The role of polymer (poly(vinylamine)) size (238-11000 units) on silicic acid condensation to yield soluble nanoparticles or composite precipitates has been explored by a combination of light scattering (static and dynamic), laser ablation combined with aerosol spectrometry, IR spectroscopy, and electron microscopy. Soluble nanoparticles or composite precipitates are formed according to the degree of polymerization of the organic polymer and pH. Nanoparticles prepared in the presence of the highest molecular weight polymers have core-shell like structures with dense silica cores. Composite particles formed in the presence of polymers with extent of polymerization below 1000 consist of associates of several polymer-silica nanoparticles. The mechanism of stabilization of the "soluble" silica particles in the tens of nanometer size range involves cooperative interactions with the polymer chains which varies according to chain length and pH. An example of the use of such polymer-poly(silicic acid) nanoparticles in the generation of composite polymeric materials is presented. The results obtained have relevance to the biomimetic design of new composite materials based on silica and polymers and to increasing our understanding of how silica may be manipulated (stored) in the biological environment prior to the formation of stable mineralized structures. We suspect that a similar method of storing silicic acid in an active state is used in silicifying organisms, at least in diatom algae.

Silicon is among the most abundant elements on the Earth. It occurs in many minerals and plays an important role in several biochemical processes. Some living organisms use silicon dioxide as a substrate for building elements of their bodies. Unicellular diatom algae build frustules from silicon dioxide. The skeleton of siliceous sponges is a silicaprotein composite. Similarly, rice hulls which protect seeds, contain silica as an important component. The living organisms assimilate silicon from the environment in the form of silicic acid. However, the biochemical mechanisms involved in the transformation of silicic acid to solid siliceous materials are still poorly understood.Evidently, condensation of silicic acid in the living organisms proceeds under control of biopolymers and it is important to know how various types of polymers influence the condensation. Bio-inspired chemistry involving the interaction between polymeric silicic acid and functional polymers results in interesting composite materials, including nanoparticles and bulk materials. This review contains a brief description of the mechanism of silicic acid condensation in aqueous medium and also includes a discussion on various precursors of silicic acid. The main focus of the review is on the influence of polymers bearing nitrogen and oxygen-containing functional groups on silicic acid condensation starting from monomer to three-dimensional polymer. Influence of molecular weight of the organic polymer on the condensation and structure of the resulting product is also elaborated. The biological importance of the obtained data and strategies for novel applications of the synthesized composite materials are described in the concluding section of the review. The biomimetic condensation processes open up new vistas for development of novel materials and applications in the biomedical and process industries.

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Polymeric amines are intensively studied due to various valuable properties. This study describes the synthesis of new polymeric amines and ampholytes by the reaction of poly(acryloyl chloride) with trimethylene-based polyamines containing one secondary and several (1-3) tertiary amine groups. The polymers contain polyamine side chains and carboxylic groups when the polyamine was in deficiency. These polymers differ in structure of side groups, but they are identical in polymerization degree and polydispersity, which facilitates the study of composition-properties relationships. The structure of the obtained polymers was confirmed with 13 C nuclear magnetic resonance infrared spectroscopy, and acid-base properties were studied with potentiometry titration. Placement of the amine groups in the side chains influences their acid-base properties: protonation of the amine group exerts a larger impact on the amine in the same side chain than on the amines in the neighboring side chains. The obtained polymers are prone to aggregation in aqueous solutions tending to insolubility at definite pH values in the case of polyampholytes. Silicic acid condensation in the presence of new polymers results in soluble composite nanoparticles and composite materials which consist of ordered submicrometer particles according to dynamic light scattering and electron microscopy. Polymeric amines, ampholytes, and composite nanoparticles are capable of interacting with oligonucleotides, giving rise to complexes that hold promise for gene delivery applications.

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