Intermolecular interactions, quantitative

Essential progress has been made recently in the area of molecular level modeling of capillary condensation. The methods of grand canonical Monte Carlo (GCMC) simulations [4], molecular dynamics (MD) [5], and density functional theory (DFT) [6] are capable of generating hysteresis loops for sorption of simple fluids in model pores. In our previous publications (see [7] and references therein), we have shown that the non-local density functional theory (NLDFT) with properly chosen parameters of fluid-fluid and fluid-solid intermolecular interactions quantitatively predicts desorption branches of hysteretic isotherms of nitrogen and argon on reference MCM-41 samples with pore channels narrower than 5 nm. 

The non-local density functional theory (NLDFT) with properly chosen parameters of fluid-fluid and fluid-solid intermolecular interactions quantitatively predicts both adsorption and desorption branches of capillary condensation isotherms on MCM-41 materials with the pore sizes from 5 to 10 nm. Both experimental branches can be used for calculating the pore size distributions in this pore size range. However for the samples with smaller pores, the desorption branch has an advantage of being theoretically accurate. Thus, we recommend to use the desorption isotherms for estimating the pore size distributions in mesoporous materials of MCM-41 type, provided that the pore networking effects are absent. 

Promise to determine intra- and intermolecular interactions quantitatively. 

The applications of quantitative structure-reactivity analysis to cyclodextrin com-plexation and cyclodextrin catalysis, mostly from our laboratories, as well as the experimental and theoretical backgrounds of these approaches, are reviewed. These approaches enable us to separate several intermolecular interactions, acting simultaneously, from one another in terms of physicochemical parameters, to evaluate the extent to which each interaction contributes, and to predict thermodynamic stabilities and/or kinetic rate constants experimentally undetermined. Conclusions obtained are mostly consistent with those deduced from experimental measurements. 

It is known that several intermolecular interactions are responsible for cyclodextrin complexation, acting simultaneously. These interactions are separable from one another by quantitative structure-reactivity analysis. Furthermore, correlations obtained by the analysis can be discussed in direct connection with actual interactions already elucidated experimentally for the action site of cyclodextrin. Thus, the results must serve to make the background of the correlation analysis more concrete. 

As shown above, quantitative structure-reactivity analysis is very useful in elucidating the mechanisms of cyclodextrin complexation and cyclodextrin catalysis. This method enables us to separate several intermolecular interactions, acting simultaneously,... 

It was concluded that the filler partition and the contribution of the interphase thickness in mbber blends can be quantitatively estimated by dynamic mechanical analysis and good fitting results can be obtained by using modified spline fit functions. The volume fraction and thickness of the interphase decrease in accordance with the intensity of intermolecular interaction. 

Thermodynamics describes the behaviour of systems in terms of quantities and functions of state, but cannot express these quantities in terms of model concepts and assumptions on the structure of the system, inter-molecular forces, etc. This is also true of the activity coefficients thermodynamics defines these quantities and gives their dependence on the temperature, pressure and composition, but cannot interpret them from the point of view of intermolecular interactions. Every theoretical expression of the activity coefficients as a function of the composition of the solution is necessarily based on extrathermodynamic, mainly statistical concepts. This approach makes it possible to elaborate quantitatively the theory of individual activity coefficients. Their values are of paramount importance, for example, for operational definition of the pH and its potentiometric determination (Section 3.3.2), for potentiometric measurement with ion-selective electrodes (Section 6.3), in general for all the systems where liquid junctions appear (Section 2.5.3), etc. 

An alternative approach is to replace an accurate but expensive first-principle-based technique by a reliable model potential. Such potentials, broadly referred to as molecular mechanics (MM), generally cannot account for bond-breaking, but can, in principle, account for the range of intermolecular interactions. However, using a fitted pair-wise potential may result in losing quantitative accuracy, predictability, and the underlying physics. 

Ferenczy GG, Winn PJ, Reynolds CA, Richter G (1997) Effective distributed multipoles for the quantitative description of electrostatics and polarisation in intermolecular interactions. Abs Papers Am Chem Soc 214 38-COMP... 

Next, a quantitative model, referred to as the E and C equation, is presented for predicting and correlating the enthalpies of adduct formation. The use of this equation and the interpretation of the parameters which result is discussed. Exceptions to the correlation are considered and the valuable insight about intermolecular interactions that can be gained by firmly establishing these exceptions is demonstrated. The parameters we obtain and valid transformations of these parameters are considered in the light of both the HSAB model and Donor Strength model of acid-base chemistry. Both of these concepts are shown to be at best incomplete models of coordination. The relationship between our parameters and the a—q Hammett parameters is quantitatively demonstrated. 

Next, we shall describe why the magnitudes of the E and C numbers are not just quantitative manifestations of the HSAB concept, but give insight into intermolecular interactions which are absent in the qualitative soft-soft and hard-hard labeling of interactions. As can be seen from the data in Tables 3 and 4, each acid and base has both a C and an E number which could be thought to correspond to possessing properties of softness and hardness. If this were the case, ammonia, which Pearson labels hard, has a larger Cb value than benzene, which is labeled soft. 

The moments of a charge distribution provide a concise summary of the nature of that distribution. They are suitable for quantitative comparison of experimental charge densities with theoretical results. As many of the moments can be obtained by spectroscopic and dielectric methods, the comparison between techniques can serve as a calibration of experimental and theoretical charge densities. Conversely, since the full charge density is not accessible by the other experimental methods, the comparison provides an interpretation of the results of the complementary physical techniques. The electrostatic moments are of practical importance, as they occur in the expressions for intermolecular interactions and the lattice energies of crystals. 

Structural chemists have nowadays at their disposal a wide range of reliable methods for the quantitative estimation of intermolecular interaction energies. 

The relationship between odour quality and chemical structure is of considerable practical and theoretical interest. A numt r of methods have been used to determine quantitatively the relationships between the structure of a molecule and its odour quality (7). Though quantitative results were not obtained, a number of interesting theories were present in that the intermolecular interaction in olfaction involved electrostatic attraction, hydrophobic bonding, van der Waals forces, hydrogen bonding, and dipole-dipole interactions. Hydrophobic interactions also appeared to be a major force for substrate binding in olfaction. It had previously been shown that lipophilicity and water solubility were factors diat significandy influenced the odour thresholds of the pyrazines (8),... 

In the field of food colloids, the use of molecular thermodynamics provides a set of qualitative and quantitative relationships describing fundamental phenomena occurring in the equilibrium state of systems for which the intermolecular interactions of biopolymers (proteins and polysaccharides) play a key role. The phenomena and processes amenable to discussion from the thermodynamic point of view are ... 

A knowledge of the magnitude of these quantities and their quantitative contributions to /uE can give insight into the detailed character of the intermolecular interactions in a biopolymer solution, including the means by which their properties may be manipulated. The sign of the second virial coefficient provides a simple indicator of the type of interactions... 

Part Two outlines the fundamental principles and practices underlying the study of biopolymer interactions. Chapter four characterizes the different kinds of intermolecular forces that can occur between biopolymers in bulk aqueous media, including the interfacial region. Chapter five sets out the thermodynamic parameters that can describe these interactions quantitatively, together with the experimental methods available for their determination. 

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