Academic literature on the topic 'Enthalpy of solvation'

Electrochemical measurements have been playing an increasingly important role in the thermodynamic study of reactions in solution, not only because they provide data that are difficult (or even impossible) to obtain by other methods but also because these data can often be compared with the values determined for the analogous gas-phase reactions, thus yielding information on solvation energetics. Figure 16.1 was adapted from a scheme proposed by Griller et al. It summarizes the thermochemical information on the R–X bond that can be probed by electrochemical methods. The vertical arrows represent homolytic cleavages, and the horizontal arrows depict reduction or oxidation potentials. The authors have appropriately called the scheme in figure 16.1 a “mnemonic,” rather than a “thermochemical cycle,” because not all arrow combinations define thermochemical cycles. This can be made more clear by inspecting figure 16.2, where true thermochemical cycles are defined. For example, the enthalpy of reaction 7 is not the sum of the enthalpies of reactions 1 and 4 (as might be suggested by figure 16.1) but their sum minus the enthalpy of reaction 12. In fact, true thermochemical cycles in figure 16.1 can only be defined by considering parallelograms confined either to the upper or the lower part of the mnemonic. For instance, the enthalpy of reaction 7 is given by the enthalpy of reaction 4 plus the enthalpy of reaction 9 minus the enthalpy of reaction 3, but it is not equal to the enthalpy of reaction 6 minus the enthalpy of reaction 11 plus the enthalpy of reaction 10. Also, the enthalpy of reaction 1 (the homolytic dissociation of the R–X bond in the neutral molecule RX) can be given by the sum of the enthalpies or reaction 5 and 11 minus the enthalpy of reaction 3 or, for example, by the sum of the enthalpies of reactions 7 and 12 minus the enthalpy of reaction 4. The attractive feature of the mnemonic in figure 16.1 (or the thermochemical cycles in figure 16.2) is that it depicts the seven possible R–X cleavage reactions of RX, RX−, and RX+, as well as their relationships.

In any reversible reaction such as . . . vA A + vB B ↔ vR R + vS S [2.1] . . . the system inevitably moves toward a state of equilibrium, or maximum probability. This equilibrium state is very important in analyzing chemical reactions because it defines the limit to which any reaction can proceed. Organic reactions, particularly those constituting a synthetic scheme for a fine chemical, usually involve molecules reacting in the liquid phase. The effects of reactant structure and of the solvent (medium) in which the reaction occurs (the solvation effects) are not included in the conventional macroscopic approach to thermodynamics. Therefore, the treatment of liquid-phase reactions tends to be less exact than that of gas-phase reactions involving simpler molecules without these influences. A convenient way of approaching this problem is to start with the conventional macroscopic or thermodynamic approach and add enough microscopic detail to allow for the effects of solute (reactant) structure and the medium. This approach is called the extrathermodynamic approach and may be regarded as bridging the gap between the two rather disparate fields of rates and equilibria represented by kinetics and thermodynamics, respectively. Such an approach is particularly useful in organic synthesis and forms the subject matter of this chapter. An important consideration in process calculations is the change that results in the basic thermodynamic properties, internal energy (U), enthalpy (H), Helmholtz work function (A), and Gibbs free energy (G) when a closed system of constant mass moves from one macroscopic state to another. For a homogeneous fluid, these change equations can be expressed in terms of four differential equations, which then can be written in difference form by employing the operator Δ to represent the change from state 1 to state 2: Of these, the enthalpy and free energy change equations are the most frequently used in the analysis of reactions.

In this work, molecular dynamics simulation (MD) was used to study the encapsulation of fat-soluble vitamins D3 (vD3) and E (a-TOC) into cucubit[7]uril (CB[7]) in an aqueous solution. Cucurbiturils is a class of macrocyclic molecules largely used as carrier and controlled release agent in order to improve the solubility and chemoprotective of drugs. Along 50 ns of MD trajectory, the vitamins formed a stable complex with CB[7] without significantly altering its structure. Moreover, the second solvation shell of the CB[7] was not disrupted by the inclusion of the vitamins. The solvation enthalpy