Molecular imprinting method

To prepare artificial enzymatic systems possessing molecular recognition ability for particular molecules, molecular imprinting methods that create template-shaped cavities with the memory of the template molecules in polymer matrices, have been developed [22, 30-35] and established in receptor, chromatographical separations, fine-chemical sensing, etc. in the past decade. The molecular... 

Molecular recognition has drawn much attention with regard to separation chemistry. One of the promising approaches to create molecular-recognising materials is the molecular imprinting method, the concept of which was proposed by Wulff et al. about 20 years ago. The new methodology does not require a precise... 

Native enzymes, which can spatially and chemically recognize substrate molecules, are powerful catalytic systems in many biochemical processes under mild reaction conditions. The preparation of artificial enzymatic catalysts with the capability of molecular recognition capability, by a molecular-imprinting method, which creates cavities with a similar shape and size to the template molecule in polymer matrices has been developed [1-14]. The technique has been mainly established in the field of analytical chemistry - molecular receptors [15-23], chromatographic separations [24-28], fine chemical sensing [29-33]. All of the methods rely on the selective adsorption of target molecules on imprinted adsorption sites. The number of papers reported per year on molecular imprinting is summarized in Fig. 22.1. 

The application of the molecular imprinting method for the synthesis of heterogeneous catalysts has been investigated examples of molecularly imprinted catalysts are summarized in Table 22.1. In addition to acid-base catalysts with acid and/or... 

The molecular imprinting method can be used to synthesize enantioselective solid materials for asymmetric organic synthesis. The first attempt to use a metal complex with an attached chiral ligand as a template was attempted by Lemaire [52]. The Rh complex, ((15,25)-V,V -dimethyl-l,2-diphenylethane diamine)-[Rh(CgHj2)Cl]2 coordinated with optically pure l-(5)-phenylethoxide or phenylethoxide (Rh 1-phenylethanolate) (template) was polymerized in the presence of isocyanate, and the polyurea-supported Rh complex is reacted with isopropanol to extract the template from the polymer backbone. They reported the influence of molecular imprinting on catalytic performance (conversion and enantiomeric excess) for the asymmetric transfer hydrogenation (Table 22.2). The imprinted polymer exhibited higher enantioselectivity compared to a nonimprinted... 

Polyakov [31] has a priority in preparation of the sorbents in the presence of molecular imprints. The sorbents obtained show specificity toward the substance that is used as an imprint. Since then the molecular imprinting methods has been successfully used in adsorption [32,33] and catalysis [34-37]. 

Nakano,T., Satoh,Y., Okamoto, Y. Synthesis and Chiral Recognition Ability of a Cross-Linked Polymer Gel Prepared by a Molecular Imprint Method Using Chiral Helical Polymers as Templates, Macro-molecules, 2001, 34, 2405—2407. 

Dobashi A, Nishida S, Kurata K, Hamada M (2002) Chiral separation of enantiomeric 1,2-diamines using molecular imprinting method and selectivity enhancement by addition of achiral primary amines into eluents. Anal Sci 18(l) 32-35... 

A molecular imprinting method has recently been developed to provide versatile receptors efficiently and economically. In principle, movements of molecules are frozen in polymeric structures so that they are immobilized in a desired fashion. This method is so unique and challenging that the scope of future applications is hard to predict precisely at the present time. This chapter deals with the current status of relevant sciences so that the reader can confirm the importance of the molecular imprinting method. 

As described above, the molecular imprinting method is of two types, depending on the nature of adducts between functional monomer and template (either covalent or non-covalent). Typical examples of these two kinds of methods are presented in Figs. 2.2 and 2.3. Both have advantages and disadvantages, and thus the choice of the best method strongly depends on various factors (see below). 

In the past, chemists were familiar with so-called template effects , although the term molecular imprinting was not used. When some molecules are added to reaction mixtures, chemical reactions are accelerated and/or product distribution is notably altered. Here, these additives interact with the reactants, and place them in mutual conformations which efficiently lead to one of the possible products. Alternatively, they stabilize certain products and promote their formation. Apparently, these phenomena are associated with the concept of molecular imprinting. However, it was the pioneering works by Wulff, Shea, Mos-bach, and others that made the molecular imprinting method as popular as it is today. 

Of course, the current molecular imprinting method has not yet been perfected with respect to its strictness in the freezing . The shutter speed of our camera must be further increased and the shut-ter timing must be more precisely controlled. We also have to know much more about the mechanism of imprinting. However, this area has been growing so rapidly in depth and breadth that these factors should be solved soon. No doubt, this versatile method will be still more widely used for a great many purposes in the near future. It is hoped that this book will help to achieve this goal. 

We should like to thank a number of people who have worked for the development of the molecular imprinting method . Our sincere appreciation is also extended to the staff members and students in our laboratories for helping with... 

The authors noted "...This enantioselective catalysis should extend the seope of our strategy for tailored specific catalysts by the molecular imprinting method...". A review of these works exists Indeed, these results are of great interest, but it is necessary to note that Kaiser and Anderson were unable to repeat the results with the benzamide imprinted silicas. Their failure probably was the result of a short lifetime for the specific properties of such Al-doped silica gels. 

Nakano, T. Satoh, Y. Okamoto, Y. Synthesis and chiral recognition ability of a cross-linked polymer gel prepared by a molecular imprint method using chiral helical polymers as templates. Macromolecules 2001, 34, 2405-2407. 

Lin, J.M. Uchiyama, K. Hobo, T. Enantiomeric resolution of dansyl amino acids by capillary electrochromatography based on molecular imprinting method. Chromatographia 1998, 47, 625-629. 

Frigeri, A. Kobayashi, H. Shinkai, S. Reinhoudt, D.N. From solutions to surfaces A novel molecularly imprinting method based on the conformational changes of boronic-acid-appended poly (L-lysine). Angew. Chem. Int. Ed. 2001, 40, 4729-4731. 

A. Friggeri, H. Kobayashi, S. Shinkai and D. N. Reinhoudt, From Solutions to Surfaces A Novel Molecular Imprinting Method Based on the Conformational Changes of Boronic-Acid-Appended Poly(l-lysine), Angew. Chem., Int. Ed., 2001,40(24), 4729-4731. 

On the basis of these pioneering works, further improvements of the binding activity and selectivity, as well as the applications of molecular imprinting method to still more versatile purposes, have been... 

The imprinted j8-CyD polymers, prepared with the use of cholesterol as the template, bound cholesterol in water far more efficiently than did the polymer obtained in the absence of the template. The effect of molecular imprinting is evident. Cholesterol is too large to be accommodated in the cavity of one -CyD molecule. Thus, two (or more) )8-CyD molecules must simultaneously interact with one cholesterol molecule in order to bind cholesterol efficiently. Only when the molecular imprinting method is used and several )8-CyD molecules are placed in the desired positions, eminent and practically useful polymeric receptors can be obtained. 

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