Molecular field correction

Here the notation [GC y indicates that the system to be treated is only the inner-shell volume, and the material enclosed is described by an ensemble of fluctuating composition - as with the grand canonical ensemble - under the influence of the molecular-field p. With longer-ranged interactions, a correction for those... 

Very recently, new descriptors have successfully been derived from 3-D molecular fields. These descriptors were correlated with the experimental permeation data by discriminant partial least-squares methods. The training set consisted of 44 compounds. The authors were able to deduce a simple mathematical model that allows external prediction. More than 90% of blood-brain permeation data were correctly predicted [77]. 

Some of the most difficult structural problems in the indole alkaloid field are associated with the bisindole alkaloids of the vobtusine type. Since 1955, vobtusine has been isolated on numerous occasions, often in large quantities, from the Apocynaceae species Callichilia, Conopharyngia, Rejoua, and Voacanga A correct molecular formula could only be determined by high-resolution mass spectrometry. In 1966 a partial structure was proposed for the alkaloid and later in the same year a complete structure was put forward. An unambiguous structural proof is, however, still lacking. The difficulty arises from the complete resistance of the alkaloid and its derivatives to cleavage, in contrast, for example, to the dimers of the voacamine and vinblastine types. Non-cleavable dimers occur also in calabash-curare but in these cases chemical correlation with cleavable alkaloids has been possible (see Section 2, p. 209). To date no bisindole alkaloid related to vobtusine has been found which can be split into monomeric units. 

The corrections mentioned, however, are rather approximate and thus one can enlarge the set of magnetic parameters for a temperature-independent term amol which compensates these uncertainties. Also, some cooperative ordering applicable at a low temperature can be included through the molecular field correction Z so that the theoretical function to be considered becomes... 

Disiloxane (SiH3)0(SiH3) has been the subject of many electronic structure calculations. The Si-O-Si bond angle in disiloxane is very flexible and thus the geometry is a challenge to predict correctly. Molecular mechanics force fields... 

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