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The roles of nucleic acid radicals in DNA and RNA damage cannot be properly understood in the absence of knowledge of the C-H bond strengths depicting the energy cost to generate each of these radicals. However, previous theoretical studies on the relative energies of different nucleic acid radicals are not fully convincing mainly because of the use of oversimplified model compounds. In the present study we chose nucleoside 3',5'-bisphosphates as model compounds for DNA and RNA, in which the effects of both the nucleobase and phosphorylation were taken into consideration. Using the newly developed ONIOM-G3B3 methods, we calculated the gas-phase bond dissociation enthalpies and solution-phase bond dissociation free energies of all the carbohydrate C-H bonds in the model compounds. It was found that the monoanionic phosphate group (OPO3H-) was a better radical stabilization group than the OH group by 1.3 kcal/mol, whereas the neutral phosphate group (OPO3H2) was a significantly worse radical stabilization group than OH by 4.4 kcal/mol. Due to these reasons, the relative thermodynamic susceptibility of H-abstraction from deoxyribonucleotides and ribonucleotides varied considerably depending on the phosphorylation state and the charge carried by the phosphate groups. Strikingly, the bond dissociation free energy of C2'-H in ribonucleotides was dramatically lower than that of all the other C-H bonds by 5-6 kcal/mol regardless of the phosphorylation state and the charge carried by the phosphate group. This explained the previous experimental finding that radiation damage of RNA occurs mainly via H-abstraction at H-2'. A model study suggested that the strength of the hydrogen bonding interaction between the 2'-OH and 3-phosphate groups should dramatically increase from ribonucleoside 3',5'-bisphosphate to its C2' radical. The strengthened hydrogen bonding stabilized the C2' radical, rendering the C2'-H bond of RNA extraordinarily vulnerable to H-abstraction. 相似文献
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具有条纹磁畴结构的磁性薄膜表现出面内转动磁各向异性,对于解决高频电子器件的方向性问题起着至关重要的作用.本文采用射频磁控溅射的方法,研究了NiFe薄膜的厚度、溅射功率密度、溅射气压等制备工艺参数对条纹磁畴结构、面内静态磁各向异性、面内转动磁各向异性、垂直磁各向异性的影响规律.研究发现,在功率密度15.6 W/cm~2与溅射气压2 mTorr(1 Torr=1.33322×102Pa)下生长的NiFe薄膜,表现出条纹磁畴的临界厚度在250 nm到300 nm之间.厚度为300 nm的薄膜比250 nm薄膜的垂直磁各向异性场增大近一倍,从而磁矩偏离膜面形成条纹磁畴结构,并表现出面内转动磁各向异性.高溅射功率密度可以降低薄膜出现条纹磁畴的临界厚度.在相同功率密度15.6 W/cm~2下生长300 nm的NiFe薄膜,随着溅射气压由2 mTorr增大到9 mTorr,NiFe薄膜的垂直磁各向异性场逐渐由1247.8 Oe(1 Oe=79.5775 A/m)增大到3248.0 Oe,面内转动磁各向异性场由72.5 Oe增大到141.9 Oe,条纹磁畴周期从0.53μm单调减小到0.24μm.NiFe薄膜的断面结构表明柱状晶的形成是表现出条纹磁畴结构的本质原因,高功率密度下低溅射气压有利于柱状晶结构的形成,表现出规整的条纹磁畴结构,高溅射气压会导致柱状晶纤细化,面内转动磁各向异性与面外垂直磁各向异性增强,条纹磁畴结构变得混乱. 相似文献
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The roles of ribonucleoside and deoxyribonucleoside radicals in DNA and RNA damage cannot be properly understood in the absence of knowledge of the C-H and N-H bond dissociation enthalpies (BDEs) depicting the energy cost to generate each of these radicals. However, because the nucleoside radicals tend to be extremely short-lived and it is very difficult to separate and identify different nucleoside radicals, experimental BDEs for nucleosides have remained elusive. Herein, we developed an ONIOM-G3B3 method in order to reliably predict the BDEs of nucleosides and we carefully benchmarked this new method against over 60 experimental BDEs of diverse sizable molecules. It was found that the accuracy of the ONIOM-G3B3 method was about 1.4 kcal/mol for BDE calculations. Using the ONIOM-G3B3 method, a full scale of C-H and N-H BDEs were obtained for the first time for ribonucleosides and deoxyribonucleosides with an estimated error bar of +/-1.4 kcal/mol. Discussions were then made about the interesting connections between these BDE values and previously reported experimental observations concerning radical-mediated DNA and RNA lesions. The significance of the work is twofold: (i) Nucleosides represent one of the most important groups of compounds in science. A full scale of reliable bond dissociation enthalpies for nucleosides is of fundamental importance. (ii) This work demonstrates the feasibility to accurately predict the bond strength of various sizable molecules ranging from nanosize molecular devices to biologically significant compounds. 相似文献
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Xiao-Wu Lei Guo-Hua Zhong Min-Jie Li Jiang-Gao Mao 《Journal of solid state chemistry》2008,181(9):2448-2455
Two new ternary ytterbium transition metal stannides, namely, Yb3CoSn6 and Yb4Mn2Sn5, have been obtained by solid-state reactions of the corresponding pure elements in welded tantalum tubes at high temperature. Their crystal structures have been established by single-crystal X-ray diffraction studies. Yb3CoSn6 crystallizes in the orthorhombic space group Cmcm (no. 63) with cell parameters of a=4.662(2), b=15.964(6), c=13.140(5) Å, V=978.0(6) Å3, and Z=4. Its structure features a three-dimensional (3D) open-framework composed of unusual [CoSn3] layers interconnected by zigzag Sn chains, forming large tunnels along the c-axis which are occupied by the ytterbium cations. Yb4Mn2Sn5 is monoclinic space group C2/m (no. 12) with cell parameters of a=16.937(2), b=4.5949(3), c=7.6489(7) Å, β=106.176(4)°, V=571.70(8) Å3, and Z=2. It belongs to the Mg5Si6 structure type and its anionic substructure is composed of parallel [Mn2Sn2] ladders interconnected by unusual zigzag [Sn3] chains, forming large tunnels along the c-axis, which are filled by the ytterbium cations. Band structure calculations based on density function theory methods were also made for both compounds. 相似文献
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This paper investigates experimentally high-order harmonic generation(HHG) of neon gas with 5-fs and 25-fs driving laser pulses.It has been demonstrated that the cutoff energy of the harmonic extreme ultraviolet photons is extended to 131 eV and the HHG spectrum near the cutoff region becomes continuum as the driving laser pulse duration is 5 fs;whereas much lower cutoff photon energy and discrete harmonic spectrum near the cutoff region are presented as the laser pulse duration is 25 fs.The results can be explained by the fact that neutral atoms can be exposed to more intense laser field before they are depleted by ionization because of the extremely short rising time of the few-cycle pulse.The 5-fs driving laser pulse paves the way of generation of coherent x-ray in the water window and single attosecond pulse. 相似文献
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Min-Jie Chen Prof. Gang-Gang Chang Li-Yan Chen Ke-Xin Huang Chun Pu Dan Li Yao Yao Jia-Xin Li Prof. Xiao-Yu Yang Prof. Banglin Chen 《化学:亚洲杂志》2021,16(22):3743-3747
Process intensification, targeting the maximization of spatial-temporal productivity utilizing minimum energy and resources has always been the constant trends especially in chemical industry. In this regard, tandem reactions that are able to perform a multi-step reaction in a single pot by eliminating costly separation steps have been viewed as a typical paradigm. However, a spatial isolation of varied active sites with a controlled manner in a single catalyst to avoid deactivation and work synergistically is a challenging problem yet sometimes being overlooked. In this work, a spatial base-metal core-shell structured catalyst with wrinkled surface was successfully fabricated by a direct homoepitaxial growth method in an acid/water system, which exhibited increased hydrophobicity, exposure of active sites and significantly improved product selectivity towards one-pot Knoevenagel condensation-hydrogenation tandem reaction compared with the uncoated catalyst. Meanwhile, the catalytic performance was largely retained and the structural stability was maintained even after successive 8 cycles, which shows great promise for industrial applications. 相似文献
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Zhong-Gao LI Tian LU Heng GAO Qing ZHANG Min-Jie LI Wei REN Wen-Cong LU 《物理化学学报》2017,33(9):1789-1795
This work describes the characteristics of benzobisthiadiazole analogues with different heteroatom substitution patterns as electronwithdrawing anchoring groups in dye-sensitized solar cells (DSSCs). In order to provide a systematic analysis of the effect of the designed anchoring groups, the widely used anchor cyanoacrylic acid was used as the reference. Theoretical calculations show that the newly designed anchors are capable of displaying a decent level of light absorption covering the entire visible range up to the near-IR region of 1000 nm. More importantly, an ultrafast electron injection is observed from the dyes SPN and SPS into the TiO2 surface. The quantum dynamics of the interfacial electron transfer (IET) reveal that SPN and SPS anchors provide efficient IET performance. About 90% of the electron injection occurs in the first 15 fs, and is complete after ~100 fs. Furthermore, the pathway of electron injection is direct, leading to very efficient transfer of the wavepacket through the TiO2 semiconductor. Therefore, the performances of both the anchors, SPN and SPS, are equivalent and even superior to that of cyanoacrylic acid. These findings are important in the context of providing guidelines for the design of metal-free organic dye sensitizers for high efficient DSSCs. 相似文献
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In this study, reduced grapheme oxide (RGO)/BiVO4 composite was prepared and characterized by FT-IR, XRD, and UV spectrum. Photo-chemically-mediated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully performed at 25°C in N,N-dimethylformamide (DMF) with RGO/BiVO4 as photoinitiator, FeCl3·6H2O/triphenylphosphine (PPh3) as catalyst, and ethyl 2-bromoisobutyrate as ATRP initiator. MMAs were polymerized in a controlled manner under ultraviolet (UV) light and sunlight conditions. The results show that a first-order kinetics model was obeyed up to higher conversion. The reaction gave well-controlled PMMA with Mn,GPC close to the theoretical value and a narrow MWD (Mw/Mn<1.5). The experiments of light on and off reveal the photoredox cycle between Fe(III) and Fe(II) species. The living character was further verified by the chain extension experiments. 相似文献