2,6-dicyano-1,5-dimethylsemibullvalene as a probe for homoaromatic molecules of the Dewar-Hoffman type

The 2,6-dicyano-1,5-dimethylsemibullvalene (2d) synthesized via the bicyclo[3.3.0]octanedione 7 exists as a classical ground state which is lower in energy by less than 5 kcal/mole than the homoaromatic transition of the Cope rearrangement of 2d.     

The synthesis of “stretched-out” analogs of lumazine, 6,7-dimethyllumazine and 2-amino-5,6,7,8-tetrahydro-6,7-dimethyl-4-pteridinone

The synthesis of pyrazino[2,3-g]quinazolin-2,4-(1H,3H)dione ( 4 ) and its 7,8-dimethyl derivative ( 5 ), as linear benzo-separated lumazines, is reported. Also described is the preparation of 2-amino-6,7,8,9-tetrahydro-7,8-dimethylpyrazino[2,3-g]quinazolin-4-one ( 6 ), as a linear benzo-separated analog of a synthetic cofactor for phenylalanine hydroxylase. All of the syntheses began with ethyl 2,4,5-triaminobenzoate ( 8 ) and proceeded through the appropriate derivatives of ethyl 6-aminoquinoxaline-7-carboxylate ( 9, 10 , and 11 ) which were subsequently ring closed to 4, 5 , and 6 .     

Chemical reducing pedoenvironment in a peatland influenced by hematitic phyllite lithology in the southern Espinhaço chain,Brazil

A peatland in Pinheiro, Diamantina City, Minas Gerais State - Brazil, was sampled at different depths of two profiles with diverse vegetation coverings (grassland field and bush) in order to collect materials that might reflect changes in the chemical states of iron over the peat formation coming from original minerals such as hematitic phyllite surrounding the boggy pedon. Samples collected were chemically, structurally and magnetically characterized. The results show that both series of peats are composed of organic matter and minerals such as quartz, kaolinite, gibbsite, rutile and muscovite. Deeper layers present only quartz. Mössbauer spectroscopy shows that iron is present in both electron states, Fe²⁺ and Fe³⁺, under both vegetations, each valence appearing in the spectra in the form of a discrete doublet. No hyperfine magnetic splitting was observed in any spectrum at room temperature. The Mössbauer subspectral area of Fe²⁺ tended to increase from the upper to deeper layers. Magnetic measurements reveal that the magnetic response of the surface samples is the highest, displaying a sharp decrease below 15 cm and that the magnetic signal is a superposition of (super)paramagnetic and ferrimagnetic contributions. Samples from the grassland field also show a diamagnetic component for the deeper layers.     

Quantification of curium isotopes in environmental samples: drawbacks,speciation and specific tracer

Journal of Radioanalytical and Nuclear Chemistry - In this study, drawbacks of the use of 243Am as a tracer in order to quantify curium isotopes during a complex chemical procedure were...     

A Convenient Synthesis of the Important Retinoid Synthon Ethyl trans-3-formyl-2-butenoate

The efficient, high-yield synthesis of the important retinoic acid synthon ethyl trans-3-formyl-2-butenoate by Wadsworth-Emmons methodology is described.     

Optimization of Sr-90 precipitation in nitric acid using design of experiments for radioactive waste characterization method

Journal of Radioanalytical and Nuclear Chemistry - 90Sr radiochemical method using nitric acid for Sr and Ca separation was optimized using design of experiments methodology. Nitric acid...