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Comparative CD and Fourier transform ir (FTIR) spectroscopic data on N-Boc protected linear peptides with or without the (Pro-Gly) beta-turn motif (e.g., Boc-Tyr-Pro-Gly-Phe-Leu-OH and Boc-Tyr-Gly-Pro-Phe-Leu-OH) are reported herein. The CD spectra, reflecting both backbone and aromatic contributions, were not found to be characteristic of the presence of beta-turns. In the amide I region of the FTIR spectra, analyzed by self-deconvolution and curve-fitting methods, the beta-turn band showed up between 1639 and 1633 cm-1 in trifluoroethanol (TFE) but only for models containing the (Pro-Gly) core. This band was also present in the spectra in chloroform but absent in dimethylsulfoxide. These findings, in agreement with recent ir data on cyclic models and 3(10)-helical polypeptides and proteins in D2O [see S. J. Prestrelski, D. M. Byler, and M. P. Thompson (1991), International Journal of Peptide and Protein Research, Vol. 37, pp. 508-512; H. H. Mantsch, A. Perczel, M. Hollósi, and G. D. Fasman (1992), FASEB Journal, Vol. 6, p. A341; H. H. Mantsch, A. Perczel, M. Hollósi, and G. Fasman (1992), Biopolymers, Vol. 33, pp. 201-207; S. M. Miick, G. V. Martinez, W. R. Fiori, A. P. Todd, and G. L. Millhauser (1992), Nature, Vol. 359, pp. 653-655], suggest that the amide I band, with a major contribution from the acceptor C = O of the 1<--4 intramolecular H bond of beta-turns, appears near or below 1640 cm-1, rather than above 1660 cm-1.(ABSTRACT TRUNCATED AT 250 WORDS)

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New banana‐shaped monomers 1a–1f, based on the 1,3‐phenylene bis{4‐[4′‐(alkenyloxy)benzoyloxy]}benzoate bent structure were prepared. The central 1,3‐phenylene ring was either unsubstituted (1a, 1b) or had a 2‐methyl substituent (1c, 1d) or a 4‐chloro substituent (1e, 1f), respectively. The occurrence of mesophases greatly depended on the chemical structure of the banana‐shaped molecules. Whilst 1,3‐phenylene bis{4‐[4′‐(10‐undecenyloxy)benzoyloxy]}benzoate (1b, acronym Pbis11BB) formed a monotropic B2 phase, the 4‐chloro derivatives showed conventional nematic and SmC phases. In contrast, the 2‐methyl derivatives did not form any kind of mesophases. MOPAC/AM1 semi‐empirical calculations allowed evaluation of the value and orientation of the electric dipole vectors and of the twist angles of the central phenyl ring with respect to the outer rings. Electro‐optical investigations showed that the B2 phase of 1b was antiferroelectric with a 45° tilt angle between 91–75 °C (P = 320 nC · cm−2) and a switching time in the range of 50 μs in a E = 15 V · μm−1 field.