DPPC Liposomes Research Articles

Interaction mechanism of three egg protein derived ACE inhibitory tri-peptides and DPPC membrane using FS, FTIR, and DSC studies.

Understanding the interaction of food derived angiotensin converting enzyme (ACE) inhibitory peptides and intestinal epithelial cell membrane may help to improve their absorption. This research aimed to study the molecular interaction of ACE inhibitory tri-peptides ADF, FGR, and MIR with DPPC membrane during absorption process. The DPPC liposome was prepared and characterized, then used as a model membrane. The permeability of tri-peptides across the membrane was investigated using Fluorescence spectroscopy. The effect of tri-peptides on the structure and dynamics of DPPC bilayers was determined using Fourier transform infrared spectroscopy. The effect of tri-peptides on the phase transition temperature in the DPPC membrane was also analyzed using Differential scanning calorimetry. The results showed that ACE inhibitory tri-peptides ADF, FGR, and MIR can penetrate into both the membrane-water interface and hydrophobic region of DPPC bilayer, and the tri-peptide FGR have higher permeability across the membrane.

Comparison of structural properties of cyclosporin A and its analogue alisporivir and their effects on mitochondrial bioenergetics and membrane behavior

The paper considers the effect of the MPT pore inhibitor cyclosporin A (CsA) and its non-immunosuppressive analogue alisporivir (Ali) on the functioning of rat skeletal muscle mitochondria. We have shown that both agents at a standard in vitro concentration of 1 μM increase the calcium capacity of organelles and have no effect on the parameters of oxidative phosphorylation. However, an increase in their concentration to 5 μM leads to the suppression of oxygen consumption by mitochondria, which is more pronounced in the case of Ali. This effect is accompanied by a decrease in the membrane potential of organelles and, apparently, is based on the inhibition of electron transport along the mitochondrial respiratory chain due to limited mobility of coenzyme Q. We have noted that both agents do not affect the production of hydrogen peroxide by isolated mitochondria. NMR spectroscopy and molecular dynamics simulation did not reveal significant differences in the structure and backbone flexibility of CsA and Ali. Both agents decrease the overall fluidity of the membrane of DPPC liposomes, inducing an increase in laurdan generalized polarization parameter. A similar effect was also found in the case of mitochondrial membranes. We suggested that these effects of CsA and Ali, associated with their lipophilic nature and the ability to accumulate in the lipid phase of membranes, may cause a decrease in the efficiency of electron transport in the respiratory chain of mitochondria and suppression of the bioenergetics of these organelles.

Preferential adsorption of L-tryptophan by L-phospholipid coated porous polymer particles

Chiral selective adsorption of L-amino acid, tryptophan (Trp) was achieved using phospholipid membrane-coated porous polymer particles (PPPs). PPPs with numerous pores were prepared by in situ polymerization of divinylbenzene, and then coated with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC, L-phospholipid) via the impregnation method. Elemental mapping of energy dispersive X-ray (EDX) analysis revealed that DPPC molecules were distributed to the surface and the inner part of PPPs, where almost all the DPPC molecules applied for impregnation were deposited on PPPs. The phospholipid membrane properties of DPPC-PPPs were characterized using the fluorescence probe 6-lauroyl-2-dimethylaminonaphthalene (Laurdan). The results show that DPPC-PPPs possessed a lipid membrane-like environment similar to pure DPPC liposomes, especially at temperatures below 35 °C. DPPC-PPPs slightly adsorbed L-Trp and D-Trp at 45 °C, while DPPC-PPPs significantly adsorbed L-Trp but not D-Trp at 30 °C: enantio excess (e.e.) was 75.0%. The time course of Trp adsorption was investigated: for both enantiomers, similar adsorption behaviors were observed for 30 h, thus suggesting surface adsorption onto DPPC-PPPs. L-Trp adsorption continued after 30 h, suggesting that L-Trp could be distributed in the inner part of DPPC-PPPs. Interestingly, the reused DPPC-PPPs featured improved adsorption performance, suggesting that the deposited DPPC membranes on PPPs could act as chiral selectors for L-Trp. The optical resolution of L-/D-Trp was performed using DPPC-PPPs, resulting in the e.e. of D-Trp was > 60%. Thus, DPPC-PPPs have the potential of chiral selective adsorption of L-amino acid, which can be used as chiral separation materials.

High-Resolution Ultrasound Spectroscopy for the Determination of Phospholipid Transitions in Liposomal Dispersions.

High-resolution ultrasound spectroscopy (HR-US) is a spectroscopic technique using ultrasound waves at high frequencies to investigate the structural properties of dispersed materials. This technique is able to monitor the variation of ultrasound parameters (sound speed and attenuation) due to the interaction of ultrasound waves with samples as a function of temperature and concentration. Despite being employed for the characterization of several colloidal systems, there is a lack in the literature regarding the comparison between the potential of HR-US for the determination of phospholipid thermal transitions and that of other common techniques both for loaded or unloaded liposomes. Thermal transitions of liposomes composed of pure phospholipids (dimyristoylphosphatidylcholine, DMPC; dipalmitoylphosphatidylcholine, DPPC and distearoylphosphatidylcholine, DSPC), cholesterol and their mixtures were investigated by HR-US in comparison to the most commonly employed microcalorimetry (mDSC) and dynamic light scattering (DLS). Moreover, tramadol hydrochloride, caffeine or miconazole nitrate as model drugs were loaded in DPPC liposomes to study the effect of their incorporation on thermal properties of a phospholipid bilayer. HR-US provided the determination of phospholipid sol-gel transition temperatures from both attenuation and sound speed that are comparable to those calculated by mDSC and DLS techniques for all analysed liposomal dispersions, both loaded and unloaded. Therefore, HR-US is proposed here as an alternative technique to determine the transition temperature of phospholipid membrane in liposomes.

Cholesterol Significantly Affects the Interactions between Pirfenidone and DPPC Liposomes: Spectroscopic Studies

In this work, we studied the effect of as on the interaction of membrane DPPC with the key antifibrotic drug pirfenidone. Liposomal forms of pirfenidone were obtained using passive loading. The addition of cholesterol reduces the loading efficiency of pirfenidone by 10%. The main binding site of pirfenidone in DPPC liposomes is the carbonyl group: the interaction with PF significantly increases the proportion of low-hydrated carbonyl groups as revealed by ATR-FTIR spectroscopy. The phosphate group acts as an additional binding site; however, due to shielding by the choline group, this interaction is weak. The hydrophobic part of the bilayer is not involved in PF binding at room temperature. Cholesterol changes the way of interaction between carbonyl groups and pirfenidone probably because of the formation of two subpopulations of DPPC and causes a dramatic redistribution of carbonyl groups onto the degrees of hydration. The proportion of moderately hydrated carbonyl groups increases, apparently due to the deepening of pirfenidone into the circumpolar region of the bilayer. For the first time, a change in the microenvironment of pirfenidone upon binding to liposomes was shown: aromatic moiety interacts with the bilayer.

Synergic fabrication of multifunctional liposomes nanocomposites for improved radiofrequency ablation combination for liver metastasis cancer therapy

The field of biomedical research has recently been interested in nanoplatforms with various functionalities, such as cancer drug carriers and MRI and optical imaging, as well as thermal treatment, among other things. As a result of the present investigation, a unique multifunctional liposome (MFL) was established in this investigation. Using radiofrequency-induced imaging and drug release based on magnetic field impact, a dual drug delivery targeted with tumor multi-mechanism treatment was made more effective. The C60 (fullerene) surface was coated with iron nanocomposites to establish the proposed nanosystems, and PEGylation was used (Fe3O4-C60-PEG2000). For fullerene radiofrequency-triggered drug release, thermosensitive DPPC liposomes with folate-DSPE-PEG2000 enveloped the binary nanosystems and doxorubicin (DOX). The in vitro cytotoxicity of the nanocomposites was confirmed by the liver metastasis in HT-29 colon cancer cells using radiofrequency. The flow cytometry analysis confirmed the apoptosis cell death mechanism. The thermal treatment combined chemotherapeutic MFL nano framework transformed radiofrequency radiation from thermoresponsive liposomes, which was noticed both in vivo and in vitro. Due to their superior active tumor targeting and magnetic targeting characteristics, the MFL could also selectively destroy cancerous liver cells in highly co-localized targets.

The spatial arrangement of astaxanthin in bilayers greatly influenced the structural stability of DPPC liposomes

Liposomes are regarded as the ideal nanocarrier for concurrent or separate delivery of nutraceuticals in the food industries. Precise control of the structural stability is essential for the processing, storage, and nutrition delivery of liposomes. Astaxanthin was found to significantly affect the membrane stability of liposomes by inserting into the phospholipid bilayers in a similar way to cholesterol. Compared with cholesterol, astaxanthin could significantly improve the phase transition temperature, membrane fluidity, and membrane compactness of liposomes. Additionally, the membrane stability was well modulated by controlling the distribution patterns of astaxanthin (monomers, H- and J-aggregates) in bilayers. For instance, astaxanthin H-aggregates could endow the liposomal membrane with highest rigidity and compactness. Additionally, astaxanthin aggregates, especially J-aggregates could greatly improve storage stability of liposomes, thus providing a novel strategy to regulate and optimize the stability of liposomes for their diversified applications.

The interaction of evodiamine and rutaecarpine with DPPC liposomes

Evodiamine and rutaecarpine, derived from the traditional chinese medicine Euodia rutaecarpa (Juss.) Benth, have many similar pharmacological effects, but their pharmacological mechanisms are not exactly the same. In this study, liposomes were used as the model of biomembrane. DSC, synchrotron XRD and FTIR techniques have been employed to investigate and compare the interaction of evodiamine and rutaecarpine with DPPC liposomes. The results show that evodiamine and rutaecarpine remarkably affect the DPPC in a concentration-dependent manner. But the concentration dependence of the two drugs is obviously different. The effect of rutaecarpine on liposome membrane was stronger than that of evodiamine, which might be related to the different pharmacological mechanism of evodiamine and rutaecarpine. This study will play an important role in the further investigation of interaction of drugs with biomimetic membranes and further investigation of pharmacological mechanisms of drugs.

Liposome-Mediated Delivery of MERS Antigen Induces Potent Humoral and Cell-Mediated Immune Response in Mice.

The advancements in the field of nanotechnology have provided a great platform for the development of effective antiviral vaccines. Liposome-mediated delivery of antigens has been shown to induce the antigen-specific stimulation of the humoral and cell-mediated immune responses. Here, we prepared dried, reconstituted vesicles (DRVs) from DPPC liposomes and used them as the vaccine carrier system for the Middle East respiratory syndrome coronavirus papain-like protease (DRVs-MERS-CoV PLpro). MERS-CoV PLpro emulsified in the Incomplete Freund’s Adjuvant (IFA-MERS-CoV PLpro) was used as a control. Immunization of mice with DRVs-MERS-CoV PLpro did not induce any notable toxicity, as revealed by the levels of the serum alanine transaminase (ALT), aspartate transaminase (AST), blood urea nitrogen (BUN) and lactate dehydrogenase (LDH) in the blood of immunized mice. Immunization with DRVs-MERS-CoV PLpro induced greater antigen-specific antibody titer and switching of IgG1 isotyping to IgG2a as compared to immunization with IFA-MERS-CoV PLpro. Moreover, splenocytes from mice immunized with DRVs-MERS-CoV PLpro exhibited greater proliferation in response to antigen stimulation. Moreover, splenocytes from DRVs-MERS-CoV PLpro-immunized mice secreted significantly higher IFN-γ as compared to splenocytes from IFA-MERS-CoV PLpro mice. In summary, DRVs-MERS-CoV PLpro may prove to be an effective prophylactic formulation to prevent MERS-CoV infection.

Interaction of DPPC liposomes with cholesterol and food protein during in vitro digestion using Dynamic Light Scattering and FTIR spectroscopy analysis

The influence of cholesterol (CHO), bovine serum albumin (BSA) and lactoferrin (LF), on the phase transition temperature (Tm) and structure of DPPC liposomes during in vitro digestion was investigated using Dynamic Laser Scattering (DLS) and Fourier Transform Infrared Spectroscopy technologies (FTIR). CHO enhanced bilayers thickness and acyl chain order, especially in DPPC:CHO of 6:1, with the average size increase to 1.77 ± 0.20 μm and broaden of phase transition (Tm 45.8 °C). Protein critically impacted on the liposomal structure through formation of hydrogen bonds between in DPPC and protein. Liposomal size and Tm were significantly changed after simulated gastric digestion, whereas the pancreatic incubation can broaden transition phase and weaken functional groups of liposomes. Our data provided a better understanding on structure changes of CHO-containing membrane and protein addition by revealing Tm and chemical bonds details, and added to current knowledge for evaluating the different component on liposomal digestibility in food area.

Shorter Alkyl Chains Enhance Molecular Diffusion and Electron Transfer Kinetics between Photosensitisers and Catalysts in CO2 -Reducing Photocatalytic Liposomes.

Covalent functionalisation with alkyl tails is a common method for supporting molecular catalysts and photosensitisers onto lipid bilayers, but the influence of the alkyl chain length on the photocatalytic performances of the resulting liposomes is not well understood. In this work, we first prepared a series of rhenium‐based CO2‐reduction catalysts [Re(4,4’‐(CnH2n+1)2‐bpy)(CO)3Cl] (ReCn ; 4,4’‐(CnH2n+1)2‐bpy=4,4’‐dialkyl‐2,2’‐bipyridine) and ruthenium‐based photosensitisers [Ru(bpy)2(4,4’‐(CnH2n+1)2‐bpy)](PF6)2 (RuCn ) with different alkyl chain lengths (n=0, 9, 12, 15, 17, and 19). We then prepared a series of PEGylated DPPC liposomes containing RuCn and ReCn , hereafter noted Cn , to perform photocatalytic CO2 reduction in the presence of sodium ascorbate. The photocatalytic performance of the Cn liposomes was found to depend on the alkyl tail length, as the turnover number for CO (TON) was inversely correlated to the alkyl chain length, with a more than fivefold higher CO production (TON=14.5) for the C9 liposomes, compared to C19 (TON=2.8). Based on immobilisation efficiency quantification, diffusion kinetics, and time‐resolved spectroscopy, we identified the main reason for this trend: two types of membrane‐bound RuCn species can be found in the membrane, either deeply buried in the bilayer and diffusing slowly, or less buried with much faster diffusion kinetics. Our data suggest that the higher photocatalytic performance of the C9 system is due to the higher fraction of the more mobile and less buried molecular species, which leads to enhanced electron transfer kinetics between RuC9 and ReC9 .

Liposomes with cyclodextrin channels and polyethyleneimine (PEI) improves cytoplasmic vaccine delivery and induces anti-cancer immune activity in mice

Cancer vaccines have been developed as an additional method of treatment in the fight against cancer. However, an important barrier to an effective vaccine is the inefficient presentation of exogenous antigen by dendritic cells to cytotoxic CD8 T cells. In this study, DPPC liposomes were modified with channels and loaded with polyethyleneimine (PEI) and 5,6-dimethylxanthenone-4-acetic acid (DMXAA) to produce a vaccine carrier. The liposomes were designed to be pH responsive to facilitate delivery of antigens directly to the cytoplasm of antigen presenting cells, bypassing the cross-presentation pathway and improving cellular immune responses. The lysis of liposomes in acidic cell-free conditions was measured using a validated dynamic light scattering assay in order to gain an insight into the mechanism of PEI-mediated lysis. Dendritic cell stimulation and T cell proliferation was investigated in vitro and the potential of this formulation to stimulate a therapeutic anti-cancer immune response was examined in a murine melanoma model. The modified formulation stimulated T cell activation in vitro and induced a small but significant increase in survival in immunized mice. Overall, liposomes modified with PEI and channels successfully delivered antigen to the cytoplasm of dendritic cells, which subsequently led to the development of an appropriate immune response.

Electroporation-enhanced entrapment of diclofenac sodium and ascorbic acid into DPPC liposomes

The effect of electroporation on the physical characteristics of 1,2-dipalmitoyl-Sn-glycerol-3- phosphocholine (DPPC) liposome loading diclofenac sodium, ascorbic acid and Rhodamine B was studied. Group one liposomes were incubated with diclofenac sodium, group two liposomes were incubated with ascorbic acid and group three: liposomes were incubated with Rhodamine B. The three groups were subjected to electroporation protocol. Samples were exposed to different field strengths at pulses 30, 60 and 90 pulses respectively with pulse duration 4 milliseconds. After electroporation, liposomes were separated from unentrapped drugs and form the dye through centrifugation. Physical characteristics of liposomes were examined using Transmission electron microscope (TEM), Confocal laser scanning microscopy (CLSM) and particle size analysis. Liposomes are entrapping ascorbic acid with high efficiency at the values of 900 V/0.2 cm with 60 pulses, 800 and 1000 V/ 0.2 cm at 90 pulses. Diclofenac sodium was entrapped at 800 V/0.2 cm and 90 pulses. Rhodamine B was entrapped at 500 and 1000 V/0.2 cm at 30 pulses. Based on the present results, entrapping of diclofenac sodium and ascorbic acid into liposomes can be controlled efficiently by electroporation technique. Optimum entrapping occurred at 800 V/0.2 cm and 90 pulses for ascorbic acid and DS at 900 V/0.2 cm and 30 pulses for Rh-B.

Bipolar Imidazolium-Based Lipid Analogues for Artificial Archaeosomes.

Archaeal lipids have harvested biomedical and biotechnological interest because of their ability to form membranes with low permeability and enhanced temperature and pressure stability. Because of problems in isolating archaeal lipids, chemical synthesis appears to be a suitable means of producing model lipids that mimic the biological counterparts. Here, we introduce a new concept: we synthesized bipolar alkylated imidazolium salts of different chain lengths (BIm10-32) and studied their structure and lyotropic phase behavior. Furthermore, mixtures of the bolalipid analogues with phospholipid model biomembranes of diverse complexity were studied. DSC, fluorescence and FTIR spectroscopy, confocal fluorescence microscopy, DLS, SAXS, and TEM were used to reveal changes in lipid phase behavior, fluidity, the lipid's conformational order, and membrane morphology over a wide range of temperatures and for selected pressures. It could be shown that the long-chain BImN32 can form monolayer sheets. Integrated in phospholipid membranes, it reveals a fluidizing effect. Here, the two polar head groups, connected by a long alkyl chain, enable the integration into the bilayer. Interestingly, addition of BImN32 to fluid DPPC liposomes increased the lipid packing markedly, rendering the membrane system more stable at higher temperatures. The membrane system is also stable against compression as indicated by the high-pressure stability of the system, mimicking an archaeal lipid-like behavior. BImN32 incorporation into raft-like anionic model biomembranes led to marked changes in lateral membrane organization, topology, and fusogenicity of the membrane. Overall, it was found that long-chain imidazolium-based bolalipid analogues can help adjust membrane's biophysical properties, while the imidazolium headgroup provides the ability for crucial electrostatic interaction for vesicle fusion or selective interaction with membrane-related signaling molecules and polypeptides in a synthetically tractable manner. The results obtained may help to develop new approaches for rational design of extremophilic bolalipid-based liposomes for various applications, including delivery of drugs and vaccines.

PEGylated DPPC/Anti-SNAP25 Antibody Targeted Liposomes from Langmuir Monolayer Study to Formulations

Background: Molecule compatibility is an important factor to be considered before preparing antibody-targeted liposomes, stealth-liposomes, and stealth antibody-targeted liposomes. Objective: To determine the intermolecular interaction of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamide- N-[methoxy(polyethyleneglycol)-2000] (ammonium salt), DOPE PEG2000 and Anti-SNAP25 (AS25) in 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine (DPPC) monolayer, and their liposomes. Methods: In this study, DPPC was used to create a monolayer mimicking the half membrane of liposomes to investigate its interactions with a polyclonal antibody, AS25, and DOPE PEG2000, which are based on Langmuir-Blodgett (LB) techniques. The surface morphology of DPPC-AS25 and DPPC-DOPE PEG2000-AS25 bilayers were also imaged and analyzed by using atomic force microscopy (AFM) to support the LB findings. The LB findings were then utilized as a reference to prepare DPPC liposomes in this work. Results: The best mole ratio of DPPC-DOPE PEG2000, determined to be 50 to 1, was used to study the interaction with the polyclonal antibody AS25. The free energy of mixing (ΔGmix) of DPPC- DOPE PEG2000-AS25 was more negative than DPPC-AS25 in the entire investigated ranges, indicating that the ternary mixture of DPPC-DOPE PEG2000-AS25 was more compatible than the binary mixture of DPPC-AS25. The presence of DOPE PEG2000 in DPPC-AS25 increased the fluidity of the membrane, which resulted in a greater interaction of AS25 with DPPC. Conclusion: The constant values of particle size and zeta potential measurements of DPPC-DOPE PEG2000-AS25 liposomes showed agreement with the LB findings, indicating that LB is a good technique to predict precise liposomal formulations.

The Interaction of Baicalein with Dipalmitoylphosphatidylcholine Liposomes: Differential Scanning Calorimetry, Synchrotron X-ray Diffraction, and Fourier Transform Infrared Studies

Baicalein is an important flavonoid compound extracted from the roots of Scutellaria baicalensis. The interaction between baicalein and DPPC liposomes has been studied by differential scanning calorimetry, synchrotron X-ray diffraction and Fourier transform infrared spectroscopy. The results showed the phase states of liposomes change under the disturbance of baicalein. When the molar percentage of baicalein (x) is not more than 5%, the baicalein molecules promote the hydration degree of the head groups. At x=5%, the liposomes undergo a change from Lβ′ to Lβ phase. When x is between 5% and 10%, the liposomes are in Pβ′ phase. When x is more than 10%, the baicalein molecules alter the hydration state of head groups. Meanwhile, the phase states shift from Pβ′ to Pβ. This study is of great significance to further study the interaction between drugs and biomimetic membranes and to further investigate the phase transition mechanisms of DPPC liposome.

Liposomes with Water as a pH-Responsive Functionality for Targeting of Acidic Tumor and Infection Sites.

A lipid named DCPA was synthesized under microwave‐assisted heating. DCPA possesses a pyridine betaine, hydrophilic group that can be complexed with water through hydrogen bonding (DCPA‐H2O). DCPA‐H2O liposomes became protonated relatively fast already at pH<6.8, due to the high HOMO binding energy of DCPA‐H2O. In murine models, DCPA‐H2O liposomes had longer blood circulation times than natural DPPC or cationic DCPM liposomes, while after tail‐vein injection DCPA‐H2O liposomes targeted faster to solid tumors and intra‐abdominal infectious biofilms. Therapeutic efficacy in a murine, infected wound‐healing model of tail‐vein injected ciprofloxacin‐loaded DCPA‐H2O liposomes exceeded the ones of clinically applied ciprofloxacin as well as of ciprofloxacin‐loaded DPPC or DCPM liposomes.

Liposomes with Water as a pH‐Responsive Functionality for Targeting of Acidic Tumor and Infection Sites

AbstractA lipid named DCPA was synthesized under microwave‐assisted heating. DCPA possesses a pyridine betaine, hydrophilic group that can be complexed with water through hydrogen bonding (DCPA‐H2O). DCPA‐H2O liposomes became protonated relatively fast already at pH&lt;6.8, due to the high HOMO binding energy of DCPA‐H2O. In murine models, DCPA‐H2O liposomes had longer blood circulation times than natural DPPC or cationic DCPM liposomes, while after tail‐vein injection DCPA‐H2O liposomes targeted faster to solid tumors and intra‐abdominal infectious biofilms. Therapeutic efficacy in a murine, infected wound‐healing model of tail‐vein injected ciprofloxacin‐loaded DCPA‐H2O liposomes exceeded the ones of clinically applied ciprofloxacin as well as of ciprofloxacin‐loaded DPPC or DCPM liposomes.

Phase Transitions and Structural Changes in DPPC Liposomes Induced by a 1-Carba-Alpha-Tocopherol Analogue.

Steady-state emission spectroscopy of 1-anilino-8- naphthalene sulfonate (ANS) and 1,6-diphenyl-1,3,5-hexatriene (DPH), fluorescence anisotropy, and DSC methods were used to characterize the interactions of the newly synthesized 1-carba-alpha-tocopherol (CT) with a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membrane. The DSC results showed significant perturbations in the DPPC structure for CT concentrations as low as 2 mol%. The main phase transition peak was broadened and shifted to lower temperatures in a concentration-dependent manner, and pretransition was abolished. Increasing CT concentrations induced the formation of new phases in the DPPC structure, leading to melting at lower temperatures and, finally, disruption of the ordered DPPC structure. Hydration and structural changes of the DPPC liposomes using ANS and DPH fluorescent probes, which are selectively located at different places in the bilayer, were studied. With the increased concentration of CT molecules in the DPPC liposomes, structural changes with the simultaneous formation of different phases of such mixture were observed. Temperature studies of such mixtures revealed a decrease in the temperature of the main phase transition and fluidization at decreasing temperatures related to increasing hydration in the bilayer. Contour plots obtained from concentration–temperature data with fluorescent probes allowed for identification of different phases, such as gel, ordered liquid, disordered liquid, and liquid crystalline phases. The CT molecule with a modified chromanol ring embedded in the bilayer led to H-bonding interactions, expelling water molecules from the interphase, thus introducing disorder and structural changes to the highly ordered gel phase.

Effect of trace amounts of ionic surfactants on the zeta potential of DPPC liposomes

Surfactants are commonly found in today's world as an essential component of cleaning detergents, cosmetics and drug delivery systems. They can penetrate into lipid membranes, thus changing their properties. The aim of this paper is to compare the effect of addition of small amounts of cationic (DTAB) and anionic surfactants (SDS) with the same alkyl chain length on the zeta potential of DPPC liposomes with their influence on the corresponding DPPC monolayers. It was found that the addition of ionic surfactants with an initial concentration in the solution equal to 2.3, 4.5 and 9.1 μM to the liposome suspension changes their electrokinetic potential significantly. These changes increase with the increasing surfactant concentration and are greater for the anionic surfactant. This indicates the incorporation of surfactants into the structure of liposomes. Based on the analysis of π-area isotherms of DPPC monolayers it was proved that the ionic surfactant molecules are irreversibly integrated into the DPPC monolayer.