厚壳贻贝贝壳的微结构及光谱分析

Microstructure and spectral analysis of Mytilus coruscus shell

贝类的贝壳是一种由碳酸钙晶体和有机质组成的高度有序的天然纳米复合材料,历来是生物材料和组织工程研究的重点对象.利用扫描电子显微镜、傅里叶红外光谱分析以及X射线衍射分析等,对厚壳贻贝(Mytilus coruscus)贝壳的微观结构、碳酸钙晶体构型以及有机质结构特征进行分析.厚壳贻贝贝壳主要包含珍珠质层、肌棱柱层和斜棱柱层;不同层次的结构在外形、碳酸晶体构型、有机质分布等方面具有不同的特征.在后闭壳肌-贝壳连接部位,肌肉与贝壳碳酸钙晶体之间由一层有机质膜连接,且该膜质地明显有别于珍珠质层表面的膜.厚壳贻贝各层结构中的蛋白质均以β-折叠为优势构象,且肌棱柱层中蛋白质的β-折叠含量最高.上述研究为深入了解贝壳的生物矿化机制以及肌肉-贝壳界面的无机相-有机相连接机理奠定了基础.

To understand the mierostructural characteristics of mussel shells correlating to the muscle-shell attach- ment, we have investigated and compared the microstructure, polymorph, organic matrix of adductor muscle atta- ched scar （AMS） and non-muscle attached zone in the adult M. coruscus shell. The adductor muscle scar has a hier- archically complex multilayer which is composed of organic matrix and three distinct mineral layers, including the nacre, myostracum and fibrous prismatic layers. Fourier transform infrared spectroscopy （FTIR） and X-Ray powder diffraction （XRD） results show that the inorganic compounds of nacre and myostracum layers are composed of arag- onite and the fibrous prismatic layer adopt calcite mineral. The adductor muscle attaches to the myostracum layer through an organic film, which forms a muscle-film-shell junction. The film adheres firmly to the myostracum layer surface and shows a very smooth texture, which is different from the film on nacre surface. The mineral phase of the M. coruscus shell is intimately associated with some organic matrixes, such as chitin and proteins. The amide region of FTIR spectra from the decalcified shell samples is analyzed. We can see that the shell proteins in vivo are in the higher structural ordered state, and the β-parallel structure is predominant in each shell layer. Furthermore, the β- parallel structure of the shell proteins in myostracum layer present the highest percentage. Based on these results, a structural model of muscle-shell attachment is proposed. The information obtained from this study will be valuable for the marine bio-mineralogists and material scientists.