ALKALOID

An alkaloid is any of a class of nitrogen-containing natural product of plant origin that have an alkaline, or basic, chemical nature. Some alkaloid are simple, monocyclic (one-ring) amines (see cyclic compounds), but many are very complex, polycyclic amines.

Occurrence

More than 200 alkoloids are known. They are present in only about 10 to 15 % of all vascular plants. Often found in the dicotyledone group of the angiosperm, or flowering plants, they seldom occur in monocotyledone or in other plant groups, such as gymnosperms. The most actively growing parts of such plants usually contain the highest percentage of the compounds. Among the more familiar alkaloid are aconitine (From monkshood), atropine (from belladonna), codeine, morphine, and papaverine (from opium poppy), nicotine (From tobacco) quinidine and quinine (from cinchona bark), solanine (from potate and tomato), ricinine (from castor bean) and strychnine and brucine (from Nux fomica).

Function.

Why certain plants contain alkaloids remains a mystery, although a number of theories have been formulated; that alkaloids are by-product of plant metabolism ; that they are mean of defense of plants against animal and insect attack; or that they are reservoirs for protein synthesis, regulators of growth and reproduction, or detoxifying agents.

Uses.

Alkaloids are most widely employed for physiological effects, which range from poisonous to sedative to hallucicinogenic. Socrates was killed by the alkaloid coniine, from poison hemlock. The poisons aconitine and strychnine were once used medically but are now generally considered too hazardous .

Morphine and codeine are analgesics, atropine is a pupil dilator, and scopolamine (from henbane) is a sedative. Lysergic acid, an ergot alkaloid, is a starting material in synthesizing lysergic acid diethylamide, a powerful hallucinogen. Another hallucinogenic alkaloid is mescaline (From peyote).

Chemical Ionic Bond

A chemical bond is formed when separate atoms are brought together and the sharing or transfer of electrons occurs. Chemical bonds can be weak or strong, depending on the nature of the interactions. The chemical bond itself happen cause by a chemical reaction between atom. The physical and chemical properties of most compounds are due, in large part, to these bonding forces.

Ionic Bonding

When two or more atoms combine, a competition for the available electrons can occur that leads to a nearly complete transfer of one or more electrons. The resulting formation of an ionic bond involves the removal of an electron from one atom, a process known as ionization potential of the atom. The other atom gains an electron, and the measure of its ability to do so is known as its electron affinity. An ionic bond result from the strong electrostatic forces of attraction between the negatively charged anions and positively charged cations. When atoms of sodium and chlorine are brought together, for example, tablet salt (NaCl) is formed; a more proper representation might be Na⁺Cl^-.

Ionic bonding is common in inorganic compounds such as salt, where the charges are easily accommodates on relatively small ions. In more complex solid the ions form three dimensional arrays in which a basic framework is repeated to generate the observed structures so obvious in crystals. A single anion may shared by several adjacent cations, so that the network of packing leads to very simple lattice structures. Because the forces are relatively strong, ionic solids tend to be strong materials, to have definite patterns of cleavage, and to have melting points.

The formation of an ionic bond is the result of the competition for available electrons. A useful measure of this property is known as the electronegativity of an atom. In general, a more electronegative element will take a large share of any bonding electrons when forming a chemical bond. If a great disparity exist between the electronegativities of the atoms in a particular compound, the uneven sharing will likely result in a complete transfer of one or more electrons and the formation of an ionic bond. In laboratory this reaction can try by using of many chemical tools.

Chemical Reaction Rate

From an engineering viewpoint, reaction kinetics has these principal functions:
Establishing the chemical mechanism of a reaction obtaining experimental rate data
Correlating rate data by equations or other means; Designing suitable reactors, Specifying operating conditions, control methods, and auxiliary equipment to meet the technological and economic needs of the reaction process.

Reactions can be classified in several ways. On the basis of mechanism they may be:
1. Irreversible
2. Reversible
3. Simultaneous
4. Consecutive

A further classification from the point of view of mechanism is with respect to the number of molecules participating in the reaction, the molecularity:
1. Unimolecular
2. Bimolecular and higher

Related to the preceding is the classification with respect to order. In the power law rate equation r = k(Ca)p. (Cb)q, the exponent to which any particular reactant concentration is raised is called the order p or q with respect to that substance, and the sum of the exponents p + q is the order of the reaction. At times the order is identical with the molecular, but there are many reactions with experimental orders of zero or fractions or negative numbers. Complex reactions may not conform to any power law. Thus, there are reactions of:

1. Integral order
2. Nonintegral order
3. Non–power law; for instance, hyperbolic

With respect to thermal conditions, the principal types are:
1. Isothermal at constant volume
2. Isothermal at constant pressure
3. Adiabatic
4. Temperature regulated by heat transfer

According to the phases involved, reactions are:
1. Homogeneous, gaseous, liquid or solid
2. Heterogeneous:

• Controlled by diffusive mass transfer
• Controlled by chemical factors

A major distinction is between reactions that are:
1. Uncatalyzed
2. Catalyzed with homogeneous or solid catalysts

Equipment is also a basis for differentiation, namely:
1. Stirred tanks, single or in series
2. Tubular reactors, single or in parallel
3. Reactors filled with solid particles, inert or catalytic:

• Fixed bed
• Moving bed
• Fluidized bed, stable or entrained

Finally, there are the operating modes:
1. Batch
2. Continuous flow
3. Semibatch or semiflow

Clearly, these groupings are not mutually exclusive. The chief distinctions are between homogeneous and heterogeneous reactions and between batch and flow reactions. These distinctions most influence the choice of equipment, operating conditions, and methods of design.

Tools of Chemistry

Chemistry is a precise laboratory science, and the equipment of a chemical laboratory is usually involved with measurement. Balances are used to measure mass, pipettes and burettes to measure volume, and thermometers to measure temperature changes. Advances in electronics and computer technology have enabled the development of scientific instruments that determine the chemical properties, structure, and content of substances accurately and precisely.

Most modern chemical instrumentation has three primary components; a source of energy, a sample compartment within which a substance is subjected to the energy, and some sort of detector to determine the effect of the energy on the sample. An X-ray diffractometer, for instance, enables the chemist to determine the arrangement of atoms, ions, and molecules that constitute crystals by means of scattering X-rays. Most modern laboratories contain ultraviolet, visible, and infrared spectrophotometers, which use light of various wavelengths on gaseous or liquid samples. By such a mean the chemist can determine the electron configuration and the arrangement of atoms in molecules. A nuclear magnetic resonance spectrometer subject a sample in a strong magnetic field to radio frequency radiation. (Magnetic Resonance Spectroscopy under spectroscopy). Other instruments include mass spectrometers, which use electrons as an energy source, and differential thermal analyzers, which use heat.

An entirely different class of instruments are those which use chromatography to separate complex mixtures into their components. Chemists are also using extremely short pulses of laser light to investigate the atomic and molecular processes taking place in chemical reactions at the microsecond level. These and other devices generate so much data that chemists frequently must use computers to help analyze the results.