Hai-Chou Chang

Bio: Hai-Chou Chang is an academic researcher from National Dong Hwa University. The author has contributed to research in topics: Ionic liquid & Hydrogen bond. The author has an hindex of 20, co-authored 40 publications receiving 1208 citations. Previous affiliations of Hai-Chou Chang include National Taiwan University of Science and Technology & Technische Universität München.

Infrared Spectra of H+(H2O)5-8 Clusters: Evidence for Symmetric Proton Hydration

Abstract: Protonated water clusters, H+(H2O)n (n = 5−8), from a supersonic expansion have been investigated by vibrational predissociation spectroscopy and ab initio calculations. The experimental spectra were obtained at an estimated cluster temperature of 170 ± 20 K. Recorded absorption bands at the frequency range of 2700−3900 cm-1 are attributed to the free- and hydrogen-bonded-OH stretches of the ion core and the surrounding solvent molecules. Ab initio calculations, performed at the B3LYP/6-31+G* level, indicate that geometries of the H+(H2O)5-8 isomers are close in energy, with the excess proton either localized on a single water molecule, yielding H3O+(H2O)n-1, or equally shared by two molecules, yielding H5O2+(H2O)n-2. Systematic comparison of the experimental and computed spectra provides compelling evidence for both cases. The unique proton-transfer intermediate H5O2+(H2O)4 was identified, for the first time, by its characteristic bonded-OH stretching absorptions at 3178 cm-1. The existence of five-membe...

Hydrogen bond stabilization in 1,3-dimethylimidazolium methyl sulfate and 1-butyl-3-methylimidazolium hexafluorophosphate probed by high pressure: the role of charge-enhanced C-H...O interactions in the room-temperature ionic liquid.

Abstract: The hydrogen bonding structures of room-temperature ionic liquids 1,3-dimethylimidazolium methyl sulfate and 1-butyl-3-methylimidazolium hexafluorophosphate have been studied by infrared spectroscopy. High-pressure infrared spectral profiles and theoretical calculations allow us to make a vibrational assignment of these compounds. The imidazolium C−H bands of 1,3-dimethylimidazolium methyl sulfate display anomalous non-monotonic pressure-induced frequency shifts. This discontinuity in frequency shift is related to enhanced C−H···O hydrogen bonding. This behavior is in contrast with the trend of blue shifts in frequency for the methyl C−H stretching mode at ca. 2960 cm-1. Our results indicated that the imidazolium C−H groups are more favorable sites for hydrogen bonding than the methyl C−H groups in the pure 1,3-dimethylimidazolium methyl sulfate. Nevertheless, both methyl C−H and imidazolium C−H groups are favorable sites for C−H···O hydrogen bonding in a dilute 1,3-dimethylimidazolium methyl sulfate/ D2O...

Structural organization in aqueous solutions of 1-Butyl-3-methylimidazolium halides: a high-pressure infrared spectroscopic study on ionic liquids.

Abstract: High-pressure infrared spectroscopy was applied to study the hydrogen-bonding structures of 1-butyl-3-methylimidazolium halides/D2O mixtures. No drastic changes were observed in the concentration dependence of the alkyl C-H band frequency at high concentration of 1-butyl-3-methylimidazolium chloride. Nevertheless, the alkyl C-H exhibits an increase in frequency upon dilution at low concentration. These observations may indicate a clustering of the alkyl groups at high concentration and the formation of a certain water structure around alkyl C-H groups in the water-rich region. The imidazolium C-H band at ca. 3051 cm(-1) displays a monotonic blue-shift in frequency as the sample was diluted at high concentration of 1-butyl-3-methylimidazolium chloride. That is, water can be added to change the structural organization of 1-butyl-3-methylimidazolium chloride in the ionic liquid-rich composition region by introducing water-imidazolium C-H interactions. Analyzing the pressure dependence of the imidazolium C-H stretches yielded anomalous nonmonotonic pressure-induced frequency shifts. This result may reflect the strengthening of C-H-O interactions between imidazolium C-H groups and the water clusters. Density functional theory calculations also revealed that the characteristic bonded C2-H vibration may be shifted via the modification of C2-H-Cl- associations.

Evidence of rotational isomerism in 1-butyl-3-methylimidazolium halides: a combined high-pressure infrared and Raman spectroscopic study.

Abstract: High-pressure methods were applied to investigate the rotational isomerism and the hydrogen-bonding structures of 1-butyl-3-methylimidazolium bromide and 1-butyl-3-methylimidazolium chloride, respectively. Conformation changes of the butyl chain were observed above a pressure of 0.3 GPa. Under ambient pressure, Raman spectra indicate that the more thermodynamically stable butyl structure of the cations is the gauche−anti (GA) and all-anti forms for 1-butyl-3-methylimidazolium bromide and 1-butyl-3-methylimidazolium chloride, respectively. Nevertheless, the high-pressure phases arise from the perturbed GA conformer. The imidazolium C−H bands of 1-butyl-3-methylimidazolium chloride display anomalous nonmonotonic pressure-induced frequency shifts. This discontinuity in the frequency shift is related to the modification of the imidazolioum C−H---Cl- contacts upon compression. The alkyl C−H---Cl- interactions are suggested to be a compensatory mechanism to provide additional stability. Density-functional-theor...

C−H- - -O Hydrogen Bonds in β-Sheetlike Networks: Combined X-ray Crystallography and High-Pressure Infrared Study

Abstract: Close interactions of the Cα−H- - -O type have been analyzed via X-ray crystallography and high-pressure infrared spectroscopy. The results demonstrate that the Cα−H- - -O interactions can offer an...

Biological Activity of Ionic Liquids and Their Application in Pharmaceutics and Medicine.

Abstract: Ionic liquids are remarkable chemical compounds, which find applications in many areas of modern science. Because of their highly tunable nature and exceptional properties, ionic liquids have become essential players in the fields of synthesis and catalysis, extraction, electrochemistry, analytics, biotechnology, etc. Apart from physical and chemical features of ionic liquids, their high biological activity has been attracting significant attention from biochemists, ecologists, and medical scientists. This Review is dedicated to biological activities of ionic liquids, with a special emphasis on their potential employment in pharmaceutics and medicine. The accumulated data on the biological activity of ionic liquids, including their antimicrobial and cytotoxic properties, are discussed in view of possible applications in drug synthesis and drug delivery systems. Dedicated attention is given to a novel active pharmaceutical ingredient-ionic liquid (API-IL) concept, which suggests using traditional drugs in ...

Spectral signatures of hydrated proton vibrations in water clusters.

Abstract: The ease with which the pH of water is measured obscures the fact that there is presently no clear molecular description for the hydrated proton. The mid-infrared spectrum of bulk aqueous acid, for example, is too diffuse to establish the roles of the putative Eigen (H 3 O + ) and Zundel (H 5 O 2 + ) ion cores. To expose the local environment of the excess charge, we report how the vibrational spectrum of protonated water clusters evolves in the size range from 2 to 11 water molecules. Signature bands indicating embedded Eigen or Zundel limiting forms are observed in all of the spectra with the exception of the three- and five-membered clusters. These unique species display bands appearing at intermediate energies, reflecting asymmetric solvation of the core ion. Taken together, the data reveal the pronounced spectral impact of subtle changes in the hydration environment.

Electronic Basis of Improper Hydrogen Bonding: A Subtle Balance of Hyperconjugation and Rehybridization

Abstract: The X−H bond length in X−H..Y hydrogen bonded complexes is controlled by a balance of two main factors acting in opposite directions. “X-H bond lengthening” due to n(Y)→σ*(H−X) hyperconjugative interaction is balanced by “X-H bond shortening” due to increase in the s-character and polarization of the X−H bond. When hyperconjugation dominates, X−H bond elongation is reflected in a concomitant red shift of the corresponding IR stretching frequency. When the hyperconjugative interaction is weak and the X-hybrid orbital in the X−H bond is able to undergo a sufficient change in hybridization and polarization, rehybridization dominates leading to a shortening of the X−H bond and a blue shift in the X−H stretching frequency.

Review of recent advances in carbon dioxide separation and capture

Abstract: This review provides a comprehensive assessment of recently improved carbon dioxide (CO2) separation and capture systems, used in power plants and other industrial processes. Different approaches for CO2 capture are pre-combustion, post-combustion capture, and oxy-combustion systems, which are reviewed, along with their advantages and disadvantages. New technologies and prospective “breakthrough technologies”, for instance: novel solvents, sorbents, and membranes for gas separation are examined. Other technologies including chemical looping technology (reaction between metal oxides and fuels, creating metal particles, carbon dioxide, and water vapor) and cryogenic separation processes (based on different phase change temperatures for various gases to separate them) are reviewed as well. Furthermore, the major CO2 separation technologies, such as absorption (using a liquid solvent to absorb the CO2), adsorption (using solid materials with surface affinity to CO2 molecules), and membranes (using a thin film to selectively permeate gases) are extensively discussed, though issues and technologies related to CO2 transport and storage are not considered in this paper.

Ionic Liquid Crystals: Versatile Materials.

Abstract: This Review covers the recent developments (2005-2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive overview of the "state-of-the-art" in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.