Mineralized organisms, nanoscale

The three-tier assembly documented for mother-of-pearl can be extended to the nanoscale architectures of other mineralized organisms. The sponge skeletal organization of echinoderms, for example, is composed of calcific nanobricks of one, single Mg-bearing calcite crystal. Three species of echinoderms and one shell of a sea urchin were analyzed using FESEM, field emission TEM (FETEM), SAED... 

The way in which the iron core in ferritin might build up and the structure of the mineral and its properties have been considered by many researchers over the years and yet there are still many questions that remain to be answered satisfactorily. From one viewpoint the subject belongs in the area of biomineralization, from a different standpoint the nanoscale properties have been of interest, and a third important area of research concerns the health aspects of iron storage and homeostasis. For this latter field the problems of too much or too little are to the fore, with iron overload disease a serious problem in much of Africa and the Middle East while in the Western world iron deficiency is more likely to be a problem. A key aspect to such health problems concerns the response of the organism to local iron levels and is regulated in healthy subjects by an iron response element (IRE) which also seems to involve metalloproteins within the so-called iron response protein. However, this has but little bearing on coordination chemistry aspects of ferritins that we are considering here whereas the chemical questions behind the mineralization processes and the measurement and interpretation of the physical properties of such nanoscale particles are of intense interest. It turns out to be helpful to consider these two aspects in tandem, as one tends to inform the other. 

Because of their ubiquitous presence in natural materials and their strong surface reactions with cations and organic molecules, clay minerals are involved in many environmentally important phenomena (1). A nanoscale particle size with large specific surface area (ca. 750 m g ) is typical for clay minerals. Therefore, cation exchange and swelling processes occur readily, governed by the electrical double layer in the interlayers of the hydrated clay mineral. 

One particular asset of structured self-assemblies is their ability to create nano- to microsized domains, snch as cavities, that could be exploited for chemical synthesis and catalysis. Many kinds of organized self-assemblies have been proved to act as efficient nanoreactors, and several chapters of this book discnss some of them such as small discrete supramolecular vessels (Chapter Reactivity In Nanoscale Vessels, Supramolecular Reactivity), dendrimers (Chapter Supramolecular Dendrlmer Chemistry, Soft Matter), or protein cages and virus capsids (Chapter Viruses as Self-Assembled Templates, Self-Processes). In this chapter, we focus on larger and softer self-assembled structures such as micelles, vesicles, liquid crystals (LCs), or gels, which are made of surfactants, block copolymers, or amphiphilic peptides. In addition, only the systems that present a high kinetic lability (i.e., dynamic) of their aggregated building blocks are considered more static objects such as most of polymersomes and molecularly imprinted polymers are discussed elsewhere (Chapters Assembly of Block Copolymers and Molecularly Imprinted Polymers, Soft Matter, respectively). Finally, for each of these dynamic systems, we describe their functional properties with respect to their potential for the promotion and catalysis of molecular and biomolecu-lar transformations, polymerization, self-replication, metal colloid formation, and mineralization processes. 

A field of growing attention is the development of polymer-clay nanocomposites due to the significant technological applications of these materials. Therefore, composite systems produced by organic polymers and clay minerals prepared at the nanoscale level, which typically present a unique layered structure, rich intercalation chemistry and availability at low cost, have been used to develop plastic materials with superior mechanical properties, molecular barrier behavior, fire retardant abilities, enhanced thermal stability, among other properties, compared to the individual polymeric materials [3-5]. 

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