Secondary Electrostatic Interaction Model Revised: Prediction Comes Mainly from Measuring Charge Accumulation in Hydrogen-Bonded Monomers

Abstract

The secondary electrostatic interaction (SEI) model is often used to predict and explain relative hydrogen bond strengths of self-assembled systems. The SEI model oversimplifies the hydrogen-bonding mechanisms by viewing them as interacting point charges, but nevertheless experimental binding strengths are often in line with the model’s predictions. To understand how this rudimentary model can be predictive, we computationally studied two tautomeric quadruple hydrogen-bonded systems, DDAA-AADD and DADA-ADAD. Our results reveal that when the proton donors D (which are electron-donating) and the proton acceptors A (which are electron-withdrawing) are grouped together as in DDAA, there is a larger accumulation of charge around the frontier atoms than when the proton donor and acceptor groups are alternating as in DADA. This accumulation of charge makes the proton donors more positive and the proton acceptors more negative, which enhances both the electrostatic and covalent interactions in the DDAA dimer. The SEI model is thus predictive because it provides a measure for the charge accumulation in hydrogen-bonded monomers. Our findings can be understood from simple physical organic chemistry principles and provide supramolecular chemists with meaningful understanding for tuning hydrogen bond strengths and thus for controlling the properties of self-assembled systems.

The Nature of Hydrogen Bonds: A Delineation of the Role of Different Energy Components on Hydrogen Bond Strengths and Lengths

“…However,t here are also cases in which this dipole-dipole interpretation fails to explain the geometricala nd energetic trends, such as the nonlinearity of the HF dimer [14] or the large energetic differences between dimers with similard ipole moments. [10] More recently,T iwari and Vanka [25] proposed to use the electrostatic force (whichh as directionality) rathert han the electrostatic interaction for the description of noncovalent interactions. Good correlations were found between the electrostatic forces and the binding energy for aw ide range of systems, including 28 base pairs that were studied in ref.…”

“…[75][76][77][78][79] When these factorsa re comparable, the dispersion interactions are usually of similar strength. [10,76] However,w hen one or more of these factors are significantly different, dispersion might even determine the trend in interaction strength.T hisw as shown by Hoja et al by studying( XOH) 2 with X = H, Me, Et, nPr, nBu, iPr and tBu. [76] They found that the interaction energy between two H-bonded monomers becomes 58 %s tronger when going from the smallest dimer (H 2 O) 2 to the bulkiest dimer (tBuOH) 2 (Figure 7).…”

“…Despitet hese valid criticisms, experimental binding strengthsa re often in line with the model's predictions. [10,86,87] Recently,w es howed that this predictive power can be understood from the charges eparationi nt he monomers. [10] When HB donor atoms (whicha re electron donating in nature) are grouped, there is al arger accumulation of positive charge aroundt heir frontier atoms.…”

“…[10,86,87] Recently,w es howed that this predictive power can be understood from the charges eparationi nt he monomers. [10] When HB donor atoms (whicha re electron donating in nature) are grouped, there is al arger accumulation of positive charge aroundt heir frontier atoms. Likewise, whenH Ba cceptora toms (which are electron withdrawing in nature)a re grouped,t here is al arger accumulation of negative chargea roundt heir frontier atoms (Figure 8).…”

Supramolecular Architecture in a Ni(II) Complex with a Weakly Bonded N,N′-(1,4-phenylenedi- carbonyl)Diglycinate Counter-Anion: Crystal Structure Investigation and Hirshfeld Surface Analysis

“…(Figures 3 and 5). The two water molecules coordinated by the Ni II atom and hydrogen bonded to the carboxylate show an attractive secondary electrostatic interaction [44,45] in the formed hydrogen-bonding pattern. The arrangement is similar to that found in the hydrogen bonded complex between the guanine and cytosine of nucleic acids [44,46].…”