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1.
Ioana Negru Mircea Teodorescu Paul O. Stǎnescu Constantin Drăghici Anamaria Lungu Andrei Sârbu 《Colloid and polymer science》2013,291(11):2523-2532
Novel triblock copolymers with PEG middle blocks of 1–10 kDa and poly(N-isopropylacrylamide-co-t-butylacrylamide) statistical copolymer side arms with DPn?≈?88 and different compositions, were synthesized by SET-LRP. The thermogelation properties of their aqueous solutions depended on both hydrophobic monomer content of the side blocks and molecular weight (MW) of the poly(ethylene glycol) (PEG) middle block, as proven by dynamic rheometry, DSC, and tube inversion method measurements. At constant PEG chain length, increasing TBAM proportions led to a gelation process occurring at progressively lower temperatures, as well as to a lower stability of the forming hydrogels in the case of shorter-PEG-chain block copolymers. By employing longer PEG blocks (MPEG ≥6,000 Da), stable hydrogels with the gelation temperature below 37 °C could be obtained. For a constant composition of the copolyacrylamide blocks, the dependence of the phase transition temperature (Tph) on MPEG displayed a different shape at different polymer solution concentrations, because of the stronger variation of Tph with polymer concentration as MPEG increased. Also, the viscoelastic properties of the hydrogels resulting from 20 wt.% polymer aqueous solutions at 37 °C were stronger affected by the MW of the PEG middle block than by the hydrophobic character of the thermosensitive side blocks. 相似文献
2.
A new N-heterocyclic initiator N-[2-(8-heptadecenyl)-4,5-dihydro-1H-imidazole-1-ethyl]-2-bromoisobutyramide was synthesized and immobilized on the surface of iron. Methyl methacrylate was grafted from iron substrates via surface-initiated atom transfer radical polymerization (ATRP). The first-order kinetics of poly(methyl methacrylate) (PMMA) grafting from iron revealed the control of ATRP throughout the reaction, and the polymerization reached a high conversion producing polymers with good control of molecular weights (M n?=?68,800) and low polydispersity indexes (M w/M n?<?1.32). The thickness of the polymer brush films was greater than 47 nm after 7 h of reaction time. The grafting density was estimated to be 0.48 chains?nm?2. The iron surfaces at various stages of modification were characterized by scanning electron microscopy and energy dispersive spectrometer. The analytical results were consistent with a thin compact polymer coating on the surface of iron. Iron surface with grafted PMMA coating showed significant corrosion resistance. This work demonstrated that the surface-initiated ATRP is a versatile means of the surface modification of active metals with well-defined and functionalized polymer brushes. 相似文献
3.
V. L. Volkov G. S. Zakharova M. V. Kuznetsov A. Jin Q. Zhu W. Chen 《Russian Journal of Inorganic Chemistry》2006,51(9):1339-1344
Layered nanocomposites of V1.67M0.33O5±δ · nH2O (M = Ti or Mo) xerogels intercalated with hydroquinone (HQ) and poly(vinyl alcohol) (PVA) are synthesized. When the organic component is intercalated, proper positively charged radicals substitute for the protons of the xerogel. IR and Raman spectroscopy is used to analyze the structural reorganization of the precursors upon composite formation. X-ray photoelectron spectroscopy shows that the composite contain vanadium(V) and vanadium(IV) whose V2p binding energies are lower than in the precursor xerogels. The ac conductivity of nanocomposite films is measured at 1 kHz. V1.67Ti0.33O4.83 · nH2O/HQ has the highest conductivity at 25°C: 0.13 S/m along layers and 1.7 × 10?2 S/m in the normal direction. The thermal properties of the composites in air are considered. 相似文献
4.
Carboxymethyl cellulose-silver nanoparticle (AgNp)-silica hybrids have been synthesized in a modified Stöber process. The hybrid synthesis was optimized to obtain an efficient immobilization matrix for diastase alpha amylase, a multimeric enzyme of high technological significance. The synthesized hybrids were characterized using FTIR, XRD, SEM, TGA and BET studies. The enzyme immobilization was done by adsorption and using the immobilized enzyme, the hydrolysis of soluble starch has been optimized in comparison to free enzyme. The optimum usable pH for the immobilized enzyme ranged from pH 4 to 5, while pH 5 was optimum pH for the free enzyme activity. The kinetic parameters for the immobilized, (K M = 3.4610 mg ml?1; V max = 6.3540 mg ml?1 min?1) and free enzyme (K M = 4.1664 mg ml?1; V max = 4.291 mg ml?1 min?1) hydrolysis indicated that the immobilization at the nanohybrid has significantly improved the catalytic property of the enzyme. In the immobilized state, the enzyme remained usable for many repeated cycles like our previous material, gum acacia-gelatin-AgNp-silica. Storage experiments indicated that the immobilization has increased the stability of the enzyme and also that AgNps play a role in stabilizing the immobilized enzyme. 相似文献
5.
Study on the stoichiometry and affinity of the arsenicals bound to HSA is an important step toward a better understanding of arsenic toxic effects. After incubation of AsIII or AsV with HSA at the physiological conditions (pH 7.43 and 37 °C), the free arsenicals and arsenic-HSA complexes were separated and detected by the combined techniques of microdialysis and liquid chromatography with hydride generation atomic fluorescence spectroscopy (MD–LC–HGAFS). The decrease of AsIII peak response rather than AsV indicated that HSA reacted with AsIII but not AsV. The binding plots indicated that the binding between HSA and AsIII was in Scatchard pattern when the concentration ratios of AsIII to HSA were ≤1:1. The strong binding sites (n 1) were 1.6 and the stability constant (K 1) was 1.54 × 106 M?1. When the concentration ratios of AsIII to HSA were >1:1, the binding was in Plasvento pattern with the stability constant K 2 ? 0 and no specific binding of AsIII with HSA. On the contrary, AsV did not show binding with HSA. The results showed that AsIII reacted with HSA more readily than AsV, which provides a chemical basis for arsenic toxicity. 相似文献
6.
For designing the responsive polymer brushes, and tuning the local and chemical surface responses to the external stimuli, the epitaxial single crystals were patterned by combination of bared surfaces of poly(ethylene glycol) (PEG) substrate, polymer homo-brushes constructed from poly(ethylene glycol)-b-polystyrene (PEG-b-PS) as well as poly(ethylene glycol)-b-poly(methyl methacrylate) (PEG-b-PMMA), and PEG-b-PS/PEG-b-PMMA mixed-brush channels. To achieve this target, various single crystals and epitaxial structures grown from dilute solutions through self-seeding approach were utilized as seeds to fabricate the next channels. The characteristics and morphologies of different channels were detectable by atomic force microscopy (AFM). The influence of chemical (solvent quality and interaction of substrate with different brushes) and physical (presence of brushes from another type in their vicinity) environments on crystallization was studied. Due to the effect of chemical environment, the PS brushes hampered the growth of PEG crystals at M n PS?=?10,000 g/mol. However, the PMMA brushes allowed PEG crystals to grow completely at M n PMMA =13,100 g/mol, and indicated their hindrance at higher molecular weights (here, M n PMMA?=?17,100 g/mol). It was feasible to neutralize the mentioned hindrance through fabricating the channels with brushes having the highest hindrance (M n PS?=?14,800 g/mol and M n PMMA?=?17,100 g/mol), and altering the physical environment from homo- to mixed-brush morphology. The characteristics (thickness, tethering density, and domain size) of developed channels from a certain material, in all arrangements and in various channels were in good agreement with those of corresponding non-epitaxial single crystals grown under the same conditions. 相似文献
7.
Yan-Xia Zhao Xun-Lei Ding Yan-Ping Ma Zhe-Chen Wang Sheng-Gui He 《Theoretical chemistry accounts》2010,127(5-6):449-465
Density functional theory (DFT) calculations are applied to study the structure and bonding properties of groups 3–7 transition metal oxide clusters M x=1–3O y q and Sc x=4–6O y q with 2y ? nx + q = 1, in which n is the number of metal valence electrons and q is the charge number. These clusters include MO2, M 2O3 +, M 2O4 ?, and M 3O5 (M = Sc, Y, La); MO2 +, MO3 ?, M 2O4 +, M 2O5 ?, M 3O6 +, and M 3O7 ? (M = Ti, Zr, Hf), and so on. The obtained lowest energy structures of most of these clusters are with character of oxygen-centered radical (O·). That is, the clusters contain oxygen atom(s) with the unpaired electron being localized on the 2p orbital(s). Chromium and manganese oxide clusters (except CrO4 ?) do not contain O· with the adopted DFT methods. The binding energies of the radical oxygen with the clusters are also calculated. The DFT results are supported by available experimental investigations and predict that a lot of other transition metal oxide clusters including those with mixed-metals (such as TiVO5 and CrVO6) may have high oxidative reactivity that has not been experimentally identified. The chemical structures of radical oxygen over V2O5/SiO2 and MoO3/SiO2 catalysts are suggested and the balance between high reactivity and low concentration of the radical oxygen in condensed phase catalysis is discussed. 相似文献
8.
A proton-conducting nanocomposite gel polymer electrolyte (GPE) system, [35{(25 poly(methylmethacrylate) (PMMA) + 75 poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP))?+?xSiO2}?+?65{1 M NH4SCN in ethylene carbonate (EC) + propylene carbonate (PC)}], where x?=?0, 1, 2, 4, 6, 8, 10, and 12, has been reported. The free standing films of the gel electrolyte are obtained by solution cast technique. Films exhibit an amorphous and porous structure as observed from X-ray diffractometry (XRD) and scanning electron microscopy (SEM) studies. Fourier transform infrared spectrophotometry (FTIR) studies indicate ion–filler–polymer interactions in the nanocomposite blend GPE. The room temperature ionic conductivity of the gel electrolyte has been measured with different silica concentrations. The maximum ionic conductivity at room temperature has been observed as 4.3?×?10?3?S?cm?1 with 2 wt.% of SiO2 dispersion. The temperature dependence of ionic conductivity shows a typical Vogel-Tamman-Fulcher (VTF) behavior. The electrochemical potential window of the nanocomposite GPE film has been observed between ?1.6 V and 1.6 V. The optimized composition of the gel electrolyte has been used to fabricate a proton battery with Zn/ZnSO4·7H2O anode and PbO2/V2O5 cathode. The open circuit voltage (OCV) of the battery has been obtained as 1.55 V. The highest energy density of the cell has been obtained as 6.11 Wh?kg?1 for low current drain. The battery shows rechargeability up to 3 cycles and thereafter, its discharge capacity fades away substantially. 相似文献
9.
The ionic conductivity of polycrystalline Li7BiO6 pellets has been measured by complex impedence method. The conductivity is 5.7 × 10?3 (Ω cm)?1 and 300°C and 3.8 × 10?6 (Ω cm)?1 at 100°C. Li7BiO6 is the best lithium conductor among the structurally related LinMO6 compounds. 相似文献
10.
We examine theoretically the three channels that are associated with the detachment of a single water molecule from the aqueous clusters of the alkaline earth dications, [M(H2O) n ]2+, M = Mg, Ca, Sr, Ba, n ≤ 6. These are the unimolecular water loss (M2+(H2O) n?1 + H2O) and the two hydrolysis channels resulting the loss of hydronium ([MOH(H2O) n?2]+ + H3O+) and Zundel ([MOH(H2O) n?3]+ + H3O+(H2O)) cations. Minimum energy paths (MEPs) corresponding to those three channels were constructed at the Møller–Plesset second order perturbation (MP2) level of theory with basis sets of double- and triple-ζ quality. We furthermore investigated the water and hydronium loss channels from the mono-hydroxide water clusters with up to four water molecules, [MOH(H2O) n ]+, 1 ≤ n ≤ 4. Our results indicate the preference of the hydronium loss and possibly the Zundel-cation loss channels for the smallest size clusters, whereas the unimolecular water loss channel is preferred for the larger ones as well as the mono-hydroxide clusters. Although the charge separation (hydronium and Zundel-cation loss) channels produce more stable products when compared to the ones for the unimolecular water loss, they also require the surmounting of high-energy barriers, a fact that makes the experimental observation of fragments related to these hydrolysis channels difficult. 相似文献
11.
Sayed Yahya Kazemi Seyed Mohammad Abedirad 《Journal of the Iranian Chemical Society》2013,10(2):251-256
In the present work, the effect of fsDNA (fish sperm DNA) on kinetic parameters of chemiluminescence (CL) of the luminol–hydrogen peroxide system catalyzed by Mn(III)–Tetrakis (4-sulfonatophenyl)-porphyrin was investigated. These parameters including pseudo first-order rise and fall rate constant for the chemiluminescence burst, maximum level intensity, time to reach maximum intensity, total light yield, and values of the intensity at maximum CL were evaluated by computer fitting of the resulted intensity–time plots. Results reveal that CL parameters are dramatically affected due to interaction of metalloporphyrin with DNA. In order to observe quenching effect of DNA on CL intensity, Stern–Volmer plot with k Q value of 1.18 × 105 M?1 was calculated in the quencher concentration range of 4 × 10?6–8.5 × 10?5 M. 相似文献
12.
Well-dispersed resorcinol-formaldehyde-based carbon spheres (RFCs) have been prepared by the polycondensation of resorcinol and formaldehyde with ammonia as catalyst and subsequent carbonization of the obtained polymer. In situ polymerization of the aniline occurred in the suspension of the RFC, and RFC was surrounded by the polyaniline (PANI) wires. The PANI and RFC hybrid network (PRFC) formed gradually. In a three-electrode mode, the specific capacitance (C sp) of PRFC reaches 315 F g?1 at a current density of 1 A g?1 in 2 M H2SO4, much higher than that of pure PANI (225 F g?1) and RFC (121.7 F g?1). Furthermore, the C sp of PRFC retains 80.0 % after 1000 charge-discharge processes at a current density of 5 Ag?1. The enhanced electrochemical performance of the PRFC came from its homogeneous three-dimensional hierarchical network structure, good electric conductivity of the PANI around the RFC, and the synergistic effect between the RFC and PANI. 相似文献
13.
Xiaokang Gao Qian Li Xinfeng Zhao Jingjing Huang Liujiao Bian Jianbin Zheng Zijian Li Youyi Zhang Xiaohui Zheng 《Chromatographia》2014,77(17-18):1235-1239
The interaction between drugs and receptors is particularly important in revealing the drug acting mechanism and developing new leads. In this work, α 1-Adrenoceptor (α 1-AR) from HEK293 cell line is purified and immobilized on the surface of macro-pore silica gel to prepare an high-performance affinity chromatography stationary phase for the pursuit of drug–receptor interactions by competition zonal elution. Naftopidil is found to have only one type of binding site to α 1-AR with an association constant of 1.45 × 106 M?1 and a concentration of binding sites of 1.56 × 10?6 M, while terazosin hydrochloride proves to present two kinds of binding site on the receptor at which the association constants are determined to be 1.61 × 105 M?1 and 2.06 × 103 M?1, and the corresponding concentrations of the binding sites are 1.56 × 10?6 M and 1.11 × 10?3 M, respectively. It is concluded that the stationary phase containing attached α 1-AR can be used to realize the binding of a drug to the receptor. 相似文献
14.
Amanda Emmanuelle Sales Fabiana América Silva Dantas de Souza José Antônio Teixeira Tatiana Souza Porto Ana Lúcia Figueiredo Porto 《Applied biochemistry and biotechnology》2013,170(7):1676-1688
Fibrinolytic proteases are enzymes that degrade fibrin; these enzymes are a promising alternative for thrombolytic therapy, and microorganisms produce them. The aim of this study was to evaluate the optimum conditions for the integrated production and purification of fibrinolytic protease from Bacillus sp. UFPEDA 485. Extractive fermentation was carried out in a culture medium containing soybean flour and by adding polyethylene glycol (PEG) and Na2SO4 according to a 23 experimental design. In all assays, the enzyme preferentially partitioned to the bottom phase (K?<?1), with an optimum activity of 835 U ml?1 in the bottom phase (salt-rich phase). The best conditions for extractive fermentation were obtained with 18 % PEG 8000 and 13 % Na2SO4. Characterization showed that it is a metalloprotease, as a strong inhibition—residual activity of 3.13 %—occurred in the presence of ethylenediaminetetraacetic acid. It was also observed that enzymatic activity was stimulated in the presence of ions: CaCl2 (440 %), MgCl2 (440 %), FeSO4 (268 %), and KCl (268 %). The obtained results indicate that the use of a low-cost substrate and the integration of fermentation with an aqueous two-phase system extraction may be an interesting alternative for the production of fibrinolytic protease. 相似文献
15.
Sayed Yahya Kazemi 《Journal of the Iranian Chemical Society》2013,10(5):915-920
The present work deals with the first attempt to study the effect of l-tyrosine on the characteristics of the peroxyoxalate chemiluminescence. Berberine was applied as an efficient fluorophore. The investigated parameters include rise and fall rate constant for the chemiluminescence burst, theoretical and experimental maximum intensity, the time needed to reach maximum intensity and the total light yield emission, which is theoretically evaluated using the pooled intermediate model by a computerized non-linear least-squares curve fitting program (KINFIT). Furthermore, based on the observed quenching effect of tyrosine, the Stern–Volmer plot with K Q value of 7.7 × 104 M?1 in the quencher concentration range 4 × 10?6–5 × 10?5 M. Moreover, this method is applied to determinate tyrosine in biological samples successfully. 相似文献
16.
Kie Yong Cho Hyun-Ji Kim Xuan Huy Do Jin Young Seo Jae-Woo Choi Sang-Hyup Lee Ho Gyu Yoon Seung Sang Hwang Kyung-Youl Baek 《Research on Chemical Intermediates》2018,44(8):4663-4684
Two series of water-soluble metalloporphyrin-cored amphiphilic star block copolymers were synthesized by controlled radical polymerizations such as atom transfer radical polymerization (ATRP) and reversible addition fragmentation chain transfer (RAFT), which gave eight amphiphilic block copolymer arm chains consisting of poly(n-butyl acrylate-b-poly(ethylene glycol) methyl ether methacylate) (PnBA-b-PEGMEMA, Mn,GPC = 78,000, Mw/Mn = 1.2, 70 wt% of PPEGMEMA) and poly(styrene-b-2-dimethylamino ethyl acrylate) (PS-b-PDMAEA, Mn,GPC = 83,000, Mw/Mn = 1.2, 67 wt% of PDMAEA), yielding porphyrin(Pd)-(PnBA-b-PPEGMEMA)8 and porphyrin(Pd)-(PS-b-PDMAEA)8, respectively. Obtained metalloporphyrin polymer photocatalysts were homogeneously solubilized in water to apply to the removal of chlorophenols in water, and was distinguished from conventional water-insoluble small molecular metalloporphyrin photocatalysts. Notably, we found that the water-soluble star block copolymers with hydrophobic–hydrophilic core–shell structures more effectively decomposed the chlorophenol, 2,4,6-trichlorophenol (2,4,6-TCP), in water under visible light irradiation (k = 1.39 h?1, t1/2 = 0.5 h) in comparison to the corresponding water-soluble star homopolymer, because the hydrophobic core near the metalloporphyrin effectively captured and decomposed the hydrophobic chlorophenols in water. 相似文献
17.
A k 0-RNAA procedure was developed to determine 129I in a mixed resin sample. CH4 extraction and (NH4)2SO3 back-extraction were used to separate 129I in ashed samples. The 129I target sample for irradiation in the reactor was prepared by heating the (NH4)2SO3 back-extraction solution to reduce its volume and then to dry it in a quartz ampoule. No MgO and LiOH were needed during the target sample preparation. After irradiation, the nuclide 130I was purified by combining hydrated antimony pentoxide column and CH4 extraction separations. A k-factor was determined for the reaction of 127I (n, 2n) 126I and used for iodine chemical yield determination. The apparent 129I concentrations of five nuclear reaction interferences were calculated. The relative standard deviation of three 129I determinations was found to be 3.5 %. The 129I content in the analyzed resin was found to be 1.36 × 10?9 g/g (8.63 × 10?3 Bq/g) with a relative uncertainty of 9.1 %. The detection limit of 129I was calculated to be 7.4 × 10?13 g (4.7 × 10?6 Bq) in a k 0-RNAA of a blank sample. 相似文献
18.
Ashok Kumar Singh Prerna Singh Sameena Mehtab 《Journal of inclusion phenomena and macrocyclic chemistry》2009,63(1-2):87-95
Novel polymeric membrane electrode (PME) and coated graphite electrode (CGE) for nickel ion were prepared based on 2,9-(2-methoxyaniline)2-4,11-Me2-[14]-1,4,8,11-tetraene-1,5,8,12-N4 as a suitable neutral ionophore. The addition of lipophilic anion excluder (NaTPB) and various plasticizers viz o-nitrophenyloctylether (o-NPOE), dioctylphthalate (DOP), dibutylphthalate (DBP), 1-chloronaphthalene (CN) and tri-n-butylphosphate (TBP) have found to improve the performance of the sensors. The best performance was obtained for the membrane sensor having a composition of I:NaTPB:TBP:PVC in the ratio 6:4:100:90 (w/w; mg). The electrodes exhibit Nernstian slopes for Ni2+ ions over wide concentration ranges of 4.6 × 10?7–1.0 × 10?1 M for PME and 7.7 × 10?8–1.0 × 10?1 M for CGE with limits of detection of 2.7 × 10?7 M for PME and 3.7 × 10?8 M for CGE. The response time for PME and CGE was found to be 10 and 8 s respectively. The potentiometric responses are independent of the pH of the test solution in the pH range 3.0–8.0. The proposed electrodes revealed good selectivities over a wide variety of other cations including alkali, alkaline earth, transition and heavy metal ions. The coated graphite electrode was used as an indicator electrode in the potentiometric titration of nickel ion with EDTA and in direct determination in different fruit juices and wine samples. 相似文献
19.
Ruchi Gaur G. N. Gupta M. Vamsikrishnan S. K. Khare 《Applied biochemistry and biotechnology》2008,151(2-3):160-166
Highly active Pseudomonas aeruginosa lipase protein-coated microcrystals (PAL PCMC) have been prepared by immobilization of protein onto K2SO4 as excipient solid support carrier and n-propanol as precipitating solvent. Transmission electron micrographs confirmed the formation of PAL PCMC. These PCMC were found to be a catalytically more active and stable preparation for p-nitrophenyl palmitate hydrolysis in n-heptane, compared to free lipase. The V max, K m, and temperature optimum for PAL PCMC increased from 0.49 to 5.66 nmol min?1 mg?1, 589 to 679.8 mmol, and 40°C to 45°C, respectively. These were thermally more stable with 4.65, 2.56, and 1.24-fold improvement in half lives at 45°C, 55°C, and 60°C compared to free P. aeruginosa PseA lipase. Their catalytic efficiency was enhanced by tenfold over that of free enzyme. PAL PCMC offer a simple and effective technique for obtaining stable and efficient lipase preparation for biocatalysis in nonaqueous medium. 相似文献
20.
A. Stamatovic P. Scheier T. D. Märk 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1987,6(4):351-362
Electron attachment to SO2 clusters formed by nozzle expansion was investigated (n up to 8) in a molecular-beam electron-ionization mass-spectrometer system. Electron ionization of SO2 clusters was also studied (n up to 18) showing no pronounced structure in the mass spectra and no strong dependence on electron energy, the dominant positive ion being the (SO2) n + series. Also present but less abundant are the fragment ion series (SO2) n SO+, (SO2) n S+ and (SO2) n O+ with decreasing intensities in that order. The dominant negative ion is (SO2) n ? . The homologous series (SO2) n O? and (SO2) n SO? are less abundant, the series (SO2) n S? has not been observed at all (except SO2·S? produced in the background gas via secondary processes). The negative ion mass spectra show a strong dependence on electron energy due to a rich resonance like structure of the attachment cross sections involved. These attachment cross sections have been determined (up to 40 eV) and they show significant differences for the different homologous series. The most striking feature is that for instance (SO2) n SO? ions do not show any signal at the first main resonance of SO? from SO2. Likewise (SO2) n O? ions only show a strongly diminished signal at the first main resonance of O? from SO2. This is in contrast to results in O2, CO2 and N2O. Conversely, (SO2) n ? ions show — besides peaks at the position of the first and second O? resonance — additional resonances below and above these peaks. In addition, (SO2) 5 ? and larger ones show a zero energy peak consisting of stoichiometric SO2 cluster ions similar to observations in O2, CO2 and H2O. The attachment cross section of S? from SO2 has been found to show an additional previously undetected peak at ~1 eV. Moreover, the present study revealed the existence of a S n ? (n up to 8) series being produced with nearly zero energy electrons via volume and surface processes in and around the ion source. 相似文献