Amino acid , electron distribution

Azolecarboxylic acids can be quite strongly acidic. Thus l,2,5-thiadiazole-3,4-dicar-boxylic acid has first and second values of 1.6 and 4.1, respectively <68AHC(9)107). The acidic strengths of the oxazolecarboxylic acids are in the order 2>5>4, in agreement with the electron distribution within the oxazole ring <74AHC( 17)99). Azolecarboxylic acids are amino acids and can exist partly in the zwitterionic, or betaine, form e.g. 394). 

A semi-empirical molecular orbital method for the correlation of charge distributions with 13C shifts in amino acids was described [95]. Plotting of chemical shift parameters versus charge density changes of a-carbon atoms relative to the corresponding atoms in the parent hydrocarbons permits prediction of the chemical shifts of the a-carbons with an accuracy of about 10%. However, the slope (280 ppm per electron) in Fig. 5.12 is... 

The distribution of partial electronic charges within an amino acid gives rise to various permanent electronic dipole and higher order multipole... 

F. Kjeldsen, K. F. Sorensen, and R. A. Zubarev, Distribution of Iie/Leu amino acid residues in the PP3 protein by (hot) electron capture dissociation in Fourier transform ion cyclotron resonance mass spectrometry, Anal. Chem., 75 (2003) 1267-1274. 

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