Interaction of Zn(II) and Cu(II) with ε-poly-L-lysine and properties of the complexes

ε-Poly-L-lysine (ε-PL) is a natural food preservative with high safety to humans and a wide antimicrobial spectra. It was found that ε-PL could form precipitates when it contacted to Cu(II) and Zn(II). Thus in this study, two complexes of ZnCl2 and CuCl2 with ε-poly-L-lysine having molecular weights between 2 and 5 kDa were prepared and characterized by elemental analysis (EA), atom absorption spectrometry (AAS), chlorine assay, etc. The results show that the compositions of two complexes can be expressed as [ NH-(CH2)5-CO ] 2n•(ZnCl2)n•2nH2O and [ NH-(CH2)5-CO ] 2n•(CuCl2)n•2nH2O (n=6-18), respectively. The results of FT-IR reveal that the formation of Zn-N and Cu-N coordination bonds. X-RD patterns indicat that the two complexes are new phases different from the raw ε-PL material. On the basis of TG-DTA curves, the complexes have a coordination reaction. From the results of the bacteriostatic test, ε-PL-Zn(II) and ε-PL-Cu(II) have similar antibacterial activity to ligand ε-PL.