Page 78 |
Save page Remove page | Previous | 78 of 200 | Next |
|
small (250x250 max)
medium (500x500 max)
Large (1000x1000 max)
Extra Large
large ( > 500x500)
Full Resolution
All (PDF)
|
This page
All
|
show almost equal weights of the two dominant configurations, : : : (HOMO)2 and
: : : (HOMO)1(LUMO)1 at TS. The HOMO and LUMO at the TS differ considerably
from those at the equilibrium geometry (shown in Fig. 2.3) — they become localized
on the imidazolin and phenyl rings, respectively. Thus, (HOMO)2 and (LUMO)2 cor-respond
to the two charge-localized configurations, and their interaction results in less
ionic electron distribution. The ionicity is also reduced by (HOMO)1(LUMO)1.
A stability analysis of the Hartree-Fock wavefunction at the TS shows an RHF-UHF
instability with a negative eigenvalue of 0:037. The DFT/PBE0 solution, however,
proves to be stable, which means that using the symmetry broken unrestricted solution
to achieve better description of the barrier will not be useful in this case. Therefore,
a multiconfigurational approach is necessary not only for describing excited-state iso-merization
of the GFP-like chromophores, but also for modeling isomerization in the
ground state.
Although the CASSCF wave function is capable of capturing the multiconfigura-tional
character of the wave function, it needs to be augmented by dynamical correlation
to provide accurate energy differences. We included dynamical correlation correction
via multireference perturbation theory (MRMP2) for the Etc and Ea energies (at the
CASSCF geometries). This yields an activation energy of Ea = 26:2 kcal/mol, which is
3.7 kcal/mol higher than the CASSCF result.
The CASSCF results represent an improvement over DFT, however, there is still
a considerable discrepancy between the theoretical (22–26 kcal/mol) and experimental
(15.4 kcal/mol) values for Ea, as noted by the authors of experimental studies20, 39, 41.
Below we demonstrate that this discrepancy is resolved when solvent effects are taken
into account.
68
Object Description
| Title | Development of predictive electronic structure methods and their application to atmospheric chemistry, combustion, and biologically relevant systems |
| Author | Epifanovskiy, Evgeny |
| Author email | epifanov@usc.edu; epifanov@usc.edu |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Chemistry |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2011-03-21 |
| Date submitted | 2011 |
| Restricted until | Unrestricted |
| Date published | 2011-04-28 |
| Advisor (committee chair) | Krylov, Anna I. |
| Advisor (committee member) |
Wittig, Curt Johnson, Clifford |
| Abstract | This work demonstrates electronic structure techniques that enable predictive modeling of the properties of biologically relevant species. Chapters 2 and 3 present studies of the electronically excited and detached states of the chromophore of the green fluorescent protein, the mechanism of its cis-trans isomerization, and the effect of oxidation. The bright excited ππ∗ state of the chromophore in the gas phase located at 2.6 eV is found to have an autoionizing resonance nature as it lies above the electron detachment level at 2.4 eV. The calculation of the barrier for the ground-state cis-trans isomerization of the chromophore yields 14.8 kcal/mol, which agrees with an experimental value of 15.4 kcal/mol; the electronic correlation and solvent stabilization are shown to have an important effect. In Chapter 3, a one-photon two-electron mechanism is proposed to explain the experimentally observed oxidative reddening of the chromophore. Chapter 4 considers the excited states of uracil. It demonstrates the role of the one-electron basis set and triples excitations in obtaining the converged values of the excitation energies of the nπ∗ and ππ∗ states. The effects of the solvent and protein environment are included in some of the models.; Chapter 5 describes an implementation of the algorithm for locating and exploring intersection seams between potential energy surfaces. The theory is illustrated with examples from atmospheric and combustion chemistry. |
| Keyword | electronic structure theory; coupled clusters theory; equation of motion theory; organic chromophore; green fluorescent protein; uracil |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m3801 |
| Contributing entity | University of Southern California |
| Rights | Epifanovskiy, Evgeny |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Epifanovskiy-4557 |
| Archival file | uscthesesreloadpub_Volume14/etd-Epifanovskiy-4557.pdf |
Description
| Title | Page 78 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | show almost equal weights of the two dominant configurations, : : : (HOMO)2 and : : : (HOMO)1(LUMO)1 at TS. The HOMO and LUMO at the TS differ considerably from those at the equilibrium geometry (shown in Fig. 2.3) — they become localized on the imidazolin and phenyl rings, respectively. Thus, (HOMO)2 and (LUMO)2 cor-respond to the two charge-localized configurations, and their interaction results in less ionic electron distribution. The ionicity is also reduced by (HOMO)1(LUMO)1. A stability analysis of the Hartree-Fock wavefunction at the TS shows an RHF-UHF instability with a negative eigenvalue of 0:037. The DFT/PBE0 solution, however, proves to be stable, which means that using the symmetry broken unrestricted solution to achieve better description of the barrier will not be useful in this case. Therefore, a multiconfigurational approach is necessary not only for describing excited-state iso-merization of the GFP-like chromophores, but also for modeling isomerization in the ground state. Although the CASSCF wave function is capable of capturing the multiconfigura-tional character of the wave function, it needs to be augmented by dynamical correlation to provide accurate energy differences. We included dynamical correlation correction via multireference perturbation theory (MRMP2) for the Etc and Ea energies (at the CASSCF geometries). This yields an activation energy of Ea = 26:2 kcal/mol, which is 3.7 kcal/mol higher than the CASSCF result. The CASSCF results represent an improvement over DFT, however, there is still a considerable discrepancy between the theoretical (22–26 kcal/mol) and experimental (15.4 kcal/mol) values for Ea, as noted by the authors of experimental studies20, 39, 41. Below we demonstrate that this discrepancy is resolved when solvent effects are taken into account. 68 |
