Surface plasmon resonance spectroscopy and quartz crystal microbalance study of streptavidin film structure effects on biotinylated DNA assembly and target DNA hybridization

Surface plasmon resonance (SPR) spectroscopy is employed for the study of biotinylated DNA assembly on streptavidin modified gold surfaces for target DNA hybridization. Two immobilization strategies are involved for constructing streptavidin films, namely, (1) physical adsorption on biotin-containing thiol treated surfaces through biotin-streptavidin links and (2) covalent attachment to 11-mercaptoundecanoic acid (MUA) treated surfaces through amine coupling. To understand the structural properties of the streptavidin films, a quartz crystal microbalance with energy dissipation monitoring (QCM-D) is used to monitor the streptavidin immobilization procedures. The simultaneously measured frequency (Deltaf) and dissipation factor (DeltaD) changes, together with the SPR angle shifts (Deltatheta), suggest that the streptavidin film assembled on the biotin-containing surface is highly rigid with a well-ordered structure while the streptavidin film formed through amine coupling is highly dissipative and less structured. The subsequent biotinylated DNA (biotin-DNA) assembly and target hybridization results show that the streptavidin film structure has distinct effects on the biotin-DNA binding amount. On the streptavidin matrix, not only the probe DNA density but also the strand orientation mediated by the streptavidin films has distinct effects on hybridization efficiency. Particularly, the molecularly ordered streptavidin films formed on the biotin-containing surfaces ensure a well-ordered DNA assembly, which in turn allows for a higher efficiency in target DNA capture and for a higher sensitivity in the hybridization analysis when compared to the biotin-DNA assembled on the less structured streptavidin films formed through amine coupling.     

Cu2(μ-dppb)2(μ-Cl)2的合成、晶体结构及非线性光学性质

The complex Cu₂(μ-dppb)₂(μ-Cl)₂ has been synthesized from the reaction of CuCl， dppb and (n-Bu)₄NCl. The crystal belongs to the triclinic with space group P1. The unit cell parameters are: a=9.939(4)?， b=10.083(6)?， c=14.104(5)?， α=76.46(3)°， β=71.02(2)°， γ=70.87(5)°. The single crystal X-ray diffraction analysis reveals that it has a bi-ring structure with a symmetry center at the middle of two Copper atoms. The outer ring is a 14-membered ring of Cu-dppb-Cu-dppb， and the inner ring is a 4-membered ring composed of two Cl^- and two Cu(Ⅰ). Investigation of third-order optical nonlinearity shows that it exhibits considerable nonlinear absorptive and self-defocusing effect with α₂=1.75×10^-13m·W^-1 and n₂=3.19×10^-18m²·W^-1. CCDC: 193113.     

~(13)C-NMR研究聚丁二烯长支链支化

本文研究了用不同催化体系制备的聚丁二烯和加氢的聚丁二烯的~(13)C-NMR谱图。结合GPC测定支化度的数据,提出了二种可能的支化结构。以Ni及Co催化体系聚合的试样,支化点可能位于顺-1,4主链双键的α-次甲基上;而由Ni+Mo催化体系聚合的试样,可能为1,2-乙烯基的双键打开接长支链。     

Molecular dynamics simulations of the mononuclear zinc-beta-lactamase from Bacillus cereus complexed with benzylpenicillin and a quantum chemical study of the reaction mechanism

Herein, we present results from MD simulations of the Michaelis complex formed between the B. cereus zinc-beta-lactamase enzyme and benzylpenicillin. The structural and dynamical effects induced by substrate-binding, the specific role of the conserved residues, and the near attack conformers of the Michaelis complex are discussed. Quantum chemical methods (HF/6-31G* and B3LYP/6-31G*) are also applied to study the hydrolysis reaction of N-methylazetidinone catalyzed by a monozinc system consisting of the side chains of the histidine residues (His86, His88, and His149) complexed with Zn-OH and the side chains of Asp90 and His210. From this model system, we built molecular-mechanics representations of the prereactive complex and transition state configurations docked into the active site. Linear-scaling semiempirical calculations coupled with a continuum solvent model were then performed on these static models. We propose that the experimental rate data for the B. cereus enzyme is compatible with a one-step mechanism for the hydrolysis of beta-lactam substrates in which His210 acts as a proton donor.     

Intramolecular hydrogen abstraction. Iodosobenzene diacetate,an efficient and convenient reagent for alkoxy radical generation

Photolysis of several hydroxy compounds in presence of iodosobenzene diacetate and iodine leads to alkoxy radical derivatives which undergo intramolecular hydrogen abstraction to produce cyclic ethers in good yield.     

Quantitative structure-property relationships for colour reagents and their colour reactions with cerium using computational neural networks

Quantitative structure-activity/property relationships (QSAR/QSPR) studies have been exploited extensively in the designs of drugs and pesticides, but few such studies have been applied to the design of colour reagents. In this work, the topological indices A(x1) - A(x3) suggested in this laboratory were applied to multivariate analysis in structure-property studies. The topological indices of 43 phosphone bisazo derivatives of chromotropic acid were calculated. The structure-property relationships between colour reagents and their colour reactions with cerium were studied using A (x1 a (x)3) indices with satisfactory results. The purpose of this work was to establish whether QSAR can be used to predict the contrasts of colour reactions and in the longer term to be a helpful tool in colour reagent design.     

Rapid detection of Escherichia coliform with a bulk acoustic wave sensor based on the gelation of Tachypleus amebocyte lysate

A new sensing method (BAW-TAL technique), which combined the bulk acoustic wave (BAW) technique with the gelation reaction of Tachypleus amebocyte lysate (TAL), was used for viscosity and density measurement and applied to the detection of Escherichia coliform (E. coli). This method depended on the fact that the viscosity and density of the mixture increased, and as a result, the resonance frequency decreased correspondingly after TAL was mixed with the heated E. coli solution that contained endotoxin. Results showed that the frequency shift was linearly related to the logarithm of E. coli concentration in the range of 2.7x10(4)-2.7x10(8) cells/ml. The correlation coefficient was 0.996. This BAW-TAL method was compared with the standard pour plate counts (PPC) method. The proposed method was much more rapid and simpler for detection of E. coli than the traditional methods.     

Steam Reforming Reactions of Methanol Over Nickel and Copper Catalysts

Steam-reforming reactions of methanol over NiO/Al₂O₃ and CuO/ZnO have been investigated. Over the nickel catalyst, the reaction rate is of zero kinetic order with respect to either methanol or steam, and the activation energy is 12.4 kJmol^?1, whereas with copper catalyst, the rate is expressed according to the literature as kP_a/(1 + K_aP_a + K_b+P_b) in which “a” and “b” are methanol and steam, respectively. The rate-controlling step of the reaction is assigned to the dissociation of O-H bond with dehydrogenation of C-H bond proceed rapidly to form carbon oxides. With copper catalyst the intrinsic participation of a water molecule during the dehydrogenation of C-H bond leads to the formation of carbon dioxide. With nickel catalyst, the dehydrogenation proceed more rapidly than the migration of a water molecule from an alumina site to a nickel site and causes almost exclusively the formation of carbon monoxide and hydrogen at a lower reaction temperature.     

Effect of Ce<Superscript>3+</Superscript> on spectral characteristic of D1/D2/Cytb559 complex from spinach

It was studied by spectroscopy that PSII reaction center complex consisting of three polypeptides, D₁, D₂ and Cytb559, were purified from PSII particle of CeCl₃ treated spinach. The results of the experiment show that Ce³⁺ could improve the growth of spinach, and accelerate electron transport of PSII particles. Of chl-a of UV-Vis spectrum of D1/D2/Cytb559 complex, Soret band was blue-shifted by 3 nm and Q band by 2 nm, respectively, and the fluorescence emission peak was blue-shifted by 5 nm in CeCl₃-treated spinach compared with the one in control. By the extended X-ray absorption fine structure (EXAFS) spectroscopy methods, it has been found that Ce³⁺ is coordinated with 8 nitrogen atoms in the first coordination shell with Ce-N bond length of 0.253 nm, and Ce³⁺ with 6 oxygen atoms in the second coordination shell with Ce-O bond length of 0.32 nm. However, the secondary structure of D1/D2/Cytb559 complex by circular dichroism (CD) spectroscopy has no significant change after CeCl₃ treated. It might be that Ce³⁺ binds to porphyrin rings of chlorophyll and oxygen of amino acid residue of polypeptide in D1/D2/Cytb559 complex, and then accelerates the primary reaction of PSII, intensifies function of P680⁺ primary electron donor of D1/D2/Cytb559, but there is little change in conformation of PSII reaction center complex.     

On the order supergraph of the power graph of a finite group

Ricerche di Matematica - The power graph $${\mathcal {P}}_{G}$$ of a finite group G is the graph whose vertex set is G, two distinct vertices are adjacent if one is a power of the other. The order...