Neutral Dipalmitoylphosphatidylcholine Research Articles

The influence of a biomimetic pulmonary surfactant modification on the in vivo fate of nanoparticles in the lung

Direct biomimetic modification of nanoparticles (NPs) with endogenous surfactants is helpful to improve the biocompatibility of NPs and avoid damage to the physiological function of the lung. Therefore, the objective of this study is to investigate the influence of biomimetic endogenous pulmonary surfactant phospholipid modification on the in vivo fate of NPs after lung delivery. Here, two neutral phospholipids (dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylamine (DPPE)) and two negatively charged phospholipids (dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphatidylserine (DPPS)) were selected to modify paclitaxel (PTX)-loaded PLGA NPs with different molar ratio. DPPC, DPPE, and DPPG improved mucoadhesion, in contrast, DPPS improved the mucus permeability of the NPs. Neutral DPPC and DPPE reduced, but negatively charged DPPS and DPPG increased the uptake by alveolar macrophages, all types of phospholipid increased the uptake by lung epithelial cells and increased PTX retention in the whole lung. Whereas, DPPC, DPPE, and DPPG promoted PTX retention in bronchoalveolar lavage fluid (BALF), while DPPS promoted PTX absorption in the lung tissue. Only DPPS-PLGA (1:1) NPs remarkably increased PTX systemic exposure. A good correlation between PTX percentage in the supernatant of BALF and PTX concentration in plasma was established, implying PTX entered the system circulation mainly in molecular form. Phospholipid modification had no effect on extrapulmonary organ distribution of PTX. Taken together, our study disclosed that different phospholipid modification can endow the NPs mucoadhesive or mucus penetration and cellular uptake properties, with tunable retention in BALF and absorption in the lung tissue, providing the scientific background for translational nanocarrier design for inhalation as required. Statement of significanceInhaled nanomedicines will inevitably interact with pulmonary surfactant and form “surfactant corona”. However, the contribution of individual pulmonary surfactant phospholipid on the in vivo fate of nanomedicines is still unclear. In this regard, the most abundant pulmonary surfactant phospholipid dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylamine, and dipalmitoylphosphatidylglycerol and dipalmitoylphosphatidylserine were selected to modify the paclitaxel loaded PLGA nanoparticles and the effect of these pulmonary surfactant phospholipids on their in vivo fate was investigated. It was demonstrated that different phospholipid modification can endow the nanoparticles mucoadhesive or mucus penetration properties, with tunable retention in bronchoalveolar lavage fluid, alveolar macrophages uptake and absorption in the lung tissue. The present study provided a comprehensive understanding for the role of pulmonary surfactant phospholipid on inhaled nanomedicines.

Moxifloxacin interacts with lipid bilayer, causing dramatic changes in its structure and phase transitions

Most drugs besides their intended activity, express undesired side effects, including those with the engagement of cell membrane. Previously, such undesired nonspecific effects on the membrane have been shown for a number of widely used nonsteroidal anti-inflammatory drugs. In this paper, we study the mechanism of interaction between moxifloxacin (Mox), antibacterial drug of broad specificity, with lipid bilayer of the liposomes of various compositions as a model of cell membrane using a combination of spectroscopy methods, including ATR-FTIR spectroscopy, circular dichroism, UV and fluorescence spectroscopy. The fine structure of the moxifloxacin-liposome complex, localization of the drug in bilayer and the main sites of Mox interaction with lipid membrane were determined. Lipid composition of the liposome plays a key role in the interaction with moxifloxacin, drastically affecting the loading efficiency, strength and character of drug binding, lipid phase segregation and phase transition parameters. In case of anionic liposomes composed of dipalmitoylphosphatidylcholine (DPPC) and cardiolipin (CL2−) the electrostatic interaction of negatively charged nitrogen in heterocycle moiety of moxifloxacin with cardiolipin phosphate groups is a crucial factor for stable complex formation. The study of moxifloxacin-liposome complex behavior at phase transition in bilayer by DSC method revealed that in DPPC/CL2− liposomes system two microphases with different content of CL2- coexist and Mox interacts with both of these microphases resulting in the formation of two types of complexes with different structure and phase transition temperature. This binding stabilized the gel-state of the lipid bilayer with increasing the phase transition temperature Tm up to 3−5 °C. A different situation is observed for neutral DPPC liposomes: drug interaction with bilayer results in defects formation and a fluidization effect in lipid bilayer, resulted to decrease the Tm value by 2−4 °C. Moxifloxacin is not firmly binding in the membrane of DPPC and drug releases rapidly.

Nanoparticle Wettability Influences Nanoparticle-Phospholipid Interactions.

We explored the influence of nanoparticle (NP) surface charge and hydrophobicity on NP-biomolecule interactions by measuring the composition of adsorbed phospholipids on four NPs, namely, positively charged CeO2 and ZnO and negatively charged BaSO4 and silica-coated CeO2, after exposure to bronchoalveolar lavage fluid (BALf) obtained from rats, and to a mixture of neutral dipalmitoyl phosphatidylcholine (DPPC) and negatively charged dipalmitoyl phosphatidic acid (DPPA). The resulting NP-lipid interactions were examined by cryogenic transmission electron microscopy (cryo-TEM) and atomic force microscopy (AFM). Our data show that the amount of adsorbed lipids on NPs after incubation in BALf and the DPPC/DPPA mixture was higher in CeO2 than in the other NPs, qualitatively consistent with their relative hydrophobicity. The relative concentrations of specific adsorbed phospholipids on NP surfaces were different from their relative concentrations in the BALf. Sphingomyelin was not detected in the extracted lipids from the NPs despite its >20% concentration in the BALf. AFM showed that the more hydrophobic CeO2 NPs tended to be located inside lipid vesicles, whereas less hydrophobic BaSO4 NPs appeared to be outside. In addition, cryo-TEM analysis showed that CeO2 NPs were associated with the formation of multilamellar lipid bilayers, whereas BaSO4 NPs with unilamellar lipid bilayers. These data suggest that the NP surface hydrophobicity predominantly controls the amounts and types of lipids adsorbed, as well as the nature of their interaction with phospholipids.

Demixing and crystallization of DODAB in DPPC-DODAB binary mixtures.

The crystallization mechanism of one lipid component within multicomponent lipid mixtures remains unclear. To shed light on this issue, we studied the demixing and crystallization behaviors of a binary lipid system using neutral dipalmitoylphosphatidylcholine (DPPC) and cationic dioctadecyldimethylammonium bromide (DODAB) as model molecules. The results indicate that when DODAB is no more than equimolar (e.g., DPPC/DODAB = 2/1 and 1/1), DPPC is miscible with DODAB and hinders the crystallization of DODAB, and the samples undergo reversible gel-fluid phase transitions upon heating and cooling. However, when DODAB is dominant in the mixture (DPPC/DODAB = 1/2), cooling of the mixed fluid phase results in the formation of a DODAB-rich gel domain and a DPPC-DODAB mixed gel domain. Such phase-separated mixed gels can undergo further demixing and crystallization, producing a DODAB-rich crystalline domain and a DPPC-rich tilted gel domain upon prolonged (or plus low-temperature) incubation. Besides, evidence has been given that the crystallized DODAB-rich domain remains in the same lipid bilayer as the DPPC-rich domain. All the three binary lipid mixtures can hold large amounts of water in the lipid interlamellar regions, allowing the incorporation of a large number of water-soluble substances such as DNA or proteins, which can be used for the fabrication of functional biofilms and biomaterials. Influences of water content and salt concentration on the phase structures (e.g., repeat distances) of the binary mixtures have also been studied.

In Situ Unfolded Lysozyme Induces the Lipid Lateral Redistribution of a Mixed Lipid Model Membrane

Redistribution of charged lipids induced by polyelectrolytes is an intriguing phenomenon. Proteins, due to their nature as polyelectrolytes, should also have this capacity. But their highly ordered structures may bring about more complex mechanisms. We studied the interaction between positively charged lysozyme and liposomes consisting of neutral dipalmitoylphosphatidylcholine (DPPC) and negatively charged dioleoylphosphatidylglycerol (DOPG). Interestingly, the enrichment of DOPG cannot be induced by the native and ex situ unfolded (unfolded in the absence of liposomes) lysozyme, but requires that lysozyme undergo an in situ unfolding process (unfolding in the presence of liposomes). These observations suggest that, for proteins, the capacity to induce lipid redistribution relies on not only the net charges but also the spatial distribution of the charges. During the in situ unfolding process, lysozyme reorganizes its structure into a specially unfolded structure that is rich in flat β-sheets and more "rigid" in the presence of lipid membrane. This special spatial structure changes the charge distribution and is advantageous to the protein-membrane electrostatic interaction and thus can induce lipid redistribution.

The role of lateral tension in calcium-induced DPPS vesicle rupture.

We assess the role of lateral tension in rupturing anionic dipalmitoylphosphatidyserine (DPPS), neutral dipalmitoylphosphatidylcholine (DPPC), and mixed DPPS-DPPC vesicles. Binding of Ca(2+) is known to have a significant impact on the effective size of DPPS lipids and little effect on the size of DPPC lipids in bilayer structures. In the present work we utilized laser transmission spectroscopy (LTS) to assess the effect of Ca(2+)-induced stress on the stability of the DPPS and DPPC vesicles. The high sensitivity and resolution of LTS has permitted the determination of the size and shape of liposomes in solution. The results indicate a critical size after which DPPS single shell vesicles are no longer stable. Our measurements indicate Ca(2+) promotes bilayer fusion up to a maximum diameter of ca. 320 nm. These observations are consistent with a straightforward free-energy-based model of vesicle rupture involving lateral tension between lipids regulated by the binding of Ca(2+). Our results support a critical role of lateral interactions within lipid bilayers for controlling such processes as the formation of supported bilayer membranes and pore formation in vesicle fusion. Using this free energy model we are able to infer a lower bound for the area dilation modulus for DPPS (252 pN/nm) and demonstrate a substantial free energy increase associated with vesicle rupture.

Decorporation and therapeutic efficacy of liposomal-DTPA against thorium-induced toxicity in the Wistar rat

Purpose: This study examined the effect of liposomal encapsulation of 99mTc-labeled diethylenetriaminepentaacetic acid (metastable technetium labeled DTPA) on its organ distribution and therapeutic effect of optimized neutral liposomal-DTPA against thorium (232Th)-induced liver toxicity and its accumulation in rat animal model.Materials and methods: 99mTc-DTPA was encapsulated in neutral (dipalmitoylphosphatidylcholine:cholesterol) and positively (dipalmitoylphosphatidylcholine:cholesterol:stearylamine) charged liposomes using thin film hydration method. Comparative efficacy of liposomal and free DTPA (11.2 mg/kg) was examined in terms of its effect on 232Th accumulation and subsequent toxicity in the liver and blood of rat administered with 232Th-nitrate (600 μg/kg). Organ distribution of free or liposomal 99mTc-DTPA was determined by solid scintillation counting and 232Th accumulation by Inductively Coupled Plasma-Atomic Emission Spectroscopy.Results: Neutral liposomes encapsulated with 99mTc-DTPA showed more uptake in liver, spleen and blood than with positively charged liposomal- and free- 99mTc-DTPA. Administration of 232Th-nitrate to rat significantly increased the levels of liver toxicity markers and of oxidative injury, which were found to be restored more significantly by neutral liposomal-DTPA than free-DTPA. The accumulation of 232Th in liver and blood of contaminated mice was found to be decreased more significantly by neutral liposomal-DTPA than by free-DTPA.Conclusions: Decorporation and consequent mitigation of 232Th induced toxicity may be significantly improved by liposomal encapsulation of DTPA, a chelating agent.

Convulsant agent pentylenetetrazol does not alter the structural and dynamical properties of dipalmitoylphosphatidylcholine model membranes

Pentylenetetrazol (PTZ) is an epileptogenic agent, which is widely used in the determination of epilepsy-induced alterations and in the assessment of anticonvulsant agents in epileptic studies. Even though PTZ is suggested to induce repetitive firing of nerve fibers and shorten the refractory, its mechanism of action is only partially understood. In the literature there are discrepancies for its action mechanism. While some studies stated that primary sites of PTZ are membrane proteins, some reports indicated that PTZ acts on membrane lipids. In order to gain new insight for this we tested the possibility of interaction of PTZ with a simplified model system called dipalmitoylphosphatidylcholine (DPPC) multilamellar vesicles (MLVs) at agent concentrations (0–24 mol%) using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), electron spin resonance (ESR) and steady-state fluorescence spectroscopy. The results showed that PTZ at concentrations used (1–24 mol%), does not cause any significant change in lipid phase behavior, lipid dynamics (fluidity), lipid acyl chain flexibility (order), hydration state of the head group and/or the region near the head group of DPPC MLVs. These results clearly revealed that PTZ does not change the structural and dynamical parameters of neutral DPPC lipid vesicles and does not locate within the bilayer.

Ghrelin–liposome interactions: Characterization of liposomal formulations of an acylated 28‐amino acid peptide using CE

Ghrelin is a pharmacologically interesting peptide hormone due to its effects on appetite and metabolism. The cationic, octanoylated 28 amino acid peptide has a short biological half-life; thus, prolonged release formulations are of interest. Acylated peptides have been suggested to bind to or be incorporated into liposomes. Formulations based on neutral dipalmitoylphosphatidylcholine (DPPC) liposomes and phosphatidylcholine:cholesterol (70:30 mol%) liposomes, and negatively charged dipalmitoylphosphatidylcholine:dipalmitoylphosphatidylserine (DPPC:DPPS) (70:30 mol%) liposomes (2 mM total lipid concentration) were characterized using ACE. Pre-equilibrium CZE and frontal analysis CE methods circumventing capillary wall adsorption of the peptide and the liposomes and suitable for characterizing ghrelin-liposome interactions were developed. The cationic peptide exhibited low affinity (<10% bound) for DPPC and phosphatidylcholine:cholesterol (70:30 mol%) liposomes whereas electrostatic interactions caused a higher affinity for DPPC:DPPS (70:30 mol%) liposomes. Studies on desacyl ghrelin instead of ghrelin demonstrated the significance of the n-octanoyl side chain as an affinity providing moiety towards DPPC:DPPS liposomes (48 and 73% bound peptide, respectively). CE experiments showed that the binding was characterized by rapid dissociation kinetics.

Stability, liposome interaction, and in vivo pharmacology of ghrelin in liposomal suspensions

Ghrelin is an appetite-stimulating peptide hormone. It is a pharmacologically interesting peptide because of its involvement in e.g. appetite and metabolism, but it has a very short half-life in the body. Ghrelin carries a Ser-3-octanoyl group, and it has previously been suggested that acylated peptides can bind to or be incorporated into liposomes. Therefore, neutral dipalmitoylphosphatidylcholine (DPPC) liposomes and phosphatidylcholine:cholesterol (PC:Chol) (70:30) liposomes as well as negatively charged dipalmitoylphosphatidylcholine:dipalmitoylphosphatidylserine (DPPC:DPPS) liposomes (70:30) were prepared, and ghrelin was added. The chemical and physical stability of ghrelin was examined. Affinity capillary electrophoresis (ACE) revealed an interaction between ghrelin and the negatively charged (DPPC:DPPS) liposomes, whereas only very small affinities were discerned in the other liposomal formulations of ghrelin. Differential scanning calorimetry showed no changes in phase transitions ( T m). In vivo pharmacokinetics following subcutaneous administration of ghrelin in buffer and in the liposomal formulations was examined in rats. The PC:Chol formulation had a longer-lasting effect as compared to the ghrelin buffer solution and the other two liposomal formulations. The prolonged effect of the PC:Chol formulation is suggested not to be caused by association between ghrelin and the liposome.

Chitosan as a Removing Agent of β-Lactoglobulin from Membrane Models

Many chitosan biological activities depend on the interaction with biomembranes, but so far it has not been possible to obtain molecular-level evidence of chitosan action. In this article, we employ Langmuir phospholipid monolayers as cell membrane models and show that chitosan is able to remove beta-lactoglobulin (BLG) from negatively charged dimyristoyl phosphatidic acid (DMPA) and dipalmitoyl phosphatidyl glycerol (DPPG). This was shown with surface pressure isotherms and elasticity and PM-IRRAS measurements in the Langmuir monolayers, in addition to quartz crystal microbalance and fluorescence spectroscopy measurements for Langmuir-Blodgett (LB) films transferred onto solid substrates. Some specificity was noted in the removal action because chitosan was unable to remove BLG incorporated into neutral dipalmitoyl phosphatidyl choline (DPPC) and cholesterol monolayers and had no effect on horseradish peroxidase and urease interacting with DMPA. An obvious biological implication of these findings is to offer reasons that chitosan can remove BLG from lipophilic environments, as reported in the recent literature.

The Surfactant Peptide KL4 in Lipid Monolayers: PHASE BEHAVIOR, TOPOGRAPHY, AND CHEMICAL DISTRIBUTION

Studies of different fragments and mutants of SP-B suggest that the function related structural and compositional characteristics in SP-B are its positive charges with intermittent hydrophobic domains. KL4 ([lysine-(leucine)4]4-lysine) is a synthetic peptide based on SP-B structure and is the major constituent of Surfaxin, a potential therapeutic agent for respiratory distress syndrome in premature infants. There is, however, no clear understanding about the possible lipid-KL4 interactions behind its function, which is an inevitable knowledge to design improved therapeutic agents. To examine the phase behavior, topography, and lipid specificity of KL4/lipid systems, we aimed to study different surfactant model systems containing KL4, neutral dipalmitoylphosphatidylcholine (DPPC) and/or negatively charged dipalmitoylphosphatidylglycerol (DPPG) in the presence of Ca2+ ions. Surface pressure-area isotherms, fluorescence microscopic images, scanning force microscopy as well as time-of-flight secondary ion mass spectrometry suggest (i) that KL4 is not miscible with DPPC and therefore forms peptide aggregates in DPPC/KL4 mixtures; (ii) that KL4 specifically interacts with DPPG via electrostatic interactions and induces percolation of DPPG-rich phases; (iii) that existing DPPG-Ca2+ interactions are too strong to be overcome by KL4, the reason why the peptide remains excluded from condensed DPPG domains and passively colocalizes with DPPC in a demixed fluid phase; and (iv) that the presence of negatively charged lipid is necessary for the formation of bilayer protrusions. These results indicate that the capability of the peptide to induce the formation of a defined surface-confined reservoir depends on the lipid environment, especially on the presence of anionic lipids.

The psychotropic drug olanzapine (Zyprexa®) increases the area of acid glycerophospholipid monolayers

The typical antipsychotics chlorpromazine (CPZ) and trifluoperazine (TFP) increase the mean molecular area (mma) of acidic, but not neutral, glycerophospholipids in monolayers at pH 7.36 measured by the Langmuir technique. The atypical antipsychotic olanzapine (OLP 1 1 The uncharged and positively charged forms of OLP are designated OLP 0 and OLP +, respectively. ) is structurally similar to TFP. We have therefore studied the effects of OLP on glycerophospholipid monolayers and in comparison with CPZ. Olanzapine (10 µM, in subphase, pH 7.36) influenced the isotherms (surface pressure versus mma) in monolayers of the neutral dipalmitoyl phosphatidylcholine (DPPC) and the acidic dipalmitoyl phosphatidylserine (DPPS) or 1-palmitoyl-2-oleoylphosphatidylserine (POPS) in the increasing order of mma: DPPS < DPPC < POPS at both lower and higher temperature. Thus, presence of an unsaturated acyl in PS increased the drug-induced effect on mma. The mma in the absence of drugs was lower at lower temperatures than at higher temperatures. OLP affected mma to a greater extent than CPZ, and caused the greatest interaction at surface pressure of 30 mN/m at higher temperatures. In contrast, CPZ gave the largest effect in the monolayers at surface pressure 30 mN/m at lower temperatures. CPZ did not alter the isotherms of DPPC, at lower or higher temperature, and only affected the packing of the DPPS and POPS monolayers. In contrast, OLP altered the isotherms of DPPC. It is suggested that the drugs affect the monolayer packing by intercalating between the glycerophospholipid molecules. Since CPZ has major side effects, while OLP has few, this may indicate that there is poor correlation between side effects and effects of the drugs on phospholipid monolayers.

Interaction of Myelin Basic Protein with Phospholipid Monolayers: Mechanism of Protein Penetration

The myelin basic protein (MBP) is the second most abundant protein in the myelin sheath of the central nervous system and is believed to be important for the compactness and integrity of the membrane. We investigated the mechanism of the interaction of lipid-free MBP with phospholipid monolayers at the air/water interface; in particular, we studied the process of MBP adsorption onto monolayers made up either of neutral dipalmitoylphosphatidylcholine (DPPC) or of negatively charged dipalmitoylphosphatidylserine (DPPS) monolayers. They are natural constituents of the myelin membrane, and sharing an identical hydrophobic chain, they differ only in headgroup composition. The MBP−lipid interaction is investigated for the first time by means of nullellipsometric measurements, monitoring in real time the effect of adsorbed molecules in the insoluble monolayer at different monolayer conditions, such as surface pressure and molecular area. The different behavior of monolayer thickness and surface pressure confirmed the hypothesis of a different interaction mechanism of MBP with the two kind of lipids. While in the presence of neutral DPPC the protein seems to penetrate among the lipid domains, in the case of negatively charged DPPS the electrostatic interaction appears to be the driving force, because protein intimately associates with the headgroups and binds to the Langmuir layer as a specific lipid−protein complex. Results with DPPS were confirmed by FTIR spectroscopy measurements, performed after transferring phospholipid multilayers onto a solid substrate by the Langmuir−Schaefer method.

Reversibility of structural rearrangements in the negative vesicular membrane upon electrostatic adsorption/desorption of the polycation

Interaction of small unilamellar vesicles (SUVs), composed of negative diphosphatidylglycerol (cardiolipin, CL 2−) and neutral dipalmitoylphosphatidylcholine (DPPC), with poly( N-ethyl-4-vinylpyridinium bromide) (PEVP) was studied in water solution above and below the vesicular membrane melting point by means of differential scanning calorimetry, photon correlation spectroscopy, microelectrophoresis, conductometry, and fluorescence techniques. It has been found that CL 2− species are homogeneously distributed within DPPC-CL 2− SUV membrane leaflets and between them. Interaction of PEVP with DPPC-CL 2− SUVs led to drastic structural rearrangements in the membrane if it was in the fluid state (liquid SUVs). Negative CL 2− molecules migrated from the inner to the outer membrane leaflet and segregated in the vicinity of adsorbed PEVP chains. In addition, PEVP adsorption terminated completely the exchange of lipid molecules between the SUVs. At the same time, the integrity of liquid SUVs contacting PEVP remained unchanged. Since the interaction of PEVP with liquid SUVs was predominantly electrostatic in nature, the polycation could be completely removed from the vesicular membrane by addition of an excess of polyacrylic acid (PAA) polyanions forming a more stable electrostatic complex with PEVP. Removal of PEVP resulted in complete resumption of the original distribution of lipids in lateral and transmembrane directions as well as intervesicular lipid exchange. In contrast, PEVP interacting with DPPC-CL 2− SUVs formed defects in the vesicular membrane if it was in the gel state (solid SUVs). Such interaction was contributed not only by electrostatic but most likely by hydrophobic interactions involving the defected membrane sites. PEVP kept contacting solid SUVs in the presence of an abundant amount of PAA. The established phenomena may be important for understanding the biological effects of polycations.

Interaction of a Multiple Antigenic Peptide of Hepatitis A Virus with Monolayers and Bilayers of Acidic, Basic, and Zwitterionic Phospholipids

The interaction of the synthetic multiple antigenic peptide construct MAP4-VP1(11-25) with lipid membranes was studied by a combination of spectroscopic and biophysical techniques. MAP4-VP1 showed an important surface activity when spread in an air–water interface, indicative of an amphipatic conformation. Since this peptide has a net anionic charge, we studied the degree of interaction with model membranes of zwitterionic dipalmitoylphosphatidylcholine (DPPC), anionic phosphatidylinositol (PI and DPPC/PI 9:1), or cationic stearylamine (SA and DPPC/SA 9:1). MAP4-VP1 was readily soluble in aqueous buffer, yet spontaneously inserted from an aqueous subphase into cationic and zwitterionic monolayers up to limiting pressures of 20–30 mN/m. The induced surface pressure increases were in the order cationic > zwitterionic > anionic monolayers. This indicates that the interaction is mainly driven by electrostatic forces, although there is an important hydrophobic component, responsible for the penetration in monolayers of neutral DPPC. Interaction of MAP4-VP1 with unilamellar vesicles of DPPC, DPPC/SA (9:1), and DPPC/PI (9:1) labeled with 1,6-diphenyl-1,3,5-hexatriene (DPH) or with 1-anilino-8-naphthalene sulfonic acid (ANS) was determined by changes in fluorescence polarization as a function of temperature. Results showed that the presence of the positively charged SA in the membrane strongly enhances the incorporation of MAP4-VP1 and that the peptide increases the fluidity of the bilayer and decreases the temperature of the phase transition.

Photoinduced electron transfer from alkylpyrenes embedded into DHP, DPPC and DODAC vesicles studied with electron paramagnetic resonance and electron spin echo modulation spectroscopies

Photoinduced electron transfer from alkylpyrene derivatives solubilized in cationic dioctadecyldimethylammonium chloride (DODAC), neutral dipalmitoylphosphatidylcholine (DPPC) and anionic dihexadecylphosphate (DHP) vesicles to interface water (D2O) was monitored by changing the pendant alkyl chain length of the alkylpyrenes and the interface charge of the vesicles. The amount of photoproduced pyrene cation radical defined as the photoyield decreased with increasing alkyl chain length of the alkylpyrene and with the interface charge from cationic DODAC to neutral DPPC to anionic DHP vesicles. The interpretation is that the increased alkyl chain length of alkylpyrene increases the electron transfer distance between the pyrene moiety as an electron donor and the interface water (D2O) as an electron acceptor. This occurs by deeper penetration of the alkylpyrene into the hydrophobic region of the vesicles for longer alkyl chains due to greater hydrophobic interaction of the alkylpyrene with the surfactant alkyl chains. This interpretation is supported by a decreasing deuterium modulation depth trend. The decreasing photoyields of alkylpyrene from DODAC to DPPC to DHP vesicles are due to an increasing energy barrier for electron transfer through the vesicular interface.

Photoionization of (p-Alkylphenyl)triphenylporphyrins in Neutral and Positively and Negatively Charged Vesicles: Effects of Alkyl Chain Length and Addition of Chloroalkanes

The photoionization of (p-alkylphenyl)triphenylporphyrins (CnPtPP) in cationic dioctadecyldimethylammonium chloride (DODAC), neutral dipalmitoylphosphatidylcholine (DPPC), and anionic dihexadecyl p...

Interaction of dipyridamole with lipids in mixed Langmuir monolayers

Dipyridamole (DIP), a well known coronary vasodilator and coactivator of anti-tumor activity of a number of drugs, forms stable Langmuir monolayers with the zwitterionic lipid dipalmitoylphosphatidylcholine (DPPC) and the negatively charged dipalmitoylphosphatidylglycerol (DPPG) at an air/aqueous solution interface. The drug binds to the lipid molecules and change their packing density in the monolayer in the process of compression, the effect depending on the drug location in the monolayer, protonation of the drug and also on the charge state of the lipid. The incorporation of dipyridamole (DIP) into neutral DPPC monolayers causes them to be more expanded at low DIP concentrations but more condensed at high concentrations, resembling the effect of cholesterol. Maximum expansion occurs for a DIP concentration of 2 mol%. For slightly charged DPPG monolayers spread on ultra pure water, the monolayers become increasingly more expanded with increasing DIP concentrations. For the negatively charged DPPG monolayers spread on buffer solutions, the incorporation of DIP has similar effects to that observed for DPPC monolayers. This is probably due to the interaction between the charged DPPG molecules and the protonated DIP molecules. Also, introduction of protonated DIP brings an increase in surface potential of DPPG monolayers because the negative contribution from the double layer is decreased. The results indicate that DIP molecules are located deeper in the hydrophobic region of DPPC monolayers, whereas in DPPG ones they appear to be located very close to the polar head region. Due to the electrostatic interaction of protonated DIP with the charges on the polar heads of lipids it is inclined with respect to the plane of the monolayer.

ChemInform Abstract: Comparative Electron Spin Resonance and Electron Spin Echo Modulation Studies of the Photoionization of Positively and Negatively Charged and Neutral Alkylphenothiazines in Cationic Dioctadecyldimethylammonium Chloride, Neutral Dipalmitoylphosphatidylcholine, and Anionic Dihexadecyl Phosphate Vesicles at 77 K.

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