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6318597 
Journal Article 
Effect of electrophilic and nucleophilic substituents on the protonation microequilibria of tyrosine derivatives 
Sipos, P; Peintler, G; Tóth, G 
1992 
0 
International journal of peptide and protein research
ISSN: 0367-8377 
39 
3 
207-210 
English 
1328096 
The microscopic protonation constants of 10 tyrosine-like, unusual amino acids used in the syntheses of opioid peptides have been determined by using a combined pH-metric-spectrophotometric method, at 0.10 mol dm-3 (NaCl) ionic strength and 25.0 degrees. The role of the different electrophilic and nucleophilic substituents on the individual basicity of the aliphatic amine and phenolic hydroxylate basic centers is discussed in detail. The interactivity parameters between these two groups correlate fairly well with the structure of the skeleton and the distance between the two basic centers, but they were found to be substituent-independent. This finding made it possible to extend the calculations to compounds having non-overlapping protonation equilibria.