Mutual orientation

The K factors in (C3.4.1) represent another very important facet of tire energy transfer [4, H]. These factors depend on tire orientations of tire donor and acceptor. For certain orientations tliey can reduce tire rate of energy transfer to zero—for otliers tliey effect an enhancement of tire energy transfer to its maximum possible rate. Figure C3.4.1 exhibits tire angles which define tire mutual orientation of a donor and acceptor pair in tenns of Arose angles the orientation factors and are given by [6, 7]... 

In light of tire tlieory presented above one can understand tliat tire rate of energy delivery to an acceptor site will be modified tlirough tire influence of nuclear motions on tire mutual orientations and distances between donors and acceptors. One aspect is tire fact tliat ultrafast excitation of tire donor pool can lead to collective motion in tire excited donor wavepacket on tire potential surface of tire excited electronic state. Anotlier type of collective nuclear motion, which can also contribute to such observations, relates to tire low-frequency vibrations of tire matrix stmcture in which tire chromophores are embedded, as for example a protein backbone. In tire latter case tire matrix vibration effectively causes a collective motion of tire chromophores togetlier, witliout direct involvement on tire wavepacket motions of individual cliromophores. For all such reasons, nuclear motions cannot in general be neglected. In tliis connection it is notable tliat observations in protein complexes of low-frequency modes in tlie... 

The catalytic subunit then catalyzes the direct transfer of the 7-phosphate of ATP (visible as small beads at the end of ATP) to its peptide substrate. Catalysis takes place in the cleft between the two domains. Mutual orientation and position of these two lobes can be classified as either closed or open, for a review of the structures and function see e.g. [36]. The presented structure shows a closed conformation. Both the apoenzyme and the binary complex of the porcine C-subunit with di-iodinated inhibitor peptide represent the crystal structure in an open conformation [37] resulting from an overall rotation of the small lobe relative to the large lobe. 

As a consequence of such interaction there are some preferential mutual orientation disturbed by the thermic motion of the molecules. 

Since niobates and tantalates belong to the octahedral ferroelectric family, fluorine-oxygen substitution has a particular importance in managing ferroelectric properties. Thus, the variation in the Curie temperature of such compounds with the fluorine-oxygen substitution rate depends strongly on the crystalline network, the ferroelectric type and the mutual orientation of the spontaneous polarization vector, metal displacement direction and covalent bond orientation [47]. Hence, complex tantalum and niobium fluoride compounds seem to have potential also as new materials for modem electronic and optical applications. 

Another important factor to determine the charge separation efficiency is the distance between and the mutual orientation of the donor and the acceptor in the geminate ion-pair state. The rate of charge recombination depends on whether... 

Usually, dilute polymer solutions are isotropic systems, i.e. macromolecular chains can exist in these solutions independently of each other with a random distribution of orientations of the long axes of coils. The solutions of flexible-chain polymers remain isotropic when the solution concentration increases whereas in concentrated solutions of macromolecules of limited flexibility the chains can no longer be oriented arbitrarily and some direction of preferential orientations of macromolecular axes appears, i.e. the mutual orientations of the axes of neighboring molecules are correlated. This means that... 

The formation of ECC is not only an extension of a portion of the macromolecule but also a mutual orientational ordering of these portions belonging to different molecules (intermolecular crystallization), as a result of which the structure of ECC is similar to that of a nematic liquid crystal. After the melt is supercooled below the melting temperature, the processes of mutual orientation related to the displacement of molecules virtually cannot occur because the viscosity of the system drastically increases and the chain mobility decreases. Hence, the state of one-dimensional orientational order should be already attained in the melt. During crystallization this ordering ensures the aggregation of extended portions to crystals of the ECC type fixed by intermolecular interactons on cooling. 

OS 90] [R 31] [P 70] At weak electrical field, the propagation velocity of a reaction front in a capillary-flow reactor was increased or decreased depending on the mutual orientation of the electrical field and the reaction zone propagation [68]. The movement of two reaction fronts was given by optical images in [68]. 

The H+-H2O bond has the special feature that although the bond energy is high, the proton will readily hop from one water molecule in the hydration complex to a neighboring water molecule. This hop is a quantum motion and will occur only when the water molecules have a favorable mutual orientation. It will occur predominantly... 

The structure of metallic deposits is determined primarily by the size, shape (faceting), type of arrangement, and mutual orientation of the crystallites. Two factors may influence the orientation and spatial alignment of the microcrystals in electrocrystallization the field direction (or direction of the electric current) and the nature of the substrate. The deposits are said to have texture when the crystallites are highly oriented in certain directions. Epitaxy implies that the lattice is altered under the influence of the substrate. 

The high catalytic activity of enzymes has a number of sources. Every enzyme has a particular active site configured so as to secure intimate contact with the substrate molecule (a strictly defined mutual orientation in space, a coordination of the electronic states, etc.). This results in the formation of highly reactive substrate-enzyme complexes. The influence of tfie individual enzymes also rests on the fact that they act as electron shuttles between adjacent redox systems. In biological systems one often sees multienzyme systems for chains of consecutive steps. These systems are usually built into the membranes, which secures geometric proximity of any two neighboring active sites and transfer of the product of one step to the enzyme catalyzing the next step. 

The mutual orientation of different symmetry elements is expressed by the sequence in which they are listed. The orientation refers to the coordinate system. If the symmetry axis of highest multiplicity is twofold, the sequence is x-y-z, i.e. the symmetry element in the x direction is mentioned first etc. the direction of reference for a reflection plane is nomal to the plane. If there is an axis with a higher multiplicity, it is mentioned first since it coincides by convention with the z axis, the sequence is different, namely z-x-d. The symmetry element oriented in the x direction occurs repeatedly because it is being multiplied by the higher multiplicity of the z axis the bisecting direction between x and its next symmetry-equivalent direction is the direction indicated by d. See the examples in Fig. 3.7. 

Fig. 8 a shows the preferred mutual orientations at large and small C-C distance, and Fig. 8b the energy variation along the least-motion and minimum-energy paths. 

Fig. 8. a) Non-least-motion approach of two methylenes. The sequence 1-2—3 shows the mutual orientation of the two fragments with decreasing distance, b) Energy variation along the least-motion path (i) and along the least-energy path (2). The abscissa scale is the C-C distance (A). The vertical bar is 1 eV on the ordinate energy scale. 

Thermal effects (dielectric heating) can result from dipolar polarization as a consequence of dipole-dipole interactions of polar molecules with the electromagnetic field. They originate in dissipation of energy as heat, as an outcome of agitation and intermolecular friction of molecules when dipoles change their mutual orientation at each alternation of the electric field at a very high frequency (v = 2450 MHz) [10, 11] (Scheme 3.1). 

Scheme 3.1 Effects ofthe surrounding electric field on the mutual orientation ofdi-poles (a) without constraint (b) submitted...

The first possibility is an increase in the pre-exponential factor, A, which represents the probability of molecular impacts. The collision efficiency can be effectively influenced by mutual orientation of polar molecules involved in the reaction. Because this factor depends on the frequency of vibration of the atoms at the reaction interface, it could be postulated that the microwave field might affect this. Binner et al. [21] explained the increased reaction rates observed during the microwave synthesis of titanium carbide in this way ... 

At some stage during a cycloaddition reactions, an interaction between two molecular species must occur. Let us imagine that two possible mutual orientations of the reacting molecules are possible that lead to... 

---