ORIGIN OF LIFE

We salute the spirit of inquisitiveness of man, which gave birth to the discipline of science. The same spirit of questioning also led man to often wonder how life or the first organism came into existence. This quest led him to find answers to how, when and where life originated.

        For centuries, it was believed that life originated de novo. In addition several other scientific and non-scientific theories were also put forward.

Some of them are:

(i) Theory of special creation: (or Biblical Theory) – It was put forward by Father Suarez, a

Spanish Monk.

(ii) Theory of spontaneous generation (or Abiogenesis): (Gr, ‘a’ – absence, “bios” – life,

“genesis” – origin) or origin from non-living matter.

(iii) Theory of Panspermia or Cosmozoic Theory: According to this theory, life came from some

other planet. It’s still believed to be true by some scientists like Wikramsinghe, Francis Crick

and Leslie Orgel.

(iv) Biogenesis: Francesco Redi and Louis Pasteur laid the foundation for the Theory of

Biogenesis, which propounded that living organisms arise from pre-existing ones and not from

non-living matter.

(v) Chemosynthetic Theory or Chemogeny: This theory proposed that first form of life originated

from inorganic chemical elements by formative action of some external physical force viz.

lightening or cosmic rays, etc. It was put forward by A.I. Oparin and J.B.S. Haldane and the

experimental evidence was provided by Stanley Millar & Harold Urey. For example, Mighi

meteorite in Ukraine and analysis of another meteorite content viz. Murchison, Victoria in

Australia by space biologists also revealed similar composition indicating that similar processes

are still occurring elsewhere in space. However, in this case, although the presence of amino

acids and polynucleotide are similar to DNA, these are of chemical origin and therefore have

identical strands instead of complementary strands.

 SAVIOURS OF BIODIVERSITY

Environmental pollution is causing a lot of distress not only to humans but also to animals, driving many animal species to endangerment and even extinction. Methods are being devised to save this precious biodiversity.

GREEN CHEMISTRY

Green Chemistry is a specific type of prevention of pollution. It involves the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances. It has been applied to a wide range of industrial and consumer goods, including paints, dyes, fertilizers, pesticides, plastics, medicines, electronics, dry cleaning, energy generation and water purification.

          Hazard is simply another property of a chemical substance. As properties of chemicals are because of their specific molecular structure, they can be modified by changing that structure. Various types of hazards that can be handled by Green Chemistry include physical hazards (being explosive or inflammable), toxicity (being carcinogenic or cancer causing, or lethal) or global hazards (climate change or stratospheric ozone depletion). Like a substance can be designed to have a low melting point or green colour, it can also be designed to be non-toxic.

Tools used in Green Chemistry

By choosing an alternate synthetic design, we focus not on the ultimate molecule but on the synthetic pathway used to create it. Modification of the synthesis can lead to the same final product, yet reduce or eliminate toxic starting materials, by-products and wastes. The following tools can be used to modify a synthesis:

1. Alternative Feedstocks (Starting Materials) The selection of a feedstock, i.e., the starting material used for the manufacture of a product, determines what hazards will be faced while handling this substance. A feedstock must be evaluated to determine whether it possesses chronic toxicity, carcinogenicity, ecotoxicity, etc. Currently, most of the organic chemicals are made from petroleum feedstocks. Petroleum undergoes oxidation during conversion to useful organic chemicals. This oxidation step is one of the most environmentally polluting steps of chemical synthesis. It has contributed to the risk to human health and the environment, mainly through the use of heavy metals, like chromium, as oxidising agents. It is, therefore, important to reduce the use of petroleum-based products. Agricultural and biological feedstocks are excellent alternative starting materials. They are already highly oxygenated. Therefore, their use eliminates the need for the polluting oxygenation step. A raw material or feedstock should be renewable rather than depleting. Petroleum and other fossil-fuel based feedstocks are depleting and feedstocks based on biomass and agricultural wastes are renewable. At present a host of agricultural products like soy, potatoes, corn and molasses are being transformed through a variety of processes into consumer products like textiles, nylon etc.

2. Alternative Reagents Alternative reagents are being increasingly used to carry out synthesis. For example, heavy metals, used in petroleum oxidation processes, are quite toxic and carcinogenic. They are being replaced by light to carry out the required transformation.

3. Alternative Solvents Many solvents commonly used in synthesis are volatile organic compounds (VOCs) that cause smog when released in air. Individuals with respiratory problems suffer great distress because of this environmental effect. Solvents like methylene chloride, chloroform, carbon tetrachloride, benzene, etc. have been identified as suspected human carcinogens. The uses of chlorofluorocarbons (CFCs) range from cleaning solvent, propellant, blowing agent for moulded plastic foams, to refrigeration. CFCs have very low direct toxicity to humans and wildlife, and are both nonflammable and non-explosive. However, CFCs are known culprits of ozone layer depletion. Some of the alternatives to these organic solvents include the use of supercritical or dense phase fluids, such as supercritical carbon dioxide. This system is not harmful from human health and environmental point of view.

            Supercritical fluids are obtained by subjecting small molecules, like carbon dioxide, to the appropriate temperature and pressure to attain the critical point at which the molecules possess the character of a fluid which is a cross between a liquid and a gas. The properties of this fluid (solvent) can be adjusted by adjusting the parameters of temperature and pressure. Supercritical solvent systems are now replacing a variety of other traditional organic solvents.

                Now methods are being developed where the reagents and feedstocks serve as the solvent as well. In some cases the reagents and feedstocks are made to react in the molten state to ensure proper mixing and optimal reaction conditions, or on solid surfaces such as specialised clays. Thus, ways are being designed to carry out reactions in solventless systems. If a solvent is essential for a particular synthesis, then the most innocuous one must be selected. Water is the safest solvent possible. A major problem with many solvents in relation to human health and the environment is their ability to volatilise. The use of immobilised solvents may serve as a solution. Immobilisation can be done by binding the solvent molecule to a solid support (polymer), so that it becomes non-volatile. Some polymers are beingdeveloped which have solvent properties and are not hazardous.

4. Alternative Product (Target Molecule) While designing safer chemicals (target molecules), the object is to maximise the functional benefits of a molecule and minimise or eliminate its toxicity or other hazards. This is done by identifying the part or parts of the molecule that produce toxic effects, and also those that are responsible for its desired function. The part related to the toxic effect can be avoided or suitably changed to reduce or eliminate the toxic effect.

        Another way to reduce hazardous effects of a substance is to minimize its bioavailability. If a toxic substance is not able to reach its target organ (e.g. heart, lungs, liver), where it can manifest its toxicity, then it is rendered innocuous for all purposes. By changing the physical and chemical properties of a molecule, like solubility in water and polarity, the absorption of molecules through biological membranes and tissues can be made difficult or impossible. Elimination of absorption and bioavailability leads to reduction in toxicity.

5. Green Analytical Chemistry The detection, measurement and monitoring of chemicals in the environment is done through Analytical Chemistry. Instead of determining environmental problems after they occur, Green Chemistry seeks to prevent the formation of toxic substances. Even minute amounts of toxic substances are detected with the help of sensors and process controls are adjusted to minimise or stop its formation.

6. Alternative Catalysts Catalysis has increased the level of efficiency of chemical synthesis, and has also brought about environmental benefits. Use of new catalysts has eliminated the need for large quantities of reagents that would have been otherwise required to carry out those syntheses. Such large amounts of regents would have increased the bulk of the waste stream.

7. Minimal Energy Requirements Energy requirements of a synthetic procedure should be minimised because energy generation and consumption bring about a major environmental effect. The advantage of using a catalyst is that it lowers the energy of activation needed to accomplish a reaction, and therefore, minimises the thermal energy required for the transformation.

        Microwave energy is now being utilised in order to effect chemical reactions rapidly, and generally in the solid state. This eliminates prolonged heating necessary to carry out a reaction. Through the use of ultrasonic energy, the conditions of the reactants are considerably changed to promote a chemical transformation.

8. Alternative Methodology Unnecessary use of blocking groups, protecting groups, additional functional groups should be avoided, because this requires use of materials (often hazardous) to make the substance and generates a waste in the regeneration of the original substance.

        Some methods make use of toxic chemicals such as cyanide or chlorine. In addition, these methods at times generate large quantities of hazardous wastes. For example, the pulp and paper industry uses chlorine compounds in processes that generate toxic chlorinated organic waste. Green chemists have developed a new technology that converts wood pulp into paper using oxygen, water, and polyoxometalate salts. Water and carbon dioxide are the only by-products. Substances used in a chemical process should be chosen so as to minimise the chances of chemical accidents, including explosions and fires.

9. Designing for Biodegradability Chemical products should be designed so that after their function is over they do not persist in the environment and do not accumulate in plant or animal systems, but break down into innocuous degradation products. Plastics are known for their durability and long life. That is why they cause environmental concerns in oceans and other aquatic media. Pesticides tend to bioaccumulate in many plant and animal species, thereby causing damage to the species itself, or, to humans if consumed. These products should be designed so that they do not remain in their initial state in the environment after their useful life is over. Their degradation products also should not be toxic or hazardous.

10. Green Chemistry Evaluation Whether dealing with a reagent, solvent, product, starting material or the process itself, the following essential characteristics need to be known to conduct a Green Chemistry evaluation:

(i) Toxicity to humans

(ii) Toxicity to wildlife

(iii) Effects on the local environment

(iv) Global environmental effects 

 ENVIRONMENTAL POLLUTION

Pollution is the introduction of contaminants into the environment that cause harm or discomfort to humans or other living organisms, or that damage the environment. India has been ranked as the seventh most environmentally hazardous country in the world. Brazil is the worst, United States is second worst and China is third. Singapore has been found to be the best.

There are three major types of environmental pollution:

Air Pollution

Water Pollution

Soil Pollution

Air Pollution

Some of the most important air pollutants are Sulphur dioxide, nitrogen dioxide, carbon monoxide, ozone, volatile organic compounds (VOCs) and airborne particles. Radioactive pollutants are the most destructive ones specially when produced by nuclear explosions. Carbon dioxide and water vapour present in the atmosphere, strongly absorb a large fraction of the earth’s emitted radiation. This absorbed radiation is partly re-emitted to the earth’s surface. The net result is that the earth’  surface gets heated up by a phenomenon called the Greenhouse Effect.

Deforestation and combustion of fossil fuels (oil, gas, coal) have a cumulative effect on the net increase in carbon dioxide content. Forests are the areas where a great deal of photosynthesis occurs, which helps in maintaining a balance in the atmospheric carbon dioxide level.

Trees and animals contribute large quantities of hydrocarbons (mainly methane) to the atmosphere. Harmful effects of hydrocarbon pollution are due to the photochemical reactions in which they are involved. Large quantities of automobile exhausts in the atmosphere exposed to intense sunlight leads to the formation of photochemical oxidants. This gives rise to photochemical smog (Characterised by brown, hazy fumes) which irritates the eyes and lungs, leads to the cracking of rubber and extensive damage of plant life. Smog is a combination of smoke and fog. Smog containing high levels of sulphur dioxide is called reducing smog. Peroxyacyl nitrate (PAN) is a potent eye irritant found in photochemical smog.

Oxides of nitrogen and sulphur entering the atmosphere are converted into nitric acid and sulphuric acid respectively. They combine with hydrochloric acid from HCl emission to generate acidic precipitation known as acid rain. Acid rain is now a major pollution problem in some areas. It causes extensive damage to buildings and sculptural materials of marble, limestone, slate, mortar, etc. It is harmful for aquatic plants and animals, and causes soil acidification.

Small solid particles and liquid droplets are collectively called particulates. These are present in large amounts in the atmosphere and sometimes pose a serious air-pollution problem. Examples of processes which inject particulate matter into the atmosphere: volcanic eruptions, blowing of soil and dust by wind, formation of fly ash from power plants, smelters and mining operations, and smoke from incomplete combustion processes. Airborne asbestos (a fibrous silicate mineral) and toxic metals like beryllium are carcinogenic. Fine particles (less than 3 microns) are the worst causes of lung damage. Coal miners’ black-lung disease, and asbestos workers’ pulmonary fibrosis are associated with the accumulation of such small particles. Very fine particulate matter, which is less than 2.5 microns in size, is called PM 2.5 and is known to cause diabetes and cardiovascular diseases. 

Air in Delhi is choking with pollutant PM 2.5. Any kind of combustion, especially of vehicular origin, contains this particle. If PM 2.5 is not regulated it will increase the number of patients suffering from asthma and lung cancer. It brings about lead deposition in the lungs. Particulates accelerate corrosion of metals and cause damage to buildings, sculptures, paints, etc. Particulates in the atmosphere reduce visibility and influence the climate through the formation of clouds, rain and snow.

Burning CNG has the highest rates of potentially hazardous carbonyl emissions. Retrofitted CNG car engines emit 30% more methane than original CNG engines. Almost all CNG car engines in India are retrofitted. Coal pollution kills more than 300,000 people every year. Nitrogen and sulphur oxides emitted by aircrafts, at an altitude of 35,000 ft, combine with other gases in the atmosphere to create harmful pollutants.

Vehicle emission is responsible for 70% of the air pollution in India. Bangalore is called the asthma capital of India. The levels of suspended particulate matter are above permissible limits in Mumbai. 

Bhopal gas tragedy was the greatest industrial disaster in the world that took place at a Union Carbide pesticide plant in the Indian city of Bhopal, Madhya Pradesh. On 3rd December, 1984 (midnight), the plant accidentally released methyl isocyanate (MIC) gas. Within a week about 10,000 people died, 1,000 became blind while more than 1 lakh continued to suffer from various disorders. This was the deadliest man made environmental disaster in history.

On 14 July 2010, chlorine gas leaked from the Sewri industrial area on land owned by the Mumbai Port Trust and approximately 76 people were treated in hospital. Rice crop yields in Southern India are decreasing as brown clouds are increasingly blocking the sunlight. The brilliant white of the famous Taj Mahal is slowly fading to a sickly yellow. The Supreme Court ordered the closure of more than 200 factories to save the Taj Mahal from being polluted by fumes.

There has been a drastic fall in the number of butterflies in the Western Himalayas, famous for their biodiversity. In areas of Himachal Pradesh, and Jammu and Kashmir, the population of 50% of the 288 species has declined more than half in just 10 years. Over 700 million people in India suffer from high levels of indoor air pollution as 75% homes use biomass fuel like wood, crop residue and dung cakes.

Excessive ultraviolet radiation coming from the sun through the ozone layer in the upper atmosphere, which is eroded by some air pollutants, may cause skin cancer in wildlife and damage to trees and plants. Ozone in the lower atmosphere may damage lung tissues of animals, and adversely affect plant respiration and photosynthesis.

Water Pollution

Water pollutants include insecticides and herbicides, food processing waste, pollutants from livestock operations, volatile organic compounds (VOCs), heavy metals, chemical waste, disease causing agents, sewage, Detergents, oil, sediments and radioactive materials. Beryllium, boron, cadmium, chromium, cyanide, lead, mercury, selenium, silver, sulphide, vanadium and zinc are some of the toxic water pollutants.

Waterborne diseases caused by polluted drinking water are typhoid, amoebiasis, giardiasis, ascariasis, hookworm, hepatitis, encephalitis, gastroenteritis and Diarrhoea. Conditions related to water polluted by chemicals are cancer, hormonal problems, and damage to liver, kidney, nervous system and DNA. Water polluted by mercury can lead to Parkinson’s disease, Alzheimer’s disease, heart disease, etc.

According to a United Nations report released on 22 March 2010 on World Water Day, contaminated and polluted water kills more people than all forms of violence including wars. 80% of urban waste in India ends up in rivers.

The river Ganga is dying slowly due to unchecked pollution. Samples taken from the river Ganga near Varanasi showed that levels of fecal coliform, a dangerous bacterium that comes from untreated sewage, were some 3,000 per cent higher than what is considered safe for bathing.

Chemical contamination in water can cause declines in frog biodiversity. Persistent organic pollutants (POPs) may cause declines, deformities and death of fish life. Plants and animals may be killed by too much sodium chloride (ordinary salt) in water. Plants may be killed by herbicides in water. Water pollution may disrupt photosynthesis in aquatic plants.

Soil Pollution

Soil pollutants include hydrocarbons, solvents and heavy metals. Soi contamination causes cancer. Lead in soil damages the brain, and mercury leads to kidney damage. It causes headache, nausea, fatigue, eye irritation, skin rashes, and depression of the central nervous system. It may alter plant metabolism and reduce crop yields. It can alter the metabolism of microorganisms. Trees and plants may absorb soil contaminants and pass them up the food chain. This may lead to increased mortality rates and even animal extinction.

Fossil Fuel Pollution

Fossil fuels (oil, gas, coal) are used in vehicles, power-generating plants, and in the manufacture of products like plastics, solvents, detergents, lubricating oils, etc. Fossil fuels contribute to soil contamination and water pollution.

When oil is transported by pipelines, an oil leak from the pipeline may occur and pollute the soil, and subsequently the groundwater. When oil is transported by tankers in an ocean, an oil spill may occur and pollute ocean water. Transport and power-generating plants are the biggest sources of fossil fuel pollution. Fossil fuel combustion is also a major source of carbon dioxide emissions (air pollution) and perhaps the most important cause of global warming.

 CHEMICAL THREATS TO BIODIVERSITY

Chemistry has brought about a medical revolution which resulted in the average life expectancy rising from 47 in 1900 to 75 in the 1990s. The explosive expansion of world’s food supply has been because of development of chemicals that protect crops and enhance growth. In almost every area (food, clothing, shelter, transportation, communication, etc.) chemistry has brought about an improvement in the quality of life of people.

The Toxics Release Inventory (TRI), USA, established under the Emergency Planning and Community Right-to-Know Act, tracks the release of chemicals by different sectors of industry. Of the top ten industrial sectors tracked by the TRI, the chemical industry releases a greater amount of waste to the environment than the other nine industrial sectors combined.

 CHEMICAL TOXICOLOGY

There are various chemicals in the environment, some of which are toxic.These toxic chemicals are released by industries into air, water and soil. They upset the complex system of chemical reactions occurring in the human body. They can cause discomfort, illness, disability or even death. Chemical Toxicology is the science of the study of toxic chemicals and their modes of action.

Toxic Chemicals in Air Some of the extremely hazardous substances in the atmosphere are acrylonitrile, arsenic, asbestos, benzene, beryllium, cadmium, chlorinated solvents, chlorofluorocarbons, chromates, coke oven emissions, ethylene dibromide, ethylene oxide, lead, mercury, ozone, sulphur dioxide, vinyl chloride and toxic waste disposal emissions.  Toxic Chemicals in Water ,The toxic elements found in natural and waste waters are arsenic, cadmium, beryllium, boron, chromium, copper, fluorine, lead, manganese, mercury, molybdenum, selenium and zinc. The water bodies contain pesticides, mainly from the drainage of agricultural land.

Effect of Toxic Chemicals on Enzymes

Toxic chemicals attack enzymes, inhibiting their essential function. Heavy metal ions like Hg2+, Pb2+ and Cd2+ act as effective enzyme inhibitors.

Classification of Toxic Substances

1. Corrosive Poisons Corrosive poisons are toxic substances which destroy tissues, e.g., strong acids and alkalies, and many oxidants which can destroy tissues. Concentrated mineral acids such as sulphuric acid and bases like sodium hydroxide attack cellular structures. The cell dies because the proteins are hydrolysed by the acid or the base

2. Metabolic Poisons Metabolic poisons cause illness or death by interfering with a vital biochemical mechanism to such an extent that it ceases to function or does not function efficiently.

3. Neurotoxins Some metabolic poisons limit their action to the nervous system. These include poisons such as strychnine and curare. Neurotoxins act at the point where two nerve fibres come together (called a synapse).

Neurotoxins such as atropine and curare occupy the receptor sites on nerve endings of organs that are normally occupied by the impulse carrying acetylcholine. When atropine or curare occupies the receptor site, no stimulus is transmitted to the organ. Neurotoxins of this type are useful in medicines. For example, atropine is used to dilate the pupil of the eye to facilitate examination of its interior. When applied to the skin, atropine salts relieve pain by deactivating sensory nerve endings on the skin. Curare is used as a muscle relaxant. Nicotine is a natural compound that blocks receptor sites as is done by atropine and curare. This powerful poison causes stimulation and then depression of the central nervous system. Nicotine is present in tobacco and insecticides

4. Mutagens Mutagens are chemicals that can change the genes and chromosomes (hereditary pattern) to cause abnormalities in the offspring. They alter the structures of DNA and RNA, which compose the genes that transmit the traits of parent to offspring. Nitrous acid is a potent mutagen in bacteria, viruses, moulds and other organisms. It reacts with nitrogenous bases of DNA to produce new compounds. The result is an alteration in the genetic coding of DNA, so that a different protein is formed. Sodium nitrite is used as a preservative, colour enhancer or colour fixative in meat and fish products. Sodium nitrite is converted to nitrous acid by hydrochloric acid in the human stomach. Some examples of mutagens: Aflatoxin (from mould), Benzo (α) pyrene (from cigarette and coal smoke), Caffeine, Captan (a fungicide), Chloroprene, Dimethyl sulphate (used for methylation), LSD (lysergic acid diethylamide), Maleic hydrazide (plant growth inhibitor), Mustard gas (dichlorodiethyl sulphide), Ozone, solvents in glue (like toluene, acetone, cyclohexane, hexane and ethyl acetate), and TEM (triethylene melamine, an anticancer drug).

5. Teratogens The chemicals which affect reproduction are called teratogens. The study of birth defects produced by chemical agents is called Teratology. There are three known classes of teratogens: radiation, viral agents and chemical substances. Any chemical that can cross the placenta is a potential teratogen. Smoking a cigarette results in higher-than-normal blood levels of such substances as carbon monoxide, hydrogen cyanide, cadmium, nicotine and benzo (α) pyrene. Many of these substances are present in polluted air as well. Other examples of teratogens: Arsenic, Cobalt, Gallium, Lead, Lithium, Mercury,Thallium, Zinc, Caffeine, DES (diethyl stilbestrol) and PCBs (polychlorinated biphenyls).

6. Carcinogens Carcinogens are chemicals that cause cancer in animals and humans. An abnormal growth is classified as cancerous or malignant when examination shows it is invading neighbouring tissue. A growth is said to be benign if it is localised at its original site. Some compounds cause cancer at the point of contact. Other compounds cause cancer in an area remote from the point of contact. The liver, the site at which most toxic chemicals are removed from the blood, is particularly susceptible to such compounds.

7. Hallucinogens Hallucinogens can produce temporary changes in perception, thought and mood. They destroy one’s sense of judgement. LSD has been linked with birth defects.

8. Alcohols Methyl alcohol is highly poisonous and is a cumulative poison in human beings. It has a toxic effect on the optic nerve and large doses can cause blindness. In the body, it gets oxidised first to formaldehyde and then to formic acid, which is eliminated in the urine. The toxic effect on the optic nerve is caused by the oxidative products.

50 Expected Questions on Chemistry| Chemistry Questions and Answers