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Journal of Thermal Analysis and Calorimetry
Authors:
H. El-Boraey
,
F. El-Saied
, and
S. Aly

Abstract  

UO2(VI), Sn(IV), Th(IV) and Li(I) complexes of 4-azomalononitrile antipyrine (L) have been isolated and characterized based on IR spectra, 1H NMR, elemental analyses, molar conductance and thermal analysis (DTA/TG). The study revealed that the ligand behaves as a neutral bidentate one and coordination takes place via the carbonyl atom of pyrazolone ring >C=O and the azomethine nitrogen >C=N. The thermal stability of the metal complexes were investigated by thermogravimetry (TG), differential thermal analysis (DTA) techniques and infrared spectra, and correlated to their structure. The thermal study revealed that Th(IV) complexes show lower thermal stability than both UO2(VI) and Sn(IV) complexes.

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Summary  

Indomethacin was successfully labeled with 125I. This labeling reaction was carried out via electrophilic substitution of hydrogen atom with the iodonium atom I+. The reaction was found to be strongly dependent on pH of the reaction medium. At neutral pH value, 7 the labeling yield was maximum. This may be due to the good solubility of indomethacin, good protonation and good working of the oxidizing agent at this pH value. Towards the acidic pH value, the yield decreased and towards the alkaline pH value the yield decreased due to the decomposition of the indomethacin. The labeling reaction is very fast but needs five minutes for completion. The produced 125I-indomethacin was found stable in-vivo as the thyroid gland uptake did not exceed 2%. Labeled indomethacin shows a good localization in inflamed muscle, either septic or sterile. It excretes mainly via liver and to some extent via kidney. The imaging must be carried out at 24-hour post injection, after that time, the background activity has cleared and the activity is concentrated in the target site.

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Summary  

Piroxicam was labeled effectively with 99mTc due to the presence of electron donating atoms such as sulfur, nitrogen, and oxygen in its structure. The labeling yield was found to be influenced by different factors such as the amount of piroxicam, stannous chloride dihydrate, pH of the reaction mixture, reaction time and reaction temperature. The suitable amount of stannous chloride dihydrate required to produce high labeling yield of 99mTc-piroxicam was 50 μg, above this quantity (200 μg) a colloidal solution was formed. Another factor which plays a significant role in this labeling reaction is the pH of the reaction medium. The labeling reaction was done only at alkaline pH range from 9-11, because piroxicam was not soluble at acidic or neutral pH. The labeling reaction proceeded well at room temperature and the complex was decomposed by heat. The labeled piroxicam (99mTc-piroxicam ) showed good localization in inflamed foci and good imaging must be taken at 24-hour post injection, as the ratio of both types of inflammation (sterile and septic) to the background are 10.6 and 8.7, respectively.

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Summary  

This investigation focused on the labeling of pefloxacin, a fluoroquinolone antibacterial agent, with 99mTc to form 99mTc-pefloxacin complex. The labeling process was done by direct addition of pertechnetate in isotonic solution to Sn-pefloxacin solution. The labeling technique is effective, as a high labeling yield (98%) was obtained after 30-minute reaction time. Different factors were found that influenced this labeling reaction: 0.5 mg pefloxacin or more must be used to prevent the formation of colloids in the reaction medium. Fifty micrograms of stannous chloride dihydrate were found to be sufficient to reduce all pertechnetate with activity ranging from 37 to 3700 MBq without the detection of free pertechnetate or colloids in the reaction mixture. The pH of the reaction medium was found to play an important role in the labeling process. The labeling reaction proceeds well at neutral pH (pH 6) but at acidic pH value (pH 4 or below) the yield of 99mTc-pefloxacin complex decreased markedly to a labeling yield of 5%. The reaction mixture must be heated to 100 °C in an oil bath to enhance the formation of the 99mTc-pefloxacin complex. The biodistribution data show that 99mTc labeled pefloxacin was retained in infectious focus. The retention was specific since the abscess uptake of 99mTc-pefloxacin remained high as compared to the uptake of aseptic foci at 24-hour post injection. Also, the clearance of the tracer from other tissues is rapid on the contrary to its clearance from the septic focus. This supports the hypothesis that 99mTc-pefloxacin is retained at the infectious site because of its specific binding to the gyrase enzymes of bacterial cells.

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