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MOST IMPORTANT SCIENTIFIC DISCOVERIES
Photosynthesis. History and essence of scientific discovery
Directory / The most important scientific discoveries For several years the French chemists Peltier (1788–1842) and Cavantoux (1795–1877) worked together. This fruitful collaboration led to the discovery of strychnine and brucine. The greatest glory was brought to them by the discovery of quinine, a sure remedy against malaria. In 1817, scientists published "A Note on the Green Matter of Leaves". It was Peltier and Kavant who discovered chlorophyll, the substance that gives all plants their green color. True, they did not attach too much importance to this. Scientists doused fresh leaves with alcohol. The alcohol turned green, and the leaves became completely colorless. In addition, Peltier and Kavantu washed the semi-liquid green mass obtained with water. After removing water-soluble impurities, they then dried it and got a green powder. Scientists called this substance chlorophyll (from the Greek "chloros" - green and "phyllon" - leaf). A start was made. Wilstetter (1872–1942), the son of a textile merchant, a German biochemist, connected his scientific interests with plant pigments (chlorophyll is one of them). In 1913, together with his closest student Arthur Stoll, he published the fundamental work "Investigations of Chlorophyll". In 1915, Wilstetter was awarded the Nobel Prize in Chemistry for this work. The scientific results of the Wilstetter school were significant. Timiryazev wrote later that Willstetter's work "will remain for a long time the starting point in the further study of chlorophyll, and the future historian will note two periods in this study - before Willstetter and after" him "". “First of all, Wilstetter,” writes Yu G Chirkov, “distinguished two principles in greenery - chlorophyll a (it is the most important) and chlorophyll b. The second achievement: Wilstetter established the chemical composition of the chlorophyll molecule. The presence of carbon, hydrogen, nitrogen, and oxygen in chlorophyll was expected. But magnesium was a surprise for scientists! Chlorophyll was the first compound in living tissue containing this element. And finally, the third: Wilstetter set out to determine whether all plants have the same chlorophyll? After all, how many different plants are on the planet, how much their living conditions vary, so do they really all cost the same, so to speak, standard chlorophyll molecule? And here Willstetter again showed his scientific character. Neither contemporaries nor descendants should have had even a shadow of doubt about the reliability of the facts obtained by him! The gigantic work lasted for two whole years. In Zurich, where Wilstetter was working at that time, numerous assistants delivered the darkness of plants from various places. Plants are terrestrial and aquatic, from valleys and mountain slopes, from north and south, from rivers, lakes and seas. And from each specimen obtained, chlorophyll was extracted and its chemical composition was carefully analyzed." As a result, the scientist was convinced that the composition of chlorophyll is the same everywhere! Heme is responsible for the red color of blood. Both heme and chlorophyll are based on porphin. "... Hans Fischer studied heme at the beginning," notes Chirkov. attached to the eight corners of the porphine... Fisher's work on the decoding and synthesis of heme was crowned with the Nobel Prize. But the scientist did not want to rest on his laurels: now he was fascinated by the mystery of chlorophyll. It was quickly established: the basis of chlorophyll is still the same porphyrin IX, however, instead of an iron atom, a magnesium atom is "interspersed" in it (the presence of the latter was proved by Wilstetter) ... ... Continuing his scientific research, Fisher became convinced that in the place where a three-carbon tail hangs on a heme molecule, a huge tail sticks out on a chlorophyll molecule - a twenty-carbon chain called phytol ... Now in any textbook on plant physiology you can find a "portrait" of this famous molecule. The structural formula of chlorophyll takes up a whole page. Although its true dimensions are extremely modest - 30 angstroms ... The chlorophyll molecule is similar to a tadpole: it has a flat square head (chlorophyllin) and a long tail (phytol). In the center of the head, like the eye of a cyclops or a diamond in a royal crown, a magnesium atom flaunts. If we tear off the phytol tail from the tadpole, and replace the magnesium atom with an iron atom, we get heme. And as if by magic, the color of the pigment will change: green will become red! The American Draper, followed by the Englishman Daubeny and the Germans Sachs and Pfeffer, as a result of the experiments, concluded that photosynthesis occurs most intensively in the yellow rays of sunlight. The Russian scientist Timiryazev did not agree with this opinion. Kliment Arkadyevich Timiryazev (1843–1920) was born into an old noble family. The boy received his primary education at home. Then Clement entered the natural department of the Physics and Mathematics Faculty of St. Petersburg University. Natural science students have always been characterized by democratic sentiments, and this faculty was considered the traditional beginning of the path of Russian raznochintsy. In his second year, Timiryazev refused to sign a pledge that he would not engage in anti-government activities. For this he was expelled from the university. However, given the outstanding abilities of the young man, he was allowed to continue his education as a volunteer. Since in Russia the scientific career for Timiryazev turned out to be closed due to his unreliability, immediately after graduating from the university he went abroad. The young scientist works in the laboratories of the largest French biologists - P. Berthelot and J. Bussingault, and also undergoes an internship in Germany with the physicist Kirchhoff and the physiologist Helmholtz. In one of the German universities, he is awarded a doctorate degree. Returning to Russia, Timiryazev began working at the Petrovsky Agricultural and Forestry Academy. In 1871, after defending his thesis "Spectral Analysis of Chlorophyll," he was elected an extraordinary professor at the Petrovsky Agricultural Academy. Today, this academy bears the name of Timiryazev. In 1875, after defending his doctoral dissertation "On the assimilation of light by a plant," Timiryazev became an ordinary professor. Timiryazev's first book is dedicated to the popularization of ideas Charles Darwin. He was practically the first to open them to Russian science and was the first to introduce Darwinism as a curriculum for students. Timiryazev devoted most of his life to the study of chlorophyll. His brilliant book Plant Life (1878) went through dozens of editions in Russian and foreign languages. In it, with vivid examples, he showed how a green plant feeds, grows, develops and reproduces. Timiryazev possessed the rare gift of a popularizer scientist, who was able to explain scientific phenomena very simply even to an inexperienced reader. In order to refute the conclusion that the photolysis maximum occurs in yellow rays, and to prove that this maximum occurs in red rays, Timiryazev carried out a whole series of carefully thought-out experiments. He himself creates the most accurate instruments for practical proof of the correctness of his theoretical conclusions. Timiryazev showed that Draper's erroneous conclusions were the result of incorrectly set experiments. An indispensable condition for the success of these experiments is the purity of the spectrum. In order for the spectrum to be clean, that is, for each section to be clearly delimited from the others, the slit through which the light beam passes must be no wider than 1–1,5 millimeters. Using the methods of gas analysis known at the time, Draper was forced to use a gap up to 20 millimeters in diameter. As a result, the spectrum turned out to be extremely impure. In this case, the greatest mixing of the rays took place in the middle, yellow-green part, which became almost white from this, slightly colored yellow. It was here that Draper found the maximum effect of photosynthesis. Timiryazev succeeded in his experiments in eliminating the error made by Draper. In his study of the relative importance of the different rays of the spectrum in the process of photosynthesis, carried out in the summer of 1868, he achieves this by the use of so-called light filters. In this case, the study of the intensity of photosynthesis in different rays of sunlight is carried out not in the spectrum, but in separate rays, isolated from the rest of the rays with the help of colored liquids. Timiryazev managed to establish that chlorophyll most completely absorbs red rays. It was in these rays that he also discovered the highest intensity of photosynthesis, which indicated the decisive role of chlorophyll in the phenomenon under study. Having revealed the fallacy of Draper's experiments, Timiryazev understood perfectly well at the same time that accurate results confirming his hypothesis about the dependence of photosynthesis on the degree of absorption of these rays by a green leaf and on the amount of their energy can be achieved only with the help of experiments carried out directly in the spectrum. Having conceived a whole range of studies in this regard, Timiryazev, first of all, pays attention to the study of the properties of chlorophyll. Timiryazev's research clearly demonstrated, as he himself said, "the cosmic role of plants." He called the plant an intermediary between the sun and life on our planet. "A green leaf, or rather, a microscopic green grain of chlorophyll, is a focus, a point in world space, into which the energy of the sun flows from one end, and all manifestations of life on earth originate from the other. A plant is an intermediary between heaven and earth. It is true Prometheus, who stole fire from the sky. The ray of the sun he stole burns both in a flickering torch and in a dazzling spark of electricity. The ray of the sun sets in motion both the monstrous flywheel of a giant steam engine, and the artist's brush, and the poet's pen. Thanks to Timiryazev's research, the view of the plant as a wonderful accumulator of solar energy has firmly established itself in science. Today there is no doubt: the chloroplast is a device for photosynthesis created by nature, and this now obvious position was proved in 1881 by Theodor Wilhelm Engelmann (1843–1909), a German physiologist, author of outstanding works on animal physiology. As Chirkov notes: “The solution to the problem was extremely ingenious. Bacteria helped. They do not have photosynthesis, but they, like people and animals, need oxygen. And oxygen is released by plant cells. In which places? And this is what gotta find out! Engelman reasoned as follows: bacteria will gather in those parts of the plant cell where oxygen is released, these places will be the centers of photosynthesis. Bacteria and a plant cell are placed in a drop of water. All this was covered with glass, the edges were carefully smeared with petroleum jelly: to prevent the access of oxygen under the glass from the air. If now the whole device is kept in the dark for a while, then the bacteria, having consumed all the oxygen in the liquid, will stop moving. Now the decisive thing: let's transfer our device to the microscope stage and illuminate the plant cell so that the rays of light fall on its various parts (and the rest is in shadow). And it's easy to make sure that bacteria begin to move only when a beam of light falls on one of the chloroplasts... So, finally, it was clearly shown: chloroplasts are those factories where the plant skillfully melts a beam of light into chemicals, and the chlorophyll contained in chloroplasts catalyzes this process. The Russian botanist Andrei Sergeevich Famintsin (1835–1918) proved that this process can also take place under artificial lighting. In 1960, newspapers in the United States and other countries informed the world that the famous American organic chemist Robert Berne Woodward (1917) had achieved an unprecedented synthesis of chlorophyll. Author: Samin D.K.
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