An asymmetric synthesis of the diterpene (S)-geranylcitronellol 1a and its acetate 1b is reported. The chirality is induced by TMSI-promoted conjugate addition of a homoallylic monoorganocopper reagent to 2-naphthyl-exo-bornylcrotonate, which proceeds with more than 98% diastereomeric excess.
The crystal structure of cholesteryl dodecanoate has been determined. The compound shows a co-packing of cholesterol skeleta and hydrocarbon chains. There are two molecules in the asymmetric unit both almost fully extended. The hydrocarbon chain axes are however somewhat bent in order to get a good close-packing side by side with the rigid cholesterol skeleta. The two non-symmetry related skeleta show different packing surroundings. One skeleton packs with both hydrocarbon chains and other skeleta while the other skeleton is completely surrounded by hydrocarbon chains. The latter packing is of particular interest as it is considered to indicate important packing principles in biological lipid bilayers.
Polar lipids, e.g. phospholipids, monoglycerides and long-chain esters of fruit acids, are important food additives. In these applications, they are usually classified as food emulsifiers although other effects than emulsification often are utilized, such as complex formation with proteins and starch. Emulsions based on polar lipids are also used in the topological administration of drugs. Knowledge of the structure of the lipid film at the oil/water interface is necessary in order to understand the physical properties of these emulsions, such as stability, rheology and diffusion of substances through the interfacial layer. The molecular arrangement of lipids at interfaces will be considered here and a procedure for identification of the structure corresponding to the highest emulsion stability will be demonstrated. Polar lipids used for formation of emulsions give aqueous phases with water which can be characterized by X-ray diffraction, and they form condensed monolayers at the air/water interface which can be studied by surface balance technique. Boyd and coworkers’ have studied the rheological properties of surface films, and on this basis, have been able to correlate increasing emulsion stability with increasing surface viscosity and elasticity. The occurrence of multilamellar liquid-crystalline particles above the limit of swelling of monoglycerides and related emulsifiers have been demonstrated,6 and the importance of such films with regard to emulsion stability has been pointed out by Friberg and Rydhag.3 In systems corresponding to food emulsions, however, there is often an interfacial film with crystalline hydrocarbon chains.” Such a film can be formed by lipid crystals, exposing a hydrophobic surface towards the oil phase and hydrophilic surface groups towards water. This possibility of formation of two alternative surface structures of lipid crystals (with dominating surfaces parallel to the bimolecular unit layers) means that the crystalline state exhibits emulsification properties, a feature which seems to have been neglected previously. The interfacial film can also be formed by lipid bilayers with crystalline hydrocarbon chains alternating with water layers, a structure characterizing the gel state.6 The hydrocarbon chains in the gel phase possess some degree of disorder, and such a multilamellar inter-facial film is therefore more flexible than that formed by true crystals. This type of structure seems to correspond to the highest emulsion stability as will be demonstrated below.
The most general method available for synthesis of chiral long-chain compounds is based on chain extension of completely resolved precursors. A large number of optically pure compounds may thus be prepared from a small number of chiral key molecules, and resolution steps, uncertain and often laborious, are few, or may be avoided if an optically active natural product is used as starting material.86 Pioneering and extensive work in the field was carried out by the Stenhagens from the middle of the 1940s. They started by synthesizing branched-chain fatty acids,1*73 and began experiments with hydroxy compounds in 1950. At that time, it had been found convenient to use the anodic Kolbe reaction for chain extension of optically active carboxylic acids with branching beyond the or-position,‘*s2*7s and they then tried 3-hydroxybutanoic acid in a Kolbe synthesis. 68 When difficulties arose because of skin formation at the electrodes, the acetate was tried instead, and found to react normally.68 They initiated its resolution by means of quinine, and then asked me to continue the work. At the same time, they proposed that a key molecule allowing chain extension in both directions should be synthesized, and suggested an acetylated monoester of 3-hydroxyglutaric acid.68 This review briefly outlines the preparation of twelve key molecules (1-12, enantiomers included) and lists some fifty long-chain hydroxy compounds synthesized from them. A few new compounds (4d, 11, lla) are included, and previously unpublished physical data have been added for some known compounds (6a, 7a, b, d). Prominent features and compounds of special interest are commented on. Other reviews do not overlap with the present one to any great extent. It has most in common with a survey of optically active long-chain natural compounds by C. R. Smith,” published in 1970, and with a chapter on use of the Kolbe electrosynthesis for assignment of absolute configuration by J. H. Brewster,“” published in 1972. Information from readers concerning errors and new or overlooked compounds and publications belonging to the field under review will be appreciated.
Foam formation in surface water bodies has become a global phenomenon, but the solutions to this crisis are often insufficient. Foam formation in water bodies is attributed to surfactants and requires a comprehensive assessment of various sources of surfactants to evolve mitigation strategies. The study is focused on thoroughly analyzing surfactants in the water and foam fractions of a large waterbody in Bangalore (India) spanning around 1000 acres (400 ha), which has been foaming for two decades. Results revealed that the key surfactants originate predominantly from anthropogenic sources with a small component emerging from naturogenic sources. Anthropogenic surfactants were found to be predominant (96.5%), with linear alkylbenzene sulphonates (LAS) of various C-chain lengths 12–20 being the most prevalent. Naturogenic surfactants derived from bacterial genera Pseudomonas exhibited significant microbial diversity, accounting for over 19% of total bacterial population in both the water and organic sediments of the lake. Modelling studies and field validation efforts were carried out to understand the fate of LAS in the foaming lake. The results indicated that these surfactants donot degrade under the prevailing conditions and timeframe as wastewater traverses through the lake, and their presence was also observed in the organic sludge sediment. Modeling the underlying processes revealed that a minimum dissolved oxygen (DO) concentration of 3.5 mg/l enables the degradation of over 90% of surfactants within the residence time of 8–10 days in Lake. Additionally, the process of desludging could contribute to an additional increase to the overall efficiency of surfactant removal, simultaneously removing legacy sorbed surfactants to sediments.
II. LIPID STRUCTURE A. Composition of head oil lipids I. Lipid class pattern (a) Pilot whale (b) Other odontocetes 2. Fatty acids (a) Pilot whale (b) Other odontocetes 3. Fatty alcohols 4. Hydrocarbons 5. Waxes 6. Triglycerides (a) Pilot whale (b) Other odontocetes 7. Other lipid classes B. Compositional topography of melon lipids 1. Relation to jaw and blubber fat 2. Lipid content 3. Lipid class 4. Fatty acids
Jojoba oil differs from all known seed oils by its almost complete absence of glycerides, making it more a liquid wax than a fat. It has become important as a possible substitute for sperm-whale oil to produce lubricants, lubricant additives and other products. The plant occurs naturally in southern Arizona and N.W. Mexico and its oil has long been used by Indians for medicinal, culinary, ritual and other purposes. It tolerates extreme daily fluctuations of temperature and grows well under the difficult soil and moisture conditions of the region. In the first part of this review the plant and its uses are described, including its floral, fruit and seed anatomy and the use of liquid wax during germination. Stored coryledon wax is used up by the embryo as a linear function of time during the first 30 days of germination and growth. Before germination, seeds weight about 0.59 mg and contain about 54% wax. The second and greater part of the review deals with jojoba oil (its extraction, properties, molecular description, toxicity and composition), jojoba meal, which remains after the oil has been extracted, and the chemical modification of the oil.
