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The effect of carrageenan concentration on thermal phase transitions of the iota carrageenan gels was investigated by using fluorescence technique. During heating and cooling processes, scattered light, I_(sc), and fluorescence in...
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The effect of carrageenan concentration on thermal phase transitions of the iota carrageenan gels was investigated by using fluorescence technique. During heating and cooling processes, scattered light, I_(sc), and fluorescence intensity, I_p, were monitored against temperature to investigate phase transitions. Transition temperatures from the derivative of the transition paths were determined. Two regions were observed during the heating and cooling processes. At the first step of the heating, dimers were converted into double helix by undergoing dimer to double helix (d-h) transition. At the higher temperature region, double helix to coil (h-c) transition took place. During the cooling process, these transitions are arranged in the order of coil to double helix (c-h) and double helix to dimer (h-d). A hysteresis was observed between (h-d) and (d-h) transitions. The critical gel fraction exponents, β, were found to be independent of the system by indicating that they all fall into the same universality class.
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Fluorescein-, benzothiazole-, quinoline-, stilbene-, and carbazole-containing fluorescent gelators have been synthesized by connecting gelation-driving segments, including l-isoleucine, l-valine, l-phenylalanine, l-leucine residue...
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Fluorescein-, benzothiazole-, quinoline-, stilbene-, and carbazole-containing fluorescent gelators have been synthesized by connecting gelation-driving segments, including l-isoleucine, l-valine, l-phenylalanine, l-leucine residue, cyclo(l-asparaginyl-l-phenylalanyl), and trans-(1R,2R)-diaminocyclohexane. The emission behaviors of the gelators were investigated, and their gelation abilities studied against 15 solvents. The minimum gel concentration, variable-temperature spectroscopy, transmission electron microscopy, scanning electron microscopy, fluorescence microscopy (FM), and confocal laser scanning microscopy (CLSM) were used to characterize gelation. The intermolecular hydrogen bonding between the N-H and C=O of amide, van der Waals interactions and pi-pi stacking play important roles in gelation. The colors of emission are related to the fluorescence structures of gelators. Fibrous aggregates characterized by the color of their emission were observed by FM. 3D images are produced by the superposition of images captured by CLSM every 0.1 mu m to a settled depth. The 3D images show that the large micrometer-sized aggregates spread out three dimensionally. FM observations of mixed gelators are studied. In the case of gelation, two structurally related gelators with the same gelation-driving segment lead to the gelators build up of the same aggregates through similar hydrogen-bonding patterns. When two gelators with structurally different gelation-driving segments induce gelation, the gelators build up each aggregate through individual hydrogen-bonding patterns. A fluorescent reagent that was incorporated into the aggregates of gels through van der Waals interactions was developed. The addition of this fluorescent reagent enables the successful observation of nonfluorescent gelators' aggregates by FM.
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A systematic study of the separation of double-stranded DNA in hydroxypropylcellulose (HPC) with a molecular mass of 10(6) was undertaken, using a variety of concentrations (from 0.1 to 1%) and different electric fields (from 6 to...
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A systematic study of the separation of double-stranded DNA in hydroxypropylcellulose (HPC) with a molecular mass of 10(6) was undertaken, using a variety of concentrations (from 0.1 to 1%) and different electric fields (from 6 to 540 V/cm). The data show that at high polymer concentrations (greater than or equal to 0.4%) and low fields, the separation mechanism is similar to that occurring in gels. The results are in good agreement with theoretical models, and in particular with a recently proposed theory for gels with a pore size smaller than the persistence length of DNA. For more dilute solutions and high fields, however, the separation pattern cannot be explained by existing theories. The existence of an original mechanism was confirmed by the direct observation of the conformation of double-stranded DNA molecules in the polymer solution by fluorescence videomicroscopy. Practical conclusions for the capillary electrophoretic separation of duplex DNA are drawn. [References: 19]
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Biocompatible fluorescent active and pH sensitive gel has been developed using covalently attached riboflavin as proficient fluorophore on crosslinked glycogen. The chemically crosslinked glycogen (cl-Gly/PMAc) has been synthesise...
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Biocompatible fluorescent active and pH sensitive gel has been developed using covalently attached riboflavin as proficient fluorophore on crosslinked glycogen. The chemically crosslinked glycogen (cl-Gly/PMAc) has been synthesised by grafting of methacrylic acid (MAc) followed by crosslinking using ethylene glycol dimethacrylate (EGDMA) through free radical polymerization. Afterward, the fluorescent active hydrogel (cl-Gly/PMAc-RB) has been synthesised by post-polymerization modification of cl-Gly/PMAc with riboflavin. The gel properties have been explored by determining rheological parameters. pH responsive swelling and reversible swelling behaviours of cl-Gly/PMAc-RB have been investigated by executing swelling/deswelling/reswelling studies. In-vitro cell cytotoxicity study predicts that the material is non-toxic and biocompatible. cl-Gly/PMAc-RB gel demonstrates excellent release profile towards the release of dual drugs (metronidazole: release similar to 75% after 24 h and ciprofloxacin: release similar to 55% after 24 h) in colonic region, which is evidenced from in vitro and in-vivo studies. Finally, ab-initio molecular dynamics study has been carried out to investigate the intricate details of the probable drugs-hydrogel interaction and pH responsive release profile of dual drugs from cl-Gly/PMAc-RB hydrogel in molecular level.
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Novel cationic and neutral analogues of bile acids (1-6) were synthesized and their aggregation properties studied. Cations 1 and 2 formed thermoreversible gels in aqueous salt solutions, whereas neutral 4 formed gels in water in ...
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Novel cationic and neutral analogues of bile acids (1-6) were synthesized and their aggregation properties studied. Cations 1 and 2 formed thermoreversible gels in aqueous salt solutions, whereas neutral 4 formed gels in water in the presence of organic solvents such as ethanol, methanol, DMSO, and DMF. The gels derived from 1 and 4 have been investigated by SEM and with pyrene as a fluorescent probe. [References: 21]
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The construction and evaluation of a capillary electrophoresis instrument for the facile optimization of DNA separations is described herein. This instrumentation allows for convenient translation of the detection zone with little...
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The construction and evaluation of a capillary electrophoresis instrument for the facile optimization of DNA separations is described herein. This instrumentation allows for convenient translation of the detection zone with little loss in detectability. Changing the effective capillary length is shown to be important when complete resolution of specified DNA fragments in a sample, in the minimum time, is desired, Efficiency is found to decrease with column length in accordance with limits imposed by axial diffusion. However, complete resolution of the fragments in a Phi X-174-HeaIII digest is accomplished in 155 s at moderate held strengths and an effective capillary length of 15 cm. It is also demonstrated that in situ gradients can be established using this instrumentation. The general chromatographic elution problem is addressed with gradients, resulting in further improvements in separation performance relative to isocratic separations.
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Films of (x/2)Er_2O_3-100ZrO_2 (x = 0, 0.1, 1 and 5) were prepared by the sol-gel and dip-coating methods, and the influences of the type of ZrO_2 phase on Er~(3+) spectroscopic properties were investigated. X-ray diffraction patt...
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Films of (x/2)Er_2O_3-100ZrO_2 (x = 0, 0.1, 1 and 5) were prepared by the sol-gel and dip-coating methods, and the influences of the type of ZrO_2 phase on Er~(3+) spectroscopic properties were investigated. X-ray diffraction patterns show the existence of metastable tetragonal phase at low temperatures, which are probably caused by both the excess surface energy due to the small crystallite-size effect (J. Phys. Chem. 4 (1965) 1238) and the stabilization of ZrO_2 with the addition of Er_2O_3 (J. Phys. Chem. B 106 (2002) 1909; J. Ceram. Soc. Jpn. 107 (1999) 1111). Under excitation at 488 nm, the green (525 + 545 nm) downconversion fluorescence due to the (~2H_(11/2) + ~4S_(3/2)) → ~4I_(15/2) transition and the red (670 nm) downconversion fluorescence due to the ~4F_(9/2) → ~4I_(15/2) transition were observed, and their intensities increased with increasing the heat-treatment temperature regardless of the type of the ZrO_2 phase. On the other hand, the intensity of red upconversion fluorescence also increased monotonically with the heat-treatment temperature under excitation at 780 nm, while the green upconversion fluorescence was hardly observed in the tetragonal phase (for the film with x=1, below 800℃; x = 5, below 700℃), but was observed in the cubic (x=1, at 800℃ or above; x = 5, at 700℃ or above) and monoclinic (x = 0.1, at 600℃ or above) phases under excitations at 647 and 780 nm. The reason is probably that the f-f transition probability concerning the ~4I_(13/2), from which the excited state absorption occurs, varied sensitively with the local structure of Er~(3+) ions in the different phase of ZrO_2.
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A passive signal enhancement device for the standoff detection of uranium in soil was developed and tested. The device consists of a spherical ball lens half-coated with a polymer-silica gel composite. The nanoporous silica gel, w...
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A passive signal enhancement device for the standoff detection of uranium in soil was developed and tested. The device consists of a spherical ball lens half-coated with a polymer-silica gel composite. The nanoporous silica gel, when placed in contact with moist soil, absorbs water and dissolved uranyl ions and significantly enhances the fluorescence intensity of the uranyl. The ball lens focuses the UV excitation energy to the focal point of the lens located within the silica gel layer and directs the resulting fluorescence signal back towards the excitation source. Our results show that this 'Directed Fluorescence' (DF) device can be used to enhance the uranyl fluorescence signal intensity by more than 200 times. Consequently, the maximum standoff detection distance is increased by more than an order of magnitude.
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Bioluminescence is widespread in nature such as the jellyfish, which inspires scientists to design polymer hydrogels with tunable fluorescence. However, it remains a big challenge to develop white-light-emitting hydrogels with loc...
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Bioluminescence is widespread in nature such as the jellyfish, which inspires scientists to design polymer hydrogels with tunable fluorescence. However, it remains a big challenge to develop white-light-emitting hydrogels with local tunability of the fluorescent behavior. Herein, we report a white fluorescent hydrogel prepared by one-pot micellar copolymerization of hydrophilic acrylamide and hydrophobic single donor-acceptor chromophore monomer, in which the unimer and the dimer of the chromophore coexist and generate high- and low-energy emission, respectively, under excitation. The fluorescent behavior of the hydrogel can be well tuned by phototreatment or heat treatment that induces unimer-to-dimer transformation of the chromophore and thus variation of the fluorescent color from blue to white and then to yellow. The fluorescence can also be reversibly switched off by forming terpyridine-Cu2+ chelate complexes and recovered by using chelating agent to extract the Cu2+ ions out of the gel matrix. These properties afford patterning the fluorescent hydrogel, which is transparent under daylight yet shows the pattern under ultraviolet light. These patterned fluorescent hydrogels should find applications in protected message display for improved information security.
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In this study, we synthesised ZnS nanocrystals and embedded them in polyacrylamide (PAAm) hydrogel to stabilise the fluorescence emission for biomedical applications. ZnS nanoparticles have strong emission but they lose it in time...
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In this study, we synthesised ZnS nanocrystals and embedded them in polyacrylamide (PAAm) hydrogel to stabilise the fluorescence emission for biomedical applications. ZnS nanoparticles have strong emission but they lose it in time, so generally they are capped with polymers. We capped ZnS nanoparticles with (3-mercaptopropyl)-trimethoxysilane (MPS) and then dispersed them through the PAAm hydrogel. The average size of nanoparticles was found 4.06 nm, but the particles got larger (around similar to 16 nm) when they were placed in the gel. FT-IR results show that PAAm strands changed the surface of MPS-capped ZnS during the PAAm polymerisation. Fluorescence studies show that ZnS nanoparticles keep their emission after 3 months, when they are stored in the gel. This feature makes the ZnS nanoparticles suitable as a long-term stable and non-toxic material for medical application.
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