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Titolo:
Conformational distortions of metalloporphyrins with electron-withdrawing NO2 substituents at different meso positions. A structural analysis by polarized resonance Raman dispersion spectroscopy and molecular mechanics calculations
Autore:
Schweitzer-Stenner, R; Lemke, C; Haddad, R; Qiu, Y; Shelnutt, JA; Quirke, JME; Dreybrodt, W;
Indirizzi:
Univ Puerto Rico, Dept Chem, San Juan, PR 00931 USA Univ Puerto Rico San Juan PR USA 00931 Dept Chem, San Juan, PR 00931 USA Univ Bremen, FBI, Inst Phys Expt, D-28359 Bremen, Germany Univ Bremen Bremen Germany D-28359 st Phys Expt, D-28359 Bremen, Germany Sandia Natl Labs, Biomol Mat & Interfaces Dept, Albuquerque, NM 87185 USA Sandia Natl Labs Albuquerque NM USA 87185 Dept, Albuquerque, NM 87185 USA Univ New Mexico, Dept Chem, Albuquerque, NM 87131 USA Univ New Mexico Albuquerque NM USA 87131 Chem, Albuquerque, NM 87131 USA Florida Int Univ, Dept Chem, Miami, FL 33199 USA Florida Int Univ Miami FL USA 33199 Univ, Dept Chem, Miami, FL 33199 USA
Titolo Testata:
JOURNAL OF PHYSICAL CHEMISTRY A
fascicolo: 27, volume: 105, anno: 2001,
pagine: 6680 - 6694
SICI:
1089-5639(20010712)105:27<6680:CDOMWE>2.0.ZU;2-Z
Fonte:
ISI
Lingua:
ENG
Soggetto:
NONPLANAR NICKEL(II) PORPHYRINS; DEPOLARIZATION RATIO; EXCITATION PROFILES; PLANAR; MACROCYCLE; FUNDAMENTALS; PROTEINS; SPECTRA; TERMS; MODES;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
38
Recensione:
Indirizzi per estratti:
Indirizzo: Schweitzer-Stenner, R Univ Puerto Rico, Dept Chem, Rio Piedras Campus,POB 23346, San Juan, PR 00931 USA Univ Puerto Rico Rio Piedras Campus,POB 23346San Juan PR USA 00931
Citazione:
R. Schweitzer-Stenner et al., "Conformational distortions of metalloporphyrins with electron-withdrawing NO2 substituents at different meso positions. A structural analysis by polarized resonance Raman dispersion spectroscopy and molecular mechanics calculations", J PHYS CH A, 105(27), 2001, pp. 6680-6694

Abstract

The meso substituted NI(II)(5,15-diNO(2)-octaethylporphyrin) coexists in at least three different conformers in CS2. To explore the structural properties of these conformers, we measured the resonance excitation profiles anddepolarization ratio dispersions of various prominent Raman lines of Ni(5,15 diNO(2)-octaethylporphyrin) in CS2. The data were analyzed by a theoretical approach, which formulates the Raman tenser in terms of vibronic coupling parameters that depend on static deformations along the normal coordinates. The coupling parameters were determined by simultaneously fitting the depolarization ratio dispersion data and the corresponding resonance excitation profiles. We have also performed molecular mechanics calculations to identify all possible stable conformers of the molecule. To quantify the out-of-plane distortions of the calculated structures, we subjected them to normal coordinate deformation analysis (Jentzen, W.; Song, X.-Z.; Shelnutt, J. A. J. Phys. Chem. B 1997, 101, 1684). The results obtained from the Raman data and from molecular modeling are consistent in showing that the most stable conformers are strongly affected by rhombic in-plane (0.3 Angstrom) and ruffling (2;1 Angstrom) and doming (0.5-0.6 Angstrom) out-of-plane distortions. Additionally, smaller contributions from saddling were also obtained(similar to0.1 Angstrom). The three conformers detectable from the analysis of the Raman spectra most likely differ in terms of saddling and doming. The lowest-energy calculated conformers all show a horizontal orientation and out-of-plane position of the NO2 groups with respect to the macrocycle, but the conformers differ in the orientations of the ethyl substituents. Conformers with vertical orientations of the NO2 groups are calculated to be slightly higher in energy. INDO/s calculations reveal that the horizontal NO2 group orientation, and to a lesser extent the vertical orientation, gives rise to a strong admixture between porphyrin and NO2 molecular orbitals, enhancing the above distortions and leading to a break down of the 4-orbital model. A comparison with monosubstituted Ni(II)(5-NO2-OEP) reveals that all distortions increase with increasing number of nitro substituents. Altogether, this study demonstrates that meso nitro substitution of metalloporphyrins has a significant impact on electronic as well as structural properties of the ground and excited electronic states.

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Documento generato il 21/09/20 alle ore 18:14:06