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    Home > JACS: a novel phase sensitive membrane probe based on conjugated polyimide

    JACS: a novel phase sensitive membrane probe based on conjugated polyimide

    • Last Update: 2018-09-06
    • Source: Internet
    • Author: User
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    Polymer is a kind of compound which is usually formed by one or more simple units linked repeatedly by covalent bond, such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC) and so on, which are often used in daily life This kind of chemical compound with stable physical and chemical properties not only provides convenience for our life, but also brings many hazards Different from this kind of polymer, the polymer (dynamers) formed by dynamic covalent bond not only has the characteristics of general polymer, but also can switch freely between polymer and monomer under certain conditions / stimulation Therefore, they are widely used in self-healing materials, degradable materials, highly ordered porous frames and other fields Recently, Naomi Sakai and Stefan matile from the University of Geneva, Switzerland, jointly reported a phase sensitive fluorescent probe based on conjugated polyimides The fluorescent parent of the probe is fluorene The aldehyde group and amino group are modified at both ends of the probe, so the probe can form imine polymer through condensation reaction under certain conditions The experimental results show that the probe tends to form polymer in ordered bilayer phospholipid membrane, while it tends to exist as monomer in disordered environment This achievement was published in the Journal of the American Chemical Society (DOI: 10.1021 / JACS 8b06668) under the title of "coherent polymer dyes as phase sensitive membrane probes" Fig 1 A) synthesis route of the probe; b) mass spectrum; c) GPC spectrum; d) ultraviolet absorption spectrum (source: J am Chem SOC.) the synthesis of the probe starts with 2,7-dibromofluorene 2 Firstly, the alkyl chain (C8) and triethylene glycol (TEG) were modified at position 9 of 2 to make them amphiphilic After that, the intermediate 3 was reacted with cuprous cyanide to obtain the intermediate 4 4 reacted with t-butyl carbamate to obtain another intermediate 5 whose bromine was substituted by amino group Then the author transformed cyano group into aldehyde group by diisobutylaluminium hydride, and finally removed BOC protecting group to obtain monomer 1 m (Fig 1a) The mass spectrum of 1 shows that it has a typical polymer peak (Fig 1b), which shows that polymerization can take place at 1 m Gel permeation chromatography (GPC) showed that the probe could form polymers with molecular weights up to 30 kDa (Figure 1C, solid line), and polymers could be further decomposed into monomers under acidic conditions (1C, dashed line) In addition, we also found that the UV absorption spectrum of the probe changed with the degree of polymerization (Fig 1D) Fig 2 A) UV absorption spectrum of probe in DPPC luvs at different temperatures; b) maximum absorption wavelength of probe in DPPC, DOPC and Sm / CL luvs at different pH values; c) maximum absorption wavelength of probe in different probe / liposome molar ratio (source: J am Chem SOC.) After obtaining the probe and having a basic understanding of its properties, the author selected three different materials to study the polymerization behavior of the probe in the phospholipid bilayer membrane The three materials are: DPPC large monolayer vesicles (luvs) with a phase change temperature of about 41 ° C; DOPC with a phase change temperature of about - 17 ° C Luvs: a mixture of sphingomyelin (SM) / cholesterol (CL) (SM: CL = 1:1) in an orderly state within the experimental temperature range The results show that in the ordered environment, the maximum absorption peak of the probe is around 425 nm, while in the disordered environment, the maximum absorption peak is about 375 nm (Fig 2a) In addition, the author also found that the polymerization behavior was related to the relative concentration of probe monomer and phospholipid (Fig 2C) Fig 3 A) excitation and emission spectra of probe in buffer, DOPC and DPPC at 25 ° C; b) fluorescence intensity of probe in DOPC at different probe / liposome molar ratio; c) fluorescence emission spectra of probe in DOPC at different osmotic stress; d) fluorescence intensity ratios of probe at 460 nm and 530 nm at different osmotic stress (source: J am Chem SOC.) in addition to the ultraviolet absorption characteristics, the author also explored the fluorescence characteristics of the probe under different conditions, and found that the environment where the probe is located has a great impact on its fluorescence spectrum Firstly, in the absence of luvs, the fluorescence of the probe can hardly be observed, and the presence of luvs will greatly enhance the fluorescence signal of the probe Secondly, the fluorescence of the probe is also different in different luvs The maximum emission wavelength in DPPC luvs is at 460 nm, while the strong fluorescence emission signal appears at 460 nm and 530 nm in DOPC film (Fig 3a), which indicates that the probe will show unique photophysical characteristics for different phase environments Based on this fluorescence characteristic, the author tried to apply the probe to the detection of membrane tension (Fig 3C, d) Because the membrane is very sensitive to osmotic stress, the author applied different osmotic stress to DOPC luvs The results showed that under different osmotic stress, the fluorescence intensity of the probe did not change significantly at 530 nm, which indicated that the change of osmotic stress did not affect the polymerization behavior of the probe It was also found that the fluorescence signal of the probe at 460 nm changed regularly with the change of osmotic stress According to the reports of related literature, under different osmotic stress, lipid will expand or contract, thus affecting the fluorescence signal of probe Highlight of this paper: the fluorescent probe with dynamic polymerization dissociation ability was obtained by simple steps It was found that the UV absorption spectrum and fluorescence emission spectrum of the probe will change with the polymerization degree Based on this characteristic, the molecule has been successfully developed into a probe for detecting membrane tension Full text author: naomisakai and Stefan matile
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