Adsorption of the diazo dye Direct Red 23 onto a zinc oxide surface: A spectroscopic study

The adsorption of the diazo dye Direct Red 23 onto a zinc oxide surface at 30 °C in the dark was investigated. The color reduction was monitored by spectrophotometry at 503 nm. The FTIR and Raman spectra of the Direct Red 23 adsorption as a function of ZnO concentration were registered. From the PM3 semi-empirical calculations of the atomic charge density and dipole moment of the Direct Red 23 molecule, it was demonstrated that the azo dye molecule may be adsorbed onto the ZnO surface through molecule geometry modifications, enhancing the interfacial area causing a variation in the bonding frequencies.     

Anomalous diffusion in an electrolyte saturated paper matrix

Diffusion of colored dye on water saturated paper substrates has been traditionally exploited with great skill by renowned water color artists. The same physics finds more recent practical applications in paper-based diagnostic devices deploying chemicals that react with a bodily fluid yielding colorimetric signals for disease detection. During spontaneous imbibition through the tortuous pathways of a porous electrolyte saturated paper matrix, a dye molecule undergoes diffusion in a complex network of pores. The advancing front forms a strongly correlated interface that propagates diffusively but with an enhanced effective diffusivity. We measure this effective diffusivity and show that it is several orders of magnitude greater than the free solution diffusivity and has a significant dependence on the solution pH and salt concentration in the background electrolyte. We attribute this to electrically mediated interfacial interactions between the ionic species in the liquid dye and spontaneous surface charges developed at porous interfaces, and introduce a simple theory to explain this phenomenon.     

Ratiometric Fluorescent Probe Based on Novel Red-emission BODIPY for Determination of Bovine Serum Albumin

A novel red-emission boron-dipyrromethene（BODIPY） dye with a pyrrole ring was synthesized simply via one-pot reaction. The spectral properties of it were investigated under the conditions of different solvents. The results show that the as-prepared BODIPY dye is extremely sensitive to solvent polarity, and the fluorescent emission enhances with the decrease of solvent polarity. In aqueous buffer, the addition of bovine serum albumin leads to a ratiometric change in absorption spectra with an association constant of 1.16×10^6 L/mol. Meanwhile, the fluorescence emission increases greatly at 622 nm but changes slightly at 575 nm. The response time is very short（less than 3 min）, and the changes of color can be noticed by naked eyes. Bovine serum albumin can be detected by this ratiometric fluorescence probe, but other proteins or enzymes cannot be detected by this method, which indicates that this novel dye has high selectivity towards bovine serum albumin. The reason is that bovine serum albumin has suitable hydro- phobic cavities for binding with the dye. In addition, the dye molecule can penetrate cell membrane easily and make a fast fluorescent stain, which makes it a potential probe for living-cell fluorescence imaging.     

Heteroassociates of singly- and doubly-charged anions of alizarin red S with the pinacyanol cation

The formation of heteroassociates of singly- and doubly-charged anions of alizarin red S with the cation of the cyanine dye pinacyanol in an aqueous solution was considered. The most probable structure of the heteroassociates was proposed on the basis of the data of spectrophotometry and theoretical calculations (quantum chemical methods of determination of the geometry of the structures and the enthalpy of formation). The destructive effect of the ionic surfactants on the heteroassociates was established, and the kinetics of their destruction was studied.     

Thermally controlled preferential molecular aggregation state in a thiacarbocyanine dye

Herein we report the experimental and theoretical study of the temperature dependence of a thiacarbocyanine dye in its monomer, H- and J-aggregates states. We demonstrate the ability to control the ratio of monomer, H- and/or J-aggregates with heat. We link such a control to the conformation dependence of the molecule. An alternative way to gain access to the dominating species without changing the concentration as a complete switching mechanism between all the present species is proposed. The results presented in this work lead to a better understanding of thiacarbocyanine dye's behavior.     

Quenching and blinking of fluorescence of a single dye molecule bound to gold nanoparticles

A fluorescein derivative (SAMSA) bound to gold nanoparticles of different diameters is investigated by time-resolved fluorescence at the single molecule level in a wide dynamic range, from nanosecond to second time scale. The significant decrease of both SAMSA excited state lifetime and fluorescence quantum yield observed upon binding to gold nanoparticles can be essentially traced back to an increase of the nonradiative deactivation rate, probably due to energy transfer, that depends on the nanoparticle size. A slow single molecule fluorescence blinking, in the ms time scale, has a marked dependence on the excitation intensity both under single and under two photon excitation. The blinking dynamics is limited by a low probability nonlinear excitation to a high energy state from which a transition to a dark state occurs. The results point out a strong coupling between the vibro-electronic configuration of the dye and the plasmonic features of the metal nanoparticles that provide dye radiationless deactivation channels on a wide dynamic range.     

Spectrophotometric determination of arsenic in water samples based on micro particle formation of ethyl violet-molybdoarsenate.

In this study, a simple and sensitive method for the determination of arsenic in water samples was developed. The method is based on the formation of micro particles of Ethyl Violet and molybdoarsenate, which gives an apparently homogeneous blue color to the solution. The absorption of the excess dye gradually decreases due to its conversion to a colorless carbinol species under strongly acidic conditions. Consequently, the sufficiently low reagent blank enables the spectrophotometric determination of arsenic with the detection limit of 4 microg l(-1). The coefficient of variation for the spectrophotometry at 50 microg l(-1) was 3.5% (n = 5). Furthermore, it is possible to detect concentrations as low as 10 microg l(-1) of arsenic visually. Our method will be useful as a simple, rapid, and cost-effective field test of arsenic, requiring no complex apparatus or skilled laboratory support.     

Single-molecule conformations probe free volume in polymers

In this communication, we showed that the conformational dynamics of the tetraphenoxy-perylenetetracarboxy diimide single dye molecule embedded in different polymer matrixes allows a direct visualization of the local free volume. By monitoring the fluorescence lifetime of the dye molecule in time and at different locations in the matrix, different lifetimes were observed. Attributed to two distinct stable conformations of the dye molecule, the lifetime variations permitted characterization of the spatial distribution and temporal dynamics of free volume.     

The Fluorophore 4′,6‐Diamidino‐2‐phenylindole (DAPI) Induces DNA Folding in Long Double‐Stranded DNA

DAPI (4′,6‐diamidino‐2‐phenylindole) is a widely used fluorescent dye, whose complicated binding features to DNAs and RNAs have been the object of debates and are still not fully understood. In this study, different approaches were employed, including binding equilibrium measurements (spectrofluorometry), melting experiments (spectrophotometry), viscometric measurements, circular dichroism, and T‐jump kinetic analyses; all data concur in shedding light on the complex mechanistic aspects of the binding mode of DAPI to natural DNA. Conditions are found that induce the mode of the DAPI/DNA interaction to change from groove binding to intercalation. Moreover, it is observed, for the first time, that DAPI is able to induce the formation of a rather compact polymer–dye adduct under particular conditions. The results suggest that this form is a folded or coiled DNA structure stabilized by DAPI dye bridges.     

CuNPs as an activator of K2S2O8 for the decolorization of diazo dye in aqueous solution

Degradation of trypan blue (TB) by persulfate/CuNPs system was investigated as a function of TB concentration, persulfate concentration, CuNPs concentration, pH, and reaction temperature in aqueous solution. The rate of the decolorization and destruction of aromatic ring were studied spectrophotometrically. The dye mineralization was performed with potassium dichromate for the determination of chemical oxygen demand (COD) in solution. The blue color reaction mixture became red-chocolate, purple, light blue to dark blue as a function of time. The CuNPs acted as an activator of K₂S₂O₈ and generates various reactive oxygen and/or sulphur species. Decolorization of dye starts due to the cleavage of azo bond by the generated radical species. The role of sulfate radicals (SO₄^?-), and hydroxyl radicals (HO^?) were established by using different radical scavengers. Degradation and mineralization of dye follows first-order kinetics. These results can support the design of remediation processes and also assist in predict their fate in environment.     

Recognition of alkaline metals and amines by a chromogenic homooxacalix[3]arene receptor

[structure: see text] The artificial host molecule 1, consisting of homooxacalix[3]arene and pyridinium N-phenolate dye (Reichardt dye E(T)1) has been prepared. Host 1 contains a proton-ionizable phenol group that acts as a chemical switch to generate color change against alkaline metals and various kind of amines.     

Anaerobic biological treatment of dye bearing water in anaerobic sequencing batch reactor: Performance and kinetics studies

Textile and dye industries are main sources of dye bearing effluent. In present studies the anaerobic biological degradation of Acid Red 3BN dye water (AR3BNDW) and mixed dye water (MDW) for reduction of color and COD were studied in sequential batch reactor (SBR). The sludge as sources of microorganism was arranged from maize processing bio methanation wastewater treatment plant, which was acclimatized for treatment of AR3BNDW and MDW. After the acclimatization, dyes degradation were studied in SBR At optimum operation condition of hydraulics retention time (HRT) = 2.5 d, and treatment time (t_R) = 16 h, AR3BNDW have gone maximum 87% color reduction of 500 mg/L dye, and 82.8% COD reduction of 380 mg/L COD. At same operating condition, 84.5% color reduction of 500 mg/L dye, and 79.42% COD reduction of 413 mg/L COD achieved for MDW. The second order Grau model was fitted well for COD and dye reductions. The kinetics parameter were evaluated for both the dye water.     

A Mechanochromic Luminescent Dye Exhibiting On/Off Switching by Crystalline–Amorphous Transitions

A mechanochromic luminescent dye based on a simple aminomaleimide skeleton was readily synthesized in a one‐pot process. It exhibited an on/off mechanochromic luminescent switching property dependent on external stimuli, unlike a traditional mechanochromic color change. The green emission was turned on by grinding in a mortar and turned off by heating or treatment with dichloromethane. In the crystalline state, two molecules were stacked by cofacial π–π interactions, which caused concentration self‐quenching. The crystalline‐to‐amorphous transition induced by grinding removed cofacial π–π stacking, which led to intensive emission. Crystallizing processes recovered the cofacial π–π stacking, resulting in elimination of the emission. Theoretical calculations and X‐ray diffraction analyses revealed that the dye molecule was distorted in the crystalline state; thus even a mechanical stimulus caused the crystalline‐to‐amorphous transition.     

Resonance energy transfer from a fluorescent dye to a metal nanoparticle

A quantum mechanical theory of the rate of excitation energy transfer from a fluorescent dye molecule to the surface plasmonic modes of a spherical metal nanoparticle is presented. The theory predicts the distance dependence of the transfer rate to vary as 1/d(sigma), with sigma=3-4 at intermediate distances, in partial agreement with the recent experimental results. F?rster's 1/d(6) dependence is recovered at large separations. The predicted rate exhibits nontrivial nanoparticle size dependence, ultimately going over to an asymptotic, a(3) size dependence. Unlike in conventional fluorescence resonance energy transfer, the orientational factor is found to vary between 1 and 4.     

Dynamics of molecular diffusion of rhodamine 6G in silica nanochannels

We describe a method to study diffusion of rhodamine 6G dye in single silica nanochannels using arrays of silica nanochannels. Dynamics of the molecules inside single nanochannel is found from the change of the dye concentration in solution with time. A 10(8) decrease in the dye diffusion coefficient relative to water was observed. In comparison to single fluorescent molecule studies, the presented method does not require fluorescence of the diffusing molecules.     

Immunoenzymatic assay of dyes currently used in affinity chromatography for protein purification.

Cibacron Blue F3-GA, Basilen Blue E3-G and Procion Red HE-3B are dyes currently used in affinity purification, and are commonly determined by spectrophotometry with limited sensitivity. An assay method is described based on a specific immunochemical recognition of the dyes amplified by a final enzymatic reaction. The sensitivity is close to 1 ng/ml of dye and the method is applicable any time that sensitive and accurate results are necessary. This method has actually been applied with success to the determination of trace amounts of dyes in the presence of affinant protein. The method was also applied to the demonstration of dye leaching from affinity sorbents when treated under acidic and/or alkaline conditions.     

Influence of the environment on photoinduced electron transfer: comparison between organized monolayers at the air-water interface and monolayer assemblies on glass

Photoinduced electron transfer (PET) has been investigated in organized monolayers at the air-water interface and in monolayer assemblies on glass in an effort to evaluate the influence of solvent reorganization and molecular dynamics on PET. The donor monolayer contained an amphiphilic thiacyanine dye, and the electron acceptors were methyl viologen and dioctadecyl viologen, respectively. The distance dependence is described here by a hard disk model, where an acceptor molecule within a disk with a radius rDA around the excited donor molecule quenches the donor fluorescence due to electron transfer. Acceptor molecules outside the disk are considered ineffective. The critical radius rDA is larger in monolayer assemblies on glass (rDA = 1.97 nm) than at the air-water interface (rDA = 1.15 nm) as evaluated from steady-state fluorescence quenching. This large difference indicates that the time between thermal collisions generating and destroying the energetic match required for electron tunneling from the excited donor molecule to the acceptor is quite different in the two systems that are compared.     

L-Proline promoted fluorescent sensor for Mg2+ detection in a multicomponent sensory system

Mg(2+) can lead to the fluorescence enhancement of a dye molecule as high as 47.3-fold while L-proline acts as a promoter in this multicomponent sensory system. The fluorescence color could be easily detected by the naked eye under a UV-lamp.     

On the study of the Metal-complex Dye Polyurethane Ionomer

The reaction of toluene diisocyanate with polyester, dimethylol propionic acid, metal-complex dye and other additives to form the structure of metal-complex dye polyurethane ionomer molecule has been proven by FT-IR spectra. In aqueous solution, the surface tension of metal-complex dye polyurethane ionomer molecule is seen to slightly increase with increasing concentrtion of metal-complex dye and neopentyl glycol, respectively. This is because the adsorption of hydrophobics of ionomer molecules at the surface of aqueous solution becomes even more order. Under the same experimental condition, the surface tension of metal-complex dye polyurethane ionomer molecule in aqueous solution appears to slightly decrease with increasing NCO/OH ratio, as a result of increased hydrophobics of ionomer molecule adsorbed at the surface of aqueous solution.     

Resonance energy transfer from a fluorescent dye molecule to plasmon and electron-hole excitations of a metal nanoparticle

The authors study the distance dependence of the rate of electronic excitation energy transfer from a dye molecule to a metal nanoparticle. Using the spherical jellium model, they evaluate the rates corresponding to the excitation of l=1, 2, and 3 modes of the nanoparticle. The calculation takes into account both the electron-hole pair and the plasmon excitations of the nanoparticle. The rate follows conventional R(-6) dependence at large distances while small deviations from this behavior are observed at shorter distances. Within the framework of the jellium model, it is not possible to attribute the experimentally observed d(-4) dependence of the rate to energy transfer to plasmons or electron-hole pair excitations.