Lipids isoprenoid-chained

Molecular Dynamics Study of Isoprenoid-Chained Lipids Salient Features of Isoprenoid Chains As Compared with Ordinary Alkyl Chains... 

Synthetic isoprenoid-chained lipids are a new class of lipids, which have recently been attracted increasing attention [1-25). A salient feature of the isoprenoid-chained Hpids lies in their regularly branched chains consisting of poly-isoprenoid (C5) hydrophobic chains, which are remarkably different from those of ordinary lipids with linear hydrocarbon chains of variable length, different degree of unsaturation. 

I 9 Molecular Dynamics Study of Isoprenoid-Chained Lipids... 

Essentially the same consideration appUes to an inverted bicontinuous cubic phase (Qn) and an inverted hexagonal (Hn) phase, which are usually formed with lipids with long hydrophobic chains. Qn and Hn phases have recently received growing attention in the pharmaceutical or biological fields, for instance, as new carriers for drug-deUvery systems, and matrices for membrane protein crystallization [37-42]. The conventional (e.g., monoolein) Qn phase, however, often transforms into a soUd phase at low temperatures around 4°C [43-47], where temperature-sensitive proteins or actives are most preferably handled and preserved. It has recently been confirmed that isoprenoid-chained lipids can in fact give a range of Qn phases that are stable at low temperatures [13]. 

Another possibihty is that the first membranes arose from phospholipid-like molecules produced by primitive metabolism. Phosphate, with or without additional components, could have provided the hydrophilic heads of the molecules. As to their hydrophobic tails, the French chemist Guy Ourisson has built a strong case in favor of polyisoprenoid molecules, the building blocks of ether lipids, as opposed to long-chain fatty acids, the main constituents of ester lipids (see Ourisson and Nakatani, 1994 Chapter 19, this volume). In nature, isoprenoid chains arise from isopentenyl pyrophosphate, a relatively simple precursor. 

The formation of ether-type polar lipids that occur in the membranes of Archaea remains elusive. The enantiomeric glycerol-phosphate backbone, ether linkages, and isoprenoid chains are distinguishing features of archaeal lipids. Carbonaceous meteorites contain up to several percent of their mass as organic carbon, mainly polycyclic aromatic hydrocarbons. Material extracted from the Murchison meteorite by organic solvents contains amphiphiles that form membrane-like vesicles in aqueous solution. 

This chapter focuses on the use of different methods for isolation of alkylresorcinols. Alkylresorcinols are members of a lipid group called non-isoprenoid phenolic lipids. Different aspects of the extraction by classical methods and supercritical CO2 are discussed. Supercritical CO2 extraction of alkylresorcinols from rye bran is discussed for the first time. As compared to the classical extraction methods, supercritical CO2 gives higher yields and it allows the separation of the crude extrac into long- and short-chain alkylresorcinol homologues. 

For resorcinolic lipids, particularly those with long saturated side-chains, the use of polar solvents is important due to their amphiphilicity. The crude extracts in many cases are subjected to preliminary fractionation/purification either by solvent fractionation/partition or by application of chromatography. For prepurification of the material and its separation from polymerized phenolics, gel filtration on hydrophobic Sephadex or TSK gel is sometimes used. Silica gel is most frequently employed for the separation and/or purification of resorcinolic lipids, notably in some studies with Ononis species (12-14). The array of compounds reported appears partly attributable to methylation or acetylation reactions occurring during column chromatographic separation. An interesting approach for I the pre-purification and selective separation of resorcinolic lipid from phenolic lipids or resorcinolic lipids from impurities has recently been reported. A selective partitioning of different non-isoprenoid phenolic lipids... 

K. Yamauchi, Y. Yoshida, T. Moriya, K. Togawa and M. Kinoshita, Archebacterial Lipid Models Formation of Stable Vesicles from Single Isoprenoid Chain-Amphiphiles, Biochim. Biophys. Acta, 1193 41 (1994). 

Most of the prenyl lipids, such as chlorophylls, carotenoids, and prenylquinones, as well as tocopherols and vitamin Ki, which occur in plant lipid extracts, can be separated by TLC using silica gel plates or special mixtures of silica gel with other adsorbents.But, the compounds with one double bond per isoprene and others with a partially or fully unsaturated isoprenoid chain can be separated efficiently by argentation TLC. 

Rhodamine 6G long-chain hydrocarbons [169] squalene, a-amyrin [170] methyl esters of fatty acids [171] glycerides [91] sterols [172, 173] isoprenoids, quinones [HI] lipoproteins [174] glycosphingolipids [175] phenolic lipids [176] phosphonolipids [177] increasing the sensitivity after exposure to iodine vapor [178,179]... 

The hydrophobic components of many lipids consist of either isoprenoids or fatty acids and their derivatives 34 Isoprenoids have the unit structure of a five-carbon branched chain 34 Brain fatty acids are long-chain carboxylic acids that may contain one or more double bonds 34... 

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