Acenes

The acenes or polyacenes are a class of organic compounds and polycyclic aromatic hydrocarbons made up of linearly fused benzene rings.

Due to their increased conjugation length the larger acenes are also studied.Theoretically, a number of reports are available on longer chains using density functional methods. They are also building blocks for nanotubes  and graphene. Unsubstituted octacene (n=8) and nonacene (n=9.


Reference -https://en.m.wikipedia.org/wiki/Acene

Electrons shielding

The shielding effect sometimes referred to as atomic shielding or electron shielding  describes the attraction between an electron  and the nucleus in any atom with more than one electron. The shielding effect can be defined as a reduction in the effective nuclear charge on the electron cloud, due to a difference in the attraction forces on the electrons in the atom. It is a special case of electric-field screening.

Crystal Field theory

Many transition-metal complexes are coloured. This other spectroscopic properties, such as magnetism and hydration enthalpies, can be explained with the so-called crystal field theory (CFT). The CFT describes the degeneration of the d- and f-orbitals in transition-metal complexes. It does not attempt to describe any type of chemical bonds. CFT is based on the interaction of a positively charged cation and the nonbinding (negatively charged) electrons of the ligand. The general principle is that the five d orbitals are degenerated, meaning that they do not occupy the same energy level anymore. Once the ligands approach the central positively charged cation,
the electrons of the ligands will become closer to some of the d orbitals of the metal. This results in the degeneration of the d orbitals. Electrons in d orbitals that are closer to the ligands will occupy a higher energy level as the negatively charged electrons will repel each other.



Reference - Essential inorganic chemistry by katja
Page number 128

Valence Bond theory

This theory was proposed by Linus Pauling. He was awarded the Nobel  Prize for Chemistry in 1954. The theory was very widely used in the period 1940-1960. It provides a basis for simple description of small inorganic molecules.  Atoms with unpaired electrons tend to combine with other atoms which also have an unpaired electrons. In this way the unpaired electrons are paired
up, and the atoms involved all attain a stable electronic arrangement. This is usually a foll shell of electrons ( a noble gas configuration). Two
electrons shared between two atoms constitute a bond. The Number of Bond is formed by an atom is usually the same as the number of unpaired
electrons in the ground state.


Concise inorganic chemistry by JDLee

Atom bomb

Atomic bomb, also called atom bomb, weapon with great explosive power that results from the sudden release of energy upon the splitting, or fission, of the nuclei of a heavy element such as plutonium or uranium.
Structure:
An atom bomb consists of a piece of fissile material whose mass is subcritical. This piece has a cylindrical void. It has a cylindrical fissile material which can fit into this void and its mass is also subcritical. When the bomb has to be exploded, this cylinder is injected into the void using a conventional explosive.  Now, the two pieces of fissile material join to form the supercritical mass, which leads to an explosion. During this explosion tremendous amount of energy in the form of heat, light and radiation is released. A region of very high temperature and pressure is formed in a fraction of a second along with the emission of hazardous radiation like γ rays, which adversely affect the living creatures. This type of atom bombs were exploded in 1945 at Hiroshima and Nagasaki in Japan during the World War II.

 

Reference   https://www.britannica.com/technology/atomic-bomb

https://en.wikipedia.org/wiki/Nuclear_weapon

Quercetin

Quercetin is a plant flavonol from the flavonoid group of polyphenols. It is found in many fruits, vegetables, leaves, and grains; red onions and kale are common foods containing appreciable content of quercetin. Quercetin has a bitter flavor and is used as an ingredient in dietary supplements, beverages, and foods.

Quercetin is a flavonoid widely distributed in nature.The name has been used since 1857, and is derived from quercetum.It is a naturally occurring polar auxin transport inhibitor.

Quercetin is one of the most abundant dietary flavonoids,with an average daily consumption of 25–50 milligrams.

In red onions, higher concentrations of quercetin occur in the outermost rings and in the part closest to the root, the latter being the part of the plant with the highest concentration. One study found that organically grown tomatoes had 79% more quercetin than non-organically grown fruit.Quercetin is present in various kinds of honey  from different plant sources.

Reference.https://en.m.wikipedia.org/wiki/Quercetin

Types of bonds

Atoms may attain a stable electronic configuration in three different ways: 
by losing electrons, by gaining electrons, or by sharing electrons. 
Elements may be divided into: 
I. Electmpositive elements, whose atoms give up one or more electrons 
fairly readily. 
2. electronegative elements. which will accept electrons. 
3. Elements which have little tendency to lose or gain electrons. 
Three different types of bond may be formed, depending on the electropositive or electronegative character of the atoms involved.

Ionic bonding involves the complete transfer of one or more electrons from one atom to another. Covalent bonding involves the sharing of a pair 
of electrons between two atoms, and in metallic bonding the valency electrons are free to move throughout the whole crystal.



Reference-- consiceInorganic chemistry by JDLee

Page number  30-31

Cholesterol

Cholesterol is an organic molecule. It is a sterol or a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell membranes.

 Cholesterol also serves as a precursor for the biosynthesis of steroid hormones,and vitamin D. In vertebrates, hepatic cells typically produce the greatest amounts. It is absent among prokaryotes, although there are some exceptions, such as Mycoplasma, which require cholesterol for growth.
According to the lipid hypothesis, elevated levels of cholesterol in the blood lead to atherosclerosis which may increase the risk of heart attack, stroke, and peripheral vascular disease.


Reference 
https://en.m.wikipedia.org/wiki/Cholesterol

Vanadium

Vanadium, with chemical symbol V and atomic number 23, is a member of the d-block metals and belongs to group 5 of the periodic table of elements. Vanadium can be found in the earth’s crust in numerous minerals and is isolated from ores mostly as a by-product. Its main application is in the steel industry, where it is used as an alloy in combination with iron. Vanadium pentaoxide is also being used as a catalyst for the production of sulfuric acid. The metal vanadium has very similar properties to titanium. Therefore, it is not surprising that its metallocene, vanadium dichloride, was also subjected to research as a potential anticancer agent.


Reference -Wikipedia

Ionization energy

A small amount of energy is supplied to an atom, then an electron may  be promoted to a higher energy .level, but if the amount of. energy supplied 
is sufficiently large the electron may be completely removed. The energy required to remove the most loosely bound electron from an isolated 
gaseous atom is called the ionization energy. 
Ionization energies are determined from spectra and are measured in kJ mo1- 1. It is possible to remove more than one electron from most 
atoms. The first ionization energy is the energy required to remove the first electron and convert M to M+; the second ionization energy is the energy 
required to remove the second election arid convert M+ to M2+; the third ionization energy converts M2+ to M3+, and so on.

The factors that influence the ionization energy are: 
1. The size of the atom. 
2. The charge on th,e nucleus. 
3. How effectively the inner electron shells screen the nuclear charge. 
4. The type of electron involved (s. p, d or/).

Reference Inorganic chemistry by Huhee

Biology and toxicology of lanthanides

lanthanoids are used in the production of batteries, lasers and other technological devices. Some lanthanoids salts, such as the salts of lanthanum, cerium and gadolinium  are
increasingly used in a clinical setting, for example, as a phosphate binder in the treatment of renal osteodys- trophy or as MRI (magnetic resonance imaging) contrast agents. Lanthanoids (Ln) show a biological behaviour very similar to that of Ca2+, as they have similar ionic radii. Lanthanoids are mostly trivalent and therefore possess a higher charge than Ca2+. Lanthanoids display a high
binding affinity to calcium-binding sites in biological molecules and to water molecules. The coordination number for lanthanoids varies from 6 to 12. Mostly, eight or nine water molecules are coordinated to the lanthanoid ion. This is a significantly lower coordination number compared to that of calcium, which is 6.

Copper containing drug

Copper-containing drugs
Copper is a valuable metal and has been mined for more than 2000 years. It has had many uses throughout
history. Initially, copper was mainly used to make alloys such as brass and bronze, which are harder and
stronger than copper itself. Nowadays, copper is mainly used because it conducts heat and electricity  and it is corrosion-resistant.
Historically, copper was used for the treatment of a variety of diseases, including chronic ulcers, headaches,
ear infections, rheumatoid arthritis (RA), and so on. In 1832, copper workers were found to be immune to an
outbreak of cholera in Paris, which stimulated further research into the medicinal use of copper. Almost every
cell in the human body uses copper, as most contain copper-dependent enzymes. Unfortunately, excessive
amounts of copper are toxic for the human body, whereas low amounts of copper also lead to health problems,
manifested in Menkes disease.
Copper ions from food sources are processed by the liver, and transported and excreted in a safe manner.
Inorganic metallic copper from sources such as drinking water mainly enters the blood directly and can be
toxic as it can penetrate the blood–brain barrier. Typically, 50% of the daily copper intake is absorbed in the GI
tract and transported to the liver from where it is transported to the peripheral tissue bound to ceruloplasmin, a
copper-binding glycoprotein. A smaller amount of copper is also bound to albumin. Excess copper is mainly
excreted in bile into the gut and then the faeces.
Copper is an essential trace metal, and copper .

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