Electrostatic enthalpy

Finally, the non-electrostatic components of the hydration enthalpy (Ai/n.eie) and entropy (-rA5n.eie) can be determined by subtracting the electrostatic enthalpy, Atfeie, and entropy -TASele from the known experimental quantities. 

Table 4-3. Enthalpic and entropic components of the electrostatic and non-electrostatic terms of the hydration free energy (kcal/mol). The non-electrostatic enthalpy and entropy were determined by subtracting the electrostatic enthalpy and entropy from the corresponding experimental data...

The Case of g < 1 The task is now to obtain an expression for the (electrostatic) enthalpy change upon mixing ng moles of polymeric salt (in the presence of ng j moles of simple salt) with an additional amount of simple salt, ng Q(] (j, so that the ratio of (total) simple salt to polymer equivalents passes from... 

Having assessed the assumptions in the derivation of the total excess electrostatic enthalpy of a polyelectrolyte solution with C >1> we will proceed further to evaluate AfTmix of equations (11) for the... 

An interesting case of application of equations (4) and (11) is to evaluate the (excess) electrostatic enthalpy change upon proton dissociation of a weak polyacid (e.g. a carboxylated polysaccharide). 

Upon introducing as a new variable the degree of ionization, a, the electrostatic enthalpy per mole of ionizable group, Up, will read ... 

For the sphere and DAPI both the NLPB and limiting law models (infinite length polymer at infinite dilution) give a slope with salt concentration close in magnitude to the net ligand charge. However, the enthalpy/entropy breakdown of the salt dependence is quite different. In the PB model, there are considerable contributions from electrostatic enthalpy and dielectric (water reorientation) entropy, compared to the cratic entropy of ion release in the limiting law model. 

The consistent force field (CFF) was developed to yield consistent accuracy of results for conformations, vibrational spectra, strain energy, and vibrational enthalpy of proteins. There are several variations on this, such as the Ure-Bradley version (UBCFF), a valence version (CVFF), and Lynghy CFF. The quantum mechanically parameterized force field (QMFF) was parameterized from ah initio results. CFF93 is a rescaling of QMFF to reproduce experimental results. These force fields use five to six valence terms, one of which is an electrostatic term, and four to six cross terms. 

The non-bonded interaction energy, the van-der-Waals and electrostatic part of the interaction Hamiltonian are best determined by parametrizing a molecular liquid that contains the same chemical groups as the polymers against the experimentally measured thermodynamical and dynamical data, e.g., enthalpy of vaporization, diffusion coefficient, or viscosity. The parameters can then be transferred to polymers, as was done in our case, for instance in polystyrene (from benzene) [19] or poly (vinyl alcohol) (from ethanol) [20,21]. 

A thermodynamic analysis regarding the relation between enthalpy and entropy values on the one hand and non-bulk electrostatic contributions on the other leads to the same result144). 

Chloromethane. bond length of, 335 bond strength of, 335 dipole moment of, 335 dissociation enthalpy of, 195 electrostatic potential map of, 38, 143.335... 

Theoretically, the problem has been attacked by various approaches and on different levels. Simple derivations are connected with the theory of extrathermodynamic relationships and consider a single and simple mechanism of interaction to be a sufficient condition (2, 120). Alternative simple derivations depend on a plurality of mechanisms (4, 121, 122) or a complex mechanism of so called cooperative processes (113), or a particular form of temperature dependence (123). Fundamental studies in the framework of statistical mechanics have been done by Riietschi (96), Ritchie and Sager (124), and Thorn (125). Theories of more limited range of application have been advanced for heterogeneous catalysis (4, 5, 46-48, 122) and for solution enthalpies and entropies (126). However, most theories are concerned with reactions in the condensed phase (6, 127) and assume the controlling factors to be solvent effects (13, 21, 56, 109, 116, 128-130), hydrogen bonding (131), steric (13, 116, 132) and electrostatic (37, 133) effects, and the tunnel effect (4,... 

Figure 5.5 Comparing liposome-water to octanol-water partition coefficients of a series of uncharged substituted benzylalkylamines [387]. The membrane partitioning of the smaller members of the series (n — 0 3) is thought to be dominated by electrostatic and H-bonding effects (enthalpy-driven), whereas the partitioning of the larger members is thought to be directed by hydrophobic forces (entropy-driven) [387]. [Avdeef, A., Curr. Topics Med. Chem., 1, 277-351 (2001). Reproduced with permission from Bentham Science Publishers, Ltd.]...

If a substance is to be dissolved, its ions or molecules must first move apart and then force their way between the solvent molecules which interact with the solute particles. If an ionic crystal is dissolved, electrostatic interaction forces must be overcome between the ions. The higher the dielectric constant of the solvent, the more effective this process is. The solvent-solute interaction is termed ion solvation (ion hydration in aqueous solutions). The importance of this phenomenon follows from comparison of the energy changes accompanying solvation of ions and uncharged molecules for monovalent ions, the enthalpy of hydration is about 400 kJ mol-1, and equals about 12 kJ mol-1 for simple non-polar species such as argon or methane. 

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