Stabilization of phosphatidylcholine coatings in capillary electrophoresis by increase in membrane rigidity

Abstract

Divalent cations affect the stability and structure of phospholipid vesicles and also the binding and immobilization of proteins into phospholipid membranes. The effect of calcium, magnesium, and zinc on zwitterionic phosphatidylcholine (PC) coatings in fused silica capillaries for electrophoresis was the primary interest in this work. In addition, the effect of temperature on the coating stability was investigated by coating 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes at temperatures above and below the gel- to fluid-state transition. All coatings were performed with PC large unilamellar vesicles (LUV) in 40 mM N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid) (HEPES) at pH 7.4 as basic solution. HEPES (40 mM) at pH 7.4 was used as background electrolyte (BGE) throughout the study. The stability of the coating was studied by measuring the electroosmotic flow. A molar ratio of 1:3 PC/Ca2+ or PC/Mg2+ gave the best coating stability owing to the increased rigidity of the phospholipid membrane furnished by the divalent metal ions. Better results were obtained with DPPC in the more rigid gel state than in the fluid state: the electroosmotic flow was much suppressed and the PC coating was stabilized. Coating the fused silica capillary with PC liposome-metal ion buffer solutions resulted in good electrophoretic separation of basic model proteins (pI-values 7.8-11.0). The electrophoretic results demonstrate the importance of stabilizing the phospholipid coating on fused silica capillaries, either by the addition of divalent metal ions (Ca2+, Mg2+, or Zn2+) or by working in the gel-state region of the phospholipid.

Capillary ion electrophoresis of inorganic anions and uric acid in human saliva using a polyvinyl alcohol coated capillary column and hexamethonium chloride as additive of background electrolyte

“…The determinations of Br − , NO 2 − , NO 3 − and/or SCN − in human saliva have been also performed by micellar electrokinetic chromatography using zwitterionic micelles [5], capillary isotachophoresis [23] and capillary zone electrophoresis (CZE) using a high ionic strength background electrolyte [24]. For direct injection of human saliva samples in CIE, hydrophilic materials coated capillaries have often been used to minimize hydrophobic and electrostatic solute/wall interactions with protein matrices and to eliminate electro-osmotic flow (EOF) [25]. In this study, a capillary column that chemically binds polyvinyl alcohol (PVA) on the fused silica (FS) capillary wall was prepared and employed as the separation column for anions.…”

A modified supported bilayer/diblock polymer – Working towards a tunable coating for capillary electrophoresis

“…Coatings prepared from double-chain cationic surfactants are easy to form and produce stable semi-permanent coatings [12,[16][17][18]. However, the strong anodic EOF [12,16,19] overwhelms the mobility of most proteins, such that the resolution can be limited.…”

Novel adsorptive polyamine coating for enhanced capillary electrophoresis of basic proteins and peptides

“…Up to now, there are lot of physically adsorbed polymers employed to avoid the adsorption of peptides and proteins on fused silica capillaries in CE-UV applications such as derivatized cellulose polymers [12], poly(ethylene oxide) polymer (PEO) [13], PVA [14], polyethyleneimine (PEI) [15,16], polybrene [17,18], successive multiple ionic layer (SMIL) coatings formed by polybrene/dextran sulfate [19] or polybrene/polyvinylsulfonate [20], poly(diallyldimethylammonium chloride) (PDADMAC) [21], polyarginine [22], chitosan [23], quaternary ammonium-substituted agarose [24], liposomes [25], phospholipid bilayers [26] and poly-E-323 [27], polymer of 1,2-bis(3-aminopropylamino)-ethane and epichlorohydrin.…”