Silica template-free

Ordered porous carbons were synthesized by replication of colloidal templates made from 30 - 100 nm diameter silica spheres and removal of the silica templates using aqueous HP. To create the templates, the monodisperse particles were pressed into pellets and then sintered slightly at their points of contact. The silica template were filled with carbon precursor solution of divinylbenzene (DVB) and a free radical initiator, azobisisobutyronitrile (AIBN). Polymerization and carbonization of the precursor solution and subsequent dissolution of the silica templates leave a polycrystalline network of carbon with interconnected uniform pores. The degree of order of the silica template is faithfully reproduced in the carbon replicas. 

Oxides Compared to silica-based networks, nonsiliceous ordered meso-poious materials have attracted less attention, due to the relative difficulty of applying the same synthesis principles to non-sihcate species and their lower stability (227). Nonsiliceous framework compositions are more susceptible to redox reactions, hydrolysis, or phase transformations to the thermodynamically preferred denser crystalline phases. Template removal has been a major issue and calcination often resulted in the collapse of the mesostracture. This was the case for mesostractured surfactant composites of mngsten oxide, molybdenum oxide, and antimony oxide, and meso-structured materials based on vanadia that were obtained at early stages. Because of their poor thermal stability, none of these mesostructures were obtained as template-free mesoporous solids (85, 228, 229). 

Alkyl alkoxysilanes undergo quick hydrolysis and polycondensation in acidic medium. This has been exploited in combination with self-assembly of long-chain alkyl trialkoxysilanes driven by hydrophobic interactions that opened prospects for surfectant- and template-free synthesis of ordered mesoporous silicas. This approach has been developed strongly by Shimojima and Kuroda [24]. 

Among hollow inorganic particles, silica-based particles are the most extensively studied because of their ease of synthesis, structural and compositional diversities, and wide range of applications. Hollow silica particles can be synthesized by either templating or template-free methods. 

Fig. 13.6 Formation of free-standing biopolymer capsules via single-step adsorption of a biopolymer (enzymes, proteins, pol5q)eptides, polynucleotides, polysaeeharides) from aqueous solution onto bromoisobutyramide surface-modified silica templates followed by template removal. Reproduced from [73] with permission from John Wiley and Sons...

It has been previously reported [21, 22] that metal colloids are formed by radiochemical reactions in water/alcohol solutions, in which the reduction of metal salts takes place by solvated electrons and free radicals produced under UV or y-ray irradiation. Ichikawa et al. have applied this photoreduction method to the surface-mediated reaction of metallic ions and succeeded in synthesizing metal/aUoy nanowires in the constrained cavities of mesoporous supports such as FSM-16 and MCM-41 [18-20, 23-25]. The adsorbed water and alcohol work not only as solvents in the nanoscale silica void space but also as a source of reducing species for metallic ions to metals under UV-vis and y-ray [11, 18, 19] irradiation. The results indicate the dense formation of Pt nanowires inside the charmels of mesoporous supports, such as FSM-16, which act as the templates. In fact, no any Pt wire is observed on the external surface of FSM-16 or amorphous silica surface. Short wires, 10 nm long, are also observed as a minor species in the samples in the initial stage of UV and y-ray irradiation. 

If an aDNA extract frails to PCR amplify it should be tested for the presence of PCR inhibitors. This test requires the availability of an authenticated aDNA sample to be used as a positive control.8 Set up side-by-side PCR reactions containing 1) the template suspected to contain inhibitors, to which is added a volume of the ancient positive control equivalent to that of the template, 2) only the template suspected to contain inhibitors and 3) only the positive ancient control. This side-by-side comparison will allow for the preclusion of PCR failure due to factors other than inhibition (e.g. the stochastic nature of PCR amplification). If the template spiked with the positive ancient control (reaction 1) permits its amplification, while the template suspected of containing inhibitors (reaction 2) fails to amplify, the template is likely free of inhibitors and, therefore, does not contain a sufficient amount of DNA for analysis. Alternatively, if the first PCR reaction fails to amplify, whereas the third reaction does amplify, the template is concluded to contain inhibitors. In this case, the silica extraction should be repeated, as described above, and PCR reattempted. Our studies have shown that as may as four repeat silica extractions may be required to sufficiently remove PCR inhibitor from DNA extracts, despite the inherent loss of DNA yield associated with each repetition of the silica extraction (5). 

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