Preparation And Characterization Of L-Alanyl-L-Glutamine-Zn^2＋ Chelate

Free amino group and carboxy group on short peptide and amino acid can coordinate metal ion with vacant orbital to form chelate compound. This chelate compound has high bioavailability, low toxicity, and advanced biochemical stability.At present, semimicro phase equilibrium, solid-phase synthesis etc. are used frequently to prepare chelates. It was studied that the chelate compound of Ala-Gln-Zn²⁺ was synthesized with Ala-Gln and zinc sulfate by dialysis equilibrium method in this paper. Ala-Gln-Zn²⁺'s main physicochemical and biochemistry characteristics was characterized.Experimental result showed that Ala-Gln coordinate with ZnSO₄·7H₂O in aqueous solution at 60℃for 1.5 hour. Ala-Gln-Zn²⁺solution was dialysised for 30 hours. Whlie dialysis reacheed equilibrium at 30 hours the molar ratio of Ala-Gln to Zn²⁺ was 2:1. Ala-Gln-Zn²⁺ was freeze-dryed, so the stable Ala-Gln-Zn²⁺ chelate was obtained. Compare with Ala-Gln, the strongest three peaks's XRD diffraction data of Ala-Gln-Zn²⁺ had a great change, which indicated that Ala-Gln-Zn²⁺'s phase had changed. Compare with Ala-Gln, TG-DGA curves of Ala-Gln-Zn²⁺ appeared a new endothermic peak at 67.22℃, Ala-Gln's endothermic peaks at 232.67℃,366.1℃shift to 279.4℃,537.3℃in Ala-Gln-Zn²⁺; Compared with Ala-Gln, the Ala-Gln-Zn²⁺'s IR characteristic absorption peaks at 3411.1cm^-1,1111.81cm^-1of -NH₂,-NH⁺ blun shift and weakened, the stretch vibration peak at 1649.5 cm^-1,1608.53 cm^-1 of -C=O blue shift and weakened, the stretch vibration peak of -OH at 3334.28cm^-1 disappeared, it indicated that Ala-Gln's -NH2,-NH,-C=O,-OH may take part in coordination; 1HNMR showed that the H signal peak atδ=12.57ppm of -OH disappeared, peak area of -CH-,-NH-'s H signal peak increased. So the coordination mechanism of Ala-Gln-Zn²⁺ is that two Ala-Gln coordinated with one Zn²⁺, carboxyl group's -OH of Ala-Gln combined with Zn²⁺ by ionic bond, carboxyl group's -C=O and -NH-'s N coordinate with Zn²⁺ to form a stable five-membered chelating ring. The chelate structure was examined by AFM scaning, single strand structure at AFM gram is Ala-Gln, two combined single strand is Ala-Gln-Zn²⁺, and atomic radius of Ala-Gln-Zn²⁺'s conjunctive atom is about 0.24 to 0.25nm, which is near to Zn²⁺, so the conjunction atom is Zn²⁺. Thus the coordination reaction and the molar ratio 2:1 is proved again.The stability constant of Ala-Gln-Zn²⁺ determined by potentiometric titration is LogK=4.46, 74.2% larger than that of Ala-Gln; Ala-Gln-Zn²⁺'s total antioxidant activity is 2105.43 U/moL, anti superoxide anion activity is 2414.38 U/moL, and it can increase the antioxidant activity of superoxide dismutase; the hydrolysis rate of carboxypeptidase to Ala-Gln-Zn²⁺ is 4.37%, 75% lower than to Ala-Gln; Finally, experimental result showed that 0.001g/mL Ala-Gln-Zn²⁺ has obvious bacteriostasis to staphylococcus aureus and escherichia coli.