Fig. 4: Phosphatase activity of [L₂Zn₃]⁶⁺.

³¹P NMR spectra using different substrates including PhOPO₃²⁻ (spectra a–d), serine phosphate (spectra e–h), threonine phosphate (spectra i–l) and tyrosine phosphate (spectra m–p). Specific details for each ³¹P NMR spectra are as follows: Spectra a, e, i and m represent substrate alone (44 h incubated @ 37 °C); Spectra b, f, j and n represents [L₂Zn₃]⁶⁺ plus substrate (t = 0 min); Spectra c, g, k and o represents [L₂Zn₃]⁶⁺ plus substrate incubated @ 37 °C for 19 h; Spectra d, h, l and p represents [L₂Zn₃]⁶⁺ plus substrate incubated @ 37 °C for 44 h. The ³¹P NMR of [L₂Zn₃(PO₄)]³⁺ gives a signal at 8.6 ppm. The doubling up of some of the ³¹P signals in [L₂Zn₃(PO₄)]³⁺ (h, p and l) is attributed to formation of a mixture of diastereoisomers between the racemic cryptand and the resolved chiral amino acids which will form an ion-pair ([L₂Zn₃(PO₄)](RCH(NH₂)CO₂)²⁺) and does not occur with the achiral phenyl phosphate. ³¹P NMR spectra of the phosphate esters are ¹H-coupled (a, e, i and m) and the remainder are ¹H-decoupled.