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Speciation 98: Abstracts
Ivan Lukes, Jan Rohovec Mojmír Kyvala and Petr Hermann
Universita Karlova, Department of Inorganic Chemistry, Albertov 2030, 128 40 Prague 2, Czech Republic
Complexing abilities of simple aminomethyl-phosphonic/phosphinic acids and common amino acids towards transitions metals usually increase in well-known order phosphinic < carboxylic < phosphonic acids. This order follows increasing basicity of both amine and acidic groups. In addition, complexing properties of the acid derivatives or azacycles bearing the acid pendant groups are influenced by other effects e.g. hydrophobic and/or steric hindrance of a substituent on phosphorus atom in phosphinic acids and in a side chain. Here we report several examples of these effects.
Phosphonodipeptides. The acid-base and complexing properties of diastereoisomers of the phosphonodipeptides containing L-alanyl, L-leucyl, and L-phenylalanyl residue and P-terminal 1-amino-ethylphosphonic acid indicate the presence of the same types of complexes and the same trends for common dipeptides. However, in contrast to the common dipeptides, the differences found between diastereo-isomers are much higher, probably due to stronger interaction between the hydrophobic and hydrophilic parts of the molecule.
Aminomethylenephosphinic acids. The acid-base and complexing properties of a series of amino-methylene(phosphinic acids) H2NCH2P(R)O2H were compared with the results found by Kiss1 for 1-aminoethylphosphinic acids H2N-CH(CH3)-P(R)O2H, where R is hydrogen, methyl, or phenyl. The stability constant log101 for the acids with H-substituent with Cu(II) are very similar. However, these values for 1-aminoethylphosphinic acids with methyl and phenyl substituents are higher than for appropriate aminomethylphosphinic acids, probably due to hydrophobic interaction of the methyl group on the a-carbon with the substituent on the phosphorus atom.
Azacycles bearing methylenephosphinic pendant group. A large number of the macrocycles is derived from 12- or 14- membered tetraazamacrocycles "cyclen" and "cyclam". Comparison of the acid-base and complexing properties found for -CH2P(Ph)(O)OH, -CH2P(H)(O)OH and -CH2COOH pendant groups again points to the extensive hydrophobic effect and/or steric hindrance of a subtituent on phosphorus atom and effects of the macrocycle conformations.
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