Mixed acid-base properties

Electrophoresis is used primarily to analyze mix tures of peptides and proteins rather than individual ammo acids but analogous principles apply Because they incorporate different numbers of ammo acids and because their side chains are different two pep tides will have slightly different acid-base properties and slightly different net charges at a particular pH Thus their mobilities m an electric field will be differ ent and electrophoresis can be used to separate them The medium used to separate peptides and proteins is typically a polyacrylamide gel leading to the term gel electrophoresis for this technique... 

The (I)-(III)-samples sorption ability investigation for cationic dyes microamounts has shown that for DG the maximum rate of extraction is within 70-90 % at pH 3. The isotherm of S-type proves the physical character of solution process and a seeming ionic exchange. Maximal rate of F extraction for all samples was 40-60 % at pH 8 due to electrostatic forces. The anionic dyes have more significant affinity to surface researching Al Oj-samples comparatively with cationic. The forms of obtained soi ption isotherms atpH have mixed character of H,F-type chemosorption mechanism of fonuation of a primary monolayer with the further bilayers formation due to H-bonds and hydrophobic interactions. The different values of pH p for sorbents and dyes confirm their multifunctional character and distinctions in the acid-base properties of adsoi ption centers. 

Di Cosimo et al. investigated the structural requirements and reaction pathways in condensation reactions of alcohols, using Mg/Al mixed oxides obtained by decomposition in N2 at 673 K for 4 h of LDH precursors with a wide range of composition [53], and found that the mechanistic pathway of the condensation reactions is affected not only by the catalyst acid-base properties but also by the chemical nature of the alcohols as well as steric factors. 

Another example of ACE analyses of solute-bilayer interactions was described by Roberts et al. (50), who observed retardation of riboflavin by liposomes. Analyses technically similar to liposomal ACE have been performed with mixed bile salt/phosphatidylcholine/fatty acid micelles (95). The partitioning of basic and acidic drugs depended on the acid-base properties of the drug and on the shape and charge of the mixed micelles. 

The acid-base properties of a mixed solvent is also an important factor influencing the behavior of solutes. Thus, the parameters of the acidity and basicity of mixed solvents have been studied to some extent [35], Figure 2.10 shows the donor numbers of mixtures of nitromethane and other organic solvents. Because ni-tromethane has very weak basicity (DN= 2.7), the addition of small amounts of basic solvents (HMPA, DMSO, pyridine) increase the donor number remarkably. 

The acid-base properties of polymers, fillers and silane additives, as described by Fowkes [14] can be used to predict the effect of silanes on the dispersion of fillers in polymer, and viscosity of the mix. In general, opposites attract (give good dispersion) while like materials repel (poor dispersion) [15]. The effect of cationic silane (Z-6032) on the dispersion of silica (acidic filler) in this particular unsaturated polyester resin (acidic polymer) is shown in Table 6. Addition of Z-6032 in increments to a silica-filled polyester resin lowered the viscosity of the mixture to a minimum at about 0.4% silane based on the filler. 

Shen, J., Kobe, J. M., Chen, Y. and Dumesic, J. A. (1994). Synthesis and surface acid/base properties of magnesium-aluminium mixed oxides obtained from hydrotalcites. Langmuir 10, 3902. 

Considerable attention has been devoted to the nature of the solvent effects (as determined in water and in various mixed solvents) on the ionic dissociations (and related thermodynamic quantities) and other acid-base properties of aliphatic zwitterionic compounds. Such investigations include studies of tricine in 50 mass % methanol-water (1), Bes in pure water and in 50 mass % methanol-water 2,3), glycine in 50 mass % monoglyme-water (4), and glycine in pure water and in 50 mass % methanol-water (5,6, 7). The numerous factors (8,9,10) which... 

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. 

The acid-base properties of mixed metal oxides have been found to change with the nature of the constituents, with their relative concentrations and with the preparation and pre-treatment procedures [81]. Accordingly, mixed oxides can be used to obtain catalysts with the desired acid-base characteristics by appropriately choosing the above-mentioned variables. 

The acid-base properties of ceria-zirconia solid solutions [82] and ceria-lanthana co-precipitated mixed oxides have been investigated by Cutrufello and... 

Thermal treatments induce dehydration, dehydroxylation and loss of the charge-compensating anions, resulting in mixed oxides with the MgO-type structure. Hydrotalcites are consequently a class of precursors useful for the preparation of catalytically active oxides showing basic properties [94], The acid-base properties of Mg-Al mixed oxides are governed by the Mg Al molar ratio, calcination temperature and preparation conditions. The study of the influence of the acid-base properties and chemical composition on the catalytic performance of calcined hydrotalcites is thus of interest. 

The main objective of this article is to present a survey of theoretical and applied aspects of microcalorimetry to heterogeneous catalysis with particular emphasis on the determination of acid-base properties of metal oxides and mixed metal oxides. This review is not meant to be comprehensive but to provide an overview of recent work done in the area. Additional applications can be found in recent reviews 1-4). 

In most recent calorimetric studies of the acid-base properties of metal oxides or mixed metal oxides, ammonia and n-butylamine have been used as the basic molecule to characterize the surface acidity, with a few studies using pyridine, triethylamine, or another basic molecule as the probe molecule. In some studies, an acidic probe molecule like CO2 or hexafluoroisopropanol have been used to characterize the surface basicity of metal oxides. A summary of these results on different metal oxides will be presented throughout this article. Heats of adsorption of the basic gases have been frequently measured near room temperature (e.g., 35, 73-75, 77, 78,81,139-145). As demonstrated in Section 111, A the measurement of heats of adsorption of these bases at room temperature might not give accurate quantitative results owing to nonspecific adsorption. 

The acid-base properties of amorphous mixed metal oxides can be varied by choosing different metal oxide constituents at diflerent concentrations and by changing the treatment of the sample (44). Thus, it appears that, by properly choosing the aforementioned variables, mixed oxides could be used to develop new catalysts with desired acid-base properties. The use of micro-calorimetric adsorption measurements to quantify the acid-base properties of metal oxides and mixed metal oxides has been limited, to date, to a few systems. However, for some of these solids, for example, silica, alumina, and silica-alumina, several investigations have led to a satisfactory description of their acidity and acid strength. We present here a compendium of those measurements and discuss some of the important properties observed. 

Apart from zeolites and ion-exchange resins (Sections 4 and 5), the main classes of catalyst which are active for dehydration are salts (usually sulphates, phosphates, and to a lesser extent, carbonates) and oxides (single and mixed). A large proportion of research has been devoted to a correlation of acid-base properties with activity for dehydration and dehydrogenation of alcohols, the two reactions being closely associated. 

Synthesis and acid-base properties of catalysts based on magnesium and sodium-magnesium mixed phosphates... 

Various solids consisting of magnesium and sodium-magnesium mixed orthophosphates were synthesized and used as catalysts in the transformation of 2-hexanol. The solids obtained were characterized by using various elucidation techniques. In particular, acid-base properties were determined by several methods. The solids were found to be active in the dehydration and dehydrogenation of the alcohol studied, and to be highly selective towards the dehydrogenation product in some instances. In addition to surface properties, the structure and composition of the catalysts -particularly their sodium content- appear to play essential roles in their catalytic behaviour. 

The data on the state of copper-containing phases and acid—base properties of active sites occurring at the surface of mixed cement systems, which were presented above, enable us to conclude that these catalysts can be employed in the oxidative ehlorination of ethane. 

The present chapter reviews the results of an investigation devoted to the study of the photodecarboxylation of ethanoic acid adsorbed over various solids. A series of pure insulator and semiconductor oxides covering a wide range of acid-base properties and a series of mixed insulator-insulator and insulator-semiconductor oxides of various composition were used for performing reactivity studies in a continuous photoreactor working in gas-solid regime. The nature of the species adsorbed over the various solids was monitored by IR spectra. 

The chemistry behind amino acid analysis is nothing more than acid-catalyzed hydrolysis of amide (peptide) bonds. The peptide is hydrolyzed by heating in 6 M hydrochloric acid for about 24 h to give a solution that contains all the amino acids. This mixture is then separated by ion-exchange chromatography, which separates the amino acids mainly according to their acid-base properties. As the amino acids leave the chromatography column, they are mixed with ninhydrin and the intensity of the ninhydrin... 

Interactions between the precious metal and support influence the performance of the catalyst. Beil (1987) has defined metal-support interaction as depending on contact between the metal particle and the support which can be a dissolution of the dispersed metal in the lattice. The interaction could also depend on the formation of a mixed metal oxide, or the decoration of the metal particle surface with oxidic moieties derived from the support. It is possible that in this study, the differences in catalytic performance of the same active material supported on different washcoats can be attributed to any of these phenomena. Another explanation could be that the support materials exhibit different acid-base properties. According to the Bronsted and Lewis definitions, a solid acid shows a tendency to donate a proton or to accept an electron pair, whereas a solid base tends to accept a proton or to donate an electron pair. The tendency of an oxide to become positively or negatively charged is thus a function of its composition, which is affected by the preparation method and the precursors used. Refer to the section Catalyst characterization for further discussion on the influence of support material on catalyst performance. To thoroughly examine the influence of the support... 

With the aim of studying the acid-base properties of Mg-Fe mixed oxides we chose the alkylation of m-cresol with methanol as a model reaction. The distribution of products obtained may take account of the different surface properties of the catalysts [3,4]. The catalytic performances were compared with the acid and basic sites distributions, as determined by pyridine and CO2 adsorption and desorption, respectively. 

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