engleski

Effects of N,N-dialkyl chain lengthening on the stereochemistry of copper(II) alpha-alaninato complexes : a molecular mechanics study

Copper(II) chelates with N-alkylated amino acids may have catalytic ability to dismutate superoxide radicals, O2.-, that is, that they may successfully mimic superoxide dismutase (SOD), the physiological scavenger of very reactive superoxide anions. As one of the requirements for an effective SOD-mimetic compound is the solubility in cell membranes,1 we suppose that lengthy alkyl chain substituents at the amino nitrogen should make bis(aminoacidato)copper(II) complexes soluble both in water and phospholipid vesicles. In order to examine the influence of different N-alkyl substituents on properties of a copper(II) amino acid complex, ƒŃ-alanine was chosen as the amino acid. A new force field (FF1) was used to investigate the effects of N,N-dialkyl chain lengthening on the stereochemistry of bis(N,N-dialkylalaninato)copper(II) complexes (alkyl: methyl, ethyl, propyl). The FF1 force field was derived with the aim to simulate and predict properties of both cis and trans tetra-coordinated copper(II) amino acid complexes. The conformational analysis with FF1 revealed very similar strain energy distributions for copper(II) chelates with L-N,N-diethyl- and L-N,N-dipropyl-ƒŃ-alanine and predicted small difference in the stability of the two compounds. Furthermore, molecular mechanics calculations suggested that reasons for prevalence of equatorial and/or axial spatial positions of the alanine residue in the crystal state should be more readily attributed to the crystal packing preferences than to intramolecular steric hindrances caused by N-dialkyl groups. ______________________________________________________________________________1. G. Czapski and S. Goldstein, Free Rad. Res. Comms., 1991, 12-13, 167.

copper(II); N-alkylated amino acids; alanine; molecular mechanics; conformational analysis; stereoselectivity

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