RICERCA ITALIANA     

Biomineral interfaces on carbonates and sulphides

Università degli Studi di Torino

Abstract

There are two parts to the program: the first one, concerning the experiments, is shared by two Units (Torino and Cagliari) and the second one, related to the interpretation of the experimental results, which will be common among all the three Units (Torino, Cagliari and Milano).

The general plan is to do, for experimental:

1a) - Nucleation and growth of CaCO3 calcite crystals (both from aqueous solution and gel) in the presence of specific inorganic impurities (Li+, Na+, Mg2+), carboxylic acids and oligosaccharides which are reckoned to be modifiers of the growth morphology, in order to select those morphologies which are alternately dominated by one of the four main forms found in biogenic natural calcites like {10.4}, {01.2},{00.1} and {11.0}.
1b) - Examination of their surface structures, before and after the adsorption of both inorganic ions and biologically relevant molecules (aspartic and glutamic acids, serine and threonine) with the aim of determining the nano-structures and the self-assembled adsorbed layers. The presence of steps on crystal faces, generated either by 2D growth islands or spiral, their roughness, the kinked or stepped structure of the faces will be stressed, down to the nano-scale level, by means of the atomic force microscopy, along with the presence of epitaxial layers formed by the shaping action of the surface adsorption during growth.

2a) - Biologically induced precipitation of Hydrozincite >>>

Principal Investigator

Dino AQUILANO Università degli Studi di TORINO

Research Objectives

The aim of this research project consists in finding the nano-structures that forms at the interface between minerals and their mother phase in the presence of biologically relevant molecules, choosing those leading to self-assembled adsorbed phases and understanding the mechanisms forming them. The aim is of giving a contribution to the knowledge of the complex biomineralization phenomena. Since the general objective is quite elaborated, it should be better to deal with it at many levels.

The first level concerns the real knowledge of the crystal surfaces on which the biomolecular self – assembling is assumed to take place. Obtaining this preliminary step is not trivial, but fundamental. As a matter of fact, all these surfaces have to be known both experimentally and theoretically, before foreign species are adsorbed on them. Lack of one out of these two complementary aspects seriously compromises the quality of the work. In fact, if the observation is lacking the nano-scale configuration of the surface before the adsorption cannot be known and then the comparison with the same surface, after the adsorption is meaningless. On the contrary, if a preliminary theoretical knowledge of the intrinsic surface characteristics is missing ( its character, its reconstruction and relaxation, the most probable profile, the surface potential, the surface tension without adsorption), it would be hard to reasonably interpret the experimental data. Then, experiments >>>

Timescale

24 months

National and international background

The meaning of the term "biomineralization" cannot be reduced to the only minerals produced by living organisms; actually it can be extended to all mineralised products having the structure of composite materials in which both inorganic and organic components coexist. Biomineral phases, having formed under controlled conditions, often have properties such as shape, size, crystallinity, isotopic and trace element content quite unlike its purely inorganically formed counterpart.
We will deal, in this research proposal, with the "biomineral interface", namely with those nano-structures that form in the transition zone between crystal surfaces of minerals (calcite, hydrous carbonates, metal sulphides) and its mother phases when organic molecules of biological interest are present in it. A wide reference frame has been produced in the last twenty years on biomineralization, as the reader may find in some fundamental reviews [1,20].
The main requirements to be fulfilled in order to build a biomineral interface lie in the capability of inorganic crystal surface to recognize the organic molecules which have to be adsorbed on it [1]. When this condition obtains, the thermodynamic interfacial properties are so affected that, for instance, the nucleation frequency of one out of the calcium carbonate polymorphs is enhanced with respect to that of another one [2].
Determining the crystal surface conditions gains in importance. Then, at the beginning of the >>>