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1.
Chunyi Jiang Yu Feng Xiaotong Huang Yechun Xu Yaping Zhang Naiming Zhou Xu Shen Kaixian Chen Hualiang Jiang Dongxiang Liu 《Analytical and bioanalytical chemistry》2010,396(5):1745-1754
Aβ1–42 is the proteolytic cleavage product of cleavage of the amyloid precursor protein by β- and γ-secretases. The aggregation
of Aβ1–42 plays a causative role in the development of Alzheimer’s disease. To lock Aβ1–42 in a homogenous state, we embedded the Aβ1–42 sequence in an unstructured region of Bcl-xL. Both the N-terminus and the C-terminus of Aβ1–42 were constrained in the disordered region, whereas the conjunction did not introduce any folding to Aβ1–42 but maintained the sequence as a monomer in solution. With Bcl-xL-Aβ42, we developed an enzyme-linked immunosorbent assay to compare the affinity of compounds for monomeric Aβ1–42. Bcl-xL-Aβ42 was coated on a microplate and this was followed by incubation with different concentrations of compounds. Compounds binding
to Leu17-Val24 of Aβ1–42 inhibited the interaction between Bcl-xL-Aβ42 and antibody 4G8. The method can not only reproduce the activities of the reported Aβ1–42 inhibitors such as dopamine, tannin, and morin but can also differentiate decoy compounds that do not bind to Aβ1–42. Remarkably, using this method, we discovered a new inhibitor that binds to monomeric Aβ1–42 and inhibits Aβ1–42 fibril formation. As the structure of Bcl-xL-Aβ42 monomer is stable in solution, the assay could be adapted for high-throughput screening with a series of antibodies that
bind the different epitopes of Aβ1–42. In addition, the monomeric form of the Aβ1–42 sequence in Bcl-xL-Aβ42 would also facilitate the identification of Aβ1–42 binding partners by coimmunoprecipitation, cocrystallization, surface plasmon resonance technology, or the assay as described
here. 相似文献
2.
Maksim Ionov Barbara Klajnert Konstantinos Gardikis Sophia Hatziantoniou Bartlomiej Palecz Bakhtiyar Salakhutdinov Josep Cladera Maria Zamaraeva Costas Demetzos Maria Bryszewska 《Journal of Thermal Analysis and Calorimetry》2010,99(3):741-747
To investigate the molecular interaction of amyloid beta peptides Aβ1–28 or Aβ25–40 with model lipid membranes differential scanning calorimetry (DSC) and DPH and TMA DPH fluorescence anisotropy approaches
were used. The main transition temperature (T
m) and enthalpy change (ΔH) of model lipid membranes composed of DMPC/DPPG on addition of Aβ25–40 or Aβ25–40 at 10:1 (w/w) phospholipid/peptide ratio either non-aggregated or previously aggregated were examined. The effect of Aβ1–28 and Aβ25–40 on the membrane fluidity of liposomes made of DMPC/DPPG (98:2 w/w) was determined by fluorescence anisotropy of incorporated
DPH and TMA DPH. The results of this study provide information that Aβ1–28 preferentially interacts with the hydrophilic part of the model membranes, while Aβ25–40 rather locates itself in the hydrophobic core of the bilayer where it reduces the order of the phospholipids packing. 相似文献
3.
Diana C. Rambaldi Andrea Zattoni Pierluigi Reschiglian Raffaella Colombo Ersilia De Lorenzi 《Analytical and bioanalytical chemistry》2009,394(8):2145-2149
Self-assembly of the 42-amino-acid-long amyloid peptide Aβ1-42 into insoluble fibrillar deposits in the brain is a crucial event in the pathogenesis of Alzheimer's disease. The fibril
deposition occurs through an aggregation process during which transient and metastable oligomeric intermediates are intrinsically
difficult to be accurately monitored and characterised. In this work, the time-dependent Aβ1-42 aggregation pattern is studied by asymmetrical flow field-flow fractionation with on-line multi-angle light scattering detection.
This technique allows separating and obtaining information on the molar mass (M
r) and size distribution of both the early-forming soluble aggregates and the late prefibrillar and fibrillar species, the
latter having very high M
r. Preliminary results demonstrate that unique information on the dynamic aggregation process can be obtained, namely on the
M
r and size of the forming aggregates as well as on their formation kinetics.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
4.
Alberto Granzotto Silvia Bolognin Janez Scancar Radmila Milacic Paolo Zatta 《Monatshefte für Chemie / Chemical Monthly》2011,10(4):421-430
Abstract
Alzheimer’s disease is a multifactorial neurodegenerative disorder characterized by the pathological brain deposition of neurofibrillary tangles and senile plaques. The latter consist mainly of insoluble β-amyloid (Aβ) fibril deposition. Aβ aggregation and deposition can be increased by several factors, including metal ions. In this study we investigated the role played by metal ions in affecting Aβ oligomerization in the presence and in the absence of its hydrophobic fragment Aβ17–28. This was done not as a physiological investigation, but as a paradigmatic study to confirm the key role of Aβ superficial hydrophobicity as a relevant aggravating factor that contributes to the toxicity of Aβ and Aβ–metal complexes. The structural conformations of Aβ–metal complexes were monitored through fluorescence and turbidity measurements as well as transmission electron microscopy. Results reported herein indicate that various metals differentially influence Aβ conformation, with aluminum being the only metal ion for which we are able to determine a dramatic enhancement of peptide oligomer formation with a consequent toxic effect. This scenario was further enhanced by the presence of Aβ17–28, which resulted in a marked toxicity in a neuroblastoma cell culture as a consequence of the enhancement of the hydrophobicity of the amyloid and amyloid–metal complexes. 相似文献5.
Abstract
The amyloid β-peptide (Aβ) and aluminum are found, among other components, in the senile plaques of patients with Alzheimer’s disease. Aggregated Aβ and aluminum are toxic to neurons but the mechanism of accumulation and toxicity remains poorly understood. It has been proposed that Aβ and aluminum toxicity results from Aβ– and aluminum–membrane interactions. It was therefore of interest to study the effect that Aβ and aluminum could have on cell membranes. Thus, the interactions of Aβ(1-40), Aβ(1-42), and Al(III) with the human erythrocyte membrane and a molecular model of the erythrocyte membrane were examined by electron microscopy and X-ray diffraction, respectively. The molecular model consisted of bilayers built up of dimyristoylphosphatidylcholine and dimyristoylphosphatidylethanolamine, phospholipid classes located in the outer and inner monolayers of most cell membranes, respectively. Aβ(1-40) and Aβ(1-42) in the presence of Al(III) altered the erythrocyte membrane morphology and the structure of dimyristoylphosphatidylcholine bilayers, effects that were different and stronger than those induced by Aβ and Al(III) separately. 相似文献6.
E. S. Rajagopal 《Colloid and polymer science》1961,175(2):126-129
Summary A working model is given for the rate of ultrasonic emulsification, considering the dispersion at the interface (areaA) and the coagulations in the volumeV of the emulsion. A bimolecular coagulation leads to the equationc=c
∞tanhbt;c
∞=(Aα/Vβ)1/2;b=(Aαβ/V)1/2 while a monomolecular coagulation givesc=c
∞{1−exp (−at)};c
∞=Aα/Vβ;a=β.
The experiments on the dependence of c∞,a andb uponA andV favour the bimolecular coagulation. The results are satisfactorily explained on general theoretical grounds.
Zusammenfassung Ein Arbeitsmodell für die Geschwindigkeit der Ultraschallemulgierung wird entwickelt, das Dispersion in der Grenzfl?che (Fl?cheA) und Koagulation im Volumen (V) der Emulsion annimmt. Eine bimolekulare Koagulation führt zu der Gleichung:c=c ∞ tanhbt;c ∞=(Aα/Vβ)1/2;b=(Aαβ/V)1/2, eine monomolekulare dagegen zu:c=c ∞{1−exp (at−)};c ∞=Aα/Vβ;α=β. Die Versuche über die Abh?ngigkeit vonc ∞,a undb vonA undV scheinen für bimolekulare Koagulation zu sprechen. Die Ergebnisse werden auf der Basis dieser einfachen theoretischen Grundlagen befriedigend erkl?rt.相似文献
7.
Nordling E Kallberg Y Johansson J Persson B 《Journal of computer-aided molecular design》2008,22(1):53-58
Diseases associated with protein fibril-formation, such as the prion diseases and Alzheimer’s disease, are gaining increased
attention due to their medical importance and complex origins. Using molecular dynamics (MD) simulations in an aqueous environment,
we have studied the stability of the α-helix covering positions 15–25 of the amyloid β-peptide (Aβ) involved in Alzheimer’s
disease. The effects of residue replacements, including the effects of Aβ disease related mutations, were also investigated.
The MD simulations show a very early (2 ns) loss of α-helical structure for the Flemish (Aβ(A21G)), Italian (Aβ(E22K)), and
Iowa (Aβ(D23N)) forms associated with hereditary Alzheimer’s disease. Similarly, an early (5 ns) loss of α-helical structure
was observed for the Dutch (Aβ(E22Q)) variant. MD here provides a possible explanation for the structural changes. Two variants
of Aβ, Aβ(K16A,L17A,F20A) and Aβ(V18A,F19A,F20A), that do not produce fibrils in vitro were also investigated. The Aβ(V18A,F19A,F20A)
initially loses its helical conformation but refolds into helix several times and spends most of the simulation time in helical
conformation. However, the Aβ(K16A,L17A,F20A) loses the α-helical structure after 5 ns and does not refold. For the wildtype
Aβ(1–40) and Aβ(1–42), the helical conformation is lost after 5 ns or after 40 ns, respectively, while for the “familial”
(Aβ(A42T)) variant, the MD simulations suggest that a C-terminal β-strand is stabilised, which could explain the fibrillation.
The simulations for the Arctic (Aβ(E22G)) variant indicate that the α-helix is kept for 2 ns, but reappears 2 ns later, whereafter
it disappears after 10 ns. The MD results are in several cases compatible with known experimental data, but the correlation
is not perfect, indicating that multimerisation tendency and other factors might also be important for fibril formation. 相似文献
8.
Jun-Ying Ge Sai-Feng Xue Qian-Jiang Zhu Zhu Tao Jian-Xin Zhang 《Journal of inclusion phenomena and macrocyclic chemistry》2007,58(1-2):63-69
The structures and optical properties of host–guest complexes produced from cucurbit[n = 6–8]urils and some benzimidazole derivatives have been investigated by 1H NMR spectroscopy, electronic absorption spectroscopy and fluorescence spectroscopy. The experimental results reveal that
calculations of A∼NQ[n]/Nguest and If∼NQ[n]/Nguest for the same association complex both support a good fit to an identical binding model. In particular, the A∼NQ[n]/Nguest, If∼NQ[n]/Nguest calculations and the 1H NMR determinations for three Q[6]–ge(1∼3) complexes and three Q[8]–ge(1∼3) complexes all support a binding model of 1:1
and 1:2 respectively. 相似文献
9.
Watanabe K Ishikawa C Kuwahara H Sato K Komuro S Nakagawa T Nomura N Watanabe S Yabuki M 《Analytical and bioanalytical chemistry》2012,402(6):2033-2042
This article details the development of a novel method that overcomes the drawbacks of sandwich ELISA (sELISA) and allows
reliable evaluation of simultaneous quantification of the amyloid (Aβ)-peptides, total-Aβ, Aβx-38, Aβx-40, and Aβx-42, in
rat brain by optimized sample purification and column-switching liquid chromatographic-tandem mass spectrometry (LC/MS/MS).
This method provides accurate analyses of total-Aβ, Aβx-38, Aβx-40, and Aβx-42 with a linear calibration range between 0.05
and 45 ng/mL. Verification for accuracy and precision of biological samples were determined by a standard addition and recovery
test, spiked with synthetic Aβ1-38, Aβ1-40, and Aβ1-42 into the rat brain homogenate. This method showed <20% relative error
and relative standard deviation, indicating high reproducibility and reliability. The brain concentrations of total-Aβ, Aβx-38,
Aβx-40, and Aβx-42 after oral administration of flurbiprofen in rats were measured by this method. Aβx-42 concentrations (4.57 ± 0.69 ng/g)
in rats administered flurbiprofen were lower than those in untreated rats (6.48 ± 0.93 ng/g). This was consistent with several
reports demonstrating that NSAIDs reduced the generation of Aβ. We report here a method that allows not only the quantification
of specific molecular species of Aβ but also simultaneous quantification of total-Aβ, Aβx-38, Aβx-40, and Aβx-42, thus overcoming
the drawbacks of sELISA. 相似文献
10.
Conducting polypyrrole (PPy) and poly(pyrrole-2,6-dimethyl-β-cyclodextrin) [poly(Py-β-DMCD)] films were prepared by electrode
potential cycling on a gold electrode in aqueous and nonaqueous (acetonitrile) electrolyte solutions containing lithium perchlorate.
The resulting products were characterized with cyclic voltammetry, in situ UV–Vis spectroscopy, and in situ conductivity measurements.
For the electrosynthesis of poly(Py-β-DMCD), a (1:1) (mole–mole) (Py-β-DMCD) supramolecular cyclodextrin complex of pyrrole
previously characterized with proton NMR spectroscopy was used as starting material. A different cyclic voltammetric behavior
was observed for pyrrole and the poly(Py-β-DMCD) complex in aqueous and nonaqueous solutions during electrosynthesis. The
results show that in both solutions in the presence of cyclodextrin, the oxidation potential of pyrrole monomers increases.
However, the difference of oxidation potentials for films prepared in aqueous solution is larger than for the films prepared
in nonaqueous solution. In situ conductivity measurements of the films show that films prepared in acetonitrile solution are
more conductive than those synthesized in aqueous solutions. Maximum conductivity can be observed for PPy and poly(Py-β-DMCD)
films prepared in nonaqueous solution in the range of 0.10 < E
Ag/AgCl < 0.90 V and 0.30 < E
Ag/AgCl < 0.90 V, respectively. In situ UV–Vis spectroelectrochemical data for both films prepared potentiodynamically by cycling
the potentials from −0.40 < E
Ag/AgCl < 0.90 V in nonaqueous solutions are reported.
This paper is dedicated to Prof. Alan Bond on the occasion of his 65th birthday in recognition of his numerous contributions
toward electrochemistry. 相似文献
11.
Sofia Nikolaou Sérgio Hiroshi Toma Vagner Roberto de Souza Juliano B. Alves Koiti Araki Henrique Eisi Toma 《Transition Metal Chemistry》2011,36(7):775-783
The triruthenium carboxylate cluster [Ru3O(OAc)6(py)2(bpp)]+ (OAc = acetate) containing the bridging 1,3-bis(4-pyridyl)propane (bpp) ligand, and its dimeric species [{Ru3O(OAc)6(py2)}2(μ-bpp)]2+ were synthesized in order to investigate their inclusion compounds with β-cyclodextrin (β-CD). Characterization of the complexes
was carried out based on spectroscopic, electrochemical and spectroelectrochemical techniques, while the formation of inclusion
complexes was evaluated using 1H NMR/NOESY spectroscopy. Since bpp is a flexible ligand, a DFT study was carried out in order to characterize its conformational
isomers and their possible role in the host–guest chemistry with β-CD. Instead of observing the formation of inclusion compounds
with different stoichiometries, we observed the formation of 1:1 bpp/β-CD compounds in which the bpp ligand assumes different
conformations. The assembly of polymetallic rotaxane species was successfully demonstrated by monitoring the 1H NMR spectra of the monomeric cluster species in the presence of aquapentacyanoferrate(II) ions and β-CD. 相似文献
12.
Silvia Berto Francesco Crea Pier Giuseppe Daniele Concetta De Stefano Enrico Prenesti Silvio Sammartano 《Journal of solution chemistry》2009,38(10):1343-1356
The formation constants of dioxouranium(VI)-2,2′-oxydiacetic acid (diglycolic acid, ODA) and 3,6,9-trioxaundecanedioic acid
(diethylenetrioxydiacetic acid, TODA) complexes were determined in NaCl (0.1≤I≤1.0 mol⋅L−1) and KNO3 (I=0.1 mol⋅L−1) aqueous solutions at T=298.15 K by ISE-[H+] glass electrode potentiometry and visible spectrophotometry. Quite different speciation models were obtained for the systems
investigated, namely: ML0, MLOH−, ML22−, M2L2(OH)−, and M2L2(OH)22−, for the dioxouranium(VI)–ODA system, and ML0, MLH+, and MLOH− for the dioxouranium(VI)–TODA system (M=UO22+ and L = ODA or TODA), respectively. The dependence on ionic strength of the protonation constants of ODA and TODA and of
both metal-ligand complexes was investigated using the SIT (Specific Ion Interaction Theory) approach. Formation constants
at infinite dilution are [for the generic equilibrium pUO22++q(L2−)+rH+
⇌(UO22+)
p
(L)
q
H
r
(2p−2q+r);β
pqr
]: log 10
β
110=6.146, log 10
β
11−1=0.196, log 10
β
120=8.360, log 10
β
22−1=8.966, log 10
β
22−2=3.529, for the dioxouranium(VI)–ODA system and log β
110=3.636, log 10
β
111=6.650, log 10
β
11−1=−1.242 for dioxouranium(VI)–TODA system. The influence of etheric oxygen(s) on the interaction towards the metal ion was
discussed, and this effect was quantified by means of a sigmoid Boltzman type equation that allows definition of a quantitative
parameter (pL
50) that expresses the sequestering capacity of ODA and TODA towards UO22+; a comparison with other dicarboxylates was made. A visible absorption spectrum for each complex reaching a significant percentage
of formation in solution (KNO3 medium) has been calculated to better characterize the compounds found by pH-metric refinement. 相似文献
13.
1. Results of thermodynamic and kinetic investigations for the different crystalline calcium carbonate phases and their phase
transition data are reported and summarized (vaterite: V; aragonite: A; calcite: C). A→C: T
tr=455±10°C, Δtr
H=403±8 J mol–1 at T
tr, V→C: T
tr=320–460°C, depending on the way of preparation,Δtr
H=–3.2±0.1 kJ mol–1 at T
tr,Δtr
H=–3.4±0.9 kJ mol–1 at 40°C, S
V
Θ= 93.6±0.5 J (K mol)–1, A→C: E
A=370±10 kJ mol–1; XRD only, V→C: E
A=250±10 kJ mol–1; thermally activated, iso- and non-isothermal, XRD
2. Preliminary results on the preparation and investigation of inhibitor-free non-crystalline calcium carbonate (NCC) are
presented. NCC→C: T
tr=276±10°C,Δtr
H=–15.0±3 kJ mol–1 at T
tr, T
tr – transition temperature, Δtr
H – transition enthalpy, S
Θ – standard entropy, E
A – activation energy.
3. Biologically formed internal shell of Sepia officinalis seems to be composed of ca 96% aragonite and 4% non-crystalline calcium carbonate.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
YOSHINORI TAKASHIMA KAZUYA SAKAMOTO YOSHIFUMI OIZUMI HIROYASU YAMAGUCHI SHIGEHIRO KAMITORI AKIRA HARADA 《Journal of inclusion phenomena and macrocyclic chemistry》2006,56(1-2):45-53
Cyclodextrins (α-CD, β-CD and 2,6-di-O-dimethyl-β-CD (DM-β-CD)) were found to form inclusion compounds with thiophenes (thiophene (T), bithiophene (2T)) in water and in crystalline states. The structures of α-CD–T, β-CD–2T, and DM-β-CD–2T inclusion complexes were determined by X-ray crystallography. DM-β-CD forms a 1:1 cage type complex with 2T. In contrast, β-CD formed 2:3 (CD:guest) complexes with thiophene and α-CD formed 2:3 complexes, both of the channel type. These inclusion complexes were found to polymerize by FeCl3 in the inclusion compounds in water. The products were formed poly-pseudo-rotaxane between cyclodextrins and poly(thiophene) characterized by IR, 1H-NMR and 13C CP/MAS NMR. The molecular weights of the poly-pseudo-rotaxanes with poly(thiophene) were determined by the MALDI-TOF mass spectra to be 3000–5000. In comparison between poly-pseudo-rotaxane (DM-β-CD–poly(thiophene)), authentic poly(thiophene) and the washed DM-β-CD–poly(thiophene) which was washed with DMF to dethread DM-β-CD, these poly-pseudo-rotaxane was characterized by Raman, UV–vis and fluorescence spectra. The maximum emission band of DM-β-CD–poly(thiophene) shifted to a shorter wavelength. The hypsochromic shift was derived from poly-pseudo-rotaxane with DM-β-CD. 相似文献
15.
Mandeep Singh Bakshi Navjot Kaur Rakesh Kumar Mahajan Jasmeet Singh Narpinder Singh 《Colloid and polymer science》2006,284(8):879-885
The cloud point (C
P) measurements of aqueous solutions of a triblock polymer (TBP) [(PEO)2.5(PPO)31(PEO)2.5], in the presence of varying amounts of cationic surfactants (monomeric and dimeric alkylammoniumbromides) covering premicellar to postmicellar regions, have been carried out. A plot of C
P vs surfactant concentration allowed us to evaluate apparent critical micelle concentration (cmc*), which has been found to decrease with an increase in the amount of salt. The cmc* values thus obtained in the absence and presence of salt allowed us to evaluate counterion binding (β) by using the Corrin–Harkins method. β values have been further used to evaluate the thermodynamic parameters of these ionic surfactants. The results suggest that the β values evaluated using this method, especially at low [TBP], are in good agreement with those already reported in the literature. 相似文献
16.
Sargaeva NP Lin C O'Connor PB 《Journal of the American Society for Mass Spectrometry》2011,22(3):480-491
Ion-electron reaction based fragmentation methods (ExD) in tandem mass spectrometry (MS), such as electron capture dissociation
(ECD) and electron transfer dissociation (ETD) represent a powerful tool for biological analysis. ExD methods have been used
to differentiate the presence of the isoaspartate (isoAsp) from the aspartate (Asp) in peptides and proteins. IsoAsp is a
β3-type amino acid that has an additional methylene group in the backbone, forming a Cα–Cβ bond within the polypeptide chain. Cleavage of this bond provides specific fragments that allow differentiation of the isomers.
The presence of a Cα–Cβ bond within the backbone is unique to β-amino acids, suggesting a similar application of ExD toward the analysis of peptides
containing other β-type amino acids. In the current study, ECD and ETD analysis of several β-amino acid containing peptides
was performed. It was found that N–Cβ and Cα–Cβ bond cleavages were rare, providing few c and z type fragments, which was attributed to the instability of the Cβ radical. Instead, the electron capture resulted primarily in the formation of a and y fragments, representing an alternative fragmentation pathway, likely initiated by the electron capture at a backbone amide
nitrogen protonation site within the β amino acid residues. 相似文献
17.
Chengkuan Qin Jinling Chai Jingfei Chen Yan Xia Xiaoying Yu Jing Liu 《Colloid and polymer science》2008,286(5):579-586
The phase behavior and the solubilization of the microemulsion systems surfactant-like ionic liquids 1-hexadecyl-3-methylimidazolium
bromide (C16mimBr), 1-tetradecyl-3-methylimidazolium bromide (C14mimBr), or 1-dodecyl-3-methylimidazolium bromide (C12mimBr)/alcohol/alkane/brine have been studied with ɛ–β-fish-like phase diagram method at 40 °C and an oil-to-water mass ratio of 1:1. From the ɛ–β-fish-like phase diagram, the physicochemical parameters, such as the mass fraction of alcohol in the hydrophile–lipophile-balanced
interfacial layer (A
S), and the solubilities of ionic liquid (S
O) and alcohol (A
O) in alkane phase, were calculated. The solubilization of the microemulsion system has been discussed based on the ɛ–β-fish-like phase diagram. The smaller the oil molecule, the longer the alcohol chain length, and the larger the NaCl concentration
in water, the larger the solubilization of the microemulsion system. In this paper, the solubilization of the microemulsion
stabilized by both C12mimBr and sodium dodecyl sulfonate (sodium dodecyl sulfate) was also investigated with the ɛ–β-fish-like phase diagram. The unequimolar composite of anionic and cationic surfactants can avoid the sedimentation aroused
by the strong electrostatic attraction, and an obvious synergism effect in solubilization was obtained. 相似文献
18.
Yttrium
orthoborate crystallizes in the vaterite-type structure and has two polymorphous
forms, viz. a low- und a high temperature one. DTA measurements of YBO3
confirmed a reversible phase transition with a large thermal hysteresis. The
phase transition has been accurately characterized by the application of different
heating and cooling rates (β). Consequently, the extrapolation of the
experimental data to zero β yields the transition points at 986.9°C
for the heating up and at 596.5°C for the cooling down cycle. These values
correspond to samples just after treatment at 1350°C. For samples with
a different ‘thermal history’ other phase transition temperatures
are observed, (e.g. after having performed several heating and cooling cycles).
The linear relationship between the associated DTA signal ΔT=T
onset–T
offset and the square root
of the heating rate β was confirmed, but the relation between T
onset and square root of β
is not found here.
From the empirical data a good linear fitting
between T
onset and
ln(β+1) can be derived.
From the kinetic analysis (Kissinger
method) of the phase transformation of YBO3 an apparent
activation energy of about 1386 kJ mol–1
for heating and of about 568 kJ mol–1 for
cooling can be determined 相似文献
19.
K. Chrissafis K. M. Paraskevopoulos C. Manolikas 《Journal of Thermal Analysis and Calorimetry》2006,84(1):195-199
The
thermal effect accompanying the transition of Cu2–xSe
into a superionic conduction state was studied by non-isothermal measurements,
at different heating and cooling rates (β=1, 2.5, 5, 10 and 20°C
min–1). During heating the peak temperature
(Tp) remains almost
stable for all values of β, (136.8±0.4°C for Cu2Se
and 133.0±0.3°C for Cu1.99Se). A gradual
shift of the initiation of the transformation towards lower temperatures is
observed, as the heating rate increases. During cooling there is a significant
shift in the position of the peak maximum (Tp)
towards lower temperatures with the increase of the cooling rate. A small
hysteresis is observed, which increases with the increase of the cooling rate, β.
The mean value of transformation enthalpy was found to be 30.3±0.8
J g–1 for Cu2Se and
28.9±0.9 J g–1 for Cu1.99Se.
The transformation can be described kinetically by the model f(ǯ)=(1–ǯ)n(1+kcatX), with activation energy E=175 kJ mol–1,
exponent value n equal to 0.2, logA=20 and log(kcat)=
0.5. 相似文献
20.
A new flow injection chemiluminescent immunoassay was developed for the detection of 17β-estradiol (E2). The method uses p–iodophenol (PIP) as enhancer and is based on a solid-phase immunoassay format in which an E2–OVA immobilized immunoaffinity column inserted in the flow system is used to trap unbound horseradish peroxidase (HRP)-labeled
anti-E2 antibody after an off-line incubation of E2 with HRP-labeled anti-E2 antibody. The trapped enzyme conjugate was detected by injecting substrates to produce an enhanced chemiluminescence (CL)
response. The linear range for E2 was 10.0–1,000.0 ng mL−1 with a correlation coefficient of 0.996 and a detection limit of 3.0 ng mL−1. The sampling and chemiluminescence detection time for one sample was 400 s after a pre-incubation procedure of 30 min. Serum
samples detected by this method were in good agreement with the results obtained by EIA with E2–biotin.
相似文献