Photokinetic voltammetric method for the determination of thiocyanate

Thiocyanate traces have a strong inhibitory effect on the oxidation of Neutral Red by potassium bromate under UV irradiation in diluted phosphoric acid. Neutral Red exhibits a sensitive second derivative oscillopolarographic wave at -0.6 V(vs. SCE) in diluted phosphoric acid and sodium acetate solution. The oscillopolarographic behavior of Neutral Red was selected as indicator component for its photo-activated oxidation. The photochemical reaction rate equation was determined. A detection limit of 0.3 ng mL(-1) (3sigma/k) and a linear calibration curve from 2.0-48.0 ng mL(-1) thiocyanate were obtained. The method was applied to the determination of thiocyanate in urine, saliva and serum with satisfactory results.     

Photokinetic voltammetric method for the determination of thiocyanate

Thiocyanate traces have a strong inhibitory effect on the oxidation of Neutral Red by potassium bromate under UV irradiation in diluted phosphoric acid. Neutral Red exhibits a sensitive second derivative oscillopolarographic wave at –0.6 V(vs. SCE) in diluted phosphoric acid and sodium acetate solution. The oscillopolarographic behavior of Neutral Red was selected as indicator component for its photo-activated oxidation. The photochemical reaction rate equation was determined. A detection limit of 0.3 ng mL^–1 (3σ/k) and a linear calibration curve from 2.0–48.0 ng mL^–1 thiocyanate were obtained. The method was applied to the determination of thiocyanate in urine, saliva and serum with satisfactory results.     

Equilibrium (NAD+/NADH) potential on poly(Neutral Red) modified electrode

The electrochemical regeneration of nicotinamide adenine dinucleotide (NAD⁺/NADH) has been one of the central subjects of bioelectrochemistry during past three decades. We report on the unique chemical electrocatalyst for NAD⁺/NADH regeneration based on electropolymerized Neutral Red. Using poly(Neutral Red) modified electrodes, the reversible polarographic waves of nicotinamide adenine dinucleotide reduction–oxidation and the equilibrium (NAD⁺/NADH) potential were observed. This was impossible using all known catalytic and mediator systems. The unique poly(Neutral Red) based electrocatalyst allowed us to determine the standard (NAD⁺/NADH) potential more precisely (E^′≅0.59 V SCE, pH 6.0).     

Phototransformations of Neutral Red dye in aqueous solutions in the presence of cucurbit[7]uril

Russian Chemical Bulletin - Photophysical properties and photochemical transformations of Neutral Red (NR) dye in water in the presence of cucurbit[7]uril (CB7) were studied by absorption,...     

Salt-induced guest relocation from a macrocyclic cavity into a biomolecular pocket: interplay between cucurbit[7]uril and albumin

The binding affinity of Neutral Red with cucurbit[7]uril (CB7) can be fine-tuned by addition and competitive binding of metal ions, which leads also to a pK(a) shift of the dye; this can be exploited to relocate the dye from the macrocyclic cavity of CB7 to the biomolecular pocket of bovine serum albumin.     

Titration of oxidants with the reduced species of phenosafranine and neutral red,generated by electrochemical and photochemical techniques

Summary The generation of the reduced species of phenosafranine and Neutral Red by coulometric and photolytic methods is described. The electrogeneration is done at a platinum or mercury cathode, and the photogeneration by photochemical reaction between EDTA and the dye. The redox potentials for phenosafranine and Neutral Red are very low. The reduced dyes are suitable as reductimetric titrants and have been applied in coulometric and photochemical titrations of periodate, chromium(VI), iron(III), cobalt(III) and 2,6-dichloroindophenol.

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Die Titration von Oxydantien mit den reduzierten Formen von Phenosafranin und Neuralrot und deren elektrochemische bzw. photochemische Herstellung

Zusammenfassung Die Herstellung der reduzierten Formen von Phenosafranin und Neutralrot mit coulometrischen bzw. photolytischen Methoden wurde beschrieben. Ersteres erfolgt an einer Platin- oder Quecksilberkathode, letzteres durch photochemische Reaktion zwischen EDTA und dem Farbstoff. Die Redox-potentiale für Phenosafranin und für Neutralrot sind sehr niedrig. Die reduzierten Farbstoffe eignen sich als reduktometrische Titranten und wurden für coulometrische und photochemische Titrationen von Perjodat, Chrom(VI), Eisen(III), Kobalt(III) und 2,6-Dichlorindophenol verwendet.

     

Spectrophotometric and thermodynamic study on the dimerization equilibrium of ionic dyes in water by chemometrics method

The monomer-dimer equilibrium and thermodynamic of several ionic dyes (Neutral Red, Nile Blue A, Safranine T and Thionine) has been investigated by means of spectrophotometric and chemometrics methods. The dimerization constants of these ionic dyes have been determined by studying the dependence of their absorption spectra on the temperature in the range 20-75 degrees C at concentrations of Neutral Red (1.73 x 10(-5) M), Nile Blue A (3.94 x 10(-5) M), Safranine (6.59 x 10(-5) M) and Thionine (6.60 x 10(-5) M). The monomer-dimer equilibrium of these dyes has been determined by chemometrics refinement of the absorption spectra obtained by thermometric titrations performed. The processing of the data carried out for quantitative analysis of undefined mixtures, based on simultaneous resolution of the overlapping bands in the whole set of absorption spectra. The enthalpy and entropy of the dimerization reactions were determined from the dependence of the equilibrium constants to the temperature (van't Hoff equation).     

An electrochemical aptasensor for cytochrome C,based on pillar[5]arene modified with Neutral Red

An electrochemical aptasensor is developed for the highly sensitive determination of cytochrome C, using a change in the redox current of Neutral Red covalently bound to terminal carboxyl groups of decasubstituted pillar[5]arene as a signal. The inclusion of the analyte into the complex with an aptamer reduces peaks of redox current of the dye through the dissociation of electron transfer chain in the surface layer. The aptasensor enables the determination of 1 nM to 1.0 mM of cytochrome C in the presence of 1000-fold excesses of albumin, polyethylene glycol, and lysozyme as models of interfering components in biological fluids.     

Solvent effect on the spectral properties of Neutral Red

Background  

The study was aimed at investigating the effect of various solvents on the absorption spectra of Neutral Red, a dye belonging to the quinone-imine class of dyes. The solvents chosen for the study were water, ethanol, acetonitrile, acetone, propan-1-ol, chloroform, nitrobenzene, ethyleneglycol, acetic acid, DMSO and DMF.     

Photoprotective nanoemulsions containing microbial carotenoids and buriti oil: Efficacy and safety study

Photoprotective nanoemulsions are able to attenuate skin damage from overexposure to the sun, thus avoiding the immediate effects caused by ultraviolet radiation. The global cosmetics market understands that there is a demand and greater acceptance by consumers for formulations containing natural products compatible with the skin. Consequently, there is an increasingly need to develop such products that are safe and effective. Furthermore, there is a growing interest in nanoemulsions (NE) in the pharmaceutical industry, due the versatility of incorporating lipophilic substances into cosmetic formulations. In the present work, oil-in-water photoprotective nanoemulsions containing microbial carotenoids, buriti oil and chemical filters were developed and characterized. The essential physical properties of the droplets, the transmission electronic microscopy (TEM), the sun protection factor (SPF) as well as the stability of the formulations were determined. In vitro phototoxicity was evaluated using Balb 3 T3 with relative cell viability estimated by Neutral Red Uptake, with the Photo Irritation Factor (PIF) and the Medium Photo Effect Factor (MPF) as the measurement parameters. Nanoemulsion 3 (NE3) showed spherical morphology with an average droplet size of 142.11 ± 0.92 nm and polydispersity index (PDI) of 0.198 ± 0.017. This nanoemulsion containing microbial carotenoids and buriti oil exhibited a SPF of 36 ± 1.5. Neutral Red Uptake revealed that the cells kept their viability even after irradiation and those nanoemulsions containing the microbial carotenoids and buriti oil were not phototoxic. The addition of microbial carotenoids and buriti oil in nanoemulsions was positive in increasing the mean SPF values compared to the control formulation.     

Kinetic Spectrophotometric Determination of Trace Amounts of Nitrite Ion Using Its Reaction With Neutral Red

Abstract

A rapid, simple, sensetive and selective method for the determination of trace amounts of nitrite ion(30-800 ng/ml) is developed. It depends on the reaction of nitrite with Neutral Red. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance at 530 nm by a fixed time method. The limit of detection is 14 ng/ml. The method is used for the determination of nitrite ion in waste water.     

Vanadium compounds in reductimetric titrations-II Standardisation of vanadium(II) sulphate with common oxidising agents and determination of binary mixtures

Methods for the standardisation of vanadium(II) sulphate are described. With weak oxidising agents, e.g., Fe(III)/Fe(II) in phosphoric acid, vanadium(II) undergoes a one-electron change, which is satisfactorily indicated by Neutral Red, Phenosafranine or Safranine T, or by potentiometry. Stronger oxidising agents oxidise vanadium(II) to vanadium(IV); Variamine Blue, Methylene Blue, o-dianisidine, cacotheline, ferroin, bis(alpha,alpha'-bipyridyl)iron(II) and ammonium molybdate are satisfactory indicators. Binary mixtures of oxidising agents can be determined.     

Superabsorbent amphoteric nanohydrogels: Synthesis,characterization and dyes adsorption studies

The goal of the present research is to remove high percentage of cationic and anionic dyes such as,Neutral Red, Safranin O and Indigo Carmine from aqueous solutions by poly(NIPAAm/N,Ndiallylpyrrolidinium bromide/AA) superabsorbent amphoteric nanohydrogels synthesized using the inverse microemulsion polymerization method. Effect of various parameters such as, treatment time,initial dye concentration, p H and adsorbent dose were investigated. Furthermore, kinetics and isotherms adsorption models were applied to determine the maximum adsorption and mechanism for adsorption,which shows that adsorption obeyed the pseudo-second order kinetics. From the results, removal of dyes within the nanohydrogel was found to be in the order: AB-74 BR-2 BR-5.     

Preconcentration of aqueous dyes through phase-transfer liquid-phase microextraction with a room-temperature ionic liquid

In this study, we employed the room-temperature ionic liquid [bmim][PF₆] as both ion-pair agent and an extractant in the phase-transfer liquid-phase microextraction (PTLPME) of aqueous dyes. In the PTLPME method, a dye solution was added to the extraction solution, comprising a small amount of [bmim][PF₆] in a relatively large amount of CH₂Cl₂, which serves as the disperser solvent to an extraction solution. Following extraction, CH₂Cl₂ was evaporated from the extractant, resulting in the extracted dyes being concentrated in a small volume of the ionic liquid phase to increase the enrichment factor. The enrichment factors of for the dye Methylene Blue, Neutral Red, and Methyl Red were approximately 500, 550 and 400, respectively; their detection limits were 0.014, 0.43, and 0.02 μg L⁻¹, respectively, with relative standard deviations of 4.72%, 4.20%, and 6.10%, respectively.     

Effect of light-harvesting complex II on ion transport across model lipid membranes

The effect of the incorporation of the major light-harvesting complex of photosystem II (LHCII) to planar bilayer lipid membranes (BLMs) formed from soybean asolectin and unilamellar small liposomes formed from egg-yolk phosphatidylcholine on ion transport across the lipid bilayer has been studied. The specific conductivity of the BLM rises from 5.2 +/- 0.8 x 10(-9) up to 510 x 10(-9) O(-1) cm(-2) upon the incorporation of LHCII. The conductivity of the membrane with LHCII depends upon the ionic strength of the bathing solution and is higher by a factor of five when the KCl concentration increases from 0.02 to 0.22 M. Such a strong effect has not been observed in the same system without LHCII. The liposome model is also applied to analyse the effect of LHCII on the bilayer permeability to protons. Unilamellar liposomes with a diameter less than 50 nm have been prepared, containing (trapped inside) Neutral Red, a pigment sensitive to proton concentration. A gradient of protons on the membrane is generated by the acidification of the liposome suspension and spectral changes of Neutral Red are recorded in time, reflecting the penetration of protons into the internal space of liposomes. Two components of proton permeation across liposome membranes are observed: a fast one (proceeding within seconds) and a slow one (operating on the time scale of minutes). The rate of both components of proton transport across LHCII-containing membranes is higher than for liposomes alone. The enhancement effect of LHCII on the ion transport across the lipid membrane is discussed in terms of aggregation of the pigment-protein complexes. The possible physiological importance of such an effect in controlling ion permeability across the thylakoid membrane is discussed.     

Poly(neutral red) on passivated nickel films. New insights through EQCM measurements

Poly(Neutral Red) (PNR) has been electrogenerated on a passivated Ni surface. PNR was chosen due to the fact that its electroactivity region overlaps with the Ni dissolution/deposition process. Therefore, both electrochemical processes can compete and by this way, there are evidences about the formation of a Ni(OH)₂/PNR composite. It was investigated by classical EQCM and the instantaneous mass/charge ratio (F(dm/dQ)) analysis shed light on the active/passive transition and nickel trans-passive dissolution mechanisms.     

UV-Vis spectroscopic and chemometric study on the aggregation of ionic dyes in water

The monomer-dimer equilibrium in several ionic dyes (Methylene Blue, Acridine Orange, Nile Blue A, Neutral Red, Rhodamine 6G and Safranine O) has been investigated by means of UV-Vis spectroscopy. The data have been processed by a recently developed method for quantitative analysis of undefined mixtures, based on simultaneous resolution of the overlapping bands in the whole set of absorption spectra. In the cases of Acridine Orange a second chemometric approach has been used as a reference. It is based on a decomposition of the recorded spectra into a product of target and projection matrices using non iterative partial least squares (NIPALS). The matrices are then rotated to give the correct concentrations, spectral profiles of the components and the equilibrium constant. The dimeric constants determined by the two methods were in excellent agreement, evidencing the accuracy of the analysis. From the calculated dimeric constant and monomer and dimer spectra, the structures of the dimeric forms of the studied dyes are estimated.     

Indirect Kinetic–Spectrophotometric Determination of Resorcinol, Catechol, and Hydroquinone

A rapid, simple, and sensitive method for the determination of trace amounts of resorcinol, catechol, and hydroquinone in aqueous media has been proposed. The method is based on their reaction with nitrite. The excess nitrite is then determined by a kinetic method based on its reaction with Neutral Red. The reaction is monitored spectrophotometrically by measuring the decrease in the absorbance at 530 nm by a fixed time method. Resorcinol, catechol, and hydroquinone could be determined by the proposed method in the ranges of 0.1–2.0 mg/mL, 0.25–2.0 mg/mL and 0.1–3.0 mg/mL, respectively. The method was applied to the determination of resorcinol and catechol in pharmaceutical formulations with satisfactory results.     

Electrophoretic exclusion for the selective transport of small molecules

A novel method capable of differentiating and concentrating small molecules in bulk solution termed “electrophoretic exclusion” is described and experimentally investigated. In this technique, the hydrodynamic flow of the system is countered by the electrophoretic velocity to prevent a species from entering into the channel. The separation can be controlled by changing the flow rate or applied electric field in order to exclude certain species selectively while allowing others to pass through the capillary. Proof of principle studies employed a flow injection regime of the method and examined the exclusion of Methyl Violet dye in the presence of a neutral species. Methyl Violet was concentrated almost 40 times the background concentration in 30 s using 6 kV. Additionally, a threshold voltage necessary for exclusion was determined. The establishment of a threshold voltage enabled the differentiation of two similar cationic species: Methyl Green and Neutral Red.     

Hybridization detection of DNA by measuring organic small molecule amplified resonance light scattering signals

The interaction of organic small molecules (OSMs) with a biological molecule is very important. In this contribution, quinone-imine dyes including Acridine Yellow (AY), Neutral Red (NR), Acridine Orange (AO), Brilliant Cresyl Blue (BCB), Thionin (TN), Azur A (AA), Azur B (AB), and Methylene Blue (MB) respectively with double strand DNA (dsDNA) and single strand DNA (ssDNA) were investigated based on the measurements of enhanced resonance light scattering (RLS) and TEM. Mechanism investigations have shown that groove binding occurs between dsDNA and these OSMs, which depends on G-C sequences of dsDNA and the volumes of OSMs. With the amplified RLS signals resulting from the interactions of OSMs with DNA, a new technique has been proposed to detect the hybridization and mismatch of DNA labeling neither the target nor the probe DNA. The results have suggested that the extent of the amplified RLS signals of dsDNA by AY is the maximum among these eight OSMs, and therefore, it has been selected as a typical model system for further discussions.