NMR spectroscopic study of the inclusion complex of desloratadine with β-cyclodextrin in solution

Desloratadine (DES) is an antihistamine used in the treatment of allergies and chronic urticaria. ¹H NMR spectroscopic study of varying ratios of DES and β-Cyclodextrin (β-CD) in D₂O suggests the formation of a 1:1 inclusion complex formed by the penetration of Cl-substituted aromatic ring into the β-CD cavity. The stoichiometry and binding constant of the complex were determined by Scott’s method.     

Enantioselective separation on a naturally chiral surface

Kinked-stepped, high Miller index surfaces of metal crystals are chiral and, therefore, exhibit enantiospecific properties. Previous temperature-programmed desorption (TPD) spectra have shown that the desorption energies of R-3-methylcyclohexanone (R-3-MCHO) on the chiral Cu(643)(R) and Cu(643)(S) surfaces are enantiospecific (J. Am. Chem. Soc. 2002, 124, 2384). Here, a comparison of the TPD spectra from Cu(111), Cu(221), Cu(533), Cu(653)(R&S), and Cu(643)(R&S) surfaces reveals that the enantiospecific desorption occurs from the chiral kink sites on the Cu(643) surfaces. Titration of the chiral kink sites with I atoms confirms this assignment of desorption features in the TPD spectra. Finally, the enantiospecific difference in the desorption energies of R- and S-3-MCHO has been used as the basis for demonstration of an enantioselective, kinetic separation of racemic 3-MCHO into its purified components during adsorption and desorption on the Cu(643)(R&S) surfaces.     

Complexation of Fluvastatin Sodium with β-Cyclodextrin: NMR Spectroscopic Study in Solution

¹H NMR spectroscopic study of fluvastatin sodium (FLU), β-Cyclodextrin (β-CD) and their mixtures confirmed the formation of FLU/β-CD inclusion complex in solution. The stoichiometry of the complex was determined to be 1:1 and the overall binding constant (K _s) was calculated to be 340 M⁻¹. Two dimensional COSY, ROESY and DEPTO experiments were performed for the unambiguous assignment of aromatic proton resonances and it was found that two isomeric forms of FLU are present in solution. It was confirmed with the help of ROESY spectral data that only F-substituted aromatic ring penetrates the β-CD cavity and there is chiral differentiation by the β-CD as one of the isomer binds more strongly, which is indicated by the intensity of correlation peaks. The mode of penetration of the guest into the β-CD cavity was also established and structure of the complex has been proposed.     

Enantioselective synthesis of (R)-phenylephrine hydrochloride

An efficient method for the synthesis of enantiomerically pure (R)-phenylephrine hydrochloride 1 is described using a Sharpless asymmetric dihydroxylation as the key step.     

Oxidation of lysine by ferricyanide in presence of osmium(VIII)

Osmium(VIII) catalysed oxidation of lysine by ferricyanide in excess ferrocyanide shows a complex kinetics. The order in lysine falls, from 1 to 0 while that in ferricyanide increases from 0 to 2 with large increase in lysine concentration. The rates were directly proportional to [Os(VIII)] and {Const.+[Fe(CN) ₆ ⁴ ]}. A suitable mechanism is proposed and discussed.

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Oxidation von lysin mittels ferricyanid in der gegenwart von osmium(VIII)

Zusammenfassung Die von Os(VIII) katalysierte Oxidation von Lysin mit Ferricyanid in überschüssigem Ferrocyanid zeigt eine komplexe Kinetik. Bei starker Steigerung der Lysinkonzentration fällt die Ordnung bezüglich Lysin von 1 auf 0, während bezüglich Ferricyanid eine Erhöhung, von 0 auf 2 festzustellen ist. Die Geschwindigkeitskonstanten waren direkt proportional zu [Os(VII)] und {Const.+[Fe(CN) ₆ ⁴ ]}. Es wird ein möglicher Mechanismus vorgeschlagen und diskutiert.

     

Role of palladium in the redox electrochemistry of ferrocene monocarboxylic acid encapsulated within ORMOSIL networks

We report herein the effect of palladium on the redox electrochemistry of ferrocene monocarboxylic acid encapsulated within an organically modified sol-gel glass network (ORMOSIL). It has been found that amount of palladium and its geometrical distribution significantly alter the redox electrochemistry of FcMCA. The geometrical distribution of palladium has been controlled by two methods: (i) palladium is allowed to link within nanostructured network of the ORMOSIL which was subsequently availed from the reactivity of palladium chloride and trimethoxysilane; (ii) palladium powder is encapsulated together FcMCA thus allowing the presence of palladium within the nanoporous domain. The content of palladium is varied by controlling the reaction dynamics of palladium chloride and trimethoxysilane interaction. For this we initially allowed to trigger hydrolysis, condensation and poly-condensation of trimethoxysilane and dimethyldiethoxysilane in acidic medium and subsequently partially dried ORMOSIL film was allowed to interact with palladium chloride. Even with partially dried ORMOSIL derived from trimethoxysilane and dimethyldiethoxysilane undergoes rapid interaction with palladium chloride and the transparent color of ORMOSIL changed to a black colour due to the formation of palladium silicon linkage. The palladium-silicon linkage has been identified by NMR, UV-VIS and transmission electron spectroscopy. The electrochemistry of FcMCA encapsulated within such an ORMOSIL matrix has been studied. Excellent redox electrochemistry of ferrocene monocarboxylic acid having peak potential separation tending to 0 for a multilayered electrode was investigated. The palladium content has been found to affect the redox electrochemistry of ferrocene as well as electrocatalytic efficiency of new ORMOSIL material. The electroanalysis of NADH is reported. The modified electrode is very sensitive to NADH with lowest detection limit of < 1 microM.     

Effect of environmental factors and carbohydrate on gellan gum production

Submerged culture fermentation studies were carried out in batch mode for optimizing the environmental parameters and carbon source requirement by Pseudomonas elodea for the production of gellan gum. The maximum production of gellan gum was obtained with 16-h-old culture and 8% inoculum at 30°C and pH 7.0 after 52 h of incubation (6.0 g/L). Of the various carbon sources tested, 2% sucrose, glucose, and soluble starch yielded considerably high amounts of gellan. Studies on the concentration of various carbohydrates on gellan gum production indicated that the optimum concentration of glucose and starch was 3%, whereas for sucrose it was 4%. The addition of glucose in the medium above 3% had a detrimental effect on gellan yield. The investigation of intermediate two-step addition of glucose under identical conditions of fermentation showed an enhanced production of gellan (8.12 g/L) as compared with the control (6.0 g/L). To optimize the recovery of gellan from fermented broth, different solvents were tested for precipitation of gellan gum. Among the various solvents tested, tetrahydrofuran gave better recovery of gellan (82%) as compared with the conventional solvent isopropanol (49%).     

Palladium(II) inhibition during cerium(IV) oxidation of aldoses: a kinetic study

Summary The kinetics of oxidation of aldoses, namely xylose, arabinose, galactose and glucose, by Ce^IV have been studied in HClO₄ + H₂SO₄ medium and in the presence of Pd^II. The reactions exhibit a first order rate dependence with respect to oxidant. The rate is inversely dependent on the [HSO _inf4 ^sup– ][H⁺] ratio. The order of reaction with respect to aldose decreases at higher [aldose]. Due to the formation of a complex between Ce^IV and Pd^II, a retarding effect of [Pd^II] on the rate of disappearance of [Ce^IV] has been observed. A mechanism consistent with the observed kinetic data is proposed.     

Kinetics of the Ru(III) catalyzed oxidation of formaldehyde and acetaldehyde by alkaline hexacyanoferrate(III)

The kinetics of ruthenium(III) catalyzed oxidation of formaldehyde and acetaldehyde by alkaline hexacyanoferrate(III) has been studied spectrophotometrically. The rate of oxidation of formaldehyde is directly proportional to [Fe(CN) _3– ⁶ ] while that of acetaldehyde is proportional tok[Fe(CN) _3– ⁶ ]/{k +k[Fe(CN) _3– ⁶ ]}, wherek, k andk are rate constants. The order of reaction in acetylaldehyde is unity while that in formaldehyde falls from 1 to 0. The rate of reaction is proportional to [Ru(III)] _T in each case. A suitable mechanism is proposed and discussed.

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Die Kinetik der Ru(III)-katalysierten Oxidation von Formaldehyd und Acetaldehyd mittels alkalischem Hexacyanoferrat(III)

Zusammenfassung Die Untersuchung der Kinetik erfolgte spektrophotometrisch. Die Geschwindigkeitskonstante der Oxidation von Formaldehyd ist direkt proportional zu [Fe(CN) _3– ⁶ ], währenddessen die entsprechende Konstante für Acetaldehyd proportional zuk[Fe(CN) _3– ⁶ ]/{k +k[Fe(CN) _3– ⁶ ]} ist, wobeik,k undk Geschwindigkeitskonstanten sind. Die Reaktionsordnung für Acetaldehyd ist eine erste, die für Formaldehyd fällt von erster bis zu nullter Ordnung. Die Geschwindigkeitskonstante ist in jedem Fall proportional zu [Ru(III)] _T . Es wird ein passender Mechanismus vorgeschlagen.

     

Highly Selective and Sensitive Graphene Based Electrochemical Sensor for Quantification of Receptor Agonist Rizatriptan

A highly selective and sensitive electrochemical sensor has been developed by modification of a glassy carbon electrode (GCE) with graphene (GRP) for quantification of Rizatriptan. The significant increase of the peak current and the improvement of the oxidation peak potential indicate that the electrochemical sensor facilitates the electron transfer of Rizatriptan. The oxidation peak current was proportional to the Rizatriptan concentration in the range from 100 to 600 µg/mL with detection (LOD) and quantification limit (LOQ) of 36.52 and 121.73 µg/mL, respectively. The developed method was successfully employed for quantification of Rizatriptan in pharmaceutical formulations. The sensor shows great promise for simple, sensitive and quantitative detection of Rizatriptan.