Structural properties of biologically controlled hydrozincite: An HRTEM and NMR spectroscopic study

Abstract

The microscopic properties of biomineral hydrozincite [Zn(5)(CO(3))(2)(OH)(6)] from Naracauli Creek (SW Sardinia) were investigated by using X-ray diffraction (XRD), nuclear magnetic resonance spectroscopy (NMR), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). Because the biomineral hydrozincite turned out to significantly deviate from the ideal structure of hydrozincite, synthetic and geologic hydrozincite samples were also investigated for comparison.\ud \ud SEM imaging shows that biomineral hydrozincite is made of small platelet-shaped crystallites having a 20-50 nm long side at the shortest and other sides measuring hundreds of nanometers long. These are interlaced to form sheaths several micrometers long. HRTEM analysis of the biomineral samples shows an imperfectly oriented aggregation of the nanocrystals that is discussed in terms of mesocrystals. Transmission electron microscopy (TEM) and XRD analysis indicate a progressive decrease in the size of the particles in the biomineral compared to the synthetic and geologic hydrozincite samples, with coherent diffraction domains in the biomineral hydrozincite that are smaller by 30-50% than in the other samples investigated in this study. (13)C magic angle spinning (MAS) and cross polarization magic angle spinning (CPMAS) NMR spectra show more than one peak for all the investigated samples, despite the fact that carbon atoms have a unique crystallographic position in the hydrozincite structure. The additional peaks can reflect the presence of lattice defects typical of nanocrystals as indicated by the HRTEM images, where high concentration of lattice defects, such as grain boundaries and stacking modes, can be observed both in the biomineral and in the synthetic samples. Further additional peaks in the NMR spectra of biomineral samples are attributed to organic molecules, relicts of the biomineralization process, in agreement with the filaments observed in SEM images of biomineral samples

Self-preservation strategies during bacterial biomineralization with reference to hydrozincite and implications for fossilization of bacteria

“…The hydrozincite displays a characteristic morphology consisting of botryoidal masses with a porous texture (figure 2a). As shown in previous studies [1,2,9], the spherical precipitates adhere to the bacterial sheath and are also associated with a meshwork of EPS (figure 2b), clearly demonstrating their biological origin. At high magnification, each sphere is made up of numerous nanoplates/ rsif.royalsocietypublishing.org J. R. Soc.…”

“…Hydrozincite precipitation is due to photosynthetic alkalinization of the cyanobacterial cell surface [1,2] and probably serves to detoxify dissolved Zn, resulting in a polished discharge into the Mediterranean [1]. However, the precipitate also encrusts cells, which in the wider context of most microbes and particularly bacteria could potentially lead to death and entombment.…”

Binding of bis-(2-ethylhexyl) phthalate at the surface of hydrozincite nanocrystals: An example of organic molecules absorption onto nanocrystalline minerals

“…Natural or synthesized HY is generally formed by nanosized crystals, with chemical impurities, grain boundaries, line and planar defects such as stacking faults [9][10][11][12][13][14][15][16]. Fig.…”

“…Fig. 1b shows the HY structure [9][10][11][12][13][14][15][16][17], which is made of T-O-T (tetrahedral-octa hedral-tetrahedral) layers that are held together by distorted carbonate molecules [17]. HY crystal growth typically leads to platelet mesocrystals flattened onto the (1 0 0) crystal surfaces that are parallel to T-O-T structures [11,[18][19][20].…”

The growth of the screw dislocation of nacreous layer on Pteria penguin

“…Because of the influence of such environmental factors as offshore wave, circumfluence, air-ocean coupling and the vortices on the surface of the shallow sea [1, 2], the characteristics of the microstructure displayed on the surface of the nacreous layer on Pteria penguin are quite different from those of the inland freshwater pearl shell (Hyriopsis cumingii). The former is characterized by the screw dislocation growth structure (Figure 2), whereas the nacreous layer of the latter (including the nacreous layer of some of the mollusks in the ocean) shows the "brick wall"-like parallel interbedding growth structure, which means that the aragonite microsheet on the nacreous layer arrays in irregular polygonal or hexagonal layers along the crystallization direction in the form of the two-dimensional nucleation because of the adjustment and control of the organic films [3][4][5][6][7][8][9][10]. Axis C of the aragonite microsheet is almost vertical to the nacreous layer.…”