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.     

HKC细胞损伤对草酸钙晶体成核和聚集的促进作用

采用H2O2对人肾小管上皮细胞(HKC)进行损伤. HKC损伤后,其活力降低,并表达骨桥蛋白(OPN). 损伤细胞促进草酸钙晶体的成核、聚集,并促进一水草酸钙(COM)晶体的形成,但对晶体生长的促进作用不明显. 本文结果提示,HKC细胞损伤后增加了肾结石形成的危险性.     

生物活性复合材料在生物矿化过程中的微观形貌与离子浓度变化

采用3-羟基丁酸酯-3-羟基戊酸酯的共聚物(PHBV)与磷酸三钙(TCP)、羟基磷灰石(HA)、生物活性玻璃(BG)等进行复合,获得了性能优良的生物活性骨组织工程支架材料和骨修复材料.研究和比较了3种复合材料在体外模拟生理环境中发生的生物矿化反应,对比了反应前后因矿化物的形成导致的表面微观形貌的变化,通过检测反应液离子浓度的变化对不同材料的矿化过程和生物活性进行了定量表征.研究结果表明,3种复合材料在模拟生理溶液中发生生物矿化的过程和程度不同,其中PHBV/BG的生物活性反应最为明显.     

早期生物矿化过程中紫外吸收动力学曲线上的负峰现象

近年来, Jens等[1]利用紫外光度法测定生物矿化溶液的吸光度(即混浊度)的变化, 实时地记录生物矿物形成过程的信息, 从而研究其矿化规律. 实验发现, 胶原/羟基磷灰石矿化的紫外吸收动力学曲线并不是胶原和磷酸钙沉淀混浊度的简单迭加, 而是一条平滑的阶梯形曲线, 它反映了有机相和无机相相互作用的过程特征. 在采用紫外光度法研究生物矿化过程中首次发现, 阶梯形矿化曲线上还有更精细的变化: 在一定条件下, 矿化曲线起峰时出现一个负峰. 本文还研究了磷酸钙浓度、胶原浓度及入射光波长对该负峰峰位和峰值的影响. 研究该负峰与系统参数的相关性, 对于了解早期生物矿化的机理和优化新型骨及牙齿等组织工程框架材料的制备工艺[2]都具有重要的意义.     

Structure and composition of calcareous sponge spicules: a review and comparison to structurally related biominerals

Since the early 19th century, the skeletons of calcareous sponges (Porifera: Calcarea) with their mineralized spicules have been investigated for their morphologies, structures, and mineralogical and organic compositions. These biomineral spicules, up to about 10 mm in size, with one to four rays called actines, have various specific shapes and consist mainly of magnesium-calcite: in only one case has an additional phase of stabilized amorphous CaCO₃ (ACC) been discovered. The spicules are invariably covered by a thin organic sheath and display a number of intriguing properties. Despite their complex morphologies and rounded surfaces without flat crystal faces they behave largely as single crystal individuals of calcite, and to some degree crystallographic orientation is related to morphology. Despite their single-crystalline nature, most spicules show nearly isotropic fracture behaviour, not typical for calcite crystals, indicating enhanced fracture resistance. These unusual morphological and mechanical properties are the result of their mechanism of growth. Each spicule is formed by specialized cells (sclerocytes) that supply mineral ions or particles associated by organic macromolecules to extracellular cavities, where assembly and crystallization in alignment with an initial seed crystal (nucleus) takes place. As a result of discontinuous mineral deposition, cross-sections of larger spicules display concentric layering that mantles a central calcitic rod. On a smaller scale, the entire spicule displays a ‘nano-cluster’ structure with crystallographically aligned and putatively semicoherent crystal domains as well as a dispersed organic matrix intercalated between domain boundaries. This ultrastructure dissipates mechanical stress and deflects propagating fractures. Additionally, this nano-cluster construction, probably induced by intercalated organic substances, enables the formation of complex crystal morphologies independent of crystal faces. In this review, the current knowledge about the structure, composition, and formation of calcareous sponge spicules is summarised and discussed. Comparisons of calcareous sponge spicules with the amorphous silica spicules of sponges of the classes Hexactinellida and Demospongiae, as well as with calcitic skeletal elements of echinoderms are drawn. Despite the variety of poriferan spicule mineralogy and the distant phylogenetic relationship between sponges and echinoderms, all of these biominerals share similarities regarding their nano-scale construction. Furthermore, echinoderm skeletal elements resemble calcareous sponge spicules in that they represent magnesium-bearing calcite single-crystals with extremely complex morphologies.     

泌尿系统尿酸结石研究中的化学基础

尿酸结石是指尿酸及其盐在泌尿系统的异常矿化和积聚。本文从尿酸结石研究中涉及的化学问题入手,讨论了pH、过饱和度、尿大分子抑制剂和基因突变等方面对尿酸结石形成的分子机理,从抑制尿酸结石成核、生长和聚集的角度,讨论了尿酸结石的化学模型和动物实验模型。     

不同种类羧酸钠对草酸钙结晶过程中晶相的影响

采用X射线衍射法研究了水溶液中不同种类羧酸钠对尿结石主要成份草酸钙结晶的影响，这些羧酸钠分别为含有一、二、三和四个羧基的羟基乙酸钠（NaGly）、酒石酸钠（Na2Tart）、柠檬酸钠（Na3Cit）和EDTA二钠盐（Na2EDTA）.结果表明，随着羧酸钠浓度的增加，草酸钙的晶相均发生规律性的变化：从最稳定的一水草酸钙（COM），到不稳定的二水草酸钙（COD），最后转化为次稳定的三水草酸钙（COT）.不同结构羧酸钠抑制COM生长、促进COD生成的顺序为:Na3Cit >Na2Tart >Na2EDTA >NaGly.该结果将为临床上选择防结石药物提供新的思路.     

Atomistic Simulation Study of Calcium,Phosphate and Fluoride Ion Association to the Teleopeptide‐Tails of Collagen – Initial Steps to Biomineral Formation

The attachment of single ions to putative adsorption sites in the tails of collagen fibers is investigated by means of molecular dynamics simulations and discussed with respect to the very early steps of apatite/collagen biomineral formation. Our studies clearly demonstrate an increased flexibility of the tails of the triple‐helical collagen protein. Apart from the termini of the backbone, several side chains were also observed to be freely accessible to ion attachment from aqueous solution. The teleopeptide was systematically scanned for suitable adsorption sites for calcium, phosphate and fluoride ions. Association of these ions was then explored from potential of mean force calculations. The resulting energy profiles reveal a variety of favorable protein‐ion bonds and hint at the suitability of the collagen tails to promote apatite aggregation.     

In-site mineralization of amorphous calcium carbonate particles: A facile and efficient approach to fabricate poly(l-lactic acid) based hybrids

The aim of this investigation is to obtain a polymer-based hybrid material with biodegradability, biocompatibility, and good mechanical properties and this object was realized via. in-situ introduction of the unmodified calcium carbonate (CaCO₃) into a poly(l-lactic acid) (PLLA) matrix. As verified by the measurements from scanning electron microscopy (SEM), optical microscopy, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), the hybrid films which possesses a uniform dispersion of calcium carbonate CaCO₃ in nano-meter scale, mechanically robustness and thermal stability could be fabricated by a mineralization-alike process. For example, the storage modulus increases from 441 MPa of neat PLLA to 1034 MPa of hybrid film containing 2% (w/w) CaCO₃. In addition, the hybrid films display a significant improvement in its UV-exposure resistance.