Structural and Functional Analysis of Pyrimidine Nucleoside Phosphorylases of the NP-I and NP-II Families in Complexes with 6-Methyluracil

The structure of bacterial uridine phosphorylase (UPh) belonging to the NP-I family in complex with 6-methyluracil was determined for the first time at 1.17 Å resolution. The structural features of bacterial UPh from the bacterium Vibrio cholerae (VchUPh) responsible for selectivity toward 6-methyluracil acting as a pseudosubstrate were revealed. The repulsion between the hydrophilic hydroxyl group of the active-site residue Thr93 of VchUPh and the hydrophobic methyl group of 6-methyluracil prevents the oxygen atom O4' of the ribose moiety and the phosphate oxygen atom O3P of ribose 1-phosphate from forming hydrogen bonds with OG1_Thr93, which are essential for the enzymatic reaction. This, apparently, makes VchUPh inactive in the enzymatic synthesis of 6-methyluridine from 6-methyluracil. Hence, Thr93 is the residue, the modification of which will allow VchUPh to catalyze the biotechnologically important synthesis of 6-methyluridine from 6-methyluracil. Taking into account high structural homology of the functionally significant regions of bacterial UPhs, this conclusion is also true for other bacterial UPhs. It was demonstrated that bacterial thymidine phosphorylases of the NP-II family cannot bind 6-methyluracil in a proper conformation required for the catalysis because of a close contact between the 6-methyl group and Phe210.     

Crystallization in Microgravity and the Atomic-Resolution Structure of Uridine Phosphorylase from Vibrio cholerae

Crystallography Reports - Uridine phosphorylases are known as key targets for the development of new anticancer and antiparasitic agents. Crystals of uridine phosphorylase from the pathogenic...     

Small-Angle X-ray Scattering Study of Changes in the Quaternary Structure of Nucleotide-Regulated Pyrophosphatase from Desulfitobacterium hafniense upon Ligand Binding in Solution

Crystallography Reports - The regulation of nucleotide-regulated inorganic pyrophosphatases at a molecular level has been extensively studied in order to establish the mechanism of signal...     

Erratum to: Crystallization in Microgravity and the Atomic-Resolution Structure of Uridine Phosphorylase from Vibrio cholerae

Crystallography Reports - An Erratum to this paper has been published: https://doi.org/10.1134/S1063774521070270     

Conformational Mobility and Phase Transitions in Alkyloxybenzoate of Cholesterol

Abstract

The structural particularities of polymorphic modifications and cholesterol liquid crystal phase have been investigated by theoretical and experimental IR spectroscopy methods. The spectra were recorded in the interval of temperatures 293–523 K within the range of 600–3600 cm^?1. The frequencies of normal modes and intensities in the IR spectra have been calculated for the alkyloxybenzoate of cholesterol conformers, which may be realized under certain temperatures. Comparison of results of theoretical modelling and recorded spectra confirmed suggestion about conformational mobility basically defined with changing of steroid kennel orientation comparatively stayed part of molecule in the different phase state.     

X-Ray Structure and Molecular Dynamics Study of Uridine Phosphorylase from Vibrio cholerae in Complex with 2,2'-Anhydrouridine

Crystallography Reports - The high-resolution three-dimensional structure of uridine phosphorylase from the pathogenic bacterium Vibrio cholerae in complex with the competitive inhibitor...     

SiC衬底上近自由态石墨烯制备及表征的研究进展

石墨烯材料自问世以来,一直处于学界研究的焦点,在微电子器件领域,通过SiC衬底制备的近自由态石墨烯具有较大的应用潜力.本文介绍了SiC热解法制备石墨烯的优势与劣势,说明了近自由态石墨烯制备的原因.综合阐述了目前制备近自由态石墨烯的常用方法,并对比了各种制备方法的特点.最后,概述了近自由态石墨烯的常用表征手段.     

阳极氧化铝基板的制备及在LED散热领域的应用

利用阳极氧化技术制备了普通阳极氧化铝基板,并在此基础上结合图形转移的方法制备出了选择性阳极氧化铝基板.借助电镜扫描并通过冷热循环冲击试验对铝材与阳极氧化膜界面处在高低温突变情况下的界面形貌进行了分析.利用结温测试仪、积分球系统、功率计、半导体制冷温控台等仪器设备,通过结温及热阻测试对比研究了两种铝基板与普通MCPCB(Metal Core PCB,金属芯印刷电路板)对LED模组散热效果的影响情况.结果表明,两种基板在经低温-55 ℃,高温125 ℃,1000次冷热循环后,氧化膜无裂纹滋生,氧化膜与铝材界面结合完好;对于驱动功率为3 W的LED灯珠,普通MCPCB、普通阳极氧化铝基板与选择性阳极氧化铝基板所对应的芯片结温分别为46.5 ℃、42.03 ℃和38.52 ℃,对应模组的热阻则分别为9.29 ℃/W、7.49 ℃/W和5.85 ℃/W.     

利用基板法在V型热解火焰中合成碳纳米管的实验研究

利用V型热解火焰合成碳纳米管是一项新的技术和方法,实验中采用304不锈钢片作为取样基板,将硝酸镍溶液均匀涂敷在取样基板上作为催化剂,利用扫描电镜和透射电镜对碳纳米管进行形态和结构表征。实验中得到了典型形态及特殊形态的碳纳米管,催化剂颗粒的直径在为5~8 nm之间。实验结果表明,取样时间为10 min,温度约为1150 K时最有利于产生碳纳米管。最后分析讨论了特殊形态的碳纳米管的结构及可能的形成机理。     

金刚石膜/硅基体热残余应力场有限元分析

运用ANSYS软件建立了有限元模型,对化学气相沉积在硅基体上的金刚石膜内部和膜/基交界面处的各热残余应力分量的分布作了计算与分析.所建模型与已有的一维解析模型都能得出厚度截面上的法向应力分量的分布,且吻合较好,而前者的优点在于它还能模拟切向应力和剪应力等其它应力分量,这对分析膜/基界面的粘附与失效是至关重要的.     

QF1基底上可见光区宽带增透膜研究

本文以QF1为基底设计了一种宽带可见光区增透膜,即:增透波长0.4～0.8 μm,工艺实现采用了电子束蒸发物理气相沉积的方法,薄膜材料仅含有TiO2和SiO2,并分别作为高低折射率材料.利用Edinburgh光谱仪对双面镀制该膜系样品的透过率进行测量,测试结果表明平均透过率达98.43;,通过SEM的膜层截面证实膜层比设计略偏厚,导致测试透过率与设计相比略有红移,但实际样品的光学特性与设计结果基本相符,具有宽带的增透特性.环境测试表明:薄膜具有良好的稳定性和牢固度.该增透膜可以应用于可靠性要求较高的环境中.     

HFCVD系统中衬底接触热阻的研究

建立了热丝CVD大面积金刚石膜沉积的衬底温度场模型,对影响衬底温度场的接触热阻及其他相关沉积参数进行了模拟计算。根据实验结果,对接触热阻的计算公式进行了修正。当ζ=0.75时,计算结果和实验结果基本上吻合。在仿真条件下,考虑衬底三维热传导以及热丝温度的不均匀分布使衬底温度场的均匀性明显优于纯热辐射下的温度场。这些计算结果为制备大面积高质量的金刚石薄膜提供了理论基础。     

Conformational Behavior of N1-(Diphenylphosphoryl)acetyl-N4-phenyl-thiosemicarbazide in Various Crystal Environments

Crystallography Reports - Three crystal modifications of phenyl-substituted diphenylphosphoryl thiosemicarbazide (compound (1) and two its solvates with dimethyl sulfoxide (2, 3)) have been...     

Role of twinning in plastic deformation

A new concept of the structure of yttrium-aluminum garnet (Y₃Al₅O₁₂) has demonstrated the possibility of forming inversion twins in the (111) plane. The twinning processes are shown to be responsible for stress relaxation during the growth and plastic deformation of Y₃Al₅O₁₂ single crystals. This way of stress relaxation can be used to describe the plastic deformation of other crystals, at least cubic ones.     

Conformational flexibility of the 17,18-benzo-1,13-diaza-4,7,10,16,20-pentaoxacycloheneicosa-2,12-dione in solution and in solid state

The recent method of synthesis of diazacoronands by macrocyclization of primary,-diamines with dimethyl esters of,-diacids was used for the preparation of the title compound (3).¹H and¹³C NMR in solution, as well as X-ray diffraction studies for three different crystals were undertaken. The centrosymmetric space groupPnma was chosen during structure determination although there are some indications that noncentrosymmetric space groupPna2₁ is also possible. In solution, dynamically averaged structure with twofold symmetry is observed. In the solid state, two independent molecules in the asymmetric unit show planar symmetry, and are conformationally different. An internal cavity represents a good receptor for a water molecule. Two various hydrogen bonding patterns of different stabilities were found. In the basic pattern, the water oxygen atom is bounded by two amide hydrogen atoms and water molecule uses one of its hydrogen atoms to form an additional hydrogen bond with 01. In the second pattern, water hydrogen atoms are nonbonded.     

HFCVD系统中衬底温度场及气相空间场的数值分析

探讨了典型气氛中热丝辐射、气体热传导与对流、化学反应生热等因素对衬底温度的影响,建立了三维热丝辐射和二维热流耦合有限元模型,研究了各工艺参数对衬底温度场及气相空间场的影响.结果表明H2占主导地位的气氛中衬底表面的氢原子重组放热对衬底温度有较大影响,氩气气氛中原子重组放热对衬底温度影响很小;热丝温度对衬底温度的影响最大;进气口到衬底的距离及进气口气体流速对衬底附近的流场影响最大,适当提高进气口到衬底的距离有助于提高衬底附近流场均匀性,增大进气速度有助于突破热障提高衬底表面流速,但同时加剧了衬底附近流场的不均匀性.     

Role of Dimensionality in Dimerized Two-Band Systems

Abstract

We have studied the ground state properties of Pd(dmit)₂ salts using an effective dimer model. This model describes low-energy excitations of the two-band Hubbard model and is derived by a strong coupling expansion. Dimensionality of the Fermi surface, density-of-states singularity, and magnetic frustration in the dimer model are simultaneously controlled by substituting the cation.     

直流弧光放电PCVD金刚石膜制备中基底控温系统的研制与应用

基于直流弧光放电PCVD金刚石薄膜沉积设备的特点,设计开发了基底自动控温系统.将该系统应用于金刚石薄膜的制备中,并采用SEM、Raman光谱等测试方法对所制备的薄膜的形貌、品质进行了表征.结果证明该系统具有较好的稳定性,其应用时所制备的金刚石薄膜的品质明显得到提高,具有广泛的应用前景.