Raman spectroscopy in combination with multivariate curve resolution (Raman-MCR) is used to explore the interaction between water and various kosmotropic and chaotropic anions. Raman-MCR of aqueous Na-salt (NaI, NaBr, NaNO3, Na2SO4, and Na3PO4) solutions provides solute-correlated Raman spectra (SC-spectra) of water. The SC-spectra predominantly bear the vibrational characteristics of water in the hydration shell of anions, because Na(+)-cation has negligible effect on the OH stretch band of water. The SC-spectra for the chaotropic I(-), Br(-), and NO3(-) anions and even for the kosmotropic SO4(2-) anion resemble the Raman spectrum of isotopically diluted water (H2O/D2O = 1/19; v/v) whose OH stretch band is largely comprised by the response of vibrationally decoupled OH oscillators. On the other hand, the SC-spectrum for the kosmotropic PO4(3-) anion is quite similar to the Raman spectrum of H2O (bulk). Comparison of the peak positions of SC-spectra and the Raman spectrum of isotopically diluted water suggests that the hydrogen bond strength of water in the hydration shell of SO4(2-) is comparable to that of the isotopically diluted water, but that in the hydration shell of I(-), Br(-), and NO3(-) anions is weaker than that of the latter. Analysis of integrated area of component bands of the SC-spectra reveals ∼80% reduction of the delocalization of vibrational modes (intermolecular coupling and Fermi resonance) of water in the hydration shell of I(-), Br(-), NO3(-), and SO4(2-) anions. In the case of trivalent PO4(3-), the vibrational delocalization is presumably reduced and the corresponding decrease in spectral response at ∼3250 cm(-1) is compensated by the increased signal of strongly hydrogen bonded (but decoupled) water species in the hydration shell. The peak area-averaged wavenumber of the SC-spectrum increases as PO4(3-) < SO4(2-) < NO3(-) < Br(-) < I(-) and indeed suggests strong hydrogen bonding of water in the hydration shell of PO4(3-) anion.

Heterodyne-detected vibrational sum frequency generation spectroscopy was applied to the water surface for measuring the imaginary part of second-order nonlinear susceptibility (Im χ((2))) spectrum in the bend frequency region for the first time. The observed Im χ((2)) spectrum shows an overall positive band around 1650 cm(-1), contradicting former theoretical predictions. We further found that the Im χ((2)) spectrum of NaI aqueous solution exhibits an even larger positive band, which is apparently contrary to the flip-flop orientation of surface water. These unexpected observations are elucidated by calculating quadrupole contributions beyond the conventional dipole approximation. It is indicated that the Im χ((2)) spectrum in the bend region has a large quadrupole contribution from the bulk water.

Familial vitamin E deficiency (AVED) causes ataxia and peripheral neuropathy that resembles Friedreich's ataxia. AVED is thought to be caused by a defect in the transport of vitamin E in liver cells, which is the probable function of alpha-tocopherol transfer protein (alphaTTP). We have cloned the cDNA and several genomic phage clones covering the entire human alphaTTP gene and determined the junctions between the five exons and four introns that composed the gene for human alphaTTP. Three mutations in three unrelated North American families with AVED were identified. Two mutations, 485delT and 513insTT, cause a frame shift and a premature stop codon and the third mutation 574G-->A would substitute Arg192 to His in alphaTTP. The 2 patients with a severe form of AVED were homozygous with 485delT and 513insTT, respectively, while the patient with a mild form of the disease was compound heterozygous with 513insTT and 574G-->A. These findings have identified the underlying genetic defect in AVED and have confirmed the role of alphaTTP in AVED.

The hydration energy of an ion largely resides within the first few layers of water molecules in its hydration shell. Hence, it is important to understand the transformation of water properties, such as hydrogen-bonding, intermolecular vibrational coupling, and librational freedom in the hydration shell of ions. We investigated these properties in the hydration shell of mono- (Cl(-) and I(-)) and bivalent (SO4(2-) and CO3(2-)) anions by using Raman multivariate curve resolution (Raman-MCR) spectroscopy in the OH stretch, HOH bend, and [bend+librational] combination bands of water. Raman-MCR of aqueous Na-salt (NaCl, NaI, Na2SO4, and Na2CO3) solutions provides ion-correlated spectra (IC-spectrum) which predominantly bear the vibrational characteristics of water in the hydration shell of respective anions. Comparison of these IC-spectra with the Raman spectrum of bulk water in different spectral regions reveals that the water is vibrationally decoupled with its neighbors in the hydration shell. Hydrogen-bond strength and librational freedom also vary with the nature of anion: hydrogen-bond strength, for example, decreases as CO3(2-) > SO4(2-) > bulk water ≈ Cl(-) > I(-); and the librational freedom increases as CO3(2-) ≈ SO4(2-) < bulk water < Cl(-) < I(-). It is believed that these structural perturbations influence the dynamics of coherent energy transfer and librational reorientation of water in the hydration shell of anions.

Preferential orientation and expulsion/accumulation of trimethylamine N-oxide (TMAO; a protecting osmolyte) and tert-butyl alcohol (TBA; a denaturant) have been investigated at the hydrophobic air–water interface by phase-sensitive heterodyne-detected vibrational sum frequency generation (HD-VSFG) spectroscopy. The imaginary χ(2) spectrum (Imχ(2); χ(2) is the second order electric susceptibility), which is directly obtainable from the HD-VSFG measurement, provides the accurate absorption characteristics of interfacial molecules, and the sign of Imχ(2) reveals the net orientation of these molecules at the interface. For the aqueous TMAO and TBA solutions, the Imχ(2) spectra in the CH-stretch region show a negative sign, which demonstrates that both TMAO and TBA orient in the same manner at the air–water interface, by pointing their methyls away from the aqueous phase (“methyl-up” orientation). Nevertheless, they affect the interfacial water quite differently: TMAO increases the H-bond strength and preferential H-down orientation of interfacial water, while the dangling OH remains almost unperturbed. TBA, on the other hand, does not affect the H-bond strength and preferential orientation of interfacial water, but reduces the propensity of the dangling OH at the air–water interface. The preferential orientation of TMAO and TBA and their distinct effect on the interfacial water have been correlated with their hydration characteristics in bulk water by retrieving the vibrational spectrum of water in their respective hydration shells, using Raman multivariate curve resolution (Raman-MCR) spectroscopy. The MCR-retrieved hydration water spectra clearly show that the water around TBA has strong water–water interaction (hydrophobic hydration) and that around TMAO has a hydrophobic hydration around the N-methyl ((CH3)3N+−) group and a hydrophilic hydration around the N-oxide group (strong H-bonding of water with the N-oxide group). The different hydration characteristic of the N-methyl and N-oxide groups orients the TMAO molecules as “methyl-up” at the air–water interface. Moreover, the strong hydration of the N-oxide group leads to a depletion of TMAO from the hydrophobic water surface, such that the preferentially oriented TMAO molecules are located beneath the topmost water layer at the air–water interface. As a result, the topmost water molecules are largely unaware of the presence of TMAO at the interface, even at very high bulk concentration of TMAO (5.0 mol dm–3). In the case of TBA, the hydrophobic hydration leads to an accumulation of TBA at the water surface, mainly affecting the topmost water molecules.

Water in the presence of electrolytes plays an important role in biological and industrial processes. The properties of water, such as the intermolecular coupling, Fermi resonance (FR), hydrogen-bonding, and Raman cross section were investigated by measuring the Raman spectra in the OD and OH stretch regions in presence of alkali halides (NaX; X = F, Cl, Br, I). It is observed that the changes in spectral characteristics by the addition of NaX in D2O are similar to those obtained by the addition of H2O in D2O. The spectral width decreases significantly by the addition of NaX in D2O (H2O) than that in the isotopically diluted water. Quantitative estimation, on the basis of integrated Raman intensity, revealed that the relative Raman cross section, σ(H)/σ(b) (σ(H) and σ(b) are the average Raman cross section of water in the first hydration shell of X(-) and in bulk, respectively), in D2O and H2O is higher than those in the respective isotopically diluted water. These results suggest that water in the hydration shell has reduced FR and intermolecular coupling compared to those in bulk. In the isotopically diluted water, the relative Raman cross section increases with increase in size of the halide ions (σ(H)/σ(b) = 0.6, 1.1, 1.5, and 1.9 for F(-), Cl(-), Br(-), and I(-), respectively), which is assignable to the enhancement of Raman cross section by charge transfer from halide ions to the hydrating water. Nevertheless, the experimentally determined σ(H)/σ(b) is lower than the calculated values obtained on the basis of the energy of the charge transfer state of water. The weak enhancement of σ(H)/σ(b) signifies that the charge transfer transition in the hydration shell of halide ions causes little change in the OD (OH) bond lengths of hydrating water.

Recently, there has been controversy over whether the HOH bend signal of water in the vibrational sum frequency generation (VSFG) spectrum arises from the conventional dipole mechanism or the quadrupole mechanism. Here, we show that the Im χ (2) (the imaginary part of the second-order nonlinear susceptibility) spectra of the HOH bend mode of water at oppositely charged monolayer/water interfaces all exhibit positive bands, irrespective of the difference in the sign of the charge at the interface. Furthermore, it is found that the peak frequency of the HOH bend band substantially changes depending on the chemical structure of the charged headgroup located at the interface. These results demonstrate that the VSFG signal of the HOH bend vibration is generated from interfacial water with the interfacial quadrupole mechanism that is associated with the large field gradient of incident lights localized in a very thin region at the interface.

Hydrogen-bonding and intra/intermolecular vibrational coupling of water next to a hydrophobic molecule (tert-butyl alcohol, TBA) have been studied by Raman multivariate curve resolution (Raman-MCR) and isotopic dilution spectroscopy. Raman-MCR provides the vibrational spectrum of water pertinent to the hydration shell of TBA, which shows a distinct Raman band at around 3660 cm(-1) corresponding to the dangling OH in the hydration shell. The presence of positive charge on the hydrophobe decreases the propensity of dangling OH in the hydration shell, presumably due to unfavorable electrostatic interaction. Analysis of the dangling OH band with isotopic dilution reveals that the 'dangling OH' is intramolecularly coupled with the 'H-bonded OH' of the same water molecule. The hydration water spectrum in the H-bonded OH stretch region (3000-3600 cm(-1)) shows a depletion of weakly H-bonded water (∼3580 cm(-1)) and an increase of strongly H-bonded water (∼3250 cm(-1)), making the average H-bonding stronger in a hydrophobic hydration shell than that in bulk. This strongly H-bonded hydration water exhibits weaker intra- and intermolecular vibrational coupling than that of bulk water.