Enantioselective lipase catalysis, in either aqueous or organic media, is becoming increasingly important in preparative synthetic chemistry. Despite poor enantiotopic selectivity in hydrolyzing triacylglycerols, lipases proved to be remarkable asymmetric agents in resolving carboxylic acids and alcohols. Thus, this article discusses (1) the general catalytic features of lipases, (2) the basic principles that govern the stereochemical selectivity of lipase catalysis in aqueous and organic media for the preparation of optically active compounds, and (3) experimental parameters important to lipase-catalyzed enantioselective esterification in organic solvents.
Plant lipoxygenases catalyze hydroperoxidation of fatty acids. The lipid hydroperoxides are metabolized to a number of physiologically active compounds. Isolation of plant lipoxygenase genes enabled us to analyze the structure and function of these enzymes at the molecular level. Lipoxygenases are also of relevance to the food and medical industries. This paper describes the plant lipoxygenase pathway and potential applications of lipoxygenase gene manipulation to industry.
Lipid peroxidation in biological system proceeds via enzymatic and nonenzymatic reaction resulting in the formation of biologically active substances. Peroxidation of biomembrane phospholipids happens by the attack of active oxygens and thereby function of biomembranes are damaged. However, this reaction seems to be of physiologically importance. For example, enzymatic peroxidation of membrane phospholipids occurs in the maturation of red cells. Platelet activating factor (PAF) -like phospholipid peroxidation products can be formed by nonenzymatic process. Pathological and physiological aspects should be evaluated in the peroxidation of membrane phospholipids.
Living organisms are cell aggregates functionally assembled, and each cell can survive and play roles due to its normal membrane functions. Since the membrane functions are controlled by the lipid microenvironment in lipid bilayers, altered lipid composition which could take place in senescence should result in the decrease of membrane and cellular functions, and eventually in the diminished activities of organs and whole bodies. Focused on aging brain inthis article, the changes in membrane lipids will be correlated with the decreases in membrane functions, and the importance of so-called “brain plasticity” will be discussed by describing an example in which a modification of membrane lipids appeares to improve synaptic functions.
There is now an increasing number of evidence which suggests that active oxygens and free radicals are involved in a progression of a variety of pathological events, cancer and aging. In this review are introduced the formation of various active oxygens and free radicals, their reactions with biological molecules such as lipids, proteins and DNA, the oxidative damage induced by them, and the defense systems in vivo against these oxidative damage. It is also briefly mentioned that active oxygens and free radicals are, like oxygen molecule, the double edge sword and can be used in the therapy.
Recent developments in the design of highly selective enzymelike catalysts are having an important impact on synthetic chemistry. Particulary, antibody reagents have been used as selective catalysts for acyl transfers, carbon-carbon bond cleavages, Diels-Alder reactions and Claisen rearrangements. The transition-state analogue concept has been established as a valuable approach on the design of enzymelike catalysts for stereoselective chemical transformations. Antibody-catalyzed enantioselective transformations of fluorinated materials facilitate the assembly of contiguous stereocenters with high relative as well as absolute stereocontrol.
Some interfacial chemical and physicochemical properties of various phospholipids which are used as a model biomembrane, as a emulsifier for intravenous fat emulsion and lipid emulsion, and as a main ingredient of liposomes (lipid vesicles) were reviewed. The hydrophile-lipophile balance (HLB) number of various phospholipids was calculated according to quantity of inorganic characters. The relation between the dynamic molecular shape and the HLB of phospholipid for stability of an emulsion was demonstrated.
The general aspects and recent developments of enzymatic reactions in organic solvents are reviewed as a new technique for utilization of enzymes as synthetic catalysts. Characteristic features of different reaction systems are described in view of the interactions between the reaction components, that is enzyme, substrate, organic solvent, and water. Significant attention is focused on the effects of the nature of organic solvent and water content on activity and specificity of proteases for synthetic and hydrolytic reactions of esters and peptides. Effects of immobilization and complex formation of enzymes with solid materials in organic solvents are also described in terms of activity and stability of the enzymes.
As temperature is used in cooking, pressure is also useful for food processing and preservation. The philosophy of the use of pressure (P) in addition to temprerature (T) has been accepted in food science and technology in the recent several years and R & D rapidly progresses in food industries and the related governmental and academic institutions especially in Japan. At present several commercial products using the high pressure technique are on the market. In this report, the principle and the versatile possibilities of high pressure food processing are described, and the present conditions of R & D in Japan are surveyed and finally the combination use of P and T is discussed.
Fatty acid is considered to be a building block as a long carbon -chain unit in total syntheses of naturally occurring compounds. This review surveys some examples of such total syntheses focusing on the routes from 10 -undecenoic acid.
The Ni (II) or Ca (II) complex-catalyzed C-2 epimerization of aldose and ketose have been investigated using 13C-enriched substrates. During our studies on this reaction, it became apparent that (1-13C) -D-glucose changed into (2-13C) -D-mannose or vice versa and (2-13C) -fructose converted into 2-13C- (hydroxymethyl) -D-ribose (hamamelose). These results said that the product sugars were prepared not via the ene-diol rearrangement but via stereospecific one. It was also elucidated that the coordination state of the intermediate complex consisting of metal, ligand, and sugar played an important role during the reaction. With more hydrophobic ligands such as N, N, -dimethyl-N'-higher alkylethylenediamine and N-higher alkyltrimethylenediamine, the epimerization were smoothly proceeded not only in methanolic solution also in aqueous solution, where ordinary hydrophilic complex could not show effective epimerization ability. The excellently organized reaction system due to their self aggregation ability like micelles would present a proper environment for the sugar epimerization.
Allylation reaction is one of the most important process in organic synthesis due to the synthetic flexibility of allylic systems. Described herein are the new methods to control regio-and stereochemistry of allylic compounds for efficient synthesis of acyclic terpenes. (1) Remarkable SN2'-, (E) -, and antiselectivities are observed in the coupling reaction between Grignard reagents and allylic phosphates in the presence of a copper (I) salt. (2) Stereochemically homogeneous mono-and di-substituted allylmetals can be directly prepared from the corresponding allylic halides and reactive metals at low temperature. (3) Allylic barium reagent reacts with a variety of carbonyl compounds to produce the homoallylic alcohol with remarkably high α -selectivity with retention of stereochemistry of the starting halides.
Recent progress in chromatography of lipid components is reviewed. Analyses of higher molecular weight components, separations unsaturation factors on : number, location and geometrical configuration of unsaturated bonds, and stereospecific analysis of triacylglycerols by recognition with chiral high performance-liquid chromatography are described. The unresolved problems remaining in the field of the chromatography of lipids is discussed.
It has been passed many years since much interests were paid on lipid hydroperoxidation in some research fields such as foods, medicines, cosmetics and their related industries. During these decades, there are many reports on development and modification of lipid hydroperoxides determination methods, which is able to perform precise and reproducible analysis with a very small sample size. Those methods are contributing for not only evaluation of toxicity or effect of lipid hydroperoxides on living bodies but also quality control of oil and fat products. However, some methods used with halogen-containing solvents, for example the official and tentative methods for peroxide value measurement have to make further modification based on looking for alternative solvent since environmental pollution by halogen compounds is proceeding rapidly. In the present review, some popular or novel methods which are classified into titrimetric, colorimetric, enzymatic and instrumental methods are introduced and characterized.
Carbontetrachloride and chloroform have been recognized as carcinogenic solvents by I.A.R.C. recently. New methods for the determination of I.V. and P.V. of fats are proposed by authors to eliminate such alkyl halide as solvent and alternate with cyclohexane or isooctane.
Many microorganisms growing on water-insoluble hydrocarbons or fatty acids as the sole source of carbon have been known to produce several kinds of surface-active compounds. These surface-active compounds are generally called as biosurfactants. The common lipophilic moiety is the hydrocarbon chain of one or more fatty acids, which may be saturated, unsaturated, hydroxyrated or branched; the hydrophilic group is derived from the esters or alcohol functional groups of neutral lipids, the carboxylate group of fatty acids or amino acids, the phosphate-containing portions of phospholipids, and the carbohydrates of glycolipids. Recently, biosurfactants have been received increasing attention owing to their special properties over their chemically synthesized counterparts. The properties include low-toxicity, biodegradability, biological activity, a wide variety of possible structures, and ease of synthesis from inexpensive, renewable resources.
Recent progress in colloidal molecular assemblies such as micelles, emulsions, vesicles, liquid crystals used in many fields is summarized. This paper deals mainly with kinds, properties of colloidal molecular assemblies, relation between the structure of surfactants and the structure of colloidal molecular assemblies, colloidal enhanced ultrafiltration, membrane emulsification, novel application of vesicles.
A review is given of the recent Langmuir-Blodgett (LB) film studies together with the outline of the LB technique and its merits and demerits from the viewpoint of developing the molecular assembly technology to arrange the molecules according to the need. Trials of systematic control of the film quality are now emerging on the basis of the recent advances in the characterization techniques. The analytic model of flow orientation effect is touched upon as an example of research along this line.
Effects of carrier type and membrane solvent on carrier-mediated transport of trivalent rare earth ions through liquid membranes are described. The liquid membranes are the supported type and the solvent polymeric membrane which consists of cellulose triacetate containing a plasticizer. In counter-transport of rare earth and hydrogen ions using β-diketones as carriers, the difference in flux among rare earths is slight, with the exception of Sc. In the transport using hinokitiol, the fluxes for the lanthanides from Sm to Lu are much higher than those from La to Nd. The flux using flavonol increases with an increase in atomic number. In these transport processes, the flux is affected by the composition of membrane solvent and by the pH and added anion in the source phase. In co-transport of rare earth and thiocyanate ions using phosphoric acid triesters as carriers, only scandium is transported.
Chlorofluorocarbons (CFCs) and chlorinated hydrocarbons are believed to contribute to the depletion of the stratospheric ozone layer. This paper reviews recent knowledges on 1) mechanisms of ozone layer depletion and the Antarctic ozone hole phenomenon, 2) the scientific bases for determining the scenario of CFCs restriction, and 3) developing technologies for accomplishing the CFCs phase-out.
The important derivatives from fats and oils are fatty acids, fatty acid methyl esters, fatty alcohols, fatty amines, and glycerol. The derivatives from these materials are discussed. These are mainly used in the surfactant field and will develop further as the gentle products for the earth. As the subject-matter in the future, highly purification, triacylglycerols in the medical field and the long chain (C20<) fatty compounds are proposed.
It is well known that lipase catalyzes not only the hydrolysis of fats and oils but also the interesterification and the ester-synthesis. Recently, a number of bioreactor system using the lipase has been investigated in the food processing field. In the field of fats and oils for food purpose, the interesterification process using lipase, especially 1, 3 positional-specific lipase, has been developed as a newly established technology. It has become possible to manufacture the following products by using bioreactor process in industrial scale. 1) Cocoa butter equivalent, hard butters 2) BOB (1, 3-Dibehenoyl-2-oleoylglycerol) fat-powder in a stable crystal form having special functions such as seeding effect and anti-blooming 3) Plastic fats for margarine and shortening processed from palm oils. In this paper, some applications of bioreactor process under anhydrous condition are intro-duced.