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Thayer MP McGuire C Stennett EM Lockhart MK Canache D Novak M Schmidtke SJ 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,84(1):227-232
The local environment dictates the structural and functional properties of many important chemical and biological systems. The impact of pH on the photophysical properties of a series of para-aminobenzoic acids is examined using a combination of experimental spectroscopy and quantum chemical calculations. Following photoexcitation, PABA derivatives may undergo an intramolecular charge transfer (ICT) resulting in the formation of a zwitterionic species. The thermodynamics of the excited state reaction and temperature-dependence of the radiative emission processes are evaluated through variable temperature fluorescence spectroscopy carried out in a range of aqueous buffers. Quantum chemical calculations are used to analyze structural changes with modifications at the amine position and different protonation states. The ICT is only observed in the tertiary amine, which calculations show has more sp(2) character than the primary or secondary amines. Thermodynamic analysis indicates the ICT reaction is driven by entropy. 相似文献
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Strategies for the synthesis of bi- and triarylic materials starting from commercially available phenols 总被引:1,自引:0,他引:1
Alicia B. Chopa Gustavo F. Silbestri María T. Lockhart 《Journal of organometallic chemistry》2005,690(17):3865-3877
A series of arylstannanes have been synthesized, through an SRN1 mechanism, in good to excellent yields (74%-99%) by the photostimulated reaction of trimethyl stannyl ion with substrates supporting different nucleofugal groups. The arylstannanes thus obtained were suitable intermediates for Stille cross-coupling reactions leading to asymmetric bi- and triaryl compounds in acceptable global yields. An attractive feature of this route is that simple commercially available benzenediols, chloro- and methoxy phenols might be useful starting substrates, leading the latter to higher global yields of products in fewer steps. The strategies proposed open a broad synthetic tool. 相似文献
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Radiotracer experiments show that self-diffusion in the rotator crystalline phase of adamantane proceeds by a vacancy mechanism. The results are in good agreement with those determined from NMR experiments. 相似文献
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Lo Fiego MJ Badajoz MA Silbestri GF Lockhart MT Chopa AB 《The Journal of organic chemistry》2008,73(22):9184-9187
The exceptional leaving group ability of the trimethylstannyl group in electrophilic aromatic substitutions makes possible the synthesis, in a single step, of bi- and triaroylarenes through the catalyst-free, regioselective reaction of bi- and tristannylarenes with different aroyl halides in o-dichlorobenzene as solvent. Specific di- and triketones are obtained in good to excellent yields (45-83%). 相似文献
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Viviana B. Dorn María T. Lockhart Adriana B. Pierini 《Journal of organometallic chemistry》2008,693(14):2458-2462
The reaction of trimethyltinsodium (1) with 1-(diethoxyphosphoryl)oxy-1,3-cyclohexadienes in liquid ammonia under irradiation affords the corresponding 1-trimethylstannylcyclohexadienes. We suggest that these reactions occur by an SRN1 mechanism. On the other hand, 2-(diethoxyphosphoryl)oxy-1,3-cyclohexadiene reacts very slowly towards 1 and the substitution product decomposes under the reaction conditions employed. Thus, structurally similar compounds do not behave in the same way under ET conditions. We suggest that this behavior is mainly due to differences in spin density of their radical anions, which affect their fragmentation rates. Our results are supported by computational calculations. 相似文献
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Wendy Lockhart 《电子产品世界》2009,16(10):51-52,55
描述了混合信号FPGA在临场医疗设备中的应用,并以血液透析仪为例加以说明。 相似文献