Spectral Studies of Lanthanide Interactions with Membrane Surfaces

Abstract

We have monitored the interactions of the series of trivalent lanthanide cations with the thylakoid membrane surface of spinach chloroplasts using two complementary spectral techniques. Measurements of the fluorescence emission of the extrinsic probe 2-p-toluidinonaphthalene-6-sulfonate (TNS) and the absorbance of the intrinsic chromophore chlorophyll provide two sensitive means of characterizing the dependence of the cationmembrane interaction on the nature of the cation. In these systems, added lanthanide cations adsorb onto the membrane surface to neutralize exposed segments of membrane-embedded protein complexes. The lanthanideinduced charge neutralization increases the proximity of added TNS anion to the membrane surface as evidenced by variations in the TNS fluorescence level and wavelength of maximum emission. Our results reveal a strong dependence of TNS fluorescence parameters on both lanthanide size and total orbital angular momentum L value. Lanthanides with greater charge density (small size and/or low L value) enhance the TNS fluorescence level to a greater extent. A possible origin for the lanthanide-dependent TNS fluorescence levels is suggested in terms of a heterogeneity in the number and type of TNS binding sites. In the absence of the probe TNS, lanthanide-induced changes in the chlorophyll absorption spectrum reflect the shrinkage of chloroplasts accompanying thylakoid membrane stacking. Absorbance increases in the 500-660 nm region, attributed to increases in light scattering arising from the membrane structural reorganization, reveal a dependence on lanthanide identity. The data are consistent with the proposal that larger lanthanides with smaller enthalpies of hydration induce more significant membrane appression. These investigations illustrate a novel utilization of lanthanides in cation binding studies by employing their chemical and physical differences rather than their similarities in luminescence properties

Biologically Relevant Lyotropic Liquid Crystalline Phases in Mixtures of n-Octyl β-d-Glucoside and Water. Determination of the Phase Diagram by Fluorescence Spectroscopy

“…Furthermore, the observed fluorescence signal can be simultaneously indicative of multiple aggregates as a consequence of the measurable fluorescence intensity in a range of solvents and the sensitivity of the wavelength of maximum emission (λ max ) to the polarity of prodan’s environment 17–23 . For example, the emission λ max ranges from 402 nm in the nonpolar solvent cyclohexane to 522 nm in aqueous solution 17,19–21 . The fluorescence signature of prodan in surfactant aggregates is thus a composite spectrum with contributions from the probe populations within various microdomains of the aggregate(s) present.…”

“…The fluorophore prodan (6-propionyl-2-(dimethylamino)naphthalene, Figure ) is an ideal probe for examining the phase behavior of aqueous surfactant systems. Prodan’s solubility in a wide range of solvents enables its distribution into an array of single-phase and multiphasic regions having different polarities. − Furthermore, the observed fluorescence signal can be simultaneously indicative of multiple aggregates as a consequence of the measurable fluorescence intensity in a range of solvents and the sensitivity of the wavelength of maximum emission (λ max ) to the polarity of prodan’s environment. − For example, the emission λ max ranges from 402 nm in the nonpolar solvent cyclohexane to 522 nm in aqueous solution. ,− The fluorescence signature of prodan in surfactant aggregates is thus a composite spectrum with contributions from the probe populations within various microdomains of the aggregate(s) present. Thus, the significant advantages of this innovative approach include (1) the use of a single technique to demarcate distinct phase regions of the binary system, (2) the application of a more generally accessible instrumental technique to the study of phase behavior, (3) the utilization of a technique with the sensitivity to identify both single-phase and multiphase regions, and (4) the determination of a phase diagram in a more rapid and streamlined fashion.…”

Blocking effect of a phospholipid monolayer on ion transfer at a liquid | liquid interface and its electrochemical control

“…It is well known that the binding of a multivalent cation to a phopholipid membrane promotes a structure change of the membrane, which has been investigated by nuclear magnetic resonance [12,13], calorimetry [14], spectrophotometry [15], atomic force microscopy [16] and electrochemistry at lipid-supported electrodes [17,18]. However, the serious effect of the multivalent cation on the permeability across the PC monolayer adsorbed at a liquid j liquid interface has not been observed.…”

Uptake and distribution of rare earth elements in rice seeds cultured in fertilizer solution of rare earth elements

“…The rapid growth responses of oats treated with La 3 , Ca 2 , K and NH 4 were measured and it was found that La did not behave like super calcium in its action upon the spontaneous growth response (Harmet, 1979). The series interactions of trivalent lanthanide cations with the thylakoid membrane surface of spinach chloroplasts veri®ed that the added lanthanide cations were adsorbed onto the membrane surface to neutralize exposed segments of the membrane-embedded protein complex (Karukstis et al, 1995). Selective biosorption of lanthanide from an aqueous solution was studied and the lanthanide biosorption equilibrium obeyed the Brunaure±Emmett±Teller isotherm model, which indicated multilayer adsorption (Texier et al, 1999).…”