Raman Spectral Change of Crown Ethers and Related Polyethylene Glycol Dialkyl Ethers Due to Accommodation of Water

Fukushima, Kunio; Ito, Masami; Sakurada, Koji; Shiraishi, Shigeki

doi:10.1246/cl.1988.323

Cited by 15 publications

(9 citation statements)

References 5 publications

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“…43 Vibrational spectra of 18c6, free and its metal complexes, have been the focus of many studies. 46 The experimental structure of 18c6, in the free and in the metal-complex state, [47][48][49][50] has been reported. X-ray structural data of free 18c6 at room temperature 47 and at 100 K 48 indicated that free 18c6 in the solid phase has a C i structure.…”

Section: Introductionmentioning

confidence: 99%

Conformational Study of the Structure of Free 18-Crown-6

2005

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A conformational search was performed for 18-crown-6 using the CONLEX method at the MM3 level. To have a more accurate energy order of the predicted conformations, the predicted conformations were geometry optimized at the HF/STO-3G level and the 198 lowest energy conformations, according to the HF/STO-3G energy order, were geometry optimized at the HF/6-31+G level. In addition, the 47 nonredundant lowest energy conformations, according to the MP2/6-31+G energy order at the HF/6-31+G optimized geometry, hereafter the MP2/6-31+G//HF/6-31+G energy order, were geometry optimized at the B3LYP/6-31+G level. According to the MP2/6-31+G//B3LYP/6-31+G energy order, three conformations had energies lower than the experimentally known Ci conformation of 18c6. At the MP2/6-31+G//B3LYP/6-31+G level, the S6 lowest energy conformation is more stable by 1.96 kcal/mol than this Ci conformation. This was confirmed by results at the MP2/6-31+G level with an energy difference of 1.84 kcal/mol. Comparison between the structure of the S6 conformation of 18c6 and the S4 lowest energy conformation of 12-crown-4, as well as other important conformations of both molecules, is made. It is concluded that the correlation energy is necessary to have an accurate energy order of the predicted conformations. A rationalization of the conformational energy order in terms of the hydrogen bonding and conformational dihedral angles is given. It is also suggested that to have a better energy order of the predicted conformations at the MM3 level, better empirical force fields corresponding to the hydrogen bond interactions are needed.

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Section: Introductionmentioning

confidence: 99%

Conformational Study of the Structure of Free 18-Crown-6

2005

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“…The solvation, or more specifically the hydration, of simple crown ethers such as 12-crown-4 (12C4), 15-crown-5 (15C5), and 18-crown-6 (18C6) is of particular interest to understanding chemical recognition phenomena and the stability of host-guest complexes. The hydration has a strong effect on the conformation of the crown ring, which is best expressed for 18C6 aqueous solutions and has been well documented by a number of experimental techniques including Raman spectroscopy, [1][2][3][4][5][6] infrared spectroscopy, 7 X-ray diffraction, 8 quasielastic neutron scattering, 9 and ultrasonic velocity. 10,11 Computer simulations employing molecular mechanics, 12,13 molecular dynamics, [14][15][16][17] and Monte Carlo calculations 18,19 have successfully complemented the experimental studies.…”

Section: Introductionmentioning

confidence: 99%

FTIR-ATR Studies of the Hydration of 15-Crown-5 and 18-Crown-6 in Aqueous Solutions

Nickolov

Ohno

1999

J. Phys. Chem. A

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The hydration of 15-crown-5 (15C5) and 18-crown-6 (18C6) in aqueous solutions has been studied by FTIR-ATR spectroscopy. A model of decomposition of the O−H stretching band of water into four components, accounting for bound and bulk water in the solutions, has been employed in the analysis of the spectra. The dependencies of the relative areas and peak wavenumbers of the resolved components on concentration reveal similarities and differences in the hydration of the two crown ethers. The number of water molecules influenced by the hydration is ca. 18−20 for 18C6 solutions and ca. 12−15 for 15C5 solutions at sufficiently high dilutions. The immediate hydration shell for both crown ethers consists of 4−5 water molecules directly H-bonded to the crown ring. The most probable hydration structure around 18C6 is composed of two bridging water molecules and two other water molecules singly bound to the ring, while, due to differences in its conformational structure, 15C5 is hydrated mostly by singly H-bonded water molecules.

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“…In earlier calculations, such an approach allowed us to predict that the Du form of 18C6, of comparable intrinsic stability as the C, form, was significantly better hydrated and should, therefore, display the highest population in water,15 in agreement with subsequent theoretical studies16'33-34 and consistent with several experimental observations. [35][36][37] We consider conformers of 18C6 and 222 extracted from solid-state structures12 and solvated in acetonitrile. For 18C6, the simulation is run for 2 ns, which is the longest simulation reported so far to our knowledge for 18C6 in solution.…”

Section: Introductionmentioning

confidence: 99%