IRON (FE) CHEMICAL INFORMATION - THE CHEMISTRY OF IRON

What Is Iron? All you need to know about the element Iron (Fe)

Iron, a familiar metal, tends to rust, as everybody has seen. What happens chemically when iron rusts? Iron atoms in the metallic iron carries no electric charge Fe(0), in which 26 electrons (negatively charged) are orbiting around a nucleus that contains 26 protons (with positive charge) and 30 neutrons (with no electric charge).

This applies to an isotope 26Fe56, the most abundant isotope of element iron. But iron atom can lose its electrons. This process (loss of electrons) is called “oxidation.” Iron becomes either Fe(II) by losing two electrons or Fe(III) by losing three electrons (under normal conditions), though it can take Fe(I) (under special conditions).

Fe(0) is said to have been oxidized to Fe(II) or Fe(III). [Fe(II) means an iron atom that carries two positive charges; this is so because there are now only 24 electrons (negative charges), but there are still 26 positive charges at the nucleus.]

For this to happen you have to have a chemical entity that removes the electrons from the iron atom. Such an entity is called an oxidant or oxidizing agent. The iron atom is said to be a reductant or reducing agent in this process, for a chemical reaction in which a chemical entity (oxidant) gains electron(s) is called “reduction.”

Hence, oxidation and reduction reactions occur simultaneously and are like “head and tail” of a coin. Iron (Fe) reacts with oxygen in the air and is oxidized first to Fe(II) and then Fe(III) ending up with iron oxide Fe2O3. [Fe(II) can also be expressed as Fe2+ or FeII, and such a state is called an “oxidation state”; in this case, the oxidation state of iron atom is +2 or II. Likewise, Fe(III)=FeIII=Fe3+.

We will usually use Roman numerals to express the oxidation states in this book]. Here oxygen (O2) in the air is the oxidizing agent. In the process, oxygen O2 which is in “zero” oxidation state gains four electron and is reduced to two of O−II (−2 oxidation state); therefore, the chemical reaction is + → III ( −II ) 2 2 3 4Fe(0) 3O 2Fe O . In this chemical reaction, 12 electrons are exchanged between four iron atoms and three oxygen molecules.

When this is not purely oxide and contains hydroxide Fe(OH)O or Fe2(OH)2O2, it shows that rust color, brown. Pure oxide Fe2O3 forms an ore called “hematite,” which is red. The red bed is found in many geological locations.

These descriptions suggest that iron, when forming chemical compounds, takes the form of Fe(II) or Fe(III). And it can go back and forth between Fe(II) and Fe(III) readily. Fe(II) gives off an electron to become Fe(III), and Fe(III) becomes Fe(II) when it accepts an electron. This kind of process is also called “electron transfer” reaction.

Hence, iron (in the form of Fe(II) and Fe(III)) can readily undergo an “electron transfer” reaction or alternatively an “oxidation–reduction” reaction, because the process of Fe(II)s becoming Fe(III) is an oxidation and the reverse (Fe(III) → Fe(II)) is a reduction reaction.

Some of you might have experienced, as this author has, to have your toilet bowl and others stained brown by your well water. The water underground can contain (depending on the location and other conditions) iron compounds; the iron is in the form of Fe(II), which is dissolved in water and almost colorless. It remains as Fe(II) in the underground, because no oxidant such as oxygen in the air is available.

However, once pumped out above ground and being exposed to the air, the iron soon turns into Fe(III) (through oxidation by oxygen). Fe(III) in water (neutral water, that is) is not stable, and soon reacts with water itself and forms iron hydroxide Fe(OH)3, which is brown and precipitates.

This is the brown stain. And the fact of the easy formation of iron stain suggests an easy affinity or reaction of Fe(II) with oxygen O2. This is indeed the basis of the usefulness of iron in the biological systems and our health.

DNA REPLICATION - HOW IS DNA REPLICATED? BASIC INFORMATION AND TUTORIALS

Really. Just how dna is replicated?

This is quite clear at least in principle by now. It is based on the specific interaction between A and T, and between G and C. That is, take, for example, the double helix in figure below.

Let us label the left strand as “l” strand and the other “r” strand. (This is the complementary strand of “l”). Suppose that you separate the two strands and the “l” strand is isolated. Then you provide a pool of components A, C, G, and T and a means to bind nucleotides (enzyme called DNA polymerase) for the “l” strand.

This enzyme binds nucleotides one by one sequentially. The top bead A on the “l” strand binds a bead T (laterally through hydrogen bond), and next another bead on “l” binds laterally a bead T. Beads T and T are then connected through the phosphate group by the enzyme.

Next the bead G on “l” binds a bead C, and the bead C then is connected to the previous T on the right hand by the enzyme. This is repeated; then you see that an “l” strand will reproduce the complementary “r” strand. The reverse will also be true; i.e., an “r” strand will reproduce the corresponding “l” strand.

Thus, a double strand will have been replicated. How this is accomplished, i.e., mechanics of these chemical reactions are currently very intensely studied, is beyond the level of this book.

Hence, this topic will not be pursued further here. But, the very basic reason why we are like our parents or in other words why a gene molecule (DNA) is (almost) faithfully replicated and transmitted to a progeny can be understood as in the previous paragraph.

This replication mechanism of DNA, however, applies to only cell division. The issue of inheritance in sexual organisms like us is a little more complicated, because we get half of the gene from mother and the other half from father.

But again we are not able to elaborate on this issue here. The issue is more of biology (so-called genetics) than chemistry. The chemical principles are about the same.

We said, “DNA is (almost) faithfully replicated” in the paragraph above. The qualification “almost” implies that replication may not always be exact. In other words, a cell may make mistakes in replicating a DNA. It happens not very often, but frequently enough. If this happens, a wrong DNA may form, which would give
wrong information.

Mistakes can be caused by some factors (some cancer causing factors, for example) or without any particularly cause. The distinction between the right combination A–T/G–C and wrong combinations such as A–C/G–T is not quite definite.

Chemically speaking, the difference in interaction energy between the right and the wrong combination is not very great. Hence, there is some chance that the DNA-making mechanism may simply connect wrong nucleotides occasionally. This may be disastrous to the organism.

Therefore, many DNA-making mechanisms (DNA polymerases) contain in it three functions. One is polymerizing nucleotides (making DNA chain), of course.

The other two are monitoring and repairing mechanisms. It monitors what nucleotides are connected and can identify a wrong one. When it has recognized a wrong one, the repairing mechanism snips off the wrong one.

And then the polymerase portion reconnects another; this time a right one, hopefully. There are many other mechanisms known in organisms that repair “damaged” DNAs. All these are chemical reactions, but too complex to be talked about here. It is also to be noted that these occasional changes in DNA are the ultimate cause of change of species, i.e., evolution.