Circular dichroism (CD)
and Raman scattering were applied to the aqueous solution of minimalist LK peptidesconstructed with successive KL repeats leading to the following generic primary sequence: (KL)
nK. Threepeptides of this family, a 3-mer (
n = 1), a 9-mer (
n = 4),
and a 15-mer (
n = 7), are analyzed in this report.Raman spectra of the 3-mer (KLK, a r
andom chain)
and its labile-hydrogen deuterated species yield a set ofinteresting information for analyzing longer peptides of this series. Although the CD spectrum of the 9-mer(KLKLKLKLK) reveals a signal traditionally assigned to a r
andom structure, the corresponding Ramanspectrum allows finding a mixture of conformations in solution, adopting predominantly
![](/images/gifchars/beta2.gif)
-type structures.This fact proves the utility of Raman spectroscopy to eliminate eventual ambiguity concerning conformationalassignments in peptides based only on the use of CD technique. Finally, the 15-mer (KLKLKLKLKLKLKLK)gives rise to CD
and Raman spectra clearly assignable to a
![](/images/gifchars/beta2.gif)
-type structure. On the basis of all the observedresults on the 15-mer, we can confirm that this peptide may exist as isolated
![](/images/gifchars/beta2.gif)
-str
ands at low concentration(sub-micromolar), flat-oriented at the air/water interface, whereas at high concentrations (millimolar), non-H-bonded immersible aggregates might be formed. A hypothetical model for these
![](/images/gifchars/beta2.gif)
-str
and aggregates couldbe proposed as stabilized by an interior hydrophobic core
and a hydrophilic external face, formed by leucine
and lysine side chains, respectively.