Interaction energy achieving

Another important feature of some random copolymers is the abihty to achieve miscibility in either a homopolymer or a second random copolymer. This "copolymer effect" has been shown empirically for quite some time, eg, PVC is miscible with random copolymers of ethylene and vinyl acetate (52). Such systems are effective because repulsions between the dissimilar segments in the copolymer are enough to overcome the repulsions between these segments and those of the second component in the mixture. In other words, in the above example, the ethylene units "hate" vinyl acetate units more than either of them "hate" PVC. Thus there is a net negative interaction energy and the two materials are miscible (53). 

Enantioseparation is typically achieved as a result of the differences in interaction energies A(AG) between each enantiomer and a selector. This difference does not need to be very large, a modest A(AG) = 0.24 kcal/mol is sufficient to achieve a separation factor a of 1.5. Another mechanism of discrimination of enantiomers involves the preferential inclusion of one into a cavity or within the helical structure of a polymer. The selectivity of a selector is most often expressed in terms of retention of both enantiomers using the separation factor a that is defined as ... 

Computational analysis of binding site interactions is achieved by calculating the relative binding free energy (AAGbind) for a ligand L with an... 

However, significant stabilization is also contributed by nN—>-szn donor-acceptor interactions, each with estimated second-order interaction energy 49.4 kcal mol-1, as depicted in Fig. 4.52. Each ammine ligand thereby donates about 0.061 e to the zinc cation, primarily to the vacant 4s orbital which acquires about 0.371 e total occupancy. As before, the high formal hypervalency at the metal center is achieved within the limits of the duodectet rule, i.e., without significant involvement of extravalent metal p orbitals. 

The postulated transition state of the tt—a bond conversion occurs when the plane of the rotating benzene molecule is approximately at 45° to the catalyst surface. The electronic hybridization changes involved in this process (Fig. 4) are similar to those proposed by Melander 22) for homogeneous substitution reactions and show how resonance interactions may achieve a lowering in the activation energy. This aspect has previously been discussed in terms of the Lennard-Jones theory where the activation energy is lowered more effectively by resonance effects... 

The term interaction is sometimes used almost synonymously with cooperativity. In this book we reserve the term interaction to mean direct interaction energy between two (or more) particles. Indeed, sometimes interaction, in the above sense, is the sole source of cooperativity, in which case the two terms may be used interchangeably. However, in most cases of interest in biochemistry, interaction in the above sense is almost negligible, such as in two oxygen molecules in hemoglobin. Cooperativity in such systems is achieved by indirect routes of communication between the ligands. 

If separation according to functionality cannot be achieved because of a small difference between the interaction energies of the functional group and the chain groups, one can try to improve the efficiency of the separation system, but it is necessary to choose another stationary phase which is more selective with respect to functional groups. 

Under equilibrium conditions in a stressed b.c.c. Fe crystal, interstitial C atoms are generally unequally distributed among the three types of sites identified in Fig. 8.86. This occurs because the C atoms in sites 1, 2, and 3 in Fig. 8.86 expand the crystal preferentially along the x, y, and 2 directions, respectively. These directions are oriented differently in the stress field, and the C atoms in the various types of sites therefore have different interaction energies with the stress field. In the absence of applied stress, this effect does not exist and all sites are populated equally. In Exercise 8.22 it was shown that when the stress on an equilibrated specimen is suddenly released, the relaxation time for the nonuniformly distributed C atoms to achieve a random distribution, t, is t = 2/(3r), where T is the total jump frequency of a C atom in the unstressed crystal. 

On the other hand, intense fluid phases interaction is achieved, (at the cost of increased energy consumption) and TBRs are more and more used in fine chemicals, for hydrogenations at higher pressures than in STRs. 

Initially, an energetically favorable interaction was achieved by manual manipulation of the ligand with respect to hemin. Consideration of a large number of artemisinin analogues required an assumption that the peroxide docked to the hemin iron in a manner identified by Shukla et al.132 Docking was complete when the minimal combined electrostatic and steric docking energies were found. 

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