Neutral hydrogen bonds

A fuzzier atom type participating in these descriptors has been defined that is pharmacologically relevant - the physicochemical type at near-neutral pH [24], which is one of the following seven binding property classes 1 = cation 2 = anion 3 = neutral hydrogen-bond donor 4 = neutral H-bond acceptor ... 

Fig. 10. Pharmacophores for angiotension-converting enzyme. Distances in nm. (a) The stmcture of a semirigid inhibitor and distances between essential atoms from which one pharmacophore was derived (79). (b) In another pharmacophore, atom 1 is a potential zinc ligand (sulfhydryl or carboxylate oxygen), atom 2 is a neutral hydrogen bond acceptor, atom 3 is an anion (deprotonated sulfur or charged oxygen), atom 4 indicates the direction of a hydrogen bond to atom two, and atom 5 is the central atom of a carboxylate, sulfate, or phosphate of which atom 3 is an oxygen, or atom 5 is an unsaturated carbon when atom 3 is a deprotonated sulfur. The angle 1- -2- -3- -4 is —135 to —180° or 135 to 180°, and 1- -2- -3- -5 is —90 to 90°.

In addition to metal centres and covalent approaches, anions such as Cl may also be used as templating auxiliary linkages.80 Paul Beer and co-workers from the University of Oxford, UK, recognised that ion pairing in non-polar solvents such as acetone allowed the coordination of a neutral hydrogen bond donor such as 10.110 to the pyridinium salt 10.109, with a binding constant... 

Scheme 10.23 Strong ion-pairing in the pyridinium salt in non polar solvents allows the coordination of a neutral hydrogen bond donor and hence the creation of the precursor to a crossover in a catenane using the chloride ion as an auxiliary linkage.80...

Fig. 2.1.3. Chiral artificial receptors for the recognition of carbohydrates via neutral hydrogen bonds [1, 3d, 3g].

Concerning ab initio calculations on neutral hydrogen-bonded complexes we consider the simplest example, the hydrogen fluoride dimer (Table 3). Both the equilibrium geometry and energy of interaction strongly depend on the quality of the basis set... 

Another way of avoiding the problems of pH range and counterion competition is to use a neutral hydrogen-bonding receptor based on amide functionalities. Peptide groups from the protein backbone are, of course, well known to be involved in enzyme anion binding as discussed earlier. Amide involve-... 

The first ester functionalized cobaltocenium receptor (74) developed by us in 1989, was based solely on electrostatic interactions (as discussed earlier) (9, 186). It was therefore decided to append the cobaltocenium moiety with secondary amide functionalized arms . In this manner, the receptors became more resistant to hydrolysis (a recurrent problem with ester-based systems), and also incorporated neutral hydrogen-bond donors capable of coordinating anions. [An interaction between a secondary amide (acetamide) and the bromide anion was physically investigated (by IR spectroscopy) as long ago as 1961 (211)]. We made the first report of this novel type of receptor (91 and 92) in 1992 (212), which was, in fact, the first class of inorganic anion receptor that incorporated hydrogen-bonding functionalities. 

Benefit of making a neutral hydrogen bond of ideal geometry -4.7... 

C. J. Gruenloh, F. C. Hagemeister, and T. S. Zwier, Size and conformation-selective infrared spectroscopy of neutral hydrogen-bonded clusters, in Recent Theoretical and Experimental Advances in Hydrogen-Bonded Clusters, edited by S. S. Xantheas (Kluwer, The Netherlands, 2000), pp. 83-99. 

Binding property torsions (bt) are binary descriptors for the presence/absence ofTinear sequences of four interconnected non-hydrogen atoms. These descriptors were proposed as an extension of topological torsions by assigning atoms to seven different types of potential pharmacophore points cations, anions, neutral hydrogen-bond donors and acceptors, polar atoms (both donor and acceptor, e.g., hydroxyl oxygen), and hydrophobic atoms and others [Kearsley, Sallamack et al, 1996]. 

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