Protein adsorption onto silica nanoparticles: conformational changes depend on the particles' curvature and the protein stability

We have analyzed the adsorption of protein to the surfaces of silica nanoparticles with diameters of 6, 9, and 15 nm. The effects upon adsorption on variants of human carbonic anhydrase with differing conformational stabilities have been monitored using methods that give complementary information, i.e., circular dichroism (CD), nuclear magnetic resonance (NMR), analytical ultracentrifugation (AUC), and gel permeation chromatography. Human carbonic anhydrase I (HCAI), which is the most stable of the protein variants, establishes a dynamic equilibrium between bound and unbound protein following mixture with silica particles. Gel permeation and AUC experiments indicate that the residence time of HCAI is on the order of approximately 10 min and slowly increases with time, which allows us to study the effects of the interaction with the solid surface on the protein structure in more detail than would be possible for a process with faster kinetics. The effects on the protein conformation from the interaction have been characterized using CD and NMR measurements. This study shows that differences in particle curvature strongly influence the amount of the protein's secondary structure that is perturbed. Particles with a longer diameter allow formation of larger particle-protein interaction surfaces and cause larger perturbations of the protein's secondary structure upon interaction. In contrast, the effects on the tertiary structure seem to be independent of the particles' curvature.     

Predicting crystal structures with data mining of quantum calculations

Predicting and characterizing the crystal structure of materials is a key problem in materials research and development. It is typically addressed with highly accurate quantum mechanical computations on a small set of candidate structures, or with empirical rules that have been extracted from a large amount of experimental information, but have limited predictive power. In this Letter, we transfer the concept of heuristic rule extraction to a large library of ab initio calculated information, and we demonstrate that this can be developed into a tool for crystal structure prediction.     

Distance dependence of the interaction between single atoms: gold dimers on NiAl(110)

The importance of substrate-mediated adsorbate-adsorbate interactions on electronic states has been demonstrated for Au dimers on NiAl(110) with a scanning tunneling microscope and density functional calculations. An unoccupied resonance observed in single Au atoms splits into a doublet in Au dimers. The energy splitting depends inversely on the distance between the two adatoms, revealing the relative importance of direct and substrate-mediated interactions. Spatially resolved conductance measurements of Au dimers reveal the symmetric and antisymmetric characters of the doublet states.     

Structure and bonding in solution of dioxouranium(VI) oxalate complexes: isomers and intramolecular ligand exchange

Structural isomers of [UO(2)(oxalate)(3)](4-), [UO(2)(oxalate)F(3)](3-), [UO(2)(oxalate)(2)F](3-), and [UO(2)(oxalate)(2)(H(2)O)](2-) have been studied by using EXAFS and quantum chemical ab initio methods. Theoretical structures and their relative energies were determined in the gas phase and in water using the CPCM model. The most stable isomers according to the quantum chemical calculations have geometries consistent with the EXAFS data, and the difference between measured and calculated bond distances is generally less than 0.05 A. The complex [UO(2)(oxalate)(3)](4-) contains two oxalate ligands forming five-membered chelate rings, while the third is bonded end-on to a single carboxylate oxygen. The most stable isomer of the other two complexes also contains the same type of chelate-bonded oxalate ligands. The activation energy for ring opening in [UO(2)(oxalate)F(3)](3-), deltaU++ = 63 kJ/mol, is in fair agreement with the experimental activation enthalpy, deltaH++ = 45 +/- 5 kJ/mol, for different [UO(2)(picolinate)F(3)](2-) complexes, indicating similar ring-opening mechanisms. No direct experimental information is available on intramolecular exchange in [UO(3)(oxalate)(3)](4-). The theoretical results indicate that it takes place via the tris-chelated intermediate with an activation energy of deltaU++ = 38 kJ/mol; the other pathways involve multiple steps and have much higher activation energies. The geometries and energies of dioxouranium(VI) complexes in the gas phase and solvent models differ slightly, with differences in bond distance and energy of typically less than 0.06 A and 10 kJ/mol, respectively. However, there might be a significant difference in the distance between uranium and the leaving/entering group in the transition state, resulting in a systematic error when the gas-phase geometry is used to estimate the activation energy in solution. This systematic error is about 10 kJ/mol and tends to cancel when comparing different pathways.     

Maximally aligned states in 99Ag

Excited states of ⁹⁹Ag were populated via the ⁵⁰Cr + ⁵⁸Ni (261 MeV) reaction using the NORDBALL detector array equipped with charged-particle and neutron detector systems for reaction channel separation. On the basis of the measured γγ-coincidence relations and angular distribution ratios a significantly extended level scheme has been constructed up to E _x ∼ 7.8 MeV and I = 35/2. The experimental results were described within the framework of the shell model. Candidates for states fully aligned in the πg _9/2 ^-3ν(d _5/2, g _7/2)² valence configuration space were found at 4109 and 6265 keV. Received: 18 June 2002 / Accepted: 11 October 2002 / Published online: 4 February 2003 RID="a" ID="a"e-mail: sohler@atomki.hu Communicated by J. ?yst?     

Adapting high Z methods for a {\user1{g}_\user1{J} } factor prediction for C5+, S15+ and Ca19+

We present a ${\user1{g}_\user1{J} } $ factor prediction for the ground state of C⁵⁺, S¹⁵⁺ and Ca¹⁹⁺. For this purpose we have developed a subtraction scheme within the QED calculations which is outlined in this contribution. Current theoretical limits are mentioned.     

Kv1.1 null mice have enlarged hippocampus and ventral cortex

Background  

Mutations in the Shaker-like voltage-gated potassium channel Kv1.1 are known to cause episodic ataxia type 1 and temporal lobe epilepsy. Mice that express a malfunctional, truncated Kv1.1 (BALB/cByJ-Kv1.1 ^mceph/mceph ) show a markedly enlarged hippocampus and ventral cortex in adulthood.     

第22卷B辑第三者期(2001)目次和提要

该文研究形如-div(a(x,x/ε,x/ε2,Duε))非线性单调算子的重迭代齐性化 J. L. Lions D. Lukassen L. E. Persson P. Wall该文研究形如-div(a(x,x/,x/2, Du))=f的非线性方程的重迭代齐性化,这里a关于前两个变量是周期的, 关于第3个变量是单调的. 证明了当 0时,u在W1,p()中(甚至在某种多尺度意义上)弱收敛于一个极限问题的解.此外, 还给出了这个极限问题的显式表达和主要结果的完整证明. 线性弹性壳动力学问题的渐近分析---动力学弯曲壳方程的验证 肖黎明 从三维弹性壳动力学方程出发, 在某些条件下用渐近分析方法给出了动力学弯曲壳方程的验证. 等变上同调和对称群的表示 M. Atiyah 作者在最近一篇论文中, 构造了一个从3维空间中, n个不同的有序点的构形空间到酉群U(n)的旗流形的连续映射, 该映射与对称群的作用相容, 它也与旋转群SO(3)适当的作用相容. 该文研究了在SO(3)-等变上同调中的诱导同态, 并证明了这个同态包含了许多涉及对称群的表示的有趣信息. 超线性可逆系统解的有界性     

On the Friedrichs inequality in a domain perforated aperiodically along the boundary. Homogenization procedure. Asymptotics for parabolic problems

This paper is devoted to the asymptotic analysis of functions depending on a small parameter characterizing the microinhomogeneous structure of the domain on which the functions are defined. We derive the Friedrichs inequality for these functions and prove the convergence of solutions to corresponding problems posed in a domain perforated aperiodically along the boundary. Moreover, we use numerical simulation to illustrate the results. The work of the first author was partially supported by RFBR. The work of the first and the second authors was partially supported by the program “Leading Scientific Schools” (NSh-1698.2008.1).     

Callable risky perpetual debt with protection period

Issuances in the USD 260 Bn global market of perpetual risky debt are often motivated by capital requirements for financial institutions. We analyze callable risky perpetual debt emphasizing an initial protection (‘grace’) period before the debt may be called. The total market value of debt including the call option is expressed as a portfolio of perpetual debt and barrier options with a time dependent barrier. We also analyze how an issuer’s optimal bankruptcy decision is affected by the existence of the call option by using closed-form approximations. The model quantifies the increased coupon and the decreased initial bankruptcy level caused by the embedded option. Examples indicate that our closed form model produces reasonably precise coupon rates compared to numerical solutions. The credit-spread produced by our model is in a realistic order of magnitude compared to market data.