Intermolecular noncovalent interactions with carbon in solution
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One of the most familiar carbon-centered noncovalent interactions (NCIs) involving an antibonding π*-orbital situated at the Bürgi-Dunitz angle from the electron donor, mostly lone pairs of electrons, is known as n → π* interactions, and if it involves a σ* orbital in a linear fashion, then it is known as the carbon bond. These NCIs can be intra- or inter-molecular and are usually weak in strength but have a paramount effect on the structure and function of small-molecular crystals and proteins. Surprisingly, the experimental evidence of such interactions in the solution phase is scarce. It is even difficult to determine the interaction energy in the solution. Using NMR spectroscopy aided with molecular dynamics (MD) simulation and high-level quantum mechanical calculations, herein we provide the experimental evidence of intermolecular carbon-centered NCIs in solution. The challenge was to find appropriate heterodimers that could sustain room temperature thermal energy and collisions from the solvent molecules. However, after several trial model compounds, the pyridine-N-oxide:dimethyltetracyanocyclopropane (PNO-DMTCCP) complex was found to be a good candidate for the investigation. NBO analyses show that the PNO:DMTCCP complex is stabilized mainly by intermolecular n → π* interaction when a weaker carbon bond gives extra stability to the complex. From the NMR study, it is observed that the NCIs between DMTCCP and PNO are enthalpy driven with an enthalpy change of -28.12 kJ mol-1 and dimerization energy of ∼-38 kJ mol-1 is comparable to the binding energies of a conventional hydrogen-bonded dimer. This study opens up a new strategy to investigate weak intermolecular interactions such as n → π* interaction and carbon bonds in the solution phase.Keywords:
Intermolecular interaction
Non-covalent interactions
Energetics
Carbon fibers
This paper introduces a new approach to probing intermolecular interactions based on a framework of two-dimensional (2D) synchronous spectroscopy. Mathematical analysis performed on 2D synchronous spectra using variable concentration as an external perturbation shows that the cross-peaks are composed of two parts. The first part reflects intermolecular interactions that manifest in the form of deviation from the Beer–Lambert law. The second part is related simply to the concentration variations of the solutes and is responsible for the generation of interfering cross-peaks not related to the intermolecular interactions in the system. It is the second part that prevents the reliable identification of intermolecular interactions. We propose a way of selecting the concentrations of solutes so that the resultant dynamic concentration vectors of different solutes become orthogonal to one another. Therefore, the contribution of the second part to the cross-peaks can be effectively removed by the dot product of orthogonal vectors. Our new approach has been tested on a simulated chemical system and a real chemical system. The results demonstrate that interfering cross-peaks can be successfully removed from a 2D synchronous spectrum so that the cross-peaks can be used as a reliable tool to characterize or probe intermolecular interactions.
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While virgin and aged binders are blended together, the old molecular associations of binders may be broken and new ones rebuilt due to intermolecular interactions. In this study, the intermolecular interactions between virgin and aged binders were investigated using Gel Permeation Chromatography (GPC). Results indicate that intermolecular interactions occurred between virgin and aged binders when virgin and aged binders were blended together in solvent. The factors affecting the degree of interaction included difference in chemical composition between the two binders, aged binder content, and molecular size. The degree of intermolecular interaction increased with the increase in the difference in chemical structure between virgin and aged binders. The intermolecular interactions were more likely to happen between large molecules than other molecules. For large and medium molecules, it is found that there was a good liner relationship between the degree of their intermolecular interaction and the aged binder content.
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One of the most familiar carbon-centered noncovalent interactions (NCIs) involving an antibonding π*-orbital situated at the Bürgi-Dunitz angle from the electron donor, mostly lone pairs of electrons, is known as n → π* interactions, and if it involves a σ* orbital in a linear fashion, then it is known as the carbon bond. These NCIs can be intra- or inter-molecular and are usually weak in strength but have a paramount effect on the structure and function of small-molecular crystals and proteins. Surprisingly, the experimental evidence of such interactions in the solution phase is scarce. It is even difficult to determine the interaction energy in the solution. Using NMR spectroscopy aided with molecular dynamics (MD) simulation and high-level quantum mechanical calculations, herein we provide the experimental evidence of intermolecular carbon-centered NCIs in solution. The challenge was to find appropriate heterodimers that could sustain room temperature thermal energy and collisions from the solvent molecules. However, after several trial model compounds, the pyridine-N-oxide:dimethyltetracyanocyclopropane (PNO-DMTCCP) complex was found to be a good candidate for the investigation. NBO analyses show that the PNO:DMTCCP complex is stabilized mainly by intermolecular n → π* interaction when a weaker carbon bond gives extra stability to the complex. From the NMR study, it is observed that the NCIs between DMTCCP and PNO are enthalpy driven with an enthalpy change of -28.12 kJ mol-1 and dimerization energy of ∼-38 kJ mol-1 is comparable to the binding energies of a conventional hydrogen-bonded dimer. This study opens up a new strategy to investigate weak intermolecular interactions such as n → π* interaction and carbon bonds in the solution phase.
Intermolecular interaction
Non-covalent interactions
Energetics
Carbon fibers
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The systematic ab initio studies of intermolecular interaction energy components in the model unsaturated hydrocarbon complexes have been performed. The influence of the weak intermolecular interactions on the optical properties has been analyzed within the supermolecular approach. The estimated interaction energy components and electric properties of the studied systems indicate the substantial influence of the intermolecular forces on the optical response of the studied systems. The obtained results could be important for understanding the properties of the organic materials exploited for the purposes of the nonlinear optics.
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The role of noncovalent gold–hydrogen and aurophilic interactions in the formation of extended molecular systems of gold complexes was studied. Three new gold compounds with a heterocyclic thione ligand N-methylbenzothiazole-2-thione (mbtt), namely, [AuCl(mbtt)] (1), [AuBr(mbtt)] (2), and [Au(mbtt)2][AuI2]1–n[I3]n (3), were synthesized and characterized. The halide ligand had a considerable effect on the complex structures and thus to noncovalent contacts. Intermolecular C–H···Au and aurophilic Au···Au contacts were the dominant noncovalent interactions in structures 1–3 determining the supramolecular arrays of the gold complexes. In 1 and 2, unusual intermolecular C–H···Au gold–hydrogen contacts linked the adjacent mononuclear molecules to a chain structure, while in 3 the change in the ligand coordination induced the formation of an intermolecular aurophilic interaction. Au···I, π–π, halogen–halogen, and hydrogen bonding interactions supported further the supramolecular array of 3. The interactions were analyzed with theoretical calculations using the Quantum Theory of Atoms in Molecules (QTAIM). The results thus obtained were consistent with the experimental data clarifying both the nature and the role of noncovalent interactions in structures 1–3.
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Halogen bond
Atoms in molecules
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Abstract Closely related structures, like esters and lactones, have vastly different physical properties. This is apparently due to differences in the intermolecular interactions. The intermolecular interactions of methyl acetate, β‐propiolactone, ethyl acetate, and γ‐butyrolactone have been studied using the AM1 semiempirical method. Some of the “arranged clusters” were also compared to possible covalently bound trimers and tetramers of β‐propiolactone and γ‐butyrolactone. © 1992 John Wiley & Sons, Inc.
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