Stabilizing Fluorine–π Interactions

A series of N-arylimide molecular balances were designed to study and measure fluorine–aromatic (F–π) interactions. Fluorine substituents gave rise to increasingly more stabilizing interactions with more electron-deficient aromatic surfaces. The attractive F–π interaction is electrostatically driven and is stronger than other halogen–π interactions.     

Recognition Interactions of Metal-complexing Imprinted Polymer

Molecularly imprinted polymer, exhibiting considerable enantioselectivity for L-mandelic acid, was prepared using metal coordination-chelation interaction. By evaluating the recognition characteristics in the chromatographic mode, the recognition interactions were proposed: specific and nonspecific metal coordination-chelation interaction and hydrophobic interaction were responsible for substrate binding on metal-complexing imprinted polymer; while the selective recognition only came from specific metal coordination-chelation interaction and specific hydrophobic interaction.     

Interactions of HCl with 1-Butanol and Group Additivity Analysis for the HCl–Alcohol Interactions

An electromotive force (emf) method was used to determine thermodynamic parameters of interaction of HCl with normal 1-butanol (n-BuOH) in water between 5 and 45°C. A comparison of pair interaction parameters for HCl–n-BuOH with those for HCl–t-BuOH (tert butyl alcohol) showed that there is an obvious difference between them. This was interpreted in terms of steric structure of their carbon chains. The group Gibbs free energy parameters ( and ) for the HCl–alcohol–water systems were derived according to the Savage–Wood group additivity principle. These group parameters can be used to evaluate pair interaction parameters of HCl with alcohol molecules.     

Do Deuteriums Form Stronger CH-π Interactions?

The D/H isotope effect for the CH-π interaction was studied experimentally and computationally. First, a series of molecular balances that are very sensitive to changes in the strength of the CH-π interactions in solution were designed. Balances with deuterated and non-deuterated alkyl groups were synthesized, and their intramolecular CH-π interactions were compared. The geometries of their intramolecular CH-π and CD-π interactions were characterized in the solid state by X-ray analysis, and the strength of each interaction was characterized in solution by the folded/unfolded ratio as measured by (1)H NMR spectra. Second, the relative strengths of the CH-π and CD-π interactions were also assessed computationally using dispersion-corrected DFT (PDE-D2/6-31+G*). No significant differencee was observed in either the experimental or theoretical studies, indicating that the D/H isotope effect for the CH-π interaction is either very small or nonexistent.     

Characterization of Molecular Interactions by Inverse Liquid Chromatographic Method

Inverse chromatography (IC) has been widely applied to characterize surface, interface, and bulk characteristics of technologically important materials. Probe molecules with known properties are injected into an isothermal chromatographic system with the material of interest as     

Anagostic Interactions under Pressure: Attractive or Repulsive?

Square‐planar d⁸‐ML₄ complexes might display subtle but noticeable local Lewis acidic sites in axial direction in the valence shell of the metal atom. These sites of local charge depletion provide the electronic prerequisites to establish weakly attractive 3c–2e M⋅⋅⋅H C agostic interactions, in contrast to earlier assumptions. Furthermore, we show that the use of the sign of the ¹H NMR shifts as major criterion to classify M⋅⋅⋅H C interactions as attractive (agostic) or repulsive (anagostic) can be dubious. We therefore suggest a new characterization method to probe the response of these M⋅⋅⋅H C interactions under pressure by combined high pressure IR and diffraction studies.     

Anagostic Interactions under Pressure: Attractive or Repulsive?

Square‐planar d⁸‐ML₄ complexes might display subtle but noticeable local Lewis acidic sites in axial direction in the valence shell of the metal atom. These sites of local charge depletion provide the electronic prerequisites to establish weakly attractive 3c–2e M???H? C agostic interactions, in contrast to earlier assumptions. Furthermore, we show that the use of the sign of the ¹H NMR shifts as major criterion to classify M???H? C interactions as attractive (agostic) or repulsive (anagostic) can be dubious. We therefore suggest a new characterization method to probe the response of these M???H? C interactions under pressure by combined high pressure IR and diffraction studies.     

Monoprotonated Sapphyrin–Pertechnetate Anion Interactions in Aqueous Media

The addition of aqueous pH 7 solutions of 7.2×10^-3?M pertechnetate to dilute aqueous 2.5% MeOH solutions containing a water-solubilized sapphyrin, 3,12,13,22-tetraethyl-8,17-bis[bis(hydroxyethyl)-amino)carbonylethyl]-2,7,18,23-tetramethylsapphyrin (1), gives rise to spectroscopic changes in the UV–Vis spectrum of 1 that are consistent with anion-binding and sapphyrin deaggregation. The spectroscopic changes induced by pertechnetate were found to differ dramatically from those induced by the addition of either pure water or dilute nitric acid; however, they were found to parallel those seen when sodium phosphate was added to solutions of 1 under analogous experimental conditions. Fits of the spectroscopic titration data to a 1:1 binding profile revealed that the effective K describing the interaction of pertechnetate anion with 1 was ca. 3900±300?M^-1; this value compares to the effective K of 23000±3000?M^-1 that describes the corresponding interaction of sodium phosphate with 1.     

Spodium Bonds: Noncovalent Interactions Involving Group 12 Elements

The term spodium (Sp) bond is proposed to refer to a net attractive interaction between any element of Group 12 and electron-rich atoms (Lewis bases or anions). These noncovalent interactions are markedly different from coordination bonds (antibonding Sp–ligand orbital involved). Evidence is provided for the existence of this interaction by calculations at the RI-MP2/aug-cc-pVTZ level of theory, atoms-in-molecules, and natural bond orbital analyses and by examining solid-state structures in the Cambridge Structure Database.     

Characterization of Phenosafranine–Hemoglobin Interactions in Aqueous Solution

Binding of the drug phenosafranine to hemoglobin (Hb) in aqueous solutions was investigated by fluorescence, UV/vis and circular dichroism (CD) spectral methods at pH=7.4. The fluorescence data showed that fluorescence quenching of Hb by phenosafranine is the result of formation of a phenosafranine–Hb complex with a 1:1 molar ratio. Thermodynamic analysis implied that hydrophobic, electrostatic and hydrogen bond interactions are all involved in stabilizing the complex. The molecular distance (r=4.29 nm) between the donor (Hb) and acceptor (phenosafranine) was calculated according to Förster’s theory. The features of phenosafranine-induced secondary structure changes of Hb have been studied by synchronous fluorescence, CD and three-dimensional fluorescence spectroscopy. This study improves our knowledge of the interaction dynamics of phenazinium drugs to the physiologically important protein Hb.     

Fluorine–Fluorine Interactions: NMR and AIM Analysis

The structure of a number of compounds that show experimental FsF coupling constants across the space has been studied using HF-DFT methods (B3LYP) and Atoms in Molecules (AIM) methodologies. For all the cases with strong coupling constants a bond critical point and the corresponding bond path between the fluorine atoms involved has been found in the electron density map. In an attempt to predict NMR properties, new compounds for which no experimental F-F coupling constants are available, but with the same characteristics in the electron density maps, have been calculated.     

Detecting Protein–Glycolipid Interactions Using Glycomicelles and CaR-ESI-MS

This study reports on the use of the catch-and-release electrospray ionization mass spectrometry (CaR-ESI-MS) assay, combined with glycomicelles, as a method for detecting specific interactions between water-soluble proteins and glycolipids (GLs) in aqueous solution. The B subunit homopentamers of cholera toxin (CTB₅) and Shiga toxin type 1 B (Stx1B₅) and the gangliosides GM1, GM2, GM3, GD1a, GD1b, GT1b, and GD2 served as model systems for this study. The CTB₅ exhibits broad specificity for gangliosides and binds to GM1, GM2, GM3, GD1a, GD1b, and GT1b; Stx1B₅ does not recognize gangliosides. The CaR-ESI-MS assay was used to analyze solutions of CTB₅ or Stx1B₅ and individual gangliosides (GM1, GM2, GM3, GD1a, GD1b, GT1b, and GD2) or mixtures thereof. The high affinity interaction of CTB₅ with GM1 was successfully detected. However, the apparent affinity, as determined from the mass spectra, is significantly lower than that of the corresponding pentasaccharide or when GM1 is presented in model membranes such as nanodiscs. Interactions between CTB₅ and the low affinity gangliosides GD1a, GD1b, and GT1b, as well as GD2, which served as a negative control, were detected; no binding of CTB₅ to GM2 or GM3 was observed. The CaR-ESI-MS results obtained for Stx1B₅ reveal that nonspecific protein-ganglioside binding can occur during the ESI process, although the extent of binding varies between gangliosides. Consequently, interactions detected for CTB₅ with GD1a, GD1b, and GT1b are likely nonspecific in origin. Taken together, these results reveal that the CaR-ESI-MS/glycomicelle approach for detecting protein–GL interactions is prone to false positives and false negatives and must be used with caution.

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Bondings and Interactions in Fe-CO:Pairing versus Unpairing Mechanism

Therehavebeenagreatdealofexperimenta1aswellastheoreticaleffortsincharacterizingthenatureofbondingsandinteractionsintheM-COIS[l'2].ItisnowgenerallyacceptedthattheM-CObondingismainlyduetothettbackdonationfromthemetald.orbitalstotheCO2x*andthemetal-COa..interactionisrepu1sive[3].AsshownbyBlombergetal,anefficientwaytoreducethisarepulsionisthe4s-3d.hybridization[41.SofarasFe-COmolecuIeisconcerned-therearealargenumberofpaperspubIished[1'2].ThetwolowestelectronicstatesofFe-COarepredictedtobe…     

An Exceptional Peroxide Birefringent Material Resulting from d–π Interactions

Birefringent materials, which can modulate the polarization of light, are almost exclusively limited to oxides. Peroxides have long been overlooked as birefringent materials, because they are usually not stable in air. Now, the first peroxide birefringent material Rb₂VO(O₂)₂F is reported, the single crystals of which keep transparency after being exposed in the air for two weeks. Interestingly, Rb₂VO(O₂)₂F does not feature an optimal anisotropic structure, but its birefringence (Δn=0.189 at 546 nm) exceeds those of the majority of oxides. According to the first-principles calculations, this exceptional birefringence should be attributed to the strong electronic interactions between localized π orbital of O₂²⁻ anions and V⁵⁺ 3d orbitals, which may be also favorable to the stability in the air for Rb₂VO(O₂)₂F. These findings distinguish peroxides as a brand-new class of birefringent materials that may possess birefringence superior to the traditional oxides.     

Aryl–Aryl Interactions in (Aryl-Perhalogenated) 1,2-Diaryldisilanes

Three 1,2-diaryltetramethyldisilanes X₅C₆-(SiMe₂)₂-C₆X₅ with two C₆H₅, C₆F₅, or C₆Cl₅ groups were studied concerning the importance of London dispersion driven interactions between their aryl groups. They were prepared from 1,2-dichlorotetramethyldisilane by salt elimination. Their structures were determined in the solid state by X-ray diffraction and for free molecules by gas electron-diffraction. The solid-state structures of the fluorinated and chlorinated derivatives are dominated by aryl–aryl interactions. Unexpectedly, Cl₅C₆-(SiMe₂)₂-C₆Cl₅ exists exclusively as an eclipsed syn-conformer in the gas phase with strongly distorted Si-C₆Cl₅ units due to strong intramolecular interactions. In contrast, F₅C₆-(SiMe₂)₂-C₆F₅ reveals weaker interactions. The contributions to the total interaction energy were analyzed by SAPT calculations.