Evidence for temperature dependent anisotropic diffusive motion of heme iron in crystals of myoglobin through Mossbauer spectroscopy

A careful investigation of Mössbauer absorption of⁵⁷Fe in an assembly of unaligned crystals of deoxymyoglobin has revealed asynimetric shapes of the spectra in the range of temperatures between –25C and 25C, which includes the physiological significant temperatures. The asymmetry increases with temperature. The spectral shapes, displaying wide wings, show the presence of modes of collective diffusive motion in which the Fe atoms participate. The results are interpreted in terms of temperature-dependent anisotropic dynamics of the slow collective diffusive modes, based on a model of bounded diffusion assuming absorption in an anisotropic harmonic oscillator in Brownian motion. For example, assuming eqQ > 0, and axial symmetry, we obtain at 20C,=0.040Ų and <x ₁ ² > = 0.016Ų.     

Study of thermally treated dickite by infrared and micro-Raman spectroscopy using curve-fitting technique

The products of dickite heated in air at 1000 to 1300°C were studied using curve-fitting of transmission and photoacoustic infrared and micro-Raman spectra. The spectra were compared with those of mullite, Al-spinel, corundum, cristobalite, amorphous silica and meta-dickite. Bands that characterize crystalline phases appeared at 1100°C and became stronger with increasing temperature. Mullite, Al-spinel, corundum and amorphous silica were identified by their characteristic bands. The characteristic IR bands of cristobalite overlap those of mullite and amorphous silica, and its presence was therefore established from intensity ratios of the appropriate bands. The research clearly demonstrated the advantage of using curve-fitting for the identification of high temperature phases in the study of the thermal treatment of kaolin-like minerals by infrared and Raman spectroscopy. This technique seems to be a useful method for materials analysis in the ceramic industry.This revised version was published online in November 2005 with corrections to the Cover Date.     

A Fifth OH-Stretching Band in IR Spectra of Kaolinites

Transmission infrared spectra of different kaolinites were studied by curve fitting. These spectra generally exhibit four hydroxyl stretching bands. In this article we show that a fifth OH band (already identified in Raman and photoacoustic IR spectra of kaolinites) is also observed in transmission IR spectra of hydrothermal and authigenic kaolinites, which have a high degree of crystallinity. This additional band is weak or undetectable for kaolinites with a low degree of crystallinity. Copyright 1999 Academic Press.     

Thermal analysis of the interaction between stearic acid and pyrophillite or talc. IR and DTA studies

Pyrophyllite and talc sorb stearic acid on edge surfaces. The grinding of clay-stearic acid associations in the presence of alkali halides converts some of the acid into the ionic form, this occurring more readily with talc than with pyrophyllite. Heating in a closed or semi-closed system causes dissociation of stearic acid adsorbed on talc, but not on pyrophyllite. The infrared absorption frequencies of the adsorbed ionic form vary with the clay mineral and the amount of water present. The thermal stabilities of the clay-stearic acid associations depend on the rate of escape of the acid, which is determined by the strength of bonding to the clay and the nature of the system, and on the degree of dissociation of the acid on the clay surfaces.

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Zusammenfassung Pyrophyllit und Talk adsorbieren Stearinsäure an den Kantenoberflächen. Beim Verreiben von Ton-Stearinsäure-Assoziaten in Gegenwart von Alkalihaliden wird ein Teil der Säure in die ionische Form überführt, und zwar leichter mit Talk als mit Pyrophyllit. Aufheizen im geschlossenen oder halbgeschlossenen System bewirkt eine Dissoziation der an Talk, aber nicht der an Pyrophyllit adsorbierten Stearinsäure. IR-Absorptionsfrequenzen der adsorbierten ionischen Form sind abhängig vom Tonmineral und der anwesenden Wassermenge. Die thermische Stabilität der Ton-Stearinsäure-Assoziate hängt von der Geschwindigkeit der Abgabe der Säure ab, die durch die Stärke der Bindung an das Tonmineral, also der Natur des Systems, und durch den Dissoziationsgrad der Säure an der Tonmineraloberfläche bedingt ist.

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Coupled-wave formalism for optical waveguiding by transverse Bragg reflection

A formalism is presented for optical waveguiding by means of Bragg reflection. The theory provides analytic expressions for field modal profiles, dispersion, and attenuation. Waveguiding in line defects of photonic bandgap crystals, a special case of the theory, is used as an example. Quantized allowed widths of the guiding channel are predicted.     

Emanation thermal analysis study of Na-montmorillonite and montmorillonite saturated with various cations

Emanation thermal analysis (ETA) and thermogravimetry measured in the range 20–1000°C was used to characterize the thermal behaviour of Na-montmorillonite (Upton Wyoming, USA) and homoionic montmorillonite samples prepared by saturation with cations Li⁺ , Mg²⁺ , Al³⁺ , respectively. It was confirmed that the presence of cations used for montmorillonite saturation (Li⁺ , Mg²⁺ , Al³⁺ ) influenced the thermal behaviour of the samples. The results that indicated the decrease of radon release rate corresponding to a collapse of the interlayer space between the silicate sheets after water release and the crystallization of meta-montmorillonite in the respective temperature intervals were compared. From the ETA results it followed that the thermal stability of intermediate microstructure depends on the type of exchanged cation. A mathematical model was used to evaluate the ETA data.     

Investigation of micelle formation by fluorescence correlation spectroscopy

We show that noncovalently bound dye molecules can be used as labels in single-molecule fluorescence experiments for the determination of aggregate formation in standard surfactant systems. Aqueous solutions of sulfosuccinic acid bis(2-ethylhexyl) ester sodium salt, hexadecyltrimethylammonium chloride, and pentaethylene glycol monododecyl ether have been studied by fluorescence correlation spectroscopy using commercially available dyes. The translational diffusion coefficient and the critical micelle concentrations have been determined and compare well to values reported in the literature. The respective charges of the surfactant and of the dye molecule are crucial for the effectiveness of the presented method.     

The use of thermo-XRD-analysis in the study of organo-smectite complexes

Summary Thermo-XRD-analysis is applied to identify whether or not the adsorbed organic species penetrates into the interlayer space of the smectites mineral. In this technique an oriented smectite sample is gradually heated to temperatures above the irreversible dehydration of the clay, and after each thermal treatment is diffracted by X-ray at ambient conditions. In the thermal treatment of organo-clays, under air atmosphere at temperatures above 250°C, the organic matter is in part oxidized and charcoal is formed from the organic carbon. In inert atmosphere e.g. under vacuum above 250°C the organic matter is pyrolyzed and besides small molecules, charcoal is formed. If the adsorbed organic compound is located in the interlayer space, the charcoal is formed in that space, preventing the collapse of the clay. A basal spacing of above 1.12 nm suggests that during the adsorption the organic compound penetrated into the interlayer space. Thermo-XRD-analyses of montmorillonite complexes with anilines, fatty acids, alizarinate, protonated Congo red and of complexes of other smectites with acridine orange are described. To obtain information about spacings of the different tactoids that comprise the clay mixture, curve-fitting calculations on the X-ray diffractograms were adapted.     

Thermo-X-ray-diffraction analysis of dimethylsulfoxide-kaolinite intercalation complexes

DMSO-kaolinite complexes of low- and high-defect Georgia kaolinite (KGa-1 and KGa-2, respectively) were investigated by thermo-XRD-analysis. X-ray patterns showed that DMSO was intercalated in both kaolinites with a d(001)-value of 1.11 nm (type I complex). The samples were gradually heated up to 170°C and diffracted by X-ray at room-temperature. With the rise in temperature, due to the thermal evolution of the guest molecules, the relative intensity of the 1.11 nm peak decreased and that of the 0.72 nm peak (neat kaolinite) increased indicating that the fraction of the non-intercalated tactoids increased. The 1.11 peak disappeared at 130–140°C. During the thermal treatment of both complexes two additional peaks appeared at 110 and 120°C, respectively, with d-values of 0.79–0.94 and 0.61–0.67 nm in DMSO-KGa-1 and 0.81–0.86 and 0.62–0.66 nm in DMSO-KGa-2, indicating the formation of a new phase (type II complex). The new complex was obtained by the dehydration of type I complex and was composed of intercalated DMSO molecules which did not escape. The new peaks disappeared at 150–160°C indicating the complete escape of DMSO.