Guest Exchange Mechanisms in Mono‐Metallic PdII/PtII‐Cages Based on a Tetra‐Pyridyl Calix[4]pyrrole Ligand

Planar pyridyl N‐oxides are encapsulated in mono‐metallic Pd^II/Pt^II‐cages based on a tetra‐pyridyl calix[4]pyrrole ligand. The exchange dynamics of the cage complexes are slow on both the NMR chemical shift and EXSY timescales, but encapsulation of the guests by the cages is fast on the human timescale. A “French doors” mechanism, involving the rotation of the meso‐phenyl walls of the cages, allows the passage of the planar guests. The encapsulation of quinuclidine N‐oxide, a sterically more demanding guest, is slower than pyridyl N‐oxides in the Pd^II‐cage, and does not take place in the Pt^II counterpart. A modification of the encapsulation mechanism for the quinuclidine N‐oxide is postulated that requires the partial dissociation of the Pd^II‐cage. The substrate binding selectivity featured by the cages is related to their different guest uptake/release mechanisms.     

Catalytic Hydrogenation of meso‐Octamethylporphyrinogen (Calix[4]pyrrole)

Hydrogenation of meso‐octamethylporphyrinogen (calix[4]pyrrole) with a number of heterogeneous catalysts under different experimental conditions has been investigated. GC‐MS analyses of the reaction mixtures showed the formation of one to four products in low to moderate yields: three of them were diastereoisomers of the product derived from half‐hydrogenation of the substrate, and displayed alternating pyrrolidine and pyrrole rings, while the fourth was the all‐cis saturated product. An acidic medium was necessary to achieve hydrogenation. However, the use of too strongly acidic solvents or additives was detrimental to the stability of the substrate and/or the catalyst.     

Tetrakis(bicyclo[2.2.2]oct‐2‐ene)‐Fused Calix[4]pyrrole

Tetrakis(bicyclo[2.2.2]oct‐2‐ene)‐fused calix[4]pyrrole, 5 , was obtained starting from (E)‐1,2‐bis(phenylsulfonyl)ethylene. This new calixpyrrole derivative is the prospective precursor of tetrabenzocalix[4]pyrrole, a potential ion‐pair receptor and an attractive species as a possible deep‐walled ‘molecular container’.     

Mono Halogen Substituted Calix[4]pyrroles: Fine-tuning the Anion Binding Properties of Calix[4]pyrrole

Abstract

Single halogen atom (i. e. I, Br, Cl and F) substituted calix[4]pyrroles, compounds 2, 3, 4 and 5, were synthesized. Studies of these systems reveal that replacement of a single β-pyrrolic hydrogen atom can increase the anion binding ability of calix[4]pyrroles for a variety of anions (e. g. Cl^?, Br^?, H₂PO₄ ^? and HSO^? ₄) relative to normal non-halogen substituted calix[4]pyrrole 1. In the case of chloride anion, the expected relative affinity sequence of 5 > 4 > 3 > 2 was observed. This was not found to be true for Br^?, H²PO^? ₄, and HSO^? ₄. Here, the chlorine substituted calix[4]pyrrole 4 was found to display a slightly higher affinity in the case of each anion than the fluorine-bearing derivative 5. This was rationalized in terms of intermolecular NH … F hydrogen bonding interactions being present in CD₂Cl₂ solutions of 5. Support for this latter conclusion came from concentration and temperature-dependent NMR spectroscopic studies.

A matched set of mono halogen substituted calix[4]pyrroles was used to study in detail, the extent to which halogen substituents may be used to fine-tune the anion binding properties of calix[4]pyrroles.     

An Electrochemical Sensing Platform for the Detection of Lead Ions Based on Dicarboxyl‐Calix[4]arene

A simple and highly sensitive electrochemical sensor COOH−C4 derived from dicarboxyl‐calix[4]arene modified on a screen printed gold electrode (Au) was developed for the determination of lead ions in water samples. A 3‐mercaptopropionic acid (MPA) monolayer was used as a template on the gold electrode for the surface modification with dicarboxyl‐calixarene. The modified electrodes were surface‐characterized using Fourier Transform infrared spectroscopy (FTIR). The data obtained proved the confirmation of each stage of the electrode modification. The electrochemical analyses of the COOH−C4 electrode showed an enhanced electrocatalytic activity and higher current towards Pb²⁺ ions as compared to the bare Au and MPA/Au electrodes. Under optimum conditions, the differential pulse voltammetry response of COOH−C4 displayed a wide linear response ranging from 280–2500 μg/L for Pb²⁺ with a detection limit of 6.2 μg/L. In addition, the fabricated electrode showed a high selectivity and stability towards the Pb²⁺ ions in presence of possible interfering species. The present method was successfully applied to determine Pb²⁺ ions in real samples with satisfactory precision, with a relative standard deviation of 3.12 % and an acceptable recovery of 92 %, which demonstrated the potential application of dicarboxyl‐calix[4]arene modified on electrodes for heavy‐metal sensing.     

杯[4]吡咯大环化合物的合成和性能

通过改进的吡咯与酮缩合反应制备了一系列杯[4]吡咯大环主体分子,并由元素分析、IR、^1H NMR,MS确证结构。作为一类新型的阴离子和中性分子的受体,其性能通过光谱滴定实验进行了初步研究。     

Coordination‐Driven Switching of a Preorganized and Cooperative Calix[4]pyrrole Receptor

The study of preorganization in receptors, particularly in cooperative receptors, and their reversible control by external stimuli is important for elucidating design strategies that can lead to increased sensitivity and external control of molecular recognition. In this work we present the design, synthesis, and operation of an asymmetric tetrathiafulvalene (TTF)–calix[4]pyrrole receptor appended with a pyridine moiety. ¹H NMR spectroscopy was employed to demonstrate that intramolecular complexation between the receptor and the pyridine moiety leads to a preorganized receptor. Absorption and ¹H NMR spectroscopy along with a computational investigation were used to demonstrate the ability of the receptor to complex the substrate 1,3,5‐trinitrobenzene (TNB) and that the receptor can be reversibly modulated between negative and positive cooperativity by employing external stimuli in the form of Zn^II. Fitting procedures incorporating multiple datasets and fitting to multiple equilibria simultaneously have been employed to quantitatively determine the preorganization effects.