Investigations into the mechanisms of molecular recognition with imprinted polymers

Macromolecules

Volumn 32, Issue 12, 1999, Pages 4113-4121

  Katz, Alexander ^a   Davis, Mark E ^a  

^a California Institute of Technology   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ADSORPTION; CHEMICAL BONDS; CROSSLINKING; FOURIER TRANSFORM INFRARED SPECTROSCOPY; MOLECULES; MONOMERS; ORGANIC POLYMERS; PHASE SEPARATION; POLYMERIZATION; SINGLE CRYSTALS; X RAY CRYSTALLOGRAPHY;

BINDING MONOMER; IMPRINTED POLYMERS; MOLECULAR RECOGNITION;

MOLECULAR DYNAMICS;

EID: 0032678647     PISSN: 00249297     EISSN: None     Source Type: Journal    
DOI: 10.1021/ma981445z     Document Type: Article

References (47)

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26. -1 have been observed for the N-H stretching vibrations corresponding to each of the three functional groups involved in the hydrogen bonding between the adenine and uracil derivatives 2,6-diamino-9-ethylpurine and 1-cyclohexyl-5-bromouracil, respectively (Kyogoku, Y.; Lord, R. C.; Rich, A. Proc. Natl. Acad. Sci. U.S.A. 1967, 57, 250).
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29. 13C NMR in deuterated chloroform was used to corroborate the FTIR results. To avoid accidental overlap of the carbonyl carbon resonances between the amide 3 and the acid 2, a titration experiment was performed with the structurally similar propionic acid and 3 using the same experimental conditions described in the paper for the FTIR titration. It has been previously established that a hydrogen bond involving the C=O functional group shifts the carbonyl carbon resonance downfield (Kalinowski, H.; Berger, S.; Braun, S. Carbon-13 NMR Spectroscopy; John Wiley & Sons: New York, 1988). No downfield shift in the amide carbonyl carbon resonance of 3 was observed during the course of titrating up to 4 mol equiv of propionic acid.
30. 1H NMR of the crystals isolated from the polymer was performed under the same conditions as discussed for the NMR acid titration experiment (the crystal was dissolved at the same concentration of 3 in deuterated chloroform). Integration of the exchangeable proton yielded approximately three protons indicative of a 1:1 molar ratio of 2 and 3 in the crystal. By measuring the chemical shift of the exchangeable proton at 23°C to be 5.24 ppm under the same conditions as in Figure 4a (see Supplementary Information where 5.27 ppm is predicted from the NMR acid titration experiment in deuterated chloroform), it was determined that the crystals comprised a 1:1 molar ratio of 2 and 3.
31. In an attempt to resolve any potential differences between crystals grown in the polymer during material synthesis and crystals grown for the single crystal study as described in the paper, X-ray powder diffraction on the single crystals and the collected material from the polymer synthesis was performed. The overlap in the X-ray powder diffraction patterns indicates that the material formed under polymerization conditions is indeed structurally the same with that synthesized under more careful conditions to yield larger single crystals.
32. Félix, O.; Hosseini, M. W.; DeCian, A.; Fischer, J. Angew. Chem., Int. Ed. Engl. 1997, 36, 102.
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37. Further Soxhlet extraction of P1 in a mixture of 7:3 MeOH: acetic acid (v:v) for 24 h and chloroform for 36 h resulted in a polymer posessing an imprint adsorption capacity differing by less than 1% relative to P1. Furthermore, no increase in the enantioselectivity was observed by comparison to P1 upon imprint rebinding. Confocal fluoresence microscopy (Biorad 600 confocal fluoresence microscope using excitation wavelength of 568 nm and emission wavelength of long-pass filter 50% level at 587 nm) was used to observe occluded imprint following extraction. An imprinted polymer was synthesized and processed for this purpose according to the same experimental procedure as for P1 only using L-phenylalanine β-naphthylamide (Sigma) as the imprint. The faint fluorescence observed in the extracted polymer signifies that some imprint still remains in the polymer after extraction.
38. Sellergren, B.; Ekberg, B.; Mosbach, K. J. Chromatogr. 1985, 347, 1.
39. As determined by Wulff et al. (ref 16), the reference polymer P3 did not possess enantioselectivity for 3 at the adsorption conditions used in this investigation. This result does not preclude the validity of either Scheme 1 or Scheme 2, since imprint has not been extracted for the creation of void spaces.
40. -3 mmol of theoretical binding sites per 40 mg of extracted imprinted polymer (based on the amount of imprint originally in the polymer prior to extraction). P1 adsorbed the equivalent 1.68% of the theoretical maximum of sites with 3 while P2 adsorbed the equivalent of 1.88% of the theoretical maximum of sites with 3. Calculating the difference between these two polymers and dividing it by the fraction of 4 in P2 (0.01%) gives 19 ± 11 molecules of 3 adsorbed per fragment of 4.
41. The mechanism represented by Scheme 2 affords a nonlinear adsorption isotherm, as the environment an adsorbing molecule experiences in such a case is strongly dependent on the number of molecules already adsorbed adjacent to the binding site in Scheme 2.
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47. Prior to extracting any of the polymers, the rates of mass transfer under the adsorption conditions used (at room temperature) were investigated. The time to achieve mass-transfer-limited equilibration in a L-PheNHPh imprinted polymer (prepared identically to the procedure given for P1) was less than 10 min for both the L- and D-enantiomers of 3 (with the particle sizes used in this work).