The interfacial behavior of a short-chain poly(ethylene oxide) (PEO) lipopolymer, PEO (molecular weight 2000) grafted distearoylphosphatidylethanolamine (PEO2K-DSPE), and its mixtures with distearoylphosphatidylcholine (DSPC) have been studied using Langmuir film balance and surface tension methods. Surface pressure-area isotherms for pure PEO2K-DSPE and PEO2K-DSPE/DSPC mixtures (with 2, 5, 10, 15, or 20 mol % of PEO2K-DSPE) revealed two phase transitions. The simple additivity in the molecular area of lipid mixtures with increasing incorporation of PEO lipopolymer below the low-pressure transition indicates the existence of a two-dimensional thin layer of PEO and lipid. The low-pressure transition is interpreted as desorption of surface-adsorbed PEO molecules into the aqueous subphase. Correlation of film balance experiments with PEO lipopolymer and surface tension experiments with PEO aqueous solutions suggests dehydration of the PEO in the lipopolymer film by expulsion of PEO-associated water molecules as surface pressure increases. Theoretical models, based on scaling theories of polymers at interfaces, fit the observed isotherms well in the low-pressure regime below the first transition but poorly in the high-pressure regime above the first transition. The high-pressure transition is interpreted as ordering of lipid tails in lipopolymers, as driven by the enthalpic gain from lipid alignment and balanced by the entropic loss for lipid ordering and most importantly by dehydration of the PEO chains.

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Me thods for extracting total RNA from various tissues of satsuma mandarin and kiwifruit were examined. Satisfactory yields in total RNA were obtained from tissues with the exception of the albedo tissue of satsuma mandarin, by using a modification of the conventional extraction method devised for fruit tissues by Lopez-Gomez and Gomez-Lim (1992). In the albedo tissue, the polysaccharides may interfere with RNA extraction but further modification of the extraction method improved its yield. The modification involved repeated back extraction, chloroform/isoamyl alcohol extraction, and increasing the volume of the aqueous phase before precipitating RNA with LiCl (3 M final concentration). From the total RNA, poly(A)+RNA was purified using an oligo(dT)-cellulose column. The poly(A)+RNA could be successfully used for Reverse Transcription-Polymerase Chain Reaction (RT-PCR) and the construction of a cDNA library. This modified protocol is applicable to other fruit tissues rich in polysaccharides.

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The surface active properties of novel poly(ethylene oxide) (PEO) containing surfactant polymers were investigated at the air-water and graphite-water interfaces. The surfactant polymers are comblike polymers consisting of a poly(vinylamine) backbone with 2 kDa PEO and hexanal side chains. The polymers were prepared with various grafting ratios of the two side chains. Surface pressure isotherms were obtained for spread monolayers for the range of polymer compositions. Two transitions are observed at 5 and 11 mN/m, which are interpreted as stages of desorption for the PEO side chains from the interface into the aqueous subphase. It is demonstrated that it is possible to scale the isotherms quantitatively to provide an accurate determination of the side chain composition. We characterized the adsorption process of two of the surfactant polymers at the water-graphite interface, using tapping mode atomic force microscopy (AFM). With high hexanal:PEO content (e.g., 8:1), the surfactant polymer rapidly forms a compact and complete monolayer 1.2 nm thick. At lower hexanal:PEO content (e.g., 4:1), a disordered layer is formed. After several hours, this layer rearranges into small scattered domains with banded structures. The structure of these layers is interpreted using a model of surface adsorption and the surface pressure isotherms.