Profile Structures of Thin Multilayer Films by X-ray Diffraction Using Direct and Refinement Methods of Analysis

Meridional x-ray diffraction data from Langmuir-Blodgett multilayers containing two to ten molecular monolayers of arachidic acid were analyzed by two independent methods. A Patterson function deconvolution technique uniquely provided the electron density profile (8A resolution) of the average, symmetric bilayer repeated in the multilayer. This average bilayer appeared to disorder as the number of bilayers in the multilayer decreased. A refinement technique, which does not assume a centrosymmetric structure or the existence of a unit cell, uniquely provided the profile structure of the multilayer itself. In particular it could distinguish the individual monolayers in the multilayer. Meridional x-ray scattering data from Langmuir-Blodgett multilayers composed of arachidic acid and either \u27myristic acid or polymerized 10,12 pentacosadiynoic acid were also analyzed by the refinement technique. It found that only the last monolayer in the depostion sequence (ie. the surface monolayer) was disordered and that ordering of the surface monolayer can be induced by the deposition of an additional monolayer. In addition, an application of Langmuir-Blodgett multilayer thin films and their characterization by x-ray scattering is discussed with regards to the structural study of membrane-membrane interactions and the triggering of cellular components of the immune system

Rat cerebral cortical synaptoneurosomal membranes. Structure and interactions with imidazobenzodiazepine and 1,4-dihydropyridine calcium channel drugs

Small angle x-ray scattering has been used to investigate the structure of synaptoneurosomal (SNM) membranes from rat cerebral cortex. Electron micrographs of the preparation showed SNM with classical synaptic appositions intact, other vesicles, occasional mitochondria, and some myelin. An immunoassay for myelin basic protein placed the myelin content of normal rat SNM at less than 2% by weight of the total membrane present. X-Ray diffraction patterns showed five diffraction orders with a unit cell repeat for the membrane of 71 to 78 A at higher hydration states. At lower hydration, 11 orders appeared; the unit cell repeat was 130 A, indicating that the unit cell contained two membranes. Electron density profiles for the 130-A unit cell were determined; they clearly showed the two opposed asymmetrical membranes of the SNM vesicles. SNM membrane/buffer partition coefficients (Kp) of imidazobenzodiazepine and 1,4-dihydropyridine (DHP) calcium channel drugs were measured; Kp's for DHP drugs were approximately five times higher in rabbit light sarcoplasmic reticulum than in SNM. Ro 15–1788 and the DHP BAY K 8644 bind primarily to the outer monolayer of vesicles of intact SNM membranes. Nonspecific equilibrium binding of Ro 15–1788 occurs mainly in the upper acyl chain of the bilayer in lipid extracts of SNM membrane

A review of a carbonaceous chondrite: what can we learn from the Kaba meteorite?

The Tenth Symposium on Polar Science/Poster presentations: [OA] Antarctic meteorites, Wed. 4 Dec. / Entrance Hall (1st floor), National Institute of Polar Researc

Bilayer characteristics of a diether phosphonolipid analog of the major lung surfactant glycerophospholipid dipalmitoyl phosphatidylcholine.

Thermal and lyotropic phase behavior was studied by X-ray diffraction and differential scanning calorimetry for a diether phosphonolipid analog (DEPN-8) of the major lung surfactant glycerophospholipid dipalmitoyl phosphatidylcholine (DPPC). DEPN-8 differs in an ether, rather than an ester, bond at the acyl chain-backbone linkage and a headgroup phosphonate (isosteric methylene substitution) versus phosphate constituent. Analysis of lamellar diffraction maxima demonstrated that at high relative humidity (98%) and temperatures below the liquid crystal phase transition (approximately 45 degrees C), DEPN-8 formed interdigitated bilayers with a characteristic periodicity of 41.9-46.5 A. At low humidity the gel phase DEPN-8 bilayers were characteristic of a normal L beta phase with a periodicity equivalent to DPPC (57-59 A). Above the liquid crystal thermal phase transition, bilayer spacing for both DEPN-8 and DPPC was 51-52 A, characteristic of the L alpha phase. Complete assessments of both lamellar and in-plane X-ray scattering used to construct electron density profiles and structure-factor plots for DEPN-8 defined more fully the interdigitated bilayer state at high humidity and low temperature. Compared to DPPC, it is energetically favorable for DEPN-8 to form interdigitated bilayers under conditions of excess water and low temperature. The flexible character of the ether bonds in DEPN-8 allows increased hydrophobic interactions between acyl chains, without generating a steric penalty from the increased packing density of the molecules. Additionally, the ether bond and the phosphonate moiety may allow for more energetically favorable interactions between the choline portion of the headgroup and water. The DEPN-8 ether linkage may also contribute to the improved adsorption and film respreading found previously for this phosphonolipid compared to DPPC

Pressure Induced Hydration Dynamics of Membranes

Pressure-jump initiated time-resolved x-ray diffraction studies of dynamics of the hydration of the hexagonal phase in biological membranes show that (i) the relaxation of the unit cell spacing is non-exponential in time; (ii) the Bragg peaks shift smoothly to their final positions without significant broadening or loss in crystalline order. This suggests that the hydration is not diffusion limited but occurs via a rather homogeneous swelling of the whole lattice, described by power law kinetics with an exponent $\beta = 1.3 \pm 0.2$.Comment: REVTEX 3, 10 pages,3 figures(available on request),#

Bilayer structure and physical dynamics of the cytochrome b5 dimyristoylphosphatidylcholine interaction

Cytochrome b5 is a microsomal membrane protein which provides reducing potential to delta 5-, delta 6-, and delta 9-fatty acid desaturases through its interaction with cytochrome b5 reductase. Low angle x-ray diffraction has been used to determine the structure of an asymmetrically reconstituted cytochrome b5:DMPC model membrane system. Differential scanning calorimetry and fluorescence anisotropy studies were performed to examine the bilayer physical dynamics of this reconstituted system. These latter studies allow us to constrain structural models to those which are consistent with physical dynamics data. Additionally, because the nonpolar peptide secondary structure remains unclear, we tested the sensitivity of our model to different nonpolar peptide domain configurations. In this modeling approach, the nonpolar peptide moiety was arranged in the membrane to meet such chemically determined criteria as protease susceptibility of carboxyl- and amino-termini, tyrosine availability for pH titration and tryptophan 109 location, et cetera. In these studies, we have obtained a reconstituted cytochrome b5:DMPC bilayer structure at approximately 6.3 A resolution and conclude that the nonpolar peptide does not penetrate beyond the bilayer midplane. Structural correlations with calorimetry, fluorescence anisotropy and acyl chain packing data suggest that asymmetric cytochrome b5 incorporation into the bilayer increases acyl chain order. Additionally, we suggest that the heme peptide:bilayer interaction facilitates a discreet heme peptide orientation which would be dependent upon phospholipid headgroup composition