1,720,973 research outputs found
Capillary Zone Electrophoresis Study of Cyclodextrin-lipoic acid Host-guest Interaction
No full textLipoic acid is a naturally occurring compound which is being widely investigated for its therapeutic effects in the treatment or prevention of a variety of diseases associated with oxidative injury, particularly diabetes. The diversity of therapeutic applications of lipoic acid requires an appropriate formulation to control its bioavailability, site-targeting delivery and to overcome its inherent chemical instability. In this regard, cyclodextrins (CDs) are ideally suitable due to their well-documented ability to include in their cavity proper guest molecules and protect them from physical or chemical damages. Lipoic acid forms 1:1 inclusion complexes with betaCD as shown in a previous report of an extended investigation that also indicated the suitability of capillary zone electrophoresis (CZE) for the study of such host-guest interactions. In view of these possible applications, we extended the CZE analysis to determine the strength of binding, in a pH 9 phosphate buffer, of lipoic acid with other CD derivatives such as alphaCD, gammaCD and the alkylated derivatives of betaCD, namely (2-hydroxypropyl)-beta-CD (HPbetaCD), and heptakis(2,3,6-tri-O-methyl)-beta-CD (TMbetaCD). Once established that the easily available betaCD is the most suitable receptor for lipoic acid, we set up and here describe a simple and reliable procedure for the quantitative determination of lipoic acid in commercial dietary supplement tablets containing also other active substances and excipients
A highly sensitive method for the analysis of nitrite ions by capillary zone electrophoresis using water-soluble aminophenylporphyrin derivative as chromogenic reagent.
No full textThe water soluble 5-paminophenyl)-10,15,20-tris(psulfonatophenyl) porphyrin, 4, acts as an extremely efficient chromogenic reagent for the detection of very low amounts of nitriles. The amino group of porphyrin 4 reacts smoothly with nitrite in acidic conditions 0.2 M HCl) producing the corresponding diazo-porphyrin derivative which is stable and does not show any appreciable hydrolysis to phenol within 6 h. The reaction is carried out in the presence of 25 mM heptakis-(2,6-di-O-methyl)-beta-cyclodextrin that prevents precipitation of the protonated form of porphyrins 4 or 5 due to the formation of strong inclusion complexes. The capillary zone electrophoresis of the diazoporphyrin and amino-porphyrin mixture shows severe peak tailing. However, symmetrical peaks can be obtained by adding 5 mM beta-cyclodextrin to the background electrolyte (20 mM phosphate buffer, pH 7.0). Calibration curve for nitrite analysis is linear up to 0.25 mM nitrite and the detection limit (at a signal-to-noise ratio of 3) has been estimated to be a 1 mu M (50 ppb) of nitrite concentration in aqueous solutions
On the behaviour of organotin compounds with cyclodextrins Part 1. The complex between allyl-di-n-butyltin chloride and beta-cyclodextrin
No full textA complex between allyl-di-n-butyltin chloride and beta-cyclodextrin has been obtained in good yield by the coprecipitation method in aqueous solution at room temperature. The stoichiometry, determined by NMR and elemental analysis, was found to be 1:1. The complex was characterised by means of several techniques, such as TCA, DSC, ESIMS, SEM, NMR, and Mossbauer spectroscopy. On the basis of these results, we suggest a structure for this complex where the tin derivative is included in the cyclodextrin, replacing about six of the ca. nine water molecules coordinated to it and where the metal centre displays a pentacoordination, probably due to Sn ... O long range contacts with the hydroxyl groups of the rim of the macrocycle
Synthesis of 6(I)-amino-6(I)-deoxy-2(I-VII)-tetradeca-O-methyl-cyclomaltoheptaose
No full textThe preparation of 6(I)-amino-6(I)-deoxy-2(I-VII),3(I-VII)-tetradeca-O-methyl-cyclomaltoheptaose is reported. Two different routes (A and B), both starting from beta-cyclodextrin (betaCD), have been examined. Route A involved: (i) synthesis of heptakis(6-0-tert-butyldimethylsilyl)-betaCD from betaCD; (ii) permethylation of the secondary hydroxyl groups with methyl iodide and sodium hydride; (iii) desilylation of the primary hydroxyls with ammonium fluoride; (iv) monotosylation at O-6 position of per-(2,3-O-methyl)-betaCD,- (5) nucleophilic replacement of the tosyl group with azide anion; (v) reduction of the azido group by catalytic transfer hydrogenation using hydrazine hydrate in the presence of Pd/C in methanol/water. Route B started from the known 6(I)-monoazido-6(I)-monodeoxy-beta-CD (two steps from beta-CD) and entailed: (i) protection of the remaining primary hydroxyls using tert-butyldimethylsilylchloride (TBDMSCI); (ii) exhaustive methylation of the secondary hydroxyls with methyl iodide and sodium hydride; (iii) removal of the TBDMS protecting groups with ammonium fluoride; (iv) reduction of the azido group as above. Route A was found to be less convenient than Route B due to the inherent difficulty of controlling the monotosylation of per-(2,3-O-methyl)-betaCD
Synthesis, characterization and chemisorption on gold of a Beta-cyclodextrin-lipoic acid conjugate.
No full textMono-6-lipoyl-amido-2,3,6-O-permethyl-beta -cyclodextrin, TM beta CDLA, was synthesized in 79% isolated yield by coupling the mono-6-amino-permethyl-beta -cyclodextrin with lipoic acid in the presence of 1-(3-dimethylamino)ethyl carbodiimide. The identity of cyclodextrin-lipoic acid conjugate was confirmed by NMR spectroscopy and electrospray mass spectrometry. Chemiadsorption of TM beta CDLA on colloidal gold was shown to occur by colloid flocculation test analysis
Supramolecular Catalysis: Enantioselective Oxidation of Thioanisole in Water by Hydrogen Peroxide Catalyzed by Mo(VI) in the Presence of beta Cyclodextrin-based Ligand
No full textModerate enantioselectivity promoted by cyclodextrins in the Zn-Barbier allylation reaction of aldehydes in aqueous medium
No full textThe effects exerted by native and trimethylated (-cyclodextrins in the Zn-Barbier allylation reaction of aldehydes in aqueous solution has been studied. The rates of conversion were, generally, depressed in the presence of the cyclodextrins, especially TMCD, but the chemical yields of the products were very satisfactory, in all cases. Moderate enantioselectivity effects were also obtained in the presence of TMCD, whereas native (CD showed to be practically inactive. The results can be rationalised in terms of formation of inclusion complexes between the substrates and the CDs and of their interaction with the surface of the metal
Very strong binding and mode of complexation of water-soluble porphyrins with a permethylated beta-cyclodextrin
No full textHeptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin a pH=7.0 aqueous solution binds meso-tetrakis(4-carboxyphenyl) porphyrin and its zinc complex to yield 2:1 complexes with exceptionally high binding constants. The made of binding, involving the inclusion of two opposite aryl groups in the cyclodextrin cavity, is clearly defined by a detailed NMR analysis
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