Cationic surfactants are being used in various applications industrially and domestically for a long time. Pyridinium salts come under the category of cationic surfactants. These are unsaturated heterocyclic compounds having different functional groups present either on pyridine ring or at nitrogen atom. Initially, they were only considered as effective germicides. Several researches have been done for the modification of the properties of these salts, making them important for various applications. This paper reviews the types, synthesis, properties, and applications of quaternary pyridinium salts.

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A small amount of sediment occurs in refined coconut oil stored in a large-scale tank for a long term. This sediment is different from that generally called Cocos Wax, is insoluble in various organic solvents, and has an m.p. of about 100°C. In this report, we have done a structural analysis of this sediment. The sediment was carried out by hydrolyzing with a KOH/ethyl alcohol solution including toluene. Samples were analyzed by elemental analysis, IR spectroscopy, EI-MS, CI-MS, field desorption mass spectrometry (FD-MS), and MALDI/TOF-MS. The hydrolyzates were a compound including an oxo group, and its relative molecular mass was 382 for the acid part and 412 for the unsaponified matter according to EI-MS (ionization energy was 70 eV and 15 eV) and CI-MS (reagent gases were i-butane, ammonia, and nitrogen monoxide). The relative molecular mass of the sediment was 1140 according to the mass spectrometry of FD, EI, and MALDI. It was elucidated based on the characteristic absorption analysis by IR and the fragmentation behavior of the EI-MS that the sediment was a wax ester, 3, 9-di-9-oxotetradocosanecarboxy-11-oxohexacosane, consisting of an acid part of 9-oxotetradocosanecarboxylic acid and an unsaponified matter of 3, 9-di-hydroxy-11-oxohexacosane.

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Effects of oil-droplet size, the weight ratio of oil to wall material and the storage temperature on the oxidation of methyl linoleate microencapsulated with maltodextrin by spray-drying were examined. The oxidation of methyl linoleate was more retarded for the microcapsules prepared from the emulsion having smaller oil droplets. The oxidation was more suppressed for the microcapsules having a lower weight ratio of oil to wall material. The fraction of unoxidized methyl linoleate leveled off after 10- to 15-days storage. The level, Y_∞, depended on the weight ratio. The dependence of Y_∞ on the weight ratio was analyzed based on the percolation theory, and the three-dimensional model of the theory was suitable to express the dependence. The effect of the storage temperature on the oxidation of microencapsulated methyl linoleate was also examined, and the activation energy was evaluated. The value of the energy suggested that the oxidation itself was a rate-limiting step for the oxidation of methyl linoleate encapsulated with maltodextrin.

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A new synthetic polymer of aromatic polyether (APE), having a narrow distribution of molecular weight, formed a specific self-assembly of Langmuir film (L film) on a water surface, which was subjected to surface pressure relaxation when the L film was compressed over 16.5 mN m^-1 at 15°C. This self-assembly was capable of transferring on silicon-wafers as LB films. We found that, because the XRD patterns for fabricated LB films depended on the crystal face of the silicon-wafer used and moreover increased in diffraction intensity with the increasing number of built-up layers in the LB film, the present LB films showed a kind of epitaxy-like phenomenon. We propose the molecular mechanism explaining that the formation of an ionic supuramolecular structure of APE occurs only on a silicon wafer surface.

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Monomeric thiol surfactants, [C_nH_2n+1N(CH₃)₂CH₂CH₂SH]Br, were produced by the cleavage of gemini surfactant containing a disulfide bond in the spacer chain, [C_nH_2n+1N(CH₃)₂CH₂CH₂SSCH₂CH₂N(CH₃)₂C_nH_2n+1]2Br. The disulfide bond was completely reduced by the addition of four times moles of dithiothreitol in water at room temperature. The critical micelle concentrations of monomeric surfactants were significantly increased in comparison with original gemini surfactants. The monomeric thiol surfactants were stable in the presence of dithiothreitol, whereas they returned gradually to their original gemini surfactants within several days due to air oxidation in water without dithiothreitol. The micelle formation induced by the disulfide linkage formation was suggested by the fluorescence intensity ratio of pyrene. The time course of decrease in thiol concentration associated with the recovery of gemini surfactants was confirmed by the absorption spectra utilizing the reactions with 4,4’-dithiopyridine.

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In this paper, thermotolerant fungal strains which can grow on glycerol as the sole carbon source were isolated from soil samples. Morphological and molecular phylogenetic analyses of ten isolated strains showed that all strains belong to Aspergillus fumigatus. Analysis of their cellular fatty acid composition revealed that all the strains accumulated lignoceric acid (C24:0), suggesting that the isolated strains can be used to produce this high-value long-chain fatty acid from glycerol.

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A comparative study of oxidative decomposition behavior of a wide range of vegetable oils and its correlation to iodine value (IV) using thermogravimetric analysis (TGA) was described. The oxidative decomposition of saturated fatty acids shows weight loss before 385°C while oxidative decomposition of unsaturated fatty acids shows lower rate of weight loss (dWt/dt) compared to saturated fatty acids due to the oxidation process (‘up taking ’ of oxygen) involving breaking down of double bond to form primary and secondary oxidation products, which leads to some weight gain in the sample before being decomposed. The relative differences in the dWt/dt (%/min) of the both fatty acids give different decomposition steps in TGA thermogram, enabling IV to be determined through the percentage weight loss of saturated fatty acids per 100% of total sample weight (excluding weight loss from moisture and volatile compounds). Therefore, TGA method can be used as an alternative method for IV determination with no sample pre-dilution and solvent consumption. Using the TGA methods, good correlation (r = 0.9889) with standard AOCS method was achieved.

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