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E M Arnett

Publications and source records attributed to E M Arnett.

3 recordsLinked to original sources
PubMed1988

Stereoselective recognition in phospholipid monolayers.

During the past ten years we have investigated the stereochemistry of intermolecular interactions in monolayers at the air-water interface, a field which has never been developed explicitly before to our knowledge. Although we demonstrated clear enantiomeric and diastereomeric interactions for a number of chiral surfactants, we found no evidence whatsoever for stereoselective interaction in dipalmitoylphosphatidylcholine (DPPC) monolayers or vesicles by standard monolayer techniques, differential scanning calorimetry or ultra-highfield NMR. The present article extends these observations to dimyristoyl- and dilauroylphosphatidylcholine. Results from dynamic surface tension studies are also reported. In no case could chiral recognition be demonstrated using the 95% confidence limit as the criterion. In our previous study of DPPC mixtures with another chiral surfactant the question arose as to whether chiral interactions could be transmitted through intervening phospholipid molecules. This question is addressed by examining the force-area curves for a variety of mixed monolayers composed of chiral surfactants and phospholipids. We conclude that the chiral discrimination observed in some of these mixed monolayers is due to the direct interaction of chiral centers, and not due to the transmission of chirality from one stereocenter to the next through intermediate achiral molecules. Finally, we will consider the question of why phospholipids, the most ubiquitous of natural chiral surfactants, should show so little chiral discrimination in view of the wide occurrence of high stereoselectivity in many natural processes.

Dimyristoylphosphatidylcholine↗
PubMed1986

No phospholipid monolayer-sugar interactions.

Studies by a number of workers using the Langmuir film balance have shown that when carbohydrates, such as sucrose or glycerol, are dissolved in a subphase on which a phospholipid is spread, film expansion occurs (Cadenhead & Demchak, 1969; Cadenhead & Bean, 1972; Maggio et al., 1976; Maggio & Lucy, 1978). Recently such effects have been observed again, particularly with the carbohydrates galactose and trehalose (Johnston et al., 1984). The origin of these film expansions was uncertain, and various suggestions have been made to explain them. One idea was that they might be due to interactions which these carbohydrates have with the water molecules close to the polar head groups of the lipids. Recent studies in our two laboratories, described here, show that the magnitude of the expansion effects is variable and that in general they arise from surfactant impurities in the sugars. These impurities are observed in carbohydrates which are reputedly of high grade; the amount of impurity present can vary from batch to batch, and sometimes they can be difficult to remove. Film balance techniques or subphase preparation can mask the detection of minor impurities. The presence of surfactant impurities in reputedly pure carbohydrates needs to be considered in other biochemical and biophysical studies of lipids and cell membranes.

Carbohydrates↗