Miscibility behavior of dipalmitoylphosphatidylcholine with a single-chain partially fluorinated amphiphile in Langmuir monolayers

Surface pressure-area, surface potential-area, and dipole moment-area isotherms were obtained for monolayers made from a partially fluorinated surfactant, (perfluorooctyl)undecyldimorpholinophosphate (F8H11DMP), dipalmitoylphosphatidylcholine (DPPC), and their combinations. Monolayers, spread on a 0.15 M NaCl subphase, were investigated at the air/water interface by the Wilhelmy method, ionizing electrode method, and fluorescence microscopy. Surface potentials were analyzed using the three-layer model proposed by Demchak and Fort. The contribution of the dimorpholinophosphate polar head group of F8H11DMP to the vertical component of the dipole moment was estimated to be 4.99 D. The linear variation of the phase transition pressure as a function of F8H11DMP molar fraction (X(F8H11DMP)) demonstrated that DPPC and F8H11DMP are miscible in the monolayer. This result was confirmed by deviations from the additivity rule observed when plotting the molecular areas and the surface potentials as a function of X(F8H11DMP) over the whole range of surface pressures investigated. Assuming a regular surface mixture, the Joos equation, which was used for the analysis of the collapse pressure of mixed monolayers, allowed calculation of the interaction parameter (xi=-1.3) and the energy of interaction (Delta epsilon =537 Jmol(-1)) between DPPC and F8H11DMP. The miscibility of DPPC and F8H11DMP within the monolayer was also supported by fluorescence microscopy. Examination of the observed flower-like patterns showed that F8H11DMP favors dissolution of the ordered LC phase domains of DPPC, a feature that may be key to the use of phospholipid preparations as lung surfactants.     

Impact of the structure of phospholipid dispersions on the stability of fluorocarbon/phospholipid emulsions for biomedical uses

The preparation of injectable fluorocarbon emulsions includes the dispersion of the phospholipids in the aqueous phase, then the admixing of the fluorocarbon to produce a crude premix; emulsification is then achieved using a high pressure mechanical procedure, followed by final heat-sterilization. In this work we report that, depending on the procedure used and energy applied, the dispersions of phospholipids consist of poorly organized unclosed “pre-liposomes”, multilamellar vesicles (MLV), or small unilamellar vesicles (SUV). This has a significant impact on the stability of the final fluorocarbon emulsions (90% (w/v) concentration), those prepared from “pre-liposomes” being more stable than those prepared from MLV or SUV. The first emulsion is shown to contain less fluorocarbon-free phospholipid vesicles than the other two. These free vesicles have previously been reported to have a detrimental effect on the stability of concentrated fluorocarbon emulsions.     

Near infrared Raman spectra of human brain lipids

Human brain tissue, in particular white matter, contains high lipid content. These brain lipids can be divided into three principal classes: neutral lipids including the steroid cholesterol, phospholipids and sphingolipids. Major lipids in normal human brain tissue are phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, phosphatidic acid, sphingomyelin, galactocerebrosides, gangliosides, sulfatides and cholesterol. Minor lipids are cholesterolester and triacylglycerides. During transformation from normal brain tissue to tumors, composition and concentration of lipids change in a specific way. Therefore, analysis of lipids might be used as a diagnostic parameter to distinguish normal tissue from tumors and to determine the tumor type and tumor grade. Raman spectroscopy has been suggested as an analytical tool to detect these changes even under intra-operative conditions. We recorded Raman spectra of the 12 major and minor brain lipids with 785 nm excitation in order to identify their spectral fingerprints for qualitative and quantitative analyses.     

Practical cobalt carbonyl catalysis in the thermal Pauson--Khand reaction: efficiency enhancement using Lewis bases

In this report we have shown that the commercially available Co(2)(CO)(8) and Co(4)(CO)(12), and enyne--Co(2)(CO)(6) complexes, are sufficiently effective in catalyzing the Pauson--Khand reaction under one atmosphere of CO pressure. It was further demonstrated that the efficiencies of these cyclization protocols could be enhanced by the presence of cyclohexylamine. These procedures have also rendered more practical and highly convenient alternatives for the catalytic Pauson--Khand reaction. Most importantly, we have dispelled the common belief that Co(4)(CO)(12) is inactive in the Pauson--Khand reaction under one atmosphere of carbon monoxide. Of mechanistic importance is that these studies have also shown that the probable formation of Co(4)(CO)(12) is not necessarily a dead end pathway in the Co(2)(CO)(8)-catalyzed Pauson--Khand reaction. It is also of interest that substoichiometric amounts of Co(2)(CO)(8), in DME and in the presence of cyclohexylamine, are sufficient for the cyclocarbonylation of enynes under a nitrogen atmosphere. Our findings have provided more practical protocols for the Pauson-Khand reaction using catalytic amounts of cobalt carbonyl complexes and a better understanding of the influence of Lewis bases on their efficiency. These reports on the activity of Co(4)(CO)(12) are anticipated to develop into a convenient and practical alternative for Co(2)(CO)(8) catalysis.     

Highly fluorinated compounds induce phase separation in,and nanostructuration of liquid media. Possible impact on,and use in chemical reactivity control

Liquid perfluorocarbons‐like supercritical CO₂‐provide valuable reaction media that can facilitate the separation of reaction products and the recovery of catalysts. Chemistry in fluorous media requires that some of the protagonist molecules, and in particular the catalysts, be grafted with one or more perfluoroalkylated chains. These chains, due to powerful hydrophobic and lipophobic effects, tend to self‐assemble and induce the formation of a variety of nanocompartmented supramolecular architectures and colloids, such as micelles, vesicles, tubules, monolayers, and emulsions, thus generating microheterogenicity in the reaction medium. Fluorinated amphiphiles are, for example, known to generate fibrous gels in fluorous, organic, and aqueous media. Phase separation, nanocompartmentation, and interface‐driven parameters can thus complicate otherwise simple chemistry. Conversely, they can provide useful micro‐ and nanoreactors and templates. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4251–4258, 2006     

Differentiation of individual human mesenchymal stem cells probed by FTIR microscopic imaging

Objective of this study is the novel application of Fourier transform infrared (FTIR) microscopic imaging to identify the differentiation state of individual human mesenchymal stem cells with or without osteogenic stimulation. IR spectra of several hundred single cells with lateral resolution of 5-10 microm were recorded using a FTIR imaging spectrometer coupled to a microscope with a focal plane array detector. A classification model based on linear discriminant analysis was trained to distinguish four cell types by their IR spectroscopic fingerprint. Without stimulation two cell types dominated, showing low or high levels of glycogen accumulation at the cell periphery. After stimulation, the protein composition in the cells changed and some cells started expressing calcium phosphate salts such as octacalciumphosphate, a precursor of the bone constituent hydroxyapatite. Few cells were identified which remained in their non-stimulated state. This study demonstrated for the first time that FTIR microscopic imaging can probe stem cell differentiation at the single cell level rapidly, non-destructively and with minimal preparation.