Ligand K-edge X-ray absorption spectroscopy and DFT calculations on [Fe3S4]0,+ clusters: delocalization, redox, and effect of the protein environment

Ligand K-edge XAS of an [Fe3S4]0 model complex is reported. The pre-edge can be resolved into contributions from the í2Ssulfide, í3Ssulfide, and Sthiolate ligands. The average ligand-metal bond covalencies obtained from these pre-edges are further distributed between Fe3+ and Fe2.5+ components using DFT calculations. The bridging ligand covalency in the [Fe2S2]+ subsite of the [Fe3S4]0 cluster is found to be significantly lower than its value in a reduced [Fe2S2] cluster (38% vs 61%, respectively). This lowered bridging ligand covalency reduces the superexchange coupling parameter J relative to its value in a reduced [Fe2S2]+ site (-146 cm-1 vs -360 cm-1, respectively). This decrease in J, along with estimates of the double exchange parameter B and vibronic coupling parameter ì2/k-, leads to an S ) 2 delocalized ground state in the [Fe3S4]0 cluster. The S K-edge XAS of the protein ferredoxin II (Fd II) from the D. gigas active site shows a decrease in covalency compared to the model complex, in the same oxidation state, which correlates with the number of H-bonding interactions to specific sulfur ligands present in the active site. The changes in ligand-metal bond covalencies upon redox compared with DFT calculations indicate that the redox reaction involves a two-electron change (one-electron ionization plus a spin change of a second electron) with significant electronic relaxation. The presence of the redox inactive Fe3+ center is found to decrease the barrier of the redox process in the [Fe3S4] cluster due to its strong antiferromagnetic coupling with the redox active Fe2S2 subsite.

Nota sobre antígeno relacionado à hepatite (HB Ag) e anticorpo (HB Ab) em população do território Federal do Amapá

53 amostras de soro, provenientes de Ferreira Gomes, no Amapá, foram testados para antígeno HB Ag e anticorpo HB Ab, com uma positividade de 3,7% para HB Ag, sub-tipo D. Os autores acentuam a necessidade de inquéritos em populações brasileiras a fim de estabelecer os sub-tipos associados à hepatite.

Martini Vahlii, profess. botan. Haun. membr. societ. lit. plur. Enumeratio plantarum :vel ab aliis, vel, ab ipso observatum, cum earum differentiis specificis, synonymis selectis et descriptionibus succinctis.

v.1

Martini Vahlii, profess. botan. Haun. membr. societ. lit. plur. Enumeratio plantarum :vel ab aliis, vel, ab ipso observatum, cum earum differentiis specificis, synonymis selectis et descriptionibus succinctis.

v.2

Plantae Preissianae sive Enumeratio plantarum quas in Australasia occidentali et meridionali-occidentali annis 1838-1841 :collegit Ludovicus Preiss /Partim ab aliis partim a se ipso determinatas descriptas illustratas edidit Christianus Lehmann.

v.1

Plantae Preissianae sive Enumeratio plantarum quas in Australasia occidentali et meridionali-occidentali annis 1838-1841 :collegit Ludovicus Preiss /Partim ab aliis partim a se ipso determinatas descriptas illustratas edidit Christianus Lehmann.

v.2

Index filicum,sive, Enumeratio omnium generum specierumque filicum et Hydropteridum ab anno 1753 ad finem anni 1905 descriptorium : adjectis synonymis principalibus, area geographica, etc. /Carl Christensen.

Fascicles 1-12, 1753-1906

Index filicum,sive, Enumeratio omnium generum specierumque filicum et Hydropteridum ab anno 1753 ad finem anni 1905 descriptorium : adjectis synonymis principalibus, area geographica, etc. /Carl Christensen.

Suppl. 1906-12

Index filicum,sive, Enumeratio omnium generum specierumque filicum et Hydropteridum ab anno 1753 ad finem anni 1905 descriptorium : adjectis synonymis principalibus, area geographica, etc. /Carl Christensen.

Suppl. prelim. 1913-17

Index filicum,sive, Enumeratio omnium generum specierumque filicum et Hydropteridum ab anno 1753 ad finem anni 1905 descriptorium : adjectis synonymis principalibus, area geographica, etc. /Carl Christensen.

Suppl. 3 1917-33

Index filicum,sive, Enumeratio omnium generum specierumque filicum et Hydropteridum ab anno 1753 ad finem anni 1905 descriptorium : adjectis synonymis principalibus, area geographica, etc. /Carl Christensen.

Suppl. 4 1934-60

Systema laurinarum /exposuit Christianus Godofredus Nees ab Esenbeck, Dr.

1836

Mexicanas plantas nuper a collectoribus expeditionis scientificae allatas :aut longis ab annis in herbario musei parisiensis depositas /praeside J. Decaisne ; enumerandas curavit Eug. Fournier.

v.1 1872

Mexicanas plantas nuper a collectoribus expeditionis scientificae allatas :aut longis ab annis in herbario musei parisiensis depositas /praeside J. Decaisne ; enumerandas curavit Eug. Fournier.

v.2 1886