Direct reaction field implementations

The design and implementation of a portable fiber-optic cholinesterase biosensor for the detection and determination of pesticides carbaryl and dichlorvos was presented by Andreou81. The sensing bioactive material was a three-layer sandwich. The enzyme cholinesterase was immobilized on the outer layer, consisting of hydrophilic modified polyvinylidenefluoride membrane. The membrane was in contact with an intermediate sol-gel layer that incorporated bromocresol purple, deposited on an inner disk. The sensor operated in a static mode at room temperature and the rate of the inhibited reaction served as an analytical signal. This method was successfully applied to the direct analysis of natural water samples (detection and determination of these pesticides), without sample pretreatment, and since the biosensor setup is fully portable (in a small case), it is suitable for in-field use. 

The model outlined above and its simple extension contain a theoretical possibility of how to direct the production of SPS towards the required product synthon. This very serious problem is partially overcome by making use of the concept of reaction distance only those new SPS are taken into account that have a smaller distance than their predecessor with respect to the product synthon. Recently, our activity in this field has been concentrated on an application of tools of logical programming for implementation of some principal rules of chemical reactivity. 

Every PGDB object has a stable nniqne identifier (ID), that is, a symbol that identifies that object nniqnely within the PGDB. Example nniqne IDs inclnde TRP (an identifier for a metabolite), RXNO-2382 (an identifier for a reaction), and PWYO-1280 (an identifier for a pathway). Relationships within a PGDB are implemented nsing IDs. Eor example, to state that the TRP (tryptophan) object is a reactant in the reaction RXNO-2382, a field of RXNO-2382 called LEFT (meaning reactants ) contains the valne TRP. Many PGDB relationships exist in both forward and backward directions for example, the TRP object contains a field called APPEARS-IN-LEFT-SIDE-OF that lists all reactions in which TRP is a reactant. The fields LEFT and APPEARS-lN-LEFT-SlDE-OF are called inverses. 

A number of excellent reviews on the Car-Parrinello method have been published during the years and an overview of the development of the field through the last decade is presented in Ref A comprehensive article has appeared recently that features the underlying theory and many details of the practical implementation ex plified with the ab initio molecular dynamics code CPMD developed in Parrinello s group. Another currrait review is especially addressed to the chemical engineaing community. Several overview articles are also available that siunmarize Car-Parrinello applications to specific topics, such as applications to clusters," fullerenes, liquids, semiconductor surfeces, smface reactions and biological systems. The present article is particularly directed to newcomers to the field of Car-Parrinello simulations who would like to get an introductory summary of the basic ideas, learn what one can do with this method and get to know which codes are currraitly available. 

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