Thermodynamic measurements acid-base interaction

Retention of Rohrschneider-McReynolds standards of selected chiral alcohols and ketones was measured to determine the thermodynamic selectivity parameters of stationary phases containing (- -)-61 (M = Pr, Eu, Dy, Er, Yb, n = 3, R = Mef) dissolved in poly(dimethylsiloxane) . Separation of selected racemic alcohols and ketones was achieved and the determined values of thermodynamic enantioselectivity were correlated with the molecular structure of the solutes studied. The decrease of the ionic radius of lanthanides induces greater increase of complexation efficiency for the alcohols than for the ketone coordination complexes. The selectivity of the studied stationary phases follows a common trend which is rationalized in terms of opposing electronic and steric effects of the Lewis acid-base interactions between the selected alcohols, ketones and lanthanide chelates. The retention of over fifty solutes on five stationary phases containing 61 (M = Pr, Eu, Dy, Er, Yb, n = 3, R = Mef) dissolved in polydimethylsiloxane were later measured ". The initial motivation for this work was to explore the utility of a solvation parameter model proposed and developed by Abraham and coworkers for complexing stationary phases containing metal coordination centers. Linear solvation... 

The NMR technique can alco be used to advantage in many cases to follow acid-base interactions [SI 72]. If the NMR chemical shift of the free acid or the complex formed does not depend on the temperature, in addition to the equilibrium constants fairly accurate thermodynamic data can be obtained from the data measured at different temperatures. 

Sinicki and Berg varied the Lewis acid-base interactions systematically and found a correlation between adhesion measured by peel testing and the calculated thermodynamic work of adhesion [118]. 

Inverse gas chromatography analysis at very high dilution and at finite concentrations of probe injection was carried out on a series of polymers and pigments used in paint formulations. Values of dispersion surface energies, and of acid-base interaction parameters were obtained for the materials, and pair interaction parameters were calculated from the results. The dispersion stability of each pigment/ polymer combination was measured and correlated with the acid-base interaction parameters of the materials, and is shown to justify the availability of fundamental thermodynamic interaction data to optimise performance aspects of protective coatings. 23 refs. 

In addition to the base-pairing disruption, this melting also destroys the stacking of bases in fixed orientations relative to one another that is observed in the duplex. Later, we will present an argument based upon thermodynamic measurements of the stabilities of synthetic oligonucleotides (small pieces of synthetic nucleic acids) that the next-nearest neighbor interactions observed in the base stacking sequence are a major contributor to the relative stabilities of duplexes. 

In order to try to clarify the different types of mechanism involving either redox cycles and/or acid-base properties, a study of the surface chemistry of single, doped and mixed oxides is of much interest. The calorimetric technique, by allowing heat transfer measurements, can provide very informative data on the thermodynamics of solid-gas interactions and for the study of the surface and reactivity of these metal oxides. 

Overall the polymers investigated were predominantly basic since they interacted most strongly with the acidic probes. Nitromethane, which is slightly basic but has the same acid strength as methylene chloride, had an enthalpy of interaction lower than that for the methylene chloride. This indicated that the basicity of nitromethane resulted in a less favorable interaction with the basic polymer surfaces. The non-dispersive interactions were not determined for polyetherimide since all of these probes resulted in nonsymetric, tailing peaks. Perhaps the polyetherimide is quite a strong base and attracted the acidic probes sufficiently to prevent equilibrium thermodynamic measurements. 

Inverse gas chromatography involves the sorption of a known probe molecule (adsorbate, vapour) and an unknown adsorbent stationary phase (solid sample). IGC may be experimentally configured for finite or infinite dilution concentrations of the adsorbate. The latter method is excellent for the determination of thermodynamic properties such as surface energies and Lewis acid-base parameters. Measurements in this range are extremely sensitive due to the low concentration regime where the highest energy sites of the surface interact with the probe molecules. 

This book presents coverage of the dynamics, preparation, application and physico-chemical properties of polymer solutions and colloids. It also covers the adsorption characteristics at and the adhesion properties of polymer surfaces. It is written by 23 contemporary experts within their field. Main headings include Structural ordering in polymer solutions Influence of surface Structure on polymer surface behaviour Advances in preparations and appUcations of polymeric microspheres Latex particle heterogeneity origins, detection, and consequences Electrokinetic behaviour of polymer colloids Interaction of polymer latices with other inorganic colloids Thermodynamic and kinetic aspects of bridging flocculation Metal complexation in polymer systems Adsorption of quaternary ammonium compounds art polymer surfaces Adsorption onto polytetrafluoroethylene from aqueous solutions Adsorption from polymer mixtures at the interface with solids Polymer adsorption at oxide surface Preparation of oxide-coated cellulose fibre The evaluation of acid-base properties of polymer surfaces by wettability measurements. Each chapter is well referenced. 

The thermodynamic and analytical aspects of acid-base reactions in aprotic solvents are surveyed in reviews by Davis [1, 2]. The correlation of acid-base strength in water and aprotic solvents is of major importance. Early kinetic work by Bell and co-workers on the acid catalysis of (i) the ethyldiazoacetate-phenol interaction [3] (ii) the rearrangement of N-bromoacetanilide [4] and (iii) the inversion of /-menthone [5] established an order of acid strengths in aprotic media and the importance of intra-molecular hydrogen bonds e.g in picric acid). A thermodynamic method using reference acids and bases is more direct, and Bell and Bayles [6] employed the indicator acid Bromophenol Blue to obtain a basicity order for weak amine bases. Kinetic measurements on these systems have recently been made, and are considered in detail in Section 7. 

QM calculations (on nucieobase dimers) reveal the binding energy between two bases in the gas phase, i.e., in complete isolation. They thus describe the intrinsic interactions of the systems with no perturbation by external effects such as solvent. The intrinsic intermolecular stabilities are directly linked to moiecuiar structures and can be derived in any selected geometry. However, the gas phase interaction energies do not correspond to the stability of the interactions in nucleic acids, as measured by thermodynamics experiments. It is not possible to easily correlate the QM calculations with measured base pairing and stacking stabilities in nucleic acids. The apparent (measured) strength of the base-base interactions in nucleic acids in various experiments is determined by a complex interplay of many factors and the intrinsic base-base term is only one of them. Many researchers incorrectly believe that the experiments reflect the true stabilities of base-base interactions and vice versa. 

A combination of uncertainty in thermodynamic data accuracy at elevated temperatures and overall lack of completeness with respect to organic compound class and interaction types (complex formation, adsorption, solid precipitate) poses some real limitations in the use of chemical and reaction path models. Thus, a cautionary note is that to compare results of different numerical studies it is necessary to know whether similar thermodynamic data bases were used. As we will show below, apparently discrepant conclusions drawn from modeling studies probably result from the use of more or less complete thermodynamic data. Of concern in the investigation of organic acid interactions in silicate rocks is the complete lack of any equilibrium measurements of silica-organic acid anion interactions, although dissolution rate measurements have been made (Bennett et al. 1988 Bennett 1991). 

The reactivity of the ring opening toward a cationic mechanism is mainly dictated by the nucleophilicity or the basicity of the monomer. The nucleophilicity of a monomer, that is, its ability to combine with electrophilic species, is determined by kinetically controlled conditions, and unfortunately, no general order of nucleophilicity is known. The monomer basicity, that is, its ability to interact with a proton, can be measured from thermodynamically controlled conditions. The most common method used to determine the basicity is based on the proportion of hydrogen-bonded compound measured at equilibrium. The basicity decreases in the following order R3N > R3P > R2O > R2S, although R2S is more basic than R2O when the ability of bonding with softer acids is measured. Tn the case of cyclic eth s, the ba city order is as follows 2)3 > ( 2) > <5 112)5 >... 

From the results summarized in Table I, apparently the Brpnsted relationship will hold for all combinations of nucleophiles and electrophiles. Because, as pointed out previously, the Hammett equation is really a special case of the Brpnsted relationship, all the legion of nucleophile-electrophile, rate-equilibrium Hammett correlations that have been studied also fall under the scope of the Brpnsted relationship. For example, nucleophilicities of ArO , ArS , ArC(CN)2 , and the other families listed in footnote c of Table I have generally been correlated by the Hammett equation, where the acidities of benzoic acids in water are used as a model for substituent interactions with the reaction site (a), and the variable parameter p is used to define the sensitivity of the rate constants to these substituent effects. The Brpnsted equation (equation 3) offers a much more precise relationship of the same kind, because this equation does not depend on an arbitrary model and allows rate and equilibrium constants to be measured in the same solvent. Furthermore, the Brpnsted relationship is also applicable to families of aliphatic bases such as carboxylate ions (GCH2C02 ), alkoxide ions (GCH20 ), and amines (GCH2NH2). In addition, other correlations of a kinetic parameter (log fc, AGf, Ea, etc.) can be included with various thermodynamic parameters (pKfl, AG°, Eox, etc.) under the Brpnsted label. 

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