Group interactions

When using a switching function in a molecular simulation with a residue-based cutoff it is important that the function has the same value for all pairs of atoms in the two interacting groups. Otherwise, severe fluctuations in the energy can arise when the separation is within the cutoff region. These two contrasting situations can be formally expressed as follows ... 

Alternatively, using a polyethylene glycol stationary phase, aromatic hydrocarbons can also be retained and separated primarily by dipole-induced dipole interactions combined with some dispersive interactions. Molecules can exhibit multiple interactive properties. For example, phenyl ethanol possesses both a dipole as a result of the hydroxyl group and is polarizable due to the aromatic ring. Complex molecules such as biopolymers can contain many different interactive groups. 

The cyclocondensation of iodoaminopyrazole with copper acetylides and the cyclization of aminopyrazolylacetylene with different mutual arrangement in the ring of interacting groups have been studied (83IZV688). 

As a substrate, 4-amino-5-acetylenylpyrazole 71 was chosen in this compound the position of interacting groups is the most favorable for intramolecular cyclization. Indeed, 4-amino-l,3-dimethyl-5-phenylethynylpyrazole 71 isomerized into l,3-dimethyl-5-phenylpyrrolo[3,2-c]pyrazole 70 in 65% yield under heating in DMF for 4 h in the presence of Cul (83IZV688). The authors have noticed that the cyclization of 71 is accelerated by the addition of CuC=CPh. 

For this reason, the heterocyclization of acetylenic derivatives of pyrazolecar-boxylic acids with different arrangements in the ring of the interacting groups was studied (Table XXVI). The reaction is carried out in boiling pyridine in the presence of catalytic amounts of PhC=CCu (81IZV1342). 4-Acetylenyl-l-methylpyrazole-5-carboxylic acids (Scheme 121) are fully isomerized into the pyranopyrazoles in 20 min in 62-84% yields. 

On occasion, the broad choice of existing phases is not enough to resolve a particular problem successfully. Derivatization with achiral reagents can be useful to introduce additional interacting groups in a poorly functionalized substract, or to... 

The present review intends to be illustrative rather than comprehensive, and focuses on the results of this study leading to the hypothesis 9 — the three-dimensional shape similarity between interacting groups in reacting molecules is responsible for more specific and precise molecular recognition than would otherwise be achieved — and on the explanation of biological recognition on this basis. 

The similarity recognition hypothesis presented here would be applicable to the specific and precise discrimination in chemical and biological systems. It is hoped that this review will serve to stimulate further work on the physicochemical origin of the shape-similarity effect on specific molecular recognition, for example, work on weak interactions specific for the three-dimensional shape of interacting groups. 

S.J. Tauster, S.C. Fung, and R.L. Garten, Strong metal-support interactions. Group 8 noble metals supported on T1O2, JACS 100, 170-175 (1978). 

G.L. Haller, and D.E. Resasco, Metal-Support Interaction Group VIII Metals and Reducible Oxides, Advances in Catalysis 36, 173-235 (1989). 

The more useful types of chirally active bonded phases are those based on the cyclodextrins. There are a number of different types available, some of which have both dispersive or polar groups bonded close to the chirally active sites to permit mixed interactions to occur. This emphasizes the basic entropic differences between the two isomers being separated. A range of such products is available from ASTEC Inc. and a separation of the d and / isomers of scopolamine and phenylephrine are shown in figure 4. The separations were carried out on a cyclodextrin bonded phase (CYCLOBOND 1 Ac) that had been acetylated to provide semi-polar interacting groups in close proximity to the chiral centers of the cyclodextrin. The column was 25 cm long, 4.6 mm in diameter and packed with silica based spherical bonded phase particles 5pm in diameter. Most of the columns supplied by ASTEC Inc. have these dimensions and, consequently, provide a... 

Bionanomaterials and Surface Interactions Group, Nanotechnology Research Institute,... 

An interesting pair of compounds is caffeine and theophylline [97] these compounds are relatively polar compounds with different functional groups (tertiary and secondary amine). In a few cases, more appropriate comparisons have been made such as between androstenedione/testoster-one and methyl benzoate/anisole these compounds are expected to be different in Snyder interaction groups. 

A number of researchers have also used a proposed ASTM test mixture, benzaldehyde, acetophenone, methyl benzoate, dimethyl terphtha-late, benzyl alcohol, and benzene to demonstrate separation on a column [98]. However the first four compounds are from the same interaction group and should behave in the same way on changing conditions. The first three have almost constant indices (respectively 760, 800, and 890) so that in effect they create an index scale with constant differences against which the last two compounds can be compared [96,99]. 

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