Hydride stretch infrared spectra in the excited electronic states of indole and its derivatives: Direct evidence for the 1ps* state

نویسندگان

  • Brian C. Dian
  • Asier Longarte
  • Timothy S. Zwier
چکیده

The hydride stretch infrared spectra of indole, indole–H2O, 3-methyl indole, 3-methyl indole–H2O, the main conformer of tryptamine ~TRA!, two conformers of N-acetyl tryptophan amide ~NATA!, and three conformers of N-acetyl tryptophan methyl amide ~NATMA!, have been recorded in the electronically excited singlet states using excited-state fluorescence-dip infrared spectroscopy. NATA and NATMA are methyl-capped dipeptides of tryptophan that have conformational flexibility and exhibit sensitivity in their electronic spectra to the conformation of the dipeptide backbone. In the indole monomer, the indole NH stretch fundamental at the S1 origin is shifted from its ground-state value ~3525 cm! to 3478 cm. The corresponding band in the indole–H2O complex appears at 3387 cm, shifted by a similar amount from its ground-state position ~3436 cm!. Higher vibronic levels within 1500 cm of the S1 origin, which have been identified previously @B. J. Fender et al., Chem. Phys. Lett. 239, 31 ~1995!# as being Lb or La in character, all show similar excited state indole NH stretch absorptions. The corresponding spectra in 3-methyl indole, 3-methyl indole-H2O, TRA, and in the C5 conformers of NATA and NATMA all are missing the indole NH stretch absorption. In its place, a broad background absorption appears, spread over the entire 2800–3800 cm region. In these molecules, other CH stretch or amide NH stretch absorptions remain sharp, appearing in their expected frequency ranges. Finally, the C7 conformations of NATA and NATMA, which possess an intramolecular hydrogen bond in the dipeptide backbone, have all infrared transitions washed out, replaced by a stronger broad background absorption. The entire data set can be explained by the presence of an excited ps* state which is dissociative along the indole NH stretch coordinate, as recently predicted by Sobolewski and Domcke @Chem. Phys. Lett. 315, 293 ~1999!#. In the weak coupling case ~indole, indole–H2O), the gap between the ps* state and the S1 origin is too large to be reached by infrared excitation. The selective loss of the indole NH stretch in the intermediate coupling case reflects the strong coupling of the Lb state NH stretch (v51) level to the ps* state, which is dissociative along the NH stretch coordinate. In the NATA and NATMA C7 conformers, an inversion of ordering of the electronic states occurs, pushing the La state below the Lb origin, and strengthening the coupling of all hydride stretch vibrational levels to the ps* dissociative continuum. These results highlight the important influence of the conformation of the polypeptide backbone on the photophysics of tryptophan in polypeptides. © 2003 American Institute of Physics. @DOI: 10.1063/1.1536616#

برای دانلود رایگان متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Microscopic Parameters in the Excited State of Toluene and Some of Its Haloderavatives

The Ultraviolet-visible (UV) spectra of toluene, ortho-bromo and para-bromo toluene in different solvents have been studied. The electric dipole moments and polarizabilities in the molecular excited electronic states were determined. It was found that the electric dipole moments for the excited states (µ*) and the ground states (µ) of these compounds are equal, and the change in dipole moment i...

متن کامل

Quantum-Chemical and Solvatochromic analysis of solvent effects on the Electronic Absorption Spectra of Some Benzodiazepine Derivatives

ABSTRACT The solvatochromic behaviour of two ketonic derivatives of benzodiazepine namely 7-chloro-1-methyl-5-phenyl-1,5-benzodiazepine-2,4-dione (Clobazam®) and 5,(2-chlorophenyl)-7-nitro-2,3-dihydro-1,4-benzodiazepine-2-one (Clonazepam®) were analysed in some selected solvents of different polarities using UV-Visible spectroscopy and DFT computational techniques. The solute-solvent interacti...

متن کامل

The Effect of Structural Parameters on the Electronic States and Oscillator Strength of a Resonant Tunneling Quantum Well Infrared Photodetector

In this paper a resonant tunnelling quantum well infrared photodetector (RT-QWIP) is discussed. Each period of this photodetector structure comprises of a resonant tunnelling structure (AlAs/AlGaAs/AlAs) nearby a quantum well (AlGaAs/GaAs). In this photodetector, photocurrent is produced when an electron makes a transition from the ground state of the well to an excited state which is coupled t...

متن کامل

Torsion–rotation analysis of OH stretch overtone–torsion combination bands in methanol

We report rotationally resolved spectra of jet-cooled methanol for the OH stretch overtones, 2v1 and 3v1 , and for the torsional combinations, 2v11v12 , 2v112v12 , 3v11v12 , and 3v112v12 . The spectra are obtained by direct excitation from the vibrational ground state with an infrared laser pulse. Population in the resulting upper state levels is detected by infrared laser assisted photofragmen...

متن کامل

Fe3O4 magnetic nanoparticles (MNPs) as an effective catalyst for synthesis of indole derivatives

The principal aim of this research is the application of Fe3O4 (MNPs) in the synthesis of some indole derivatives. Fe3O4 MNPs were prepared by Co-Precipitation method from the reaction of FeCl2.4H2O and FeCl3.6H2O in ammonia solution. Morphology and structure of Fe3O4 MNPs were determined by FT-IR, X-Ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy ...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 2003