Integrated QM/polarizable MM/continuum approaches to model chiroptical properties of strongly interacting solute–solvent systems

Abstract

Solvent effects on chiroptical properties and spectroscopies can be huge, and affect not only the absolute value but the sign of molecular chiroptical responses. Therefore, the definition of reliable theoretical models and computational protocols to calculate chiroptical responses and assist the assignment of the chiral absolute configuration cannot overlook the effects of the surrounding environment. Continuum solvation methodologies are successful in case of weakly interacting solute-solvent couples, whereas in case of strongly interacting systems, such as those dominated by explicit hydrogen bonding interaction, a change of strategy is required to gain a reliable modeling.In this review, a recently developed integrated Quantum-Mechanical/Polarizable molecular mechanics (MM)/polarizable continuum model (PCM) method is discussed, which combines a fluctuating charge approach to the MM polarization with the PCM. Its theoretical fundamentals, and issues related to the calculation of chiroptical responses are summarized, and the application to few representative test cases in aqueous solution is discussed.aqueous solutions, chirality, polarizable embedding, solvent effects, quantum mechanical/molecular mechanics | I N T R O D U C T I O NThe calculation of chiroptical properties and chiral spectra by means of Quantum-Mechanical (QM) methods [1][2][3][4][5] is a mature research field.Many theoretical developments have been reported in the literature, focusing on the different aspects (accuracy in the description of the molecular Hamiltonian, choice of the basis set, inclusion of environmental effects) [3,[6][7][8][9] which may contribute to reach an accurate description of chirality. The definition of accurate protocols is nowadays accompanied by several applications, which demonstrate that a significant level of accuracy is accessible, so that QM calculations are universally accepted as a powerful methodology to assist the determination of the molecular absolute configuration.[10]In case of standard (non-chiral) spectroscopies, the most relevant information which is extracted from spectra is mainly related to peak positions (energies), whereas peak intensities play a secondary role. This is reflected in the computational methodologies which have been developed so far, which are mainly interested in getting an accurate reproduction of peak positions (infrared/Raman wavenumbers, UV-Vis transition energies, NMR chemical shieldings, etc.), reserving instead much less attention to spectral intensities. [11][12][13] In case of chiroptical properties/spectroscopies, an opposite situation occurs, in fact not only the absolute value but also especially the sign of the spectroscopic response is the most relevant information taken from the spectra. This feature makes chiroptical properties among the most challenging for theoretical models, and the difficulties in their accurate modeling are further increased by that fact that they are formally mixed electricmagnetic properties, where the effects of both the fields are ...

Simulating vertical excitation energies of solvated dyes: From continuum to polarizable discrete modeling

“…The FQ model provides a computationally efficient and chemically consistent way of introducing polarization effects within both classical dynamics simulations and QM/MM calculations. [44,54] In the FQ model, each atom is endowed with a charge that is allowed to fluctuate. Such fluctuation is ruled by the difference in atomic electronegativities.…”

“…Such models can be based on distributed multipoles, [35][36][37][38] induced dipoles, [39][40][41][42] Drude oscillators, [43] or fluctuating charges (FQ). [44] The FQ model was first developed into a 3-layer fully polarizable approach with nonperiodic boundary conditions (QM/FQ/PCM). The method has subsequently been extended to allow calculations of numerous molecular properties by including features like analytical first and second derivatives, [45] response equations, [46] magnetic perturbations with Gauge including atomic orbitals (GIAOs), [47] excitation energies (at the TD-DFT and equation-of-motion coupled cluster model with single and double substitutions levels of theory), [48,49] vibrational optical activity, [50,51] excitation energy gradients.…”

Recent Trends in Chiroptical Spectroscopy: Theory and Applications of Vibrational Circular Dichroism and Raman Optical Activity

“…[57][58][59][60] The "explicit" clusters can also be surrounded by a PCM continuum, to account for longer-range solvent effects. Polarizable force fields or three layer polarizable models further increase precision of the calculations, [61][62][63] similarly as for the fluctuating point charge model. [64] The explicit approach is usually based on geometries obtained by molecular dynamics (MD) simulations and many solute-solvent clusters ("snapshots") need to be averaged for realistic simulations.…”

Theoretical and computational chemistry in Italy

“…As mentioned above, the extension of methods for treating isolated molecules to condensed phases is one of the most well known contributions of Italian theoretical chemistry. New developments in this connection are described by Chiara Cappelli in her contribution . The development of effective methods allowing the treatment of dynamical effects is another key development of recent years.…”

“…New developments in this connection are described by Chiara Cappelli in her contribution. [7] The development of effective methods allowing the treatment of dynamical effects is another key development of recent years. In this connection Emilia Sicilia discusses the kinetics of complex reactions, [8] Dimitrios Skouteris reviews recent developments of time-independent and time-dependent approaches for isolated systems, [9] and Rocco Martinazzo analyzes analogous tools for processes at solid surfaces.…”