Small-molecule , generally

This material on main group molecular mechanics is divided into two major parts applications on small molecules (generally organized by group number, with a couple of miscellaneous subdivisions at the end covering several groups) and larger systems, subdivided into extended lattices and polymers. 

Three channels have been implicated as potentially having a role in the access to the active site of CAT. The perpendicular (relative to the plane of the heme) or main channel has been considered as an access channel. The lateral or minor channel has been shown to be important, possibly as an inlet channel, in HPII and in small-subunit enzymes. A third channel has been identified, leading from the heme to the central cavity of the tetramer [200]. All three channels are quite narrow, particularly as they approach the heme-containing active-site cavity, and this restricts accessibility to relatively small molecules, generally not much larger than H2O2. Subtle differences in the size and shape of the channels may influence substrate entry or product exit, contributing to the differences in the reaction rates between different CATs [201]. 

It is appropriate at this point to indicate our personal motivation for carrying out structural studies, the types of compounds we study, and the experimental conditions we employ. In a very general sense we are interested in the bonding of small molecules and ions, e.g., 02, N2, NO, N2 R+, olefins, and acetylenes, to transition-metal complexes. Because of our interest in bonding, we seek the best solutions we can attain. Rapid, qualitative answers to conformational problems are not our interest. Since those transition-metal systems that bind small molecules generally have the metal in a low oxidation state, and since a low oxidation state is usually stabilized by ligands of the type PR3 (R = alkyl or aryl), solution to our problems involves typically the determination of a large number of structural parameters. With only a few exceptions the intensity data are obtained at room temperature on a Picker FACS-1 computer-controlled diffractometer. Usually the ratio of observations to variables is at least 10, and it is often 20 to 30. 

Several different effects are important. Small molecules generally show a monotonic decrease in heat of adsorption with loading (see Fig. 7a). For nonpolar species such as methane this is probably due to energetic heterogeneity arising from the presence of structural defects. On polar adsorbents the magnitude of the decline is greater for quadrupolar and polar sorbates,... 

Biotechnology (hereinafter, biotech) can loosely be defined as the science of very large and very complicated biological molecules. The patent concepts that have developed over the decades to deal with a myriad of inventions covering organic compounds (i.e. small molecules ) generally can be, and have been, adapted to cover biotech inventions. However, biotech inventions have two basic types of problems one technological, the other societal. 

Coenzyme. A coenzyme is a small molecule, generally a derivative of a B-type vitamin, required for the catalytic activity of some enzymes. The coenzyme is generally tightly bound to the enzyme. The complex enzyme-coenzyme forms the holoenzyme, while the free enzyme is the apoenzyme. Sometimes, the term coenzyme is used interchangeably with the term cofactor . The latter includes in addition to coenzymes metal factors such as Mg or Ca " that are often required for enzyme activity. 

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