Organotin models

Table 17.6 Bacterial inhibition results for organotin model...

EXAFS data were analyzed by using multishell models up to 300 pm. These results are the first structural data (bond lengths) on complexes formed with organotin(lV)-DNA and related compounds.Some data are collected in Table 6. The proposed structures are similar to those depicted in Figure 6. 

Because of the influence of the ligand, physicochemical properties and environmental fate modelling derived from them are often uncertain for the organotins. 

As most organotins decompose, boiling points of 250 °C were assumed in the absence of a "true boiling point. The values for Henry s law constant and organic carbon/water partition coefficient were all derived from EUSES unless otherwise indicated. The chlorides were chosen as soluble salts in this table toxicity is independent of salt (see section 8), and soluble salts maximize likely environmental exposure, giving worst case in modelling environmental fate. 

The BUSES model has been run for each of the organotins under consideration. This involved developing use patterns for each compound, together with appropriate emission factors (based on the results presented above) and data on the properties of each of the compounds. The data upon which the analysis is based are the usage of each compound by application. More details on the method can be found in the source document (EC, 2003). Regional PECs for fresh water are summarized in Table 16. 

Pieters RHH, Bol M, Penninks AH (1994b) Immunotoxic organotins as possible model compounds in studying apoptosis and thymocyte differentiation. Toxicology, 91 (2) 189-202. 

Gabrielska, J., Sarapuk, J. and Przestalski, S. (1997). Role of hydrophobic and hydrophilic interactions of organotin and organolead compounds with model lipid membranes, Z. Naturforsch. C., 52, 209-216. 

Sarapuk, J., Kleszczynska, H. and Przestalski, S. (2000). Stability of model membranes in the presence of organotin compounds, Appl. Organomet. Chem., 14, 40 17. 

Antifouling performance of these organotin carboxylate polymers indicates that their mode of action corresponds to the bulk abiotic bond cleavage model proposed by Castelli and Yeager (8). The controlling factors to be considered here are ... 

Antifouling performance of organotin carboxylate polymers show that their mode of action corresponds to the "bulk abiotic bond cleavage" model. All the controlling factors are analyzed. 

The mode of action of the antifouling polymers thus conforms to the bulk abiotic bond cleavage model. All the controlling factors, viz., diffusion of water into the polymer matrix, hydrolysis of the tributyltin carboxylate, diffusion of tributyltin species from the matrix to the surface, phase transfer of the organotin species, and its migration across the boundary layer, are analyzed. It is found that the transport of the mobile tributyltin species in the matrix is the rate limiting factor. 

The first section, Chemical Reactions on Polymers, deals with aspects of chemical reactions occurring on polymers—aspects relating to polymer size, shape, and composition are described in detail. One of the timely fields of applications comprises the use of modified polymers as catalysts (such as the immobilization of centers for homogeneous catalysis). This topic is considered in detail in Chapters 2, 3, 8, 9, and 11 and dealt with to a lesser extent in other chapters. The use of models and neighboring group effect(s) is described in detail. The modification of polymers for chemical and physical change is also described in detail in Chapters 2 (polystyrene) 4 (polyvinyl chloride) 5 (polyacrylic acid, polyvinyl alcohol, polyethyleneimine, and polyacrylamide) 6 (polyimides) 7 (polyvinyl alcohol) 8 (polystyrene sulfonate and polyvinylphosphonate) 10 (polyacrylamide) and 12 (organotin carboxylates). 

The development of the hypervalency concept was discussed in general. This model was concerned with the group 14 elements . The ability of the tin atom to expand the coordination sphere in organotin compounds was established in the early 1960s, when an oligomeric structure was suggested for trimethyltin fluoride and trimethyltin carboxylates" on the basis of IR data. It should be pointed out that the trimethyltin chloride-pyridine adduct was the first pentacoordinate organotin compound structurally characterized by X-ray diffraction in 1963". ... 

There has been controversy on the stereochemistry of the transmetallation of alkylmetals. Transmetallation from Hg to Pd is reported to proceed in THF with retention of configuration [27]. By contrast, cross-coupling reactions of organotin reagents are assumed to take place with inversion in HMPA [28] but with retention in toluene [29]. We consider that the organosilicon-based coupling reaction would be a useful model for examining the stereochemistry of the transmetallation process. 

Receptor 16 was reported to form a 1 1 complex with chloride ions in chloroform (K = 500 M ), exhibiting fast exchange on the NMR time scale (73). Such hosts, containing four tin binding sites, were shown to be considerably more effective than mononuclear organotin compounds for chloride binding. In 1991, Newcomb and co-worker (74) published modeling studies for these tin based hosts as well as a crystal structure of 17. 

A number of organotin hydrides which carry a chiral group, usually menthyl or nor-bomyl, have been prepared for use in asymmetric synthesis.42 An example is shown in equation 15-19 the enantioselectivity in this reaction is enhanced by the presence of a Lewis acid (e.g. BF3 or Cp2ZrCl2), and ee values of up to about 80 have been achieved.43 Force field and MO methods have been used to model the transition state for hydrogen transfer in such reactions.44... 

The results with organotin compounds (Table 20-7) can be discussed using SnH4 as a model.83-85... 

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