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A study was conducted on the spatial requirements of the B12 region in insulin and the biological properties of synthesized insulin analogues in which other hydrophobic amino acid residues replaced the B11 and B12 residues. The analogues that resulted from alpha-aminoisobutyric acid, D-Ala and Phe substitution of B12 Val were found to exhibit biological activities of 8.5%, 2% and 0.2%, respectively compared to natural insulin, while the analogue formed by inverting the B11-B12 sequence, had 3.3% activity. Results indicate that the B12 position's Val residue plays a role in the special side-chain packing requirements that contributes to insulin's structural stability.

The fluorescence properties of (tryptophan2)oxytocin were studied using intensity decay parameters and 1H NMR results. It was shown that results of fluorescence studies using a tryptophan analogue are compatible with the rotamer model of (Tyr2)oxytocin. The X2 conformers of the tryptophan analogue do not significantly affect fluorescence decay kinetics and three decay constants can be found in the three X1 rotamers of tryptophan.