Photodimerization of Anthryl Moieties in a Poly(methacrylic acid) Derivative as Reversible Cross-linking Step in Molecular Imprinting

Abstract

A methodology for reversible molecular imprinting is presented. A molecularly imprinted polymer (MIP) is prepared by photo-cross-linking poly(methacrylic acid) (PMAA) with anthryl moieties as photo-cross-linking sites in the presence of an antimalarial drug cinchonidine as a template molecule, resulting in enhanced binding capacity to cinchonidine, compared with non-imprinted polymers. MIP is then ''initialized'' by exposure to shortwave UV that cleaves the anthracene-dimer-based crosslinks, resulting in the reduced binding capacity comparable to the non-imprinted polymers.Molecular imprinting is a methodology to produce a polymer with functional groups arranged for recognition of specific target molecules.1 Polymers obtained by molecular imprinting (molecularly imprinted polymers, MIPs) have often been compared to enzymes and antibodies, and utilized in various applications ranging from analysis 2 to catalysis. 3 In typical MIP syntheses, functional monomers, complexed with a template molecule, are polymerized (cross-linked) to preserve the arrangement of the monomers complementary to the template molecule. Even after removal of the template molecule from the resultant network polymer, it is believed that the complementarity can be still preserved in terms of both shape and functionality, allowing the polymer to specifically bind the template molecule. Cross-linking manners are greatly important for constructing binding sites, and have been the central theme for establishing the imprinting techniques. 4 Although radical polymerization has been the most commonly used in the MIP synthesis, the reaction is not quite appropriate for controlling and monitoring cross-linking degree. Furthermore, once the radical polymerization proceeds, the structure and property of resultant MIPs can not be changed due to inert cross-links. To date, however, few cross-linkers controllable by external stimuli have been reported. 5In this study, aiming at performing reversible molecular imprinting upon external stimuli, we examine [4 þ 4] photodimerization of anthryl groups as cross-linking step (Figure 1). It is known that anthracene and its derivatives form a dimer upon exposure to longwave UV and the dimer is restored to an original monomer by irradiation of shortwave UV.6 Various polymeric materials have been reported utilizing this reaction, 7,8 and our design of molecular imprinting is based on these studies demonstrating interesting reversible properties. Another point in our design is a use of a linear polymer with cross-linkable moieties (a pre-polymer); it is appropriate to use pre-polymers as MIP precursors rather than monomers for constructing network structure by dimerization-based cross-linking. We previously reported that poly(methacrylic acid) (PMAA) with styryl moieties can be used for preparing cinchonidine-selective MIPs, 9 in which carboxyl moieties of PMAA are supposedly immobilized as complementary to cinchonidine by cross-linking. 10 In this study, we designed a PMAA-based pre-polymer bearing anthryl moieties t...

Photochemical Behavior of High Quantum Yield SWNTs Functionalized with Anthracene Salts

“…Photodimerization of the precursor salt [bamim]Cl was achieved under the same conditions, and photoinduced scission of the formed polymer was also partially reversible (see the Supporting Information, Figures S2 and S3). Similar phenomena have also been previously observed, and although the reasons for the partial reversibility remain unclear, [36,37] it is possible that only the dimers on the surface of the polymer can be cleaved, although one might expect that as those on the surface cleave, the dimers buried inside the polymer become susceptible to scission.…”

“…The irradiation of SWNT-[bamim] was monitored by UV/ Vis spectrophotometry (Figure 1). Irradiation of SWNT-[bamim] in ethanol at 365 nm (8 W) resulted in a gradual decrease of the absorption peak at 248 nm and the bands in the region 320-400 nm became slightly blue-shifted (Figure 1 a), [36] thus indicating that the anthracene groups have dimerized leading to a new SWNT system: SWNT-[bamim]-A. Notably, the peaks in the region 320-400 nm represent the characteristic conjugate structure, and the blue shift can be attributed to a shortening in the effective conjugated length.…”

Reversible Photocycloadditions, a Powerful Tool for Tailoring (Nano)Materials

“…Another linear polymer was synthesized by esterification of poly(methacrylic acid) with 9‐chloromethylanthracene as the side group 43. Although, after photodimerization of several of these chains, full decrosslinking was not achieved, the reversibility was very efficient and the changes in the degree of crosslinking in the generated network were highly repetitive, as shown in Figure 9.…”

Towards the Generation of Self‐Healing Materials by Means of a Reversible Photo‐induced Approach

“…Photo-induced mending structures have been reported in the literature using small molecules, linear polymers with end-or pending photo-active functional groups as well as in star polymers. [2,7,23,28,29] Nevertheless, we are unaware of the use of dendritic polymers focusing on these re-mending properties. The self-healing ability of our system was tested by introducing an artificial scratch (4.5 Â 1 mm 2 , Figure 3) in a beforehand crosslinked film of PG-An.…”