Equivalent chain length

A similar method was described by Rezanka and Podojil (100) and by Wiley et al. (101), including choline chloride as the source of the quaternary ammonium counterion. The molecular species of PE, PC, and PI were separated by a mixture of methanol, 286 mM aqueous choline chloride, and acetonitrile in a 90.5/7/2.5 ratio. Graphs of the logarithm of the relative retention time versus the equivalent chain length of the fatty acid found in the 1-position yields a straight line for a given fatty acid in the 2-position. For different fatty acids in the 2-position, a series of parallel straight lines is obtained. 

The structures deduced from the mass spectra must account for the observed equivalent chain length (ECL) or Kovats indices (KI) (Carlson et al., 1998 Katritzky and Chen, 2000 Zarei and Atabati, 2005). The values for monomethylalkanes (Mold et al., 1966 Szafranek et al., 1982) can be used to estimate the expected ECL or KI for a di-, tri- or tetramethyl-alkane structure proposed from a mass spectrum. For example, a dimethylalkane, such as 3,11 -dimethylnonacosane, with 31 carbons, would have its elution time decreased by about 0.3 carbons for the 3-methyl group and about 0.7 carbons for the 11-methyl group. Thus, the predicted ECL is approximately 30 and this is the ECL observed. 

We have optimized the geometry using ab initio methods as we did for compound 5a-g in this chapter and then calculated their 3 using ZINDO/CV/SCRF methods. The plot of experimental and theoretical 3 in cis and trans form with n is shown in the Figure 7. First hyperpolarizabiUties of cis conformers are about (50-60)% of trans conformers with equivalent chain lengths and the trends in 3 values with chain length are the same for both conformers. Even in the cis form, the theoretical 3 values are much higher than the experimentally measured values, whereas the... 

For commercial POE nonionics with different types of hydrophobic groups of approximately equivalent chain length and the same degree of oxyethylenation (9 mol EO), the order of decreasing nonpolar soil removal from polyester/ cotton was nonylphenol adduct > secondary Cn — C15 alcohol adduct > linear primary C12 — C15 alcohol adduct. This was the order of decreased effectiveness of equilibrium jow reduction and of reduced rate of yow reduction (Dillan, 1984). 

The importance of the heat of combustion in calculating the heat of formation of an organic molecule was pointed out in Chapter 2. A method of estimating it has been proposed (Cardozo, 1986) in which an equivalent chain length of a molecule is defined as... 

Species N number of components equivalent chain length. 

Wolff, RL Ghristie, WW. Structure, practical sources (Gymnosperm seeds), gas-chromatographic data (equivalent chain lengths), and mass spectrometric characteristics of all-cA A5-olefinic acids. Eur. J. Lipid Sci. Technol, 2002, 104, 234-244. 

The equivalent chain-lengths (ECL) of the methyl ester derivatives of 79 unsaturated fatty acids have been determined by GC with fused silica columns coated with Carbowax 20M (polyethylene glycol), Silar 5CP, CP-Sil 84 (Chrompak/Vaiian) and a 5% phenyl-methyl silicone (Christie, 1988). CP-Sil 84 is equivalent to AT-SILAR-90, DB-23, Rtx-2330, SP-2330 [poly(80% biscyanopropyl)-20% cyanoptroylphenyl siloxane] (Grace, 2011). 

Christiansen, K Mahadevan, V. Viswanathan C.V. Holman, R.T. (1969). Mass spectrometry of long-chain aliphatic aldehydes, dimethyl acetals and alk-l-enyl ethers. Lipids, Vol.4, No.6, (November 1969), pp. 421-427, ISSN 1558-9307 Christie, W.W. (1988). Equivalent chain-lengths of methyl ester derivatives of fatty acids on gas chromatography A reappraisal. Journal of Chromatography A, Vol.447, pp. 305-314, ISSN 0021-%73... 

Gas-liquid chromatography is widely used in the study of fatty acids and can furnish useful structural information. Retention data are usually recorded in the form of equivalent chain length (Miwa et al., 1960) and generalizations of fatty acid behaviour can be made. Usually fatty acids are chromatographed as their methyl esters but the analyses of short (C2-C6) and medium (C8-Ci2)-chain fatty acids pose particular problems. It is necessary to take special precautions in the analysis of these acids to avoid... 

ECL (= Equivalent chain length of unknown peak, x n = Chain length of preceding n-alkane rt = Retention time of peak, x rt = Retention time of preceding n-alkane rt = Retention time of next n-alkane... 

Figure 10 Equations for Kovats indices and equivalent chain length.

Equivalent chain lengths according to Dobson, Christie and Sebedio (1996a, 1996c). 

CFAM = cyclic fatty acid monomers ECL = equivalent chain length FTIR = Fourier transform infra-red (spectroscopy) GC = gas chromatography ND = not determined. 

Alternatively, the identification of FAMEs is possible using the concept of equivalent chain length (ECL), by expressing their elution positions relative to those of known straight-chain saturated FAMEs, under isothermal conditions. Details for the calculation of ECL and tables for a large number of FAMEs are available in specialized reports.Recently a method was developed that allows this identification with temperature and pressure programming on a single capillary column. 

The distribution of radioactivity between substrate and product was measured by gas-liquid radiochromatography in a Packard apparatus with a proportional counter. The fatty acids were identified by comparison with standards and equivalent chain length determination. From the conversions found the speed of the reactions were calculated. Substrate concentrations that saturated the enz3nne were determined and used throughout the experiment to measure the specific activities. 

An aliquot of the corresponding fraction of the samples was counted in a Packard Tricarb Scintillation counter. Other aliquots were esterified. The distribution of the radioactivity between the fatty acids was determined by gas liquid radiochromatography (Alaniz et al, 1976). The labeled methyl esters were identified by equivalent chain length determination and comparison with authentic standards. The fatty acid composition of serum, HTC cells and lipid fractions of culture cells was analyzed by gas liquid chromatography. The specific radioactivities for linoleic and arachidonic acids were calculated with those data after measuring the radioactivity in an aliquot in which the mass distribution of the fatty acids had previously been determined by gas liquid chromatography in the presence of an internal standard of eicosaenoic acid. 

Christie, W.W. (1988) Equivalent chain-lengths of methyl ester derivatives of fatty adds on gas chromatography. J. Chromatogr. 447, 305-314. 

Strdnsk, K., Jursik, T., Vftek, A. and Skofepa, J. (1992) An improved method of characterizing fatty acids by equivalent chain length values. J. High Resolut. Chromatogr. 15, 730-740. 

FCL. By definition the equivalent chain length (ECL) of a saturated acid/ester is equal to the number of carbon chains in the acid. Thus, for stearic esters it is 18.00. The ECL of oleic acid and its esters is a non-integral number where the actual value depends on the chromatographic conditions, especially the nature of the stationary phase. For example it may be 18.53 on one polar stationary phase. The value +0.53 is then the FCL corresponding to a selected stationary phase and a particular stmctural unit, in this case a cis double bond in the A9/co9 position. 

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