1H–13C–29Si triple resonance and REDOR solid-state NMR—A tool to study interactions between biosilica and organic molecules in diatom cell walls

Triple resonance solid-state NMR experiments using the spin combination ¹H–¹³C–²⁹Si are still rarely found in the literature. This is due to the low natural abundance of the two heteronuclei. Such experiments are, however, increasingly important to study hybrid materials such as biosilica and others. A suitable model substance, ideally labeled with both ¹³C and ²⁹Si, is thus very useful to optimize the experiments before applying them to studies of more complex samples such as biosilica. Tetraphenoxysilane could be synthesized in an easy, two-step synthesis including double isotope labelling. Using tetraphenoxysilane, we established a ¹H–¹³C–²⁹Si double CP-based HETCOR experiment and applied it to diatom biosilica from the diatom species Thalassiosira pseudonana. Furthermore, we carried out ¹H–¹³C{²⁹Si} CP-REDOR experiments in order to estimate the distance between the organic matrix and the biosilica. Our experiments on diatom biosilica strongly indicate a close contact between polyamine-containing parts of the organic matrix and the silica. This corroborates the assumption that the organic matrix is essential for the control of the cell wall formation.     

Chemical promenades: Exploring potential-energy surfaces with immersive virtual reality

The virtual-reality framework AVATAR (Advanced Virtual Approach to Topological Analysis of Reactivity) for the immersive exploration of potential-energy landscapes is presented. AVATAR is based on modern consumer-grade virtual-reality technology and builds on two key concepts: (a) the reduction of the dimensionality of the potential-energy surface to two process-tailored, physically meaningful generalized coordinates, and (b) the analogy between the evolution of a chemical process and a pathway through valleys (potential wells) and mountain passes (saddle points) of the associated potential energy landscape. Examples including the discovery of competitive reaction paths in simple A + BC collisional systems and the interconversion between conformers in ring-puckering motions of flexible rings highlight the innovation potential that augmented and virtual reality convey for teaching, training, and supporting research in chemistry.     

Nonbiofouling surface based on amphiphilic alkanethiol self‐assembled monolayers

A series of novel amphiphilic alkanethiols used for preparation of nonbiofouling surfaces have been synthesized and characterized. Surface properties of the resultant self assembled layers have been studied by multiple characterization techniques, such as XPS, Grazing angle infrared spectroscopy (GA‐FTIR) and contact angle measurements. The antifouling performance of surfaces grafted with terminally fluorinated alkanethiols were assayed employing the fouling diatom Nitzschia and ubiquitous Staphylococcus aureus. The results indicated that amphiphilic alkanethiol‐grafted surfaces could effectively reduce the bacterial adhesion and settlement of the fouling diatom. Copyright © 2010 John Wiley & Sons, Ltd.     

氨基化硅藻基As(Ⅴ)印迹复合材料的制备与性能

采用硅藻作为材料载体、选取氨基丙基三甲氧基硅烷(APS)作为功能单体、As(Ⅴ)为模板离子、环氧氯丙烷(ECH)为交联剂通过表面印迹组合,制备了砷离子印迹复合材料,并将其应用于二元体系中对砷离子的选择吸附。采用扫描电镜、X射线光电子能谱、傅立叶变换红外光谱及N_2吸附-脱附实验对材料进行表征,探究了硅藻基表面印迹法的搭接方式:氨基丙基三甲氧基硅烷首先通过缩合反应脱去甲氧基,与硅藻表面的活性羟基形成了(Si-O)_3≡Si-R结构,在硅藻表面形成有效接枝,通过环氧氯丙烷与APS中的氨基交联形成印迹结合位点,从而在硅藻表面形成了具有As(Ⅴ)选择性的复合印迹孔穴。采用选择性系数法,得出离子印迹复合材料对砷离子(As(Ⅴ))的去除率为98%,相对选择性系数(k′)均大于1.5。     

An algebraic description of anharmonic diatom–diatom inelastic collisions in the semiclassical approximation

An algebraic model to describe inelastic collisions between two anharmonic diatomic molecules in the semiclassical approximation is presented. The interactions for the diatomic systems are modelled in terms of Morse potentials, while an exponential repulsive potential is taken for the interactions between the nearest atoms of the diatomic systems. This problem is treated in the interaction potential framework, where an approximation in terms of the generators of three SU(2) groups is proposed, two corresponding to the Morse oscillators and the other to the interaction. The transition probabilities are given in terms of a sum of the products of three Wigner's d(β) functions corresponding to the three SU(2) groups. As an example the systems N₂?+?N₂ and H₂?+?H₂ are described and compared with exact quantum mechanical calculations.     

An extension of the grid empowered molecular simulator to quantum reactive scattering

Within the activities of the D37 COST Action, we have further developed the quantum dynamics framework of the grid empowered molecular simulator (GEMS) implemented on the segment of the European grid available to the COMPCHEM (computational chemistry) virtual organization. GEMS does now include in a full ab initio approach, the evaluation of the detailed quantum (both time dependent and time independent) dynamics of small systems starting from the calculation of the electronic structure properties as well as the direct calculation of thermalized properties. Illustrative, full dimensional applications of the extended simulator to the H + H(2) , N + N(2) , and O + O(2) systems are presented.     

Macromolecule mediated bioinspired silica synthesis using a diol-modified silane precursor

Following recent investigations on the role of synthetic and biological macromolecules in silicification and biosilicification, we report here the bioinspired synthesis of silica structures under ambient conditions and neutral pH mediated by two synthetic macromolecules. In this research ethylene glycol modified silane (EGMS) was used as the silica precursor. The macromolecules used were either poly(allylamine hydrochloride) (PAH) or poly-l-lysine (PLL), both being cationically charged at neutral pH in an aqueous medium. Mild conditions that constitute the bioinspired or biomimetic synthesis were used to compare the behaviour of the EGMS to other silica precursors. The products were characterised by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Fourier Transform Infrared Spectroscopy (FTIR). The formation of well-defined spherical silica particles (for both PAH and PLL) and hexagons (for PLL only), was shown by electron microscopy. In addition, it was also found that these macromolecules were incorporated into the silica products, thus fulfilling the dual role of catalysts and structure directing agents in a similar fashion to that described in the literature for the formation of (bio)silica, as facilitated by (bio)macromolecules.This paper is dedicated to Mike Owen on occasion of his winning the DeBruyn medal, the first silicon chemist to do so.     

Synthesis of Ordered Biosilica Materials

Biogenic silica with amazing diversity of nanostructure shells,fibers and granules in diatoms and sponges is mediated by proteins and polysaccharides and forms at ambient pressure and temperatures.Chemical synthetic methods,in contrast,have to rely on extreme pH and /or surfactants to induce the condensation of silica precurors into specific patterns.One kind of benign synthesis method through plant cell wall template-directed ordered biosilica materials under ambient conditions in intriguing in this context.Organized silica materials in intercellular spaces of epidermal cells of tall fescue leaves were synthesized through molecular recognition between Si-OH and polysaccharide-OH or glycoprotein-OH of main components of plant cell walls and cellular processing as well when Si(OEt)4 was supplied rather than monosilicic acid.The biosynthesis of structural silica in tall fescue plant was correlated with the Si species applied,reflecting the slower condensation from tetraethoxysilane (TEOS) and thus providing greater opportunities for structural control by the underlying matrix of cell walls.The composition was estimated by energy dispersive X-ray(EDX) spectra on a scanning electron microscope.All organized structures showed carbon,oxygen and silicon peaks,indication that their formations differ from natural siliceous process.     

硅藻遗骸的稳定性对硅藻土形成环境的指示

硅藻遗骸的稳定性对于理解硅藻土矿的全球分布十分重要. 作者在不同 p H值和温度条件下,对硅藻遗骸的稳定性进行了研究结果表明: 温度高于 40℃或者 p H> 12时 ,硅藻遗骸的溶解度成倍地增加. 它指示着硅藻土矿主要分布于中高纬度地区 ,不仅是因为那里的冷水域有丰富的营养盐 ,有利于硅藻的生长繁殖,还因为低温有利于硅藻遗骸的保存而不至于被溶解.     

Preparation of composite monoliths of quaternized chitosan and diatom earth for protein separation

In this study, composite monoliths with porous structures were prepared using quaternized chitosan and diatom earth for protein separation. Quaternized chitosan (N-[(2-hydroxy-3-trimethylammonium)propyl] chitosan chloride) dissolved in water was mixed with diatom earth and crosslinked with glutaraldehyde under low-temperature conditions to form a cryogel. Interconnected porous monoliths were obtained after removing ice crystals from the cryogel. The monoliths adsorbed bovine serum albumin selectively from the solution mixture of bovine serum albumin and bovine ɤ-globulin, and bovine ɤ-globulin was recovered in the flow-through fraction. The adsorption selectivity was enhanced by changing the solution pH from 6.8 to 5.5. The adsorption of bovine serum albumin by the monolith was replicated at least five times following its washing with a buffer containing 400 mM NaCl and subsequent regeneration with a 10 mM acetate buffer. The composited monolith is a promising adsorbent for the removal of acidic proteins, such as serum albumin contamination in neutral proteins, for example, ɤ-globulins, in bioproduction processes.