Effects of phase Separation and devitrification processes in oxide glasses on ESR spectra

The consequences of phase Separation and devitrification processes for the ESR patterns of Fe³⁺ ions and oxygen hole centres in giassy and glassy-crystalline Systems are discussed. Analysis of the Fe³⁺ spectra by Simulation (including 4th order terms) allows their model-based Interpretation for homogeneous, phase-separated and devitrified samples as well. It is even possible to estimate the ratio of Fe³⁺ ions incorporated into the giassy matrix to those localized in the crystalline phase. An influence of irreversible structural reorganization in glasses on γ-irradiation-induced oxygen hole centres is detectable by studying their Saturation behaviour For the example of a barium Silicate glass studied here, pronounced passage effects could be detected at 77 K. In contrast, a devitrified sample of the same composition after γ Irradiation yielded the same spectral pattern at low microwave power, but only Saturation broadening was to be observed when rising the microwave power. In an annealed sample of anorthite composition (in mol%: 25CaO, 25AI₂O₃, 50SiO₂) progressive crystal growth was detectable using Fe³⁺ ions as probes

On the interaction of glasses with high-energy radiation - Combined ESR and optical studies

This paper will discuss some aspects of the induced physical processes and chemical reactions which are observed when Silicate and aluminosilicate glasses are exposed to UV radiation (248 nm; excimer laser), γ radiation (⁶⁰Co) and pulses of fast electrons (3.8 MeV). The stimulated emission and absorption of short-lived defects and Čerenkov radiation are detected in the optical ränge between 200 and 800 nm and on the microsecond time scale. Stahle hole centres (Si-0⁻/h⁺, Si-O-Al/h⁺) and electron centres (among others Zn⁺, Cd⁺, (Fe³⁺)⁻) are detected by ESR spectroscopy at room temperature. They show surprising differences in regard to their thermal stability, i.e., the distribution and mean value of their trap depths. Induced absorption in the UV/VIS range exhibits broad and overlapping bands, some of which can be partially assigned to centres detected by ESR spectroscopy. Therefore, UV/VIS spectroscopy provides complementary information, an induced absorption at 300 nm for example, which has no analogy in ESR measurements

Effects of dental probing on occlusal surfaces - A scanning electron microscopy evaluation

The aim of this clinical-morphological study was to investigate the effects of dental probing on occlusal surfaces by scanning electron microscopy (SEM). Twenty sound occlusal surfaces of third molars and 20 teeth with initial carious lesions of 17- to 26-year-old patients (n = 18) were involved. Ten molars of each group were probed with a sharp dental probe (No. 23) before extraction; the other molars served as negative controls. After extraction of the teeth, the crowns were separated and prepared for the SEM study. Probing-related surface defects, enlargements and break-offs of occlusal pits and fissures were observed on all occlusal surfaces with initial carious lesions and on 2 sound surfaces, respectively. No traumatic defects whatsoever were visible on unprobed occlusal surfaces. This investigation confirms findings of light-microscopic studies that using a sharp dental probe for occlusal caries detection causes enamel defects. Therefore, dental probing should be considered as an inappropriate procedure and should be replaced by a meticulous visual inspection. Critical views of tactile caries detection methods with a sharp dental probe as a diagnostic tool seem to be inevitable in undergraduate and postgraduate dental education programmes. Copyright (c) 2007 S. Karger AG, Basel

Influence of irradiation sterilization on a semi-solid poly(ortho ester)

Viscous poly(ortho ester) (POE), a promising polymer for controlled release is being investigated as an injectable drug delivery system for peptides, for antiproliferative agents after glaucoma filtering surgery and for antibiotics in the treatment of periodontitis. Due to the chemical lability of POE, the strategies for obtaining a sterile product are limited to aseptic processing and terminal sterilization using high energy radiation. In the first part of the present investigation, we used electron-paramagnetic-resonance (EPR) spectroscopy to evaluate radical formation and radical-induced polymer degradation after irradiation treatment. Due to the viscous nature of POE, radicals were only found at low temperatures or by using the method of ‘spin-trapping'. Several radical species could be distinguished by a variation of the microwave power and the differences of the thermal stability of the radicals. The incorporation of 5-fluorouracil accelerates the degradation of the polymer. In the second part, we have compared the effects of the two commonly applied methods for irradiation sterilization (i.e. gamma and beta rays) on POE and on POE with incorporated 5-fluorouracil and compared these methods to aseptically prepared devices. In addition, we have checked the possibility of preventing radical-induced degradation using two different protecting agents: α-tocopherol at a concentration of 0.1% (w/w) and sterilization under nitrogen monoxide. The weight and number average molecular weight of POE decreased drastically after irradiation treatment and subsequent to irradiation, an accelerated degradation was observed. Generally it was found that higher molecular weight polymers are more affected and that gamma irradiation leads to more degradation than beta treatment. Also, the addition of protecting agents did not significantly prevent polymer degradation. Therefore, we have concluded that irradiation sterilization of POE is not a viable process and aseptic preparation is preferred. Without sterilization POE is stable for about 1 year when kept as monodoses at low temperatures

Isotope Effects in ESR Spectroscopy

In order to present the relationship between ESR spectroscopy and isotope effects three levels are considered: (i) ESR spectroscopy is described on a general level up to the models for interpretation of the experimental spectra, which go beyond the usually used time and mass independent spin-Hamilton operator, (ii) the main characteristics of the generalized isotope effects are worked out, and finally (iii) the basic, mainly quantum mechanical effects are used to describe the coupling of electron spins with the degrees of freedom, which are accessible under the selected conditions, of the respective paramagnetic object under investigation. The ESR parameters and the respective models are formalized so far, that they include the time and mass depending influences and reflect the specific isotope effects. Relations will be established between the effects in ESR spectra to spin relaxation, to spin exchange, to the magnetic isotope effect, to the Jahn-Teller effects, as well as to the influence of zero-point vibrations. Examples will be presented which demonstrate the influence of isotopes as well as the kind of accessible information. It will be differentiated with respect to isotope effects in paramagnetic centres itself and in the respective matrices up to the technique of ESR imaging. It is shown that the use of isotope effects is indispensable in ESR spectroscopy