Sum Frequency Generation (SFG) Vibrational Spectroscopy of Planar Phosphatidylethanolamine Hybrid Bilayer Membranes under Water

Kett, Peter J. N.; Casford, Michael T. L.; Davies, Paul B.

doi:10.1021/la1003512

Cited by 25 publications

(35 citation statements)

References 56 publications

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“…This is indicative of a highly ordered conformation of AHL- d n in the bilayer without gauche defects and kinks that would otherwise lead to the presence of CD 2 bands. 27, 60 …”

Section: Resultsmentioning

confidence: 99%

Interkingdom Signaling: Integration, Conformation, and Orientation of N-Acyl-l-homoserine Lactones in Supported Lipid Bilayers

Barth

Jakubczyk²,

Kubas³

et al. 2012

Langmuir

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N-Acyl-l-homoserine lactones (AHLs) are small cell-to-cell signaling molecules involved in the regulation of population density and local gene expression in microbial communities. Recent evidence shows that contact of this signaling system, usually referred to as quorum sensing, to living eukaryotes results in interactions of AHL with host cells in a process termed "inter-kingdom signaling". So far details of this process and the binding site of the AHLs remain unknown; both an intracellular and a membrane-bound receptor seem possible, the first of which requires passage through the cell membrane. Here, we used sum-frequency-generation (SFG) spectroscopy to investigate the integration, conformation, orientation, and translocation of deuterated N-Acyl-L-homoserine lactones (AHL-dn) with varying chain length (8, 12, and 14 C atoms) in lipid bilayers consisting of a 1:1 mixture of POPC:POPG supported on SiO2 substrates (prepared by vesicle fusion). We found that all AHL-dn derivatives are well-ordered within the supported lipid bilayer (SLB) in a preferentially all-trans conformation of the deuterated alkyl chain and integrated into the upper leaflet of the SLB with the methyl terminal groups pointing downwards. For the bilayer system described above, no flip-flop of AHL-dn from the upper leaflet to the lower one could be observed. Spectral assignments and interpretations were further supported by Fourier transform infrared and Raman spectroscopy.

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“…This is indicative of a highly ordered conformation of AHL- d n in the bilayer without gauche defects and kinks that would otherwise lead to the presence of CD 2 bands. 27, 60 …”

Section: Resultsmentioning

confidence: 99%

Interkingdom Signaling: Integration, Conformation, and Orientation of N-Acyl-l-homoserine Lactones in Supported Lipid Bilayers

Barth

Jakubczyk²,

Kubas³

et al. 2012

Langmuir

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“…Hence, having a chemical group with its transition dipole moment (TDM) oriented towards or away from the substrate leads to a constructive (peak) or a destructive (dip) interference, respectively. 39,40 …”

Section: Methodsmentioning

confidence: 99%

Nonfouling Poly(ethylene oxide) Layers End-Tethered to Polydopamine

Pop‐Georgievski

Verreault

Diesner³

et al. 2012

Langmuir

102

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Nonfouling surfaces capable of reducing protein adsorption are highly desirable in a wide range of applications. Coating of surfaces with poly(ethylene oxide) (PEO), a water-soluble, nontoxic, and nonimmunogenic polymer, is most frequently used to reduce nonspecific protein adsorption. Here we show how to prepare dense PEO brushes on virtually any substrate by tethering PEO to polydopamine (PDA)-modified surfaces. The chain lengths of heterobifunctional PEOs were varied in the range of 45−500 oxyethylene units (M n = 2000−20 000). End-tethering of PEO chains was performed through amine and thiol headgroups from reactive polymer melts to minimize excluded volume effects. Surface plasmon resonance (SPR) was applied to investigate the adsorption of model protein solutions and complex biologic medium (human blood plasma) to the densely packed PEO brushes. The level of protein adsorption of human serum albumin and fibrinogen solutions was below the detection limit of the SPR measurements for all PEO chains end-tethered to PDA, thus exceeding the protein resistance of PEO layers tethered directly on gold. It was found that the surface resistance to adsorption of lysozyme and human blood plasma increased with increasing length and brush character of the PEO chains end-tethered to PDA with a similar or better resistance in comparison to PEO layers on gold. Furthermore, the chain density, thickness, swelling, and conformation of PEO layers were determined using spectroscopic ellipsometry (SE), dynamic water contact angle (DCA) measurements, infrared reflection− absorption spectroscopy (IRRAS), and vibrational sum-frequency-generation (VSFG) spectroscopy, the latter in air and water.

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“…10 In OTS supported lipid monolayers, the inherent asymmetry in fluidity properties of the two layers can either serve to (1) decouple interleaflet interactions or (2) induce strong coupling by forcing the monolayers to adopt preferred packing density determined by the tight packing of the underlying OTS monolayer. In very differently prepared lipid monolayer configurations on hydrophobic substrates, [33][34][35][36] indeed, such coupling, including interdigitation between the lipid monolayer and the underlying substrate layer, 35,36 and increase in fluidity transition temperatures is implied. In our case -representing equilibrated monolayers obtained on hydrophobic substrates obtained by vesicle fusion -the second scenario can be ruled out since increased molecular density would result in an increase, rather than the observed decrease, in T ft .…”

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confidence: 99%

A comparison of lateral diffusion in supported lipid monolayers and bilayers

Babayco

Turgut²,

Smith³

et al. 2010

Soft Matter

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Lipid monolayers and bilayers exist in distinct physical states differentiated by the differences in the manner in which translational fluidity relates to their phase transition and how cholesterol influences the two. Work presented here suggests that intra-leaflet diffusion and cholesterol interactions are modulated by the nature of inter-leaflet coupling. Our results also provide an important practical caveat in the comparisons of membrane physical properties deduced using the two, mono-and bilayer, model membrane configurations.Understanding the physical basis of lateral fluidity of bilayer-forming lipids in biological membranes is important because of its central role in many important functions including signaling, transport, and intermembrane interactions. 1,2 A significant body of work now establishes that the membrane fluidity at physiological temperatures is primarily determined by two key factors: (1) physical properties of the constituent lipids (e.g., degree of unsaturation, length of the acyl tail, head-group electrostatics) and (2) the amount of cholesterol. The bulk of our understanding, to this end, comes from studies of temperature-dependent diffusivity of single lipids (and their mixtures with cholesterol) typically using model membrane configurations all of which present symmetric bilayers (e.g., vesicles, black lipid membranes, supported bilayers). These studies treat long-range lateral diffusion of lipids as the reciprocal of the structural order and of the lateral packing of acyl chains. This in turn relates lateral diffusion to the gel (low fluidity phase) to liquid-crystalline or l.c. (high fluidity phase) main phase transition and attendant chain conformational transition of the bilayer 3,4 The role of cholesterol, within this framework, is understood to be that of a substitutional ''impurity'' which tends to decouple the conformational transition from the packing transition 5 of the host bilayer. Specifically, introduction of cholesterol induces a condensing effect on disordered lipids resulting in denser packing and conversely fluidizes ordered lipids by disrupting their packing habit. 6,7 Implicit in these studies is the assumption that diffusion of membrane lipids is directly linked to their thermotropic phase transition. 8The main phase transition in pure lipids is a cooperative process, strongly influenced by the smectic coupling of two apposed monolayers comprising the bilayer. 9-11 Indeed, previous theoretical efforts show that the inter-monolayer interactions are critical for the transitions, otherwise absent in uncoupled monolayers. 11 But biological membranes are both compositionally and structurally asymmetric across the two leaflets. 12 For instance, in red blood cells, phosphatidylethanolamines and serines are located primarily in the cytosolic leaflet whereas cholines and glycolipids tend to concentrate in the exoplasmic monolayer. Moreover the inner leaflet is also structurally constrained by the underlying cytoskeleton. These structural and compositional asymmetries in ce...

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Sum Frequency Generation (SFG) Vibrational Spectroscopy of Planar Phosphatidylethanolamine Hybrid Bilayer Membranes under Water

Cited by 25 publications

References 56 publications

Interkingdom Signaling: Integration, Conformation, and Orientation of N-Acyl-l-homoserine Lactones in Supported Lipid Bilayers

Interkingdom Signaling: Integration, Conformation, and Orientation of N-Acyl-l-homoserine Lactones in Supported Lipid Bilayers

Nonfouling Poly(ethylene oxide) Layers End-Tethered to Polydopamine

A comparison of lateral diffusion in supported lipid monolayers and bilayers

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