Circular Dichroism of Heterodetic Cyclic Cystinyl TripeptidesThe circular dichroism of two series of heterodetic cyclic tripeptides, t‐butoxycarbonyl‐l‐cysteinyl‐X‐cysteine disulfide methyl esters [X = Ala, Val, Leu, Phe, Glu(Obut), Lys(Z)] and l‐cysteinyl‐X‐cysteine disulfide methyl ester formates, and a corresponding series of t‐butoxycarbonyl‐l‐cysteinyl‐(glycyl)n‐cysteine disulfide methyl esters (n= 1–5) was investigated. The interaction between the disulfide group and the amide bonds results in a long‐wavelength Cotton effect at 300 nm. which exhibits a strong solvent dependence. In contrast to the long‐wavelength disulfide band and to the n‐π* amide Cotton effect a bathochromic shift is observed from less polar to strongly polar solvents. Within the series of N‐terminal protected tripeptide esters the influence of the central chiral amino acid X is small, but it increases in the non‐protected peptide esters. The circular dichroism is dominated by the influence of the conformation of the disulfide ring, which is essentially the same in both series. Due to interactions of the disulfide group with the amide chromophores, the sign of the long‐wavelength disulfide Cotton effect ca
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