First-order rate constants as large as 124000 s~1 (f1/2 ~5.6 µß) and second-order rate constants as large as 2 X 10® M"1 s'1 are measured with a pulsed-accelerated-flow (PAF) spectrometer. The method uses a variation of flow velocity during data collection to resolve reaction rate constants from mixing rate constants. The validity of the method Is demonstrated by calibration reactions under pseudo-first-order and second-order (equal and unequal concentration) conditions. The performance and limitations of a twin-path mixing/observation cell and the PAF method are reported.

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The proton and copper(II) association constants are measured for eight peptides and four peptide amides, which contain the -aminoisobutyric acid (Aib) residue. The Aib peptides are slightly stronger bases than the corresponding glycyl peptides with a greater difference in the protonation constants for the carboxylate group (0.5-0.6 log unit) than for the amine functional group (0.0-0.25 log unit). The stepwise formation constants for the copper(II)-Aib" peptide complexes indicate that both inductive and steric properties of the -carbon methyl groups influence the relative stability of the copper(II) complexes of Aib peptides and glycyl peptides. The fully formed Aib complexes are 2.5-63 times more stable than the glycyl complexes. Steric interference to coordination is seen in the copper(II)-Aib4 complex, where the third peptide nitrogen does not coordinate to copper(II) because of the bulk presented by the -carbon methyl groups in the fourth residue.

Die Proton‐ und Cu(II)‐Assoziations‐ konstanten für die 12 Liganden Ala‐Aib, Aib2, GlyAibGly, AlaAib2, Aib3 , Glyz‐ Aib‐Gly, Aib3‐Gly, Aib4, Aib‐NH2, Ala‐Aib‐NH2, Aibz‐NH2 und Aib3 ‐NH2 (Aib = α‐Aminoisobuttersäure) werden gemessen und mit den entsprechenden Werten für die Glycylpeptide und ‐peptidamide sowie Alanylpeptide verglichen.