RESUMO
Zinc is required for virtually all biological processes. In plasma, Zn2+ is predominantly transported by human serum albumin (HSA), which possesses two Zn2+-binding sites of differing affinities (sites A and B). Fatty acids (FAs) are also transported by HSA, with seven structurally characterized FA-binding sites (named FA1-FA7) known. FA binding inhibits Zn2+-HSA interactions, in a manner that can impact upon hemostasis and cellular zinc uptake, but the degree to which binding at specific FA sites contributes to this inhibition is unclear. Wild-type HSA and H9A, H67A, H247A, and Y150F/R257A/S287A (FA2-KO) mutant albumins were expressed in Pichia pastoris. Isothermal titration calorimetry studies revealed that the Zn2+-binding capacity at the high-affinity Zn2+ site (site A) was reduced in H67A and H247A mutants, with site B less affected. The H9A mutation decreased Zn2+ binding at the lower-affinity site, establishing His9 as a site B ligand. Zn2+ binding to HSA and H9A was compromised by palmitate, consistent with FA binding affecting site A. 13C-NMR experiments confirmed that the FA2-KO mutations prohibited FA binding at site FA2. Zn2+ binding to the FA2-KO mutant was unaffected by myristate, suggesting binding at FA2 is solely responsible for inhibition. Molecular dynamics studies identified the steric obstruction exerted by bound FA in site FA2, which impedes the conformational change from open (FA-loaded) to closed (FA-free) states, required for Zn2+ to bind at site A. The successful targeting of the FA2 site will aid functional studies exploring the interplay between circulating FA levels and plasma Zn2+ speciation in health and disease.
Assuntos
Ácidos Graxos , Albumina Sérica Humana , Zinco , Zinco/metabolismo , Humanos , Sítios de Ligação , Ácidos Graxos/metabolismo , Albumina Sérica Humana/metabolismo , Albumina Sérica Humana/química , Ligação ProteicaRESUMO
Mucin expression and glycosylation patterns on cancer cells differ markedly from healthy cells. Mucin 1 (MUC1) is overexpressed in several solid tumors and presents high levels of aberrant, truncated O-glycans (e.g., Tn antigen). Dendritic cells (DCs) express lectins that bind to these tumor-associated carbohydrate antigens (TACAs) to modulate immune responses. Selectively targeting these receptors with synthetic TACAs is a promising strategy to develop anticancer vaccines and to overcome TACA tolerance. In this work, we prepared, via a solid phase peptide synthesis approach, a modular tripartite vaccine candidate, incorporating a high-affinity glycocluster based on a tetraphenylethylene scaffold, to target the macrophage galactose-type lectin (MGL) on antigen presenting cells. MGL is a C-type lectin receptor that binds Tn antigens and can route them to human leukocyte antigen class II or I, making it an attractive target for anticancer vaccines. Conjugation of the glycocluster to a library of MUC1 glycopeptides bearing the Tn antigen is shown to promote uptake and recognition of the TACA by DCs via MGL. In vivo testing revealed that immunization with the newly designed vaccine construct bearing the GalNAc glycocluster induced a higher titer of anti-Tn-MUC1 antibodies compared to the TACAs alone. Additionally, the antibodies obtained bind a library of tumor-associated saccharide structures on MUC1 and MUC1-positive breast cancer cells. Conjugation of a high-affinity ligand for MGL to tumor-associated MUC1 glycopeptide antigens has a synergistic impact on antibody production.
Assuntos
Mucina-1 , Vacinas , Humanos , Mucina-1/química , Galactose/metabolismo , Glicopeptídeos/química , Antígenos Glicosídicos Associados a Tumores/química , Lectinas Tipo C/metabolismo , Células Dendríticas , Macrófagos/metabolismoRESUMO
The comprehension of molecular recognition phenomena demands the understanding of the energetic and kinetic processes involved. General equations valid for the thermodynamic analysis of any observable that is assessed as a function of the concentration of the involved compounds are described, together with their implementation in the AFFINImeter software. Here, a maximum of three different molecular species that can interact with each other to form an enormous variety of supramolecular complexes are considered. The corrections currently employed to take into account the effects of dilution, volume displacement, concentration errors and those due to external factors, especially in the case of ITC measurements, are included. The methods used to fit the model parameters to the experimental data, and to generate the uncertainties are described in detail. A simulation tool and the so called kinITC analysis to get kinetic information from calorimetric experiments are also presented. An example of how to take advantage of the AFFINImeter software for the global multi-temperature analysis of a system exhibiting cooperative 1:2 interactions is presented and the results are compared with data previously published. Some useful recommendations for the analysis of experiments aimed at studying molecular interactions are provided.
Assuntos
Calorimetria/métodos , Proteínas/química , Software , Fenômenos Biofísicos , Cinética , Ligação Proteica , Temperatura , TermodinâmicaRESUMO
We have studied the kinetics of phase separation and gel formation in a low-dispersity colloid - non-adsorbing polymer system with long range attraction using small-angle light scattering. This system exhibits two-phase and three-phase coexistence of gas, liquid and crystal phases when the strength of attraction is between 2 and 4kBT and gel phases when the strength of attraction is increased. For those samples that undergo macroscopic phase separation, whether to gas-crystal, gas-liquid or gas-liquid-crystal coexistence, we observe dynamic scaling of the structure factor and growth of a characteristic length scale that behaves as expected for phase separation in fluids. In samples that gel, the power law associated with the growth of the dominant length scale is not equal to 1/3, but appears to depend mainly on the strength of attraction, decreasing from 1/3 for samples near the coexistence region to 1/27 at 8kBT, over a wide range of colloid and polymer concentrations.
RESUMO
Heparin is the most common anticoagulant used in clinical practice but shows some downsides such as short half-life (for the high molecular weight heparin) and secondary effects. On the other hand, its low molecular weight analogue cannot be neutralized with protamine, and therefore cannot be used in some treatments. To address these issues, we conjugated polyethylene glycol (PEG) to heparin reducing end (end-on) via oxime ligation and studied the interactions of the conjugate (Hep-b-PEG) with antithrombin III (AT) and protamine. Isothermal titration calorimetry showed that Hep-b-PEG maintains the affinity to AT. Dynamic light scattering demonstrated that the Hep-b-PEG formed colloidal stable nanocomplexes with protamine instead of large multi-molecular aggregates, associated with heparin side effects. The in vitro (human plasma) and in vivo experiments (Sprague Dawley rats) evidenced an extended half-life and higher anticoagulant activity of the conjugate when compared to unmodified heparin.
Assuntos
Heparina , Protaminas , Animais , Ratos , Humanos , Heparina/efeitos adversos , Protaminas/química , Ratos Sprague-Dawley , Anticoagulantes/farmacologia , Anticoagulantes/químicaRESUMO
The neuronal calcium sensor 1 (NCS-1), an EF-hand Ca2+ binding protein, and Ric-8A coregulate synapse number and probability of neurotransmitter release. Recently, the structures of Ric-8A bound to Gα have revealed how Ric-8A phosphorylation promotes Gα recognition and activity as a chaperone and guanine nucleotide exchange factor. However, the molecular mechanism by which NCS-1 regulates Ric-8A activity and its interaction with Gα subunits is not well understood. Given the interest in the NCS-1/Ric-8A complex as a therapeutic target in nervous system disorders, it is necessary to shed light on this molecular mechanism of action at atomic level. We have reconstituted NCS-1/Ric-8A complexes to conduct a multimodal approach and determine the sequence of Ca2+ signals and phosphorylation events that promote the interaction of Ric-8A with Gα. Our data show that the binding of NCS-1 and Gα to Ric-8A are mutually exclusive. Importantly, NCS-1 induces a structural rearrangement in Ric-8A that traps the protein in a conformational state that is inaccessible to casein kinase II-mediated phosphorylation, demonstrating one aspect of its negative regulation of Ric-8A-mediated G-protein signaling. Functional experiments indicate a loss of Ric-8A guanine nucleotide exchange factor (GEF) activity toward Gα when complexed with NCS-1, and restoration of nucleotide exchange activity upon increasing Ca2+ concentration. Finally, the high-resolution crystallographic data reported here define the NCS-1/Ric-8A interface and will allow the development of therapeutic synapse function regulators with improved activity and selectivity.
Assuntos
Cálcio , Fatores de Troca do Nucleotídeo Guanina , Cálcio/metabolismo , Fosforilação , Fatores de Troca do Nucleotídeo Guanina/metabolismo , Transdução de Sinais , Chaperonas Moleculares/metabolismoRESUMO
We have studied the interplay between phase separation and crystallization in a colloid-polymer mixture along one kinetic pathway in samples which exhibit three-phase equilibrium coexistence. In analogy with atomic systems, the range of the effective attractive interaction between colloids is sufficiently long to allow for a stable liquid phase. By direct imaging in microgravity on the International Space Station, we observe a unique structure, a "crystal gel," that occurs when gas-liquid phase separation arrests due to crystallites within the liquid domain spanning the cell. From the initial onset of spinodal decomposition until arrest caused by this structure, the kinetics of phase separation remain largely unaffected by the formation of the third phase. This dynamic arrest appears to result from the stiffness of the crystalline strands exceeding the liquid-gas interfacial tension.
RESUMO
The study of the interaction of a cationic polymer as PEI with phospholipids membranes is of special relevance for gene therapy because the PEI is a potential nonviral vector to transfer DNA in living cells. We used light scattering, zeta potential, and electron transmission microscopy to characterize the interaction between DMPG and DOPC liposomes with PEI as a function of the charge molar ratio, pH, temperature, initial size of the liposomes, and headgroup of the lipids. Unexpectedly, a double charge inversion and two different ranges of PEI-liposome concentrations where an aggregation occurs were found, when the proper pH and initial size of the liposomes were chosen. The interaction is analyzed in terms of the interaction potential proposed by Velegol and Thwar for colloidal particles with a nonuniform surface charge distribution. Results show a remarkable dependence of the stability on pH and the initial size of the liposomes, which explains the low reproducibility of the experiments if no special care is taken in preparing the samples. Comparatively small changes in the pH or in the liposomes size lead to a completely different stability behavior.
Assuntos
Lipossomos/química , Polietilenoimina/química , Concentração de Íons de Hidrogênio , Luz , Lipossomos/síntese química , Tamanho da Partícula , Espalhamento de Radiação , Propriedades de Superfície , TemperaturaRESUMO
Polyethylenimine (PEI) has been demonstrated as an efficient DNA delivery vehicle both in vitro and in vivo. There is a consensus that PEI-DNA complexes enter the cells by endocytosis and escape from endosomes by the so-called "proton sponge" effect. However, little is known on how and where the polyplexes are de-complexed for DNA transcription and replication to occur inside the cell nucleus. To better understand this issue, we (i) tracked the cell internalization of PEI upon transfection to human epithelial cells and (ii) studied the interaction of PEI with phospholipidic layers mimicking nuclear membranes. Both the biological and physicochemical experiments provided evidence of a strong binding affinity between PEI and the lipidic bilayer. Firstly, confocal microscopy revealed that PEI alone could not penetrate the cell nucleus; instead, it arranged throughout the cytoplasm and formed a sort of aureole surrounding the nuclei periphery. Secondly, surface tension measurements, fluorescence dye leakage assays, and differential scanning calorimetry demonstrated that a combination of hydrophobic and electrostatic interactions between PEI and the phospholipidic monolayers/bilayers led to the formation of stable defects along the model membranes, allowing the intercalation of PEI through the monolayer/bilayer structure. Results are also supported by molecular dynamics simulation of the pore formation in PEI-lipidic bilayers. As discussed throughout the text, these results might shed light on a the mechanism in which the interaction between PEI and the nucleus membrane might play an active role on the DNA release: on the one hand, the PEI-membrane interaction is anticipated to facilitate the DNA disassembly from the polyplex by establishing a competition with DNA for the PEI binding and on the other hand, the forming defects are expected to serve as channels for the entrance of de-complexed DNA into the cell nucleus. A better understanding of the mechanism of transfection of cationic polymers opens paths to development of more efficiency vectors to improve gene therapy treatment and the new generation of DNA vaccines.
Assuntos
Polietilenoimina , Vacinas de DNA , Endossomos , Terapia Genética , Humanos , TransfecçãoRESUMO
The interaction between polyethylenimine (PEI) and phospholipid bilayers plays an important role in several biophysical applications such as DNA transfection of target cells. Despite considerable investigation into the nature of the interaction between PEI and phospholipid bilayers, the physical process remains poorly understood. In this paper, we study the impact of PEI on 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) vesicles as a function of salt concentration using several techniques including dynamic (DLS) and static (SLS) light scattering, differential scanning calorimetry (DSC), and nuclear magnetic resonance (NMR). At low salt concentration, vesicles aggregate, leading to the formation of stable clusters whose final size depends on the PEI concentration. At high salt concentration the system does not aggregate; DSC and NMR data reveal that the PEI penetrates into the bilayer, and SLS measurements are consistent with PEI crossing the bilayer. The transfectional ability of PEI is discussed in terms of these results.
Assuntos
Bicamadas Lipídicas , Fosfolipídeos/química , Polietilenoimina/química , Varredura Diferencial de Calorimetria , DNA/genética , Espectroscopia de Ressonância Magnética , TransfecçãoRESUMO
An understanding of the thermodynamics of the complexation process utilized in sustaining drug release in clay matrices is of great importance. Several characterisation techniques as well as isothermal calorimetry were utilized in investigating the adsorption process of a model cationic drug (diltiazem hydrochloride, DIL) onto a pharmaceutical clay system (magnesium aluminium silicate, MAS). X-ray powder diffraction (XRPD), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and optical microscopy confirmed the successful formation of the DIL-MAS complexes. Drug quantification from the complexes demonstrated variable behaviour in the differing media used with DIL degrading to desacetyl diltiazem hydrochloride (DC-DIL) in the 2 M HCl media. Here also, the authors report for the first time two binding processes that occurred for DIL and MAS. A competitor binding model was thus proposed and the thermodynamics obtained suggested their binding processes to be enthalpy driven and entropically unfavourable. This information is of great importance for a formulator as care and consideration should be given with appropriate media selection as well as the nature of binding in complexes.
RESUMO
This study reports the use of ITC in understanding the thermodynamics occurring for a controlled release system in which complexation has been exploited. In this study, a model drug, propranolol hydrochloride (PPN) was complexed with magnesium aluminium silicate (MAS) and these complexes were used in combination with polyethylene oxide (PEO) as a hydrophilic carrier at various concentrations to sustain the release of PPN. DSC, XRPD, ATR-FTIR and SEM/EDX were successfully used in characterising the produced complexes. 2D- SAXS data patterns for MAS and the produced complexes were shown to be symmetric and circular with the particles showing no preferred orientation at the nanometre scale. ITC studies showed differences between PPN adsorption onto MAS compared with PPN adsorption onto a MAS-PEO mixture. At both temperatures studied the binding affinity Ka was greater for the titration of PPN into the MAS-PEO mixture (5.37E + 04 ± 7.54E + 03 M at 25 °C and 8.63E + 04 ± 6.11E + 03 M at 37 °C), compared to the affinity obtained upon binding between PPN and MAS as previously reported suggesting a stronger binding with implications for the dissolution process. MAS-PPN complexes with the PEO polymer compacts displayed desired manufacturing and formulation properties for a formulator including, reduced plastic recovery therefore potentially reducing the risk of cracking/splitting and on tooling wear, controlled release of PPN at a significantly low (5%) polymer level as well as a zero-order release profile (case II transport) using up to 50% polymer level.
Assuntos
Compostos de Alumínio/análise , Liberação Controlada de Fármacos , Compostos de Magnésio/análise , Nanocompostos/análise , Polímeros/análise , Espalhamento a Baixo Ângulo , Silicatos/análise , Compostos de Alumínio/metabolismo , Compostos de Magnésio/metabolismo , Polímeros/metabolismo , Silicatos/metabolismo , Espectroscopia de Infravermelho com Transformada de Fourier/métodosRESUMO
The interaction between two serum blood proteins, namely human serum albumin (HSA) and human immunoglobulin G (IgG), with 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) liposomes has been studied in detail using dynamic light scattering, flow cytometry, enzyme-linked immunosorbent assay (ELISA), electrophoretic mobility, differential scanning calorimetry (DSC), and surface tension measurements. HSA and IgG interact with liposomes forming molecular aggregates that remain stable at protein concentrations beyond those of total liposome coverage. Both HSA and IgG penetrate into the liposome bilayer. An ELISA assay indicates that the Fc region of IgG is the one that is immersed in the DMPC membrane. The liposome-protein interaction is mainly of electrostatic nature, but an important hydrophobic contribution is also present.
Assuntos
Dimiristoilfosfatidilcolina/química , Imunoglobulina G/química , Lipossomos/química , Albumina Sérica/química , Varredura Diferencial de Calorimetria , Ensaio de Desvio de Mobilidade Eletroforética , Ensaio de Imunoadsorção Enzimática , Citometria de Fluxo , Humanos , Luz , Espalhamento de Radiação , Tensão Superficial , TemperaturaRESUMO
In this chapter, we describe an original protocol based on ITC experiments and data analysis with the software AFFINImeter to get information of heparin-AT interactions relevant for the elucidation of the anticoagulant activity of heparins. This protocol is used to confirm the presence of the bioactive pentasaccharide with anticoagulant activity in heparins and to determine the amount of this pentasaccharide in the sample. Here we have applied this protocol to the characterization of low molecular weight heparins.
Assuntos
Anticoagulantes/química , Calorimetria/métodos , Heparina de Baixo Peso Molecular/química , Polissacarídeos/química , Humanos , SoftwareRESUMO
Standard molecular binding isothermal titration calorimetric (ITC) experiments are designed to get thermodynamic information: changes in Gibbs energy, enthalpy, and entropy associated to the studied process. Traditionally, the kinetic information contained in the ITC raw signal has been ignored. For a usual one-step process, this corresponds to the rate constants for the association and the dissociation of the complex (kon and koff). The availability of highly sensitive ITC instruments with low response time, together with the development of theoretical methods and of public software for the proper analysis of the signal, cancels any reason for not retrieving this kinetic information. Here we describe how to further exploit ITC experiments of simple one-step interactions by using the software AFFINImeter.The method is exemplified using a standard reference system for thermodynamic and kinetic molecular binding analysis: the interaction of carbonic anhydrase (CA) with its inhibitor 4-carboxybenzenesulfonamide (4-CBS) at several temperatures. It is to be emphasized that old experiments initially designed and executed just for thermodynamic analysis can be readily recycled by using AFFINImeter to retrieve the previously ignored kinetic information.
Assuntos
Calorimetria/métodos , Proteínas/química , Software , Termodinâmica , Entropia , Cinética , Ligação Proteica , TemperaturaRESUMO
A study of the fractal dimension of the aggregation of three different types of large unilamellar vesicles, formed by egg yolk phosphatidylcholine (EYPC), dimyristoyl-phosphocholine (DMPC), and dipalmitoyl-phosphocholine (DPPC), in the presence of La3+, is presented. Aggregate liposome fractal dimensions were calculated by two methods, aggregation kinetics, using the approaches diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation (RLCA) and angle-scattering light dispersion. Electrophoretic measurements show a similar variation of the zeta potential (zeta potential) for EYPC and DPPC, with a small increase of initial positive values. However, the zeta potential of DMPC changes from a initial negative value to near zero with increasing La3+ concentration. The evolution of the aggregate sizes was followed by light scattering. DPPC and DMPC show a RLCA regimen growth at low La3+ concentrations and a DLCA regimen at higher concentrations. In the case of EYPC, the final size of aggregation strongly depends on La3+ concentration. The calculated fractal dimension is in the range 1.8 to 2.1.
Assuntos
Coloides/química , Cristalização/métodos , Lantânio/química , Modelos Químicos , Modelos Moleculares , Fosfolipídeos/química , Lipossomas Unilamelares/química , Simulação por Computador , Fractais , Fluidez de Membrana , Tamanho da PartículaRESUMO
Lanthanide ions such as La3+ and Gd3+ are well known to have large effects on the structure of phospholipid membranes. Unilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC) were prepared by sonication method and confirmed by transmission electron microscopy. The effects of concentration of gadolinium ions Gd3+ on DPPC unilamellar vesicles in aqueous media were studied by different techniques. As physical techniques, photon correlation spectroscopy, electrophoretic mobility, and differential scanning calorimetry were used. The theoretical predictions of the colloidal stability of liposomes were followed using the Derjaguin-Landau-Verwey-Overbeek theory. Changes in the size of liposomes and high polydispersities values were observed as Gd3+ concentration increases, suggesting that this cation induces the aggregation of vesicles. Electrophoretic mobility measurements on unilamellar vesicles as a function of Gd3+ ion concentration show that the vesicles adsorb Gd3+ ions. Above Gd3+ concentrations of 0.1 mol dm-3, the zeta potential and light scattering measurements indicate the beginning of aggregation process. For comparison with similar phospholipids, the zeta potential of phosphatidylcholine interacting with Gd3+ was measured, showing an analogous behavior. Differential scanning calorimetry has been used to determine the effect of Gd3+ on the transition temperature (Tc) and on the enthalpy (DeltaHc) associated with the process.
Assuntos
1,2-Dipalmitoilfosfatidilcolina/química , Cátions/química , Gadolínio/química , Lipossomos/química , Fosfatidilcolinas/química , Varredura Diferencial de Calorimetria , Coloides , Microscopia Eletrônica de Transmissão , TemperaturaRESUMO
The aim of this study is to characterize vesicles obtained by the incorporation of the semifluorinated alkane, (perfluoro-n-hexyl)ethane (diblock F6H2) to a standard lipid, egg yolk phosphatidylcholine (PC). Large unilamellar vesicles (LUVs), prepared by extrusion, were characterized by fluorescence spectroscopy, zeta potential (zeta-potential) and light scattering. By using the fluorescence spectroscopy technique, the anisotropy of l,6-diphenyl-l,3,5-hexatriene (DPH) probe at different temperatures was determined. It was demonstrated that F6H2 is placed inside of the lipid bilayer and that the hydrocarbon acyl chain in the bilayers has higher viscosity in the presence of fluoroalkane. The zeta-potential of the PC-F6H2 system is negative and increases (in absolute value) from -10 to -19 mV when the temperature rises from 10 to 25 degrees C, this last value keeping practically constant with a further increase of temperature. The adsorption of K+ ions on the liposome surface was measured by zeta-potential. This adsorption originates a sudden increase of the initial zeta-potential followed by a slight decrease with K+ concentration. The application of the DLVO theory of colloidal stability showed a growing dependence of the DLVO potential with K+ concentration and consequently a increasing stability.
Assuntos
Alcanos/química , Fluorocarbonos/química , Lipossomos/química , Micelas , Fosfatidilcolinas , Alcanos/metabolismo , Difenilexatrieno/química , Difenilexatrieno/metabolismo , Fluorocarbonos/metabolismo , Cinética , Luz , Bicamadas Lipídicas/química , Bicamadas Lipídicas/metabolismo , Lipossomos/metabolismo , Espalhamento de Radiação , Espectrometria de Fluorescência , Temperatura , TermodinâmicaRESUMO
Isothermal titration calorimetry (ITC) has long been used for kinetic studies in chemistry, but this remained confined to enzymatic studies in the biological field. In fact, the biological community has long had the tendency of ignoring the kinetic possibilities of ITC considering it solely as a thermodynamic technique, whereas surface plasmon resonance is seen as the kinetic technique par excellence. However, the primary signal recorded by ITC is a heat power which is directly related to the kinetics of the reaction. Here, it is shown how this kinetic signal can be recovered by using kinITC, the kinetic extension of ITC. The theoretical basis of kinITC is detailed for the most common situation of a second-order reaction A+B Ω C characterized by kinetic parameters kon, koff. A simplified kinITC-ETC method based upon the determination of an "Equilibration Time Curve" (ETC) is presented. The ETC is obtained by automatic determination of the "effective end" of each injection. The method is illustrated with experimental results with a comparison to Surface Plasmon Resonance (SPR) data. kon values were obtained in a wide range, from 10(3) to 0.5×10(6) M(-1) s(-1). All procedures were implemented in the program AFFINImeter (https://www.affinimeter.com/).
Assuntos
Calorimetria/métodos , CinéticaRESUMO
The influence of La(3+) on the colloidal stability of liposomes made up by two zwitterionic phospholipids, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-palmitoyl-2-[16-fluoropalmitoyl-phosphatidylcholine (F-DPPC), in aqueous media has been investigated by dynamic light scattering and electrophoretic mobility. The critical aggregation concentration (c.a.c.) of La(3+) for F-DPPC and DPPC liposomes were experimentally obtained, and the results were compared with theoretical predictions using the Derjaguin-Landau-Verwey-Overbeek theory. In order to evaluate the influence of the state of the bilayer on the stability of liposomes, all experiments were performed at temperatures below and above the chain-melting phase-transition temperature of lipids (transition temperature of lipids). Changes in the size of both types of liposomes and high values of polydispersity in the presence of La(3+) showed that these ions induce aggregation of liposomes at 25 °C and at 60 °C. At 25 °C, when the bilayer of F-DPPC liposomes is interdigited, DPPC liposomes are more resistant to aggregation than the liposomes formed with F-DPPC. However, this difference disappears at 60 °C, when both bilayers have the same conformation. The experimental results also indicate that the c.a.c. is higher at 60 °C than at 25 °C for both types of liposomes. In fact, it has been observed by dynamic light scattering measurements that aggregation of liposomes at 25 °C can be prevented by increasing the solution temperature for La(3+) concentrations near to the c.a.c. Moreover, the behavior of these liposomes in the presence of the ion was studied at temperatures above and below the transition temperature of the phospholipids.