Chemical strategies

Among the various other syntheses achieved by mild chemical routes, mention must be made of the synthesis of hydrides of metals and alloys using borohydride reduction in aqueous medium (Murphy et al, 1993). The reaction seems to proceed as follows  

It is significant that a hydriding power equivalent to 20-30 atm. of H2 is obtained in a reaction of this kind using aqueous BH4 in an open beaker. 

The ideal condition for carrying out a solid state reaction in order to obtain a homogeneous product in the shortest time at the lowest possible temperature is to ensure homogeneous mixing of the reactants on an atomic scale. This, however, cannot be achieved in the ceramic method or its modifications. The only way to achieve this is to prepare a single phase (a chemical compound) in which the reactants are present in 

Chevrel compounds of the general formula A MogSg with A = Cu, Pb, La etc. are difficult to prepare in very pure state by the ceramic procedure. A one-step reduction of a precursor sulphide has been found to yield these phases (Nanjundaswamy et al, 1987)  

Metal thiolates, thiocarbonates and dithiocarbonates are good precursors to prepare sulphides such as CdS and ZnS. A variety of organometallic precursors (usually metal alkyls) have been employed to prepare semiconducting materials (e.g. GaAs, InP). 

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The TCA cycle can now be completed by converting succinate to oxaloacetate. This latter process represents a net oxidation. The TCA cycle breaks it down into (consecutively) an oxidation step, a hydration reaction, and a second oxidation step. The oxidation steps are accompanied by the reduction of an [FAD] and an NAD. The reduced coenzymes, [FADHg] and NADH, subsequently provide reducing power in the electron transport chain. (We see in Chapter 24 that virtually the same chemical strategy is used in /3-oxidation of fatty acids.)... 

Whitesides, G. M., Mathias, J. P. and Seto, C. T. (1991) Molecular self-assembly and nanochemistry a chemical strategy for the synthesis of nanostructures. Science, 254, 1312-1319. 

G.J. de A. Soler-Illia, C. Sanchez, B. Lebeau, J. Patari, Chemical strategies to design textured materials from microporous and mesoporous oxides to nanonetworks and hierarchical structures. Chem. Rev. 102 (2002) 4093. 

In this chapter we have seen that enzymatic catalysis is initiated by the reversible interactions of a substrate molecule with the active site of the enzyme to form a non-covalent binary complex. The chemical transformation of the substrate to the product molecule occurs within the context of the enzyme active site subsequent to initial complex formation. We saw that the enormous rate enhancements for enzyme-catalyzed reactions are the result of specific mechanisms that enzymes use to achieve large reductions in the energy of activation associated with attainment of the reaction transition state structure. Stabilization of the reaction transition state in the context of the enzymatic reaction is the key contributor to both enzymatic rate enhancement and substrate specificity. We described several chemical strategies by which enzymes achieve this transition state stabilization. We also saw in this chapter that enzyme reactions are most commonly studied by following the kinetics of these reactions under steady state conditions. We defined three kinetic constants—kai KM, and kcJKM—that can be used to define the efficiency of enzymatic catalysis, and each reports on different portions of the enzymatic reaction pathway. Perturbations... 

Substitution of a pyridine ring for a benzene ring often is compatible with retention of biological activity and occasionally this moiety is an essential part of the pharmacophore. Such substitution of =N for CH= is an example of the common medicinal chemical strategy known as bioisosterism. 

Speers, A.E., and Cravatt, B.F. (2004a) Chemical strategies for activity-based proteomics. Chem. Bio. Chem. 5, 41 17. 

Lefebure, Victor. The Riddle of the Rhine Chemical Strategy in Peace and War. New York E.P. Dutton Company, 1923. 

A major advantage of plasma processing is that the heat input may be accomplished in an atmosphere of any desired composition and reactivity. In practice there are only a few variations of chemical strategies available for thermal processing i.e. pyrolysis, oxidation, reactions with hydrogen and water. They were already reported elsewhere [5]. The most cost effective and friendly to the environment are the approaches of plasma employing for zero-waste fuel generation or for zero-waste incineration. 

The main objective of the new EU Chemical Strategy is to ensure a high level of protection for human health and... 

A decision by the European Parliament to put restrictions on the use of six phthalate plasticisers ignores scientific risk assessments and threatens the basis for Reach, the impending European legislation on chemical strategy. The Strasbourg parliament has voted to ban DEHP, DBP and BBP in children s toys and childcare items. DINP, DIDP and DNOP will be banned from use if the toys or items can be put in the mouth by children. An EU scientific risk assessment said children were not at risk from DINP in toys. A similar study in the US by the Consumer Product Safety Commission reached the same conclusion. European Commission... 

The different 3D-shapes adopted by aminoglycosides in the RNA- and enzyme-bound states suggest a possible structure-based chemical strategy to obtain antibiotics with better activity against resistant bacteria. Assiun-ing that, in these cases, some degree of conformational distortion of the substrates is required for enzymatic activity, it should be possible to design a conformationally locked oHgosaccharide that still retains antibiotic activity, but that is not susceptible to enzymatic inactivation (Fig. 8) [41]. 

The state institutions can also offer orientation (in so far as this is done on the basis of a far-reaching discourse within society). This includes the development of a national chemicals strategy, for example, or the publication and specialised validation of priority substance lists that require special attention when designing products and processes. 

Chemical Strategy for the Determination and Synthesis of Antigenic Sites... 

Through the application or appropriate adaptations of the general chemical strategy outlined above, we found that lysozyme has three antigenic sites, each constituting spatially adjacent residues (which are otherwise distant in sequence) that occupy a... 

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