Interface structures, complex

Juo, Z. S., Kassavetis, G. A., Wang, Geiduschek, E. P. and Sigler, P. B. (2003). Crystal structure of a transcription factor lllB core interface ternary complex. Nature 422, 534-539. 

The compositional and structural complexity of these systems is their principal advantage. It is this feature which allows surface properties to be tuned in order to optimize selectivity and activity with respect to a specific reaction. At the same time, complexity is the reason of the fact that at a molecular level, an understanding of reaction kinetics at heterogeneous and porous interfaces is difficult to achieve. Consequently, the reaction kinetics on their surfaces depend sensitively on a number of structural and chemical factors including the particle size and structure, the support and the presence of poisons and promoters. 

Crystal/crystal interfaces possess more degrees of freedom than vapor/crystal or liquid/crystal interfaces. They may also contain line defects in the form of interfacial dislocations, dislocation-ledges, and pure ledges. Therefore, the structures and motions of crystal/crystal interfaces are potentially more complex than those of vapor/crystal and liquid/crystal interfaces. Crystal/crystal interfaces experience many different types of pressures and move by a wide variety of atomic mechanisms, ranging from rapid glissile motion to slower thermally activated motion. An overview of crystal/crystal interface structure is given in Appendix B. 

Supramolecular Structures Complex Polymeric Systems - Organization, Design and Formation using Interfaces and Cyclic or Complex Molecules... 

This illustrates that we are far from the point where we can develop robust and transferable semiempirical potentials for the general M/C interface. This task is fundamentally difficult because the bonding changes character at the interface, from metallic to ionic, and because of the structural complexity present. This probably requires explicit inclusion of quantum effects, at least at a low level. 

Tunneling in multilayered LB films is defect-mediated via trap sites within the conduction band of the molecules (Poole conduction), or by Schottky emission between widely spaced trap sites (Poole Frenkel conduction) in thicker samples [13]. With good molecular conductors the current from molecular conduction should dominate the small contribution from tunneling. However, the conduction mechanism between adjacent layers is not always obvious, due to the complexity of the interface structure. 

Similar conclusions apply to interface structures (Chapter 6). Textural examinations of reactant-product contact zones have revealed greater structural complexities than were recognised in earlier work. The interface model leads to the kinetic representation that the rate of product formation is directly proportional to the area of reactant-product contact and its geometric pattern of development (Chapter 3). 

A key factor in formation of structures that are not compact is the line tension between the phases, which suppresses instabilities at an interface. The addition of cholesterol to a monolayer lowers the line tension and favors the formation of ramified structures. Complex lamellar structures of many types, including spirals (Fig. 22), are formed in the LE LC transition region of phospholipids doped with cholesterol. If the amphiphiles are chiral, the spirals have a unique sense of rotation. 

To date, the limited use of the enantioselectivity of biocatalysts in polymerization conditions and the lengthy synthetic procedures required to prepare optically pure monomers have hampered full exploitation of chemo-enzymatic approaches in polymer chemistry. However, a combined multidisciplinary effort at the interface of biocatalysis, polymer chemistry and organic catalysis, will allow to convert methods well-established in organic chemistry such as tandem catalysis, to the field of polymer chemistry. Undoubtedly, in the near future the exploitation of the selectivity of enzymes and the advantages of chemo-enzymatic approaches in a wide variety of polymerization chemistries will be recognized. This may lead to a paradigm shift in polymer chemistry and allow a higher level of structural complexity in macromolecules, reminiscent to those found in Nature. 

Fig. 8.3 Crystal structure of Complex III dimer and model of putative Complex III surface that interacts with Complex IV from S. cerevisiae. (A) Dimer of Complex III based on the crystal structure (figure adapted from (Hunte, 2005)) with the interface between monomers in the center. a-Helices of different subunits within the dimer are shown as rods of different shading connected by non-helical domains. Note the positions of CL and PE (all circled) in the center front (also on back center but not shown) between the dimers and on the front right) and back left) sides of the diagram. The two bars on the right show the 36-A width of the membrane. (B) The putative interface of Complex III monomer (figure adapted from (Pfeiffer et ah, 2003)) with Complex IV with the various subunit domains labeled. This view, with a cavity containing PE and CL (both circled), corresponds to the right and left sides of the view shown in (A) and is positioned within the membrane bilayer. Bottom of both diagrams faces the mitochondrial matrix...

Note the increase in complexity of embryo formation, the interface structure and the number of steps, 6, needed to do so. In the simple case, B grows at the expense of A. However, in the second case involving parallel reactions, two embryos form from A. In the third case, at least two steps are involved in the two consecutive reactions where "A" transforms to B", which transforms to "C". 

Measurement of mineral-water interface structure during surface reactions provides direct insight into mineral reactivity and is a powerful approach for understanding complex interfacial reactions. It is currently not possible to provide a complete structural measurement with a temporal resolution of a few minutes. It is, however, possible to measure representative changes in real time in a way that provides important constraints on the dissolution process. Such measurements can also be coupled with high-resolution measurements of previously reacted surfaces to provide snapshots of the reacted surface. 

In this chapter we present a general method for solving surface/ solution equilibrium problems described by a surface complexation model, applicable for arbitrary surface layer charge/potential relationships and arbitrary surface/solution interface structures. 

H nmr studies in non-polar solvents have shown that whereas the sulphide and selenide of the heterocyclic system (224) involve intramolecular coordinative interactions between tin and sulphur or selenium, the related phosphine oxide prefers to bind intermolecularly. In the solid state, a similar situation applies.Structural studies of adducts of triphenylphosphine oxide with monoorganotrichlorostannanes have also been reported. Various types of phosphine oxides are able to complex alkali and alkaline earth metal cations, and to facilitate their transfer across aqueous/organic interfaces.Organogallium complexes of phosphine oxide ligands have been isolated from the reactions of organogallium peroxo derivatives with phosphines. ... 

TWO types of physical loss processes should be considered In the external removal of a chemical species. First, the species of Interest may be lost to the atmosphere through water-air exchange. This process depends on the Henry s Law constant for the chemical species, as well as the atmospheric concentration and the structure of the surface microlayers (. Wind stress and turbulence of the water body surface have a pronounced effect, especially for surface-active materials for which bubble scavenging and surface film ejection as aerosol takes place. Transfer rates at the air-water interface are complex problems In themselves and are not dealt with In this Chapter. 

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