Exchange attraction

Those familiar with the language of the molecular orbital picture of bonding may be surprised that no parallel to the delocalization energy seems present in our description. That effect would occur in the VB treatment only if ionic terms axe included. We thus conclude that delocalization is less important than the exchange attraction in bonding. 

An early report by Shilov et al that PtCU in CH3COOD homogeneously effected H/D exchange attracted much attention. The reaction may go via electrophilic attack of the metal on the alkane, but the details are not yet clear. 

Cellular imaging has become a topic of intensive research in recent years, and luminescent metal-based probes have been intensively utilized for such a process. The transition metal ions of ruthenium(II), rhenium(I), and iridium(III) have been particularly effective as luminescent intracellular imaging agents owing to their kinetic inertness (low rates of ligand exchange), attractive photophysical properties (large... 

The intermicellar potential U reflects the superposition of an osmotic repulsion and the exchange attraction. To obtain the second virial coefficient of micelle-micelle interactions, B, we approximate f/ as a square-well potential of width out and depth AFejchange having an infinite wall at L - Accordingly, 5 = J [1 exp(-[//jfeT)]r2dris... 

In the case of spherical starlike micelles it is possible to estimate the exchange attraction on the basis of a blobological picture, the Daoud-Cotton model. Two ingredients are involved. The concentration profile predicted by this... 

Functional fonns based on the above ideas are used in the FIFD [127] and Tang-Toeimies models [129], where the repulsion tenn is obtained by fitting to Flartree-Fock calculations, and in the XC model [92] where the repulsion is modelled by an ab initio Coulomb tenn and a semi-empirical exchange-repulsion tenn Cunent versions of all these models employ an individually damped dispersion series for the attractive... 

Thus E. is the average value of the kinetic energy plus the Coulombic attraction to the nuclei for an electron in ( ). plus the sum over all of the spin orbitals occupied in of the Coulomb minus exchange interactions. If is an occupied spin orbital, the temi [J.. - K..] disappears and the latter sum represents the Coulomb minus exchange interaction of ( ). with all of the 1 other occupied spin orbitals. If is a virtual spin orbital, this cancellation does not occur, and one obtains the Coulomb minus exchange interaction of cji. with all N of the occupied spin orbitals. 

The ability of living organisms to differentiate between the chemically similar sodium and potassium ions must depend upon some difference between these two ions in aqueous solution. Essentially, this difference is one of size of the hydrated ions, which in turn means a difference in the force of electrostatic (coulombic) attraction between the hydrated cation and a negatively-charged site in the cell membrane thus a site may be able to accept the smaller ion Na (aq) and reject the larger K (aq). This same mechanism of selectivity operates in other ion-selection processes, notably in ion-exchange resins. 

Qualitatively, the first term of Eq. (27) represents the electron exchange repulsion as a result of the Pauli principle, and the second long-range term accounts for the attractive dispersion interaction. The [12-6] formulation is only qualitatively... 

The first three terms in Eq. (10-26), the election kinetic energy, the nucleus-election Coulombic attraction, and the repulsion term between charge distributions at points Ti and V2, are classical terms. All of the quantum effects are included in the exchange-correlation potential... 

The exchange repulsion and dispersive attraction com bine in what is referred to as a van der Waals term. Sometimes a potential is added to account for hydrogen bonding explicitly while in other situations this is expected to fall out of ordinary electrostatic interactions. 

---