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1.
Andreas Markwitz Perry Davy John Kennedy Horst Baumann 《Surface and interface analysis : SIA》2008,40(5):931-934
Low‐energy lead ion implantation and high‐temperature electron beam annealing were used to study the potential of producing Pb nanostructures on Si. Pb+ ions were implanted at high dose into p‐type (100) Si to the depth of 8.0 nm. The implanted samples were annealed under high vacuum conditions with an electron beam at 200–700 °C for 15 s. Rutherford Backscattering Spectrometry (RBS) shows rapid out‐diffusion of Pb atoms above 400 °C. However, some Pb atoms are still present in the near‐surface region after annealing the implanted samples at 700 °C. Lead nanostructures were found on samples annealed above 300 °C. Annealing the samples at 450 °C causes the formation of nanostructures as tall as 4.1 ± 0.1 nm. Many of these are arranged in ‘web‐like’ strings that extend over micrometer distances. Occasionally, much larger nano‐features (as wide as 500 nm in diameter, average height of 1.5 nm) appear in the centre of the strings. Annealing samples well above the melting point of lead results in randomly distributed small nanometer‐sized Si nano‐dots. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Investigating Pb diffusion across buried interfaces in Pb(Zr0.2Ti0.8)O3 thin films via time‐of‐flight secondary ion mass spectrometry depth profiling
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John S. Mangum Stephen Podowitz‐Thomas Jason Nikkel Chuanzhen Zhou Jacob L. Jones 《Surface and interface analysis : SIA》2017,49(10):973-977
The diffusion of Pb through Pb(Zr0.2Ti0.8)O3(PZT)/Pt/Ti/SiO2/Si thin film heterostructures is studied by using time‐of‐flight secondary ion mass spectrometry depth profiling. The as‐deposited films initially contained 10 mol% Pb excess and were thermally processed at temperatures ranging from 325 to 700°C to promote Pb diffusion. The time‐of‐flight secondary ion mass spectrometry depth profiles show that increasing processing temperature promoted Pb diffusion from the PZT top film into the buried heterostructure layers. After processing at low temperatures (eg, 325°C), Pb+ counts were low in the Pt region. After processing at elevated temperatures (eg, 700°C), significant Pb+ counts were seen throughout the Pt layer and into the Ti and SiO2 layers. Intermediate processing temperatures (400, 475, and 500°C) resulted in Pb+ profiles consistent with this overall trend. Films processed at 400°C show a sharp peak in PtPb+ intensity at the PZT/Pt interface, consistent with prior reports of a Pt3Pb phase at this interface after processing at similar temperatures. 相似文献
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Characterization of the interaction of hypericin with protein kinase C in U-87 MG human glioma cells
Kocanova S Hornakova T Hritz J Jancura D Chorvat D Mateasik A Ulicny J Refregiers M Maurizot JC Miskovsky P 《Photochemistry and photobiology》2006,82(3):720-728
A fluorescence imaging technique was used to monitor intracellular localization of protein kinase C (PKC) in U-87 MG human glioma cells in the presence of hypericin (Hyp) and phorbol 12-myristate-13-acetate (PMA). It is shown that PKC localization, which reflects its activity, is influenced by Hyp and this influence is different from that observed for PMA which acts as PKC activator. Fluorescence binding experiments were used to determine the binding constants of Hyp to several isoforms of PKC. The obtained values of K(d)s (approximately 100 nM) suggest that Hyp binds with high affinity to PKC. Finally, molecular modeling was used to compare structural models of the interaction of C1B domain of PKC (PKC isoforms alpha, delta, gamma) with Hyp and our previously published model of the (C1B domain PKCgamma)/PMA complex. The influence of Hyp on PKC translocation in U-87 MG cells in comparison with PMA, colocalization fluorescence pattern of Hyp and PKC, the higher binding affinity of Hyp to PKC in comparison with known binding constants of phorbol esters, as well as the binding mode of Hyp and PMA to the C1B domain of PKC suggested by molecular modeling, support the idea that Hyp and PMA might competitively bind to the regulatory domain of PKC. 相似文献
6.
Calsavara Luiza P. V. De Moraes Flávio F. Zanin Gisella M. 《Applied biochemistry and biotechnology》2001,91(1-9):615-626
The enzyme cellobiase from Novo was immobilized in controlled pore silica particles by covalent binding with the silane-glutaraldehyde
method with protein and activity yields of 67 and 13.7%, respectively. The activity of the free enzyme (FE) and immobilized
enzyme (IE) was determined with 2 g/L of cellobiose, from 40 to 75°C at pH 3.0–7.0 for FE and from 40 to 70°C at pH 2.2–7.0
for IE. At pH 4.8 the maximum specific activity for the FE and IE occurred at 65°C: 17.8 and 2.2 micromol of glucose/(min·mg
of protein), respectively. For all temperatures the optimum pH observed for FE was 4.5 whereas for IE it was shifted to 3.5.
The energy of activation was 11 kcal/mol for FE and 5 kcal/mol for IE at pH 4.5–5, showing apparent diffusional limitation
for the latter. Thermal stability of the FE and IE was determined with 2 g/L of cellobiose (pH 4.8) at temperatures from 40
to 70°C for FE and 40 to 75°C for IE. Free cellobiase maintained its activity practically constant for 240 min at temperatures
up to 55°C. The IE has shown higher stability, retaining its activity in the sametest up to 60°C. Half-life experimental results
for FE were 14.1, 2.1, and 0.17 h at 60, 65, and 70°C, respectively, whereas IE at the same temperatures had half-lives of
245, 21.3, and 2.9 h. The energy of thermal deactivation was 80.6 k cal/mol for the free enzyme and 85.2 k cal/mol for the
IE, suggesting stabilization by immobilization. 相似文献
7.
Prodromos B. Issopoulos 《Fresenius' Journal of Analytical Chemistry》1989,334(6):554-557
Summary A spectrophotometric method for the determination of microquantities of frusemide (FRS) is described. It is based on the oxidation of the latter by the paramolybdate anion (PMA) or by the molybdatophosphoric anion (MPA). The oxidation is carried out in acid medium at 98° C ±0.5° C for a fixed time of 25 min. The blue coloured reaction product can be measured spectrophotometrically at 690 nm and 700 nm, respectively. Beer's law is obeyed over the range of 5–200 ppm of FRS. The apparent molar absorptivities and Sandell's sensitivities (in l mol–1 cm–1 and ng cm–2 per 10–3 absorbance unit, respectively) are 2.8×103 and 118.2 using PMA as oxidizing agent and 2.16×103 and 153 using MPA for the same purpose. Six replicate analyses of solutions containing seven different concentrations of FRS were realized and gave a mean correlation coefficient of 0.9999 using the first oxidant (PMA) and 0.9998 using the second one (MPA), while the slope and intercept of the regression line equation were calculated. FRS was successfully determined both in the pure form and in pharmaceutical preparations. The results demonstrated that the proposed procedure is at least as accurate, precise and sensitive as the official method, while a statistical analysis indicated that there was no significant difference between the results obtained by the recommended procedure and those of the official method.
Spektralphotometrische Bestimmung von Mikromengen Frusemid unter Verwendung von Iso- und Heteropolyanionen des Mo(VI) als Oxidationsmittel相似文献
8.
Seok Ho Park 《Journal of Dispersion Science and Technology》2018,39(7):961-969
Oil-in-water emulsions were prepared by emulsifying mineral oil in gold nanoparticle (GNP) solution using amphiphilic polymers as an emulsifier. Poly(2-hydroxyethyl acrylate) (PHEA) and poly(2-hydroxyethyl acrylate-co-propyl methacryate) (P(HEA/PMA)) having different PMA contents (2.98%, 3.29%, 6.1%, and 8.59% (mole/mole)) were prepared by a free radical polymerization, confirmed by 1H NMR spectroscopy. According to the optical density change of the polymer solution (2% (w/v)) at 20°C–80°C, only P(HEA/PMA) having a PMA content of 3.29 mole % showed its lower solution critical temperature around 31°C. The air/water interfacial activity of the amphiphilic polymers was higher as the PMA content was higher. GNP was prepared by reducing gold ions in water. The mean hydrodynamic diameter was 22.2?nm and it appeared sphere-like on TEM photo. The emulsion prepared using PHEA maintained its stability above 80% for 190 hours, whereas it was destabilized rapidly upon 60 minutes of near-infrared (NIR) irradiation and its stability decreased to below 20% in 20 hours. As the PMA content was higher, the stability of the emulsions prepared using P(HEA/PMA) became lower and NIR irradiation accelerated the destabilization more effectively. 相似文献
9.
Muhammad Asad Anam Zulfiqar Rizwan Raza Minghui Yang Akhtar Hayat Naeem Akhtar 《Electroanalysis》2020,32(1):11-18
A novel electrode based on orange peel derived C‐dots decorated CuO nanorods (CR@C‐dot) modified lead pencil (LP) electrode has been fabricated for highly sensitive and selective monitoring of dopamine (DA). Prior to the functionalization with C‐dot, electrochemical efficacy of CR was evaluated and compared with CuO nano‐needles (CN) and nano‐spheres (CS). The morphology, surface area and composition of synthesized nanoparticles was confirmed through field emission scanning electron microscopy (FE‐SEM), N2‐adsorption‐desorption isotherm, X‐ray diffraction (XRD), Raman spectroscopy and X‐ray photoelectron spectroscopy (XPS). Our results indicated that CR has high electrocatalytic activity compared to CN and CS by expositing greater fraction of catalytic active sites, large surface area and short diffusion pathways. The electrochemical efficacy of CR is further enhanced by decorating with orange peel derived C‐dots, which surprisingly lead to the integrations of surface‐active sites with current collectors with minimum resistance by acting as an electron transport mediator and providing more surface defects. The developed CR@C‐dot sensor enables highly sensitive and selective recognition of DA detection (0.0007 μM), over good linear range (5–2250 μM) with rapid response time. the developed CR@C‐dot sensor was successfully used to monitor the DA from deboned chicken, thus suggesting reliability of the developed electrode. 相似文献
10.
Selective formation of diblock copolymers using radical trap‐assisted atom transfer radical coupling
William E. Butcher Scott C. Radzinski Eric S. Tillman 《Journal of polymer science. Part A, Polymer chemistry》2013,51(17):3619-3626
Polystyrene (PSt) radicals and poly(methyl acrylate) (PMA) radicals, derived from their monobrominated precursors prepared by atom transfer radical polymerization (ATRP), were formed in the presence of the radical trap 2‐methyl‐2‐nitrosopropane (MNP), selectively forming PSt‐PMA diblock copolymers with an alkoxyamine at the junction between the block segments. This radical trap‐assisted, atom transfer radical coupling (RTA‐ATRC) was performed in a single pot at low temperature (35 °C), while analogous traditional ATRC reactions at this temperature, which lacked the radical trap, resulted in no observed coupling and the PStBr and PMABr precursors were simply recovered. Selective formation of the diblock under RTA‐ATRC conditions is consistent with the PStBr and PMABr having substantially different KATRP values, with PSt radicals initially being formed and trapped by the MNP and the PMA radicals being trapped by the in situ‐formed nitroxide end‐capped PSt. The midchain alkoxyamine functionality was confirmed by thermolysis of the diblock copolymer, resulting in recovery of the PSt segment and degradation of the PMA block at the relatively high temperatures (125 °C) required for thermal cleavage. A PSt‐PMA diblock formed by chain extenstion ATRP using PStBr as the macroinitiator (thus lacking the alkoxyamine between the PSt‐PMA segements) was inert to thermolysis. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3619–3626 相似文献
11.
A nano‐crystalline In2O3 was synthesized using calcinations methods and was used as a photocatalyst to degrade sulfan blue (SB) dye. In addition, this study addresses the conditions of the degradation and the factors that influenced the catalysis. In2O3 was prepared by calcining In(OH)3 at heat ranges of 100–700 °C for 24 h. The In2O3 was characterized using field emission scanning electron microscopy (FE‐SEM), an X‐ray diffractometer (XRD), thermogravimetric analysis (TGA), and high‐resolution X‐ray photoelectron spectroscopy (HR‐XPS). The activities of these samples were tested for the photocatalytic degradation of SB dye. The results indicated that the In(OH)3 that was calcined at 300 °C for 24 h had the best performance. 相似文献
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With the expanding application of capacitors, thermal resistant dielectric materials are in high demand due to the increasing harsh environments where the capacitors are needed and the heat generated by the capacitors. Herein, we present polyarylene ether nitrile and titanium dioxide hybrids which can be used as thermal resistant dielectrics for these capacitors. Phthalonitrile modified titanium dioxide (TiO_2-CN) and phthalonitrile end-capped polyarylene ether nitrile (PEN-Ph) are firstly prepared. After being cast into TiO_2-CN/PEN nanocomposite films,these composites self-crosslink upon heating at 320℃ for 4 h, forming the polyarylene ether nitrile and titanium dioxide hybrids (TiO_2-PEN).Improved dielectric constants which are stable from room temperature to 200℃ of these hybrids are observed, indicating the potential application of the hybrids as thermal resistant dielectrics. 相似文献
13.
Kuilin Deng Jing Liu Xiangyang Zheng Yaqin Zhang Na Jia Hua Tian Yinghai Liu 《先进技术聚合物》2008,19(8):1048-1054
Using potassium diperiodatonickelate (Ni (IV)) as an efficient initiator, the graft copolymerization of methyl acrylate (MA) onto organophilic montmorillonite (OMMT) was successfully performed in an alkaline medium. Three grafting parameters were systematically evaluated as functions of the temperature, the initiator concentration, reaction time, pH value, and the ratio of MA to OMMT substrate. The structure of the titled graft copolymers (OMMT‐g‐PMA) were confirmed by Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and thermo‐gravimetric analysis (TGA). It was found that Ni (IV) was a highly efficient initiator for graft copolymerization of the MA onto OMMT, i.e., grafting efficiency is as high as 95% and grafting percentage can be facilely controlled within 700% in this study. In addition, the highest grafting efficiency and grafting percentage were obtained when temperature adopted was over 40°C and pH was about 10.3. A single‐electron‐transfer mechanism was proposed to illustrate the formation of radicals and the initiation reaction. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
14.
H. Katsuura H. Kawamura M. Manabe H. Kawasaki H. Maeda 《Colloid and polymer science》2002,280(1):30-37
The binding of a cationic surfactant, dodecylpyridinium (C12Py) chloride, with a low-charge-density poly (methacrylic acid)
(PMA) was investigated in buffer solutions under the condition of constant pH. The binding isotherms with PMA consisted of
two and three steps at a pH lower and higher than 3.2, respectively. Bindings in the first step were independent of pH and
this step was considered to correspond to the solubilization of the hydrocarbon chains of C12Py into the nonpolar region of
the compact form of PMA. This is the indication of the compact form from the binding isotherm. At pH higher than 3.2, the
second step was discriminated and it depended on the pH. In the third step, a sharp rise in the degree of binding (β) was
observed accompanying the solubilization of the precipitates of the PMA–C12Py complex. The binding with poly(acrylic acid)
(PAA) and PMA in conventional unbuffered NaCl solutions was also examined and the pH profile of the solution during the binding
process was determined. In the case of unbuffered NaCl solutions, the binding with PAA took place cooperatively at the critical
association concentration (cac). The binding isotherm consisted of two steps and the pH decreased with the increase in β.
The binding isotherm of PMA, on the other hand, consisted of three steps: the pH decreased slightly in the first step and
considerably in the second step with the increase in β but it increased with β in the third step, exhibiting a pH minimum
around 3.2. The binding in the first step coincided with that obtained in the buffered solutions. Linear relationships between
β and the pH were found for both polymers. In the case of PMA, no cac was observed in both buffered and unbuffered NaCl solutions.
Received: 24 January 2001 Accepted: 23 May 2001 相似文献
15.
Poly(methyl acrylate) (PMA) and 1:1 poly(styrene-co-methyl acrylate) (PSMA) were prepared by solution and bulk polymerization, respectively. The copolymer was analyzed with NMR to ascertain its composition and microstructure. The solution properties of unfractionated PMA and fractionated PSMA in ethyl acetate were investigated by light-scattering and viscosity techniques at 35°C. Narrow composition heterogeneity as revealed from the light-scattering measurements in different solvents justified the use of a single solvent for the copolymer characterization. The equations relating the limiting viscosity number to molecular weight, the molecular dimension to molecular weight, etc., were found for homopolymer and copolymers in ethyl acetate at 35°C. In the evaluation of the Flory constant K for the unperturbed state by methods based on Flory-Fox-Schaefgen, Kurata-Stockmayer, and Stockmayer-Fixman expressions, only the first method gave a value for PMA in ethyl acetate, consistent with that obtained in other solvents, whereas similar values of K were obtained by the three methods for PSMA in ethyl acetate. The studies indicate reduced thermodynamic interaction for PSMA–ethyl acetate compared to PMA–ethyl acetate, but increased steric effect in the copolymer compared with the homopolymer. 相似文献
16.
Bunichiro Yamada Fuminori Oku Takahiro Harada 《Journal of polymer science. Part A, Polymer chemistry》2003,41(5):645-654
The addition of propagating radicals of methyl acrylate (MA) and styrene (St) to CH2?C(CO2CH3)CH2? and CH2?C(C6H5)CH2? ω‐end groups of poly(methyl methacrylate) (PMMA) and polystyrene (PSt) was investigated. The end groups were as reactive as MA and St toward the poly(methyl acrylate) (PMA) and PSt radicals, respectively. The adduct radical derived from the two types of PMMA end groups and PMA radicals underwent β fragmentation exclusively to yield PMMA radicals and end groups bound to PMA chains. The addition of PSt radicals to PMMA with CH2?C(CO2Me)CH2? end groups resulted in adduct radicals that underwent β fragmentation and addition to St or coupling with PSt radicals. Adduct radicals formed by the addition of PMA radicals to both types of end groups of PSt exclusively formed C? C bond by coupling with PMA radicals to form branched structures or by addition to MA monomer to give a copolymer. The fate of the adduct radicals was highly dependent on the type of polymer chain and the substituent bound to the end group. Steric congestion of the adduct radical arising from the α‐methyl group of the PMMA chain was considered to be crucial for fragmentation to expel the PMMA radical. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 645–654, 2003 相似文献
17.
R. Parise Filho A. A. S. Araújo M. Santos Filho J. R. Matos M. A. B. Silveira C. A. Brandt 《Journal of Thermal Analysis and Calorimetry》2004,75(2):487-494
Oxamniquine (OXA) is a schistosomicide agent that causes some adverse effects in central nervous system. Intending to improve
OXA therapeutic properties, a polymeric prodrug was designed. Currently, there is an increasing interest of thermal analytical
techniques in the pharmaceutical area, so differential thermal analysis (DTA) and thermogravimetry (TG) were carried out to
evaluate the thermal behavior of OXA, polymethacrylic acid (PMA), [poly(methacrylic-co-oxamniquine methacrylate)acid] (PMOXA)
and physical mixture (OXA+PMA). The thermoanalytical profile of the physical mixture showed characteristic events of the thermal
decomposition of OXA and PMA. Distinctly, PMOXA DTA curve did not show an endothermic peak at 148.5°C indicating that the
drug was incorporated into the polymeric system. These results were corroborated by the IR spectroscopy and X-ray diffraction
data.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
Zhong Jie Zhang Peng Cui Xiang Ying Chen Jian Wei Liu 《Journal of Solid State Electrochemistry》2013,17(6):1749-1758
High-performance activated carbon for electrochemical double-layer capacitors (EDLC) has been prepared from cation exchange resin by carbonization and subsequent activation with KOH. The activation temperature has a key role in the determination of porous carbon possessing high surface areas, and large pore structures. The porous carbon activated at 700 °C (carbon-700-1:4) has high surface area (2236 m2?g?1) and large total pore volume (1.15 cm3?g?1), which also displays best capacitive performances due to its well-balanced micro- or mesoporosity distribution. In details, specific capacitances of the carbon-700-1:4 sample are 336.5 F?g?1 at a current density of 1 A?g?1 and 331.8 F?g?1 at 2 A?g?1. At high current density as 20 A?g?1, the retention of its specific capacitance is 68.4 %. The carbon-700-1:4 sample also exhibits high performance of energy density (46.7 Wh?kg?1) and long cycle stability (~8.9 % loss after 3,000 cycles). More importantly, due to the amount of waste ion-exchange resins increasing all over the world, the present synthetic method might be adopted to dispose them, producing high-performance porous carbons for EDLC electrode materials. 相似文献
19.
The thermal production of 4PbO·PbSO4 was comprehensively studied and characterized for two syntheses routes, i.e. either heating 3PbO·PbSO4·H2O, or a mixture of 4PbO:PbSO4, in air to about 700 °C. In the 3PbO·PbSO4·H2O approach, the formation of an intermediate amorphous phase occurred at around 210 °C with the loss of H2O from the hydrated structure. Formation of 4PbO·PbSO4 initiated at around 270 °C with predominantly 4PbO·PbSO4 and 13% residual PbO·PbSO4 existing at 700 °C. With the synthesis route of mixing a stoichiometric ratio of 4PbO with PbSO4, an intermediate phase of PbO·PbSO4 formed at around 300 °C, before the 4PbO·PbSO4 phase started to form at around 500 °C. Upon further heating, 4PbO·PbSO4 was the predominant phase with 8% of PbO·PbSO4 remaining. Both samples decomposed upon further heating to 850 °C. Powder neutron diffraction studies of the final 4PbO·PbSO4 products from the two different synthesis routes showed similar crystallographic unit cell lattice parameters with slight differences in the PbO:PbSO4 contents. This could possibly be linked to differences observed in the microscopic crystallite shapes from the two synthesis routes. 相似文献
20.
Polymaleimide (PMAI) was synthesized by reacting polymaleic anhydride (PMA) with urea via a solvent-free reaction at 180 °C. The conversion of PMA could reach 95%. This method is simple, practical and environmentally-friendly. The structure of the resulting PMAI was characterized by 1H-NMR and IR. 相似文献