Membranes theophylline-imprinted

Fig. 16 SEM image of the cross section of a theophylline-imprinted membrane asymmetric structure of imprinted membrane prepared by the wet phase inversion process. Reproduced with permission from [217]...

Selectively permeable membranes can be produced using a molecular imprinting approach. Using a phase inversion method, a poly(acrylonitrile-co-acrylic acid) ultrafiltration membrane was imprinted with theophylline [52], When solutions of theophylline and caffeine were filtered, a significantly greater amount of theophylline was retained within the membrane (Figure 6.33). 

Figure 6.33 Selective filtration through a theophylline imprinted membrane. TH= theophylline, CA = caffeine [52]...

Theophylline-imprinted membranes were prepared by phase inversion of poly(acrylonitrile-co-acrylic acid). The copolymer and the template molecule, theophylline, dissolved in dimethylsulfoxide, was spread on a glass plate about 0.1 mm thick and coagulated in water. After removal of the theophylline by washing with 0.1 %(v/v) acetic acid, a theophylline-imprinted polymer membrane was obtained [46], Instead of poly(acrylonitrile-co-acrylic acid), Nylon-6 was also used in this technique to prepare L-glutamine-imprinted polymer membranes [47]. 

An ultrathin-film composite membrane selective for theophylline has been reported [48]. The theophylline-imprinted polymer was prepared inside pores of a microporous alumina support membrane with a thickness of 500 nm and a pore size of 20 nm, in which pores of the membrane were filled by the polymerization solution containing the template theophylline, methacrylic acid, and ethylene glycol dimethacrylate, and the membrane was illuminated with UV light for 1 h, followed by immersion in methanol containing 10 %(v/v) acetic acid to remove the template and any excess monomer. Because the membrane is extremely thin, the flux rate is high, being at least two orders of mag-... 

The molecular recognition capabilities of polyelectrolyte multilayers have also been investigated by Laschewesky [55], while imprinted films have been grown on membrane surfaces in approaches similar to the phase inversion method for preparing a membrane imprinted with theophylline. Wang et al. [56] adopted an acrylonitri-le/dithiocarbamoyl-methylstyrene copolymer (Fig. 16) to effect separation of caffeine from the theophylline-imprinted membrane. 

Several selective interactions by MIP membrane systems have been reported. For example, an L-phenylalanine imprinted membrane prepared by in-situ crosslinking polymerization showed different fluxes for various amino acids [44]. Yoshikawa et al. [51] have prepared molecular imprinted membranes from a membrane material which bears a tetrapeptide residue (DIDE resin (7)), using the dry phase inversion procedure. It was found that a membrane which contains an oligopeptide residue from an L-amino acid and is imprinted with an L-amino acid derivative, recognizes the L-isomer in preference to the corresponding D-isomer, and vice versa. Exceptional difference in sorption selectivity between theophylline and caffeine was observed for poly(acrylonitrile-co-acrylic acid) blend membranes prepared by the wet phase inversion technique [53]. 

The group of Ciardelli prepared MIP nanoparticles imprinted with theophylline or caffeine by precipitation polymerisation and coated them onto a poly-MMA-co-AA membrane (Fig. 18) [217, 255, 256]. 

Liquid crystalline imprinted materials have been synthesized (Fig. 24) from polysiloxanes with mesogenic side-chains. In some of them, acetophenone was chosen as template and was covalently linked to the mesomorphous network via a ketal link [ 199]. In the others, the templates (carbobenzoxy-L-phenylala-nine, 1,8-diaminonaphthalene or theophylline) were in interaction with the mesomorphous polymer via hydrogen bonding [200]. All the imprinted networks were obtained as dense membranes. 

T. Kobayashi, H.Y. Wang, N. Fujii, Molecular imprinting of theophylline in acrylonitrile-acrylic acid co-polymer membrane. Chemistry Letters 10 (1995)... 

Pore-filling MIP composite membranes had been first prepared by Dzgoev and Haupt [100]. They casted the reaction mixture into the pores of a symmetric microfiltration membrane from polypropylene (cutoff pore size 0.2 pm) and performed a cross -linking copolymerization of a functional polyacrylate for imprinting protected tyrosine. Hattori et al. [101] had used a commercial cellulosic dialysis membrane (Cuprophan) as matrix and applied a two-step grafting procedure by, (i) activation of the cellulose by reaction with 3-methacryloxypropyl trimethoxysilane from toluene in order to introduce polymerizable groups into the outer surface layer, (ii) UV-initiation of an in situ copolymerization of a typical reaction mixture (MAA/EDMA, AIBN) for imprinting theophylline. 

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