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2.B.31 The Synthetic Linear Ionophoric Peptide (LIP) Family 

Two linear synthetic peptides, N-tBoc-Pro-Gly-Ala-NHCH3 and N-tBoc-Pro-D-Ala-Ala-NHCH3, complex Ca2+ and form 2:1 (peptide:calcium) complexes. They also bind Pr3+ (praseodymium, a soft, silvery, malleable and ductile metal).  Like most rare earth elements, praseodymium most readily forms the +3 oxidation state, which is the only stable state in aqueous solution.  These peptides mediate transport of Pr3+ across dimyristoylphosphatidylcholine unilamellar vesicles via a 2:1 ion-sandwich complex (Shastri et al. 1986).

References associated with 2.B.31 family:

Shastri, B.P., P.H. Rehse, S.K. Attah-Poku, and V.S. Ananthanarayanan. (1986). Acyclic model peptides with ionophoretic activity. Pr3+ transport by N-tBoc-Pro-Xxx-Ala-NHCH3. FEBS Lett. 200: 58-62. 3699165