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1.
M. G. Voronkov A. V. Vlasov N. N. Vlasova 《Russian Journal of Organic Chemistry》2010,46(12):1838-1842
Reactions of acetyl iodide with pyridine at room temperature and with quinoline both at 20–25°C and on cooling to −50°C involve
dehydrohalogenation of acetyl iodide with formation of ketene and pyridinium or quinolinium iodides. The reaction of acetyl
iodide with pyridine at −5 to −50°C led to the formation of N-acetylpyridinium iodide. Benzoyl iodide reacted with both pyridine and quinoline at both −50°C and at 20–25°C to form stable
N-benzoylpyridinium and N-benzoylquinolinium iodides. The reaction of pyrrole with acetyl iodide under analogous conditions was accompanied by polymerization. 相似文献
2.
Penna Thereza Christina Vessoni Chiarini Eb Machoshvili Irene Alexeevna Ishii Marina Pessoa Adalberto 《Applied biochemistry and biotechnology》2002,98(1-9):791-802
The recombinant green fluorescent protein (gfp
uv
) was expressed by Escherichia coli DH5-α cells transformed with the plasmid pGFPuv. The gfp
uv
was selectively permeabilized from the cells in buffer solution (25 mM Tris-HCl, pH 8.0), after freezing (−70°C for 15 h), by four freeze (−20°C)/thaw cycles interlaid by sonication. The average
content of released gfp
uv
(experiment 2) was 7.76, 34.58, 39.38, 12.90, and 5.38%, for the initial freezing (−70°C) and the first, second, third and
fourth freeze/thaw cycles, respectively. Superfusion on freezing was observed between −11°C and −14°C, after which it reached
−20°C at 0.83°C/min. 相似文献
3.
G. Bognár Cs. Pintér B. Horváth T. Sydo E. Ligeti J. Pulai D. Lőrinczy 《Journal of Thermal Analysis and Calorimetry》2009,95(3):769-774
Osteonecrosis (ON) of the femoral frequently occurs after steroid medication. One of the final pathways leading to steroid
induced ON is thought to be pathologic fat metabolism. The pathobiological mechanism underlying the induction of fat metabolism
outslides by steroids leading to ON has not been fully elucidated. The purpose of this study was to examine the intraoperative
obtained gluteal fat tissue from ON patients with histology, gas chromatography (GC) and differential scanning calorimetry
(DSC) and to compare them with otherwise healthy patient’s samples. The histological sections showed no significant differences
compared with the control group. GC revealed that fraction of saturated fatty acids decreased in ON samples from mean values
of controls of 24% to 21, the polyunsaturated fraction from 20 to 14%. The monounsaturated acids showed an increase from mean
rate of 52% of the controls to 65% of steroid treated samples. DSC curves correlate with chromatographic analysis of the tissue
fatty acids (Steroid treated, heating between 0–100°C: T
m=5.7°C, ΔH= −15.8J/g−1; heating between −20–100°C: Tm= −9.96 and 5.85°C, ΔH= −59.17 and −16.2 J g−1. Non-necrotic, heating between 0–100°C: two separable transition with Tm=5.7 and 9.9°C, total ΔH= −20.8 J g−1; heating between −20–100°C: Tm= −10.9 and 4.95°C, total ΔH= −75.8 J g−1.)
Our preliminary findings are rather tendentious. Further investigations are needed with higher sample rate and under other
anamnestic circumstances too. 相似文献
4.
The electrical conductivity of polycrystalline MgO between 350 and 750°C is determined by the transport of surface electronic
and hole defects and depends on the applied voltage. Near 620°C at low applied voltages, the conductivity decreases by 1–2
orders of magnitude in a narrow temperature range (ΔT = 75°C), and this is accompanied by a change of the sign of the surface charge carriers. The “ignition” of the catalytic
activity of magnesium oxide in free radical generation in radical chain hydrocarbon pyrolysis is observed in the same temperature
range. It is assumed that the change of the sign of the charge carriers is due to the existence of an isoelectric temperature
T
i
and that, at T > T
i
, OO· defects come out to the magnesium oxide surface. 相似文献
5.
3-Iodolevoglucosenone reacts with the sodium derivative of ethyl cyanoacetate at −60°C to give a tetrasubstituted cyclopropane
derivative; similar reactions of the sodium derivatives of ethyl acetoacetate and acetylacetone at −60 °C afford the expected
transformed Michael adducts, while at 20 °C,O,C-dialkylated products of the oxetene series are formed.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp 152–156, January, 1999. 相似文献
6.
Starch or pullulan was hydrolyzed using glucoamylase or pullulanase immobilized on N-isopropylacrylamide gel. The gel used is temperature sensitive; its mesh size becomes smaller at higher temperatures (30 °C)
and larger at lower temperatures (20 °C). The molecular weight distribution of starch is wide and it consists of high-molecular-weight
amylopectin, amylose and glucose. From the change in the chromatograms for the substrate and products, it was found that the
hydrolysis rate at 30 °C was faster than that at 20 °C for amylose, though it was the reverse for amylopectin. This finding
suggests that the smaller molecular sized amylose can enter the gel phase at both temperature, while the larger molecular
sized amylopectin can hardly do so; only the end group, which can partly enter the gel phase at 20 °C (larger mesh size),
was hydrolyzed. Further, several molecular weight pullulans (monodisperse) were hydrolyzed and the experimental chromatograms
for substrate and products confirm the hydrolysis mechanism estimated.
Received: 14 July 1998 Accepted in revised form: 26 August 1998 相似文献
7.
The sensitivity and precision of headspace solid-phase micro extraction (HS-SPME) at an analyte solution temperature (T
as) of +35 °C and a fiber temperature (T
fiber) of +5 °C were compared with those for HS-SPME at T
as and T
fiber of −20 °C for analysis of the volatile organic compounds benzene, 1,1,1-trichloroethane, trichloroethylene, toluene, o-xylene, ethylbenzene, m/p-xylene, and tetrachloroethylene in water samples. The effect of simultaneous fiber cooling and analyte solution freezing
during extraction was studied. The compounds are of different hydrophobicity, with octanol/water partition coefficients (Kow) ranging from 126 and 2511. During a first set of experiments the polydimethylsiloxane (PDMS) SPME fiber was cooled to
+5 °C with simultaneous heating of the aqueous analyte solution to +35 °C. During a second set of experiments, both SPME fiber
holder and samples were placed in a deep freezer maintained at −20 °C for a total extraction time of 30 min. After approximately
2 min the analyte solution in the vial began to freeze from the side inwards and from the bottom upwards. After approximately
30 min the solution was completely frozen. Analysis of VOC was performed by coupling HS-SPME to gas chromatography-mass spectrometry
(GC-MS). In general, i.e. except for tetrachloroethylene, the sensitivity of HS-SPME increased with increasing compound hydrophobicity
at both analyte solution and fiber temperatures. At T
as of +35 °C and T
fiber of +5 °C detection limits of HS-SPME were 0.5 μg L−1 for benzene, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene, 0.125 μg L−1 for toluene, and 0.025 μg L−1 for ethylbenzene, m/p-xylene, and o-xylene. In the experiments with T
as and T
fiber of −20 °C, detection limits were reduced for compounds of low hydrophobicity (Kow<501), for example benzene, toluene, 1,1,1-trichloroethane, and trichloroethylene. In the concentration range 0.5–62.5 μg
L−1, the sensitivity of HS-SPME was enhanced by a factor of approximately two for all compounds by performing the extraction
at −20 °C. A possible explanation is that freezing of the water sample results in higher concentration of the target compounds
in the residual liquid phase and gas phase (freezing-out), combined with enhanced adsorption of the compounds by the cooled
fiber. The precision of HS-SPME, expressed as the relative standard deviation and the linearity of the regression lines, is
increased for more hydrophobic compounds (Kow>501) by simultaneous direct fiber cooling and freezing of analyte solution. Background contamination during analysis is
reduced significantly by avoiding the use of organic solvents. 相似文献
8.
J. D. Menczel 《Journal of Thermal Analysis and Calorimetry》2000,59(3):1023-1027
Fibers drawn form poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole] (PBI) were studied by DSC and DMA. PBI is a high temperature polymer T
g is between 387 and450°C depending on the measurement technique used. The as-spun fiber is free of orientation. The oriented
fiber exhibits considerable dependence on whether the DSC measurements were carried out in free-to-shrink or fixed-length
modes. The β-relaxation is at 290°C, and was associated with loss of water. The γ-transition at 20°C was not identified, while
theδ-transition at –90°C seems to correspond to rotation of the m-phenylene ring.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Morphology of micron-sized monodispersed poly(butyl methacrylate)/polystyrene composite particles produced by seeded dispersion polymerization 总被引:1,自引:0,他引:1
In order to develop the seeded dispersion polymerization technique for the production of micron-sized monodispersed core/shell
composite polymer particles the effect of polymerization temperature on the core/shell morphology was examined. Micron-sized
monodispersed composite particles were produced by seeded dispersion polymerizations of styrene with about 1.4-μm-sized monodispersed
poly(n-butyl methacrylate) (Pn-BMA) and poly(i-butyl methacrylate) (Pi-BMA) particles in a methanol/water (4/1, w/w) medium in the temperature range from 20 to 90 °C. The composite particles,
PBMA/polystyrene (PS) (2/1, w/w), consisting of a PBMA core and a PS shell were produced with 2,2′-azobis(4-methoxy-2,4-dimethyl
valeronitrile) initiator at 30 °C for Pn-BMA seed and with 2,2′-azobis(isobutyronitrile) initiator at 60 °C for Pi-BMA seed. The polymerization temperatures were a little above the glass-transition temperatures (T
g) of both Pn-BMA (20 °C) and Pi-BMA (40 °C). On the other hand, when the seeded dispersion polymerizations were carried out at much higher temperatures than
the T
g of the seed polymers, composite particles having a polymeric oil-in-oil structure were produced.
Received: 14 October 1998 Accepted in revised form: 2 June 1999 相似文献
10.
Homopolymerization of methyl methacrylate (MMA) was carried out in the presence of triphenylstibonium 1,2,3,4-tetraphenyl-cyclopentadienylide
as an initiator in dioxane at 65°C±0·l°C. The system follows non-ideal radical kinetics (R
p
∝ [M]1·4 [I]0·44
@#@) due to primary radical termination as well as degradative chain-transfer reaction. The overall activation energy and average
value ofk
2
p
/k
t
were 64 kJmol−1 and 0.173 × 10−3 1 mol−1 s−1 respectively 相似文献
11.
Many semicrystalline polymers undergo a process of aging when they are stored at temperatures higher than their glass-transition
temperature (T
g). Syndiotactic polypropylene was quenched from the melt to −40 °C, crystallized from the glassy state at 20 or 40 °C and
stored at the respective temperature for different aging times up to 7200 h. A significant increase in the tensile modulus
and stress at yield and a decrease in strain at yield were observed for both aging temperatures. Differential scanning calorimetry
(DSC) scans of aged material showed an endothermic annealing peak 15–30 °C above the previous aging temperature, the maximum
temperature and enthalpic content of which increased with aging time. The position and the shape of the melting peak were
not affected by aging. Scans of the storage modulus obtained from dynamic mechanical analyser measurements indicated a softening
process starting at about 20 °C above the aging temperature and correlating with the annealing peak detected by DSC. Density
measurements and wide-angle X-ray scattering investigations revealed that neither the crystallinity increased significantly
nor did the crystal structure change. So the observed property changes induced by aging are attributed to microstructural
changes within the amorphous phase. Furthermore, it could be shown by annealing experiments carried out at 60 °C, that aging
above T
g is, analogous to aging below T
g (physical aging), a thermoreversible process.
Received: 18 September 2000 Accepted: 2 January 2001 相似文献
12.
Yu. V. Tomilov I. V. Kostyuchenko G. P. Okonnishnikova E. V. Shulishov E. A. Yagodkin O. M. Nefedov 《Russian Chemical Bulletin》2000,49(3):472-477
Hydrochlorination of spiro(1-pyrazoline-3,1′-cyclopropanes) proceeds regioselectively at the azocyclopropane group to form 3-(2-haloethyl)pyrazoline derivatives. If the latter contain a halogen atom in the heterocycle, they are readily converted into (2-haloethyl)pyrazole hydrohalides. Bromination of 3-cyanospiro(2-pyrazoline-5,1′-cyclopropane) withN-bromosuccinimide at 20°C proceeds with retention of the cyclopropane ring to form 3-bromo-3-cyanospiro(1-pyrazoline-5,1′-cyclopropane), which is converted into (2-bromoethyl)cyanopyrazole in ∼60% yield at ∼20°C after 3–4 days. 相似文献
13.
H. Bayram M. Önal G. Üstünışık Y. Sarıkaya 《Journal of Thermal Analysis and Calorimetry》2007,89(1):169-174
An industrial raw material taken from Sivrihisar (Eskişehir, Turkey) region was heat-treated at different temperatures in
the range of 100–1000°C for 2 h. The volumetric percentage of the particles having a diameter below 2 μm after staying in
an aqueous suspension of the material was determined as 67% by the particle size distribution analysis. The mineralogical
composition of the material was obtained as mass% of 32% palygorskite, 10% metahalloysite, 35% magnesite, 20% dolomite and
3% interparticle water by using the acid treatment, X-ray diffraction and thermal analysis (TG, DTA) data.
The temperature ranges were determined for the endothermic dehydrations for the interparticle water as 25–140°C, for the zeolitic
water as 140–320°C, and for the bound water as 320–480°C, in the palygorskite. The temperature range for the endothermic dehydroxylation
and exothermic recrystalization of the palygorskite is 780–840°C. The temperature range for the endothermic dehydroxylation
of the metahalloysite and calcinations of magnesite are coincided at 480–600°C. Dolomite calcined in the temperature range
of 600–1000°C by two steps. The zig-zag changes in the specific surface area (S/m2 g−1) and specific micro and mesopore volume (V/cm3 g−1) as the temperature increases were discussed according to the dehydrations in the palygorkskite, dehydroxylation of palygorskite
and metahalloysite, and calcinations in magnesite and dolomite. 相似文献
14.
A. O. Barabanova I. P. Tishchenko V. P. Glazunov T. F. Solov’eva I. M. Ermak 《Chemistry of Natural Compounds》2010,46(4):509-513
Polysaccharides isolated by successive extraction with water at 20 and 80°C from freshly collected and dried alga T. crinitus were compared. It was shown that the yield of polysaccharides from freshly collected alga was 40–44%; from dried material,
less than 25%. It was found that the amount of extracted polysaccharides and their molecular weights decreased upon storage
of dried alga for three years. Polysaccharides isolated from freshly collected and dried alga had identical structures and
were a mixture of κ/β- and a new X-type of carrageenan. It was shown that protein, the amount of which reached 24% in the extracts obtained at
20°C, was strongly bound to the carrageenan. The amino-acid compositions of the proteins associated with the polysaccharides
isolated at 20 and 80°C were identical and had an elevated content of serine, glutamic acid, glycine, and alanine. 相似文献
15.
Poly(styrenechromiumtricarbonyl) was synthesized by radical homopolymerization of styrenechromiumtricarbonyl in AcOEt at 50
°C in the presence of AIBN and triisobutylboron.
Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1319–1320, July, 2000. 相似文献
16.
The carborane–siloxane copolymers Dexsil 300, a 34.5% bis(dimethylsilyl)-m-carborane–65.5% dimethylsiloxane copolymer, and Dexsil 400, a 24.9% bis(dimethylsilyl)-m-carborane–50.8% dimethyl, 24.3% methylphenylsiloxane copolymer, were coated on fused silica capillary columns and their gas
chromatographic properties were evaluated. Their selectivity was evaluated using both Rohrschneider–McReynolds constants and
triacylglycerol indices. The bis(dimethylsilyl)-m-carborane unit turned out to be equivalent to two dimethylsiloxy units and one half of a diphenylsiloxy unit. The m-carborane unit was found to cause a 15–25 K shift in the elution temperature between 120 and 360 °C. The working range was
from 20 and 0 °C to 380 °C for Dexsil 300 and Dexsil 400, respectively. The column bleeding levels at 380 °C were below 20
and 15 pA for Dexsil 300 and Dexsil 400, respectively. 相似文献
17.
Submicron-sized, comparatively monodisperse poly (methyl methacrylate) particles were produced by dispersion polymerization
of methyl methacrylate with a poly(dimethylsiloxane)-based azoinitiator in supercritical carbon dioxide at 30 MPa for 24 h
at 65 °C. The initiator operated not only as a radical initiator but also as a colloidal stabilizer, and was named an “inistab”.
Received: 13 February 2001 Accepted: 20 June 2001 相似文献
18.
S. Olmez Aytas S. Akyil M. Eral 《Journal of Radioanalytical and Nuclear Chemistry》2004,260(1):119-125
Adsorptive behavior of natural clinoptilolite-rich zeolite from Balikesir deposites in Turkey was assessed for the removal
of uranium from aqueous solutions. The uranium uptake and cation exchange capacities of zeolite were determined. The effect
of initial uranium concentrations in solution was studied in detail at the optimum conditions determined before (pH 2.0, contact
time: 60 minutes, temperature: 20 °C). The uptake equilibrium is best described by Langmuir adsorption isotherm. Some thermodynamic
parameters (ΔH°, ΔS°, ΔG°) of the adsorption system were also determined. Application to fixation of uranium to zeolite was performed. The uptake
of uranium complex on zeolite followed Langmuir adsorption isotherm for the initial concentration (25 to 100 μg/ml). Thermodynamic
values of ΔG°, ΔS° and ΔH° found show the spontaneous and exothermic nature of the process of uranium ions uptake by natural zeolite.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
Stop-flow techniques are occasionally needed in combinations of LC-NMR and LC-MS. During the interval when there is no flow
on the column, axial diffusion of components not yet eluted can be expected to take place. In this paper the size of the band
broadening which is caused by diffusion during stop-flow has been determined for two peptides on reversed-phase packed micro
columns. Within a temperature range of 20–40 °C, stop-flow could be extended to 30 minutes for peptides having k values in the range of 0.7–5.1 with little increase in band width on 1.0 mm i.d. columns at isocratic conditions. Stop-flow
for 6 h at 20 °C increased the peak width of bradykinin and leucine-enkephalin by 25% and 60%, respectively, depending on
the secondary interactions of the peptides. The peak broadening increased with increasing temperature (from 20 to 40 °C),
as expected, and the impact was significant at stop-flow times larger than 2 h. Stop-flow during gradient elution resulted
in less increase in peak width than isocratic elution due to the peak compression obtained when re-entering the gradient.
At 20 °C the effective diffusion coefficients of leucine-enkephalin and bradykinin were determined to 6.5 × 10−7cm 2/s and 5.5 × 10−7 cm2/s, respectively, on the packed micro column. 相似文献
20.
R. Mu?oz Olivas Philippe Quevauviller O. F. X. Donard 《Fresenius' Journal of Analytical Chemistry》1998,360(5):512-519
Long term stability of organic selenium compounds (selenocystine, selenomethionine, trimethylselenonium ion) has been studied
over a one year period for 2 analyte concentrations: 25 and 150 μg/L Se, at pH 4.5 in the dark, under different storage conditions:
temperature of –20°C, 4°C, 20°C, 40°C; in Pyrex, Teflon, or polyethylene containers; in an aqueous matrix or in the presence
of a chromatographic counter ion (pentyl sulfonate at 10–4 mol/L concentration). Light effects have also been tested. The stability of the selenium species was monitored by HPLC-ICP/MS.
Storage conditions can drastically alter the stability of organic selenium species. Organoselenium compounds were shown to
be stable in the dark over a one year period in an aqueous matrix at pH 4.5 in Pyrex containers at both 4°C and 20°C. Pyrex
vials exposed to natural sunlight at room temperature resulted in a steady decrease of the selenoamino acid concentration.
Teflon containers caused losses of less than 25% at both 4° C and 20° C in the dark. However, polyethylene vials presented,
at all temperatures tested, a rapid decrease of the TMSe+ concentration. The stability of the Se species studied did not show significant differences between 4° C and 20° C in any
container material used. Storage of solutions at 40° C led to slight differences between the Pyrex and Teflon containers.
However, polyethylene presented a drastic decrease of the three species over time at this higher temperature. Solutions frozen
at –20° C in polyethylene vials did not stabilize the TMSe+ signal. Finally, concentrations and matrices of the samples did not significantly affect the stability of the species.
Received: 15 July 1996 / Revised: 14 July 1997 / Accepted: 18 July 1997 相似文献