Synthesis and photoisomerization of dithienylethene-bridged diporphyrins

Dithienylethene-bridged diporphyrins 1-6 were prepared as photochemical switching molecules. Porphyrin and dithienylethene are directly linked in 1, and linked, respectively, through a 1,4-phenylene spacer in 2, through a 4-ethynylphenylene spacer in 3, and through a di-4-phenylethynylene spacer in 4, while meso-ethynylated porphyrin and dithienylethene are directly connected in 5 and linked through a 1,4-phenylene spacer in 6. Compounds 1, 2, and 5 do not undergo any photochemical isomerization, probably due to efficient quenching of the excited dithienylethene by the attached porphyrin moiety via intramolecular energy transfer. Compounds 4 and 6 undergo open-to-closed and closed-to-open photoisomerizations in quantum yields of 4.3 x 10(-)(2) and 1.8 x 10(-)(3), and 2.6 x 10(-)(3) and 7.5 x 10(-)(4), respectively, by irradiation with 313 and 625 nm light, which are considerably smaller than quantum yields of 0.52 and 3.8 x 10(-)(3) for reference dithienylethene molecule 7. The fluorescence of 4 was regulated in a reversible manner by the photoisomerization of the dithienylethene moiety. In addition, the absorption properties of the porphyrin in 6 changed in response to the photochromic reaction of the dithienylethene bridge.     

483—Monitoring cell potential of Escherichia coli with use of an electrode sensitive to tetraphenyl phosphonium: Change by addition of various sugars

An electrode sensitive to tetraphenyl phosphonium cation (TPP⁺) was applied to the determination of the membrane potential of E. coli (strain B, IAM 1268). This strain did not require EDTA (ethylenediamine tetraacetic acid)-treatment for accumulation of TPP⁺. As reported previously, some part of the TPP⁺-uptake was due to the binding to cell envelopes. The time course of TPP⁺-uptake by cells on addition of sugars was analysed, and the result indicated that the additional binding of TPP⁺ no longer occured. The change in the membrane potential on addition of various sugars was evaluated.     

Construction of a functional IgG-binding luciferase fusion protein for the rapid detection of specific bacterial strains

A fusion protein consisting of two IgG-binding domains of streptococcal protein G and firefly luciferase was constructed, and a simple and specific bioluminescent immunodetection system for bacterial strains was developed.     

Strategy for Molecular Design of Photochromic Diarylethenes Having Thermal Functionality

Thermal reactivities of photochromic diarylethene closed‐ring isomers can be controlled by the introduction of substituents at the reactive positions. Diarylethenes having bulky alkyl groups undergo thermal cycloreversion reactions. When bulky alkoxy groups are introduced, the diarylethenes have both thermal cycloreversion reactivities and low photocycloreversion quantum yields. Such photochromic compounds can be applied to thermally reusable photoresponsive‐image recordings. The thermal cycloreversion reactivity of the closed‐ring isomers can be evaluated using specific steric substituent constants and be correlated with the parameters. By introduction of trimethylsilyl or methoxymethyl groups at the reactive positions, the diarylethene closed‐ring isomers undergo thermal irreversible reactions to produce by‐products at high temperatures. These diarylethenes may be useful for secret‐image recordings. Furthermore, thiophene‐S,S‐dioxidized diarylethenes having secondary alkyl groups at the reactive positions undergo thermal by‐product formation reactions, in addition to the photostability of the colored closed‐ring isomers. Such materials may be used for light‐starting thermosensors. The thermal by‐product formation reactivity can be evaluated by the specific substituent constants and theoretical calculations of quantum chemistry. These results supply the strategy for the molecular design of the photochromic diarylethenes having thermal functionality.

     

Plasmonic enhancement of gold nanoparticles on photocycloreversion reaction of diarylethene derivatives depending on particle size, distance from the particle surface, and irradiation wavelength

We newly synthesized various sized gold nanoparticles covered with photochromic polymers consisting of diarylethenes with various structures to investigate an effect of the gold nanoparticles on the photocycloreversion reaction of the diarylethene chromophores upon irradiation with visible light. The gold nanoparticles covered with the photochromic polymers exhibited reversible changes in localized surface plasmon resonance (LSPR) absorption along with the photochromic reaction depending on the diameter of the particle, the distance between the gold surface and the chromophore, and the structure of the diarylethene chromophore. The rate of the photocycloreversion reaction of the chromophores around the particle was enhanced by the gold nanoparticles and the degree of the enhancement was affected by the diameter of the particle and the distance from the gold surface, while a structural difference in the diarylethene chromophore had no effect on the degree of the enhancement. The larger enhancement of the photocycloreversion reaction was observed by irradiation at longer wavelength side than visible light corresponding to the LSPR frequency.     

Solvent effect on photochromism of a dithienylperfluorocyclopentene having diethylamino group

Some photochromic diarylethenes having polar substituents were synthesized, and their photochromic behavior was examined. They exhibited photochromism with the similar photoreactivity in a non-polar solvent. However, the photocyclization quantum yield of dithienylperfluorocyclopentene having diethylamino group was found to decrease in polar solvents. The yield in acetonitrile was estimated to be 60 times smaller than that in hexane. The yields determined in various solvents were found to be correlated with the solvent polarity parameter E_T(30). Such an effect was not observed in dithienylfluorocyclopentenes bearing methoxy or acetoxy group and in non-fluorinated dithienylcyclopentene bearing diethylamino group.     

Recombination System Based on Cre α Complementation and Leucine Zipper Fusions

A gene encoding β-1,3-1,4-glucanase was cloned by polymerase chain reaction (PCR) from Bacillus subtilis MA139. Sequencing result showed 97% homology to the corresponding gene from Bacillus licheniformis. The open reading frame (ORF) of the gene contained 690 bp coding for a 226 amino-acid matured protein with the estimated molecular weight of 24.44 kDa. The β-1,3-1,4-glucanase gene was subcloned into an expression vector of pET28a and expressed in Escherichia coli BL21 and then purified by metal affinity chromatography using a nickel–nitrilotriacetic acid (Ni–NTA) column. The purified β-1,3-1,4-glucanase demonstrated 24.05 and 12.52 U ml^-1 activities for the substrates of barley β-glucan and lichenan, respectively, and the specific activities were 728.79 and 379.1 U mg^-1 for them, respectively. The optimal temperature and pH of the purified enzyme were 40°C and 6.4, respectively. When barley β-glucan was used as the substrate, K _m was 5.34 mg ml^-1, and K _cat showed 7,206.71 S^-1, thus the ratio of K _cat and K _m was 1,349.67 ml s^-1 mg^-1. The activity of β-1,3-1,4-glucanase was affected by a range of metal ions or ethylenediaminetetraacetic acid (EDTA).     

Two-photon photochromism of two simple chromene derivatives

Two kinds of typical chromene derivatives, 5a,9-dimethyl-5aH-benzo[b]chromene (1) and 7a,11-dimethyl-7aH-dibenzo[b,f]chromene (2), were synthesized to understand the relationship between molecular structures and two-photon photochromism for chromene derivatives. The photochromic performances of 1 and 2 in hexane were investigated by measuring ultraviolet (UV)–visible absorption and ¹H nuclear magnetic resonance spectral changes upon UV irradiation. The results indicate that 1 showed the two-photon photochromic reaction, whereas the main photochemical reaction of 2 was the isomerization between the open-E and open-Z isomers. Density functional theory (DFT) calculations suggest that these different photochromic performances are attributed to the differences in relative stabilities of closed, open-Z and open-E isomers for 1 and 2. Combined with DFT calculations for 12aH-12a-methyl-naphtho[3,2]chromene (3), the most typical chromene derivative well exhibiting two-photon photochromism, we conclude that chromene derivatives show the best two-photon photochromic performances only if closed isomers are more stable than open-Z and open-E isomers.     

Polymerization of 2-(substituted methyl)acrylate bearing ω-methoxyoligoethyleneoxy groups as side chains to new low Tg polymer

The polymerization of methyl 2-(ω-methoxyoligoethleneoxymethyl)acrylates, which were synthesized from reactions of methyl 2-bromomethylacrylate with ω-methoxyoligoethylene glycol, was investigated. All these monomers polymerized readily to high molecular weight despite expectation of the considerable steric hindrance against propagation. No influence of ceiling temperature was observed. The 2-(2-methoxyethyleneoxymethyl)acrylate exhibited similar reactivities to methyl 2-alkoxymethylacrylate reported previously in copolymerization with styrene and methyl methacrylate. The homopolymers synthesized, except for those from methyl 2-methoxymethyl- and 2-(2-methoxyethyleneoxymethyl)acrylates, were soluble in water, and all were soluble in benzene. These polymers were thermally less stable than poly(methyl methacrylate) as confirmed by thermogravimetric analysis, and all showed glass transition temperatures below 0°C. © 1993 John Wiley & Sons, Inc.