Página 1 dos resultados de 5 itens digitais encontrados em 0.001 segundos

‣ New extractants for separation of platinium-group metals from chloride solutions and their application to recycling processes

Paiva, A. P.; Carvalho, G. I.; Schneider, A. L.; Costa, M. Clara; Costa, A. M.; Assunção, A. F.; Nogueira, C. A.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em 10/09/2012 Português
Relevância na Pesquisa
39.32146%
In this paper some results on the application of four N,N’-tetrasubstituted malonamide derivatives for the extraction and separation of platinum-group metals (PGMs) are presented. The above mentioned extractants were specifically synthesized in order to evaluate their efficiency for the extraction of a specific metal, or group of metals, from aqueous chloride matrices. Different behaviours were obtained towards platinum(IV) and/or palladium(II) extraction, all the N,N’-tetrasubstituted malonamide derivatives allowing the mutual separation of the two metal ions, depending on the HCl concentration. Generally, extraction experiments were carried out involving initial aqueous phases containing 100 mg/L of each metal isolate, in varying 1M to 8M HCl concentration ranges, and 0.05M extractant in 1,2- dichloroethane solutions. From the preliminary results obtained, one can conclude that HCl concentrations and the structure of the malonamide derivative play a crucial role on the efficiency shown for Pt(IV) and/or Pd(II) extraction. The efficiency of the stripping stage of the loaded organic phases is variable, depending on the N,N’-tetrasubstituted malonamide derivative, as well as on the metal ion involved; for Pt(IV), distilled water and 1M HCl were generally successful...

‣ The solvent extraction performance of N,N’-dimethyl-N,N’-dibutylmalonamide towards platinum and palladium in chloride media

Paiva, A. P.; Carvalho, G. I.; Costa, M. Clara; Costa, Ana M. Rosa da; Nogueira, C. A.
Fonte: Taylor & Francis Publicador: Taylor & Francis
Tipo: Artigo de Revista Científica
Publicado em //2014 Português
Relevância na Pesquisa
27.613052%
The solvent extraction performance of N,N’-dimethyl-N,N’-dibutylmalonamide (DMDBMA) in 1,2-dichloroethane (1,2-DCE) towards platinum(IV) and palladium(II) in hydrochloric acid media was systematically evaluated. Pt(IV) extraction (%E) increases with the HCl concentration in the aqueous phases, being always higher than 72%, whereas Pd(II) extraction decreases from 65% at 1 M HCl to 22% at 8 M HCl. Several stripping agents for the two metals were tested: Pt(IV) is successfully recovered by a 1 M sodium thiosulfate solution, whereas the best result for Pd(II) was achieved with 0.1Mthiourea in 1MHCl. The loading capacity of DMDBMA for Pt(IV) is high, and data obtained from successive extraction-stripping cycles suggest a good DMDBMA stability pattern. Attempts to replace 1,2-DCE by more environmentally-friendly diluents showed, in general, worse %E for Pt(IV). The dependence of Pt(IV) distribution coefficients on DMDBMA and chloride ion concentrations, as well as on acidity, are the basis of a proposal for the composition of Pt(IV) extracted species.

‣ Synthesis and elaboration of peptidomimetic units

RAMADORI, FEDERICO
Fonte: La Sapienza Universidade de Roma Publicador: La Sapienza Universidade de Roma
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
17.613053%
Retro-peptides are peptidomimetics that present the direction of the amino acidic sequence reversed. A classical retro modification can be obtained by the introduction of the malonyl unit followed by a gem-diaminic unit, that can result in an increase of proteolysis resistance of the related parent peptide, retarding degradation and consequently enhancing therapeutic efficacy.This thesis aims at developing synthetic stategies to synthesize new interesting building blocks for the construction of peptidomimetics containing a retro modification.In this field Meldrum’s acid is recently reported as a useful scaffold to obtain non-symmetric disubstituted malonamides rAA-mGly-AA′ as building blocks for the synthesis of retro-peptides. The attention has been turned towards the synthetic elaboration of different rAA-mGly-AA′ with the aim of introducing, into the malonamide backbone, the olefinic moiety by a Knoevenagel condensation, obtaining correspondig malonyl dehydro peptides MDHPs.The investigation of a further elaboration was carried out to obtain the corresponding epoxy and aziridino peptides,interesting building blocks containing electrophilic sites known to react with nucleophilic amino acids within the active site of proteases. Starting from L-amino acids...

‣ Extracção líquido-líquido de iões metálicos de soluções aquosas cloretadas por derivados de ditiomalonamida N,N'-tetrassubstituídos

Ortet, Osvaldo Arlindo Lopes
Fonte: Universidade de Lisboa Publicador: Universidade de Lisboa
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em //2009 Português
Relevância na Pesquisa
28.332612%
Tese de mestrado em Química (Química Aplicada ao Património Cultural), apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2009; Este trabalho subdividiu-se em duas partes, primeiramente incidiu-se na síntese e caracterização de dois derivados de malonamida N,N'-tetrassubstituídas, a N,N'-dimetil-N,N'-difenilmalonamida (DMDPHMA) e a N,N'-dimetil-N,N'-diciclohexilmalonamida (DMDCHMA), seguida da conversão desses derivados em ditiomalonamidas, obtendo-se a N,N'-dimetil-N,N'-difenilditiomalonamida (DMDPHDTMA) e a N,N'-dimetil-N,N'-diciclohexilditiomalonamida (DMDCHDTMA), respectivamente, sendo que o método eficaz para a referida conversão foi através do uso do reagente de Lawesson. Todos os compostos sintetizados foram analisados e caracterizados por técnicas espectroscópicas, tais como infravermelho com transformada de Fourier (FTIR) e ressonância magnética nuclear (RMN) de 1H e de 13C. Determinaram-se também os respectivos pontos de fusão. Os derivados de ditiomalonamida foram também analisados pela técnica de espectrometria de massa com ionização por electrospray (ESI-MS). A segunda parte do trabalho baseou-se na investigação das capacidades extractivas dos derivados de ditiomalonamida para a recuperação de iões metálicos seleccionados (Ag(I)...

‣ Liquid-Liquid Extraction of Platinum from Chloride Media by N,N'-Dimethyl-N,N'-Dicyclohexyltetradecylmalonamide

Costa, M. Clara; Assunção, Ana; Costa, Ana M. Rosa da; Nogueira, C. A.; Paiva, A. P.
Fonte: Taylor & Francis Publicador: Taylor & Francis
Tipo: Artigo de Revista Científica
Publicado em //2013 Português
Relevância na Pesquisa
27.613052%
Liquid-liquid extraction of platinum(IV) from chloride media was carried out using N,N'-dimethyl-N,N'-dicyclohexyltetradecylmalonamide (DMDCHTDMA) in 1,2-dichloroethane. Platinum can be effectively extracted by DMDCHTDMA without addition of tin(II) chloride, since extraction percentages (%E) of 88% and 99% have been achieved from 6 M and 8 M HCl, respectively. Moreover, platinum can be successfully stripped through a simple contact with a 1 M HCl solution. The effect of some experimental parameters such as equilibration time, diluent, extractant and HCl concentrations was systematically investigated. The loading capacity of DMDCHTDMA was also evaluated. Data obtained from successive extraction-stripping cycles suggest a good stability pattern of DMDCHTDMA. Preliminary extraction data achieved with single metal ion solutions pointed out to a possible separation of platinum(IV) from palladium(II).