"In developing structural chemistry we have not drawn a line between inorganic and organic substances, and at first most of our work, covering compounds of all elements, dealt with organic compounds to only a small extent. However, our methods have been found to be particularly valuable in the treatment of the complicated problems of organic chemistry, and we are now devoting the major part of our effort to those problems."

Linus Pauling. "Brief Account of Research in Chemistry Supported by Grant from the Rockefeller Foundation." October 24, 1933.

"We are ready to make an intensive attack on the structure of hemoglobin."

Linus Pauling. Letter to The Rockefeller Foundation. October 22, 1934.

"The picture is, however, still very far from definite - she suggests various alternatives and does not make any definite predictions."

Linus Pauling. Letter to Warren Weaver. March 6, 1937.

"[Delbrück's] training in physics is good and he attacks biological problems in a sensible way. He understands their nature, whereas Dr. Wrinch does not."

Linus Pauling. Letter to Warren Weaver. February 23, 1938.

"It has been recognized by workers in the field of modern structural chemistry that the lack of conformity of the cyclol structures with the rules found to hold for simple molecules makes it very improbable that any protein molecules contain structural elements of the cyclol type."

Linus Pauling Carl G. Niemann. "The structure of proteins." Journal of the American Chemical Society, 61, 1860-1867. 1939.

"I think that this synthesis of antibodies in vitro can be considered pretty important."

Linus Pauling. Letter to Warren Weaver. November 18, 1941.

"Although the chances that our work on artificial antibodies will lead to results of practical value in the immediate future are not great, there does exist some possibility that the researches will have practical application."

Linus Pauling. Letter to Frank Blair Hanson. May 29, 1942.

"It does not seem to us that we should consider going in for the support of immunology on a broad front at the present time."

Frank Blair Hanson. Letter to Linus Pauling. May 7, 1943.

"...I must confess to a good deal of skepticism as to whether it is possible or desirable to carry over, into peace-time research, many of the elements of organization and control which properly and inevitably characterize war-time work."

Warren Weaver. Letter to Linus Pauling. September 21, 1944.

"It may be emphasized that this explanation for specificity, as due to a complementariness in structure which permits non-specific intermolecular forces to come into fuller operation than would be possible for non-complementary structures, is the only explanation which the present knowledge of molecular structure and intermolecular forces provides."

Linus Pauling. "Molecular Structure and Intermolecular Forces." In The Specificity of Serological Reactions, by Karl Landsteiner, 2nd ed. Cambridge, Mass.: Harvard University Press. 1945.

"Even the sense of taste and odor are based upon molecular configuration rather than upon ordinary chemical properties. A molecule that has the same shape as a camphor molecule will smell like camphor even though it may be quite unrelated to camphor chemically."

Linus Pauling. "Analogies between Antibodies and Simpler Chemical Substances." Chemical and Engineering News, 24:1064. 1946.

"I think it has really been very much worthwhile for me to get away for this period of time, under circumstances favorable to my thinking over questions and trying to find their solution."

Linus Pauling. Letter to Robert Corey. March 3, 1948.

"The mechanism of obtaining [immunological specificity] is one of moulding a plastic material, the coiling chain, into a die or mould, the surface of the antigen molecule. I believe that the same process of moulding of plastic materials into a configuration complementary to that of another molecule which serves as a template, is responsible for all biological specificity. I believe that the genes serve as the templates on which are moulded the enzymes which are responsible for the chemical characters of the organism."

Linus Pauling. "Molecular Architecture and the Processes of Life," the Twenty-First Sir Jesse Boot Foundation Lecture. May 28, 1948.

"Proteins hold the key to the whole subject of the molecular basis of biological reactions."

Linus Pauling. "Signs of Life." Electronic Medical Digest, 35-36. 1949.

"The difference between our two predicted configurations and the others that have been described in the literature is that ours are precise, whereas the others are more or less vague. I feel in a sense that this represents the solution of the problem of the structure of proteins."

Linus Pauling. Letter to Warren Weaver. March 8, 1951.

"In reply to your letter of January 24, 1952, you are informed that your request for a passport has been carefully considered by the Department. However, a passport of this Government is not being issued to you since the Department is of the opinion that your proposed travel would not be in the best interests of the United States."

Ruth B. Shipley. Letter to Linus Pauling. February 14, 1952.

"We have been having a lot of fun in our work on the structure of proteins. There now seems to be pretty general agreement that some of our structures are correct, although a few people, namely the workers at Courtaulds, are still complaining."

Linus Pauling. Letter to Thomas Taylor. July 2, 1952.

"Polypeptide Configuration Conference...Jim Watson will arrive before March & stay. Invite him, but no money."

Linus Pauling. Diary entry. August 1952.

"His attitude toward the patient always dominated his work, and the Clinic for Renal Diseases at Stanford University held its sessions right in the laboratory, in the midst of the experiments. On Clinic days, the laboratory was unique and a sight to be remembered. It was humming with activity. Patients sat all about, watching with interest the tests, both those which were routine and those which were part of some special research project, being made in front of their eyes. Then, when Dr. Addis saw his patient, the information about his condition was up-to-the-minute."

Linus Pauling. "Biographical Notes re: Thomas Addis." February 1955.

"The human body contains many other kinds of proteins. Perhaps each human being has as many as 100,000 different kinds of proteins inside of him....Now the hemoglobin molecule contains about 10,000 atoms. Nobody knows, even yet, how these atoms are attached together in space. Nobody knows the complete structure. Yet, during the last twenty-five years, many pieces of information about the hemoglobin molecule have been gathered together and I have been especially interested in this."

Linus Pauling. National Film Board of Canada interview. 1960.

"In the 1930s already, I began work on the question of the nature of antibodies, antitoxins, how the human body protects itself against invasion by infection. There is a very interesting natural mechanism that is involved here. Doctor Karl Landsteiner of the Rockefeller Institute for Medical Research, who is the man who discovered the blood groups and made it possible to give transfusions of blood from one human being to another, is the man who got me interested in this field of immunology."

Linus Pauling. National Film Board of Canada interview. 1960.

"I think that we shall be able to get a more thorough understanding of the nature of disease in general by investigating the molecules that make up the human body, including the abnormal molecules, and that this understanding will permit...the problem of disease to be attacked in a more straightforward manner such that new methods of therapy will be developed."

Linus Pauling. National Film Board of Canada interview. 1960.

"Twenty-five years ago I began work on the question of how the four iron atoms in the hemoglobin molecule are related to the other atoms. My students and I investigated hemoglobin by measuring its magnetic properties - whether it is attracted by a magnet or not - and we were successful in finding out something about the nature of the bonds connecting the four iron atoms - there are four iron atoms in the molecule - with the other atoms that surround the iron atoms in the hemoglobin molecule. And also we found out something about the nature of the bonds between the iron atoms and molecules of oxygen. Hemoglobin in the blood combines with oxygen molecules from the air, in the lungs...then as the blood flows out to the tissues, the oxygen is carried along. In the tissues, the hemoglobin molecule gives up the oxygen molecules to the tissues where it serves to support the oxidation of worn out molecules and to provide energy to muscle and do the other jobs that are part of the physiological activity of the human being or other animals. Then the hemoglobin, the blood, flows back to the lungs, and the hemoglobin again picks up a load of oxygen."

Linus Pauling. National Film Board of Canada interview. 1960.

"But after some years, at the end of the war, in connection with my interest in application of chemistry to medicine, I learned about the disease sickle cell anemia. As soon as I learned about this disease, the very evening - it was at a dinner in New York where a medical research committee, of which I was a member, a committee which had been appointed by President Roosevelt to study medical research in the United States, was holding a meeting. At this dinner I learned about the disease sickle cell anemia and immediately I thought, 'Could it be possible that this disease, which seems to be a disease of the red cell because the red cells in the patients are twisted out of shape, could really be a disease of the hemoglobin molecule?' Nobody had ever suggested that there could be molecular diseases before, but this idea popped into my head. I thought, 'Could it be that these patients manufacture a certain kind of hemoglobin such that the molecules are sticky and clamp onto one another to form long rods which then line up side-by-side to form a long, needle-like crystal which, as it grows inside the red cell, becomes longer than the diameter of the cell and thus twists the red cell out of shape.' Well, I said to the man who was talking about the disease, Dr. Castle, 'Has anyone ever suggested that this might be a disease of the hemoglobin molecule?' And he said not so far as he had ever heard and I said, 'Do you think it would be alright if I were to look at the hemoglobin from these patients and see?' And he said 'I don't see why not.' So when I got back to Pasadena, it turned out that a young M.D., a young medical man wanted to come work with me in chemistry and get his Ph.D. degree. I said to him - his name is Harvey Itano - I said to him 'Why don't you work on the hemoglobin that you get from patients with the disease sickle cell anemia and see whether it is the same as hemoglobin in other humans or its different?' Nobody had ever found any difference between the hemoglobin of one person and another before that time. Well Dr. Itano did that, together with the two other young men in our laboratory - Dr. Singer and Dr. Wells. Pretty soon - it wasn't an easy job, these proteins are hard substances to work with - but after a while Dr. Itano and Dr. Singer and Dr. Wells were able to show that if they put a drop of hemoglobin solution from a patient with this disease in a little trough containing salt solution and applied an electric field - putting electrodes into this trough - the hemoglobin from the sickle cell anemia patients would move in one direction in this trough and that from ordinary individuals would move in the other direction. This was the proof that these patients have a different kind of hemoglobin; they manufacture a special kind of hemoglobin molecule which is the cause of their disease. This was the first molecular disease to be identified, that is the first disease to be shown due to the manufacture by the patient of an abnormal molecule."

Linus Pauling. National Film Board of Canada interview. 1960.

"[Pauling] had already proved himself in the early years to have such an ingrown sense of the realities of the quantum as applied to chemistry that he did not need to think about detailed derivations but thought automatically in quantum terms."

J. D. Bernal. "The Pattern of Linus Pauling's Work in Relation to Molecular Biology." Structural Chemistry and Molecular Biology: A Volume Dedicated to Linus Pauling By His Students, Colleagues and Friends (San Francisco: W. H. Freeman). 1968.

"This show, like all of his dazzling performances, delighted the younger students in the audience. There was no one like Linus in all the world. The combination of his prodigious mind and his infectious grin was unbeatable. Several fellow professors, however, watched this performance with mixed feelings....A number of his colleagues quietly waited for the day when he would fall flat on his face by botching something important."

James D. Watson. The Double Helix 1968.

"It can be said that, by and large, Pauling's idea played an essential role in the working out of protein structure. But it did far more. It broke away from the limitation imposed by crystallographers on the integral nature of the turns of a helix. It eventually led to a new generalization of crystallography that was to have immense repercussions. It might be said, 'Only a crystallographer could have predicted this development, but if they were good crystallographers, they would have been bound to reject it.' Indeed, Pauling's generalization opened the field to a new and much more wide-sweeping account of semiregular structures that are similar to the helical."

J. D. Bernal. "The Pattern of Linus Pauling's Work in Relation to Molecular Biology." Structural Chemistry and Molecular Biology: A Volume Dedicated to Linus Pauling By His Students, Colleagues and Friends (San Francisco: W. H. Freeman). 1968.

"I found that Landsteiner and I had a much different approach to science: Landsteiner would ask, 'What do these experimental observations force us to believe about the nature of the world?' and I would ask, 'What is the most simple, general and intellectually satisfying picture of the world that encompasses these observations and is not incompatible with them?'"

Linus Pauling. "Fifty Years of Progress in Structural Chemistry and Molecular Biology." Daedalus, 99, 1005. 1970.

"He and I together decided that he should work on the determination of the structure of some crystals of amino acids and simple peptides. When I say that he and I together made this decision, I may not be quite right. It is not unlikely that he had already made the decision, and that he arranged to have me agree with him, in such a way that I would think that we had made the decision together. I learned later that he was very good at this..."

Linus Pauling. "Robert Brainard Corey." May 3, 1971.

"To my father, nucleic acids were just interesting chemicals, just as sodium chloride is an interesting chemical."

Peter Pauling. "DNA - The Race that Never Was." New Scientist May 31, 1973.

"What I'm telling you now is that I was thinking of the alpha helix in hemoglobin, and I refrained from saying anything to Max, not because I wanted to keep him from having significant information, but because there's no use disturbing people about something unless you feel happy with it yourself."

Linus Pauling. Interview with Horace Freeland Judson. December 23, 1975.

"As I lay there in bed, I had an idea about a new way of attacking the problem. Back in 1937 I had been so impressed by the fact that the amino-acid residues in any position in the polypeptide chain may be of any of 20 different kinds that the idea that with respect to folding they might be nearly equivalent had not occurred to me. I accordingly thought to myself, what would be the consequence of the assumption that all of the amino-acid residues are structurally equivalent, with respect to the folding of the polypeptide chain?"

Linus Pauling. "The Discovery of the Alpha Helix." September 1982.

"On my return to Pasadena in the fall of 1948 I talked with Professor Corey about the alpha helix and the gamma helix, and also with Dr. Herman Branson, who had come for a year as a visiting professor. I asked Dr. Branson to go over my calculations, and in particular to see if he could find any third helical structure. He reported that the calculations were all right, and that he could not find a third structure."

Linus Pauling. "The Discovery of the Alpha Helix." September 1982.

"...[T]hree ways of folding polypeptide chains have turned out to constitute the most important secondary structures of all proteins. Dr. Corey, to some extent with my inspiration, designed molecular models of several different kinds that were of much use in the later effort to study other methods of folding polypeptide chains. I used these units to make about 100 different possible structures for folding polypeptide chains."

Linus Pauling. "The Discovery of the Alpha Helix." September 1982.

"[Corey and I] reached the conclusion, as did Crick, that in the alpha-keratin proteins the alpha helices are twisted together into ropes or cables. This idea essentially completed our understanding of the alpha-keratin diffraction patterns."

Linus Pauling. "The Discovery of the Alpha Helix." September 1982.

"Pauling was a more important figure in molecular biology than is sometimes realized. Not only did he make certain key discoveries (that sickle cell anemia is a molecular disease, for example), but he had the correct theoretical approach to these biological problems."

Francis Crick. What Mad Pursuit: A Personal View of Scientific Discovery (New York: Basic Books). 1988.

"Time has shown that, so far, Pauling was right and Delbrück was wrong, as indeed Delbrück acknowledged in his book, Mind into Matter. Everything we know about molecular biology appears to be explainable in a standard chemical way."

Francis Crick. What Mad Pursuit: A Personal View of Scientific Discovery (New York: Basic Books). 1988.

"During a period of about a decade, beginning in 1926, my principal research effort was an attack on the problem of the nature of life, which was, I think, successful, in that the experimental studies carried out by my students and me provided very strong evidence that the astonishing specificity characteristic of living organisms, such as an ability to have progeny resembling themselves, is the result of a special interaction between molecules that have mutually complementary structures. In a world that is not in thermodynamic equilibrium, such as our earth, parts of which are heated by sunlight, it is possible for certain chemical reactions to be favored, for example by the action of enzymes or other catalysts. A molecule or group of molecules that can catalyze its or their own production is thereby able to prosper. This process, over a period of four billion years, has led to the existence of human beings. So we are here, in this wonderful world, with its millions of different kinds of molecules and crystals, the mountains, the plains and the oceans, and the millions of species of plants an animals. We have developed a degree of intelligence that permits us to understand the wonder of the world, and also that has given us the power to destroy the world and the human race. With Benjamin Franklin I say, 'O that moral Science were in as fair a way of improvement, that men would cease to be wolves to one another, and that human beings would at length learn what they now improperly call humanity'."

Linus Pauling. "The Meaning of Life." In The Meaning of Life: Reflections in Words and Pictures on Why We Are Here, David Friend and the Editors of Life, eds. (Boston: Little, Brown). 1991.

"Propelled by Dionysian forces far stronger than any of his colleagues', Pauling's intellectual ambition was reinforced by bold managerial maneuvers that placed him and Caltech at the forefront of Rockefeller support and of the production of molecular knowledge."

Lily E. Kay. The Molecular Vision of Life: Caltech, The Rockefeller Foundation and the Rise of the New Biology (New York: Oxford University Press). 1993.

"In suggesting that hydrogen bonds determined the three-dimensional configuration of proteins - and thus their biological specificity - Pauling and Mirsky enunciated a fundamental relation between molecular structure and biological function. It was also one of the cornerstones of Pauling's conception of molecular architecture, a metaphor and method for explaining life in health and disease, which would lend legitimacy to the molecular biology enterprise."

Lily E. Kay. The Molecular Vision of Life: Caltech, The Rockefeller Foundation and the Rise of the New Biology (New York: Oxford University Press). 1993.

"Wooden and plastic balls of all colors were designed and made at the laboratories and shops of the chemistry division, their scales and shapes represented such atoms as carbon, oxygen and nitrogen as they exist in proteins. They could be added and subtracted at will, thereby bringing some order to the process of building by trial and error without a clear blueprint."

Lily E. Kay. The Molecular Vision of Life: Caltech, The Rockefeller Foundation and the Rise of the New Biology (New York: Oxford University Press). 1993.

"During a single year, using his own x-ray equipment, Corey made great strides into the protein puzzle. He showed that in the crystalline dipeptide diketopiperazine (a simplified analogue of amino acids), the amide bonds were coplaner, strongly suggesting the presence of a resonance structure - observations that fit precisely with Pauling's studies of the amide bond in urea during the early 1930s."

Lily E. Kay. The Molecular Vision of Life: Caltech, The Rockefeller Foundation and the Rise of the New Biology (New York: Oxford University Press). 1993.

"Pauling's model-building approach was novel to both crystallography and biological research. It became crucial to the investigations of protein structure, allowing precise visualization of the molecular arrangements and interactions hitherto hidden."

Lily E. Kay. The Molecular Vision of Life: Caltech, The Rockefeller Foundation and the Rise of the New Biology (New York: Oxford University Press). 1993.

"For about forty years I have been thinking of writing a book on the molecular basis of biological specificity, and I am trying to settle down to writing it. My tentative title now is The Nature of Life, Including My Life. I felt that biological specificity was the characteristic property of living organisms, and that it needed to be explained. I think our immunochemical work did that job."

Linus Pauling. Letter to Lily Kay. January 1993.

"This was a fortunate arrangement. Not only did Mirsky teach me how to handle proteins in the laboratory - they are far more delicate than inorganic substances - but he also gave me a great amount of information about the properties of proteins and especially about denaturation of proteins."

Linus Pauling. "How My Interest in Proteins Developed." January 12, 1993.

"I felt that I knew enough about the structure of polypeptide chains to be able to determine the structure of alpha-keratin by analyzing Astbury's diffraction photographs and similar ones made in our own x-ray laboratory, and I spent a good part of the summer of 1937 in this effort."

Linus Pauling. "How My Interest in Proteins Developed." January 12, 1993.

"Todd says that he told Bragg that the amide group was planar, but apparently Bragg did not understand what he said. I was fortunate in having a good understanding of two fields, structural chemistry and x-ray diffraction. My recommendation to young scientists is that they get a thorough knowledge of one field, and also some knowledge of other fields of science."

Linus Pauling. "How My Interest in Proteins Developed." January 12, 1993.

"I don't think it's right, really, to discuss the impact of Linus Pauling on molecular biology. Rather he was one of the founders of molecular biology. It wasn't that it existed in some way and he came down and put something on it. He was one of the founders who got the whole discipline going."

Francis Crick. "The Impact of Linus Pauling on Molecular Biology." February 28, 1995.

"While my own work at Caltech had nothing to do with protein structure, Pauling used to talk to me occasionally about his models and what one could learn from them. In his lecture, he had talked about spirals. In conversation a few days later, I told him that for me the word "spiral" referred to a curve in a plane. As his polypeptide coils were three-dimensional figures, I suggested they were better described as "helices." Pauling's erudition did not stop at the natural sciences. He answered, quite correctly, that the words "spiral" and "helix" are practically synonymous and can be used almost interchangeably, but he thanked me for my suggestion because he preferred "helix" and declared that he would always use it henceforth. Perhaps he felt that by calling his structure a helix there would be less risk of confusion with the various other models that had been proposed earlier. In their 1950 short preliminary communication, Pauling and Corey wrote exclusively about spirals, but in the series of papers published the following year the spiral had already given way to the helix. There was no going back. A few years later we had the DNA double helix, not the DNA double spiral. The formulation of the α-helix was the first and is still one of the greatest triumphs of speculative model building in molecular biology, and I am pleased that I helped to give it its name."

Jack Dunitz. "La Primavera." (unpublished manuscript) 2011.