Coulomb interactions acids

ACID DYES Commercial acid dyes contain one or more sulfonate groups, thereby providing solubility in aqueous media. These dyes are apphed in the presence of organic or mineral acids (pH 2—6). Such acids protonate any available cationic sites on the fiber, thereby making possible bonding between the fiber and the anionic dye molecule. Wool, an animal fiber, is an amphoteric coUoid, possessing both basic and acidic properties because of the amino and carboxylic groups of the protein stmcture. In order to dye such a system, coulombic interactions between the dye molecule and the fiber must take place ie, H2N" -wool-COO + H2N" -wool-COOH. The term acid dye is appHed to those that are capable of such interactions. Acid dyes... 

This quick glance at the acid-base properties of some (poly)azamacro-cycles already suggests which parameters will determine the p a of macrocyclic and related acids and bases. Hydrogen bonds will probably be very important and in polyions Coulomb interactions have to be taken into consideration. But the geometry of the acid-base function has to be defined. In Sections 2, 3 and 4 we shall therefore focus on compounds with intra-annular acid-base functionalities (the 1,3-xylyl trick). 

The case of succinic acid cannot be discussed in terms of Coulombic interactions alone. Here, conformational changes induced by the binding process can contribute significantly to the correlation. Note also that g(l, 1) [or W(l, 1)] of succinic acid is not an average of the correlations in maleic and fiimaric acids. This could be partially due to the configurational changes in the succinic acid, induced by the binding process. We shall discuss below a simple two-state model for succinic acid, and a continuous model in the next subsection. 

An alternative view is provided by a pair of electrostatic potential maps. Electron-rich heteroatoms line up with the electron-poor (acidic) hydrogens. Attraction between the two bases may be thought of as due to favorable Coulombic interactions. 

Hence, 4-keto flavonoids can be partially dissociated at neutral pH and eventually involved in attractive coulombic interactions with positively charged amino acid residues. 

Figure 4 shows our 3D model of human 11P-HSD types 1 and 2. These models identify residues important in preference of 1 ip-HSD-1 for NADPH and 1 ip-HSD-2 for NADH. In 11P-HSD type 1, lysine-44 and arginine-66 have favorable coulombic interactions with the 2 -phosphate on NADP+ that stabilize binding (Figure 4a). Moreover, their positively charged side chains compensate for the negative interaction between glutamic acid-69 and the 2 -phosphate group. Tanaka et al. [37] found a similar function for lysine-14 and arginine-39 in the preference of mouse carbonyl reductase for NADPH.

Real proteins are built up both from hydrophobic and polar amino acid residues, some of the latter can be charged. Many of the conformational and collective properties of proteins are due to a complex interplay between short-range (hydrophobic) effects and long-range (Coulomb) interactions. Electrostatic effects can also determine some of the unique solution properties of globular proteins. We have already discussed the results of simulations... 

Both poly(l-butyl-5-vinylimidazole), poly(lB-5IM), and poly(l-methyl-5-vinyl-imidazole), poly(lM-5IM), have no quatemizable nitrogen, so that the coulombic interaction with the substrate is not necessarily to be considered. Using these polymers, hydrolyses of several 3-nitro-4-acyloxy benzoic acid having various acyl chain length (8) (n = 0,5,10,16) have been made (55). The apparent rates of hydrolyses are tabulated in Table 7. 

Contributions of both the hydrophobic and the coulombic interaction are indicated in the hydrolyses of 3-nitroacyloxy benzoic acid (8) by poly(5(6)-vinyl-benzimidazole) (67) and of 3-acyloxy-N-trimethylanilinium iodide (acyloxy group in lieu of acetoxy group in ANTI (6)) by poly(5(6)-vinylbenzimidazole-co-acrylic acid), poly(BI-ac) (68). 

For most vapor-phase complexes of type (6) the Coulomb interaction compensates only part of the proton transfer energy AE and we expect to find neutral type complexes (NC). The only candidates for ionic complexes (IC) or intermediate cases are the associations of strong bases with strong acids, e.g. the complexes between ammonia or aliphatic amines and HC1, HBr or HJ (Table 1). 

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