Base properties

Ireland J F and Wyatt PAH 1976 Acid-base properties of electronically excited states of organic molecules Adi/. Rhys. Org. Chem. 12 131-221... 

This basic LFER approach has later been extended to the more general concept of fragmentation. Molecules are dissected into substructures and each substructure is seen to contribute a constant inaement to the free-energy based property. The promise of strict linearity does not hold true in most cases, so corrections have to be applied in the majority of methods based on a fragmentation approach. Correction terms are often related to long range interactions such as resonance or steric effects. 

Furthermore, QSPR models for the prediction of free-energy based properties that are based on multilinear regression analysis are often referred to as LFER models, especially, in the wide field of quantitative structure-activity relationships (QSAR). 

Acid-Base Properties of Amino Acids with Neutral Side Chains... 

Individual ammo acids differ m their acid-base properties This is important m peptides and proteins where the properties of the substance depend on its ammo acid constituents especially on the nature of the side chains It is also important m analyses m which a complex mixture of ammo acids is separated into its components by taking advantage of the differences m their proton donating and accepting power... 

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... 

Acid-Base Properties of Ammo Acids (Tables 27 2 and 27 3, p 1059)... 

Now the overall effects due to hydrogen bonding, dipole moment, acid-base properties, and molecular configuration can be expressed as... 

Conditional Metal—Ligand Formation Constants Recognizing EDTA s acid-base properties is important. The formation constant for CdY in equation 9.11 assumes that EDTA is present as Y . If we restrict the pH to levels greater than 12, then equation 9.11 provides an adequate description of the formation of CdY . for pH levels less than 12, however, K overestimates the stability of the CdY complex. 

To correct the formation constant for EDTA s acid-base properties, we must account for the fraction, ayi-, of EDTA present as Y . 

As with EDTA, which we encountered in Chapter 9, o-phenanthroline is a ligand possessing acid-base properties. The formation of the Fe(o-phen)3 + complex, therefore, is less favorable at lower pH levels, where o-phenanthroline is protonated. The result is a decrease in absorbance. When the pH is greater than 9, competition for Fe + between OH and o-phenanthroline also leads to a decrease in absorbance. In addition, if the pH is sufficiently basic there is a risk that the iron will precipitate as Fe(OH)2. 

In the most general sense, a molecular-based property prediction method can be thought of as any method in which the physical features of a molecule (or... 

The acid-base properties of isoxazole and methylisoxazoles were studied in proton donor solvents, basic solvents or DMSO by IR procedures and the weakly basic properties examined (78CR(Q(268)613). The basicity and conjugation properties of arylisoxazoles were also studied by UV and basicity measurements, and it was found that 3-substituted isoxazoles were always less basic than the 5-derivatives. Protonation increased the conjugation in these systems (78KGS327). 

Usually the acid-base properties of poly electrolyte are studied by potentiometric titrations. However it is well known, that understanding of polyelectrolyte properties in solution is based on the knowledge of the thermodynamic properties. Up to now, there is only a small number of microcalorimetry titrations of polyelectrolyte solutions published. Therefore we carried out potentiometric and microcalorimetric titrations of hydrochloric form of the linear and branched polyamines at 25°C and 65°C, to study the influence of the stmcture on the acid-base properties. 

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. 

Primary amines are stronger bases than secondary amines, which arc stronger than tertiary amines. Amines with stronger base properties will be more reactive toward CO2 and H2S gases and will form stronger chemical bonds. 

Classification according to Br nsted acid-base properties is useful. 

Proteins are the indispensable agents of biological function, and amino acids are the building blocks of proteins. The stunning diversity of the thousands of proteins found in nature arises from the intrinsic properties of only 20 commonly occurring amino acids. These features include (1) the capacity to polymerize, (2) novel acid-base properties, (3) varied structure and chemical functionality in the amino acid side chains, and (4) chirality. This chapter describes each of these properties, laying a foundation for discussions of protein structure (Chapters 5 and 6), enzyme function (Chapters 14-16), and many other subjects in later chapters. 

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