Energetic Ordering of Hydrogen Bond Strengths in Methanol-Water Clusters: Insights via Molecular Tailoring Approach

In this work, we examine the strength of various types of individual hydrogen bond (HB) in mixed methanol-water M_nW_m, (n+m=2 to 7) clusters, with an aim to understand the relative order of their strength, using our recently proposed molecular tailoring-based approach (MTA). Among all the types of HB, it is observed that the O_M−H…O_W HBs are the strongest (6.9 to 12.4 kcal mol⁻¹). The next ones are O_M−H…O_M HBs (6.5 to 11.6 kcal mol⁻¹). The O_W−H…O_W (0.2 to 10.9 kcal mol⁻¹) and O_W−H…O_M HBs (0.3 to 10.3 kcal mol⁻¹) are the weakest ones. This energetic ordering of HBs is seen to be different from the respective HB energies in the dimer i. e., O_M−H…O_M (5.0 to 6.0 kcal mol⁻¹)>O_W−H…O_M (1.5 to 6.0 kcal mol⁻¹)>O_M−H…O_W (3.8 to 5.6 kcal mol⁻¹)>O_W−H…O_W (1.2 to 5.0 kcal mol⁻¹). The plausible reason for the difference in the HB energy ordering may be attributed to the increase or decrease in HB strengths due to the formation of cooperative or anti-cooperative HB networks. For instance, the cooperativity contribution towards the different types of HB follows: O_M−H…O_W (2.4 to 8.6 kcal mol⁻¹)>O_M−H…O_M (1.3 to 6.3 kcal mol⁻¹)>O_W−H…O_W (−1.0 to 6.5 kcal mol⁻¹)>O_W−H…O_M (−1.2 to 5.3 kcal mol⁻¹). This ordering of cooperativity contribution is similar to the HB energy ordering obtained by the MTA-based method. It is emphasized here that, the interplay between the cooperative and anti-cooperative contributions are indispensable for the correct energetic ordering of these HBs.     

Interaction between bovine transferrin and cefonicid sodium by multi-spectroscopy

In the Tris-HCl buffer solution with pH = 7.4, the reaction mechanism of cefonicid sodium with bovine transferrin was investigated by multi-spectroscopic methods at different temperatures (298, 303, and 310 K). The results demonstrated that non-radiative energy transfer occurred between cefonicid sodium and bovine transferrin, which gradually quenched the fluorescence of bovine transferrin, and the quenching mechanism was a static quenching progress. During the quenching progress, the electrostatic force played a dominant role in this system, and the number of binding sites in the system was close to 1. Moreover, ultraviolet visible absorption spectroscopy and synchronous fluorescence spectroscopy showed that the structure of bovine transferrin was changed. The polarity around amino acid residues increased and the hydrophobicity decreased. Circular dichroism spectroscopy also showed that cefonicid sodium changed the secondary structure of bovine transferrin. However, the structure of the bovine transferrin was also predominantly α-helical even after binding to cefonicid sodium. The values of Hill’s coefficients were less than 1, indicating that drugs had negative cooperativity for subsequent ligands in the system.     

Enhanced Emission Induced by FRET from a Long-Lifetime, Low Quantum Yield Donor to a Long-Wavelength, High Quantum Yield Acceptor

We report observation of high quantum yield, long-lifetime fluorescence from a red dye BO-PRO-3 excited by resonance energy transfer (RET). The acceptor fluorescence was highly enhanced upon binding to the donor-labeled DNA. A ruthenium complex (Ru) was chosen as a donor in this system because of its long fluorescence lifetime. Both donor and acceptor were non-covalently bound to DNA. Emission from the donor-acceptor system (DA) at wavelengths exceeding 600 nm still preserves the long-lifetime component of the Ru donor, retaining average fluorescence lifetimes in the range of 30–50 ns. Despite the low quantum yield of the Ru donor in the absence of acceptor, its overall quantum yield of the DA pair was increased by energy transfer to the higher quantum yield acceptor BO-PRO-3. The wavelength-integrated intensity of donor and acceptor bound to DNA was many-fold greater than the intensity of the donor and acceptor separately bound to DNA. The origin of this effect is due to an efficient energy transfer from the donor, competing with non-radiative depopulation of the donor excited state. The distinctive features of DA complexes can be used in the development of a new class of engineered luminophores that display both long lifetime and long-wavelength emission. Similar DA complexes can be applied as proximity indicators, exhibiting strong fluorescence of adjacently located donors and acceptors over the relatively weak fluorescence of separated donors and acceptors.     

Tuning of tetrel bonds interactions by substitution and cooperative effects in XH3Si···NCH···HM (X = H,F, Cl,Br; M = Li,Na, BeH and MgH) complexes

In this work, the interplay between the tetrel bond and the dihydrogen bond is investigated in ternary XH₃Si···NCH···HM complexes, where X = H, F, Cl, Br and M = Li, Na, BeH, MgH. The nature of Si···N and H···H interactions is studied by molecular electrostatic potential (MEP), noncovalent interaction and electron localisation function analyses. All binding distances in the ternary complexes are shorter than those of isolated XH₃Si···NCH and NCH···HM systems. That is, the two types of interactions have a cooperative effect on each other. The results of the MEP analysis indicate that the enhancement of the Si···N and H···H bonds can mainly be attributed to the electrostatic interaction. The plot of the reduced density gradient versus sign (λ₂)ρ indicates that the location of the spike associated with each interaction in the ternary systems moves slightly towards the negative (λ₂)ρ values with respect to the binary systems. This confirms that both Si···N and H···H interactions in the ternary complexes are strengthened by the presence of other. Besides, cooperative effects lead to a considerable change in the ¹⁴N nuclear quadrupole coupling constant values of the ternary complexes relative to the XH₃Si···NCH complexes.     

Relationship between cation–π and anion–π interactions: individual binding energies in the π–Mz+–π–X−–π system

The mutual influence of cation–π and anion–π interactions in the π–M^z+–π–X^?–π system (M^z+ = Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, Ca²⁺ and X^? = F^?, Cl^?) has been studied by quantum mechanical calculations. Both geometric parameters and energy data reveal that cation–π and anion–π interactions enhance each other in the π–M^z+–π–X^?–π system. Individual binding energies (E_ion···π) have been estimated in the quintuplet system using a simple new method from electron charge densities calculated at the bond critical points (BCPs) of the ion···π interaction by the atoms in molecules (AIM) method at the M062X/6-31+G(d) level of theory. With respect to the obtained individual binding energies, the strength of an ion···π interaction depends on the cooperative effects of other components.     

The effect of hydrogen-bonding cooperativity on the strength and properties of σ-hole interactions: an ab initio study

Ab initio calculations at the MP2/aug-cc-pVTZ level of theory are performed to investigate the effect of hydrogen-bonding cooperativity on the strength and bonding properties of σ-hole interaction in linear FCl???(NCH)_n=2–5, FHS???(NCH)_n=2–5, FH₂P???(NCH)_n=2–5 and FH₃Si???(NCH)_n=2–5 clusters. It is found that the cooperative effects in the hydrogen-bonding tend to strengthen the σ-hole interaction. However, these effects are almost saturated in the larger clusters (n > 5). For a given cluster, the amount of bond contraction in FCl???(NCH)_n is more important than other systems. A nice linear relationship is found between the σ-hole bond energies and absolute ¹⁵N chemical shieldings or spin–spin coupling constants across the σ-hole bond.     

Tuning of pnicogen and chalcogen bonds by an aerogen-bonding interaction: a comparative ab initio study

Using high-level ab initio calculations, the cooperativity effects between an aerogen-bonding and a pnicogen- or chalcogen-bonding interactions are studied in ternary Y···PH₂CN···ZO₃ and Y···SHCN···ZO₃ complexes (Y?=?NH₃, N₂ and Z?=?Ar, Kr, Xe). A detailed analysis of the structures, interaction energies and bonding properties is performed on these systems. For each set of the complexes, a favourable cooperativity is observed between Z···N and P/S···N interactions, especially in complexes involving NH₃ and XeO₃ molecules. It is found that for a given Y or Z, the amount of cooperativity effects in Y···PH₂CN···ZO₃ complexes are important than Y···SHCN···ZO₃ ones. For each ternary complex considered, the effect of a Z···N aerogen bond on a P/S···N bond is more pronounced than that of a P/S···N bond on a Z···N bond. The mechanism of the cooperativity effects in the ternary complexes is studied by electron density difference, quantum theory of atoms in molecules and natural bond orbital analyses. The solvent effects are also studied on the interaction energy and cooperativity of Z···N and P/S···N bonds in the ternary systems.     

Cl~–…苯氰…H_2O中阴离子氢键协同效应与芳香性理论研究

本文采用DFT-B3LYP和MP2(full)方法对三聚体Cl–…苯氰…H2O中O/C–H…Cl–阴离子氢键与传统氢键O–H…N和C–H…O之间的协同效应、热力学性质以及芳香性进行了研究.结果表明阴离子氢键O/C–H…Cl–对O–H…N或C–H…O相互作用的影响更显著.在线性结构中发生正协同效应,熵变是促进热力学协同效应的主要因素,而在环状结构中发生反协同效应,焓变成为主要因素.在三聚体形成过程中,苯氰环的芳香性是减弱的,而苯氰中π→π*共轭效应是增强的.结果表明,协同效应能Ecoop.分别与Rc(NICS(1)ternary/NICS(1)binary),ΔΔδ(Δδternary-Δδbinary),Rc'((NICS(1)ternary-NICS(1)binary)/NICS(1)binary)和RBDE(C–CN)(BDE(C–CN)ternary/BDE(C–CN)binary)均具有良好的线性关系.同时,AIM的分析也佐证了协同效应的存在.     

Theoretical evaluation to improve the performance of composite wax powder: cooperativity effects involving the strong Na+···π/σ and weak hydrogen-bonding interactions in the complex of graphene oxide with Na+ and CH4

ABSTRACT

To provide a reasonable design scheme to improve the performance of composite wax powder, the ternary complex Na⁺···graphene oxide (GO)···CH₄ was selected as a model system to evaluate the cooperativity effect between the Na⁺···σ/π and H-bonding interactions in the composite wax powder doped with GO at the M06-2X/6-311++G(2d,p) and MP2/6-311++G(2d,p) levels. The cooperativities in GO···(CH₄)_n (n?=?1～10) and thermodynamic cooperativity effects in Na⁺···GO···CH₄ were also investigated. Although the changes of the absolute values of H-bonding interactions were slight, from those of relative values, the influence of the Na⁺···π or Na⁺···O interaction on the C–H···π, O–H···C or C–H···O interaction was notable upon the formation of ternary systems. The anti-cooperativity effect was found in the cyclic structure, while the cooperativity effect appeared in the linear conformation. The Na⁺···σ/π and H-bonding interactions as well as cooperativities in Na⁺···GO···CH₄ were stronger than those in Na⁺···coronene···CH₄. The formation of Na⁺···GO···CH₄ is a thermodynamic cooperativity process driven by the enthalpy change. Therefore, it could be inferred that, when graphite powder or carbon black was replaced by GO, the compatibilities could be strengthened among various components, and thus the performance of casting moulds could be improved. Atoms-in-molecules (AIM) and reduced density gradient (RDG) analyses confirmed the cooperativity effect and revealed the nature of the improved performance of composite wax powder with GO. The GO···(CH₄)_n (n?=?1～3) are positively cooperative, while the negative cooperativity is shown when n?=?4～10.