Interaction of merocyanine 540 with cations of physiological solutions

Merocyanine 540 adsorbed on polyethylenimine-functionalized graphene oxide nanocomposites as a turn-on fluorescent sensor for bovine serum albumin

We suggest a simple, fast, sensitive and selective BSA sensor designed by assembling MC540 molecules on PEI–GO nanocomposites.

Temperature dependence of the lipid packing in thylakoid membranes studied by time- and spectrally resolved fluorescence of Merocyanine 540

The lipid packing of thylakoid membranes is an important factor for photosynthetic performance. However, surprisingly little is known about it and it is generally accepted that the bulk thylakoid lipids adopt the liquid-crystalline phase above -30 degrees C and that a phase transition occurs only above 45 degrees C. In order to obtain information on the nature of the lipid microenvironment and its temperature dependence, steady-state and time-resolved fluorescence measurements were performed on the fluorescence probe Merocyanine 540 (MC540) incorporated in isolated spinach thylakoids and in model lipid systems (dipalmitoyl phosphatidylcholine and dioleoyl phosphatidylethanolamine) adopting different phases. It is demonstrated that the degree and way of incorporation differs for most lipid phases--upon selective excitation at 570 nm, the amplitude of the fluorescence component that corresponds to membrane-incorporated MC540 is about 20% in gel-, 60% in rippled gel-, and 90% in liquid-crystalline and inverted hexagonal phase, respectively. For thylakoids, the data reveal hindered incorporation of MC540 (amplitude about 30% at 7 degrees C) and marked spectral heterogeneity at all temperatures. The incorporation of MC540 in thylakoids strongly depends on temperature. Remarkably, above 25 degrees C MC540 becomes almost completely extruded from the lipid environment, indicating major rearrangements in the membrane.

Multispectral imaging of ion transport in neutral carrier-based cation-selective membranes

BACKGROUND

High-resolution spectroscopic imaging of the cross section of ion-selective membranes during real-time electrochemical measurements is termed spectroelectrochemical microscopy (SpECM). SpECM is aimed for optimizing the experimental conditions in mass transport controlled ion-selective electrode (ISE) membranes for improved detection limit.

METHODS

The SpECM measurements are performed in a thin layer electrochemical cell. The key element of the cell is a membrane strip spacer ring assembly which forms a two compartment electrochemical cell. The cell is placed onto the stage of a microscope and the membrane strip is positioned in the center of the field of view. A slice of the image is focused onto the entrance slit of the imaging spectrometer.

RESULTS

SpECM has been used for the determination of the diffusion coefficients of different membrane ingredients and for the quantitative assessment of the charged site concentrations in ISE membranes and membrane plasticizers. In addition, changes in the concentration profiles of the ionophore (free and complexed) and charged mobile sites inside the ISE membranes are documented upon the application of large external voltages.

CONCLUSIONS

This account demonstrates the power and advantages of SpECM, a multispectral imaging method for investigations of mass transport processes in ISE membranes during electrochemical measurements.

pH, serum proteins and ionic strength influence the uptake of merocyanine 540 by WiDr cells and its interaction with membrane structures

It has been suggested that selective uptake of photosensitizers is due to significantly lower pH of the interstitial fluid in tumors compared to normal tissue. Therefore, the cellular uptake of merocyanine 540 (MC 540) was examined at two pH values: 6.8+/-0.1 and 7.4+/-0.1. There was no difference in spectral properties (absorption and fluorescence maxima positions, fluorescence intensity) of the drug in the presence of increasing amounts of either human blood plasma or FCS (0-2%) at the two pH values investigated. Nevertheless, significantly higher amounts of the drug were taken up by WiDr cells at pH 6.8+/-0.1, both in the presence of 10% FCS and in the absence of FCS. The absorption spectra of MC 540 in the presence of egg phosphatidylcholine (PC) liposomes turned out to be NaCl concentration-dependent (0.00-0.30 mol l(-1)). Membrane fluidity, as measured by fluorescence anisotropy of diphenylhexatriene (DPH), was unchanged within the experimental error in the NaCl concentration range 0.01-0.30 mol l(-1). The spectral changes indicated an enhancement of the incorporation of MC 540 into lipid membranes with increasing ionic strength. Such a salt concentration dependence suggests a possible involvement of the surface potential in the interaction of MC 540 with lipid membranes. The results might provide an explanation of the pH dependency of the cellular uptake of MC 540 observed in this study.

A spectroscopic study of the fluorescence quenching interactions between biomedically important salts and the fluorescent probe merocyanine 540

The effects of several biologically important inorganic salts, including NaCl, NaI, NaBr, KCl, MgCl2, MgSO4 and CaCl2 on the electronic absorption and fluorescence spectra of Merocyanine 540 (MC-540) have been investigated in aqueous media at 25 degrees C. Depending on both the MC-540 concentration and the nature of salt, a new absorption band appears at about 515 nm, above the critical salt concentration (CSC), corresponding to salt-induced MC-540 aggregation. Several types of MC-540 fluorescence quenching by the salts are observed, according to their cationic charge and the nature of anion: in the case of monovalent ions (Na+, K+), a non-linear Stern-Volmer behaviour is observed, indicating variable contributions of dynamic and static quenching mechanisms, whereas for divalent alkaline-earth (Mg2+, Ca2+) ions, linear Stern-Volmer relationships are obtained. Using these results, an analytical quenchofluorimetric approach is proposed for the determination of magnesium ions.