Vitamin immobilization

Biosensor-based analysis is becoming more and more important in the food industry, and one of the fields of application is in vitamins analysis. The method for vitamin analysis is a label-free, inhibition assay (Kalman et al., 2006). The SPR biosensor monitors interactions of a specific binding protein with the vitamin immobilized on a CMS sensor chip. The prepared samples are mixed with a fixed concentration of the vitamin binding protein by the autosampler and injected over the chip surface. The vitamin present in the sample binds to the protein and subsequently inhibits it from binding to the surface of the sensor chip. The higher the concentration of the vitamin is in the sample, the higher the level of inhibition, and hence the lower the response of the biosensor (O Kane and Wahlstrom, 2011). A regeneration step prepares the chip surface for the next sample. Quantification is performed by multilevel caHbration with the vitamin standards. 

The concept of the hybrid electrode was extended to a vitamin-immobilized system by Hisaeda and co-workers (Fig. 5), in which heptapropyl and heptaoctyl esters of vitamin B12 derivatives with a Co(II) or Co(III) center were used. Investigation of ti-A isotherms of these compounds with the alkoxysilane monolayers suggested that stable accommodation of the vitamin functionality in the lipid monolayer can be achieved by the introduction of long chains at the vitamin B core. The mixed monolayers of the long chain-substituted vitamin B12 and organosilane amphiphile were transferred as an x-type LB film onto a quartz plate and showed reasonable UV absorbance. Monolayers similarly immobilized on an indium-tin-oxide (ITO) electrode possessed a... 

Two techniques for sorption-spectroscopic determination of ascorbic acid have been proposed. The first one is the recovery by silica modified with tetradecyl ammonium nitrate of blue form of molibdophosphoric HPA in the presence of vitamin C. And the second one is the interaction between the ascorbic acid in solution and immobilized on silica ion associate of molibdophosphoric acid with lucigenine. The detection limits of vitamin C are 0.07 and 2.6 mg respectively. The techniques were successfully applied to the determination of ascorbic acid in fmit juices. 

Armario, A., Campmany, L., Borras, M. and Hidalgo, J. (1990). Vitamin E-supplemented diets reduce lipid peroxidation but do not alter either pituitary-adrenal, glucose, and lactate responses to immobilization stress or gastric ulceration. Free Rad. Res. Commun. 9, 113-118. 

The heterogeneous catalytic system iron phthalocyanine (7) immobilized on silica and tert-butyl hydroperoxide, TBHP, has been proposed for allylic oxidation reactions (10). This catalytic system has shown good activity in the oxidation of 2,3,6-trimethylphenol for the production of 1,4-trimethylbenzoquinone (yield > 80%), a vitamin E precursor (11), and in the oxidation of alkynes and propargylic alcohols to a,p-acetylenic ketones (yields > 60%) (12). A 43% yield of 2-cyclohexen-l-one was obtained (10) over the p-oxo dimeric form of iron tetrasulfophthalocyanine (7a) immobilized on silica using TBHP as oxidant and CH3CN as solvent however, the catalyst deactivated under reaction conditions. 

D-Pantolactone and L-pantolactone are used as chiral intermediates in chemical synthesis, whereas pantoic acid is used as a vitamin B2 complex. All can be obtained from racemic mixtures by consecutive enzymatic hydrolysis and extraction. Subsequently, the desired hydrolysed enantiomer is lactonized, extracted and crystallized (Figure 4.6). The nondesired enantiomer is reracemized and recycled into the plug-flow reactor [33,34]. Herewith, a conversion of 90-95% is reached, meaning that the resolution of racemic mixtures is an alternative to a possible chiral synthesis. The applied y-lactonase from Fusarium oxysporum in the form of resting whole cells immobilized in calcium alginate beads retains more than 90% of its initial activity even after 180 days of continuous use. The biotransformation yielding D-pantolactone in a fixed-bed reactor skips several steps here that are necessary in the chemical resolution. Hence, the illustrated process carried out by Fuji Chemical Industries Co., Ltd is an elegant way for resolution of racemic mixtures. 

The electroreductive dehalogenation of a-haloacetic acids has been achieved with cobalamin [387]. The hydrophobic vitamin B12 Co complex immobilized on a glassy carbon electrode (252) may catalyze the electrochemical carbon-skeleton rearrangements of... 

Scheme 94 Cathodic dehalogenation with immobilized vitamin Bn-...

Incorporation of biologically important molecules into LDHs has become of interest in recent years and materials such as DNA [189], ATP [190], amino acids or enzymes [191,192] and vitamins [193] can be stabilized in the interlayer space of LDHs. If enzymes and proteins, for example, can be immobilized in the interlayer galleries of LDHs, new types of selective catalysts (see Sect. 2.2) as well as new delivery systems and carrier materials can be expected. 

Some ISEs containing no inner reference solution, as well as tubular potentiometric sensors, has been used in conjunction with FI systems for the determination of vitamins B, and Bg in pharmaceutical preparations. The membranes used for this purpose were prepared from the vitamin tetra(2-chlorophenyl)borate dissolved in o-nitrophenyloctyl ether and immobilized in PVC. The intrinsic behaviour of the tubular electrodes was assessed by using a low-dispersion single-channel FI manifold and compared with those of conventionally-shaped electrodes using the same membrane the results provided by both were very similar [119]. 

For the first biosensor shown in Table 17.2, L-ascorbic acid has been determined in fruit juices and vitamin tablet, by immobilizing a slice of cucumber (Cucumis sativus) onto an 02 electrode in the pH range 6.0-6.5 (phosphate buffer solution) [11] ... 

The avidin-biotin interaction has also been used to immobilize antibodies and proteins, especially in commercial systems based on surface plasmon resonance (SPR) measurements (e.g., the BIAcore). The extraordinary affinity (Kl 10-15 M) of avidin (or its bacterial relative, streptavidin) for the vitamin biotin is the basis of this immobilization procedure. A solid support (e.g., glass beads, sensor chip, optical fiber) covered with avidin can be used as an activated carrier for a very sturdy immobilization of previously biotinylated antibodies. In spite of the many methods for biotinylating proteins described in the literature, the use of biotinyl N-hydroxysuccinimide ester (BNHS) and similar derivatives, remains the most useful [65]. 

HYDROPHOBIZED SILICA NANOCOMPOSITES WITH IMMOBILIZED ANTIOXIDANTS (VITAMINS C AND E)... 

Abstract. Adsorption of antioxidants (vitamins C and E) from aqueous and ethanol solutions on unmodified and partially hydrophobized nanosilica A-200 was studied using UV spectroscopy and quantum chemical methods with consideration for the solvent effects. Antioxidant power of silica nanocomposites with immobilized vitamins was evaluated by measuring the total polyphenolic index following the Folin-Ciocalteu method. It has been shown that immobilization of vitamins on silica surface leads to their stabilization. Being released from the carrier molecules of vitamins do not lose their antioxidant properties... 

Oxidative stress or imbalance between formation and deactivation of free radicals is considered to be one of the main causes of many known human diseases.1,2 Vitamins E and C are among the most attractive objects for prophylactic drug development.2,3 Aside from being natural antioxidants of direct action, their combination results in a synergistic effect.4 However, obtaining stable formulations remains a challenge since these vitamins are readily oxidized in a liquid medium. Immobilization of such biomolecules on solid surfaces may result in enhanced stabilization. 

Highly disperse silica is widely used in pharmaceutical formulations as a filler, adsorbent, thickener etc.5 Their high hydrophilicity and the absence of emulsifying ability restrict their application. In contrast to hydroxylated silica, partially or fully hydrophobized silica may exhibit improved properties as a drug carrier. The main goal of this work is to study hydrophobized silica nanocomposites with immobilized vitamins C and E. Investigations of adsorption-desorption processes which involve silica nanoparticles and the antioxidants are described. Factors affecting the antioxidant stability have also been carefully considered. 

Antioxidant activity of silica nanocomposites with immobilized vitamin C was tested using the polyphenolic activity index.8 After adsorption of ascorbic acid on the silica surface and centrifugation, the excess solution was removed to obtain the suspension of a fixed volume (2 ml). Distilled water, sodium carbonate solution, and Folin-Ciocalteu s phenol reagent were subsequently added to suspensions and to the reference Vitamin C solution. The suspensions were then stored for 30 min, and the optical density of supernatant was measured at X = 750 nm. The reference solution of ascorbic acid was used to compare antioxidant activity of vitamin-containing nanocomposites with the activity of dissolved vitamin C. 

Unmodified silica was found to have a low adsorptive capacity with respect to vitamin E. In the case of modified silica the quantity of immobilized biomolecules is significantly increased (Figure 2). The adsorption of vitamin E does not prevent interaction of silica with vitamin C (Figure 3). It was found that the adsorption of vitamin C from ethanol solution, on the surface of modified silica with preadsorbed vitamin E, is thermodynamically favourable (AGads = -31 kJ/mol). 

To obtain silica nanocomposites with immobilized antioxidants, and to test their antioxidant activity, vitamins C and E were adsorbed onto nanosilica from ethanol solution containing both vitamins. A desorption experiment was then carried out. After the desorption of ascorbic acid from modified silica (0tms -0.40) into aqueous medium, the solvent was changed and the desorption of vitamin E into ethanol was studied. As one can see (Figure 6), both vitamins can be released from the surface for 1-2 hours. It should be noted that no increase in vitamin C concentration was detected in aqueous solution after its contact with A-200 for more than 30 min. Thus, as is the case for vitamins Bj and B6, desorption of vitamin C from the surface of modified silica is slower in... 

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