Development of carbon-11 labelled PET tracers-radiochemical and technological challenges in a historic perspective.

The development of positron emission tomography (PET) from being an exclusive and expensive research tool at major research institutes to a clinically useful modality found at most major hospitals around the world is largely dependent on radiochemistry and synthesis technology achievements by a few pioneer researchers starting their PET careers 40 to 50 years ago. Especially, the introduction of [(11) C]methyl iodide resulted in a quantum jump in the history of PET tracer development enabling the smooth labelling of a multitude of useful tracers. A more recent and still challenging methodological improvement is transition metal mediated (11) C-carbonylations, having a large synthetic potential that has, however, not yet been realized in the clinical setting. This mini-review focuses on the history of carbon-11 radiochemistry and related technology developments and the role this played in PET tracer developments, especially emphasizing radiolabelling of endogenous compounds. A few examples will be presented of how the use of radiolabelled endogenous substances have provided fundamental information of in vivo biochemistry using the concept of position-specific labelling in different positions in the same molecule.

Clouds, airplanes, trucks and people: carrying radioisotopes to and across Mexico.

The aim of this paper is to describe the early stages of Mexican nuclearization that took place in contact with radioisotopes. This history requires a multilayered narrative with an emphasis in North-South asymmetric relations, and in the value of education and training in the creation of international asymmetrical networks. Radioisotopes were involved in exchanges with the United States since the late 1940s, but also with Canada. We also describe the context of implementation of Eisenhower's Atoms for Peace initiative in Mexico that opened the door to training programs at both the Comisión Nacional de Energía Nuclear and the Universidad Nacional Autónoma de México. Radioisotopes became the best example of the peaceful applications of atomic energy, and as such they fitted the Mexican nuclearization process that was and still is defined by its commitment to pacifism. In 1955 Mexico became one of the 16 members of the atomic fallout network established by the United Nations. As part of this network, the first generation of Mexican (women) radio-chemists was trained. By the end of the 1960s, radioisotopes and biological markers were being produced in a research reactor, prepared and distributed by the CNEN within Mexico. We end up this paper with a brief reflection on North-South nuclear exchanges and the particularities of the Mexican case.

Clouds, airplanes, trucks and people: carrying radioisotopes to and across Mexico

The aim of this paper is to describe the early stages of Mexican nuclearization that took place in contact with radioisotopes. This history requires a multilayered narrative with an emphasis in North-South asymmetric relations, and in the value of education and training in the creation of international asymmetrical networks. Radioisotopes were involved in exchanges with the United States since the late 1940s, but also with Canada. We also describe the context of implementation of Eisenhower´s Atoms for Peace initiative in Mexico that opened the door to training programs at both the Comisión Nacional de Energía Nuclear and the Universidad Nacional Autónoma de México. Radioisotopes became the best example of the peaceful applications of atomic energy, and as such they fitted the Mexican nuclearization process that was and still is defined by its commitment to pacifism. In 1955 Mexico became one of the 16 members of the atomic fallout network established by the United Nations. As part of this network, the first generation of Mexican (women) radio-chemists was trained. By the end of the 1960s, radioisotopes and biological markers were being produced in a research reactor, prepared and distributed by the CNEN within Mexico. We end up this paper with a brief reflection on North-South nuclear exchanges and the particularities of the Mexican case (AU)

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Otto Hahn (1879-1968): pioneer in radiochemistry and discoverer of radiotherapeutic mesothorium.

Otto Hahn was a German innovative chemist. He had discovered various radioactive elements, as well as the nuclear fission. He finally received the Nobel Prize for his participation in the atomic energy project, which Hahn and others considered that could be a factor used for peaceful means like cheap electricity and cheap industrial products. His greatest discovery though in oncology was mesothorium, a radioactive element that had been used to treat all cancer types at the beginning of the 20th century.

Carbohydrate radicals: from ethylene glycol to DNA strand breakage.

Radiation-induced DNA strand breakage results from the reactions of radicals formed at the sugar moiety of DNA. In order to elucidate the mechanism of this reaction investigations were first performed on low molecular weight model systems. Results from studies on deoxygenated aqueous solutions of ethylene glycol, 2-deoxy-d-ribose and other carbohydrates and, more relevantly, of d-ribose-5-phosphate have shown that substituents can be eliminated from the ß-position of the radical site either proton and base-assisted (as in the case of the OH substituent), or spontaneously (as in the case of the phosphate substituent). In DNA the C(4') radical undergoes strand breakage via this type of reaction. In the presence of oxygen the carbon-centred radicals are rapidly converted into the corresponding peroxyl radicals. Again, low molecular weights models have been investigated to elucidate the key reactions. A typical reaction of DNA peroxyl radicals is the fragmentation of the C(4')-C(S') bond, a reaction not observed in the absence of oxygen. Although OH radicals may be the important direct precursors of the sugar radicals of DNA, results obtained with poly(U) indicate that base radicals may well be of even greater importance. The base radicals, formed by addition of the water radicals (H and OH) to the bases would in their turn attack the sugar moiety to produce sugar radicals which then give rise to strand breakage and base release. For a better understanding of strand break formation it is therefore necessary to investigate in more detail the reactions of the base radicals. For a start, the radiolysis of uracil in oxygenated solutions has been reinvestigated, and it has been shown that the major peroxyl radical in this system undergoes base-catalysed elimination of [Formula: see text], a reaction that involves the proton at N(l). In the nucleic acids the pyrimidines are bound at N(l) to the sugar moiety and this type of reaction can no longer occur. Therefore, with respect to the nucleic acids, pyrimidines are good models only in acid solutions where the [Formula: see text] elimination reaction is too slow to compete with the bimolecular reactions of the peroxyl radicals. Moreover, the long lifetime of the radical sites on the nucleic acid strand may allow reactions to occur which are kinetically of first order, and which cannot be studied in model systems at ordinary dose rates. It is therefore suggested to extend model system studies to low dose rates and to oligonucleo-tides. Such studies might eventually reveal the key reactions in radical-induced DNA degradation.

Clemens von Sonntag and the early history of radiation-induced sugar damage in DNA.

PURPOSE: This article reviews the early history of ionizing radiation-induced sugar damage in DNA in dedication to Prof. Clemens von Sonntag, who recently passed away. It covers the time between 1968 and 1978, during which most of the work on the ionizing radiation-induced damage to polyalcohols, carbohydrates and the 2'-deoxyribose moiety in DNA was performed. Methodologies using gas chromatography-mass spectrometry (GC-MS) were developed to identify and quantify the radiation-induced products that had previously remained elusive. Products were identified by GC-MS either directly or after reduction of samples with NaBH(4) or NaBD(4). Incorporation of deuterium atoms by NaBD(4)-reduction facilitated the identification of aldehyde, keto, carboxyl and deoxy groups in the molecules. Numerous products of a polyalcohol and carbohydrates were identified and quantified. Mechanisms of product formation were proposed. Several products of the 2'-deoxyribose moiety in DNA were identified, indicating that they were released from DNA strand, not bound to it. Alkali labile sites and products still remaining within DNA or bound to DNA as end groups were also elucidated by first reducing irradiated samples with NaBD(4) followed by alkali treatment and GC-MS analysis. CONCLUSION: The knowledge of the products of the 2'-deoxyribose moiety in DNA led to the first mechanistic understanding of various pathways of hydroxyl radical-induced DNA strand breakage. To this date, some of these mechanisms still remain the most-widely studied mechanisms of DNA damage. Prof. von Sonntag's contributions to the understanding of the radiation chemistry of carbohydrates and DNA helped shape this field of science for years to come.

[Notable radiophysicists and radiochemists in Croatia by 1945]. / Znameniti radiofizicari i radiokemicari u Hrvatskoj do 1945.

Physicists and chemists were among the first potential victims of occupational exposure to ionising radiation and they were also the first to warn about the harmful effects of radiation on living organisms. This review presents the work of the first notable scientists in the field of radiation science in Croatia from the discovery of radiation (Henry Becquerel in 1896) to 1945. The beginning of radiation science and radiation protection in Croatia can be traced to the end of the 19th century. Our research of the archived material and literature not only gave a deeper insight to the life and work of some of these notable scientists, but also gave a glimpse of previously unknown facts and details important for the history and development of radiation science, radiation protection, as well as medical physics. Our research has shown that Croatian scientists not only kept pace with contemporary scientific knowledge but also made notable contributions from the very beginning.