Feasibility of Single-Walled Carbon Nanotubes as Materials for CO2 Adsorption: A DFT Study

[eng] The adsorption of CO2 by zigzag and armchair singlewalled carbon nanotubes (SWNTs) of different diameters (4.70−10.85 Å) has been studied using DFT with empirical dispersion correction (B97-D/SVP). Different binding sites have been considered, namely, in the interior (side-on and end-on binding modes) and on the surface (parallel or perpendicular) of the nanotube. Our calculations predict larger interaction energies for interior than exterior adsorption, with the strongest interactions observed for the (9,0) and (5,5) SWNTs (−12.8 and −12.5 kcal·mol−1, respectively). Therefore, these SWNTs can be considered to be very good potential candidates for carbon capture and storage in reducing CO2 emissions, as corroborated by the computed ΔH and ΔG adsorption energies. Moreover, we predict that interior adsorption would be more favorable than interstitial adsorption in bundles for (9,0), (10,0), (11,0), and (5,5) nanotubes. Furthemore, the diffusion of CO2 from the outside to the interior of the (5,5) SWNT is an energetically barrierless and favorable process. We have also analyzed the interplay between CO2·SWNT and CO2·CO2 interactions when more than one CO2 molecule is inside the tube, showing interesting cooperativity effects for SWNTs with large diameters. Finally, the symmetryadapted perturbation theory partition scheme was used to investigate the physical nature of the interactions and to analyze the different energy contributions to the binding energy

Cation-pi and anion-pi interactions

[eng] In this review, we analyze the interaction of ions with aromatic rings from several points of view.We start with a short history of cation-π and anion-π interactions and continue with a description of the main forces involved in these interactions. The comprehension of these forces allows us to rationalize the requirement that both the ion and the aromatic compound should have improved the interaction. Some physical properties of both the aromatic rings and the interacting ion are directly related with the strength of the interaction. An interesting part of this review is the study of the interplay of the ion-π interactions with other noncovalent forces. The strength of the ion-π interaction is considerably influenced by the presence of hydrogen bonding or other weaker interactions. These influences can be used to tune the interaction, either weakening or strengthening it.We give some experimental examples that illustrate this point. C 2011 John Wiley & Sons, Ltd. WIREs Comput Mol Sci 2011 1 440-459 DOI: 10.1002/wcms.1

Interplay between ion-pi and Ar/pi Van der Waals interactions

[eng] This article analyzes the interplay between cation-pi or anion-pi interactions and Ar/pi Van der Waals interactions. Interesting cooperativity effects are observed when cation-pi/anion-pi and Ar/pi Van der Waals interactions coexist in the same complex. These effects are studied theoretically in terms of energetic and geometric features of the complexes, which are computed by ab initio methods. The symmetryadapted perturbation theory (SAPT) partition scheme was utilized to analyze the different energy contributions to the binding energy and to investigate the physical nature of the interplay between the interactions. By taking advantage of all aforementioned computational methods, the present study examines how these interactions mutually influence each other. Finally, our computational results at the SCS-RI-MP2/aug-cc-pwCVTZ level of theory for the Benzene/Ar complex (D0 = 0.90 kcal/mol and Re = 3.595 Å) are in a very good quantitative agreement with the experimental dissociation energy (0.90 ± 0.02 kcal/mol) and equilibrium distance (3.586 Å)

Interplay between edge-to-face aromatic and hydrogen-bonding interactions

[eng] The interplay between two important noncovalent interactions involving aromatic rings is studied by means of MP2/6-31++G** ab initio calculations. They indicate that synergistic effects are present in complexes where edge-to-face aromatic interactions and hydrogen-bonding interactions coexist. These synergistic effects have been studied bu using the atoms in molecules theory and the molecular interaction potential with polarization partition scheme. Experimental evidence for such interactions has been obtained from the Cambridge Structural Database

A novel fluoride selective optical chemosensor based on internal charge transfer signaling

[eng] A new internal charge transfer probe, NAPH-1, synthesized by incorporating photoemitive naphthalimide core with an acidic imidazolium ring, offers highly selective colorimetric and ratiometric 'off-on' signaling for targeting F-, while Cl-,Br-,I-, HSO4-, SCN-, AcO-, and NO3 do not appreciably perturb the photophysical properties of the probe even at relatively higher concentrations than the F-. Deprotonation of the imidazolium ring, supported by the 1H NMR and theoritical studies, seems to cause the spectral modulations

Interplay between cation-pi and hydrogen bonding interactions

[eng] The interplay between two important non-covalent interactions involving aromatic rings is studied by means of ab initio calculations (MP2/6-31++G**). They demonstrate that synergetic effects are present in complexes where cation-p and hydrogen bonding interactions coexist. These synergetic effects have been studied using the 'atoms-in-molecules' theory and the Molecular Interaction Potential with polarization partition scheme

Is the use of diffuse functions essential for the properly description of noncovalent interactions involving anions?

[eng] It is commonly assumed that theoretical DFT or ab initio calculations involving anions require the utilization of diffuse functions in order to obtain reliable results. In large systems, the use of diffuse functions in the calculations increases the computational cost and, more importantly, sometimes provokes self-consistent-field (SCF) convergence problems, especially in open shell systems. Nowadays, the popular and often used bases for studying noncovalent interactions are the correlation-consistent polarized basis sets of Dunning and co-workers, denoted as cc-pVXZ (X = D, T, etc.), and the Turbomole def2 basis set family (def2-SVP and def2-TZVP). In this paper we study the effect of the utilization of diffuse functions on the energetic and geometric features of several noncovalent complexes, including hydrogen, halogen, and pnicogen bonding, lithium bonds, anion−π interactions, and van der Waals interactions

Long range effects in anion-pi interactions: their crucial role in the inhibition mechanism of Mycobacterium tuberculosis malate synthase

[eng] The glyoxylate shunt is an anaplerotic bypass of the traditional Krebs cycle. It plays a prominent role in Mycobacterium tuberculosis virulence, so it can be exploited for the development of antitubercular therapeutics. The shunt involves two enzymes: isocitrate lyase (ICL) and malate synthase (GlcB). The shunt bypasses two steps of the tricarboxylic acid cycle, allowing the incorporation of carbon, and thus, refilling oxaloacetate under carbon-limiting conditions. The targeting of ICL is complicated; however, GlcB, which accommodates the pantothenate tail of acetyl-CoA in the active site, is easier to target. A catalytic Mg2+ unit is located at the bottom of the cavity, and plays a very important role. Recently, the development of effective antituberculosis drugs based on phenyldiketo acids (PDKAs) has been reported. Interestingly, all the crystal structures of GlcB-inhibitor complexes exhibit close contact between the carboxylate of Asp633 and the face of the aromatic ring of the inhibitor. Remarkably, the replacement of the phenyl ring in PDKA by aliphatic moieties yields inactive inhibitors, suggesting that the aromatic moiety is crucial for inhibition. However, the aromatic ring of PDKA is not electron-deficient, and consequently, the anion-p interaction is expected to be very weak (dominated only by polarization effects). Herein, through a combination analysis of the recent X-ray structures of GlcB-PDKA complexes retrieved from the protein data bank (PDB) and computational ab initio studies (RI-MP2/def2-TZVP level of theory), we demonstrate the prominent role of the Mg2+ ion in the active site, which promotes long-range enhancement of the anion-p interaction

Halogen bonding versus chalcogen and pnicogen bonding: a combined Cambridge structural database and theoretical study

[eng] In this manuscript we analyze the Cambridge Structural Database (CSD) to compare the relative importance of halogen, chalcogen and pnicogen bonding. The three interactions can be explained in terms of electrostatic effects, considering the halogen, chalcogen or pnicogen as a Lewis acid due to the presence of a sigma hole (s-hole). We have studied the behaviour of the three interactions considering two types of Lewis bases: amines and arenes. Combining the CSD search and a comprehensive theoretical study (DFT-D3) we conclude that the halogen bonding interaction is the energetically most favourable when the electron donor is an amine. In contrast, the pnicogen bond is the most favourable if the Lewis base is benzene (pnicogen-p interaction)

Quadrupole Moment versus Molecular Electrostatic Potential: strange behaviour of ethynyl-substituted benzenes

[eng] In this Letter we demonstrate that the quadrupole moment (Qzz) of aromatic compounds shows a strong correlation with the MEP value computed along the main symmetry axis perpendicular to the ring plane. The Qzz value correlates well with both the LUMO energy level and the dipoles created by the substituents. Latter result allows conciliating two different points of view regarding the source of the electrostatic contribution to the total interaction energy ion-p complexes of substituted benzenes. The ethynyl group presents a strange behavior that is analyzed in this Letter, using several tools including MEP and SAPT analysis among others