Chlorophyll Overview Chlorophyll (KLOR-uh-fill) is the pigment that gives plants, algae, and cyanobacteria their green color. The name comes from a combination of two Greek words, chloros, meaning "green" and phyllon, meaning "leaf." Chlorophyll is the substance that enables plants to create their own food through photosynthesis. At least five forms of chlorophyll exist. They are:
chlorophyll a (also known as α-chlorophyll), with a formula of C55H72O5N4Mg chlorophyll b (also known as β-chlorophyll), with a formula of C55H70O6N4Mg Chlorophyll c1, with a formula of C35H30O5N4Mg Chlorophyll c2, with a formula of C35H28O5N4Mg Chlorophyll d, with a formula of C54H70O6N4Mg
Key Facts Formula:
Varies; see Overview. Elements:
Carbon, hydrogen, oxygen, nitrogen, magnesium Compound Type:
Organic State:
Solid Molecular Weight:
608.96-907.47 g/mol Melting Point:
Chlorophyll a: 152.3°C (306.1°F); Chlorophyll b: 125 C (257°F) Boiling Point:
Not applicable Solubility:
Chlorophyll a and b are insoluble in water, soluble in alcohol, ether, and oils
Chlorophyll a occurs in all types of plants and in algae. Chlorophyll b is found primarily in land plants. Chlorophyll c1 and chlorophyll c2 are present in various types of algae. Chlorophyll d is found in red algae. All forms of chlorophyll have a similar chemical structure. They have a complex system of rings made of carbon and nitrogen known as a chlorin ring. The five forms of chlorophyll differ in the chemical groups attached to the chlorin ring. These differences result in slightly different colors of the five chlorophylls. French chemists Pierre-Joseph Pelletier (1788–1842) and Joseph-Bienaimé Caventou (1795–1877) first isolated chlorophyll in 1817. In 1865, German botanist Julius von Sachs (1832–1897) demonstrated that chlorophyll is responsible for photosynthetic reactions that take place within the cells of leaves. In the early 1900s, Russian chemist Mikhail Tsvett (1872–1920) developed a technique known as chromatography to separate different forms of chlorophyll from each other. In 1929, the German chemist Hans Fischer (1881– 1945) determined the complete molecular structure, making possible the first synthesis of the molecule in 1960 by the American chemist Robert Burns Woodward (1917–1979).
Interesting Facts
The chemical structure of chlorophyll is very similar to that of hemoglobin, the molecule that transports oxygen in the red blood cells of mammals. The major difference between the two is that hemoglobin contains an atom or iron at the center of a large ring compound, while chlorophyll has an atom of magnesium in the same location. Leaves contain compounds called carotenoids that are red, orange, and yellow in color. These colors are masked by the green color of chlorophyll. In fall, plants stop producing chlorophyll, and the red, orange, and yellow of carotenoids become visible. Carotenoids do not perform photosynthesis, although they do transmit light energy to chlorophyll, where photosynthesis takes place.
How It Is Made Plants make chlorophyll in their leaves using materials they have absorbed through their roots and leaves. The synthesis of chlorophyll requires several steps involving complex organic compounds. First, the plant converts a common amino acid, glutamic acid (COOH(CH2)2CH(NH2)COOH) into an alternative form known as 5-aminolevulinic acid (ALA). Two molecules of ALA are then joined to form a ring compound called porphobilinogen. Next, four molecules of porphobilinogen are joined to form an even larger ring structure with side chains. Oxidation of the larger ring structure introduces double bonds in the molecule, giving it the ability to absorb line energy. Finally, a magnesium atom is introduced into the center of the ring and side chains are added to the ring to give it its final chlorophyll configuration.
Yahoo answer: Chlorophyll. Chlorophyll, the green pigment of plants, plays an important role in their synthesis of carbohydrates. The cells of the mesophyll of the leaf contain chloroplasts or chlorophyll-corpuscles, the nucleus, other substances, and the cell liquid with its dissolved materials. The chloro-plasts contain four pigments, two green ones, chlorophyll a and chlorophyll b, and two yellow ones, carotene and xanthophyll. Solubility of chlorophyll. Chlorophyll is not soluble in water. Very little green color is found in the water in which green vegetables have been cooked. Pure isolated chlorophyll is soluble in acetone, ether and benzene. In extracting the pigment from thoroughly dry leaves it is necessary to add about 20 per cent of water to the acetone or other solvent. One explanation for this is that chlorophyll is in the colloidal state in the leaf, and the mineral constituents of the leaf, dissolved in the water, peptize it, rendering it soluble. Onslow states that "the condition of chlorophyll is altered by plunging into boiling water. The pigment is then much more soluble, in ether, etc., even when the leaves are subsequently dried. It is supposed that the chlorophyll has diffused out from the plastids, and is in true solution in the accompanying waxy substances which have become liquid owing to change in temperature."
This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon:Experimental cookery.
Plant Pigments Chlorophyll. Chlorophyll, the green pigment of plants, plays an important role in their synthesis of carbohydrates. The cells of the mesophyll of the leaf contain chloroplasts or chlorophyll-corpuscles, the nucleus, other substances, and the cell liquid with its dissolved materials. The chloro-plasts contain four pigments, two green ones, chlorophyll a and chlorophyll b, and two yellow ones, carotene and xanthophyll. Solubility of chlorophyll. Chlorophyll is not soluble in water. Very little green color is found in the water in which greenvegetableshave been cooked. Pure isolated chlorophyll is soluble in acetone, ether and benzene. In extracting the pigment from thoroughly dry leaves it is necessary to add about 20per centof water to the acetone or other solvent. One explanation for this is that chlorophyll is in the colloidal state in the leaf, and the mineral constituents of the leaf, dissolved in the water, peptize it, rendering it soluble. Onslow states that "the condition of chlorophyll is altered by plunging intoboilingwater. The pigment is then much more soluble, in ether, etc., even when the leaves are subsequently dried. It is supposed that the chlorophyll has diffused out from the plastids, and is in truesolutionin the accompanying waxy substances which have become liquid owing to change in temperature." When green vegetables are dropped into boiling water a change takes place nearly instantly, the green color being intensified. Various explanations have been offered for the phenomenon. One is that the hot water has melted waxy constituents of the leaf so the chlorophyll escapes from the cell more readily or may become more soluble. Or the hot water may have dissolved salts or other substances in contact with the chlorophyll so that it diffuses more readily. For peas, Kohman states that one factor in the intensification of the green color is the removal of air from the pea when it is dropped in the boiling water. The outer skin of the pea is transparent, the space
beneath this being impregnated with air which is removed when the peas are blanched. That this change in color is caused by removal of the air can be shown by subjecting the peas to an adequate vacuum under cold water and releasing the vacuum while the peas are still under the water. Composition of chlorophyll. Willstatter, whose work gave us the formula for and thechemicalreactions of chlorophyll, reports that it exists in two forms, depending upon the degree of oxidation in the plant cells: form (a) and form (b). The former exists in the proportion of three to one of the latter.
Chlorophyll contains 2.7 per cent of the metal magnesium. It contains two ester groups, one of methyl alcohol (COOCH3) and one of phytol alcohol (COOC20H39). Reactions of chlorophyll with alkalies. Chlorophyll is a neutral substance but gives characteristic reactions when treated with alkalies or acids. Will-statter designates the parent substance of chlorophyll as chlorophyllin. The reaction of chlorophyllin with methyl and phytol alcohols gives the ester chlorophyll. Chlorophyll, when treated in the cold with alkalies, gives alkaline salts of chlorophyllin. The color change is first brown, followed by a return of the green, but it is no longer fluorescent. When chlorophyll is saponified with hot alcoholic alkalies, isochlorophyllins are formed, which are fluorescent.
When the green-colored vegetables are cooked in water with an alkaline reaction, or in water to which a small amount of soda is added, they develop a bright, intense green color. Reaction of chlorophyll with acids. Chlorophyll reacts with acids to give an olive-colored product, without fluorescence, called phaeophytin. The magnesium of the chlorophyll is replaced by hydrogen. From phaeophytin, Willstatter has obtained two decomposition groups: the first, designated as phytochlorins, are olive green and derived from chlorophyll a; the second, the phytorhodins, are red and derived from chlorophyll b.
Theeffect of heatupon chlorophyll. The chlorophyll is changed to the olive-green color by two means, (1) by hydrogen ions or an acid reaction and (2) byheat. As previously given, the hydroxyl ions, or an alkaline reaction, produces chlorophyll salts with bright green color. In general, the more acid the reaction, the more rapid is this change in color when the vegetable is heated; or, vice versa, the more alkaline the reaction, the more slowly the chlorophyll changes to olive-green. Thus in order that the bright green color be retained in cooking green vegetables, they should be cooked for as short a time as possible and contact with acids should be avoided as far as possible. It is also possible that other ions than the hydrogen and hydroxyl ions may affect the stability of the chlorophyll, for some vegetables with nearly the same pH, cooked in water from the same source, and with other conditions standardized are more stable to heat than others. In cooking certain procedures may aid in decreasing the acidity of the cooking water. The vegetables contain both volatile and non-volatile acids, which in the plant are prevented from uniting with the chlorophyll but are liberated when the plant tissues are heated. If the cooking vessel is not covered, the volatile acids may escape with the steam, thus decreasing the acidity. It has been found that the highest percentage of these volatile acids passes off during the first few minutes of cooking. Hence, if the cooking vessel needs to be covered for a part of the time, it is preferable to have the uncovered period the first few minutes. Certain water, such as hard water, softened water, or water from many streams, is alkaline in reaction. Rain water, snow, oricewater is usually about neutral. If the cooking water contains alkaline salts, these salts may neutralize the non-volatile acids, and if there is a slight excess of alkaline salts the green color is intensified. To a certain extent the intensification depends upon the quantity of water used, for the larger quantity of water contains a greater quantity of alkaline salts. If the water is only slightly alkaline theplant acidsmay not all be neutralized and the olive-green color may develop. If the water is very alkaline and considerable water is used, not enough volatile and non-volatile acids will be liberated to neutralize the alkalinity of the water, the cover can be kept on during cooking, and the product will be bright green. With longer cooking the heat may have more effect upon the chlorophyll than the alkaline salts of the water. The addition of sodium bicarbonate (baking soda), Experiment 17A, 5, also intensifies the green color. Canned spinach, asparagus, peas, and string beans have a deep olive-green color due to the retention of the plant acids during processing and to the high temperature at which they are processed. Green vegetables like cabbage, Brussels sprouts, and spinach cooked inmilkmay remain a bright green color. Owing to the ease with which milk scorches and boils over there is usually less tendency to cook the vegetables too long when milk is used.
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Chlorophyll Pickup in Extractions I have been having a discussion on another forum, on how it is possible for water to pickup chlorophyll in an extraction, when chlorophyll is basically a hydrocarbon, which is mostly insoluble in water. I did enough research to know that I was in over my head with chemistry that I took on the late fifties and early sixties, so I asked Joe, our budding biochemist, to take a run at it. In quick summary, before Joe’s response, “define soluble?” The word soluble means different things in biochemistry, than it does in inorganic chemistry, because of the behavior of the molecules of life.
The chlorophyll molecule has a magnesium (Mg) at its rings center, which makes it ionic and water-loving (hydrophilic) and a ring that is water fearing (hydrophobic) with carbonyl groups near a tail that make it polar (also hydrophilic). It is held in place in the plant within a water-soluble material known as water-soluble chlorophyll-binding protein (WSCP). WSCP is soluble in water, and mostly insoluble in polar alkane alcohols and non polar alkanes.
Chlorophyll is readily soluble in alcohol, mostly insoluble in non polar alkanes like butane and hexane, and has some special relationships with polar water, because of its polar and ionic groups. Mostly is a key word in all cases, because of chlorophylls charged polar end and non polar hydrocarbon ring with the ionic Mg. Before I finish summarizing, here is Joe’s response to the question of how water can remove and transport basically insoluble chlorophyll molecules, as well as how saturating water with NaCl table salt aids in the process of washing unwanted chlorophyll out of extractions that have gone awry: Chlorophyll Info by Joe Chlorophyll is an intra-membrane chemical within a thylakoid. A thylakoid is a membranebound compartment inside chloroplasts.
The thylakoid membranes of higher plants are composed primarily of phospholipids and galactolipids that are asymmetrically arranged along and across the membranes.
Chlorophyll is shown as photosystem I and II in this illustration. Both phospholipids and galatolipids have hydrophilic (water-loving) heads and hydrophobic (water fearing) tails. In biology this theme is used in almost all life forms to compartmentalized for energy storage, isolate invaders or encase their genome to protect it and many others reasons. Solubility is a term that has more than one definition. In inorganic chemistry it refers to waters (or another compound) ability to break covalent and ionic bonds of most compounds, dependent on time temperature and pH. The “solublized” atoms are then bonded to their polar opposite ion H3 (+) or OH (-) and are in solution. In biology however, it is used in the first tense but, it is also used to describe the ability of an organic molecule or complex to form an association with water and be in solution but not be “solubilized” by it. Proteins and other organic molecules use charged ions such as phosphate (PO4) and Sodium (Na) to form micelles. Micelles are little balls of hydrophobic molecules surrounded by a charged ion. Just like a cell’s membrane bilayer. Sometimes micelles are formed by complexes of proteins surrounding a small molecule for transport through water.
Chlorophyll specifically, is only able to form complexes with other molecules to stay in solution at biological pH (7.4). Its natural environment is at a pH of around 4 not 7.4. At this pH it has a net charge of -2 so that it can form a chemo-gradient for electron transport during photosynthesis. So since pH =-log [OH-/ H+] when at pH 4 the [H+] concentration is higher than the [OH] thus creating an environment that is more likely to associate with the (-) charged area of the chlorophyll molecule. Hence the low solubility of unbound chlorophyll in water, the large hydrophobic areas compress together and present their hydrophilic areas to exclude water from the center, becoming a mass that will sediment in water. The point of this is to illustrate that while purified chlorophyll is not likely to stay in solution in pure water; we don’t extract pure chlorophyll and we don’t use pure water. We use brine to keep the charge on the phospholipid bilayer (Na+ with PO4-3) and no detergents. The alcohol (ROH+) wants nothing to do with Na+ while in its protonated (H+) state. Non polar solvents for obvious reasons won’t either and also won’t form much of an emulsion with alcohols in their bent state because; the alcohol is denser and forms a micelles like layer to protect itself from the charged Na+. If there is an excess of alcohol it will start forming an emulsion layer at the upper interface. The phospholipid bilayer of the chloroplasts and of the thylakoid being intact or mostly so, prevent the chlorophyll from being disassociated with the Na+ water and are able to be excluded from alcohol or non-polar solvents . Alcohol is able to associate with chlorophyll and proteins in its native conformation but not when bent by Na+ because the electron pool concentrated at the (O-) repels the (-) region of the chlorophyll molecule and the PO4-3 of the membrane bilayer. If the membranes have been broken up by a detergent or broken down by enzymes then the only way to exclude chlorophyll from a non-polar solvent or alcohol is with lots of Na+ and water. Because of the large non polar area of the chlorophyll molecule it can more easily form a hydrophobic interface and shield the charge in the center. The salt exposes the charge (because ionic is a stronger bond than Van Der Wals forces) and precipitates the chlorophyll into water. So in conclusion, chlorophyll is not wholly soluble in water, but in its biological complex is able to associate with it. By manipulating charge/charge interactions chlorophyll can be forced into solution with water and away from polar organic and non-polar solvents. While it doesn’t meet the inorganic chemistry definition of solubility, it will form micelles complexes with an ionic solution and it can be precipitated from that solution under the right conditions. From a biological perspective chlorophyll can also be solubilized by any solvent under the right conditions. Sooooo, back to my summary, it appears that some solvents can wash away the cement binding the chlorophyll in the plant cells and free the chlorophyll to be washed away as a micelles, but it also exposes the chlorophyll to the solvent, which in the case of alcohol, will readily dissolve it and hold it in solution. Freezing the material prior to an extraction, may be holding both the chlorophyll and the WSCP locked up in ice, so that neither the water present or the solvent can reach the chlorophyll. Merck Index lists chlorophyll as practically insoluble in non polar solvents, so the difference between practically and totally insoluble may offer a clue, as well as butanes practically insolubility in water.
While most sources list n-Butane as insoluble in water, its actual solubility is 0.0325 vol/vol, at 1 atmosphere pressure and 20C/68F. That is 32 ml/liter, which may be enough to account for the light electric green hue that occurs, by both washing away the WSCP and holding some of the chlorophyll in suspension. When we saturate the water with salt, before washing a polar extract suspended in a non polar solvent like hexane, it forces the chlorophyll into solution and washes it away. explanation by Joe, summarized by Graywolf Share this:
