Loredana Erra

Structural Effects of Proline Substitution and Metal Binding on Hexameric Cyclic Peptoids

L-Proline and N-methoxyethyl glycine have been included in novel cyclic hexameric peptoids. Supramolecular coordination with Na(+) triggered the formation of the first 1D metal-organic framework based on peptoids.

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.

Solid state assembly of cyclic α-peptoids

The solid state assembly of free and metal coordinated cyclic α-peptoids has been examined with the aim to find common underlying features and to direct the design of new functional biomimetic materials with desired properties in terms of molecular recognition, drug delivery and catalysis. The lack of the amide proton prevents the formation of NH⋯OC hydrogen bonds and weaker interactions play a key role in the intermolecular recognition and assembly. Inter-annular CH⋯OC hydrogen bonds provide face to face or side by side arrangement of macrocycles in a way that can be considered the peptoid counterpart of β-sheet secondary structure in proteins. The choice of side chains is crucial for the solid state properties of α-cyclic peptoids. Side chains have a strong influence on the solid state assembly of peptoid macrocycles: they may provide competing interactions to CH⋯OC inter-annular hydrogen bonds, leading either to a T-shape or to a tubular arrangement of the peptoid macrocycles. The size of the macrocycle is another important factor influencing the tubular arrangement. In particular, a larger size of the macrocycle promotes side by side with respect to T-shape interactions. Hirshfeld surfaces and their fingerprint analysis allowed the analysis of the contributions of weak intermolecular interactions, such as weak CH⋯OC hydrogen bonds and CH–pi interactions, towards the crystal packing.

Cocrystals of gabapentin with C -alkylresorcin[4]arenes

The synthesis of cocrystals of gabapentin (GBP) with resorcin[4]arenes (RsCn) with different tail lengths, C-hexylresorcin[4]arene (RsC6) and C-propylresorcin[4]arene (RsC3), is reported. The structural elucidations of the two cocrystals show differences in packing arrangements and host–guest interactions.

Determination of the distribution of elements with similar electron counts: a practical guide for resonant X‐ray scattering

This article attempts to present straightforward and easy-to-understand guidelines for the determination of element distribution in compounds lacking X-ray scattering contrast because they have similar electron counts. Different sources of anomalous dispersion correction terms (especially Δf′ values) are compared with respect to their suitability, reliability and quality. Values from databases are compared with Δf values calculated from fluorescence spectra and those refined from single-crystal diffraction data, using both reference crystals without scattering contrast problems and crystals containing elements with similar electron counts. The number of data sets required to determine reliably the element distribution and the optimum wavelengths to be used are discussed. Joint multiple data set refinements are suitable for the refinement of multiply mixed occupancies of elements lacking scattering contrast. The most straightforward method of obtaining Δf′ values depends on the complexity of the problem to be solved and the precision required.

Pyrogallol[4]arenes as Frustrated Organic Solids

Two forms of interdigitated layered arrangements of C-pentylpyrogallol[4]arene (PgC5) have been structurally elucidated and show variations in packing arrangements and host-guest interactions. Molecular dynamics simulations reveal a propensity for formation of self-included dimers, with or without incorporated solvent. Combined gas sorption and PXRD results show the presence of seven forms of PgC5, with and without CO2 (and their interconversions). This is the first CO2 gas sorption study of pyrogallol[4]arenes, and it provides evidence that pyrogallol[4]arenes may act as frustrated organic solids.

A solid-state molecular capsule based on p-sulfonatocalix[7]arene and dicationic Diquat guest

An extended framework of molecular capsules based on p-sulfonatocalix[7]arene and a dicationic Diquat guest has been obtained. One Diquat guest molecule is encapsulated inside two trimeric ¾-cone subunits of two different p-sulfonatocalix[7]arene caps. The molecular capsules are sealed electrostatically by means of interactions between anionic sulfonato groups and Ba2+ cations. Interestingly, the extended capsular framework gives rise to cavities hosting water molecules.

Inclusion properties of volatile organic compounds in a calixarene-based organic zeolite.

The inclusion properties of a calixarene-based porous material have been studied to investigate the adsorption and the desorption of carbon tetrachloride, chloroform, and water in the zeolite-like structure. Uptake and release processes have been studied both by time-resolved powder X-ray diffraction and by thermogravimetric analysis to obtain structural and kinetic information. The selected guests are able to enter the structure with an increase in the host cell volume and with time-dependent diffusivity coefficients. Chloroform molecules act as a permanent porosity switch promoting a phase transition to non-porous triclinic form.

Finding crystal structures from few diffraction data by a combination of a random search with genetic algorithms.

A new procedure for performing structural analysis of crystalline materials from diffraction data by random search and genetic algorithms is described.

Solid-state assembly of 4,4’-bipyiridine and proximal p-tert-butylcalix[4]dihydroquinone units*

Abstract The solid state structure of the co-crystal between proximal p-tert-butylcalix[4]dihydroquinone, ethylacetate and 4,4’-bipyridine shows an interesting interplay of H-bond and van der Waals interactions that allow to rationalise the assembly possibilities of the calixarene compound under study.