Amino-substituted, circular dichroism

Protein stability is the free energy difference (AG) between the folded and unfolded states at physiological conditions, and it is in the range of 5-25 kcal/mol. Site-directed mutagenesis experiments provided a wealth of data for understanding the importance of chemical interactions for the stability of proteins during amino acid substitutions. Protein stability is experimentally measured with differential scanning calorimetry, circular dichroism, fluorescence spectroscopy, and so forth. The availability of such data in an electronically accessible database would be a valuable resource for the analysis and prediction of protein mutant stability. 

The principle of exciton coupling between vicinal benzoate chromophores has been extended to other aromatic carboxylic acid derivatives , including those of ring-substituted benzoic acids, 9-anthranoic acid (141) and p-methoxycinnamic acid (142). These derivatives have been widely used for the determination of the absolute stereochemistry in polyol natural products. The circular dichroism of the A -p-bromobenzoyl group combined with various 0-, 0,0 -di- and 0,0, 0"-tii-(p-bromobenzoyl) derivatives of 2-amino-2-deoxygalactopyranoside and an iV-anthranoyl group combined with tri-, tetra- and penta-p-methoxycinnamoyl derivatives of acyclic 1-amino polyols were studied to improve and develop microscale CD methods for the structural study of amino sugars. 

Treatment of a number of covalent polymers substituted with molecular recognition capability with suitable guests leads to chiral induction. The same crown ether-amino acid complementary pair described for the rosettes above was employed in the form of crown-ether pendant cis-transoidai poly(phenylacetylene). When the achiral polymer is treated with amino acids (in the form of their hydroperchlorate salts in acetonitdle) a large induced CD signal is observed in the backbone of the polymer. The polymer is sensitive to small enantiomeric excesses in the amino acid, as little as 0.005% enantiomeric excess of alanine can be detected. In a similar vein, c/5-transoidal poly(carboxyphenylacetylene) shows induced circular dichroism when treated with nonracemic chiral amines In addition, the system displays chiral memory, in that treatment of the complex with achiral amino alcohols results in retention of the chiral polymer backbone. 

Electronic circular dichroism for compounds without a chromophore To determine the absolute configuration of compounds without a chromophore in the accessible spectral region one or more proper groups can be derivatized to obtain an appropriate chromophoric system. The substitution of di-hydroxysteroids with two p-methoxybenzoates can be mentioned as an example. The substitution leads to an inherent dissymmetric chromophore for which the exciton chirality method can be applied. For chiral diols and amino alcohols another interesting possibility does exist. Complexing of these diols and amino alcohols with a transition metal... 

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