Photoinduced Reversible Bending and Guest Molecule Release of Azobenzene-Containing Polydiacetylene Nanotubes.
ABSTRACT: Creation of hollow, one-dimensional nanomaterials has gained great recent attention in the chemical and material sciences. In a study aimed at discovering new functional materials of this type, we observed that an amphiphilic diacetylene (DA) derivative, containing an azobenzene moiety and an oligo-ethylene group, self-assembles to form nanotubes and undergoes photopolymerization to form hollow polydiacetylene (PDA) nanotubes with a uniform wall thickness and diameter. The azobenzene-PDA nanotubes are photoresponsive in that on-and-off UV-irradiation leads to a reversible morphological change between straight and bent forms in association with E-Z photoisomerization of the azobenzene group. Owing to the UV-induced structural change feature, the new DA and PDA nanotubes serve as a controlled release material. Accordingly, fluorescent rhodamine B encapsulated inside the nanotubes are effectively released by using repeated on-off UV irradiation. Furthermore, photo-release of rhodamine B was shown to occur in an artemia (brine shrimp).
Project description:Conjugated polydiacetylene (PDA) possessing stimuli-responsive properties has been intensively investigated for developing efficient sensors. We report here fluorescence resonance energy transfer (FRET) in liposomes synthesized using different molar ratios of dansyl-tagged diacetylene and diacetylene-carboxylic acid monomers. Photopolymerization of diacetylene resulted in cross-linked PDA liposomes. We used steady-state electronic absorption, emission, and fluorescence anisotropy (FA) analysis to characterize the thermal-induced FRET between dansyl fluorophores (donor) and PDA (acceptor). We found that the monomer ratio of acceptor to donor ( R ad) and length of linkers (functional part that connects dansyl fluorophores to the diacetylene group in the monomer) strongly affected FRET. For R ad = 10 000, the acceptor emission intensity was amplified by more than 18 times when the liposome solution was heated from 298 to 338 K. A decrease in R ad resulted in diminished acceptor emission amplification. This was primarily attributed to lower FRET efficiency between donors and acceptors and a higher background signal. We also found that the FRET amplification of PDA emissions after heating the solution was much higher when dansyl was linked to diacetylene through longer and flexible linkers than through shorter linkers. We attributed this to insertion of dansyl in the bilayer of the liposomes, which led to an increased dansyl quantum yield and a higher interaction of multiple acceptors with limited available donors. This was not the case for shorter and more rigid linkers where PDA amplification was much smaller. The present studies aim at enhancing our understanding of FRET between fluorophores and PDA-based conjugated liposomes. Furthermore, receptor tagged onto PDA liposomes can interact with ligands present on proteins, enzymes, and cells, which will produce emission sensing signal. Therefore, using the present approach, there exist opportunities for designing FRET-based highly sensitive and selective chemical and biochemical sensors.
Project description:We report here the synthesis and characterization of polydiacetylene (PDA) films and nanotubes using layer-by-layer (LBL) chemistry. 10,12-Docosadiyndioic acid (DCDA) monomer was self-assembled on flat surfaces and inside of nanoporous alumina templates. UV irradiation of DCDA provided polymerized-DCDA (PDCDA) films and nanotubes. We have used zirconium-carboxylate interlayer chemistry to synthesize PDCDA multilayers on flat surfaces and in nanoporous template. PDCDA multilayers were characterized using optical (UV-vis, fluorescence, ellipsometry, FTIR) spectroscopies, ionic current-voltage ( I- V) analysis, and scanning electron microscopy. Ellipsometry, FTIR, electronic absorption and emission spectroscopies showed a uniform DCDA deposition at each deposition cycle. Our optical spectroscopic analysis indicates that carboxylate-zirconium interlinking chemistry is robust. To explain the disorganization in the alkyl portion of PDCDA multilayer films, we propose carboxylate-zirconium interlinkages act as "locks" in between PDCDA layers which restrict the movement of alkyl portion in the films. Because of this locking, the induced-stresses in the polymer chains can not be efficiently relieved. Our ionic resistance data from I- V analysis correlate well with calculated resistance at smaller number of PDCDA layers but significantly deviated for thicker PDCDA nanotubes. These differences were attributed to ion-blocking because some of the PDCDA nanotubes were totally closed and the nonohmic and permselective ionic behaviors when the diameter of the pores approaches the double-layer thickness of the solution inside of the nanotubes.
Project description:Recognition of nucleic acids remains an important endeavor in biology. Nucleic acids adopt shapes ranging from A-form (RNA and GC rich DNA) to B-form (AT rich DNA). We show, in this contribution, shape-specific recognition of A-U rich RNA duplex by a neomycin (Neo)-polydiacetylene (PDA) complex. PDA assemblies are fabricated by using a well-known diacetylene (DA) monomer, 10,12-pentacosadiynoic acid (PCDA). The response of poly(PCDA) assemblies is generated by mixing with a modified neomycin-PCDA monomer (Neo-PCDA). The functionalization by neomycin moiety provides specific binding with homopolyribonucleotide poly (rA) - poly (rU) stimulus. Various types of alcohols are utilized as additives to enhance the sensitivity of poly(PCDA)/Neo-PCDA assemblies. A change of absorption spectra is clearly observed when a relatively low concentration of poly (rA)-poly (rU) is added into the system. Furthermore, poly(PCDA)/Neo-PCDA shows a clear specificity for poly (rA)-poly (rU) over the corresponding DNA duplex. The variation of linker between neomycin moiety and conjugated PDA backbone is found to significantly affect its sensitivity. We also investigate other parameters including the concentration of Neo-PCDA and the DA monomer structure. Our results provide here preliminary data for an alternative approach to improve the sensitivity of PDA utilized in biosensing and diagnostic applications.
Project description:Superchiral light, generated by the interference of two counter-propagating circularly polarized light (CPL) with same frequency, opposite handedness and different intensity, exhibits enhanced dissymmetry in its interaction with chiral molecules, and has the potential for ultrasensitive detection and characterization of chiral molecules. It is anticipated that the enhanced optical dissymmetry in superchiral light (SCL) field may be utilized to promote asymmetric photochemical reactions efficiency. Herein we reported SCL impart greater chiral bias to trigger asymmetric photo-polymerization reaction from initially achiral diacetylene (DA) monomer, and the enhanced optical dissymmetry for whole polydiacetylene (PDA) films could be achieved. An explanation based on the chiral transfer and amplification of chiral bias from SCL during the polymerization process has been proposed. Moreover, thus formed chiral PDA films polymerized by SCL exhibited enhanced enantioselective recognition ability, and can serve as a direct visual probe for the discrimination of some specific enantiomers.
Project description:Chiral noble metal nanoparticles has recently gained great interest due to their potential applications including ultrasensitive chiral recognition and asymmetric synthesis. We anticipate that they could be utilized to induce asymmetric photo-polymerization reactions with high enantioselectivity and reactivity. Here, we report such a system. By employing silver nanoparticles modified with cysteine as the chiral inducer, polydiacetylene (PDA) with high chiral asymmetry was obtained from achiral diacetylene monomers triggered with unpolarized UV light. Furthermore, the helical sense of chirality can be controlled by varying the wavelength of UV irradiation. This enables a feasible and economical method to fabricate programmable 2D patterns of chiral PDA with tailored chirality distributions, such as smooth gradients in chirality and micropatterns with tailorable circularly polarized luminescence. Our finding not only opens a pathway for producing programmable chiroptical micropatterns, but also is highly valuable for deeper understanding of symmetry breaking in enantioselective photochemical reactions.
Project description:The structure of a self-assembly formed from a cationic azobenzene derivative, 4-cholesterocarbonyl-4'-(N,N,N-triethylamine butyloxyl bromide) azobenzene (CAB) and surfactant sodium dodecyl sulfate (SDS) in aqueous solution was studied by cryo-TEM and synchrotron radiation small-angle X-ray scattering (SAXS). Both unilamellar and multilamellar vesicles could be observed. CAB in vesicles were capable to undergo reversible trans-to-cis isomerization upon UV or visible light irradiation. The structural change upon UV light irradiation could be catched by SAXS, which demonstrated that the interlamellar spacing of the cis-multilamellar vesicles increased by 0.2-0.3?nm. Based on this microstructural change, the release of rhodamine B (RhB) and doxorubicin (DOX) could be triggered by UV irradiation. When incubated NIH 3T3 cells and Bel 7402 cells with DOX-loaded CAB/SDS vesicles, UV irradiation induced DOX release decreased the viability of both cell lines significantly compared with the non-irradiated cells. The in vitro experiment indicated that CAB/SDS vesicles had high efficiency to deliver loaded molecules into cells. The in vivo experiment showed that CAB/SDS vesicles not only have high drug delivery efficiency into rat retinas, but also could maintain high drug concentration for a longer time. CAB/SDS catanionic vesicles may find potential applications as a smart drug delivery system for controlled release by light.
Project description:Polydiacetylenes (PDAs) are conjugative polymers that demonstrate color changes as a response to an external stimulus. In this study, 10,12-pentacosadiynoic acid (PCDA) was mixed with a supporting polymer including poly(ethylene oxide) (PEO) and polyurethane (PU), and the mixture solution was electrospun to construct fiber composites. The electrospun fibers were then photopolymerized using UV irradiation to produce PEO-PDA and PU-PDA nanofiber mats with a fiber diameter ranging from 130 nm to 2.5 ?m. The morphologies of both PEO-PDA and PU-PDA nanofibers were dependent on electrospinning parameters such as the ratio of PCDA to PEO or PCDA to PU and the total polymer concentrations. Scanning electron microscopy images showed beaded fibers of PEO-PDA and PU-PDA at 2 and 18 w/v % concentrations, respectively. Smooth fibers were found when the solvent concentration was increased to 3.75 w/v % in PEO-PDA and 25 w/v % in PU-PDA fibers. Both PEO-PDA and PU-PDA nanofiber composites demonstrated excellent colorimetric responses to the presence of Escherichia coli ATCC25922 bacterial cells and the changes in pH as external stimuli. The nanofibers underwent a rapid colorimetric response when exposed directly to E. coli ATCC25922 grown on Luria-Bertani agar. The comparison between the PEO-PDA and PU-PDA suggested that the combination of PEO and PDA is favorable because it provides a sensitive response to the presence of E. coli. The results were compared with samples of a PDA polymer in the absence of a matrix polymer. The colorimetric response was similar when the PDA polymer and the PDA nanofiber composites were exposed to pH changes, and the color change was found to occur at pH 10 and enhanced at pH 11-13. The PDA-containing nanofiber composites showed stronger colorimetric responses than those of the PDA polymer only, suggesting their potential as biosensors and chemosensors.
Project description:Porous self-assembled ?-Fe2O3 hollow microspheres were fabricated via an ionic liquid-assisted solvothermal reaction and sequential calcinations. The concentration of the ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate [C4Mim]BF4) was found to play a crucial role in the control of these ?-Fe2O3 hollow structures. Trace amounts ionic liquid was used as the soft template to synthesize ?-Fe2O3 hollow spheres with a large specific surface (up to 220 m2/g). Based on time-dependent experiments, the proposed formation mechanisms were presented. Under UV light irradiation, the as-synthesized ?-Fe2O3 hollow spheres exhibited excellent photocatalysis in Rhodamine B (RhB) photodegradation and the rate constant was 2-3 times higher than ?-Fe2O3 particles. The magnetic properties of ?-Fe2O3 hollow structures were found to be closely associated with the shape anisotropy.
Project description:We report a new polydiacetylene (PDA) sensor strip for simple visual detection of zinc ions in aqueous solution. The specificity of this sensor comes from Zn(2+) DNA aptamer probes conjugated onto PDA. Effects of aptamer length and structure on the sensitivity of PDA's color transition were first investigated. PDA conjugated with the optimal aptamer sequence was then coated onto a strip of polyvinylidene fluoride membrane and photopolymerized by UV exposure. The newly developed sensor successfully exhibited a blue-to-red chromatic change in a semi-quantitative manner in response to zinc ions. No discernable change was observed in solutions containing other common ions. Advantages of this sensor include its ease of fabrication, high specificity, and equipment-free detection, all of which are desirable for in-field applications and use in resource-limited settings.
Project description:In this study, benefiting from the sensitive molecular conformation transversion in azobenzene, a new strategy for fabricating alginate gels with the abilities of splicing and photo-responsive mechanical adjustment is reported. Firstly, a 4,4'-azobis(benzoylhydrazide) (Azo-hydrazide) linker was used to crosslink alginate physically via the electrostatic interaction between hydrazide groups and carboxyl groups. It was then shaped and transferred in situ to a chemically crosslinked gel via 450 nm light irradiation. Under the irradiation, the molecular conformation change of azobenzene in the linker was able to form covalent bonds at the crosslinking points of the gels. Furthermore, the reversible conformation transformation of azobenzene was able to induce the increase and decrease of the storage modulus under irradiation with 365 nm light and 450 nm light, respectively, while also providing gel-like mechanical properties, depending upon the irradiation time and given wavelength. Meanwhile, the results also indicated that active groups could contribute to the splicing ability of the gel and construct a hollow cavity structure. It is believed that this work could provide a versatile strategy for preparing photo-responsive gels with reversibly tunable mechanical properties.