The diploma thesis deals with the preparation and characterization of catanionic complexes and their possible application to pharmaceutics and medicine. The catanionic complexes were prepared by mixing two oppositely charged surfactants with the concentration of 20 mmol·dm­3 in various volume ratios. Two systems were analyzed – CTAB + SDS and Septonex + SDS. Both systems were prepared in an aqueous and physiological environment. The turbidimetric analyses provided results of the intensity of turbidity of the prepared mixtures. The size and stability of the prepared particles were determined by DLS and ELS measurements. CTAB-rich samples showed significant viscosity changes and they were therefore characterized by rheological measurements. The results of this work show that the asymmetry of alkyl chains, surfactant selection, temperature, and ionic strength have a significant influence on the properties and self-assembly of surfactants in catanionic complexes.

Spinové vlny mají potenciál být použity jako nová platforma pro přenos a zpracování dat, protože mohou dosáhnout vlnových délek v rozsahu nanometrů a frekvencí v rozsahu terahertzů. K tomu, aby bylo možné navrhnout zařízení a logické obvody založené na spinových vlnách, je zapotřebí získat informace o prostorovém rozložení intenzity spinové vlny a pokud je to možné, také o jejich fázi. To lze měřit pomocí fázově rozlišeného fokuso-vaného Brillouinova rozptylu světla (µ -BLS). Předložená práce se zabývá rozšířením stávající optické sestavy o možnost měření fáze, kde doposud bylo možné měřit pouze intenzitu. Toto rozšíření sestavy je důkladně popsáno a charakterizováno. Schopnosti optické sestavy jsou demonstrovány ve studii šíření spinových vln skrz Néelovu doménovou stěnu. Získané 2D mapy intenzity spinových vln ukazují, že propagace přes doménovou stěnu je ovlivněna topologicky vynucenou kruhovou Blochovou čarou ve středu doménové stěny a že režim propagace závisí na frekvenci spinových vln. V prvním režimu propagace se vytvoří dva svazky spinových vlny šířící se kolem kruhové Blochovy čáry, zatímco ve druhém režimu se spinové vlny šíří pouze středem. Fázově rozlišené µ-BLS měření odhaluje fázový po- sun spinových vln pro oba režimy. Mikromagnetické modelování spinových vln ukazuje rozrušení jejich fázových vlnoploch, které je třeba brát v úvahu při interpretaci měření a navrhování potenciálních zařízení. Mikromagnetické simulace ukazují, že vnější magnetické pole může být použito k pohybu kruhové Blochovy čáry ve stěně domény, a tedy k manipulaci spinových vln.

Humic acids are part of the natural organic matter occurring all around us. The aim of this thesis is to study the molecular organization, conformation of humic acids in aqueous solutions, that always raise a number of questions. For a long time, the scientists all over the world argue, if humic acid are polymers, micelles or supramolecules. Over time, thanks to new technologies, their opinions are moving away from a polymer model and tend rather to supramolecular arrangement of humic acids. Studying humic complex systems is not easy, because they are polydisperse and heterogeneous, which significantly complicates any characterization. Moreover, its molecular organization is affected by many factors such as e.g. pH, ionic strength and etc. For the study of the conformation of humic acids, concentration series of IHSS (International humic substances asociation) Leonardite humic acids stamdards in four different mediums were prepared: 0,1 M NaOH, humic acids in water with pH modified to 12 (basic medium), 0,1 M NaOH + 0,1 M HCl, 0,1 M NaCl (neutral environment). Furthermore it has been performed the fractionation of humic acids for the purpose of simplifying the complicated structure. Prepared concentration series were characterized with several analytical methods such as ultraviolet and visible spectroscopy, dynamic light scattering, electrophoretic light scattering, microrheology, gel permeation chromatography, potentiometric pH determination and direct conductometry. Diploma thesis is built on the previous bachelor thesis in which different sample of humic acids was studied. The measured results indicate that the studied systems show supramolecular behavior and in some cases are subject to aggregation into larger units (micelles).

Exosomer är extracellulära vesiklar i nanostorlek som frigörs från cellerna till den extracellulära matrisen. Exosomer är laddade med nukleinsyror, proteiner, och lipider, och fungerar som kommunikatorer mellan celler. Det har gjort dem mycket attraktiva for forskning inom terapi, diagnostik och transport av läkemedel. För att använda exosomer i kliniska tillämpningar behöver standardiserade metoder för isolering, rening och analys av exosomer att utvecklas.  Detta projekt syftar till att sätta upp en snabb metod som använder "multiangle light scattering" (MALS) i kombination med kromatografi for att bestämma storleken på exosomer. Olika storlekskromatografi (SEC)/jonbyte (IEX)-kolonner kommer att undersökas och användas for analys av storlekar på exosomer. Partikelstorleken som erhålls från MALS kommer sedan att verifieras med nanoparticle tracking analysis (NTA).  För SEC-MALS-analyserna eluerades exosomerna i dödvolymen. IEX-MALS-metoden separerade exosomerna enligt resultatet. Exosomer i storlek mellan 60-110 nm eluerades ut med 800 mM NaCl. Större exosomer och eventuella aggregat i storlek 120-200 nm eluerades ut med 1200 mN NaCl.  Resultatet visar att signalen från MALS indikerar var exosomer i kromatogrammen elueras ut och kan ge värdefull information om storleksfördelningen i en topp. SEC-MALS-resultatet är dock inte reproducerbart, eftersom det ibland sker en förändring i storleksfördelningen över toppen. Resultatet har också visat att arean for toppen i dödvolymen varierar mellan körningarna, vilket förmodligen orsakats av att exosomer interagerar med den stationära fasen eller filtret i kolonnen. Förskjutningen i storleksfördelning observerades också i IEX­MALS-metoden. Medelvärdet av partikelstorlekarna som beräknades från SEC-MALS överensstämmer med storlekarna beräknade med NTA. SEC-MALS-metoden behöver förbättras för att fa reproducerbara resultat. Den beräknade storleken från IEX-MALS stämde inte överens med storleken från NT A. Jonbytesanalysen skulle kunna upprepas och fraktioner skulle kunna analyseras med andra tekniker för att verifiera resultatet i framtida arbete. Effekten av den höga saltkoncentrationen på exosomerna behöver också undersökas ytterligare. / Exosomes are nanosized extracellular vesicles released from the cells into the extracellular space. Exosomes are loaded with nucleic acids, proteins, and lipids, and work as communicators among cells. This has made them very attractive for research in therapeutics, diagnostics and drug delivery applications. Standardised exosome isolation, purification, and analysis methods need to be developed to use exosomes in clinical applications.  This project aimed to set up a quick method using multiangle light scattering (MALS) combined with chromatography techniques to determine exosome sizes. Different size exclusion (SEC)/ion exchange (IEX) columns will be investigated and used to analyse exosome sizes. The particle size obtained from MALS will then be verified with nanoparticle tracking analysis (NTA).  For the SEC-MALS analysis, the exosomes were eluted in the void volume. The IEX-MALS method separated the exosome sample. The exosome eluted with 800 mM NaCl ranged between 60-110 nm in diameter. The exosomes eluted with 1200 mM NaCl ranged between 120-200 nm in diameter. The result shows that the light scattering intensity from MALS indicates where the exosomes elute in the chromatograms and gives valuable information about the size distribution in a peak. However, the SEC-MALS result is not reproducible, as sometimes, a shift in the size distribution over the peak occurs.  The result has also shown that the void peak area varies between the runs, caused mainly by the exosomes interacting with the resin or the column's filter. The shift in size distribution was also observed in the IEX-MALS method.  The average sizes calculated from SEC-MALS agree with the sizes calculated with NTA. The SEC-MALS method needs to be improved to obtain reproducible results. The calculated size from IEX-MALS did not agree with the size from NTA. The ion exchange analysis could be repeated and further analysed with other techniques to verify the result in future work. The effect of the high salt concentration on the exosomes also needs to be further investigated.

No description available.

A β2GPI é uma glicoproteína que circula livre ou em lipoproteínas. Adsorve em superfícies negativas, tem efeitos anticoagulantes e moduladores da inflamação. Neste trabalho caracterizou-se a interação de moléculas da proteína entre si e com superfícies lipídicas. O SDS-PAGE e o imunoblot da β2GPI identificaram monômeros, dímeros e oligômeros. Técnicas de espalhamento de luz (estático, dinâmico, Raios-X) revelaram que β2GPI forma soluções aquosas de macroagregados anisométricos. Seca sobre mica, a β2GPI forma elipsóides prolatos, observáveis por microscopia de força atômica. A forma e o tamanho das partículas dependeram de pH e concentração de proteína. A interação entre a β2GPI e superfícies lipídicas foi estudada por microgravimetria. Superfícies de fosfatidilcolina pura adsorveram β2GPI mais fracamente do que ouro ou misturas com fosfatidilserina. A adsorção de lipoproteínas artificiais à β2GPI foi dependente de pH. Sugere-se que os efeitos biológicos da β2GPI sejam mediados por interações proteína-proteína e proteína-lipídio, e dependentes de pH. / β2GPI is a blood glycoprotein circulating free or bound to lipoproteins. β2GPI adsorbs to negatively charged surfaces, acting as anticoagulant and modulator of inflammation. This work was designed to characterize the interaction between protein molecules and among protein molecules and lipid surfaces. The β2GPI SDS-PAGE and immunoblot revealed monomer, dimer and oligomers. Light scattering methods (static, dynamic and X-ray) showed that β2GPI generates aqueous solutions of anisometric macroaggregates. Atomic force microscopy showed that β2GPI dried on muscovite surfaces assembles itself in prolate ellipsoids. The particle shape and size depended both on the pH and protein concentration. The interaction among β2GPI and lipid surfaces was studied by microgravimetry. β2GPI adsorption to pure phosphatidylcholine was weaker than to gold or phosphatidylcholine/phosphatidylserine surfaces. Artificial lipoproteins adsorbed to β2GPI in a pH dependent manner. Results suggest that β2GPI biological effects could be mediated by protein-protein interactions and lipid surface binding, and pH dependent.

This thesis focuses on the study of the interactions between polyelectrolytes and surfactants in aqueous solutions and at interfaces, as well as on the structural changes these molecules undergo due to that interaction. Small–angle neutron scattering, dynamic, and static light scattering were the main techniques used to investigate the interactions in bulk. The first type of polymer studied was a negatively charge glycoprotein (mucin); its interactions with ionic sodium alkyl sulfate surfactants and nonionic surfactants were determined. This system is of great relevance for several applications such as oral care and pharmaceutical products, since mucin is the main component of the mucus layer that protects the epithelial surfaces (e.g. oral tissues). Sodium dodecyl sulfate (SDS) on the other hand, has been used as foaming agent in tooth pastes for a very long time. In this work it is seen how SDS is very effective in dissolving the large aggregates mucin forms in solution, as well as in removing preadsorbed mucin layers from different surfaces. On the other hand, the nonionic surfactant n-dodecyl β-D-maltopyranoside (C12-mal), does not affect significantly the mucin aggregates in solution, neither does it remove mucin effectively from a negatively charge hydrophilic surface (silica). It can be suggested that nonionic surfactants (like the sugar–based C12-mal) could be used to obtain milder oral care products. The second type of systems consisted of positively charged polyelectrolytes and a negatively charged surfactant (SDS). These systems are relevant to a wide variety of applications ranging from mining and cleaning to gene delivery therapy. It was found that the interactions of these polyelectrolytes with SDS depend strongly on the polyelectrolyte structure, charge density and the solvent composition (pH, ionic strength, and so on). Large solvent isotopic effects were found in the interaction of polyethylene imine (PEI) and SDS, as well as on the interactions of this anionic surfactant and the sugar–based n-decyl β-D-glucopyranoside (C10G1). These surfactants mixtures formed similar structures in solutions to the ones formed by some of the polyelectrolytes studied, i.e. ellipsoidal micelles at low electrolyte concentration and stiff rods, at high electrolyte and SDS concentrations. / QC 20100901

This thesis reports light-scattering experiments and visual investigations close to the critical point, in the solvophobic systems, 3-methylpyridine (3MP) + heavy water (D2O) + sodium bromide (NaBr) and methyl ethyl ketone (MEK) + water (W) + secondary butyl alcohol (sBA). The system 3MP + D2O + NaBr was chosen in order to throw more light on the reported crossover from mean-field to Ising-type of critical behaviour shown by this system and to investigate the existence of a mean-field tricritical point in it at an NaBr weight fraction of X = 0.1700, two issues that have been the subject of an intense scientific debate in recent years. The system MEK + W + sBA is the result of our search for a system, other than, the well known 3-methylpyridine (3MP) + water (W) + heavy water (HW) + potassium iodide (KI), in which a quadruple critical point (QCP) can potentially be realized. In addition to this the thesis provides exhaustive details regarding the design, fabrication, and characterization, of a microkelvin thermostat in which a temperature stability of the order of a few microkelvin is achievable despite its relatively simple thermal design. The thesis is organized into 6 Chapters. Chapter 1 provides an introduction to the field of critical phenomena in liquid mixtures. The critical phenomena observed in various systems such as simple fluids, ionic fluids, polymer blends and polymer solutions, and micellar and microemulsion systems, are discussed in brief. Particular attention has been paid to the investigations by various researchers, into, the crossover from Ising to mean-field critical behaviour in electrolyte and polymer solutions, and in amphiphilic systems. Recent theoretical attempts at modeling ionic criticality have also been cited and summarized. A brief discussion on the various types of special critical points and multicritical points that are observed in multicomponent liquid mixtures and other condensed matter systems has been provided. The appealing possiblity of the presence of multicritical points in ionic fluids leading to crossover behaviour is also discussed. The chapter ends with a statement on the goals of this thesis. Chapter 2 describes the instrumentation and other aspects of the experimental techniques used for the light-scattering studies reported in this thesis. Details about the thermal instrumentation such as the water bath and the silicone-oil bath used for the visual investigation experiments and the metal thermostat used for the light-scattering experiments have been provided. The important design considerations relating to the achievement of a high degree of temperature stability (Formula) have been elucidated clearly. The modifications made to the design of the light-scattering thermostat, that enables achievement of a temperature stability of ± 2.5 mK at temperatures 19 ≤ T ≤ 24°C has been discussed. A section has been devoted to the description of the calibration of the temperature sensors we used in our experiments. The light-scattering instrumentation has been discussed in depth. The difficulties associated with the light-scattering techniques when it is used as a tool to study critical phenomena have been detailed. This is followed by a description of the method we used in correcting our light-scattering data for double-scattering effects. A description of the sample cells used for visual investigations and light-scattering experiments along with the sample filling and cleaning procedures followed by us has been described. Chapter 3 deals with the first of the three important problems discussed in this thesis. The chapter is aimed at investigating the crossover behaviour of the solvo-phobic system 3-methylpyridine (3MP)+ water (H2O) + sodium bromide (NaBr), by means of light-scattering studies on the strongly motivated and non-trivial system of 3-methylpyridine (3MP) + heavywater (D2O) + sodium bromide (NaBr). The replacement of H2O by D2O in 3MP + D2O + NaBr, is expected to accentuate the crossover behaviour reportedly displayed by 3MP + H2O + NaBr, and thereby, provide conclusive evidence regarding the existence or otherwise of a crossover between the Ising- and the mean-field-types of critical behaviour in this system. The chapter begins with a detailed literature survey on the topic of the crossover behaviour shown by the system 3MP + H2O + NaBr. We also provide a survey of the effect of the iso-topic H→D substitution on the critical behaviour of binary and quasibinary systems. Through an argument based on small-angle neutron scattering (SANS) studies and the Kirkwood-Buff integrals (KBIs), a strong and cogent motivation is established, which proves that, if the reported crossover behaviour in 3MP + H2O + NaBr is assumed to be correct, then the system 3MP + D2O + NaBr should display not just the same crossover behaviour as shown by the undeuterated system 3MP + H2O + NaBr, but, in addition, also a more pronounced dependence of the crossover temperature on the concentration of NaBr in the mixture than that seen in 3MP + H2O + NaBr. This approach to understand the crossover behaviour of 3MP + H2O + NaBr, has not been used by any of the previous investigators. The coexistence curve data for the system 3MP + D2O + NaBr are obtained at six different values of the NaBr weight fractions viz. X = 0, 0.0250, 0.0800, 0.1200, 0.1500, and 0.1800. The closed-loop immiscibility loop obtained for X = 0, agrees well with the reported phase diagram for 3MP + D2O in the literature. A comparison between the lower-critical lines obtained for the deuterated and the undeuterated system has been provided. Within error bars, no perceptible dip was observed in the critical line at X = 0.1700 in the case of the system 3MP + D2O + NaBr. Hence, our study does not indicate the presence of a mean-field tricritical point that has been reported at X = 0.1700 in the system 3MP + H2O + NaBr. A large section of Chapter 3 is devoted to the results and discussions of our extensive light-scattering experiments on the system 3MP + D2O + NaBr. The experiments were performed on 13 different samples of 3MP + D2O + NaBr with NaBr weight fractions in the range of 0 ≤ X ≤ 0.1900. The choice of the X values were guided by the NaBr concentrations at which earlier investigators have done light-scattering experiments on the system 3MP + H2O + NaBr. Detailed light-scattering experiments reveal that the system 3MP + D2O + NaBr shows a simple Ising-type critical behaviour with γ ' 1.24 and ν ' 0.63 over the entire NaBr concentration range 0 ≤ X ≤ 0.1900. The crossover behaviour is predominantly nonmonotonic, and the crossover is completed well outside the critical domain. An analysis in terms of the effective susceptibility exponent (γeff) showed that the crossover behaviour is nonmonotonic for 0 ≤ X ≤ 0.1793 and tends to become monotonic for X > 0.1793. The correlation length amplitude, ξo, has a value of (Formula) for 0.0250 < X ≤ 0.1900, whereas for (Formula). Since isotopic H—> D substitution is not expected to change the critical behaviour of the system, our results shows that the system 3MP + H2O + NaBr should exhibit universal Ising-type critical behaviour that is typical for aqueous solutions. Our search for a new system in which a quadruple critical point (QCP) could possibly be realized forms the subject matter of the Chapter 4 of the thesis. The system methyl ethyl ketone (MEK) + water (W) + secondary butyl alcohol (sBA) is identified as a very promising candidate-system for this purpose. The chapter begins with a brief survey of the various types of multicritical points and special critical points realizable in multicomponent liquid mixtures. The importance of investigating special critical points such as the QCP is motivated. A detailed coexistence surface for MEK + W + sBA was developed by generating the coexistence curves corresponding to five different, but onstant, values of MEK weight fractions XM = 0.0500, 0.1000, 0.1750, 0.2300, and 0.3000, respectively. The complete isobaric coexistence surface (at 1 atm) for the system MEK + W + sBA was visualized in the form of a prismatic phase diagram. The surface is found to display a tunnel-like appearance in the MEK weight fraction range of 0.0500 ≤ XM ≤ 0.1750, with the tunnel being the narrowest at the point (XM,XW,XSBA) = (0.1750, 0.5801, 0.2449), where, xw and XSBA are, respectively, the weight fractions of water and sBA in the mixture. An analysis of the order parameter data showed that MEK + W + sBA shows near Ising-type of critical behaviour near their upper critical solution temperatures, TU's. It was seen that the critical temperature Tc shows a low drift with time (Formula)/day and that the tunnel-like portion in the phase diagram of MEK + W + sBA was very symmetric. These two features make (MEK + W + sBA) a considerably more promising system than (3MP + W + HW + KI )for the realization of the QCP. It may be recalled that 3MP + W + HW + KI is the only system in which QCP studies have been reported so far in literature. The light-scattering investigations in MEK + W + sBA near the lower critical solution temperatures TL are described next. We corrected our light-scattering data for both turbidity as well as double-scattering effects. Our experiments revealed that (MEK + W + sBA) shows near three-dimensional-Ising type of critical behaviour at the lower critical solution temperatures, with the susceptibility exponent (γ) in the range of 1.217 ≤ γ ≤ 1.246. The correlation length amplitudes (ξo) and the critical exponent (ν) of the correlation length (ξ) were in the ranges of 3.536 ≤ ξo ≤ 4.611 A and 0.619 ≤ ν ≤ 0.633, respectively. An analysis in terms of the effective susceptibility exponent (γeff) results in the interesting result, namely that, the critical behaviour of (MEK + W + sBA ) is of the Ising-type for MEK concentrations in the ranges of 0.1000 ≤ XM ≤ 0.1250 and XM ≥ 0.3000; but, for the intermediate range of 0.1750 < XM < 0.3000, the system shows a tendency towards mean-field type of critical behaviour. This behaviour is interesting because both the constituent binary systems of the ternary system (MEK + W + sBA), namely, (MEK + W) and (W + sBA) show Ising-type of critical behaviour. Chapter 5 discusses another crucial objective of this thesis, namely, the fabrication and characterization of a microkelvin thermostat, which has been built for the purpose of performing light-scattering studies exceptionally close to the critical temperature. At the outset, the need for a temperature stability of the order of a few microkelvin for performing reliable critical point phenomena experiments very close to the critical point, is justified and demonstrated. This is followed by an in-depth account of the thermal design of the thermostat and the electronic circuitry used in the temperature controller. The variations in the ambient temperature and the stability of the bridge excitation source are identified and demonstrated to be crucial factors that affect the long-term temperature stability of the thermostat. A simple compensation scheme to nullify the effects of ambient temprature variations on the controller performance is suggested. It is demonstrated that the thermostat gives a temperature stability of (Formula) and ±60−90 µK for 7 − 14 h over a broad range of 25 − 103 °C. A detailed profile of thermal gradients within the sample recess is provided. It is shown that the parameter ∆Teff [i.e., the difference between the maximum (minimum if ∆Teff has a negative value) temperature within the sample recess and the temperature just outside the sample recess] is a more relevant parameter than ∆T (i.e., the temperature difference between the inner and the outer stages) in understanding the behaviour of multistage thermostats. The most important result that emerges from our study is that the thermal gradients and the transient response of the controller, can both be tuned by varying ∆Teff (or by varying ∆T). The best horizontal and vertical thermal gradient performance observed within our thermostat were 250 and 100 µK/mm, respectively, which are observed for a ∆Teff = 4.46 mK. The transient response of the controller is almost invariant for ∆Teff > 0 but it shows a dramatic decrease of almost 50% when ∆Teff < 0. It is seen that, the limit ∆Teff →>• 0, provides the best operating conditions of the thermostat from the standpoints of temperature stability, transient response and gradient performance. An error analysis relevant to the circuitry used by us is provided at the end of the chapter, which clearly indicates the efficacy of the compensations scheme proposed by us to nullify the effects of ambient temperature variations. Chapter 6 summarizes the important results obtained in this thesis. It also presents a range of open problems that need to be explored further in order to fully understand the results that are reported in this thesis, especially, regarding the type of crossover behaviour seen in the systems 3MP + D2O + NaBr and MEK + W + sBA.

Novel, tailored titanium dioxide pigments with controllable nanoscale morphological features were shown to significantly enhance the optical and strength properties of paper. The opacifying power of synthesized polycrystalline TiO2 particles in a cellulose matrix was found experimentally to be superior to that of a commercial rutile pigment, depending on the crystal structure of the synthesized particles. High aspect ratio polycrystalline rutile pigments composed of a linear linkage of several individual rutile crystals gave 6% more opacity than the commercial rutile pigment. Theoretical light scattering calculations using the T-Matrix Method showed the light scattering efficiency of linearly arranged polycrystalline rutile particles to depend on number and size of crystals composing the particle and confirmed the higher efficiency of the synthesized polycrystalline rutile pigments over commercial rutile. The opacifying power of hollow polycrystalline rutile particles was found experimentally to be superior to that of a commercial rutile pigment in a highly pressed bleached fiber matrix, depending on cavity size, while the opacifying power of silica-rutile titania core-shell particles was found comparable to commercial rutile at constant titania loading. The light scattering efficiency of titania core-shell particles was shown to be dependant on the light scattering efficiency of the core material. The overall particle shape and aspect ratio of titania core-shell and hollow nanoparticles were shown to be tunable by choosing an appropriate template and coating thickness in layer-by-layer or sol-gel templating synthesis. Inorganic-cellulose core-shell and hollow cellulose nanoparticles were prepared by self-encapsulation with regenerated cellulose via precipitation of cellulose in a polyacrylic acid hydrogel layer surrounding inorganic particle templates in 4-Methylmorpholine N-oxide (NMMO) monohydrate solution. This discrete encapsulation of inorganic pigments with a thin, uniform cellulose shell was found to increase the bondability improvement between the particles and a polysaccharide substrate. The crystallinity of several carbohydrate polymers was shown to significantly affect the bondability of encapsulated core-shell particles.

A &#946;2GPI é uma glicoproteína que circula livre ou em lipoproteínas. Adsorve em superfícies negativas, tem efeitos anticoagulantes e moduladores da inflamação. Neste trabalho caracterizou-se a interação de moléculas da proteína entre si e com superfícies lipídicas. O SDS-PAGE e o imunoblot da &#946;2GPI identificaram monômeros, dímeros e oligômeros. Técnicas de espalhamento de luz (estático, dinâmico, Raios-X) revelaram que &#946;2GPI forma soluções aquosas de macroagregados anisométricos. Seca sobre mica, a &#946;2GPI forma elipsóides prolatos, observáveis por microscopia de força atômica. A forma e o tamanho das partículas dependeram de pH e concentração de proteína. A interação entre a &#946;2GPI e superfícies lipídicas foi estudada por microgravimetria. Superfícies de fosfatidilcolina pura adsorveram &#946;2GPI mais fracamente do que ouro ou misturas com fosfatidilserina. A adsorção de lipoproteínas artificiais à &#946;2GPI foi dependente de pH. Sugere-se que os efeitos biológicos da &#946;2GPI sejam mediados por interações proteína-proteína e proteína-lipídio, e dependentes de pH. / &#946;2GPI is a blood glycoprotein circulating free or bound to lipoproteins. &#946;2GPI adsorbs to negatively charged surfaces, acting as anticoagulant and modulator of inflammation. This work was designed to characterize the interaction between protein molecules and among protein molecules and lipid surfaces. The &#946;2GPI SDS-PAGE and immunoblot revealed monomer, dimer and oligomers. Light scattering methods (static, dynamic and X-ray) showed that &#946;2GPI generates aqueous solutions of anisometric macroaggregates. Atomic force microscopy showed that &#946;2GPI dried on muscovite surfaces assembles itself in prolate ellipsoids. The particle shape and size depended both on the pH and protein concentration. The interaction among &#946;2GPI and lipid surfaces was studied by microgravimetry. &#946;2GPI adsorption to pure phosphatidylcholine was weaker than to gold or phosphatidylcholine/phosphatidylserine surfaces. Artificial lipoproteins adsorbed to &#946;2GPI in a pH dependent manner. Results suggest that &#946;2GPI biological effects could be mediated by protein-protein interactions and lipid surface binding, and pH dependent.