Crystal structure and thermodynamics of reversible molecular capsules

Journal of the American Chemical Society

Volumn 120, Issue 25, 1998, Pages 6252-6260

  Chapman, Robert G ^a   Olovsson, Gunnar ^a   Trotter, James ^a   Sherman, John C ^a  

^a UNIVERSITY OF BRITISH COLUMBIA   (Canada)

Author keywords

[No Author keywords available]

Indexed keywords

ARTICLE; COMPLEX FORMATION; CROSS LINKING; CRYSTAL STRUCTURE; HYDROGEN BOND; THERMODYNAMICS;

EID: 0032126687     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja980081n     Document Type: Article

References (43)

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22. Abbreviations: GDS, guest determining-step (the GDS is also the product-determining step; we use GDS because our focus is on the guest or template effect in the assembly process; just as a product ratio reflects the relative rates of a product-determining step, in our system, the template ratios reflect the relative rates of the GDS); NMP, N-methylpyrrolidinone; DBU, 1,8-diazabicyclo[5.4.0]undec-7-ene; CHB, charged hydrogen bond; Δδ, the difference in chemical shifts, usually between free and entrapped guests; DMA, dimethylacetamide; TBA, tetrabutylammonium; CPK, Corey-Pauling-Koltun.
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24. 1H NMR spectrometer at 200 K before acquisition of the spectrum.
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28. The chemical shift of the CHB protons was highly sensitive to small amounts of water (the sample was run containing molecular sieves, which catalyze H/D exchange with acetone as well as the condensation of acetone, which generates more water). Thus, the Δδ of protons versus deuterons, which is an indication of hydrogen bond strength, was not possible. See: (a) Cleland, W. W. Biochemistry 1992, 31, 317-319. (b) Smirnov, S. N.; Golubev, N. S.; Denisov, G. S.; Benedict, H.; Schah-Mohammedi, P.; Limbach, H.-H. J. Am. Chem. Soc. 1996, 118, 4094-4101.
29. + further complicated the spectrum.
30. The doubly charged bis-bowl species observed by ESI have some kinetic stability, but are not likely to be thermodynamically stable enough to be observed in solution, according to the data presented in Figure 2.
31. Chapman, R. G.; Sherman, J. C. Manuscript in preparation.
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33. Resolution enhancement of these signals indicated they were coupled, J = 1 Hz. Enhancement was done by performing a Gaussian multiplication (GB = 0.5) of the free-induction decay and setting line broadening to -1.
34. Hz is the separation of the signals in Hz. See: Abraham, R. J.; Fisher, J.; Loftus, P. Inlroduction to NMR Spectroscopy; Wiley: New York, 1990; pp 194-197.
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39. 1H NMR signals for the host signals of complex 3b•guest. Guest 1 and guest 2 were added in ratios that yield a ∼ 1:1 ratio of complex 3b•guest 1:complex 3b•guest 2, and such that the total amount of free species that remained represented less than 15% of the total concentration of host.
40. The exchange rate of pyrazine is assumed to be the slowest of the guests at all temperatures, and decomplexation is assumed to be the slowest step in achieving equilibrium (i.e., the in-rates of all guests are much faster than the out-rate of pyrazine at all concentrations of guests studied). The decomplexation rate of pyrazine from complex 3b•pyrazine was shown to be much slower than the decomplexation rates of dioxane or DMSO from complexes 3b•dioxane and 3b•DMSO, respectively, at ambient temperature (see Experimental Section).
41. Reichardt, C. Solvents and Solvent Effects in Organic Chemistry, 2nd ed.; VCH: New York, 1988.
42. 5.
43. 2+ salt, which would have remained on the silica gel during column chromatography.