Sedimentation field flow fractionation monitoring of bimodal wheat starch amylolysis.

Enzymatic starch granule hydrolysis is one of the most important reactions in many industrial processes. In this study, we investigated the capacity of sedimentation field flow fractionation (SdFFF) to monitor the amylolysis of a bimodal starch population: native wheat starch. Results demonstrated a correlation between fractogram changes and enzymatic hydrolysis. Furthermore, SdFFF was used to sort sub-populations which enhanced the study of granule size distribution changes occurring during amylolysis. These results show the interest in coupling SdFFF with particle size measurement methods to study complex starch size/density modifications associated to hydrolysis. These results suggested different applications such as the association of SdFFF with structural investigations to better understand the specific mechanisms of amylolysis or starch granule structure.

Sedimentation field flow fractionation monitoring of rice starch amylolysis.

Enzymatic starch granule hydrolysis is one of the most important reactions in many industrial processes. In this work, we investigated the capacity of SdFFF to monitor the native rice starch amylolysis. In order to determine if fractogram changes observed were correlated to granule biophysical modifications which occurred during amylolysis, SdFFF separation was associated with particle size distribution analysis. The results showed that SdFFF is an effective tool to monitor amylolysis of native rice starch. SdFFF analysis was a rapid (less than 10 min), simple and specific method to follow biophysical modifications of starch granules. These results suggested many different applications such as testing series of enzymes and starches. By using sub-population sorting, SdFFF could be also used to better understand starch hydrolysis mechanisms or starch granule structure.

Size- and shape-dependent separation of TiO2 colloidal sub-populations with gravitational field flow fractionation.

The simplest field flow fractionation technique, which uses the earth's gravity as the external field is applied to isolate two populations, which differ in both shape and size, from a polydisperse sub-micron TiO2 powder of homogenous density. The fraction eluted first is spherical with an average diameter of 0.31 microm while the second fraction is ellipsoidal and can be associated with a 0.45 microm hydrodynamic diameter. Elution conditions appeared to be very sensitive to electrolyte and surfactant characteristics in the carrier phase as well as on the sample concentration. Using 25 microl (1%, w/w) sample suspension, separations of spherical from ovoid particles was performed in almost 2 h with a mobile phase of 0.001 M KNO3-0.01% (v/v) Fl-70 in water in a 0.025-cm thick channel made of polystyrene walls.

Antithyroid action of tamoxifen in the rat: in vivo and in vitro studies.

The influence of administration of tamoxifen (TAM) on thyroid metabolism was investigated. The potential action of TAM on iodine in the thyroid gland was evaluated by determination of the equilibrium constant of the charge transfer complex formed with molecular iodine and by computational studies. Adverse effects of TAM on thyroid function parameters were also investigated in female Wistar rats. Rats were treated for seven weeks with 5 mg/kg/day of TAM. Irrespective of the iodine content of the diet, administration of TAM led to goitre and a significant increase in levels of T4 and TSH. Similar results, albeit more marked, were observed after administration of an inhibitor of thyroid peroxidase. We also showed that TAM forms charge transfer complex with iodine (Kc = 876 liters/mol). We concluded that under our experimental conditions, TAM exerts antithyroid activity from an action on thyroid peroxidase. Nevertheless, when the exogenous iodine contribution is restricted, TAM may sequester iodine in the form of charge transfer complexes, thereby enhancing hypothyroidism.

Elution characteristics of natural cyclodextrins on porous graphitic carbon

The retention behavior of natural alpha-, beta-, and gamma-cyclodextrins on a porous graphitic carbon (PGC) stationary phase is investigated. Unusual retention properties for reversed-phase chromatographic conditions are observed with acetonitrile-methanol and water-methanol mixtures as mobile phases. It is assumed that the retention process is governed not only by the standard solvophobic effect but also by specific interactions described as "CD-PGC" effect. The retention factor versus the volumetric methanol fraction in the mobile phase show second-order curves expressing this double mechanism hypothesis. van't Hoff plots demonstrate the contribution of these two retention processes. The retention factor of each natural cyclodextrin is shown to depend on the mobile phase property to act as a proton acceptor, according to the solvent selectivity classification described by Snyder. The "CD-PGC" effect is interpreted as an equilibrium between different interactions: cyclodextrin-PGC stationary phase, London dispersion forces, and cyclodextrin-mobile phase hydrogen bonding. The balance of these interactions may monitor the orientation of the cyclodextrin molecule facing the carbon surface, which is therefore suspected to be the major parameter of this retention mechanism.

Chromatographic study of terpene derivatives on porous graphitic carbon stationary phase with beta-cyclodextrin as mobile phase modifier.

The stoichiometric coefficients and apparent formation constants (Kf) of alpha-terpineol, thymol, geraniol and linalool complexes with beta-cyclodextrin (beta-CD) were determined using HPLC with a porous graphitic carbon (PGC) chromatographic support. Measurements were performed with four different methanol-water mobile phases. All the terpene derivatives under study form 1:1 guest-CD complexes. Graphs of Kf as a function of the mobile phase composition appeared different from those classically described for RP-C18 and suggest that the PGC stationary phase could play an active role in the complexation process. Solute-CD inclusion and solute-stationary phase interactions may be involved in this specific behavior.

Influence of dietary iodine on drug-induced hypothyrodism in the rat.

Several compounds of pharmaceutical importance from a variety of chemical families, for example chlorpromazine and clomipramine, have been found to form charge-transfer complexes with iodine. We have investigated the influence of dietary iodine on thyroid-gland dysfunction induced by clomipramine, chlorpromazine or 2-thiazoline-2-thiol. We suggest that iodine is partly diverted from its metabolic pathway by complexation with drugs, and so the urinary concentration of iodide is increased. Both chlorpromazine and clomipramine, at doses which do not inhibit thyroperoxidase, enhanced urinary iodine excretion when dietary iodine was restricted (3.944+/-0.96 microg/day for chlorpromazine-tested rats, 3.43+/-1.33 microg/day for clomipramine-tested rats, compared with 2.34+/-0.11 microg/day in control rats). Concurrently, these pharmaceutical compounds increased the level of free thyroid-stimulating hormone (TSH) in comparison with controls and induced histological modifications in, and enlargement of, the thyroid gland. We have demonstrated that drug-induced loss of iodine in the urine was associated with antithyroid action when iodine intake was limited.