RESUMO
During the last decade, experimental and theoretical studies on the unimolecular decomposition of cumulenes (H(2)C(n)H(2)) from propadiene (H(2)CCCH(2)) to hexapentaene (H(2)CCCCCCH(2)) have received considerable attention due to the importance of these carbon-bearing molecules in combustion flames, chemical vapor deposition processes, atmospheric chemistry, and the chemistry of the interstellar medium. Cumulenes and their substituted counterparts also have significant technical potential as elements for molecular machines (nanomechanics), molecular wires (nano-electronics), nonlinear optics, and molecular sensors. In this review, we present a systematic overview of the stability, formation, and unimolecular decomposition of chemically, photo-chemically, and thermally activated small to medium-sized cumulenes in extreme environments. By concentrating on reactions under gas phase thermal conditions (pyrolysis) and on molecular beam experiments conducted under single-collision conditions (crossed beam and photodissociation studies), a comprehensive picture on the unimolecular decomposition dynamics of cumulenes transpires.
Assuntos
Alcadienos/química , Polienos/química , Polienos/síntese química , Alcadienos/efeitos da radiação , Modelos Químicos , Peso Molecular , Fotoquímica , Polienos/efeitos da radiação , Espectrofotometria Ultravioleta/métodos , Raios UltravioletaRESUMO
Container/closure systems are extensively characterized in terms of their propensity to contribute leachable substances to the drug products they contain. Such a characterization is relevant until a change occurs in the composition or production of the container/closure system itself or the raw materials it is comprised of. When such a change occurs, it is necessary to ascertain the impact that the change would have on the validity and applicability of the previously performed leachables assessment. A general methodology for performing change control evaluations is developed in this manuscript and is illustrated via the use of a case study.
Assuntos
Contaminação de Medicamentos , Embalagem de Medicamentos , Armazenamento de Medicamentos , Polienos/química , Cromatografia Líquida , Misturas Complexas/análise , Raios gama , Cromatografia Gasosa-Espectrometria de Massas , Concentração de Íons de Hidrogênio , Polienos/efeitos da radiação , Solubilidade , Solventes/análise , Solventes/química , Espectrofotometria Ultravioleta , Esterilização , Oligoelementos/análiseRESUMO
Three different cation-exchange membranes with carboxylic acid, phosphoric acid, and sulfonic acid groups, and one anion-exchange membrane with a triethylamine group were prepared by radiation-induced graft polymerization. The maximum capacities of the carboxylic acid, phosphoric acid, sulfonic acid, and triethylamine groups were 3.0, 2.30, 2.43, and 1.42 mmol/g, respectively. The physico-chemical properties of the polyalkene non-woven fabric membrane with four different ion-exchange groups were examined by thermogravimetric analysis, X-ray photoelectron spectrometry (XPS), and scanning electron microscopy. The prepared ion-exchange membrane was applied to the removal of terephthalic acid in dyeing wastewater.
Assuntos
Polienos/química , Ácidos Carboxílicos/química , Fenômenos Químicos , Físico-Química , Etilaminas/química , Troca Iônica , Espectrometria de Massas , Membranas Artificiais , Microscopia Eletrônica de Varredura , Ácidos Fosfóricos/química , Ácidos Fosfóricos/efeitos da radiação , Ácidos Ftálicos/química , Polienos/síntese química , Polienos/efeitos da radiação , Ácidos Sulfônicos/química , Propriedades de Superfície , TermogravimetriaAssuntos
Antibacterianos/farmacologia , Antibacterianos/efeitos da radiação , Soluções Tampão , Fenômenos Químicos , Físico-Química , Estabilidade de Medicamentos , Armazenamento de Medicamentos , Concentração de Íons de Hidrogênio , Polienos/farmacologia , Polienos/efeitos da radiação , Soluções , Luz Solar , Temperatura , Raios UltravioletaAssuntos
Carotenoides/efeitos da radiação , Clorofila/efeitos da radiação , Cumarínicos/efeitos da radiação , Fotoquímica , Polienos/efeitos da radiação , Porfirinas/efeitos da radiação , Purinas/efeitos da radiação , Pirimidinas/efeitos da radiação , Espectroscopia de Ressonância Magnética , Conformação Molecular , Espectrometria de Fluorescência , Análise Espectral , Análise Espectral RamanRESUMO
Deep effect of gamma-rays on polyenic antibiotics was studied. It was shown that gamma-radiation induced radiation-chemical oxidation of the substances. The chromatographic analysis showed that the levorin degradation products were identical to the polyenic products of the antibiotic oxidative destruction. As for mycoheptin and amphotericin B, destruction of their molecules to non-polyenic products was observed. It was found that toxicity of the levorin aromatic heptaen did not practically change after gamma-irradiation in high doses. The toxicity of mycoheptin and amphotericin B, non-aromatic heptaens increased after exposure to high doses of gamma-rays.