Role of the Template in Model Biomineralization: Synchrotron X-ray Scattering Experiments.

摘要

Synthesis of functional nanoparticles in cheap and environment friendly ways is one of the big challenges we face today. Interestingly, many biological systems are already expert at this task. Living organisms can grow nanocrystals of inorganic minerals with certain orientations and shapes and use them together with organic material to build structures with properties superior to the sum of their components. This process is called biomineralization. It has been previously shown that floating monolayers of amphiphilic molecules (Langmuir monolayers) can be used to simulate this process. This project covers the study of three different minerals, calcium oxalate, hydroxyapatite and gold, in an attempt to understand the role of the organic template in the model biomineralization experiments. We used in situ synchrotron x-ray scattering techniques to monitor the organic-inorganic interface during nucleation and growth of inorganic crystals. We also used scanning and transmission electron microscopy to study the structure of mature crystals ex situ .;Although kidney stones (mostly calcium oxalate) are pathological in humans and animals, their microscopic structures exhibit considerable orientation and order, probably caused by organic molecules. Our x-ray scattering experiments revealed, first time, that in the early stages of the crystallization calcium oxalate crystals adapt a structure different from their known bulk structures. In the later stages, the crystals relax back to the bulk structure while changing the organization of the organic molecules next to them. We developed a model that explains these interactions in terms of the organic-inorganic interface potential energy.;Hydroxyapatite is the main inorganic constituent of the vertebrate bone. In spite of the vast literature about bone mineralization, there is little known about the organic-inorganic interactions at the molecular level. In this thesis, we report the first in situ x-ray scattering experiments during model hydroxyapatite biomineralization. We studied the interactions between the organic template and the pre-nucleation clusters in the calcium phosphate solution depending on the temperature and the subphase concentration. Our results show how the organic-inorganic interface becomes more suitable for oriented hydroxyapatite crystallization under physiological conditions.;One of the main reasons to study biomineralization is to use the knowledge obtained to develop new methods for nano-engineering. As a demonstration of this idea, we used Langmuir monolayer of alkylthiols to grow (111)-oriented gold nanoparticles from solution in a biomimetic way. The organic molecules we used make the gold nanoparticles grow with a specific orientation. However, they also change their organization to minimize the interaction potential at the organic-inorganic interface. In fact the final structure they adapt is very similar to self-assembled monolayers of alkylthiol molecules on gold crystal surfaces, so one can say that we "reversed" the self-assembly process.;It has long been assumed, although not directly observed, that the organic template controls the growth of the inorganic crystals. Our studies, taken together, show that the interaction between the organic template and the crystals is not a one way street; rather, both organic and inorganic structures may change to lower the interaction potential energy at the interface. This is usually accomplished through a structural match between the surface lattices.