毛细管电色谱聚丙烯酰胺类整体柱对芳香酮类化合物分离性能考察

在N-甲基甲酰胺与三(羟甲基)胺基甲烷(Tris)组成的混合体系中合成了聚丙烯酰胺类毛细管电色谱柱,以实验室自行合成的N,N-二乙基丙烯酰胺取代传统的丙烯酰胺,增强了固定相的疏水性,使分离更彻底.实验考察了电场强度、乙腈浓度、pH值等参数对电渗流的影响,同时对电渗流的重现性及柱寿命进行了评价,实现了7种芳香酮类(含单酮及1,2-二酮)化合物的快速基线分离.

Preparation of Hollow Silica Microspheres via Poly（N-isopropylacrylamide）

Core-shell structured SiO2/poly（N-isopropylacrylamide） （SiO2/PNIPAM） microspheres were successfully fabricated through hydrolysis and condensation reaction of tertraethyl orthosilicate （TEOS） on the surface of PNIPAM template at 50 ~C. The PNIPAM template can be easily removed by water at room temperature so that SiO2 hollow microspheres were finally obtained. The transmission electron microscope and scanning electron microscope observations indicated that SiO2 hollow microspheres with an average diameter of 150 nm can be formed only if there are enough concentration of PNIPAM and TEOS, and the hy- drolysis time of TEOS. FTIR analysis showed that part of PNIPAM remained on the wall of SiO2 because of the strong interaction between PNIPAM and silica. This work provides a clean and efficient way to prepare hollow microspheres.

Rheological behavior of ZnO suspension with thermosensitive poly(N-isopropylacrylamide) for colloidal processing of ceramics

Novel colloidal processing using thermosensitive poly（N-isopropylacrylamide） （PNIPAM） as a coagulating agent has beendeveloped to prepare complex-shaped ceramic components. In this work, the properties of PNIPAM aqueous solutions and therheological behavior of ZnO suspensions with PNIPAM were investigated. The results show that the PNIPAM solutions exhibitobvious thermosensitivity and its transition temperature is around 32℃. When the temperature is above 40℃ （Tc, the criticaltransition temperature of thermosensitive suspension）, the 50% ZnO （volume fraction） suspension with 8 mg/mL PNIPAM has asharp increase in viscosity and reaches up to 11.49 Pa·s at 50℃, displaying strong elasticity. The main reasons are the increase ofeffective volume fraction attributed to precipitation of PNIPAM segments and the flocculation between ZnO powder particles. Inaddition, the maximum solid loading （volume fraction） at 20 ℃ is higher than that at 40℃, which proves that the phase transition ofPNIPAM can induce the flocculation of suspension.

Thermo-responsive functionalized PNIPAM@Ag/Ag3PO4/CN-heterostructure photocatalyst with switchable photocatalytic activity

It is extremely important for photocatalysts to exhibit intelligent responsiveness to their environment. Herein, a poly N-isopropyl acrylamide(PNIPAM)-modified Ag/Ag3PO4-20/CN hybrid material with excellent convertible photocatalytic activity is prepared. PNIPAM has good hydrophilicity below the lower critical solution temperature(LCST);this increases the capacity of the photocatalyst for adsorbing tetracycline(TC) molecules. In addition, the PNIPAM-modified Ag/Ag3PO4-20/CN can prevent the loss of Ag3PO4. The dispersity is improved by loading g-C3N4 nanosheets(CN) for enhancing the efficiency of photocatalytic activity. Furthermore, a Z-scheme heterostructure is formed between CN and Ag3PO4, accelerating the separation efficiency of the holes and electrons. Ag nanoparticles can be used as electron-shuttle mediators, and electrons receiving more energy are transferred via the localized surface plasmon resonance(LSPR) effect. Furthermore, the PNIPAM@Ag/Ag3PO4-20/CN photocatalyst exhibits an excellent degradation rate for the degradation of TC when the temperature is lower than the LCST. The photoluminescence spectra and photocurrent curves prove that the carrier-separation efficiency of PNIPAM@Ag/Ag3PO4-20/CN is higher than those of Ag/Ag3PO4/CN and CN. The main active species of ·O2-and h+ are detected to reveal the plausible mechanism of the PNIPAM@Ag/Ag3PO4-20/CN hybrid material system. This work provides a way to develop intelligent materials for switchable photocatalytic applications.

Effect of Graft Yield on the Thermo-Responsive Permeability Through Porous Membranes with Plasma-Grafted Poly(N-isopropylacrylamide)Gates

The effect of graft yield on both the thermo-responsive hydraulicpermeability and the therrno-responsive diffusional permeability through porous membranes withplasma-grafted poly(N-isopropylacrylamide) (PNIPAM) gates was investigated. Both thermo-responsiveflat membranes and core-shell microcapsule membranes with a wide range of graft yield of PNIPAM wereprepared using a plasma-graft pore-filling polymerization method. The grafted PNIPAM was formedhomogeneously throughout the entire thickness of both the flat polyethylene membranes and themicrocapsule polyamide membranes. Both the hydraulic permeability and the diffusional permeabilitywere heavily dependent on the PNIPAM graft yield. With increasing the graft yield, the hydraulicpermeability (water flux) decreases rapidly at 25℃ because of the decrease of the pore size;however, the water flux at 40℃ increases firstly to a peak because of the increase ofhydrophobicity of the pore surface, and then decreases and finally tends to zero because of the poresize becoming smaller and smaller. For the diffusional permeability, the temperature showsdifferent effects on the diffusional permeability coefficients of solutes across the membranes. Whenthe graft yield was low, the diffusional coefficient of solute across the membrane was higher attemperature above the lower critical solution temperature (LCST) than that below the LCST; however,when the graft yield was high, the diffusional coefficient was lower at temperature above the LCSTthan that below the LCST. It is very important to choose or design a proper graft yield of PNIPAMfor obtaining a desired thermo-responsive 'on/off' hydraulic or diffusional permeability.

Temperature-triggered Protein Adsorption and Desorption on Temperature-responsive PNIPAAm-grafted-silica:Molecular Dynamics Simulation and Experimental Validation

Poly(N-isopropylacrylamide)(PNIPAAm) grafted onto silica,which may be used for reverse phase chromatography(RPC),was simulated and synthesized for protein separation with temperature-triggered adsorption and desorption.Molecular dynamics simulation at an all-atom level was performed to illustrate the adsorption/desorption behavior of cytochrome c,the model protein,on PNIPAAm-grafted-silica,a temperature responsive adsorbent.At a temperature above the lower critical solution temperature(LCST),the PNIPAAm chains aggregate on the silica surface,forming a hydrophobic surface that is favorable for the hydrophobic adsorption of cytochrome c,which has a high exposure of hydrophobic patches.At temperatures below the LCST,the PNIPAAm chains stretch,forming hydrophilic surface due to hydrogen bonding between PNIPAAm and surrounding water.Desorption of cytochrome c on the PNIPAAm-grafted-silica surface occurs as a result of competition with water,which forms hydrogen bonds with the protein.The conformational transitions of both cytochrome c and PNIPAAm are monitored,providing molecular insight into this temperature-responsive RPC technique.PNIPAAm-grafted-silica beads were synthesized and used for the adsorption and desorption of cytochrome c at approximately 313 K and 290 K,respectively.The experimental results validate the molecular dynamics simulation.In comparison to conventional RPC,using temperature as a driving force for RPC reduces the risk of protein denaturation caused by exposure to chaotropic solvents.Moreover,it simplifies the separation process by avoiding the buffer exchange operations between the steps.

Swelling properties and molecular simulation of PNIPA porous hydrogels

A series of porous intelligent hydrogels, which exhibited appropriate lower critical solution temperature (LCST) and fast response behavior, were synthesized by radiation method. The structure and surface morphology of hydrogels were examined by the infrared radiation and the scanning electron microscopy, respectively. The influences of the content of crosslinking agent and relative molecular mass of polyethylene glycol (PEG) on the swelling properties of hydrogels were discussed. The molecular mechanics simulations were performed to investigate the phase transformation mechanism of poly(N-isopropyl acrylamide) (PNIPA) hydrogel. The results show that macropores are observed in hydrogels, whereas hydrogels prepared without using PEG have a dense surface. LCST of hydrogels increases with the increase of relative molecular mass of PEG. The swelling mechanism of PNIPA porous hydrogels follows non-Fickian diffusion model. The theoretical maximum water absorption S∞ is approximately consistent with experimental value according to the second-order kinetics model established by Schott. The molecule chains of PNIPA hydrogel begin folding and curling, resulting in volume shrinkage at 305 K. There are much intramolecular nonbonding interactions in molecule chains of hydrogels. The porous hydrogels are expected to be applied in the field of artificial intelligence material.

New Insights into Folding Kinetics of α,ω Dye-Functionalized Poly(N-isopropylacrylamide)

Two narrowly-distributed poly(N-isopropylacrylamide)(PNIPAM) samples were prepared via atom transfer radical polymerization (ATRP) with a novel dansyl functionalized initiator. The other end of the PNIPAM was functionalized by dabcyl group via click reaction. From the static fluorescence measurements, the fluorescence intensity of dansyl group and energy transfer efficiency between dansyl and dabcyl groups increased when the temperature increased from 36 °C to 45 °C, indicating that the microenvironment surrounding dansyl became hydrophobic and the distance between dansyl and dabcyl decreased. The kinetics of the conformational change of the dye-labeled PNIPAM was studied by a home-made laser-induced temperature jump device with fluorescent measurement. Our results revealed that the characteristic transition time was 3.8 and 5.8 ms for PNIPAM with degrees of polymerization of 85 and 142, respectively, indicating that the characteristic transition time was related to the chain length. Besides, characteristic transition time for the change of the energy transfer efficiency was 2.9 ms for PNIPAM with the degree of polymerization of 85, suggesting that the energy transfer efficiency change was faster than the fluorescence intensity change of dansyl group.

Poly(N-isopropylacrylamide)-based thermo-responsive surfaces with controllable cell adhesion

Poly(N-isopropylacrylamide)(PNIPAAm)-based thermo-responsive surfaces can switch their wettability(from wettable to non-wettable) and adhesion(from sticky to non-sticky) according to external temperature changes. These smart surfaces with switchable interfacial properties are playing increasingly important roles in a diverse range of biomedical applications; these controlling cell-adhesion behavior has shown great potential for tissue engineering and disease diagnostics. Herein we reviewed the recent progress of research on PNIPAAm-based thermo-responsive surfaces that can dynamically control cell adhesion behavior. The underlying response mechanisms and influencing factors for PNIPAAm-based surfaces to control cell adhesion are described first. Then, PNIPAAm-modified two-dimensional flat surfaces for cell-sheet engineering and PNIPAAm-modified three-dimensional nanostructured surfaces for diagnostics are summarized. We also provide a future perspective for the development of stimuli-responsive surfaces.

Preparation of poly (N-isopropylacrylamide) brush bonded on silicon substrate and its water-based lubricating property

The poly (N-isopropylacrylamide) brush was covalently bonded on an initiator-coated silicon wafer via surface-initiated atom transfer radical polymerization. The polymer brush was (76.2±0.1) nm in thickness (by ellipsometer) with a grafting density of ca. 0.27 chains/nm 2 . The tribological properties of the poly (N-isopropylacrylamide) brush were investigated by means of ball-on-disk tests in a rotational mode under water lubrication for tribological application. The experimental results exhibited a low friction coefficient of ca. 0.03. The excellent lubrication property of the brush was due to its amide groups in the polymer chains. It was supposed that the good lubrication property of the brush was attributed to the cross-linked polymer network formed by the hydrogen bond association of N-H…O==C and the water molecular layer adsorbed by the terminal amide groups in the brush. The poly (N-isopropylacrylamide) solution also exhibits a lubrication property due to physical adsorption of the polymer chains.

Synthesis of multifunctional ABC stars with a reduction-labile arm by consecutive ROP, RAFT and ATRP processes

This study aims at versatile synthesis of 3-arm ABC-type （A=poly（c-caprolactone）, PCL; B=poly（N-isopropylacrylamide）, PNIPAM; C=poly（tert-butyl acrylate）, PtBA, or poly（acrylic acid）, PAA） miktoarm star copolymers with a reducible disulfide linkage. Using 2-（（2-（（2-hydroxymethyo-2-（（2-bromo-2-methyl）propionyloxy）methyl）propionyloxy）ethyl）disulfanyl）ethyl 4- cyano-4-（phenylcarbonothioylthio）pentanoate （HBCP） as a heterotrifunctional initiator, consecutive ring-opening polymerization （ROP） of g-caprolactone （CL）, reversible addition-fragmentation chain transfer （RAFT） polymerization of N-isopropy- lacrylamide （NIPAM） and atom transfer radical polymerization （ATRP） of tert-butyl acrylate （tBA） afforded ABC1 star, and followed by a subsequent hydrolysis to give ABC2 star. IH nuclear magnetic resonance （IH NMR） and gel permeation chromatography （GPC） analyses revealed the desired stars and their precursors had well-controlled molecular weight and relatively low polydispersity （PDI≤1. 12）. As confirmed by GPC analysis, the disulfide linkage in ABCI star could be efficiently cleaved upon reductive stimulus, during which the topology was converted from star terpolymer to mixtures of homopolymer （B） and diblock copolymer （AC1）. In addition to acting as nanocarriers for stimuli-triggered drug delivery systems, ABC stars with terminal bromide, dithiobenzoate and hydroxyl functionalities are expected to form other reduction-cleavable multicomponent copolymers such as （BC-graft-A）m and dendritic graft copolymers via postpolymerization modification. Our research affords a straightforward ＂core-first＂ method to construct multifunctional star terpolymers with stimuli-responsive arms and reduction-labile linkage.

Wide range temperature detection with hybrid nanoparticles traced by surface-enhanced Raman scattering

We report on the fabrication of a class of surface-enhanced Raman scattering(SERS)active thermometers,which consists of60 nm gold nanoparticles,encoded with Raman-active dyes,and a layer of thermoresponsive poly(N-isopropylacrylamide)(PNIPAM)brush with different chain lengths.These SERS-active nanoparticles can be optimized to maintain spectrally silent when staying as single particles in dispersion.Increasing temperature in a wide range from 25 to 55°C can reversibly induce the interparticle self-aggregation and turn on the SERS fingerprint signals with up to 58-fold of enhancement by taking advantage of the interparticle plasmonic coupling generated in the process of thermo-induced nanoparticles self-aggregation.Moreover,the most significative point is that these SERS probes could maintain their response to temperature and present all fingerprint signals in the presence of a colored complex.However,the UV-Vis spectra can distinguish the differences faintly and the solution color shows little change in such complex mixture.This proof-of-concept and Raman technique applied here allow for dynamic SERS platform for onsite temperature detection in a wide temperature range and offer unique advantages over other detection schemes.

New insights into the effects of molecular weight and end group on the temperature-induced phase transition of poly(N-isopropylacrylamide) in water

In an attempt to clarify issues related to the molecular weight dependence of the phase transition of poly(N-isopropylacrylamide) (PNIPAM) in water,we prepared a library of PNIPAM samples of well-controlled molecular weight (7000 to 45000 g/mol) bearing identical groups on each chain end.The polymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAM) with a bifunctional chain tranfer agent and further end group modification.The effects of the end group chemical structure,hydroxyethyl (HE),propargyl (Pr),chloroethyl (CE),n-butyl (nBu),n-hexyl (nHe),and isobutylsulfanylthiosulfanyl (IBS) on the phase transition temperature of aqueous PNIPAM solutions were investigated by high-sensitivity differential scanning calorimetry (HS-DSC),yielding the enthalpy ΔH and the endotherm maximum temperature (T M),and turbidimetry,providing the cloud point (T CP) of each solution.The T CP and T M of the PNIPAM sample of lowest molar mass (M n 7,000 g/mol,0.5 g/L) ranged,respectively,from 38.8 to 22.5 °C and 42.2 to 26.0 °C,depending on the structure of the end-group,whereas H showed no strong end-group dependence.The phase transition of all polymers,except,-di(n-butyl-PNIPAM),exhibited a marked dependence on the polymer molar mass.

Polyrotaxane-based triblock copolymers synthesized via ATRP of N-isopropylacrylamide initiated from the terminals of polypseudorotaxane of Br end-capped pluronic 17R4 and β-cyclodextrins

Thermo-responsive polyrotaxane （PR）-based triblock copolymers were synthesized via the atom transfer radical polymeriza- tion （ATRP） of N-isopropylacrylamide initiated with self-assemblies made from a distal 2-bromoisobutyryl end-capped Plu- ronic 17R4 （PPOI4-PEG24-PPOI4） with a varying amount of β-cyclodextrins （β-CDs） in the presence of Cu（I）C1/PMDETA at 25 ~C in aqueous solution. The molecular structure was characterized by means of ~H NMR, FTIR, WXRD, GPC, TGA and DSC analyses. About half of [3-CDs are still entrapped on the Pluronic 17R4 chain while the number of incorporated NIPAAm monomers is nearly a double feed value in the resulting copolymers. The aggregate morphologies in aqueous solution were evidenced by TEM observations. A two-step thermo-responsive transition arising from a combination of a polypseudorotaxane middle block with poly（N-isopropylacrylamide） flanking blocks was also demonstrated by turbidity measurements. Given their thermo-responsive behavior in aqueous solution, these PR-based triblock copolymers show the potential to be used as smart materials for the controlled drug delivery systems, biosensors, and the like.