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61.
Irradiation (lambda = 670 or >613 nm) of 4,5-benzodiazocycloheptatriene (15), matrix isolated in argon at 10 K, produces primarily 2,3-benzobicyclo[4.1.0]hepta-2,4,6-triene (9) accompanied by small amounts of triplet 4,5-benzocycloheptatrienylidene (2) and 2-naphthylcarbene (10). A reversible photoequilibrium is established in which 9 is converted to 10 at lambda = 290 nm and then regenerated at lambda = 360 nm. Similarly, matrix-isolated 2,3-benzodiazocycloheptatriene (16) produces 4,5-benzobicyclo[4.1.0]hepta-2,4,6-triene (11) at lambda = 670 or >613 nm, but without detection of 2,3-benzocycloheptatrienylidene (4). Irradiation of 11 at lambda = 290 nm induces ring opening to triplet 1-naphthylcarbene (12), which, in turn, cyclizes back to 11 at lambda = 342 or >497 nm. The diazo compounds and photoproducts are characterized by IR, UV/visible, and ESR spectroscopy, where appropriate, and by comparison of the experimental and B3LYP/6-31G calculated IR spectra for each species. Alternate rearrangement products such as allenes 6, 7, and 8 are not detected in the photolysis of either diazo compound. 相似文献
62.
Ion cyclotron resonance trapped electron spectra for carbonylfluoride, trifluoroacetyl fluoride, hexafluoroacetone, acetyl fluoride and I,I.I-trifluoroacetone are reported. Comparisons of data obtained for 3(π → π*) vertical excitation energies are used in conjunction with photoelectron spectroscopic data to deduce the effects of fluorine and trifluoromethyl groups on the energies of σ, π and π* orbitals associated with the carbonyl group. 相似文献
63.
Oligosaccharide and glycoprotein microarrays as tools in HIV glycobiology; glycan-dependent gp120/protein interactions. 总被引:11,自引:0,他引:11
Eddie W Adams Daniel M Ratner Heidi R Bokesch James B McMahon Barry R O'Keefe Peter H Seeberger 《Chemistry & biology》2004,11(6):875-881
Defining HIV envelope glycoprotein interactions with host factors or binding partners advances our understanding of the infectious process and provides a basis for the design of vaccines and agents that interfere with HIV entry. Here we employ carbohydrate and glycoprotein microarrays to analyze glycan-dependent gp120-protein interactions. In concert with new linking chemistries and synthetic methods, the carbohydrate arrays combine the advantages of microarray technology with the flexibility and precision afforded by organic synthesis. With these microarrays, we individually and competitively determined the binding profiles of five gp120 binding proteins, established the carbohydrate structural requirements for these interactions, and identified a potential strategy for HIV vaccine development. 相似文献
64.
Aqueous solutions of the industrially important chelating agent N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine exhibit basic properties. The proton dissociation constants were determined to be 8.99 +/- 0.04 (pK(1)) and 4.30 +/- 0.04 (pK(2)) by potentiometric titration at 25 degrees in 0.15M sodium chloride. 相似文献
65.
66.
Shane Bermingham Robert O'Connor Fiona Regan Gillian P. McMahon 《Journal of separation science》2010,33(11):1571-1579
An online SPE‐LC method that can determine both anthracyclines and taxanes simultaneously in human serum samples is reported. The entire method of extraction, separation and UV detection was achieved online by column switching between an SPE column (Biotrap 500 (20×4 mm)) and an analytical column (Zorbax XDB C18, 150×4.6 mm, 5 μm) with a 23 min total cycle time. The method is linear (r2>0.998) over the range of 0.5–25 μg/mL. The analytes of interest are retained on the SPE column with good recovery (84–117%), while proteins and other serum components elute to waste. This online clean‐up is much faster (150 s) and less manual than traditional off‐line extraction methods. Using 0.1 mL spiked serum samples, the LOQ was 0.5 μg/mL. Intra‐ and inter‐day precision were acceptable (≤15% RSD) at and above the LOQ. The method was applied to the analysis of serum samples from patients undergoing chemotherapy with these agents. 相似文献
67.
Bouchoux G Guillemin JC Lemahieu N McMahon TB 《Rapid communications in mass spectrometry : RCM》2006,20(8):1187-1191
The gas-phase basicity (GB) of aminoacetonitrile (NH2CH2CN, 1) has been determined from measurement of proton transfer equilibrium constants in an ion cyclotron resonance mass spectrometer (GB(1) = 789.3 +/- 1.0 kJ x mol(-1)). Molecular orbital calculations up to the G2 level demonstrate that protonation occurs preferentially on the nitrogen atom of the NH2 group, and provide a theoretical proton affinity (PA(1)) of 824.0 kJ x mol(-1). Exact calculation of the entropy associated with hindered rotations and consideration of Boltzman distribution of conformers allow a theoretical estimate of the molar protonation entropy S degrees (1H+) - S degrees (1) = 8.6 J x mol(-1) x K(-1). Combining this value with experimental GB(1) leads to an 'experimental' proton affinity of 819.2 kJ x mol(-1), in close agreement with the G2 expectation. 相似文献
68.
The apparent Michaelis constant, K(M), for glutamate oxidase (GluOx) immobilised on Pt electrodes increased systematically with enzyme loading. The effect was due, at least in part, to electrostatic repulsion between neighbouring oxidase molecules and the anionic substrate, glutamate (Glu). This understanding has allowed us to increase the Glu sensitivity of GluOx-based amperometric biosensors in the linear response region (100+/-11 nA cm(-2)microM(-1) at pH 7.4; SD, n=23) by incorporating a polycation (polyethyleneimine, PEI) to counterbalance the polyanionic protein. Differences in the behaviour of glucose biosensors of a similar configuration highlight a limitation of using glucose oxidase as a model enzyme in biosensor design. 相似文献
69.
This paper reports the findings of an investigation of 11 preservice secondary school teachers' interpretations of the development of proportional reasoning strategies used by middle school students. The preservice teachers examined samples of solution strategies generated by middle school students in proportional reasoning situations and prepared written responses of their views concerning the developmental levels indicated in the students' work. Each preservice teacher also participated in an hour‐long interview, in which the researchers asked for elaboration and clarification of the written responses and, in some cases, challenged the preservice teachers to consider alternative interpretations for the middle school students' work. The interviews were audiotaped for later analysis by the investigators, and key aspects of both the written and audiotaped responses were entered into a spreadsheet and later tabulated into categories indicating trends in the preservice teachers' interpretations. Some implications for the preparation of preservice middle school science and mathematics teachers are included. 相似文献
70.
Yoshifuku S Chen S McMahon EM Yoshikawa A Sengupta PP Korinek J Belohlavek M 《Ultrasonics》2007,46(2):109-118