Ab initio calculations are used to analyze the CH···O interaction between FnH3-nCH as proton donor and H2O, CH3OH, and H2CO as acceptor. The interaction is quite weak with CH4 as donor but is enhanced by 1 kcal/mol with each F added to the donor. The CH···O interaction behaves very much like a conventional OH···O H-bond in most respects, including shifts in electron density that accompany the formation of the bond and the magnitudes of the various components of the interaction energy. The two sorts of H-bonds also gravitate toward a similar equilibrium geometry and are comparably sensitive to deformations from that structure. In a quantitative sense, while both CH···O and OH···O prefer a linear configuration, the former is somewhat more easily bent and is less sensitive to stretches from its equilibrium H-bond length. Whereas the OH bond has been shown to stretch and undergo a red shift in its vibrational frequency upon formation of a H-bond, the CH bond of the molecules studied here follows the opposite ...

Fundamental Properties of the CH···O Interaction: Is It a True Hydrogen Bond?

Alcohol based cosolvents, such as trifluoroethanol (TFE) have been used for many decades to denature proteins and to stabilize structures in peptides. Nuclear magnetic resonance spectroscopy and site directed mutagenesis have recently made it possible to characterize the effects of TFE and of other alcohols on polypeptide structure and dynamics at high resolution. This review examines such studies, particularly of hen lysozyme and beta-lactoglobulin. It presents an overview of what has been learnt about conformational preferences of the polypeptide chain, the interactions that stabilize structures and the nature of the denatured states. The effect of TFE on transition states and on the pathways of protein folding and unfolding are also reviewed. Despite considerable progress there is as yet no single mechanism that accounts for all of the effects TFE and related cosolvents have on polypeptide conformation. However, a number of critical questions are beginning to be answered. Studies with alcohols such as TFE, and 'cosolvent engineering' in general, have become valuable tools for probing biomolecular structure, function and dynamics.

Trifluoroethanol and colleagues: cosolvents come of age. Recent studies with peptides and proteins

I. Characterization of Hydrogen Bonding: From van der Waals Interactions to Covalency, R. Parthasarathi and V. Subramanian II. Intramolecular Hydrogen Bonds. Methodologies and Strategies for their Strength Evaluation, Giuseppe Buemi III. Changes of Electron Properties in the Formation of Hydrogen Bonds, Luis F. Pacios IV. Weak to Strong Hydrogen Bonds, Han Myoung Lee, N. Jiten Singh, Kwang S. Kim V. The Nature of the C-H...X Intermolecular Interactions in Molecular Crystals. A Theoretical Perspective, Fernando Mota, Emiliana D'Oria VI. Weak hydrogen bonds involving transition elements, Maria Jose Calhorda VII. Contribution of CH**X Hydrogen Bonds to Biomolecular Structure, Steve Scheiner VIII. Neutral Blue-Shifting and Blue-Shifted Hydrogen Bonds, Eugene S. Kryachko IX. Hydrogen-Hydrogen Bonding: the Non-Electrostatic Limit of Closed-Shell Interaction Between two Hydrogen Atoms (A Review), Cherif F. Matta X. Potential Energy Shape for the Proton Motion in Hydrogen Bonds Reflected in Infrared and NMR Spectra, Gleb S. Denisov, Janez Mavri and Lucjan Sobczyk XI. Molecular Geometry - Distant Consequences of H-Bonding, Tadeusz M. Krygowski and Joanna E. Zachara XII. Topology of X-ray charge density of hydrogen bonds, Tibor S. Koritsanszky XIII. Structure-Property Relations for Hydrogen-Bonded Solids, Andrzej Katrusiak XIV. Unrevealing the Nature of Hydrogen Bonds: p -Electron delocalization Shapes H-Bond Features. Intramolecular and Intermolecular Resonance-Assisted Hydrogen Bonds, Slawomir J.Grabowski and Jerzy Leszczynski

Hydrogen Bonding - New Insights

Coil−globule transition of poly(N-isopropylacrylamide) (PIPA), followed by intermolecular association in H2O and D2O, was investigated by Fourier transform infrared (FTIR) spectroscopy. IR spectra of the solutions were measured as a function of temperature, and spectral changes induced by the transition were observed. The intensities of the difference IR bands due to the vibrational modes of isopropyl and amide groups critically increased at the lower critical solution temperature (LCST). Heating of the PIPA solutions above the LCST led shifts of the amide II, C−H-stretching, and C−H-bending bands to lower wavenumbers during a shift of the amide I band to a higher wavenumber. The amide I band of the PIPA observed below the LCST could be fitted with a single component centered at 1625 cm-1, whereas two components (1625 and 1650 cm-1) were necessary to fit the band above the LCST. These components may be assigned to the CO group which is bound to water molecules as the solvent (1625 cm-1) and to the N−H in ...

Change in Hydration State during the Coil−Globule Transition of Aqueous Solutions of Poly(N-isopropylacrylamide) as Evidenced by FTIR Spectroscopy†

Rechargeable aqueous batteries are an up-and-coming system for potential large-scale energy storage due to their high safety and low cost. However, the freeze of aqueous electrolyte limits the low-temperature operation of such batteries. Here, we report the breakage of original hydrogen-bond network in ZnCl2 solution by modulating electrolyte structure, and thus suppressing the freeze of water and depressing the solid-liquid transition temperature of the aqueous electrolyte from 0 to –114 °C. This ZnCl2-based low-temperature electrolyte renders polyaniline||Zn batteries available to operate in an ultra-wide temperature range from –90 to +60 °C, which covers the earth surface temperature in record. Such polyaniline||Zn batteries are robust at –70 °C (84.9 mA h g−1) and stable during over 2000 cycles with ~100% capacity retention. This work significantly provides an effective strategy to propel low-temperature aqueous batteries via tuning the electrolyte structure and widens the application range of temperature adaptation of aqueous batteries. Rechargeable aqueous batteries are promising for potential large-scale energy storage due to their high safety and low cost. Here the authors analyse a zinc chloride based low-temperature electrolyte for improving practicability of the aqueous batteries.

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Modulating electrolyte structure for ultralow temperature aqueous zinc batteries.

A solid-state dedicated circular dichroism (CD) spectrophotometer (J-800KCM) was designed and constructed. As a CD spectrophotometer is a polarization–modulation instrument, CD spectra are necessarily accompanied by artifacts due to macroscopic anisotropies such as linear birefringence (LB) and linear dichroism (LD) which are unique to the solid state. A photomultiplier with the least polarization characteristics and a photoelastic modulator (PEM) with the least residual static birefringence were selected for the new instrument, which was based on the electrical and optical systems of a commercially available spectrophotometer. A phased-locked loop circuit was introduced to a PEM driver, and a sample rotation holder, a stage controller, and an analyzer were installed. We have designed and built a special solid-state sample holder to enable the cancellation of artifact CD, and a lens unit for smaller samples. A set of procedures for obtaining true CD has been devised based on the Mueller matrix method, and...

A solid-state dedicated circular dichroism spectrophotometer: Development and application

NMR and FT-IR Studies of Hydrogen Bonds in Ethanol-Water Mixtures

The concentration and the temperature dependencies of 1H and 13C chemical shifts in NMR of aqueous acetone mixtures were studied, together with the concentration dependence of the frequency of the C–H stretching vibration of acetone in IR spectra. 1H and 13C chemical shifts were measured at 1 °C, 23 °C, and 48 °C by the external double reference method using a capillary with a blown-out sphere at the bottom for tetramethylsilane as the external reference substance. By this method, it is possible to determine the volume magnetic susceptibility of a sample solution at each temperature, for which the observed chemical shifts may be corrected exactly. Thus, we revealed the detailed electronic polarization in acetone as well as water as functions of concentration and temperature. On diluting acetone with water, the chemical shift of water protons, δH2O, is 3 ppm at the mole fraction of water Xw=0,05 and increases to the value for pure water, ca. 5 ppm, at Xw=0.96, with increasing Xw. In the region of Xw>0.96, ...

Hydrophobic hydration of acetone probed by nuclear magnetic resonance and infrared: Evidence for the interaction C–H⋯OH2

The Mueller matrix approach is used to analyze the problems associated with the calibration of a modern CD spectropolarimeter constructed on the basis of a modulation technique in polarization spectroscopy. As a result, the performance of the CD spectropolarimeter is found to be determined by the characteristics of the photomultiplier as a partial polarizer, the residual static strain birefringence of the modulator, and the first harmonic response of a lock‐in amplifier. Furthermore, the CD signal is greatly affected by the circular birefringence of a sample in addition to the above three factors. Thus, the necessity of checking these factors before the calibration is carried out using a standard sample is pointed out.

Circular dichroism measurements. I. Calibration of a circular dichroism spectrometer

An interesting paper on circular dichroism (CD) and linear dichroism (LD) microscopy by Livolant, Mickols, and Maestre [(1988) Biopolymers27, 1761–1969] has attracted our attention. They reported that they have succeeded in deconvoluting mathematically true CD and LD from signals obtained for their samples of strong and incompatible anisotropies. If this is true, then their method of mathematical deconvolution will open new possibilities in polarization-modulation spectroscopy. However, after carefully reading through their paper, we found the following obscure points in their results: (1) the hardware of their spectrometer; (2) the sensitivity matrix; (3) the method for separation of CD and LD by using two standards; (4) average CD curves; and (5) circular intensity differential scattering (CIDS) and linear intensity differential scattering (LIDS) in the wavelength range from 300 to 330 nm. Making use of the Mueller matrix analysis, we present our comments on the above subjects together with our data. In conclusion, we maintain that it is difficult to accept their claim of having a general and useful approach to separating true CD and LD from signals observed in macroscopically anisotropic samples.

Yohji Shindo

Papers

A solid-state dedicated circular dichroism spectrophotometer: Development and application

NMR and FT-IR Studies of Hydrogen Bonds in Ethanol-Water Mixtures

Hydrophobic hydration of acetone probed by nuclear magnetic resonance and infrared: Evidence for the interaction C–H⋯OH2

Circular dichroism measurements. I. Calibration of a circular dichroism spectrometer

Problems of CD spectrometers (V): Can we measure CD and LD simultaneously? Comments on differential polarization microscopy (CD and linear dichroism)