Biopolymer colloids for controlling and templating inorganic synthesis

Abstract

Biopolymers and biopolymer colloids can act as controlling agents and templates not only in many processes in nature, but also in a wide range of synthetic approaches. Inorganic materials can be either synthesized ex situ and later incorporated into a biopolymer structuring matrix or grown in situ in the presence of biopolymers. In this review, we focus mainly on the latter case and distinguish between the following possibilities: (i) biopolymers as controlling agents of nucleation and growth of inorganic materials; (ii) biopolymers as supports, either as molecular supports or as carrier particles acting as cores of core-shell structures; and (iii) so-called "soft templates", which include on one hand stabilized droplets, micelles, and vesicles, and on the other hand continuous scaffolds generated by gelling biopolymers.

Keywords: biomacromolecules; biopolymer; colloid; nanoparticle; organic–inorganic hybrid; template.

Figure 1

Different roles of biopolymers as controlling agents and templates in the formation of inorganic materials.

Figure 2

Schematic representation of the evolution of the morphology of calcium oxalate crystals prepared in the presence of oligo(L-glutamic acid)s of different lengths, ranging from the monomer (Glu) to the eicosamer (Glu₂₀). COD: calcium oxalate dihydrate; COT: calcium oxalate trihydrate. Reprinted with permission from [38]. Copyright 2010 American Chemical Society.

Figure 3

DNA-templated preparation of porous CdS shells on the surface of silica beads: (a) surface modification with (3-aminopropyl)trimethoxysilane (APTMS), (b) DNA deposition on the cationic particle surface, (c) CdS precipitation, and (d) dissolution of the SiO₂ core to form hollow structures. Reprinted with permission from [52]. Copyright 2011 American Chemical Society.

Figure 4

Siloxan polymerization on chitosan microspheres by using immobilized protein templates. Reprinted with permission from [61]. Copyright 2008 Elsevier.

Figure 5

Schematic representation of the procedure applied for synthesizing starch/Ag nanocapsules. Reprinted with permission from [63]. Copyright 2014 The Royal Society of Chemistry.

Figure 6

Products obtained when gold(III) is reduced in the presence of DNA toroids formed with bis(ethylenediamine)gold(III). Reprinted with permission from [66]. Copyright 2010 American Chemical Society.

Figure 7

Dark-field TEM micrograph (a) and corresponding electron diffraction pattern (b) of hydroxyapatite/gelatin particles. Reprinted with permission from [87]. Copyright 2008 John Wiley & Sons.

Figure 8

Schematic representation of aerogel preparation. A nanoporous cellulose gel is impregnated with the silica precursor TEOS (a). Afterwards, the silica formation takes place by sol–gel process (hydrolysis and condensation), yielding a cellulose–silica composite gel (b). Drying with supercritical CO₂ gives a composite aerogel (c). Macroscopic views of the prepared samples are shown in panels (e–h). Reprinted with permission from [90]. Copyright 2012 John Wiley & Sons.