R. J. Jakobsen

An Algorithm for the Reproducible Spectral Subtraction of Water from the FT-IR Spectra of Proteins in Dilute Solutions and Adsorbed Monolayers:

Spectral subtraction and baseline correction via interactive graphics programs have been extensively used for the analysis of weak IR absorption signals which are under strong bands, such as occur in aqueous protein solutions. However, personal bias and uncertainty can result in significant differences in the spectra of the same protein substracted and baseline corrected by different persons. This is demonstrated in the case of albumin adsorbed on the surface of a germanium ATR crystal in contact within pure water. A simple computer algorithm to automatically subtract the water spectrum and remove any baseline tilt or curvature, and thus remove this individual bias and uncertainty, is presented, with a comparison of the results between different persons and the algorithm.

Far infrared studies of hydrogen bonding in carboxylic acids—I formic and acetic acids

Abstract The three infrared active hydrogen bond vibrations of the cyclic dimer of formic acid have been reassigned, with the modes of vibration verified by normal coordinate analysis of the deuterated species. For acetic acid, two of the three predicted vibrations have been observed and assigned and the third vibration established by normal coordinate analysis. Another observed frequency was shown to be a combination band in Fermi resonance with a hydrogen bond fundamental. Assignments have been made for the observed frequencies of the solid polymeric forms of formic and acetic acids. Two separate polymorphic forms have been isolated for formic acid crystals and two polymorphic forms have been detected but not isolated for acetic acid. Liquid formic acid has been shown to consist of hydrogen bonded polymers and liquid acetic acid, mainly of hydrogen bonded cyclic dimers.

Fourier Transform Infrared Spectroscopy of Protein Adsorption from Whole Blood: II. Ex Vivo Sheep Studies

A Fourier transform infrared/attenuated total reflectance technique has been developed to study protein adsorption onto surfaces. The application of this technique to an ex vivo model using a beagle dog as the source of whole, flowing blood is described (currently, high-quality infrared spectra are being collected at 5-s intervals of protein adsorption). This approach has enabled the authors to identify albumin and glycoproteins as the initially adsorbing species, with the subsequent competitive replacement of part of this protein layer with fibrinogen and other proteins. The exact relationship between the pattern of protein adsorption from whole blood and the generation of a thrombus (clot) is not yet clear, but it is hoped that this type of experimental approach will help clarify the relationship.

Hydrogen bonding in solid alcohols

Abstract Polarized ir spectra of single crystals of solid alcohols have shown that the OH stretching vibration, v (OH), is always split into two components. Spectra of partially-deuterated solid alcohols have demonstrated that the appearance of two bands is due to crystal splitting. This splitting can be explained by nearest-neighbor or first-order coupling of the vibrations of adjacent OH groups along the hydrogen bond chain. The decoupled OH stretching vibration of these alcohols gives a narrow singlet absorption with a half bandwidth as low as 30 cm −1 . Thus, v (OH) of solid alcohols is not inherently broad, but gains breadth as a result (direct or indirect) of the coupling between OH groups. A study of partially-deuterated liquid alcohols indicates that coupling plays only a small part in the v (OH) bandwidth in liquids. Therefore, different mechanisms control the OH bandwidth in liquid and solid alcohols.

Infrared spectra and normal coordinate calculation of crystalline formic acid

Abstract Infrared spectra from 3000 to 70 cm−1 have been obtained on the β-polymorphs of (HCOOH)n, (DCOOH)n, and (HCOOI))n crystals. All of the observed absorption bands were assigned on the basis of an infinite hydrogen bonded chain having a factor group isomorphous to C3v. In order to verify the assignment, normal coordinate calculations were carried out for (HCOOH)n with a set of force constants obtained from the observed frequencies. These force constants were successfully used to predict the frequencies of (DCOOH)n and (HCOOI)n. Both the potential energy distribution and Cartesian displacements were calculated in order to accurately determine the modes of the vibrations, including the hydrogen bond vibrations. This represents the first sucessful calculation for a hydrogen bonded polymeric molecule in which the modes of the hydrogen bond vibration have been reasonably determined.

Far‐Infrared Spectra of Mercuric Halides and Their Dioxane Complexes

The far‐infrared spectra (600–60 cm−1) of HgCl2, HgBr2, HgI2 (red), and their one‐to‐one p‐dioxane complexes (in the solid state) were investigated. All of the observed spectra, except those of HgI2, were assigned on the base of the symmetry properties of the crystals. High‐pressure effects were investigated for the anti‐symmetric stretching vibration of HgCl2 and its dioxane complex. The frequency shifts of all of the compounds in the various states, from the gaseous state through the dioxane complex under high pressure, were elucidated in terms of the distance between the mercury atom and its nearest neighbors.

Polarized infrared spectra of single crystals of ethyl alcohol

Abstract Polarized mid-infrared spectra of single crystals of ethyl alcohol and its deuterated derivatives have been obtained using a diamond-window high-pressure cell for both the crystal growing and the spectral measurements. Lattice frequencies have been determined from the infrared spectra of polycrystalline samples at low temperatures. From the dichroic measurements, a crystal structure, C 2 h 6 - A 2/a, is proposed. All of the polarized infrared bands are interpreted on the basis of this structure, including the splitting of the OH stretching vibration into a broad and a sharp component. This latter phenomenon has been interpreted in terms of coupling and a tendency towards a tautomerism for some of the OH stretching vibrations of an infinite zigzag hydrogen-bonded chain.

Polarized ir spectra of single crystals of propanoic acid

Abstract Single Crystals of propanoic acid were grown in a diamond-window Cell under high pressure at room temperature. Polarized ir Spectra of the Single Crystals were investigated and assignments of the Bands were Made taking the Crystal Structure into Consideration. Mid- and far-IR Spectra of the acid and Some deuterated acids in various physical States were also investigated and all of the observed Bands were interpreted in terms of a hydrogen-bonded Cyclic dimer. The only exception was the vapor at about 100° which Showed a Spectrum for Monomeric acid without hydrogen Bonds. A rough Normal-coordinate Calculation was Carried out for the out-of-plane vibrations of the dimers.

High Pressure Spectroscopic Studies of Hydrogen Bonding

A diamond-window high pressure cell has been used to study the effects of pressure on the OH stretching vibration of liquid alcohols. The results of this study show that: (1) while decreasing temperature changes the polymer equilibrium of hydrogen bonded systems, increasing pressure shortens the hydrogen bond or intermolecular distance without affecting the polymer equilibrium; (2) the free OH absorption seen in these compounds arises from the OH end group of the hydrogen bonded polymer and not from monomeric molecules; and (3) the alcohols used in this study must be primarily linear polymers rather than cyclic hydrogen bonded structures and these chains must be fairly short otherwise the free OH end group absorption would not be observed.

Past Results and Future Prospects of the Far-Infrared Studies of Hydrogen Bonding

In the past five years the number of papers concerned with far-ir studies of hydrogen bonding has increased by an order of magnitude. The results of some of these papers are presented in this review. Most of this work is concerned with the assignment of low frequency hydrogen bond vibrations. Since the major problem is reliable assignments, we discuss techniques used in making the assignments and emphasize the past work in which attempts have been made to substantiate those assignments. These assignments are discussed in terms of the different hydrogen bond vibrations associated with various types of hydrogen bonds. The main needs for future far ir hydrogen bond studies are listed.