A Novel Dimeric BINOL for Enantioselective Recognition of 1,2‐Amino Alcohols

A novel auxillary chiral dimeric binol has been designed, synthesized, and used to enantioselectively recognize 1,2‐amino alcohols through the three point of interactions, the reversible imine bond, resonance assisted hydrogen bonding and the hydrogen bonding by the additional chiral moiety introduced at the receptor. The enantioselectivities were comparable to those of the previous reported receptors.     

基于杯[4]芳烃和S-联萘酚的荧光传感器的合成及其对N-Boc保护谷氨酸阴离子的对应选择性识别性能研究

合成了一种基于杯[4]芳烃和S-联萘酚单元的新型手性大环受体4,并用荧光光谱和核磁氢谱研究了该受体与阴离子的键合性质。非线性曲线拟合结果表明受体4与N-Boc保护L-和D-谷氨酸阴离子都能通过多重氢键形成1:1的络合物,而且对N-Boc保护谷氨酸阴离子对映体显示了较好的对应选择性识别性能（Kass(L) / Kass(D) = 4.65）。不同的荧光响应表明受体4可以用作N-Boc保护谷氨酸阴离子的对应选择性的荧光化学传感器。     

Anion Receptor with Xylene Bridged Two Imidazolium Rings

A m-xylene bridged imidazolium receptor 1 has been designed and synthesized. The receptor 1 utilizes two imidazole (C–H)⁺—anion hydrogen bonds and one aromatic hydrogen—anion hydrogen bond. The major driving force of complexation between the receptor 1 and anions comes from two imidazole (C–H)⁺—anion hydrogen bonding. However, some hydrogen bonding energy between aromatic hydrogen and anion exists, although it is expected to be much smaller than that of imidazole (C–H)⁺—anion hydrogen bonds.

     

Head‐to‐Tail Intermolecular Hydrogen Bonding of OH and NH Groups with Fluoride

To explore the anion‐recognition ability of the phenolic hydroxyl group and the amino hydrogen, we synthesized three different acridinedione (ADD) based anion receptors, 1 , 2 and 3 , having OH, NH, and combination of OH and NH groups, respectively. Absorption, emission and ¹H NMR spectral studies revealed that receptor 1 , having only a phenolic OH group, shows selective deprotonation of the hydroxyl proton towards F^?, which results in an “ON–OFF”‐type signal in the fluorescence spectral studies. Receptor 2 , which only has an amino hydrogen, also shows deprotonation of the amino hydrogen with F^?, whereas receptor 3 (having both OH and NH groups) shows head‐to‐tail intermolecular hydrogen bonding of OH and NH groups with F^? prior to deprotonation. The observation of hydrogen bonding of the OH and NH groups in a combined solution of 1 and 2 with F^? in a head‐to‐tail hetero‐intermolecular fashion, and the absence of head‐to‐head and tail‐to‐tail intermolecular hydrogen bonding in 1 and 2 with F^?, prove that the difference in the acidity of the OH and NH protons leads to the formation of an intermolecular hydrogen‐bonding complex with F^? prior to deprotonation. The presence of this hydrogen‐bonding complex was confirmed by absorption spectroscopy, 3D emission contour studies, and ¹H NMR titration.     

Synthesis of high surface area NiO nanoparticles through thermal decomposition of mixed ligand Ni(II) Complex, [Ni(binol)(bpy)]∙CH<Subscript>3</Subscript>OH

The present work focuses on the synthesis of high surface area NiO nanoparticles through thermal decomposition of [Ni(binol)(bpy)]?CH₃OH complex as a new precursor. [Ni(binol)(bpy)]?CH₃OH (where binol = racemic-1,1′-bi-2-naphtholate and bpy = 2,2′-bipyridine) was synthesized from reaction of NiCl₂(bpy) with rac-Na₂(binol). The complex was characterized by elemental analysis and spectroscopy techniques of IR, UV-Vis, mass, ¹H and ¹³C NMR. The results revealed that [Ni(binol)(bpy)]?CH₃OH was a paramagnetic tetrahedral complex. The physicochemical properties of the nanoparticles were characterized by various analysis techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and BET specific surface area. The used synthetic rout is facile and economic that makes it suitable for large scale production of pure nickel oxide nanoparticles.     

Effect of Hydrogen Binding on Selective Recognition of Halide Anions

The interplay of molecular rigidity enforced by interior or exterior hydrogen bonding and affinity for binding halide anions is described to demonstrate the effect of intramolecular hydrogen bonding in anion recognition process. To this end pyridine‐2,6‐dicarboxamides 1 and 2 , and aromatic oligoamides 3 and 4 containing intramolecular hydrogen bonds were explored for their ability in associating with tetrabutylammonium halide (Cl^?, Br^?, and I^?). Binding constants in chloroform solution were calculated using nonlinear curve‐fitting method based on ¹H NMR titration experiments. The trimeric amide 3 , which adopts a crescent conformation as revealed by single‐crystal X‐ray diffraction analysis, strongly binds chloride anion with binding constant as high as 379 L·mol^?1. This is more than 6 times greater than the binding constant for the control receptor 2 with a backbone that is only partially rigidified. The comparative data provided supportive information for rationalizing the observed affinity difference in binding halide anions in terms of local preorganization effected by interior or exterior hydrogen bonding.     

Chalcogen Bond Mediated Enhancement of Cooperative Ion-Pair Recognition

A series of heteroditopic receptors containing halogen bond (XB) and unprecedented chalcogen bond (ChB) donors integrated into a 3,5-bis-triazole pyridine structure covalently linked to benzo-15-crown-5 ether motifs exhibit remarkable cooperative recognition of halide anions. Multi-nuclear ¹H, ¹³C, ¹²⁵Te and ¹⁹F NMR, ion pair binding investigations reveal sodium cation–benzo-crown ether binding dramatically enhances the recognition of bromide and iodide halide anions, with the chalcogen bonding heteroditopic receptor notably displaying the largest enhancement of halide binding strength of over two hundred-fold, in comparison to the halogen bonding and hydrogen bonding heteroditopic receptor analogues. DFT calculations suggest crown ether sodium cation complexation induces a polarisation of the sigma hole of ChB and XB heteroditopic receptor donors as a significant contribution to the origin of the unique cooperativity exhibited by these systems.     

Electrochemical measurement of switchable hydrogen bonding in an anthraquinone-based anion receptor

The electrochemistry of a novel anion receptor is presented. The receptor 1,3-diphenylcarboxamidoanthraquinone (AAR) in the absence of an appropriate anion behaves as an anthraquinone system in the presence of a strong hydrogen bond donor. In this case, the electrochemical evidence supports the suggestion that the hydrogen bonding with the anthraquinone occurs at least partially through intra- or intermolecular interactions. It is suggested that these interactions stabilise both the semiquinone and dianion species resulting from reduction of AAR. However, in the presence of a suitable competitive anion (specifically F⁻), the hydrogen-bond donor groups bind to the anion rather than the quinone oxygen atoms. This removes the hydrogen bonding interaction to the redox-active quinone centre and hence alters the electrochemistry significantly. In the presence of F⁻, two one-electron quasireversible electrochemical processes are observed.     

Thiourea Based Tweezer Anion Receptors for Selective Sensing of Fluoride Ions

Three 3,3＇-di（4-substituted-phenyl）-1,1＇-isophthaloylbis（thiourea） compounds were designed as novel neutral anion receptors, and synthesized by simple steps in good yields. The single crystal structure of receptor 1 shows that a solvent molecule was captured by the host molecule through intermolecular hydrogen bonding. Moreover, it was self-assembled as a supramolecular system for the presence of abundant inter- and intramolecular hydrogen bonding and π-π interactions between phenyl groups. Their application as anion receptors has been examined by UV-Vis and ^1H NMR spectroscopy, showing that they had a higher selectivity for fluoride than other halides. The host and guest formed a 1 ： 1 stoichiometry complex through hydrogen bonding interactions in the first step, then following a process of deprotonation in presence of an excess of F^- in the solvent of DMF.     

Chalcogen Bond Mediated Enhancement of Cooperative Ion‐Pair Recognition

A series of heteroditopic receptors containing halogen bond (XB) and unprecedented chalcogen bond (ChB) donors integrated into a 3,5‐bis‐triazole pyridine structure covalently linked to benzo‐15‐crown‐5 ether motifs exhibit remarkable cooperative recognition of halide anions. Multi‐nuclear ¹H, ¹³C, ¹²⁵Te and ¹⁹F NMR, ion pair binding investigations reveal sodium cation–benzo‐crown ether binding dramatically enhances the recognition of bromide and iodide halide anions, with the chalcogen bonding heteroditopic receptor notably displaying the largest enhancement of halide binding strength of over two hundred‐fold, in comparison to the halogen bonding and hydrogen bonding heteroditopic receptor analogues. DFT calculations suggest crown ether sodium cation complexation induces a polarisation of the sigma hole of ChB and XB heteroditopic receptor donors as a significant contribution to the origin of the unique cooperativity exhibited by these systems.     

From a Tb<Superscript>3+</Superscript> chelated compound to a hybrid material: selective emission responses to anions

A novel terbium 2-hydroxymethyl-benzoimidazole-6-carboxylic acid complex has been designed and unique emission changes to fluoride anions in comparison with HSO₄⁻, AcO⁻, Cl⁻, Br⁻, and I⁻ were observed. Then, the complex was encapsulated into an inorganic matrix. The novel hybrid material, with strong green emission was successfully synthesized as an anions receptor in water. More importantly, this hybrid material not only gave luminescence response to F⁻, but also to HSO₄⁻. Spectroscopic studies demonstrated that the recognition process for fluoride ions can be mainly ascribed to its hydrogen bonding interactions with hydrogen bond donor units (NH and OH). In case of hydrogen sulfate, the sensing effects can be probably attributed to its acidity instead of hydrogen bonding interactions.     

Salicylaldehyde-indole-2-acylhydrazone: a simple,colorimetric and absorption ratiometric chemosensor for acetate ion

A simple anion receptor (i.e. salicylaldehyde-indole-2-acylhydrazone) was synthesised and its recognition properties were investigated by naked-eye observation, UV–vis titration spectra, ¹H NMR spectroscopy and DFT calculations. The obtained results indicated that this receptor could realise the selective colorimetric sensing and absorption ratiometric response towards AcO^?  in CH₃CN–DMSO medium, by virtue of threefold intermolecular hydrogen bonding interactions formed with phenolic OH, indole NH and amide NH.     

Synthesis and Structure of a 1,3-alternate-Thiacalix[4]arene diamide Derivative

A novel receptor possessing two complexation sites and bearing 1,3-alternate conformation based on thiacalix[4]arene, confirmed by single crystal X-ray analysis, was prepared. The tetrathiacalix[4]arene diamide shows strong intramolecular hydrogen bonding. The binding behavior towards K⁺ and halides has been examined by ¹H NMR titration experiments.     

Evaluation of the individual hydrogen bonding energies in N-methylacetamide chains

The individual hydrogen bonding energies in N-methylacetamide chains were evaluated at the MP2/6-31+G** level including BSSE correction and at the B3LYP/6-311++G(3df,2pd) level including BSSE and van der Waals correction. The calculation results indicate that compared with MP2 results, B3LYP calculations without van der Waals correction underestimate the individual hydrogen bonding energies about 5.4 kJ mol^?1 for both the terminal and central hydrogen bonds, whereas B3LYP calculations with van der Waals correction produce almost the same individual hydrogen bonding energies as MP2 does for those terminal hydrogen bonds, but still underestimate the individual hydrogen bonding energies about 2.5 kJ mol^?1 for the hydrogen bonds near the center. Our calculation results show that the individual hydrogen bonding energy becomes more negative (more attractive) as the chain becomes longer and that the hydrogen bonds close to the interior of the chain are stronger than those near the ends. The weakest individual hydrogen bonding energy is about ?29.0 kJ mol^?1 found in the dimer, whereas with the growth of the N-methylacetamide chain the individual hydrogen bonding energy was estimated to be as large as ?62.5 kJ mol^?1 found in the N-methylacetamide decamer, showing that there is a significant hydrogen bond cooperative effect in N-methylacetamide chains. The natural bond orbital analysis indicates that a stronger hydrogen bond corresponds to a larger positive charge for the H atom and a larger negative charge for the O atom in the N-H?O=C bond, corresponds to a stronger second-order stabilization energy between the oxygen lone pair and the N-H antibonding orbital, and corresponds to more charge transfer between the hydrogen bonded donor and acceptor molecules.     

Quantitative decomposition of resonance-assisted hydrogen bond energy in β-diketones into resonance and hydrogen bonding (π- and σ-) components using molecular tailoring and function-based approaches

Using the molecular tailoring and function-based approaches allows one to divide the energy of the O─H⋯O═C resonance-assisted hydrogen bond in a series of the β-diketones into resonance and hydrogen bonding components. The magnitude of the resonance component is assessed as about 6 kcal mol⁻¹. This value increases by ca. 1 kcal mol⁻¹ on going from the weak to strong resonance-assisted hydrogen bonding. The magnitude of the hydrogen bonding component varies in the wide range from 2 to 20 kcal mol⁻¹ depending on the structure of the β-diketone in question.     

Dynamic Inversion of Stereoselective Phosphate Binding to a Bisurea Receptor Controlled by Light and Heat

A chiral bisurea anion receptor, derived from a first‐generation molecular motor, can undergo photochemical and thermal isomerization operating as a reconfigurable system. The two possible cis configurations in the isomerization cycle are opposite in helicity, as is shown by CD spectroscopy. ¹H NMR titrations demonstrate that the P and M helical cis isomers hold opposite enantioselectivity in the binding of binol phosphate, while anion complexation by the intermediate trans isomer is not selective. The difference in the binding affinity of the enantiomers was rationalized by DFT calculations, revealing very distinct binding modes. Thus, the enantiopreferred substrate binding in this receptor can be inverted in a dynamic fashion using light and heat.     

A pH-Switchable Triple Hydrogen-Bonding Motif

A stimuli responsive linear hydrogen bonding motif, capable of in situ protonation and deprotonation, has been investigated. The interactions of the responsive hydrogen bonding motif with complementary partners were examined through a series of ¹H NMR experiments, revealing that the recognition preference of the responsive hydrogen bonding motif in a mixture can be switched between two states.     

Importance of aliphatic C–H hydrogen bonding on anion recognition

We have designed and synthesised new anion receptors 1 and 2, both of their C–H groups were at the α positions to carbonyl groups and further polarised by the attached polarising substituents. This enabled us to study hydrogen bonding donor ability of C–H bonds. The polarising substituents are electron withdrawing cyano group for host 1, while charged pyridinium group for host 2. As expected from charge effects, host 2 shows roughly an order of magnitude higher binding constants against various anion guests than those of receptor 1. Since the magnitude of polarisation change should be greatest for C–H group among various hydrogen bonding groups, this indicates the importance of C–H hydrogen bonding. In contrast, the relative order of binding constants was the same for both host 1 and 2. The order of association constants was found to be (CH₃)₂POO^? > CH₃COO^? > C₆H₅COO^? > Cl^? > Br^?. DFT calculation results were in good agreement with experimental binding constants and confirmed the importance of charged group substitution. In addition, receptor 1 showed the highest association constant for dimethyl phosphinate, which is implicated in many metabolic diseases.     

RuII and IrIII Complexes Containing ADA and DAD Triple Hydrogen Bonding Motifs: Potential Tectons for the Assembly of Functional Materials

The synthesis and characterisation of a series of [Ru^II(bpy)₂L] and [Ir(ppy)₂L] complexes containing ligands L with the potential to engage in triple hydrogen bonding interactions is described. L1 and L2 comprise pyridyl triazole chelating units with pendant diaminotriazine units, capable of donor‐acceptor‐donor (DAD) hydrogen bonding, while L3 and L4 contain ADA hydrogen bonding units proximal to N^N and N^O cleating sites, respectively. X‐ray crystallography shows the L1 and L2 containing Ru^II complexes to assemble via hydrogen bonding dimers, while [Ru^II(bpy)₂L 4 ] assembles via extended hydrogen bonding motifs to form one dimensional chains. By contrast, the expected hydrogen bonding patterns are not observed for the Ru^II and Ir^III complexes of L3 . Spectroscopic studies show that the absorption spectra of the complexes result from combinations of MLCT and LLCT transitions. The L1 and L2 complexes of Ir^III and Ru^II complexes are emissive in the solid state and it seems likely that hydrogen bonding to complementary species may facilitate tuning of their ³ILCT emission. Low frequency Raman spectra provide further evidence for ordered interactions in the solid state for the L4 complexes, consistent with the results from X‐ray crystallography.     

A pseudo‐quadruple hydrogen‐bonding motif consisting of six N—H⋯O hydrogen bonds in trimethoprim formate

The title compound, trimethoprim (TMP) formate [systematic name: 2,4‐di­amino‐5‐(3,4,5‐tri­methoxy­benzyl)­pyrimidin‐1‐ium formate], C₁₄H₁₉N₄O₃⁺·CHO₂^?, reveals a pseudo‐quadruple hydrogen‐bonding motif consisting of six N—H?O hydrogen bonds involving two unpaired TMP cations and two formate anions which are symmetrically disposed. The hydrogen‐bonding motif is strikingly comparable with that observed in other TMP salts where the amino­pyrimidine moieties of the TMP cations are centrosymmetrically paired. These conserved hydrogen‐bonding motifs may serve as robust synthons in crystal engineering and design. The characteristic pseudo‐quadruple hydrogen‐bonding motif and other intermolecular hydrogen bonds operating in the crystal form a two‐dimensional supramolecular sheet structure.