77iS
Chemistry
of Life
a C&EN
J-(ow Life Originated on Earth and in the "World Beyond
chemical science series
With this article describing the earliest development of living organisms, C&EN concludes its three-part series on the chemistry of life. In the first part, published two weeks ago, the CirEN staff surveyed the question of how living cells synthesize proteins. Last week, Dr. Heinz Fraenkel-Conrat and Dr. Wendell M. Stanley of the University of California (Berkeley) discussed what they and others are learning about the RNA viruses and also about the way in which genetic information is transmitted from one cell to another 96
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The particular sequence of thoughts indicated by the title of this article has its origin in my interest in the process of photosynthesis. It began when I asked the question: Which came first, the plants or t h e animals? This question has been answered in a great variety of ways. Yet, one can't help b u t wonder, as one learns more and more about the detailed mechanisms by which living organisms store energy and use it, how these organisms got started in the first place. These thoughts began long before w e heard of Sputnik and all of its
successors. However, it will soon be possible for us to know—probably within five years—whether there are organic chemicals on the moon and what t h e genetic nature of t h e living material on Mars might be ( I am assuming there is s o m e ) . Therefore, it becomes a much more pressing matter for us to surmise how life got here (on earth) so w e will have some clue as to w h a t to look for in outer space. This is another driving force for inquiry in this direction, and a very pressing driving force it is. To know what w e should look for,
DR. MELVIN CALVIN, University of California, Berkeley, Calif.
we should extract some basic idea of the essential features of living material as w e know it on earth. W e can then devise the proper instrument to go ahead and look for it elsewhere. Chemical
Evolution
Roughly 5 to 6 billion years ago, the earth was formed and hardened into its present shell. Immediately after the formation of the earth's crust, the processes of increasing t h e complexity of organic chemical formation began. This long span of time, which included the Archeozoic and Protero-
zoic geologic eras, was the period of chemical evolution. It was t h e time when chemicals were transformed from relatively simple, primitive molecules into very complex ones. These complex molecules evolved somewhere in the middle of this period into a complex system which had enough of the properties we usually attribute to living organisms to call it alive. At this point, organic evolution (Darwinian evolution) began. Our discussion will b e concerned mainly with t h e portion of t h e time scale which I have called chemical evolution, for
which we have no fossil record on the surface of the earth. This evolutionary period covered from 2 to 4 billion years. Thoughts about the nature of life itself—really the first serious ones in the modern day—stem from Darwin. This is the idea that living organisms develop in an evolutionary sequence over long periods of time. Shortly after publication of Darwin's thesis, Louis Pasteur, in about 1863, did an experiment in which h e showed definitely that no life could originate on the earth's surface, under conditions MAY 2 2, 1 9 6 1
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Ammonia
Water
Glycine
Formic dad
PRIMEVAL MOLECULES. These are some of the chemicals in the early atmosphere of the earth (top) and some of the simple organic molecules (bottom) that can be derived from them. In experiments in 1950, Dr. Melvin Calvin irradiated carbon dioxide and water in a cyclotron and produced formic acid, acetic acid, and other reduced compounds. In 1953, when Dr. Stanley Miller put ammonia into a system simulating a reduced atmosphere, he obtained glycine, alanine, j8-alaninef and other amino acids that are among the building blocks of living organisms
existing in modern times, except from pre-existing life. (As far as we know, he did not concern himself with primitive conditions.) After Pasteur's work, no one dared think seriously that living material could be created from anything except living material. Speculation on the matter came to an end at that point. One of the basic questions, of course, is: When are we justified in calling something alive? Some people believe that a thing must be selfreproducing to be alive. Others say it must convert energy into negative entropy. Others emphasize that it must have the property of irritability (the ability to respond to environmental stimuli). And a variety of other such descriptions have been used by research workers to define living matter. Actually, it is the aggregation of a sufficient number of these properties in a single system that gives rise to what we would call a living organism. I shall not try to define how many of these properties are necessary because ideas differ, depending on your point of view. If you are a chemist, you have one viewpoint; if you are a geneticist, you have another. There is no ambiguity, of course, in distinguishing the living from the nonliving at higher levels. Only at the primitive level do we have this difficulty because of the very nature of living material, being, as it is, an aggregation of a more or less arbi98
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trarily sufficient number of properties in one system. Let us consider how the chemical systems we call living matter could have arisen on earth. Then, let us take a look at other astral bodies to see if there is any possibility (or hope) that similar systems might exist or may have existed elsewhere. We have every reason to suppose that the primitive earth had on its surface only simple organic molecules. If the earth had a reducing atmosphere (and it seems to be generally agreed now that it did), most of the carbon was very largely in the form of methane or carbon monoxide. Some of the carbon could have been combined as carbon dioxide, but the contention now is that most of it was reduced. The nitrogen was mainly in the form of ammonia. There was a great deal of hydrogen, and the oxygen was all (or very nearly all) in the form of water. These, presumably, were the primitive molecules from which the more complex ones, such as proteins, developed. A short 10 years ago, we first began looking for ways to reproduce this developmental sequence experimentally in the laboratory. We started with carbon dioxide and water to determine whether or not reduced carbon compounds could be made in the absence of a photosynthetic system. By irradiating solutions of carbon dioxide and hydrogen with high energy ionizing radiation or ultraviolet light, we obtained reduced carbon.
Today, experiments of this type are easier to perform because we now believe that the atmosphere of primeval earth was a reduced one. Using methane (in place of carbon dioxide), ammonia, water, and hydrogen, we can get a whole variety of chemicals in the presence of similar ionizing radiations. In 1953, Dr. Stanley Miller, then at Columbia and now at the University of California (La Jolla), performed the first experiment with the reduced atmosphere and ammonia. In our experiment with carbon dioxide and water, which was done in the cyclotron in 1950, we obtained formic acid, acetic acid, and other reduced carbon compounds. When Dr. Miller put ammonia into the gas mixture to simulate a reduced atmosphere, he got glycine, alanine, /^-alanine, and several other amino acids. All these carbon skeletons are the simple metabolites that are very often rearranged by present-day living organisms. These materials are also the very first molecules that show up in a random synthesis, the kind of synthesis that begins with the ripping apart of existing simple molecules. The resulting fragments fall together to form metastable structures—metastable, that is, under very highly ionizing conditions. A few of these compounds are caught in this metastable condition and can be used in further synthesis. Molecules with Survival
Value
This random synthesis can go on for quite a while. But eventually, enough carbon is present in these metastable forms so that the very processes which took the precursor molecules apart now start tearing the products apart. A few of the molecules become more complex, but some of them start degrading to the more primitive forms. Hence, some kind of process must exist which permits the selection of those molecules which have some self-perpetuating survival value. Chemists recognize the existence of such a process and have given it a name: autocatalysis. Any product which has a catalytic function in its own formation helps to transform the raw materials to itself. Although, to a chemist, there is nothing profound about this idea—it seems almost primitive—it is a rather important concept. It is, in essence, the biologist's concept of self-reproduction. The catalytic properties of the primitive materials may themselves have
been rather simple, as, for example, the ability of a simple hydrated ferric ion to decompose hydrogen peroxide and produce water and oxygen, or to act as a peroxidase (oxidation catalyst). Simple aqueous ferric ion has a catalytic activity which may be expressed by the number 10~5, If, however, the iron ion is surrounded by a suitable organic grouping—in this case, heme, a tetrapyrrole—the catalytic ability of the iron is enhanced by a factor of 1000, reaching 1 0 2 . If the heme is built into a still more complex structure with a protein around it, the catalytic ability of the iron is increased several more powers of 10. Thus, the catalytic power residing in the iron for a simple reaction can be enhanced by the environment in which the iron is placed. How can this enhancement of iron's catalytic ability come about in a natural, evolutionary way? The answer is by autocatalysis and self-selection. The sequence of reactions involves simple condensation, decarboxylation, another condensation (really a double condensation), and a series of oxidation steps—all of which lead finally to a tetrapyrrole. Once this process begins, some of these steps may be catalyzed by iron. And if the iron porphyrin structures turn out to be better catalysts for any of these steps than the bare iron itself, the sequence's autoselection enhances the transformation of the succinic acid and glycine into 8-aminolevulinic acid and finally into the porphyrin. Thus, in the presence of iron and oxygen (or iron and water, for that matter) and ionizing radiation or even ultraviolet light, small amounts of porphyrin are synthesized nonenzymatically—that is, by the primitive catalytic abilities of the iron and the iron porphyrins themselves acting on 8-aminolevulinic acid. Capable of Transferring
Evolution of a Catalyst In this simple reaction . . . H2fj2 —+ H20 + 1/2O2 . . . aqueous ferric ion . . .
. . . has a catalytic activity of 10*' Surround it with heme, a tetrapyrrole •
, . and the catalytic activity increases to 10* Surround it with a more complex structure such as the protein, catalase . . .
Energy
The ability of the living organism to transfer energy is frequently considered one of its main properties. This property is often described in terms of the ability of the organism to change chemical energy from one form to another, usually from the form of sugar into the form of pyrophosphate linkage. This is what most organisms are able to do. The question arises: How does this change come about? Here, again, by observing primitive catalytic abilities, we can see how a development of
. . . and the activity rises to 105 Thus, the catalytic power of iron can be increased by changing the environment in which it is placed. Some such process would have enhanced the build-up of more complex molecules during the period of chemical evolution, billions of years ago
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FOSSIBLH POINTS FOR CATALYTIC
FUNCTION]
OF F&
AUTOCATALYSIS. In this way, compounds randomly synthesized by radiation, such as succinic acid and glycine, may have been transformed into porphyrins. If any of these steps is catalyzed by iron and if the iron porphyrin structures turn out t o be better catalysts than bare iron itself, the process catalyzes itself once it begins (as it would have begun here by random synthesis and condensation)
energy-coupling systems could lead to the more sophisticated systems we recognize today. All or part of the energy involved in the oxidation of iron (the removal of an electron from ferrous iron to make ferric iron) may be used to condense two phosphate linkages to form a phosphoric anhydride linkage—a pyrophosphate bond. The suggestion that iron is able to do this was made six or eight years ago. We actually tried using bare, or hydrated, iron ions to synthesize pyrophosphate by oxidizing iron in the presence of orthophosphate to see if we could make any pyrophosphate. But we were unsuccessful. Recently, however, Dr. John A. Barltrop at Oxford, using a slightly different technique, succeeded, at least tentatively. Instead of using the bare iron, as we did, he used an iron porphyrin. He was able to show the appearance of pyrophosphate when a ferrous porphyrin was oxidized to ferric porphyrin in the presence of phosphate. If this turns out to be a confirmed and successful experiment, we will have a clue as to how iron porphyrin evolved and how the energy of oxidation of iron is stored in the formation of pyrophosphate. We have now discussed several aspects of the generation of living material: • Conversion of simple compounds into more complex ones in a random fashion. • Autoselection, which leads to the formation of certain compounds from the precursors, which themselves have some autocatalytic function. • A way in which the energy conversion and storage processes might have had their beginnings. Creating an Organized
ENERGY STORAGE. This shows how iron porphyrin might have evolved and how the energy of oxidation of iron can be stored in the formation of pyrophosphate. Dr. John A. Barltrop at Oxford has shown tentatively that pyrophosphate appears when ferrous protoporphyrin is oxidized to ferric protoporphyrin in the presence of phosphate. Elsewhere, efforts to synthesize pyrophosphate involved the use of bare, or hydrated, iron ions, but the experiments proved unsuccessful
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Structure
Thus far, we have considered the generation of living material in terms of molecules in random solution—that is, organic molecules dissolved in water. These organic molecules are not oriented with respect to each other. But another aspect of a living organism is the fact that it is not random—it is not just a big bag full of molecules behaving haphazardly. Whenever you look at the outside of a living organism (at the whole man, in other words) or into the innermost part (whether it be a man or a microbe), you find it is a highly organized structure in which all of the elements are
related to one another in a specific way. How did the order in living organisms arise in the first place? Perhaps a consideration of crystallization and how it gives rise to order will help to answer this question. The order of a crystal resides in the nature and symmetry of the molecular interaction which, in turn, is the property of the molecule's structure—its shape, its force fields, and the like. Thus, the nature of the order is really built into the molecule itself. We must, therefore, look into the construction of molecules to see if anything is there that might give rise to the kind of order we see in living things. The structure of living organisms is based on three kinds of macromolecules: protein, nucleic acid, and carbohydrate. Possibly the most important of these is protein. Proteins are made up of amino acids in polypeptide linkage. The secondary structure of protein is the helical structure, and the tertiary structure is the fold in the helix. The helical structure depends at least partly on the particular geometry of the peptide structure. When these helixes are properly packed, they can give rise to struc-
tures that are visible macroscopically. Within the last year or so, Dr. Sidney W. Fox of Florida State University has been experimenting with the conversion of simple amino acids into proteinaceous material under nonbiological conditions. Dr. Fox calls these "prebiological conditions." He has taken a mixture of 18 to 20 amino acids and heated them in molten glutamic acid. Under these conditions, the amino acids hook together to form polypeptides of rather large structure - 3 0 0 0 to 10,000 molecular weight. He was able to reduce the temperatures needed to perform this experiment by putting in some polyphosphate. With polyphosphate in the reaction mixture, he produced proteinoids out of mixtures of amino acids at temperatures of 70° to 80° C. These proteinoids are relatively high molecular weight materials. If a hot solution of these proteinoids is cooled, they will come out of solution in the form of spherules which, says Dr. Fox, resemble spherical bacteria (cocci). Furthermore, they behave in some physical respects as if they were spherical organisms. In the proteinoid material itself, one can begin
PRIMITIVE CHANGES. Chemists are attempting to find out how simple molecules might have been converted to more complex ones in earliest times. Here, a photographer records experimental work being done in this field by William
to see structural features built into the molecular structure itself. The protein also affects the catalytic properties of the elements with which it may be associated. Both aspects depend on the protein's construction. When the amino acids are hooked together by dehydration (the removal of a water molecule between the acid and the amino group), peptide linkages are formed. When there is a long chain, because of the tendency of the hydrogen on the amide nitrogen to form a bond with the amide carbonyi of a suitably placed peptide group (more or less three residues are removed from the hydrogen), the well known a-helix forms. This is a built-in element of order—built into the polypeptides because of the very nature of the structure of the peptide linkage. Another macromolecule of living organisms about which we have heard a great deal in the past decade is the genetic material itself—the nucleic acid, which presumably carries the information used by the organism in reconstructing itself. The structure of this substance also has certain built-in elements of order, resulting from the structure of its component
Everette (center) and Dr. Christof Palm at the University of California (Berkeley). They are arranging a tube containing a "primitive earth atmosphere," made up of methane, ammonia, hydrogen, and water, for electron bombardment MAY
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parts. This is discussed in the first article of this three-part series (C&EN, May 8, page 80), which summarizes current thinking on the role of ribonucleic and deoxyribonucleic acids (RNA and DNA) in protein synthesis. Given these two ordered systemsprotein with its amino acids in polypeptide linkage and the nucleic acids with their hydrogen-bonded base pairs —a question arises, then, as to the relationship between the RNA and DNA helixes on the one hand and the protein structure on the other. How does nucleic acid determine the structure of protein, or how does protein build nucleic acid? Furthermore, which came first? In evolutionary terms: How could nucleic acid evolve without protein; how could the relationship between nucleic acid and protein have arisen?
PROBING METEORITES. In various laboratories, scientists have been analyzing meteorites to see if they might show whether living organisms exist elsewhere in the universe. Especially useful in this research is the carbon-containing Murray meteorite, which fell in the U.S. in 1950. A sample of this meteorite is being examined here by (left to right) Dr. Frederick D. Sisler of the U.S. Geological Survey, Edward P. Henderson of the Smithsonian Institution, and a visiting scientist, Dr. Paul Ramdohr of the University of Heidelberg, Germany
METEORITE IR ABSORPTION. Infrared absorption spectrum of a carbon tetrachloride extract of the Murray meteorite (partially indicated here m two discontinuous graphs) shows that it is a complex mixture. A definite carbon-hydrogen absorption occurs at a wave number of about 2900 c m r 1 (graph at left). Also observed is a carbonyl absorption that takes place at about 1725 c m . 1 (graph below)
3800 3400 3000 Wave number, cm.- 1 JLUU
J
S 6
Transmission
80
-i 20
\
Currently, this is a very active field of study. One of the more fruitful areas along these lines has evolved around the tobacco mosaic virus (TMV), which is composed of 5% ribonucleic acid and 95% protein. Dr. Heinz Fraenkel-Conrat and Dr. Wendell Stanley, in their contribution to this series (C&EN, May 15, page 136), have shown clearly that both the nucleic acid and protein structures are needed to give the correct total structure to the TMV particle. And as both previous articles point out, the interaction between these two substances to bring about the final construction is not related to some unknown "force." Rather, it is a coding or a lock-and-key arrangement—in analogy with a molecular crystallization phenomenon, if you like. But we know very little about noncrystalline (colloidal) and surface chemistry and what role such chemistry plays in making structural features. This is one area where more research is obviously needed. We have now gone through chemical evolution right up to the point where we have formed a primitive organism of some sort. From here on, the Darwinian selection mechanism can take over, and I shall not delve further into this aspect of the discussion. With this information as a background, we can proceed to the next step. Life Beyond the Earth
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Is it possible that similar events have occurred elsewhere in the universe? For this sequence of events to
occur, we require at least a certain temperature range, a certain type of atmosphere, and a variety of other factors, all of which are now definable. The sequence of events occurs because of the nature of carbon atoms, nitrogen atoms, and hydrogen atoms, giving rise, as they do, to reactions going from methane to acetic acid to formic acid to malic acid to glycine. These, in turn, give rise to proteinoids and to the nucleic acid type of molecules, thus building up in structure the order of living organisms and the interaction of molecules of the required type. All this hinges on the nature of the elements with which we are dealing— namely, carbon, hydrogen, nitrogen, oxygen, iron, and phosphorus. If earthlike conditions (both physical and chemical) exist, we can expect this sequence of events to occur elsewhere in the universe. The question we have to answer is: Are there any other places where this set of conditions might occur? Here we must turn to the astronomers. They tell us that in our solar system the only places we are likely to find a set of conditions corresponding to the ones which we have just described are on our two neighboring planets, Venus and Mars. Possibly, these conditions might be closely enough approached on each of these two planets so that a similar sequence of events could have occurred or might even be occurring now. There is some evidence already that organic compounds, varying with the geography of the surface and with the seasons, exist on the surface of Mars. However, we are so limited in our ability to observe Mars that we can just barely make out, for example, a CH frequency in its reflection spectrum. We would like to be able to do better, and I think we will, within
COMBINED REPRINTS . . . . . . of this article, together with Parts I and II published in the past two weeks, are available at the following prices: One to nine copies—$1.00 each 10 to 49 copies—15% discount 50 to 99 copies—20% discount
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a few years. It should be pointed out that there are other uses for high flying vehicles and satellites besides looking down; you can also look up. Meteorite
Experiments
Of course, we would like to be able to go out into space and collect bits of various planets and other celestial bodies. We could then bring them back to earth to see if they contain any organisms. Or, if not organisms, perhaps they might possess the prebiological environment mentioned earlier. Unfortunately, we cannot quite do that yet, and it will probably be more than five years before we can. But materials are already on hand that can give us some kind of information about what is out there. These, of course, are the meteorites. We can't place a purchase order for meteorites. We have to take them when and where they come, and that is not very often. Furthermore, they get into museums, and once there, you usually can't get them out. (I don't blame the museum keepers. Actually, if they gave out the meteorites to everyone who asked for them, there would be none left. Their reluctance is not unreasonable. It's just too bad they don't have more meteorites.) Fortunately, we were able to get samples of two meteorites. From the Smithsonian Institution, we obtained a sample of the Murray meteorite, which fell in 1950. From Paris, we received a sample of the Orgueil meteorite, which fell in 1864. The main reason for looking at these particular meteorites is that they contain carbon. Unfortunately, the meteorites do not contain much carbon—about 2% of the total weight of the meteorite is carbon. What is worse is that, of the 2%, a large fraction of the carbon is not easily extractable. The carbon is not in the form of carbide but is in some other form which cannot be recovered under the mild conditions we must use. However, from these two meteorites, one can extract with water enough of the carbon fraction to permit it to be analyzed spectroscopically. The Orgueil meteorite contains salt which is mostly magnesium sulfate. The water extract from the Murray meteorite contains a salt, mostly calcium sulfate. The water extracts of the two meteorites do not have the same carbon content. However, both meteorites show ultraviolet and infrared absorbing ma-
DR. MELVIN CAL-
VIN has been director of the bioorganic chemistry group at the University of California (Berkeley) Radiation Laboratory since 1946. In addition, he has been professor of chemistry at the University of California since 1947. He is widely recognized for his research on photosynthesis and plant physiology. He has also made important contributions to the fields of catalysis, photochemistry, reaction mechanisms, and physical and organic chemistry. Coauthor of such books as "Isotopic Carbon'' "Chemistry of the Metal Chelate Compounds," and "Path of Carbon in Photosynthesis," he has written over 260 scientific publications. He holds a Ph.D. in chemistry from the University of Minnesota and honorary doctorates from three other universities. Over the years, he has received numerous honors, including the ACS Award for Nuclear Applications in Chemistry, the Nichols Medal, and the T. W. Richards Medal.
terial, which might lead one to believe that a wide variety of compounds are present in these water extracts, including hydrocarbons and heterocyclic bases. The infrared absorption spectrum of a carbon tetrachloride extract of the Murray meteorite shows a definite carbon-hydrogen absorption (at about 2900 cm. - 1 ) and a carbonyl absorption as well (at about 1725 c m r 1 ) . This extract is a rather complex material—a mixture of many things. The ultraviolet absorption of the water extract, taken at various pH's, shows that there is a pH-sensitive absorption band where cytosine absorbs. Furthermore, it behaves very much like a cytosine type of absorption. But I do not think this is cytosine. It is not pure material, for one thing, but a mixture. Our meteorite analysis is continuing. Unfortunately, we do not have enough of either one of these meteorites, so I cannot give a definitive statement about the nature of the cytosinelike material in the meteorite. I can describe only the general character of the compounds found in these meteorites. We have discovered no amino acids MAY 22, 1961 C & E N
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Series of Self-Additions of HCN May Lead to Formation of Adenine Two HCN additions across a third HCN produce the known but unstable trimer, aminomalonitrile:
This reaction could be followed by an addition of the resulting amino group across a fourth HCN to produce 4-amino-5-cyanoimidazole (possibly the parent of the two imidazoles that have been found):
4AMINO-5CYANOI IMIDAZOLE Addition of the amino group thus formed across another HCN, with ring closure, leads to adenine:
ADENINE
in their aqueous extracts. This harks back to the question of which came first—the protein or the nucleic acid. On the other hand, the aqueous extracts showed hydrocarbon-like material in the infrared spectrum, as well as in the mass spectrum when examined up to C 12 . Synthesis
Under Primitive
Conditions
Actually, a good deal of organic material is present in the solar system and interstellar space. We can recognize it in the form of light emission from the comets, for example. There is much CH emission and much cyanide in the comet tails. This is a rather important observation. According to experiments by Dr. Miller (he irradiated methane, ammonia, and water and formed glycine, alanine, and a 104
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few other amino acids), these amino acids represent an extremely small fraction of the methane that has been converted to organic material—less than V/c Most of it consists of other materials, as yet undetermined. The mechanism for forming these amino acids, however, is relatively simple. But here, again, it is subject to uncertainty. Presumably, it is an HCN addition to an aldehyde in the presence of ammonia to produce an amino acid—a Strecker type of synthesis. This means that when you expose methane and ammonia to ionizing radiation you get HCN. HCN and ammonia is a very sensitive mixture. This sensitivity has been demonstrated by a number of people, but most recently by Dr. John Oro of the University of Houston. Dr. Oro was able to show that mild heating (below
100° C.) of a mixture of ammonia and HCN (about I N equivalent ammonium cyanide) produces, in addition to a large amount of black polymer, several identifiable compounds in small quantities. By extraction and chromatography, he was able to identify adenine and two imidazoles. Adenine is isomeric with a pentamer of HCN—that is, it has the empirical formula (HCN) 5 . The two imidazoles can be formulated in terms of a sequence of self-additions of HCN, and they might very well be intermediates on the way to the formation of adenine. In our laboratory at Berkeley, Dr. Christof Palm, using an electron accelerator, has carried out a 5-m.e.v. bombardment experiment, starting with a mixture of methane, ammonia, hydrogen, and water. He has found a small amount of amino acids of the general distribution that Dr. Miller reported. By using paper chromatography, he has also found a large number and variety of other compounds. These have been located by using radioactive methane but have not as yet been identified. Possibly, some of these compounds will turn out to be aromatic heterocyclics of the type reported by Dr. Oro. Indications are that the heterocyclic compounds, as well as the amino acids, may have been formed in the very earliest stages of chemical evolution. It thus appears that the two apparently distinct evolutionary processes—(1) the development of the catalytic function of the proteins arising from the amino acids and (2) the code development of the polynucleotides arising from the purine and pyrimidine bases—were initiated by the same chemistry and grew simultaneously. This could account for the very close relationship that exists between these two classes of substances in living organisms. We have reason to hope that earthbound laboratory studies of chemical evolution, such as those described here—as well as information which we may be able to gather concerning the nature of the organic matter and possible living matter in other parts of the solar system—will contribute to our understanding of the method by which the code contained in the polynucleotides is translated into the chemically versatile protein. Such understanding will also contribute much to our fundamental knowledge of the nature of life itself.
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end. W t . 1 3 ^ lbs 5 K ' " x 1 4 H " ( 2 8 0 c u . in.) M" pipe opening one end.. . WtTsHlbs 3 eavy Carbon E X T R A H I G H PRESSURE, 3 0 0 Steel, 0 PSI 8 " port. Equipped w i t h ff Q Cfl 1 • " ,lve. W t . 8 lbs., Spec J 0.3U XA" pipe thread port. >n steel, X O 3 J>" x 1 9 " Heavy carbon C A 7R w t : 8 ibs ' ••••• -L w : s ibs * *-,a t Same as H-2 but 4 " x 2 4 " heavy carbon steel, A" n Same thread as H-2opening. but 4 " x 2W 4 "t heavy carbon steel, A" ff C IE pipe . 1 0 Ibs 1pipe 3 H "thread x 3J2"—stainless steel—with -L opening. W t . 1 0 Ibs hi pressure brass J3 - , J i o valve 1 3 1 4 "A" x 3 thrds A"—stainless steel—with hi pressure brass ff-in QC I U 3 3 QW xV,' 1 2thrds " stainless a l l o y — 2 0 0 0 p s i - K " thrd. openings *t U Q A-Z valve ' C top, bottom and side *0 a d
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THE INDEX TO ANALYTICAL CHEMISTRY'S YEARS OF GREATEST GROWTH Now you can open the door to the recent literature on analytical chemistry in one operation, saving hours of searching. Analytical Chemistry's new FifteenYear Index unfolds the panorama of analytical work for the important years 1944 through 1958. The growing role of the analytical chemist is shown in the fact that this index covers two and one half times the number of pages on original research as the preceding 15-year index. There have been major changes in scope. Physical methods using complex instruments have forged ahead. This period, which also marks the rise of the new atomic era, has ushered in the use of radioactivation analysis. It has witnessed the arrival of such important analytical tools as gas chromatography, polarography, and magnetic resonance spectrometry. New techniques have come forth to meet the need for trace analysis in parts per million or per billion. These are just some of the reasons why no analytical chemist—nor those who supply him with information—can afford to miss this compact guide to research progress. It covers the years most vital to analytical work today. It will save time, save effort, save costs—and furnish new ideas for forward planning. Analytical Chemistry Fifteen-Year Collective Index, Volumes 16-30 174 pages paper bound $9.00 Note: This index can be purchased together with the first 15-year collective index (1929-1943), giving the whole sweep of 30 years of analytical work. Bound together, the two indexes are priced at $11.50. Order from: S p e c i a l I s s u e s S a l e s American Chemical Society 1155 S i x t e e n t h S t r e e t , N.W. W a s h i n g t o n 6, D.C.
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1961
Don't blindfold him! T
HE MAN in this picture is a cancer research scientist. T h e device he is using looks like something out of science-fiction —but actually, it's an electron microscope. It shows him the sub-microscopic detail of a cancer cell —magnified 100,000 times. The cost of one electron microscope is $35,000. Some of the equipment needed for cancer research, a n d purchased with A m e r i c a n Cancer Society funds, is even more expensive. T h e American Cancer Society g r a n t s millions of dollars for research to some 1300 scientists who a r e at this m o m e n t w o r k i n g to find t h e cause of cancer—and ultimately, ways to prevent cancer. Your help is needed to enable the American Cancer Society to continue this support. D o n ' t b l i n d f o l d c a n c e r research. Give to it. Send your contribution now to CANCER, c/o your local post office. AMERICAN CANCER S O C I E T Y
