iron 26 fe 55.845(2) mn fe co tc ru rh fe (d ) fe (d
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Iron26Fe55.845(2)
Mn Fe Co Tc Ru Rh
The essentials
Name: iron Symbol: Fe Atomic number: 26 Atomic weight: 55.845 (2) Group number: 8 Group name: (none) Period number: 4 Block: d-block
Fe3+ (d5) Fe2+ (d6)
IsotopesNaturally occurring iron consists of four isotopes: 5.845% of radioactive 54Fe (half-life: >3.1×1022 years), 91.754% of stable 56Fe, 2.119% of stable 57Fe and 0.282% of stable 58Fe. 60Fe is an extinct radionuclide of long half-life (1.5 million years).
Standard state: solid at 298 K Colour: lustrous, metallic, greyish tinge Classification: Metallic
Availability:
Iron is available in many forms including foil, chips, sheet, wire, granules, nanosized activated powder, powder, and rod. Small and large samples of iron foil, sheet and wire (also Iron alloy in foil form and stainless steel alloys in foil, sheet, wire, wire straight cut lengths, insulated wire, mesh, rod, tube and powder form) can be purchased.
Iron is a relatively abundant element in the universe. It is found in the sun and many types of stars in considerable quantity.
Iron nuclei are very stable. Iron is a vital constituent of plant and animal life, and is the key component of haemoglobin.
The pure metal is not often encountered in commerce, but is usually alloyed with carbon or other metals. The pure metal is very reactive chemically, and rapidly corrodes, especially in moist air or at elevated temperatures.
Iron in biology
Iron is essential to nearly all known organisms.
In cells, iron is generally stored in the centre of metalloproteins, because "free" iron -- which binds non-specifically to many cellular components -- can catalyse production of toxic free radicals.
In animals, plants, and fungi, iron is often incorporated into the heme complex. Heme is an essential component of cytochrome proteins, which mediate redox reactions, and of oxygen carrier proteins such as hemoglobin, myoglobin, and leghemoglobin.
Inorganic iron also contributes to redox reactions in the iron-sulfur clusters of many enzymes, such as nitrogenase (involved in the synthesis of ammonia from nitrogen and hydrogen) and hydrogenase. Non-heme iron proteins include the enzymes methane monooxygenase(oxidizes methane to methanol), ribonucleotide reductase (reduces ribose to deoxyribose; DNA biosynthesis), hemerythrins (oxygen transport and fixation in marine invertebrates) and purple acid phosphatase (hydrolysis of phosphate esters).
Iron distribution is heavily regulated in mammals, partly because iron has a high potential for biological toxicity. Iron distribution is also regulated because many bacteria require iron, so restricting its availability to bacteria (generally by sequestering it inside cells) can help to prevent or limit infections. A major component of this regulation is the protein transferrin, which binds iron absorbed from the duodenum and carries it in the blood to cells.
Iron in biology
Electron Transfer
Enzymes
Iron-Sulfur Proteins (non-heme iron)
Heme Proteins (heme iron)
Nutrition and dietary sources
Good sources of dietary iron include red meat, fish, poultry, lentils, beans, leaf vegetables, tofu, chickpeas, black-eyed peas, potatoes with skin, bread made from completely whole-grain flour, molasses, teff and farina. Iron in meat is more easily absorbed than iron in vegetables.
Iron provided by dietary supplements is often found as iron (II) fumarate, although iron sulfate is cheaper and is absorbed equally well. Elemental iron, despite being absorbed to a much smaller extent, is often added to foods such as breakfast cereals or "enriched" wheat flour (and will be listed as "reduced iron" in the list of ingredients). Iron is most available to the body when chelated to amino acids (available as an iron supplement).
The RDA for iron varies considerably based on age, gender, and source of dietary iron (heme-based iron has higher bioavailability). Infants will require iron supplements if they are not breast-fed.
??????como os metais se coordenam às cadeiras laterais dos aminoácidos em proteínas ??????
influência do campo de ligandos
As funções dos elementos químicos nos sistemas biológicosInteracção com os sistemas biológicos
Iões metálicos e geometrias mais frequentes
ião metálico geometrias mais frequentes
Cu2+ Tetragonal > Coordenação 5 > Tetraédrica Ni2+ Octaédrica > restantes Co2+ Octaédrica > Tetraédrica > restantes Zn2+ Tetraédrica > Octaédrica Mn2+ Octaédrica > restantes Fe3+ Octaédrica > Tetraédrica
Ligandos preferidos por diversos iões metálicos em biologia
Iões metálicos Ligandos biológicos preferidos Na+ K+
Ligandos oxigenados neutros ou com carga -1
Mg2+ Mn2+ Grupos carboxilatos, fosfato e dadores azotados (porfirinas) Ca2 Grupos carboxilato e fosfato Fe2+ Grupos -S- e grupos >NH (imidazol, porfirinas) Fe3+ Co3+ Fenóis (tirosina), carboxilatos, porfirinas Cu+ Grupos -S- (cisteína) e aminas aromáticas Cu2+ Aminas, imidazol, grupos >N- Zn2+ Aminas, imidazol, grupos -S- Ag+, Hg2+, Cd2+ Grupos -S- e aminas Pb2+ Grupos carboxilato e -S-
Campo esférico Octaédrico - Oh
e - duplamente degeneradot - triplamente degenerado
eg
t2g
Campo esférico Tetraédrico - T
ΔTet <<< ΔOct (ΔTet = 4/9 ΔOct)
Na presença de um campo eléctrico (devido aos ligandos) os níveis d não são degenerados.
Para complexos OCTAÉDRICOS os grupos de orbitais t e e estão separados pela diferença Δoct.
Há tendência para preencher os orbitais de mais baixa energia (t) obdecendo àregra de Hund.
[Ti(H2O)6]3+ [V(H2O)6]3+ [Cr(H2O)6]3+
Δoct Δoct Δoct
e
t2
d1 d2 d3
[Mn(H2O)6]3+ d4 Para onde vai o 4º electrão? (t ou e ?)
O factor que vai determinar a ocupação do nível d é o valor relativo de Δoct com a energia de emparelhamento electrónico (P).
Δoct > P vai para t
Δoct < P vai para e
Se o acoplamento for o processo preferencial obtêm-se
“ COMPLEXOS DE SPIN BAIXO ”,
caso contrário obtêm-se “
COMPLEXOS DE SPIN ALTO ”.
• Configuração electrónica: d4 duas configurações possíveis
e
t
3/5 Δoct
2/5 Δoct
e
t
3/5 Δoct
2/5 Δoct
Spin-alto S = 2
Spin-baixo S = 1
P é a energia necessária para emparelhar 2 electrões
Δ < P
Δ > P
• Configuração electrónica: d6 Fe2+, Co3+
eg
t2g
3/5 Δoct
2/5 Δoct
eg
t2g
3/5 Δoct
2/5 Δoct
Spin-alto S = 2
Spin-baixo S = 0
Δ > P
Δ < P
S = 1/2
S = 5/2 SA
S = 1/2 SB
S = 2 SA
S = 0 SB
S = 3/2 SA
S = 1/2 SB
S = 1/2
S = 0
Mo(V) 4d1
Fe(III) 3d5
Mn(II)
Fe(II) 3d6
Co(II) 3d7
Cu(II) 3d9
Cu(I) 3d10
MET
AIS
DE
TRA
NSI
ÇÃ
O
Mononuclear non-heme Iron Centers in Biology
Nitrile as substrateNitrile as substrate
Undefined functionUndefined function
Dioxygen as substrateDioxygen as substrate
Mononuclear non-heme Iron Centers in Biology
Electron TransferElectron Transfer
Superoxide as substrateSuperoxide as substrate
Rubredoxin (Rd)
Monomeric protein containing 1 Fe(S-Cys)4 center
Adman, E.T. et al. (1991)
NH2 Cys – X – X – Cys COOH
Cys
Cys
Cys
Cys
The Fe(S-Cys)4 center: Electron Transfer
Cys – X – X – Cys
NN--terminalterminal
N
C
CC--terminalterminal
S-Cys9 S-Cys12
S-Cys28
S-Cys29
Nε-His48
Nε-His74
Nε-His68
Nδ-His118
S-Cys115
center II
center I
Dfx - Desulfoferrodoxin - a modular protein
N terminalC terminalover-expression
Coelho, A.V. et al. (1996)
Schematic presentation of primary structures
Rubredoxin (Rd)
Desulforedoxin (Dx)
Desulfoferrodoxin (Dfx)
CxxC CxxC
CxxC CC
ExHCxxC CC H H C H
Schematic presentation of primary structures
Rubredoxin (Rd)
Desulforedoxin (Dx)
Desulfoferrodoxin (Dfx)
Neelaredoxin (Nlr) – D. gigas
Treponema pallidum
CxxC CxxC
CxxC CC
EKHCxxC CC H H C H
Methanococcus jannaschii
EKH H H C H
EKKH H H C H
EKH H H C H
CEN
TRO
S FE
RRO
-EN
XO
FRE
Rubredoxinas - redutases de superóxido
Ferredoxinas (plantas)
Ferredoxinas
Ferredoxinas - bacterianas
+3+2.5+2
IRON-SULFUR CLUSTERS
• CLUSTER INTERCONVERSIONS
[3Fe-4S] [4Fe-4S]
• SYNTHESIS OF HETEROMETALLIC CLUSTER[M,3Fe-4S](in proteins and model compounds)
M = Fe, Co, Ni, Zn, Cd, Ga, V, Re, Tl
3Fe and 4Fe CLUSTERS
[Fe-S] CLUSTERS VERSATILE COORDINATION
Versatile coordinationN (HIS), COO- (ASP, GLU)
HETEROMETALLIC CLUSTERS
NEWSPIN STATESOXIDATION STATESMAGNETIC PROPERTIES
MODEL COMPOUNDS
UNUSUAL [Fe-S] ClusterMixed Coordination
Pereira, Tavares, Moura, Huynh
SYNTHESIS OF HETEROMETALLIC CLUSTERS[3Fe-4S] center as a template
INTERCONVERSION 3Fe into 4Fe CLUSTER
FROM APO-PROTEIN
ISOTOPIC LABELLING OF A [Fe-S] CORE
Mild conditionsThe [3Fe-4S] core as TEMPLATE