Photosynthetic light-harvesting and energy transfer

Phycocyanin 645 (PC645) is the principal light-harvesting antenna in unicellular cryptophyte Chroomonas CCMP270 algae.

In photosynthesis, special antennae proteins that contain multiple light-absorbing molecules (chromophores) are able to capture sunlight and transfer the excitation energy to reaction centers with almost 100% quantum efficiencies. Traditionally, electronic energy transfer is modeled using Förster theory, developed more than 60 years ago, which describes an energy hopping mechanism mediated by dipole-dipole interactions between the interacting chromophores. Whereas this description is well-suited for a variety of systems, recent evidence from theory and experiment, for instance the recently developed 2D electronic spectroscopy, have unveiled the many interesting subtleties of closed packed multichromophoric aggregates that go beyond Förster theory, including coherence effects, deviations from the dipole approximation or environment screening effects. In this context, we work in the development of accurate quantum chemical tools aimed at describing such processes  in molecular detail.

Selected references:

1) C. Curutchet and B. Mennucci, Quantum Chemical Studies of Light Harvesting, Chem. Rev., 2017, 117 (2), 294–343.

2) L. Viani, C. Curutchet and B. Mennucci, Spatial and Electronic Correlations in the PE545 Light-Harvesting Complex, J. Phys. Chem. Lett. 2013, 4 (3), 372–377.

3) C. Curutchet, V. I. Novoderezhkin, J. Kongsted, A. Muñoz-Losa, R. van Grondelle, G. D. Scholes and B. Mennucci, Energy Flow in the Cryptophyte PE545 Antenna is Directed by Bilin Pigment Conformation, J. Phys. Chem. B (Paul Barbara Memorial Issue) 2013, 117(16), 4263-4273.

4) C. Curutchet, J. Kongsted, A. Muñoz-Losa, H. Hossein-Nejad, G. D. Scholes and B. Mennucci, Photosynthetic light-harvesting is tuned by the heterogeneous polarizable environment of the protein, J. Am. Chem. Soc. 2011, 133(9), 3078-3084.

5) D. L. Andrews, C. Curutchet and G. D. Scholes, Resonance Energy Transfer: Beyond the Limits, Laser & Photonics Reviews, 2011, 5, 114-123.

6) D. Beljonne, C. Curutchet, G. D. Scholes and R. J. Silbey, Beyond Förster resonance energy transfer in biological and nanoscale systems, J. Phys. Chem. B Feature Article, 2009, 113(19), 6583–6599.

Charge and energy transfer in DNA


Charge and energy transfer reactions are key in order to understand the behaviour of DNA photophysics leading to oxidative or photoinduced damage

In the  last decade, much progress has been made in the understanding of DNA excited-state dynamics. In this context, theoretical studies focused both on the photophysical properties of individual nucleobases as well as on the relevant interactions in assemblies of two or more bases have been a valuable tool for exploring decay mechanisms of excited states in DNA. However, there are still many open questions related to the behaviour of charge and energy transfer reactions along DNA, or in DNA-protein complexes. In this research line, we aim at advancing in this area by applying molecular modelling techniques able to describe both energy and charge migration in complex biological environments.

Selected references:

1) M. Corbella, A.A. Voityuk and C. Curutchet, Single Amino Acid Mutation Controls Hole Transfer Dynamics in DNA-Methyltransferase HhaI Complexes, J. Phys. Chem. Lett. 2015, 6(18), 3749–3753.

2) C. Curutchet and A. A. Voityuk, Triplet–Triplet Energy Transfer in DNA: A Process That Occurs on the Nanosecond TimescaleAngew. Chem. Int. Ed. 2011, 50(8), 1820-1822.

Electronic energy transfer in model systems

We also study intra and intermolecular energy transfer mechanisms in small model systems in which the chromophoric units are linked by a bridge. In such cases, bridge-mediated mechanisms (charge-transfer, superexchange) play an important role. In addition, the fixed arrangement between donor-acceptor moieties, or the possibility to perform single-molecule spectroscopy experiments,make them excellent model systems to test modern theory of energy transfer.

Selected references:

1) C. Curutchet and A. A. Voityuk, Distance Dependence of Triplet Energy Transfer in Water and Organic Solvents: A QM/MD Study, J. Phys. Chem. C 2012, 116(42), 22179-22185.

2) C. Curutchet, F. A. Feist, B. Van Averbeke, B. Mennucci, J. Jacob, K. Müllen, T. Basché and D. Beljonne, Superexchange-mediated electronic energy transfer in a model dyad, Phys. Chem. Chem. Phys. 2010, 12(27), 7378-7385.

3) C. Curutchet, B. Mennucci, G.D. Scholes and D. Beljonne, Does Förster theory predict the rate of electronic energy transfer for a model dyad at low temperature?, J. Phys. Chem. B 2008, 112(12), 3759-3766.

4) V. Russo, C. Curutchet and B. Mennucci, Towards a molecular scale interpretation of excitation energy transfer in solvated bichromophoric systems. II. The through bond contribution, J. Phys. Chem. B 2007, 111(4), 853-863.

5) C. Curutchet and B. Mennucci, Towards a molecular scale interpretation of excitation energy transfer in solvated bichromophoric systems, J. Am. Chem. Soc. 2005, 127(47), 16733-16744.

Development of continuum solvation models

In continuum models, the solvent environment is modelled as a dielectric medium.

The description of solvent (or more generally enviromnent) effects is key in condensed phase chemistry. We develop quantum mechanical continuum solvation models for the description of solvent effects in a variety of applications, from the prediction of solvation free energies to the study of solvatochromic effects in excited states, or the investigation of screening effects in electronic energy transfer.

Selected references:

1) A. Klamt, B. Mennucci, J. Tomasi, V. Barone, C. Curutchet, M. Orozco and F. J. Luque, On the Performance of Continuum Solvation Methods. A Comment on Universal Approaches to Solvation Modeling, Acc. Chem. Res., 2009, 42(4), 489–492.

2) G.D. Scholes, C. Curutchet, B. Mennucci, R. Cammi and J. Tomasi, How solvent controls electronic energy transfer and light harvesting, J. Phys. Chem. B 2007, 111(25), 6978-6982.

3) C. Curutchet, M. Orozco, F. J. Luque, B. Mennucci and J. Tomasi, Dispersion and repulsion contributions to the solvation free energy: Comparison of quantum mechanical and classical approaches in the polarizable continuum model, J. Comput. Chem. 2006, 27(15), 1769-1780.

4) C. Curutchet, C. J. Cramer, D. G. Truhlar, M. Ruiz Lopez, D. Rinaldi, M. Orozco and F.J. Luque, Electrostatic Component of Solvation: Comparison of SCRF Continuum Models, J. Comput. Chem. 2003, 24(3), 284-297.

Development of combined QM/MM models

In combined QM/MM models, the solvent molecules are explicitly described through classical force fields.

We also develop combined quantum mechanics/molecular mechanics (QM/MM) approaches to describe environment effects. QM/MM methods allow an efficient description of the enviroment through classical force fields, while still describing quantum-mechanically the molecules or parts of the system where we want to focus our attention. Such strategy is specially convinient in highly heterogeneous enviromnents like proteins, where a continuum dielectric description obscures the often critical role of local molecular structure.

Selected references:

1) S. Caprasecca, C. Curutchet and B. Mennucci, Toward a Unified Modeling of Environment and Bridge-mediated Contributions to Electronic Energy Transfer: a Fully Polarizable QM/MM/PCM Approach, J. Chem. Theory and Comput. 2012, 8(11) 4462-4473.

2) C. Curutchet, A. Muñoz-Losa, S. Monti, J. Kongsted, G. D. Scholes and B. Mennucci, Electronic energy transfer in condensed phase studied by a polarizable QM/MM model, J. Chem. Theory Comput. 2009,  5(7), 1838-1848.

3) I. Soteras, C. Curutchet, A. Bidon-Chanal, F. Dehez, J. G. Ángyán, M. Orozco, C. Chipot and F. J. Luque, Derivation of distributed models of atomic polarizability for molecular simulations, J. Chem. Theory Comput. 2007, 3(6), 1901-1913.