Oligomer separation

I Plot DI H aiwlag out FIGURE 13.29 Nylon oligomer separation. 

Figure 4-8. 1NDO/SCI simulation of the wavcfunclion y/(x,xi, = 16, chain I) of the lowest charge transfer-excited stale in a cofacial dimer formed by two five-ring PPV oligomers separated by 4A. Ili/(x,x/, - 16, chain 1) represents the probability amplitude in finding an electron on a given site xt. assuming the hole is centered on site 16 of chain I. The site labeling is the same as that reported on top of Figure 4-7.

The oligomer separation procedure was performed according to the protocol described elsewhere [27]. Polygalacturonic acid (O.lg) was dissolved in 10 mL of citric-citrate buffer pH... 

Okada, T. (1990). Chromatographic oligomer separation of poly(oxyethylenes) on potassium ion-form cation-exchange resin. Anal. Chem. 62(4), 327-331. 

A novel homogeneous process for the catalytic rearrangement of 3,4-epoxy-l-butene to 2,5-dihydrofuran has been successfully developed and scaled-up to production scale. A tri(n-alkyl)tin iodide and tetra-(n-alkyl)phosphonium iodide co-catalyst system was developed which met the many requirements for process operation. The production of a minor, non-volatile side product (oligomer) was the dominating factor in the design of catalysts. Liquid-liquid extraction provided the needed catalyst-oligomer separation process. 

There are numerous examples for isocratic oligomer separations by molar mass on polar adsorbents, i.e., under the conditions of adsorption chromatography. One of the first examples reported 14) is shown in Fig. 3. 

For the synthesis of the D-C portion, two different concepts were followed either by modification of laminaribiose (166) [89] or by a stereospecific P, 1 ->3-glycosylation [20]. Laminaran is isolated from seaweeds or from Poria cocos Wolf, degraded by selective acetolysis, and the lower oligomers separated by preparative HPLC [90]. Following acetylation, the heptaacetyl laminaribiosyl bromide is prepared and transformed into the disaccharide glycal 167 by the classical approach in 93 % yield. The 2-deoxy-2-iodo-a-glycoside is formed by application of the NIS procedure after deprotection and subsequent 4,6-0-benzylidenation, the precursor 168 for the radical formation of the 6,6 -dibromo-6,6 -dideoxy derivative is at hand. This compound may be further reduced to methyl-3-0-(P-D-chinovosyl)-a-D-olivoside (169). 

Promising applications of SFC include group separations (paraffins, olefins and aromatics) in petrochemical samples, monitoring of supercritical extraction processes (caffeine from coffee, nicotine from tabacco) and oligomer separations. However, it is in the field of applications that SFC has yet to prove its value. Unique separations that can be accomplished with SFC, but not with either GC or LC, have yet to be demonstrated. 

The molar mass distributions of the functionality fractions were determined by preparatively separating the fractions and subjecting them to SEC. The SEC chromatograms of fractions 1-9 are summarized in Fig. 23. For a number of fractions oligomer separations were obtained, which could be used to calibrate the SEC system. 

The analysis of a technical poly(ethylene oxide) with respect to chemical composition and degree of polymerization has been performed by Pasch and Hiller [210]. This investigation was conducted under conditions which are common for HPLC separations, i.e. sufficiently high flow rate, moderate sample com-centration, and on-flow detection. Using an octadecyl-modified silica gel as the stationary phase and an eluent of acetonitrile/deuterium oxide 50 50 (v/v), the sample was separated into different functionality fractions (see Fig. 38). The major fraction of the sample eluting between 14 and 25 min exhibited a partial oligomer separation. 

Fig. 3-113. Separation of maltose oligomers. - Separator column CarboPac PA-1 eluent (A) 0.1 mol/L NaOH, (B) 0.1 mol/L NaOH + 1 mol/L NaOAc gradient 100% A for 2 min isocratically, then linearly to 100% B in 200 min flow rate 1 mL/min detection and injection volume see Fig. 3-105 solute concentrations 166 ppm each of maltose (1), maltotriose (2), maltotetraose (3), maltopentaose (4), maltohexaose (5), and maltoheptaose (6).

Since Nielsen et al introduced peptide nucleic acids (PNA), this area has received vast attention, and continues to do so. More recently, the main area of interest has been in novel analogues, and many new ones have been reported. The solid phase synthesis of DNA-3 -PNA chimeras have been described, in which the DNA is attached to the amino terminal of the PNA via the 3 -phosphate or thiophosphate. All chimeras were shown to have superior thermal stability towards either DNA or RNA than a DNA oligomer, and the phosphodiester linkage was more stable than the phosphorothioate. Hybridisation studies with PNA and PNA-DNA chimeras demonstrate that there is a sequence effect for the junction between PNA and DNA on duplex stability. A decamer pyrimidine bis-PNA oligomer, separated by a linker, when targeted to complementary dsDNA formed three distinct structures. One structure contained two bis-PNA units, and the other two were believed to be structural isomers. 

Indirect foliKomcr contenn 3. Degradation, oligomer separation/... 

Several workers have compared the performance of SEC and HPLC in oligomer separations. HPLC will give a much greater degree of separation. Van der Maeden et al [36] achieved separation of novolacs to n = 16, epoxy... 

Of these eluent systems, n-pentane-1, 4-dioxane has been found to be particularly successful for separating individual oligomers up to a molecular mass of 5500 [53]. Figure 9.13 shows the type of oligomer separation which can be achieved. 

Figure 9.20 HPLC separation of phthalate derivatives of polypropylene glycol. oligomers separated in Figure 9.5 [37]. By permission of Dr Alfred Hiithig Verlag GmbH.

Figure 3.7 shows an example of an oligomer separation achieved by this method for various POE-HPLC has also been applied to the determination of oligomers in polyesters [34], alkylphenyl formaldehyde resins [35, 36] and polyethylene terephthalate [37, 38]. 

Fig. 3-180. Separation of maltose oligomers. - Separator column CarboPac PAl eluant ...

Figure 4. Comparison of linear (M) and cyclic (CD) oligomers separations on a Biogel 2 column.

The utility of gel electrophoresis in long chain oligonucleotides has relegated TLC to smaller chain species. Intermediate chain oligonucleotides are nicely handled by HPLC, but many smaller ones are not. This is the province of TLC. Silica gel TLC has been important in oligomer separations well up to decamers. 

Cemulsols Lutensols Nonylphenolethoxylates typically 1-30 ethoxy-groups Partlsll-10 PAC (10 jjm) CH3CN-CH3OH 1.6 (95 5) + 40 nM NaClOij Oligomer separation ca. 1... 

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