Limited information is available on the prevalence of waterborne pathogens in aquatic environments in developing countries. In this study, water samples were collected from nine shallow wells and a river in the Kathmandu Valley, Nepal, during the rainy season in 2009 and were subjected to detection of waterborne protozoa, viruses and coliphages using a recently developed method for simultaneous concentration of protozoa and viruses in water. Escherichia coli and total coliforms were also tested as indicator bacteria. At least one type of the five pathogens tested (Cryptosporidium, Giardia, human adenoviruses, and noroviruses of genogroups I and II) was detected in five groundwater samples (56%) (1000 ml each) from shallow wells. Compared with groundwater samples, the pathogens were more abundant in the river water sample (100ml); the concentrations of Cryptosporidium and Giardia were 140 oocysts/l and 8500 cysts/l, respectively, and the mean threshold cycle (Ct) values in real-time RT-PCR were 34.3, 36.8 and 34.0 for human adenoviruses and noroviruses of genogroups I and II, respectively. Genotyping of F-RNA coliphages by real-time RT-PCR was successfully used to differentiate human and animal faecal contamination in the samples. Moreover, for the groundwater samples, protozoa and viruses were detected only in E. coli-positive samples, suggesting that E. coli may be an appropriate indicator of pathogen contamination of valley groundwater.
Self-assembling characteristics of dodecylguanidine hydrochloride (C 12G), a cationic surfactant with a guanidine group in its molecule, were investigated and compared with those of dodecyltrimethylammonium chloride (DTAC) and sodium dodecylsulfate (SDS). Introduction of a guanidine group into the surfactant molecule was found to increase its assembly formability more than that of the trimethylammonium group on the basis of the experimental results on the phase diagram, Kraft point, area occupied per molecule at the air-water interface, and micellar aggregation number of C 12G. Thermodynamic parameters for micelle formation suggested that an attractive force acts between guanidine groups of C 12G molecules to facilitate their assembly formation. The presence of this force was evidenced by changes in the (1)H NMR and IR spectra before and after micelle formation of the guanidine-type (G-type) surfactant, indicating that the increased assembly formability is caused by an increase in hydrogen bonding between guanidine groups of the surfactant via water molecules.
For the purpose of estimating the reaction mechanism of the direct ethoxylation of a fatty ester in the presence of an Al-Mg composite oxide catalyst, a labeled fatty methyl ester C 11 H 23 CO 18 OCH 3 containing 18 O isotope was synthesized and directly ethoxylated. The product was evaluated by gas chromatography-mass spectrometry (GC-MS). The GC-MS spectra showed that the 18 O isotope label was present only in the methoxy group at the molecular end of the ethoxylated fatty methyl ester. This supports the reaction mechanism of coordination anionic polymerization where the bond between the acyl and methoxy groups of the fatty methyl ester molecule was broken, caused by the bifunctional effect of the acid-base active sites; an intermediate chemisorption species was formed; and then ethylene oxide was addition-polymerized sequentially, in parallel. JAOCS 74, 19-24 (1997). KEY WORDS:Al-Mg composite oxide catalyst, coordination anionic polymerization, direct ethoxylation, ethoxylated fatty methyl ester, ethoxylation, ethylene oxide, fatty methyl ester, nonionic surfactant, reaction mechanism, solid catalyst.In the previous paper (1), we reported that the direct ethoxylation of a fatty methyl ester without active hydrogens in the molecule did not proceed in the presence of an ordinary homogeneous catalyst, such as NaOH (2), but readily proceeded over the novel metal ion-containing MgO, especially an Al ion-containing MgO catalyst. The resultant ethoxylated fatty methyl ester was a monoester-type nonionic surfactant which was substantially completely homogeneous.Also, the possibility was proposed that the reaction proceeded by a coordination anionic polymerization mechanism on the surface of the solid catalyst, and that ethylene oxide was directly inserted between the acyl and methoxy groups of the fatty methyl ester.In this paper, the tracer experiment with the 18 O stable isotope was carried out to reveal the insertion position of the ethylene oxide on the solid catalyst and to establish the ethoxylation reaction mechanism (3-5). EXPERIMENTAL PROCEDURESSynthesis of labeled methyl ester. The method used for synthesizing the fatty acid methyl ester labeled with an 18 O stable isotope (relative isotopic abundance 0.20%) is shown in Scheme 1 (6-7). To 80 mL of a solution of 0.6 g of 18 O-labeled methanol (EURISCO-TOP, Saint-Aubin Cedex, France: 18 O concentration 98.7 atom %, purity 99.1%) and 8.94 g of ordinary methanol (refined by distillation of methanol for high-performance liquid chromatography (HPLC), manufactured by Kanto Chemical, Tokyo, Japan) in pyridine (special grade pyridine, manufactured by Junsei Chemical (Tokyo, Japan) with added CaH 2 , and distilled to be refined), 178 g (0.357 mol, 1.2 equivalents) of n-dodecanoyl chloride (special grade n-dodecanoyl chloride, manufactured by Tokyo Chemical Industry, Tokyo, Japan, and distilled to be refined) was added dropwise gradually for 1 h while the solution was vigorously stirred. Immediately after the addition of acid chloride was completed, 100 mL water was ad...
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