Dynamic and 2D NMR Studies on Hydrogen-Bonding Aggregates of Cholesterol in Low-Polarity Organic Solvents

Giordani, Cristiano; Wakai, Chihiro; Okamura, Emiko; Matubayasi, Nobuyuki; Nakahara, Masaru

doi:10.1021/jp062607t

Cited by 17 publications

(22 citation statements)

References 18 publications

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“…This suggests formation of cholesterol aggregates, in agreement with reports in the literature. [69][70][71][72][73][74] In contrast, the particle size does not change for cholesterol in 1-octanol as a function of concentration, consistent with the interpretation that cholesterol disperses as monomers in 1-octanol. 70 With cholesterol's solution behavior in both cyclohexane and 1-octanol as reference points, we investigated the mixed AOT reverse micelle/cholesterol system.…”

Section: Resultssupporting

confidence: 66%

Coexisting Aggregates in Mixed Aerosol OT and Cholesterol Microemulsions

et al. 2010

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Dynamic light scattering and NMR spectroscopic experimental evidence suggest the coexistence of two compositionally different self-assembled particles in solution. The self-assembled particles form in solutions containing water, Aerosol OT (AOT, sodium bis(2-ethylhexyl) sulfosuccinate) surfactant, and cholesterol in cyclohexane. In a similar series of studies carried out in 1-octanol only one aggregate type, that is, reverse micelles, is observed. Dynamic light scattering measurements reveal the presence of two different types of aggregates in the microemulsions formed in cyclohexane, demonstrating the coexistence of two compositionally distinct structures with very similar Gibbs energies. One particle type consists of standard AOT reverse micelles while the second type of particle consists of submicellar aggregates including cholesterol as well as small amounts of AOT and water. In microemulsions employing 1-octanol as the continuous medium, AOT reverse micelles form in a dispersed solution of cholesterol in 1-octanol. Although the size distribution of self-assembled particles is well-known for many different systems, evidence for simultaneous formation of two distinctly sized particles in solution that are chemically different is unprecedented. The ability to form microemulsion solutions that contain coexisting particles may have important applications in drug formulation and administration, particularly as applied to drug delivery using cholesterol as a targeting agent.

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Section: Resultssupporting

confidence: 66%

Coexisting Aggregates in Mixed Aerosol OT and Cholesterol Microemulsions

et al. 2010

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“…Another interesting example of solvent effect on the extent of aggregation has been reported by Nakahara and co-workers studying cholesterol in low-polarity organic solvents that mimic the membrane bilayer hydrophobic core. 24 They found that cholesterol forms aggregates in chloroform and cyclohexane but it does not in 1-octanol. The aggregation process is driven by the hydrogen bonding.…”

Section: Changing Solventmentioning

confidence: 99%

Determining accurate molecular sizes in solution through NMR diffusion spectroscopy

et al. 2008

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This tutorial review deals with the methodological procedures that can be used to obtain accurate molecular sizes in solution from diffusion NMR spectroscopy. The critical aspects associated with the estimation of the size of molecules from the measured translational self-diffusion coefficient, using the Stokes-Einstein equation, are highlighted and discussed. From a theoretical point of view, it is shown how to take into account the size of the solute with respect to that of the solvent and its non-spherical shape using the appropriate correction factors in the frictional coefficient. From a practical point of view, the advantages of introducing an internal standard in the sample are presented. Initially, non-aggregating systems are considered in an attempt to clarify what hydrodynamic dimensions mean. Successively, aggregating systems are addressed showing how it is possible to understand the aggregation level and derive the thermodynamic parameters for some illustrative aggregation processes.

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“…Ion Pairing and Salt Structure in Organic Salts first example of the use of 195 Pt relaxation characteristics for this purpose. [36] X-ray study of 6 c: Relative to the CF 3 SO 3 À anion, the CH 3 SO 3 À anion is not frequently used. Consequently we have determined the solid-state structure of salt 6 c and show this in Figure 14a along with selected bond lengths and bond angles.…”

Section: Full Papermentioning

confidence: 99%

Ion Pairing and Salt Structure in Organic Salts through Diffusion, Overhauser, DFT and X‐ray Methods

Moreno

Pregosin

Veiros³

et al. 2009

Chemistry A European J

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Pulsed gradient spin-echo (PGSE) diffusion characteristics for a) the new [brucinium][X] salts 6 a-f [a: X = BF(4)(-); b: X = PF(6)(-); c: X = MeSO(3)(-), d: X = CF(3)SO(3)(-); e: X = BArF(-); f: X = PtCl(3)(C(2)H(4))(-)], b) 4-tert-butyl-N-benzyl analogue, 7 and c) the aryl carbocations (p-R-C(6)H(4))(2)CH 9 a (R = CH(3)O) and 9 b (R = (CH(3))(2)N), (p-CH(3)O-C(6)H(4))(x)CPh(3-x)(+) 10 a-c (x = 1-3, respectively) and (p-R-C(6)H(4))(3)C(+) 11 (R = (CH(3))(2)N) and 12 (R = H) all in several different solvents, are reported. The solvent dependence suggests strong ion pairing in CDCl(3), intermediate ion pairing in CD(2)Cl(2) and little ion pairing in [D(6)]acetone. (1)H, (19)F HOESY NMR spectra (HOESY: heteronuclear Overhauser effect spectroscopy) for 6 and 7 reveal a specific approach of the anion with respect to the brucinium cation plus subtle changes, which are related to the anion itself. Further, for carbocations 9-12, (all as BF(4)(-) salts) based on the NOE results, one finds marked changes in the relative positions of the BF(4)(-) anion. In these aryl cationic species the anion can be located either a) very close to the carbonium ion carbon b) in an intermediate position or c) proximate to the N or O atom of the p-substituent and remote from the formally positive C atom. This represents the first example of such a positional dependence of an anion on the structure of the carbocation. DFT calculations support the experimental HOESY results. The solid-state structures for 6 c and the novel Zeise's salt derivative, [brucinium][PtCl(3)(C(2)H(4))], 6 f, are reported. Analysis of (195)Pt NMR and other NMR measurements suggest that the eta(2)-C(2)H(4) bonding to the platinum centre in 6 f is very similar to that found in K[PtCl(3)(C(2)H(4))]. Field dependent T(1) measurements on [brucinium][PtCl(3)(C(2)H(4))] and K[PtCl(3)(C(2)H(4))], are reported and suggested to be useful in recognizing aggregation effects.

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Dynamic and 2D NMR Studies on Hydrogen-Bonding Aggregates of Cholesterol in Low-Polarity Organic Solvents

Cited by 17 publications

References 18 publications

Coexisting Aggregates in Mixed Aerosol OT and Cholesterol Microemulsions

Coexisting Aggregates in Mixed Aerosol OT and Cholesterol Microemulsions

Determining accurate molecular sizes in solution through NMR diffusion spectroscopy

Ion Pairing and Salt Structure in Organic Salts through Diffusion, Overhauser, DFT and X‐ray Methods

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