Solvent, screening effect

Neugebauer J et al (2010) A subsystem TDDFT approach for solvent screening effects on excitation energy transfer couplings. J Chem Theory Comput 6 1843-1851... 

A length characteristic of the solvent screening effect is the Bjerrum length ... 

Also use constant dielectric Tor MM+aiul OPLS ciilciilatimis. Use the (lislance-flepeiident dielecinc for AMBER and BlO+to mimic the screening effects of solvation when no explicit solvent molecules are present. The scale factor for the dielectric permittivity, n. can vary from 1 to H(l. IlyperChem sets tt to 1. .5 for MM-r. Use 1.0 for AMBER and OPLS. and 1.0-2..5 for BlO-r. 

Before running a molecular dynamics simulation with solvent and a molecular mechanics method, choose the appropriate dielectric constant. You specify the type and value of the dielectric constant in the Force Field Options dialog box. The dielectric constant defines the screening effect of solvent molecules on nonbonded (electrostatic) interactions. 

Baldridge et al.185 studied the effect of the solvent screening on the interactions between the formaldehyde and Na+ or Ca++ cations. In these studies, the cation and the formaldehyde molecule were localized inside the cavity of molecular shape. The reaction field po-... 

Baldridge, K., R. Fine, and A. Hagler. 1996. The Effect of Solvent Screening in Quantum Mechanical Calculations in Protein Systems. J. Comp. Chem. 1216. 

The increase in the anion concentration results in higher values of Cj at the maximum and in the shift of the maximum toward the zero charge density. The shift of the peak with increasing concentration is caused by the screening effect of the anions, accumulated in the diffuse layer and linked to the positive ends of the solvent dipoles. However, the changes in the shape of the C, vs. plots are greater on the negative than on the... 

Electron-deficient oxazoline thiourea 222 turned out to be the most effective catalyst concerning activity (93% yield/48h/THF) and asymmetric induction (88% ee/rt) in contrast to 218-221, which gave poor results (Figure 6.62). The solvent screening revealed aprotic THF to be the solvent of choice, while polar prohc... 

Femtosecond spectroscopic investigations in the spectral range 400-880 ran have permitted to discriminate specific OH effects on the dynamics of short lived UV excited CTTS states and transient near-IR (HO e )H20 pairs. The complex nature of ultrafast prehydration elementary redox reactions with nascent OH radical (strong acid) must be contemplated in the framework of ion-pairs dynamics, ion-solvent correlation function, short-range ordering water molecules, solvent screening or anisotropic electric field effects and short-time vibronic couplings. 

When selecting a desorption solvent, the effect of the solvent on recovery of sample matrix contaminants should be considered. If available, a control sample matrix should be screened against potential elution solvents to assess which solvents can be used to maximize recovery of the analyte of interest and minimize the elution of sample contaminants. 

The inclusion of electrostatic attraction depends on the assumed screening effect of the solvent, a problem similar to that of the Coulomb term in the free energy equations. This remains one of the major questions in the theory of e.t. reactions, and it may be safer to avoid any discussion of the kinetics of separation of ion pairs in polar solvents until this is resolved. 

This longitudinal relaxation time differs from the usual Debye relaxation time by a factor which depends on the static and optical dielectric constants of the solvent this is based on the fact that the first solvent shell is subjected to the unscreened electric field of the ionic or dipolar solute molecule, whereas in a macroscopic measurement the external field is reduced by the screening effect of the dielectric [73]. 

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