Water zeolite complexes

A new zeolite model, that features the a and c channels of clinoptilolite has been used to study the possible interactions of aspirin-water-zeolite, in order to know the behavior of the drug in a more complex system and the influence of water present in the zeolite channel. The calculations have been performed using the AMI semi-empirical method and acid and sodic clinoptilolite models. The results showed that the adsorption entalphy of aspirin in the acid structure is in the same order than that obtained for the sodic structure, although the nature of the interaction is different in each structure. The ester and aromatic groups were preferentially oriented to the model. In any case the chemical stability of aspirin is affected by the presence of water molecules in the system. 

Zeolites are complex inorganic minerals whose crystals contain pores that are regular and molecule-sized. The first natural zeolite was discovered in 1756 by the Swedish chemist Axel Frederic Cronstedt (1703-68). Heating a sample of the mineral using a blowpipe he watched it literally boil off water ( zeolite is derived from the Greek boiling stone ). In 1932, James W. McBain (1882-1953), at Bristol, discovered that zeolites have the ability to separate ( sieve ) molecules on the basis of size and shape and... 

The structural complexity of the 3D framework aluminosilicates precludes a detailed treatment here, but many of the minerals are of paramount importance. The group includes the feldspars (which are the most abundant of all minerals, and comprise 60% of the earth s crust), the zeolites (which find major applications as molecular sieves, desiccants, ion exchangers and water softeners), and the ultramarines which, as their name implies, often have an intense blue colour. All are constructed from Si04 units in which each O atom is shared by 2 tetrahedra (as in the various forms of Si02 itself), but up to one-half of the Si... 

Among the three-dimensional silicates are the zeolites, which contain cavities or tunnels in which Na+ or Caz+ ions may be trapped. Synthetic zeolites with made-to-order holes are used in home water softeners. When hard water containing Ca2+ ions flows through a zeolite column, an exchange reaction occurs. If we represent the formula of die zeolite as NaZ, where Z represents a complex, three-dimensional anion, the water-softening reaction can be represented by the equation... 

With lower heat-flux ratings and higher ratios of internal water volume to heating surface than is the norm today, complex external treatment was not always necessary where deemed necessary, it was often limited to basic sedimentaion or filtration techniques employing inorganic coagulants and flocculants, typically followed by the use of natural zeolites (see sections 9.2.3.1 and 9.2.5 for additional information). 

In principle, the soil removal for the a-ester sulfonates increases appreciably in soft water as chain length increases. In hard water the results for C16 and C18 ester sulfonates are nearly the same with and without zeolite A, a builder for complexing Ca2+ ions (Fig. 8) [58]. 

Supported metal carbonyl clusters are alternatively formed from mononuclear metal complexes by surface-mediated synthesis [5,13] examples are [HIr4(CO)ii] formed from Ir(CO)2(acac) on MgO and Rh CCOlie formed from Rh(CO)2(acac) on y-Al203 [5,12,13]. These syntheses are carried out in the presence of gas-phase CO and in the absence of solvents. Synthesis of metal carbonyl clusters on oxide supports apparently often involves hydroxyl groups or water on the support surface analogous chemistry occurs in solution [ 14]. A synthesis from a mononuclear metal complex precursor is usually characterized by a yield less than that attained as a result of simple adsorption of a preformed metal cluster, and consequently the latter precursors are preferred when the goal is a high yield of the cluster on the support an exception is made when the clusters do not fit into the pores of the support (e.g., a zeolite), and a smaller precursor is needed. 

Krossner, M., Sauer, J., 1996, Interaction of Water With Brpnsted Acidic Sites of Zeolite Catalysts. Ab Initio Study of 1 1 and 2 1 Surface Complexes , J. Phys. Chem., 100, 6199. 

The category of builders consists predominantly of several types of materials -specific precipitating alkaline materials such as sodium carbonate and sodium silicate complexing agents like sodium triphosphate or nitrilotriacetic acid (NTA) and ion exchangers, such as water-soluble polycarboxylic acids and zeolites (e.g., zeolite A). 

Fig. 27 Competition by water and sulfide for cation complexed persulfoxide and its effect on the sulfoxide/sulfone ratio as a function of zeolite loading.

In general, the 2 1 clays are not very simple systems in which to study the interaction of water and surfaces. They have complex and variable compositions and their structures are poorly understood. Water occurs in several different environments zeolitic water in the interlayer regions, water adsorbed on the external surfaces of the crystallites, water coordinating the exchangeable cations, and, often, as pore water filling voids between the crystallites. Thus, there are many variables and the effects of each on the properties of water are difficult to separate. 

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