Destabilization of Polyelectrolyte Multilayers Formed at Different Temperatures and Ion Concentrations

Cornelsen, Matthias; Helm, Christiane A.; Block, Stephan

doi:10.1021/ma9027883

Cited by 26 publications

(46 citation statements)

References 43 publications

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“…It has the appearance of a surface-induced phase separation (spinodal decomposition) between the two polyelectrolytes, and this mechanism was, indeed, recently put forward. 52 …”

Section: Resultsmentioning

confidence: 99%

Homogeneity, Modulus, and Viscoelasticity of Polyelectrolyte Multilayers by Nanoindentation: Refining the Buildup Mechanism

2012

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Atomic force microscopy, AFM, and nanoindentation of polyelectrolyte multilayers, PEMUs, made from poly(diallyldimethylammonium), PDADMA, and poly(styrene sulfonate), PSS, provided new insight into their surface morphology and growth mechanism. A strong odd/even alternation of surface modulus revealed greater extrinsic (counterion-balanced) charge compensation for fully hydrated multilayers ending in the polycation, PDADMA. These swings in modulus indicate a much more asymmetric layer-by-layer growth mechanism than previously proposed. Viscoelastic properties of the PEMU, which may contribute to cell response, were highlighted by variable indentation rates and minimized by extrapolating to zero indentation rate, at which point the surface and bulk equilibrium moduli were comparable. Variations in surface composition were probed at high resolution using force mapping and the surface was found to be uniform, with no evidence of phase separation. AFM comparison of wet and dry films terminated with PSS and PDADMA revealed much greater swelling of the PDADMA-terminated PEMU by water, with collapse of surface roughness features in dry conditions. Dynamic and static contact angle measurements suggested less rearrangement for the glassy PSS surface.

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“…It has the appearance of a surface-induced phase separation (spinodal decomposition) between the two polyelectrolytes, and this mechanism was, indeed, recently put forward. 52 …”

Section: Resultsmentioning

confidence: 99%

Homogeneity, Modulus, and Viscoelasticity of Polyelectrolyte Multilayers by Nanoindentation: Refining the Buildup Mechanism

2012

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“…21,22 Briefly, the script scans over the images identifying the highest points within a moving 17 3 17 rectangle (supplemental Figure 1), giving the position and maximum height of the samples adsorbed to mica. To avoid cross-talk with measurement noise, a 0.9-nm threshold (the standard deviation of the background noise in the AFM images) was used in this study.…”

Section: Atomic Force Microscopymentioning

confidence: 99%

Binding of anti–platelet factor 4/heparin antibodies depends on the thermodynamics of conformational changes in platelet factor 4

Kreimann¹,

Brandt²,

Krauel³

et al. 2014

Blood

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Key Points• Besides clustering, platelet factor 4/polyanion complexes require input of energy to become immunogenic. • Minute differences in chain length determine the induction of antigenicity of PF4.The chemokine platelet factor 4 (PF4) undergoes conformational changes when complexing with polyanions. This can induce the antibody-mediated adverse drug effect of heparin-induced thrombocytopenia (HIT). Understanding why the endogenous protein PF4 becomes immunogenic when complexing with heparin is important for the development of other negatively charged drugs and may also hint toward more general mechanisms underlying the induction of autoantibodies to other proteins. By circular dichroism spectroscopy, atomic force microscopy, and isothermal titration calorimetry we characterized the interaction of PF4 with unfractionated heparin (UFH), its 16-, 8-, and 6-mer subfractions, low-molecular-weight heparin (LMWH), and the pentasaccharide fondaparinux. To bind anti-PF4/heparin antibodies, PF4/heparin complexes require (1) an increase in PF4 antiparallel b-sheets exceeding ∼30% (achieved by UFH, LMWH,, (2) formation of multimolecular complexes (UFH,, and (3) energy (needed for a conformational change), which is released by binding of ‡11-mer heparins to PF4, but not by smaller heparins. These findings may help to synthesize safer heparins. Beyond PF4 and HIT, the methods applied in the current study may be relevant to unravel mechanisms making other endogenous proteins more vulnerable to undergo conformational changes with little energy requirement (eg, point mutations and post-translational modifications) and thereby predisposing them to become immunogenic. (Blood. 2014;124(15):2442-2449 IntroductionHeparin, widely used clinically as a parenteral anticoagulant, 1-3 is a polyanion consisting of iduronic acid, glucuronic acid, and glucosamine residues carrying sulfate groups. Pharmaceutical heparin is obtained from porcine gut mucosa and, as biological material, is composed of polysaccharide chains with variable length. Degradation of unfractionated heparin (UFH) results in less polydisperse and smaller low-molecular-weight heparins (LMWHs). The pentasaccharide fondaparinux consists of the shortest sequence able to catalyze the activity of antithrombin. It was the first synthesized heparin approved for clinical use. 4 Currently, several other heparin-based, synthesized polysaccharides are in preclinical development. 5,6 Beside their anticoagulant activity, heparins have other biological effects including potential antitumor activity, 7 which, however, differs depending on the chain length. Clinically, beside bleeding, heparin-induced thrombocytopenia (HIT) is the most important adverse effect of heparin.8 HIT is a lifethreatening immune-driven adverse effect, which occurs in up to 3% of patients receiving UFH after major surgery. 9 HIT is caused by antibodies that recognize platelet factor 4 (PF4), a CXC chemokine family protein, in ultralarge multimolecular complexes with heparin. 10Several of these pathogenic antib...

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“…1,15 With in situ ellipsometry, we can monitor the thickness of a deposited polycation/ polyanion bilayer in the linear growth regime. Figure 4 shows the temperature dependence of d BL .…”

Section: ' Experimental Setupmentioning

confidence: 99%

“…This destabilization is characterized by a drastic increase in layer roughness and frequently, even a detachment or partial dewetting of the PEM is observed. 1 Hence, the investigation of the temperature effect requires in situ techniques like ellipsometry, neutron, or optical reflectometry, which are capable of exploring PEMs in its liquid environement.…”

Section: ' Introductionmentioning

confidence: 99%

Temperature-Induced Transition from Odd–Even to Even–Odd Effect in Polyelectrolyte Multilayers Due to Interpolyelectrolyte Interactions

2012

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Within a liquid cell the linear growth of polyelectrolyte multilayers from poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) is observed with multiple angle null ellipsometry. The salt content is varied between 1 and 4 mol/L NaCl and the temperature between 20 and 55 °C. In the linear growth regime, the outermost layer is investigated. At low temperature, a top PSS layer is twice as thick as a top PAH layer (odd-even effect), consistent with the respective monomer volumes and the same water content for both kinds of top polyelectrolyte layers as confirmed by refractive index measurements. On heating, the thickness of a polycation/polyanion bilayer increases. For temperatures exceeding a crossover temperature, a top PAH layer is thicker than a top PSS layer (even-odd effect). Simultaneously, the index of refraction of the respective top layers indicates a compact PSS and a swollen PAH layer. It is suggested that, at elevated temperature and high salt conditions, secondary forces gain importance in comparison to electrostatic forces: therefore, a transition from an odd-even to an even-odd effect occurs, as well as the decreased film stability on drying as described before (Cornelsen, M., et al. Macromolecules 2010, 43, 4300). The ellipsometric data indicate that PAH/PSS layer pairs exceeding 8.6 nm thickness in solution are unstable in air.

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Destabilization of Polyelectrolyte Multilayers Formed at Different Temperatures and Ion Concentrations

Cited by 26 publications

References 43 publications

Homogeneity, Modulus, and Viscoelasticity of Polyelectrolyte Multilayers by Nanoindentation: Refining the Buildup Mechanism

Homogeneity, Modulus, and Viscoelasticity of Polyelectrolyte Multilayers by Nanoindentation: Refining the Buildup Mechanism

Binding of anti–platelet factor 4/heparin antibodies depends on the thermodynamics of conformational changes in platelet factor 4

Temperature-Induced Transition from Odd–Even to Even–Odd Effect in Polyelectrolyte Multilayers Due to Interpolyelectrolyte Interactions

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