide) (PLLA/PDLA) blends were prepared by adding small amounts of PDLA with different structures into linear PLLA matrix. The effect of PDLA on rheological behavior, crystallization behavior, nucleation efficiency and spherulite growth of PLLA was investigated. Rheological results indicated that PLLA/PDLA blends showed solid‐like viscoelastic behavior at low temperature (<200°C), and the cross‐linking density of PLLA/PDLA melt at 180°C followed the order: PLLA/6PDLA > PLLA/L‐PDLA > PLLA/3PDLA > PLLA/4PDLA. No‐isotherm and isotherm crystallization results indicated that the crystallization capacity of PLLA/PDLA blends was strongly related to the PDLA structure, crystallization temperature and thermal treatment temperature. Furthermore, the dimension of crystal growth during isotherm crystallization presented the obvious dependent on the PDLA structure. The nucleation efficiency of sc‐crystallites in the blends and spherulite density during isothermal crystallization were also studied. Nucleation efficiency of sc‐crystallites in the PLLA/S‐PDLA blends showed the obvious dependent on thermal treatment temperature with respect to PLLA/L‐PDLA, and nucleation efficiency sc‐crystallites in the PLLA/S‐PDLA blends first decreased and then increased as the thermal treatment temperature increased. Spherulite density of PLLA/PDLA blends was also related to thermal treatment temperature and the PDLA structure. This study has discussed the temperature dependence of the stereocomplex networks between PLLA and PDLA with different structure, and then its consequential influence on rheology and crystallization capacity of PLLA, which would provide the theoretical direction for PLA processing. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation and characterization of poly(propylene carbonate)/montmorillonite nanocomposites by solution intercalation

Poly(propylene carbonate) (PPC) is a new biodegradable aliphatic polycarbonate. However, the poor thermal stability and low glass transition temperatures (T_g) have limited its applications. To improve the thermal properties of PPC, organophilic montmorillonite (OMMT) was mixed with PPC by a solution intercalation method to produce nanocomposites. An intercalated-and-flocculated structure of PPC/OMMT nanocomposites was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal and mechanical properties of PPC/OMMT nanocomposites were investigated by thermal gravimetric analysis (TGA), differential scanning calorimetric (DSC), and electronic tensile tester. Due to the nanometer-sized dispersion of layered silicate in polymer matrix, PPC/OMMT nanocomposites exhibit improved thermal and mechanical properties than pure PPC. When the OMMT content is 4 wt%, the PPC/OMMT nanocomposite shows the best thermal and mechanical properties. These results indicate that nanocomposition is an efficient and convenient method to improve the properties of PPC.     

The synthesis of 4,4′-arylmethylene-bis(3-(trifluoromethyl)-1-phenyl-1H-pyrazol-5-ol) in aqueous media without catalyst

The synthesis of 4,4′-arylmethylene-bis(3-(trifluoromethyl)-1-phenyl-1H-pyrazol-5-ol) was performed effectively in aqueous media without catalyst by the reaction of aryl aldehydes and 1-phenyl-3-trifluoromethylpyrazol-5-one. All of the compounds obtained were characterized by elemental analysis, FTIR and ¹H NMR. The structure of compound 3g was further confirmed by the X-ray single crystal diffraction. The method has the advantages of mild condition, without any catalyst, high yields and environmentally benign procedure.     

Miscibility and Crystallization in Binary Crystalline Blends of Poly(butylene terephthalate) with Poly(butylene terephthalate-e-caprolactone)

Poly(butylene terephthalate)/poly(butylene terephthalate-e-caprolactone) is a new A/AxB1-x binary crystalline blend with intra-molecular repulsion interaction. Using the mean-field binary interaction model, the value of interaction parameter between the butylene terephthalate and caprolactone structural unit was first reported to be 0.305. This blend exhibited different crystallization behavior from a typical homopolymer/copolymer blend, which was carefully investigated by di?erential scanning calorimetry. It was found that poly(butylene terephthalate-e-caprolactone) copolymers have a great effect on the pure poly(butylene terephthalate) chain mobility and poly(butylene terephthalate) crystalline lattice packing. In the meantime, the crystallization of butylene terephthalate segments in copolymers was restricted by the previously formed poly(butylene terephthalate) crystallites. The two constituents for blending can not form a co-crystal in the range of composition even if they have the same butylene terephthalate unit. It can be concluded that longersegments in a copolymer would be beneficial for the formation of a co-crystal in blends.     

Probing the two-stage transition upon crossing the glass transition of polystyrene by solid-state NMR

A two-stage transition upon crossing the glass transition of polystyrene with increasing temperature was precisely determined and interpreted by using solid-state nuclear magnetic resonance(SSNMR), ~1H-~1H dipolar couplings based double quantum-filtered(DQF) and dipolar filter(DF) experiments and ~(13)C chemical shift anisotropy(CSA) based centerband-only detection of exchange(CODEX) experiment are used to fully characterize the time scale of molecular motions during the glass transition. While differential scanning calorimetry(DSC) and CODEX experiment predicted the first stage of glass transiton, DQF and DF experiments provided the evidence for the second stage transition during which the time scale of molecular motions changed from very slow(t ms) to very fast(t μs). The first stage of glass transition begins with the occurrence of remarkable slow re-orientation motions of the polymer backbone segments and ends when the degree of slow motion reaches maximum. The onset and endpoint of the conventional calorimetric glass transition of polystyrene can be quantitatively determined at the molecular level by SSNMR. In the second stage, a subsequent dramatic transition associated with the melting of the glassy components was observed. In this stage liquid-like NMR signals appeared and rapidly increased in intensity after a characteristic temperature T_f(~1.1T_g). The signals associated with the glassy components completely disappeared at another characteristic temperature T_c(~1.2T_g).