Calixarenes structure

Hydrogen bonds keeping most calixarene structures in the cone conformation can also be characterized by the position of the vOH band in IR spectra and the hydroxyl proton signal in the NMR spectra both are shifted with respect to the corresponding values for the free phenolic OH [lc]. 

The structure of the tetranitro derivative was confirmed by X-ray diffraction in the solid state, this compound does not possess any symmetry element. The conformation of the calixarene structure is less symmetrical than for calix[4]arene(bis crown-6). The nitro groups appear to strongly modify the usual conformation of this calixarene, and a decrease in the preorganization toward cesium complexation can be expected. 

Complexation studies were carried out by electrospray ionization mass spectrometry (ESI-MS) with three lanthanides (La, Eu, and Yr) at a concentration of 10 4 M, while the ratio of concentration of CPw2 versus calixarene (r = [calix]org/[Ln]aq) was varied between 0.1 and 10.165 The behavior of the three lanthanides is the same the 1 1 Ln calix-CMPO complex is always predominant in the range of concentration studied the 2 1 Ln calix-CMPO appears in the case of metal excess with a maximum for r = 0.5, while the percent of 1 2 Ln calix-CMPO increases as the concentration of ligand increases, but does not exceed 10% for r = 10. These studies show that two factors play a key role in the selectivity of CMPO derivatives, firstly the presence of phenyl groups on the phosphorus atom, which confers the selectivity to CMPO ligands, secondly the calixarene structure, which amplifies this selectivity due to its preorganization. Indeed the noncyclic derivative (Os2), in spite of the presence of phenyl units, does not display noticeable selectivity. 

Bott, S. G., Coleman, A. W., Atwood, J. L., Inclusion of both cation and neutral molecule by a calixarene - structure of the para leu Inily11neihoxycalix[4]aiene sodium loluene I cation.././Irn. Chem. Soc. 1986, 108, 1709-1710. 

VIII. MOLECULES CONSISTING OF SEVERAL CALIXARENE STRUCTURES A. Double Calixarenes... 

The functional groups and reactions discussed above have been used to synthesize various molecules consisting of two or more covalently linked calixarene structures . Figure 13 gives a schematic representation of the main types that have been realized. 

Figure 3.3 Calixarene structures calix[5]arene (top Left), 4-t-butyLcaLix[6]arene (bottom Left), 4-t-butyLcaLix[12]arene (right)...

Calixarenes have been extensively studied as solvent extractants for inorganic ions, stationary phases for capillary gas chromatography (GC), selectivity modifiers in CE, and as components of HPLC. The calixarene structure is quite versatile in that the lower rim can be modified to adjust solubility and the phenol groups on the upper rim are suitable for many chemical modihcations that may introduce specific selectivity. Here, we describe the application of modified calixarenes to ion chromatographic separations. 

The analysis of over 4000 entries classified as organic compounds reveals that calixarene structures are in great majority (approx. 2900 entries). Among them about 2270 entries refers to calix[4]arenes. The number of entries referring to the number of aromatic residues in the macrocyclic ring is presented in Table 38.1. 

Among calix-type compounds other than calixarenes represented in CSD the largest group consists of calixpyrroles. The number of entries in CSD for non-calixarene structures are listed in Table 38.2. 

Calixarenes Structure of an Acetonitrile Inclusion Complex and Some Transition Metal Rimmed Derivatives ... 

Xu, W., Puddephatt, R.J., Manojlovic-Muir, L., Muir, K.W., and Frampton, C.S. - Calixarenes Structure of an Acetonitrile Inclusion Complex and Some Metal Rimmed Derivatives 277... 

Fig. 16.16 (a) Examples of macrocyclic compounds used to modify CPEs. (b) Example highlighting the chemical structure of a simple calixarene from which it is easy to see the cup shape of the molecule likely to act as a host for guest species. The symbol R is not a single element but represents a group of atoms. The structure of the R group can be varied to give the basic calixarene structure a more selective action rather than simply working on the basis of size... 

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