Environmental Engineering Reference
In-Depth Information
25
Catalyst Design BaseD on nano-sizeD
inorganiC Core of enzymes: Design of
environmentally frienDly Catalysts
Mohammad Mahdi Najafpour
Department of Chemistry, Center for Research in Climate Change and Global Warming, and Institute for Advanced Studies
in Basic Sciences (IASBS), Zanjan, Iran
Catalysts are very important compounds in our life [1-3]. Catalysts with new pathways enable the highly selective formation
of desired products at rates that are commercially viable [1-3]. Some important reactions in human life are water oxidation,
water reduction, nitrogen reduction, and carbon dioxide reduction, which function very efficiently at moderate temperature in
organisms. We need efficient, stable, environmentally friendly, low-cost, and multielectron transfer catalysts to perform tasks
at an industrial scale. Multielectron transfer catalysts have the ability to accommodate, accumulate, and transfer multiple elec-
trons to reaction substrates at the same time. The compounds that catalyze multielectron reactions are prone to structural rear-
rangement and instability during turnover.
While heavy metals are widely used as catalysts, organisms manage to use abundant, low-cost, and environmentally friendly
transition metals for the same purpose. Biomimetics is biologically inspired design that could be defined as the study of the
structure and function of biological systems as models for the design and engineering of materials and machines [4]. For bio-
logically inspired catalyst designs, we could look at enzymes as they are the most efficien catalysts.
Probably, the first enzymes had broad substrate specificity and were not efficient [5]. It is believed that a relatively small
number of enzymes might have sufficed to support the metabolic network of the first proto-organisms. These first enzymes were
known as generalists, which changed to
modern enzymes
[5]. Metal clusters are used as the active sites of some
modern
enzymes
. Over past years, the clusters were studied by many methods, most importantly X-ray diffraction methods. The struc-
tures may serve as a helpful and fundamental basis for a better understanding of the mechanism and provide a framework for
generating hypotheses for catalysis design.
From a certain viewpoint, we may consider enzymes to be nano-sized inorganic cores in a protein matrix. To understand the
subject we should find the chemistry of interactions between proteins and solid surfaces.
Interactions between proteins and solid surfaces were studied using many methods by several groups [6-11]. Interactions of
proteins with clays or minerals have been reviewed by a few authors [12, 13]. Many reports indicated that enzyme molecules
were not intercalated in the mineral structure but were immobilized at the external surfaces and at the edges of the mineral oxide [14].
This result also showed the protein's molecular conformation after binding to the mineral colloid surfaces.
The solid surfaces might have an important role in the origin of life and the formation of biomolecules [15]. Wächtershäuser's
group proposed that the earliest form of life originated in a volcanic hydrothermal flow at high pressure and high temperature
(~100°C). In this condition, a composite of mineral compounds with catalytic transition metal centers could play important
roles in forming the first biological molecules [16, 17]. Cairns-Smith's group also proposed that imperfect clay crystals were
the first genes [18]. It was also known that minerals and clays could induce selection, concentration, and organization of
