“…Upon heating, the spectrum shifts to the red, this shift being linearly dependent on the temperature (Figure ). Such behavior is a manifestation of the so-called quadratic electronic−vibrational coupling: , the presence of normal coordinates ( q i ), along which the force-field constants of the ground electronic state differ from those of the excited one. , Moreover, the fact that the whole spectrum rigidly shifts implies 24 that the displacements along the q coordinates are characterized by considerably smaller force-field constants than those along the Q coordinates. 2 Temperature dependence of the main peak position of wt-GFP (□) and its linear fit (line).…”
The fluorescence spectra of the wild-type green fluorescence protein (wt-GFP) and the anionic form of p-hydroxybenzylidenedimethylimidazolone (p-HBDI), which models the protein chromophore, were obtained in the 80-300 K temperature range in glycerol/water solvent. The protein spectra have pronounced and well-resolved vibronic structure, at least at lower temperatures. In contrast, the chromophore spectra are very broad and structureless even at the lowest temperatures. Analysis of the spectra shows that the experimentally observed red-shift of the protein spectrum upon heating is apparently caused by quadratic vibronic coupling of the torsional deformation (TD) of the phenyl single bond of the chromophore to the electronic transition. The broad spectra of the chromophore manifest the contribution of different conformations in the glycerol/water solvent. In particular, the lowest-temperature spectrum reflects the distribution over the same TD coordinate in the excited electronic state, which essentially contributes to the asymmetry of the spectrum. Upon heating, motion along this coordinate leads to a configuration from which the radiationless transition takes place. This narrows the distribution along the TD coordinate, causing a more symmetric fluorescence spectrum. We were able to reconstruct the broad, structureless fluorescence spectra of p-HBDI in glycerol/water solutions at various temperatures by convoluting the original wt-GFP spectra with the function describing the distribution of the transition energies of the p-HBDI chromophore. Thus, both the fluorescence broadening and increase in radiationless transition upon removal of the protein chromophore to bulk solvent are consistent with decay by a barrierless TD of the phenyl single bond.
“…Upon heating, the spectrum shifts to the red, this shift being linearly dependent on the temperature (Figure ). Such behavior is a manifestation of the so-called quadratic electronic−vibrational coupling: , the presence of normal coordinates ( q i ), along which the force-field constants of the ground electronic state differ from those of the excited one. , Moreover, the fact that the whole spectrum rigidly shifts implies 24 that the displacements along the q coordinates are characterized by considerably smaller force-field constants than those along the Q coordinates. 2 Temperature dependence of the main peak position of wt-GFP (□) and its linear fit (line).…”
The fluorescence spectra of the wild-type green fluorescence protein (wt-GFP) and the anionic form of p-hydroxybenzylidenedimethylimidazolone (p-HBDI), which models the protein chromophore, were obtained in the 80-300 K temperature range in glycerol/water solvent. The protein spectra have pronounced and well-resolved vibronic structure, at least at lower temperatures. In contrast, the chromophore spectra are very broad and structureless even at the lowest temperatures. Analysis of the spectra shows that the experimentally observed red-shift of the protein spectrum upon heating is apparently caused by quadratic vibronic coupling of the torsional deformation (TD) of the phenyl single bond of the chromophore to the electronic transition. The broad spectra of the chromophore manifest the contribution of different conformations in the glycerol/water solvent. In particular, the lowest-temperature spectrum reflects the distribution over the same TD coordinate in the excited electronic state, which essentially contributes to the asymmetry of the spectrum. Upon heating, motion along this coordinate leads to a configuration from which the radiationless transition takes place. This narrows the distribution along the TD coordinate, causing a more symmetric fluorescence spectrum. We were able to reconstruct the broad, structureless fluorescence spectra of p-HBDI in glycerol/water solutions at various temperatures by convoluting the original wt-GFP spectra with the function describing the distribution of the transition energies of the p-HBDI chromophore. Thus, both the fluorescence broadening and increase in radiationless transition upon removal of the protein chromophore to bulk solvent are consistent with decay by a barrierless TD of the phenyl single bond.
SynopsisIt is postulated from energetic considerations that the anhydrocellobiose unit in cellulose I has a conformation differing from that in cellulose 11. Conformation I has two intramolecular hydrogen bonds, while conformation I1 has only one. This difference a r k s from a different orientation of the C(6)-hydroxyl group in the two conformations. Their interconversion is shown to be dependent upon the polarity of the medium. The assignment of conformation I to cellulose I and conformation I1 to cellulose I1 and the equilibrium between them appear to be consistent with a number of experimental observations reported in the literature.
synopsisAn examination of powder x-ray diff ractograms of native and hydrolyzed cellulosic materials obtained from widely different sources revealed the presence of materials having a higher degree of molecular order than ramie hydrolyzate, the conventional crystalline standard for cellulose. With the use of these materials as new crystalline standards, a critical reappraisal has been made of the validity of the application of the two-phase (i.e., fringed-micelle) hypothesis to the fine structure of cotton and related cellulosic materials. It is concluded that the lattice structure of cotton and related celluloses of plant or bacterial origin is liquid-like or paracrystalline.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
