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Functional Study (functional + study)
Kinds of Functional Study Selected AbstractsA Density Functional Study of the Hydrogenation of Ketones Catalysed by Neutral Rhodium-Diphosphane ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2006Francine Agbossou-Niedercorn Abstract The potential energy profile of RhI -catalysed hydrogenation of ketones has been computed for the simple model system [Rh{H3POCH2CH2N(H)PH3}(Cl)] using DFT calculations. The general sequence of the catalytic cycle involves coordination of the carbonyl derivative to the neutral RhI complex followed by oxidative addition of molecular hydrogen providing rhodium dihydride intermediates. The latter are converted into alkoxy hydrides by a migratory insertion reaction. Reductive elimination of the alcohol and substitution of the latter by the incoming substrate completes the catalyticcycle. Intermediates and transition states of all catalyticsteps have been located. Two isomeric derivatives bearingthe model substrate have been found for the [Rh{H3POCH2CH2N(H)PH3}(Cl)(H2CO)] complex. Eight diastereomeric pathways have been followed for the cis addition of molecular hydrogen to [Rh{H3POCH2CH2N(H)PH3}(Cl)(H2CO)] leading to eight distinct isomeric dihydride intermediates. Four dihydride complexes can be considered as the more accessible compounds. The site preference for migratory insertion and transition states discriminates the main path of the catalytic reaction. Migratory insertion to form the alkoxy hydride constitute the turn over limiting step of the process. The potential energy profile has been found to be smooth without excessive activation barriers. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Density Functional Study of the Complexation Reaction of Sn(CH3)3X (X = F, Cl, Br and I) with Halide AnionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2003Frank De Proft Abstract The Lewis acid-base reaction between Sn(CH3)3X and Y, (with X, Y = F, Cl, Br and I) has been studied using quantum chemical calculations. Complexation energies were calculated at the Density Functional Theory (DFT) level and rationalized on the basis of a local application of the hard and soft acids and bases principle. It was observed that smaller differences in the local softness of the interacting sites in the Lewis acid and base correspond to stronger interactions. Moreover, the calculated sequences in complexation energies can be reproduced using equations containing chemical concepts introduced within the framework of conceptual density functional theory and rooted in the hard and soft acids and bases principle and referring only to the reactants. A method of treating the electronegativity and softness of the halide anions is presented based on a Taylor expansion of the electronegativity of the neutral halogens and the softness-polarizability proportionality. Experimental evidence for the calculated sequences was gathered from measured 117Sn chemical shifts and 1J (13C- 119/117Sn) coupling constant changes upon complexation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] A Density Functional Study of Ethylene Insertion into the M-methyl (M = Ti, Zr) Bond for Different Catalysts, with a QM/MM Model for the Counterion, B(C6F5)3CH3,ISRAEL JOURNAL OF CHEMISTRY, Issue 4 2002Kumar Vanka Single site homogeneous catalysts have been studied extensively in recent years as alternatives to traditional heterogeneous catalysts. The current theoretical study uses density functional theory to study the insertion process of the ethylene monomer into the titanium-carbon chain for contact ion-pair systems of the type [L1L2TiCH3 -,-CH3 -B(C6F5)3], where L1, L2, are Cp, NPH3, and other ligands. Different modes of approach cis and trans to the ,-CH3 bridge were considered. The counterion, B(C6F5)3CH3,, was modeled by QM/MM methods. The value of ,Htot,the total barrier to insertion,was found to be positive (in the range of 4,15 kcal/mol). The ability of the ancillary ligands, L1 and L2, to stabilize the ion-pair was found to be an important factor in determining the value of ,Htot. On replacing the titanium metal center with zirconium, the ,Htot values were found to be lowered (in the range of 2,9 kcal/mol), indicating that they would be better catalysts than their titanium analogues. The size of the ligands L1 and L2 was increased by replacing hydrogens in the ligands with tertiary butyl groups. The value of ,Htot was found to increase (in the range of 10,28 kcal/mol) in contrast to the simple systems, for both the cis and trans cases of approach, with the cis mode of approach giving lower values of ,Htot. Solvent effects were incorporated with cyclohexane (, = 2.023) as the solvent, and were found to have a minor influence, ±(0.5,1.5) kcal/mol) on the insertion barrier for all the cases studied. [source] ChemInform Abstract: A Density Functional Study of ,-Mg(BH4)2.CHEMINFORM, Issue 46 2008Michiel J. van Setten Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Impurity Effects on Small Pd Clusters: A Relativistic Density Functional Study of Pd4X, X: H, C, O.CHEMINFORM, Issue 44 2008Alexander Genest Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: A Density Functional Study of the Various Forms of UN4O12 Containing Uranyl NitrateCHEMINFORM, Issue 2 2008Joel J. Berard Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Density Functional Study of Structural and Electronic Properties of Small Bimetallic Silver,Nickel ClustersCHEMINFORM, Issue 44 2007M. Harb Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Density Functional Study of Small Neutral and Charged Silver Cluster Hydrides.CHEMINFORM, Issue 52 2006Shuang Zhao Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Density Functional Study of 8- and 11-Vertex Polyhedral Borane Structures: Comparison with Bare Germanium Clusters.CHEMINFORM, Issue 2 2006R. B. King No abstract is available for this article. [source] Density Functional Study of the Structures of Lead Sulfide Clusters (PbS)n (n = 1,9).CHEMINFORM, Issue 21 2005Hongxia Zeng No abstract is available for this article. [source] High Covalence in CuSO4 and the Radicalization of Sulfate: An X-Ray Absorption and Density Functional Study.CHEMINFORM, Issue 9 2005Robert K. Szilagyi Abstract For Abstract see ChemInform Abstract in Full Text. [source] Ab initio and Density Functional Study of Thionitroso XNS and Thiazyl Isomers XSN, X: H, F, Cl, Br, OH, SH, NH2, CH3, CF3, and SiF3.CHEMINFORM, Issue 33 2004Pablo A. Denis No abstract is available for this article. [source] Exchange Coupling of Paramagnetic Ions in a Polyoxometalate Matrix: Density Functional Study of Diiron(III) Substituted ,-Silicotungstates.CHEMINFORM, Issue 26 2004Ekaterina M. Zueva No abstract is available for this article. [source] Density Functional Study of Palladium ClustersCHEMINFORM, Issue 43 2003Paola Nava Abstract For Abstract see ChemInform Abstract in Full Text. [source] Magnetism of URhSi and URhGe: A Density Functional Study.CHEMINFORM, Issue 48 2002M. Divis No abstract is available for this article. [source] A Density Functional Study of Phosphorus Nitride P3N5: Refined Geometries, Properties, and Relative Stability of ,-P3N5 and ,-P3N5 and a Further Possible High-Pressure Phase ,-P3N5 with Kyanite-Type Structure.CHEMINFORM, Issue 41 2002Peter Kroll No abstract is available for this article. [source] ChemInform Abstract: Reaction of Sc+ (1D,3D) with H2O, NH3, and CH4: A Density Functional Study.CHEMINFORM, Issue 26 2001Nino Russo Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] 103Rh NMR Chemical Shifts in Organometallic Complexes: A Combined Experimental and Density Functional StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2004Laura Orian Dr. Abstract Experimental 103Rh NMR chemical shifts of mono- and binuclear rhodium(I) complexes containing s - or as -hydroindacenide and indacenediide bridging ligands with different ancillary ligands (1,5-cyclooctadiene, ethylene, carbonyl) are presented. A protocol, based on density functional theory calculations, was established to determine 103Rh NMR shielding constants in order to rationalise the effects of electronic and structural variations on the spectroscopic signal, and to gain insight into the efficiency of this computational method when applied to organometallic systems. Scalar and spin,orbit relativistic effects based on the ZORA (zeroth order regular approximation) level have been taken into account and discussed. A good agreement was found for model compounds over a wide range of chemical shifts of rhodium (,10,000 ppm). This allowed us to discuss the experimental and calculated ,(103Rh) in larger complexes and to relate it to their electronic structure. [source] Electron Tunneling through Molecular Media: A Density Functional Study of Au/Dithiol/Au SystemsCHEMPHYSCHEM, Issue 9 2005Qiang Sun Dr. Abstract We report a density functional theory study of the electronic properties of n -alkanedithiols (CnS2, with n=4, 8 and 12) sandwiched between two Au(111) infinite slab electrodes. We investigate the influence of the distance between the two electrodes and of the molecular chain length, tilt angle, and coverage on the local density of states (LDOS) at the Fermi energy (Ef). We find that the (small) value of the LDOS at Efnear the center of the molecular wires,a quantity that is related to the tunneling current,is mainly determined by the length n of the alkane chains: it originates from the tails of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) which are broadened by the interaction with the electrodes, and decays exponentially with the length of the molecular wire. This opens a nonresonance tunneling channel for charge transport at small bias voltages. While the length of the hydrocarbon chain appears to be the determining factor, the tilt angle of the molecular wires with respect to the electrode surfaces, and therefore the distance between these, has a small influence on the LDOS at the center of the molecule, while the effect of coverage can be ignored. The picture which emerges from these calculations is totally consistent with a through-bond tunneling mechanism. [source] Density Functional Study of Two Seven-Membered Unconventional Fullerenes C58F17CF3 and C58F18CHINESE JOURNAL OF CHEMISTRY, Issue 8 2010Chunmei Tang Abstract The density functional method is used to study the structure, electronic properties, static linear polarizabilities, and optical absorption spectra of two seven-membered unconventional fullerene derivatives C58F17CF3 and C58F18. It is calculated that three sites chosen to locate the CF3 are isoenergetic. The energy gaps of C58F18 and C58F17CF3 are much larger than that of C58, indicating the fluorination and trifluoromethylation of C58 can remarkably enhance the kinetic stability. The density of states explore that the influence of CF3 to the energy levels is mainly distributed in the energy range from ,10 to ,2 eV. However, when the CF3 substitutes for F in C58F18, the bond lengths, energy gaps, static linear polarizabilities, and optical absorption spectra all show small variety. [source] [(Pyridylcarbonyl)pyridyl]triazolopyridines, Useful Ligands for the Construction of Polynuclear Coordination Compounds , Synthesis, Crystal Structure and Magnetic Properties of a Novel Tetranuclear Copper(II) Cubane,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29 2007Belén Abarca Abstract A new tetranuclear cubane Cu4O4 complex has been synthesised from assembly of CuII ions and the polydentate ligand (pyridin-2-yl){6-([1,2,3]triazolo[1,5- a]pyridin-3-yl)pyridin-2-yl}methanone. Crystallographic analysis indicates that the Cu4O4 unit has an S4 symmetry. The magnetic properties have been analysed using the H = ,2,i,jJijSiSj spin Hamiltonian. Two distinct coupling constants, 2J1,3 = ,37.4 cm,1 and 2J1,2 = ,2.6 cm,1, obtained from the fitting of the experimental data have been rationalised on the basis of a density functional study of magnetostructural correlations in cubane complexes containing the Cu4O4 core. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] A Theoretical Study of the Nearest Cu···Cu Antiferromagnetic Exchange Coupling Interactions in [LaCu6] and [YCu6]EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2007Yi-Quan Zhang Abstract A density functional study of the exchange coupling interactions between the two nearest CuII centers in [LaCu6] and [YCu6] is presented. Two approaches show that the Cu···Cu antiferromagnetic interactions increase with a decrease of the ionic radius of the diamagnetic central LaIII and YIII ions. However, the influence of the central ions on the Cu···Cu interactions is small compared to that of their structures according to our calculations. We therefore conclude that the stronger antiferromagnetic interactions between the two nearest CuII centers in [LaCu6] than in [YCu6] are not a result of the central LaIII ion but the structure. The antiferromagnetic contributions of the direct overlap between the two nearest CuII magnetic orbitals also play a major role according to the calculations of the overlap integral Sij based on Kahn's theory.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] A Theoretical Study of the Exchange Coupling in Hydroxo- and Alkoxo-Bridged Dinuclear Oxovanadium(IV) CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2004Antonio Rodríguez-Fortea Abstract A density functional study of exchange coupling in hydroxo- and alkoxo-bridged dinuclear oxovanadium(IV) compounds is presented. Coupling constants calculated for full unmodeled structures are in good agreement with experimentally reported values, confirming the ability of the computational strategy used in this work to predict the exchange coupling in dinuclear VIV compounds. The influence of the configuration of the [VO(,-OR)2VO]2+ core in compounds with two edge-sharing octahedrally coordinated oxovanadium(IV) centers, of the nature of the terminal ligands and of structural distortions on the coupling constant have been analyzed through model calculations. The results indicate that the coupling constant is less affected by these factors than for hydroxo- and alkoxo-bridged CuII compounds. The calculations support the orbital models usually employed in qualitative interpretations of magneto-structural correlations, showing good correlations between the calculated coupling constants and the overlap between the two magnetic orbitals or the square of the orbital gap. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Structural and functional evidence for a singular repertoire of BMP receptor signal transducing proteins in the lophotrochozoan Crassostrea gigas suggests a shared ancestral BMP/activin pathwayFEBS JOURNAL, Issue 13 2005Amaury Herpin The transforming growth factor , (TGF-,) superfamily includes bone morphogenetic proteins, activins and TGF-,sensu stricto (s.s). These ligands, which transduce their signal through a heteromeric complex of type I and type II receptors, have been shown to play a key role in numerous biological processes including early embryonic development in both deuterostomes and ecdyzozoans. Lophochotrozoans, the third major group of bilaterian animals, have remained in the background of the molecular survey of metazoan development. We report the cloning and functional study of the central part of the BMP pathway machinery in the bivalve mollusc Crassostrea gigas (Cg- BMPR1 type I receptor and Cg- TGF,sfR2 type II receptor), showing an unusual functional mode of signal transduction for this superfamily. The use of the zebrafish embryo as a reporter organism revealed that Cg- BMPR1, Cg- TGF,sfR2, Cg- ALR I, an activin Type I receptor or their dominant negative acting truncated forms, when overexpressed during gastrulation, resulted in a range of phenotypes displaying severe disturbance of anterioposterior patterning, due to strong modulations of ventrolateral mesoderm patterning. The results suggest that Cg- BMPR1, and to a certain degree Cg- TGF,sfR2 proteins, function in C. gigas in a similar way to their zebrafish orthologues. Finally, based on phylogenetic analyses, we propose an evolutionary model within the complete TGF-, superfamily. Thus, evidence provided by this study argues for a possible conserved endomesoderm/ectomesoderm inductive mechanism in spiralians through an ancestral BMP/activin pathway in which the singular, promiscuous and probably unique Cg- TGF,sfR2 would be the shared type II receptor interface for both BMP and activin ligands. [source] NUB1-mediated targeting of the ubiquitin precursor UbC1 for its C-terminal hydrolysisFEBS JOURNAL, Issue 5 2004Tomoaki Tanaka NEDD8 is a ubiquitin-like protein that controls vital biological events through its conjugation to target proteins. Previously, we identified a negative regulator of the NEDD8 conjugation system, NEDD8 ultimate buster-1 (NUB1), that recruits NEDD8 and its conjugates to the proteasome for degradation. Recently, we performed yeast two-hybrid screening with NUB1 as bait and isolated a ubiquitin precursor UbC1 that is composed of nine tandem repeats of a ubiquitin unit through ,-peptide bonds. Interestingly, NUB1 interacted with UbC1 through its UBA domain. Further study revealed that the UBA domain interacted with ,-peptide bond-linked polyubiquitin, but not with isopeptide bond-linked polyubiquitin, indicating that the UBA domain of NUB1 is a specific acceptor for the linear ubiquitin precursor. A functional study revealed that an unidentified protein that was immunoprecipitated with NUB1 served as a ubiquitin C-terminal hydrolase for UbC1. Thus, NUB1 seems to form a protein complex with the unidentified ubiquitin C-terminal hydrolase and recruit UbC1 to this complex. This might allow the ubiquitin C-terminal hydrolase to hydrolyze UbC1, in order to generate ubiquitin monomers. Northern blot analysis showed that the mRNAs of both NUB1 and UbC1 were enriched in the testis. Furthermore, in situ hybridization showed that both mRNAs were strongly expressed in seminiferous tubules of the testis. These results may imply that the UbC1 hydrolysis mediated by NUB1 is involved in cellular functions in the seminiferous tubules such as spermatogenesis. [source] Abstract no.: 6 Endothelium-dependent relaxation by purinergic receptors in the aorta of apolipoprotein E-deficient miceFUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 3 2005A. Korda Previously we reported that the acetylcholine-induced relaxation in the isolated aorta of apolipoprotein E-deficient (apoE -/- ) mice deteriorates after the development of atherosclerotic plaques, but remains normal in adjacent, plaque-free segments. The present study investigated the presence of functional purinergic receptors in the murine aorta, and whether their function changes before or after the development of atherosclerosis. Endothelium-dependent relaxation was measured in aorta segments of apoE -/- , C57BL6 (WT) and human apoAI-overexpressing apoE -/- mice (apoAI/apoE -/- ) on regular chow. Rings were isometrically contracted with phenylephrine to 50% of their maximum force before performing cumulative concentration-response curves to different nucleotides or their stable analogues. After the functional study, the cross-sectional area of the plaque was determined in every segment. The nucleotides induced complete (UTP, UDP, ATP) or partial (ADP) relaxation that was abolished by endothelial cell removal or nitric oxide (NO) synthase inhibition. The responses pointed to the presence of functional P2y1, P2y2 or P2y4 receptors on endothelial cells. RT-PCR confirmed the presence of P2y1 and P2y4 mRNA in the aorta of WT mice. Nucleotide responses were unaltered in lesion-free apoE -/- mice (5 months). However, in atherosclerotic segments of apoE -/- mice (18 months), the relaxation to ATP was impaired compared to age-matched WT controls (maximum amplitude (Emax) 25 ± 14%, n = 6 vs. 90 ± 3%, n = 5, P < 0.01). A similar defect was seen for the stable analogue ATP-gamma-S (Emax 36 ± 12% vs. 86 ± 3%, P < 0.01). Atherosclerotic apoE -/- segments were less sensitive to the NO donor spermineNONOate (pD2 6.74 ± 0.18) than WT segments (7.25 ± 0.20), but maximum relaxation was unaltered. In non-atherosclerotic aorta segments of the same apoE -/- mice all relaxation responses remained normal and were not different from WT. Strong negative correlations (P < 0.001) existed between lesion size and the Emax for ATP (rs = ,0.82) and ATP-gamma-S (rs = ,0.73) in apoE -/- mice. ApoAI overexpression improved the purinergic responses (Emax ATP 64 ± 9%, ATP-gamma-S 64 ± 10%, n = 5) and these were not different from WT (P > 0.05). An analysis of covariance with plaque size as covariate suggested that this benefit was secondary to the strongly reduced plaque formation in apoAI/apoE -/- mice. It is concluded that functional P2 y receptors are present on murine aortic endothelium. Furthermore, endothelium-dependent purinergic relaxation declines after plaque development. This deterioration involves decreased bioavailability of NO rather than enhanced ATP degradation. The defect is, however, not systemic since the responses remain unaltered in plaque-free segments of atherosclerosis-prone apoE -/- mice. [source] Highly Emitting Neutral Dinuclear Rhenium Complexes as Phosphorescent Dopants for Electroluminescent DevicesADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Matteo Mauro Abstract A series of neutral, dinuclear, luminescent rhenium(I) complexes suitable for phosphorescent organic light emitting devices (OLEDs) is reported. These compounds, of general formula [Re2(µ -Cl)2(CO)6(µ -1,2-diazine)], contain diazines bearing alkyl groups in one or in both the , positions. Their electrochemical and photophysical properties are presented, as well as a combined density functional and time-dependent density functional study of their geometry, relative stability and electronic structure. The complexes show intense green/yellow emissions in toluene solution and in the solid state and some of the complexes possess high emission quantum yields (,,=,0.18,0.22 for the derivatives with disubstituted diazines). In butyronitrile glass, at 77,K, due to the charge transfer character of the lowest (emitting) excited state, strong blue shift of the emission is observed, accompanied by a strong increase in the lifetime values. The highest-performing emitting complex, containing cyclopentapyridazine as ligand, is tested in a polymer-based light-emitting device, with poly(9-vinylcarbazole) as matrix, as well as in a device obtained by vacuum sublimation of the complex in the 2,7-bis(diphenylphosphine oxide)-9-(9-phenylcarbazol-3-yl)-9-phenylfluorene (PCF) matrix. This represents the first example of devices obtained with a rhenium complex which can be sublimed and is solution processable. Furthermore, the emission is the bluest ever reported for electrogenerated luminescence for rhenium complexes. [source] Octamer 4 (Oct4) mediates chemotherapeutic drug resistance in liver cancer cells through a potential Oct4,AKT,ATP-binding cassette G2 pathway,HEPATOLOGY, Issue 2 2010Xiao Qi Wang Chemoresistance presents a major obstacle to the efficacy of chemotherapeutic treatment of cancers. Using chemotherapeutic drugs to select drug-resistant cancer cells in hepatocellular carcinoma (HCC) and several other cancer cell lines, we demonstrate that chemoresistant cells displayed cancer stem cell features, such as increased self-renewal ability, cell motility, multiple drug resistance, and tumorigenicity. Octamer 4 (Oct4) messenger RNA (mRNA) levels were dramatically increased in chemoresistant cancer cells due to DNA demethylation regulation of Oct4. By functional study, Oct4 overexpression enhanced whereas Oct4 knockdown reduced liver cancer cell resistance to chemotherapeutic drugs in vitro and in xenograft tumors. It is known that the Oct4-TCL1-AKT pathway acts on embryonic stem cells and cancer stem cells in cell proliferation through inhibition of apoptosis. We further demonstrate that Oct4 overexpression induced activation of TCL1, AKT, and ABCG2 to mediate chemoresistance, which can be overcome by addition of the PI3K/AKT inhibitor; therefore, a direct pathway of Oct4-TCL1-AKT-ABCG2 or a combination of Oct4-TCL1-AKT with the AKT-ABCG2 pathway could be a potential new mechanism involved in liver cancer cell chemoresistance. Moreover, the clinical significance of the Oct4-AKT-ABCG2 pathway can be demonstrated in HCC patients, with a strong correlation of expression patterns in human HCC tumors. The role of the Oct4-AKT-ABCG2 axis in cancer cell chemoresistant machinery suggests that AKT pathway inhibition (PI3K inhibitors) not only inhibits cancer cell proliferation, but may also enhance chemosensitivity by target potential chemoresistant cells. Conclusion: Oct4, a transcriptional factor of pluripotent cells, can mediate chemoresistance through a potential Oct4-AKT-ABCG2 pathway. (HEPATOLOGY 2010;) [source] On the binding mode of urease active site inhibitors: A density functional studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2008M. Leopoldini Abstract The way with which boric acid, a rapid reversible competitive inhibitor, binds the urease active site was explored at density functional B3LYP level of theory. The catalytic core of the enzyme was simulated by two models of different size. In both cases, amino acid residues belonging to the inner and to the outer coordination spheres of nickel ions were replaced by smaller molecular species. Contrary to the experimental indication that attributes the inhibitory ability of this acid to the lack of a nucleophilic attack by the enzyme to the boron atom, we instead found that another possibility exists based on the presence of a strong covalent , bond between boron and urease that we think can be hardly broken to allow any course of the reaction. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Density functional study of the heme moiety of cytochrome c,,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005Anil Kumar Abstract A model of cytochrome c (Cyt-c) including the porphyrin ring, a methionine residue (Met), and the imidazole ring of histidine (His), the latter two being situated above and below the iron (Fe) atom of the porphyrin ring, was studied using Density Functional Theory (DFT). The geometries of the model Cyt-c complex with the Fe atom in two different charge states were fully optimized, i.e., in singlet and triplet states for Fe and in doublet and quartet states for Fe3+. The B3LYP method of DFT along with the 3-21G* basis set for C, H, N, and O atoms and the Lanl2dz basis set for the Fe atom was used. We found that with Fe3+, the doublet spin state is the ground state and the quartet state lies slightly above it. The geometry of the singlet spin state is similar to that of the doublet and quartet states. However, methionine has different conformations when Fe has zero charge (singlet, triplet states) relative to the situation when Fe has +3 charges (doublet, quartet states). The Met chain is folded instead of remaining extended in going from the singlet or triplet spin state to the doublet or quartet state and the folding is stabilized by an intramolecular CH..O hydrogen bond. The optimized geometrical parameters of the model of Cyt-c are usually in satisfactory agreement with those observed experimentally. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] | ||||||||||||||||