Synthesis of Phospho‐Polypeptides via Phosphate‐Containing N‐Carboxyanhydride: Application in Enzyme‐Induced Self‐Assembly, and Calcium Carbonate Mineralization

Abstract

An easy synthetic strategy was developed to synthesize the phosphate-functionalized amino acid N-carboxyanhydride (NCA), using simple primary amine initiators to obtain homo and block phospho-polypeptides with controlled molecular weight and molecular weight distribution. The methodology was extended to the synthesis of the end-functionalized homo polypeptides (15 to 50 repeat unit) and block co-polypeptides with PEG (0.7 K, 2 K, and 5 K) and glycopolypeptide (15-unit mannose glycopolypeptide) as one of the blocks. The deprotected fully water-soluble anionic phosphate-based polypeptides showed pH-dependent helical conformation with a helical content of 20 %, which further changed to β-sheets upon addition of the enzyme alkaline phosphatase (ALP) due to dephosphorylation. The block co-polypeptide containing PEG as one of the blocks led to its self-assembly into colloidal structures, such as vesicles with a hydrodynamic diameter of 250 nm, due to the formation of amphiphilic block co-polymer upon dephosphorylation. The nature of the colloidal structures formed can be temporally controlled by the extent of dephosphorylation. Finally, the phospho-polypeptides serve as a template for the mineralization of calcium carbonate with varying polymorphs and morphologies.[a] B. Mondal, S. Panda, T. Dutta, Dr.

Using High Molecular Precision to Study Enzymatically Induced Disassembly of Polymeric Nanocarriers: Direct Enzymatic Activation or Equilibrium-Based Degradation?

“…These results demonstrate that once the polymers become amphiphilic and start to self-assemble, the residual phosphate groups, which are linked to the core-forming block, become inaccessible to the enzyme, and their cleavage rate becomes negligible. Similar trends in enzymatic degradation of phosphorylated polypeptides due to limited accessibility of the enzyme to the phosphate side groups were recently reported by Gupta and co-workers …”

“…Similar trends in enzymatic degradation of phosphorylated polypep-tides due to limited accessibility of the enzyme to the phosphate side groups were recently reported by Gupta and co-workers. 43 On the basis of these results, one could argue that the design of polymeric assemblies that contain enzymatically cleavable lipophilic groups is not realistic as the activating enzyme will not be able to reach the hydrophobic core, which is expected to accommodate the cleavable groups. This limited accessibility was also demonstrated for polymeric assemblies with enzyme-cleavable shells as reported by the group of Heise for amphiphilic polymers containing hydrophilic peptides as the hydrophilic block and polystyrene (PS) or poly(n-butyl acrylate) as the hydrophobic block.…”