Intriguing Intermolecular Interplay in Guanine Quartet Complexes with Alkali and Alkaline Earth Cations

Abstract

The possibility to target noncanonical guanine structures with specific ligands for therapeutic purposes inspired numerous theoretical and experimental investigations of a guanine quartet and its stacked composites. In this work, we employed the interacting quantum atoms methodology to study interactions among different fragments in complexes composed of a guanine quartet and alkali (Li+, Na+, K+) or alkaline earth (Be2+, Mg2+, Ca2+) cations in vacuo: metal–quartet interaction, influence of the cation on guanine–guanine interaction, as well as hydrogen bond cooperativity in the guanine quartet and its complexes with metal ions. Interestingly, although the presence of a cation intensifies interaction among guanine molecules, it lowers their binding energy because of notable quartet’s distortion which is responsible for guanines’ substantial deformation energy. This phenomenon is particularly pronounced with Be2+ which, out of the six analyzed cations, enhances hydrogen bond cooperativity to the greatest extent.

Modulating Excited Charge-Transfer States of G-Quartet Self-Assemblies by Earth Alkaline Cations and Hydration

“…62 We believe that the instability of Li + -coordinated G-octets originates from the inability of the Li + cation to coordinate all oxygen atoms and subsequently the lack of G-quartet rigidity, which is crucial for G-quartet stacking. In the case of the Mg 2+ cation, the stability might be even more reduced since it was previously shown that G-quartets with earth alkaline cations only exist because of strong cation−guanine attraction 9 and this cation also does not coordinate all oxygen atoms. We will show below that the earth alkaline cations even reduce the strengths of the inner hydrogen bonds in the G-octets relative to those of G-octets coordinated with alkaline cations.…”

“…Although the latter interaction is dominated by electrostatics, 6,9 it also has a partially covalent nature. Selected geometrical parameters related to these interactions are collected in Table 1.…”

“…Particularly, monovalent and divalent cations dictate the self-assembly of guanines into a cation-templated G-quartet structure (see Figure ). The stability of this supramolecular structure is determined by cooperative hydrogen bonding, the size of the cation, and its hydration energy. − …”

Proton leap: shuttling of protons onto benzonitrile

“…All quantum chemical calculations were performed at the M06-2X/6-311++G(d,p) level 42–47 with the Gaussian program package 48 using an ultrafine integration grid. It has been demonstrated that M06-2X functional successfully describes charged particles, 36,49,50 but also systems with various types of interactions. 31,39,51–57 IQA analysis was performed with the AIMAll software 58 by employing the promega5 basin integration method.…”

“…For this purpose, the Interacting Quantum Atoms methodology 21,22 (IQA) was employed, which has so far been successfully utilized for analysis of diverse systems, properties and processes. 23–41 It enables quantification of classical and non-classical interaction terms among selected fragments (the fragments being BN & PCH + , BN & H + , PC & H + , or BN & H + & PC), but also energetical properties of the fragments themselves when their geometry and the environment modify upon reaction advancement. The paper is organized as follows: Section 2 contains details of the computational procedure; the results and their discussion are presented in Section 3; the conclusions are summarized in Section 4.…”