Infrared and Raman spectroscopy of carbohydrates. Part VI: Normal coordinate analysis of V-amylose

A normal coordinate analysis of V-amylose has been performed for an isolated 6₁ helical chain. Negligible splitting from interactions of vibrations of successive residues is expected between A and E vibrational species due to the large size of the monomer unit. As a result, calculation of only the totally symmetric A modes represents an adequate approximation to the vibrational spectrum of helical polysaccharides. Using this method together with a valence force field we have obtained good agreement between the observed and calculated frequencies. In addition, the computed potential energy distribution and Cartesian displacement coordinates match previous experimental assignments, based on deuterium exchange. The analysis also supports the proposed mechanism for conversion of V-amylose to the more extended B-form. This conversion results in an observed frequency shift for the Raman line at 946 cm^?1 which is predicted by the calculations.     

Infrared and raman spectra of specifically deuterated 1,2-dipalmitoyl-sn-glycero-3-phosphocholines

Deuterated methylene groups have been introduced synthetically in selected positions of the sn-2 palmitoyl chain of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and deuterated methyl groups in the sn-1 and sn-2 palmitoyl chains as well as in the sn-3 phosphocholine group.The vibrational spectra of seven such deuterium labelled derivatives of the title compound have been studied as the assignment of the C–D stretching vibrations is discussed.     

Characterization of the three major polymorphic forms and liquid state of tristearin by Raman spectroscopy

Raman spectroscopy was used to distinguish the differences in the molecular organization of the α, β′ and β polymorphs, as well as the liquid state, of tristearin with focus placed on the CO, CH and CC Raman-active stretching regions. The ester carbonyl stretching region permitted polymorphic discrimination due to significant differences in the number of modes, their relative frequencies and their full-widths at half-maximum. In the liquid state, the absence of obvious signatures in this region indicated that many local micro-environments likely exist about the ester carbonyl of molten tristearin. The ratio between the symmetrical and asymmetrical CH stretching modes was linearly correlated with the enthalpy of fusion for each polymorph. The CC stretching modes, which provided insight into the trans/gauche content, were polymorph independent, but changed significantly upon transition into the liquid state (p < 0.05). Overall, Raman spectroscopy allowed for the quick discrimination of tristearin polymorphs from a conformational and thermodynamic perspective.     

Infrared and Raman spectra of phosphatidyl-ethanolamine and related compounds.

Infrared and Raman spectra of phosphatidylethanolamine from Escherichia coli, L-alpha-glycero-phosphorylethanolamine and 0-phosphorylethanolamine were obtained. Most of the bands were assigned to each vibrational mode based on the N deuteration effect, comparison of the intensity in the infrared and Raman spectra and the depolarization degree measurement in the Raman spectra. The spectra of phosphatidylethanolamine can be interpreted by assuming that the molecule takes the dipolar ionic structure both in non-polar solvent and in solid.     

On the blue color of triiodide ions in starch and starch fractions. III. Resonance Raman spectra of bluing species in amylose

In order to clarify the characteristics of the basic units responsible for the blue coloring of iodine/iodide in amylose, we made a resonance Raman spectroscopic study at several KI concentrations using excitation by Ar⁺, He-Ne, and Kr⁺ lasers and amyloses with the degrees of polymerization (DP) of 30, 100, 300, and 1000. Similar Raman spectra were observed, regardless of the KI and I₂ concentrations, DP, and excitation wavelengths. Four Raman lines appearing at 159, 111, 55, and 27 cm^?1 were obviously fundamental tones, with a degree of depolarization ρ of ca. 1/3 for every spectrum. However, the internal ratios of the intensities of the 159, 55, and 27 cm^?1 lines to that of the 111-cm^?1 line decreased with increasing KI concentration. Based on the value of ρ, the assignment of the fundamental lines was made by taking a schematic model of the true motions as a projection in separately analyzing the modes of stretching and bending vibrations for a pseudolinear polyiodide chain, which we found to be perturbed by the external forces of the amylose lattice. In accordance with the variation of the force constants from the assignment of the spectra associated with the change in the composition of the bound species, it was concluded that the basic unit changed from I to I through I with decreasing KI concentration.     

Infrared and raman spectra of metal 1,2,4,5-benzenetetracarboxylates: Evidence for very short,strong hydrogen bonds

Salts of 1,2,4,5-benzenetetracarboxylic acid with copper, aluminum, ammonium, cobalt(II), thallium(I), tin(II), uranyl ion, zinc, manganese, iron(II), nickel, potassium and sodium have been prepared and characterized by their IR spectra. The salts of aluminum, ammonium, thallium(I), tin(II), zinc, iron(II), nickel, potassium and sodium had not been reported before with adequate characterization. Raman spectra of selected compounds also aided structural interpretation. The IR spectra of Na₂C₁₀H₄O₈·2H₂O, Fe(C₁₀H₅O₈)₂·12H₂O, Zn(C₁₀H₅O₈)₂·12H₂O, Ni(C₁₀H₅O₈)₂·12H₂O, (NH₄)₃C₁₀H₃O₈·H₂O and CoC₁₀H₄O₈·6H₂O indicate very short, strong hydrogen bonds in these compounds. The IR and Raman spectra can be used to determine the mode of coordination (if any) of the carboxylate groups of 1,2,4,5- benzenetetracarboxylate to metal ions.     

Low-frequency Raman spectra of lysozyme.

New techniques in laser Raman spectroscopy are used to obtain spectra of aqueous solutions of lysozylme for frequency shifts as small as 5 cm^?1. In addition, Raman measurements are made on two crystalline forms of hen egg white lysozyme. The spectra obtained from the solution and from the crystal are found to be similar for frequencies above 100 cm^?1. However, a low-frequency band at 25 cm^?1 observed in crystalline lysozyme is not found in the solution, indicating that this band cannot be attributed to an internal molecular vibration.     

Conformation-dependent features in the raman spectra of simple lipids

Raman spectroscopy is shown to be a useful method in order to study the conformation in hydrophobic regions of lipid systems. The most sensitive part of the spectra in this respect is formed by the C-H stretching vibrations. Different close-packing arrangements of the hydrocarbon chains can thus be identified in the solid state, and the successive increase in the degree of disorder at transitions into liquid-crystalline and micellar phases can be seen from changes in the spectra. Even when the phases contain more than 90% (w/w) of water, well resolved spectral contributions from the lipids are obtained, and direct analyses of biological systems are therefore possible. Some applications are also demonstrated.     

Differences in the polymorphic forms of metallothionein

Metallothionein induced in rat liver by metal ions can be resolved into two forms, referred to as isoforms I and II. These polymorphic forms differ in several properties. Sequence analysis of the CNBr-digested thionein isoforms revealed seven differences in the first 25 amino acids between isoforms I and II of Cd-induced thionein. The sequence of the first 25 amino acids in isoform II of Cu-induced thionein was identical to that of isoform II of Cd-induced thionein, suggesting that the same polymorphic forms are induced with different metal ions. Isoform II of Cd,Zn-thionein exhibited a reproducibly greater Stokes radius (17 Å) by gel filtration compared to isoform I (16.2 Å), whereas isoform II of Cu-thionein eluted with a Stokes radius of 16.2 Å. The isoforms also differ in Zn-binding affinity. Isoform I of several preparations of Cd,Zn-thionein and Zn-thionein invariably reconstituted greater esterase activity in apo-carbonic anhydrase than did isoform II. In Cd,Zn-thionein samples, only the Zn²⁺ ions were transferred to apo-carbonic anhydrase. Similarity, the Zn²⁺ ions in isoform I were more reactive with EDTA compared to isoform II. The greater reactivity of isoform I with EDTA was evident kinetically from spectrophotometric assays as well as thermodynamically from equilibrium dialysis experiments. The significance of these differences is unclear, but it is conceivable that the dissimilarities in the conformational and Zn-binding affinity of rat liver metallothionein may correlate with a functional distinction.     

Infrared spectroscopy of heparin-cation complexes.

Hydrated and partially hydrated films and aqueous solutions of heparin, heparans and N-desulphated preparations of these polymers were studied by near- and fundamental-region-i.r. spectroscopy in the presence of a range of countercations. The results suggest that ion binding is not explicable solely in terms of simple electrostatic theory, and that specific cation effects, and the hydration pattern of the polymer-cation complex need to be taken into account.     

Resonance Raman spectra of whole mitochondria.

The resonance Raman spectra of reduced cytochromes b and c and cytochrome oxidase in whole mitochondria have been recorded without any instrument modifications. The contributions of the individual cytochromes have been identified by comparison with the characteristic features observed in partially purified preparations including: (i) the strong dependence of the intensity patterns on excitation wavelength relative to the peak positions of the alpha, beta, and gamma absorption bands of the cytochromes; and (ii) the presence of marker bands for heme type. Since the Raman spectra can be used as an intrinsic indicator of interaction between hemes, the ability to record spectra in intact mitochondria opens the possibility to study heme-heme interactions in the functioning membrane in situ.     

Infrared spectroscopy of collagen and collagen-like polypeptides.

The set of synthetic polytripeptides and polyhexapeptides which can adopt a triple-helical form constitute a good model system for investigating collagen structure. Here we consider previous and new infrared spectroscopic studies on collagen and present the infrared spectra of a number of polymers with collagen-like features. The amide A band position for all triple-helical polypeptides is higher than that observed for most proteins and polypeptides, and this high frequency appears to be related to the degree of supercoiling of the triple helix. It is possible that with increased supercoiling of the three chains the angles between the groups involved in the intramolecular hydrogen bonds become less favorable, or these bonds may become unusually long. The frequency of the amide I band varies considerably for triple-helical polypeptides with different amino acid sequences, and often minor bands are observed. This finding contrasts with the observations for polypeptides in a pleated sheet or α-helical form, where the same amide I frequency is observed regardless of the amino acid composition. An explanation for this variation is proposed in terms of the hydrogen bonding properties of imino acids. Significant spectral changes in the amide I region are observed on hydration in the spectra of some triple-helical polypeptides, but corresponding changes have not been found in the collagens examined.