Surface Effect of Alumina on the First Electronic Transition of Liquid Water Studied by Far-Ultraviolet Spectroscopy

The first electronic transition (<i>Ã</i> ← <i>X̃</i>) of liquid water (H₂O and D₂O) on an α-alumina substrate was studied using variable angle attenuated total reflection far-ultraviolet (VA-ATR-FUV) spectroscopy in the wavelength region 140–180 nm (8.86–6.89 eV). A variation in the penetration depth of the evanescent wave of a probe light (25–19 nm) directly determined individual FUV spectra associated with bulk water (distance from the alumina surface >2 nm) and interfacial water (<2 nm). We found that the <i>Ã</i> ← <i>X̃</i> band of the interfacial water was markedly blue-shifted and red-tailed relative to the bulk water. The electronic state difference of the interfacial water from the bulk water mainly arose from the hydrogen-bond structure and energy affected by the alumina surface

Electronic Transitions of Protonated and Deprotonated Amino Acids in Aqueous Solution in the Region 145–300 nm Studied by Attenuated Total Reflection Far-Ultraviolet Spectroscopy

The electronic transitions of 20 naturally occurring amino acids in aqueous solution were studied with attenuated total reflection far-ultraviolet (ATR-FUV) spectroscopy in the region from 145 to 300 nm. From the measured ATR spectra of sample solutions, the FUV absorption spectra attributed to the amino acids were separated from the intense solvent absorption by using a modified Kramers–Kronig transformation method. The FUV absorption spectra of the amino acids reflect the protonation states of the backbone and side-chain structures. The contributions of the side chains to the spectra were also examined from the difference spectra subtracting the corresponding Gly spectrum from each spectrum. The observed spectra were compared mostly with the electronic transition studies of the molecular fragments of the amino acids in gas phase. The FUV spectra of the amino acids exhibited the intra- and intermolecular electronic interactions of the solute–solute as well as the solute–solvent, and those are essential factors to elucidate UV photochemical processes of the amino acids in aqueous solution

Hydration States of Poly(<i>N</i>‑isopropylacrylamide) and Poly(<i>N</i>,<i>N</i>‑diethylacrylamide) and Their Monomer Units in Aqueous Solutions with Lower Critical Solution Temperatures Studied by Infrared Spectroscopy

The coil-to-globule transition of poly­(<i>N</i>-isopropylacrylamide) (PNiPA) and poly­(<i>N</i>,<i>N</i>-diethylacrylamide) (PdEA) in aqueous solutions has recently received substantial interest in its drastic change in the hydration state from a hydrated random coil to a hydrophobic globule for practical applications: drug delivery and tissue engineering. In this report, the hydration states of PNiPA and PdEA in aqueous solutions were investigated by IR spectroscopy in the amide I, N–H and C–H stretching band regions as compared with those of their repeat units, <i>N</i>-isopropylpropionamide (NiPP) and <i>N</i>,<i>N</i>-diethylpropylacrylamide (dEP) in aqueous and cyclohexane solutions in combined with their phase diagrams. The IR spectral changes in the amide I and C–H stretching band regions of <i>N</i>-alkylamides and <i>N</i>,<i>N</i>-dialkylamides including NiPP and dEP in aqueous solutions with varying concentration was characteristic due to different amide–amide interaction; the amide–amide interaction for <i>N</i>-alkylamide (CO···H–N hydrogen bond) is stronger than that for <i>N</i>,<i>N</i>-dialkylamide (dipolar interaction). It is found that almost all amide groups of PNiPA in aqueous solution forms the intramolecular CO···H–N hydrogen bond even in the coil state and that the amide group of PNiPA is less hydrated than that of PdEA in spite of the similar degree of hydration to alkyl groups. The IR spectral changes in the amide I and C–H stretching band regions of PNiPA and PdEA in aqueous solutions with heat are ascribed to the dehydration of the amide and alkyl groups from the coil state to the globule one