共查询到20条相似文献,搜索用时 15 毫秒
1.
Attila Sipos Miklós Tóth Franziska K. U. Mueller Jochen Lehmann Sándor Berényi 《Monatshefte für Chemie / Chemical Monthly》2009,140(4):473-478
Abstract The synthesis of 4H-thiochromene derivatives of apomorphines, a novel class of isoquinoline alkaloid-related compounds, has been achieved by
different O-dealkylation methods applied on previously published heteroring-fused aporphinoids. Detailed DFT study has been presented
regarding the mechanism of the L-selectride-mediated multiple O-dealkylation of a seven-ring aporphine analogue. Dopamine-binding tests confirmed the essential function of 11-hydroxy moiety
of the aporphine skeleton and revealed a remarkable D1 over D2 specificity for the derivative having the 4H-thiochromene ring system attached to positions 2 and 3 of the aporphine backbone.
Graphical Abstract
相似文献
Attila SiposEmail: |
2.
Ilana Abayev Arie Zaban Vladimir G. Kytin Alexey A. Danilin Germà Garcia-Belmonte Juan Bisquert 《Journal of Solid State Electrochemistry》2007,11(5):647-653
Results on the density of sates of nanostructured TiO2 as a function of particle size and temperature are reported. In TiO2 nanoparticles with a mean diameter 10 nm, the density of states (DOS) is strongly temperature-dependent, indicating a rearrangement
of the bandgap states in which the exponential energy parameter (width of the distribution) increases from 0.080 to 50 °C.
For nanoparticles with mean diameters of 20 and 30 nm the DOS is much closer to an exponential distribution, and is much less
sensitive to temperature variations. It is suggested that nanometer confinement has a significant influence on the density
of electronic states for 10-nm particles, while band tailing is similar to that occurring in bulk semiconductors for the larger
particles.
相似文献
Juan BisquertEmail: |
3.
Edward B. Nikitin Sanjeev K. Dey David A. Lightner 《Monatshefte für Chemie / Chemical Monthly》2009,140(1):97-110
Abstract Six 10-nor-bilirubin analogs have been synthesized and investigated. Lacking the C(10) CH2 group, these linear tetrapyrroles have a bipyrrole core rather than a dipyrrylmethane core and thus a different shape. Whereas
the propionic acid groups of bilirubin are well engaged in intramolecular hydrogen bonding to the dipyrrinones, molecular
modeling studies of the 10-nor-rubins predict that propionic acid chains are too short to engage the CO2H hydrogen fully in intramolecular hydrogen bonding with the dipyrrinones. Butyric acid chains, however, can and do lead to
a stabilized conformation with a bipyrrole dihedral angle of approximately 115°. Spectroscopic studies verify the predictions
and vapor pressure osmometry indicates that the 10-nor-rubins with butyric acids are monomeric in CHCl3.
Graphical abstract
相似文献
David A. LightnerEmail: |
4.
1. | It has been shown that, the lifetime of a negatively charged molecular ion, is related to the following molecular parameters: the electron affinity, the electronic-vibrational interaction constants, the active vibration frequencies, and the value of the nonadiabaticity. depends critically on the electron affinity, increasing monotonically as the latter rises. |
2. | The rate of ion breakdown along each of the decomposition channels increases with an increase in the energy of the impinging electron and/or the initial vibrational energy of the molecule. There is an increase in the number of breakdown channels under these same conditions, but it is not large. |
3. | The lifetime of the negatively charged molecular ion can be used to get a highly precise determination of the electron affinity of the molecule. |
4. | The distribution of emitted electrons over energies is essentially exponential, the characteristic width being given by /ln(E 1/E 1 Ne).). |
5.
Yan Gao Sabrina Reischmann Johannes Huber Tobias Hanke Rudolf Bratschitsch Alfred Leitenstorfer Stefan Mecking 《Colloid and polymer science》2008,286(11):1329-1334
Single semiconductor quantum dots were embedded into polymer particles with diameters below 0.1 μm by an emulsion polymerization
procedure or via a secondary dispersion approach. The photoluminescence properties of the nanocrystals are retained upon encapsulation,
as demonstrated by fluorescence confocal microscopy.
相似文献
Stefan MeckingEmail: |
6.
The molecular structure and vibrational characteristics of monomeric and dimeric tin diiodide, SnI2 and Sn2I4, were determined by high-level computational methods. For the dimer molecule two low-energy geometries were found, one with
C
s and the other with C
2v symmetry, the former with somewhat lower energy; their relative energy is strongly dependent on the computational method.
Thermodynamic functions for both species and their dimerization reaction were calculated based on the computed structures.
相似文献
Magdolna HargittaiEmail: |
7.
In the present work, an important point concerning the NEMCA effect is addressed. We analyse the reasons why the changes in the work function of the gas exposed catalyst-electrode surface are one to one related to the changes in the catalyst working electrode potential E with respect to a reference electrode. It is concluded that this is due to the unique properties of the catalyst/solid electrolyte interface: the structure of the double layer in this region is very different from that in liquid electrolytes, being the potential difference at this interface mainly determined by the specific adsorption of the mobile species in the solid electrolyte.
相似文献
Ezequiel P. M. LeivaEmail: |
8.
N. Bunjes S. Paul J. Habicht O. Prucker J. Rühe W. Knoll 《Colloid and polymer science》2004,282(8):939-945
Neutron reflectivity measurements have been performed with polystyrene (PS) brushes of different graft densities ranging from =0.020 to =0.051 in contact with toluene/methanol mixtures of different composition. The brushes were prepared by a grafting-from procedure resulting in linear chains of average molecular weight
n=300,000 g mol–1. The recorded reflectivity curves could be analyzed to a first approximation by assuming a flat scattering length density profile within the brush normal to the surface with a moderate Gaussian smearing of the interface brush/solvent. With increasing toluene content a substantial thickness increase was found with the swollen brush at 70 vol.% being 3.7 times thicker than the dry collapsed film. At low toluene contents the preferential incorporation of this good solvent for the PS brush exceeds a factor 3.5 relative to the molar ratio of the bulk solvent mixture with methanol.
相似文献
W. KnollEmail: |
9.
Hiroyuki Takeno Shin Nakazato Toshiaki Dobashi Masahiro Nobe Atsumi Wakabayashi 《Colloid and polymer science》2007,285(9):1029-1036
We investigated the self-assembling processes of solutions of poly(vinyl methyl ether) in mixed solvents of 2-butanone and
water with and without zirconium oxide (ZrO2) particles with average size of 75 nm during vaporization of the solvents by means of optical microscopy. The self-assembling
processes can be classified into three regimes: (1) early stage (nucleation and growth regime), (2) intermediate stage (regularly
arranged regime), and (3) late stage (aggregation and coalescence regime). In the intermediate stage, the water droplets,
including the ZrO2 particles, were regularly arranged with an almost constant spacing. The mechanism of the self-assembling processes is discussed
on the basis of experimental results.
相似文献
Hiroyuki TakenoEmail: |
10.
O. S. Morozova A. A. Kadushin V. A. Khalif E. L. Aptekar' L. Ya. Margolis O. V. Krylov 《Russian Chemical Bulletin》1976,25(4):722-725
1. | The surface of a SnO2-Sb2O4 catalyst is uniformly homogeneous with respect to the heats of adsorption of isobutylene. The heats vary from 50 to 20 kcal/mole as the degree of coverage is increased to 18% of a monolayer. |
2. | Isobutylene is adsorbed on SnO2-Sb2O4 in two forms: reversible (desorbed in the range 79–100° with Edes=21 kcal/mole) and irreversible. |
3. | Irreversibly chemisorbed isobutylene exists on the surface primarily in the form of the-methallyl complex. |
11.
The emission spectra of a series of molybdenum(II) chloride clusters containing thiolate ligands, [Mo6(μ3-Cl)8(SR)6]2− (R = Et, Bu, Ph, Bn), have been recorded. These complexes all show a broad emission at ~700 nm after excitation at 337, 400
and 410 nm. Determination of the excited state lifetimes and quantum yields of these complexes in acetonitrile reveals that
(Bu4N)2[Mo6(μ3-Cl)8(SPh)6] displays the longest excited state lifetime of this series (26 μs at 296 K).
相似文献
Lisa F. SzczepuraEmail: |
12.
José I. Martínez-López Héctor Moncada-Hernández Javier L. Baylon-Cardiel Sergio O. Martínez-Chapa Marco Rito-Palomares Blanca H. Lapizco-Encinas 《Analytical and bioanalytical chemistry》2009,394(1):293-302
Insulator-based dielectrophoresis (iDEP), an efficient technique with great potential for miniaturization, has been successfully
applied for the manipulation of a wide variety of bioparticles. When iDEP is applied employing direct current (DC) electric
fields, other electrokinetic transport mechanisms are present: electrophoresis and electroosmotic flow. In order to concentrate
particles, iDEP has to overcome electrokinetics. This study presents the characterization of electrokinetic flow under the
operating conditions employed with iDEP; in order to identify the optimal conditions for particle concentration employing
DC-iDEP, microparticle image velocimetry (μPIV) was employed to measure the velocity of 1-μm-diameter inert polystyrene particles
suspended inside a microchannel made from glass. Experiments were carried out by varying the properties of the suspending
medium (conductivity from 25 to 100 μS/cm and pH from 6 to 9) and the strength of the applied electric field (50–300 V/cm);
the velocities values obtained ranged from 100 to 700 μm/s. These showed that higher conductivity and lower pH values for
the suspending medium produced the lowest electrokinetic flow, improving iDEP concentration of particles, which decreases
voltage requirements. These ideal conditions for iDEP trapping (pH = 6 and σ
m = 100 μS/cm) were tested experimentally and with the aid of mathematical modeling. The μPIV measurements allowed obtaining
values for the electrokinetic mobilities of the particles and the zeta potential of the glass surface; these values were used
with a mathematical model built with COMSOL Multiphysics software in order to predict the dielectrophoretic and electrokinetic
forces exerted on the particles; the modeling results confirmed the μPIV findings. Experiments with iDEP were carried out
employing the same microparticles and a glass microchannel that contained an array of cylindrical insulating structures. By
applying DC electric fields across the insulating structures array, it was seen that the dielectrophoretic trapping was improved
when the electrokinetic force was the lowest; as predicted by μPIV measurements and the mathematical model. The results of
this study provide guidelines for the selection of optimal operating conditions for improving insulator-based dielectrophoretic
separations and have the potential to be extended to bioparticle applications.
Figure Comparison of experimental measurements and mathematical modeling of electrokinetic and dielectrophoretic effects on microparticles
相似文献
Blanca H. Lapizco-EncinasEmail: |
13.
T. N. Drebushchak M. A. Mikhailenko V. A. Drebushchak E. V. Boldyreva 《Structural chemistry》2007,18(4):449-456
The paper summarizes recent results on crystallization and characterization of two polymorphs of the sulfathiazole:pyridine
(1:1) adducts with substantially different space groups (P41 and P21/c) and packing. Intermolecular interactions in the adducts are compared. These two forms were obtained from solutions containing
different ratios of n-propanol, not participating directly in crystallization but obviously controlling the polymorphism, and pyridine. The adducts
are also formed by the contact of pure solid sulfathiazole (different polymorphs) with pyridine vapor. In air, the adducts
decompose giving initially the metastable polymorph I of sulfathiazole, and then the stable sulfathiazole-III.
相似文献
E. V. BoldyrevaEmail: |
14.
Conjugated C3 symmetric molecules have been pursued for their fluorescent and electrochemical properties. The synthesis of conjugated C3 symmetric aryl tripyrroles has been performed by a route featuring three steps from trimethyl 1,3,5-benzene tricarboxylate 6: copper-catalyzed cascade addition of vinylmagnesium bromide to convert the carboxylates into γ,δ-unsaturated ketones, Tsuji–Wacker olefin oxidations to form tris(1,4-dione) 9, and Paal–Knorr condensation with ammonia and different amines to furnish the final tripyrroles (30–60% yields). In addition, incomplete reaction of vinylmagnesium bromide to 6 provided benzoate 8 possessing two γ,δ-unsaturated ketones, which were similarly converted to 3,5-dipyrrolylbenzoates 11. The absolute fluorescence quantum yields (Φfl) and electrochemical properties of 5a–c and 11a–c were investigated. The Φfl are the first reported for such compounds and they ranged between 2 and 40%, contingent on structure and solvent polarity. Cyclic voltammetry revealed that the compounds could be both oxidized and reduced, albeit irreversibly. The oxidation potentials (Eox) varied between 0.73 V and 1.2 V and the reduction potentials (Ered) varied from −0.83 V to −1.36 V. The lowest redox processes were measured for the NH–pyrrole 5a. Moreover, tripyrrole 5a was air stable and on oxidative doping with ferric chloride exhibited a 50 nm bathochromic shift in its absorbance spectrum. 相似文献
15.
1. | Substituted thiazoles are formed when N-acyl--aminoketones are heated with thioacetic acid and ZnCl2 in ether dioxane or ethyl acetate. |
2. | The reaction of acetamidoacetone with thioacetic acid and ZnCl2 at 20° leads to 2,5-dimethyl-5-acetylmercapto-2-thiazoline. |
3. | -Formamidoketones are formed when-aminoketone hydrochlorides are heated with orthoformic ester. |
16.
H. P. Zhang L. C. Yang L. J. Fu Q. Cao D. L. Sun Y. P. Wu R. Holze 《Journal of Solid State Electrochemistry》2009,13(10):1521-1527
Recent progress in studies of several types of core-shell structured electrode materials, including TiO2/C, Si/C, Si/SiO
x
, LiCoO2/C, and LiFePO4/C nanocomposites, including details of their preparation and their electrochemical performance is briefly reviewed. Results
clearly show that the coating shell can effectively prevent the aggregation of the nanosized cores, which are the electrochemically
active materials. In addition, the diffusion coefficients of lithium ions can be increased, and the reversibility of lithium
intercalation and deintercalation is improved. As a result, the cycling behavior is greatly improved. The reviewed results
suggest that core-shell nanocomposites are a good starting point for further development of new promising electrode materials.
相似文献
Y. P. WuEmail: |
R. Holze (Corresponding author)Email: |
17.
Poly(ethylene oxides), PEO, end-capped with hexadecyl dimethylammonium, HDDMA+, and trimethylammonium hexyldimethylammonium, THA2+, changed distinctly the sol–gel transition of sodium montmorillonite dispersions. In the presence of HDDMA+-PEO 1,500 and 4,000, domains of sol with increased salt tolerance (c
k=550–1,000 mmol NaCl/l) were found at high polymer and low montmorillonite contents. The corresponding PEO of higher molar mass (20,000 and 35,000) led to extended fields of flocs. THA2+-PEO 1,500 formed attractive gels at polymer concentrations >2–5 g/l and montmorillonite contents >0.5%. These gels showed very high yield values. THA2+-PEO of higher molar mass acted as stabilizing agents. The salt tolerance was highest (300–750 mmol/l) in the presence of THA2+-PEO 20,000. The observed sol–gel diagrams reveal the interplay between polymer end-group fixation on the clay mineral particles, polymer conformation, and colloidal stabilization and destabilization mechanisms.
相似文献
G. LagalyEmail: Phone: +49-431-8807445Fax: +49-431-8801608 |
18.
19.
K. O. Hiller B. Masloch H. J. M?ckel 《Fresenius' Journal of Analytical Chemistry》1976,280(4):293-297
Aliphatische Di- und Polysulfide lassen sich im reverse-phase-Verfahren an einer chemisch gebundenen Octadecylphase (Micro-Pak-CH) mit MeOH-H2O als Eluens sauber trennen. Die qualitative Zuordnung der Peaks wird durch folgende Effekte vereinfacht:
Bei Auswahl eines geeigneten Eluensgradienten können homologe Reihen wie R
2
S
2 mit R = Methyl bis R = Hexyl oder R
2
S
x mit x = 2–7 mit einer Auflösung Res 2 zwischen allen Komponenten getrennt werden. 相似文献
1. | log k nimmt bei konstanter S-Zahl linear mit der C-Zahl zu; |
2. | log k nimmt bei konstantem Alkylrest linear mit der S-Zahl zu; |
3. | log k fällt linear mit zunehmendem Gehalt des Eluens an MeOH. |
20.
K. B. Piotrovskii M. P. Ronina G. F. Bannikov G. A. Nikiforov V. V. Ershov 《Russian Chemical Bulletin》1976,25(11):2285-2287
1. | Phenol-substituted silanes with formula RnSiPh4–n (R=[-(4-oxy-3,5-di-tert-butylphenyl)propoxy] group and n=1–4), especially RSiPh3, are effective polybutadiene oxidation inhibitors. |
2. | Maximum synergism in mixtures of RnSiPh4–n with N-phenyl--naphthylamine is observed with stoichiometric proportions of phenyl and amine groups in the mixture components, diminishing in the order R2SiPh2>RSiPh3-R3SiPh > R4Si. |