1,721,078 research outputs found
Synthesis of polyaromatic hydrocarbons with a central rotor
No full textA series of molecular landers comprising a central mobile part has been synthesised. The two rigid main boards consist of acenaphtho[1,2-k]fluoranthene groups, each substituted in positions 7 and 14 by 3,5-di-tert-butylphenyl groups. The boards are linked by a diethynylanthracene, a phenyl, or a biphenyl rotor
Recognition of Amides By New Rigid Calix[4]arene-based Cavitands
No full textThe synthesis of new hosts specifically designed for the recognition of amides, characterized by two binding regions: a rigid calix[4]arene cavity and a sidearm, inserted at its rim, able to form strong hydrogen bonds, is described. The binding abilities of the new receptors toward amides of general structure R1CONR2R3 have been investigated in CDCl3 solution by 1H NMR spectroscopy. When the additional binding site is the N-phenylureido group spaced by a methylene unit from the apolar cavity, binding constants up to 756 M-1 were measured. Neither the two separate potential binding sites, nor the model host, where the calix[4]arene skeleton is flexible show detectable binding ability toward the series of guests examined. The rigidity of the calix[4]arene apolar cavity is the key control element in determining the efficiency of these molecular recognition processes. The presence of NH groups in the guest controls the efficiency and selectivity of binding
Selective Mass Sensitive Devices Obtained by Calix[4]arene-based Coatings” in Sensors and Microsystems
No full textAnion Effects on the Recognition of Ion Pairs by Calix[4]arene-Based Heteroditopic Receptors
No full textA novel heteroditopic receptor (5) based on a rigid calix[4]arene cavity bearing at the upper rim four arylsulfonamido binding sites has been synthesized. The binding abilities of this new host have been investigated in apolar solvents toward a series of tetramethylammonium salts (tosylate, chloride, acetate, trifluoroacetate, and picrate) and compared with those of monotopic and heteroditopic calix[4]arene-bis(crown-3)-based receptors 1 and 2 in order to evaluate the role of the anion on ion-pair recognition. While monotopic host 1 shows an efficiency order toward the different salts that increases when the anion is less interactive (Hofmeister trend), an opposite role of the counteranion on the recognition process was observed with host 5 (anti-Hofmeister trend). A more complex behavior is experienced by host 2, which shows a high and leveled efficiency for all the anions tested. The results obtained were explained on the basis of the different types of ion pairs present in the recognition process. Further information on the role of the anion were obtained by the "dual host" strategy utilizing the tri-n-butylthioureido derivative of tren 7, which forms a stable complex with chloride anion. The very high efficiency shown by these heteroditopic hosts opens new routes in supramolecular projects and is a very interesting tool in the molecular recognition of ion-pairs and its applications
Triazole-enabled, iron-catalysed linear/branched selective C-H alkylations with alkenes
No full text: Iron-catalysed C-H alkylations with alkenes were achieved on benzamides by N-triazole assistance. A notable switch of the regioselectivity from linear to branched was observed depending on the nature of the olefin employed. The approach allowed for the synthesis of a family of decorated benzamides with ample scope and high levels of chemo-, regio- and site-selectivity
Chlorosulfonation of 2-acylthiophenes: an examination on the reaction regiochemistry
No full textChlorosulfonation of thenoyltrifluoroacetone with neat chlorosulfuric acid was found to give a 25:75 mixture of 3- and 2-chlorosulfonated thenoyltrifluoroacetone isomers in 33% overall yield. The use of dichloromethane as solvent for the chlorosulfonation reaction gave only the 2-chlorosulfonated isomer in 45% yield. On the contrary, the reaction of 2-acetylthiophene with neat chlorosulfuric acid gave only the 3-chlorosulfonated-5-acetylthiophene in 35% yield. The identity of these chlorosulfonated compounds was unambiguously established by NMR techniques and confirmed by the crystal structure determination of the 2-chlorosulfonated isomer
CALIX[6]ARENE-BASED PSEUDOROTAXANES: A SOLID STATE STRUCTURAL INVESTIGATION
No full textTriphenylureido-calix[6] arene derivatives act as a heteroditopic and asymmetrical wheel. They are able to form pseudorotaxanes with dialkylviologen salts. These supramolecular complexes are stabilised by several noncovalent interactions whose nature and role has been evidenced through single crystal X-ray diffraction and computational methods
Ion-Pair Selective Conformational Rearrangement of Sulfonamide Calix[6]arene-Based Pseudorotaxanes
Full text linkWe describe the synthesis of a new class of trisulfonamide calix[6]arene-based wheels that can bind dialkylviologen salts, in apolar media. The threading process occurs through a selective ion-pair recognition, established by the sulfonamide groups with the counterions of the bipyridinium salts, that dictates a conformational rearrangement of the corresponding pseudorotaxanes
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