pH-responsive poly(methacrylic acid)-grafted hollow silica vesicles

Poly(methacrylic acid)-grafted hollow silica vesicles (PMAA-g-hollow silica vesicles) were obtained through a grafting-from approach. PMAA brushes were formed by performing atom-transfer radical polymerisation of sodium methacrylate with an initiator attached to the hollow silica spheres. PMAA-g-hollow silica vesicles were characterised by using TEM, thermogravimetric analysis (TGA) and FTIR spectroscopy. pH-dependent ξ potential and (1)H NMR spectra of PMAA-g-hollow silica vesicles were measured, and the results indicated that MAA brushes in PMAA-g-hollow silica vesicles had a lower ionisation degree and low solubility in acidic aqueous solution, for example, pH 3.4, but a higher ionisation degree and high solubility when the pH was higher than 7. Also it was demonstrated that calcein blue and fluorescein isothiocyanate (FITC) labelled dextran (M(n):10 kDa) could be encapsulated in the interiors of the PMAA-g-hollow silica vesicles with a negligible amount in PMAA brushes at pH 2, and pH-triggered release of calcein blue and FITC-labelled dextran from PMAA-g-hollow silica vesicles was observed at pH 7.4.     

Few cycle pulse compressor based on hollow-core fiber waveguide results in pulse tails

The hollow-core fiber structure influence of few-cycle pulse compressor on pulse contrast is investigated experimentally. It is found that a periodic structure of pulses at the tail of the main pulse extended hundreds of picoseconds away. It can be due to the fiber structure and could be eliminated by modifying the structure.     

Maintaining maximum signal-to-noise ratio in uncooled vertical-cavity surface-emitting laser-based self-mixing sensors

We demonstrate a method for maintaining the maximum signal-to-noise ratio (SNR) of the signal obtained from the self-mixing sensor based on a vertical-cavity surface-emitting laser (VCSEL). It was found that the locus of the maximum SNR in the current-temperature space can be well approximated by a simple analytical model related to the temperature behavior of the VCSEL threshold current. The optimum sensor performance is achieved by tuning the laser current according to the proposed model, thus enabling the sensor to operate without temperature stabilization in a wide temperature range between -20 °C and +80 °C.     

High-temporal-quality injector generated by optical parametric amplification with hollow-core-fiber compression

We demonstrate a 100 μJ, <10 fs, high-temporal-contrast injector. The experimental setup is based on an optical parametric amplification system followed by a standard hollow-core-fiber compressor and a frequency-doubling crystal. Pulses near 800 nm with FWHMs of about 160 nm are generated. More than 11 orders of magnitude of the contrast ratio, which is limited by the measurement device, are obtained over a large temporal range extending from <1 ps ahead of the main pulse. The broad spectral bandwidth and the high contrast of this device make it a good front-end injector for a few-cycle, high-power laser system.     

N‐alkylpyridinium quaternization for assisting electrospray ionization of sterols in oil by quadrupole‐time of flight mass spectrometry

Rationale: The illegal cooking oil has become a serious social problem and raised widespread alarm recently. However, an efficient and sensitive technique for identifying the potential illegal cooking oil is still unavailable, especially when mixed with the ordinary ones; there is an urgent need to develop an efficient method for identifying the illegal cooking oil. Sterols in the cooking oil could be used as an indicator to identify the source and quality of oil by detecting the kinds of phytosterols and zoosterols. However, those sterols are difficult to be ionized by electrospray ionization, which resulted in the low sensitivity in electrospray ionization (ESI)‐mass spectrometric (MS) analysis. Methods: N‐alkylpyridinium isotope quaternization was extended to charge label sterols in different cooking oil and attached N‐cationic pyridinium tag onto the sterols in the presence of trifluoromethanesulfonic anhydride (Tf₂O); the kinds of sterols were identified and quantified by comparing d₀/d₅ pairs and product scan from ESI‐quadrupole‐time of flight (Q‐TOF) MS analysis. Results: The derivatized sterols were attached with permanent charge, resulting in the significant enhancement of ionization in ESI‐Q‐TOF MS analysis. The detection limits of analytes were improved to 0.02–0.05 ng/mL; different kinds of phytosterol, zoosterol and oxides were identified and quantified by comparing d₀/d₅ pairs from full scan and product scan. The method was applied in the detection of zoosterol for identifying the potential recycled cooking oil, even when the illegal oil has been blended into the ordinary one. More zoosterol was detected in the recycled oil compared with other cooking oil. Conclusions: The use of N‐alkylpyridinium isotope quaternization method provided an alternative method for identifying the potential illegal cooking oil. Copyright © 2013 John Wiley & Sons, Ltd.     

Efficient synthesis of highly enantiopure β-lactam derivatives from biocatalytic transformations of amides and nitriles

Catalyzed by Rhodococcus erythropolis AJ270, a nitrile hydratase and amidase containing microbial strain, under mild conditions, kinetic resolution of racemic amides provides an efficient and scalable route to highly enantioenriched R-4-carboxymethyl-β-lactams and S-4-carbamoylmethyl-β-lactams despite the substrates contain a stereogenic center that is β-positioned to amide functionality. Synthetic potential of the method was demonstrated by the constructions of novel β-lactam-fused heterocyclic compounds through convenient and practical chemical transformations.     

Switching of the Magnetocaloric Effect of MnII Glycolate by Water Molecules

The transformation of Mn^II glycolates (glc) between the three‐dimensional coordination polymer [Mn(glc)₂]_n ( 1 ) and discrete mononuclear phase [Mn(glc)₂(H₂O)₂] ( 2 ) can be reversibly switched by water molecules, which dramatically change the magnetocaloric effect (MCE) of Mn^II glycolates from the maximum of 6.9 J kg^?1 K^?1 in 1 to 60.3 J kg^?1 K^?1 in 2 . This case example reveals that the effect of magnetic coupling on MCE plays a dominant role over that of other factors such as magnetic density for 3d‐type magnetic refrigerants.     

Resonance hyper-Raman spectra of zinc phthalocyanine

Hyper-Raman spectra were obtained for zinc phthalocyanine in a dilute pyridine solution at excitation wavelengths that are two-photon resonant with the one-photon-allowed B band (360-380 nm) as well as with the two-photon absorption near 440 nm reported by Drobizhev et al. ( J. Chem. Phys. 2006, 124, 224701 ). In both regions, the hyper-Raman spectra were very different from the linear resonance Raman spectra at the corresponding excitation frequencies. While the resonance Raman spectra show only g symmetry modes, almost all of the hyper-Raman frequencies can be assigned as fundamentals of E u symmetry that also are observed in the infrared absorption spectrum or E u symmetry combination bands. These results contrast sharply with previous observations of highly noncentrosymmetric push-pull conjugated molecules and are consistent with a structure for phthalocyanine in solution that is centrosymmetric or nearly so. The hyper-Raman spectra show different intensity patterns in the two excitation regions, consistent with different Franck-Condon and/or vibronic coupling matrix elements for the different resonant states.     

Highly sensitive and quantitative detection of rare pathogens through agarose droplet microfluidic emulsion PCR at the single-cell level

Genetic alternations can serve as highly specific biomarkers to distinguish fatal bacteria or cancer cells from their normal counterparts. However, these mutations normally exist in very rare amount in the presence of a large excess of non-mutated analogs. Taking the notorious pathogen E. coli O157:H7 as the target analyte, we have developed an agarose droplet-based microfluidic ePCR method for highly sensitive, specific and quantitative detection of rare pathogens in the high background of normal bacteria. Massively parallel singleplex and multiplex PCR at the single-cell level in agarose droplets have been successfully established. Moreover, we challenged the system with rare pathogen detection and realized the sensitive and quantitative analysis of a single E. coli O157:H7 cell in the high background of 100?000 excess normal K12 cells. For the first time, we demonstrated rare pathogen detection through agarose droplet microfluidic ePCR. Such a multiplex single-cell agarose droplet amplification method enables ultra-high throughput and multi-parameter genetic analysis of large population of cells at the single-cell level to uncover the stochastic variations in biological systems.     

Schiff Base Structured Acid–Base Cooperative Dual Sites in an Ionic Solid Catalyst Lead to Efficient Heterogeneous Knoevenagel Condensations

An acid–base bifunctional ionic solid catalyst [PySaIm]₃PW was synthesized by the anion exchange of the ionic‐liquid (IL) precursor 1‐(2‐salicylaldimine)pyridinium bromide ([PySaIm]Br) with the Keggin‐structured sodium phosphotungstate (Na₃PW). The catalyst was characterized by FTIR, UV/Vis, XRD, SEM, Brunauer–Emmett–Teller (BET) theory, thermogravimetric analysis, ¹H NMR spectroscopy, ESI‐MS, elemental analysis, and melting points. Together with various counterparts, [PySaIm]₃PW was evaluated in Knoevenagel condensation under solvent and solvent‐free conditions. The Schiff base structure attached to the IL cation of [PySaIm]₃PW involves acidic salicyl hydroxyl and basic imine, and provides a controlled nearby position for the acid–base dual sites. The high melting and insoluble properties of [PySaIm]₃PW are relative to the large volume and high valence of PW anions, as well as the intermolecular hydrogen‐bonding networks among inorganic anions and IL cations. The ionic solid catalyst [PySaIm]₃PW leads to heterogeneous Knoevenagel condensations. In solvent‐free condensation of benzaldehyde with ethyl cyanoacetate, it exhibits a conversion of 95.8 % and a selectivity of 100 %; the conversion is even much higher than that (78.2 %) with ethanol as a solvent. The solid catalyst has a convenient recoverability with only a slight decrease in conversion following subsequent recyclings. Furthermore, the new catalyst is highly applicable to many substrates of aromatic aldehydes with activated methylene compounds. On the basis of the characterization and reaction results, a unique acid–base cooperative mechanism within a Schiff base structure is proposed and discussed, which thoroughly explains not only the highly efficient catalytic performance of [PySaIm]₃PW, but also the lower activities of various control catalysts.