Starch Biocatalyst Based on α-Amylase-Mg/Al-Layered Double Hydroxide Nanohybrids

The application of conventional or magnetic materials to support immobilization of amylolytic enzymes for batch and continuous operation of starch hydrolysis processes

In the production of ethanol, starches are converted into reducing sugars by liquefaction and saccharification processes, which mainly use soluble amylases. These processes are considered wasteful operations as operations to recover the enzymes are not practical economically so immobilizations of amylases to perform both processes appear to be a promising way to obtain more stable and reusable enzymes, to lower costs of enzymatic conversions, and to reduce enzymes degradation/contamination. Although many reviews on enzyme immobilizations are found, they only discuss immobilizations of α-amylase immobilizations on nanoparticles, but other amylases and support types are not well informed or poorly stated. As the knowledge of the developed supports for most amylase immobilizations being used in starch hydrolysis is important, a review describing about their preparations, characteristics, and applications is herewith presented. Based on the results, two major groups were discovered in the last 20 years, which include conventional and magnetic-based supports. Furthermore, several strategies for preparation and immobilization processes, which are more advanced than the previous generation, were also revealed. Although most of the starch hydrolysis processes were conducted in batches, opportunities to develop continuous reactors are offered. However, the continuous operations are difficult to be employed by magnetic-based amylases.

Coherent-interface-induced second hardening deformation of Al-Mg-Al nanolayers by molecular dynamics simulations

Thermal diffusion plays an important role in the determination of the structures and properties of interfaces and nanolayers. Here we report results from molecular dynamics simulations of the tensile behavior of Al-Mg-Al nanolayers with their Al/Mg interfaces being joined by the thermal diffusion of atoms. We find that a different deformation mechanism applies in each case: low thermal diffusion temperatures (300 ≤ T1 < 664 K) and high thermal diffusion temperatures (664 ≤ T1 ≤ 846 K). The formation of coherent Al/Mg interfaces in the case of high T1 induces the second hardening deformation of Al-Mg-Al nanolayers before the stress reaching the tensile strength, significantly enhancing the tensile properties of Al-Mg-Al nanolayers in comparison to the case of low T1. This difference would provide guidance on the improvement of the mechanical properties of Al-Mg layered systems.

Magnetic layered double hydroxide nanosheet as a biomolecular vessel for enzyme immobilization

Magnetic nanoparticle coated with manganese‑aluminum layered double hydroxide (Fe3O4/Mg-Al-CO3-LDH) was prepared and used as porous support for ficin (EC 3.4.22.3) as a model enzyme. Structural characteristics were studied by XRD, FTIR, SEM and light scattering. The quantity of immobilized ficin on the mentioned LDH and non-magnetic LDH was measured and enzyme activity, stability and reusability were compared. Results revealed that the core and shell structure of Fe₃O₄/Mg-Al-CO₃-LDH makes it better dispersion compared to the pristine Mg-Al-CO₃-LDH. Ficin showed strong affinity to absorption of the surface of mentioned LDHs nanosheet especially magnetic LDH, confirmed that the existence of Fe₃O₄ in the core structure of magnetic Fe₃O₄/Mg-Al-CO₃-LDH caused better dispersion of LDH nanocrystal shell compared to pristine LDH moreover, enzyme which immobilized on the magnetic LDH supports, can be recovered by magnetic interaction. The storage stability of free ficin, immobilized ficin on the Mg-Al-CO₃-LDH and Fe₃O₄/Mg-Al-CO₃-LDH during a period of 120 days lost about 75%, 30%, and 20% of their initial activities, respectively.

Melting at Mg/Al interface in Mg-Al-Mg nanolayer by molecular dynamics simulations

The melting at the magnesium/aluminum (Mg/Al) interface is an essential step during the fabrications of Mg-Al structural materials and biomaterials. We carried out molecular dynamics simulations on the melting at the Mg/Al interface in a Mg-Al-Mg nanolayer via analyzing the changes of average atomic potential energy, Lindemann index, heat capacity, atomic density distribution and radial distribution function with temperature. The melting temperatures (Tm) of the nanolayer and the slabs near the interface are significantly sensitive to the heating rate (vh) over the range ofvh ≤ 4.0 K ps^-1. The distance (d) range in which the interface affects the melting of the slabs is predicted to be (-98.2, 89.9) Å atvh→0,if the interface is put atd = 0 and Mg (Al) is located at the left (right) side of the interface. TheTmof the Mg (Al) slab just near the interface (e.g.d=4.0Å) is predicted to be 926.8 K (926.6 K) atvh→0,with 36.9 K (37.1 K) below 963.7 K for the nanolayer. These results highlight the importance of regional research on the melting at an interface in the nanolayers consisting of two different metals.

Assembly of nitroreductase and layered double hydroxides toward functional biohybrid materials

The development of new multifunctional materials integrating catalytically active and selective biomolecules, such as enzymes, as well as easily removable and robust inorganic supports that allow their use and reuse, is a subject of ongoing attention. In this work, the nitroreductase NfrA2/YncD (NR) from Bacillus megaterium Mes11 strain was successfully immobilized by adsorption and coprecipitation on layered double hydroxide (LDH) materials with different compositions (MgAl-LDH and ZnAl-LDH), particle sizes and morphologies, and using different enzyme/LDH mass ratios (Q). The materials were characterized and the immobilization and catalytic performance of the biohybrids were studied and optimized. The nitroreductase-immobilized on the nanosized MgAl-LDH displayed the best catalytic performance with 42-46% of catalytic retention and>80% of immobilization yield at saturation values of enzyme loading Cs ≈ 0.6 g NR/g LDH (Q = 0.8). The adsorption process displayed high enzyme-LDH affinity interactions yielding to a stable biohybrid material. The increase in the amount of enzyme loading favoured the catalytic performance of the biohybrid due to the better preservation of the native conformation. The biohybrid was reused several times with partial activity retention after 4 cycles. In addition, the biohybrid was successfully dried maintaining the catalytic activity for several weeks when it was stored in its dry form. Finally, thin films of NR@LDH biohybrid deposited on glassy carbon electrodes were evaluated as a modified electrode applied for nitro-compound detection. The results show that these biohybrids can be used in biotechnology applications to efficiently detect compounds such as dinitrotoluene. The search for new non-hazardous chemical designs preventing or reducing the use of aggressive chemical processes for human being and the environment is the common philosophy within sustainable chemistry.

Interactions between Biological Cells and Layered Double Hydroxides: Towards Functional Materials

This review highlights the current research on the interactions between biological cells and Layered Double Hydroxides (LDH). The as-prepared biohybrid materials appear extremely attractive in diverse fields of application relating to health care, environment and energy production. We describe how thanks to the main features of biological cells and LDH layers, various strategies of assemblies can be carried out for constructing smart biofunctional materials. The interactions between the two components are described with a peculiar attention to the adsorption, biocompatibilization, LDH layer internalization, antifouling and antimicrobial properties. The most significant achievements including authors' results, involving biological cells and LDH assemblies in waste water treatment, bioremediation and bioenergy generation are specifically addressed.

Synthesis and formulation of functional bionanomaterials with superoxide dismutase activity

Layered double hydroxide (LDH) nanoparticles were prepared and used as solid support for superoxide dismutase (SOD) enzymes. Structural features were studied by XRD, spectroscopic methods (IR, UV-Vis and fluorescence) and TEM, while colloidal stability of the obtained materials was investigated by electrophoresis and light scattering in aqueous dispersions. The SOD quantitatively adsorbed on the LDH by electrostatic and hydrophobic interactions and kept its structural integrity upon immobilization. The composite material showed moderate resistance against salt-induced aggregation in dispersions, therefore, heparin polyelectrolyte was used to improve the colloidal stability of the system. Heparin of highly negative line charge density strongly adsorbed on the oppositely charged hybrid particles leading to charge neutralization and overcharging at appropriate polyelectrolyte loading. Full coverage of the composite platelets with heparin resulted in highly stable dispersions, which contained only primary particles even at elevated ionic strengths. Our results indicate that the developed bionanocomposite of considerable enzymatic function is a suitable candidate for applications, wherever stable dispersions of antioxidant activity are required for instance in biomedical treatments or in chemical manufacturing processes.