Chemical Engineering: February 2016

Monday, 29 February 2016

Intramolecular Catalysis

Intramolecular Catalysis:

The acceleration of a chemical transformation at one site of a MOLECULAR ENTITY through the involvement of another FUNCTIONAL (“catalytic”) GROUP in the same molecular
entity, without that group appearing to have undergone change in the reaction product. The use of the term should be restricted to cases for which analogous INTERMOLECULAR CATALYSIS by CHEMICAL SPECIES bearing that catalytic group is observable. Intramolecular catalysis can be detected and expressed in quantitative form by a comparison of the reaction rate with
that of a comparable model compound in which the catalytic group is absent, or by measurement of the EFFECTIVE MOLARITY of the catalytic group.

Insulin:

A protein hormone produced in the pancreas by beta cells, located in the islets of Langerhans, that stimulates cellular utilization of glucose by body cells by converting glucose and other carbohydrates to energy, and that helps control blood sugar levels by acting antagonistically with glucagons, the chief source of stored fuel in the liver. It is released by various signals that are sensitive to the intake and digestion of food. It also acts as an important regulator of protein and lipid metabolism. Insulin is used as a drug
to control insulin-dependent diabetes mellitus, a disorder that is caused by the insufficient production of insulin. Without insulin, cells do not absorb glucose. Diabetic individuals may have type I diabetes (juvenile), comprising about 10 percent of the population,
or type II diabetes (adult). Presently some 16 million Americans have diabetes, with 1,700 new cases being diagnosed daily. Diabetes has been linked to the development of a variety of diseases, including heart disease, stroke, peripheral vascular disease, and neurological disorders.

Inductomeric effect:

A molecular polarizability effect occurring by the inductive mechanism of electron displacement. The consideration of such an effect and the descriptive term have been regarded as obsolescent or even obsolete, but in recent years theoretical approaches have reintroduced substituent polarizability as a factor governing reactivity, etc., and its parameterization has been proposed.

Imbalance

Imbalance:

The situation in which REACTION parameters
that characterize different bond-forming or
bond-breaking processes in the same reaction have
developed to different extents as the TRANSITION
STATE is approached along some arbitrarily defined
reaction coordinate. For example, in the nitroalkane
anomaly, the Bronstedβ exponent for proton removal
is smaller than the Bronstedα for the nitroalkane
because of imbalance between the amount of bond
breaking and resonance delocalization in the transition
state. Imbalance is common in elimination, addition,
and other complex reactions that involve proton
(hydron) transfer.

Ideal Gas:

A hypothetical gas that appears to obey perfectly the ideal gas law as the pressure nears zero; a gas characterized by a complete absence of cohesive forces between molecules; no gas has met this requirement.

Gibbs energy diagram:

A diagram showing the relative standard Gibbs energies of reactants, TRANSITION STATEs, reaction INTERMEDIATEs, and products in the same sequence as they occur in a CHEMICAL REACTION. These points are often connected by a smooth curve (a “Gibbs energy profile,” still commonly referred to as a
“free energy profile”), but experimental observation can provide information on relative standard Gibbs energies only at the maxima and minima and not at the configurations between them. The abscissa expresses the sequence of reactants, products, reaction intermediates, and transition states and is usually undefined or
only vaguely defined by the REACTION COORDINATE
(extent of bond breaking or bond making). In some adaptations, however, the abscissas are explicitly defined as BOND ORDERs, Bronsted exponents, etc. Contrary to statements in many textbooks, the highest point on a Gibbs energy diagram does not necessarily
correspond to the transition state of the RATE-LIMITING
STEP. For example, in a STEPWISE REACTION consisting
of two reaction steps
1. A + B C
2. C + D → E

Fractional Distillation:

Using a fractionating column DISTILLATION to separate a liquid mixture into component parts that have different boiling points. When a mixture of liquids is boiled, the vapor will be richer in the component with the lower boiling point, but it will

still be a mixture. By successive CONDENSATION and revaporization steps (usually in a column called a fractionating

column), the vapor becomes increasingly rich in the lower-boiling component and can eventually be collected in pure form.

Fermentation:

The anaerobic decomposition of complex organic substances by microorganisms such as bacteria, molds, or yeast (called ferments) on a fermentation substrate that produces simpler substances or
other desired effects, such as the yielding of ethanol and carbon dioxide from yeast for commercial purposes, the production of ATP and energy production, and the development of antibiotics and enzymes. Fermentation is used by microflora of the large intestine to break down indigestible carbohydrates. Large fermentors are used to culture microorganisms for the production of some commercially valuable products such as bread, beer, wine, and other beverages.

Faraday’s law:

of electrolysis Relates to the number of electrons required to discharge one mole of an element. One equivalent weight of a substance is produced at each electrode during the passage of 96,487 coulombs of charge through an electrolytic cell.

Fatty Acid:

Fatty acids are the components of two LIPID types mostly found in cells in the form of large lipids or small amounts in free form: storage fats and structural phospholipids. They consist of long hydrocarbon chains of varying length (from four to 24 carbon atoms), containing a terminal CARBONYL GROUP at one end, and they may be saturated (having only a single carbon-tocarbon
bond), or unsaturated (one or more double or triple carbon-to-carbon bonds). The number and location of double bonds also vary. More than 70 different kinds have been found in cells. Saturated fatty acids cause higher levels of blood CHOLESTEROL, since they have a regulating effect on its synthesis, but unsaturated
ones do not have that effect and nutritionally are promoted more. Some fatty acids are palmitic acid, palmitoleic acid, alpha-linolenic acid, eleostearic acid, linoleic acid, oleic acid, and elaidic acid. Three fatty acids linked to a glycerol molecule form FAT.

Evaporative Cooling:

Temperature reduction that occurs when water absorbs latent heat from the surrounding air as it evaporates; cooling of the skin from
the evaporation of sweat is evaporative cooling and is a process for the body to lose excess heat.

Eutrophication:

The accelerated loading or dumping of nutrients in a lake by natural or human-induced causes. Natural eutrophication will change the character of a lake very gradually, sometimes taking centuries, but human-induced or cultural eutrophication speeds
up the aging of a lake, changing its qualities quickly, often in a matter of years.

Ethylene:

(C2H4) A reactive chemical made from natural gas or crude oil components (occurs naturally in both petroleum and natural gas) that acts as a plant hormone. The only gaseous hormone, it is used for accelerating fruit ripening (bananas), maturing citrus fruit color, leaf abscission, aging, and increasing the growth rate of seedlings, vegetables, and fruit trees.

Entropy:

The amount of energy in a closed system that is not available for doing work; disorder and randomness in a system. The higher the entropy, the less energy is available for work. The second law of thermodynamics states that the entropy of the universe will
always increase.

Enzyme:

A macromolecule that functions as a BIOCATALYST by increasing the reaction rate, frequently containing or requiring one or more metal ions. In general, an enzyme catalyzes only one reaction type (reaction specificity) and operates on only a narrow range of SUBSTRATEs (substrate specificity). Substrate molecules
are attacked at the same site (regiospecificity), and only one, or preferentially one of the ENANTIOMERs of CHIRAL
substrate or of RACEMIC mixtures, is attacked (enantiospecificity).

Encounter Complex:

A COMPLEX of MOLECULAR ENTITIES produced at an ENCOUNTER-CONTROLLED RATE that occurs as an intermediate in a reaction MECHANISM. When the complex is formed from two molecular entities, it is called an encounter pair. A distinction between encounter pairs and (larger) encounter
complexes may be relevant in some cases, e.g., for mechanisms involving PRE-ASSOCIATION.

Electrophilicity

Electrophilicity:

(1) The property of being electrophilic. (See ELECTROPHILE.)
(2) The relative reactivity of an electrophilic reagent. (It is also sometimes referred to as “electrophilic power.”) Qualitatively, the concept is related to LEWIS ACIDITY. However, whereas Lewis acidity is measured by relative equilibrium constants, ELECTROPHILICITY is measured by relative RATE CONSTANTs for reactions of different electrophilic reagents toward a common SUBSTRATE (usually involving attacking a
carbon atom).

Electron-nuclear double resonance:

(ENDOR) A magnetic resonance spectroscopic technique for the
determination of HYPERFINE interactions between electrons
and nuclear spins. There are two principal techniques.
In continuous-wave ENDOR, the intensity of an ELECTRON PARAMAGNETIC RESONANCE (EPR) signal, partially saturated with microwave power, is measured as radio frequency is applied. In pulsed ENDOR, the radio frequency is applied as pulses, and the EPR signal is detected as a spin echo. In each case an enhancement
of the EPR signal is observed when the radio frequency is in resonance with the coupled nuclei.

Electronegativity:

Each kind of atom has a certain attraction for the electrons involved in a chemical bond. This attraction can be listed numerically on a scale of electronegativity. Since the element fluorine has the greatest attraction for electrons in bond-forming, it
has the highest value on the scale. Metals usually have a low electronegativity, while nonmetals usually have high electronegativity. When atoms react with one another, the atom with the higher electronegativity value will always pull the electrons away from the atom that has the lower electronegativity value.

Efficacy:

Describes the relative intensity with which AGONISTs vary in the response they produce, even when they occupy the same number of RECEPTORs with the same AFFINITY. Efficacy is not synonymous withINTRINSIC ACTIVITY.
Efficacy is the property that enables DRUGs to produce responses. It is convenient to differentiate the properties of drugs into two groups: those that cause them to associate with the receptors (affinity) and those that produce stimulus (efficacy). This term is often used to characterize the level of maximal responses induced
by agonists. In fact, not all agonists of a receptor are capable of inducing identical levels of maximal responses. Maximal response depends on the efficiency of receptor coupling, i.e., from the cascade of events that, from the binding of the drug to the receptor, leads to the observed biological effect.

Dynein:

A molecular motor, a complex believed to be made of 12 distinct protein parts, that performs basic transportation tasks critical to the cell. Converts chemical energy stored in an ATP (adenosine triphosphate) molecule into mechanical energy that moves material
through the cell along slender filaments called microtubules.
One of the most important functions occurs during cell division, when it helps move chromosomes into proper position. It also plays a part in the movement of eukaryotic flagella and cilia.
Molecular motors play a critical role in a host of cell functions such as membrane trafficking and cell movement during interphase, and for cell asymmetry development. During cell division, they are responsible for establishing the mitotic or meiotic spindle, as well
as segregating chromosomes and dividing the cell at cytokinesis. It is the last part of the mitotic cycle, during which the two daughter cells separate. Motors either move along actin tracks (members of the myosin superfamily) or microtubules (the dynein and kinesin
superfamilies). Based on the Greek dunamis, meaning power.

Diffraction:

The scattering of light from a regular array of points or lines that can produce a constructive or destructive interference. X-ray diffraction is a technique used for seeing the structures of crystalline solids. X rays of a single wavelength are directed at a crystal to obtain a diffraction pattern in which interatomic
spaces are then determined.

Dipole–Dipole Interaction

Dipole–Dipole Interaction:

Intermolecular or intramolecular interaction between molecules or groups having a permanent electric DIPOLE MOMENT. The
strength of the interaction depends on the distance and relative orientation of the dipoles. The term applies also to intramolecular interactions between bonds having permanent dipole moments.

Digestion:

The process by which living organisms break down ingested food in the alimentary tract into more easily absorbed and assimilated products using enzymes and other chemicals. Digestion can occur in
aerobic conditions, where waste is decomposed by microbial action in the presence of oxygen, or anaerobic conditions, where waste is decomposed under microbial action in the absence of oxygen. In anaerobic conditions such as in a large-animal facility (i.e., dairy
farm), the by-product, a biogas, a low-energy gas that is made with the combination of methane and carbon dioxide, can be used as an energy source. In analytical chemistry, the term digestion is used to describe the process of decomposing materials and bringing them
into solution by heating with a liquid reagent, usually an acid.

Depolarization:

A process where an electrical charge of a neuron becomes less negative as the MEMBRANE potential moves from resting potential (70 mV) toward 0 mV; a decrease in voltage. The loss of membrane polarity is caused by the inside of the cell membrane
becoming less negative in comparison with the outside. Depolarization is caused by an influx of Na+ions through voltage-gated Na+ channels in axons.

Chromatography

Chromatography:

A method of chemical analysis where compounds are separated by passing a mixture in a suitable carrier over an absorbent material. Compounds with different absorption coefficients move at
different rates and are separated.
See also GAS CHROMATOGRAPHY; HIGH-PERFORMANCE
LIQUID CHROMATOGRAPHY.

Cholesterol:

A soft, waxy, fat-soluble steroid formed by the liver and a natural component of fats in the bloodstream (as LIPOPROTEINs); the most common steroid in the human body and used by all cells in permeability of their membranes. It is used in the formation of many products such as bile acids, vitamin D, progesterone,
estrogens, and androgens. In relation to human health, there is “good,” high-density cholesterol (HDL), which protects the heart, and “bad,” low-density cholesterol (LDL), which causes heart disease and other problems.

Chemical Relaxation:

If the equilibrium mixture of a CHEMICAL REACTION is disturbed by a sudden change, especially of some external parameter (such as temperature, pressure, or electrical field strength), the system will readjust itself to a new position of the chemical equilibrium or return to the original position, if the
perturbation is temporary. The readjustment is known as chemical relaxation.
In many cases, and in particular when the displacement
from equilibrium is slight, the progress of the system toward equilibrium can be expressed as a first-order law
[Ct–(Ceq)2] = [(Ceq)1–(Ceq)2]e–t/τ

Celsius scale:

(centigrade scale) A temperature scale with the range denoted by °C, as seen in the above figure. The normal freezing point of water is 0°C, and the normal boiling point of water is 100°C. The scale was named after ANDERS CELSIUS, who proposed it in 1742
but designated the freezing point to be 100 and the boiling point to be 0 (reversed after his death).

Capillary Action:

The rising of a liquid up the inside of a small-bore tube or vertical space when adhesive forces (the attractive forces between the capillary material and the liquid) exceed cohesive forces (the attractive forces between the molecules of the liquid itself).

Cell

Cell:

The basic unit of life, capable of growing and multiplying. All living things are either single, independent cells or aggregates of cells. A cell is composed of cytoplasm and a nucleus and is surrounded by a membrane or wall. Cells can be categorized by the presence of specific cell surface markers called clusters of differentiation.

Catalyst:

A substance that participates in a particular CHEMICAL REACTION and thereby increases its rate, but without a net change in the amount of that substance in the system. At the molecular level, the catalyst is used and regenerated during each set of MICROSCOPIC CHEMICAL EVENTs leading from a MOLECULAR ENTITY of reactant to a molecular entity of product.

Carbon Dioxide:

(CO2) A colorless, odorless gas that makes up the fourth most-abundant gas in the atmosphere, used by plants in carbon fixation. Atmospheric CO2 has increased about 25 percent since the early
1800s due to burning of fossil fuels and deforestation.Increased amounts of CO2 in the atmosphere enhance the greenhouse effect by blocking heat from escaping into space, thus contributing to the warming of Earth’s lower atmosphere and having an effect on the world’s biota. This is a major issue currently being debated by
scientists around the world.

Boiling Point:

The temperature at which the vapor pressure of a liquid is equal to the external atmospheric pressure. A normal boiling point is considered to be the boiling point at normal atmospheric pressure (101.325 kPa).

Barometer:

An instrument that measures atmospheric pressure and was discovered by Evangelista Torricelli in 1643 in Florence.

Biotechnology

Biotechnology:

The industrial or commercial manipulation and use of living organisms or their components to improve human health and food production either on the molecular level (genetics, gene splicing, or
use of recombinant DNA) or in more visible areas such
as cattle breeding.

Biomass:

The dry weight of organic matter in unit area or volume, usually expressed as mass or weight, comprising a group of organisms in a particular habitat.Also refers to organic matter that is available on a
renewable basis, such as forests, agricultural crops,wood and wood wastes, animals, and plants, for example.

Biological Magnification:

The increase in the concentration of heavy metals (i.e., mercury) or organic contaminants (i.e., chlorinated hydrocarbons [CHCs])
in organisms as a result of their consumption within a food chain/web. Another term for this is BIOACCUMULATION. An excellent example is the process by which contaminants such as PCBs accumulate or magnify as they move up the food chain. For example, PCBs concentrate in tissue and internal organs, and as big fish eat little fish, they accumulate all the PCBs that have been eaten by everyone below them in the food chain.

DNA:

Strand with another pair of nucleotides. The bases are one of five compounds—adenine, guanine, cytosine, thymine, and uracil—that form the genetic code in DNA and RNA.

Bacteria:

One of two prokaryotic (no nucleus) domains, the other being the ARCHAEA. Bacteria are microscopic, simple, single-cell organisms. Some bacteria are harmless or, often, are beneficial to human beings. Others are pathogenic, causing disease and even
death. All play a major role in the cycling of nutrients in ecosystems via AEROBIC and ANAEROBIC decomposition (saprophytic). Some species form symbiotic relationships with other organisms, such as legumes, and help them survive in the environment by fixing atmospheric nitrogen. Many different species exist as single
cells or colonies, and they fall into four shapes based on the shape of their rigid cell wall: coccal (spherical), bacillary (rod-shaped), spirochetal (spiral/helical or corkscrew), and vibro (comma-shaped). Bacteria are also classified on the basis of oxygen requirement (aerobic vs. anaerobic).

Atomic Number:

The atomic number is equal to the number of positively charged protons in an atom’s nucleus and determines which element an atom is. The atomic number is unique for each element and is designated by a subscript to the left of the elemental symbol.
The atomic number for hydrogen is 1; it has one proton.
Elements are substances made up of atoms with
the same atomic number. Most of the elements are metals
(75 percent), and the others are nonmetals.

Atomic Mass Unit

(amu) One-twelfth of a mass of an atom of the carbon-12 (12C) isotope; a unit used for stating atomic and formula weights; also called a dalton.

Anabolism:

The processes of METABOLISM that result
in the synthesis of cellular components from precursors
of low molecular weight.

AIDS

(acquired immunodeficiency syndrome) AIDS is

the name given to the late stages of HIV (human

immunodeficiency virus) infection, a disease discovered

and discussed in 1981 in Los Angeles, California. By

1983 the retrovirus responsible for HIV was first

described, and since then millions of adults and children

worldwide have died from contracting the disease. It is

thought to have originated in central Africa from monkeys

or developed from contaminated vaccines used in

the world’s first mass immunization for polio.

Abstraction Defination

Abstraction
A CHEMICAL REACTION or TRANSFORMATION,
the main feature of which is the bimolecular
removal of an atom (neutral or charged) from a
MOLECULAR ENTITY. For example: proton abstraction
from acetone
CH3COCH3 + (i-C3H7)2N– →
(CH3COCH2)– + (i-C3H7)2NH
hydrogen abstraction from methane
CH4 + Cl. → H3C. + HCl