Current research at LCPP is centered on the idea that the most efficient and yet tunable photochemical systems know in nature are biological photoreceptors (i.e. visual and sensory pigments and ion-pumps). For this reason two parallel research lines are pursued. The first line focuses on the investigation of the molecular mechanism making a photoreceptor (a protein) or its mutants efficient in terms of color tuning (both in absorption and emission), reaction selectivity, time scale and quantum yield.
The second and parallel research line uses the same computational tools to design novel synthetic molecules that mimic the behavior of biological photoreceptors and can be employed as bio-mimetic molecular devices. For instance,
one of the LCPP targets is the development of a library of photo-responsive unnatural amino-acids to be employed in biological or medical research. Due to its research and the need for efficient computer programs and hardware, LCPP constitutes a potential environment for interdisciplinary work involving the Computer Sciences, Biology and Chemistry including organic synthesis.
To pursue the above targets, LCPP uses innovative computational protocols. These protocols, whose efficiency in treating large molecular systems has been demonstrated, aim to the simulation of the behavior of an entire population of photo-excited molecules thus overcoming the limitations of ordinary single molecule simulations. While, presently, this represents a brute-force computational effort, such development is foreseen to dominate the computer aided design of photoresponsive material in the near future. We believe that this is apparent when considering that: (i) the majority of the technological application of photo responsive materials involve the coherent (laser) or incoherent light irradiation of an entire sample and (ii) the availability of larger and larger arrays of fast processors (i.e. of computer clusters) will enable the simultaneous modeling of a statistically meaningful number of excited state molecules and, in turn, of an excited state population.
Research Projects at LCPP include:
Computational investigation of the "primary event" in biological photoreceptors.
Structure of potential energy surfaces near conical intersections.
Development and application of accurate QM/MM methods for investigating excited states and photochemical reactivity.
Computer Design and Synthesis of Biomimetic Molecular Motors and Switches.
Methods for the Design of Photoreceptors Mutants with Programmed Optical and Photochemical Properties.
LCPP is a bi-national Lab which exploits the computer facilities both at the Department of Biotechnology, Chemistry and Pharmacy, University of Siena (UNISI), Italy, and at the Center for Photochemical Sciences, Department of Chemistry, Bowling Green State University (BGSU), Ohio. The laboratory, equipped with a pool of Linux-based servers including a 26 nodes – 134 cores High Performance Computer Cluster based on Intel Xeon (Woodcrest and Clovertown) CPUs and installed at the BGSU campus. The currently most advanced software tool used in the laboratory is a quantum-mechanics/molecular-mechanics software based on multiconfigurational quantum chemistry.
This facilities allow for the construction of realistic (i.e. quantitative) computer models of photo-excited chemical and biological systems. Most important LCPP aims at the creation of specific tools capable to track the time-evolution of the system making the lab activity highly complementary to that of the Ohio Laboratory of Kinetic and Spectrometry to which the LCPP has access. A larger number of processors and an improved software performance are being pursued to allow for a routinely affordable simulation time of excited state molecular population dynamics.
Three different objectives have been achieved over the years. The first objective aimed to a deeper understanding of the Woodward-Hoffmann selection rules (W.-H. rules) for pericyclic reactions to the development of new computational tools capable of treating reactivity problems in small to medium size (few hundred atoms) organic molecules.
The second objective involved the development of protocols for mapping excited state energy surfaces and a systematic characterization of the photochemical reactivity of different classes of organic and biological chromophores.
The third and present objective includes the development and application of excited state reaction path and trajectory computations using a quantum mechanics/molecular-mechanics protocol. In this context the group represents one of the first and few with expertise in the development and applications of quantum mechanics/molecular mechanics methods for excited states and in particular for photochemical reactions occurring in complex matrices such as a protein environment. Notice that the quantum mechanical part is usually treated at the ab initio multiconfigurational level (mainly CASPT2 and CASPT2//CASSCF protocols). This methodology is being intensively exploited for the investigation of photoisomerizations and luminescence reactions in biological photoreceptors and for the design of novel photoresponsive materials. Recently, the group has reported in the Science Magazine. For recent (last 10 years) work in these areas see:
Frutos L. M. et al. (2007) Tracking the excited-state time evolution of the visual pigment with multiconfigurational quantum chemistry. Proc. Natl. Acad. Sci. USA 104:7764-7769.
Sinicropi A. et al. (2008) An Artificial Molecular Switch that Mimics the Visual Pigment and Completes its Photocycle in Picoseconds. Proc. Nat. Acad. Sci. USA 105:17642-17647.
Melloni, A. et al. (2010) Modeling, Preparation and Characterization of a Dipole Moment Switch Driven by Z/E Photoisomerization J. Am. Chem. Soc. 132:9310-9319.
Altoè, P. et al. (2010) An aborted double bicycle-pedal isomerization with hydrogen bond-breaking is the primary event in the Bacteriorhodopsin proton-pumping Proc. Natl. Acad. Sci. USA 107:20172-20177.
Strambi, A. et al. (2010) Anabaena sensory rhodopsin is a light-driven unidirectional rotor Proc. Natl. Acad. Sci. USA 107:21322-21326.
Schapiro, I. et al. (2011) The Ultrafast Photoisomerizations of Rhodopsin and Bathorhodopsin are Modulated by Bond Alternation and HOOP driven Electronic Effects J. Am. Chem. Soc. 133:3354-3364.
Grilj, J. et al. (2011) Fluorescence of Radical Ions in Liquid Solution: Wurster's Blue as a Case Study Angew. Chem. Int. Ed. 50:4496-4498.
Gozem S., Schapiro, I., Ferré, N. & Olivucci, M. (2012) The Molecular Mechanism of Dark Noise in Rod Photoreceptors. Science 337:1225-1228.
Rinaldi S., Melaccio, F., Gozem, S., Fanelli, F. & Olivucci, M. (2014) Comparison of the isomerization mechanisms of human melanopsin and invertebrate and vertebrate rhodopsins Proc. Natl. Acad. Sci. USA 111:1714-1719.
Luk H. L., Melaccio, F., Rinaldi, S., Gozem, S. & Olivucci, M. (2015) Molecular bases for the selection of the chromophore of animal rhodopsins. Proc. Natl. Acad. Sci. USA 112:15297-15302.