Solvation studies polarized continuum model

While these studies give good estimates for the IPs, it has been shown that the properties of DNA components are affected by the first few waters of hydration which mimic the first hydration shell around the molecule. For example, each water that acts as a net hydrogen bond donor to a base results in an elevation of the IP while each water that acts as a net hydrogen bond acceptor will tend to lower the IP [54], The solvation model, e.g., PCM (polarized continuum model), which takes into account the effect of the bulk solvent on the solute lacks these specific interactions and has the effect of substantially lowering the IP. Nevertheless, these first waters need to be included for a good accounting of IPs and EAs. 

The aqueous solvation free energies of the four tautomers available to the 5-(2H)-isoxazolone system have also been studied using a variety of continuum models (Table 7). Hillier and co-workers - " have provided data at the ab initio level using the Born-Kirkwood-Onsager model, the classical multipolar expansion model (up to I = 7), and an ab initio polarized continuum model. We examined the same BKO model with a different cavity radius and the AMl-SMl and AMl-SMla o- models, and Wang and Ford have performed calculations with the AMl-PCM model. 

The continuum model, in which solvent is regarded as a continuum dielectric, has been used to study solvent effects for a long time [2,3]. Because the electrostatic interaction in a polar system dominates over other forces such as van der Waals interactions, solvation energies can be approximated by a reaction field due to polarization of the dielectric continuum as solvent. Other contributions such as dispersion interactions, which must be explicitly considered for nonpolar solvent systems, have usually been treated with empirical quantity such as macroscopic surface tension of solvent. 

Solvent continuum models are now routinely used in quantum mechanical (QM) studies to calculate solvation effects on molecular properties and reactivity. In these models, the solvent is represented by a dielectric continuum that in the presence of electronic and nuclear charges of the solute polarizes, creating an electrostatic potential, the so-called reaction field . The concept goes back to classical electrostatic schemes by Martin [1], Bell [2] and Onsager [3] who made fundamental contributions to the theory of solutions. Scholte [4] and Kirkwood [5] introduced the use of multipole moment distributions. The first implementation in QM calculations was reported in a pioneer work by Rivail and Rinaldi [6,7], Other fundamental investigations were carried out by Tapia and Goscinski [8], Hilton-McCreery et al. [9] and Miertus et al. [10], Many improvements have been made since then (for a review,... 

No systematic study of the effect of different solvation models has been performed. A few reports have compared specific cases such as the study of cationic and anionic alanines, which shows a significant improvement in the chemical shift prediction using polarized continuum method (PCM) or better stiU a hybrid solvation approach (Section 1.4.3). However, the linear scaling correction discussed below can often account for the systematic solvent effect and so sometimes one can get away without any solvent computation at all. 

In the gas phase the neutral form is energetically favored, while in condensed phases, such as solutions in polar solvents and crystals, the ionic form is more stable. Glycine and alanine are zwitterionic in water solutions and their description is a rather challenging task for continuum solvation models. In the following we summarize the results of a study we have published on Theochem on structures and energies of tautomers of glycine and alanine in the framework of the lEF version of the Polarizable Continuum Model. 

Numerous theoretical studies on DMABN have been carried out, and many of them confirm the greater validity of the TICT model. The main body of such calculations, however, has been limited to the isolated system, while few examples including solvent effects can be quoted. " On the contrary, the phenomenon is strongly related to solvation and thus explicit considerations of solvent interactions are very important to get a more accurate understamding of the experimental evidence on the specific effects due to the presence of polar solvents. Here we summarize the results of the correlated study of DMABN both in vacuo and in solution we have published on the Journal of American Chemical Society. In this study we have used the multireference perturbation configuration interaction (Cl) method, known with the CIPSI acronym, which has been coupled to the PCM-IEF solvation continuum model. ... 

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