The precipitation of alkaline-earth metal and transition metal oxalates from aqueous solution. Induction periods and nucleation rates

The precipitation of magnesium, calcium, strontium and barium oxalates and of manganous, ferrous, cobalt, nickel and copper oxalates was studied from equivalent aqueous solutions at 22°C: the initial overall concentrations (C) generally varied from 0.001 to 0.2 M and the saturation ratios (S_mox) varied from <10 to >3000. The induction periods before the main growth surge were measured and nucleation rates were determined from final crystal numbers and induction periods. Precipitation occurred through homogenous nucleation: the critical nuclei in supersaturated alkaline-earth metal oxalate solutions were formed by aggregation of 6–8 M⁺⁺Ox⁻ ion-pairs while the critical nuclei in supersaturated transition metal oxalate solutions were formed by aggregation of 6–8 MOx complexes (to units of 3–4 M⁺⁺MOx₂⁻ ion-pairs). Over the range studied, the nucleation rates then varied with saturation ratios according to the relation, Nucleation rates at any saturation ratio decreased in the order Mg > Sr, Ba > Ca and Fe > Mn > Co, Cu > Ni; that is, generally in the order of increasing M⁺⁺–Ox⁻ and M⁺⁺–MOx₂⁻ bond strengths and increasing surface energies of the metal oxalate crystals. Induction periods decreased with increasing-concentration and saturation ratio; over The factors t _C1 and t _S1 depended in turn on the ‘rate constants’ for nucleation and growth during the induction periods and on metal oxalate solubilities.     

Enantioselective synthesis of (L)-Fmoc-α-Me-Lys(Boc)-OH via diastereoselective alkylation of oxazinone as a chiral auxiliary

Benzyl (2R,3S)-(−)-6-oxo-2,3-diphenyl-4-morpholinecarboxylate (4) was successively alkylated with methyl iodide and 1,4-diiodobutane using a base. In each alkylation step anti-alkylated product formed exclusively. The iodo group was displaced with azide, which served as a precursor for the side-chain amino function. Catalytic hydrogenation with concomitant cleavage of the chiral auxiliary afforded (L)-α-Me-Lys-OH (9) in a total of four steps in good yield. (L)-Fmoc-α-Me-Lys(Boc)-OH (16) was obtained from 9 via regioselective benzyloxycarbonylation. Alternately, (L)-Fmoc-α-Me-Lys(Boc)-OH (16) was obtained via Staudinger reduction of azide (8) in a total of six steps in good yield.     

Alkylenedithiophosphate derivatives of arsenic(III), antimony(III) and bismuth(III)

Tris(alkylenedithiophosphates) of arsenic(III), antimony(III) and bismuth(III),

have been synthesized by the reactions of alkylenedithiophosphoric acids with metal oxides and chlorides and of their ammonium salts with metal chlorides in suitable solvents. Mixed chloride alkylenedithiophosphates of arsenic(III) and antimony(III),

have been obtained by the reactions of metal chlorides with ammonium alkylenedithiophosphates at 1 : 1 and 1 : 2 molar ratios or alternatively by the co-disproportionations reactions of metal chlorides with metal tris(alkylenedithiophosphates) at different (2 : 1 and 1 : 2) molar ratios. These new compounds have been characterized by elemental analyses, molecular weight measurements and spectroscopic (IR, and ¹H and ³¹P NMR) data. Chelated structures with bidentate alkylenedithiophosphate groups have been proposed for all these derivatives.     

Potassium carbonate mediated unusual transformation of 2,3-dihydroquinazolinone via cascade reaction

An unusual potassium carbonate mediated transformation of 2,3-dihydroquinazolinone by a one-pot operation is reported under mild conditions. In addition, it is interesting to report the regioselective transformation of 3-(2-bromophenyl)-2-isopropyl-2,3-dihydroquinazolin-4(1H)-one from compound 16.     

Advances in [4+3]‐Annulation/Cycloaddition Reactions Leading to Homo‐ and Heterocycles with Seven‐Membered Rings

In this review, we summarize advances in [4+3] and a few other annulation/cycloaddition reactions for the construction of seven membered rings, with an emphasis on the literature subsequent to the year 2010. The type of products include the following: azepines, diazepines, benzazepinones, 1,2‐diazepinones, oxazepinones, benzothiazepines, benzodiazepinones, benzoxopinones, cyclohepta[b]indoles, benzoxazepines, azepino‐indoles, oxepines/oxazepanes, triazepines oxepinoindolones/azepinoindolones, oxadiazepines, azabicyclooctanes. Emphasis is also given to cover diverse types of annulations; possible intermediates are displayed in the illustrated schemes to aid future work.     

Refractometric studies of molecular complexes ofDDT with some compounds of biological interest

Formation of molecular complexes betweenDDT as acceptor and indole, 2-methylindole, 3-methylindole, benzene and naphthalene as donors have been studied in carbon tetrachloride using refractometric and differential refractometric measurements. Titration techniques through these measurements have indicated11 stoichiometry of these complexes. Equilibrium constants (K ₁) and extent of electronic polarization were calculated. Two types of complexes were observed, one association involving primarily the benzhydryltrichloromethyl grouping ofDDT with a polar complexing agents, and the other interaction of theDDT aromatic -electron system with -electrons of donors in the complexing molecule. These data support the charge-transfer complex formation hypothesis for the mode of action ofDDT on molecular level.

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Refraktometrische Untersuchungen an Molekülkomplexen von DDT mit einigen biologisch relevanten Verbindungen

Zusammenfassung Es wurde die Bildung von Molekülkomplexen zwischenDDT als Acceptor und Indol, 2-Methyl-indol, 3-Methyl-indol, Benzol und Naphthalin als Donor in CCl₄ mittels Refraktometrie und differenzieller Refraktometrie untersucht. Es wurde11-Stöchiometrie der Komplexe festgestellt, Gleichgewichtskonstanten und das Ausmaß der Elektronenpolarisation wurden berechnet. Zwei Typen von Komplexen wurden beobachtet; in einem Fall erfolgt die Assoziation primär über die Benzhydryltrichlormethyl-Gruppierung desDDT, im anderen Fall über -Elektronenwechselwirkungen. Die Daten unterstützen ein chargetransfer-Modell der Komplexbildung vonDDT mit geeigneten Donormolekülen.

     

Minireview: Whole-cell,Nucleotide, and Enzyme Inhibition-based Biosensors for the Determination of Arsenic

Arsenic is a natural and highly toxic environmental contaminant and is intensely connected with human health. It can cause DNA damage, mutations, neurological disorders, and cancer. In previous few decades, large numbers of biosensors for recognition and identification of arsenic both qualitatively and quantitatively have been developed. The biosensor is a logical device that is usually used for identification of a particular or a group of analytes in samples. This review aims at various advancements made in the improvement of biosensors for arsenic detection such as whole cell-based, nucleotide-based, and enzyme inhibition-based biosensors. The review focuses on the technology used for development of arsenic biosensor along with their advantages and limitations.     

Synthesis and Characterization of Toluene-3,4-dithiolatoarsenic(III) Derivatives of Dialkyldithiophosphates

Replacement reactions of toluene-3,4-dithiolatoarsenic(III) chloride and sodium salts of dialkyldithiophosphoric acids in 1:1 molar ratio in refluxing anhydrous benzene yielded toluene-3,4-dithiolatoarsenic(III) dialkyldithiophosphate derivatives of the general formula overline{SC_{6}H_{3}(CH_{3})SA} sS 2 P(OR) 2 [where R = Et, Pr n , Pr i , Bu n and Bu i ]. These newly synthesized derivatives are soluble in organic solvents like benzene, chloroform, and dichloromethane. These derivatives have been characterized by elemental analysis (C, H, S, and As) as well as IR and NMR ( 1 H, 13 C and 31 P) spectral studies.     

A theoretical study for one-dimensional modeling for VOC in a catalytic converter

Modeling for catalytic oxidation of a volatile organic compound, acetaldehyde for the purpose of controlling tail-pipe emissions from vehicular exhaust was carried out. The model developed was one-dimensional unsteady state model, using mass and energy balance equations to predict results for acetaldehyde conversion in an adiabatic monolith operating under warm-up conditions. The equations consisted of a set of partial differential equations that are coupled and solved using Backward Implicit Scheme. Analysis of the behavior of the converter during warm up period was carried out and it was observed that the warm up was faster for a fresh catalyst and this warm up period could be reduced by introducing hot incoming exhaust gas at higher temperature.