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71.
72.
Lenz T Bonnist EY Pljevaljcić G Neely RK Dryden DT Scheidig AJ Jones AC Weinhold E 《Journal of the American Chemical Society》2007,129(19):6240-6248
We report the crystal structure of the DNA adenine-N6 methyltransferase, M.TaqI, complexed with DNA, showing the fluorescent adenine analog, 2-aminopurine, flipped out of the DNA helix and occupying virtually the same position in the active site as the natural target adenine. Time-resolved fluorescence spectroscopy of the crystalline complex faithfully reports this state: base flipping is accompanied by the loss of the very short ( approximately 50 ps) lifetime component associated with fully base-stacked 2-aminopurine in DNA, and 2-aminopurine is subject to considerable quenching by pi-stacking interactions with Tyr108 in the catalytic motif IV (NPPY). This proves 2-aminopurine to be an excellent probe for studying base flipping by M.TaqI and suggests similar quenching in the active sites of DNA and RNA adenine-N6 as well as DNA cytosine-N4 methyltransferases sharing the conserved motif IV. In solution, the same distinctive fluorescence response confirms complete destacking from DNA and is also observed when the proposed key residue for base flipping by M.TaqI, the target base partner thymine, is substituted by an abasic site analog. The corresponding cocrystal structure shows 2-aminopurine in the active site of M.TaqI, demonstrating that the partner thymine is not essential for base flipping. However, in this structure, a shift of the 3' neighbor of the target base into the vacancy left after base flipping is observed, apparently replicating a stabilizing role of the missing partner thymine. Time-resolved fluorescence and acrylamide quenching measurements of M.TaqI complexes in solution provide evidence for an alternative binding site for the extra-helical target base within M.TaqI and suggest that the partner thymine assists in delivering the target base into the active site. 相似文献
73.
An extensive computational study of the conformational preferences of N-acetylphenylalaninylamide (NAPA) is reported, including conformational and anharmonic frequency analyses, as well as calculations of excitation energies of the four NAPA conformers lowest in energy. Particular attention is paid to the influence of hydrogen-bonding interactions on the relative stability of the conformers, which was found to be very sensitive to both the level of quantum chemical computations and the anharmonic treatment of molecular vibrations. The assignments of the UV spectral peaks are well supported by the multireference CASSCF/MS-CASPT2 calculations. Upon consideration of the second-order M?ller-Plesset (MP2) and density functional theory (DFT) structures, overall energetics, and harmonic and anharmonic corrections, we found no conclusive theoretical evidence for the assumed conformational propensity of small model peptides toward extended beta-strand structures. 相似文献
74.
Bykov A. A. Strygin I. S. Goran A. V. Rodyakina E. E. Nomokonov D. V. Marchishin I. V. Abedi S. Vitkalov S. A. 《JETP Letters》2019,110(10):672-676
JETP Letters - The effect of microwave radiation on low-temperature electron magnetotransport in a square antidot lattice with a period of d ≈ 0.8 µm based on a GaAs quantum well with... 相似文献
75.
Synthesis, characterization and cytotoxicity of surface amino-functionalized water-dispersible multi-walled carbon nanotubes 总被引:2,自引:0,他引:2
Goran Vukovi? Maja Obradovi? Miodrag ?oli? Petar S. Uskokovi? 《Applied Surface Science》2009,255(18):8067-8075
Surface functionalization of multi-walled carbon nanotubes (MWCNTs), with amino groups via chemical modification of carboxyl groups introduced on the nanotube surface, using O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (N-HATU) and N,N-diisopropylethylamine (DIEA) is reported. The N-HATU coupling agent provides faster reaction rate and the reaction occurs at lower temperature compared to amidation and acylation-amidation chemistry. The amines, 1,6-hexanediamine (HDA), diethylenetriamine (DETA), triethylenetetramine (TETA) and 1,4-phenylenediamine (PDA) were used. The resulting materials were characterized with different techniques such as FTIR, XRD, elemental analysis, TGA, TEM, UV-vis spectroscopy and cyclic voltammetry. MWCNTs functionalized with PDA posses the best dispersibility and electron transfer properties in comparison to the others amines. Functionalized MWCNTs, at the concentrations between 1 and 50 μg ml−1, were not cytotoxic for the fibroblast L929 cell line. However, the concentrations of MWCNTs higher of 10 μg ml−1 reduced cell growth and this effect correlated positively with the degree of their uptake by L929 cells. 相似文献
76.
Károly Lázár Andjelka Toma?evi? Goran Bo?kovi? Ern? Kiss 《Hyperfine Interactions》2009,192(1-3):23-29
Catalytic performances of Fe-AlPILC (14 wt.% Fe) and Fe-ZSM-5 (5 wt.% Fe) catalysts are compared in the wet oxidative degradation of methomyl. Fe-ZSM-5 exhibits outstanding whereas Fe-AlPILC shows only mediocre activity. Positions of iron are analysed in the two catalysts by Mössbauer spectroscopy. Iron is in highly dispersed state in Fe-AlPILC whereas in the other case a hematite/ZSM-5 composite is formed. The catalytic activity is attributed to iron located and stabilized in ionic dispersion. 相似文献
77.
Santiago Gómez-Ruiz Goran N. Kalu?erovi? ?eljko ?i?ak Zorica D. Jurani? Mariano Fajardo 《Journal of organometallic chemistry》2009,694(13):1981-1987
The alkenyl-substituted titanocene complex [Ti(η5-C5H5)(η5-C5H4{CMe2(CH2CH2CHCH2)})Cl2] (1) has been synthesized and characterized using traditional methods. The reaction of 1 with 9-BBN gave the boryl substituted complex [Ti(η5-C5H5)(η5-C5H4{CMe2(CH2CH2CH2CH2BC8H14)})Cl2] (2). The cytotoxic activity of 1 and 2 was tested against tumour cell lines human adenocarcinoma HeLa, human myelogenous leukemia K562, human malignant melanoma Fem-x, human breast carcinoma MDA-MB-361 and normal immunocompetent cells peripheral blood mononuclear cells PBMC and compared with those of the reference complexes [Ti(η5-C5H5)2Cl2] (R1), [Ti(η5-C5H4Me)2Cl2] (R2) and [Ti(η5-C5H5)(η5-C5H4SiMe3)Cl2] (R3). Complex 1 showed higher cytotoxic activities on HeLa, Fem-x and K562 (IC50 values from 96.6 ± 3.4 to 149.2 ± 2.9 μM) than the reference complexes R1, R2 and R3 which presented IC50 values from 173.3 ± 6.0 to >200 μM. On the other hand, boryl substituted complex 2, present slightly lower cytotoxic activities than 1 on HeLa, Fem-x and K562 (IC50 values from 155.6 ± 5.5 to 167.9 ± 4.2 μM). However, 2 was the most active of the studied complexes against MDA-MB-361 (IC50 value of 161.1 ± 0.1 μM). Structural studies based on DFT calculations of 1 and 2 have also been carried out in order to gain a possible insight into the relationship between metal complex structure and cytotoxicity. 相似文献
78.
Dejan Jeremi Goran N. Kaluderovi Santiago Gmez‐Ruiz Ilija Br
eski Katarina K. Andelkovi 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(4):m143-m145
The structure of the title compound, [Ca(C10H15O4S)2(H2O)4], is the first example in which two d ‐camphor‐10‐sulfonate anions are coordinated to a metal ion, in this case with direct Ca—O bonding. The molecule has crystallographically imposed twofold symmetry with the Ca atom on the twofold axis. Hydrogen bonds are formed between the coordinated water molecules and the O atoms of the SO3− groups of adjacent molecules, leading to the formation of a two‐dimensional layered network. The compound displays sharp wavelength‐selective transparency in the UV–visible spectrum, offering the potential for application as an optical filter. 相似文献
79.
Nicolaou KC Chen DY Li Y Uesaka N Petrovic G Koftis TV Bernal F Frederick MO Govindasamy M Ling T Pihko PM Tang W Vyskocil S 《Journal of the American Chemical Society》2006,128(7):2258-2267
The key building blocks (6, 7, and 8) for the intended construction of the originally proposed structures of azaspiracid-1, a potent marine-derived neurotoxin, were coupled and the products elaborated to the targeted compounds (1a,b) and their C-20 epimers (2 and 3). The assembly of the three intermediates was accomplished by a dithiane-based coupling reaction that united the C(1)-C(20) (7) and C(21)-C(27) (8) fragments, followed by a Stille-type coupling which allowed the incorporation of the C(28)-C(40) fragment (6) into the growing substrate. Neither of the final products (1a,b) matched the natural substance by TLC or (1)H NMR spectroscopic analysis, suggesting one or more errors in the originally proposed structure for this notorious biotoxin. 相似文献
80.
Nonlinear magnetotransport of two-dimensional electrons in modulation-doped GaAs/AlAs heterostructures with anisotropic mobility is investigated. The mobility attains its maximum and minimum values in the $\left[ {1\bar 10} \right]$ and [110] directions, respectively. It is found that, upon an increase in the direct electrical current I dc though Hall bars oriented along the [110] direction, the transition of the two-dimensional system to the state with differential resistance r xx ≈ 0 in a magnetic field occurs at a lower value of I dc and is accompanied by a more pronounced “plunge” into the region of negative r xx values as compared to bars oriented along the $\left[ {1\bar 10} \right]$ direction. The results are explained by the impact of mobility on the spectral diffusion of nonequilibrium charge carriers. 相似文献