Monomers, dimers, and trimers

Currently, there is continuing work on an iadustry standard method for the direct determination of monomer, dimer, and trimer acids. Urea adduction (of the methyl esters) has been suggested as a means of determining monomer ia distilled dimer (74). The method is tedious and the nonadductiag branched-chain monomer is recovered with the polymeric fraction. A micro sublimation procedure was developed as an improvement on urea adduction for estimation of the polymer fraction. Incomplete removal of monomer esters or loss of dimer duriag distillation can lead to error (75). 

With bulky diphosphines Bu2P(CH2) PBu2 (n = 8-12), similar reactions of the diphosphines with MCl2(PhCN)2 give separable mixtures of monomer, dimer and trimer. With small phosphines (n = 5-7) dimers predominate (Figure 3.48). 

Gonzalez-Barrio R, Beltran D, Cantos E, Gil MI, Espin JC and Tomas-Barberan F A. 2006. Comparison of ozone and UV-C treatments on the postharvest stilbenoid monomer, dimer, and trimer induction in var. Superior white table grapes. J Agric Food Chem 54(12) 4222 t228. 

Gacon, K., Peleg, H., and Noble, A.C., Bitterness and astringency of flavan-3-ol monomers, dimers and trimers. Food Qual. Prefer. 7, 343, 1996. 

Although a crystal structure has been reported for the hexamer,1 at least two distinctly different crystalline forms exist and molecular weight studies indicate that monomers, dimers, and trimers exist in equilibrium in solution. For these reasons, the complexes are referred to herein as in an indefinite state of aggregation, that is [CuH(PR3)]. ... 

Similar results obtained with lysozyme (a protein of molecular weight 14,600) in a 75% ethanol-25 % water solution are shown in Figure 5. The vertical bars indicate the repelling voltage required to stop singly charged monomers, dimers, and trimers of lysozyme traveling at the calculated beam velocity of 754 meters/sec. Sharp dropoffs are seen to... 

Energy Requirements. The production of dimer acids is quite energy-intensive. A standard operation sequence normally results in the expenditure of about 18.6 MJ (17.600 Btu) (equivalent to 0.67 kg coal or 0.33 kg natural gas of fuel oil) to produce each kg of crude dimer and to separate it into monomer, dimer, and trimer. 

Size-exclusion chromatography (SEC) has been used by several workers to separate monomer, dimer, and trimer. Bartosiewics (65) reported the determination of monomer and dimer acids with cross-linked polystyrene beads but did not attempt quantitative analysis. 

Aitzetmuller (69,70) indicated that SEC can be used as a measure and indication of the extent of heating and polymerization of heated fats and oil. Harris et al. (71) achieved SEC separation of monomer, dimer, and trimer acids within 3 h, and quantitation was possible with the use of heptanoic acid as internal standard. 

A special type of polymeric antioxidant is anoxomer, which consists of 1,4-benzenediol, 2-(l,l-dimethylethyl)-polymer with diethylbenzene, 4-(l,l-dimethyl-ethyl)phenol, 4-methoxy-phenol, 4,4 -(l-methylethylidene)bis(phenol), and 4-methylphenol prepared by condensation polymerization of divinylbenzene (m- and p-) with tert-butylhydroquinone, tert-butylphenol, hy-droxyanisole, p-cresol, and 4,4 -isopropylidenediphenol. Total monomers, dimers, and trimers below 500 are not more than 1%. Anoxomer is permitted in the United States as an antioxidant in food at a level of not more than 5 ppm of fat and oil content of the food. 

Formed from the imine using LDA in hexane, NMR studies reveal complex solvent-dependent distributions of monomers, dimers, and trimers in several ethereal solvents, although a mono-solvated dimer can be selected by appropriate choice of solvent. Study of C-alkylation rates suggests that both monomer- and dimer-based mechanisms operate. The lithioimines were compared with the isostructural lithium dialkylamides, but were shown to be not simply vinylogous analogues thereof. 

Fig. 3 The molecular weight distribution of chitosan-EC>45 as determined by GPC. The peak corresponding to unmodified chitosan as well as the peaks corresponding to monomers, dimers, and trimers and 15-mers of conjugates of glukosamine and MPEO of chitosan-EO45 are indicated...

Photoionization and Photoelectron Spectroscopy of Alkali Halide Monomers, Dimers, and Trimers... 

This manuscript summarizes the most significant current experimental information regarding the photoionization behavior of alkali halide monomers, dimers and trimers. Some data exist on higher ionization potentials, (30) and ionic model calculations have also been applied to these higher levels. (19, 30)... 

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