Weak Interaction Energies Research Articles

Chiral fluorescent carbon dots for tyrosine enantiomers: Discrimination, mechanism and cell imaging

The development of chiral analytical methods for tyrosine enantiomers, characterized by superior recognition performance and selectivity, holds significant potential for application in the biochemical and biomedical domains associated with tyrosine. Herein, a straightforward and effective strategy for tyrosine enantiomers identification and purity analysis by chiral carbon dots (CDs) fluorescence sensor were reported. The chiral CDs were designed by using L-cysteine and 2,4-diaminophenol hydrochloride through a gentle one-step synthesis strategy at room temperature. The resulting chiral CDs exhibited completely different fluorescence response to L-tyrosine and D-tyrosine, that is, L-tyrosine could enhance the fluorescence of the chiral CDs, but D-tyrosine made no difference. The fluorescent differential recognition factor for enantiomers was as high as 23.2, which was the highest be achievement to our best knowledge so far. The varying discriminatory capabilities of chiral CDs towards tyrosine enantiomers were also applicable to HeLa cells. To confirm the recognition mechanism of chiral CDs to tyrosine enantiomers, the chiral CDs-modified SiO2 stationary phase were synthesized and applied to separate the tyrosine enantiomers in reverse-phase HPLC mode. Furthermore, density functional theory was combined with the fluorescence spectroscopy and chromatographic results to verify that the recognition ability was related to the difference of weak interaction energy and Gibbs free energy between the precursor molecule of the chiral CDs and the tyrosine enantiomers. This cost-effective and highly selectivity assay not only provided a valuable tool for tyrosine enantiomers identification and purity analysis, but also delivered an important reference for the recognition and purity identification of other chiral drugs.

Understanding the adsorption properties of CO2 and N2 by a typical MOF structure: Molecular dynamics and weak interaction visualization

An extensible molecular dynamics (MD) force field for a typical metal–organic framework (MOF) has been developed and verified in comparison with experimental data. The visualization of the important weak interactions based on density functional theory (DFT) calculations is performed. The dynamic process of CO2 and N2 adsorption by MOF was then studied by MD methods. The gas adsorption and desorption during temperature and pressure swing were also investigated. It is found that the structural features of MOF have an important effect on the regional range and strength of the weak interactions, and the region of the van der Waals potential surface of the MOF can determine the gas density distribution. The adsorption is dominated by van der Waals interactions on the whole and the variation of the total weak interaction energy can reflect that of the adsorbed amount. The sorption/desorption responds more slowly to temperature swing than to pressure swing.

Electrolyte Dependence of Li+ Transport Mechanisms in Small Molecule Solvents from Classical Molecular Dynamics.

As demands on Li-ion battery performance increase, the need for electrolytes with high ionic conductivity and a high Li+ transference number (tLi) becomes crucial to boost power density. Unfortunately, tLi in liquid electrolytes is typically <0.5 due to Li+ migrating via a vehicular mechanism, whereby Li+ diffuses along with its solvation shell, making its diffusivity slower than the counteranion. Designing liquid electrolytes where the Li+ ion diffuses independently of its solvation shell is of significant interest to enhance the transference number. In this work, we elucidate how the properties of the solvent influence the Li+ transport mechanism. Using classical molecular dynamics simulations, we find that a vehicular mechanism can be increasingly preferred with a decreasing solvent viscosity and increasing interaction energy between the solvent and Li+. Thus, a weaker interaction energy can enhance tLi through a solvent-exchange mechanism, ultimately improving Li-ion battery performance. Finally, metadynamics simulations show that in electrolytes where a solvent-exchange mechanism is preferable, the energy barrier to changing the coordination environment of Li+ is much lower than in electrolytes where a vehicular mechanism dominates.

Is there a Covalent Au(I)-Au(I) Bond in the trans-(AuX)2 (X = F, Cl, Br, I) Structure? A Post-Hartree-Fock and Density Functional Theory Study.

We present an exhaustive exploration of the driving forces dominating the interaction between gold atoms in the trans-(AuX)2, where X is a halogen ligand. This work provides insights into the nature of the gold-gold contact in the trans-(AuX)2. The geometries and energies were calculated at the MP2, CCSD(T), and DFT-D3(BJ) (B3LYP, PBE, and TPSS) levels of theory. The results show a short Au-Au distance, typical of a covalent bond, but with a weak interaction energy associated with noncovalent interactions. It is established that the physical contributions from polarization and the electronic correlation forces are the most relevant at the post-Hartree-Fock level of theory. Also, the electrostatic term is attractive but with low contribution. Finally, the Wiberg indices and NBO analysis exposed a small covalent character between the gold atoms, revealing that this contribution is insufficient to explain the stability of the dimers. It is concluded that a sum of contributions makes it possible to establish an attraction between the gold atoms in the dimers studied beyond a classical aurophilic interaction.

Polymer‐supported Quaternary Phosphonium Ionic Liquid Catalysts for Efficient Fixation of CO2 into Cyclic Carbonates

AbstractThe chemical conversion of CO2 into cyclic carbonate is an effective method for the resource utilization of CO2 and the production of cyclic carbonates. Herein, a series of polymer‐supported quaternary phosphonium ionic liquid catalysts with high grafting amount have been systematically designed and synthesized, and all catalysts could promote efficient fixation of CO2 into cyclic carbonate. According to the results of the experiment and simulation, it was found that the high catalytic activity was ascribed to the weak interaction energy of the anion and cation of the catalyst. Among them, PS−TPP−Cl, with lower interaction energy of 72.2 KJ/mol, showed better performance. Yet even after being recycled five times, its conversion of propylene oxide with little loss was still above 95 %. Furthermore, a possible cycloaddition mechanism for the synergetic effect of cation‐anion coordination has been proposed. This work will shed new light on the development of novel heterogeneous catalysts with promising properties for industrial applications.

Simple, Efficient, and Universal Energy Decomposition Analysis Method Based on Dispersion-Corrected Density Functional Theory.

Energy decomposition analysis (EDA) is an important class of methods to explore the nature of interaction between fragments in a chemical system. It can decompose the interaction energy into different physical components to understand the factors that play key roles in the interaction. This work proposes an EDA strategy based on dispersion-corrected density functional theory (DFT), called sobEDA. This method is fairly easy to implement and very universal. It can be used to study weak interactions, chemical bond interactions, open-shell systems, and interactions between multiple fragments. The total time consumption of sobEDA is only about twice that of conventional DFT single-point calculation for the entire system. This work also proposes a variant of the sobEDA method named sobEDAw, which is designed specifically for decomposing weak interaction energies. Through a proper combination of DFT correlation energy and dispersion correction term, sobEDAw gives a ratio between dispersion energy and electrostatic energy that is highly consistent with the symmetry-adapted perturbation theory, which is quite popular and robust in studying weak interactions but expensive. We present a shell script sobEDA.sh to implement the methods proposed in this work based on the very popular Gaussian quantum chemistry program and Multiwfn wavefunction analysis code. Via the script, theoretical chemists can use the sobEDA and sobEDAw methods very conveniently in their study. Through a series of examples, the rationality of the new methods and their implementation are verified, and their great practical values in the study of various chemical systems are demonstrated.

The van der Waals interaction and absorption and electron circular dichroism spectra of two-dimensional bilayer stacked structures

van der Waals (vdW) heterojunctions based on two-dimensional (2D) materials, graphene and transition metal dichalcogenides (TMDs), are a research hotspot for future optoelectronic and exciton devices. Bond-free vdW interactions are key to 2D material heterojunction device reliability and stability. However, most of the current research on 2D stacked materials heterostructures mainly focuses on optical properties and electronic structure. Furthermore, vdW interaction in 2D heterostructures is studied and understood on the basis of qualitative description and energy ranges from the literature. There are few studies on the nature of vdW interaction based on practical calculations of the quantitative strength and microscopic mechanism of vdW interaction between 2D stacked materials. Therefore, this paper explores the vdW interaction between 2D material stacked bilayer structures, including bilayer graphene, graphene/MoS2 and graphene/WS2 heterostructures, focusing on quantitative analysis of the energy components of the vdW interaction. We first visually observed the weak interactions in the three stacked bilayer structures through noncovalent interaction (NCI) analysis, and found that the interactions are concentrated in the binding region between the two-layer structures. We mainly decomposed the weak interaction energy in the three 2D material bilayer heterostructures through energy decomposition analysis based on the force field (EDA-FF) method and obtained the energy values and proportions of the three components-electrostatic energy, exchange repulsion energy and dispersion energy of the total binding energy between the 2D stacked bilayer structures. The vdW interaction energy is the sum of the exchange repulsion energy and dispersion energy, and the dispersion energy of the vdW interaction accounts for more than 60% of the binding energy of the weak interaction between the 2D bilayer stacked structures. The vdW strengths in the bilayer structures are on the order of 177.07, 123.85, and 133.93 kJ/mol, approxmately 1–2 orders of magnitude larger than the classically defined vdW energies of 0.1–10 kJ/mol. Furthermore, we calculate the density of states of the three 2D stacked structures, and further obtained HOMO-LOMO information; to further understand the electronic structures of the graphene/MoS2 and graphene/WS2 heterostructures, we calculated their optical absorption spectra and electron circular dichroism (ECD) spectra. According to the calculation results, the two heterostructures have strong absorption peaks in the visible region, and the charge transfer forms at the strong absorption peak can be determined according to the charge transfer diagram. The ECD spectra indicate that the configurations of the graphene/MoS2 and graphene/WS2 heterostructures have large chirality. Our work contributes to a deeper understanding of the nature of the weak interactions and optical properties in 2D stacked materials, which plays a fundamental role in promoting the construction of stable 2D heterostructure configurations and the development of multifunctional 2D devices. The research is conducive to further promoting the basic research and practical development of strong optoelectronic and excitonic 2D heterojunctions devices.

Molecular Dynamics Simulation Study on Thermal Transport in Graphyne/Polyaniline Composite System

AbstractGraphyne (GY) is a new carbon material with excellent electrical conductivity and low thermal conductivity (TC). The doping of GY into polymers to improve the thermoelectric properties of the material has become a hot research trend. In this study, molecular dynamics (MD) and nonequilibrium MD are used to study the effect of the number of oxidation units of polyaniline (PANI) on TC and heat transfer of PANI and GY/PANI systems. The geometric structure of polymer, interaction energy, and heat transport of all systems are studied and analyzed. It is found that (1) as the number of oxidation units of PANI increases, the interchain and intrachain heat transfers of PANI are decreased thereby decreasing the heat transfer of the PANI chains; (2) the weak interaction energy at the interface hinders the heat flux transfer, and the phonon vibration of GY and PANI mismatch at the interfaces; eventually the above reasons lead to low interface TC; (3) the doping of GY can effectively reduce the TC of the system. This study provides some research ideas and theoretical exploration for the application of polymer doped with GY composites in the field of thermoelectricity.

Modeling of an Er3+-Doped ZBLAN Fiber Laser With Ion Clustering Effect

In this study, we proposed a numerical model incorporating ion clustering effect for an Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped ZBLAN fiber laser. Our proposed model does not use weak-interaction (WI) energy transfer parameters, instead, it is based on two separate rate equations for isolated and clustered ions, respectively, using conventional ionic interaction parameters, unlike the previously proposed WI model. We verified the efficacy of our proposed model by comparing the numerically calculated output curves with the experimentally measured ones in a Fabry-Pérot laser setup based on two different lengths of commercially available Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped ZBLAN fiber. The proposed model can readily provide an accurate prediction of the laser output performance without using WI energy transfer parameters. In addition, with the numerical calculation of the model, the relative number of clustered ions in a commercial ZBLAN fiber was indirectly found to be ∼18.1%. Lastly, we compared the calculation results of our model with those with strong-interaction (SI) and WI model, which are commonly used for Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped ZBLAN fiber lasers.

Electrochemical and CD-spectroelectrochemical studies of the interaction between BSA and the complex [Cu(Bztpen)]2+, (Bztpen = (N-benzyl-N, N′, N′-tris (pyridin-2-ylmethyl) ethylenediamine)

In this work we report the electrochemical, spectroscopical and spectro-electrochemical studies of a model complex [CuΙΙ(Bztpen)]2+, (Bztpen = (N-benzyl-N,N′,N′-tris(pyridin-2-ylmethyl)ethylenediamine) in order to propose a methodology to evaluate the interaction of potential metal based anticancer agents during electron transfer processes, with transport proteins such as Bovine Serum Albumin (BSA). It was possible to establish a reversible electron transfer [CuΙΙ(Bztpen)]2+ +1e → [CuΙ(Bztpen)]+ and a weak interaction energy between BSA and [CuΙΙ(Bztpen)] and [CuΙ(Bztpen)] species, with no adsorption of protein over the electrode surface. Circular Dichroism (CD) Spectroelectrochemistry, not reported before, reveals no significant changes in BSA structure during the electron transfer [CuΙΙ(Bztpen)]2+ + 1e → [CuΙ(Bztpen)]+. CD experiments at variable temperature for BSA denaturalization in the absence and in the presence of [CuΙΙ(Bztpen)]2+, shown no change in thermodynamic parameters due to low interaction between the transport protein and copper complex.

Carbon Material With Ordered Sub-Nanometer Hole Defects.

A holey carbon material with ordered sub-nanometer hole defects was synthesized from oxidative cyclodehydrogenation of a polyhexaphenylbenzene precursor. Band gap of around 2.2 eV is formed due to the narrow connection between the hexabenzocoronene subunits. It has weak interlayer interaction energy compared with graphene and shows easy dispersion in a wide range of solvents, surprisingly including water. Density functional theory calculations confirmd the excellent dispersion of this material in water. This new carbon material was then proved as effective support for various inorganic nanoparticles of small sizes. The supported iron nanoparticles showed enzyme-like catalysis behavior in nitrophenyl reduction reaction by NaBH4, exemplifying the great potential of this new material in catalysis.

Molecular dynamics study of droplet electrocoalescence in the oil phase and the gas phase

• Dispersive attraction and steric effect of oil molecules affect droplet coalescence. • Solvent accessible surface area could determine when droplets contact and coalesce. • The migration of molecules causes uneven distribution of charges in water droplets. • The electro-coalescence behavior of droplets in oil and gas are highly similar. Under a uniform electric field, water droplets in a water-in-oil (W/O) emulsion approach and coalesce by dipole–dipole forces, which fundamentally affect the efficiency of electric dehydration. In order to unravel the molecular mechanism of droplet electrocoalescence, we explored the coalescence behavior of droplets in the oil phase and the simplified oil phase (nitrogen) under an external electric field using molecular dynamics (MD) simulations. The results indicated that the coalescence process of droplets can be divided into three stages based on the solvent accessible surface area (SASA), before coalescence, coalescing and after coalescence. The two droplets completely coalesced when the center-of-mass distance between droplets was 2.73 nm. Weak interaction and interaction energy analysis revealed that the electrostatic attraction between water molecules dominated the coalescence process of water droplets due to the significant characteristics of electrostatic potential (ESP). The dispersion attraction of C 6 H 14 H 2 O and C 6 H 14 C 6 H 14 was very pronounced while the interactions related to nitrogen molecules were negligible, which was the underlying reason for the differences between droplet coalescence behaviors in the two media. Nevertheless, the coalescence behaviors of a droplet pair in oil and gas had a high level of similarity, which implied that the MD simulation results of the electric coalescence based on nitrogen is acceptable to some extent. The field-induced hydrogen and oxygen atoms migrated toward both ends of the droplet, causing the redistribution of charges and changing the overall dipole moment of the droplets. This study made it possible to use oil-phase molecules for MD simulation study on the electrostatic coalescence behavior of droplets in the W/O emulsion, and confirmed the feasibility of nitrogen replacing with the oil phase.

Probing the molecular basis for sulfonamides recognition in surface molecularly imprinted polymers using computational and experimental approaches

The computer-aided design of surface molecularly imprinted polymers (SMIPs) of sulfadimethoxine (SDM) using methacrylic acid (MAA), 4-vinylpyridine (4-VP) or 4-aminostyrene (AS) as functional monomers was performed using Gaussian software, and the corresponding materials were innovatively prepared by surface-initiated supplemental activator and reducing agent atom transfer radical polymerization (SI-SARA ATRP) using an Fe(0)/Cu(II) catalytic system. Sulfonamides were selected as template molecules because of their stable nuclear parent and regular side chain changes, which could help explore the molecular mechanism of imprinting and recognition from the perspective of structural differences. The imprinted systems were calculated using Gaussian software to obtain parameters related to intermolecular interactions. The morphology and physicochemical properties of SMIPs were determined by scanning electron microscope (SEM), oxygen bomb combustion-ion chromatography (OBC-IC) and thermogravimetric analyzer (TGA). The relevant adsorption mechanism was evaluated using the Langmuir–Freundlich (LF) isotherm. The adsorption capacities (Q) of the three SMIPs for nine other sulfonamides were evaluated by experiments, and the weak interaction energy between other sulfonamide molecules and the molecularly imprinted pores generated by SDM was simulated. Compared with the two other functional monomers, MAA demonstrated advantages in Q, pore uniformity, and imprinting factor. Weak interaction energies between the drug and functional monomer, as the main influencing factor, and steric hindrance as a secondary factor, influenced the Q, difficulty of template elution, and selective adsorption of the polymers for the nine other sulfonamides. Quantum chemical calculation data revealed that the number of hydrogen bonds generated, the participation of other weak interactions, and the charge of hydrogen bond donors had great influence on the weak interaction energy.

Stabilizing Role of Water Solvation on Anion−π Interactions in Proteins

In this work, anion−π interactions between sulfate groups (SO42–) and protein aromatic amino acids (AAs) (histidine protonated (HisP), histidine neutral (HisN), tyrosine (Tyr), tryptophan (Trp), and phenylalanine (Phe)) in an aqueous environment have been analyzed using quantum chemical (QC) calculations and molecular dynamics (MD) simulations. Sulfates can occur naturally in solution and can be contained in biomolecules playing relevant roles in their biological function. In particular, the presence of sulfate groups in glycosaminoglycans such as heparin and heparan sulfate has been shown to be relevant for protein and cellular communication and, consequently, for tissue regeneration. Therefore, anion−π interactions between sulfate groups and aromatic residues represent a relevant aspect to investigate. QC results show that such an anion−π mode of interaction between SO42– and aromatic AAs is only possible in the presence of water molecules, in the absence of any other cooperative non-covalent interactions. Protonated histidine stands out in terms of its enhancement in the magnitude of interaction strength on solvation. Other AAs such as non-protonated histidine, tyrosine, and phenylalanine can stabilize anion−π interactions on solvation, albeit with weak interaction energy. Tryptophan does not exhibit any anion−π mode of interaction with SO42–. The order of magnitude of the interaction of aromatic AAs with SO42– on microsolvation is HisP > HisN > Tyr > Trp > Phe. Atoms in molecules (AIM) analysis illustrates the significance of water molecules in stabilizing the divalent SO42– anion over the π surface of the aromatic AAs. MD simulation analysis shows that the order of magnitude of the interaction of SO42– with aromatic AAs in macroscopic solvation is HisP > HisN, Tyr, Trp > Phe, which is very much in line with the QC results. Spatial distribution function analysis illustrates that protonated histidine alone is capable of establishing the anion−π interaction with SO42– in the solution phase. This study sheds light on the understanding of anion−π interactions between SO42– and aromatic AAs such as His and Tyr observed in protein crystal structures and the significance of water molecules in stabilizing such interactions, which is not feasible otherwise.

Cisplatin uptake and release in pH sensitive zeolitic imidazole frameworks

Cancer remains hard to treat, partially due to the non-specificity of chemotherapeutics. Metal-organic frameworks (MOFs) are promising carriers for targeted chemotherapy, yet, to date, there have been few detailed studies to systematically enhance drug loading while maintaining controlled release. In this work, we investigate which molecular simulation methods best capture the experimental uptake and release of cisplatin from UiO-66 and UiO-66(NH2). We then screen a series of biocompatible, pH-sensitive zeolitic imidazolate frameworks (ZIFs) for their ability to retain cisplatin in healthy parts of the patient and release it in the vicinity of a tumor. Pure-component GCMC simulations show that the maximum cisplatin loading depends on the pore volume. To achieve this maximum loading in the presence of water, either the pore size needs to be large enough to occupy both cisplatin and its solvation shell or the MOF-cisplatin interaction must be more favorable than the cisplatin-shell interaction. Both solvated and non-solvated simulations show that cisplatin release rates can be controlled by either decreasing the pore limiting diameters or by manipulating framework-cisplatin interaction energies to create strong, dispersed adsorption sites. The latter method is preferable if cisplatin loading is performed from solution into a pre-synthesized framework as weak interaction energies and small pore window diameters will hinder cisplatin uptake. Here, ZIF-82 is most promising. If it is possible to load cisplatin during crystallization, ZIF-11 would outcompete the other MOFs screened as cisplatin cannot pass through its pore windows; therefore, release rates would be purely driven by the pH triggered framework degradation.

Modeling the aluminum-doped and single vacancy blue phosphorene interactions with molecules: a density functional theory study.

Structural, electronic, binding energies and magnetic properties of aluminum-doped and single vacancy blue phosphorene interacting with pollutant molecules are investigated using the density functional theory (DFT) with periodic boundary conditions. Acetylene, ozone, sulfur trioxide, hydrogen selenide, and sulfur dichloride molecules are considered to show the efficiency and enhancement of the sensing properties in comparison with the pristine blue phosphorene. Acetylene, sulfur trioxide, hydrogen selenide, and sulfur dichloride show chemisorption (> 0.5eV/molecule) when interacting with the aluminum-doped system, but the ozone molecule dissociates in all configurations and symmetry sites. On the other hand, the acetylene, ozone, and sulfur trioxide with the single vacancy blue phosphorene exhibit chemisorption, the hydrogen selenide molecule exhibit a weak interaction energy, and the sulfur dichloride dissociates in all configurations and symmetry sites. In all the cases, the enhancement in the interaction energy was achieved when compared to other results for the same molecules. Finally, the single vacancy blue phosphorene shows a magnetic moment of ~1 μB/supercell, as induced by the vacancy.

Integrating redox-response in crown ethers by disulfide incorporation: a computational approach

Reducing properties are investigated for the minimum energy conformers of selected thiacrown systems with redox-responsive disulfide linkage. The adiabatic electron affinity values of the investigated host systems in the gas phase lie in a range that makes them capable to undergo reversible redox reactions. In water, these show a high propensity to get reduced. Their binding energy with different alkali metal ions (Li+, Na+, and K+) is also determined under gas and aqueous phase conditions. The computational analysis reveals the weak metal binding interactions of disulfide systems than the parent thiacrown ethers. Such weak interaction energies in host-guest complexes indicate the possibility of reversible complexation-decomplexation. This assumably assists the fast release of guest molecules from the disulfide systems in response to the redox stimuli. Possibilities of incorporating such disulfide incorporated moieties in thiacalixarenes are also discussed. The results discussed in the present work are valuable for further development in the practical applications of crown ether–based host materials.

Experimental and theoretical studies of chitosan dissolution in ionic liquids: Contribution ratio effect of cations and anions

Typical hydrogen bonding information (hydrogen bonds, hydrogen bond lengths, and average bond lengths) and weak interaction energy (ΔH) of four ionic liquids (ILs), anion/chitobiose, cation/chitobiose, and IL/chitobiose complexes were determined using density functional theory (DFT) calculations to elucidate the contribution ratio effect of ions (cations or anions of ILs) upon chitosan dissolution.For [Emim]Ac and [Bmim]Ac with same acetate anion, contribution ratio (Rc) values of cations in [Bmim]Ac and [Emim]Ac increased from 37.88% to 38.14%. For [Bmim]Cl and [Etmim]Cl with same chloride anion, contribution ratio (Rc) values of cations increased slightly from 39.39% to 41.65%. As for [Bmim]Cl and [Bmim]Ac with same cation, contribution ratio (Rc) values of Cl- anion in [Bmim]Cl (60.61%) was lower than that of acetate anion in [Bmim]Ac (62.12%).These changes revealed that cations of ILs played more important role in chitosan dissolution.Hydrogen-bond basicity values (β values) of ILs were closely related to the DFT simulation results (weak interaction energy and average hydrogen bond length values) of ILs. Chitosan dissolved faster in acetate based imidazolium ILs ([Emim]Ac and [Bmim]Ac) than the chloride based ILs ([Bmim]Cl and [Etmim]Cl). The chitosan dissolution performance in ILs was consistent with DFT simulation results (weak interaction energy values and average hydrogen bond length values) of IL/chitobiose and hydrogen-bond basicity values of ILs.

Intermolecular Non-Covalent Carbon-Bonding Interactions with Methyl Groups: A CSD, PDB and DFT Study.

A systematic evaluation of the CSD and the PDB in conjunction with DFT calculations reveal that non-covalent Carbon-bonding interactions with X–CH3 can be weakly directional in the solid state (P ≤ 1.5) when X = N or O. This is comparable to very weak CH hydrogen bonding interactions and is in line with the weak interaction energies calculated (≤ –1.5 kcal·mol−1) of typical charge neutral adducts such as [Me3N-CH3···OH2] (2a). The interaction energy is enhanced to ≤–5 kcal·mol−1 when X is more electron withdrawing such as in [O2N-CH3··O=Cdme] (20b) and to ≤18 kcal·mol−1 in cationic species like [Me3O+-CH3···OH2]+ (8a).

From Hierarchical Helicates to Functional Supramolecular Devices.

Catechol ligands with aldehyde, ketone or ester groups attached in 3-position form, in the presence of titanium(IV) triscatecholate, titanium(IV) complexes. If lithium cations are the counterions, they can bind in a successive step to the salicylate units of the complex and form a dimeric triple-lithium-bridged dinuclear helicate. In solution, the dimer is in equilibrium with the monomer and the thermodynamics of the dimerization can be easily evaluated. Thus, the hierarchically assembled titanium(IV) helicates represent a lithium-dependent molecular switch. The investigation of different derivatives of the complex allows for an estimation of the influence of side chain functionalities on the energetics of the dimerization. Thus, the hierarchically assembled helicates can be used as a kind of molecular balance to determine weak interaction energies (solvophobic effects and even dispersive effects). In addition, tethering of two ligands leads to "classical" helicates. Removal or addition of lithium cations allows for a reversible switching between a compressed and expanded state, which in the case of chiral ligands can be even performed stereospecifically.