Levan structure

The constant pattern concept has also been extended to circumstances with nonplug flows, with various degrees of rigor, including flow profiles in tubes [Sartory, Jnd. Eng. Chem. Fundam., 17, 97 (1978) Tereck et al., Jnd. Eng. Chem. Res., 26, 1222 (1987)], wall effects [Vortmeyer and Michael, Chem. Eng. ScL, 40, 2135 (1985)], channeling [LeVan and Vermeulen in Myers and Belfort (eds.). Fundamentals of Adsorption, Engineering Foundation, New York (1984), pp. 305-314, AJChE Symp. Ser No. 233, 80, 34 (1984)], networks [Aviles and LeVan, Chem. Eng. Sci., 46, 1935 (1991)], and general structures of constant cross section [RudisiU and LeVan, Jnd. Eng. Chem. Res., 29, 1054 (1991)]. 

The structure of the levan synthesized by the action of B. subtilis on sucrose was determined by Hibbert and Brauns.89 Levan, in a yield of 60-65% calculated on the D-fructose part of the sucrose, was obtained by precipitation of the concentrated culture into methanol, and purified by reprecipitation and electrodialysis. Hydrolysis of purified levan with 0.5% aqueous oxalic acid for one hour at 100° gave a 99% yield of crystalline D-fructose. Triacetyllevan was prepared by treatment with acetic anhydride in pyridine, and deacetylation with alcoholic alkali yielded material identical with the original levan.940... 

The levan synthesized by B. subtilis from raffinose was shown by Mitchell and Hibbert100 to be identical in structure with that obtained from sucrose. 

Challinor, Haworth and Hirst101 determined the chemical structure of the levan produced by the action of B. mesentericus on sucrose. Methylated levan appeared homogeneous when fractionally precipitated from mixed solvents. Fractional distillation of the hydrolytic products of methylated levan yielded tetramethyl-D-fructofuranose in an amount corresponding to a levan chain length of from ten to twelve fructofuranose units, joined as previously940 shown through the 2- and 6-positions. 

Other levans produced by widely different organisms all have similar structures, e. g., the levans1020 produced from sucrose by B. megatherium, Phytomonas pruni and P. prunicola, and those1020 produced from sucrose... 

Polymers of D-fructose are important carbohydrate reserves in a number of plants. Inulins and levans are two major types that differ in structure. D-Fructans require only relatively mild conditions for their hydrolysis, for example, levan was qualitatively hydrolyzed by hot, dilute, aqueous oxalic acid. Permethylated fructans could be hydrolyzed with 2 M CF3CO2H for 30 min at 60°. Fructan oligosaccharides were hydrolyzed in dilute sulfuric acid (pH 2) at 70 (see Ref. 53) or 95° (0.1 M). D-Fructans from timothy haplocorm (where they comprise 63% of the water-soluble carbohydrates) could be hydrolyzed with 0.01 M hydrochloric acid at 98°. 

Structure. The nmr spectra, shown in Figure 2, indicates that essentially all fructose molecules in the polymers are in the same conformation. In Table I, nmr peaks from fructan are compared to peaks from known inulin 0-(l->2) linked) and bacterial levan (P-(2->6) linked). Data clearly show the fructan to be of the p-(2- 6) type (27). (Sec Table II.)... 

Fructans are polysaccharides composed of o-fructofuranose units. They are important in short-term energy reserves for grasses and some plants. Inulin, found in dahlias, and levans from grasses are examples of fructans. Levans are short linear polysaccharides composed of (3 2 1 linked fructose units as illustrated in structure 9.21. 

Bacterial levans, as distinct from other polyfructoses, may be molecules possessing highly branched structures and very high molecular weights. 

Jarrell, H.C., Conway, T.F., Moyna, P., and Smith, I.C.P., Manifestation of anomeric form, ring structure, and linkage in the carbon-13 NMR spectra of oligomers and polymers containing D-fructose, maltulose, isomaltulose, sucrose, leucrose, 1-kestose, nystose, inulin, and grass levan, Carbohydrate Res., 76, 45-57, 1979. 

If one compares Figs. 6 and 7, it is apparent that with the IgA myelomas individual dextrans precipitate different total quantities of antibody N, whereas with the IgM antidextran myelomas all dextrans that can react, regardless of structure, will precipitate all the myeloma antidextran. This difference is ascribable to the presence, in the IgA myelomas of monomers and polymers, the monomers partially inhibiting precipitation as discussed earlier. This distinctive behavior of IgA myelomas holds for antifructosans. With the IgG2a antifructosan myeloma UPCIO, all levans tested, including ryegrass levan, precipitated all the antibody when added... 

Inulin, levan, graminan, phlein, andkestoses are classified as fructans [12]. Inulin exists either as a linear, branched, or cyclic fructan whereas the structure of the remaining fructans are linear and branched (O Table 2) [13]. 

On the other hand, the quantitative prediction of competitive isotherm behavior for the components of binary mixtmes is not possible using the competitive Langmuir isotherm model when the difference between the column satmation capacities for the two components exceeds 5 to 10%. For example, the adsorption isotherms of pure cis- and trans-androsterone on sihca are well accoimted for by the Langmuir model [9]. However, the two column saturation capacities differ by 30%, due to the nearly flat structure of the trans isomer compared to the folded structure of the cis isomer. As a consequence, the competitive Langmuir model accounts poorly for the competitive adsorption data [9,10]. Much improved results are obtained with the more complex LeVan-Vermeulen isotherm (Section 4.1.5). Another approach could use the random adsorption site model, with different exclusion siuface areas for the competing molecules [12],... 

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