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Raman spectra of D and L amino acid copolymers. Poly‐DL‐alanine, poly‐DL‐leucine, and poly‐DL‐lysine

The Raman spectrum of poly‐DL‐alanine (PDLA) in the solid state is interpreted in terms of the disordered chain conformation, in analogy with the spectrum of mechanically deformed poly‐L‐alanine. The polymer is largely disordered with only a small α‐helical content in the solid state. When PDLA is dissolved in water, the spectra suggest that short α‐helical segments are formed upon dissolution. These helical regions might be stabilized by hydrophobic bonds between side‐chain methyl groups. Addition of methanol to the aqueous PDLA solutions results in a Raman spectrum resembling that of solid PDLA. This result suggests that the methanol disrupts the helical regions by breaking the hydrophobic bonds.