Carmine Gaeta

Pseudorotaxanes with self-sorted sequence and stereochemical orientation.

Partner preferences in pseudorotaxane formation were exploited to establish an integrative self-sorting system able to discriminate simultaneously at the sequence and stereochemical level (see picture). It was found that calix[6]arenes were threaded selectively with a preferred orientation onto bisammonium axles, even when the structural differences between the possible building blocks were small and located remote from the binding sites.

Fixed or Invertible Calixarene-Based Directional Shuttles

The first examples of rotaxanes based on calixarenes threaded by dialkylammonium ions, which also represent the first examples of calixarene-based molecular shuttles, are reported. The base/acid treatment demonstrated that these systems act as molecular shuttles, which move between three sites on the axle. When small OMe groups are appended at the calix[6]arene lower rim an unprecedented inversion of its shuttling direction is observed, which occurs through a cone-to-cone inversion of the macrocycle.

Stereoprogrammed direct synthesis of calixarene-based [3]rotaxanes.

Directional calixarene wheels were threaded along a bis(benzylalkylammonium) axle in a stereoprogrammed way to obtain the first examples of calixarene-based [3]rotaxanes. The base/acid treatment demonstrated that these systems act as nanosized molecular shuttles. An unprecedented switching between the tail-to-tail and head-to-head relative orientation of the calix-wheels was observed.

Absolute configuration assignment of inherently chiral calix[4]arenes using DFT calculations of chiroptical properties.

The racemate of an inherently chiral meta-substituted calix[4]arene derivative 3 has been resolved via enantioselective HPLC. Measured optical rotation dispersion and electronic circular dichroism have been compared with DFT theoretical predictions. The comparison indicates that the absolute configuration of the dextrorotatory enantiomer (+)-3 is cS. The procedure has been successfully tested against a literature precedent confirming the validity of the method.

Methane Adsorption in a Supramolecular Organic Zeolite

Gas storage in solids is an increasingly important research area with applications in the field of energy, environment, biology and medicine. Because it concerns the adsorption of methane, the main component of natural gas fuels, the storage target for any solid to be effective in energy applications and compete with the compressed form is approximately 35 wt % or 180 v/v. Several different types of porous materials such as carbon materials, zeolites, silica gels, MOFs and polymers have been recently examined in addition to organic crystalline microporous solids and nonporous ones, but no ideal candidates have emerged so far. In this paper we wish to report on the methane adsorption properties of a new microporous organic zeolite based on 1,2-dimethoxy-p-tert-butylcalix[4]dihydroquinone (Scheme 1), which has been recently characterised by our research group. The crystalline solid has a cubic structure (a= 36.412(4) ) with networked channels and hydrophobic cages. The channels have minimum and maximum diameter of 3.9 and 8.5 , respectively, excluding van der Waals radii, and they are filled with easily removable water molecules. The hydrophobic cages show a gate diameter of 2.2 and can reach a maximum diameter of 11.2 (excluding van der Waals radii), and the estimated cage volume is about 1000 . Interestingly, the supramolecular framework is also preserved after the removal of channel water molecules. Previous studies showed that the BET surface area corresponds to 230 m g 1 (N2 at 77 K) and that carbon dioxide can be absorbed at room temperature inside its nanochannels with high selectivity with respect to H2 gas, [9] encouraging further studies towards methane adsorption. Methane adsorption measurements were performed by using a home-made volumetric system. Sorption isotherms have been carried out at 298, 278 and 203 K. Data have been collected at initial pressures between 0.5 and 3 atm. The adsorption isotherm at 203 K is reported in Figure 1, (see the Supporting Information for adsorption isotherms at 298 and 278 K). At 1 atm and 298 K our compound adsorbs 0.11 methane molecules for each calixarene molecule. For comparison, p-tert-butylcalix[4]arene adsorbs 0.14 methane molecules for each calixarene molecule under the same conditions. Under the mild conditions of ambient pressure and temperature our sample shows an efficiency for methane storage of 0.29 wt %, whereas in the case of CO2 molecules the value was 0.5 wt %. The adsorption isotherm at 203 K is not of type I. The adsorption step at 2 atm could be interpreted by considering that at first the methane molecules enter the channels, interacting with the most favourite sites, and then upon increasing the pressure the channels are progressively filled. Note that there are 90 methane molecules in the unit cell at 3 atm pressure, which approximately corresponds to a 1:2 ratio between calixarene molecules and methane molecules. [a] Dr. C. Tedesco, Dr. L. Erra, Dr. V. Cipolletti, Dr. C. Gaeta, Prof. P. Neri Department of Chemistry and Nano_MATES Research Center University of Salerno, 84084 Fisciano (Italy) Fax: (+39) 089-969603 E-mail : ctedesco@unisa.it neri@unisa.it [b] Dr. M. Brunelli, Prof. A. N. Fitch European Synchrotron Radiation Facility 38043 Grenoble (France) [c] Prof. J. L. Atwood Department of Chemistry University of Missouri-Columbia Columbia, Missouri 65211 (USA) [d] Dr. M. Brunelli Current address: ILL Institut Laue-Langevin BP 156, 38042 Grenoble Cedex 9 (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200903218. Scheme 1. 1,2-Dimethoxy-ptert-butylcalix[4]dihydroquinone.

Conformational features and recognition properties of a conformationally blocked calix[7]arene derivative.

The shaping of a calix[7]arene macrocycle into cone-like structure 3, through exhaustive alkylation of doubly bridged calix[7]arene derivative 2 with bulky groups, has been investigated. Conformational details about the structure adopted by calix[7]arene derivative 3 in solution have been obtained by using chemical shift surface maps, as previously reported by our group. Thus, chemical shift contour plots indicated that 3 adopted a cone-shaped structure in solution analogous to that adopted by the known p-tert-butylcalix[7]arene heptacarboxylic acid derivative 4. Interestingly, the X-ray structure of derivative 3 showed a high degree of similarity to the theoretical structure, which confirmed the validity of the contour plots method. The preorganized calix[7]arene host 3 showed interesting recognition abilities toward both organic and alkali cations. In fact, an unprecedented endo-cavity complexation of linear and branched alkyl ammonium cations with a larger calix[7]arene host was evidenced. A comparable affinity for branched tBuNH(3)(+) and linear nBuNH(3)(+) guests was observed.

Convenient regioselective functionalization at the upper-rim of p-tert-butylcalix[8]arene through a protection–deprotection procedure

Abstract A viable method to obtain calix[8]arenes selectively functionalized at the upper rim of 1,5-aromatic rings is reported. The procedure relies on protected, readily accessible 1,5-xylylene-bridged derivatives, which are easily deprotected by hydrogenolysis. The method allowed the synthesis of the first examples of calix[8]arenes partially substituted with p-nitro, p-amino, quinone and hydroquinone functionalities.

Polyoxomolybdate-Calix[4]arene Hybrid: A Catalyst for Sulfoxidation Reactions with Hydrogen Peroxide

An easily accessible polyoxomolybdate-calix[4]arene hybrid 1 has been synthesized and applied as a heterogeneous catalyst in the sulfoxidation of thioethers to sulfoxides and to sulfones under strictly stoichiometric amounts of 30% H2O2 in CH3CN as the solvent. This study represents the first promising example of successful employment of calixarenes-polyoxometalate (POM) hybrid materials in the area of catalytic oxidations.

Conformationally locked calixarene-based histone deacetylase inhibitors.

Alkyl- and arylamidocalix[4]arene derivatives 1-11 have been designed and theoretically evaluated by docking studies as potential histone deacetylase inhibitors (HDACi). On the basis of the trimodal distribution of the calculated inhibition constants (K(i)), five alkyl- or arylamido derivatives (3, 7, 8, 9, and 11) were synthesized and tested. A qualitative accordance between the experimental results and the theoretical predictions was obtained, confirming that appropriately substituted arylamidocalix[4]arenes are active HDACi.

Regioselective intramolecular bridging of p-tert-butylcalix[7]arene

The first examples of doubly bridged calix[7]arenes 2a–h have been obtained by base-promoted O-alkylation of p-tert-butylcalix[7]arene 1 or 1,4-tetramethylene-bridged calix[7]arene 3a with a variety of bis-electrophiles including BrCH2Cl, oligoethylene glycol ditosylates, and 1,2-bis(bromomethyl)benzene. In the presence of Cs2CO3 as the base, in acetone, the syn-1,4:2,3-bis-bridged regioisomer was obtained in yields up to 76%. Assignment of bridging pattern was based on chemical shift of OH groups in conjunction with chemical correlations with known compounds. Stereochemical and conformational features were investigated with the aid of 2D and Dynamic NMR studies and MM3 calculations.