Silica biological synthesis

Biology produces a remarkable diversity of silica structures [1, 2], many of which are strikingly beautiful. The biological synthesis of the wide variety of shells, spines and granules made by diatoms, other unicellular organisms, sponges, mollusks and plants is remarkable in three respects ... 

Equally remarkable is the scale of this biological synthesis of silica. Earth s biota produce gigatons of silica annually much of this production occurs in the world s oceans, where it contributes an estimated 3 km to the ocean floor sediments each year. Ancient deposits of diatomite thousands of meters thick are mined today for industrial purposes. 

In addition to the QM structure of the natural terpene QMs, the reactive oxygen species (ROS) may also play a significant role in the observed biological activities. In the synthesis of taxodione and taxodone, QMs were formed from the catechol precursors through the spontaneous oxidation in the presence of silica gel.7, 8,49-51... 

Rieux, L., Niederlander, H., Verpoorte, E., Bischoff, R. (2005). Silica monolithic columns Synthesis, characterisation and applications to the analysis of biological molecules. J. Sep. Sci. 28, 1628-1641. 

As mentioned earlier, biological systems have developed optimized strategies to design materials with elaborate nanostructures [6]. A straightforward approach to obtaining nanoparticles with controlled size and organization should therefore rely on so-called biomimetic syntheses where one aims to reproduce in vitro the natural processes of biomineralization. In this context, a first possibility is to extract and analyze the biological (macro)-molecules that are involved in these processes and to use them as templates for the formation of the same materials. Such an approach has been widely developed for calcium carbonate biomimetic synthesis [13]. In the case of oxide nanomaterials, the most studied system so far is the silica shell formed by diatoms [14]. 

Nakamura M, Shono M, Ishimura K (2007) Synthesis, characterization, and biological applications of multifluorescent silica nanoparticles. Anal Chem 79 6507-6514... 

Preparation of nonracemic epoxides has been extensively studied in recent years since these compounds represent useful building blocks in stereoselective synthesis, and the epoxide functionality constitutes the essential framework of various namrally occurring and biologically active compounds. The enantiomericaUy enriched a-fluorotropinone was anchored onto amorphous KG-60 silica (Figure 6.6) this supported chiral catalyst (KG-60-FT ) promoted the stereoselective epoxidation of several trans- and trisubstituted alkenes with ees up to 80% and was perfectly reusable with the same performance for at least three catalytic cycles. 

Another assay commonly referred to as in vitro is the chemical synthesis assay of p-hematin. Developed by Egan et al. [64], a heme substrate solution, with or without inhibitors, is prepared in 0.1 M NaOH. The substrate is added to a pre-equilibrated (60 °C) acetate buffer (final concentration 4.5 M) reaction mixture and stirred for 10-30 minutes. After cooling on ice, the precipitate is filtered, washed with water and dried over silica gel or P2O5. The dried reaction mixture is analyzed by FT-IR and for solubility in 0.1 M sodium bicarbonate (pH 9.1). Several researchers have expressed concerns about extrapolating biologically... 

Table I shows the distribution of silica in biological systems. In direct contrast to the abundance of siliceous structures observed in lower plants and animals, no silicified structures have been observed in bacteria. Why this should be so is not clear however, because siliceous structures in unicellular organisms require the synthesis of special membrane-bound compartments, the lower structural organization of prokaryotic cells may be an important factor inhibiting the formation and organization of silica in these organisms.

Improvement in LC-MS and LC-MS/MS analysis throughput has been reported by the use of monolithic silica columns to increase the speed of chromatography separation [156-158]. The substimtion of an SFC front end to MS in lieu of HPLC has been a growing trend in compound library analysis. It is possible that the use of SFC-MS will be extended to in vitro and in vivo evaluation of library compounds such as ADME and DMPK. CE-MS has not been widely used in the analysis of combinatorial libraries. To date, the application of CE-MS has been frequently in the analysis of mixture-component libraries derived from split synthesis and in the affinity screening of libraries through ACE. However, with the miniaturization of biological screening in the lab-on-a-chip format, CE-MS may find renewed interest... 

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