Ligand sites

The van der Waals parameters of the metal in a liganded site may be significantly... 

Although Cu (aq) is a poor catalyst, it has been established that certain complexes of Cu(II) with a free ligand site can reduce H2O2, i.e. that the electron transfer is inner-sphere in character The rate law depends on the other ligands, e.g. 

The rate of a catalytic reaction depends on the rate of diffusion of both substrates and products to and from the catalytic sites. Therefore it is of outmost importance that the catalytically active sites are freely accessible for reactions. Only dendrimers of low generation number can possibly be expected to be suitable carriers for catalytically active sites, especially when these are located in the interior. In high-generation dendrimers with crowded surfaces catalytic activity of an internal site would be prevented. On the other hand, a crowded surface will not only hinder access to an interior ligand site but will also cause steric hindrance between groups attached to it and thus prevent high reactivity of sites at the periphery. 

Gamble, D. S., Underdown, A. W. and Langford, C. H. (1982). Copper(II) titration of fulvic acid ligand sites with theoretical, potentiometric and spectro-photometric analysis, Anal. Chem., 52, 1901-1908. 

Step 1. The substrate, RH, associates with the active site of the enzyme and perturbs the spin-state equilibrium. Water is ejected from the active site and the electronic configuration shifts to favor the high-spin form in which pentaco-ordinated heme Fe3+ becomes the dominant form-binding substrate. In this coordination state, Fe3+ is puckered out and above the plane in the direction of the sixth ligand site. The change in spin state alters the redox potential of the system so that the substrate-bound enzyme is now more easily reduced. 

Li W, Palmer G. 1993. Spectroscopic characterization of the interaction of azide and thiocyanate with the binuclear center of cytochrome oxidase evidence for multiple ligand sites. Biochem 32(7) 1833-1843. 

A number of groups have reported the preparation and in situ application of several types of dendrimers with chiral auxiliaries at their periphery in asymmetric catalysis. These chiral dendrimer ligands can be subdivided into three different classes based on the specific position of the chiral auxiliary in the dendrimer structure. The chiral positions may be located at, (1) the periphery, (2) the dendritic core (in the case of a dendron), or (3) throughout the structure. An example of the first class was reported by Meijer et al. [22] who prepared different generations of polypropylene imine) dendrimers which were substituted at the periphery of the dendrimer with chiral aminoalcohols. These surface functionalities act as chiral ligand sites from which chiral alkylzinc aminoalcoholate catalysts can be generated in situ at the dendrimer periphery. These dendrimer systems were tested as catalyst precursors in the catalytic 1,2-addition of diethylzinc to benzaldehyde (see e.g. 13, Scheme 14). 

Schuller, D. J., Grant, G. A., and Banaszak, L.J. (1995). The allosteric ligand site in the Vmax-type cooperative enzyme phosphoglycerate dehydrogenase. Nat. Struct. Biol. 2, 69-76. 

For each symmetry element of the second kind (planes of reflection and improper axes of rotation) one counts according to Eq. (1) the pairs of distinguishable ligands at ligand sites which are superimposable by symmetry operations of the second kind. 

It should be noted that upon reaction with an electron-rich cyclobutenone (R1 = R3 = H, R2 = OEt), the major product formed was a cobaltacyclopen-tenone, which may also be considered to be an 772-vinylketene complex. A similar restructure was isolated after heating 114.a with a large excess of triphenylphosphine, which replaces the ligand site vacated by the central C2 unit. Interestingly, such 772-vinylketene complexes are the expected products from the analogous insertion of rhodium into cyclobutenones (e.g., 7). 

We present here a simple model where long-range and nonadditivity of the correlations can be studied explicitly in terms of the ligand-ligand, and ligand-site interactions. With this model we can clearly see the different behavior of the three models discussed in previous sections and, by generalization, we shall see that the same mechanism applies for correlations between particles in the liquid state. 

The understanding of three-dimensional molecular structure and the explanation of ligand-site affinity on hand of shape and functional group complementarity ( lock and key hypothesis) naturally lead to the introduction of the pharmacophore concept in medicinal chemistry and implicitly in computational chemistry see [6] and references therein. The specific physicochemical mechanisms controlling the macromolecule-ligand interactions could be, in principle, understood on a purely... 

When DHB is bound to serine or threonine cyclization may occur resulting in an oxazoline ring cf. above anachelin, Sect. 2.3, and mycobactins, Sect. 2.8). It has been discussed whether the oxazoline nitrogen atom may act as a ligand site (see below, (505)). This would explain why DHB is replaced by a salicylic acid residue in some cases. 

N-Alkylated 2-oxoglutaric acid derivatives cyclize at neutral pH values to two epimeric 5-carboxy-5-hydroxy-2-oxopyrolidine structures (Chart 4). In this way, ot-hydroxycarboxylic acid groupings are formed that can act as ligand sites for Fe ". ... 

The linkage of binding energy at multiple ligand sites is commonly referred to as cooperativity, and the free en-... 

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