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91.
A new approach for studying the effect of temperature on electrochemical processes is presented in this paper. Using an in-house developed electrode holder, experiments are performed under conditions of applied and controlled electrode temperature. This new approach provides an improved temperature control during the experimental study and, additionally, allows distinguishing both the influences of the electrolyte and electrode temperatures. The advantages of the applied electrode temperature approach are illustrated by considering porous anodizing of aluminium. In a broad temperature range the electrochemical behaviour of the aluminium electrodes, recorded during the new and the conventional way of anodizing, are compared. Differences between the anodic potential evolutions in both approaches are observed, and are explained by a heat flux to the surroundings during the experiments at uncontrolled electrode temperature. These results illustrate the advantage of applying the electrode temperature. If the influence of temperature on a process is investigated by merely varying the electrolyte temperature, the electrode temperature is only indirectly influenced and can significantly differ from the electrolyte temperature. Therefore, when evaluating the influence of temperature on an electrochemical system the electrode temperature should be considered, and preferentially also controlled. 相似文献
92.
Schmidt D Conrad J Klaiber I Beifuss U 《Chemical communications (Cambridge, England)》2006,(45):4732-4734
5-Hydroxy-3-oxopent-4-enoic acid esters can be efficiently transformed into the stable bis-potassium salts of the corresponding 5-hydroxy-3-oxopent-4-enoic acids, from which the sensitive acids are released in situ, the latter being converted into substituted 4-hydroxy-2H-pyran-2-ones, pyrazoles and isoxazoles under mild conditions; the efficiency of this method is demonstrated by the first synthesis of two naturally occurring pyrones. 相似文献
93.
Iron complexes of porphyrins (and corroles to a lesser extent) are the first catalysts to utilize ammonia for the synthesis of N-free amino acid esters. 相似文献
94.
95.
Rudzevich Y Rudzevich V Schollmeyer D Thondorf I Böhmer V 《Organic & biomolecular chemistry》2006,4(21):3938-3944
The crystal structure of the homodimer formed by the tritolylurea 3a proves the existence of a belt of six bifurcated hydrogen bonds between both NH and the O=C groups of the adjacent urea residues. For the tritosylurea 3b, four additional three-center hydrogen bonds, also involving the SO2 oxygen, are found in the crystalline state. Molecular dynamics simulations in a chloroform box confirm these patterns of the hydrogen bonds and the resulting elongation of the dimer 3b. 3b in comparison to 3a x 3a. The calculated complexation energies for the three dimeric combinations are nearly identical in agreement with the simultaneous formation of heterodimer 3a x 3b in a mixture of 3a and 3b. 相似文献
96.
The dithiol trypanothione can reduce an antiparasitic pentavalent antimony agent to trivalent rapidly; this reduction process is both pH and temperature dependent and trypanothione may therefore play an important role in the activation of the drug. 相似文献
97.
Oleg Kasyan Iris Thondorf Michael Bolte Vitaly Kalchenko Volker Bhmer 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(5):o289-o294
The structures of three syn‐1,3‐dialkoxythiacalix[4]arenes with unusual conformations in the solid state are reported. The pinched cone conformation of syn‐22,42‐dihydroxy‐12,32‐bis(prop‐2‐enyloxy)thiacalix[4]arene, C30H24O4S4, (3a), is stabilized by two intramolecular hydrogen bonds, remarkably formed from both OH groups to the same ether O atom. In syn‐22,42‐dihydroxy‐15,25,35,45‐tetranitro‐12,32‐bis(prop‐2‐enyloxy)thiacalix[4]arene acetone disolvate, C30H20N4O12S4·2C3H6O, (3b1), the molecule is found in the 1,3‐alternate conformation. The crystallographic C2 symmetry is due to a twofold rotation axis running through the centre of the calixarene ring. The hydroxy groups cannot form intramolecular hydrogen bonds as in (3a) and both are bonded to an acetone solvent molecule. The molecule of the pseudo‐polymorph of (3b1) in which the same compound crystallized without any solvent, viz. (3b2), is located on a crystallographic mirror plane. Only one of the two hydroxy groups forms a hydrogen bond, and this is with a nitro group of a neighbouring molecule as acceptor. Molecular mechanics calculations for syn‐1,3‐diethers suggest a preference of the 1,3‐alternate over the usual cone conformation for thiacalix[4]arene versus calix[4]arene and for para‐nitro versus para‐H derivatives. 相似文献
98.
A catalytic DNA-templated reaction of hydrolysis of an ester group in an N-modified peptide nucleic acid, which is activated by a Cu2+ complex-PNA, has been discovered and optimized. Both the ester-containing PNA and the metal complex PNA bind neighboring sites on a template DNA. This brings the reacting groups (the ester and the Cu2+ complex) in proximity to each other and accelerates the hydrolysis of the ester approximately 500 times in comparison with its hydrolysis in the absence of the template. The hydrolysis reaction provides >10(2)-fold kinetic discrimination between DNAs that are different from each other at a single nucleotide position. Natural enzyme T4 DNA ligase is slightly less selective. On the basis of this reaction a fully homogeneous and sensitive assay for sequence-specific DNA detection has been developed (10 fmol DNA). Identification of one of four DNAs (variation at one position) can be done in a single experiment. Since the Cu2+ ion is tightly bound in an associate containing the ester PNA, the metal complex PNA, and the template DNA, application of this method in buffers containing other Cu2+-binding ligands, e.g., PCR buffer and physiological buffer, is possible. 相似文献
99.
Miroslav Novakovic Iris Djordjevic Nina Todorovic Snezana Trifunovic Boban Andjelkovic Boris Mandic 《Natural product research》2019,33(19):2837-2844
New aurone epoxide, 2,10-oxy-10-methoxysulfuretin (14), and new auronolignan (15), named cotinignan A, were isolated by silica gel column and semipreparative HPLC chromatography from the methylene chloride/methanol extract of Cotinus coggygria Scop. heartwood. In addition, thirteen known secondary metabolites namely sulfuretin, 2,3-trans-fustin, fisetin, butin, butein, taxifolin, eriodictyol, 3',5,5',7–tetrahydroxyflavanone, 3',4',7-trihydroxyflavone, 3-O-methyl-2,3-trans-fustin, 3-O-galloyl-2,3-trans-fustin, β-resorcylic acid and 3-O-β-sitosterol glucoside were isolated as well. Their structures were elucidated by 1D and 2D NMR, HR-ESI-MS, IR and UV. Ten out of eleven isolated flavonoids possess 7, 3' and 4' hydroxy groups. These structural features could be considered as chemotaxonomic characteristic of flavonoids from C. coggygria. Cotinignan A (15) represents new subclass of secondary metabolites - auronolignans.
100.
Scheele I Conjusteau A Callegari C Schmied R Lehmann KK Scoles G 《The Journal of chemical physics》2005,122(10):104307
The nu(5)+nu(9) spectra of ethylene, C(2)H(4), and its dimer, solvated in helium nanodroplets, have been recorded in the wavelength region near 1.6 microm. The monomer transitions show homogeneous broadening of approximately 0.5 cm(-1), which is interpreted as due to an upper state vibrational relaxation lifetime of approximately 10 ps. Nearly resonant vibrational energy transfer (nu(5)+nu(9)-->2nu(5)) is proposed as the relaxation pathway. The dimer gives a single unresolved absorption feature located 4 cm(-1) to the red of the monomer band origin. The scaling of moments of inertia upon solvation in helium is 1.18 for the monomer and >2.5 for the dimer. In terms of the adiabatic following approximation, this classifies the monomer as a fast rotor and the dimer as a slow rotor. 相似文献