Composition, structure, and luminescence of montmorillonites saturated with different aggregates of methylene blue

The distribution of various aggregates (dimers, trimers, and tetramers) of methylene blue (MB) formed in aqueous solution at various concentrations of dye has been calculated using the equilibrium aggregation constants betaq. Two montmorillonite samples with different cation exchange capacities, surface areas, and interlayer distances d001, Na-SWy, and Ca-Cheto, were saturated with methylene blue (MB) solutions with various ratios between monomers and higher aggregates of dye. The total amount of MB in the intercalated montmorillonite samples (MB-SWy and MB-Cheto) increases with increasing concentration of dye in water solutions, i.e., with increasing aggregates/monomers ratio of MB in water solution. In all intercalated montmorillonite samples with methylene blue except guest qth aggregate cations [MBqq+] low contents of Na+ (in MB-SWy) and Ca2+ (in MB-Cheto) cations were also determined. A very good positive correlation between the basal spacing d001 and the MB/montmorillonite molar ratio was revealed for saturated MB-montmorillonite samples. Structural analysis using a combination of diffraction data with molecular modeling revealed the differences in the interlayer arrangement of MB guests in MB-SWy and MB-Cheto intercalates. Also, fluorescence measurements showed the strong effect of the silicate layer charge on the spectroscopic behavior of MB guests intercalated in montmorillonite. Methylene blue exhibits a certain luminescence in MB-SWy samples with cation exchange capacity 0.80 meq g-1 and almost no luminescence in MB-Cheto samples with higher cation exchange capacity 1.50 meq g-1.     

Effect of dye aggregation on triarylmethane-mediated photoinduced damage of hexokinase and DNA

The observation that enhanced mitochondrial membrane potential is a prevalent cancer cell phenotype has provided the conceptual basis for the development of mitochondrial targeting as a novel therapeutic strategy for both chemo- and photochemotherapy of neoplastic diseases. Cationic triarylmethane (TAM(+)) dyes represent a series of photosensitizers whose phototoxic effects develop at least in part at the mitochondrial level. In this report we describe how the molecular structure of four representative TAM(+) dyes (Crystal Violet, Ethyl Violet, Victoria blue R, and Victoria pure blue BO) affects their efficiency as mediators of the photoinduced inactivation of two model mitochondrial targets, hexokinase (HK) and DNA. Our results have indicated that TAM(+) dyes efficiently bind to HK and DNA in aqueous media both as dye monomers and aggregates, with the degree of aggregation increasing with increasing the lipophilic character of the photosensitizer. The efficiency with which HK and DNA are damaged upon 532 nm photolysis of biopolymer-TAM(+) complexes was found to decrease upon increasing the degree of dye aggregation over these macromolecular templates. Comparative experiments carried out both in water and in D(2)O, and in air-equilibrated and nitrogen-purged samples have also indicated that, at least when Crystal Violet is used as the photosensitizer, the mechanism of macromolecular damage does not require the involvement of molecular oxygen to operate. This finding makes Crystal Violet a potential candidate for use in photochemotherapy of hypoxic or poorly perfused tumor areas.     

Intriguing H-aggregate and H-dimer formation of coumarin-481 dye in aqueous solution as evidenced from photophysical studies

Photophysical properties of coumarin-481 (C481) dye in aqueous solution show intriguing presence of multiple emitting species. Concentration and wavelength dependent fluorescence decays and time-resolved emission spectra and area-normalized emission spectra suggest the coexistence of dye monomers, dimers, and higher aggregates (mostly trimers) in the solution. Because of the efficient intramolecular charge transfer (ICT) state to twisted intramolecular charge transfer (TICT) state conversion, the dye monomers show very short fluorescence lifetime of ~0.2 ns. Fluorescence lifetimes of dimers (~4.1 ns) and higher aggregates (~1.4 ns) are relatively longer due to steric constrain toward ICT to TICT conversion. Observed results indicate that the emission spectra of the aggregates are substantially blue-shifted compared to monomers, suggesting H-aggregation of the dye in the solution. Temperature-dependent fluorescence decays in water and time-resolved fluorescence results in water-acetonitrile solvent mixtures are also in support of the dye aggregation in the solution. Though dynamic light scattering studies could not recognize the dye aggregates in the solution due to their small size and low concentration, fluorescence up-conversion measurements show a relatively higher decay tail in water than in water-acetonitrile solvent mixture, in agreement with higher dye aggregation in aqueous solution. Time-resolved fluorescence results with structurally related non-TICT dyes, especially those of coumarin-153 dye, are also in accordance with the aggregation behavior of these dyes in aqueous solution. To the best of our knowledge, this is the first report on the aggregation of coumarin dyes in aqueous solution. Present results are important because coumarin dyes are widely used as fluorescent probes in various microheterogeneous systems where water is always a solvent component, and the dye aggregation in these systems, if overlooked, can easily lead to a misinterpretation of the observed results.     

A new type of aggregates of cyanine dyes

It was shown that aggregates of a new type are formed in an aqueous solution upon the interaction of dimers of thiamonomethinecyanines and thiapentamethinecyanines. The detected aggregates from the dimers of various dyes are named “heterocontact dimers.” It was concluded that the formation of the heterocontact aggregates is energetically favored over the J aggregates of individual dyes.     

Solvent effect on the electronic spectra of azine dyes under alkaline condition

Thiazine dye, methylene blue (MB), oxazine dye, nile blue (NB), and phenazine-based dye, neutral red (NR), bear a similar basic dye skeleton with a distinctively different central heteroatom. All of them are extracted into nonpolar organic solvent from alkaline solution. The role of the heteroatom on the respective dye skeletons and redox potentials of the dyes has been examined to signature the stability of the species in organic solvent and the results have been substantiated through geometry optimization and wave function analysis at the density functional theory level. The effect of solvent polarity on the electronic absorption spectra of the three nonionic benzenoid species has been investigated with an intention to investigate the solvatochromic behavior of these compounds.     

The role of the methylene blue and toluidine blue monomers and dimers in the photoinactivation of bacteria

The interactions between the phenothiazine dyes, methylene blue (MB) and toluidine blue (TB), and bacteria (Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus faecalis, Hemophilus influenzae, Escherichia coli and Pseudomonas aeruginosa) were studied spectrophotometrically. This demonstrated that a metachromatic reaction took place between the dyes and bacteria. Furthermore, bacteria induced additional dimerization of MB and TB. The effective dimerization constants of MB and TB were evaluated in the presence of each bacterial strain at a concentration of 10(8) CFU/ml. The analysis of the effective dimerization constants for MB and TB in the presence of bacteria indicated that the ability to form dimers was greater for TB than for MB. Gram-negative bacteria induced the dye dimerization more intensely than gram-positive bacteria. There was a correlation between the ability of each dye to form dimers in the presence of bacteria and the relative photobactericidal efficacy of each dye against these bacteria. These results provide evidence confirming the essential role of the dye dimers in bacterial photodamage.     

J-aggregation of anionic ethyl meso-thiacarbocyanine dyes induced by binding to proteins

The effects of ribonuclease A (RNase), lysozyme, trypsin, and bovine serum albumin (BSA) on the J-aggregation behavior of 3,3'-bis[sulfopropyl]-5-methoxy-4',5'-benzo-9-ethylthiacarbocyanine (1), 3,3'-bis[sulfopropyl]-4,5,4',5'-dibenzo-9-ethylthiacarbocyanine (2), and 3,3'-bis[sulfopropyl]-5,5'-dimethoxy-9-ethylthiacarbocyanine (3) were studied in aqueous solution. The formation of J-aggregates at pH 6 is induced by RNase for 1-3, by lysozyme for 1 and 2, and by trypsin for 2. The formation of J-aggregates correlates with decay of the dimers and is supported by induced circular dichroism spectra. The concentration of J-aggregates for lysozyme/1 increases with an increase in the protein/dye concentration ratio, reaches a plateau, and then gradually decreases. J-aggregates are characterized by relatively weak fluorescence; e.g., Phi(f) = 0.01 for lysozyme/1, and by a small Stokes shift of 6-8 nm, indicating almost resonance fluorescence. J-aggregation proceeds in the range of seconds to minutes with sigmoidal type kinetic curves for trypsin/2 and nonsigmoidal kinetics in the other cases. The presence of BSA, in contrast to RNase, lysozyme, and trypsin, results in deaggregation of dimers of 1-3 and formation of bound monomers and exhibits intense fluorescence from the trans-monomer; e.g., Phi(f) = 0.22 for BSA/1. Generally, the binding of 1-3 to the proteins is a cooperative process, where the number of binding sites changes from n = 15 for lysozyme/1 to n = 6 for trypsin/2 and n = 0.3 and 1 for BSA/3.     

光波导分光光谱技术研究染料分子在玻璃表面的吸附特性

光波导分光光谱技术利用光波导表面的消逝场敏感地测定有色物质亚单分子吸附层的偏振吸收光谱, 非常适合于研究染料、颜料、荧光分子、量子点、金属纳米粒子、带色基的蛋白质等在固/液界面的吸附行为. 本文使用宽频带卤钨灯、棱镜耦合的薄膜玻璃光波导和基于电荷耦合器件(CCD)的光谱分析仪设计制作了具有时间分辨本领的光波导分光光谱装置, 并利用该装置实时监测了罗丹明6G(R6G)和亚甲基蓝(MB)在玻璃表面的吸附特性. 通过比较在横电(TE)和横磁(TM)偏振模式下的吸收光谱, 发现R6G主要以二聚体和单体的形式吸附在玻璃表面, 而MB主要以多聚体的形式吸附在玻璃表面, 并分别估算了它们的平均取向角.     

Micellar electrokinetic chromatography with diode laser-induced fluorescence detection as a tool for investigating the fluorescence labeling of proteins

We describe the use of micellar electrokinetic chromatography with diode laser-induced fluorometry (MEKC-DLIF) as a tool to characterize a labeling reaction between sulfoindocyanine succinimidyl ester (Cy5), a cyanine fluorescent dye, and a model protein, bovine serum albumin (BSA). To decrease the influence of imprecise injection, methylene blue was added as an internal standard. Labeled BSA was completely separated from the unconjugated Cy5, and methylene blue under optimized conditions. A kinetic study of the reaction was performed by changing some parameters, such as reaction buffer pH, reaction buffer concentration and the initial concentration of BSA. A comparison between the current method and traditional methods was made.     

Investigation of micelle formation by fluorescence correlation spectroscopy

We show that noncovalently bound dye molecules can be used as labels in single-molecule fluorescence experiments for the determination of aggregate formation in standard surfactant systems. Aqueous solutions of sulfosuccinic acid bis(2-ethylhexyl) ester sodium salt, hexadecyltrimethylammonium chloride, and pentaethylene glycol monododecyl ether have been studied by fluorescence correlation spectroscopy using commercially available dyes. The translational diffusion coefficient and the critical micelle concentrations have been determined and compare well to values reported in the literature. The respective charges of the surfactant and of the dye molecule are crucial for the effectiveness of the presented method.     

The effect of chromophore-chromophore interaction on the spectral luminescent properties of oxazine dye dimers

Spectral and luminescent properties were studied for chemical dimers and molecular aggregates of Nile Red oxazine dye in solutions. Chemical bonding of two oxazine dye molecules leads to the formation of a dimer whose spectral behavior is in close agreement with the exciton model constructed for “physical” molecular aggregates. Chemical dimers luminesce, whereas dimers formed because of van der Waals interactions do not.     

New phosphonate-substituted tricarbocyanines and their interaction with bovine serum albumin

New tricarbocyanine dyes with phosphonate groups (2, 3) were synthesized and their binding constants to bovine serum albumin (BSA) were determined. The binding constants of the synthesized tricarbocyanines and cardiogreen (1) (K_b ~ 10⁵ M^–1) are similar, indicating an insignificant contribution of the Coulomb interaction to the complex formation, which is determined by the polymethine chain interaction with BSA. The fluorescence lifetimes attest to the formation of two types of complexes: the lifetime of the dye complex with BSA with a major contribution (~80%) is 740–800 ps, and a lifetime of ~210 ps corresponds to the complex of dye aggregates with BSA.     

Aggregation of sensitizing dyes in solution and their adsorption onto silver halides

The formation of dye dimers and higher aggregates in solution as a function of dye structure and environmental variables are considered. These factors, together with silver halide composition and crystal habit, are also examined in regard to their influence on surface spectra, dye orientation and forces involved in adsorption of dyes at silver halide substrates.     

Adsorption behavior of methylene blue and its congeners on a stainless steel surface

Methylene blue and its congeners as model dyes were adsorbed onto stainless steel particles at different ionic strengths, pH values, and ethanol contents, and the adsorption mechanism was investigated. A Fourier transform infrared spectroscopy (FTIR) analysis of the dyes adsorbed on the stainless steel plate was carried out to determine the orientations of the adsorbed dyes on stainless steel surface. The adsorption isotherms for all the dyes tested were approximated by a Langmuir equation (Q=Kq(m)C/(1+KC)) in most cases except under strongly basic conditions. From the ionic strength and ethanol content dependencies of the K value in the Langmuir equations, both the electrostatic and hydrophobic interactions were indicated to contribute to the adsorption of the dyes at neutral pH. By comparing the K and q(m) values for the methylene blue congeners and with the aid of the FTIR analyses, it was found that the kind of substituent groups at most positions of the polyheterocycles of methylene blue strongly affects the adsorption behavior, particularly the area occupied by an adsorbed dye molecule, the affinity for the stainless steel surface, and the orientation of the adsorbed dye molecule on the stainless steel surface.     

Comparative studies on biophysical interactions between 4-dicyanomethylene-2,6-dimethyl-4H-pyran (DDP) with bovine serum albumin (BSA) and human serum albumin (HSA) via photophysical approaches and molecular docking techniques

Photophysical studies of 4-Dicyanomethylene-2,6-Dimethyl-4H-Pyran (DDP) dye with globular proteins, Human Serum Albumin (HSA) and Bovine Serum Albumin (BSA) were carried out in aqueous solution. An isosbestic point resulted on the addition of serum albumins, which signifies a complex or an equilibrium state of DDP dye with albumin. Addition of BSA to DDP dye results in a fluorescence enhancement accompanied with a significant hypsochromic shift, whereas with that of HSA, a fluorescence quenching with a considerable blue shift resulted. Excited state studies of DDP dye with serum albumins portray that the role of binding sites of dye with albumins vary considerably and the nature of interaction is presumably attributed to combined hydrogen-bonding and hydrophobic interactions. Molecular docking studies of DDP dye with albumins and two other derivatives 4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) dye and 4-(Dicyanomethylene)-2-methyl-6-(4-t-buyl)-4H-pyran (DCT) dyes with BSA and HSA elucidates that the hydrogen-bonding interaction accompanied with several hydrophobic, pi–pi an pi–alkyl interactions coexist between dye and albumins. The binding energy, intermolecular energy and stability of the DDP, DCM and DCT dyes through docking techniques with albumins authenticate that the dye predominantly acts as hydrogen-bonding acceptor site and the protein molecule as the donor. DDP dye prefers to exist in four different binding sites of HSA, whereas, in the case of BSA, the most preferred site is found to be hydrophobic domain (site I). Interestingly, the most preferred site of DCT dye is III A subdomain of HSA, whereas DCM dye is oriented towards I B subdomain. DDP and DCT are smaller in size and reside in the domain preferred for smaller ligands (II A and IIIA) as resulted in several drugs-HSA interaction whereas DCM dye which is categorized as medium to larger ligand based on the extended structure resides in the most favoured site IB. Fluorescence techniques in combination with molecular docking methods elucidate binding characteristics and the domain in which the dye resides in a micro heterogeneous environment is established in this study.     

Potentiometric determination of the stability constants of the fluoroborate-dye complexes used in colorimetric analysis for boron

An extensive bibliography on the determination of boron by means of tetrafluoroborate-dye complexes is given. The stability constants of the fluoroborate—dye complexes are calculated from potentiometric measurements with an Orion fluoroborate ion-selective electrode, for the following nineteen dyes: methylene blue, methylene green, new methylene blue N, thionine, toluidine blue O, malachite green, brilliant green, crystal violet, fuchsine, methyl green, methyl violet, Victoria blue B, brilliant cresyl blue, Nile blue A, rhodamine B, rhodamine 6G, pyronine Y, safranine T and Janus green B. The solubilities of these dyes have been determined by spectrophotometry.     

Supramolecular organization of toluidine blue dye in solid amorphous phases

Toluidine blue (TB) dye molecules are intensively utilized for large-area photophysics applications such as carcinoma detection, photoinactivation of bacteria, biosensors, and photovoltaic cells. Understanding the nature of the TB aggregation state becomes an essential point of the research process in order to know the structure-function relationship and to foresee technological applications of this class of metachromatic-dye molecules. However, no structural information on toluidine blue is available in the literature, maybe because of the poor crystalline character of the aggregate. Here, we present the first structural determination of TB organic molecules using the energy dispersive X-ray diffraction technique. The investigation highlights dimeric arrangements of stacked molecules in antiparallel fashion, forming a superstructure of two dimers in a transverse arrangement. The behavior of the TB higher aggregates indicates that these dye molecules, in spite of repulsion due to similar charge (cationic dyes), undergo self-aggregation to form helical conformations.     

Effect of Poly(methacrylic acid) on Photoinduced Processes with Cyanine Dyes in Aqueous Solutions

The cyanine dyes thiamonomethinecyanine (I), thiacarbocyanine (II), and thiadicarbocyanine (III) in an aqueous poly(methacrylic acid) (PMA) solution form different molecular species: monomers anchored to PMA, dimers, and H aggregates, in proportions determined by the [dye]/[PMA] concentration ratio. Each molecular species is characterized by its own probabilities of radiative and nonradiative transitions: the absence of photoisomerization for I–IIIdimers and H aggregates, the absence of fluorescence for H aggregates of IIand III, the capability of transition to a triplet state for PMA-anchored monomers I–III, and considerable enhancement of intersystem crossing to the triplet state for the dimers of II.     

Supramolecular host-guest systems as frameworks for excitation energy transfer.

The antenna behavior of rhodamine 6G and methylene blue loaded novel host supramolecular frameworks is investigated. The geometrical constraints of these supramolecular hosts allows the cationic dye molecules encapsulating within the parallel channels to form novel host-guest systems. The cationic dyes are close together that self-quenching of electronic excitation energy can occur. The excitation energy transfer occurs from rhodamine 6G as a donor (D) to methylene blue as an acceptor (A) within supramolecular systems filled with a mixture of both dyes.     

Interaction between dyes and polyelectrolytes. XIII. Effect of dye aggregation on the excitation energy transfer between bound dyes

Effect of polyanions on the aggregation of methylene blue (MB) was investigated spectrophotometrically. The following polyanions were used: potassium poly(vinyl sulfate), potassium poly(styrenesulfonate), sodium poly(methacrylate), and sodium poly(acrylate). The state of aggregation was largely dependent on the kind of polyanion and polyanion-MB ratio. MB-photo-sensitized isomerization of cis-p-(phenylazo)phenyltrimethylammonium iodide(cis-PTA) to the transisomer was used advantageously to investigate the effect of dye aggregation on the triplet excitation energy transfer between cationic dyes bound to polyanions. Although the efficiency of the excitation energy transfer between MB and cis-PTA was enhanced by the addition of polyanions, the formation of highly aggregated MB reduced the efficiency of the excitation energy transfer. Correlation with the dye aggregation induced by polyanions and the efficiency of excitation energy transfer between dyes was discussed.