Imprinting, hydrophobic interactions

Molecular imprinting can be accomplished in two ways (a), the self assembly approach and (b), the preorganisation approach3. The first involves host guest complexes produced from weak intermolecular interactions (such as ionic or hydrophobic interaction, hydrogen bonding) between the analyte molecule and the functional monomers. The self assembled complexes are spontaneously formed in the liquid phase and are sterically fixed by polymerisation. After extraction of the analyte, vacant recognition sites specific for the imprint are established. Monomers used for self assembly are methacrylic acid, vinylpyridine and dimethylamino methacrylate. 

However, the theophylline-imprinted polymer beads also bound more caffeine than theophylline, pointing out the fact that nonspecific hydrophobic interactions may play a role in the absorption phenomenon. 

In another report published near the same time, this group demonstrated the electrochemical detection of electroactive enantiomers, d- and L-3,4-dihydroxypheny-lalanine (DOPA) and (R)- and (.S )-A, A /-dimcthylfcrroccnylcthylamine (FcN) in imprinted sol-gel-derived thin films.68 To improve response times, the imprinted films were made to be very thin, — 70 nm, which is about 3 to 10 times thinner than typical sol-gel-derived films. The functional monomer used to imprint DOPA was PTMOS (Fig. 20.2) because it was expected to exhibit tt-tt and hydrophobicity interactions. For the ferrocene derivative, both PTMOS (Fig. 20.2) and carboxyethylsila-netriol sodium salt (CTES) were used for hydrophobicity and tt-tt interactions and electrostatic interactions between the amine and carboxy groups, respectively.68... 

As well as the more common oil in water suspension methods, it is also possible to make stable water in oil suspensions by choosing alternative surfactants with much lower hydrophilic/lipophilic balance values, combined with solvents such as hydrocarbons as the dispersing phase. These can be used to make beaded polymers from water-soluble monomers such as acrylamide. Although little work has been done to date with imprinting in aqueous conditions (using hydrophobic interactions... 

Non-covalent molecular imprinting relies on multiple non-covalent interactions between the print molecules and the monomers. The monomers are chosen to allow hydrogen bonds, ionic interactions, n-n interactions and/or hydrophobic interactions with the print molecules. Before polymerisation, the monomers and the print... 

Many planar dye molecules are bound to double-stranded DNA by being accommodated between adjacent Watson-Crick base pairs. These non-covalent interactions (intercalation) are used for molecular imprinting [11], Various hydrophobic interactions are also useful for the purpose [12],... 

The seed latexes used as the cores of the imprinted particles were prepared from hydrophilic or hydrophobic polymers. The hydrophilic seeds were prepared from methyl methacrylate and methyl methacrylate/ethyleneglycol dimethacrylate copolymers, while the hydrophobic seeds were composed of polystyrene or styre-ne/divinyl benzene copolymers. Hydrophilic- and hydrophobic-imprinted shells were then laid over these cores. It was found that the best cholesterol recognition was obtained with a hydrophilic-imprinted shell and a poly(methyl methacrylate) core. However, the performance deteriorated when the core was lightly cross-linked with ethyleneglycol dimethacrylate. In a second paper [10], imprinted polymers were prepared by the noncovalent approach with cholesterol rebinding relying upon hydrophobic interactions between cholesterol and the imprinted shell. To achieve this, the template was modified to give it the characteristics of a surfactant. The structure of the template surfactant is illustrated in Fig. 2. 

Yu, C. Ramstrom, O. Mosbach, K. Enantiomeric recognition by molecularly imprinted pol miers using hydrophobic interactions. Anal. Lett. 1997, 30, 2123 2140. 

Despite the fact that water interferes with many noncovalent imprinting systems, there have been numerous examples of noncovalent MIP beads prepared by suspension polymerization in water [15-18]. In almost all the cases, either a strong ionic, or hydrophobic interaction, or a combination of both (between template and monomers) were gainfully utilized. To generate larger MIP beads for chromatographic separation of metal ions, Yoshida et al. [19] developed a water-in-oil-in-water (W/O/W) multiple emulsion polymerization method, where a functional host... 

It should be stressed again that in many cases the increase of hydrophobic interactions could involve not only the binding sites, but also the polymeric backbone, resulting in pronounced nonspecific binding, often in the form of total retention of all hydrophobic compounds with a complete loss of selectivity. Such nonspecific adsorption can be reduced by the addition of organic modifiers or surface-active agents. This effect can be used when imprinted columns are prepared for on-line solid... 

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