金属离子(Na+、K+、Mg2+、Ca2+)与鸟嘌呤活性位点相互作用的理论研究

本文用量子化学从头算方法对金属离子与碱基活性位点的相互作用及其形成配合物的结构和性质进行理论研究.用HF/6-311G*优化鸟嘌呤及其金属离子(Na 、K 、Mg2 、Ca2 )配合物.在HF水平上,运用6-311G*基组计算Ⅰa和Ⅱa族金属离子(Na 、K 、Mg2 、Ca2 )与鸟嘌吟(Guanine)活性位点的相互作用.结果表明:Mg2 、Ca2 离子引起配位体的变形较Na 、K 离子大;Mg2 、Ca2 离子配合物比Na 、K 离子配合物稳定.     

Effect of B2O3 on the structural and in vitro biological assessment of mesoporous bioactive glass nanospheres

In this paper, the boron-containing mesoporous bioactive glass (MBG) nanospheres have been successfully synthesized by modified sol-gel method assisted by surfactant, and the effect of boron substitution on structure and bioactivity was evaluated by combining experiments and ab initio molecular dynamics (AIMD) simulations. All of the samples exhibit regularly uniform mesoporous spherical microstructure with an average size of about 60 nm, and the boron-containing MBGs show higher specific surface area with the value up to 416.20 m²/g. The simulated body fluid (SBF) immersion test confirms that the deposited hydroxyapatite (HA) evidently increases with the increasing of boron content, indicating that the biological behavior has been significantly improved resulting from incorporation of boron. Additionally, our results also reveal that B₂O₃ substitution has positive impact on cell proliferation of human periodontal ligament cells (hPDLCs) at lower extracted concentration. Furthermore, AIMD simulation is employed to understand the relationship between structural changes and in vitro bioactivity in terms of structural information, especially the boron coordination number. The results illustrate that the boron-containing MBG nanospheres with excellent bioactivity are great potential for biomedical applications.     

Chain Vacancies in 2D Crystals

Defects in bulk crystals can be classified into vacancies, interstitials, grain boundaries, stacking faults, dislocations, and so forth. In particular, the vacancy in semiconductors is a primary defect that governs electrical transport. Concentration of vacancies depends mainly on the growth conditions. Individual vacancies instead of aggregated vacancies are usually energetically more favorable at room temperature because of the entropy contribution. This phenomenon is not guaranteed in van der Waals 2D materials due to the reduced dimensionality (reduced entropy). Here, it is reported that the 1D connected/aggregated vacancies are energetically stable at room temperature. Transmission electron microscopy observations demonstrate the preferential alignment direction of the vacancy chains varies in different 2D crystals: MoS₂ and WS₂ prefer direction, while MoTe₂ prefers direction. This difference is mainly caused by the different strain effect near the chalcogen vacancies. Black phosphorous also exhibits directional double‐chain vacancies along 〈01〉 direction. Density functional theory calculations predict that the chain vacancies act as extended gap (conductive) states. The observation of the chain vacancies in 2D crystals directly explains the origin of n‐type behavior in MoTe₂ devices in recent experiments and offers new opportunities for electronic structure engineering with various 2D materials.     

Ab initio calculation of the BCC Fe–Al–Mo (Iron–Aluminum–Molybdenum) phase diagram: Implications for the nature of the phase

The metastable phase diagram of the BCC-based ordering equilibria in the Fe–Al–Mo system has been calculated via a truncated cluster expansion, through the combination of Full-Potential-Linear augmented Plane Wave (FP-LAPW) electronic structure calculations and of Cluster Variation Method (CVM) thermodynamic calculations in the irregular tetrahedron approximation. Four isothermal sections at 1750 K, 2000 K, 2250 K and 2500 K are calculated and correlated with recently published experimental data on the system. The results confirm that the critical temperature for the order–disorder equilibrium between Fe₃Al–D0₃ and FeAl–B2 is increased by Mo additions, while the critical temperature for the FeAl–B2/A2 equilibrium is kept approximately invariant with increasing Mo contents. The stabilization of the Al-rich A2 phase in equilibrium with overstoichiometric B2–(Fe,Mo)Al is also consistent with the attribution of the A2 structure to the τ₂ phase, stable at high temperatures in overstoichiometric B2–FeAl.     

The interpretation of X-ray photoelectron spectra of pyrolized S-containing carbonaceous materials

Theoretical models and ab initio Hartree-Fock wavefunctions have been used to investigate the S(2p) core level binding energies (BE), of pyrolized S-containing, carbonaceous materials. Comparison between experimental and calculated data for thiophene permits the accuracy of the present approach to be established. A systematic study of different situations demonstrates that, in these materials, non-oxidized S atoms can show peaks at very high BE relative to the C(1s) peak at 285.0 eV. This study confirms that the peak at 164.1 eV corresponds to ‘thiophenic’ S atoms. On the other hand, it shows that the peaks at higher BE could correspond to S atoms replacing C atoms in three-coordinated structures of graphene layers, in agreement with the arguments suggested in the experimental works. The energetic similarity between the two peaks at very high BE makes it difficult to differentiate between them, although the results of the present study seem to suggest that the peak at experimental BE ≈ 166 eV could correspond to S atoms coordinated to two C and one H atoms at the edge of graphene layers, while the peak at ≈ 169 eV would correspond to S atoms replacing C atoms in inner positions of the graphene layers, and it is bonded to three C atoms.     

茂金属卡宾配合物{(eta~5-C_5H_5)MoX(CO)_2[C(CH_2)_2CH_2O]}(X:Cl、Br、I)的电子结构研究

运用G98W程序,采用Lanl2dz基组,对茂金属配合物{(eta~5-C_5H_5)MoX(CO)_2[C(CH_2)_2CH_2O]}(X:Cl、Br、I)进行从头算研究,探讨配合物结构单元的稳定性、分子轨道能量、原子净电荷布居规律,以及一些前沿分子轨道的组成特征等。结果表明,标题配合物结构在能量上是稳定的,因而能作为结构单元而存在。为茂金属配合物的合成、分子组装提供理论参考。     

Substitution of nickel in Mg2Ni and its hydride with elements from groups XIII and XIV: An ab initio study

We have performed ab initio calculations with equilibrium supercells of the Mg₂Ni compound and its hydride Mg₂NiH₄ doped with elements X = Al, Ga, In, Si, Ge and Sn. Two concentrations of X in both structures have been set: (1) every 16th, and (2) every fourth Ni atom has been substituted by X. Total energy calculations yielded the Mg₂NiH₄ hydrogen absorption enthalpy ΔH_abs according to the chemical reaction Mg₂Ni + 2H₂ → Mg₂NiH₄. Reduction of the hydrogen absorption enthalpy was reported for both concentrations of X. When doping the Mg₂NiH₄ hydride with X = In in a low concentration (1), the value of hydrogen desorption enthalpy decreases from 68.22 to 55.96 kJ(mol H₂)^?1. Doping with X = In in a high concentration (2) further decreases the hydrogen desorption enthalpy to 5.50 kJ(mol H₂)^?1. Further, the electronic structure of Mg₂(Ni–In)H₄ hydride with a low In concentration indicates weaker Ni–H bonds in comparison with the pristine Mg₂NiH₄. Attraction between H and In atoms induced enhanced bonding between Mg and H atoms compared to the pristine Mg₂NiH₄.