Surface dipole moments of lipids at the argon-water interface. Similarities among glycerol-ester-based lipids

Smaby, Janice M.; Brockman, Howard L.

doi:10.1016/s0006-3495(90)82365-1

Cited by 102 publications

(120 citation statements)

References 45 publications

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“…This is evident from the finding that pregnanolone partitions more avidly to cholesterol-containing monolayers for which the phospholipid head group spacing is higher, but ⌿ is lower than for 6-ketocholestanol-containing films. In addition, despite practically equal effective dipole moments of DPPC and POPC (469 and 468 mD), and therefore higher ⌿ values for DPPC caused by weaker packing of POPC at equal surface pressures (Smaby and Brockman, 1990;Smaby et al, 1994), pregnanolone seems to favor partitioning into POPC monolayers. In keeping with the weaker lateral packing (higher area per molecule) for POPC, one would expect larger head-group spacing and free volume in the head-group region, and therefore more efficient binding for pregnanolone, as observed.…”

Section: Discussionmentioning

confidence: 98%

Dipole Potential and Head-Group Spacing Are Determinants for the Membrane Partitioning of Pregnanolone

Alakoskela¹,

Söderlund²,

Holopainen³

et al. 2004

Molecular Pharmacology

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The membrane interactions of pregnanolone, an intravenous general anesthetic steroid, were characterized using fluorescence spectroscopy and monolayer technique. di-8-ANEPPS [4-[2-[6-(dioctylamino)-2-naphthalenyl]ethenyl]-1-(3-sulfopropyl)-pyridinium], a membrane dipole potential (⌿)-sensitive probe, revealed pregnanolone to decrease ⌿ similarly as reported previously for other anesthetics. The decrement in ⌿ was approximately 16 and 10 mV in dipalmitoylphosphatidylcholine (DPPC) and DPPC/cholesterol (90:10, mol/mol) vesicles, respectively. Diphenylhexatriene anisotropy indicated pregnanolone to have a negligible effect on the acyl chain order. In contrast, substantial changes were observed for the fluorescent dye Prodan, thus suggesting pregnanolone to reside in the interfacial region of lipid bilayers. Langmuir balance studies indicated increased association of pregnanolone to DPPC monolayers containing cholesterol or 6-ketocholestanol at surface pressures Ͼ 20 mN/m as well as to monolayers of the unsaturated 1-palmitoyl-2-oleoylphosphatidylcholine. In the same surface pressure range, the addition of phloretin, which decreases ⌿, reduced the penetration of pregnanolone into the monolayers. These results suggest that membrane partitioning of pregnanolone is influenced by the spacing of the phosphocholine head groups as well as by membrane dipole potential. The latter can be explained in terms of electrostatic dipole-dipole interactions between pregnanolone and the membrane lipids with their associated water molecules. Considering the universal nature of these interactions, they are likely to affect membrane partitioning of most, if not all, weakly amphiphilic drugs.Pregnanolone (Fig. 1) is a steroid-based progesterone metabolite that is used as an intravenous general anesthetic (Hering et al., 1996). Because of its low solubility into water, it is administered in an oil-in-water emulsion (eltanolone). Hydrophobicity of compounds is directly linked to their membrane partitioning, and thus, pregnanolone can be expected to favor association with lipid bilayers. However, as far as we are aware, no studies on pregnanolone-lipid interactions have been reported. Other general anesthetics such as isoflurane and halothane have been shown to interact with lipid membranes (Cafiso, 1998). Although many different modes of action have been suggested, the exact mechanism of action of general anesthetics has remained unresolved. The proposed mechanisms include interactions between anesthetics and proteins, interactions between anesthetics and lipids, and effects of anesthetics on the lipid-protein interface (Makriyannis et al., 1990;Ueda et al., 1994). Cantor (1997) suggested a mechanism linking the membrane lateral-pressure profile to the action of membrane proteins. The importance of nonspecific interactions mediated by the amino acid residues in the lipid-water-protein interface was highlighted in a recent molecular-dynamics simulation of the effects of an anesthetic on gramicidin channels in membranes (Tang and Xu,...

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Section: Discussionmentioning

confidence: 98%

Dipole Potential and Head-Group Spacing Are Determinants for the Membrane Partitioning of Pregnanolone

Alakoskela¹,

Söderlund²,

Holopainen³

et al. 2004

Molecular Pharmacology

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“…Table 1 summarizes the values of m ± and DV 0 , obtained from plots of the dipole potential versus inverse crosssectional molecular area (V 2 A 21 ). DV 0 values for B7-PC were 551 mV, compared with 24 mV for PB-PC (26) and 110-140 mV for the fluid nonfluorescent phosphatidylcholines lacking docosahexenoyl acyl chains (30,33,34). However, the dipole moment, m ± , of B7-PC was found to be 2850 milliDebyes, compared with 874 milliDebyes for PB-PC (26) and 480-550 milliDebyes for phosphatidylcholines lacking docosahexenoyl acyl chains (30,33,34).…”

Section: Probe Lateral Packing and Spectral Properties In Monolayersmentioning

confidence: 99%

“…Surface pressure and area calibration of the film balance were performed as detailed previously (30,31). Fluorescence emission measurements were performed using a slightly modified set-up compared with that described by Dahim et al (32).…”

Section: Monolayer Conditionsmentioning

confidence: 99%

“…where DV is the potential measured in millivolts and m ± is the dipole moment (in milliDebyes) perpendicular to the lipid-water interface and can be determined from the slope of DV versus 1/A plots (30). The intercept term, DV 0 , is lipid-specific and appears to arise from an epitaxial ordering of interfacial water molecules (30,33).…”

Section: Analyses Of Monolayer Isothermsmentioning

confidence: 99%

“…The intercept term, DV 0 , is lipid-specific and appears to arise from an epitaxial ordering of interfacial water molecules (30,33). DV versus 1/A plots of various liquid-expanded lipids are linear from ?1 mN/m up to surface pressures at which the second derivative of the p-A isotherms (d 2 p/dA 2 ) goes from positive to negative values (p d ) (33,34).…”

Section: Analyses Of Monolayer Isothermsmentioning

confidence: 99%

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New BODIPY lipid probes for fluorescence studies of membranes

Болдырев

Zhai

Momsen

et al. 2007

Journal of Lipid Research

100

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Many fluorescent lipid probes tend to loop back to the membrane interface when attached to a lipid acyl chain rather than embedding deeply into the bilayer. To achieve maximum embedding of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) fluorophore into the bilayer apolar region, a series of sn-2 acyl-labeled phosphatidylcholines was synthesized bearing 4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene-8-yl (Me 4 -BODIPY-8) at the end of C 3 -, C 5 -, C 7 -, or C 9 -acyl. A strategy was used of symmetrically dispersing the methyl groups at BODIPY ring positions 1, 3, 5, and 7 to decrease fluorophore polarity. Iodide quenching of the phosphatidylcholine probes in bilayer vesicles confirmed that the Me 4 -BODIPY-8 fluorophore was embedded in the bilayer. Parallax analysis of Me 4 -BODIPY-8 fluorescence quenching by phosphatidylcholines containing iodide at different positions along the sn-2 acyl chain indicated that the penetration depth of Me 4 -BODIPY-8 into the bilayer was determined by the length of the linking acyl chain. Evaluation using monolayers showed minimal perturbation of ,10 mol% probe in fluid-phase and cholesterol-enriched phosphatidylcholine. Spectral characterization in monolayers and bilayers confirmed the retention of many features of other BODIPY derivatives (i.e., absorption and emission wavelength maxima near 498 nm and ?506-515 nm) but also showed the absence of the 620-630 nm peak associated with BODIPY dimer fluorescence and the presence of a 570 nm emission shoulder at high Me 4 -BODIPY-8 surface concentrations. We conclude that the new probes should have versatile utility in membrane studies, especially when precise location of the reporter group is needed. Fluorescent lipid probes have proven to be valuable tools in membrane studies (see Ref. 1 for review). Because the determination of depth-dependent parameters of bilayers can benefit the understanding of membranous structures (2), sets of probes bearing the same fluorophore at different distances from the bilayer surface are potentially quite useful. Ideally, such fluorophores should be apolar enough to localize at the membrane depth that reflects the apolar nature of the surrounding acyl chain region without being strongly influenced by the transbilayer polarity gradient (3). The first probe set designed to achieve this goal was a series of n-(9-anthroyloxy) fatty acids synthesized by Thulborn and Sawyer (4), who showed that the fluorophore resided in the bilayer at a graded series of depths that coincided with the attachment point of the anthroyloxy fluorophore along the acyl chain. Other widely used fluorophores, such as N-dansyl (5) or N-NBD (6, 7), have been shown to have polar characteristics that interfere with localization deep inside the bilayer even when attached to the end of the acyl chain.During the past decade, BODIPY (4,4-difluoro-4-bora3a,4a-diaza-s-indacene) fluorophore probes have found a wide range of applications in cell biology and biophysics, even though this zwitterionic fluorophore wa...

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Molecular dynamics simulation of hydrated DPPC monolayers using charge equilibration force fields

et al. 2011

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We present results of molecular dynamics simulations of a model DPPC-water monolayer using charge equilibration (CHEQ) force fields which explicitly account for electronic polarization in a classical treatment of intermolecular interactions. The surface pressure, determined as the difference between the monolayer and pure water surface tensions at 323 K, is predicted to be 22.92 ± 1.29 dyne/cm, just slightly below the broad range of experimental values reported for this system. The surface tension for the DPPC-water monolayer is predicted to be 42.35 ± 1.16 dyne/cm, in close agreement with the experimentally determined value of 40.9 dyne/cm. This surface tension is also consistent with the value obtained from DPPC monolayer simulations using state-of-the-art nonpolarizable force fields. The current results of simulations predict a monolayer-water potential difference relative to the pure water-air interface of 0.64 ± 0.02 Volts, an improved prediction compared to the fixed-charge CHARMM27 force field, yet still overestimating the experimental range of 0.3 to 0.45 Volts. Since the charge equilibration model is a purely charge-based model for polarization, the current results suggest that explicitly-modeled polarization effects can offer improvements in describing interfacial electrostatics in such systems.

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Surface dipole moments of lipids at the argon-water interface. Similarities among glycerol-ester-based lipids

Cited by 102 publications

References 45 publications

Dipole Potential and Head-Group Spacing Are Determinants for the Membrane Partitioning of Pregnanolone

Dipole Potential and Head-Group Spacing Are Determinants for the Membrane Partitioning of Pregnanolone

New BODIPY lipid probes for fluorescence studies of membranes

Molecular dynamics simulation of hydrated DPPC monolayers using charge equilibration force fields

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