Structure and dynamics of hexafluoroisopropanol-water mixtures by x-ray diffraction, small-angle neutron scattering, NMR spectroscopy, and mass spectrometry

Abstract

The structure and dynamic properties of aqueous mixtures of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) have been investigated over the whole range of HFIP mole fraction (xHFIP) by large-angle x-ray scattering (LAXS), small-angle reutron scattering (SANS), F19-, C13-, and O-NMR17 chemical shifts, O-NMR17 relaxation, and mass spectrometry. The LAXS data have shown that structural transition of solvent clusters takes place at xHFIP∼0.1 from the tetrahedral-like hydrogen bonded network of water at xHFIP⩽∼0.1 to the structure of neat HFIP gradually formed with increasing HFIP concentration in the range of xHFIP⩾0.15. The Ornstein–Zernike plots of the SANS data have revealed a mesoscopic structural feature that the concentration fluctuations become largest at xHFIP∼0.06 with a correlation length of ∼9 Å, i.e., maximum in clustering and microhetrogeneities. The F19 and C13 chemical shifts of both CF3 and CH groups of HFIP against xHFIP have shown an inflection point at xHFIP∼0.08, implying that the environment of HFIP molecules changes due to the structural transition of HFIP clusters. The O17 relaxation data of water have shown that the rotational motion of water molecules is retarded rapidly upon addition of HFIP into water up to xHFIP∼0.1, moderately in the range of ∼0.1<xHFIP≲0.3, and almost constant at xHFIP≳0.3, reflecting the structural change in the solvent clusters at xHFIP∼0.1. The mass spectra of cluster fragments generated in vacuum from HFIP-water mixtures have shown that the predominant clusters are A1Wn (n<12, A=HFIP, W=water) and water clusters Wn (n=5–8) at xHFIP=0.09 and 0.20 and only HFIP oligomers in a water-rich region of xHFIP=0.005∼0.01. From all the information obtained in the present study, the models are proposed for the aggregation of HFIP and water molecules in HFIP-water mixtures.

Structure of Hexafluoroisopropanol–Water Mixtures by Molecular Dynamics Simulations

“…This finding shows a disruption of the tetrahedral-like structure of water due to the inclusion of HFIP molecules into the structure of water. According to the previous LAXS and SANS studies [17], the structural transition of the solvent appeared at x HFIP ≈ 0.1, which is not consistent with the composition estimated from the present MD simulation. As discussed in the previous section, this is probably because the water-water pairs are less perturbed by HFIP in the present simulation than expected from the NDIS study.…”

“…The structural and dynamic properties of aqueous mixtures of HFIP were investigated over the entire range of HFIP mole fractions from comprehensive measurements with large-angle X-ray scattering (LAXS), small-angle neutron scattering (SANS), 19 F, 13 C, and 17 O nuclear magnetic resonance (NMR) chemical shifts, 17 O NMR relaxation, and mass spectrometry [17]. Overall, clustering and microheterogeneities are found to be most enhanced at x HFIP ≈ 0.1, where a structural transformation of solvent clusters occurs from the tetrahedral-like structure of water to the neat structure of HFIP.…”

Amyloid-β Protofibrils Differ from Amyloid-β Aggregates Induced in Dilute Hexafluoroisopropanol in Stability and Morphology

“…Previously reported biophysical analyses of aqueous HFIP solutions also support a microdroplet structure. NMR and small angle neutron scattering data have indicated microheterogeneities that are maximized at HFIP concentrations of about 35% (v/v), with clusters involving hydrophobic CF 3 groups aggregated in an inside core and hydrophilic OH groups forming hydrogen bonds with surrounding water molecules (68). Below these concentrations, mass spectrometry revealed hydrated HFIP oligomers of stoichiometry (HFIP) m (H 2 O) n .…”

“…Below these concentrations, mass spectrometry revealed hydrated HFIP oligomers of stoichiometry (HFIP) m (H 2 O) n . At 2-4% HFIP (v/v), oligomers with m ϭ 2-4 and n ϭ 5-20 were detected, but larger oligomers were not explored because of the limited mass number range employed (68).…”

Morphology‐Specific Inhibition of β‐Amyloid Aggregates by 17β‐Hydroxysteroid Dehydrogenase Type 10

“…[47] However, the formation of HFIP micro-droplets acting as adsorption platforms for bovine serum albumin has already been discussed using TEM [42] and micro-heterogeneities in HFIP-water mixtures have been studied in detail using NMR and small angle neutron scattering (SANS) experiments revealing a correlation in lengths ranging from 7 to 10 Å. [54] Interesting these lengths match the diameter (8-9 Å) of -CD cavities which are known to promote the characteristic enhancement in ThT emission. [45] From NMR and SANS data it has been suggested that these micro-heterogeneities are maximized at HFIP concentrations of 30-35 % (v/v) and that the clusters organize with the trifluoromethyl (CF 3 )…”