Götz Milkereit

Synthesis and mesogenic properties of glycosyl diacylglycerols

We synthesised glycosyl diacylglycerols bearing unsaturated or chiral methyl branched fatty acid chains. The thermotropism was measured with polarising microscopy and additionally the lyotropism with the contact preparation method. The synthesised compounds displayed thermotropic S(A) (lamellar), cubic and columnar phases and investigation of the lyotropic phase behaviour led to the observation of inverted bicontinuous cubic V(II) phases, lamellar L(alpha) phases and normal bicontinuous cubic V(I) phases. The phases are discussed with respect to the chemical structures that have been varied systematically to derive structure--property relationships.

Effects of carbohydrate headgroups on the stability of induced cubic phases in binary mixtures of glycolipids

This paper is part in a series of papers, investigating the influence of carbohydrate headgroups on the mesogenic properties of glycolipids. While previous papers focussed on the synthesis and mesogenic properties of the pure compounds, we will discuss here our results obtained with binary mixtures. Mixtures of compounds, one forming a lamellar phase and the other one a columnar phase in their pure state, displayed always an induced cubic phase. The stability of this induced cubic phase depends significantly on the structure of the carbohydrate headgroup of both components. Thus it was possible to derive structure-property relationships by comparison of the phase diagrams that have been obtained, if the carbohydrate headgroup of one component was changed systematically. We observed an interesting effect of galactose headgroups which might be of great biological importance. Furthermore, the observed kind of kinetic of the S(A)-->cub transition might also be of great biological relevance.

Phase diagrams of monoacylated amide-linked disaccharide glycolipids

A series of monoacylated glycolipids with even-numbered acyl chain lengths ranging from saturated C11 to C15 and an unsaturated C17:1 fatty acid connected by an amide in linkage to the disaccharide head groups maltose, melibiose and lactose were synthesized. The structural polymorphism of the glycolipids was investigated using Fourier-transform infrared spectroscopy and differential scanning calorimetry for the detection of the gel to liquid-crystalline acyl chain melting behaviour and small-angle X-ray scattering for the elucidation of the physical structure of the lipid aggregates. Also, the phase morphology was studied by polarizing microscopy in contact preparations. The data clearly show the existence of uni- and multilamellar structures. Although only one acyl chain is present, there is no evidence for the existence of micelles - of spherical or of cylindrical (H(I)) type - or of interdigitated phases. The preference for lamellar phases seems to be correlated with the intrinsic high conformational order of the amide linkage of these compounds which inhibits the formation of highly curved structures.

An Improved Synthetic Procedure for the Preparation of N‐Acyl (2‐aminoethyl)‐β‐d‐glycopyranoside Lipids and Characterization of Their Mesogenic Properties

Abstract A modified synthetic procedure was used for the synthesis of N‐acyl (2‐aminoethyl) glycosides bearing lactose, maltose, and melibiose carbohydrate headgroups and different acyl chains. The lipid glycosides were prepared in gram scale and investigated for their liquid crystalline properties. It was found that the polar spacer suppresses polymorphism, and the resulting simplified phase behavior was found in the pure state upon heating, as well as for the lyotropic phases

Structural polymorphism of hydrated monoacylated maltose glycolipids.

The physico-chemical properties of three fully hydrated monoacyl maltoside glycolipids were investigated with Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS). The different synthesized maltoside glycoconjugates vary in the length and saturation of the fatty acid moiety, whereas the constant head group region contains a beta-linked maltose with a OC(2)-NH spacer. The compounds with saturated acyl chains showed a complex pattern of temperature-dependent behaviour, regarding the adopted three-dimensional aggregate structure of the molecules and the main phase transition from the gel to liquid crystalline phase of the acyl chains. A substitution of the saturated acyl chain with an unsaturated acyl chain led to a complete change of the structural preferences, from a high ordered stacking of the bilayers to an unilamellar arrangement of completely disordered and fluid membranes. The presence of the NH group in the spacer, compared to the compounds lacking the NH group allows the formation of a hydrogen bonding network, which influences the observed phase properties. The results of these studies of the hydrated monoacylated maltose glycolipids are discussed in relation to the thermotropic phase properties of the pure compounds in the absence of water.