Carboxyl-carboxylate interactions

Interactions between charges and simple dipoles also occur in proteins, and carboxyl-carboxylate interactions (which are acid salts of monobasic carboxylic acids) were examined by Sawyer and James (1982). Fersht et al. (1985) have estimated the free energy change due to a hydrogen bond involving a charged donor or acceptor to be approximately -3 kcal/mol. 

Fig. 23. (continued)—(b) An axial projection of the unit cell shows that the helices associate via car-boxylate potassium water carboxylate interactions. 

Two helices are packed antiparallel in the orthorhombic unit cell. Association of the helices occurs through a series of periodic carboxylate potassium water - carboxylate interactions. An axial projection of the unit-cell contents (Fig. 23b) shows that the helices and guest molecules are closely packed. This is the first crystal structure of a polysaccharide in which all the guest molecules in the unit cell, consistent with the measured fiber density, have been experimentally located from difference electron-density maps. The final / -value is 0.26 for 54 reflections, of which 43 are observed, and it is based on normal scattering factors.15... 

Zinc carboxylate interactions have been exploited as part of a fluorescent molecular sensor for uronic acids. The sensors feature two interactions coordination of the carboxylate to the zinc and a boronic acid diol interaction.389 Photoluminescent coordination polymers from hydrothermal syntheses containing Zn40 or Zn4(OH)2 cores with isophthalate or fumarate and 4,4 -bipyridine form two- and three-dimensional structures. Single X-ray diffraction of both dicarboxylates identified the network structure.373... 

Guanidine forms salts with such relatively weak acids as nitromethane, phthalimide, phenol and carbonic acid [20], Interactions between carboxylate anions of proteins and added guanidinium ion are thought [19, 56] to be weaker than the interactions with ammonium ions the role of guanidinium-carboxylate interactions in stabilizing natural protein conformations has been discussed [36c]. A few reports of metal complex formation by guanidines [57-60], and aminoguanidines [61] have appeared. 

The contoured scatterplots showed that the most likely arrangements of metal cations are those designated syn, anti, and direct. The percentages of directionalities of metal liganding for a total of 1558 metal-carboxylate interactions are 62.9% syn, 22.7% anti, and 14.4% direct. Minimum metal ion-ligand distances are given in Table IX(a). syn is generally preferred, except when the distances are short... 

Einspahr, H., and Bugg, C. E. (1981). The geometry of calcium-carboxylate interactions in crystalline complexes. Acta Crystallogr. Sect. B 37, 1044-1052. 

Another crude model, this time for estimating the strength of tyrosyl-carboxylate interactions, was proposed by Wetlaufer (1956), who showed (1) a qualitatively weak interaction in the miscibility of phenol and aqueous sodium acetate solution, but (2) on the basis of the comparison of the solubility of tyrosine in sodium chloride and sodium acetate solutions, a maximum association constant no greater than 0.10 (assumed binary association) between tyrosine and acetate. By a comparison of salt effects... 

The primarily ionic nature of the RE(III)-carboxylate interaction suggests that a direct relationship between the ionic radii of the RE(III) and the stability of their complexes with car-boxylates should exist the stability constants of the complexes would increase monotonously from La(III) to Lu(III). However, the experimental results obtained indicate that this is only true for light rare earth metals from La(III) to Eu(III). Three different trends are observed for heavy rare earths from Gd(III) to Lu(III), that is, upward, flat, and downward. This is the so called gadoliniumbreak. Acetate, malonate, succinate, glutarate, and adipate complexes fall into the second category. The log Pi of the complexes remain almost unchanged from Gd(III) to Lu(III) (Table 3.2). There have been various interpretations of these trends, and the most widely accepted one is the change in the number of the hydration water molecules [98, 99]. 

Melo, A., and Ramos, M. J., Proton transfer in arginine-carboxylate interactions, Chem. Phys. Lett. 245, 498-502 (1995). 

Figure 5 Active-site model of cytochrome P450-IID6 with 16 substrates (23 metabolic reactions (A) fitted onto the template molecules debrisoquine and dex-trometorphan (B). Basic nitrogen atoms and , oxidation sites negative molecular electrostatic potentials as well as carboxylate interaction with the protein (Oj and OJ are indicated. (From Koymans et al., 1992.)...

In the past, considerable significance was attached to the syn-carboxylate interaction. Candour (1981) suggested that the syn electron pair may be more basic than the anti pair by a factor 10 -10. This seemed to explain the enhanced basicity of imidazole. However, studies of databases (Allen and Kirby, 1991) and model compounds (Zimmerman et ai, 1991) indicate that the difference in the relative basicities between syn- and anti-carboxylates is marginal (0.4—0.6 units). The hPL triad and the Asp-His couple in the active center of phospholipase A2 appear to support this view. Thus, the preference toward syn-type bonds observed in most serine proteinases may be due to packing effects in the active centers rather than to stereoelectronic effects. 

Although Bi(Hlac)3 is formally homoleptic, two lactate ligands are bound more tightly [Bi-Ocarboxyiate 2.205(7) A, Bi-Ohydroxy 2.474(8) A Bi-Ocarboxylate 2.364(8) A, Bi-Ohydroxy 2.457(9) A] than the third [Bi-Ocarboxylate 2.628(9) A, Bi-Ohydroxy 2.800(1) A], which bridges a second bismuth center via a bidentate carboxylate interaction 162). A carboxylate oxygen interacts with a third bismuth center, giving bismuth a total coordination number of 9 (49) and resulting in a complex three-dimensional network. 

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