Hydrogen Bonds and Other Weak Interactions

Hydrogen bonds play a major role in the interactions of a substrate with its biological target. This latter is generally a protein, which bears many possible sites for potential hydrogen bonds. 

Moreover, fluorine substitution reduces polarizability, increases the hydrophobic surface, and provides an enhanced driving force for desolvation (estimated driving force 0.2-0.5 kcal/mol).  

Values of the parameter, which represents the ability of a substituent to be a donor of hydrogen bonds, show that the presence of fluorine atoms notably enhances the hydrogen bond donor ability of a hydroxyl group. Conversely, values of P2, which represents the ability to accept hydrogen bonds, are lowered by the presence of fluorine atoms. 

The acidic character of fluorinated alcohols, and consequently the excellent ability to donate hydrogen bonds, justifies their use as central peptidomimetic units in inhibitors of serine and aspartyl proteases. An enhancement of of the OH-1 IjS of 

9-fluorocorticoids has also been invoked to explain their pharmacological properties. 

---

Complexes of Heavier Transition Metals Electrochemical Studies Luminescence Studies IV. Hydrogen Bonding and Other Weak Interactions in Complexes of Squaric Acid and Its Monosubstituted Derivatives References... 

Generally, specific proteins can bind to each other In the body to form dimers (duplex structures), trimers, tetramers, or even larger multiples. These subunit proteins may be of identical or different structure. The different proteins in these mullimeric structures arc bound to each other by hydrogen bonds and other weak interactions. Ihese multimers often perform physiological functions that cannot be carried out by the individual separated proteins. 

High temperature disrupts the hydrogen bonds and other weak interactions that maintain protein structure. 

As a rule, it is then possible to note that intermolecular interaction can be considered as the sum of two components a dispersive (or nonpolar, superscript L) component, i.e., attributable to London force, and a specific (or polar, SP) component owing to all other types of interactions (Debye, Keesom, hydrogen bonding, and other weakly polar effects)... 

We will present examples of tapes, ribbons, and sheets based on hydrogen bonding and other intermolecular interaction patterns. The use of both strong hydrogen bonding groups such as carboxylic acids and amides, as well as, weak interactions such as C-H---0 hydrogen bonds and iodo---nitro polarization interactions will be covered. 

Over the past decade, there have been numerous books and arti-cles " reviewing ab initio and density functional theory (DFT) computations of hydrogen bonding and other weak noncovalent interactions. In fact, the very first chapter of this entire review series examines basis sets for noncovalent interactions between atoms and/or molecules," while a chapter in the second volume reviews ab initio methods for hydrogen bonding." Three thematic issues of Chemical Reviews have been dedicated to van der Waals interactions (Vol. 88, No. 6, 1988 Vol. 94, No. 7, 1994 and Vol. 100, No. 11, 2000). Two articles in the centennial issue of the Journal of Physical Chemistry discuss weakly bound clusters and solvation." " It is also worth noting that 7i-type stacking interactions are very topical at the moment and are the subject not only of a separate chapter in this volume of Reviews in Computational Chemistry" but also of a special issue of Physical Chemistry Chemical Physics (Vol. 10, No. 19, 2008). 

A confirmation of the soundness of electronic theory was derived from a recent study, performed by Bogotaj et al. [46], They measured the zeta potential of different polymer dispersions and mucosal homogenates and found a correlation between such a parameter and the force necessary to detach a polymer dispersion from the biological substrate. The adsorption theory states that the bioadhesive bond is due to van der Waals interactions, hydrogen bonds, and other related weak interactions [44],... 

The no-bond function includes the electronic energy of the component molecules, plus terms representing the effect of dipole interactions, dispersion forces, hydrogen bonding and other intermolecular forces. The dative bond functions represent states where an electron has been transferred from the donor molecule to the acceptor, introducing electrostatic interactions and forming a weak covalent link between the resulting radical ions ... 

Lastly, it is conceivable that the size of the anion may have an influence over coordination polymer structure. Such an effect can be difficult to assess, and in particular, de-convolute from other factors, most noticeably from weak interactions with the polymer structure such as CH acceptor interactions. If the size of an anion is influencing a structure, it is likely that it is in close contact with the polymer and therefore the formation of hydrogen bonds, or other supramolecular interactions, could be the main factor in affecting the structure. 

The key to CTeating a flexible framework is to utilize weak molecular interactions in addition to the strong covalent and coordination bonds. Actually, coordination bonds in PCPs are frequently supported by hydrogen bonds, n-n stacking, van der Waals forces and other weak interactions. Intermolecular links with these weaker interactions produce flexible parts in a framework, so that the system can exist in two or more sohd phases. Depending on the external perturbations and guest molecules, the systan will be in one of the multiple solid phases. 

---