Presence Of DPPC Research Articles

Supramolecular Catalysis: New Directions and Developments

Fluorescence Resonance Energy Transfer (FRET) between two organic dyes Fluorescein and Rhodamine 6G were successfully investigated in aqueous solution in presence and absence of 1,2-Dipalmitoyl-sn-glycero-3-phosphorylcholine (DPPC) at different pH. Spectroscopic studies suggest that both the dyes were present mainly as monomer in solution. FRET occurred from Fluorescein to Rhodamine 6G in solutions. Energy transfer efficiency increases in presence of DPPC and the maximum efficiency was 59.3% when the concentration of DPPC was 1.4×10−4 M at ambient condition. pH plays a crucial role in this investigation as the energy transfer efficiency was found to change in presence of DPPC at different pH. It has been demonstrated that with proper calibration it is possible to use the present system under investigation to realize various ionic states of DPPC by observing the change in FRET efficiency between these two dyes.

The effect of the monocyclic monoterpene tertiary alcohol γ-terpineol on biointerfaces containing cholesterol

The compound γ-terpineol, which presents potential as microbicide and anticancer drug, was incorporated in cholesterol Langmuir monolayers, pure or mixed with DPPC. The compound expands the monolayers at higher molecular areas, but condenses them at lower areas, indicating a structural molecular rearrangement of γ-terpineol at the-water interface upon compression. Such effect was confirmed with rheological, surface potential, Brewster angle microscopy and infrared data, which indicated, respectively, reduction of the compressional modulus of the lipid monolayer, decrease of the surface potential, formation of aggregates, and alteration of the trans/gauche conformers ratio for methylene groups. Distinctive effects were observed for cholesterol monolayers without or with the presence of DPPC. Such results may help understand how the interaction of γ-terpineol with lipidic surfaces is modulated by lipids able to mediate the packing state of biointerfaces.

Investigation on ionic states of 1,2-Dipalmitoyl-sn-glycero-3-phosphorylcholine (DPPC) using organic laser dyes: A FRET study

Fluorescence Resonance Energy Transfer (FRET) between two organic dyes Fluorescein and Rhodamine 6G were successfully investigated in aqueous solution in presence and absence of 1,2-Dipalmitoyl-sn-glycero-3-phosphorylcholine (DPPC) at different pH. Spectroscopic studies suggest that both the dyes were present mainly as monomer in solution. FRET occurred from Fluorescein to Rhodamine 6G in solutions. Energy transfer efficiency increases in presence of DPPC and the maximum efficiency was 59.3% when the concentration of DPPC was 1.4×10−4M at ambient condition. pH plays a crucial role in this investigation as the energy transfer efficiency was found to change in presence of DPPC at different pH. It has been demonstrated that with proper calibration it is possible to use the present system under investigation to realize various ionic states of DPPC by observing the change in FRET efficiency between these two dyes.

Interaction between a Cationic Surfactant-like Peptide and Lipid Vesicles and Its Relationship to Antimicrobial Activity

We investigate the properties of an antimicrobial surfactant-like peptide (Ala)6(Arg), A6R, containing a cationic headgroup. The interaction of this peptide with zwitterionic (DPPC) lipid vesicles is investigated using a range of microscopic, X-ray scattering, spectroscopic, and calorimetric methods. The β-sheet structure adopted by A6R is disrupted in the presence of DPPC. A strong effect on the small-angle X-ray scattering profile is observed: the Bragg peaks from the DPPC bilayers in the vesicle walls are eliminated in the presence of A6R and only bilayer form factor peaks are observed. All of these observations point to the interaction of A6R with DPPC bilayers. These studies provide insight into interactions between a model cationic peptide and vesicles, relevant to understanding the action of antimicrobial peptides on lipid membranes. Notably, peptide A6R exhibits antimicrobial activity without membrane lysis.

Structure and stability studies of mixed monolayers of saturated and unsaturated phospholipids under low-level ozone

In the present study, stability and structure of single and binary mixed monolayers of an unsaturated phospholipid, DOPC, and a saturated phospholipid, DPPC-d75, on the water surface, were explored using the π-A isotherm, atomic force microscopy (AFM) and sum frequency generation (SFG) vibrational spectroscopy in various environments. Our results demonstrated that DOPC in the monolayers becomes unstable after the exposure to a low concentration of ozone (20 ± 10 ppb) or even to ambient laboratory air, which has a similar ozone level, but is stable in nitrogen or oxygen. DOPC can be selectively oxidized by a trace amount of ozone in the ambient environment but can be partially inhibited by the presence of DPPC in the monolayer. The present study provides useful information for understanding the physicochemical properties of the cell membranes.

The role of palmitic acid in pulmonary surfactant systems by Langmuir monolayer study: Lipid–peptide interactions

Palmitic acid (PA) has been widely used as an useful and effective additive to pulmonary surfactants (PS) such as Survanta and Surfaxin. Moreover, PA has well-known biological and physicochemical properties, and its simple chemical structure allows its manufacture at low cost. However, the role and significance of PA in PS formulations are still controversial. In the present study, the PS model preparation containing PA has been investigated to clarify its additional effect (molecular recognition and interaction in particular) employing the Langmuir monolayer technique. The elucidation of the PA effect is performed by comparison with the data from its analogue (or homologue) lipids; i.e. three fatty acids and four fatty alcohols. The surface pressure (π)-molecular area (A) and surface potential (ΔV)−A isotherms for the eight DPPC/fatty lipid systems containing a PS model peptide (Hel 13-5) have been measured. In addition, the morphology and phase behavior are examined with in situ fluorescence and ex situatomic force microscopy. As a result, it is found that a balance between the hydrophilicity of the headgroup and the hydrophobicity of the tail group in the lipids is an important factor in pulmonary functions. In particular, the dissociation degree of the fatty acids, which depends on the pH or the surface pH, strongly affects their electrostatic interaction with positively charged Hel 13-5. The chain length is also significant and the carbon number 16 is found to be most appropriate. The present molecular-level information on the interaction between the lipids and Hel 13-5 in the presence of DPPC indicates that PA takes on a hydrophile–lipophile balance suitable for the PS preparation.

Comparison of n-tetradecane/electrolyte emulsions properties stabilized by DPPC and DPPC vesicles in the electrolyte solution

The properties of n-tetradecane/electrolyte emulsions with DPPC or DPPC vesicles in the electrolyte solution were investigated. The DPPC molecules form different aggregates, which possess different surface affinity, size and structure, and therefore we assumed some differences in the adsorption at the oil droplet/water interface. The n-tetradecane emulsions in 1:1, 1:2 and 1:3 electrolytes were prepared by mechanical stirring in the presence of DPPC at natural pH. Electrokinetic properties of the systems were investigated taking into account the effective diameter and multimodal size distribution of the droplets as well as the zeta potentials using the dynamic light scattering technique. The zeta potential of the droplets was negative in all systems with NaCl. In the emulsions with CaCl2 at a higher concentration of electrolyte and emulsions with LaCl3 with all investigated concentrations, positive values were observed.Similar measurements were performed for DPPC vesicles in the electrolyte solution. The pH and ionic strength changes induce those in the electrical charge of DPPC layer or vesicle surface. This is due to the fact that the DPPC molecule contains –PO− and –N(CH3)3 groups, which are in equilibrium with H+ and OH−, as well as other ions present in the solution, i.e. Na+, Ca2+, La3+ or Cl−. In the n-tetradecane/electrolyte emulsion stabilized by DPPC or DPPC vesicles the zeta potential may be also related to acid–base interactions. The effect of the ions from the solution on the DPPC layer adsorbed on n-tetradecane droplets or DPPC vesicles is discussed.

Interaction between nystatin and natural membrane lipids in Langmuir monolayers—The role of a phospholipid in the mechanism of polyenes mode of action

Nystatin (NYS), a polyene antifungal antibiotic, has been investigated in Langmuir monolayers alone and in mixtures with mammalian and fungi membrane sterols (cholesterol and ergosterol, respectively) as well as with a model phospholipid (DPPC). The interactions between film molecules have been examined both in a qualitative and quantitative way with the excess area per molecule ( A Exc), excess free energy of mixing (Δ G Exc) and the interaction parameter ( α). The obtained results have been compared with those previously reported for another polyene antimycotic: amphotericin B (AmB) mixed with lipids. Higher affinity of NYS has been observed for ergosterol vs. cholesterol, however, the strongest attractions were found for its mixtures with DPPC. The obtained results have been verified with biological studies reported previously for both antibiotics (NYS and AmB). A thorough analysis of the Langmuir experiment results performed for both polyenes enabled us to conclude that the presence of DPPC can be considered as a key factor affecting their antifungal activity as well as their toxicity towards host cells.

Stereoselectivity Aspects in the Condensation of Racemic NCA−Amino Acids in the Presence and Absence of Liposomes

In previous work dealing with the liposome-assisted polycondensation of NCA (N-carboxyanhydride)−amino acids, it has been shown that racemic NCA−Trp condensation affords chains with preferential homochiral sequences: the homochiral blocks become increasingly over-represented with increasing oligomer length if compared with the statistically (Bernoullian) distributions. The present paper deals with three questions related to this stereoselective NCA−Trp condensation. The first question concerns the kinetic mechanism that is responsible for the over-representation of homochiral sequences in the presence as well as in the absence of liposomes. To this aim, we have investigated whether and to what extent the selection of the entering chiral monomer unit is governed by the chirality of the penultimate residue. This analysis allows one to suggest that the polycondensation corresponds to a second- or higher-order Markov process. The second question considered in this paper is whether the preferential formation of homochiral sequences, originally found in NCA−Trp−amino acid condensations, is observed also for amino acids other than Trp as well as for mixtures of different amino acids. To clarify this point, we have analyzed by liquid chromatography mass spectrometry (LC-MS) the condensation products of racemic NCA−d-Leu/perdeuterated NCA−l-Leu and racemic NCA−d-Ile/perdeuterated NCA−l-Ile in an aqueous solution without liposomes. This analysis permits us to show that the preferential homochiral growth occurs also with Leu and Ile. By LC-MS analysis we can show that under the same conditions also mixtures of equal amounts of the l- and d-forms of different amino acids, such as Trp/Leu, Leu/Ile, and Trp/Leu/Ile, exhibit similar behavior. The third question considered in this paper is related to the effect of liposomes on the NCA−Trp condensation, addressing the question of whether the chemical structure of the lipid in the liposomes and consequently their physical state have an influence on the stereoselectivity of the NCA−Trp condensation. To this aim, experiments are carried out at different temperatures in the presence of DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine) liposomes, below as well as above the liquid-analogue/crystalline-analogue transition temperature. The answer to the third question is that basically the same results are obtained independently of the physical state of the lipid.

Effect of phospholipid bilayers on solution conformation of branched polymeric polypeptides and peptide-polymer conjugates.

This report provides a detailed analysis on the influence of phosholipid bilayers on the conformation of poly[Lys(X(i)-DL-Ala(m))] (XAK, where X = Ser, Orn, Glu, or AcGlu) type branched polypeptides and their peptide conjugates. CD spectra of polycationic (SAK, OAK), amphoteric (EAK), or polyanionic (Ac-EAK) polylysine derivatives were recorded in 0.25M acetate buffer at pH 7.4 as well as in the presence of DPPC or DPPC/PG (95/5, 80/20 mol/mol) liposomes. Based on these data, two groups of polypeptides are described. Group one contains polypeptides with significantly ordered conformation even in buffer solution (SAK, AcEAK), which is essentially not altered by phospholipids. Group two, branched polypeptides (OAK, EAK), with only partially ordered conformation in aqueous solution in the presence of phospholipid bilayers with high PG content, could adopt more (EAK) or less (OAK) ordered alpha-helical structure depending on their charge properties. In addition, we report on the synthesis of two new sets of oligopeptide-branched polypeptide conjugates. Studies with selected conjugates suggest that these compounds are highly ordered in buffer solution almost regardless from the helix-forming ability of the carrier (AK, SAK, EAK) and from the hydrophilic/hydrophobic character of peptides attached (AVKDEL vs FWRGDLVFDFQV). Addition of phospholipid bilayers with different composition essentially had no modifying effect on conformation of conjugates. From this we can conclude that the covalently coupled oligopeptides has a predominant effect of the conformational properties of conjugates.

Membrane interaction of synthetic peptides related to the putative fusogenic region of PH-30 alpha, a protein in sperm-egg fusion.

In order to investigate the relationship between structure and function of a putative fusogenic region of PH-30a, a protein active in sperm-egg fusion, two peptides, SFP22 and SFP23, whose sequences correspond to the residues 90-111 and 89-111 of PH-30 alpha, respectively, were chemically synthesized. An analog of SFP23, SFP23AA, which has an Ala-Ala sequence instead of the Pro-Pro sequence in SFP23, was also prepared. The CD study indicated that SFP22 and SFP23 mainly took a beta-structure in the presence of DPPC and DPPC/DPPG (3/1) vesicles, while SFP23AA showed an alpha-helical pattern though the alpha-helical content calculated was low (25-30%). alpha-Helical CD curve was observed for these peptides in trifluoroethanol. The membrane-perturbing activity of SFP22 and SFP23 was weaker than that of SFP23AA. On the other hand, the membrane-fusogenic activity of SFP22 and SFP23 to acidic phospholipid bilayers was much stronger than that of SFP23AA. All the peptides caused very weak cell lysis. These results are consistent with the reported speculation [Blobel, C. P. et al. (1992), Nature (London) 356, 248-252] that residues 90-111 of PH-30 alpha may be the fusogenic region and suggest that the Pro-Pro sequence is one of the important factors for holding the active secondary structure of the fusogenic region of PH-30 alpha in membranes.

Determination of ethanol partition coefficients to the interior and the surface of dipalmityl-phosphatidylcholine liposomes using deuterium nuclear magnetic resonance spectroscopy

The binding of ethanol-d 6 to dipalmityl-phosphatidylcholine liposomes (DPPC) can be separated into two processes, namely, ethanol in the bilayer and on the surface of the bilayer. For the deuterons of the methylene group, the T 2 of both bound states is shorter than the respective preexchange lifetime (τ B) and therefore the amount of ethanol bound to both sites can be determined from the decrease in the methylene intensity resonance in the presence of DPPC. For the methyl resonance, however, only the T 2 of deuterons on ethanol bound to the surface is less than its τ B and the amount of surface bound ethanol-d 6 can be determined. Subtraction yields the amount of ethanol bound within the bilayer. The partion coefficient for internally bound ethanol remains constant from 0 to 3.5 m ethanol. Surface binding is, however, highly cooperative.