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Article: Molecular dynamics simulation of amphiphilic bistable [2]rotaxane Langmuir monolayers at the air/water interface

TitleMolecular dynamics simulation of amphiphilic bistable [2]rotaxane Langmuir monolayers at the air/water interface
Authors
Issue Date2005
Citation
Journal of the American Chemical Society, 2005, v. 127, n. 42, p. 14804-14816 How to Cite?
AbstractBistable [2]rotaxanes display controllable switching properties in solution, on surfaces, and in devices. These phenomena are based on the electrochemically and electrically driven mechanical shuttling motion of the ring-shaped component, cyclobis(paraquat-p-phenylene) (CBPQT4+), between a monopyrrolotetrathiafulvalene (mpTTF) unit and a 1,5-dioxynaphthalene (DNP) unit located along a dumbbell component. The most stable state of the rotaxane (CBPQT4+ @ mpTTF) is that in which the CBPQT4+ ring encircles the mpTTF unit, but a second less favored metastable co-conformation with the CBPQT4+ ring surrounding the DNP (CBPQT 4+ @ DNP) can be formed experimentally. For both co-conformations of an amphiphilic bistable [2]rotaxane, we report here the structure and surface pressure-area isotherm of a Langmuir monolayer (LM) on a water subphase as a function of the area per molecule. These results from atomistic molecular dynamics (MD) studies are validated by comparing with experiments based on similar amphiphilic rotaxanes. For both co-conformations, we found that as the area per molecule increases the thickness of the LM decreases while the molecular tilt increases. Both co-conformations led to similar LM thicknesses at the same packing area. From the simulated LM systems, we calculated the electron density profiles of the monolayer as a function of area per molecule, which show good agreement with experimental analyses from synchrotron X-ray reflectivity measurements of related systems. Decomposing the overall electron density profiles into component contributions, we found distinct differences in molecular packing in the film depending upon the co-conformation. Thus we find that the necessity of allowing the tetracationic ring to become solvated by water leads to differences in the structures for the two co-conformations in the LM. At the same packing area, the value of the overall tilt angle does not seem to be sensitive to whether the CBPQT4+ ring is encircling the mpTTF or the DNP unit. However, the conformation of the dumbbell does depend on the location of the CBPQT4+ ring, which is reflected in the segmental tilt angles of the mpTTF and DNP units. Using the Kirkwood-Buff formula in conjunction with MD calculations, we find the surface pressure-area isotherms for each co-conformation in which the CBPQT4+ @ mpTTF form has smaller surface tension and therefore larger surface pressure than the CBPQT4+ @ DNP at the same packing area, differences that decreases with increasing area per molecule, which is verified experimentally. © 2005 American Chemical Society.
Persistent Identifierhttp://hdl.handle.net/10722/332631
ISSN
2023 Impact Factor: 14.4
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ISI Accession Number ID

 

DC FieldValueLanguage
dc.contributor.authorJang, Seung Soon-
dc.contributor.authorJang, Yun Hee-
dc.contributor.authorKim, Yong Hoon-
dc.contributor.authorGoddard, William A.-
dc.contributor.authorChoi, Jang Wook-
dc.contributor.authorHeath, James R.-
dc.contributor.authorLaursen, Bo W.-
dc.contributor.authorFlood, Amar H.-
dc.contributor.authorStoddart, J. Fraser-
dc.contributor.authorNørgaard, Kasper-
dc.contributor.authorBjørnholm, Thomas-
dc.date.accessioned2023-10-06T05:13:03Z-
dc.date.available2023-10-06T05:13:03Z-
dc.date.issued2005-
dc.identifier.citationJournal of the American Chemical Society, 2005, v. 127, n. 42, p. 14804-14816-
dc.identifier.issn0002-7863-
dc.identifier.urihttp://hdl.handle.net/10722/332631-
dc.description.abstractBistable [2]rotaxanes display controllable switching properties in solution, on surfaces, and in devices. These phenomena are based on the electrochemically and electrically driven mechanical shuttling motion of the ring-shaped component, cyclobis(paraquat-p-phenylene) (CBPQT4+), between a monopyrrolotetrathiafulvalene (mpTTF) unit and a 1,5-dioxynaphthalene (DNP) unit located along a dumbbell component. The most stable state of the rotaxane (CBPQT4+ @ mpTTF) is that in which the CBPQT4+ ring encircles the mpTTF unit, but a second less favored metastable co-conformation with the CBPQT4+ ring surrounding the DNP (CBPQT 4+ @ DNP) can be formed experimentally. For both co-conformations of an amphiphilic bistable [2]rotaxane, we report here the structure and surface pressure-area isotherm of a Langmuir monolayer (LM) on a water subphase as a function of the area per molecule. These results from atomistic molecular dynamics (MD) studies are validated by comparing with experiments based on similar amphiphilic rotaxanes. For both co-conformations, we found that as the area per molecule increases the thickness of the LM decreases while the molecular tilt increases. Both co-conformations led to similar LM thicknesses at the same packing area. From the simulated LM systems, we calculated the electron density profiles of the monolayer as a function of area per molecule, which show good agreement with experimental analyses from synchrotron X-ray reflectivity measurements of related systems. Decomposing the overall electron density profiles into component contributions, we found distinct differences in molecular packing in the film depending upon the co-conformation. Thus we find that the necessity of allowing the tetracationic ring to become solvated by water leads to differences in the structures for the two co-conformations in the LM. At the same packing area, the value of the overall tilt angle does not seem to be sensitive to whether the CBPQT4+ ring is encircling the mpTTF or the DNP unit. However, the conformation of the dumbbell does depend on the location of the CBPQT4+ ring, which is reflected in the segmental tilt angles of the mpTTF and DNP units. Using the Kirkwood-Buff formula in conjunction with MD calculations, we find the surface pressure-area isotherms for each co-conformation in which the CBPQT4+ @ mpTTF form has smaller surface tension and therefore larger surface pressure than the CBPQT4+ @ DNP at the same packing area, differences that decreases with increasing area per molecule, which is verified experimentally. © 2005 American Chemical Society.-
dc.languageeng-
dc.relation.ispartofJournal of the American Chemical Society-
dc.titleMolecular dynamics simulation of amphiphilic bistable [2]rotaxane Langmuir monolayers at the air/water interface-
dc.typeArticle-
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1021/ja0531531-
dc.identifier.pmid16231934-
dc.identifier.scopuseid_2-s2.0-27144550143-
dc.identifier.volume127-
dc.identifier.issue42-
dc.identifier.spage14804-
dc.identifier.epage14816-
dc.identifier.isiWOS:000232780900056-

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