Dispersion analysis of the orthorhombic peptide single crystal Z-(Aib)3-L-Ala-OtBu

We present a dispersion analysisof the orthorhombic peptide single crystal Z-Aib-Aib-AibL-Ala-OtBu (N-benzyloxycarbonyl-α-aminoisobutyryl-α-aminoisobutyryl-L-alanine tertbutyl ester, C27H42N4O7), where Z is benzyloxycarbonyl and OtBu is the tert-butylester) in the MIR spectral region by means of adapted generalized dispersion analysis, employing the naturally grown crystal faces. Based on the results we identify the orientation of the crystal axes a, b, c within the sample, and supported by a stereographic projection of the crystal, we assign the individual axes. The gained dielectric tensor function and the oscillator parameters were confirmed by forward calculation of reflection spectra of different orientations. The orientation of the crystal axes was verified by a second stereographic projection with another crystal face in the center.