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971.
HPLC impurity profile method development for a doxorubicin-heptapeptide conjugate included significant changes of the separation profile with diluent, eluent and pH. These separation variables were also temperature-dependent with a shift in retention from 35 to 45 degrees C. There was also a direct relationship of temperature with LC retention, and a pH minimum at 5.9. Atypical dependence of the impurity profile on diluent at a k' of 18 led to further investigation. A large change in retention by several minutes was a function of both the organic eluent composition and temperature between 15 and 30 degrees C. Several Van't Hoff temperature studies from 5 to 65 degrees C on several column types resulted in non-linear plots. Analysis of the molecular subunits suggested that the peptide portion of the analyte influenced the non-linear retention behavior. The stationary phase type was not a significant factor causing non-linearity. Circular dichroism-temperature studies indicated a notable transition in ellipticity for the amine regions (198-202 nm) that occurred between 39 and 44 degrees C. This transition temperature range coincided with the results of the Van't Hoff analysis, between 35 and 44 degrees C, to indicate that these effects were not primarily stationary phase induced. 相似文献
972.
Schumacher DD Mitchell CR Xiao TL Rozhkov RV Larock RC Armstrong DW 《Journal of chromatography. A》2003,1011(1-2):37-47
A set of 28 racemic dihydrofurocoumarins in which the stereogenic center is located in the furan ring have been synthesized. Currently no effective asymmetric synthesis of this class of compounds exists, although their enantiomers are produced biologically by certain plants. Their diverse medicinal properties are being investigated in several laboratories. The enantioselective separation of these dihydrofurocoumarins by three native and six derivatized cyclodextrins has been evaluated in the reversed-phase mode, the polar organic mode, and normal-phase mode. The hydroxypropyl-beta-cyclodextrin is the most effective chiral stationary phase (CSP) at separating the dihydrofurocoumarins into enantiomers, showing some enantioselectivity for 22 dihydrofurocoumarins, and baseline resolving 16 of the 28 compounds in the reversed-phase mode. The acetyl-beta-cyclodextrin and 2,3-dimethyl-beta-cyclodextrin also showed enantioselectivity for a large number (18 and 17, respectively) of dihydrofurocoumarins in the reversed-phase mode. The native cyclodextrins are ineffective and the aromatic derivatized beta-cyclodextrins are only marginally effective at separating the furocoumarin enantiomers in the reversed-phase mode. The polar organic mode and the normal-phase mode have also been evaluated with these CSPs, but no enantioseparations were observed. 相似文献
973.
We report a laboratory measurement of the rate coefficient for the collisional removal of O(2)(X(3)Sigma(g) (-),upsilon=1) by O((3)P) atoms. In the experiments, 266-nm laser light photodissociates ozone in a mixture of molecular oxygen and ozone. The photolysis step produces vibrationally excited O(2)(a(1)Delta(g)) that is rapidly converted to O(2)(X(3)Sigma(g) (-),upsilon=1-3) in a near-resonant electronic energy-transfer process with ground-state O(2). In parallel, a large amount of O((1)D) atoms is generated that promptly relaxes to O((3)P). Under the conditions of the experiments, only collisions with the photolytically produced O((3)P) atoms control the lifetime of O(2)(X(3)Sigma(g) (-),upsilon=1), because its removal by molecular oxygen at room temperature is extremely slow. Tunable 193-nm laser light monitors the temporal evolution of the O(2)(X(3)Sigma(g) (-),upsilon=1) population by detection of laser-induced fluorescence near 360 nm. The removal rate coefficient for O(2)(X(3)Sigma(g) (-),upsilon=1) by O((3)P) atoms is (3.2+/-1.0)x10(-12) cm(3) s(-1) (2sigma) at a temperature of 315+/-15 K (2sigma). This result is essential for the analysis and correct interpretation of the 6.3-mum H(2)O(nu(2)) band emission in the Earth's mesosphere and indicates that the deactivation of O(2)(X (3)Sigma(g) (-),upsilon=1) by O((3)P) atoms is significantly faster than the nominal values recently used in atmospheric models. 相似文献
974.
Kawakami M Byrne K Khatri BS Mcleish TC Radford SE Smith DA 《Langmuir : the ACS journal of surfaces and colloids》2005,21(10):4765-4772
The dynamical nature of biomolecular systems means that knowledge of their viscoelastic behavior is important in fully understanding function. The linear viscoelastic response can be derived from an analysis of Brownian motion. However, this is a slow measurement and technically demanding for many molecular systems of interest. To address this issue, we have developed a simple method for measuring the full linear viscoelastic response of single molecules based on magnetically driven oscillations of an atomic force microscope cantilever. The cantilever oscillation frequency is periodically swept through the system resonance in less than 200 ms allowing the power spectrum to be obtained rapidly and analyzed with a suitable model. The technique has been evaluated using dextran, a polysaccharide commonly used as a test system for single molecule mechanical manipulation experiments. The monomer stiffness and friction constants were compared with those derived from other methods. Excellent agreement is obtained indicating that the new method accurately and, most importantly, rapidly provides the viscoelastic response of a single molecule between the tip and substrate. The method will be a useful tool for studying systems that change their structure and dynamic response on a time scale of 100-200 ms, such as protein folding and unfolding under applied force. 相似文献
975.
Macho S Miguel D Gómez T Rodríguez T Torroba T 《The Journal of organic chemistry》2005,70(23):9314-9325
[Structure: see text]. The 1,5- and 1,7-s-hydrindacenedione dioximes reacted with S2Cl2 and iBu3N to give the first examples of bis[1,2,3]dithiazolo-s-indacenes; one of them was a near-infrared dye. In contrast, the silylated bicyclo[3.3.0]octan-2,6-dione dioxime reacted with S2Cl2 and Et3N to give a bicyclic 4-cyanoethylcyclopenta[1,2,3]dithiazole or, after addition of Li2S, a tricyclic 4-cyanoethyl-5,6-pentathiepinocyclopenta[1,2,3]dithiazole, also obtained from 2-cyanoethylcyclopentanone oxime, S2Cl2, and Hünig's base. In related reactions, 2-oxocyclopentylpropionate oxime gave the expected cyclopenta[1,2,3]dithiazole, in addition to an unexpected cyclopenta[c][1,2]thiazine that showed a reversible reduction wave in its CV at -0.95 V. Ethyl 2-oxocyclopentanecarboxylate oxime reacted with S2Cl2, Hünig's base, and Li2S to give a 5,6-tetrathiinocyclopenta[1,2,3]dithiazole derivative. Cyclopentathiophen-4-one oximes reacted with S2Cl2 and iBu3N to give thienocyclopenta[1,2,3]dithiazoles that showed UV-vis spectral bands that depended on the positions of the ring fusion. 相似文献
976.
The production of I(2P) in the photolysis of CH2I2 has been studied optoacoustically at excitation wavelengths between 365.5 and 247.5 nm. Bands found at 32200 and 47000 cm?1 correlate with I(2P) whilst those at 34700 and 40100 cm?1, which correlate with I(2P), give final 2P/2P ratios of 1.75 and 1.1, respectively, after curve crossing. 相似文献
977.
Carmona D Lamata MP Viguri F Rodríguez R Oro LA Balana AI Lahoz FJ Tejero T Merino P Franco S Montesa I 《Journal of the American Chemical Society》2004,126(9):2716-2717
The 1,3-dipolar cycloaddition reaction of C,N-diphenylnitrone with methacrolein is efficiently catalyzed by the rhodium diphosphine compound (SRh,RC)-[(eta5-C5Me5)Rh(R-Prophos)(H2O)](SbF6)2 [R-Prophos = (R)-(+)-1,2-bis(diphenylphosphino)-propane, 1.SbF6]; the asymmetric catalytic process occurs with reversal of regioselectivity, perfect endo selectivity, and up to 92% ee. The complete (NMR and X-ray analysis) characterization of the involved intermediate (SRh,RC)-[(eta5-C5Me5)Rh(R-Prophos)(methacrolein)](SbF6)2 (7.SbF6) allows us to interpret the observed selectivity. 相似文献
978.
Omary MA Rawashdeh-Omary MA Gonser MW Elbjeirami O Grimes T Cundari TR Diyabalanage HV Gamage CS Dias HV 《Inorganic chemistry》2005,44(23):8200-8210
Varying the coinage metal in cyclic trinuclear pyrazolate complexes is found to significantly affect the solid-state packing, photophysics, and acid-base properties. The three isoleptic compounds used in this study are [[3,5-(CF3)2Pz]M]3 with M = Cu, Ag, and Au (i.e., Cu3, Ag3, and Au3, respectively). They form isomorphous crystals and exist as trimers featuring nine-membered M3N6 rings with linear two-coordinate metal sites. On the basis of the M-N distances, the covalent radii of two-coordinate Cu(I), Ag(I), and Au(I) were estimated as 1.11, 1.34, and 1.25 angstroms, respectively. The cyclic [[3,5-(CF3)2Pz]M]3 complexes pack as infinite chains of trimers with a greater number of pairwise intertrimer M...M interactions upon proceeding to heavier coinage metals. However, the intertrimer distances are conspicuously short in Ag3 (3.204 angstroms) versus Au3 (3.885 angstroms) or Cu3 (3.813 angstroms) despite the significantly larger covalent radius of Ag(I). Remarkable luminescence properties are found for the three M3 complexes, as manifested by the appearance of multiple unstructured phosphorescence bands whose colors and lifetimes change qualitatively upon varying the coinage metal and temperature. The multiple emissions are assigned to different phosphorescent excimeric states that exhibit enhanced M...M bonding relative to the ground state. The startling luminescence thermochromic changes in crystals of each compound are related to relaxation between the different phosphorescent excimers. The trend in the lowest energy phosphorescence band follows the relative triplet energy of the three M(I) atomic ions. DFT calculations indicate that [[3,5-(R)2Pz]M]3 trimers with R = H or Me are bases with the relative basicity order Ag < Cu < Au while fluorination (R = CF3) renders even the Au trimer acidic. These predictions were substantiated experimentally by the isolation of the first acid-base adduct, [[Au3]2:toluene]infinity, in which a trinuclear Au(I) complex acts as an acid. 相似文献
979.
Barluenga J Vicente R López LA Rubio E Tomás M Alvarez-Rúa C 《Journal of the American Chemical Society》2004,126(2):470-471
A new type of metal carbene complexes of group 9, specifically a cationic Fischer carbene of rhodium(I), has been synthesized from chromium carbene complexes via double transfer of carbene and CO ligands. These complexes reveal a different reactivity than other transition metal carbenes, including their chromium precursors, toward neutral and electron-poor alkynes, giving selectively polysubstituted cyclopentenones. 相似文献
980.
González-Núñez ME Mello R Royo J Asensio G Monzó I Tomás F López JG Ortiz FL 《The Journal of organic chemistry》2004,69(26):9090-9099
The detailed study of the oxidation of thianthrene 5-oxide (1) with methyl(trifluoromethyl)dioxirane (5b) in different solvents and in the presence of (18)O isotopic tracers is reported. Thianthrene 5-oxide (1) is a flexible molecule in solution, and this property allows for transannular interaction of the sulfoxide group with the expected zwitterionic 7 and hypervalent 10-S-4 sulfurane 9 intermediates formed in the oxidation and biases the course of the reaction toward the monooxygenation pathway. 相似文献