Dichotenone-a and -b: two new enones from the marine brown alga Dictyota dichotoma (Hudson) Lamour

Marine brown alga Dictyota dichotoma (Dictyotaceae) collected from Karachi coast of Arabian Sea yielded two new (1 and 2) enones (dolastane-diterpenoids) named: dichotenone-A and -B along with an olide (loliolide, 3) as a new source. Their structures have been characterized with the aid of 2D-NMR spectroscopic techniques.     

A new method for preparation of silica potassium cobalt hexacyanoferrate composite ion exchanger from silica sol

A new method for the preparation of porous silicapotassium cobalt hexacyanoferrate (SiO₂ ^.KCoFC) composite from silica sol is described. Silica sol was first gelled with K₄Fe(CN)₆ solution. Then the resulting hydrogel, SiO₂ ^.K₄Fe(CN)₆ was reacted with Co(NO₃)₂ solution in acetone to give the composite SiO₂ ^.KCoFC hydrogel. The empirical formula of KCoFC in the composite was found to be K₁.₆₉Co _0.93Fe(CN)₆. The removal efficiency of the composite for Cs was judged by measuring its distribution coefficient, K _d in 1M HCl solution containing 10 ppm Cs. The K _d of Cs was found to be 5.73^.10⁵ ml/g-composite.     

Flow injection chemiluminescence determination of hydrazine by oxidation with chlorinated isocyanurates

A rapid and sensitive flow injection chemiluminescence (CL) method is described for the determination of hydrazine based on the CL generated during its reaction with either sodium dichloroisocyanurate (SDCC) or trichloroisocyanuric acid (TCCA) in alkaline medium. The emission intensity is greatly enhanced if dichlorofluorescein (DCF) as sensitizer is present in the reaction medium. The presence of citrate prevents the precipitation of some cations in the reaction medium and also causes an enhancement in emission intensity. The effect of analytical and flow injection variables on these CL systems and determination of hydrazine are discussed. The optimum parameters for the determination of hydrazine were studied and were found to be the following: SDCC and TCCA both 1x10(-3) M; NaOH, 2x10(-1) M; DCF, 5x10(-6) M; citrate, 1x10(-3) M and flow rate, 3.8 ml min(-1). The optimized method yielded 3sigma detection limits of 2x10(-7) and 3x10(-7) M for hydrazine with SDCC and TCCA oxidants, respectively. The method is simple, fast, sensitive, and precise and was applied to the determination of hydrazine in water samples.     

Thermochemistry of bis-arene- and arenetricarbonyl-chromium compounds containing hexamethylbenzene, 1,3,5-trimethylbenzene and naphthalene.

Microcalorimetric measurements at elevated temperatures of the heats of thermal decomposition and iodination have led to values of the standard enthalpies of formation of the following crystalline compounds (values given in kJ mol^?1) at 298K: [Cr(η⁶-1,3,5-C₆H₃(CH₃)₃)₂] = (63±12); [Cr(η⁶-C₆(CH₃)₆)₂] : -(88±12); [Cr(1,2,3,4,4a,8a-η-C₁₀H₈)₂] = (407±11); [Cr(CO)₃(1,2,3,4,4a,8a-η-C₁₀H₈)] = -(258±8). Separate measurements by the vacuum sublimation microcalorimetric technique gave the following values for the enthalpy of sublimation at 298K (kJ mol^?1) : [Cr(η⁶-1,3,5-C₆H₃(CH₃)₃)₂] = (104±1); [Cr(η⁶-C₆(CH₃)₆)₂] = (119±4); [Cr(CO)₃(1,2,3,4,4a,8a-η-C₁₀H₈)] = (107±3). From these and other data, the bond enthalpy contributions of the metal-ligand bonds in the gaseous metal complexes were evaluated as follows: [(η₆-C₆(CH₃)₆)-Cr] (155±7); [(η⁶-C₆H₃(CH₃)₃)-Cr] (151±6); [(1,2,3,4,4a, 8a-η-C₁₀H₈)-Cr](145±6) kJ mol^?1]The question of the transferability of the enthalpy contributions of chromium—ligand bonds between organochronium complexes is discussed with aid of information from structural and spectroscopic investigation. The limitations of the procedure are defined.The thermodynamic data are used to discuss various substitution, redistribution and exchange reaction of Cr(η-arene)₂ and [Cr(CO)₃(η-arene)] compounds.     

Selective spectrophotometric determination of thorium(IV) with 2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol

A spectrophotometric study of the Th(IV) complex of a new reagent 2-(5-Bromo-2- pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is presented. A reddish brown complex is formed at pH 4.86, and shows maximal absorbance at 580 nm with molar absorptivity of 1.66 × 10⁵ mol⁻¹ cm⁻¹ liter. Beer's law is obeyed over the range 0.0 to 15 μg of thorium. Rare earths ions like La³⁺, Ce³⁺, and Y³⁺ do not interfere because they form complexes with 5-Br-PADAP at higher pH's (>9.94) (1). A new method for determining trace amounts of thorium is proposed, which possesses the advantages of high sensitivity and selectivity.     

Microdetermination of some xylenols via investigation of their catalyzed reactions with iodine

The oxidation of some xylenols with iodine in aqueous ethanolic solutions in the presence of silver ions as a catalyst was investigated and used for microdetermination of these reductants. The study of these redox reactions and the microdetermination of these phenols were performed by volumetric and spectrophotometric methods. These methods were compared. The spectrophotometric method was more accurate at very low concentrations (60–488 μg). The volumetric methods used silver ions as catalyst. The potentiometric method is more accurate than the visual method. Possible schemes for the course of these redox reactions were suggested. One electron processes for oxidation of xylenols have been indicated.     

Chemische Vitamin D<Subscript>3</Subscript>-Bestimmung in Lebertran

The different aspects of Vitamin D₃ determination and the data reported in the literature are discussed. The spectrophotometric determination of Vitamin D₃ in cod-liver oil is carried out after the alkaline saponification, extraction of unsaponified parts, precipitation of accompanying sterols and the column- and thin-layer chromatographic purification and separation of vitamin D₃ on 40 cm plates from other vitamins. The dyestuff α-naphtholbenzein is suited well as standard substance for the better location and identification of vitamin D₃ zone on the thin-layer plate. The results obtained from the chemical method were checked through the simultaneous biological determination.     

Heteropolynuclear Sodium(I) Lead(II) Complex: Crystal and Molecular Structure of a Novel 3‐D Polymer, [(en)Pb(μ3‐ONO)2Na(μ3‐ONO)2Na(μ‐O2ClO2)Na]n

A novel 3D polymeric heteropolynuclear sodium(I) lead(II) complex containing different ligands, [NaPb(ClO₄)(en)(NO₂)₂] was synthesized and characterized by elemental analysis and IR, and ¹H‐, ¹³C‐, and ²⁰⁷Pb‐NMR spectroscopy. The single‐crystal X‐ray data of [NaPb(ClO₄)(en)(NO₂)₂]_n established that the complex is a three‐dimensional polymer, [(en)Pb(μ₃‐ONO)₂Na(μ₃‐ONO)₂Na(μ‐O₂ClO₂)Na]_n. The Pb and Na atoms have four‐ and eight‐coordinate geometry, respectively. The lone pair of electrons at the Pb^II atom is ‘stereochemically active’.     

Enhancing the enzymatic hydrolysis of cellulosic materials using simultaneous ball milling

One of the limiting factors restricting the effective and efficient bioconversion of softwood-derived lignocellulosic residues is the recalcitrance of the substrate following pretreatment. Consequently, the ensuing enzymatic process requires relatively high enzyme loadings to produce monomeric carbohydrates that are readily fermentable by ethanologenic microorganisms. In an attempt to circumvent the need for larger enzyme loadings, a simultaneous physical and enzymatic hydrolysis treatment was evaluated. A ball-mill reactor was used as the digestion vessel, and the extent and rate of hydrolysis were monitored. Concurrently, enzyme adsorption profiles and the rate of conversion during the course of hydrolysis were monitored. α-Cellulose, employed as a model substrate, and SO₂-impregnated steam-exploded Douglas-fir wood chips were assessed as the cellulosic substrates. The softwood-derived substrate was further posttreated with water and hot alkaline hydrogen peroxide to remove >90% of the original lignin. Experiments at different reaction conditions were evaluated, including substrate concentration, enzyme loading, reaction volumes, and number of ball beads employed during mechanical milling. It was apparent that the best conditions for the enzymatic hydrolysis of α-cellulose were attained using a higher number of beads, while the presence of air-liquid interface did not seem to affect the rate of saccharification. Similarly, when employing the lignocellulosic substrate, up to 100% hydrolysis could be achieved with a minimum enzyme loading (10 filter paper units/g of cellulose), at lower substrate concentrations and with a greater number of reaction beads during milling. It was apparent that the combined strategy of simultaneous ball milling and enzymatic hydrolysis could improve the rate of saccharification and/or reduce the enzyme loading required to attain total hydrolysis of the carbohydrate moieties.