Dark‐red‐emitting CdTe/Cd1‐xZnxS core/shell quantum dots: preparation and properties

CdTe nanocrystals (NCs) were fabricated through an organic synthesis. The growth and properties of CdTe NCs depended strongly on the preparation conditions. In a reaction system of octadecene and tetradecylphosphonic acid (TDPA), the growth was slow. CdTe NCs with cubic‐like morphology were created in trioctylamine (TOA) using octadecylphosphonic acid (ODPA)‐CdO or TDPA‐CdO as precursors. The TOA and ODPA system gives rise to NCs with high photoluminescence (PL) efficiencies (12%). A Cd_xZn_1‐xS shell coating on the CdTe core, gave rise to tunable dark red PL (630–670 nm). The morphology and PL properties of the CdTe cores were drastically affected by shell coating and this determined the properties of CdTe/Cd_xZn_1‐xS NCs. Small CdTe NCs were easily coated with Cd_xZn_1‐xS shells. The resulting core/shell NCs revealed a spherical morphology. However, shell growth became slow when large CdTe cores were used. This is ascribed to the cores with a cubic‐like morphology. CdS interlayer plays an important role for the formation of the CdTe/Cd_xZn_1‐xS NCs because the experimental result indicated it is difficult to coat CdTe NCs with a ZnS shell. The core/shell NCs benefited from a Cd_xZn_1‐xS composite shell because CdTe/CdS NCs created via a similar procedure revealed a low PL efficiency. Copyright © 2012 John Wiley & Sons, Ltd.     

CdTe1‐xSex/Cd0.5Zn0.5S core/shell quantum dots: core composition and property

Alloy CdTe_1‐xSe_x quantum dots (QDs) have been fabricated by an organic route using Cd, Te and Se precursors in a mixture of trioctylamine and octadecylphosphonic acid at 280 °C. The variation of photoluminescence (PL) peak wavelength of the CdTe_1‐xSe_x QDs compared with CdTe QDs confirmed the formation of an alloy structure. The Se component drastically affected the stability of CdTe_1‐xSe_x QDs. A Cd_0.5Zn_0.5S shell coating on CdTe_1‐xSe_x cores was carried out using oleic acid as a capping agent. CdTe_1‐xSe_x/Cd_0.5Zn_0.5S core/shell QDs revealed dark red PL while a yellow PL peak was observed for the CdTe_1‐xSe_x cores. The PL efficiency of the core/shell QDs was drastically increased (less than 1% for the cores and up to 65% for the core/shell QDs). The stability of QDs in various buffer solutions was investigated. Core/shell QDs can be used for biological applications because of their high stability, tunable PL and high PL efficiency. Copyright © 2013 John Wiley & Sons, Ltd.     

Hydrothermal synthesis for high‐quality glutathione‐capped CdxZn1 – xSe and CdxZn1 – xSe/ZnS alloyed quantum dots and its application in Hg(II) sensing

High‐quality Cd_xZn_{1 – x}Se and Cd_xZn_{1 – x}Se/ZnS core/shell quantum dots (QDs) emitting in the violet–green spectral range have been successfully prepared using hydrothermal methods. The obtained aqueous Cd_xZn_{1 – x}Se and Cd_xZn_{1 – x}Se/ZnS QDs exhibit a tunable photoluminescence (PL) emission (from 433.5 nm to 501.2 nm) and a favorable narrow photoluminescence bandwidth [full width at half maximum (FWHM): 30–42 nm]. After coating with a ZnS shell, the quantum yield increases from 40.2% to 48.1%. These Cd_xZn_{1 – x}Se and Cd_xZn_{1 – x}Se/ZnS QDs were characterized by transmission electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy and Fourier transform infrared (FTIR) spectroscopy. To further understand the alloying mechanism, the growth kinetics of Cd_xZn_{1 – x}Se were investigated through measuring the fluorescence spectra and X‐ray diffraction spectra at different growth intervals. The results demonstrate that the inverted ZnSe/CdSe core/shell structure is formed initially after the injection of Cd²⁺. With further heating, the core/shell structured ZnSe/CdSe is transformed into alloyed Cd_xZn_{1 – x}Se QDs with the diffusion of Cd²⁺ into ZnSe matrices. With increasing the reaction temperature from 100 °C to 180 °C, the duration time of the alloying process decreases from 210 min to 20 min. In addition, the cytotoxicity of Cd_xZn_{1 – x}Se and Cd_xZn_{1 – x}Se/ZnS QDs were investigated. The results indicate that the as‐prepared Cd_xZn_{1 – x}Se/ZnS QDs have low cytotoxicity, which makes them a promising probe for cell imaging. Finally, the as‐prepared Cd_xZn_{1 – x}Se/ZnS QDs were utilized to ultrasensitively and selectively detect Hg²⁺ ions with a low detection limit (1.8 nM).     

Cation Substitution of Solution‐Processed Cu2ZnSnS4 Thin Film Solar Cell with over 9% Efficiency

To alleviate the limitations of pure sulfide Cu₂ZnSnS₄ (CZTS) thin film, such as band gaps adjustment, antisite defects, secondary phase and microstructure, Cadmium is introduced into CZTS thin film to replace Zn partially to form Cu₂Zn_1?xCd_xSnS₄ (CZCTS) thin film by low‐cost sol–gel method. It is demonstrated that the band gaps and crystal structure of CZCTS thin films are affected by the change in Zn/Cd ratio. In addition, the ZnS secondary phase can be decreased and the grain sizes can be improved to some degree by partial replacement of Zn with Cd in CZCTS thin film. The power conversion efficiency of CZTS solar cell device is enhanced significantly from 5.30% to 9.24% (active area efficiency 9.82%) with appropriate ratio of Zn/Cd. The variation of device parameter as a function of Zn/Cd ratio may be attributed to the change in electronic structure of the bulk CZCTS thin film (i.e., phase change from kesterite to stannite), which in turn affects the band alignment at the CZCTS/buffer interface and the charge separation at this interface.     

Zinc and cadmium in 5-aminolevulinic acid dehydratase. Equilibrium,kinetic, and 113Cd-nmr-studies

5-Aminolevulinic acid dehydratase (ALAD) from bovine liver contains zinc that is partially lost during the isolation of the enzyme. ALAD has its maximal activity at 10^?5 M ZnCl₂. It binds 7.4 Zn per octameric protein with an association constant of 5.3 × 10⁶ M^?1. ALAD is inactivated by 1,10-phenanthroline or ethylenediaminetetraacetic acid (EDTA) but not by monodentate anions like cyanide or sulfide. After removal of zinc by chelating agents, the enzyme activity may be restored by Zn²⁺ or Cd²⁺. Removal or zinc by EDTA increases K_M 60-fold and decreases V_max to about $\text{1}\text{2}$ of its original value. The ¹¹³Cd nuclear magnetic resonance spectrum of the enzyme reconstituted with ¹¹³Cd-acetate exhibits a single sharp resonance signal at 79 ppm. It does not change by the addition of substrate but disappears when the inhibitor lead acetate is added. Therefore, an immediate interaction between the metal ion of the enzyme and the substrate is excluded, whereas lead changes the environment of cadmium and probably of zinc too.     

Zinc to cadmium replacement in the A. thaliana SUPERMAN Cys₂ His₂ zinc finger induces structural rearrangements of typical DNA base determinant positions

Among heavy metals, whose toxicity cause a steadily increasing of environmental pollution, cadmium is of special concern due to its relatively high mobility in soils and potential toxicity at low concentrations. Given their ubiquitous role, zinc fingers domains have been proposed as mediators for the toxic and carcinogenic effects exerted by xenobiotic metals. To verify the structural effects of zinc replacement by cadmium in zinc fingers, we have determined the high resolution structure of the single Cys₂His₂ zinc finger of the Arabidopsis thaliana SUPERMAN protein (SUP37) complexed to the cadmium ion by means of UV–vis and NMR techniques. SUP37 is able to bind Cd(II), though with a dissociation constant higher than that measured for Zn(II). Cd‐SUP37 retains the ββα fold but experiences a global structural rearrangement affecting both the relative orientation of the secondary structure elements and the position of side chains involved in DNA recognition: among them Ser17 side chain, which we show to be essential for DNA binding, experiences the largest displacement. © 2011 Wiley Periodicals, Inc. Biopolymers 95: 801‐810, 2011.     

Kinetic characterization of Zinc transport process and its inhibition by Cadmium in isolated rat renal basolateral membrane vesicles: In vitro and In vivo studies

We firstly characterized zinc uptake phenomenon across basolateral membrane vesicles (BLMVs) isolated from normal rat kidney. The process was found to be time, temperature, and substrate concentration dependent, and displayed saturability. Zn²⁺ uptake was competitively inhibited in the presence of 2 mM Cd with Ki of 3.9 mM. Zinc uptake was also inhibited in the presence of sulfhydryl reacting compound suggesting involvement of {–}SH groups in the transport process. Further, to elucidate the effect of in vivo Cd on zinc transport in BLMVs, Cd nephrotoxicity was induced by subcutaneous administration of CdCl₂ at dose of 0.6 mg/kg/d for 5 days in a week for 12 weeks. An indolent renal failure developed in Cd exposed rats was accompanied with a significantly high urinary excretion of Cd²⁺, Zn²⁺ and proteins. The histopathology and electron microscopy of kidneys of Cd exposed rats documented changes of proximal tubular degeneration. Notably, Cd content in renal cortex of Cd exposed rats was 215 μg/g tissue that was higher than the critical concentration of Cd in kidneys which was associated with significantly higher Zn and metallothionein (MT) contents. Zinc uptake in BLMVs isolated from kidneys of Cd exposed rats was significantly reduced. Further, kinetic studies revealed that decrease in zinc uptake synchronized with decrease in maximal velocity (V_max) and increase in affinity constant which is suggestive of decreased number of active zinc transporters. Furthermore, conformational modulation of Zn transporter in BLM was further supported by observed variation in transition temperature for zinc transport in BLMVs isolated from Cd-exposed kidney.     

Comparison of the Structures of the Metal-thiolate Binding Site in Zn(II)-, Cd(II)-, and Hg(II)-Metallothioneins Using Molecular Modeling Techniques

Abstract

The first fully energy-minimized structures for a series of structurally related metal complexes of the important mammalian metal binding protein metallothionein are described. The structures were calculated based on structural information obtained from existing spectroscopic and crystallographic data, and minimized using molecular mechanics (MM2) techniques. A two domain structure, with stoichiometrics of M(II)₃?(S_cys)₉ and M(II)₄?(S_cys)₁₁ where M = zinc(II), cadmium(II), and mercury(II), was assembled and minimized. The resultant three-dimensional structure closely resembled that of rat liver Cd₅Zn₂?MT 1 obtained by analysis of x-ray diffraction data [A. H. Robbins, D. E. McRee, M. Williamson, S. A. Collett, N. H. Xuong, W. F. Furey, B. C. Wang and C. D. Stout, J. Mol. Biol. 221, 1269–1293 (1991)]. Minimized structures for Zn₇?MT, Cd₇?MT, and Hg₇?MT are reported. Deep crevices that expose the metal-thiolate clusters are seen in each structure. However, for the mercury-containing protein, much of the mercury-thiolate structure is visible and it is proposed that this provides access for extensive interaction between solvent water molecules and the mercury(II), resulting in the observed distortion away from tetrahedral geometry for Hg₇MT. Volume calculations are reported for the protein metallated with 7 Zn(II), Cd(II), or Hg(II). A series of structural changes calculated for the step-wise isomorphous replacement of Zn(II) by Cd(II) and Hg(II) in the Zn₄S₁₁ α domain are shown.     

Development of nutritious rice with high zinc/selenium and low cadmium in grains through QTL pyramiding

Enriching zinc (Zn) and selenium (Se) levels, while reducing cadmium (Cd) concentration in rice grains is of great benefit for human diet and health. Large natural variations in grain Zn, Se, and Cd concentrations in different rice accessions enable Zn/Se‐biofortification and Cd‐minimization through molecular breeding. Here, we report the development of new elite varieties by pyramiding major quantitative trait loci (QTLs) that significantly contribute to high Zn/Se and low Cd accumulation in grains. A chromosome segment substitution line CSSL^GCC7 with the PA64s‐derived GCC7 allele in the 93‐11 background, exhibited steadily higher Mn and lower Cd concentrations in grains than those of 93‐11. This elite chromosome segment substitution line (CSSL) was used as the core breeding material to cross with CSSLs harboring other major QTLs for essential mineral elements, especially CSSL^GZC6 for grain Zn concentration and CSSL^GSC5 for grain Se concentration. The CSSL^GCC7+GZC6 and CSSL^GCC7+GSC5 exhibited lower Cd concentration with higher Zn and Se concentrations in grains, respectively. Our study thus provides elite materials for rice breeding targeting high Zn/Se and low Cd concentrations in grains.     

Phytoextraction potential of soils highly polluted with cadmium using the cadmium/zinc hyperaccumulator Sedum plumbizincicola

Abstract

A three-crop repeated phytoextraction experiment was conducted using four soils (S1–S4) highly polluted with cadmium (Cd) and two enhanced phytoextraction pot experiments using the most polluted soil (S4) to investigate the feasibility of Cd removal from highly polluted soils using the Cd/zinc (Zn)-hyperaccumulator Sedum plumbizincicola. Shoot biomass showed no significant difference during the repeated phytoextraction experiment on the four test soils and shoot Cd content showed a decreasing trend with the three consecutive crops in soils S1, S2, and S3 but not in soil S4. The Cd removal rates in soils S1, S2, S3, and S4 were 84.5, 81.6, 45.3, and 32.4%, respectively. Rice straw application increased Cd extraction efficiency by 42.6% but the addition of ethylenediaminedisuccinic acid, biochar or nitrogen had no effect on Cd remediation. Shoot Cd content increased significantly (1.57 and 1.71 times, respectively) at low (S₀-1) and high (S₀-2) sulfur addition rates. Soil extractable-Cd in S₀-1 after the experiment showed no significant difference from the control but was 2.43 times higher in S₀-2 than in the control. These results indicate that S. plumbizincicola shows good prospects for the phytoextraction of Cd from highly polluted soils and that the process can be enhanced by adding straw and/or sulfur to the soil.     

Cadmium and zinc influx characteristics by intact corn (Zea mays L.) seedlings

Summary Cadmium and zinc uptake parameters were determined for intact corn (Zea mays L.) seedlings grown for 15 and 22 in nutrient solutions containing levels of Cd and Zn that were similar to those found in soil solutions. Uptake of both elements was assumed to follow Michaelis-Menten kinetics. Calculations were based on the concentrations of free ionic Cd (Cd²⁺) and Zn (Zn²⁺) rather than the total solution concentration. Rates of Zn uptake were measured by determining depletion of Zn for periods of up to 30 h from solutions containing initial concentrations of 1.5 and 10μmol Zn 1⁻¹. Depletion curves suggested that Zn uptake characteristics were similar at both levels of Zn in solution. The Imax for Zn uptake decreased from 550 to 400 pmol m⁻² root surface s⁻¹ between 16 and 22 d of growth while Km decreased from 2.2 to 1.5 μmol Zn²⁺ 1⁻¹. Cadmium uptake parameters were measured by controlling Cd²⁺ activities in nutrient solution betwen 6.3 to 164 nmol l⁻¹ by continuous circulation of nutrient solution through a mixed-resin system. Imax for Cd uptake was 400 pmol m⁻² root surface s⁻¹ at 15 and 22 d of growth. The magnitude of Km increased from 30 to 100 nmol Cd²⁺ 1⁻¹ during this time period. The Km value suggests that corn is efficient for Cd uptake. The results of these uptake studies are consistent with the observed uptake of Zn and Cd by corn seedlings in soils.     

Expression of a Neurospora crassa zinc transporter gene in transgenic Nicotiana tabacum enhances plant zinc accumulation without co‐transport of cadmium

Zinc (Zn) is an essential micronutrient required for growth and development of all organisms. Deficiency of Zn in humans is widespread, affecting 25% of world population and efforts are underway to develop crop plants with high levels of Zn in their edible parts. When strategies for enhancing Zn in crop plants are designed, it is essential to exclude cadmium (Cd), a toxic analogue of Zn. In the present work, a high affinity and high specificity zinc transporter gene (tzn1) from Neurospora crassa was cloned and introduced into Nicotiana tabacum with the objective of enhancing the potential of plants for zinc acquisition. When grown in hydroponic medium spiked with ⁶⁵Zn, transgenic plants showed enhanced accumulation of Zn (up to 11 times) compared to control plants, which was confirmed further by environmental scanning electron microscopy coupled with Energy Dispersive X‐ray analysis. More importantly, no significant difference in uptake of Cd²⁺, Fe²⁺, Ni²⁺, Cu²⁺, Mn²⁺ and Pb²⁺ between the transgenic and control plants was observed. The present studies have shown that Neurospora crassa tzn1 is a potential candidate gene for developing transgenic plants for improving Zn uptake, without co‐transport of Cd and may have implications in Zn phytofortification and phytoremediation.     

Structural and optical properties of Cu‐doped ZnS nanoparticles formed in chitosan/sodium alginate multilayer films

Chitosan/alginate multilayers were fabricated using a spin‐coating method, and ZnS:Cu nanoparticles were generated within the network of two natural polysaccharides, chitosan and sodium alginate. The synthesized nanoparticles were characterized using an X‐ray diffractometer (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and atomic force microscopy (AFM). The results showed that cubic zinc blende‐structured ZnS:Cu nanoparticles with an average crystal size of ~ 3 nm were uniformly distributed. UV–vis spectra indicate a large quantum size effect and the absorption edge for the ZnS:Cu nanoparticles slightly shifted to longer wavelengths with increasing Cu ion concentrations. The photoluminescence of the Cu‐doped ZnS nanoparticles reached a maximum at a 1% doping level. The ZnS:Cu nanoparticles form and are distributed uniformly in the composite multilayer films with a surface average height of 25 nm. Copyright © 2013 John Wiley & Sons, Ltd.     

Biosorption of cadmium by a Cd2+-hyperresistant Bacillus cereus strain HQ-1 newly isolated from a lead and zinc mine

A Cd²⁺-hyperresistant bacterial strain HQ-1 was isolated from a lead–zinc mine. The strain was characterized and identified as Bacillus cereus based on morphology, physiological tests and 16S rRNA gene analysis. The minimal inhibitory concentration of Cd²⁺ for the bacterium was 0.012 mol/l. Isotherms for cadmium (Cd) biosorption by cells of B. cereus strain HQ-1 were investigated. The equilibrium data could be fitted by a Langmuir isotherm equation. The possible functional sites that might be influenced by the sorption were determined. The results indicate that this B. cereus strain has excellent potential for biosorption of Cd. Physiological characterization of the isolate also indicates possible application of this strain for bioremediation of sites with Cd contamination.     

Removal of Contaminating Metals from Soil by Sulfur-Based Bioleaching and Biogenic Sulfide-Based Precipitation

The potential of a hybrid process incorporating sulfur-based bioleaching and sulfide-based precipitation for treatment of metal-contaminated soil was examined in batch-type experiments. The sulfur-based soil bioleaching process with Acidithiobacillus sp. could be initiated at a wide range of initial pH from 4.0 to 6.3. After 15 days, 98% of Zn, 89% of Cu and 79% of Cd was bioleached. The gaseous sulfides recycling from Desulfovibrio sp.-mediated sulfate-reducing reactor via N₂ sparging efficiently treated metal-loaded soil leachate. With a sulfide/metal ratio of 3.0, 88% of Zn, 100% of Cu and 95% of Cd were precipitated, resulting in effluent metal concentrations of 3.5 mg Zn²⁺/L, 0.2 mg Cu²⁺/L and 0.03 mg Cd²⁺/L.

Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.     

Solid phase speciation of Zn and Cd in zinc smelter effluent-irrigated soils

Solubility of metal in contaminated soils is a key factor which controls the phytoavailability and toxic effects of metals on soil environment. The chemical equilibria of metal ions between soil solution and solid phases govern the solubility of metals in soil. Hence, an attempt was made to identify the probable solid phases (minerals), which govern the solubility of Zn²⁺ and Cd²⁺ in zinc smelter effluent-irrigated soils. Estimation of free ion activities of Zn²⁺ (pZn²⁺) and Cd²⁺ (pCd²⁺) by Baker soil test indicated that metal ion activities were higher in smelter effluent-irrigated soils as compared to that in tubewell water-irrigated soils. Identification of solid phases further reveals that free ion activity of Zn²⁺ and Cd²⁺ in soil highly contaminated with Zn and Cd due to long-term irrigation with zinc smelter effluent is limited by the solubility of willemite (Zn₂SiO₄) in equilibrium with quartz and octavite (CdCO₃), respectively. However, in case of tubewell water-irrigated soil, franklinite (ZnFe₂O₄) in equilibrium with soil-Fe and exchangeable Cd are likely to govern the activity of Zn²⁺ and Cd²⁺ in soil solution, respectively. Formation of highly soluble minerals namely, willemite and octavite indicates the potential ecological risk of Zn and Cd, respectively in smelter effluent irrigated soil.     

EFFECT OF ZINC AVAILABILITY ON GROWTH,MORPHOLOGY, AND NUTRIENT INCORPORATION IN A COASTAL AND AN OCEANIC DIATOM1

We investigated the effect of Zn availability on growth rate (μ), cell morphology, and elemental stoichiometry and incorporation rate in two marine diatoms. For the coastal diatom Skeletonema costatum (Grev.) Cleve, the half‐saturation constant (K_S) for growth was 4.1 pM Zn²⁺, and growth ceased at ≤ 2.6 pM Zn²⁺, whereas for the oceanic diatom Thalassiosira oceanica Hasle, K_S was 0.5 pM Zn²⁺, and μ remained at ～40%μ_max even at 0.3 pM Zn²⁺. Under Zn‐limiting (Zn‐L) conditions, S. costatum decreased cell size significantly, leading to an 80% increase in surface area to volume ratio (SA/V) at Zn²⁺ of 3.5 pM compared to Zn‐replete (Zn‐R) conditions (at Zn²⁺ of 13.2 pM), whereas T. oceanica’s morphology did not change appreciably. Cell quotas of C, N, P, Si, and chl a significantly decreased under Zn limitation in S. costatum (at Zn²⁺ of 3.5 pM), whereas Zn limitation in T. oceanica (at Zn²⁺ of 0.3 pM) had little effect on quotas. Elemental stoichiometry was ～85C:10N:9Si:1P and 81C:9N:5Si:1P for S. costatum, and 66C:5N:2Si:1P and 52C:6N:2Si:1P for T. oceanica, under Zn‐R and Zn‐L conditions, respectively. Incorporation rates of all elements were significantly reduced under Zn limitation for both diatoms, but particularly for Si in S. costatum, and for C in T. oceanica, despite its apparent tolerance of low Zn conditions. With [Zn²⁺] in some parts of the ocean being of the same order (～0.2 to 2 pM) as our low Zn conditions for T. oceanica, our results support the hypothesis that in situ growth and C acquisition may be limited by Zn in some oceanic species.     

A Multisite Strategy for Enhancing the Hydrogen Evolution Reaction on a Nano‐Pd Surface in Alkaline Media

The hydrogen evolution reaction (HER) on a noble metal surface in alkaline media is more sluggish than that in acidic media due to the limited proton supply. To promote the reaction, it is necessary to transform the alkaline HER mechanism via a multisite catalyst, which has additional water dissociation sites to improve the proton supply to an optimal level. Here, this study reports a top‐down strategy to create a multisite HER catalyst on a nano‐Pd surface and how to further fine‐tune the areal ratio of the water dissociation component to the noble metal surface in core/shell‐structured nanoparticles (NPs). Starting with Pd/Fe₃O₄ core/shell NPs, electrochemical cycling is used to tune the coverage of iron (oxy)hydroxide on a Pd surface. The alkaline HER activity of the core/sell Pd/FeO_x (OH)_2?2x NPs exhibits a volcano‐shaped correlation with the surface Fe species coverage. This indicates an optimum coverage level where the rates of both the water dissociation step and the hydrogen formation step are balanced to achieve the highest efficiency. This multisite strategy assigns multiple reaction steps to different catalytic sites, and should also be extendable to other core/shell NPs to optimize their HER activity in alkaline media.     

31P-NMR study of pig intestinal brush-border membrane structure: effect of zinc and cadmium ions

³¹P-NMR experiments on intact pig small intestine brush-border membrane vesicles (BBMV) and detergent-solubilized membranes gave direct insights into the organization of the phospholipids (PL) and their interaction with zinc and cadmium ions. Various endogenous PL were identified from well resolved BBM micelle spectra. These experiments revealed a strong interaction of Zn²⁺ and Cd²⁺ with the negatively charged phosphatidylinositol and phosphatidylserine. In BBM micelles, a progressive time-dependent PL degradation occurred in the absence of ions and indicated the presence of active phospholipases. The presence of zinc inhibited the degradation process whereas cadmium had the opposite influence. ³¹P spectra of BBMV were carefully characterized. Neither zinc nor cadmium affected the PL bilayer structural organization. A degradation of PL, monitored by the increase of the inorganic phosphate (P _i) signal, also occurred in vesicles but to a lesser extent than in micelles. A 2/3 internal, 1/3 external PL asymmetry was observed in the absence and presence of ions. Offprint requests to: P. Ripoche