Linked Life Data

17979283

Source:http://linkedlifedata.com/resource/pubmed/id/17979283

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PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
25
pubmed:dateCreated
2007-11-30
pubmed:abstractText
Exchange of guest molecules into capsule shaped host molecules is the most fundamental process in host-guest chemistry. Several examples of quantitative measurements of guest exchange rates have been reported. However, there have been no reports on the activation energies of these processes. A molecule known as cavitand-porphyrin (H2CP) has been reported to have a flexible host structure capable of facilitating moderate guest exchange rates suitable for kinetic measurements of the guest exchange process with 1H NMR. In this article, various kinetic and thermodynamic parameters related to the process of encapsulation of small hydrocarbons into H2CP in CDCl3 solution were determined by 2D exchange spectroscopy (EXSY): association and dissociation rate constants (k(ass) = 320 M-1 s-1, k(diss) = 1.4 s-1 for methane at 25 degrees C), the corresponding activation energies (E(a,ass) = 27 kJ.mol-1, E(a,diss) = 58 kJ.mol-1), and thermodynamic parameters for each process (DeltaG++(ass) = 59 kJ.mol-1, DeltaG++(diss) = 72 kJ.mol-1, DeltaH++(ass) = 25 kJ.mol-1, DeltaH++(diss) = 55 kJ.mol-1, DeltaS++(ass) = -113 J.K-1.mol-1, and DeltaH++(diss) = 58 J.K-1.mol-1 for methane). The thermodynamic parameters (DeltaG degrees = -13 kJ.mol-1, DeltaH degrees = -31 kJ.mol-1, DeltaS degrees = -60 J.K-1.mol-1 for methane) for this encapsulation equilibrium determined by EXSY were comparable to those for methane determined by 1D 1H NMR titration (DeltaG degrees = -11 kJ.mol-1, DeltaH degrees = -33 kJ.mol-1, DeltaS degrees = -75 J.K-1.mol-1 for methane). In addition, the structure of the methane encapsulation process was revealed by ab initio MO calculations. The activation energies for methane association/dissociation were estimated from MP2 calculations (E(a,ass) = 58.3 kJ.mol-1, E(a,diss) = 89.1 kJ.mol-1, and DeltaH degrees = -30.8 kJ.mol-1). These values are in accord with the experimentally determined values. The observed guest exchange rates and energies are compared with the corresponding values of various reported capsule-shaped hosts.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Dec
pubmed:issn
0022-3263
pubmed:author
pubmed:issnType
Print
pubmed:day
7
pubmed:volume
72
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
9448-55
pubmed:meshHeading
pubmed:year
2007
pubmed:articleTitle
Kinetic investigations of the process of encapsulation of small hydrocarbons into a cavitand-porphyrin.
pubmed:affiliation
Graduate School of Sciences, and Institute for Materials Chemistry and Engineering, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, Japan.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't