Catalysis [PDF]

Zitiervorschau

CATALYSIS AZUELO♫ FERRER ☼ MEDIANA ♦

CATALYSIS The

phenomenon in which a small amount of substance, called a “catalyst” affects the rate of chemical reaction without itself being affected.

CATALYSIS Many

everyday products depend on catalysts, thus, playing a key role in our lives; indeed, life would not be possible without them.

CATALYSIS Industrial

catalysis has been responsible for the vast growth of chemicals manufacture and petroleum refining worldwide.

HISTORY  The

first period of catalysis dates back to the dawn of civilization, at a date lost in time when mankind began to produce alcohol by fermentation. The work done during the first period of catalysis consists mainly of isolated observations that were sporadically documented without any effort made to explain these phenomena.

HISTORY  The

first period of catalysis ended stridently when Jöns Jacob Berzelius systematically investigated the recorded observations and classified them as catalysis in 1835. The conclusions drawn by Berzelius were based upon discussions and experimental work with contemporary scientists in Europe.

HISTORY 

The second period was characterized by systematic research and the discovery of new catalytic processes. During this period it became quite clear that catalysis was applicable in most chemical processes and that by implementing catalysis in an industrial process there could be significant financial gains. This new perception of catalysis was clearly formulated by Wilhelm Ostwald, who once wrote that “there is probably no chemical reaction which cannot be influenced catalytically.”

HISTORY 

The third period of catalysis begins sometime during the end of the nineteenth century, when the growth of academic knowledge translated into industrial applications. At this point the number of catalytic processes that had been developed had grown into hundreds and the economic potential of some of these processes were highly feasible. There was also a general growth in the demand for bulk chemicals and therefore minimization of by-products, by catalysis, had evident economic advantages. The industrial production of bulk chemicals of this period was at an all-time high during World War 1, when the demands on explosives based upon nitric acid reached preposterous proportions.

HISTORY 

The fourth period of catalysis began at the end of the First World War, when the demand for explosives diminished, and the industrial production shifted towards the manufacturing of synthetic fuels and new innovative processes such as Fisher- Tropsch, a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen into liquid hydrocarbons. The most significant new process innovation of this period was the FCC (Fluid Catalytic Cracking) process, which enabled the Allied forces to provide fuel to its fighters during World War Two. When the war ended there was a notable change in the trend of the catalytic industry and thus the end of the fourth period of catalysis.

HISTORY 

The fifth period, which lasted to some undefined point at the beginning of the 1970s, was strongly characterized by the petrochemical industry and various catalytic processes for the manufacturing of synthetic polymers. The dominating role of the petrochemical industry was the result of the explosive automotive market that had developed in Europe and North America after World War Two. At some point during the early 70s the world started to become aware of the impacts that industry had on the environment, partially sparked off by Rachel Carson’s “Silent Spring”. This new trend of thought gave birth to the discipline of environmental catalysis. Environmental catalysis was the first step towards the modern chemical industry where catalysis is applied to almost every process, including the production of fine chemicals for pharmaceutical applications to the production of bulk chemicals and exhaust gas catalysts.

HISTORY  The

sixth period, which started in the seventies, and that can only be characterized by continuous invention of new catalytic processes, has not yet clearly passed into a seventh stage, the use of enzymatic biocatalysis.

IN GENERAL: Catalysts generally react with one or more reactants to form intermediates that subsequently give the final reaction product, in the process regenerating the catalyst. The following is a typical reaction scheme, where C represents the catalyst, X and Y are reactants, and Z is the product of the reaction of X and Y:

X + C → XC (1) Y + XC → XYC (2) XYC → CZ (3) CZ → C + Z (4) Although the catalyst is consumed by reaction 1, it is subsequently produced by reaction 4, so for the overall reaction:

X+Y→Z

A CATALYST can be:

HETEROGENEOUS MOSTLY

solids. Mostly contain metals especially those of Group VIII of the periodic table, Pt being a prime example. Physically, these catalysts resemble sponges; small and numerous pores.

HETEROGENEOUS

PALLADIUM

PLATINUM

HOMOGENEOUS 

MOSTLY acids, bases or organic amines.



Others consist of metals particularly transition metals ex, Fe or Rh in the form of salt or organometallic compound or a metal carbon monoxide (metal carbonyl) compound.



This is most often the liquid phase, although gas phase examples are known. Ozone in the stratosphere, for example, is converted into oxygen via the catalytic action of chlorine atoms formed as a result of the photochemical destruction of chlorofluorocarbon refrigerants.

HOMOGENEOUS

ENZYMES  also

known as “ORGANOCATALYSTS”

 Enzymes

are "biological catalysts." "Biological" means the substance in question is produced or is derived from some living organism.

Enzymes, as a subclass of catalysts, are very specific in nature. Each enzyme can act to catalyze only very select chemical reactions and only with very select substances.

ENZYMES AS CATALYST WHAT ARE ENZYMES AND WHAT DO THEY DO? 

Enzymes are proteins with highly specialized catalytic functions, produced by all living organisms.



Enzymes are responsible for many essential biochemical reactions in microorganisms, plants, animals, and human beings.

ENZYMES AS CATALYST  Enzymes

are essential for all metabolic processes, but are not alive.

 Although

like all other proteins, enzymes are composed of amino acids, they differ in function in that they have the unique ability to facilitate biochemical reactions without undergoing change themselves. This catalytic capability is what makes enzymes unique.

ENZYMES AS CATALYST  Enzymes

are natural protein molecules that act as highly efficient catalysts in biochemical reactions, that is, they help a chemical reaction take place quickly and efficiently.

 Enzymes

not only work efficiently and rapidly, they are also biodegradable. Enzymes are highly efficient in increasing the reaction rate of biochemical processes that otherwise proceed very slowly, or in some cases, not at all.

ENZYMES AS CATALYST  An

enzyme has been described as a "key" which can "unlock" complex compounds. An enzyme, as the key, must have a certain structure or multi-dimensional shape that matches a specific section of the "substrate" (a substrate is the compound or substance which undergoes the change). Once these two components come together, certain chemical bonds within the substrate molecule change much as a lock is released, and just like the key in this illustration, the enzyme is free to execute its duty once again.

The Nature of Enzyme Catalysis Specific acid or base catalysis -

Enzymes are able to deprotonate or protonate a substrate.

General acid or base catalysis - It is similar from the specific acid or base catalysis, the reaction rate can be increased by adding or removing a proton.

The Nature of Enzyme Catalysis Charge Neutralization -

When a substrate is charged when it is bound to the enzyme, other residues of the opposite charge around the enzyme can help to maintain the binding.

Nucleophilic catalysis - Many enzymes binds substrates with covalent bonding. Enzymes always are nucleophilic. Substrates are electrophilic. Therefore, the enzymes attacks the electrophilic center of substrates. This reaction is very rapid.

The Nature of Enzyme Catalysis Electrophilic catalysis -

The enzyme reaction can be catalyzed by removing the electron.

Bond strain - There are different types of binding in the enzyme-catalyzed reaction present such as hydrogen bonds, hydrophobic interactions, and electrostatic interactions. When substrates bind on the active site of enzymes, their structures may not be exactly complementary to the site. These different types of binding energy contribute the binding. Further, it helps the substrates bind enzyme more tightly.

MECHANISM

SOURCES OF INDUSTRIAL ENZYMES

PLANTS

ANIMALS

MICROBIAL/ BACTERIA

Malted grains or tubers (Amylase) • Pineapple Bromelin (Protease) • Fig Tree Ficin (Protease) • Papaya Papain (Protease) •

• Liver Catalase (Peroxide Breakdown) • Calf Stomach Rennet/ Chymosin (Milk Clotting)

• Amylase • Protease • Fungi (Molds and Yeast) amylase

• Pectinase

• Hog Stomach Pepsin • Cellulase (Protease) • Isomerase • Lactase (many • Hog Pancreas types of each) Pancreatic Enzymes • Beta-glucanase (Several) • Hemicellulase • Digestive Tract Trypain (Protease)

HYDROLYZING ENZYMES

Amylase catalyzes the digestion of starch into small segments of multiple sugars and into individual soluble sugars.



Protease (or Proteinase) split

up proteins into their component amino acid building blocks.

Lipase split

up animal and vegetable fats and oils into their component part: glycerol and fatty acids.

Cellulase  breaks

down the complex molecule of cellulose into more digestible components of single and multiple sugars.

Beta-glucanase (or Gumase) digest

one type of vegetable gum into sugars and/or dextrins.

Pectinase digests

pectin and similar carbohydrates of plant origin.

PRODUCTION OF ENZYME CATALYST

Isolation of Microorganisms, Strain Development and Preparation of Inoculum Microorganisms

are isolated on culture media following the microbiological techniques.

Aim for isolating a suitable microorganism lies in: (a) production of enzyme in high amount and other metabolites in low amount, (b) completion of fermentation process in short time, and (c) utilization by the microorganism of low cost culture medium.

Isolation of Microorganisms, Strain Development and Preparation of Inoculum Strains

of microorganisms are developed by using mutagenic chemicals and ultraviolet light.

Isolation of Microorganisms, Strain Development and Preparation of Inoculum Inoculum of enzyme producing strains developed after treatment of mutagens is prepared by multiplying its spores and mycelia on liquid broth.

Medium Formulation and Preparation Culture

medium is formulated in such a way that should provide all nutrients supporting for enzyme production in high amount but not for good microbial growth.

Medium Formulation and Preparation An

ideal medium must have a cheap source of carbon, nitrogen, amino acids, growth promoters, trace elements and little amount of salts. Care must be taken to maintain pH during fermentation.

Medium Formulation and Preparation For

a specific microbe pH, temperature and formulation of culture medium is optimized prior to inoculation. Production of enzymes increases with the concentration of culture medium.

Sterilization and Inoculation of Medium, Maintenance of Culture and Fluid Filtration Medium

is sterilized batchwise in a large size fermenter.

Sterilization and Inoculation of Medium, Maintenance of Culture and Fluid Filtration After

medium is sterilized, inoculation with sufficient amount of inoculum is done to start fermentation process.

Sterilization and Inoculation of Medium, Maintenance of Culture and Fluid Filtration Fermentation

process is the same as antibiotic production.

Sterilization and Inoculation of Medium, Maintenance of Culture and Fluid Filtration  When

fermentation is over broth is kept at 5°C to avoid contamination. Fungal broth is directly filtered or centrifuged after pH adjustment.

Purification of Enzymes Enzyme purification is a complex process but the main steps of purification are:

Purification of Enzymes 1. Preparation of concentrated solution by vacuum evaporation at low temperature or by ultrafiltration

Purification of Enzymes 2. Clarification of concentrated enzyme by a polishing filtration to remove other microbe

Purification of Enzymes 3. Addition of preservatives or stabilizers

Purification of Enzymes 4. Precipitation of enzymes with acetone, alcohols or organic salts.

Purification of Enzymes

5. Drying the precipitate

Purification of Enzymes

6. Packaging

ENZYME EFFICIENCY Enzymes

work as a catalyst by lowering the Gibbs free energy of activation of the enzymesubstrate complex. On the next slide, are two figures showing a basic enzymatic reaction with and without a catalyst.

ENZYME EFFICIENCY

ENZYME EFFICIENCY Looking

at a simple enzymatic reaction:

ENZYME EFFICIENCY  German

biochemist Leonor Michaelis and Canadian biochemist Maud Menten derived an equation later known as the "Michaelis-Menten Equation", shown below.

V0=Vmax[S]/KM+[S]

ENZYME EFFICIENCY For KM we know that V0 = VMax/2 VMax/2 = (Vmax[S])/(KM + [S]) (KM + [S])(VMax/2) = (Vmax[S]) (KM + [S]) = (Vmax[S]) / (VMax/2) KM + [S] = 2[S] KM = [S]

ENZYME EFFICIENCY  The

Michaelis constant can be thought of as the rate at which the substrate becomes unbound to the enzyme, which can either be in the events of substrateenzyme complex becoming the product, or the substrate becomes unbound to the enzyme. KM can be shown as an equation.

KM =k−1+k2k1

ENZYME EFFICIENCY Graphing V0 vs [S] :

ENZYME EFFICIENCY Vmax is the maximum rate the reaction can run at, regardless of [S], meaning that even if you add more substrate, the reaction would not go any faster. That is because at Vmax all of the active sites on the enzyme are occupied.

ENZYME EFFICIENCY  After

all the explanations on various forms of enzyme kinetic equations, we arrive at our conclusion of catalytic efficiency. Referring back to the earlier reaction, we have:

ENZYME EFFICIENCY k2 is an irreversible reaction as oppose to an equilibrium expression, when compared to k-1 and k1, k2 is also known as kcat , the catalytic efficiency of enzyme. V0 is the measured reaction rate, which is the product formation over time, so we can conclude that an equation would end up looking like the following:

v0=d[P] dt=k2[E]0 Where [E]0 is the total enzyme concentration.

ENZYME EFFICIENCY VMax is observed when all of the enzymesubstrate complex disappear and turn into products, so we can make the following assumption:

VMax=k2[E]0 and after rearrangement, we have this equation:

kcat=k2=VMax[E]0

ENZYME EFFICIENCY  That

is the equation for calculating catalytic efficiency, to be used after we obtain data from experiments and after using the Michaelis-Menten Equation. With a larger kcat , the enzyme is efficient because less enzyme is needed.

FACTORS AFFECTING THE EFFICIENCY OF ENZYMES

1. Enzyme Concentration 

The amount of enzyme present in a reaction is measured by the activity it catalyzes. The relationship between activity and concentration is affected by many factors such as temperature, pH, etc. An enzyme assay must be designed so that the observed activity is proportional to the amount of enzyme present in order that the enzyme concentration is the only limiting factor. It is satisfied only when the reaction is zero order.

1. Enzyme Concentration Table I: Reaction Orders with Respect to Substrate Concentration Order Rate Equation Comments zero

rate = k

rate is independent of substrate concentration

first

rate = k[S]

rate is proportional to the first power of substrate concentration

second

rate = k[S][S]=k[S]2

rate is proportional to the square of the substrate concentration

second

rate = k[S1][S2]

rate is proportional to the first power of each of two reactants

1. Enzyme Concentration

2. Substrate Concentration 

more likely the driver of the entire reaction.



Can be interpreted and explained using the Michaelis-Menten Equation



Michaelis constants have been determined for many of the commonly used enzymes. The size of Km tells us several things about a particular enzyme.



A small Km indicates that the enzyme requires only a small amount of substrate to become saturated. Hence, the maximum velocity is reached at relatively low substrate concentrations.



A large Km indicates the need for high substrate concentrations to achieve maximum reaction velocity.



The substrate with the lowest Km upon which the enzyme acts as a catalyst is frequently assumed to be enzyme's natural substrate, though this is not true for all enzymes.

3.Inhibitors, Poisons and Promoters  Catalyst

INHIBITORS - substances that

reduce the action of catalysts (if reversible reaction)

ex. Sildenafil (Viagra), Methotrexate, penicillin

3.Inhibitors, Poisons and Promoters

3.Inhibitors, Poisons and Promoters  Catalyst

POISONS - substances that

reduce the action irreversible reaction)

of

catalysts

ex. Mercury and Lead compounds

(if

3.Inhibitors, Poisons and Promoters  PROMOTERS/ACTIVATORS-

are substances that increase the catalytic activity, even though they are not catalysts by themselves. ex. MAGNESIUM ion (Mg2+) for Phosphatase and ZINC ion (Zn2+) for carbonic anhydrase

Temperature 

Like most chemical reactions, the rate of an enzyme-catalyzed reaction increases as the temperature is raised. A ten degree Centigrade rise in temperature will increase the activity of most enzymes by 50 to 100%. Variations in reaction temperature as small as 1 or 2 degrees may introduce changes of 10 to 20% in the results.



Over a period of time, enzymes will be deactivated at even moderate temperatures. Storage of enzymes at 5°C or below is generally the most suitable. Some enzymes lose their activity when frozen.

pH 

Enzymes are affected by changes in pH. The most favorable pH value - the point where the enzyme is most active - is known as the optimum pH.



Extremely high or low pH values generally result in complete loss of activity for most enzymes. pH is also a factor in the stability of enzymes. As with activity, for each enzyme there is also a region of pH optimal stability.

pH

FOOD/FOOD INGREDIENT Sugar

syrups from

starch Meat Tenderizing

DAIRY APPLICATIONS Cheeses Cheese

flavors Lactose-free dairy products

BAKING APPLICATIONS Bromate

Replacer

BEVERAGE APPLICATIONS

Low

Calorie Beers

HOUSEHOLD & PERSONAL CARE APPLICATIONS  Lower

Temperature & No Phosphate Clothes Washing

 Milder

Dishwashing Detergents

INDUSTRIAL APPLICATIONS  Textiles

Processing  Leather Tanning with Enzymes: Dehairing, Bating

THANK YOU! :D