Synthesis,characterization and metal ion complexation and extraction capabilities of calix[4]arene Schiff base compounds

The syntheses, characterization and metal ion complexation and extraction capabilities of six new calix[4]arene Schiff base compounds, 5–10, are reported. The preparation of the compounds was achieved by the condensation of 5,17-diamino-11,23-di-tert-butyl-25,27-di-n-butoxy-26,28-dihydroxycalix[4]arene with the appropriate aldehyde (5-bromosalicylaldehyde for 5, 4-anisaldehyde for 6, 4-(dimethylamino)benzaldehyde for 7, 9-anthracenecarboxaldehyde for 8, 1-pyrenecarboxaldehyde for 9, and 9-fluorenecarboxaldehyde for 10) in refluxing ethanol. The compounds were characterized by ¹H and ¹³C NMR spectroscopy, IR spectroscopy, high-resolution mass spectrometry and elemental analysis. The X-ray crystal structures of 7, 8 and 9 (as dichloromethane solvates) revealed that the calixarene molecules adopt H-bond stabilized, distorted-cone conformations and form centrosymmetric dimers in the solid state. Compounds 5–10 did not form host–guest complexes with NEt₄[(bdt)MoO₂(OSiPh₃)] (bdt^2–=benzene-1,2-dithiolate), a potential precursor for biologically relevant oxosulfido-Mo(VI/V) enzyme models; such host–guest complexes have the potential to stabilize these sought-after but highly reactive model compounds. In addition, the capabilities of 5–10 to extract selected metal ions (Ni²⁺, Co²⁺, Cu²⁺, Zn²⁺, Ag⁺, Pb²⁺, Cd²⁺ and Hg²⁺) from an aqueous into an organic phase have been assessed by picrate extraction experiments. Compound 5 displayed exceptional selectivity towards Ni²⁺, compound 7 exhibited enhanced extraction towards all of the metal ions tested and compounds 6, 9 and 10 showed very high selectivity towards Hg²⁺. On the other hand, compound 8 exhibited negligible capacity to extract any of the metal ions tested.     

Optical studies of dynamic director configurations in ferroelectric liquid crystal devices

An investigation into the transmission spectrum of a ferroelectric liquid crystal device is undertaken. This is done both for an initial static state and during a switching process. Comparisons are made between experimental data and theoretical predictions. The dynamic internal director configurations in the device is shown to be consistent with a simple model during both monopolar and bipolar addressing pulses.     

Guest Covalent Capture by a Host: A Biomimetic Strategy for the Selective Functionalization of a Cavity

A biomimetic strategy for the monofunctionalization of a calix[6]arene core is described. It is based on host–guest chemistry (mimicking the Michaelis–Menten adduct in enzymes) and allows the finely tuned pre‐organization of the substrate (an alkyne) with respect to the reactant (three azido groups introduced at the calixarene large rim). It is shown that the thermal Huisgen reaction implemented in this work proceeds under very mild conditions with total regioselectivity of the cycloaddition process. The scope of the reaction was explored and the results suggest that such a supramolecular strategy is quite versatile and could be applied to the selective functionalization of other cavitands bearing different recognition patterns. A detailed structural, thermodynamic, and kinetic study is also reported, highlighting interesting biomimetic features: The importance of the host–guest adduct strength, the high sensitivity of the reaction to the pre‐organization of the reactive partners (alkyne vs. azide), and a significant impact of the embedment on the transition state. The self‐coordination of the monofunctionalized products was also studied and an “endo/exo” switch of the internal side‐chain could be triggered by adding competitive ligands.     

Dimensional Matching of Polycyclic Aromatics with Rectangular Metallacycles: Insertion Modes Determined by [C?H⋅⋅⋅π] Interactions

A family of Pd^II/Pt^II dinuclear receptors, designed to give a smooth increase in their cavity lengths (from 7.46–13.78 Å), is presented. Their inclusion complexes with a representative set of polycyclic aromatic substrates (naphthalene, carbazol, pyrene, and benzo[a]pyrene), were characterized and studied in aqueous solution and the solid state. By taking into account the dimensions of both receptors and substrates, an excellent complementarity was found between the size of the receptors and their ability to complex a given substrate. Furthermore, this dimensional matching results in specific binding modes depending on the ability of the guest to establish stabilizing [C? H???π] interactions with the host.     

Monoester Copillar[5]arenes: Synthesis,Unusual Self‐Inclusion Behavior,and Molecular Recognition

The self‐inclusion behavior of monoester copillar[5]arenes depends on the position of the ester group, which causes different guest selectivities. Monoester copillar[5]arenes bearing an acetate chain can form stable self‐inclusion complexes in low‐ and high‐concentration solution and exhibit high guest selectivity. However, a monoester copillar[5]arene bearing a butyrate chain can not form a self‐inclusion complex and exhibits low guest selectivity. Thus, a new class of stable self‐inclusion complexes of copillar[5]arenes was explored to improve the selectivity of molecular recognition.     

Controllable Syntheses of Porous Metal–Organic Frameworks: Encapsulation of LnIII Cations for Tunable Luminescence and Small Drug Molecules for Efficient Delivery

Two porous metal–organic frameworks (MOFs), [Zn₃(L)(H₂O)₂] ? 3 DMF ? 7 H₂O ( MOF‐1 ) and [(CH₃)₂NH₂]₆[Ni₃(L)₂(H₂O)₆] ? 3 DMF ? 15 H₂O ( MOF‐2 ), were synthesized solvothermally (H₆L=1,2,3,4,5,6‐hexakis(3‐carboxyphenyloxymethylene)benzene). In MOF ‐ 1 , neighboring Zn^II trimers are linked by the backbones of L ligands to form a fascinating 3D six‐connected framework with the point symbol (4¹².6³) (4¹².6³). In MOF‐2 , eight L ligands bridge six Ni^II atoms to generate a rhombic‐dodecahedral [Ni₆L₈] cage. Each cage is surrounded by eight adjacent ones through sharing of carboxylate groups to yield an unusual 3D porous framework. Encapsulation of Ln^III cations for tunable luminescence and small drug molecules for efficient delivery were investigated in detail for MOF‐1 .     

Water-soluble pillar[6]arene stabilized silver nanoparticles: preparation and application in amino acid detection

In the presence of a water-soluble pillar[6]arene WP6 containing 12 imidazolium groups, silver nanoparticles were successfully prepared and investigated in detail by ultraviolet visible spectroscopy, X-ray diffraction, and transmission electron microscopy. Excitingly, these pillar[6]arene stabilized silver nanoparticles were demonstrated to function as a colorimetric sensor to selectively probe glutamic acid in water.     

Tuning protonation states of tripelennamine antihistamines by cucurbit[7]uril

The formation of host–guest complexes of cucurbit[7]uril (CB7) with the antihistamine drug tripelennamine (TRP) was studied by optical and NMR spectroscopy. The experimental and computational results are consistent with inclusion of a single TRP molecule in CB7. Addition of CB7 has tuned drug protonation states associated with (de)protonation of the ethyldimethylammonium and exocyclic nitrogens with an increase in the associated pK_a values by 1.5 and 2.5 units, respectively. The incorporation of antihistamines drugs such as TRP in cucurbiturils could be utilized for switching their capability for selective binding to histamine H₁‐receptors, in the future. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and complexation of a ‘mixed’-pyridine-naphthalene homooxacalixarene

A deep-cavity ‘mixed’ octahomotetraoxacalix[2]naphthalene[2]pyridine macrocycle has been synthesised and its single-crystal X-ray structure has been determined. Molecular modeling studies suggested that this macrocycle could be an effective host for guest aromatic diol(s) similar to Wang's methylazacalixpyridines. Binding constants were determined using ¹H NMR chemical shifts changes and comparisons were made between the diols which were tested.