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排序方式: 共有70条查询结果,搜索用时 437 毫秒
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Boudet AC Cornard JP Merlin JC 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,56(4):829-839
3-Hydroxyflavone (3HF), which is the simplest molecule of the flavonol class, possesses chelating properties towards Al(III). Spectrophotometric methods have shown that the 3HF molecule forms an Al(3HF)2 complex in pure methanol. The structure of this complex, obtained by quantum semi-empirical AM1 method, indicated that complexed 3HF adopts a pyronium form. Structural and electronic modifications induced by chelation are illustrated by the important frequency shifts observed between free and complexed 3HF FT-Raman spectra and by the chemical shifts variations in the 13C NMR spectra of the two species. Complexes with the same stoichiometry were formed when AcO- or MeO- are present in the medium. However, in acidic medium the chelate composition is Al2(3HF). 相似文献
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Alves GA Amato S Anjos JC Appel JA Astorga J Bracker SB Cremaldi LM Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Halling AM Jedicke R Karchin PE Kwan S Leuking LH Mantsch PM de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A Passmore D Rafatian A dos Reis AC Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wallace A Wu Z 《Physical review D: Particles and fields》1994,49(9):R4317-R4320
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Alves GA Amato S Anjos JC Appel JA Astorga J Bracker SB Cremaldi LM Dagenhart WD Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Jedicke R Karchin PE Kennedy C Kwan S Lueking LH de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A Passmore D Rafatian A dos Reis AC Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wallace A Wu Z 《Physical review letters》1996,77(12):2388-2391
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Alves GA Amato S Anjos JC Appel JA Bracker SB Cremaldi LM Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Jedicke R Kaplan D Karchin PE Kwan S Leedom I Lueking LH Luste GJ Mantsch PM de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A Rafatian A dos Reis AC Reucroft S Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wu Z 《Physical review letters》1993,70(6):722-725
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Kim H Ralph J Lu F Ralph SA Boudet AM MacKay JJ Sederoff RR Ito T Kawai S Ohashi H Higuchi T 《Organic & biomolecular chemistry》2003,1(2):268-281
Peroxidase/H2O2-mediated radical coupling of 4-hydroxycinnamaldehydes produces 8-O-4-, 8-5-, and 8-8-coupled dehydrodimers as has been documented earlier, as well as the 5-5-coupled dehydrodimer. The 8-5-dehydrodimer is however produced kinetically in its cyclic phenylcoumaran form at neutral pH. Synthetic polymers produced from mixtures of hydroxycinnamaldehydes and normal monolignols provide the next level of complexity. Spectral data from dimers, oligomers, and synthetic polymers have allowed a more substantive assignment of aldehyde components in lignins isolated from a CAD-deficient pine mutant and an antisense-CAD-downregulated transgenic tobacco. CAD-deficient pine lignin shows enhanced levels of the typical benzaldehyde and cinnamaldehyde end-groups, along with evidence for two types of 8-O-4-coupled coniferaldehyde units. The CAD-downregulated tobacco also has higher levels of hydroxycinnamaldehyde and hydroxybenzaldehyde (mainly syringaldehyde) incorporation, but the analogous two types of 8-O-4-coupled products are the dominant features. 8-8-Coupled units are also clearly evident. There is clear evidence for coupling of hydroxycinnamaldehydes to each other and then incorporation into the lignin, as well as for the incorporation of hydroxycinnamaldehyde monomers into the growing lignin polymer. Coniferaldehyde and sinapaldehyde (as well as vanillin and syringaldehyde) co-polymerize with the traditional monolignols into lignins and do so at enhanced levels when CAD-deficiency has an impact on the normal monolignol production. The implication is that, particularly in angiosperms, the aldehydes behave like the traditional monolignols and should probably be regarded as authentic lignin monomers in normal and CAD-deficient plants. 相似文献
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The general expressions with retardation of the matrix elements for a central potential of the transitions S1/2–P1/2 and S1/2–P3/2 have been established previously for all the cases of degeneracies. Here, they are calculated, for any Z, as combinations of hypergeometric series, for the transitions between 1S1/2 and the continuum (photoeffect). A verification of the results is achieved for the approximation Z222 by using the integral representation in the complex plane of the confluent hypergeometric functions and the residues theorem. 相似文献
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Roger Boudet 《Foundations of Physics》1999,29(1):29-47
By using a geometrical form of the Darwin solutions of the Dirac equation, the general expressions with retardation of the matrix elements of the transitions S1/2-P1/2 and S1/2-P3/2 are established. The extension to the calculation with retardation of the sum rules relative to the intensities in the anomal Zeemann decomposition of the transitions between two levels is carried out. 相似文献