Turan Ünak

What is the potential use of thorium in the future energy production technology

Todays nuclear technology has principally been based on the use of fissile U-235 and Pu-239. While the natural thorium isotope Th-232 can finally be transformed to a fissile U-233 nucleus following a thermal neutron capture reaction, the existence of thorium in the nature and its potential use in the nuclear technology were not unfortunately into account with a sufficient importance. This was probably because of the geological availability of natural resources of thorium and uranium. Global distributions of thorium and uranium reserves clearly indicate that in general some developed countries such as the USA, Canada, Australia have considerable uranium reserves and contrarily only some developing countries such as Brazil, Turkey, India, Egypt have considerable thorium reserves as being totally about 70 % of the global reserve. All technical parameters obtained from the studies on thorium fuel cycle during the last 50 years indicate that thorium fuel cycle can be used in most of reactor types already operated. In addition, accelerated-driven hybrid systems promise to use the thorium based nuclear fuels. So, thorium will probably be a nuclear material much more valuable than uranium in the future. For this reason, all developing countries having thorium reserves should focus their technological attentions to the evaluation of their national thorium resources like in the case of India. In this paper a brief story on the studies of thorium and its potential use in the future energy production technology have been summarized.

Self-radioiodination of iodogen.

Iodogen (1,3,4,6-tetrachloro-3alpha,6alpha-diphenylglucoluril) is commonly used for the radioiodination of proteins as an oxidative agent. The oxidative character of iodogen is not clear, but the two carbonyl groups in its structure probably have an essential role in its oxidizing character. In this study, the self-radioiodination of iodogen has been examined. It was observed that about 10-20% of the initial iodine radioactivity was consumed for the self-radioiodination of iodogen itself. On the other hand, the radioiodinated iodogen removed by ethyl alcohol from the iodogen-coated tubes showed clearly that no thyroid uptake was observed and that it was rapidly cleared out from the whole body of a rabbit administered with the radioiodinated iodogen by injection via the ear vein.

Direct radioiodination of metabolic 8-hydroxy-quinolyl-glucuronide, as a potential anti-cancer drug.

8-Hydroxy-quinolyl-glucuronide (8-HOQ-Glu) can be deglucuronidated by the beta-glucoronidase enzyme, which has an activity that is considerably high in certain kinds of cancer cell. Owing to this enzyme activity, 8-HOQ-Glu can be considered as a potential anti-cancer drug. The combination of the radiotoxicity known of 125I nuclide with the cytotoxicity of 8-hydroxy-quinoline (8-HOQ) and particularly the selective carrying of 125I into the cancer cells is the principal aim of this study. As a first step, the metabolic 8-HOQ-Glu was extracted from the urine of rabbits treated with 8-HOQ directly radioiodinated using the iodogen method. The results showed that the radioiodination was successfully realized, and its yield was found to be about 90-95%.Abstract 8-Hydroxy-quinolyl-glucuronide (8-HOQ-Glu) can be deglucuronidated by the β-glucoronidase enzyme, which has an activity that is considerably high in certain kinds of cancer cell. Owing to this enzyme activity, 8-HOQ-Glu can be considered as a potential anti-cancer drug. The combination of the radiotoxicity known of 125 I nuclide with the cytotoxicity of 8-hydroxy-quinoline (8-HOQ) and particularly the selective carrying of 125 I into the cancer cells is the principal aim of this study. As a first step, the metabolic 8-HOQ-Glu was extracted from the urine of rabbits treated with 8-HOQ directly radioiodinated using the iodogen method. The results showed that the radioiodination was successfully realized, and its yield was found to be about 90–95%.

Synthesis and iodine-125 labelling of glucuronide compounds for combined chemo- and radiotherapy of cancer

Some types of cancer cells have high levels of beta-glucuronidase activity. This enzyme is able to deglucuronidate a variety of glucuronide derivatives on the cell membrane. Either O- or N-glucuronides can be selectively incorporated into the cancer cells. If the aglycone is cytotoxic, the glucuronide can potentially be used as a selective anti-cancer drug in cancers with high levels of beta-glucuronidase activity. Nevertheless, in vitro studies carried out by various investigators have shown that the cytotoxicities of several glucuronides in cancer cells are not sufficiently high for their use as effective anti-cancer drugs. For this reason, we have synthesized glucuronide compounds radiolabelled with iodine-125 combining the radiotoxicity of this Auger electron emitter with the chemotoxicity of the aglycone portion of the glucuronide.

Some microdosmetric data on Astatine-211.

Abstract Radionuclides which emit short range, high LET radiations such as alpha and Auger electrons have very promising applications in cancer therapy. Such radionuclides should eventually be incorporated into cell nuclei to achieve high radiotoxic effectiveness. This means that the dose distribution within the cell nucleus at microscopic levels is very important for comparison of the real differences between the radiotoxic effectiveness of different radionuclides. An experimental setup to determine real dose absorption on the microscopic scale is extremely difficult to design. For this reason, calculation procedures for microscopic dose absorption are of special interest for the diagnostic and therapeutic applications of radionuclides which emit short-range and high LET radiations. A specific calculation method for microscopic energy absorptions within the cell nucleus from Auger electrons of 125I was described earlier. In this study, the radiotoxic effectiveness of 211At and 125I has been compared using the data obtained by this calculation method. The data obtained show clearly that the radiotoxicity of the alpha and Auger emitter radionuclide 211At is comparable to that of 125I.

Microscopic energy absorption of the DNA molecules from auger electrons of iodine-125

The microscopic energy distribution along the DNA duplex due to local absorption of Auger electrons of iodine-125 incorporated into the DNA molecule, has been theoretically calculated. Our calculation method [Unak T. Nucl. Instrum. Methods A255, 274 (1987); Unak T Ibid. A255, 281 (1987)] recently presented for spatial energy distribution from low-energy electrons in different chemical systems, has also been used for these calculations. As a result, it has been determined that the maximum range of the highest energy 125I Auger electrons in a linear DNA duplex is about 38 micron, and the total energy absorbed by DNA molecule per decay is about 10.3 keV, which is approximately half of the total energy released by electrons (19.8 keV per decay). This absorbed energy is not uniformly distributed along the DNA duplex. Consequently, it has also been determined that the microscopic energy absorption per DNA base or sugar-phosphate group rapidly decreased with the distance from the 125I nuclide, and reached about 5 eV per DNA base or sugar-phosphate group at a distance of about 2 nm. On the other hand, the results also demonstrated that the local absorption of 125I Auger electrons is able to produce alone at least one double strand break (DSB) on the DNA duplex without the support of the neutralization effects of highly charged tellurium ions.Abstract The microscopic energy distribution along the DNA duplex due to local absorption of Auger electrons of iodine-125 incorporated into the DNA molecule, has been theoretically calculated. Our calculation method [Unak T. Nucl. Instrum. Methods A255, 274 (1987); Unak T. Ibid. A255, 281 (1987)](12,13) recently presented for spatial energy distribution from low-energy electrons in different chemical systems, has also been used for these calculations. As a result, it has been determined that the maximum range of the highest energy 125I Auger electrons in a linear DNA duplex is about 38 μm, and the total energy absorbed by DNA molecule per decay is about 10.3 keV, which is approximately half of the total energy released by electrons (19.8 keV per decay). This absorbed energy is not uniformly distributed along the DNA duplex. Consequently, it has also been determined that the microscopic energy absorption per DNA base or sugar-phosphate group rapidly decreased with the distance from the 125I nuclide, and reached about 5 eV per DNA base or sugar-phosphate group at a distance of about 2 nm. On the other hand, the results also demonstrated that the local absorption of 125I Auger electrons is able to produce alone at least one double strand break (DSB) on the DNA duplex without the support of the neutralization effects of highly charged tellurium ions.

Synthesis, radiolabeling and in vivo biodistribution of diethylstilbestrol phosphate derivative (DES-P)

Diethylstilbestrol (DES) is a well known, nonsteroidal estrogen with high affinity for the estrogen receptor (ER). Today DES is used to treat breast and prostate cancers. A phosphate derivative of DES [Diethylstilbestrol diphosphate (DES-P)] which is specific to tumor cells consisting alkaline phosphatase enzyme was synthesized and labeled with 99mTc using tin chloride as reducing agent. In vivo biological activity of 99mTc labeled diethylstilbestrol phosphate compound (99mTc-DES-P) was examined by biodistribution studies on Wistar Albino rats. Statistical evaluation was performed using SPSS 13 program. The percentage (%) radiolabeling yield of 99mTc-DES-P and quality control studies were done by Thin Layer Radio Chromatography (TLRC). Results showed that, 99mTc-DES-P may be proposed as an imaging agent for ER enriched tumors such as uterus and prostate and their metastases in bones.

Metabolic comparison of radiolabeled aniline- and phenol-phthaleins with 131I

The metabolic comparison of aniline- and phenol-phthaleins radiolabeled with (131)I ((131)I-APH and (131)I-PPH, respectively) has been investigated in this study. To compare the metabolic behavior of these phthaleins and their glucuronide conjugates radiolabeled with (131)I, scintigraphic and biodistributional techniques were applied using male Albino rabbits. The results obtained have shown that these compounds were successfully radioiodinated with a radioiodination yield of about 100%. Maximum uptakes of (131)I-APH and (131)I-PPH, which were metabolized as N- and O-glucuronides, were observed within 2 h in the bladder and in the small intestine, respectively. In the case of verification of considerably up taking of these compounds also by tumors developed in the small intestine and in the bladder tissues, these results can be expected to be encouraging to test these compounds, which will be radiolabeled with other radioiodines such as (125)I, (123)I and (124)I as imaging and therapeutic agents in nuclear medical applications.

Determination of the stability constants of uranyl complex with 8-hydroxyquinolinium sulfate

Abstract8-Hydroxyquinoline (8-HOQ) is known as an important chelating agent for several metal ions. This compound is practically insoluble in water. For this reason, in this study its water soluble sulfate salt has been used for complexing uranyl ions and the stability constants of the complex have been determined. The Irving-Rosotti method computing the Calvin-Bjerrum pH-titration data, was applied. Finally, the stability constants of the complex formed between (8-HOQN-H)2SO4 and uranyl ions were found to be lgK1=8.25 and lgK2=4.15, the overall stability constant being {ie55-1}.

Radioiodination and preliminary biological tests of aniline-mustard and its glucuronide conjugate as a potential anticancer prodrug

Aniline-mustard and its glucuronide conjugate were radioiodinated with 131I. The preliminary dynamic tests were carried out on rabbits. The scintigrams showed clearly that the glucuronide conjugate of aniline-mustard was very quickly cleared from the metabolism, accumulating in the bladder in about 15 minutes. The clearance time of radioiodinated aniline-mustard-glucuronide was considerably longer (about 45 min.). The results obtained from the biodistributional studies have represented interesting differences between the metabolic details of radioiodinated compounds, and indicated that the glucuronide conjugate of aniline-mustard may be a promising radioiodinated prodrug, if verification of its selective accumulation in some kinds of tumor cells can be obtained.