Combinations of Cyclodextrins with Synthetic and Natural Compounds

Host–guest compounds formed by cyclodextrins with synthetic and natural compounds are reviewed with regard to their properties, characterisation (using experimental and computational methods) and applications.     

Study on Synthesis and Intercalation Behavior of Layered Zirconium Proline-N-methylphosphonate-phosphate

Zirconium proline-N-methylphosphonate-phosphate (α-ZPMPP) was prepared in the presence of HF for the first time. The α-ZPMPP sample is highly crystallized with interlayer distance of 1.52nm. The interlayer distance of complex of α-ZPMPP with n-butylamine (α-ZPMPP-BA) is in 0.45 nm larger than that of α-ZPMPP. The α-ZPMPP possesses different intercalation behavior of host-guest compound from α-ZP.     

质子化4,4’-联吡啶盐与二苯并-24-冠-8的包合行为

通过1H NMR, ESI-MS, 紫外-可见光谱等分析手段研究了两个新的质子化联吡啶盐客体与冠醚二苯并-24-冠-8在溶液中和气态下的包合行为. 研究结果表明, 质子化的联吡啶盐与冠醚主要形成1∶1的超分子包合物, 且存在夹心式的几何结构, 双质子化的联吡啶盐比单质子化的联吡啶盐具有更强的结合冠醚的能力, 其缔合常数分别为200, 116 L•mol－1.     

Confinement inside a Crystalline Sponge Induces Pyrrole To Form N−H⋅⋅⋅π Bonded Tetramers

Based on the DFT-level-calculated molecular volume (V_mol) of pyrrole and its liquid density, pyrrole manifests the highest liquid density coefficient LD_c (defined as [V_mol×density ×0.6023]/FW) value of 0.7. Normal liquids have LD_c <0.63. This very high LD_c is due to the strong N−H⋅⋅⋅π interactions in solution, and hence pyrrole can be considered to be a pseudo-crystalline liquid. When trapped inside the confined space of a crystalline sponge, a reorientation of the N−H⋅⋅⋅π interaction is observed leading to specific cyclic N−H⋅⋅⋅π tetramers and N−H⋅⋅⋅π dimers, as verified by single-crystal X-ray crystallographic and computational methods. These tetramers are of the same size as four pyrrole molecules in the solid-state of pyrrole, yet the cyclic N−H⋅⋅⋅π intermolecular interactions are circularly oriented instead of being in the linear zigzag structure found in the X-ray structure of a solid pyrrole. The confinement thus acts as an external driving force for tetramer formation.     

The Preparation of a Water-Soluble Phospholate-Based Macrocycle for Constructing Artificial Light-Harvesting Systems

On the basis of cyclotrixylohydroquinoylene ( CTX ), a novel water-soluble phospholate-based CTX derivative ( WPCTX ) was prepared with facile synthetic procedure and satisfying yield. Several model guest molecules were selected to investigate WPCTX ′s host-guest properties. Based on the study of the host and model guest complexation, a tetraphenylethylene derivative from model guest was employed as a guest molecule ( G ) to form WPCTX⊃G nanoparticles (NPs) with WPCTX through further supramolecular self-assembly in water. Moreover, a hydrophobic fluorescent dye, Eosin Y( ESY ) or Nile red ( NiR ), was encapsulated in WPCTX⊃G NPs to construct two types of artificial light-harvesting systems. Their high antenna effect demonstrated such NPs successfully mimicked light-harvesting systems in nature.     

Temperature Dependence of the Weak Host-guest Interactions in the p‐tertbutylcalix[4]Arene 1:1 Toluene Complex

Abstract

The temperature dependence of the CH₃… π hostguest interaction in the p‐tertbutylcalix[4]arene 1:1 toluene complex has been investigated by comparison of its known molecular structure at room temperature (RT) with that at 220 K determined by single crystal X-ray diffraction. The diffraction pattern showed a phase transition when the temperature was decreased from 298 to 220 K.

The structure at 220 K could be solved assuming a twin by pseudo-merohedry with a fourfold twin axis [001] relating two monoclinic components with equal volumes of space group P 112/a a = b = 17.899(2), c = 13.827(1) Å, V = 4429.8(8) ų, Z = 2, mol. weight 741.06 a.m.u., D _calc = 1.111 g·cm^?3.

The structure refinement converged to R1 = 0.103 and wR2 = 0.256 for 1655 unique observed data.

The complex exists in two different conformations of the hosts which exhibit two different host-guest structural relationships both indicating that the most relevant differences induced by the low temperature are concerning the host-guest interaction mode.

Particularly unexpected is the different temperature dependence of the CH₃…π interactions between the tert-butyl of the host and the aromatic moiety of the guest with respect to that of the van der Waals interactions. The CH₃…π interactions, which stabilizes the complex at RT, strongly decrease as the temperature decreases.     

Determination of Binding Strengths of Host-Guest Complexes in Deep Eutectic Solvents Using Spin Probe Methodology

Electron paramagnetic resonance (EPR) and spin probe methodologies have been employed to study the complexation properties of cyclodextrins (CDs) and cucurbit[n]urils (CB[n]s) in the deep eutectic solvent (DES) choline chloride-urea. In the presence of γ-CD an affinity constant very similar to that measured in water was measured in DES with benzyl-tert-butyl nitroxide (BTBN). With β-CD, complexation of BTBN is significantly depressed, although still maintained. Complexation of TEMPO radical probe by CB[7] or CB[8] was instead almost entirely cancelled in DES. In addition, this methodology enabled for the first time to measure the single rate constants for the association and dissociation processes with CDs in DES.     

Structural Stability of the CO2@sI Hydrate: a Bottom-Up Quantum Chemistry Approach on the Guest-Cage and Inter-Cage Interactions

Through reliable first-principles computations, we have demonstrated the impact of CO₂ molecules enclathration on the stability of sI clathrate hydrates. Given the delicate balance between the interaction energy components (van der Waals, hydrogen bonds) present on such systems, we follow a systematic bottom-up approach starting from the individual 5¹² and 5¹²6² sI cages, up to all existing combinations of two-adjacent sI crystal cages to evaluate how such clathrate-like models perform on the evaluation of the guest-host and first-neighbors inter-cage effects, respectively. Interaction and binding energies of the CO₂ occupation of the sI cages were computed using DF-MP2 and different DFT/DFT−D electronic structure methodologies. The performance of selected DFT functionals, together with various semi-classical dispersion corrections schemes, were validated by comparison with reference ab initio DF-MP2 data, as well as experimental data from x-ray and neutron diffraction studies available. Our investigation confirms that the inclusion of the CO₂ in the cage/s is an energetically favorable process, with the CO₂ molecule preferring to occupy the large 5¹²6² sI cages compared to the 5¹² ones. Further, the present results conclude on the rigidity of the water cages arrangements, showing the importance of the inter-cage couplings in the cluster models under study. In particular, the guest-cage interaction is the key factor for the preferential orientation of the captured CO₂ molecules in the sI cages, while the inter-cage interactions seems to cause minor distortions with the CO₂ guest neighbors interactions do not extending beyond the large 5¹²6² sI cages. Such findings on these clathrate-like model systems are in accord with experimental observations, drawing a direct relevance to the structural stability of CO₂@sI clathrates.     

Controlling Aromatic Inclusion Within Nonaqueous Copper Iodide Coordination Polymers

Abstract

The formation and characterization of two novel coordination polymers based upon copper iodide and pyrazine have been observed that demonstrate varying aromatic inclusion. By changing the solvent from 1,2-dichlorobenzene to nitrobenzene, the ability to include the solvent as a guest molecule within the two-dimensional coordination polymer has been realized. In the nitrobenzene example, unlike the 1,2-dichlorobenzene example, honeycomb shaped cavities form along the polymeric chain that allows aromatic inclusion.     

Host‐Guest Complexations Between Pillar[6]arenes and Neutral Pentaerythritol Derivatives

It is demonstrated that three kinds of neutral pentaerythritol derivatives possess promising host‐guest complexations with pillar[6]arenes both in solution and in the solid state. The inclusion structures were characterized by NMR spectroscopy and X‐ray crystallography. The complexation properties in different solvents were also investigated.