GroEL(SP/MC), prepared by genetic and chemical modifications of group I chaperonin protein GroEL, site-specifically possesses approximately 28 photochromic (spiropyran [SP] and merocyanine [MC]) units in the entrance parts of its cavity. Addition of divalent metal ions such as Mg(2+) to a tris-HCl buffer solution of GroEL(SP/MC) results in one-dimensional (1D) assembly of GroEL(SP/MC), affording cylindrical hollow fibers with a very large aspect ratio; the longest fiber was approximately 2.5 microm long, corresponding to a 170-mer of GroEL(SP/MC) (MW approximately 1.4 x 10(8)). When such long fibers are mixed with EDTA, they are cut into short-chain oligomers and eventually into monomeric GroEL(SP/MC). Similar to GroEL, GroEL(SP/MC) possesses a large binding affinity toward denatured proteins. When GroEL(SP/MC) undergoes 1D assembly after incubation with a denatured protein, guest-containing cylindrical fibers result.
A simple modification, methylation of the nitrogen-substituted mesoporous silica SBA-15, enhances the basicity of a solid-base catalyst. The methyl group donates an electron to the nitrogen atom in the silica framework. This catalyst accelerates Knoevenagel condensation using benzaldehyde and diethyl malonate, which conventional solid-base catalysts reported to date cannot do. This report demonstrates a possible new type of base catalyst using nitrogen-substituted mesoporous silica materials.
A network polymer with photoinduced mending abilities was prepared from cinnamoyl-telechelic prepolymer of poly(butylene adipate), PBAC 2 , and a tetra-cinnamoyl linker, C 4 , by photodimerization. The photodimerization reaction of the cinnamoyl groups was analyzed using both ultraviolet (UV)/visible (vis) and infrared (IR) spectroscopy. In the reaction, the isomerization of the cinnamate group from the trans to the cis conformation competes with the dimerization reaction of cinnamates. The fractions of dimer and isomer populations estimated from the UV/vis spectra revealed that dimerization was the more preferred reaction at temperatures higher than the melting point of PBAC 2 . When a film of the network polymer was damaged by tapping, the cinnamate dimers dissociated to form cinnamate monomers due to the reversibility of the dimerization. To recover the network structure, these monomers could be dimerized once again through a photoirradiation process. These results show that cracks in the network polymer can be recovered through photoirradiation.
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