共查询到20条相似文献,搜索用时 250 毫秒
1.
Processes of direct and electrocatalytic (in the presence of electrochemically reduced Cp2TiCl2) reduction of three α-bromoketones containing the C(sp3)-Br or C(sp2)-Br bond, viz., 2-bromo-and 2,6-dibromo-4,4-dimethylcyclohexa-2,5-dien-1-ones and α-bromo-acetophenone, were studied by cyclic voltammetry
and preparative electrolysis. In all cases, the dissociative electron transfer proceeds via the concerted mechanism. Preparative electrolysis of these α-bromoketones in the presence of Cp2TiCl2 affords the reductive debromination products in 40–80% yield at low cathodic potentials (−0.85 V vs. Ag/AgCl/KCl). In the case of 2,6-dibromo-4,4-dimethylcyclohexa-2,5-dien-1-one in the potentiostatic regime, only one bromine
atom can be eliminated selectively.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 977–983, May, 2007. 相似文献
2.
Henning Wiberg Patrik Ek Frida Ekholm Pettersson Lars Lannfelt Åsa Emmer Johan Roeraade 《Analytical and bioanalytical chemistry》2010,397(6):2357-2366
We have investigated the use of isoelectric focusing and immunodetection for the separation of low molecular weight species
of amyloid-beta (Aβ) peptides from their aggregates. From solutions of Aβ1–40 or Aβ1–42 monomeric peptides, low molecular weight material appeared at a pI value of ca. 5, while the presence of aggregates was detected as bands, observed at a pI of 6–6.5. The formation of Aβ aggregates (protofibrils) was verified by a sandwich ELISA, employing the protofibril conformation-selective
antibody mAb158. In order to study the aggregation behavior when using a mixture of the monomers, we utilized the IEF separation
combined with Western blot using two polyclonal antisera, selective for Aβ1–40 and Aβ1–42, respectively. We conclude that both monomers were incorporated in the aggregates. In a further study of the mixed aggregates,
we used the protofibril conformation-selective antibody mAb158 for immunoprecipitation, followed by nanoelectrospray mass
spectrometry (IP-MS). This showed that the Aβ1–42 peptide is incorporated in the aggregate in a significantly larger proportion than its relative presence in the original
monomer composition. IP-MS with mAb158 was also performed, and compared to IP-MS with the Aβ-selective antibody mAb1C3, where
a monomeric Aβ1–16 peptide was added to the protofibril preparation. Aβ1–16 is known for its poor aggregation propensity, and acted therefore as a selectivity marker. The results obtained confirmed
the protofibril conformation selectivity of mAb158. 相似文献
3.
E. V. Starodubtseva O. V. Turova M. G. Vinogradov L. S. Gorshkova V. A. Ferapontov 《Russian Chemical Bulletin》2005,54(10):2374-2378
The rate of hydrogenation of γ-ketoesters MeCOCH2CH2COOR (R = Et, Pri, But) in the presence of the chiral RuII—BINAP catalyst (BINAP is 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) greatly increases upon the addition of 5–10 equivalents
of HCl with respect to ruthenium. In the hydrogenation of ethyl levulinate, the optically active γ-hydroxy ester initially
formed would cyclize by ∼95% to give γ-valerolactone with optical purity of 98–99% ee. When the Ru(COD)(MA)2—BINAP—HCl catalytic system is used (COD is 1,5-cyclooctadiene, MA is 2-methylallyl), complete conversion of the ketoester
(R = Et) in EtOH is attained in 5 h at 60 °C under an H2 pressure of 60–70 atm.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2301–2304, October, 2005. 相似文献
4.
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
5.
Ulrich Englich Ingo Prass Karin Ruhlandt-Senge Thorsten Schollmeier Frank Uhlig 《Monatshefte für Chemie / Chemical Monthly》2002,133(7):931-943
Summary. Hydrido substituted stannasilanes of the type or (Z = H, Me, Ph; R, R′ = alkyl, Ph) are accessible by reaction of either alkali metal stannides (MSn(Z)R
2; M = Li, Na) with halogen substituted silanes (; X = F, Cl) or chlorostannanes (R
2SnCl2, Ph3SnCl) and fluorosilanes in the presence of magnesium. Stannasilanes with halogen substituents at the silicon as well as the tin atom are formed by
treatment of the hydrido substituted stannasilanes with CHCl3 or CCl4. The hydrido substituted stannasilanes decompose in contact with air to distannanes and siloxanes or to the linear (
t
Bu2Sn(–O–
t
Bu2Si–OH)2) and cyclic ((–
t
Bu2Sn–O–
i
Pr2Si–O–)2) stannasiloxanes.
Received November 29, 2001. Accepted (revised) January 16, 2002 相似文献
6.
S. Ch. Gagieva T. A. Sukhova D. V. Savinov V. A. Tuskaev K. A. Lyssenko N. M. Bravaya Yu. N. Belokon’ B. M. Bulychev 《Russian Chemical Bulletin》2006,55(10):1794-1802
New representatives of chelate-type titanium(IV) salicylideneaniline complexes with bis(5-methyl-2-furyl)methyl substituents in the aniline fragment are synthesized. In
the presence of poly(methylalumoxane), these complexes catalyze ethylene and propylene polymerization. The effect of the position
of substituents in the ligands on the activities of the catalysts is studied. High-molecular-weight linear polyethylene (M
w ≈ 172200–300000, M
w/M
n ≈ 2–3) and high-molecular-weight atactic elastic polypropylene (M
w ≈ 1000000, M
w/M
n ≥ 7.0) are obtained.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1730–1737, October, 2006. 相似文献
7.
A. I. Ilovaisky V. M. Merkulova Yu. N. Ogibin G. I. Nikishin 《Russian Chemical Bulletin》2005,54(7):1585-1592
Electrolysis of salts of primary and secondary nitro compounds (nitroethane, 1- and 2-nitropropanes, nitrocyclohexane, and
nitrocycloheptane) in the presence of excess halide, nitrite, cyanide, and phenylsulfinate anions under undivided and divided
amperostatic electrolysis conditions in a two-phase medium (CH2Cl2/H2O) produces geminal nitrohalides (35–85% yields), dinitro compounds (15–51%), nitronitriles (6–27%), and nitrosulfones (50–70%).
The salts of secondary nitro compounds form the products of oxidative coupling with halide and phenylsulfinate anions under
the undivided electrolysis conditions. In all other cases, divided electrolysis is required.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1539–1546, July, 2005. 相似文献
8.
S. V. Basenko I. A. Gebel M. G. Voronkov L. V. Klyba R. G. Mirskov 《Russian Chemical Bulletin》1998,47(8):1571-1573
Methyl(vinyl)dichlorosilane reacts with DMSO in the presence of hexamethyldisiloxane to give the corresponding linear oligosiloxanes
of the general formula Me3Si(OSiMeVin)
n
OSiMe3 (n=1–6) as well as MeSi(OSiMe3)3 and Me3Si(MeOSiVin)
m
OSi(OSiMe3)(Me)OSiMe3 (m=1–2). The same reaction in the presence of chlorotrimethylsilane results in oligomers of the general formula Me3Si(OSiMeVin)
n
Cl (n=1–3). A possible scheme of their formation is discussed.
Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1614–1616, August, 1998. 相似文献
9.
The kinetics of the solvolytic aquation of trans-[Ru (3-Me Py)4Cl2] was studied spectrophotometrically in water – isopropanol in the range (30–90% v/v), and water acetonitrile in the range
(10–70% v/v), and in the temperature range 50–65 °C. Plots of log k versus the reciprocal of the relative permittivity and Grunwald–Winstien gave non-linear plots. This non-linearity is derived from
a large differential effect of solvent structure between the initial and transition states. The plot of log k versus water concentration was also non linear; evidence for the presence of a S
N
1
mechanism. However, extrema in the variation of enthalpy ΔH* and entropy ΔS* of activation correlate well with the extrema in physical properties of the mixtures which are related to changes in solvent
structure. Linear plots of ΔH* versus ΔS* were obtained and the iso- kinetic temperature indicates that the reaction is entropy controlled. 相似文献
10.
Sumera Mahboob Rohama Gill Muhammad Mazhar Gabriele Kociok-Köhn Kieran C. Molloy 《Monatshefte für Chemie / Chemical Monthly》2008,139(9):1019-1024
A series of trichlorogermyl-substituted dicarboxylic acids of general formula HOOC–R′–COOH where R′=–CH2CH(GeCl3)CH2– 1, –CH(CH2GeCl3)CH2– 2, –CH(GeCl3)CH2– 3 and –CH(CH3)CH(GeCl3)– 4 were synthesized by the hydrogermylation reaction of unsaturated acids, such as trans-glutaconic (2-pentenedioic acid), itaconic (methylenebutanedioic acid), fumaric (2-butenedioic acid), and citraconic (2-methyl-2-butenedioic
acid) acids with HGeCl3, which was produced in situ by the reaction of GeO2 with 37% HCl in presence of NaH2PO2 · H2O. All these compounds were characterized by melting point, CHN analysis, FTIR, and multinuclear NMR (1H; 13C; H,H-COSY). X-Ray crystal structures of 1 and 2 were analyzed to show supramolecular structures in which central Ge atom in each of these structures is four-coordinated
with a slightly distorted tetrahedral geometry. Structurally, both compounds adopt supramolecular forms via strong intermolecular O–H–O interactions through 8-membered and 22-membered hydrogen bonded rings.
Supplementary material to this paper is available in electronic form at
Correspondence: Muhammad Mazhar, Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan. 相似文献
11.
V. Kharton A. Kovalevsky E. Tsipis A. Viskup E. Naumovich J. Jurado J. Frade 《Journal of Solid State Electrochemistry》2002,7(1):30-36
Deficiency in the A sublattice of perovskite-type Sr1–
y
Fe0.8Ti0.2O3–δ (y=0–0.06) leads to suppression of oxygen-vacancy ordering and to increasing oxygen ionic conductivity, unit cell volume, thermal
expansion, and stability in CO2-containing atmospheres. The total electrical conductivity, predominantly p-type electronic in air, decreases with increasing
A-site deficiency at 300–700 K and is essentially independent of the cation vacancy concentration at higher temperatures.
Oxygen ion transference numbers for Sr1–
y
Fe0.8Ti0.2O3–δ in air, estimated from the faradaic efficiency and oxygen permeation data, vary in the range from 0.002 to 0.015 at 1073–1223 K,
increasing with temperature. The maximum ionic conductivity was observed for Sr0.97Fe0.8Ti0.2O3–δ ceramics. In the system Sr0.97Fe1–
x
Ti
x
O3–δ (x=0.1–0.6), thermal expansion and electron-hole conductivity both decrease with x. Moderate additions of titanium (up to 20%) in Sr0.97(Fe,Ti)O3–δ result in higher ionic conductivity and lower activation energy for ionic transport, owing to disordering in the oxygen sublattice;
further doping decreases the ionic conduction. It was shown that time degradation of the oxygen permeability, characteristic
of Sr(Fe,Ti)O3–δ membranes and resulting from partial ordering processes, can be reduced by cycling of the oxygen pressure at the membrane
permeate side. Thermal expansion coefficients of Sr1–
y
Ti1–
x
Fe
x
O3–δ (x=0.10–0.60, y=0–0.06) in air are in the range (11.7–16.5)×10–6 K–1 at 350–750 K and (16.6–31.1)×10–6 K–1 at 750–1050 K.
Electronic Publication 相似文献
12.
Prithwiraj Byabartta 《Transition Metal Chemistry》2007,32(8):1007-1011
Reaction of [Au(C6F5)(tht)2Cl](OTf) with RaaiR′ in CH2Cl2 medium leads to [Au(C6F5)(RaaiR′)Cl](OTf) [RaaiR′ = p-R–C6H4–N=N–C3H2–NN-1-R′, (1–3), abbreviated as N,N′-chelator, where N(imidazole) and N(azo) represent N and N′, respectively; R = H (a), Me (b), Cl (c) and R′ = Me (1), CH2CH3
(2), CH2Ph (3), tht is tetrahydrothiophen]. The maximum molecular peak of [Au(C6F5)(MeaaiMe)Cl] is observed at m/z 599.51 (100 %) in the FAB mass spectrum. Ir spectra of the complexes show –C=N– and –N=N– stretching near at 1590 and 1370 cm−1 and near at 1510, 955, 800 cm−1 due to the presence of pentafluorophenyl ring. The 1H-NMR spectral measurements suggest methylene, –CH2–, in RaaiEt gives a complex AB type multiplet while in RaaiCH2Ph shows AB type quartets. 13C-NMR spectrum of complexes confirm the molecular skeleton. In the 1H-1H-COSY spectrum as well as contour peaks in the 1H-13C HMQC spectrum for the present complexes, assign the solution structure and stereoretentive conformation. The electrochemistry
gives the ligand reduction peaks. 相似文献
13.
M. V. Tsodikov V. Ya. Kugel' E. V. Slivinskii Yu. A. Egorov V. P. Mordovin 《Russian Chemical Bulletin》1998,47(7):1322-1326
The influence of the composition of catalytic systems and the method for H2 feed into the reaction area on the degree of conversion of CO2 during its joint transformations with ethanol and on the selectivity of formation of liquid organic products (ethyl acetate,
acetaldehyde, and hydrocarbons) was studied atp=15 atm andT=573 K. A noticeable conversion of CO2 and ethanol into ethyl acetate and acetaldehyde was observed in the presence of only the intermetallic compound, its composition
with a palladium-containing catalyst, and the whole ternary catalytic system. The selectivity of the reaction changed when
the binary catalytic composition consisting of the intermetallic and γ-Al2O3 was used. In this case, the fraction of C9–C14 alkenes and alkenes with normal and iso structures was mostly formed; its content was as high as 40%. The degree of conversion
of CO2 reached 30–36% and the selectivity to liquid products was 70–80% only when the hydrogen desorbed from the intermetallic was
used.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1360–1364, July, 1998. 相似文献
14.
New divalent transition metal 3,5-pyrazoledicarboxylate
hydrates of empirical formula Mpz(COO)2(H2O)2,
where M=Mn, Co, Ni, Cu, Zn and Cd (pz(COO)2=3,5-pyrazoledicarboxylate),
metal hydrazine complexes of the type Mpz(COO)2N2H4
where M=Co, Zn or Cd and Mpz(COO)2nN2H4·H2O,
where n=1 for M=Ni
and n=0.5 for M=Cu
have been prepared and characterized by physico-chemical methods. Electronic
spectroscopic data suggest that Co and Ni complexes adopt an octahedral geometry.
The IR spectra confirm the presence of unidentate carboxylate anion (Δν=νasy(COO–)–νsym(COO–)>215
cm–1) in all the complexes and bidentate
bridging hydrazine (νN–N=985–950 cm–1)
in the metal hydrazine complexes. Both metal carboxylate and metal hydrazine
carboxylate complexes undergo endothermic dehydration and/or dehydrazination
followed by exothermic decomposition of organic moiety to give the respective
metal oxides as the end products except manganese pyrazoledicarboxylate hydrate,
which leaves manganese carbonate. X-ray powder diffraction patterns reveal
that the metal carboxylate hydrates are isomorphous as are those of metal
hydrazine complexes of cobalt, zinc and cadmium. 相似文献
15.
Voltammetry and electrochemical impedance spectroscopy were applied to investigate the inhibition activity of ethyleneglycol
and its oligomers on tin electrode in strong acidic sulfate solutions. Tetraethyleneglycol was found to be the most active
substance among compounds HO–(CH2–CH2–O)
m
–H (m≤4) that retards diffusion-controlled Sn(II) reduction due to its inhibitive adsorption. This rather slow process is controlled
both by diffusion and electrosorption steps. A comparison of exchange current densities obtained in the presence of different
polyethers shows that the length of the hydrocarbon chain is the main factor responsible for inhibition activity of such substances
on tin electrode. 相似文献
16.
Mingqi Ao Peipei Huang Guiying Xu Xiaodeng Yang Yajing Wang 《Colloid and polymer science》2009,287(4):395-402
The aggregation behavior and thermodynamic properties of micellization for the ionic liquid-type gemini imidazolium surfactants
with different spacer length ([C12–s–C12im]Br2, s = 2, 4, 6) have been investigated by means of surface tension, electrical conductivity, dynamic light scattering and fluorescence
measurements. The values of cmc, γ
cmc, Γ
max, A
min, π
cmc, pc20 and cmc/pc20 suggest that the shorter the spacer, the higher the surface activity of [C12–s–C12im]Br2 is. The cmc and γ
cmc values are decreased significantly in the presence of sodium halides, and the values decrease in the order NaCl < NaBr < NaI.
The thermodynamic parameters of micellization (, , ) indicate that the micellization of [C12–2–C12im]Br2 and [C12–4–C12im]Br2 is entropy-driven, whereas aggregation of [C12–6–C12im]Br2 is enthalpy-driven at lower temperature but entropy-driven at higher temperature. Finally, the fluorescence measurements
show that the micropolarity of micelles increases but the aggregation numbers decrease with increasing the spacer length of
[C12–s–C12im]Br2. 相似文献
17.
A. O. Terent'ev A. V. Kutkin M. M. Platonov Z. A. Starikova Yu. N. Ogibin G. I. Nikishina 《Russian Chemical Bulletin》2005,54(5):1214-1218
A procedure was developed for the synthesis of 1,1′-bishydroperoxydi(C11-C15-cycloalkyl) peroxides based on homocoupling of geminal 11–15-membered bis(hydroperoxy)cycloalkanes in the presence of BF3⋅OEt2.
Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1182–1185, May, 2005. 相似文献
18.
Gigantic colloidal single crystals (2–6 mm) are formed for fluorine-containing polymer spheres (120–210 nm in diameter) in
exhaustively deionized aqueous suspensions. The spheres used are poly(tetrafluoroethylene) (PTFEA and PTFEB), copolymer of
tetrafluoroethylene and perfluorovinylether (PFA) and copolymer of tetrafluoroethylene and perfluoropropylene (PTP). The phase
diagrams of these spheres are obtained in the deionized suspensions and also in the presence of sodium chloride for PFA. The
critical sphere concentrations of crystal melting (φ
c) for these spheres are around 0.0006 in volume fraction, which are close to, but slightly larger than, those of monodispersed
polystyrene spheres (φ
c ≈ 0.00015) and colloidal silica spheres(φ
c = 0.0002–0.0004) reported previously. The crystals are largest when the sphere concentrations are a bit higher than the φ
c value and their size decreases as the sphere concentration increases. Reflection spectra are taken in sedimentation equilibrium
as a function of the height from the bottom of the suspension. The static elastic modulus is estimated to be 10.8 and 28.7 Pa
for PTFEA and PTP spheres at the sphere concentrations 0.00325 and 0.00322 in volume fraction, respectively.
Received: 27 October 1999 Accepted in revised form: 16 November 1999 相似文献
19.
Issa Yavari Nasir Iravani S. Zahra Sayyed-Alangi Rahimeh Hajinasiri 《Monatshefte für Chemie / Chemical Monthly》2009,35(1):1199-1204
Abstract
An efficient synthesis of alkyl acylcarbamodithioates by reaction of acid chlorides with ammonium thiocyanate in the presence of thiols is described. The unusually large values of 5 J FH = 12–15 Hz, observed for alkyl (2-fluorobenzoyl)carbamodithioates provide information about Ar–C–N–H torsion in these compounds. 相似文献20.
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