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