Dipalmitoylphosphatidylcholine Multilayers Research Articles

Effect of trehalose on the phase properties of hydrated and lyophilized dipalmitoylphosphatidylcholine multilayers

The structure and thermal behavior of hydrated and lyophilized dipalmitoylphosphatidylcholine (DPPC) multilayers in the presence of trehalose were investigated by differential scanning calorimetry and X-ray diffraction methods. Trehalose enters the aqueous space between hydrated bilayers and increases the interbilayer separation (from 0.36 to 1.37 nm in the different DPPC phases at 1 M trehalose). It does not affect the lipid chain packing and also the slow isothermal conversion at 4 °C of the metastable Lβ′ phase into the equilibrium crystalline Lc phase. Addition of trehalose leads to a slight upward shift (about 1 °C at 1 M trehalose) of the three phase transitions (sub-, pre-, and main transition) in fully hydrated DPPC while their other properties (enthalpy, excess specific heat, and transition width) remain unchanged. The effect of trehalose on the thermal behavior of DPPC multilayers freeze-dried from an initially completely hydrated state is qualitatively similar to that of water. These data support the “water replacement” hypothesis about trehalose action. It is suggested that trehalose prevents the formation of direct interbilayer hydrogen bonds in states of low hydration.

Lamellar gel-lamellar liquid crystal phase transition of dipalmitoylphosphatidylcholine multilayers freeze-dried from aqueous trehalose solutions. A real-time X-ray diffraction study

The mechanism of the phase transition of dipalmitoylphosphatidylcholine multilayers freeze-dried from fully hydrated gel phase (L β′) in the presence of trehalose has been investigated by real-time X-ray diffraction methods. Sequential diffraction patterns were recorded with an accumulation time of 3 s during heating and 1.2 s during cooling between about 20 and 80°C. A transition is observed in the range 47–53°C that involves structural events typical of a lamellar gel-lamellar liquid-crystal (L β-L α) transformation. This transition is completely reversible with a temperature hysteresis of 2–3°C and thereby resembles the main phase transition of fully hydrated dipalmitoylphosphatidylcholine multilayers. The mechansim of the transition from L β to L α as seen in the wide-angle scattering profiles show that the sharp peak at about 0.41 nm, characteristic of the gel phase, broadens and shifts progressively to about 0.44 nm towards the end of the transition. A temperature jump at 6C°/s through the phase transition region of a freeze-dried dipalmitoylphosphatidylcholine: trehalose mixture (molar ratio 1:1) showed that the phase transition had a relaxation time of about 2 s which is similar to that of the main transition in the fully hydrated lipid. X-ray diffraction studies of the melting of dipalmitoylphosphatidylcholine freeze-dried from the lamellar-gel phase in the absence of trehalose showed a transition at above 70°C. The low-angle diffraction data of phospholipid/trehalose mixtures are consistent with an arrangement of trehalose molecules in a loosely packed ‘monolayer’ separating bilayers of phospholipid. Trehalose appears to reduce the direct interbilayer hydrogen bond coupling thereby modifying the thermal stability and the phase transition mechanism of the bilayers.

Formation of multilayers of dipalmitoylphosphatidylcholine using the Langmuir-Blodgett technique

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFormation of multilayers of dipalmitoylphosphatidylcholine using the Langmuir-Blodgett techniqueJ. B. Peng, M. Prakash, R. Macdonald, Pulak Dutta, and J. B. KettersonCite this: Langmuir 1987, 3, 6, 1096–1097Publication Date (Print):November 1, 1987Publication History Published online1 May 2002Published inissue 1 November 1987https://doi.org/10.1021/la00078a037RIGHTS & PERMISSIONSArticle Views151Altmetric-Citations32LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (253 KB) Get e-Alerts Get e-Alerts

Raman study of low frequency lattice modes in dipalmitoylphosphatidylcholine (DPPC) multilayers

Low frequency Raman spectra (6–30 cm−1) of macroscopically ordered multilayers of dipalmitoylphosphatidylcholine (DPPC) were taken as a function of temperature (80–270 K) and for different water contents. A weak band is observed which is shifted from 18.5 to 14 cm−1 between 80 and 270 K. This band is shifted to lower frequencies with increasing water content. In addition, a strong background appears at the Rayleigh line position which grows strongly with increasing temperature. The low frequency band can be explained (1) in terms of an optical mode associated with an antiphase in-plane vibration of two opposing monolayers or it can (2) be attributed to rotational vibrations of the hydrocarbon chains. The softening of this band is attributed to a decrease in the chain orientational order with increasing temperature. The increasing rotational freedom is expected to cause a transition from a monoclinic or orthorhombic to a hexagonal lattice and eventually triggers the Lβ′ → Lα chain melting transition (at T=340 K for 5.3 wt. % of water). The appearance of the background can also be attributed to an increasing anharmonicity of the lattice potential upon approaching the phase transition, which leads to mode coupling. The possibility of ferroelectric order due to a collective orientation of the dipole moments of the C–O groups of the glycerol backbone is discussed.

ESR and DSC comparative study of phase separation in γ-irradiated lipid membranes

ESR and DSC techniques have been applied to the study of aqueous dispersions of dipalmitoyl phosphatidylcholine multilayers both unirradiated and γ-irradiated, with TEMPO spin-label added to them. The examen of ESR spectra gave information on the molar fraction (f) of TEMPO bound to the lipid phase. While for the unirradiated samples one observes a sharp variation off at the main transition temperature, in the case of irradiated samples the speed of variation is greatly reduced, and other significant details do appear in thef vs.T curves. Moreover, always around the transition zone, the irradiation products, when in low concentration, show quite complete miscibility in the lipid bilayers. When their concentration is sufficiently higher, due to a greater irradiation dose, the products of irradiation lead to the formation of a domain-like organization of precipitates, whose composition and fluidity depend on the actual absorbed dose as well as on the temperature.

Evidence for acyl chain trans/gauche isomerization during the thermal pretransition of dipalmitoyl phosphatidylcholine bilayer dispersions

In order to clarify, in dipalmitoyl phosphatidylcholine multilayers, the effect of the 34°C thermal pretransition on the acyl chain intramolecular disordering process, Raman spectra of dipalmitoyl phosphatidylcholine gels at 20 and 34°C were compared in the 1000–1200 cm −1 skeletal C-C stretching region. In addition to an overall intensity decrease associated with a change in chain packing characteristics, the growth of intensity in the 1080–1090 and 1122 cm −1 regions in the (34-20°C) difference spectrum clearly indicates that the thermal pretransition is accompanied by an increase in the population of hydrocarbon chain gauche rotamers toward the center of the bilayer.

Structural reorganizations in lipid bilayer systems: effect of hydration and sterol addition on Raman spectra of dipalmitoylphosphatidylcholine multilayers.

Vibrational Raman spectroscopy was used in investigate the conformational behavior of dipalmitoylphosphatidylcholine (DPPC) bilayers perturbed by cholesterol and water, two membrane components whose lipid interactions involve different regions of the bilayer matrix. Upon the addition of cholesterol, an intrinsic membrane constituent, to an anhydrous bilayer in concentrations varying from 7 to 30 mol %, modifications in lateral chain interactions were observed by monitoring spectral changes in the methylene C-H stretching and the CH2 deformation regions. The perturbation in the 1460-cm-1 region was not spectroscopically observed until after the addition of 7 mol % of the sterol. Although chain-chain interactions are altered, no additional trans/gauche isomerization is developed along the hydrocarbon chains. Water, a peripheral bilayer component, was added to the multilayer assembly in the hydration range of 0.3 to 4 molecules of water per lipid molecule. Vibrational spectra characteristic of motions in the head-group, interfacial, and acyl chain regions of the lipid bilayer were observed. These data indicate that hydration confers a mobility to the head-group, glycerol, and carbonyl moieties. Shifts in the CN symmetric and PO2-antisymmetric stretching modes, occurring on the addition of approximately four molecules of water, indicate a conformational rearrangement within the polar head group. After approximately four molecules of water are added to the DPPC system, the spectral features of the gel system [70% (w/w) water] indicate that not further head-group changes nor increases in either acyl chain trans/gauche or lattice disorder arise on further hydration.

Carbon-13 nuclear magnetic resonance studies of the cholesteryl ester – phosphatidylcholine system

Using difference spectroscopy, 13C spin–lattice relaxation measurements on 40% egg phosphatidylcholine multilamellar liposomes (containing 25 mol% cholesteryl palmitate)–60% D2O indicate the ester contributes negligibly to the microviscosity of the acyl chains in the bilayers.At 37 °C, spin–spin and spin–lattice relaxation measurements have been obtained for 25 mol% cholesteryl linoleate in both egg phosphatidylcholine and dipalmitoyl phosphatidylcholine multilayers and indicate: (a) T1 values of the linoleate ester chain are 0.5 times those of the lecithin chain carbons, and (b) T2* = 16 ± 6 ms for all discernable linoleate carbons. At 52 °C, cholesteryl ring carbons C5 and C6 yield T2* values of 23 and 20 ms, respectively. These studies suggest the esters reside in an environment whose "fluidity" approaches that found in very low density lipoprotein (VLDL).

Pore formation in lipid membranes by alamethicin.

The conformation of the linear peptide antibiotic alamethicin in dipalmitoyl phosphatidylcholine multilayers was investigated in the absence of an electric field by means of infrared attenuated total reflection spectroscopy. Alamethicin was found to be incorporated into the lipid membrane not only in the dry state but also in an aqueous environment. Its molecular conformation, however, changed from a helix when dry to an extended chain when aqueous. The extended chain aggregated to di- and multimers spanning the lipid bilayer. The equilibrium concentration of alamethicin in the surrounding water was 90 nM, which is in the range of concentrations used in black film experiments. The corresponding molar ratio of lipid to peptide was 80:1. Concerning the molecular mechanism of electric field-induced pore formation, one has to conclude that the dipole model proposed by several authors is very unlikely because it is based on the assumption that the major part of alamethicin is adsorbed on the membrane surface, from which small amounts flip into the membrane under the influence of an electric field. An alternative mechanism is proposed, based on a field-induced conformational change of the peptide from the extended state to a helix. This transition is favored by the resulting dipole moment of the alamethicin helix.

Order-disorder and the pretransition in dipalmitoyl phosphatidylcholine multilayers

Using x-ray diffraction, the interaction of calcium ions with dipalmitoyl phosphatidylcholine (DPPC) multilayers in excess solution has been studied as a function of temperature over a range of concentrations. We have discovered order-disorder-order transformations as a function of both increasing temperature and calcium concentration. For pure DPPC, the pretransition is characterized by a large increase in lattice disorder. For low calcium concentrations, a similar increase in lattice distortion occurs for all temperatures. The high temperature phase is marked by a significant reduction in this disorder. Likewise ordering of the multilayer is regained at high calcium concentrations.

Angle of tilt and domain structure in dipalmitoyl phosphatidylcholine multilayers

A cooperative alignment of lipid chains in dipalmitoyl phosphatidylcholine (DPPC) bilayers was detected by using oriented multilayers containing small amounts of spin-labeled phosphatidylcholine. It is shown that a significant angle of tilt exists along the entire length of the lipid chains in DPPC. This behavior is compared with that of the more complex egg phosphatidylcholine bilayers. The lipid chains do not have the alignment of a single crystal but evidently exist in domains consisting of either clusters within a bilayer or successive layers out of register in the stacked multilayer.