Rhodamine-inspired far-red to near-infrared dyes and their application as fluorescence probes

Probes to dye for: Rhodamine-inspired Si-pyronine, Si-rhodamine, Te-rhodamine, and Changsha NIR dyes have been developed recently. These dyes show fluorescence in the far-red to near-infrared region, while retaining the advantages of the original rhodamines, such as high fluorescence quantum yield, tolerance to photobleaching, good water solubility, and exhibit great potential for biological application.     

Fluorescent probes for the stabilization and detection of G-quadruplexes and their prospective applications

This review article discusses the non-covalent interaction of various probe molecules of different structural diversity with G-quadruplex forming Guanine rich DNA sequences, revealing remarkable stimuli responsive fluorescence changes which are appropriate for sensing and other technological applications. Tailor-made probes having quadruplex inducing/stabilizing attachments of well-known dye molecules and its derivatives such as, coumarins, cyanines, thiazole orange, pyrazines, thioflavin T, triphenylmethane, tetraphenylethene, dimethylindole red etc have been employed. These probes express their modulations due to the binding to the topologically distinct G-quadruplexes through structural rigidization, aggregation propensity, binding strengths, tunability and other competitive interactions and are viewed as remarkable changes particularly in their fluorescence features. Based on this concept, several studies have reported the development of label free fluorescence sensor for the selective detection of topology specific G-quadruplexes, therapeutic, early diagnostic of cancer, cation-sensing, trace level detection of an anti-cancer drugs etc. have been accomplished. In vivo imaging is also achieved using a cholesterol attached G-quadruplex forming oligonucleotide probe labelled with specific dyes. Since the fine details of the topological information and control mechanisms of G-quadruplex forming sequences are very much essential for targeting and tuning several important biological processes relevant to cancer proliferation and developing stimuli responsive sensors, it is sure that many more contributions in this field will emerge in the coming years.     

Influence of gelator structures on formation and stability of supramolecular hydrogels

A supramolecular hydrogel(defined as G1) formed from 1,2,4,5-benzene tetracarboxylic acid (BTCA) and 2-amino-3- hydroxypyridine possessed higher T_(gel) than that of another hydrogel(defined as G2) formed from BTCA and 3-hydroxypyridine. Based on the analysis of their xerogels by ~1H NMR,IR and XRD,the higher stability of G1 was attributed to the formation of stronger hydrogen binding enhanced by the ortho amino group of 2-amino-3-hydroxypyridine.     

Principles of responsive lanthanide-based luminescent probes for cellular imaging

The advent of chemical tools for cellular imaging—from organic dyes to green fluorescent proteins—has revolutionized the fields of molecular biology and biochemistry. Lanthanide-based probes are a new player in this area, as the last decade has seen the emergence of the first responsive luminescent lanthanide probes specifically intended for imaging cellular processes. The potential of these probes is still undervalued by the scientific community. Indeed, this class of probes offers several advantages over organic dyes and fluorescent proteins. Their very long luminescence lifetimes enable quantitative spatial determination of the intracellular concentration of an analyte through time-gating measurements. Their emission bands are very narrow and do not overlap, enabling the simultaneous use of multiple lanthanide probes to quantitatively detect several analytes without cross-interference. Herein we describe the principles behind the development of this class of probes. Sensors for a desired analyte can be designed by rationally manipulating the parameters that influence the luminescence of lanthanide complexes. We will discuss sensors based on varying the number of inner-sphere water molecules, the distance separating the antenna from the lanthanide ion, the energies of excited states of the antenna, and PeT switches.

Amphiphilic ESIPT benzoxazole derivatives as prospective fluorescent membrane probes

Fluorescent amphiphilic benzoxazole derivatives were synthesized and used to produce photoactive phosphatidylcholine (PC) liposomes by reserve-phase evaporation. The dyes absorbed in the UV region and were fluorescent in the blue-green region (determined by solvent polarity). The alkyl chain length seemed to play a fundamental role in the photophysics of the benzoxazole fluorophore in reverse liposomes, and despite the same ESIPT core and phospholipid building block, each amphiphilic dye had a particular emission profile related to the dye location in the liposome. The fluorescence emission spectra from dye 5 showed that its fluorophore experienced a polar environment, due to the single normal emission, while dyes 6–7 had (in part) a normal emission, and the main fluorescent band ascribed to the ESIPT emission indicated a more hydrophobic environment. Despite the complex fluorescent profiles, the benzoxazole derivatives could be successfully introduced into the reverse liposome structure due to the interaction between the alkyl chain and PC bilayer.     

The water-soluble indolium-based fluorescence probes for detection of the extreme acidity or extreme alkalinity

In this work, 3,3′-(((1E,1′E)-(H,12H-5,11-methanodibenzo[b,f][1,5]diazocine-2,8-diyl)bis(ethene-2,1-diyl))bis(1,1-dimethyl-1H-benzo[e]indole-3-ium-2,3-diyl))bis(propane-1-sulfonate) (1), 3,3’-(((1E,1′E)-(6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine-2,8-diyl)bis(ethene-2,1-diyl))bis(3,3-dimethyl-3H-indole-1-ium-2,1-diyl))bis(propane-1-sulfonate) (2), 2,2’-((1E,1′E)-(6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine-2,8-diyl)bis(ethene-2,1-diyl))bis(1,3,3-trimethyl-3H-indol-1-ium) iodide (3) and 2,2’-((1E,1′E)-(6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine-2,8-diyl)bis(ethene-2,1-diyl))bis(1,1,3-trimethyl-1H-benzo[e]indol-3-ium) iodide (4) were designed and synthesized by ethylene bridging of the N-substituted indolium salts and the Tröger’s Base (TB) framework. The probes exhibited a longer absorption and emission wavelength and the emission wavelength of them in dichloromethane (DCM) was more than 600 nm, performed a red fluorescence. All of the probes could work on the extreme acidic and the extreme alkaline environments and showed a good liner response in the working pH range. Especially, 2 and 4 were soluble in water and manifested a good pH sensing in a water system. Also, ¹H NMR analysis illustrated how these dyes worked as the pH-sensitive fluorescence probes. In addition, they performed excellent reversibility, high selectivity and good photostability.     

Cholesteryl derivatives as phase-selective gelators at room temperature

One cholesterol-based ALS and two dimeric cholesterol-based A(LS)₂ low-molecular-mass organic gelators (LMOGs) containing phthaloyl, isophthaloyl, and terephthaloyl moieties, respectively, were prepared. Gelation test revealed that 2 and 3 are more efficient gelators than 1. Interestingly, 2 and 3 can gel several solvents spontaneously at room temperature and these gels posses thixotropic properties as revealed by rheological studies. More interestingly, 2 and 3 show selective gelation of the solvents from their mixtures with water. The network structures of some gels were investigated by SEM measurements, and the molecular packing mode of the LMOGs in the gel was studied by XRD analysis. Temperature- and concentration-dependent ¹H NMR measurements revealed that hydrogen bonding between the gelator molecules is an important driving force for the gel formation.     

Preparation and gelling properties of sugar-contained low-molecular-mass gelators: Combination of cholesterol and linear glucose

Four novel amphiphilic cholesterol-based and sugar-contained low-molecular-mass gelators (LMMGs) were designed and prepared. According to the structures of the linkers, which are ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, and 1,6-hexane- diamine, these compounds are denoted as 1, 2, 3 and 4, respectively. Gelation tests revealed that 2, 3 and 4 start to gel xylene at concentrations of 0.090%, 0.022%, and 0.016% (w/v), respectively, which are typical ‘super-gelators’. Moreover, these xylene gel systems also possess film formation property. Scanning electron microscopy (SEM) measurements demonstrated that the aggregation behaviors of the compounds are greatly affected by the structures of the linkers. ¹H NMR spectroscopy studies revealed that intermolecular hydrogen bonding formation plays an important role for the formation of the gels. X-ray diffraction (XRD) studies showed that 1 possesses a layered structure in its 1-pentanol gel, a similar structure to that of it in solid state. Gelator 3 also possesses a similar structure in its THF gel, but different from that of it in solid state. Transmission electron microscopy (TEM) observation revealed the helical nature of the nanobelt assemblies of 1 in its 1-pentanol gel.     

Fabrication of palladium nanoparticles as effective catalysts by using supramolecular gels

Two-component supramolecular gels were made through self-assembly of tetrazolyl derivatives and Pd(OAc)₂. The robust gels indicated high storage modulus(>10,000 Pa) and loss modulus, which were studied by rheological measurements. The formed Pd nanoparticles(~9 nm) obtained during the formation of the gel showed effective catalytic hydrogenation of nitrobenzene and could be recovered and reused without loss of activity.     

Photophysics of aminoxanthone derivatives and their application as binding probes for DNA

Xanthones with amino substituents were synthesized to diminish the photoreactivity of the xanthone chromophore with DNA, with the objective of using these molecules to study their binding dynamics with DNA. The aminoxanthones showed a strong solvatochromic effect on their singlet and triplet excited-state photophysics, where polar solvents led to a decrease of the energies for the excited states. Quenching of the triplet excited states by nitrite anions was used to determine the binding dynamics, and a residence time in the microsecond time domain was estimated for the bound 2-aminoxanthone with DNA. The quenching experiments performed showed that this methodology will not be applicable to study the binding dynamics of a wide variety of guests with DNA.     

Synthesis of 3-hydroxyflavone fluorescent probes and study of their fluorescence properties

<正>Direct measurement of dipole potential in biological membranes has been impossible and 3-hydroxyflavones(3HFs) have allowed detection of changes in dipole potential in biological systems.In the present study,sixteen derivatives of 3HF with aliphatic hydrocarbon chains of different lengths at 4′-position and 6-position were synthesized.The basic fluorescence properties of 3HFs are maintained in all the probes in terms of strong blue shift in maximum fluorescence emission wavelength and100 fold increase in quantum yield in organic solvents and in dioleoylphosphatidylcholine(DOPC) small unilamellar vesicles(SUV) in comparison to in aqueous Hepes buffer(15 mmol/L,pH 7.4).More importantly,the ability of the new compounds to report dipole potential changes in biological systems are also maintained,since all the new probes showed spectrum properties that are similar to yet different from that of F4N1,which potentially may allow more sensitive measurement of the dipole potential change in membranes.     

Development of FRET-based dual-excitation ratiometric fluorescent pH probes and their photocaged derivatives

Dual-excitation ratiometric fluorescent probes allow the measurement of fluorescence intensities at two excitation wavelengths, which should provide a built-in correction for environmental effects. However, most of the small-molecule dual-excitation ratiometric probes that have been reported thus far have shown rather limited separation between the excitation wavelengths (20-70 nm) and/or a very small molar absorption coefficient at one of the excitation wavelengths. These shortcomings can lead to cross-excitation and thus to errors in the measurement of fluorescence intensities and ratios. Herein, we report a FRET-based molecular strategy for the construction of small-molecule dual-excitation ratiometric probes in which the donor and acceptor excitation bands exhibit large separations between the excitation wavelengths and comparable excitation intensities, which is highly desirable for determining the fluorescence intensities and signal ratios with high accuracy. Based on this strategy, we created a coumarin-rhodamine FRET platform that was then employed to develop the first class of FRET-based dual-excitation ratiometric pH probes that have two well-resolved excitation bands (excitation separations>160 nm) and comparable excitation intensities. In addition, these pH probes may be considered as in a kind of "secured ratioing mode". As a further application of these pH probes, the dual-excitation ratiometric pH probes were transformed into the first examples of photocaged dual-excitation ratiometric pH probes to improve the spatiotemporal resolution. It is expected that the modular nature of our FRET-based molecular strategy should render it applicable to other small-molecule dual-dye energy-transfer systems based on diverse fluorescent dyes for the development of a wide range of dual-excitation ratiometric probes with outstanding spectral features, including large separations between the excitation wavelengths and comparable excitation intensities.     

Development of new sol-gel carbon composite electrodes and their application as electrochemical sensors

Microchimica Acta - Two types of modified electrodes, viz. sol-gel and sol-gel-poly(dimethyldiallylammonium chloride (PDMDAAC) carbon composite electrodes, were synthesised and characterised. In...     

Ruthenium and Osmium Podate Cyclodextrins with Dual-function Recognition Sites for Luminescent Sensing

A multifunctionalised podand cyclodextrin ligand, β-CD-(urebpy)⁷, with urea--bipyridine binding sites leads to ruthenium and osmium, {Ru[β-CD-(urebpy)⁷]}[PF⁶]² {Os[β-CD-(urebpy)⁷]}[PF⁶]², cyclodextrins. The bipyridine ligands are preorganised by the cyclodextrin cavity encapsulating the ruthenium and osmium core to give photoactive metallocyclodextrins. The podate cyclodextrin complexes show characteristic ruthenium and osmium tri-bipyridine luminescence. It is demonstrated that the ruthenium cyclodextrins participate in sensing schemes through both the cyclodextrin cavity and the urea cage at the bottom of the cyclodextrin rim. Luminescence quenching of the ruthenium emission is observed by addition of anthraquinone guests in the cyclodextrin cavity or addition of dihydrogen phosphate anion.     

Organic functionalization of luminescent oxide nanoparticles toward their application as biological probes

Luminescent inorganic nanoparticles are now widely studied for their applications as biological probes for in vitro or in vivo experiments. The functionalization of the particles is a key step toward these applications, since it determines the control of the coupling between the particles and the biological species of interest. This paper is devoted to the case of rare earth doped oxide nanoparticles and their functionalization through their surface encapsulation with a functional polysiloxane shell. The first step of the process is the adsorption of silicate ions that will act as a primary layer for the further surface polymerization of the silane, either aminopropyltriethoxysilane (APTES) or glycidoxypropyltrimethoxysilane (GPTMS). The amino- or epoxy- functions born by the silane allow the versatile coupling of the particles with bio-organic species following the chemistry that is commonly used in biochips. Special attention is paid to the careful characterization of each step of the functionalization process, especially concerning the average number of organic functions that are available for the final coupling of the particles with proteins. The surface density of amino or epoxy functions was found to be 0.4 and 1.9 functions per square nanometer for GPTMS and APTES silanized particles, respectively. An example of application of the amino-functionalized particles is given for the coupling with alpha-bungarotoxins. The average number (up to 8) and the distribution of the number of proteins per particle are given, showing the potentialities of the functionalization process for the labeling of biological species.     

Twin probes as a novel tool for the detection of single-nucleotide polymorphisms

Single-nucleotide polymorphisms (SNPs) are the most common form of DNA sequence variation. There is a strong interest from both academy and industry to develop rapid, sensitive and cost effective methods for SNP detection. Here we report a novel structural concept for DNA detection based on fluorescence dequenching upon hybridization. The so-called "twin probe" consists of a central fluorene derivative as fluorophore to which two identical oligonucleotides are covalently attached. This probe architecture is applied in homogeneous hybridization assays with subsequent fluorescence spectroscopic analysis. The bioorganic hybrid structure is well suited for sequence specific DNA detection and even SNPs are identified with high efficiency. Additionally, the photophysical properties of the twin probe were investigated. The covalent attachment of two single stranded oligonucleotides leads to strong quenching of the central fluorescence dye induced by the nucleobases. The twin probe is characterized by supramolecular aggregate formation accompanied by red-shifted emission and broad fluorescence spectra.