Water confined in the local field of ions.

Interionic distances are shorter in concentrated ionic solutions, thus instigating the interaction and overlap of hydration shells, as ions become separated by only one or two layers of water molecules. The simultaneous interaction of water with two oppositely charged ions has, so far, only been investigated by computer simulation studies, because the isolated vibrational spectroscopic signature of these molecules remains undetected. Our combined near-infrared spectroscopic and molecular dynamics simulation studies of alkali halide solutions present a distinct spectral feature, which is highly responsive to depletion of bulk water and merging of hydration shells. The analysis of this spectral feature demonstrates that absorption trends are in good agreement with the law of matching affinities, thus providing the first successful vibrational spectroscopic treatment of this topic. Combined with commonly observed near-infrared bands, this feature provides a spectral pattern that describes some relevant aspects of ionic hydration.

Quantification of anomeric structural changes of glucose solutions using near-infrared spectra.

Glucose is the most abundant carbohydrate found in living organisms. It exists as two anomers: α-D-glucose and ß-D-glucose, which differ in how the hydroxyl group on the C1 carbon is directed. In solutions, the ratio between α- and ß-D-glucose is typically 4:6 but can vary depending on the surrounding ions or temperature. In this study, we obtained near-infrared (NIR) spectra of the glucose anomers based on concentration, and analyzed the spectral difference between each anomer by spectra subtraction and principal component analysis, respectively. Moreover, by simultaneously measuring the optical rotation and NIR spectra from dissolution to equilibration, we showed that NIR spectra quantitatively estimated the specific rotations of glucose solutions using partial least-squares regression in the 1100-1800 nm wavelength range. All the analytical results indicated that the absorption at 1742 nm possess the potential to distinguish each glucose anomer quantitatively. Therefore, we addressed the prediction of the specific rotation by the absorption at 1742 nm, and demonstrated that the absorption normalized by line subtraction showed the high correlation with measured specific rotation. The absorption at 1742 nm reflects structural changes of the glucose anomers in solution. Our spectroscopy study not only provides spectral information about glucose anomers, which are the most fundamental chemical compounds in organisms, but also shows the possibility to detect the anomer ratio in vivo for the fields of agriculture and medicine by taking advantage of NIR.

Improving accuracy and reproducibility of vibrational spectra for diluted solutions.

In what appears to be a trivial operation in which the averaged spectrum of solvent is subtracted from the spectra of solutions, can be a misleading step in improving reproducibility of vibrational spectra. Near-infrared spectra of pure water and glycine solutions were used to quantify instrumental and spectral variations, and examine its influence on the reproducibility of difference spectra over a wide concentration range. Significant improvements were observed (fourfold), in comparison with the most commonly applied technique that uses an averaged spectrum of solvent. We propose a new technique, in which subtraction of the closest spectrum of solvent involves calculating the smallest area under the subtracted curve, to extract the optimal outcome. These results reveal that, contrary to common practice, reproducibility for spectra of diluted solutions can bypass even instrumental baseline shifts and render results that are limited only by the noise originating from the instrument's sensor.

Origin of the blueshift of water molecules at interfaces of hydrophilic cyclic compounds.

Water molecules at interfaces of materials exhibit enigmatic properties. A variety of spectroscopic studies have observed a high-frequency motion in these water molecules, represented by a blueshift, at both hydrophobic and hydrophilic interfaces. However, the molecular mechanism behind this blueshift has remained unclear. Using Raman spectroscopy and ab initio molecular dynamics simulations, we reveal the molecular mechanism of the blueshift of water molecules around six monosaccharide isomers. In the first hydration shell, we found weak hydrogen-bonded water molecules that cannot have a stable tetrahedral water network. In the water molecules, the vibrational state of the OH bond oriented toward the bulk solvent strongly contributes to the observed blueshift. Our work suggests that the blueshift in various solutions originates from the vibrational motions of these observed water molecules.

Unprecedented cell-selection using ultra-quick freezing combined with aquaporin expression.

Freezing is usually used for preservation and storage of biological samples; however, this process may have some adverse effects such as cell membrane damage. Aquaporin (AQP), a water channel protein, has been suggested to play some roles for cryopreservation although its molecular mechanism remains unclear. Here we show that membrane damage caused by ultra-quick freezing is rescued by the expression of AQP4. We next examine if the expression of AQP combined with ultra-quick freezing can be used to select cells efficiently under freezing conditions where most cells are died. CHO cells stably expressing AQP4 were exclusively selected from mixed cell cultures. Having identified the increased expression of AQP4 during ES cell differentiation into neuro-ectoderm using bioinformatics, we confirmed the improved survival of differentiated ES cells with AQP4 expression. Finally we show that CHO cells transiently transfected with Endothelin receptor A and Aqp4 were also selected and concentrated by multiple cycles of freezing/thawing, which was confirmed with calcium imaging in response to endothelin. Furthermore, we found that the expression of AQP enables a reduction in the amount of cryoprotectants for freezing, thereby decreasing osmotic stress and cellular toxicity. Taken together, we propose that this simple but efficient and safe method may be applicable to the selection of mammalian cells for applications in regenerative medicine as well as cell-based functional assays or drug screening protocols.