Retrieval of Reactions

WebReactions (http //www.WebReactions.net) is a new, unique reaction search system offering direct retrieval of reaction precedents through the Internet. For a limited time the 400000-reaction archive from InfoChem GmbH, Munich, is available for searching without cost. The Web-Reactions system is easy to learn and use, though it works only with Netscape Navigator, not Internet Explorer 5.0. It is virtually instantaneous in displaying matches, not just for... 

The CASTOR-system is a system for the documentation of chemical reactions. It relies on a procedure of non-prejudiced coding, indexing, classification, storage and retrieval of reaction and structure information. Its conceptual and mathematical basis is the algebraic model of chemical structure of J. Dugundji and I. Ugi, the DU-model (see next section). 

A recent SciFinder enhancement allows for the retrieval of reaction information and commercial source information via a chemical structure. 

In this section, the basic concepts of reaction retrieval are explained. The first example is concerned with finding an efficient way to reduce a 3-methy]cydohex-2-cnonc derivative to the corresponding 3-mcthylcyclohcx-2-cnol compound (see Figure 5-24). As this is a conventional organic reaction, the CIRX database should contain valuable information on how to syntbesi2e this product easily. 

First, a quei y must be drawn using the MOL" ISIS/Draw program. By using this reaction query, a eurrent reaction search " can be performed. This type of reaction retrieval compares the starting material and the product of the reaction query with all the reactions in the CIRX database. Both query structures must match exactly, including the implicit hydrogen atoms not shown in the reaction query. In this case, one hit is found in the CIRX databases. 

The next abstraction level of reaction retrieval is a so-called reaction substructure search in which both query structures arc considered as substructures. In the case of a reaction substructure search, no hydrogen atoms arc added internally during the execution of the search. Atoms which have their valencies not completely saturated are considered as open sites, where any hind ofelement could be bonded. 

With its flexible and logical search language, REACCS can retrieve molecular stmctures, the atoms and bonds that are transformed ia a reaction, relative and absolute stereochemistry, the role (reactant, product, solvent, or catalyst) of a molecule ia a reaction, reaction data (eg, temperature and yield), hterature references, and keyword descriptions of reaction types. 

After 24 h of reaction, the catalytic bed was retrieved and sieved to separate the catalyst from the diluent. The used catalyst particles were placed in a Soxhlet apparatus, washed with n-hexane for 8 hours and then dried overnight at 393 K. Their carbon content was determined by automatic titration of the CO2 formed by burning the washed sample, in a Strohlein Coulomat 702 apparatus. 

In general, the mechanism of heat and alkaline solution for DNA extraction may be based upon a hypothesis, previously proposed for the AR technique.32 Strong alkaline solution may denature and hydrolyze proteins, resulting in breaking cell and nuclear membranes as well as disrupting cross-linkages due to formalin fixation. It is no surprise to observe the similarity between retrieval of nucleic acid and retrieval of protein (antigen) based on a similar chemical reaction of formaldehyde with these two kinds of macromolecules (Fig. 3.1).15"19... 

To further illustrate how the basis-swapping algorithm can be used to balance reactions, we consider several ways to represent the dissolution reaction of pyrite, FeS2. Using the program RXN, we retrieve the reaction for pyrite as written in the llnl database... 

A critical point in the retrieving of the number of nuclear reactions in laser-solid experiments is that there is no control on the spectrum of the electrons accelerated in the interaction, as well as the acceleration mechanism is uncertain and difficult to fit in a predictable scheme. In most cases, the electron energy distribution is assumed to be Boltzmann-like and deconvolutions are performed starting from this assumption. 

The figures are annotated and little additional comment is required. Figure 4 illustrates retrieval of a structure and its supergraphs and subgraphs. Figure 5 illustrates reaction retrieval. 

Other applications of the polymer substrate technique include the synthesis of threaded macrocyclic systems (hooplanes, catenanes, knots), the retrieval of a minor component from a reaction system, and the trapping of reaction intermediates [Frechet, 1980a,b Hodge, 1988 Hodge and Sherrington, 1980 Mathur et al., 1980],... 

The control of processes involving biological systems should start from a sound knowledge of their biological properties and characteristics. It has been shown that metabolism consists of many reactions which supply both the energy and the chemical materials for the synthesis and reproduction of the cells. Central to the control of these systems is the utilisation and retrieval of information stored within the cell s DNA. 

The second operation en route to tricycle 102, retrieval of the terminal alkene function first installed through the Bubnov reaction, commenced with a survey of electrophilic reagents that might plausibly cleave (oxidize) the propyl-tin bond within 119. The problem inherent in this... 

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