It is shown that the electron density at the hydrogen bond critical point increases approximately linearly with increasing stabilization energy in going from weak hydrogen bonds to moderate and strong hydrogen bonds, thus serving as an indicator of the nature and gradual change of strength of the hydrogen bond for a large number of test intermolecular complexes.

In this perspective article, the basic theory and applications of the "Quantum Theory of Atoms in Molecules" have been presented with examples from different categories of weak and hydrogen bonded molecular systems.

In line with the charge transfer (DeltaNmax = -mu/eta) proposed by Parr et al. (Parr, R. G.; Szentpály, L. V.; Liu, S. J. Am. Chem. Soc. 1999, 121, 1922), we propose an electrophilicity-based charge transfer (ECT) descriptor in this paper and validate it through the interaction between a series of chlorophenols and DNA bases. Application of ECT can be extended to the interaction of any toxin with the biosystem.

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To verify whether the maximum or the minimum Fukui function site is better for protonation reactions or an altogether different local reactivity descriptor, viz., the charge is necessary, we calculate the Fukui functions (using a finite-difference approximation as well as a frozen-core approximation) and charges (Mulliken, Hirshfeld, and natural population analysis schemes) of several hydroxylamine derivatives, their sulfur-containing variants, and amino acids using B3LYP/6-311G(d,p) technique. While the Fukui functions provide the wrong selectivity criterion for hard−hard interactions, the charges are found to be more reliable, vindicating Klopman's idea. It is transparent from the present results that the hard−hard interactions are better explained in terms of charges, whereas the Fukui functions can properly account for soft−soft interactions known to be frontier-controlled.

We present a versatile approach for tuning the surface functionality of an atomically precise 25 atom gold cluster using specific host-guest interactions between β-cyclodextrin (CD) and the ligand anchored on the cluster. The supramolecular interaction between the Au25 cluster protected by 4-(t-butyl)benzyl mercaptan, labeled Au25SBB18, and CD yielding Au25SBB18∩CDn (n = 1, 2, 3, and 4) has been probed experimentally using various spectroscopic techniques and was further analyzed by density functional theory calculations and molecular modeling. The viability of our method in modifying the properties of differently functionalized Au25 clusters is demonstrated. Besides modifying their optoelectronic properties, the CD moieties present on the cluster surface provide enhanced stability and optical responses which are crucial in view of the potential applications of these systems. Here, the CD molecules act as an umbrella which protects the fragile cluster core from the direct interaction with many destabilizing agents such as metal ions, ligands, and so on. Apart from the inherent biocompatibility of the CD-protected Au clusters, additional capabilities acquired by the supramolecular functionalization make such modified clusters preferred materials for applications, including those in biology.

A high CO2 to CO electroreduction rate exceeding 300 mA cm−2 was achieved with single atom nickel and nitrogen doped three-dimensional porous carbon electrocatalysts.