DNA‐Based Oligochromophores as Light‐Harvesting Systems

The chromophores ethynyl pyrene as blue, ethynyl perylene as green and ethynyl Nile red as red emitter were conjugated to the 5‐position of 2′‐deoxyuridine via an acetylene bridge. Using phosphoramidite chemistry on solid phase labelled DNA duplexes were prepared that bear single chromophore modifications, and binary and ternary combinations of these chromophore modifications. The steady‐state and time‐resolved fluorescence spectra of all three chromophores were studied in these modified DNA duplexes. An energy‐transfer cascade occurs from ethynyl pyrene over ethynyl perylene to ethynyl Nile red and subsequently an electron‐transfer cascade in the opposite direction (from ethynyl Nile red to ethynyl perylene or ethynyl pyrene, but not from ethynyl perylene to ethynyl pyrene). The electron‐transfer processes finally provide charge separation. The efficiencies by these energy and electron‐transfer processes can be tuned by the distances between the chromophores and the sequences. Most importantly, excitation at any wavelength between 350 and 700 nm finally leads to charge separated states which make these DNA samples promising candidates for light‐harvesting systems.     

Fluorescent labeling of proteins with nile red and 2-methoxy-2,4-diphenyl-3(2H)-furanone: physicochemical basis and application to the rapid staining of sodium dodecyl sulfate polyacrylamide gels and Western blots

The fluorescent hydrophobic dye Nile red allows the rapid, sensitive, and general staining of proteins in sodium dodecyl sulfate (SDS)-polyacrylamide gels. Nile red staining does not preclude further electroblotting of protein bands onto polyvinylidene difluoride (PVDF) membranes. The resulting Western blot can be stained with the covalent fluorescent dye 2-methoxy-2,4-diphenyl-3(2H)-furanone (MDPF) using a simple procedure. MDPF staining allows further N-terminal microsequencing and immunodetection of specific bands. This review considers the physicochemical, structural, and analytical studies that have led to the development of Nile red and MDPF staining methods. The usefulness of these procedures is discussed in comparison to other currently available fluorescent and nonfluorescent protein detection methods.     

Fabrication of oligo‐glycerol based hydrolase responsive amphiphilic nanocarriers

Herein, we report on the synthesis of a new class of novel non‐ionic amphiphiles using triglycerol as a core, which is further functionalized with hydrophilic units poly(ethylene glycol) monomethyl ether (M_n: 350 and 550) and a pair of hydrophobic alkyl chains (C₁₈ or C₁₅) via chemo‐enzymatic approach. Fluorescence measurements and dynamic light scattering studies showed that all of the synthesized amphiphilic systems spontaneously self‐ assemble in aqueous solution, which is further confirmed by the transmission electron microscopy. Encapsulation of hydrophobic moieties like Nile red and nimodipine was studied using ultraviolet‐visible (UV‐vis) and fluorescence spectrometer techniques. A cytotoxicity study of the amphiphiles using A549, HeLa, and MCF7 cell, which showed that all of the synthesized nanocarriers are well tolerated at the concentrations studied. The release profile of encapsulated Nile red in synthesized amphiphilic system was studied in the presence of the immobilized enzyme (Novozym 435).     

Structure of microemulsions with gemini surfactant studied by solvatochromic probe and diffusion NMR

The structure of microemulsions prepared by the anionic gemini surfactant didodecyl diphenyl ether disulfonate (C12-DADS) was investigated by a solvatochromic probe and nuclear magnetic resonance (NMR) diffusion measurements. The NMR measurements indicate the presence of bicontinuous and oil-in-water microemulsions depending on microemulsion composition. The absorbance spectra of the solvatochromic probe, Nile red, indicate the solubilization of the probe in different sites, in agreement with the NMR findings. It was also found that the microemulsions were capable of dissolving the hydrophobic probe, Nile red, up to four times better than expected if it were simply dissolved in the toluene phase.     

Polymeric Photoresist Nanoparticles: Light‐Induced Degradation of Hydrophobic Polymers in Aqueous Dispersion

Nanoparticles consisting of a photoreactive polymer able to radically switch its hydrophobicity are successfully prepared by miniemulsion polymerization. Irradiation with UV light causes degradation of the particles whereat complete dissolution is achieved by changing the initial hydrophobic photoresist polymer into hydrophilic poly(methacrylic acid). Incorporation of the fluorescence‐sensitive Nile red serves as a solvatochromic probe to study the particle degradation. Diffusion of either Nile red out from or water into the former hard spherical nanoparticles is studied and not only renders the described material an ideal system for applications, where in situ dissolution of nanoparticles may be needed, but also bears the additional advantage of performing controlled burst release.     

Chemical analysis of Yemeni archaeological ceramics and the Egyptian enigma

Archaeological reconnaissance in the Yemen Arab Republic produced samples of mediaeval Islamic ceramics in a 100 km² region centred at Zabid. The ceramics dated from 700 A. D. to 1750 A. D. and initial research indicated that they were all locally made products. Twelves types of ceramics were selected for sampling on the basis of stylistic decoration; nine types were red bodied and three types were white bodied. Six laboratory samples of each type were subjected to neutron activation analysis for the short-lived isotope producing elements using the SLOWPOKE reactor at the University of Toronto. The results showed very tight sherd groupings, with all the red wares of discrete composition and all the white wares of a different discrete composition. Hence the same two clay sources have been utilized over a thousand years. However, a comparison of both ware types with Nile alluvium red ware and Aswan white ware from Egypt, tested for the same elements, produced unexpected results. Although the white wares from Egypt and Yemen were quite different chemically, the red wares showed remarkable chemical similarity. In order to subject the data to a more rigorous statistical testing, a multivariate discriminate analysis programme was applied. The analysis confirmed that the Yemeni and Egyptian white wares could easily be separated. The Yemeni red and Nile alluvium red wares were also separated into the two groups with a very high prediction rate, in spite of the fact that, on visual inspection of the data, no substantial differences were evident. It is clear, therefore, that artifact analysis must be conducted with due respect given to the archaeological context, the elemental chemistry, and sound statistical procedures.     

Synthesis of Dual‐Stimuli‐Responsive Microcontainers with Two Payloads in Different Storage Spaces for Preprogrammable Release

Stimuli‐responsive microcontainers have become a major topic of interest, from fundamental aspects to applications in materials science. However, microcontainers that enable the loading of multiple species and programmable release are mostly unexplored. Herein, we describe the design and synthesis of a dual‐responsive organic/inorganic hybrid microcontainer with two payloads in separate storage spaces that is formed by the rapid UV‐initiated polymerization of Pickering emulsions. The stellate mesopore silica nanoparticles with poly(N ‐isopropylacrylamide) grafted inside the mesopores were loaded with one compound (Nile red) and used as Pickering emulsifiers to stabilize oil‐in‐water droplets. Upon UV irradiation, pH‐responsive monomers were polymerized in the presence of 5(6)‐carboxyfluorescein diacetate (CFDA) to form hybrid colloidal microcontainers. The release of Nile red and CFDA could be selectively activated by changing the temperature or pH value.     

THE TRIPLET STATE OF 8-METHOXYPSORALEN

Abstract— Transient absorption spectra produced by laser flash photolysis of an aqueous solution of 8-methoxypsoralen (8-MOP) have been studied. The biphotonic production of hydrated electrons and of the radical ions, 8-MOP ⁺ and 8-MOP^- is reported. The hydrated electron was found to react with ground state 8-MOP with k ˜ 3 × 10¹⁰ M ^-1 s^-1. In order to obtain a true triplet-triplet absorption spectrum. contributions from the radical ions were subtracted from the overall transient absorption. In addition, contributions from e^-_aq to the transient spectrum were removed by using N₂O, low laser intensity to minimize photoionization or by measuring the transient O.D. after the electron has decayed. These three methods each produced the same triplet-triplet spectrum which differs in the red region from previously reported spectra.     

Ultrafast dynamics of single-walled carbon nanotubes dispersed in polymer films

Wavelength-resolved femtosecond transient absorption spectroscopy is used to follow the electronic dynamics of single-walled carbon nanotubes in polymers following visible photoexcitation. Electron-hole (e-h) pairs give rise to sharp features in the transient spectra that decay in amplitude and exhibit rapid spectral shifts. The decay reflects (e-h) recombination on both short (1.3 ps) and long (35 ps) time scales. Transient spectra also exhibit a broad photobleach at early times that arises from the cooling of a hot electron gas created via excitation at the red edge of a pi-plasmon band.     

Acetylcholinesterase responsive polymeric supra-amphiphiles for controlled self-assembly and disassembly

We have fabricated enzyme responsive polymeric supra-amphiphiles by mixing a block copolymer of poly(ethylene glycol)-block-poly(acrylic acid) with myristoylcholine chloride in water. The polymeric supra-amphiphiles self-assemble into spherical aggregates with sizes varying from about 40 to 150 nm. Moreover, the spherical aggregates can be disassembled triggered by acetylcholinesterase, an enzyme which can cut off the ester linkage of myristoylcholine chloride. Nile red can be loaded into the spherical aggregates and released in several hours upon the treatment of acetylcholinesterase. The releasing rate is rather fast considering that it takes more than 150 h for Nile red to diffuse out of the spherical aggregates without addition of acetylcholinesterase. It is anticipated that the new enzyme responsive polymeric supra-amphiphile may be explored as a carrier for drug delivery.     

Fluorescence probe techniques to monitor protein adsorption-induced conformation changes on biodegradable polymers

The study of protein adsorption and any associated conformational changes on interaction with biomaterials is of great importance in the area of implants and tissue constructs. This study aimed to evaluate some fluorescent techniques to probe protein conformation on a selection of biodegradable polymers currently under investigation for biomedical applications. Because of the fluorescence emanating from the polymers, the use of monitoring intrinsic protein fluorescence was precluded. A highly solvatochromic fluorescent dye, Nile red, and a well-known protein label, fluorescein isothiocyanate, were employed to study the adsorption of serum albumin to polycaprolactone and to some extent also to two starch-containing polymer blends (SPCL and SEVA-C). A variety of fluorescence techniques, steady state, time resolved, and imaging were employed. Nile red was found to leach from the protein, while fluorescein isothiocyanate proved useful in elucidating a conformational change in the protein and the observation of protein aggregates adsorbed to the polymer surface. These effects were seen by making use of the phenomenon of energy migration between the fluorescent tags to monitor interprobe distance and the use of fluorescence lifetime imaging to ascertain the surface packing of the protein on polymer.     

Development of lipid targeting Raman probes for in vivo imaging of Caenorhabditis elegans

A simple, sensitive, and highly specific lipid targeting Raman probe (Nile red coated silver nanoparticles) has been developed to image living nematode Caenorhabditis elegans (C. elegans). Our idea of imaging lipids in C. elegans is to combine the specificity of the fluorescent dye, Nile red, and the highly enhanced Raman scattering on the silver nanoparticles. Our strategy involves the fabrication of a lipid targeting probe, which is incorporated into the intracellular intestinal granules of C. elegans by incubating these worms in the solution containing Raman probes, resulting in an uptake and subsequent incorporation of these Raman probes into the intestinal granule, thus allowing fast visualization of lipid droplets through a conventional confocal imaging technique.     

How transient photoconductivity reveals significant features of the reduction of ground-state aromatic ketones by amino-alkyl radicals through a thermal electron-transfer process

The rate constants kred of the thermal electron-transfer reaction between several aminoalkyl radicals and two ground-state aromatic ketones, benzophenone (BP) and thioxanthone (TX), were measured by nanosecond transient photoconductivity in acetonitrile. The kred values were strongly at variance from those expected from the free energy change Gred of the reaction within the framework of the Marcus' theory of electron transfer. Moreover, addition of small amounts of water in acetonitrile strongly enhanced kred and the ion quantum yield. These results were rationalized by invoking a 1 : 1 complex formation between amino-alkyl radicals and water, and semi-empirical AM1 calculations were used to sustain this explanation.     

多种优化试剂显现潮湿纸张表面潜在手印的比较研究

复杂条件下潜在手印的发现及显现提取一直以来是刑事技术领域研究的热点和难点,尤其是潮湿或水中浸泡客体表面的潜在手印,往往因为环境条件的影响而无法使用常规的显现方法。因此,对于这类疑难条件下潜在手印的显现研究成为亟待解决的问题。本文分别对比了尼罗红、尼罗蓝、物理显影液三种可用于潮湿客体表面潜在手印显现的优化试剂,并对其可靠性、灵敏度及使用条件进行了详细的论证分析,为实战工作中疑难条件下潜在手印的显现提出了可靠的处理方法。     

Bulk Properties of Carboxymethylchitosan and Cationic Surfactant Mixtures: Fluorescence and Surface Tension Studies

The interactions between carboxymethylchitosan and alkyltrimethylammoniumbromides were studied in aqueous solution. The dependences of aggregation behavior on surfactant concentration, polyelectrolyte concentration, as well as surfactant chain length were investigated mainly using fluorescence spectroscopy method. The variation of I ₁/I ₃ of pyrene fully characterized the aggregation behavior of the polymer-surfactant complex. Meanwhile, based on that Nile red has the sensitivity to the environmental polarity different to pyrene, the changes of aggregates size and number can be reflected by the fluorescence spectroscopy of Nile red.     

Quantified High-Throughput Screening of Escherichia coli Producing Poly(3-hydroxybutyrate) Based on FACS

Here, we report on a highly sensitive method for the detection of P(3HB) accumulation in Escherichia coli cells based on the automated flow cytometry system using fluorescent dyes. E. coli containing P(3HB) were stained with either BODIPY or Nile red fluorescent dye, and their staining properties were analyzed under a variety of conditions. Compared with Nile red, BODIPY was much more sensitive in staining P(3HB) and overall demonstrated a more rapid staining of cells, a greater resistance to photobleaching, and greater cell viability. In addition, we also successfully monitored heterogeneity in P(3HB) accumulation within a cell population using BODIPY staining and flow cytometry. We believe this optimized staining method using BODIPY in combination with screening by high-speed flow cytometer will be helpful in the engineering of host cells toward an enhanced production of bioplastics.     

Molecular organization of hydrophobic molecules and co-adsorbed water in SBA-15 ordered mesoporous silica material

The purpose of this study was to improve our understanding of the molecular organization of hydrophobic guest molecules in the presence of co-adsorbed water inside SBA-15 ordered mesoporous silica material. Understanding this adsorption competition is essential in the development of applications of controlled adsorption and desorption. The poorly water soluble drug compound itraconazole and the fluorescent probe Nile red were selected for the study. The interaction between itraconazole and SBA-15 was investigated using FT-IR, (1)H MAS NMR and (29)Si MAS NMR spectroscopy, by determination of adsorption isotherms and release kinetics in simulated gastric fluid. The distribution and migration of the hydrophobic fluorescent probe Nile red was visualized in situ using confocal fluorescence microscopy. For both molecules, there was a pronounced influence of the co-adsorbed water on adsorption, hydrophobic aggregation and migration in SBA-15 pores. These insights contribute to the development of practical methods for loading ordered mesoporous silica materials with hydrophobic molecules.     

Visible Light-Induced Metal-Free Fluoroalkylations

Fluoroalkylation is a crucial synthetic process that enables the modification of molecules with fluoroalkyl groups, which can enhance the properties of compounds and have potential applications in medicine and materials science. The utilization of visible light-induced, metal-free methods is of particular importance as it provides an environmentally friendly alternative to traditional methods and eliminates the potential risks associated with metal-catalyst toxicity. This Account describes our studies on visible light-induced, metal-free fluoroalkylation processes, which include the use of organic photocatalysts or EDA complexes. We have utilized organophotocatalysts such as Nile red, tri(9-anthryl)borane, and an indole-based tetracyclic complex, as well as catalyst-free EDA chemistry through photoactive halogen bond formation or an unconventional transient ternary complex formation with nucleophilic fluoroalkyl source. A variety of π-systems including arenes/heteroarenes, alkenes, and alkynes have been successfully fluoroalkylated under the developed reaction conditions.     

A DNA–Fullerene Conjugate as a Template for Supramolecular Chromophore Assemblies: Towards DNA‐Based Solar Cells

A fullerene was covalently attached to a (dA)₂₀ template that serves as structural scaffold to self‐assemble an ordered and mixed array of ethynyl‐pyrene‐ and ethynyl‐Nile‐red‐nucleoside conjugates. Fluorescence spectroscopy revealed evidence for energy transfer between the two different chromophores. Moreover, fluorescence quenching is significantly enhanced by the attached fullerene in mixed assemblies of different chromophore ratios. This indicates exciton dissociation by electron transfer from the photo‐generated exciton on the chromophore stack to the fullerene. The fullerene–DNA‐conjugate was integrated as a photo‐active layer in solar cells that showed charge‐carrier generation in the spectral regime of all three components of the conjugate. This work clearly demonstrates that DNA is suitable as structural element for chromophore assemblies in future organic optoelectronic devices, such as solar cells.     

Fluorescence resonance energy transfer-a spectroscopic probe for organized surfactant media

Dyes commonly used as biological labels have been used to probe resonance energy transfer in organized media. In neat water, energy transfer between the dye pairs fluorescein (donor):Nile red (acceptor) and acridine orange (donor):Nile red (acceptor) has a very low probability of occurrence. This study shows that the rate constant of energy transfer increases by more than an order of magnitude in organized surfactant media, viz., micelles and reverse micelles of the surfactant Triton X-100. The reverse micelles provide a better medium for energy transfer than the micelles. The energy transfer studies also provide an idea about the location and proximity of donor and acceptor dyes within the various organized media. Assuming Poissonian statistics for dye distribution, the donor-acceptor distances within micelles and reverse micelles are determined from energy transfer parameters. Acridine orange has been found to function better as a donor than fluorescein. This may be due to steric and electrostatic factors.