Biological Synthesis of Silica Nanoparticles

The LCPAs are nonprotein components ( 3.5 kDa) that have been found encapsulated in the silica matrix of the diatom, and isolated through a series of H F extractions [59]. Unlike silafHns, which have a peptide backbone, these polyamines consist of linear chains of C-N-hnked PEI units that are bonded to a putrescine or putrescine derivative backbone. The chemical composition of these LCPAs is unique for each diatom species, with variable repetitions and degrees of methylation. 

Recently, synthetic or natural polypeptides have been created or modified to serve as sihca condensation templates. Examples of these include the poly(amino acids) [79], the diatom-derived R5-peptide [66], chimeric polypeptides [64, 67], block copolypeptides [71, 72, 75, 80], lanreotide [63] and even the naturally occurring protamine [65]. These polypeptides have been used to produce a variety of sihca shapes and sizes, which can be tuned to perform a variety of applications, including transport and the separation of encapsulated materials [62], or potentially for dmg dehvery [73]. 

1 Block Copolypeptides Block copolypeptides, which have been used as 

The formation of platelets or spheres with the Lys-b-Gly copolypeptide suggested that there was a morphological dependence on the phosphate concentration and solubility of the hydrophobic block. As the relative hydrophobicity was increased though the addition of Gly residues, substitution of the Gly block with the more hydrophobic Ala block, or the loss of Lys residues, the solubility of the copolypeptide was decreased, making it more susceptible to phase separation. The hydro-phobic block was more energetically stable when it was associated, rather than by 

Reproduced with permission from Ref [72] 2007, Wiley-VCH Verlag GmbH Co. KGaA. 

---