Orientation Matters

Covalent immobilization strategies typically provide superior electrocatalytic characteristics, but the tethering can sometimes hinder protein conformation [66]. In addition, the functional groups on the enzyme that are used for tethering should not be essential to catalysis, or enzyme inactivation losses will occur. The ability to tailor covalent chemistry to specific regions of a protein, however, allows some control over protein orientation. A recent tendency in protein immobilization is the specific and rational orientation of protein molecules on a selected surface [67-69]. This strategy aims to create uniformly oriented protein immobilized in a manner that may optimize catalytic efficiency [70], enhance stability [68], or increase electron transfer efficiency [71,72]. 

Oriented immobilization may be achieved by introducing reactive groups or covalent tethers to the protein surface that can then interact with a compatible functionalized surface [70,73,74]. Alternatively, by careful design of the immobilization conditions, it is possible to exploit the inherent physicochemical properties of an enzyme [68,72]. The exposed amine groups of lysine residues, for example, react readily with active ester groups, such as A-hydroxysuccinimide esters. 

FIGURE 11.6 Covalent enzyme immobilization via reaction of (a) lysine residues with NHS esters or aldehydes, (b) cysteine residues with maleimide groups, and (c) carhoxyl residue of glutamic acid or aspartic add with amine-functionalized materials via NHS-mediated ester chemistry. 

For laccase, orientation can be guided by different attachment strategies that aim specifically to attach the enzyme in a particular position [77,78]. As an example, in 2011, Pita et al. developed and optimized a strategy for oriented covalent immobilization of Trametes hirsuta laccase on gold electrodes [72]. After optimizing the immobilization for DET via the type 1 (Tl) copper site, they were able to measure current density values up to 40 pA cm for the electrocatalytic reduction of O2 in the absence of redox mediators. 

Similarly, the orientation of laccase on gold was demonstrated by recombinant expression of laccase with a six-histidine His-tag linker that then specifically orients the protein with a thiol-modified monolayer, formed on the surface of gold [79]. The oriented immobilization of the enzyme preserves catalytic activity, and the catalytic reduction of dioxygen was observed in the presence of a redox mediator. 

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A rigorous and complete mathematical treatment of the polarization of light and the interaction of light with oriented matter is outside the scope of this chapter. These subjects have been thoroughly dealt with before and can be found in a number of comprehensive texts [29-32] the reader is referred to the excellent book by Michl and Thulstrup [3] for a more detailed treatment of optical spectroscopy with polarized light. Here, a conventional, qualitative representation is given to establish the nomenclature and conventions to be used and to facilitate the understanding of the concepts presented. 

Introduction and Orientation, Matter and Energy, Elements and Atoms, Compounds, The Nomenclature of Compounds, Moles and Molar Masses, Determination of Chemical Formulas, Mixtures and Solutions, Chemical Equations, Aqueous Solutions and Precipitation, Acids and Bases, Redox Reactions, Reaction Stoichiometry, Limiting Reactants... 

Haber s breakthrough was to find the catalyst, a facilitator for the reaction, which in this specific case was an iron and iron oxide solid— rust. Solid catalysts can facilitate reactions because molecules are three-dimensional beasts, and when it comes to reactions, orientation matters. This restriction can be understood by considering interactions between other three-dimensional objects a kiss is just a kiss, but three-dimensional humans have to be oriented correctly for the kiss to be on target and effective. One advantage of a solid catalyst may be that it can hold the reactants in a favorable orientation. Automobiles use catalytic converters to convert NOx back into nitrogen and oxygen and convert poisonous carbon monoxide to carbon dioxide. 

Heinzmann U, Hoiioway S, Kieyn A W, Paimer R E and Snowdon K J 1996 Orientation in moieouie-surfaoe interaotions J. Phys. Condens. Matter 8 3245... 

Berrett J F, Molino F, Porte G, Diat O and Lindner P 1996 The shear-induced transition between oriented textures and layer-sliding-mediated flows in a micellar cubic crystal J. Phys. Condens Matters 9513-17... 

The angles ot, p, and x relate to the orientation of the dipole nionient vectors. The geonieti y of interaction between two bonds is given in Fig. 4-16, where r is the distance between the centers of the bonds. It is noteworthy that only the bond moments need be read in for the calculation because all geometr ic features (angles, etc.) can be calculated from the atomic coordinates. A default value of 1.0 for dielectric constant of the medium would normally be expected for calculating str uctures of isolated molecules in a vacuum, but the actual default value has been increased 1.5 to account for some intramolecular dipole moment interaction. A dielectric constant other than the default value can be entered for calculations in which the presence of solvent molecules is assumed, but it is not a simple matter to know what the effective dipole moment of the solvent molecules actually is in the immediate vicinity of the solute molecule. It is probably wrong to assume that the effective dipole moment is the same as it is in the bulk pure solvent. The molecular dipole moment (File 4-3) is the vector sum of the individual dipole moments within the molecule. 

This will clearly be made somehow by discormections a and b but the order of events is important. We must discoimect first, that is synthesise last, the bond with the wrong orientation - i.e. meta to the t-butyl group. The reaction will then be intramolecular and orientation doesn t matter. This gives us 399B, and 1 show one possible route from that. 

Liquid crystals represent a state of matter with physical properties normally associated with both soHds and Hquids. Liquid crystals are fluid in that the molecules are free to diffuse about, endowing the substance with the flow properties of a fluid. As the molecules diffuse, however, a small degree of long-range orientational and sometimes positional order is maintained, causing the substance to be anisotropic as is typical of soflds. Therefore, Hquid crystals are anisotropic fluids and thus a fourth phase of matter. There are many Hquid crystal phases, each exhibiting different forms of orientational and positional order, but in most cases these phases are thermodynamically stable for temperature ranges between the soHd and isotropic Hquid phases. Liquid crystallinity is also referred to as mesomorphism. 

The term glass has two meanings, ie, the material and a state of matter. The glassy or vitreous condition is where the atoms of the material have a random orientation. This amorphous or noncrystalline nature leads to physical properties typical of the product caHed glass, including unpredictable breaks, no sharp melting temperature, and no heat of fusion. 

Gupta, S.C. and Y.M. Gupta (1984), Response of Ytterbium Foils Oriented Parallel and Perpendicular to the Shock Front, in Shock Waves in Condensed Matter— 1983 (edited by J.R. Asay, R.A. Graham, and G.K. Straub) Elsevier Science, New York, pp. 237-238. 

K. J. Strandburg, ed. Bond Orientational Order in Condensed Matter Systems. New York Springer, 1992. 

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