A Combined Experimental and Theoretical Study on the Conformational Behavior of a Calix[6]arene

Role of hydrogen bonding interactions within of the conformational preferences of calix[n = 4,6,8]arene: DFT and QTAIM analysis

Understanding the interactions of the cage molecules with a variety of invited molecules is getting very important. But, the hydrogen bonds can also play a crucial role in the interaction phenomenon. In this work, natural population analysis (NPA), chemical shifts, and atom in molecules (AIM) analysis have been used to identify the role of hydrogen bonds in the stability of CX[n] molecules. According to our calculation, the ¹³C NMR spectra are also sensitive to the nature of hydrogen bonds. We note that the DFT calculations have reproduced with a very good agreement, the experimentally observed chemical shifts of CX[4].

Synthetic Evolution of the Multifarene Cavity from Planar Predecessors

The stepwise evolution of curved multifarene structures from planar precursors is demonstrated, highlighting three architectural design elements: 1) employment of various aromatic units, 2) changing the hybridization of the linking atoms from sp² to sp³ , and 3) rigidification of the system by the introduction of five-membered rings. Similar design elements have been employed to transform graphene sheets into curved carbon structures. Specifically, the stepwise synthetic evolution of multifarene[2+2], which has a curved, quite rigid structure, begins with a planar, tetraimine precursor, conversion to pairs of vicinal diamines, and the transformation of these pairs to cyclic thiourea groups. This process was probed by NMR spectroscopy and X-ray crystallography. Since varying the carbonylation conditions resulted in carbamates or thiocarbamates rather than the urea or thiourea isomers, the isomeric interconversion was studied both experimentally and by DFT computations. The carbamate versus urea preference was found to reflect either kinetic or thermodynamic control, respectively.

An experimental and theoretical study of the aggregate structure of calix[6]arenes in Langmuir films at the water/air interface

In this paper, the aggregate formation of para-tert-butylcalix[6]arene molecules (Calix6) in dimeric structures was investigated at the water/air interface using experimental and theoretical studies. A specific orientation for such Calix6 molecules was observed with an average area of 133 Å(2), which corresponds to a flat-on orientation with the OH groups parallel to the interface. By varying the pressure on the Calix6 monolayer, the molecules tend to organize at the water/air interface and subsequently, at higher pressures, aggregates were formed atop the monolayer as cluster structures. Morphological characterization by the Brewster Angle Microscopy technique showed the formation of larger domains at lower pressures. Based on such experimental evidence, molecular dynamics (MD) simulations were performed to investigate possible dimeric structures for aggregated Calix6 molecules, which are localized at the water/air interface, where one molecule remains in the water phase and the other remains in the air phase. By increasing surface pressure, experimental and theoretical results corroborate the intermolecular interactions among Calix6 molecules. These results are relevant because a dimeric structure has a molecular cavity, which is a candidate for host-guest chemistry, an ion receptor or a drug-delivery system.

Dual mode of extraction for Cs+ and Na+ ions with dicyclohexano-18-crown-6 and bis(2-propyloxy)calix[4]crown-6 in ionic liquids: density functional theoretical investigation

Experimentally observed distribution constant and theoretically predicted values of ΔG_ext for Cs⁺ and Na⁺ ions with DCH18C6 and BPC6 ligand in ionic liquid and octanol.