Iron

Iron is the chemical element with the symbol Fe and atomic number 26. It is one of the most
used metals because of the relatively low production costs and its high strength. Iron can be found in many everyday items, from food containers to screw drivers or any type of machinery. Steel is a form of iron, which is alloyed with carbon and a variety of other metals. Iron ions are a necessary trace element used by almost all living organisms with the only exceptions being a few prokaryotic organisms that live in iron-poor conditions. As an example, the lactobacilli in iron-poor milk use manganese for their catalysis processes. Iron-containing enzymes, usually containing haeme prosthetic groups, participate in the catalysis of oxidation reactions in biology and in the transport of a number of soluble gases.
Iron is a metal extracted from iron ore, and is almost never found in the free elemental state. In order to obtain elemental iron, the impurities must be removed by chemical reduction. Iron is the main component of steel, and it is used in the production of alloys or solid solutions of various metals.Iron is an essential trace element for the human body. Haemoglobin is the oxygen-transport metalloprotein in the red blood cells; myoglobin facilitates the oxygen use and storage in the muscles; and cytochromes transport electrons. Iron is also an integral part of enzymes in various tissues.

Reference: Essential inorganic chemistry by katja
Page number 148-150

Metallic Hydrides

Many of the elements in the d-block, and the lanthanide and actinide elements in the /-block, react with H2 and form metallic hydrides. How-
ever, the elements in the middle of the d-block do not form hydrides. The absence of hydrides in this part of the periodic table is· sometimes· called 
the hydrogen gap. 
Metallic hydrides are usually prepared by heating the metal with hydrogen under high pressure. (If heated to higher temperatures the hydrides decompose, and this may be used· as a convenient method of making very pure hydrogen.) 
These hydrides generally have properties similar to those of the parent metals: they are hard, have a metallic lustre, conduct electricity, and have 
magnetic properties. The hydrides are less dense than the parent metal, because the crystal lattice has expanded through the inclusion of hydrogen.

Reference _consince of inorganic chemistry
By JD Lee
Page number  252

Chemical behavior of alkali metals

Most alkali metals have a silvery white appearance with the exception of caesium which is golden yellow.
They are all soft metals and typically can be cut with a knife. The softness of the metal increases within the
group; caesium is the softest of the alkali metals.
Alkali metals are generally very reactive and oxidise in the air. The reactivity increases within the group,
with lithium having the lowest reactivity and caesium the highest. Therefore, all alkali metals except lithium
have to be stored in mineral oil. Lithium as an exception is normally stored under inert gas such as argon.
Nevertheless, lithium, sodium and potassium can be handled in air for a short time, whereas rubidium and
caesium have to be handled in an inert gas atmosphere.
All alkali metals react violently with water with the formation of the metal hydroxide and hydrogen. Again,
lithium is the least reactive alkali metal and reacts ‘only’ quickly with water, whereas potassium, rubidium
and caesium are more reactive and react violently with water.

Reference Inorganic chemistry by Huhee

Mechanisms of Enzymes

Mechanisms of Enzymes:

There are two types of mechanisms involved to explain substrate-enzyme complex formation; lock and key theory (template model), and induced-fit theory.

(i) Lock and Key Theory:

Emil Fischer (1894) explained the specific action of an enzyme with a single substrate using a theory of Lock and Key analog . According to this theory, reaction of sub-state and enzyme is analogous to lock and key. Enzyme is analogous to key, where the geometrical configuration of socket is fixed. Similarly substrate has also got fixed geo­metrical configuration like that of key. A particular lock can be opened or closed by a particular key. According to the particular substrate can be found at active site of particular enzyme forming substrate-enzyme complex. Enzyme-substrate complex remains in tight fitting and active sites of enzymes are complementary to substrate molecules. Subsequently, enzyme-substrate complexes result in the transformation of substrate into the product formation due to activity of reaction sites.

Since product has lower free energy, it is released. Enzymes are fixed to receive another molecule of substrate and thus enzyme activity continues. In this analogy, the lock is the substrate and the key is the enzyme. Only the correctly sized key (substrate) fits into the key hole (active site) of the lock (enzyme).

Smaller keys, larger keys, or incorrectly positioned teeth on keys (incorrectly shaped or sized substrate molecules) do not fit into the lock (enzyme).

Lock and Key Model for Mechanism of Enzyme Action

(ii) Induced Fit Theory:

In 1958, Koshland modified the Fischer’s model for the formation of an enzyme-substrate complex to explain the enzyme property more efficiently. According the Fischer’s model the nature of the active site of enzyme is rigid, but it is able to be pre-shaped to fit the substrate.

Koshland explains that the enzyme molecule does not retain its original shape and structure, but the contact of the substrate induces some geometrical changes in the active site of the enzyme molecule. The enzyme molecule is made to fit completely the configuration and active centers of the substrate. At the same time, other amino acid residues may become buried in the interior of the molecule.

The hydrophobic and charged group both are involved in substrate binding. A phosphoserine (-P) and SH group of cysteine residue are involved in catalysis.

Residue of the other amino acid such as lysine (Lys) and methionine (Met) are not involved in either binding or catalysis. In the absence of substrate, the substrate binding group and catalytic group are far apart from each other.

But the contact of the substrate induces a conformational changes in the enzyme molecule and aligns both the groups for substrate binding and catalysis. Simultaneously, the spatial orientation of the other region also changed. This causes the lysine and methionine much closer.

Reference http://www.biologydiscussion.com/metabolism/microbial-metabolism/enzymes-definition-mechanisms-and-classification-microbiology/65516

Clemmensen reduction

The reaction of aldehydes and ketones with zinc  (Zn/Hg alloy) in concentrated hydrochloric acid, which reduces the aldehyde or ketone to a hydrocarbon, is called Clemmensen reduction.

Syngas

Syngas, or synthesis gas, is a fuel gas mixture mainly consisting hydrogen, carbon monoxide, and carbon dioxide. Syngas is usually a product of gasification and the electricity generation. Syngas has been using instead of gasoline. It has less than half the energy density  of natural gas.

It can be produced from many sources, including natural gas, coal, biomass, or virtually any hydrocarbon feedstock, by reaction with steam, carbon dioxide  or oxygen. Syngas is a important intermediate resource for production of hydrogen, ammonia, methanol, and synthetic hydrocarbon fuels. Syngas is also used as an intermediate in producing synthetic petroleum  for use as a fuel.

Reference

Alloy

Alloy is a  metallic substance that composed of two or more elements, as either a compound or a solution atleast one of them metal.

Almost all metals are used as alloy and it is mixtures of several element because these have properties superior to pure metals.

Examples of alloys including  stainless steel, brass, bronze, white gold, and sterling silver. The principal alloying elements for steel are chromium, nickel, manganese, molybdenum, silicon, tungsten, vanadium, and boron. Some metal alloys are naturally occurring and require little processing to be converted into industrial grade materials. Ferro-alloys such as Ferro-chromium and Ferro-silicon, for instance, are produced by smelting mixed ores and are used in the production of various steels.

Over 90% of metal used is in the form of alloys. Alloys are used because their chemical and physical properties are superior for an application than that of the pure element components. Typical improvements include corrosion resistance, improved wear, special electrical or magnetic properties, and heat resistance. Alloys are used because they retain the key properties of component metals are less expensive.

The components of alloys cannot be separated using a physical means. An alloy is homogeneous and retains the properties of a metal, even though it may include metalloids or nonmetals in its composition.


Reference
 https://www.thebalance.com/metal-alloys-2340254
https://www.thoughtco.com/alloy-definition-examples-and-uses-606371
https://www.britannica.com/technology/alloy
https://en.wikipedia.org/wiki/Alloy