Self-aggregation of Methylene Blue in aqueous medium and aqueous solutions of Bu4NBr and urea

Patil, Kesharsingh J.; Pawar, Rani P.; Talap, Pandurang

doi:10.1039/b005370h

Cited by 176 publications

(142 citation statements)

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“…We found a K D value of 2.6 × 10 −4 M which is in good agreement with the value reported by Patil et al 20 (2.9 × 10 −4 M, at 27°C) and by Rabinowitch and Epstein 34 (2.8 × 10 −4 M, at 26.7°C). The ε M and ε D ∕2 values, at different wavelengths, were extracted from the slope and origin of the linear fit and used to generate the individual monomer and dimer spectra [dashed lines in Fig.…”

Section: Calculation Of Monomer and Dimer Concentrationssupporting

confidence: 82%

“…hydrogen bonding, and Van der Waals forces. 19,20 The coupling between monomers results in a splitting of the singlet excited state into two states, of lower and upper energies, which manifests by a splitting of the absorption band of the monomer (Fig. 3).…”

Section: Photoacoustic Lifetime Contrast Imagingmentioning

confidence: 99%

“…For concentrations greater than 50 μM, we observed a progressive blue shift of the isosbestic point that can be attributed to the formation of a small amount of trimers (with absorption maximum at 580 nm). 33 In this model (adapted from Patil et al 20 ), the dimer dissociation constant K D is defined as Eq. (2):…”

Section: Calculation Of Monomer and Dimer Concentrationsmentioning

confidence: 99%

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Photoacoustic lifetime contrast between methylene blue monomers and self-quenched dimers as a model for dual-labeled activatable probes

et al. 2013

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Abstract. Activatable photoacoustic probes efficiently combine the high spatial resolution and penetration depth of ultrasound with the high optical contrast and versatility of molecular imaging agents. Our approach is based on photoacoustic probing of the excited-state lifetime of methylene blue (MB), a fluorophore widely used in clinical therapeutic and diagnostic applications. Upon aggregation, static quenching between the bound molecules dramatically shortens their lifetime by three orders of magnitude. We present preliminary results demonstrating the ability of photoacoustic imaging to probe the lifetime contrast between monomers and dimers with high sensitivity in cylindrical phantoms. Gradual dimerization enhancement, driven by the addition of increasing concentrations of sodium sulfate to a MB solution, showed that lifetime-based photoacoustic probing decreases linearly with monomer concentration. Similarly, the addition of 4 mM sodium dodecyl sulfate, a concentration that amplifies MB aggregation and reduces the monomer concentration by more than 20-fold, led to a signal decrease of more than 20 dB compared to a solution free of surfactant. These results suggest that photoacoustic imaging can be used to selectively detect the presence of monomers. We conclude by discussing the implementation of the monomer-dimer contrast mechanism for the development of an enzyme-specific activatable probe.

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Section: Calculation Of Monomer and Dimer Concentrationssupporting

confidence: 82%

Section: Photoacoustic Lifetime Contrast Imagingmentioning

confidence: 99%

Section: Calculation Of Monomer and Dimer Concentrationsmentioning

confidence: 99%

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Photoacoustic lifetime contrast between methylene blue monomers and self-quenched dimers as a model for dual-labeled activatable probes

et al. 2013

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“…Absorbance was found to be proportional to concentration up to 50 M at 340 nm and at 613 nm but only up to 3 M at 663 nm. The major reason for this is that the MB monomer has a higher absorbance at 663 nm (ε ϭ 75 mM Ϫ1 cm Ϫ1 ) than the dimer (45). As the K diss of the dimer is approximately 200 M in phosphate buffers at pH 7.0, one expects low ε values when measurements are done at total MB concentrations above 50 M. This explains, e.g., the low ε value of 45 mM Ϫ1 cm Ϫ1 reported previously (51).…”

Section: Resultsmentioning

confidence: 99%

Interactions of Methylene Blue with Human Disulfide Reductases and Their Orthologues fromPlasmodium falciparum

Buchholz

Schirmer

Eubel

et al. 2008

Antimicrob Agents Chemother

150

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Methylene blue (MB) has experienced a renaissance mainly as a component of drug combinations against Plasmodium falciparum malaria. Here, we report biochemically relevant pharmacological data on MB such as rate constants for the uncatalyzed reaction of MB at pH 7.4 with cellular reductants like NAD(P)H (k ‫؍‬ 4 M ؊1 s ؊1 ), thioredoxins (k ‫؍‬ 8.5 to 26 M ؊1 s ؊1 ), dihydrolipoamide (k ‫؍‬ 53 M ؊1 s ؊1 ), and slowly reacting glutathione. As the disulfide reductases are prominent targets of MB, optical tests for enzymes reducing MB at the expense of NAD(P)H under aerobic conditions were developed. The product leucomethylene blue (leucoMB) is auto-oxidized back to MB at pH 7 but can be stabilized by enzymes at pH 5.0, which makes this colorless compound an interesting drug candidate. MB was found to be an inhibitor and/or a redox-cycling substrate of mammalian and P. falciparum disulfide reductases, with the k cat values ranging from 0.03 s ؊1 to 10 s ؊1 at 25°C. Kinetic spectroscopy of mutagenized glutathione reductase indicates that MB reduction is conducted by enzyme-bound reduced flavin rather than by the active-site dithiol Cys 58 /Cys 63 . The enzyme-catalyzed reduction of MB and subsequent auto-oxidation of the product leucoMB mean that MB is a redox-cycling agent which produces H 2 O 2 at the expense of O 2 and of NAD(P)H in each cycle, turning the antioxidant disulfide reductases into pro-oxidant enzymes. This explains the terms subversive substrate or turncoat inhibitor for MB. The results are discussed in cellpathological and clinical contexts. Methylene blue (MB or MBϩ ) [also known as methylthionine hydrochloride or 3,7-bis(dimethylamino)phenothiazin-5-ium chloride] was the very first synthetic compound to be used as a drug. Paul Ehrlich, who introduced the concept of modern target-based chemotherapy using MB as an example, and Paul Guttmann described the compound as being an effective antimalarial agent (28). Despite its beneficial antimalarial activity, the drug disappeared from the scene because up-and-coming compounds such as chloroquine were more effective; in addition, soldiers resented taking MB because of inevitable but harmless side effects: green or blue urine and bluish sclerae (47, 55).After MB was revisited as an antimalarial agent (6, 53) and found to be an inhibitor of Plasmodium falciparum glutathione (GSH) reductase (GR) (23), it was studied as a partner drug in antimalarial drug combinations (2,39,48,51).Compared with other antiparasitic agents, MB is affordable and registered in most countries (as the treatment of choice for acute and chronic methemoglobinemia [16,17,36]), and it can be made internationally available in sufficient dosages (51). The price for treating a malaria episode in a child with an MB-containing drug combination would be less than €0.50 (40). Drug resistance has not been reported for MB and could not be provoked in rodent malaria models (52, 53).Because of its favorable properties, including the differential staining of cell biological structures and protein cr...

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“…The maximum of absorbance of Azure B is also shifted from 646 to 651 nm; similar behavior has been observed before for methylene blue. 18 To understand how to maximize the system performance, we have to understand the photophysical and physicochemical behavior of the chromophore. The reaction cycle is shown in Scheme 1.…”

Section: ■ Introductionmentioning

confidence: 99%

Chaotropic Agents Boosting the Performance of Photoionic Cells

et al. 2015

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Photoionic cells are a simple and scalable concept for direct solar energy storage, where the redox fuels produced by the photoreaction are separated in different phases to prevent recombination. The presence of chaotropic agents such as urea, that break the structure of water, was found to drastically enhance the quantum yield; a 10-fold increase of quantum yield to over 13% was achieved by addition of chaotropes into a system based on the reductive quenching of Azure B by Co(II)EDTA in water and the extraction of the leuco dye in 1,2-dichloroethane. ■ INTRODUCTIONSolar energy conversion is one of the global challenges for a sustainable economy. At present, two major routes are being followed: photovoltaic (PV) systems to generate electricity and solar thermal collectors to generate heat. However, all PV technologies must immediately distribute the produced electricity either to a storage system or to the electrical grid, irrespective of demand. Recently, we have proposed a simple and scalable concept for solar energy storage: photoionic cells. 1 This is an extension of the early work of Rabinowitch et al. 2−5 and Albery et al. 6−9 on photogalvanic cells (essentially photochemical concentration cells), but in photoionic cells the charge separation takes place at the interface between two immiscible electrolyte solutions. 1 The system is based on a dye−quencher couple where, upon light excitation, the excited dye (for example thionine) is quenched in the aqueous solution by the quencher (e.g., [Co(II)EDTA] 2− ) to form both an oxidized quencher (e.g., [Co(III)EDTA] − ) and reduced neutral dye (leucothionine) that partitions to the organic phase. The two immiscible liquid phases are separated, and the redox energy is stored in the respective electrolyte solutions. These two solutions can then be electrochemically discharged in a flow cell to generate electricity on demand. The main potential advantage of photoionic cells over classical solar cells is the unique ability to convert solar energy directly into "redox fuels" that can be consumed only when electricity is required to generate electricity to meet a specific demand.The original thionine−cobalt EDTA system 1 has some drawbacks, like low potential difference between the two photogenerated redox couples and very low solubility of thionine, which limits the quantum yield of the system. Another serious issue that has to be considered is dye aggregation, leading to significant loss of performance. In order to overcome such drawbacks, in this work we have explored Azure B (H 2 AzB) as an interesting alternative in the development of systems capable of capturing, converting, and storing solar energy in the form of reduced and oxidized photoproducts separated by a polarized interface formed between two immiscible electrolyte solutions.We have systematically studied the effects of the physicochemical and photophysical properties of a dye on the quantum yield, and we have optimized the reaction conditions in the photoionic cells in order to maximize the ...

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Self-aggregation of Methylene Blue in aqueous medium and aqueous solutions of Bu4NBr and urea

Cited by 176 publications

References 11 publications

Photoacoustic lifetime contrast between methylene blue monomers and self-quenched dimers as a model for dual-labeled activatable probes

Photoacoustic lifetime contrast between methylene blue monomers and self-quenched dimers as a model for dual-labeled activatable probes

Interactions of Methylene Blue with Human Disulfide Reductases and Their Orthologues fromPlasmodium falciparum

Chaotropic Agents Boosting the Performance of Photoionic Cells

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