Quantum-Chemical Photobiology in the Excited State: Photophysics and Photochemistry of Biomolecules (BIOQCEX)
A theoretical, quantum-chemical study is proposed on the photophysics and photochemistry of several chromophores related to systems with biological interest. We will study natural processes of photoinduced character related to different aspects of vision, phototaxis, and photosynthetic regulation through the determination of the photoisomerization channels in the excited state of molecules like retinal, the PYP protein chromophore, and phytochromobiline.Also, the photophysics and photochemistry of the DNA and RNA nucleic acid bases: cytosine, thymine, uracil, adenine, and guanine, will be analyzed, together with its radiationless response to direct UV radiation and the photoinduced endogenic mutations undergone by the monomers or dimers, whether opposed or stacked.
Finally, we propose the study of the photophysics and photochemistry of several systems with prospective phototherapeutic action, like psoralen and its derivatives, porphirins, chlorins, phtalocianines, and bilirubin. The study aims to contribute to the understanding of the direct and dynamic mechanisms of antitumoral phototherapeutic action, and to help to design new pharmacons with effective photoinduced properties, trying to optimize aspects such as the proper absorption or emission energies, energy transfer to reactive oxygen, or the formation of adducts without unwanted secondary effects.
Mainly, the theoretical ab initio quantum-chemical method CASSCF/CASPT2 will be employed, whilst new techniques will be developed to more accurately search for conical intersections between potential energy hypersurfaces, considered to be responsible for the photoreactive processes.
- Project:Photoisomeriza
tions in
Biology
- Project:Photophysics and
Photochemistry
of DNA
and RNA bases
- Project:Medical Applications
of
Photochemistry:
Photodynamic
Therapy
- Project:Photosynthe
sis
- Networking:COST
Action P9: Radiation Damage in Biomolecular
Systems. A European Network.
Recent publications:
- "Computational Evidence in Favor of a Two-State, Two-Mode Model
of the Retinal Photoisomerization"
R. González-Luque, M. Garavelli, F. Bernardi, M. Merchán, M. A. Robb, and M. Olivucci. Proc. Nat. Acad. USA, 97, 9379 (2000) - "On the Absorbance Changes in the Photocycle of the Photoactive
Yellow Protein:A Quantum-Chemical Analysis"
V. Molina and M. Merchán, Proc. Nat. Acad. USA, 98, 4299 (2001) - "Ultrafast Internal Conversion of Excited Cytosine via the
Lowest pipi* Singlet State"
M. Merchán and L. Serrano-Andrés, J. Am. Chem. Soc., 125, 8108 (2003) - "Triplet State Formation Along the Ultrafast Decay of Excited
Singlet Cytosine"
M. Merchán, L. Serrano-Andrés, M. A. Robb, and L. Blancafort, J. Am. Chem. Soc., 127,1820 (2005) - "Structure, Spectroscopy, and Spectral Tuning of the Gas-phase
Retinal Chromophore: The Beta-Ionone 'Handle' and Alkyl Group
Effect".
A. Cembran, R. González-Luque, P. Altoe, M. Merchán, F. Bernardi, M. Olivucci, and M. Garavelli, Journal of Physical Chemistry A, 109, 6597-6605 (2005)
- "Propiedades Fotofísicas del Psoraleno"
J. J. Serrano-Pérez, L. Serrano-Andrés, M. Merchán, Boletín de la XIX Reunión del Grupo Espańol de Fotobiología. 28-29 Enero 2005.
Theoretical Ab Initio Spectroscopy (TEOSPEC)
Different research projects are integrated in a line that is aimed to study the spectroscopy of systems of intrinsic chemical interest and develop methodologies to account for properties of molecular electronic excited states and transitions between them. The spectroscopy, photophysics, and photochemistry of families of chemical interest are being studied.Oligothiophenes are systems of technological importance because of their photoelectrical properties. Derivatives and analogs of acridines and xanthones, such as thioxanthone, are systems of intriguing spectroscopical behavior which have been scrutinized by experimentalists because of their particular solvatochromism. Herbicides based on triazines or sulfur derivatives would be favorable destroyed, with healthy consequences for the environment, if efficient photodegradation could take place. Previous knowledge of their spectroscopical behavior is being studied in cooperation with experimental teams.
Finally, the group is interested on the development of quantum chemical methodologies able to deal with the specific and difficult properties of the excited state. An example is the efficient search of conical intersections or reaction paths with methods that include correlation at a sufficient extent. The MOLCAS program is a suitable platform to incorporate and exploit the new methodologies.
- Project:Photophysi
cs of
Oligothiophenes
- Project: Spectroscopy of
Acridines and
Xanthones
- Project:Photodegradatio
n of
Herbicides
- Project:Methodolog
ical
Development
in Quantum Chemistry.
The MOLCAS Project.
Recent publications:
- "Theoretical Analysis of the Excited States in
Maleimide"
T. Climent and M. Merchán, J. Phys. Chem. A, 107, 6995 (2003) - "The low-lying excited states of 2,2'-
bithiophene: A theoretical analysis"
M. Rubio, M. Merchán, R. Pou-Amérigo,and E.Ortí ChemPhysChem., 4, 1308 (2003) - "Theoretical Absorption and Emission Spectra of
1H- and 2H-Benzotriazole"
A. C. Borin, L. Serrano- Andrés, V. Ludwig, and S. Canuto. Phys. Chem. Chem. Phys., 5, 5001 (2003) - "Spectroscopy:
Applications"
L. Serrano-Andrés and M. Merchán, Encyclopedia of Computational Chemistry, P. v. R. Schlegel et al. Eds, Wiley, Chichester, 2004 - "On the Low-lying Excited States of sym-Triazine-Based
Herbicides"
J. M. Oliva, M. E. D. G. Azenha, H. D. Burrows, R. Coimbra, J. S. Seixas de Melo, M. Canle L., M. I. Fernández, J. A. Santaballa, and L. Serrano- Andrés,
ChemPhysChem., 6, 306-314 (2005) - "Theoretical study of the electronic excited states of
tetracyanoethylene and its radical anion".
B. Milián, R. Pou-Amérigo, M. Merchán, and E. Ortí,
ChemPhysChem, 6, 503-510 (2005) - "A Theoretical Study on the Low-lying Excited States of
2,2':5',2''-Terthiophene and 2,2':5',2'':5'',2'''-
Quaterthiophene".
M. Rubio, M. Merchán, and E. Ortí,
ChemPhysChem, 6, 1357-1368 (2005)
Adapted from: M. A. Robb, M. Olivucci, F. Bernardi, Encyclopedia of Computational Chemistry, 2056, (1998)
Molecular Direct Ab Initio Reaction Dynamics for the Excited State (RADEX)
Initial steps into the field of the molecular reaction dynamics have been performed. Our main goal is to develop efficient methodologies to compute classical trajectories based on quantum chemical information on the potential energy hypersurfaces. Typical methodologies will be CASSCF and CASPT2. The method would fit into what is known as "on-the-fly" ab initio reaction dynamics, in which the gradient/hessian is computed at the different points of the trajectory and the information used by the classical mechanics equations. Different procedures such as the Verlet algorithm are being tested. Surface-hopping techniques are also explored to account for the change of surfaces close to conical intersection situations. The development of the methodology and computer code, integrated within the MOLCAS package, and the study of photoinduced single molecular reactions based on simple organic systems are our initial goals.
