Soon Ng

Analysis of positional distribution of fatty acids in palm oil by13C NMR spectroscopy

The13C NMR spectrum of the carbonyl carbons of the acyl groups of triacylglycerols of palm oil has been shown to give the composition of saturated, oleic and linoleic acyl groups at the 1,3-positions and at the 2-position of the glycerol moiety. Except for the lack of differentiation of the saturated fatty acids, the13C NMR technique provides the same information as the tedious enzymatic hydrolysis cum fatty acid analysis. The carbonyl carbon of the linolenic acyl group (18∶3,[cis, cis, cis]-9, 12, 15) has a chemical shift which is only 0.005 ppm to low frequency of that of the linoleic acyl group (18∶2,[cis, cis]-9, 12), so that the two resonances may not be distinguishable (or resolved) even at a high magnetic field.

Analysis of epoxidized natural rubber. A comparative study of d.s.c., n.m.r., elemental analysis and direct titration methods

A comparative analysis of epoxidized natural rubber samples by 1H and 13C n.m.r., titrimetric, elemental and d.s.c. techniques has been made. Whereas the titrimetric method is only applicable at low epoxy contents (< 15 mol%) both n.m.r. methods give reasonable precision over the compositional range of 20–75 mol%. Elemental analysis appears less reliable. D.s.c. analysis through measurement of Tg provides the highest precision of measurement but requires independent calibration by one or more of the primary methods. The epoxy content may also be related to the polymer density.

High field13C nuclear magnetic resonance spectrum of the olefinic carbons of the triglycerides of palm oil

In the triglycerides of palm oil (or any vegetable oil or fat), an unsaturated fatty acid (oleic or linoleic) attached to the 2-glycerol carbon can be distinguished from one attached to the 1- or 3-glycerol carbon by high (or medium) field13C nuclear magnetic resonance (NMR) analysis of the olefinic carbons. The chemical shift difference of the olefinic carbons in the fatty acid chain is characteristic of the chains glycerol position and can therefore be used to identify the glycerol position of an unsaturated fatty acid in the triglyceride.

13C NMR spectroscopic analysis of the fatty acid composition of palm oil

Gated decoupled 13C NMR spectra of the saturated and olefinic carbons in palm oil can be used for direct determination of the composition of the fatty acids in mole fractions of the saturated, monoene and diene acid chains. The results are more informative than the conventional iodine value which is used as a measure of the total unsaturation in the fatty acids.

On the use of the modified Benesi—Hildebrand equation to process NMR hydrogen bonding data

Abstract In the hydrogen bonding between chloroform and tetrahydrofuran in cyclohexane medium, the hydrogen-bond chemical shift and the equilibrium constant obtained by processing the NMR data by means of the modified Benesi—Hildebrand equation are in agreement with those obtained by means of the “best fit” method of Drago et at. Experimental conditions for the successful application of the Benesi—Hildebrand equation are discussed.

Detection ofcis-vaccenic acid in palm oil by13C NMR spectroscopy

The NMR signals of the carbonyl and olefinic carbons of the oils of some species of palm show some relatively weak peaks at characteristic positions that have not been identified previously. These peaks are most intense in the oil of the speciesElaeis oleifera. On the basis of the chemical shift data of the carbonyl and olefinic carbons of several synthetic monoenic triacylglycerols and of the packed-column gas chromatogram of the methyl esters of the oil ofE. oleifera, the peaks in question are assigned tocis-vaccenic acid (18∶1,[cis]-11).13C NMR spectroscopy is an effective technique for the detection ofcis-vaccenic acid and other monounsaturated fatty acids in vegetable oils or fats.

The importance of Au⋯π(aryl) interactions in the formation of spherical aggregates in binuclear phosphane gold(I) complexes of a bipodal thiocarbamate dianion: a combined crystallographic and computational study, and anti-microbial activity

Binuclear phosphanegold(I) complexes of a bipodal thiocarbamate dianion, (R3PAu)2L, R = Et (1), Ph (2) and Cy (3), where LH2 is {1,4-[MeOC(S)N(H)]2C6H4}, have been synthesised, and characterised spectroscopically (NMR and IR) and by X-ray crystallography. The gold atoms are linearly coordinated within a P-,S-donor set, and are oriented toward the central ring to form intramolecular Au⋯π(aryl) interactions, rather than the intramolecular Au⋯O interactions normally observed in mononuclear analogues. This phenomenon has been investigated by theory (LC-ωPBE-XDM) for 1 which revealed that the geometry optimised species with two Au⋯π(aryl) interactions is more stable by at least 12 kcal mol−1 compared to conformations having one or more Au⋯O interactions instead. The disk diffusion, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) methods were used to observe the inhibitory effect of complexes 1–3. The disk diffusion results demonstrated that 1 exhibited a broad spectrum of anti-bacterial activity toward 24 strains of Gram-positive and Gram-negative bacteria. By contrast, the anti-bacterial activity of 2 and 3 was limited to Gram-positive bacteria. Further evaluation showed that 1 exhibited marked bactericidal activity against B. cereus, B. subtilis, E. faecalis, L. monocytogenes, S. aureus, S. saprophyticus and methicillin resistant S. aureus cf. standard antibiotics tetracycline and chloramphenicol.

Determination of iodine value of palm and palmkernel oil by carbon‐13 nuclear magnetic resonance spectroscopy

High resolution carbon-13 nuclear magnetic resonance ( 13 CNMR) can be used for characterization of palm oil and palmkernel oil in determining the iodine value (IV) of the oil. It is only necessary to obtain the quantitative 13 CNMR spectrum of the oil in dilute CDCl3 solution in the region of δ30.0-δ24.7 ppm, which pertains to the methylene carbons along the acyl chain from the β-carbonyl to the ω-4. From the peak areas in the spectrum the average number of double bonds per triacylglycerol molecule and the average molecular weight can be calculated and hence the IV. The IVs of 18 samples of palm and palmkernel oil have been determined by 13 CNMR and by the Official Method of the American Oil Chemists Society. There is good agreement between the two sets of IVs. Conditions for obtaining reliable IVs by this 13 CNMR method are given.

Measurement of hydrogen bonding to pyridine and its alkyl derivatives by NMR spectrometry

Abstract The measurement of the hydrogen bonding between chloroform and pyridine (or an alkyl derivative) by NMR spectrometry is complicated by the presence of a small extent of the interaction of chloroform at the π-site of pyridine. The interaction at the π-site is shown to introduce ambiguity in the hydrogen-bonding parameters evaluated from the experimental data on the basis of a single equilibrium, in that the equilibrium constant so obtained would be larger while the hydrogen-bond chemical shift, the enthalpy and the entropy changes would be smaller than the values that would be obtained for the interaction at the π-site in the absence of the interaction at the π-site. The chemical shift of the proton hydrogen bonded to the n-site of pyridine contains a contribution from the ring current effect, so that experimentally the true hydrogen-bond chemical shift is not obtained. The hydrogen-bonding parameters obtained on the basis of a single equilibrium for the interaction of pyridine with 2,4,6-tri- tert -butylphenol and 2,6-di-l-adamantyl-4- tert -butyl-phenol, and for the interaction of chloroform with tetrahydrofuran and pyridine and its 2-methyl, 3-methyl, 4-methyl, 4- tert -butyl, 2,6-dimethyl, and 2,4,6-trimethyl derivatives are presented. The parameters for the alkyl-pyridines are found to vary as the result of the steric, resonance, and inductive effects of the alkyl substituents, as well as the extent of the interaction of the chloroform at the π-site.

NMR measurement of the hydrogen bonding ability of the CH groups of some halogenated hydrocarbons. Limitation of the NMR method for XH2and XH3 groups

Abstract The hydrogen bonding ability of CF3CHCl2, CCl3CHCl2, CH3CHCl2, and CHClCCl2 with acetone and benzene as electron donors have been measured in cyclohexane medium by the NMR method. The hydrogen bonding ability of CH2Cl2, CCl3CH2Cl, and CHCl2CHCl2, having two equivalent activated hydrogens, have likewise been measured with the same donors. The results for the latter compounds with acetone as donor relative to benzene as donor are found to be irregular with those of the compounds having a single activated hydrogen. Similar results are obtained for the methyl group of nitromethane in the same donor solvents. The reasons for the irregularity are postulated and would point to a limitation in the NMR method for measuring the hydrogen bonding interaction of XH2 and XH3 groups with n-donors.