DNA与组蛋白相互作用的布朗动力学研究

在真核生物中,DNA按左手手征性的方式,缠绕在组蛋白八聚体的周围,形成稳定的核小体结构.文章作者运用布朗动力学,数值模拟了DNA与组蛋白相互作用最终形成核小体的动力学过程,揭示了DNA与组蛋白相互作用的详细图景,并提出了组蛋白八聚体旋转模型,以解释这一过程.文章作者还计算了组成核小体的DNA在受到拉伸力时,组蛋白被从核小体中剥离下来的动力学过程,得到了组装和剥离过程的详细图像,给出了与前人单分子实验一致的拉伸力与拉伸长度的关系曲线和拉伸台阶.此外,还通过建立的组蛋白手征性模型,模拟了核小体手征性的形成过程,发现DNA的缠绕方向强烈依赖于组蛋白的手征性,显示出环境温度对核小体手征性有重要影响.     

How can Mössbauer Spectrometry Contribute to the Characterization of Nanocrystalline Alloys?

A controlled annealing of amorphous precursors represents a simple way of obtaining nanocrystalline alloys featuring interesting magnetic properties suitable for technical applications. They stem from the presence of crystalline nanograins embedded in the amorphous residual matrix which determine the resulting macroscopic parameters. In order to understand correlation between the microstructure and the resulting magnetic behaviour, Mössbauer spectrometry is used as a method of local probe analysis. Possibilities of this technique are discussed and representative examples of investigation of NANOPERM-type nanocrystalline alloys are provided.     

Mössbauer studies of mixed-valence spin-crossover iron complexes with a hexadentate tripod ligand

The spin-crossover behaviors of mixed-valence iron compounds [Fe^IIH₃L][Fe^IIIL](NO₃)₂ (1) and [Fe^IIH₃L^Me][Fe^IIIL^Me](NO₃)₂ (2) have been investigated by ⁵⁷Fe Mössbauer spectroscopy, where H₃L is a hexadentate N₆ tripod ligand containing three imidazole groups and H₃L^Me is its 2-methylimidazole derivative. Deconvolution analyses of the Mössbauer spectra revealed that a two-step SCO (LS Fe^II–LS Fe^III→HS Fe^II–LS Fe^III→HS Fe^II–HS Fe^III) proceeds in each compound on elevating the temperature. Compound 2 exhibited lower spin-transition temperatures than 1. “Frozen-in effect” was observed below 120 and 50 K for 1 and 2, respectively.     

Substituent effect of large conjugate groups on the DNA base pair derivatives: Density functional study

The substituent effects caused by 2‐nitro‐naphthalen (aNO₂), 2‐hydroxyl‐naphthalen (aOH), 1‐nitro‐4‐vinyl‐benzene (bNO₂), and 1‐hydroxyl‐4‐vinyl‐benzene (bOH) have been investigated in this report. The geometries of various substituted base pairs have been optimized using the B3LYP method at the 6‐31G* level with no constraints. The vertical ionization potential energy has been calculated. Natural bond orbital (NBO) and CHelp analyses have also been carried out on both the neutral and cationic systems at the same level. The outcomes show that the hydrogen bond lengths of these substituted base pairs are similar to unsubstituted bases, while the geometries of the substituted bases have an interesting aspect; i.e., the substituent and the substituted base are nonplanar when the substituted base is pyrimide, while it is coplanar when the substituted base is purine. The stabilization energies changed slightly as compared with the corresponding A:T or G:C base pairs. NBO analysis shows that charge transfer is the largest in aOH‐T:A, while it is small in the other derivatives. Population analysis shows that the NPA and Mulliken charge of H has a relationship with the H‐bond lengths, while that of Chelp does not. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Information entropy of the relativistic Kozlov-Nikishin model

We calculate wave functions in the momentum representation for bound states in the relativistic Kozlov-Nikishin model. We investigate the asymptotic behavior of entropy in the coordinate and momentum representations at various limiting transitions. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 148, No. 3, pp. 444–458, September, 2006.     

赤道东太平洋厄尔尼诺—南方海涛机制的同伦解法

厄尔尼诺—南方海涛(ENSO)是涉及到赤道太平洋中的一个年际现象。本文的目的是建立一个ENSO模型的非线性方程的渐近求解方法。并在一类ENSO模型振子的基础上，借用同伦映射方法研究了对应问题的近似解。由同伦方法得到的结果去分析ENSO模型的赤道东太平洋的SST变异和气-海振子的温度深度变异。     

Mechanosynthesis of YIG and GdIG: A Structural and Mössbauer Study

We have investigated the mechanosynthesis of gadolinium and yttrium iron garnets by high-energy ball-milling of α-Fe₂O₃ and Gd₂O₃ or α-Fe₂O₃ and Y₂O₃, respectively, followed by short thermal annealings conducted at moderate temperatures. The samples were characterized by X-ray diffraction and Mössbauer spectroscopy, in order to determine the influence of the milling time and annealing conditions on the final products. For as-milled samples of each rare-earth system, the results revealed the formation of perovskite phases, in relative amounts that depend on the milling time. The formation of garnet phases was observed in as-annealed samples treated at 1000°C for 2 h or 1100°C for 3 h, i.e., at very modest annealing requirements when compared with ordinary solid-state-reaction processes performed without previous high-energy milling. Also, the occurrence was verified of a milling time for which the relative amount of garnet phases formed by annealing was maximized. This time depends on the rare-earth composing the garnet phase and on the annealing temperature.     

Some Applications of a Polynomial Inequality to Global Optimization

In this paper, we use the Ehlich-Zeller-Gärtel inequality to derive an algorithm for finding the global minima of polynomials over hyperrectangles as well as to provide a bounding method for the branch-and-bound algorithm. The latter application of the inequality results in an improved algorithm which gives simultaneously a decreasing upper bound and an increasing lower bound for the global minimum at each iteration. The algorithm can be used also to find the Lipschitz constant of a polynomial.     

Tin–DNA complexes investigated by nuclear inelastic scattering of synchrotron radiation

Nuclear inelastic scattering (NIS) of synchrotron radiation has been used to investigate the dynamics of tin ions chelated by DNA. Theoretical NIS spectra have been simulated with the help of density functional theory (DFT) calculations using 12 models for different binding sites of the tin ion in (CH₃)Sn(DNA_Phosphate)₂. The simulated spectra are compared with the measured spectrum of the tin–DNA complex.