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101.
Tritium exchange at C-8 of xanthosine, theobromine, 1-, 3- and 7-methylxanthine in water has been studied. The rates of detritiation of these compounds have been determined over a pH range at constant temperature. Several mechanisms of exchange involving various ionic forms of substrate operating at different pH have been suggested. 相似文献
102.
Magdalena Biesaga Elzbieta Stolarczyk Krystyna Pyrzyńska Marek Trojanowicz 《Analytical sciences》2002,18(2):151-154
The silica-based Fe(III)-protoporphyrin and Zn-tetraphenylporphyrin stationary phases were examined for the HPLC separation of anions. The retention of nine common inorganic anions as well as benzoate anion (BA) and its hydroxy analogues (HBA) was examined using tartrate, acetate, and succinate eluents. The retention factors of inorganic anions on the FeProP stationary phase were in the order Cl- < NO3- < ClO4- < I- < SCN- and for organic anions benzoate < p-hydroxybenzoate < m-hydoxybenzoate < o-hydroxybenzoate. The retention factors of organic anions examined for a ZnTPP column were in the order p-HBA < m-HBA < BA < o-HBA. 相似文献
103.
J. Magoński 《Journal of solution chemistry》1990,19(6):597-607
The significant role of the proton exchange and homoconjugation (formation of AHA– and A1HA
1
–
complexes) equilibria in protonic hetero systems (HA+A
1
–
) has been shown from analysis of published data and from my own simple experiments. It is concluded that there is a need to reconsider some basic hydrogen bond problems. One of these problems-the existence of heteroconjugates in polar solvents — has been verified and illustrated with suitable experimental evidence (IR and UV-VIS spectra). The most accepted experimental evidence for the double minimum potential in the hydrogen bridge has been questioned as being in disagreement with the equilibrium law. A simple relation between the heteroconjugation constant, the parent homoconjugation constants and the proton exchange constant is also postulated. This relation fulfills important theoretical requirements, however, it is not applicable in extreme cases.To the memory of Bogdan Przybyszewski. 相似文献
104.
Jolanta Obniska Krzysztof Kaminski Agnieszka Dzierzawska-Majewska 《Journal of fluorine chemistry》2006,127(3):417-425
A series of N-phenyl- and N-benzyl-2-azaspiro[4.4]nonane- and [4.5]decane-1,3-diones containing a fluoro or trifluoromethyl substituents at the aryl ring was synthesized and tested for their anticonvulsant activity in the maximal electroshock (MES) and subcutaneous metrazole (sc.Met) tests. Among them, the most active were N-benzyl derivatives with fluoro and trifluoromethyl substituents especially at position-2 of the aryl moiety. The introduction of the phenyl ring at the imide nitrogen atom resulted in less active compounds. The results obtained showed that incorporation of fluoro or trifluoromethyl substituents increased the anticonvulsant activity in comparison to respective chloro, methoxy or methyl analogues. Crystallographically obtained conformation for one active and two inactive derivatives with trifluoromethyl substituents at position-2 or -3 of phenyl ring were initially used for molecular electrostatic potentials (MEP) calculation. The MEP distribution at carbonyl oxygen atoms was different for active and inactive molecules. 相似文献
105.
ABSTRACT Novel chiral three-ring (R) enantiomers were synthesised using optically active (R)-(?)-2-octanol. Properties, such as the sequence of phases, the transition temperatures and enthalpies, were tested by a polarising optical microscope and differential scanning calorimeter. An antiferroelectric smectic phase (SmCA*) with a direct transition from the antiferroelectric to the isotropic phase (SmCA*-Iso) was observed for three esters with an achiral C3F7CH2O(CH2)3O– terminal chain. Bi- and multicomponent mixtures with a broad temperature range of the antiferroelectric phase and good electro-optical properties were formulated. Helical pitch of pure esters and mixtures was measured by spectrophotometry method. 相似文献
106.
Polyvinyl chloride samples of various tacticity have been prepared and photochlorinated in CCl4 for 4 hr. The chlorination degree correlates directly with the degree of syndiotacticity. Initial PVC with syndiotacticity about 56 per cent, which can be regarded as alternate sequences of syndiotactic and isotactic diads, is quickly chlorinated. The mechanism of chlorine attack on the macromolecula is directly connected with the stereoregularity. 相似文献
107.
Chibowski E Wiacek A Holysz L Terpilowski K 《Langmuir : the ACS journal of surfaces and colloids》2005,21(17):7662-7671
Electrical phenomena at nonionogenic hydrophobic surfaces (solid or liquid) in water, electrolyte, and/or surfactant solutions still attract research. In part 1 of this paper we described the electrokinetic behavior of paraffin wax suspension in water and electrolyte solutions (NaCl or LaCl3). On the basis of the latest data of water structure near hydrophobic surfaces it was concluded that immobilized water dipoles at the interface can play an essential role in the zeta potential formation. In this paper were investigated the zeta potentials of paraffin wax in cationic surfactants cetyltrimethylammonium bromide, C16H33(CH3)3NBr, and octadecyltrimethylammonium chloride, C18H37(CH3)3NCl, and anionic surfactant sodium dodecyl sulfate, C12H25SO4Na. Also changes in wettability of the paraffin surface due to the surfactant's adsorption were studied via wetting contact angle measurements and calculation of the surface free energy. It was concluded that at a low surfactant concentration (10(-6) M) the water dipole structure still contributes to the zeta potential, but at a higher one the zeta potential is determined by the surfactant molecules' adsorption. A special role of OH- ions is also clearly seen. Moreover, a functional relationship was found between the surface free energy of the surfactant-covered paraffin surface and the zeta potential. 相似文献
108.
Measurements of Rayleigh light scattering, nonlinear light scattering in DC magnetic fields, and the Cotton-Mouton effect were carried out for 15 mM NaCl and water solutions of ferritin at room temperature. The spherical geometry of the molecule implies that it is optically isotropic. Such a macromolecule should not manifest magnetic anisotropy; however, in solution it shows induced magnetic birefringence (Cotton-Mouton effect) and changes in the intensity of the scattered light components. The analysis of the obtained results indicates the deformation of linear optical polarizability induced in the ferritin by a magnetic field as the main source of the magneto-optical phenomena observed. Light scattering and the CM effects theoretically depend on the linear magneto-optical polarizability, chi, and the nonlinear magneto-optical polarizability, eta. Using the theory describing the phenomena as well as the experimental data, the values of the anisotropy of linear magneto-optical polarizability components, chi(parallel) - chi(perpendicular) = -(1.3 +/- 0.7) x 10(-22) [cm3] (in SI units chi(parallel) - chi(perpendicular) = -(2.0 +/- 1.2) x 10(-33) [m3]), the linear optical polarizability, alpha = (alpha(parallel) + 2alpha(perpendicular))/3 = (3.9 +/- 1.0) x 10(-20) [cm3] (in SI units alpha = (3.52 +/- 0.09)x10(-4) [Cm2 V(-1)]), and its anisotropy, kappa(alpha) = (alpha(parallel) - alpha(perpendicular))/3alpha = -(0.06+/-0.03), nonlinear magneto-optical polarizability, eta = (eta(parallel) + 2eta(perpendicular))/3 = -(4.7 +/- 0.9) x 10(-30) [cm3 Oe(-2)] (in SI units eta = -(6.7 +/- 1.3) x 10(-18) [Cm4 V(-1) A(-2)]) and its anisotropy, kappa(eta) = (eta[parallel) - eta(perpendicular))/3eta = -(0.15 +/- 0.10), were deduced. Here alpha(parallel), eta(parallel), alpha(perpendicular), eta(perpendicular) are the optical and magneto-optical polarizability components along the parallel and the perpendicular axes of the axially symmetric molecule, respectively. 相似文献
109.
Lead(II) 2,2'-bipyridine hexachloroplumba tetetrahydrate was synthesized and investigated by DTA, TG and DTG. IR spectroscopy
and other methods enabled the identification of some of the decomposition products. Comparative studies on the corresponding
chlorides: [Pb(bipy)]Cl2 and [Pb(bipy)3]Cl2, which can be considered as precursors of the hexachloroplumbate, were also undertaken. X-ray measurements enabled the tentative
determination of the crystal structure of [Pb(bipy)]Cl2. Hexachloroplumbate decomposes with the liberation of chlorine, water and organic ligands, and the process is accompanied
by the simultaneous transition of Pb(IV)→Pb(II). Chlorides release only ligands upon heating. Residues comprised always PbCl2.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
110.
Lewiński J Marciniak W Lipkowski J Justyniak I 《Journal of the American Chemical Society》2003,125(42):12698-12699
Studies on the reaction of zinc alkyls with O2 are reported which demonstrate that the selective oxygenation of organozinc compound is viable. The reaction of [EtZn(azol)]n (azol = deprotonated 1-aziridineethanol) with an excess of dry O2 in toluene affords the zinc ethylperoxide [EtOOZn(azol)]2[EtZn(azol)]2, while the analogous reaction between Me2Zn and O2 results in the isolation of the Me6Zn7(OMe)8 cluster in high yield. 相似文献