7. Conclusions

increase in the alkyl chain length to C16 resulting in a highly organized surface arrangement [99]. Monolayers containing one of these glycolipids together with immunoglobulin G were successfully formed by spreading from vesicle dispersions [100]. The presence of the immunoglobulin G in transferred monolayers was subsequently confirmed by infrared spectroscopy, and it was proposed that on compression the immunoglobulin G re-orients from a flat to standing orientation [101]. Monolayers of these derivatives were studied in mixed monolayers with phospholipids by GIXD, and it was found that addition of the glycolipid reduced the correlation length

A homologous series of dialkylglycerylethers and their β-D-glucoside and β-D-cellobioside derivatives were studied as monolayers. It was found that introduction of the sugars expanded the monolayers, and acted in opposition to the effect of increasing chain length [103]. Using pentaerythritol as a building block, a gemini glycolipid was synthesized with two C16 alkyl chains and two N-acetyl-β-D-glucosamine units [104]. Surface pressure-area isotherms showed that monolayers of the compound underwent an expanded to condensed phase transition. In a related study, glucoside lipids were created with a single hydrocarbon chain and either one or two glucose units in the head-group, presented in a branched geometry [105]. The bivalent glucoside achieved maximal binding to lectin at a lower surface fraction than did the monovalent glucoside lipid, when studied in mixed monolayers with an analog lacking sugar units.

Some studies in which glycolipid systems were transferred onto solid supports have been reported. Synthetic glycolipids bearing lactose, Lewis X, and sialyl Lewis X were synthesized containing partially fluorinated chains [106]. Mixed monolayers with phospholipids were observed by fluorescence microscopy and found to display phase separated microdomains. The monolayers were transferred onto silanized glass slides and it was found that adherence of Chinese hamster ovary cells to the supported monolayers varied with the composition and extent of microdomain formation. Langmuir-Blodgett films containing polydiacetylene derivatives that undergo a color change upon a binding induced conformational change are of interest for development of biosensors. Dioctadecyl glyceryl ether-β-glucosides (DGG) were used to form mixed monolayers with 10,12-pentacosadiynoic acid (PCDA) or tricosa-2,4-diynoic acid (TCDA) [107]. BAM showed that mixed monolayers with TCDA could be uniform, but those with PCDA showed phase separated domains. The excess Gibbs free energy of mixing was determined under varied subphase conditions. Another study reported mannosyl derivatives of PCDA in which BAM revealed highly structured dendritic like domains indicating the presence of a highly ordered phase [108]. Absorbance spectroscopy, carried out directly at the water-air

interface, showed a shift from blue to red upon irradiation of the monolayers.

for the cellular glycocalyx.

Synthetic derivatives of galactosyl ceramides with varied chain length between 11 and 33 carbons were synthesized and used to prepare monolayers, the phase behavior of the monolayers varied with overall chain length becoming more condensed with increasing chain length [109]. Synthetic glycolipids based on glycerol with two hydrocarbon chains and one, two, or three lactose units as the head-group were used to make monolayers and the interfacial viscosity was measured. With one lactose unit, a highly viscoelastic monolayer was obtained, with two a more fluid monolayer was observed, and with three a transition from viscous to elastic was observed [110]. In this study, the glycolipid monolayers were considered as a model

and hence the extent of ordering for the phospholipid component [102].

232 Cell Culture

The study of monolayers containing glycolipids provides many insights into the molecular arrangement of glycolipids in membranes. The physical state of the monolayers influences the interaction of glycolipids with binding partners, which can be studied directly by introducing these partners into the subphase. The modulation of these binding interactions is significant to the membrane biochemistry of glycolipids, and monolayers at the water surface provide a uniquely convenient and controllable environment in which to conduct such studies.
