Dielectric environments

Kelly, K.L., Coronado, E., Zhao, L.L. and Schatz, G.C. (2003) The optical properties of metal nanoparticles the influence of size, shape, and dielectric environment. The Journal of Physical Chemistry B, 107, 668-677. 

The electrical potentials assumed to exist at liquid-liquid interfaces, including inert gas or liquid dielectric environments are presented in Fig. 1. 

An interesting hypothesis may be put forward. The interfacial pA lcm (Fig. 5.1) that a solute exhibits depends on the dielectric environment of its location in the bilayer. Simple isotropic water-miscible solvents may be used to approximate p mem pure methanol (e 32), may do well for the bilayer zone containing the phosphate groups pure 1,4-dioxane (e 2) may mimic some of the dielectric properties of the hydrocarbon region. It appears that psKa values of several weak bases, when extrapolated to 100% cosolvent, do approximate pvalues [119,162,172]. Fernandez and Fromherz made favorable comparisons using dioxane [448]. This idea is of considerable practical use, and has been largely neglected in the literature. 

The SCRF approach became a standard tool167 for estimating solvent effects and was combined with various quantum chemical methods that range from semi-empirical161 to the post-Hartree-Fock ab initio ones. It can also be combined with the Kohn-Sham formalism where the Kohn-Sham Hamiltonian (Eq. 4.2) is used for the gas-phase Hamiltonian in Eq. 4.15. The effective Kohn-Sham Hamiltonian for the system embedded in the dielectric environment takes the following form ... 

To study the structural behaviour of MAPs, an adequate membrane model (see Fig. 5) is essential. Simple organic solvent systems, such as DMSO, MeOH/H20 or TFE/PLO mixtures, present a similar dielectric environment as a membrane on... 

A homogenous dielectric environment with the didctric constant of water was modded using SCRF calculations (see Wong, M. W. Frisch, M. J. Wiberg, K. B. Solvent Effects. 1. The Mediation of Electrostatic Effects by Solvents J. Am. Chon. Soc 1991,113,4776-4782). 

All stationary point geometries were fully optimized at the HF/6-31G level of theory and characterized by harmonic frequency analysis. Single point energies were evaluated at the MP2/6-31G level to account for the effects of electron correlation. Since experiments were carried out in a relatively low dielectric environment (chlorobenzene solvent), it is likely that the shape of the potential energy surface in the gas phase and solution would be comparable... 

The MPE study of the dielectric environment effects on the spin-spin coupling constants of acetylene [43] allowed for a comparison with experimentally measured gas-to-solution shifts for a series of solvents of varying polarity. It has been found in the experimental study that 1JCC changes considerably with the solvent, and that the changes correlate approximately with the solvent polarity. This tendency has been qualitatively reproduced by the MPE MCSCF linear response calculation, although the calculated changes constitute only approximately 30 % of the experimental shifts. 

At a more detailed level, we note that the solvent effects on the optical rotation have the same origins as solvent effects on the energy itself, as described in detail in other contributions to this book. Most other studies of solvent effects on natural optical activity have focused on the electrostatic contributions. These contributions can be partitioned into direct effects arising from the influence of the dielectric environment on the electronic density of the solute, and into indirect effects arising from the relaxation of the nuclear structure in the solvent. For conformationally flexible molecules, we may also consider a third possible solvent effect due to the changes in the conformational equilibria when going from the gas phase to solution. 

In contrast, EET has been historically modelled in terms of two main schemes the Forster transfer [15], a resonant dipole-dipole interaction, and the Dexter transfer [16], based on wavefunction overlap. The effects of the environment where early recognized by Forster in its unified theory of EET, where the Coulomb interaction between donor and acceptor transition dipoles is screened by the presence of the environment (represented as a dielectric) through a screening factor l/n2, where n is the solvent refractive index. This description is clearly an approximation of the global effects induced by a polarizable environment on EET. In fact, the presence of a dielectric environment not only screens the Coulomb interactions as formulated by Forster but also affects all the electronic properties of the interacting donor and acceptor [17],... 

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