Noncovalent interactions in catechol/ammonium-rich adhesive motifs: Reassessing the role of cation-π complexes?

Complexes of Alkaline and Ammonium Cations with Dopamine and Eumelanin Precursors: Dissecting the Role of Noncovalent Cation−π and Cation–Lone Pair (σ-Type) Interactions

“…The intermolecular energy curves and landscapes were computed according to the procedure described in previous works ,− and briefly summarized in the following. Unless otherwise stated, the molecular geometries of o -benzoquinone, DHI, and 22Q (see Figure ) were optimized once and for all at the DFT level, using the B3LYP functional with the 6-311G* basis set. The interaction energy Δ E between the cation (C) and the molecule (M) is computed at the mp2 mod level, i.e., employing the MP2 technique with specifically modified basis sets. ,− The low cost and reliability of the method, which allows for a wide yet accurate exploration of the Δ E multidimensional surface, are rooted in the reduced dimensions of the modified basis set, specifically tuned with reference higher level calculations purposely carried out on selected geometries. The modified basis sets were obtained in previous work from the original 6-31G­(d,p) by optimizing the α exponents of the polarization functions. ,,,, Using the notation 6-31G­(α d (C),α d (O),α d (N),α p (H)), the 6-31G­(0.27, 0.34, 0.36) basis set , was employed for the modified exponents of carbon, oxygen, and hydrogen atoms of the o -benzoquinone, whereas 6-31G­(0.27, 0.34, 0.37,0.60) , was used for DHI and 22Q. Conversely, for the considered cations, we have applied the standard def2-TZVPPD for Na + and K + and the 6-311+G­(2d,p) for NH 4 + . , All Δ E calculations were carried out within the supermolecule approach, where the E C–M is the absolute energy of the C–M complex, while E C and E M are those of the separate single C and M units.…”

“…The modified basis sets were obtained in previous work from the original 6-31G­(d,p) by optimizing the α exponents of the polarization functions. ,,,, Using the notation 6-31G­(α d (C),α d (O),α d (N),α p (H)), the 6-31G­(0.27, 0.34, 0.36) basis set , was employed for the modified exponents of carbon, oxygen, and hydrogen atoms of the o -benzoquinone, whereas 6-31G­(0.27, 0.34, 0.37,0.60) , was used for DHI and 22Q. Conversely, for the considered cations, we have applied the standard def2-TZVPPD for Na + and K + and the 6-311+G­(2d,p) for NH 4 + . , All Δ E calculations were carried out within the supermolecule approach, where the E C–M is the absolute energy of the C–M complex, while E C and E M are those of the separate single C and M units. Since absolute energies are negative, a negative value of Δ E indicates a favorable interaction energy.…”

“…The interaction energy Δ E between the cation (C) and the molecule (M) is computed at the mp2 mod level, i.e., employing the MP2 technique with specifically modified basis sets. ,− The low cost and reliability of the method, which allows for a wide yet accurate exploration of the Δ E multidimensional surface, are rooted in the reduced dimensions of the modified basis set, specifically tuned with reference higher level calculations purposely carried out on selected geometries. The modified basis sets were obtained in previous work from the original 6-31G­(d,p) by optimizing the α exponents of the polarization functions. ,,,, Using the notation 6-31G­(α d (C),α d (O),α d (N),α p (H)), the 6-31G­(0.27, 0.34, 0.36) basis set , was employed for the modified exponents of carbon, oxygen, and hydrogen atoms of the o -benzoquinone, whereas 6-31G­(0.27, 0.34, 0.37,0.60) , was used for DHI and 22Q. Conversely, for the considered cations, we have applied the standard def2-TZVPPD for Na + and K + and the 6-311+G­(2d,p) for NH 4 + . , …”

“…The modified basis sets were obtained in previous work from the original 6-31G­(d,p) by optimizing the α exponents of the polarization functions. ,,,, Using the notation 6-31G­(α d (C),α d (O),α d (N),α p (H)), the 6-31G­(0.27, 0.34, 0.36) basis set , was employed for the modified exponents of carbon, oxygen, and hydrogen atoms of the o -benzoquinone, whereas 6-31G­(0.27, 0.34, 0.37,0.60) , was used for DHI and 22Q. Conversely, for the considered cations, we have applied the standard def2-TZVPPD for Na + and K + and the 6-311+G­(2d,p) for NH 4 + . , …”

“…Computational techniques can play an important role in support of the de novo design of such catechol-based biomimetic materials, as they can in principle allow for unraveling the complex supramolecular architectures in terms of specific NCI. Indeed, a growing interest has been devoted in the past decade to setup computational methods suitable for a balanced and accurate description of intermolecular interactions. − Among others, cation−π interactions involving phenolic compounds have been investigated to a certain extent, focusing on complexes between phenol or catechol molecules with metals − or small polyatomic ions, as ammonium and protonated amines. − In this framework, we have also very recently reported − on cation–catechol complexes employing the mp2 mod method, , which allows for computing very accurate interaction energy (Δ E ) landscapes, at a feasible computational cost. The aim of such detailed 2D maps is 2-fold.…”