Catalyzing chemical reaction

Enzymes are proteins that catalyze chemical reactions in living systems. Such catalysts are not only efficient but are also extremely selective. Hence, enzymes combine the recognition and amplification steps, as needed for many sensing applications. 

Microwave catalysis is a catalytic process performed in the presence of a microwave (electromagnetic) field in which the catalyst acts as an energy convertor . It uses microwave irradiation to stimulate catalytic reactions. It is necessary to stress that any sort of electromagnetic or microwave radiation is not itself a catalyst, as has sometimes erroneously stated [1], Similarly, it is not correct to say that microwave irradiation catalyzes chemical reactions [1], The principles of microwave catalysis will be described in the following sections. 

A conceptualized cross section through a portion of the cell wall (rectangles), periplasmic space, and cell membrane (lipid bilayer with polar head groups in contact with cytoplasm and external medium, and hydrophobic hydrocarbon chains) of an aquatic microbe. Reactive functional groups (-SH, -COOH, -OH, -NH2) present on the wall consitutents and extracellular enzymes (depicted as shaded objects) attached by various means promote and catalyze chemical reactions extracellularly. 

For phase transfer catalyzed chemical reactions of pol)rmers... 

A new dimension in the development of nucleic acid based catalysts was introduced by Breaker and Joyce in 1994 when they isolated the first deoxyribozyme [111]. It is not unexpected that DNA is also able to catalyze chemical reactions because it was shown previously that ssDNA aptamers which bind to a variety of ligands can be isolated by in vitro selection [141]. In the meantime, several deoxyribozymes have been described which expand the range of chemical transformations accelerated by nucleic acid catalysts even further and raising question whether even catalytic DNA might have played some role in the pre-biotic evolution of hfe on earth [69-71]. 

Figure 1. A hypothetical reaction coordinate diagram for an enzyme-catalyzed chemical reaction.

Reclaim cannot remove metals or other ionic compounds from groundwater nor catalyze chemical reactions. Also, the success of Reclaim is in relative proportion to the permeability of the geologic components comprising the contaminated site, the hydraulic gradient, and the concentrations and vapor pressures of the contaminants. As permeability, contaminant concentrations, vapor pressure, and hydraulic gradients decrease, so does the rate of recovery. In addition, Reclaim requires vendor-supplied, on-site service and support on a periodic basis. 

The ability of phthalocyanines to transport oxygen and to accelerate oxidation reactions in the same way as heme was discovered soon after their molecular structure had been established 5>6>. The property of catalyzing chemical reactions seemed to offer promising practical applications 7>. 

Figure 17.3 Schematic representation of the change in activation energy barrier for an enzymatically mediated reaction as compared to the analogous non-catalyzed chemical reaction.

There are two fundamental conditions for life. First, the living entity must be able to self-replicate (a topic considered in Part III) second, the organism must be able to catalyze chemical reactions efficiently and selectively. The central importance of catalysis may surprise some beginning students of biochemistry, but it is easy to demonstrate. As described in Chapter 1, living systems make use of energy from the environment. Many of us, for example, consume substantial amounts of sucrose—common table sugar—as a kind of fuel, whether in the form of sweetened foods and drinks or as sugar itself. The conversion of sucrose to C02 and... 

D. The Electrode Surface as Medium catalyzing Chemical Reactions of Electrogenerated Reactive Organic Intermediates... 

Biodegradation depends on the microbial production of enzymes capable of catalyzing chemical reactions that will transform (or, ideally, mineralize) pollutants. Bioremediation technologies can be enhanced in several ways, but the existing biochemical capabilities of the organisms should be reviewed before any anticipated genetic alterations are considered. 

Thousands of different proteins make up a very large fraction of the "machinery" of a cell. Protein molecules catalyze chemical reactions, carry smaller molecules through membranes, sense the presence of hormones, and cause muscle fibers to move. Proteins serve as structural materials within cells and between cells. Proteins of blood transport oxygen to the tissues, carry hormones between cells, attack invading bacteria, and serve in many other ways. No matter what biological process we consider, we find that a group of special proteins is required. 

Layered aluminosilicates catalyze chemical reactions in various ways. They stabilize high-energy intermediates, store energy in their lattice structures and catalyze redox reactions (ref. 1). They often exhibit high surface acidity (ref. 2). 

Whereas a major function of biological membranes is to maintain the status quo by preventing loss of vital materials and entry of harmful substances, membranes must also engage in selective transport processes. Living cells depend on an influx of phosphate and other ions, and of nutrients such as carbohydrates and amino acids. They extrude certain ions, such as Na+, and rid themselves of metabolic end products. How do these ionic or polar species traverse the phospholipid bilayer of the plasma membrane How do pyruvate, malate, the tricarboxylic acid citrate and even ATP move between the cytosol and the mitochondrial matrix (see figs. 13.15 and 14.1) The answer is that biological membranes contain proteins that act as specific transporters, or permeases. These proteins behave much like conventional enzymes They bind substrates and they release products. Their primary function, however, is not to catalyze chemical reactions but to move materials from one side of a membrane to the other. In this section we discuss the general features of membrane transport and examine the structures and activities of several transport proteins. 

Catalytic antibodies, predicted by Jencks in 1969 and first discovered in 1986, can now be raised against a wide variety of haptens covering nearly every reaction. Catalytic antibodies are regarded as the best enzyme mimics, with very good selectivity, but almost always their catalytic efficiency is by far insufficient. Some natural RNA molecules act as catalysts with intrinsic enzyme-like activity which permits them to catalyze chemical reactions in the complete absence of protein cofactors. In addition, ribozymes identified through in-vitro selection have extended the repertoire of RNA catalysis. This versatility has lent credence to the idea that RNA molecules may have been central to the early stages of life on Earth. 

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