Inulin phosphates

N-Carboxymethylaminopropylated inulin Cycloinulohexaose derivatives Alkoxylated inulin Inulin phosphates Complexing agents... 

Phosphoric acid esters of the ketopentose D-ribulose (2) are intermediates in the pentose phosphate pathway (see p.l52) and in photosynthesis (see p.l28). The most widely distributed of the ketohexoses is D-fructose. In free form, it is present in fruit juices and in honey. Bound fructose is found in sucrose (B) and plant polysaccharides (e.g., inulin). 

In 1999, Carlini et al. investigated the ability of niobium-based phosphate to catalyze the selective dehydration of fructose, sucrose, and inulin to HMF (Scheme 7) [74]. Starting from fructose and using a column reactor packed with niobium phosphate catalyst, 67% selectivity to HMF was obtained at 38% conversion. This catalyst was stable in the presence of water and was successfully reused without notable change of activity. Interestingly, from sucrose and inulin, the niobium-based catalysts afforded HMF with 66% selectivity at 47% conversion. A significant improvement of both the catalyst activity and the HMF selectivity was achieved when the HMF was continuously extracted from the water phase with methylisobutylketone (MIBK). Indeed, under these conditions, HMF was produced with 98% selectivity at 60% conversion of fructose. Using the same procedure, but from inulin, HMF was obtained with 72% selectivity at 70% conversion. 

Scheme 6 Fructose can be transformed into 5-hydroxymethyl furfural (HMF) via acid-catalyzed dehydration. Solid acid catalysts applied to facilitate the reaction are zeolites, ion-exchange resins and solid inorganic phosphates. With sporadic success, notably with inorganic phosphates, other carbohydrate sources such as inulin can also be transformed into HMF.

Fuller s earth (hydrated aluminosilicate) Magnesium oxide Charcoal Alumina Magnesium trisilicate Silica gel Calcium hydroxide Magnesium carbonate Calcium phosphate Calcium carbonate Sodium carbonate Talc Inulin Sucrose = starch Petroleum ether, b 40-60°- Petroleum ether, b 60-80°. Carbon tetrachloride. Cyclohexane. Benzene. Ethyl ether. Chloroform. Ethyl acetate. Acetone. Ethanol. Methanol. Pyridine. Acetic acid. 

FIGURE 10.20 The action of fructan 1-exohydrolase and fructan fructan 1-fructosyltransferase in dormant and sprouting tubers on inulin depolymerization. Abbreviations 1-feh = fructan 1-exohydrolase 1-fft = fructan fructan 1-fructosyltransferase hk = hexokinase spp = sucrose phosphate phosphatase sps = sucrose phosphate synthase GF = sucrose G = glucose F = fructose GFF = 1-ketose GF-P = sucrose phosphate UDP-G = uridine diphosphate glucose F-6-P = fructose-6-phosphate. 

Magnesium trisilicate Silica gel Calcium hydroxide Magnesium carbonate Calcium phosphate Calcium carbonate Sodium carbonate Talc Inulin... 

In vitro and in vivo release kinetics were compared using two different approaches. In the first approach (the recovery approach) polymer implants containing a radioactively labeled substrate—,4C-labeled bovine serum albumin, /3-[14C]-lactoglobulin, or [3H]-inulin—were implanted subcutaneously into rates (in vivo) or released in phosphate-buffered saline, pH 7.4, at 37°C (in vitro). At various time points, the polymer implants were removed from the rats or the saline. They were then lyophilized to remove residual water and dissolved in xylene. When the polymer dissolved, the unreleased macromolecules precipitated to the bottom of the vial. Water was then added to dissolve the macromolecules scintillation fluid was next added, resulting in a homogeneous translucent emulsion which was counted via liquid scintillation. 

Inulin is a polysaccharide of molecular weight 5200. It is one of the very few molecules that is neither metabolized in vivo nor reabsorbed or secreted by kidney tubules. Thus, all inulin released from the polymer should be recovered in the urine. An in vivo-in vitro comparison was made by making nine identical inulin-polymer pellets. Five pellets were implanted in rats housed in metabolic cages. Four pellets were released into a physiological solution of phosphate-buffered saline (PBS) at pH 7.4 at 37°C. Both urine and PBS were collected daily. The [3H]-inulin was measured by scintillation counting. The experiment was carried out for 500 hours. (Additional experiments have been carried out for 1500 hours with similar results.) Over this period, in vivo and in vitro release rates agreed to within 1% (10) (Fig. 3). 

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