<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="6.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Hurtado, P.</style></author><author><style face="normal" font="default" size="100%">Gamez, F.</style></author><author><style face="normal" font="default" size="100%">Hamad, S.</style></author><author><style face="normal" font="default" size="100%">Martinez-Haya, B.</style></author><author><style face="normal" font="default" size="100%">Steill, J. D.</style></author><author><style face="normal" font="default" size="100%">Oomens, J.</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Multipodal coordination of a tetracarboxylic crown ether with NH4+: A vibrational spectroscopy and computational study</style></title><secondary-title><style face="normal" font="default" size="100%">Journal of Chemical Physics</style></secondary-title><alt-title><style face="normal" font="default" size="100%">J. Chem. Phys.</style></alt-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">(18-CROWN-6)-TETRACARBOXYLIC</style></keyword><keyword><style  face="normal" font="default" size="100%">ACID</style></keyword><keyword><style  face="normal" font="default" size="100%">AMINO-ACIDS</style></keyword><keyword><style  face="normal" font="default" size="100%">CAPILLARY-ELECTROPHORESIS</style></keyword><keyword><style  face="normal" font="default" size="100%">CHIRAL STATIONARY PHASES</style></keyword><keyword><style  face="normal" font="default" size="100%">COMPLEXES</style></keyword><keyword><style  face="normal" font="default" size="100%">GAS-PHASE</style></keyword><keyword><style  face="normal" font="default" size="100%">INFRARED-SPECTROSCOPY</style></keyword><keyword><style  face="normal" font="default" size="100%">METAL-CATIONS</style></keyword><keyword><style  face="normal" font="default" size="100%">NUCLEAR-MAGNETIC-RESONANCE</style></keyword><keyword><style  face="normal" font="default" size="100%">RECOGNITION</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2012</style></year><pub-dates><date><style  face="normal" font="default" size="100%">Mar</style></date></pub-dates></dates><urls><web-urls><url><style face="normal" font="default" size="100%">&lt;Go to ISI&gt;://WOS:000302214200020 </style></url></web-urls></urls><number><style face="normal" font="default" size="100%">11</style></number><volume><style face="normal" font="default" size="100%">136</style></volume><pages><style face="normal" font="default" size="100%">6</style></pages><isbn><style face="normal" font="default" size="100%">0021-9606</style></isbn><language><style face="normal" font="default" size="100%">English</style></language><abstract><style face="normal" font="default" size="100%">The elucidation of the structural requirements for molecular recognition by the crown ether (18-crown-6)-2,3,11,12-tetracarboxylic acid (18c6H(4)) and its cationic complexes constitutes a topic of current fundamental and practical interest in catalysis and analytical sciences. The flexibility of the central ether ring and its four carboxyl side arms poses important challenges to experimental and theoretical approaches. In this study, infrared action vibrational spectroscopy and quantum mechanical computations are employed to characterize the conformational structure of the isolated gas phase complex formed by the 18c6H(4) host with NH4+ as guest. The results show that the most stable gas-phase structure is a barrel-like conformation sustained by tetrapodal H-bonding of the ammonia cation with two C=O side groups and with four oxygen atoms of the ether ring in a bifurcated arrangement. Interestingly, a similar structure had been proposed in previous crystallographic studies. The experiment also provides evidence for a significant contribution of a higher energy bowl-like conformer with features resembling those adopted by 18c6H(4) in the analogous complexes with secondary amines. Such a conformation displays H-bonding between confronted side carboxyl groups and tetrapodal binding of the NH4+ with the ether ring and with one C=O group. Structures involving even more extensive intramolecular H-bonding in the 18c6H(4) substrate are found to lie higher in energy and are ruled out by the experiment. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3693518]</style></abstract><work-type><style face="normal" font="default" size="100%">Article</style></work-type><accession-num><style face="normal" font="default" size="100%">WOS:000302214200020</style></accession-num><notes><style face="normal" font="default" size="100%">ISI Document Delivery No.: 917YGTimes Cited: 0Cited Reference Count: 31</style></notes><custom1><style face="normal" font="default" size="100%">GUTHz</style></custom1><custom2><style face="normal" font="default" size="100%">Molecular Dynamics</style></custom2><auth-address><style face="normal" font="default" size="100%">[Hurtado, Paola; Gamez, Francisco; Hamad, Said; Martinez-Haya, Bruno] Univ Pablo de Olavide, Dept Phys Chem &amp; Nat Syst, Seville 41013, Spain. [Steill, Jeffrey D.] FOM Inst Plasma Phys Rijnhuizen, NL-3439 MN Nieuwegein, Netherlands. [Oomens, Jos] Univ Amsterdam, NL-1098 XH Amsterdam, Netherlands.Martinez-Haya, B (reprint author), Univ Pablo de Olavide, Dept Phys Chem &amp; Nat Syst, Seville 41013, Spainbmarhay@upo.es</style></auth-address></record></records></xml>