Search results for "cytosine"
showing 10 items of 117 documents
Kinetic and equilibrium studies for the adsorption of acid nucleic bases onto K10 montmorillonite
2011
Abstract The kinetic of the adsorption of two nucleic acid bases, namely adenine (A) and cytosine (C), on K10 montmorillonite (MMT) clay has been investigated over a wide range of nitrogenous bases concentrations, by using the spectrophotometric method. The measurements have been performed at T = 25.0 °C and pH = 4.0 where adenine and cytosine exist both in their protonated and neutral forms. Preliminary to the kinetic data treatment, the adsorption isotherms have been gathered and, then, analyzed by using the Freundlich and the Dubinin–Radushkevich model. The obtained results allow to draw the conclusion that physisorption of adenine and cytosine on MMT occurs and the process is mainly gov…
Modeling hole transfer in DNA: Low-lying excited states of oxidized cytosine homodimer and cytosine–adenine heterodimer
2008
Abstract Charge transport in DNA strands has been studied by characterizing on theoretical grounds the lowest doublet states of the oxidized cytosine homodimer (CC + ) and adenine–cytosine heterodimer (CA + ) along the intermolecular separation of the monomers. The high-level quantum-chemical ab initio CASPT2 method and accurate one-electron basis sets have been employed. Both cationic species are found to be bound with comparable binding energies as those of neutral CC and reduced CC − . The results suggest that charge transport in DNA and the distinct photophysical attributes related to the polymer can be described within the framework of a unified theory. A cooperative micro-hopping mech…
Associations between single-nucleotide polymorphisms of the VEGF gene and long-term prognosis of oral squamous cell carcinoma.
2012
Department of Otorhinolaryngology, Johannes Gutenberg-University, Mainz, GermanyINTRODUCTION: Functional polymorphisms (SNPs) ofthe vascular endothelial growth factor (VEGF) are asso-ciated with the incidence of oral squamous cell carcinoma(OSCC). An impact of VEGF-SNPs on prognosis of OSCCpatients seems possible. Therefore, correlations betweenprognostic parameters of OSCC patients and five VEGF-SNPs were determined.MATERIALS AND METHODS: In a retrospective long-term study, in 113 OSCC patients that underwentcurative resections, five VEGF-SNPs ( 1154 G/A,+405 G/C, +936 C/T, 2578 C/A, and 460 C/T) wereanalyzed. Associations between SNPs and prognosis(incidence of local recurrent disease, seco…
Phase I/II Trial of High-Dose Cytosine Arabinoside and Mitoxantrone in Adult Refractory Acute Myeloid Leukemia
1987
In spite of a high initial response rate of 60% –80% the vast majority of adult patients with acute myeloid leukemia (AML) still cannot be cured of the disease and ultimately die from recurrent and refractory leukemia. The development of new therapeutic approaches and of more effective drugs therefore seems warranted.
Genetic Analysis of Sequences in the 3′ Nontranslated Region of Hepatitis C Virus That Are Important for RNA Replication
2002
ABSTRACT The genome of the hepatitis C virus (HCV) is a plus-strand RNA molecule that carries a single long open reading frame. It is flanked at either end by highly conserved nontranslated regions (NTRs) that mediate crucial steps in the viral life cycle. The 3′ NTR of HCV has a tripartite structure composed of an about 40-nucleotide variable region, a poly(U/UC) tract that has a heterogeneous length, and a highly conserved 98-nucleotide 3′-terminal sequence designated the X tail or 3′X. Conflicting data as to the role the sequences in the 3′ NTR play in RNA replication have been reported. By using the HCV replicon system, which is based on the self-replication of subgenomic HCV RNAs in hu…
Investigations on the Mechanism of Induction of the Alkaline Phosphatase by Bromodesoxyuridine in Herpes simplex Virus Transformed Cells and the Tran…
1980
Addition of BrdUrd in combination with prednisolone to HSVi-transformed hamster embryo cells induces an alkaline phosphatase (AP). FdUrd enhances, dThd reduces the inducing capacity of BrdUrd and prednisolone. Induction is prevented by addition of cycloheximide or of cytosine arabinoside. BrdUrd reduces transport and phosphorylation of exogenously applied labeled Urd, especially the amount of UTP, UDP and Urd-diphosphate sugars. The Lineweaver-Burk-plot of uridine-uptake after addition of BrdUrd reveales the characteristics of the mixed type inhibition (competitive-noncompetitive).
Proton/Hydrogen Transfer Mechanisms in the Guanine–Cytosine Base Pair: Photostability and Tautomerism
2013
Proton/hydrogen-transfer processes have been broadly studied in the past 50 years to explain the photostability and the spontaneous tautomerism in the DNA base pairs. In the present study, the CASSCF/CASPT2 methodology is used to map the two-dimensional potential energy surfaces along the stretched NH reaction coordinates of the guanine–cytosine (GC) base pair. Concerted and stepwise pathways are explored initially in vacuo, and three mechanisms are studied: the stepwise double proton transfer, the stepwise double hydrogen transfer, and the concerted double proton transfer. The results are consistent with previous findings related to the photostability of the GC base pair, and a new contrib…
Density functional theory (DFT) prediction of structural and spectroscopic parameters of cytosine using harmonic and anharmonic approximations
2015
The applicability of popular and efficient B3LYP hybrid density functional and medium-size Pople-type basis set in combination with computationally expensive anharmonic model to obtain more accurate theoretical structure, vibrational frequencies and GIAO NMR parameters of cytosine was tested. We report on prediction of cytosine equilibrium (R e ) and rovibrationally averaged (R v ) structures and vibrational frequencies in the gas phase and DMSO solution using density functional theory combined with 6-311++G** basis set. The harmonic and anharmonic vibrational frequencies (using second-order vibrational perturbation theory, VPT2) were critically discussed. In comparison with initial harmoni…
Syntheses, Mössbauer and infrared spectroscopic investigations on tin(II) chloride adducts with purine and pyrimidine bases and nucleosides
1982
Abstract The synthesis of two types of tin(II) complex SnCl2·L·CH3OH (L = adenosine, cytidine and inosine) and SnCl2·L2·CH3OH (L = adenine and cytosine) are described. The complexes are characterised by their infrared and 119Sn Mossbauer data. The Mossbauer shift data suggest that the bonds between tin(II) chloride and the donor atoms of the ligands are relatively weak.
The role of pyrimidine nucleobase excimers in DNA photophysics and photoreactivity
2009
Abstract Quantum chemical studies using the accurate CASPT2//CASSCF procedure show that π-stacked interactions in biochromophores such as pyrimidine (Pyr) DNA/RNA nucleobases pairs yield excimer-like situations which behave as precursors of processes like charge transfer (CT) or photoreactivity and are the source of the emissive properties in DNA. Examples are the CT between adjacent DNA nucleobases in a strand of oligonucleotides and the photodimerization taking place in cytosine (C) pairs leading to cyclobutanecytosine (CBC) mutants. These processes take place through nonadiabatic photochemical mechanisms whose evolution is determined by the presence and accessibility of conical intersect…