Inorganic Models

Correlation of Partial Pyramidalization and the Incipient Bond Distance 

2 Ligand Elimination from the Tetrahedral XY4 Species Bond Length and Valence Angle Correlations 

Spontaneous breakdown of acetals is an example of the SnI type of reaction, uni-molecular elimination from a tetrahedral center. Reaction pathways for this general type of reaction have been derived by analysis of deviations from the expected symmetry of tetrahedral molecules of the YMX3 and MX4 formulation [95]. 

Another remarkable feature of the presented plots is that the smooth curves are not just correlation curves of any arbitrary form drawn to fit the data as well as possible, but are derived from a simple model of bonding. The model is based on three assumptions. The first is Pauling s relation between bond length and bond number [24]  

In the previously mentioned study, Zobetz also examined distortion pathways for the approximately C3V symmetrical O... BO3 and BO4 groups [94]. The correspond- 

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The primary reason for interest in extended Huckel today is because the method is general enough to use for all the elements in the periodic table. This is not an extremely accurate or sophisticated method however, it is still used for inorganic modeling due to the scarcity of full periodic table methods with reasonable CPU time requirements. Another current use is for computing band structures, which are extremely computation-intensive calculations. Because of this, extended Huckel is often the method of choice for band structure calculations. It is also a very convenient way to view orbital symmetry. It is known to be fairly poor at predicting molecular geometries. 

Karlin, K.D. Metalloenzymes, structural motifs, and inorganic models. Science 261 701-708, 1993. 

Chemistry of vitamin B12 and related inorganic model systems. D. G. Brown, Prog. Inorg. Chem., 1973,18, 177-286 (268). 

It is clear from the above work on B12 and the inorganic models that changing the axial Ugands has a noticeable effect on the corrin system, as evidenced by the C(10)-proton chemical shift. On the other hand,... 

Brown, Dennis G., The Chemistry of Vitamin B12 and Related Inorganic Model... 

It is noted that the redox and EPR spectroscopic characteristics of these dimeric manganese complexes have led them to acquire some importance in the formulation of inorganic models able to mimic the manganese centre involved in the photosynthetic oxidation of water (discussed in the following section). 

Robertsone aZ. defined these elaborate peptide-based inorganic model complexes using a term extracted from art and architecture, maquette,... 

Because the number of protein three-dimensional structures completed is relatively small, much of our understanding of the metal center structures comes from studies on inorganic model compounds. Although it is beyond the scope of this chapter to discuss these compounds separately, we have integrated some of the results in our discussion of the relevant protein structures. 

Biological and Biomimetic Catalysis of Manganese Redox Enzymes and Their Inorganic Models... 

Recently, workers (2) have been examining the equilibrium and kinetic factors that are important at the oxic-anoxic interface. The kinetic behavior is difficult to characterize completely due to varying rates of oxidation and absomtion above the interface and varying rates of reduction, precipitation and dissolution below the interface (2.51. Bacterial catalysis may also complicate the system (1). Although one can question the importance of abiotic thermodynamic and kinetic processes at this interface, we feel it is useful to use simple inorganic models to approximate the real system. Recently, the thermodynamics and kinetics of the H2S system in natural waters has been reviewed (0. From this review it became apparent that large discrepancies existed in rates of oxidation of H2S and the thermodynamic data was limited to dilute solution. In the last few years we have made a number of thermodynamic (7.81 and kinetic (9 101 measurements on the H2S system in natural waters. In the present paper we will review these recent studies. The results will be summarized by equations valid for most natural waters. 

As indicated below, for heterogeneous inorganic models of enzymes this circumstance is of practically no importance, i.e. the model operates in a broad range of reaction mixture parameter variation. In some cases, high effectiveness is displayed even in the gas phase (at relatively high temperature). 

Transition metal complexes are interesting as bio-inorganic model systems [155-157] and also because of their material properties (conductivity, magnetism, porosity) and as potential hosts for a variety of guests [156-161]. Whereas salt-like 2D-Cun-coordination polymers are well documented [158-162], far less is known about their neutral counterparts. 

Inorganic species are at the centre of the OEC. Moreover, inorganic model chemistry has played an important and synergistic role in studies of the OEC. 

Vrettos JS, Limburg J, Brudvig GW. Mechanism of water oxidation combining biophysical studies of photosystem II with inorganic model chemistry. Biochim Biophys Acta 2001 1503 229-45. 

Andersson KK, Barra A-L (2002) The use of high field/ frequency EPR in studies of radical and metal sites in proteins and small inorganic models. Spectrochim Acta A 58 1101-1112... 

Wikaira, J., Gorun, S M. (1999) Biological and biomimetic catalysis of manganese redox enzymes and their inorganic models, in Reedijk, J. and Bouwman, E. (eds) Bioinorganic Catalysis (2nd Edition, Revised and Expanded) Marcel Dekker, Inc., New York, N. Y., pp. 355-422. 

We have attempted to survey both the current status of studies attempting to elucidate the nature of higher oxidation Mn biomolecules, and the efforts directed toward the synthesis of satisfactory inorganic models. As we noted in Section I, this is consequently by no means an exhaustive account of all the work reported, and references to more detailed reviews of specific systems have been cited in the text. Nor have all Mn-containing or Mn-dependent biological systems been included again, more detailed and exhaustive reviews are available elsewhere (327). 

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