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J Lipkowski

Publications and source records attributed to J Lipkowski.

7 recordsLinked to original sources
PubMed2005

Influence of the electric field on a bio-mimetic film supported on a gold electrode.

A model biological membrane was formed by fusion of mixed cholesterol and DMPC (dimyristoylphosphatidylcholine) phospholipid vesicles onto a gold-coated quartz support. The gold surface was charged and the influence of the charge at the solid support on the structure and integrity of the phospholipid bilayer was investigated using the specular reflection of neutrons and electrochemical measurements. When the surface charge density is close to zero, the lipid vesicles fuse directly on the surface to form a bilayer with a small number of defects and hence low water content. When the support's surface is negatively charged the film swells and incorporates water due to the field driven poration of the membrane. When the charge density is more negative then -8 microC cm(-2) the bilayer is detached from the metal surface. However, it remains in close proximity to the metal electrode, suspended on a thin cushion of water. The film thicknesses, calculated from neutron reflectivity, have allowed us to determine the tilt angle of the lipid molecules as a function of the support's charge density. The lipid molecules are tilted 55 degrees from the surface normal at zero charge density but become significantly more perpendicular (30 degrees tilt angle) at charge densities more negative than -8 microC cm(-2). The tilt angle measurements are in very good agreement with previous IR studies. This paper describes the highlights of a more in-depth study which is fully described in [1].

Biomimetic Materials↗
PubMed2004

Electric field-driven transformations of a supported model biological membrane--an electrochemical and neutron reflectivity study.

A mixed bilayer of cholesterol and dimyristoylphosphatidylcholine has been formed on a gold-coated block of quartz by fusion of small unilamellar vesicles. The formation of this bilayer lipid membrane on a conductive surface allowed us to study the influence of the support's surface charge on the structure and hydration of the bilayer lipid membrane. We have employed electrochemical measurements and the specular reflection of neutrons to measure the thickness and water content in the bilayer lipid membrane as a function of the charge on the support's surface. When the surface charge density is close to zero, the lipid vesicles fuse directly on the surface to form a bilayer with a small number of defects and hence small water content. When the support's surface is negatively charged the film swells and incorporates water. When the charge density is more negative than -8 micro C cm(-2), the bilayer starts to detach from the metal surface. However, it remains in a close proximity to the metal electrode, being suspended on a thin cushion of the electrolyte. The field-driven transformations of the bilayer lead to significant changes in the film thicknesses. At charge densities more negative than -20 micro C cm(-2), the bilayer is approximately 37 A thick and this number is comparable to the thickness determined for hydrated multilayers of dimyristoylphosphatidylcholine from x-ray diffraction experiments. The thickness of the bilayer decreases at smaller charge densities to become equal to approximately 26 A at zero charge. This result indicates that the tilt of the acyl chains with respect to the bilayer normal changes from approximately 35 degrees to 59 degrees by moving from high negative charges (and potentials) to zero charge on the metal.

Adsorption↗
PubMed2003

Electrochemical and photon polarization modulation infrared reflection absorption spectroscopy study of the electric field driven transformations of a phospholipid bilayer supported at a gold electrode surface.

Electrochemistry and polarization modulation Fourier transform infrared reflection absorption spectroscopy (PM-FTIRRAS) was employed to investigate fusion of small unilamellar vesicles of 1,2dioyl-sn-glycero-3-phosphatidyl choline (DOPC) onto the Au(111) electrode. Electrochemical studies demonstrated that the DOPC vesicles fuse and spread onto the gold electrode surface at small charge densities -8 microC cm(-2)<sigmaM<0 microC cm(-2)(if the static electric field is <2 x 10(8) V/m) to form a bilayer. At sigmaM<-8 microC cm(-2), the film is detached from the electrode surface; however, the film remains in close proximity to the surface. The PM-FTIRRAS experiments demonstrated that the field-driven transformation of the film involves changes in hydration, orientation, and conformation in the polar headgroup region and that changes in the packing and tilt of the acyl chains are consequences of the headgroup rearrangements.

Absorption↗
PubMed2001

L-Seryl-L-leucine.

Explore the source record for details and available documents.

Journal Article↗
PubMed2000

Optical resolution of phosphorus containing calix[4]arenes by additive RP HPLC method.

The RP HPLC method (LiChrosorb RP18 or Separon SGX C18 column, acetonitrile-water 86:14 v/v mobile phase) was applied for enantiomeric separation of topologically chiral 5-bromo-25,26-bis(diethoxyphosphoryl)calix[4]arene 9 or 25-ethyl-26-dihydroxyphosphoryl-calix[4]arene 5. Separation of calixarene 9 was achieved by the addition of D-(-)-tartaric acid which formed hydrogen bonded diastereomeric associates with 9 to the mobile phase. Calixarenephosphoric acid 5 was transformed into diastereomeric salt 6 by addition of L-(-)-alpha-phenylethylamine before RP HPLC separation.

Calixarenes↗