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81.
The relative rates of H-transfer between partners in ion-neutral complexes were compared with those in intramolecular rearrangements using results of first differential photoionization mass spectrometry measurements. Complex-mediated H-transfers are inferred to have rates of the same order as those for intramolecular hydrogen rearrangements, suggesting a similar range of motion of the reactive sites in both types of reactions. It is also concluded that at their fastest H-transfers take place between the partners in ion-neutral complexes within at most the time of several rotations of the partners in the complexes. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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Ehsan Majid Keith B. Male Yew‐Min Tzeng Jesse O. Omamogho Jeremy D. Glennon John H. T. Luong 《Electrophoresis》2009,30(11):1967-1975
A CD‐modified capillary electrophoretic method has been developed for achiral and chiral analysis of seven bioactive compounds isolated from the fruiting body of Antrodia camphorata. Such important target analytes exhibit similar chemical structures and are known for their diverse properties including antioxidant and anticancer effects. The analytes were separated in 25 min using a pH 9.3, 20 mM sodium borate buffer containing 20 mM methyl‐β‐CD and 30 mM sulfobutylether‐β‐CD. With the exception of the optical isomer pairs (antcin B or zhankuic acid A, zhankuic acid C, and antcin A), the remaining bioactive compounds including the chiral pair antcin C were baseline‐separated. Analysis time was noticeably longer to baseline separate all of the above chiral pairs (~38 min) by adding 5% DMF to the running buffer. The migration order was reversed compared with the HPLC elution. More hydrophobic compounds complexed favorably with methyl‐β‐CD and emerged earlier in the electropherogram than their more hydrophilic counterparts which were strongly associated with sulfobutylether‐β‐CD. The simple capillary electrophoretic method developed was applicable for rapid separation and characterization of several important bioactive compounds isolated from the fruiting body of A. camphorata. 相似文献
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Hannu?TiitinenEmail author Anna?Mari?M?kel? Ville?M?kinen Patrick?JC?May Paavo?Alku 《BMC neuroscience》2005,6(1):62
Background
The cortical activity underlying the perception of vowel identity has typically been addressed by manipulating the first and second formant frequency (F1 & F2) of the speech stimuli. These two values, originating from articulation, are already sufficient for the phonetic characterization of vowel category. In the present study, we investigated how the spectral cues caused by articulation are reflected in cortical speech processing when combined with phonation, the other major part of speech production manifested as the fundamental frequency (F0) and its harmonic integer multiples. To study the combined effects of articulation and phonation we presented vowels with either high (/a/) or low (/u/) formant frequencies which were driven by three different types of excitation: a natural periodic pulseform reflecting the vibration of the vocal folds, an aperiodic noise excitation, or a tonal waveform. The auditory N1m response was recorded with whole-head magnetoencephalography (MEG) from ten human subjects in order to resolve whether brain events reflecting articulation and phonation are specific to the left or right hemisphere of the human brain. 相似文献85.
Blewitt G LoSecco JM Bionta RM Bratton CB Casper D Chrysicopoulou P Claus R Cortez BG Errede S Foster GW Gajewski W Ganezer KS Goldhaber M Haines TJ Jones TW Kielczewska D Kropp WR Learned JG Lehmann E Park HS Reines F Schultz J Seidel S Shumard E Sinclair D Sobel HW Stone JL Sulak L Svoboda R van der Velde JC Wuest C 《Physical review letters》1985,55(20):2114-2117
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