Hydrogels from diacylphosphatidylcholine

The formation of hydrogels from diacylphosphatidylcholine (PC) and water/glycerol mixtures and the properties of the gels are reported. The gels are formed when L_α phases from the PC in the solvent mixtures are cooled from T >55 °C below the Krafft temperature of the PC (T _m ∼52 °C). The glycerol can also be replaced by other co-solvents like butylenglycol. Above T _m, the PC spontaneously forms L_α phases with multilamellar vesicles that show a strong stationary birefringence. On cooling below T_m, the L_α phases jellify to transparent gels. DSC measurements of the gels show that the PC molecules undergo a phase transition into the crystalline state. This transition does not seem to be accompanied by a change of the morphological structure of the liquid L_α phase. The hydrogels also have a stationary birefringence. The vesicles in the gels have been imaged by the CryoTEM method. The hydrogels are already formed with as little as 1% of PC in the mixed solvent. The rheological properties of the gels were determined from oscillating rheological measurements. Samples with 10% of PC have a storage modulus of >10,000 Pa.     

DODAB and DODAC bilayer-like aggregates in the micromolar surfactant concentration domain

In the millimolar concentration domain (typically 1 mM), dioctadecyldimethylammonium bromide and chloride (DODAX, X representing Br⁻ or Cl⁻ counterions) molecules assemble in water as large unilamellar vesicles. Differential-scanning calorimetry (DSC) is a suitable technique to obtain the melting temperature (T _m) characteristic of surfactant bilayers, while fluorescence spectroscopy detects formation of surfactant aggregates, like bilayers. These two techniques were combined to investigate the assembly of DODAX molecules at micromolar concentrations, from 10 to 100 μM. At 1 mM surfactant, T _m ≈ 45 °C and 49 °C, respectively, for DODAB and DODAC. DSC and fluorescence of Nile Red were used to show the formation of DODAX aggregates, at the surfactant concentration as low as 10 μM, whose T _m decreases monotonically with increasing DODAX concentration to attain the value for the ordinary vesicles. The data indicate that these aggregates are organized as bilayer-like structures.     

The effect of storage temperature on interactions between dehydrated sugars and phosphatidylcholine

We studied the effects of storage temperature on the stability of dehydrated POPC (1-palmitoyl-2-oleoyl-phosphatidylcholine) mixed with sucrose, trehalose, or a sucrose/raffinose mixture. We used DSC to measure the gel-to-fluid phase transition temperature (T _m) of POPC after incubation either below or near the glass transition temperature (T _g) of the sugars in the mixture. Glass formation by the sugars around fluid-phase POPC led to the lowering ofT _m below that of the fully hydrated lipid. Phospholipid phase behavior did not change during storage belowT _g. In some samples stored aboveT _g, trehalose crystallized completely; in these samples, theT _g of POPC increased to that of the partially dehydrated phospholipid. Melting the crystalline sugar re-established its ability to lower POPC'sT _m. We conclude that prevention of complete sugar crystallization was important for stability in the dry state, and that storage belowT _g conferred long-term stability to the dehydrated sugar-lipid mixtures.     

Classification for molecular aggregation structure of monolayers on the water surface

The melting temperature, T_m, and the crystalline relaxation temperature, Tα_c, of palmitic acid and dipalmitoyl phosphatidylcholine monolayers on the water surface were evaluated by combination of two kinds of measurements: first, the subphase temperature, T_sp, dependence of the monolayer modulus based on the surface pressure-area (π-A) isotherm and second, the T_sp dependence of the electron diffraction, ED patterns of their monolayers. On the basis of their characteristic temperatures of the monolayers, the aggregation structure of the monolayers which were transferred onto a hydrophilic SiO substrate at various surface pressures and T_sps was investigated by means of transmission electron microscopy. The π-A isotherm for the fatty acid monolayer on the pure water surface represented the aggregating process of isolated domains grown right after spreading a solution on the pure water surface. The fatty acid monolayer on the pure water surface was classified into a crystalline monolayer (T_sp < T_m) and an amorphous one (T_sp > T_m). The crystalline monolayer was further classified into two types; crystalline domains were aligned along their crystallographic axes owing to an induced sintering at the interfacial region among monolayer domains by surface compression (T_sp < Tα_c), while not for T_sp > Tα_c. In the case of the phospholipid monolayer, the monolayer was classified into a compressing crystallized monolayer (T_sp < T_m) and an amorphous one (T_sp > T_m). The compressing crystallized monolayer is a monolayer in which crystallization was gradually induced at plateau region on the π-A isotherm by compression. Electron diffraction studies of arachidic acid monolayers in different dissociated states of hydrophilic groups revealed that formation of the compressing crystallized monolayer was attributed to an electrostatic repulsion among ionic hydrophilic groups. It was concluded that the aggregation structure of monolayers on the water surface was systematically classified into ‘the crystalline monolayer’, ‘the amorphous monolayer’ and ‘the compressing crystallized monolayer’, with respect to thermal and chemical (intermolecular repulsive) factors.     

The formation of vesicles by N-dodecyl-N-methylpyrrolidinium bromide ionic liquid/copper dodecyl sulfate and application in the synthesis of leaflike CuO nanosheets

The phase behavior of the mixed catanionic surfactants in aqueous solution, composed of the long-chain ionic liquid (IL) N-dodecyl-N-methylpyrrolidinium (C₁₂MPB) and a divalent metal surfactant copper dodecyl sulfate (Cu(DS)₂·4H₂O), was investigated. The phase diagram of the catanionic system was mapped through visual observation and electrical conductivity measurement. The formation of vesicles was confirmed in the lamellar phase (L_α) through transmission electron microscopy (TEM). Rheological measurements were used to study the macroscopic properties of the birefringent L_α phase. Electrostatic and hydrophobic interactions are regarded as the main driving forces for the formation of vesicles. Furthermore, the vesicles were successfully used as the templates to prepare the leaflike CuO nanomaterials.     

Swelling of Lalpha-phases by matching the refractive index of the water-glycerol mixed solvent and that of the bilayers in the block copolymer system of (EO)15-(PDMS)15-(EO)15

The swelling of Lalpha-phases from the block copolymer polyethylenoxide-b-polydimethylsiloxane-polyethylenoxide (EO)15-(PDMS)15-(EO)15 in water/glycerol mixtures is reported. At low and medium polymer concentrations (<60%), the block copolymer forms a turbid vesicular dispersion in water. With time, the small unilamellar vesicles (SUV) and the large multilamellar vesicles (MLV) separate into a two phase L1/Lalpha-system. The turbid dispersions of the Lalpha-phase below 60% of the compound become more and more transparent with increasing glycerol and at 60% of glycerol become completely clear. Replacement of water by the solvent glycerol thus lowers the turbidity of the dispersion and swells the interlamellar distance between the bilayers. A 20% aqueous L1/Lalpha-dispersion can thus be transformed into a single birefringent transparent Lalpha-phase. The swelling of the Lalpha-phase in water and the decrease of the turbidity of the dispersion by the addition of glycerol is explained by the matching of the refractive index of the solvent to the refractive index of the bilayers of the block copolymer. The matching of a refractive index lowers the Hamaker constant in the DLVO theory between the bilayers and therefore decreases the attraction between the bilayers what allows them to swell to a larger separation. The microstructures in the phases were determined by cryo- and FFR-TEM. The interlamellar distance between the bilayers was determined by SAXS measurements. The viscous properties of the Lalpha-phases were determined by oscillatory rheological measurements. In comparison to other Lalpha-phases from normal surfactants, the Lalpha-phases from the block copolymer (EO)15-(PDMS)15-(EO)15 have low shear moduli. This is probably due to the high flexibility of the poly dimethylsiloxane block in the bilayers what can be recognized on the non-spherical shapes of the SUV's.     

Influence of the leprosy drug, dapsone on the model membrane dipalmitoyl phosphatidylethanolamine

The influence of the sulfone drug, diamino diphenyl sulfone (DDS or dapsone) on the phase transitions and dynamics of the model membrane, dipalmitoyl phosphatidylethanolamine (DPPE)-water/buffer has been studied using DSC and (¹H and ³¹P) NMR. These investigations were carried out with DPPE dispersion in both multilamellar vesicular (MLV) and unilamellar vesicular (ULV) forms for DDS/DPPE molar ratio, R, in the range 0-0.5. DSC results indicate that the mechanism by which DDS interacted with the DPPE membrane is independent of the morphological organization of the lipid bilayer and the solvent (water or buffer) used to form the dispersion. DDS affected both the thermotropic phase transitions and the molecular mobility of the DPPE membrane. Addition of increasing amounts of DDS to the DPPE dispersion, resulted in the lowering of the gel to liquid-crystalline phase transition temperature (T_m) hence increased membrane fluidity. At all concentrations, the DDS is located close to the interfacial region of the DPPE bilayer but not in the acyl chain region. The interesting finding with MLV is that the gel phase of DPPE-water/buffer both in presence and absence of DDS, on prolonged equilibration at 25 °C, transforms to a stable crystalline subgel phase(s). The DPPE-water system forms both crystalline subgel L_LC (with transition temperature T_LC < T_m) and L_HC (with transition temperature T_HC ≥ T_m) phases, while the DPPE-buffer system forms only subgel L_LC phase. The presence of the drug seems to (i) increase the strength of the subgel L_LC phase and (ii) decrease the strength of subgel L_HC (for R < 0.5) phase. However, the value of the transition temperatures T_LC and T_HC does not change significantly with increasing drug concentration.     

Bilayer swelling of nonionic surfactant and sodium dodecylsulfate mixed system by refractive-index matching

Bilayer swelling behavior of nonionic and anionic surfactant mixed aqueous solution induced by adding glycerin was studied. The phenomenon were performed on a system, polyethylene glycol ether of tridecyl alcohol with the average number of ethylene oxide of 5 (CH₃(CH₂)₁₂(OCH₂CH₂)₅OH; abbreviation IT5) and SDS mixed aqueous solution, with white cream of the upper phase and micelles (L₁) of the lower phase. White cream containing densely packed multilamellar vesicles was revealed by freeze-fracture transmission electron microscopy and polarized microscope observations. Phase transition from white cream/L₁, two-phase, to clear unique vesicle phase can be induced by adding glycerin to replace water. The addition of glycerin lowers the turbidity of the dispersion and swells the interlamellar distance between bilayers, which could be explained by refractive-index matching between solvent and bilayers.     

Lyotropic Liquid Crystals Formed by Brij 97/PEO‐PPO‐PEO Mixtures

The phase diagrams of Brij 97/(PEO)_m(PPO)_n(PEO)_m/water/IPM quaternary systems (A L‐64: m=13, n=30; A L‐62: m=7, n=32; A L‐61: m=3.5, n=31) were determined at 25°C. The liquid crystalline phases (lamellar L_αand hexagonal H₁) were investigated by means of small angle x‐ray scattering (SAXS) and rheological techniques, with comparison of composition and component effects. The lamellar phases formed in Brij 97/A L‐64 and Brij 97/A L‐62 systems array more orderly than that of Brij 97/A L‐61 system, indicated by the stronger intensity of the second reflection peak in the SAXS patterns and the higher moduli (G′ and G″) in the dynamic rheograms. In Brij 97/A L‐64/water/IPM system, all L_α phases exhibit elastic rheograms, moreover the viscous property get increased with increase in water content. On the other hand, with this change, the H₁ phases show Maxwell and gel‐like rheograms in order, in which the latter shows mechanical and relaxation spectra typical of highly structured materials.     

Freezing point depression of water in phospholipid membranes: a solid-state NMR study

Lipid-water interaction plays an important role in the properties of lipid bilayers, cryoprotectants, and membrane-associated peptides and proteins. The temperature at which water bound to lipid bilayers freezes is lower than that of free water. Here, we report a solid-state NMR investigation on the freezing point depression of water in phospholipid bilayers in the presence and absence of cholesterol. Deuterium NMR spectra at different temperatures ranging from -75 to + 10 degrees C were obtained from fully (2)H2O-hydrated POPC (1-palmitoyl-2-oleoylphosphatidylcholine) multilamellar vesicles (MLVs), prepared with and without cholesterol, to determine the freezing temperature of water and the effect of cholesterol on the freezing temperature of water in POPC bilayers. Our 2H NMR experiments reveal the motional behavior of unfrozen water molecules in POPC bilayers even at temperatures significantly below 0 degrees C and show that the presence of cholesterol further lowered the freezing temperature of water in POPC bilayers. These results suggest that in the presence of cholesterol the fluidity and dynamics of lipid bilayers can be retained even at very low temperatures as exist in the liquid crystalline phase of the lipid. Therefore, bilayer samples prepared with a cryoprotectant like cholesterol should enable the performance of multidimensional solid-state NMR experiments to investigate the structure, dynamics, and topology of membrane proteins at a very low temperature with enhanced sample stability and possibly a better sensitivity. Phosphorus-31 NMR data suggest that lipid bilayers can be aligned at low temperatures, while 15N NMR experiments demonstrate that such aligned samples can be used to enhance the signal-to-noise ratio of is 15N chemical shift spectra of a 37-residue human antimicrobial peptide, LL-37.     

A re‐examination of the sub‐Tm exotherm in polyamide 6: The roles of thermal history,water and clay

The sub‐T_m exotherms in polyamide 6 (PA6) have been carefully re‐examined by differential scanning calorimetry and X‐ray diffraction, considering the effects of processing and thermal history, addition of water and clay. The results obtained cast doubt on Khanna's proposal that sub‐T_m exotherm in PA6 comes from the release of strain energy absorbed during processing, and suggested that the origin of sub‐T_m exotherm is the γ?α transformation at the premelting temperature, namely, the less thermodynamically stable γ‐form (γ^ns) transforming into the more thermodynamically stable α‐form (α^s). The presence of water or clay in PA6 samples facilitated the formation of γ^ns at corresponding cooling rates, and enhanced the development of sub‐T_m exotherms. During the heating scan of PA6/clay composites, the initial γ^ns can be transformed into more stable (γ^s)^t and α^s at the same time, which can be thought as the origin of their sub‐T_m events. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2385–2393, 2009     

Review of: “Physico-Chemical Properties of Selected Anionic Cationic and Nonionic Surfactants”. N.M van Os,J.R. Haak and L.M. Rupert (Eds.). Elsevier,Amsterdam, 1993, pp. viii + 608 pages. $245.75.(ISBN 0-444-89691-0)

The phase behavior in water of pentaglycerol monostearate (C₁₈G₅) and pentaglycerol monooleate (C_18:1G₅) surfactants has been studied as a function of temperature and surfactant weight fraction, W _s . The equilibrium phases present at each composition and temperature studied were characterized by means of visual observation under normal and polarized light, differential scanning calorimetry (DSC), and X‐ray scattering, both at small (SAXS) and at wide angle (WAXS). In the temperature range 0–46°C, C₁₈G₅ presents a thermotropic α‐gel structure. However, at higher temperatures, the α‐gel phase melts and a lamellar liquid crystalline (L_α) phase is formed. The amount of water that can be solubilized by α‐gel and L_α was determined by plotting the interlayer distance, d, as a function of the reciprocal of W _s . Water is soluble in the α‐gel phase up to 21 w/w% water concentration and in the L_α phase up to 30 w/w% water concentration. At higher water concentrations, excess water appears and a dispersion of α‐gel (α‐gel+W) and lamellar liquid crystal (L_α+W) in water is formed, respectively. In contrast, C_18:1G₅ is liquid in the whole range of temperatures studied (0–100°C). While at low temperatures, C_18:1G₅ presents a L_α structure, at about 63°C L_α melts and an isotropic liquid reverse micellar solution (O_m) phase is formed. The amount of water that can be solubilized by both O_m and L_α increases with temperature.     

Filling‐level effect on the physical properties of MgBr2‐ and MgCl2‐filled poly(vinyl acetate) films

The structural properties of poly(vinyl acetate) (PVAc) films filled with different levels of MgBr₂ or MgCl₂ were investigated. Differential scanning calorimetry revealed that, at certain filling levels of MgBr₂ or MgCl₂, two new transitions appeared. The first one was due to the α relaxation (T_α) associated with a crystalline region, and the second was due to the melting temperature (T_m). This implies that a crystalline phase was formed in the polymeric matrix. Changes occurring in T_α, T_m, and the melting peak area as a function of the filling level were examined. The X‐ray diffraction (XRD) pattern revealed that the pure PVAc film was amorphous. However, the addition of MgBr₂ or MgCl₂ led to the formation of a crystalline phase in the polymeric matrix that depended on the filling level. XRD also demonstrated that the structural changes depended not only on the metal ions but also on the halide ions. Scanning electron microscopy images for the studied samples were examined. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 112–119, 2003     

Long periods in slow-cooled linear and branched polyethylene: Part II

It is shown that the long periods L in slow-cooled polyethylene materials obey the general law L = L⁰ + αr_w, where r_w is the weight average dimension of the coil before crystallization, and L⁰ is a parameter of the order of l_c, the crystalline core thickness, which increases as the cooling rate V decreases. α is a parameter independent of M and V but decreasing with the number of long-chain branches per molecule. The two terms in the above relation are, respectively, the contributions of crystalline and amorphous layers. For cooling rates from 800°C/min to 0.2°C/min, it is shown that the temperature T_c of crystallization is constant; hence the change of morphology (long period, crystalline core thickness, crystallinity) cannot be explained by supercooling. The increase in long period and crystallite thickness in slow-cooled materials with decreasing cooling rate is interpreted in terms of annealing of the crystallized materials between the crystallization temperature T_c and the secondary transition temperature T_αc. Crystallization proceeds by a two-step process of solidification and annealing. During the annealing stage, the mobility of the chains in the crystalline phase is due to defects; the kinetics of thickening is then governed by the mobility (or nucleation) of the defects appearing above T_αc. In the proposed model of crystallization, the assumption that the energy of activation is proportional to T_αc explains the observed laws L ≡ l_c ≡ log t_a, where the annealing time t_a is equal to (T_c ? T_αc)/V. The model applies also to polymers crystallized from the melt and subsequently annealed.     

On the relation between the solvent parameters and the physical properties of methyl-4,6-O-benzylidene-α-d-glucopyranoside organogels

This paper reports the mechanisms of gel formation, the thermal properties and the microstructures of the networks of the gels composed of methyl-4,6-O-benzylidene-α-d-glucopyranoside and selected organic solvents: p-xylene, benzene, toluene, diphenyl ether and tetraethoxysilane. The Fourier transform infrared measurements together with simulation spectra, the air bath method and Polarized Optical Microscopy were employed in our studies. The experimental data show that the solvent has an influence on the microstructure of the gel network but there is no predictable influence of the solvent polarity on the shape of the formed gelator aggregates and correspondingly on the fibrous assemblies as revealed by the different microstructure of the gel network. Independently of the solvent polarity, the studied gelator, like other methyl-4,6-O-benzylidene derivatives of monosaccharides, formed gels through the formation of a hydrogen-bond network. The solvent parameters, such as the dielectric constant, Hildebrand solubility parameter, the polarity scale E_T and the Kamlet–Taft parameters were considered to quantify solvent effects on the gelation. The conclusions about the correlations are of interest but only to this particular sugar based gels.     

Probing the Interdigitated Phase of a DPPC Lipid Bilayer by Micropipette Aspiration

We used micropipette aspiration of giant unilamellar vesicles to directly measure the areal expansion of gel (L_β′) phase 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayers induced by exposure to ethanol/water mixtures. Areal expansion began in 7 vol% ethanol and increased monotonically as the concentration of ethanol was increased to 15 vol% at which point areal expansion reached a plateau of 50%. This ethanol concentration range is in good agreement with that of the interdigitated phase (L_βI) of DPPC, therefore, we believe that this is the first direct measurement of the areal expansion accompanying interdigitation of gel-phase lipids. Our observations are consistent with the presence of coexisting L_βI and L_β′ phases in ethanol concentrations between 7% and 15 vol% and 100% L_βI phase in 15 vol% ethanol and higher. We observed a bimodal distribution of areal expansion (0% and 20%) induced by 7 vol% ethanol indicating that at the threshold concentration, interdigitation is induced in only a portion of DPPC vesicles. Areal expansion could not be easily reversed, consistent with kinetic trapping of the L_βI phase. DPPC vesicles exposed to butanol at the known threshold and plateau concentrations for the L_βI phase displayed areal expansion behavior consistent with our ethanol observations. However, the area expanded significantly faster for DPPC bilayers exposed to butanol vs. ethanol, which we attribute to enhanced partitioning of the longer-chained butanol into the lipid headgroups. Ethanol-induced areal expansion of DPPC bilayers was inhibited by inclusion of 10 mol% and 25 mol% cholesterol in the bilayer. However, areal expansion could be induced by application of tensions (∼8 mN/m) similar to the phenomena of interdigitation induced by high pressure. The presence of 20 vol% ethanol significantly decreased surface cohesion of DPPC bilayers containing 25 mol% cholesterol as evidenced by a decreased area compressibility modulus and lysis tension.     

Probing the interaction of the potassium channel modulating KCNE1 in lipid bilayers via solid‐state NMR spectroscopy

KCNE1 is known to modulate the voltage‐gated potassium channel α subunit KCNQ1 to generate slowly activating potassium currents. This potassium channel is essential for the cardiac action potential that mediates a heartbeat as well as the potassium ion homeostasis in the inner ear. Therefore, it is important to know the structure and dynamics of KCNE1 to better understand its modulatory role. Previously, the Sanders group solved the three‐dimensional structure of KCNE1 in LMPG micelles, which yielded a better understanding of this KCNQ1/KCNE1 channel activity. However, research in the Lorigan group showed different structural properties of KCNE1 when incorporated into POPC/POPG lipid bilayers as opposed to LMPG micelles. It is hence necessary to study the structure of KCNE1 in a more native‐like environment such as multi‐lamellar vesicles. In this study, the dynamics of lipid bilayers upon incorporation of the membrane protein KCNE1 were investigated using ³¹P solid‐state nuclear magnetic resonance (NMR) spectroscopy. Specifically, the protein/lipid interaction was studied at varying molar ratios of protein to lipid content. The static ³¹P NMR and T₁ relaxation time were investigated. The ³¹P NMR powder spectra indicated significant perturbations of KCNE1 on the phospholipid headgroups of multi‐lamellar vesicles as shown from the changes in the ³¹P spectral line shape and the chemical shift anisotropy line width. ³¹P T₁ relaxation times were shown to be reversely proportional to the molar ratios of KCNE1 incorporated. The ³¹P NMR data clearly indicate that KCNE1 interacts with the membrane. Copyright © 2017 John Wiley & Sons, Ltd.     

Synthesis and UCST‐type phase behaviors of OEGylated random copolypeptides in alcoholic solvents

A series of OEGylated random copolypeptides with similar main‐chain lengths and different oligo(ethylene glycol) (OEG) molar content and chain lengths were prepared from triethylamine initiated ring‐opening polymerization (ROP) of OEGylated γ‐benzyl‐_L‐glutamic acid based N‐carboxyanhydride (OEG_mBLG–NCA, m = 2, 3) and γ‐benzyl‐_L‐glutamic acid based N‐carboxyanhydride (BLG–NCA). ¹H NMR analysis verified copolypeptides structures and determined the OEG molar content (x). FTIR analysis further confirmed the molecular structures, indicated α‐helical conformations of copolypeptides in the solid‐state, and revealed H‐bonding interactions between OEG pendants and alcoholic solvents. The copolypeptides exhibited a reversible upper critical solution temperature (UCST)‐type phase behavior in various alcoholic solvents (i.e., methanol, ethanol, 1‐propanol, 1‐butanol, and 1‐pentanol) depending on the x values and OEG side‐chain lengths (m). Variable‐temperature UV–vis analysis revealed that the UCST‐type transition temperatures (T_pts) of the copolypeptides in alcohols decreased as x or m value increased or as polymer concentration decreased. T_pts of copolypeptides with high x values (x ≥ 0.50) increased as the number of methylene of the alcoholic solvent increased from 3 (i.e., 1‐propanol) to 5 (i.e., 1‐pentanol). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3444–3453     

Calorimetric and EPR studies of the thermotropic phase behavior of phospholipid membranes

Transmission electron micrographs (TEM) showed that liposome vesicles prepared from DL-α-phosphatidylcholine dimyristoyl (1,2-ditetradecanoyl-rac-glycerol-3-phosphocholine) (DMPC) by the modified reverse-phase evaporation method (mREV) were spherical in shape and in majority of them were less than 100 nm in diameter. Differential scanning calorimetry (DSC) method was used to determine the influence of cholesterol content and pH of Tris-HCl buffer used for the preparation of liposomes on the temperature of phase transition T _C of phospholipids which form the investigated liposome vesicles. The use of DSC method made it possible to determine not only the temperature of the main phase transition of phospholipids but also the temperature of the phospholipid phase transition from the tilted gel phase(L _β′) to the ripple gel phase(P _β′). The results were compared with those obtained with EPR study. EPR study was carried out in the temperature range from 284 to 310 K i.e. below and above the phase transition temperature T _C of DMPC. On the basis of EPR spectra of spin marker 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) incorporated into the liposome, the values of parameters f were determined. Hence TEMPO can be used to observe the change in partition between aqueous and fluid lipid regions. The change in the relative values of f determined for DMPC as a function of temperature shows that this phospholipid undergoes a transition from a ‘gel phase’ to a lamellar smectic liquid crystalline phase in the presence of excess water. The EPR study of TEMPO allowed us to determine the transition temperature T _C. The results were compared with those obtained with DSC method.