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For the observation of plant material under a light microscope, free-hand sectioning is usually the fastest and most practical procedure. The staining of the obtained cuts is a crucial step and the action mechanism of the dye is variable. Toluidine blue O is a cationic dye whose metachromatic potential for free-hand sections has long been known. Thus, this work aimed at analysing the performance of Toluidine blue O for this type of sectioning with a systematic and comparative approach. The action of Toluidine blue O pH 4.0 was tested for both fresh and previously clarified free-hand sections from leaves of different species of plant. These sections were compared with sections embedded in glycol-methacrylate resin stained with the same dye or submitted to different histochemical tests. The fresh sections obtained by free-hand and stained with Toluidine blue O permitted the accomplishment of histochemical inferences, with the advantage of maintaining the natural colours from the tissues. The previously clarified sections presented the advantage of having a clearer image, allowing a better cellular delimitation. We concluded that Toluidine blue O is very informative for sections of plant material obtained by free-hand, being, therefore, a procedure that is fast, inexpensive and with excellent results. [ABSTRACT FROM AUTHOR]

This work reports the synthesis of poly (itaconic acid) by thermal polymerization mediated by 2,2′-Azobis(2-methylpropionamidine) dihydrochloride. Furthermore, physical hydrogels were prepared by using high molecular weight poly (itaconic acid) characterized by low dispersity and laponite RD. The hydrogels presented porous 3D network structures, with a high-water penetration of almost 2000 g/g of swelling ratio, which can allow the adsorption sites of both poly (itaconic acid) and laponite RD to be easily exposed and facilitate the adsorption of dyes. The water adsorption followed Schott's pseudo-second-order model. The mechanism of the adsorption process was investigated using 1H and 31P NMR. The hydrogel is able to fast adsorb by a combination of electrostatic interactions and hydrogen bonding by the synergic effect of the clay and poly (itaconic acid). Moreover, the prepared aerogels exhibited a fast removal of Basic Fuchsin, with an adsorption capacity of 67.56 mg/g and a high removal efficiency (~99 %). The adsorption followed the pseudo-second-order kinetic model and Langmuir isotherm model. Furthermore, the thermodynamic parameters showed that the BF process of adsorption was spontaneous and feasible, endothermic, and followed physisorption. These results indicated that the PIA/laponite-based aerogel can be considered a promising adsorbent material in textile wastewater treatment. [Display omitted] • Biobased poly (itaconic acid) of high molecular weight and low dispersity was prepared by thermal polymerization. • Physically crosslinked poly (itaconic acid)/laponite RD hydrogels were fabricated. • The mechanical properties can be improved by tailoring the molecular weight of the polyelectrolyte. • Strong electrostatic interactions between the cationic dyes and laponite/poly (itaconic acid) were demonstrated by NMR. • The adsorption process was found to be endothermic, fast, and spontaneous with >95 % of Basic Fuchsin eliminated after 60 min. [ABSTRACT FROM AUTHOR]

Abstract Toluidine blue (TB) staining either alone or in association with other methodologies has the potential to answer a variety of biological questions regarding the human, animal and plant tissues or cells. In this brief review, we not only report the primary use of TB to detect the anionic substrates and availability of their binding sites, but also unveil the resulting applications of TB staining in biological research. Among these applications, the uses of TB staining to identify the changes in chromatin DNA-protein complexes, nucleolus location, and extracellular matrix proteoglycan complexes associated with different physiological and pathological events are described. The usefulness of TB staining to monitor the effects elicited by environmental insults on chromatin and intercalation of drugs into the DNA is also included. [ABSTRACT FROM AUTHOR]

Charged food hydrocolloids provide structure and texture in manufactured foods by their organization and electrostatic interactions with other species and small ions. These electrostatic interactions depend on their actual charge density which cannot be predicted from pK a values of weakly charged monomers. In practice, this is circumvented by the use of an ‘apparent pK a ’ (pK a (app) ) which depends on solution ionic strength and type of counter-ions. pK a (app) values for food hydrocolloids are poorly documented, especially in low ionic strength solvents. Titration of a metachromatic alginate-ortho-toluidine blue complex revealed a sigmoidal, pH-dependent, dye metachromasy response with its centre located at pH = pK a (app) . To test the suitability of this approach for the determination of pK a (app) , five food hydrocolloids and a synthetic polyanion are analysed and the results are compared to classical methods such as potentiometric titration. Metachromasy is shown to occur when the polymer inter-charge distance is 4.5 Å; the complex stoichiometry depending on inter-charge distance. pK a (app) of stoichiometric complexes at low ionic strength (1 mM phosphate buffer) were successfully determined (alginate 4.5, sodium carboxymethylcellulose 4.6, κ-carrageenan 1.2, polyphosphate 2.1 and polyacrylic acid 5.8) and are comparable to values obtained by potentiometric titration. Further, it is shown that pK a (app) determination by metachromatic dye titration is feasible for stoichiometric polymer-dye complexes at low concentrations (20–200 μM) in low ionic strength (<10 mM) aqueous solutions. Unlike classical methods, the metachromatic dye titration approach is suitable for low polymer concentrations in aqueous solutions at low ionic strength. [ABSTRACT FROM AUTHOR]

Sodium Lauryl Ether Sulfates (SLES) are an increasingly important and versatile type of surfactants. The complexation between ortho-Toluidine blue (TBO) and a homologous series of SLES, including Sodium Lauryl Sulfate (SDS) without Ethylene Oxide (EO), has been investigated using visible spectrophotometry. Upon increasing the molar surfactant-dye-ratio (S/D), three TBO organization regimes can be identified from the absorption spectra: (i) Ion-pair formation, (ii) Pre-micellar aggregation and (iii) Micellar aggregation. The limited solubility of SDS-TBO ion pairs, leading to precipitation of ion-pair clusters, causes a decrease of the TBO monomeric peak height when S/D is increased. The better solvability of TBO-SLES ion-pairs causes the onset of precipitation to occur at higher S/D when the EO-block length increases. In an intermediate S/D range, metachromasy is observed as a result of dye-stacking onto the SDS arranged in a pre-micellar state at surfactant concentrations well below the critical micelle concentration (CMC). For SDS, the S/D range showing pre-micelles depends on TBO concentration but seems independent of variation of ionic strength (phosphate buffer, pH = 7.0, C buffer = 0.1–10 mM), whereas the metachromatic peak height increases with decreasing ionic strength. The pre-micellar region for all SLES-TBO is located at the same S/D range but the maximum metachromatic peak height follows the trend: EO 2 > EO 4 > SDS > EO 12 ≈ EO 30 . The onset of the micellar range, in which TBO is again present in monomeric form, is shown to coincide with the CMC. These findings could proof helpful in either formulation or analysis of SLES. Likewise, understanding the dyes' interactions may facilitate formulation of dyeing solutions for optimal performance, or alternatively, as part of the textile plant effluent treatment to remove, and possibly recycle, dyes. [ABSTRACT FROM AUTHOR]

This communication reports the metachromasy or the changes in shapes and positions of the absorption spectra of an anionic cyanine dye merocyanine 540 abbreviated as MC540, in aqueous solutions and in LB films when electrostatically interacted with a well-known cationic surfactant cetyltrimethylammonium bromide abbreviated as CTAB. Critical Micellar Concentration of CTAB affected largely on the dissociation of MC540 molecular aggregates in the CTAB-MC540 complex LB films. Spectroscopic studies of these LB films showed only monomeric absorption band and intense fluorescence band. This complex LB film can act as efficient fluorescence probe for several biological systems. [ABSTRACT FROM AUTHOR]

Polymeric carbon nitride in graphitic form (g-C 3 N 4 ) is an emerging visible light active photocatalyst. In this work, phosphate-modified polymeric carbon nitride (PCN) was synthesized by thermal condensation of melamine in the presence of ammonium dihydrogen phosphate (ADP). The addition of PCN to methylene blue (MB) solution showed the color intensification. The hypsochromic shift in the absorption spectrum of MB is due to metachromasy, a phenomenon in which aggregation of dye molecules occurs over the surface of a material. The polymerization of melamine into carbon nitride and MB trimerization depend on the amount of ADP and nature of phosphate species, respectively. [ABSTRACT FROM AUTHOR]

The interaction between an anionic dye Methyl Orange and two poly cations namely, Poly (N-vinyl-4-methylpyridiniumiodide), (PC1) & Poly (vinylbenzyltriphenylphosphoniumchloride), (PC2) has been investigated by spectrophotometric method. The polymers are observed to induce metachromasy in the dye as evidenced from the considerable blue shift in the absorption maximum of the dye. The interaction constant and thermodynamic parameters of interaction have been determined by absorbance measurements at the metachromatic band. The effect of additives such as ionic salts, alcohols, urea and polyelectrolytes on the reversal of metachromasy has been studied and used to determine the stability of the metachromatic complex and to understand the nature of binding.

This communication reports the effect of building matrices and nano clay platelets on the aggregation pattern of a water soluble cationic fluorescent dye Crystal Violet (CV) in Langmuir-Blodgett (LB) Films. When stearic acid (SA) was used as a building matrix, pressure induced changes in metachromasy was observed in the SA-CV complex LB films with a characteristic J-band formed at the longer wavelength side. On the other hand, clay incorporated hybrid LB films showed high degree of control over H-dimeric band. Isotherm characteristics, Brewster Angle Microscopic (BAM) images, UV–vis absorption and fluorescence characteristic studies were employed to investigate this result. [ABSTRACT FROM AUTHOR]

The surface domains of self-assembled amphiphiles are well-organized and can perform many physical, chemical, and biological functions. Here, we present the significance of chiral surface domains of these self-assemblies in transferring chirality to achiral chromophores. These aspects are probed using l- and d-isomers of alkyl alanine amphiphiles which self-assemble in water as nanofibers, possessing a negative surface charge. When bound on these nanofibers, positively charged cyanine dyes (CY524 and CY600), each having two quinoline rings bridged by conjugated double bonds, show contrasting chiroptical features. Interestingly, CY600 displays a bisignated circular dichroic (CD) signal with mirror-image symmetry, while CY524 is CD silent. Molecular dynamics simulations reveal that the model cylindrical micelles (CM) derived from the two isomers exhibit surface chirality and the chromophores are buried as monomers in mirror-imaged pockets on their surfaces. The monomeric nature of template-bound chromophores and their binding reversibility are established by concentration- and temperature-dependent spectroscopies and calorimetry. On the CM, CY524 displays two equally populated conformers with opposite sense, whereas CY600 is present as two pairs of twisted conformers in each of which one is in excess, due to differences in weak dye-amphiphile hydrogen bonding interactions. Infrared and NMR spectroscopies support these findings. Reduction of electronic conjugation caused by the twist establishes the two quinoline rings as independent entities. On-resonance coupling between the transition dipoles of these units generates bisignated CD signals with mirror-image symmetry. The results presented herein provide insight on the little-known structurally induced chirality of achiral chromophores through transfer of chiral surface information.

Metachromatic image of cell-walls were investigated for seven algae. Species; red: Acanthophora nayadiformis, Chondria capillaris, Phyllophora crispa, brown: Petalonia fascia, Cystoseira barbata, Dictyota dichotoma and green: Ulva linza. The tested methachromatic dyes were azur II, methylene blue and thioflavine. In this work, locations of algal acidic and sulfated polysaccharides in cell-wall of red and brown algae were demonstrated by metachromasy, except in green algae. The metachromatic method clearly showed the cell wall constituents of algae. Cuticle and epidermal cells intensely stained but also the inner cell wall polysaccharide accumulation clearly shown. The most obvious staining and color change was seen by azur II. [ABSTRACT FROM AUTHOR]

Abstract: Aims: After undergoing lesions, tendons have disorganized collagen fibers compared to undamaged tendons. Arrabidaea chica leaves have the aglycones carajurin and carajurone, components of the antocyanins, with a strong pharmacological potential due to their healing properties. Thus, the aim of this study was to investigate the effect of topical application of A. chica extract during tendon healing. Main methods: The calcaneal tendon of Wistar rats was partially transected with subsequent treatment with A. chica extract (2.13g/mL) followed by excision on the 7th, 14th and 21st days. Control rats received only saline treatment. Key findings: Transmission electron microscopy analysis showed the presence of a large amount of small segments of collagen fibrils in the transected region of the tendons on the 7th day in both the control and plant-treated groups. Considering the organization of the collagen fibers, higher values of birefringence were observed under polarization microscopy in the tendons of the plant-treated group on the 14th day compared to the control group. A larger quantity of dermatan sulfate was also detected after plant treatment in the same period. However, lesser dermatan and chondroitin sulfate were detected in the plant-treated group than in the control group on the 21st day. No differences were found in the values of birefringence between these groups. Intense metachromasy was observed in both transected groups on the 21st day. Significance: In conclusion, the use of A. chica extract improves collagen organization and increases the quantity of dermatan sulfate on the 14th day of the tendon healing. [Copyright &y& Elsevier]

Abstract: The influence of methylene blue adsorption to different clays on its photodegradation was studied. Methylene blue in solution was decomposed by sunlight in a zero-order process. Adsorption to some clay minerals (sepiolite and vermiculite) and a zeolite (clinoptilolite) accelerated the degradation process, and converted it to a first-order reaction. On the other hand, adsorption to other clay minerals (palygorskite and montmorillonite) stabilized the dye and prevented its degradation. Interestingly, in the clay–dye complexes that exhibited stability, clear metachromasy of the adsorbed methylene blue occurred, whereas the effect was not observed in the clay–dye complexes that underwent photodegradation. [Copyright &y& Elsevier]

The interaction of nanomaterials with DNA and proteins is an area of great interest especially in the development of novel biosensors, and recently, it has become the focus of many multidisciplinary researches. DNA intercalating agent acridine orange interrupts the normal function of cellular DNA, leading to the inhibition of gene expressions. Many carcinogenic chemicals damage DNA either by intercalation or by cross-linkage. Numerous repair strategies are available to block the progressive DNA damage caused by DNA intercalators. These strategies aimed to prevent intercalation through the scavenging of the reactive moieties of the intercalators. In this report, we demonstrate binding of halloysite nanotubes (HNT) with a DNA intercalator, acridine orange (AO), through a hydrophobic interaction referred to as 'polar bonding.' HNTs are composed of silica on their outer surface and alumina within their inner surface. The inner and outer surfaces of tubular walls confer a resultant negative charge which makes HNT polyanionic in nature, thus enhancing the potential for polar bonding between HNT and amino-substituted AO. This interaction can lead to a metachromatic shift due to π interactions between the aromatic entity of AO and the oxygen plane of the HNT. This shift was confirmed by Fourier transform infrared spectroscopy (FTIR) analysis whereby in the presence of HNT, the intercalator AO, intercalated within the DNA-AO complex, showed affinity for HNT as observed by the shift in FTIR peaks of halloysite nanotubes from 3,623, 1,722, and 1,038 cm to 3,612, 1,706, 1,083, and 963 cm. [ABSTRACT FROM AUTHOR]

The interaction between an anionic dye methyl orange and three poly cations namely, poly (N-methy-4-vinylpyridinium iodide) (PM4VPI), poly (vinylbenzyltriphenyl phosphonium chloride) (PVBTPPC) and poly (N-methy-4- vinylpyridinium iodide) (PM2VPI) has been investigated by spectrophotometric method. The polymers were observed to induce metachromasy in the dye as evidenced from the considerable blue shift in the absorption maxima of the dye. The interaction constant and thermodynamic parameters of interaction have been determined by absorbance measurements at the metachromatic band. The effect of additives such as ionic salts, alcohols, urea and polyelectrolytes on the reversal of metachromasy has been studied and used to determine the stability of the metachromatic complex and to understand the nature of binding. [ABSTRACT FROM AUTHOR]

The binding behavior of acidic capsular polysaccharide (SPS), isolated from Klebsiella serotype K43, with oppositely charged dyes and surfactants have been studied by way of absorbance and emission spectroscopic measurements. Each repeating unit of the SPS consists of three D-mannose, one D-galactose, and one D-glucuronic acid residue. The anionic polysaccharide exhibited chromotropic character and induced strong metachromasy in the cationic dye, pinacyanol chloride (PCYN) through the formation of a 1:1 stoichiometric complex. Evaluation of thermodynamic parameters, viz., changes in free energy (ΔG), enthalpy (ΔH), and entropy (ΔS), for the formation of dye-polymer complex and studies on the effect of different cosolvents were also evaluated to shed light on the binding nature as well as the extent of stability of the dye-polymer complex. Fluorescence of the cationic dye acridine orange (AO) was quenched with the progressive addition of SPS, which was found to be of Stern-Volmer type. Cationic surfactants in their pure form as well as in the mixed state with nonionic surfactant (Tween-20), replaced the dye bound to the polymer matrices; thus the original band intensities of the dyes could be reverted. Such studies revealed the involvement of both electrostatic as well as hydrophobic interactions between the dye-polymer as well as surfactant-polymer aggregates. [ABSTRACT FROM AUTHOR]

Abstract: Physico-chemical studies on the interaction of capsular polysaccharide (SPS) isolated from Klebsiella K18, with cationic dyes and surfactants have been reported. SPS is an integral component of gram-negative bacteria and having glucuronic acid as the potential anionic site, induced strong metachromasy (blue shift ∼110nm) in the cationic dye pinacyanol chloride (PCYN). Reversal of metachromasy was observed upon addition of co-solvents which provides a qualitative measurement of stability and nature of metachromatic compound associated with PCYN–SPS interaction. Thermodynamic parameters such as association constant, changes in free energy, enthalpy and entropy of dye–polymer interaction, were evaluated which revealed the nature of interaction. Studies on fluorescence quenching of acridine orange (AO) was also performed. The interaction of SPS with cationic and cationic–non-ionic mixed surfactant systems have been studied by turbidimetry, spectrophotometry, spectrofluorometry and viscosity measurements. The studies could provide an understanding on the effects of the surfactants on binding with the polymer. The binding was found to be electrostatic in origin and also hydrophobic in nature to a certain extent. [Copyright &y& Elsevier]

Abstract: The present paper shows that the aggregation behavior of methylene blue in the monomer, dimer or aggregated forms is responsible for the inconsistency in the photocatalytic performance studies in various photocatalysts materials. The aggregation behavior of MB and its influence on photocatalytic degradation of the dye during photocatalytic performance study has been characterized by UV–visible absorption spectroscopy. The results indicate that the photocatalytic degradation of dyes depends not only on the intrinsic parameters of photocatalysts but also on the aggregation behavior of the pollutant on the catalyst surface. [Copyright &y& Elsevier]

Abstract: The interactions of Acridine Orange with Sodium Alginate and Pinacyanol Chloride with Heparin have been investigated by spectrophotometric method. The polymers induce metachromasy in the dye as evidenced from the considerable blue shift in the absorption maxima of the corresponding dyes. The interaction constant and thermodynamic parameters of polymer–dye interactions have been determined. The effect of additives such as alcohols, and urea on the reversal of metachromasy has been studied. The data has been used to determine the stability of the metachromatic complex and the nature of binding. The thermodynamic parameters of interaction revealed that binding between Acridine Orange and Sodium Alginate involved only electrostatic forces while that between Pinacyanol Chloride involved both electrostatic and hydrophobic forces. The reversal studies using surfactants indicated the involvement of both electrostatic and hydrophobic forces in binding. Based on the results it can be concluded that Pinacyanol Chloride is more effective inducing metachromasy than Acridine Orange. [Copyright &y& Elsevier]

Abstract: Spectral studies on the interaction of acidic capsular polysaccharide (SPS), isolated from Klebsiella K28, with cationic dye and surfactants have been reported. The polymer induced strong metachromasy (∼100nm blue shift) in the cyanine dye pinacyanol bromide (PCYB). The SPS consists of d-glucose, d-galactose, d-mannose and d-glucuronic acid (2:1:2:1 molar ratio) in hexasaccharide repeating units. Glucouronic acid acted as potential anionic binding sites. 1:1 stoichiometry of the SPS–dye complex indicated the association of every potential anionic binding site of the polymer and its stacking conformation. Addition of different cosolvents resulted reversal of metachromasy. Oppositely charged surfactant–SPS binding was evaluated by dye incorporation technique. Cationic surfactants replaced bound dye molecules, thus the original band intensity of dye got increased. From the spectral data, binding constants of polymer–surfactant aggregates were calculated. [Copyright &y& Elsevier]

The addition of different ionenes, polycations with defined structure and charge distances, to methylorange 1 in very dilute solutions of water resulted in an observable shift of the absorption maxima from 464 nm to shorter wavelengths. The extent of this so-called metachromasy effect was found to be dependent on the nature of the hydrophobic unit of the polymer backbone. The comparison of UV/VIS spectra's of these solutions with the absorption of a film of a model substance - a dication with methylorange as counteranion - lead to the conclusion that ionenes undergo an exchange of the counteranions when added to a dilute solution of methylorange. Precipitation is slowed down, but the absorption is equivalent with solid product. The new absorption spectra of methylorange can be explained by the interaction of the quaternary nitrogen with the dye anion. [ABSTRACT FROM AUTHOR]

The interaction of acidic capsular polysaccharide isolated from Klebsiella K26 with cationic dyes pinacyanol chloride, acridine orange and phenosafranin has been studied by spectral measurements. The polymer induces metachromasy in pinacyanol chloride dye, indicating a blue shift in the visibly absorption spectrum of the dye from 600 to 500 nm. The stoichiometry of polymer/dye in the metachromatic compound, thermodynamic parameters of interaction, and effects of different cosolvents on the stability of the complex have been studied. Spectrophotometric and spectrofluorometric properties of the interaction between the polymer and all three dyes are presented. The chromotropic property of the polymer has been established. [ABSTRACT FROM AUTHOR]

Abstract: Background: In clinical settings, human serum albumin (HSA) is widely quantitated on the basis of change in the color of bromocresol purple (BCP) bound to HSA. However, the binding sites of BCP on HSA are hitherto unknown. We have identified these sites by performing binding experiments in which BCP was bound to HSA complexed with warfarin, ibuprofen, propofol, or myristic acid. Methods: The binding experiment was performed with HSA complexed with a drug in buffers at pH 4.8 and 7.2. The number of BCP binding sites (n) and the association constant (Ka) were obtained by Scatchard analysis using the absorbance data of the BCP–HSA complexes. Results: Two BCP binding sites on native HSA were identified at pH 7.2 and 1.3 sites were identified at pH 4.8. The number of sites for warfarin–HSA binding was approximately half that of native HSA at both pH values. The site numbers for myristate- and ibuprofen–HSA were 0.3 and 0.8 at pH 7.2, and 1.5 and 2.0 at pH 4.8, respectively; their Ka values were also high (18×104 and 10×104). The Ka values for all HSA samples, except for the 2 samples, arranged from 1.5×104 to 3.3×104. The n and Ka values for propofol were equivalent to those for native HSA. Conclusion: We postulate that the 2 BCP binding sites include a warfarin-binding site (drug-binding site 1) and 1 of the 2 ibuprofen-binding sites. [Copyright &y& Elsevier]

The aggregation mode of three azo dyes, methyl orange (MO), ponceau SS (PSS), and direct blue 1 (DB1) induced by three 1,4-diazabicyclo[2.2.2]octane (DABCO)-based ionene polymers having different topologies (i.e., 1,2-ionene, 1,3-ionene, and 1,4-ionene) was investigated in this work. Metachromatic behavior of the dyes in the presence of ionenes, and the stability of the ionene/dye complex were discussed as a function of ionene structure. It was demonstrated that the association of the dye molecules with the ionenes and the metachromasy were strongly influenced by both the dye structure and the ionene topology. Thus, MO, having one -SO 3 Na group per molecule, was almost stoichiometrically bound to all ionenes regardless of their topology, showing also a metachromatic effect. In sharp contrast, the interaction of PSS and DB1 molecules with ionenes was strongly dependent on the polymer topology. It was found that PSS having two -SO 3 Na groups per molecule was preferentially bound onto both 1,2-ionene and 1,3-ionene, but DB1, having four -SO 3 Na groups per molecule and a more complex structure, was efficiently bound only onto 1,2-ionene. The dye removal efficiency with each ionene was evaluated in batch mode taking into account the affinity of ionenes for azo dyes. The experimental isotherms of the dye sorption were fitted with four isotherm models, i.e., Langmuir, Freundlich, Sips, and Dubinin-Radushkevich. It was found that the best fitting of the experimental data was given by the Langmuir, Sips, and Dubinin-Radushkevich isotherm models. The maximum equilibrium sorption capacity, q m , evaluated by the Langmuir model, at 35 °C, was as follows: 985.71 mg MO/g 1,3-ionene, 483.71 mg PSS/g 1,3-ionene, 1010.49 mg PSS/g 1,2-ionene, and 976.7 mg DB1/g 1,2-ionene. Kinetic study of the dye removal indicated chemisorption as the main mechanism of sorption.