Studies in oxidation-reduction reactions: Oxidation with chloramine-b indirect determinations

Chloramine-B has been used as an oxidizing agent in hydrochloric acid medium for the indirect volumetric estimations of hydrogen peroxide, lead dioxide, manganese dioxide, selenium dioxide, sodium formate, sodium sulphide, sodium metavanadate, potassium iodate and copper sulphate using iodine monochloride as a catalyst and pre-oxidiser. Chloroform is used as an indicator. It is coloured pink owing to the liberation of iodine during the titration and becomes light pale yellow at the end-point because of the formation of iodine monochloride.     

Sodium meta-vanadate as volumetric reagent : Iodine monochloride method (Indirect determinatios)

Sodium meta-vanadate has been used as an oxidizing agent in hydrochloric acid medium for the indirect volumetric determination of hydrogen peroxide, lead dioxide, manganese dioxide, selenium dioxide, potassium persulphate, copper sulphate, sodium formate and sodium sulphide using iodine monochloride as a catalyst, pre-oxidizer and an indicator. Chloroform is coloured pink owing to the liberation of iodine during the titration and becomes light pale yellow at the end-point owing to the formation of iodine monochloride.     

Studies in spiroheterocycles. Part V. Synthesis of new fluorinated spiro[3H-indole-3,2′-oxiran]-2(1H)-ones

Reinvestigation of the reaction of 3-aroylmethyleneindol-2-ones with hydrogen peroxide has revealed that a 1:1 isomeric mixture of spiro[3H-indole-3,2′-oxiran]-2(1H)-ones is formed. The structures of the two isomers have been confirmed by their ir, pmr and mass spectral studies. Mass fragmentation patterns of these compounds are discussed.     

2,4,6-Trichloro-1,3,5-triazine Catalyzed Chemoselective Transthioacetalization of Aldehyde Acetals and Oxathioacetals

Summary. A mild and efficient transthioacetalization of aldehyde acetals and oxathioacetals was carried out using 2,4,6-trichloro-1,3,5-triazine as a mild and inexpensive catalyst. Chemoselective transacetalization is impressive as aldehyde O,O- and O,S-acetals are converted into the corresponding S,S-acetals in the presence of ketones or their acetals and oxathiocetals in nearly quantitative yields.     

Potentiometric estimation of sulfide ion using the Fe(III)-EDTA complex

The Fe(III)-EDTA complex reacts with sulfide ion in a fast electron transfer reaction, oxidising the latter to elemental sulfur and getting itself reduced to Fe(II). The reaction has been developed for the quantitative estimation of sulfide ion by titration against the Fe(III)-EDTA complex, measuring the redox potential of the system. Repeated use of a given quantity of the complex solution by the process of regeneration has been demonstrated. The possibility of its practical application in liquid phase oxidation processes of recovering sulfur from H₂S is emphasized.     

Nonlinear dynamics of confined polymer melts with attractive walls

A scaling model is presented to analyze the reversible strain-hardening phenomenon in end-tethered polymer clay nanocomposites (Krishnamoorti, R.; Giannelis, E. P. Langmuir 2001, 17, 1448). It is assumed that for attractive clay-polymer interactions a fraction of the polymer chains that span the space between opposite clay plates get adsorbed on them, thereby bridging the plates. Under large amplitude oscillatory shear, such bridges are stretched, and this results in the strain-hardening behavior. The onset of strain hardening is predicted to be dependent only on the average distance separating the two plates and is independent of the frequency of the oscillations and the polymer molecular weight.     

THE weighted histogram analysis method for free-energy calculations on biomolecules. I. The method

The Weighted Histogram Analysis Method (WHAM), an extension of Ferrenberg and Swendsen's Multiple Histogram Technique, has been applied for the first time on complex biomolecular Hamiltonians. The method is presented here as an extension of the Umbrella Sampling method for free-energy and Potential of Mean Force calculations. This algorithm possesses the following advantages over methods that are currently employed: (1) It provides a built-in estimate of sampling errors thereby yielding objective estimates of the optimal location and length of additional simulations needed to achieve a desired level of precision; (2) it yields the “best” value of free energies by taking into account all the simulations so as to minimize the statistical errors; (3) in addition to optimizing the links between simulations, it also allows multiple overlaps of probability distributions for obtaining better estimates of the free-energy differences. By recasting the Ferrenberg–Swendsen Multiple Histogram equations in a form suitable for molecular mechanics type Hamiltonians, we have demonstrated the feasibility and robustness of this method by applying it to a test problem of the generation of the Potential of Mean Force profile of the pseudorotation phase angle of the sugar ring in deoxyadenosine. © 1992 by John Wiley & Sons, Inc.     

Potentiometric studies in oxidation-reduction reactions: Oxidation with chloramine-b. indirect determinations

Chloramine-B has been used as an oxidising agent to determine indirectly potassium iodate, potassium metaperiodate, potassium, bromate, potassium dichromate, hydrogen peroxide, chloramine-T and potassium permanganate by a potentiometric method. An excess of potassium iodide added to each of the substances in an acid medium is titrated back with a standard solution of chloramine-B, using platinum foil as an oxidation-reduction electrode coupled with a saturated calomel electrode through an agar-agar potassium chloride bridge.     

Investigation of the reactions of fluorinated isatins and N-acetylisatins with thiocarbohydrazide: Synthesis of a novel spiro system: 2-oxo-1′,2′,4′,5′-tetrahydrospiro[3H-indole-3,3′-1,2,4,5-tetrazine]-6′-thione

A novel system 2-oxo-1′,2′,4′,5′-tetrahydrospiro[3H-indole-3,3′-1,2,4,5-tetrazine]-6′-thione has been synthesized by the treatment of fluorinated isatins with thiocarbohydrazide in aqueous ethanolic medium. Under exactly similar conditions, N-acetylisatin gave exclusively thiocarbohydrazone. The spiro product, on treatment with acetic acid, gave fluorinated isoindigo. Characterization of these products have been done by elemental analyses, ir, pmr and mass spectral studies.