Influence of Negatively Charged Interfaces on the Ground and Excited State Properties of Methylene Blue¶

Abstract

Properties of the ground and excited states of methylene blue (MB) were studied in negatively charged vesicles, normal and reverse micelles and sodium chloride solutions. All these systems induce dimer formation as attested by the appearance of the dimer band in the absorption spectra (lamdaD approximately 600 nm). In reverse micelles the dimerization constant (KD) corrected for the aqueous pseudophase volume fraction is two-three orders of magnitude smaller than KD of MB in water, and it does not change when W0 is increased from 0.5 to 10. Differences in the fluorescence intensity as a function of dimer-monomer ratio as well as in the resonance light scattering spectra indicate that distinct types of dimers are induced in sodium dodecyl sulfate (SDS) micelles and aerosol-OT (sodium dioctyl sulfoxinate, AOT) reversed micelles. The properties of the photoinduced transient species of MB in these systems were studied by time-resolved near infrared (NIR) emission (efficiency of singlet oxygen generation), by laser flash photolysis (transient spectra, yield and decay rate of triplets) and by thermal lensing (amount of heat deposited in the medium). The competition between electron transfer (dye*-dye) and energy transfer (dye*-O2) reactions was accessed as a function of the dimer-monomer ratio. The lower yield of electron transfer observed for dimers in AOT reverse micelles and intact vesicles compared with SDS micelles and frozen vesicles at similar dimer-monomer ratios is related with the different types of aggregates induced by each interface.

Changes in the Spin State and Reactivity of Cytochrome c Induced by Photochemically Generated Singlet Oxygen and Free Radicals

“…Diphenylacetaldehyde was purchased from Aldrich. Ile 7 -angiotensin III (AngIII), human adrenocorticotropic hormone fragments [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]), ␣-cyano-4-hydroxycinnamic acid, sinapinnic acid, and trifluoroacetic acid were obtained from Amersham Biosciences (Upsala, Sweden). Sequencing grade trypsin was purchased from Promega (Madison, WI).…”

“…Therefore, O 2 ( 1 ⌬ g )-mediated alterations in cytochrome c structure and reactivity can influence activation of caspases in the apoptosome. On the other hand, photodynamic generation of O 2 ( 1 ⌬ g ) is also accompanied by free radical production (34), and discriminating the effect of each reactive species on the cytochrome c structure still poses a challenge.…”

Optical Studies of the Methylene Blue-Semiconductor Nanocrystals Hybrid System

“…It is also a very good electron acceptor [1]. Common problems with this dye include its dimerization in the presence of interfaces [3] and its reduction to a photochemically inactive leuco-MB form under some conditions [4].…”

Plasmid DNA damage induced by singlet molecular oxygen released from the naphthalene endoperoxide DHPNO2 and photoactivated methylene blue

“…While dimeric form can predominantly generate free radical species by primary reaction mechanism, monomeric form can mainly generate 1 O 2 by secondary mechanisms in the presence of molecular oxygen ( Figure 1). 33 In the MB concentration used in this work (10 mM), MB is most likely in the monomeric form, 33 thus, generating predominantly 1 O 2 after photoactivation. Nevertheless, photo reduction of oxygen may be responsible for the production of some ROS, therefore in considering possible reactive species in photosensitized reactions, the participation of species such as H 2 O 2 , O 2 ·-and · OH must be considered along with 1 O 2 , and direct dye/substrate processes.…”