Terbium orthophosphate nanoparticles were synthesized using 1-hydroxy ethylidene-1,1-diphosphonic acid(HEDP) as a capping ligand under hydrothermal conditions at 80℃. These HEDP-capped TbPO4 nanoparticles owned a hexagonal phase structure according to the powder X-ray diffraction(XRD) results and were spherical monodispersed particles with a diameter of about 10 nm confirmed by transimission electron microscope(TEM) images. Interestingly, the luminescent intensities of the HEDP-capped TbPO4 nanoparticles decreased obviously in the presence of Pb2+ ions and such a quenching behavior of luminescence was well fitted by the Stern-Volmer equation.
A pure inorganic [P2Mo5O23]6- based cobalt complex [H8(H2O)16][Co(H2O)4(HP2Mo5O23)2] with a sandglass-like shape was synthesized and characterized by means of single-crystal X-ray diffraction, powder X-ray diffraction(PXRD), infrared spectroscopy(IR), thermogravimetry/differential scanning calorimetry(TG/DSC), ultraviolet-visible spectroscopy(UV-Vis) and cyclic voltammogram(CV). Single-crystal X-ray diffraction analysis reveals that the asymmetric unit of compound 1 consists of a half cobalt ion, one [P2Mo5O23]6- anion, two coordinated water molecules and eight lattice water molecules. It is especially intriguing to note that two [P2Mo5O23]6- clusters are symmetrical about the Co ion, like a sandglass. And a chair-like water cluster with an unprecedented centrosymmetric [H8(H2O)16]8+ can be observed in compound 1. Additionally, the electrochemical and catalytic properties of compound 1 were also investigated.
A novel hybrid material with microporous structure was fabricated from SBA-15 with mesopores via silane modification and hydrolysis. Two kinds of pores with diameters of 6.5 and 1.9 nm were found in the hybrid material. Compared to that of SBA-15, the surface area of the hybrid material increased from 395.9 m2/g to 667.4 m2/g while its porous volume decreased. The new hybrid material was found to have high efficiency in removing NaCl from solution, and the maximum adsorption capacity of it was ca. 517.5 mg/g.
The evolution of morphology and heterostructure of BiOCl was investigated during an in situ oxidation reaction. Morphology and structure transformation of regular 2D nanoflake, 0D nanosphere or 3D nanoflower was achieved by adjusting the ratio of reagent concentration or reaction temperature, respectively. The enhanced photocatalytic degradation ability and the photocurrent intensity of BiOCl nanomaterials may be attributed to the improved degree of crystallinity and the formation of Bi/BiOCl heterostructure. The photocurrent density of Schottky battery was increased due to enhancing the optical pathway and assisting during charge separation. Crystallinity also contributed to the improvement of the photoelectric conversion efficiency and reduction of the recombination rate of photogenerated electron-hole pairs.
The interaction of indocyanine green(ICG) with human serum albumin(HSA) was investigated via various spectrometric(UV-visible, fluorescence and circular dichroism) techniques. The experimental results indicate that the interaction of ICG with HSA depends on the values of R(R is defined as the molar ratio of HSA to ICG). The interaction of ICG with HSA can form two complexes with intrinsic binding constants(Ka) of 2.97×105(R≤2) and 2.63×104(R>2), respectively. The fluorescence and induced CD(ICD) spectra of ICG demonstrate that binding the first mole of HSA to ICG can form a chiral ICG-HSA complex with strong fluorescence emission, and the chirality and fluorescence of ICG-HSA complex can be significantly reduced by adding another mole of HSA to ICG. Furthermore, although both ICG and ICG-HSA complexes followed an energy-dependent endocytosis process to enter living cells, the cellular uptaken dynamic mechanism of ICG was significantly affected by the HSA conjugation.
Based on the obtained data of half-lives(t1/2) for 31 polychlorinated biphenyl congeners(PCBs), 3D quantitative structure-activity relationship(QSAR) pharmacophore was used to establish a 3D QSAR model to predict the t1/2 values of the remaining 178 PCBs, using the structural parameters as independent variables and lgt1/2 values as the dependent variable. Among this process, the whole data set(31 compounds) was divided into a training set(24 compounds) for model generation and a test set(7 compounds) for model validation. Then, the full factor experimental design was used to research the potential second-order interactional effect between different substituent positions, obtaining the final regulation scheme for PCB. At last, a 3D QSAR pharmacophore model was established to validate the reasonable regulation targeting typical PCB with respect to half-lives and thermostability. As a result, the cross-validation correlation coefficient(q2) obtained by the 3D QSAR model was 0.845(>0.5) and the coefficient of determination(r2) obtained was 0.936(>0.9), indicating that the models were robust and predictive. CoMSIA analyses upon steric, electrostatic and hydrophobic fields were 0.7%, 85.9%, and 13.4%, respectively. The electrostatic field was determined to be a primary factor governing the t1/2. From CoMSIA contour maps, t1/2 increased when substi- tuents possessed electropositive groups at the 2'-, 3-, 3'-, 5- and 5'- positions and electronegative groups at the 3-, 3'-, 5-, 6- and 6'- positions, which could increase the PCB stability in transformer insulation oil. Modification of two typical PCB congeners(PCB-77 and PCB-81) showed that the lgt1/2for three selected modified compounds increased by 13%(average ratio) compared with that of each congener and the thermostability of them were higher, validating the reasonability of the regulatory scheme obtained from the 3D QSAR model. These results are expected to be beneficial in predicting t1/2 values of PCB homologues and derivatives and in providing a theoretical foundation for further elucidation of the stability of PCBs.
A series of amino alcohol derivatives containing coumarin and benzothiophene moieties was synthesized with 5-bromosalicylaldehyde and 5-bromo-2-thiophenecarboxaldehyde as starting materials, 6-substituted-3-chroma- none and 4,5-dihydrobenzo[b]-thiophen-5(4H)-one as intermediates and Suzuki reaction and spiro-hydantoin hydrolysis as key steps. The structures of key intermediate and target compounds were confirmed by 1H NMR, 13C NMR, IR and HRMS. Their characterization as sphingosine 1-phosphate(S1P) receptor agonists was reported.
Based on the formation of 2,5-bis(trimethylsilyl)-zirconacyclopentadienes from two silylalkynes with Cp2ZrBu2 and the Cu-mediated formation of 1,4-disilylbenzene via the cycloaddition of zirconacyclopentadienes to disubstituted alkynes, a selective synthesis of 1,4-dialkyl(aryl)-hexa-substituted benzenes was achieved followed by iodination and coupling reaction. The coupling reactions were carried out with either organolithium reagent or organozinc reagent(Negishi coupling), depending on the electrophilic species.
Several novel chiral thiazoline catalysts containing thiazoline, thiourea and proline were efficiently synthesized from commercially available L-cysteine. These ligands were subsequently applied to the asymmetric Michael reaction between cyclohexanone and various β-nitrostyrene. The result shows that the optimal catalyst for this reaction is ligand 18d, the organocatalyst with thiazoline, thiourea and chiral proline motif, which efficiently promotes the enantioselective conjugate addition of cyclohexanone to various nitroalkenes to yield the corresponding addition products in high to excellent yields with enantiomeric excess(e.e.) up to 95% and diastereoselectivity ratio(dr.) up to 99:1.
We report the first trifluoroacetic anhydride-and trifluoroacetic acid-promoted cascade reaction with phloroglucinoltribenzyl ether and carboxylic acid as starting materials. By simply varying the temperature of systems containing the same starting materials, different products were produced in high yields. A three-step consecutive reaction process was also proposed.
Phosphine-catalyzed [4+2] annulations of 2-(acetoxymethyl)buta-2,3-dienoates with α-aminonitriles have been developed, in which α-aminonitriles serve as C, N-bisnucleophilic reaction partners and 2-(acetoxymethyl)buta- 2,3-dienoates as "C4 synthons" respectively. A number of α-aminonitriles could be successfully applied to giving multifunctional desired products using PPh3 as catalyst. This method provides a facile entry to access polysubstituted tetrahydropyridines bearing quaternary carbon centers. The possible reaction mechanism was also proposed.
A cost-effective and environmentally compliance FeCl3·6H2O catalyzed Friedel-Crafts alkylation of cyclic ketene dithioacetals with alcohols was developed. The reaction was efficient in the presence of catalyst loading as low as 5%(molar fraction) in CH2Cl2 solvent at room temperature or under reflux conditions. A wide range of alkylated ketene dithioacetals were synthesized in excellent yields.
To develop novel sulfonylurea herbicides, a series of chlorsulfuron derivatives was designed and synthesized through introducing tetrahydrophthalimide substructure taken from protoporphyrinogen IX oxidase(PPO) inhibitors onto the critical 5-position of the classical benzene ring. The structures of title compounds were confirmed by infrared spectroscopy, ultraviolet spectroscopy, 1H and 13C NMR spectrometry, mass spectrometry and elemental analysis. In addition, the crystal structure of compound II-5 was further determined by X-ray diffraction analysis. Bioassay results showed that individual compounds exhibited good herbicidal activities, especially compound II-8, which displayed 100% inhibition rate against Echinochloa crusgalli at 150 g/ha(1 ha=104 m2) with the method of foliage spray in the pot experiment.
In order to identify potential protein targets involved in colorectal cancer(CRC), we used a liquid chromatography coupled with mass spectrometry(LC-MS)/MS-based proteomics approach to characterize global protein expression patterns in malignant tissues and their adjacent healthy tissues from Dukes C stage CRC patients. A total number of 34 differentially expressed proteins were detected and identified by LC-MS/MS and database searching, which are supposed to be relevant to progression of colorectal tumor. Among these proteins, nucleophosmin 1(NPM1) was found to be remarkably up-regulated in colorectal carcinoma tissues, as compared with that in their normal counterparts. The results presented here could provide clues to elucidate the pathological significance of NPM1 in regulation of carcinogenesis of Dukes C stage colorectal tumors.
We prepared a cholesterol-conjugated chitosan(CHCS) material and evaluated its potential application as a bone tissue repair material by in vitro cell experiments. Cell proliferation, differentiation and morphology on CHCS membrane surfaces with different graft degrees were assessed in mouse pre-osteoblasts MC3T3-E1 cells. The results indicate that CHCS materials could promote the proliferation of MC3T3-E1 cells at low graft degrees, but the CHCS material with high graft degree inhibits the proliferation of cells in contrast to the pure chitosan membrane. However, the alkaline phosphatase(ALP) activity of MC3T3-E1 cells on different CHCS membrane surface increased with increasing graft degrees of cholesterol. The area of cells stretched onto the surface of CHCS materials was larger than on the surface of CS materials, and more microfilaments and stress fibers in cells were observed on CHCS materials than on the pure chitosan material surface. After 7 d, the expression of related osteogenic marker genes, such as runt-related transcription factor 2(Runx2), osterix(OSX), osteocalcin(OCN), osteopontin(OPN), ALP and collagen I(COL-I) were all up-regulated in CHCS materials to different degrees compared to pure chitosan material, which indicated that the CHCS materials facilitated MC3T3-E1 cell differentiation and maturation. Characterizing CHCS materials is useful in designing and developing strategies for bone tissue engineering.
Nitrogen oxide(NOx) emitted from stationary and mobile sources is a major air pollutant. Selective catalytic reduction(SCR) of NOx over a catalyst is a main technology for NOx elimination. Catalysts used for practical applications would be deactivated in flue containing SO2. In this work, three typical commercial catalysts were investigated before and after SO2 treatment. The catalysts were characterized by X-ray diffraction(XRD), X-ray fluorescene(XRF), temperature programme reduction(TPR), temperature programme desorption(TPD) and diffuse reflectance Fourier transform infrared(DRIFT) techniques. Results showed that SO2 treatment significantly influenced the performance of V2O5/TiO2 catalyst. The amount of V2O5 in the catalyst primarily affected the accumulation of sulfur species in the SO2atmosphere. The performance of catalysts with small amounts of V2O5 could be improved under the same experimental conditions for acidity enhancement.
K+-doped Bi0.02Co was investigated as catalyst for N2O decomposition. It was found that the catalytic performance of the Bi0.02Co catalyst, which was prepared by coprecipitation method, can be effectively modified by potassium cations via impregnation. The optimized K0.01Bi0.02Co catalyst exhibited much higher activity compared with Bi0.02Co and K0.01Co for the reaction in feed gas 0.2% N2O/Ar, irrespective of the presence or absence of impurity gas(volume fraction) 5%O2, 2%H2O, 0.12%NO and 10%CO2. Characterization of the catalysts with H2 temperature programmed reduction(H2-TPR) and O2 temperature programmed desorption(O2-TPD) indicate that the Co-O bond in Bi0.02Co was weakened by the K+doping, and hence the K0.01Bi0.02Co catalyst has much higher turnover frequency(TOF) than Co3O4 spinel and Bi0.02Co for the reaction.
Degradation phenomenon and poor stability of tris(8-hydroxyquinoline) aluminum(III)(Alq3)-based organic light-emitting diodes(OLEDs) have attracted much attention. In this paper, we discussed the origin of instability of the facial Alq3-based blue luminescent OLEDs with the help of first-principles calculation. The results show that environmental humidity seriously affects the luminescence stability of Alq3-based OLEDs. H2O molecules in environment can be firmly bound to the oxygen atoms of the facial Alq3, which then act as starting points for further degradation of Alq3. Moreover, the interactions between facial Alq3 and different cathode metal layers were investigated to explain the experiment phenomenon. A design guideline for diminishing the strong attraction from oxygen atoms can be proposed to protect Alq3 and improve the stability of materials applied in OLEDs.
A novel and facile method for fabricating large-area patterned silver nanocrystals was introduced and the investigation on the high sensitive and stable surface-enhanced Raman spectroscopy(SERS) of the nanocrystals was carried out. Nanostructured silicon substrate was processed by laser interference and used as a template for growing silver nanocrystals via galvanic battery reaction method. The substrate with large area for violent chemical reaction was tailored into a nanocell array. The limited reaction area hindered the growth of silver nanocrystals and made their size uniform and controllable. The size and gaps of the nanocrystals could be controlled by template period and ratio, which were easily reproduced by laser interference. Taking 10-8 to 10-11 mol/L Rh6G for example, the optimized silver arrays exhibited great potential for ultrasensitive molecular sensing in terms of its high SERS enhancement ability, favorable stability, and excellent reproducibility.
The facile preparation of Ag NPs/C via a one-pot strategy was carried out by microwave treatment of a mixed aqueous solution of AgNO3 and glucose at 180℃ for 20 min without the presence of extra reducing agent. The as-synthesized Ag NPs/C showed high catalytic performance toward the reduction of H2O2. The H2O2 sensor constructed with as-synthesized Ag NPs/C exhibited a short amperometric response time of less than 2 s. The linear range was approximately (0.1-50) mmol/L(r=0.997), and the detection limit was approximately 3.3 μmol/L at a signal-to-noise ratio of 3. A glucose biosensor was fabricated by immobilizing glucose oxidase onto Ag NPs/C- modified glassy carbon electrode to detect glucose. The glucose sensor had a wide linear response range of 2-22 mmol/L(r=0.999) and a detection limit of 190 μmol/L.
Different precursors were prepared via a simple low heat solid state reaction(LHSSR) upon changing the ligands. The ZnO photoanode films were obtained by the doctor blade technique, and their composition, thermal decomposition process and morphologies were identified by means of X-ray diffraction(XRD), thermal gravimetric analysis-differential thermal analysis(TGA-SDTA) and scanning electron microscope(SEM). The results show that the morphologies of ZnO photoanodes are irregular block, regular lamellar and irregular sheet-cluster, and the multistage structure can be found in all the photoanodes. Furthermore, there exists a genetic effect of morphology between the precursors and the corresponding photoanodes. The optimum power conversion efficiency of the sheet-cluster ZnO photoanode was 3.12% with the short circuit current density(Jsc) being 11.23 mA/cm2. The multi- stage sheet-cluster structure could result in the increase of the scattering of the incident light and provide a rapid electronic transmission channel to reduce the risk of electronic recombination. A beneficial enlightenment was obtained to simplify the process and the photoanode films with various morphologies can be prepared with lower price in the further research.
Engineering metal-organic frameworks(MOF) for heterogeneous catalysts have been of extreme interest since they have large pore size within the crystalline framework and well defined pore architecture. Ni-containing MOF Ni2(3,5-Pydc)2(H2O)8·2H2O(1·H2O) was prepared by solvothermal method from 3,5-pyridinedicarboxylic acid, D-camphoric acid and Ni(NO3)2·6H2O in dimethylformamide(DMF)/water(volume ratio 2:1). And two gold and silver functionalized 1·H2O catalysts were prepared by impregnation method. Catalysts 2.53%Au/MOF and 4.23%Ag/MOF were in-depth characterized by single crystal X-ray diffraction, powder X-ray diffraction(PXRD), thermogravimetric analysis(TGA), transmission electron microscopy(TEM), and inductively coupled plasma-atomic emission spectroscopy(ICP-AES). Their catalytic performance was examined in one-pot synthesis of structurally divergent propargylamines via three component coupling of aldehyde, alkyne, and amine(A3) in 1,4-dioxane. The results show that the catalysts all displayed high reactivities, and a selectivity of 100% for propargylamines. Catalysts 2.53%Au/MOF and 4.23%Ag/MOF have proved to be applicable to a wide range of substrates. Catalysts 2.53%Au/MOF and 4.23%Ag/MOF can be easily recycled and used repetitively at least 3 times with a slight drop in activity. These features render the catalysts particularly attractive in the practice of propargylamines synthesis in an environmentally friendly manner.
The electronic structures and spectroscopic properties of heteroleptic cyclometalated iridium(III) complexes were investigated. The geometries, electronic structures, and the lowest-lying excited states of (DBQ)2Ir(acac) and (MDQ)2Ir(acac) were investigated via density functional theory-based approaches. A series of designed models of (DBQ)2Ir(dpis), (DBQ)2Ir(tpip), (MDQ)2Ir(dpis) and (MDQ)2Ir(tpip) was also calculated for comparison. The structures in the ground and excited states were optimized via B3LYP method. The lowest absorptions and emissions spectra were evaluated via TD-B3LYP and TD-PBE1PBE methods. The computational results reveal that the emission peaks of the designed complexes are at around 585-640 nm, which belong to the orange-yellow wavelength. The frontier molecular orbital properties indicate that the Ir(III) complexes have low efficiency roll-off.
SiO2 with different nanostructures, namely hexagonal mesoporous silica(HMS), and three unordered commercial silica, were used as supports to fabricate silver catalysts using an incipient wetness impregnation method. It was found that Ag/HMS catalyst showed a high catalytic activity. Next, the HMS support was calcined at different temperatures before impregnation of AgNO3. The effect of calcination temperature of HMS support was investigated in terms of structure and catalytic activity of Ag catalysts. The support and catalysts were characterized by N2 adsorption-desorption isotherms, Thermogravimetric-differential thermal analyzer, X-ray diffraction, H2-temperature program reduction and transmission electron microscopy. The results showed that calcination of HMS at an appro- priate temperature(750℃) before catalyst preparation would benefit the formation of highly dispersive small sized Ag particles on the HMS support and markedly enhance the catalytic activity of Ag/HMS catalyst toward CO oxidation.
The influences of H2O and SO2 on CeO2/TiO2 monolith catalyst for the selective catalytic reduction(SCR) of NOx with NH3 were investigated. In the absence of SO2, H2O inhibited the SCR activity, which might be ascribed to the competitive adsorption of H2O and reactants such as NH3 and/or NOx. SO2 could promote the SCR activity of CeO2/TiO2 monolith catalyst in the absence of H2O, while in the presence of H2O it speeded the deactivation. During the SCR reaction in SO2-containing gases, Ce(III) sulfate species formed on the catalyst surface, resulting in the enhancement of Brønsted acidity. This played a significant role in the enhanced SCR activity. However, in the presence of both H2O and SO2, a large amount of ammonium-sulfate salts formed on the catalyst surface, which resulted in the blocking of catalyst pores and deactivated the catalyst. In addition, the NOx conversion was more sensitive to gas hourly space velocity in the presence of H2O than in the absence of H2O. The relatively high space velocity would result in a higher formation rate of ammonium-sulfate salts on per unit catalyst in the presence of H2O and SO2, which caused obvious deactivation of Ce/TiO2 monolith catalyst.
Cu2O/nitrogen-doped grapheme(NG) nanocomposite material was prepared via a facile one step chemical reduction and characterized by means of X-ray diffraction(XRD) and scanning electron microscopy(SEM). A new electrochemical sensor was then fabricated by coating Cu2O/nitrogen-doped graphene nanocomposite with Nafion on glassy carbon electrode(Cu2O/NG/Nafion/GCE). The electrochemical response of this modified electrode toward ofloxacin was examined by cyclic voltammetry. The results indicate that Cu2O/NG/Nafion composite-modified electrode exhibits higher catalytic activity in the electrochemical oxidation of ofloxacin compared with glassy carbon electrode(GCE), Cu2O/Nafion modified electrode(Cu2O/Nafion/GCE), and N-doped graphene/Nafion modified electrode(NG/Nafion/GCE). Under optimal conditions, the peak current was found to be linearly proportional to the concentration of ofloxacin in the 0.5-27.5 μmol/L and 27.5-280 μmol/L ranges with a lower detection limit of 0.34 μmol/L, higher sensitivity of 39.32 μA·L·mmol-1 and a shorter reaction time of less than 2 s. In addition, Nafion can enhance the stability of the modified electrode and prevent some negative species. Thus the modified electrode exhibits good selectivity and a long working life. The Cu2O/NG/Nafion composite modified electrode shows promising application in electrochemical sensors, biosensors, and other related fields because of its excellent properties.
Lanthanide-doped upconversion nanoparticles(UCNPs) are great promising to apply to biomedical imaging and therapy. We prepared NaYF4:Yb3+,Er3+ nanoparticles with different surface ligands, i.e., without any ligands(bare), coordinated with 2-aminoethyl dihydrogen phosphate(AEP), polyacrylic acid(PAA) or polyallylamine (PAAm), via a simple two-step ligand exchange of oleic acid capped NaYF4:Yb3+,Er3+ nanoparticles. Although the surface modification retained the crystal structure and transimission electron microscope(TEM) size distribution of the nanoparticles, and good dispersibility in aqueous solution and did not significantly change the upconversion luminescence, distinct differences were observed in the surface charge and hydrodynamic diameter. The cellular uptake and cytotoxicity of the nanoparticles were studied on two different cell lines, breast cancer MCF-7 and fibroblast 3T3. Confocal microscopy images demonstrate that PAAm-coordinated UCNPs can enhance the cellular uptake and endocytosis, whereas AEP- and PAA-coordinated UCNPs show a very low level of nonspecific adsorption. Biocompatibility studies based on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT) assay, however, indicate that PAAm-coordinated UCNPs are more toxic than the other two, and thus need further modifiaction(like PEG coordinating) to improve their biocompatibility. These results are important to the knowledge base required for the biomedical application of the UCNPs.
Ferrofluids, formed by magnetic nanoparticles uniformly dispersed in a liquid carrier, respond to an external magnetic field, which enable the fluid's position by applying a magnetic field. Here, ferrofluids composed of Fe3O4 nanoparticles with oleic acid and oleylamine as the surfactant and photoresist, respectively, were prepared. Under an external magnetic field, the movement and the position of ferrofluids and the injection of the fluids into complex shapes were easily achieved. The ferrofluid surfaces were distorted under the magnetic field, and the surface structue was controlled by the applied field strength. Using a photoresist as the liquid carrier, it was possible to solidify the ferrofluids by UV irradiation. The shape and the position of the solid superparamagnetic nanoparticles/polymer composites were also determined by the external magnetic field.
Fmoc or Boc mono-substituted cyclo(L-Lys-L-Lys)s were synthesized via the reaction of lysine cyclic dipeptide with Fmoc N-hydroxysuccinimide este(Fmoc-OSu) and di-tert-butyl dicarbonate[(Boc)2O], respectively. The resulted mono-substituted cyclo(L-Lys-L-Lys)s(2-4) by means of test tube inversion method served as organogelators enabled to form stable thermo-reversible organogels in alcoholic, substituted benzene and chlorinated solvents, with the minimum gelation concentration(MGC) in a range of 1%-4%(mass fraction). The transmission electron microscopy(TEM) and scanning electron microscopy(SEM) observations reveal that these gelators self-assembled into 3D nanofiber, nanoribbon or nanotube network structures. The rheological measurement exhibited that the storage modulus of gels is higher than the loss one, and the complex viscosity is reduced linearly with the increasing of scanning frequency. The fluorescence spectrum of compound 2 in 1,2-dichloroethane and benzene demonstrates that the emission peak of Fmoc at 320 nm has red-shifted and the intensity decreases gradually, while the intensity of the emission peak at 460 nm substantially enhances as a function of concentration, indicating the existence of π-π sta- cking interactions and the formation of J-type aggregates. Meanwhile, compound 4 self-assembled into nanotubes via the stacking of multiple bilayer membranes. Fmoc and Boc disubstituted cyclo(L-Lys-L-Lys)(3) holds the relatively lower MGC values, showing the stronger gelation ability in most selected organic solvents due to the presence of both Fmoc and Boc groups.
A post-photochemical cross-linking strategy was successfully demonstrated to enhance the stability of polyelectrolyte poly(allylamine hydrochloride)(PAH)/poly(vinylsulfonic acid sodium salt)(PVS) multilayers. Conventional polyelectrolyte multilayers of PAH/PVS are usually fabricated through electrostatic layer-by-layer(LbL) assembly, resulting in poor stability, especially in basic solutions, which leads to the urgent demand for converting weak electrostatic interactions into covalent bonds to enhance the stability of the multilayers. This stability problem has been ultimately addressed by post-infiltrating a photosensitive cross-linking agent, 4,4'-diazostilbene-2,2'- disulfonic acid disodium salt(DAS), into the LbL assembled films to initiate the photochemical reaction to cross-link the multilayers. The obviously improved stability of the photo-cross-linked multilayers was demonstrated through experiments with basic solution treatments. Compared to the complete decomposition of uncross-linked multilayers in basic solution, over 74.4% of the covalently cross-linked multilayers were retained under the same conditions, even after a longer duration of basic solution treatment.
The effects of the concentration of sodium chloride in an aqueous solution(cNaCl) and the temperature on the molecular size of poly(sulfobetaine methacrylate)(PSBMA) were studied via viscometry and dynamic light scattering(DLS). The morphology of single-chain PSBMA was determined by atomic force microscopy(AFM). The results demonstrate that the hydrodynamic diameter of PSBMA can be expressed as a continuous function of cNaCl, with the molecular size of PSBMA increasing and eventually approaching an asymptotic value with increasing cNaCl. The molecular size of PSBMA at a lower cNaCl(0.04 mol/L) increases with increasing temperature, which is the opposite of the temperature effect at a higher cNaCl(2.0 mol/L). Therefore, the internal structure of PSBMA chains in solutions with a low salt concentration differs from that in solutions with a high salt concentration. In addition, the morphology of single chains of PSBMA appears to be spherical, containing 89% void space, and the apparent size of the dried chains is almost identical to that in solution.
High molecular weight aliphatic segmented poly(ether ester amide)s(PEEAs) were synthesized via melt polycondensation and chain extension. An oligomeric polyamide(PA) terminated mainly with -COOH groups(HOOC-PA-COOH) was prepared from the reaction of nylon 610 salt with sebacic acid. Melt polycondensation of HOOC-PA-COOH with polyethylene glycol(PEG), such as PEG400, PEG600, PEG1000 and PEG1500, was conducted at 200℃, and several segmented PEEA prepolymers(PrePEEAs) were prepared. Chain extension of PrePEEAs was carried out at 190℃ using 2,2'-(1,4-phenylene)-bis(2-oxazoline) and adipoyl biscaprolactamate as combination chain extenders. Chain extended PEEAs(ExtPEEAs) were characterized by gel permeation chromatography(GPC), Fourier transform infrared spectrophotometer(FTIR), proton nuclear magnetic resonance(1H NMR), differential scanning calorimetry(DSC), wide angle X-ray scattering(WAXS), thermogravimetry analysis(TGA), and tensile test. The ExtPEEAs exhibited Mn up to 98700, Tm from 164.2℃ to 176.1℃, initial decomposition temperature above 320.6℃, tensile strength up to 34.80 MPa, and strain at break from 111.92% to 353.12%. Aliphatic segmented PEEAs with good thermal and mechanical properties were prepared.
High-molecular-weight aliphatic polycarbonates(APCs) were synthesized through a two-step transesterification process under solvent-free conditions. Oligomers with equal numbers of hydroxyl and phenyl carbonate terminal groups could be easily controlled by using equimolar amounts of diphenyl carbonate(DPC) and aliphatic diols as feedstocks in the first step. In the second step, the high-molecular-weight APCs can be obtained by connecting -OH with -OC(O)OC6H5 end-group upon removing the generated phenol at reduced pressure. Mg(OAc)2 was found to be the best catalyst for this process among the screened catalysts, which gave the poly(1,4-butylene carbonate)(PBC) a weight-average molecular weight(Mw) of 148600 and a yield of 84.8% under its suitable reaction conditions. In addition, based on the results of X-ray diffraction(XRD), scanning electron microscopy(SEM) and fourier transform infrared spectroscopy(FTIR), a possible reaction mechanism over Mg(OAc)2 was proposed for APCs synthesis.