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Titolo:
Diastereoselective formation of host-guest complexes between a series of phosphate-bridged cavitands and alkyl- and arylammonium ions studied by liquid secondary-ion mass spectrometry
Autore:
Irico, A; Vincenti, M; Dalcanale, E;
Indirizzi:
Univ Turin, Dipartimento Chim Analit, I-10125 Turin, Italy Univ Turin Turin Italy I-10125 timento Chim Analit, I-10125 Turin, Italy Univ Parma, Dipartimento Chim Organ & Ind, I-42100 Parma, Italy Univ Parma Parma Italy I-42100 to Chim Organ & Ind, I-42100 Parma, Italy
Titolo Testata:
CHEMISTRY-A EUROPEAN JOURNAL
fascicolo: 9, volume: 7, anno: 2001,
pagine: 2034 - 2042
SICI:
0947-6539(20010504)7:9<2034:DFOHCB>2.0.ZU;2-O
Fonte:
ISI
Lingua:
ENG
Soggetto:
FAST-ATOM-BOMBARDMENT; GAS-PHASE COMPLEXATION; ALKALI-METAL ION; CROWN-ETHERS; ELECTROSPRAY-IONIZATION; BINDING SELECTIVITIES; MOLECULAR RECOGNITION; CONFIGURATIONAL ANALYSIS; DESORPTION IONIZATION; STABILITY-CONSTANTS;
Keywords:
cavitands; diastereomers; host-guest systems; hydrogen bonds; mass spectrometry;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
71
Recensione:
Indirizzi per estratti:
Indirizzo: Vincenti, M Univ Turin, Dipartimento Chim Analit, Via Pietro Giuria 5, I-10125 Turin, Italy Univ Turin Via Pietro Giuria 5 Turin Italy I-10125 rin, Italy
Citazione:
A. Irico et al., "Diastereoselective formation of host-guest complexes between a series of phosphate-bridged cavitands and alkyl- and arylammonium ions studied by liquid secondary-ion mass spectrometry", CHEM-EUR J, 7(9), 2001, pp. 2034-2042

Abstract

The reactions occurring between a new class of cavitands that carry up to four dioxaphosphocin binding units and alkyl- and arylammonium ions was investigated by liquid secondary-ion mass spectrometry (LSIMS). As the cavitands existed as distinct diastereomers with different spatial orientation of their binding groups, these geometrical differences proved to have a dramatic influence on their chemical properties, including their ability to form host-guest complexes. In practice, only the cavitands that carry at least three P=O groups oriented toward the inside of the cavity were demonstrated to be strong no ligands toward organic ammonium ions, whereas those with only two converging binding groups (either adjacent or opposite in the cavitand structure) still formed host-guest complexes, but they were much weaker. Adjacent binding sites proved to be more effective in interacting with organic ammonium ions than those lying in opposite positions. The isomers withno converging P=O groups did not act as molecular receptors. Even the isomer with one group oriented toward the inside of the cavity did not form host-guest complexes, as the absence of synergistic hydrogen bonding made the interaction from inside the cavity energetically equivalent (or even less favorable) to the outside: binding. The presence in the cavitand structure of substituents with an electron-donating character proved to increase the proton affinity of the P=O binding groups and, consequently. their binding energy. The strong proton affinity of the cavitands led to the formation of stable host-guest complexes, as con firmed by the collisionally activated dissociation experiments. Effects of steric hindrance were weak, at least for the cavitands with three converging P=O groups. This confirmed that the cavity has a wide and readily accessible opening. The relative complexation constants were measured for the various guests, yielding scales of relativeaffinity toward each cavitand. These relative constants may represent thermodynamic values referred to the matrix used in LSIMS experiments. namely 3-nitrobenzyl alcohol (NBA), provided that kinetically controlled selvedge processes are negligible. Absolute complexation constants could not be obtained on account of the unknown pH and the protonation constant in the NEA matrix.

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Documento generato il 28/09/20 alle ore 01:50:48