23 research outputs found
Metal Complexation and H-bonding Effects on Electronic Structure of Cytosine Studied in the Gas Phase
The influence of H-bonding and complexation with cations (probed by HF, F–, Li+, Na+ and K+) on structural and π-electron changes in the six most stable cytosine tautomers has been studied in the gas phase using the B3LYP/6-311++G(2d,2p) computational level. The presence of two exo- groups (ami-no/imino and carbonyl/hydroxyl) in cytosine tautomers significantly increases their sensitivity to structur¬al changes due to intra- and intermolecular interactions. These interactions induce large changes in aroma¬ticity of the rings and in the CX (X = N, O) bond lengths of exocyclic groups. Three types of H-bonds, considering their strength, could be distinguished: (i) charge-assisted X–•••HF, X = N or O, as the strong¬est, (ii) neutral X•••HF, where X is the nitrogen atom of the ring or imino group or the keto form oxygen atom and (iii) also neutral X•••HF, where X being either amino N or alternatively hydroxylic O. Hydrogen bond energy decreases approximately twice in the above listed sequence of interactions. Structural conse¬quences of H-bonding and metal complexation have been observed not only in the immediate region of the interaction but also in other parts of the molecule (the shape of the amino group, changes in CO and CN bond lengths). Complexation of the cytosine tautomers with cations leads to monotonic changes in
aromaticity in line with an increase of their ionic radii
Why 1,2‑quinone derivatives are more stable than their 2,3‑analogues?
In this work, we have studied the relative stability
of 1,2- and 2,3-quinones. While 1,2-quinones have
a closed-shell singlet ground state, the ground state for
the studied 2,3-isomers is open-shell singlet, except for
2,3-naphthaquinone that has a closed-shell singlet ground
state. In all cases, 1,2-quinones are more stable than their
2,3-counterparts. We analyzed the reasons for the higher
stability of the 1,2-isomers through energy decomposition
analysis in the framework of Kohn–Sham molecular orbital
theory. The results showed that we have to trace the origin
of 1,2-quinones’ enhanced stability to the more efficient
bonding in the π-electron system due to more favorable
overlap between the SOMOπ of the ·C4n−2H2n–CH·· and
··CH–CO–CO· fragments in the 1,2-arrangement. Furthermore,
whereas 1,2-quinones present a constant trend with their elongation for all analyzed properties (geometric,
energetic, and electronic), 2,3-quinone derivatives present a
substantial breaking in monotonicity.European
Union in the framework of European Social Fund through the Warsaw
University of Technology Development Programme. O.A. S., H.
S. and T.M. K
Towards physical interpretation of substituent effects : the case of N- and C3-substituted pyrrole derivatives
Experimental study of radiopharmaceuticals based on technetium-99m labeled derivative of glucose for tumor diagnosis
Purpose: to study the potential utility of 1-thio-D-glucose labeled with 99mTc for cancer imaging in laboratory animals. Materials and method: the study was carried out in cell cultures of normal CHO (Chinese hamster ovary cells CHO) and malignant tissues MCF-7 (human breast adenocarcinoma MCF-7). To evaluate the uptake of 99mTc-1-thio-D-glucose in normal and tumor tissue cells, 25 MBq of 1-thio-D-glucose labeled with 99mTc was added to the vials with 3 million cells and incubated for 30 minutes at room temperature. After centrifugation of the vials with cells, the supernatant was removed. Radioactivity in vials with normal and tumor cells was then measured. In addition, the study included 40 mice of C57B 1/6j lines with tumor lesion of the right femur. For neoplastic lesions, Lewis lung carcinoma model was used. Following anesthesia, mice were injected intravenously with 25MBq of 99mTc-1-thio-D-glucose. Planar scintigraphy was performed 15 minutes later in a matrix of 512x512 pixels for 5 minutes. Results: when measuring the radioactivity of normal and malignant cells after incubation with 99mTc-1-thio-D- glucose, it was found that the radioactivity of malignant cells was higher than that of normal cells. The mean values of radioactivity levels in normal and malignant cells were 0.3±0.15MBq and 1.07±0.6MBq, respectively. All examined animals had increased accumulation of 99mTc-1-thio- D-glucose at the tumor site. The accumulation of 99mTc-1-thio-D-glucose in the tumor was on average twice as high as compared to the symmetric region. Conclusion: The present study demonstrated that 99mTc-1-thio-D-glucose is a prospective radiopharmaceutical for cancer visualization. In addition, high accumulation of 99mTc-1-thio-D-glucose in the culture of cancer cells and in tumor tissue of animals demonstrates tumor tropism of the radiopharmaceutical