Activities Structures: Three-Dimensional Works

Ice (H20) is a molecular crystalline solid. Six water molecules bond to each other to form a hexagonal pattern. This pattern is reflected in the hexagonal geometry exhibited in snowflakes. In Activity 4.1, you will construct models of basic crystalline solids and grow molecular-solid crystals. Then you will consider the basic structures of crystalline solids and look upon these structures as three-dimensional works of art. 

Although most medicinal chemists use structure-activity relationships of various sorts in drug design, very few use quantitative three-dimensional structural information in designing potentially active molecules. Three-dimensional information that is being used, comes for the most part from qualitative work with molecular models. This situation exists, not because of any lack of interest or lack of awareness among medicinal chemists, but because 1) availability of three-... 

A lot of work is currently carried out to extend this idea to fully dispersed two-dimensional (on a YSZ surface) or three-dimensional (in a porous YSZ structure) metal catalysts. The main problems to be overcome is current bypass and internal mass transfer limitations due to the high catalytic activity of such fully dispersed Pt/YSZ catalyst systems. 

Elemental and Structural Characterization Many oxidation reactions occur on mixed oxides of complex composition, such as SbSn(Fe)0, VPO, FePO, heteropolycompounds, etc. Very often the active surfaces are not simple terminations of the three dimensional structure of the bulk phases. There is need to extensively apply structural characterization techniques to the study of catalysts, if possible in their working state. 

The above examples used only a pair of molecules to illustrate the approach. To discuss three-dimensional structure-activity relationships in more detail from a strict pharmacological point of view, common pattern search trails should be conducted for a large number of molecules which have similar activities and different structures. In practice, COMPASS can work for three or more... 

The synthesis, characterization and properties of nanomaterials have become very active areas of research in the last few years. In particular, nanostructured materials assembled by means of supramolecular organization offer many exciting possibilities. These include self-assembled monolayers and multilayers with different functionalities, intercalation in preassembled layered hosts and inorganic three-dimensional networks. The reader is referred to the special issue of Chemistry of Materials91 for an overview of present day interests. There are many recent reviews on the varied aspects of nanomaterials. The work of Alivisatos92 on the structural transitions, elec-... 

Based on the earlier work of Meyer and Overton, who showed that the narcotic effect of anesthetics was related to their oil/water partition coefficients, Hansch and his co-workers have demonstrated unequivocally the importance of hydrophobic parameters such as log P (where P is, usually, the octanol/water partition coefficient) in QSAR analysis.28 The so-called classical QSAR approach, pioneered by Hansch, involves stepwise multiple regression analysis (MRA) in the generation of activity correlations with structural descriptors, such as physicochemical parameters (log P, molar refractivity, etc.) or substituent constants such as ir, a, and Es (where these represent hydrophobic, electronic, and steric effects, respectively). The Hansch approach has been very successful in accurately predicting effects in many biological systems, some of which have been subsequently rationalized by inspection of the three-dimensional structures of receptor proteins.28 The use of log P (and its associated substituent parameter, tr) is very important in toxicity,29-32 as well as in other forms of bioactivity, because of the role of hydrophobicity in molecular transport across cell membranes and other biological barriers. 

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