Extraction, template

SG sols were synthesized by hydrolysis of tetraethyloxysilane in the presence of polyelectrolyte and surfactant. Poly (vinylsulfonic acid) (PVSA) or poly (styrenesulfonic acid) (PSSA) were used as cation exchangers, Tween-20 or Triton X-100 were used as non- ionic surfactants. Obtained sol was dropped onto the surface of glass slide and dried over night. Template extraction from the composite film was performed in water- ethanol medium. The ion-exchange properties of the films were studied spectrophotometrically using adsorption of cationic dye Rhodamine 6G or Fe(Phen) and potentiometrically by sorption of protons. 

Large (stoichiometric) amounts of analyte are required to manufacture MIPs. This is an important issue if the (analyte) template is expensive, difficult to isolate, or toxic. In principle, the analyte could be recovered after template extraction although this process can also be cumbersome. 

Currently, the most widely applied technique to generate molecularly imprinted binding sites is represented by the noncovalent route. This makes use of noncovalent self-assembly of the template with the functional monomer(s) prior to polymerization. After free radical polymerisation with a cross-linking monomer, followed by template extraction, rebinding is achieved via noncovalent interactions. 

In the first step, the contact occurring between the functionalised monomers and the template molecule leads to the formation of a complex. Its structure and stability will then determine the behaviour of the future MIR The interactions involved must be sufficiently strong to remain intact during the polymerisation stage but sufficiently labile to enable template extraction and reinsertion of guest molecules in the later stages. These interactions must therefore occur rapidly and be reversible. It is crucial to optimise the choice of the different components of the system at this point. 

In addition, the synthesis of MIPs requires large quantities of guest molecule (50 to 500 pmoles per gram of polymer). So, when pure template molecule is difficult or expensive to obtain, reaching quantitative template extraction yields can be primordial. Extraction conditions must then be optimised to obtain yields of over 99% [126,127]. 

It was observed that a high proportion of template (10%) can be introduced without losing the mesomorphic order [ 199]. Moreover after template extraction, the polymorphism was quite different from that of the non-imprinted material, the variations depending on the structure of the template used and on its concentration [200]. The last point is the manifestation of a significant memory effect of the template, imprinted inside the mesomorphic structure. It arises from the interactions between template and the other parts of the network which can induce conformational constraints inside the networks during cross-linking. It occurs even though the amount of crosslinker is low (5%). Moreover, this point constitutes a means for the direct study of the imprint left in the network by the template. 

P-ll - The synthesis and hydrothermal stability of directly usable hexagonal mesoporous silica by efficient primary amine template extraction in acidified water... 

CO2 modified with a methanol/dichloromethane mixture and showed that the template extracted in this manner could be re-used for further syntheses of mesoporous silica. Treatment with supercritical CO2 alone leads to pore swelling with retention of mesostructural ordering in 2D hexagonal phase silica triblock copolymer surfactant composites. Pore swelling with supercritical CO2 has also been observed for materials templated with fluorinated surfactants. ... 

Figure 2 Screening of MiniMIPs (1) in situ template extraction (2) equilibrium batch rebinding.

Note 6. The Soxhlet extraction gives a material which is sufficiently free from residual template and suitable for chromatographic applications, considering that subsequent column washing will further reduce the amount of residual template. Do not use this material for solid-phase extraction applications, because this technique requires more exhaustive template extraction methods. 

P and Vansant, E. (2002) Template extraction from porous clay heterostructures influence on the porosity and the hydrothermal stability of the materials. Phys. Chem. Chem. Phys., 4, 2818-2823. 

Molecular imprinted polymers (MIPs) can be prepared according to a number of approaches that are different in the way the template is linked to the functional monomer and subsequently to the polymeric binding sites. The current technique makes use of noncovalent self-assembly of the template with functional monomers before polymerization, free radical polymerization with a cross-linking monomer, and then template extraction followed by rebinding by noncovalent interactions. The functional monomer is often methacrylic acid, the cross-linker is ethylene glycol dimethacrylate, the initiator is 2,2-azo-A,lV -to-isobutyronitrile. They are mixed with template and the mixture is reacted at elevated temperature. The resultant rigid polymer is ground into a sieved powder and the template enantiomer washed off. 

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