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Enrico Dalcanale

Publications and source records attributed to Enrico Dalcanale.

15 recordsLinked to original sources
PubMed2006

Grafting cavitands on the Si(100) surface.

Cavitand molecules having double bond terminated alkyl chains and different bridging groups at the upper rim have been grafted on H-terminated Si(100) surface via photochemical hydrosilylation of the double bonds. Pure and mixed monolayers have been obtained from mesitylene solutions of either pure cavitand or cavitand/1-octene mixtures. Angle resolved high-resolution X-ray photoelectron spectroscopy has been used as the main tool for the monolayer characterization. The cavitand decorated surface consists of Si-C bonded layers with the upper rim at the top of the layer. Grafting of pure cavitands leads to not-well-packed layers, which are not able to efficiently passivate the Si(100) surface. By contrast, monolayers obtained from cavitand/1-octene mixtures consist of well-packed layers since they prevent silicon oxidation after aging. AFM measurements showed that these monolayers have a structured topography, with objects protruding from the Si(100) surface with average heights compatible with the expected ones for cavitand molecules.

Journal Article↗
PubMed2006

Conformational behavior of pyrazine-bridged and mixed-bridged cavitands: a general model for solvent effects on thermal "vase-kite" switching.

The controllable switching of suitably bridged resorcin[4]arene cavitands between a "vase" conformation, with a cavity capable of guest inclusion, and a "kite" conformation, featuring an extended flattened surface, provides the basis for ongoing developments of dynamic molecular receptors, sensors, and molecular machines. This paper describes the synthesis, X-ray crystallographic characterization, and NMR analysis of the "vase-kite" switching behavior of a fully pyrazine-bridged cavitand and five other mixed-bridged quinoxaline-bridged cavitands with one methylene, phosphonate, or phosphate bridge. The pyrazine-bridged resorcin[4]arene cavitand displayed an unexpectedly high preference for the kite conformation in nonpolar solvents, relative to the quinoxaline-bridged analogue. This observation led to extensive solvent-dependent switching studies that provide a detailed picture of how solvent affects the thermal vase-kite equilibration. As for any thermodynamic process in the liquid phase, the conformational equilibrium is affected by how the solvent stabilizes the two individual states. Suitably sized solvents (benzene and derivatives) solvate the cavity of the vase form and reduce the propensity for the vase-to-kite transition. Correspondingly, the kite geometry becomes preferred in bulky solvents such as mesitylene, incapable of penetrating the vase cavity. As proposed earlier by Cram, the kite form is preferred at low temperatures due to the more favorable enthalpy of solvation of the enlarged surface. Furthermore, the kite conformation is more preferred in solvents with substantial hydrogen-bonding acidity: weak hydrogen-bonding interactions between the mildly basic quinoxaline and pyrazine nitrogen atoms and solvent molecules are more efficient in the open kite than in the closed vase form. Vase-to-kite conversion is entirely absent in dipolar aprotic solvents lacking any H-bonding acidity. Thermal vase-kite switching requires fully quinoxaline- or pyrazine-bridged cavitands, whereas pH-controlled switching is also applicable to systems incorporating only two or three such bridges.

Journal Article↗
PubMed2006

Metal-directed self-assembly of cavitand frameworks.

The self-assembly between bidentate cavitand ligands and mono/dinuclear metal precursors to give cavitand frameworks has been explored. For this purpose, two new cavitands bearing AB and AC phenylpyridyl moieties at the upper rim have been synthesized. A series of self-assembled molecular dimers featuring fac-Re(CO)(3)Br as metal corners have been prepared and characterized. Two possible dimeric structures (C-shaped and S-shaped) are possible when AB cavitand 2 is used in the self-assembly reaction; only one is obtained in the case of AC cavitand 3. In addition, the self-assembly of AB-dibridged cavitand 2 with dinuclear Pd/Pt metal precursors 5a and 5b has been studied. At this level of complexity, the self-assembly can lead to more than one structure. Several different final structures have been envisioned and their formation analyzed in silico and in solution. Out of the three possible cyclic structures (dimer, trimer, and tetramer), only the entropically favored dimer 6a (6b) is formed, as predicted from molecular modeling and demonstrated by PGSE NMR experiments.

Journal Article↗
PubMed2006

ESI-FTICR mass spectrometric study of alcohol complexation properties of mono- and diphosphonate-bridged cavitands.

Alcohol complexation properties of eight mono- and diphenyl phosphonate-bridged cavitands were studied by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR) and theoretical calculations. The cavitands varied in number and position of phenyl phosphonate bridges and their orientation with respect to the cavity, length of the lower rim alkyl chains, and substituents at apical positions of the resorcarene skeleton. The specificities of the different cavitands toward primary, secondary, and tertiary alcohols varying long of the alkyl chain were investigated, together with the stabilities of the formed complexes. The number, position, and orientation of the P = O moieties affected the complex formation of the cavitands and stability of the complexes dramatically. Methyl groups at apical positions of the resorcarene skeleton also affected the complexation properties. Although length and branching of the alkyl chain of the alcohol influenced the complex formation, the effect on stability of the complexes was negligible.

Acetonitriles↗
PubMed2005

Proton driven vase-to-kite conformational change in cavitands at an air-water interface monitored by surface SHG.

The conformational changes of quinoxaline-bridged cavitands deposited as Langmuir films were monitored at different pH values of the subphase using surface second harmonic generation during the compression of the monolayer at the water surface. A quantitative analysis of the susceptibility tensor elements was performed for methylene (MeCav)- and quinoxaline (QxCav)-bridged cavitands for pH values varying between 5.7 and 0.1. For MeCav (reference compound), no significant changes were observed for different pHs, confirming that the cavity does not undergo protonation or a drastic conformational change. For the QxCav, however, the results suggest a partial opening of the cavity on the basis of analysis of the compression curves.

Air↗
PubMed2005

Dynamic and structural NMR studies of cavitand-based coordination cages.

The interionic structure, kinetic stability, and degree of anion encapsulation of coordination cages 1 were studied by PGSE, NOE, and EXSY NMR techniques. The rate constants for the formation/dissociation processes at 296 K were obtained independently via (1)H-NOESY and (19)F-NOESY experiments giving, respectively, k(obs) = 0.30 +/- 0.04 s(-1) in CDCl(3) and k(obs) = 5.2 +/- 0.8 s(-1) in CD(3)NO(2)/CDC(13) (7.1) mixture with the proton probe, and k(obs) = 0.33 +/- 0.06 s(-1) in CDCl(3) and k(obs) = 5.0 +/- 0.8 s(-1) in CD(3)NO(2)/CDC(13) (7/1 mixture) with the (19)F probe. PGSE experiments showed that in CDCl(3) not only the encapsuled anion but also the external anions translate with the same rate as the cage. (19)F,(1)H-HOESY experiments indicated that an average of five external triflate anions are located in the equatorial sites close to the palladium moieties, while two of them approach the polar pockets formed by the alkyl chains. In a CD(3)NO(2)/CDCl(3) (7/1) mixture only one or two anions are in close proximity with the cage, while the others are solvated. In all the considered solvents (benzene, chloroform, methylene chloride, and nitromethane) the inclusion of a single unsolvated triflate anion in the cage is quantitative. (19)F,(1)H-HOESY experiments indicated that the charged guest head points toward one metal center. Therefore, while the ionic aggregation level and kinetic stability of coordination cages 1 are solvent dependent, anion encapsulation is not.

Journal Article↗
PubMed2005

Design and self-assembly of ditopic and tetratopic cavitand complexes.

The self-assembly of open ditopic and tetratopic cavitand complexes has been investigated by using monofunctionalized cavitand ligands and suitable metal precursors. In the case of ditopic complexes, self-assembly protocols, leading exclusively to the formation of both thermodynamically stable cis-Pt square-planar complexes 8 and 9 and the kinetically inert fac-Re octahedral complex 14, have been elaborated. The use of cis-[Pt(CH3)CN)2Cl2] as metal precursor led to the formation of monotopic trans-10 and ditopic trans-11 cavitand complexes, while cis-[Pt(dmso)2Cl2] afforded both cis-13 and trans-11 isomers. The self-assembly of tetratopic cavitand complexes has been achieved by using mononuclear [Pd(CH3CN)4(BF4)2] and dinuclear [M2(tppb)(OTf)4] (19: M = Pt; 20: M = Pd) metal precursors. Only the tetratopic dinuclear complexes 21 and 22 were stable. The ligand configuration with two phosphorus and two cavitand ligands at the metal centers is the most appropriate to build tetratopic cavitand complexes with sufficient kinetic stability.

Journal Article↗
PubMed2004

Cavitand-based nanoscale coordination cages.

This communication reports design, self-assembly, solution, and solid-state characterization of nanoscale coordination cages formed by tetradentate cavitand ligands and appropriate metal precursors. The preorganization of the cavitand ligand in terms of structural rigidity and relative orientation of the pyridyl units leads to the exclusive formation of coordination cages in a wide temperature and concentration range. Desired features of the cage self-assembly process, such as reversibility in the presence of a competitive ligand and self-recognition of the cavitand components, have been assessed.

Journal Article↗
PubMed2004

Surface-confined single molecules: assembly and disassembly of nanosize coordination cages on gold (111).

A cavitand functionalized with four alkylthioether groups at the lower rim, and four tolylpyridine groups on the upper rim is able to bind to a gold surface by its thioether groups, and forms a coordination cage with [Pd(dppp)(CF(3)SO(3))(2)] by its pyridine groups. The cavitand or the cage complex can be inserted from solution into a self-assembled monolayer (SAM) of 11-mercaptoundecanol on gold. The inserted molecules can be individually detected as they protrude from the SAM by atomic force microscopy (AFM). The cages can be reversibly assembled and disassembled on the gold surface. AFM can distinguish between single cavitand and cage molecules of 2.5 nm and 5.8 nm height, respectively.

Journal Article↗
PubMed2003

Investigation of the origin of selectivity in cavitand-based supramolecular sensors.

The sensing properties of functionalized cavitands have been studied by thin-film coating TMSR chemical sensors and by measuring their responses towards model analytes. We studied the relationship between the sensor performance, in terms of sensitivity and selectivity, and the molecular recognition properties of the cavitands. The Langmuir-like shape of the adsorption isotherm, obtained in the case of short-chain alcohols, demonstrated that selective binding can be achieved by the synergistic interactions of the cavity and the bridging PO(in) groups. In the absence of these substituents, the peripheral alkyl chains necessary for the formation of highly permeable thin films attenuate the cavity effect because of nonspecific dispersion interactions. This completely overrides the response originating from molecular recognition. The same effect is observed when the PO groups are oriented outward from the cavity. The use of multivariate chemometrics and the study of the correlations between sensors sensitivity and analyte properties provided further evidence of molecular recognition phenomena, whose intensity is enhanced by the permanent free volume created by the rigid cavity surrounding the PO(in) group.

2-Propanol↗
PubMed2003

Rational design of cavitand receptors for mass sensors.

This Communication describes a rational approach to the fabrication of selective mass sensors, using multiple hydrogen-bonding type interactions encoded in a single cavitand receptor. The introduction of two inward facing hydrogen bond acceptor PO groups at the upper rim of a cavitand renders the corresponding receptor layer deposited on a mass transducer highly selective toward alcohol vapors. The molecular origin of the increased selectivity has been identified in the presence of two energetically and geometrically equivalent interaction modes available to the guest, giving to the corresponding complexes an entropic advantage over their mono PO analogues.

Journal Article↗
PubMed2002

Design and self-assembly of wide and robust coordination cages.

The self-assembly of a new class of coordination cages formed from two tetrapyridyl-substituted cavitands connected through four square-planar palladium or platinum complexes is reported. The shape of the internal cavity resembles an ellipsoid with a calculated volume of 840 A(3). The four lateral portals have a diameter of about 6 A, large enough to allow the fast entrance/egress of counterions in solution. The platinum cages 3a,e cannot be disassembled using triethylamine as competitive ligand and they are kinetically stable at room temperature, whereas the palladium cages 3b-d, 3f-h are disassembled and kinetically labile under the same conditions. The different solubility properties of the cage components have allowed the extension of this self-assembly protocol to the liquid-liquid interface.

Chromatography, High Pressure Liquid↗
PubMed2001

Direct Observation of Surface-Controlled Self-Assembly of Coordination Cages by Using AFM as a Molecular Ruler We acknowledge the Nanolink Program of the MESA(+) Research Institute (University of Twente), the CNR Nanotechnology Programme, and MURST (Project Molecular Nanoelectronics) for financial support of this work. A special thanks goes to Dr. Maik Liebau (University of Twente) for the preparation of the microcontact-printed substrates and Dr. Frank Geurts (AKZO NOBEL, Central Research Arnhem, NL) for the XPS measurements.

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Journal Article↗