Methods and Results of Optical Investigations on Semiconductor Interfaces

Measurement of the state of polarization of reflected light (ellipsometry) permits the determination of the thickness and refractive index of thin layers formed on a surface. The IR absorption spectra of such thin layers, which can be measured by means of internal reflection spectroscopy (IRS), provide information about their chemical composition. These methods have been used to study adsorption processes and the formation of reaction layers at semiconductor interfaces, and may also be used for measurements of free charge carriers in the space-charge region and in surface states. Results of such investigations are given in this article.     

Absolute Rate Constants for the Addition of the 1‐(tert‐Butoxy)carbonylethyl Radical onto Cyclic Alkenes in Solution

Absolute rate constants are reported for the addition of the 1‐[(tert‐butoxy)carbonyl]ethyl (= 2‐(1,1‐dimethylethoxy)‐1‐methyl‐2‐oxoethyl) radical ^.CHMeCO₂(t‐Bu) to several cyclic and monosubstituted alkenes in MeCN as obtained by time‐resolved electron paramagnetic resonance (EPR). The activation energies for the addition of this alkyl radical are mainly governed by the addition enthalpy but are also substantially lowered by the ambiphilic effect and by relief of cyclic strain.     

Transport efficiency in femtosecond laser ablation inductively coupled plasma mass spectrometry applying ablation cells with short and long washout times

Relative mass transport efficiencies of near infrared (λ = 795 nm) femtosecond laser generated brass aerosols in helium were measured by ICP-MS applying different ablation cells with short and long washout times. It was found that the transport efficiencies are independent of the cell used within the mutual experimental uncertainties. This finding was confirmed by additional measurements providing the absolute particle mass transport efficiencies of femtosecond laser ablation in He. Here, the transport efficiencies were determined by weighing the samples before and after ablation with a micro-balance, collecting the particles by low-pressure impaction, and evaluating the impacted masses quantitatively by total reflection X-ray fluorescence. Within the experimental uncertainties (± 9–19%) the same absolute transport efficiency (about 77%) was found for all cells applied. This efficiency value can be regarded as a lower limit of the absolute mass transport efficiency since mass losses in the impactor are difficult to quantify.     

Capillary isoelectric focusing-mass spectrometry for shotgun approach in proteomics

We report on capillary isoelectric focusing-mass spectrometry (CIEF-MS) of complex peptide mixtures in the absence of carrier ampholytes. Furthermore, the use of low concentrations of carrier ampholytes as mere spacers is investigated. Carrier ampholytes are complex mixtures of amphoteric compounds with high buffering capacity. Since all peptides are amphoteric compounds by themselves, the use of carrier ampholytes may be superfluous to establish a stable pH gradient in CIEF analysis of protein digests. Our research showed that when carrier ampholytes are omitted, the analyte ions are not focused at their isoelectric point. The analytes are charged, leading to electrophoretic mobility uncharacteristic for CIEF. The method was tested for a five-protein-mixture at 0.02 mg/mL per protein and 0.05 mg/mL per protein. At the lower concentration, the analytes were stacked during the focusing process in only a limited length of the capillary. Therefore, the higher concentration led to better separation efficiency. It was found that at low concentration (0.20%) the carrier ampholytes could work as spacers. Though it led to sensitivity losses of 15-45%, this was compensated by the higher separation efficiencies seen. The method was evaluated with an eight-protein-mixture, of which all could be identified after performing MS/MS.     

固相氯化法合成氯化聚乙烯的红外光谱研究

本文研究在不同条件固相氯化聚乙烯(CPE)的红外光谱,探讨了一步和两步氯化合成的CPE的结构差别,着重讨论了两步氯化的CPE结构特点。从观察表征结晶结构和—(CH_2)_n—链段氯分布的特征频率变化表明,低温固相氯化主要发生在无定形区,并且在CPE中形成高氯化和低氯化链段(或未氯化)的嵌段结构。在两步固相氯化时,晶区受到较大程度的破坏,氯化作用已不局限在无定形区,其结晶结构的破坏主要同第二步氯化程度有关,即使CPE氯含量相同,若前后两步氯化程度不同,结构有很大差异。     

The unimolecular chemistry of protonated glycine and the proton affinity of glycine: a computational model

The potential energy hypersurface of protonated glycine, GH⁺, has been investigated. The calculated G2(MP2) value for the proton affinity (PA) of glycine, PA _calc=895kJ mol⁻¹, is in good agreement with the experimental value which has been estimated to lie in the range 864kJ mol⁻¹ < PA _exp <891kJ mol⁻¹. Ab initio quantum chemical calculations of relevant parts of the potential energy surface of GH⁺ give a reaction model which is consistent with the observed mass spectrometric fragmentation pattern. The lowest energy unimolecular reactions of GH⁺ are two distinct processes: (1) loss of CO, which has a substantial barrier for the reverse reaction, and (2) loss of CO plus H₂O, which has no barrier for the reverse reaction. Received: 15 November 1996 / Accepted: 6 May 1997     

Photodegradation of polypropylene thermal bonded non-woven fabric

Samples of thermal bonded polypropylene non-woven fabrics were exposed to light from two TUV 30W G30T8 Philips lamps (λ = 253.7 nm) in a covered open-air chamber at room temperature (25 °C and 55% relative humidity) for different periods of time. In order to determine the state of degradation, the samples were examined by optical microscopy, scanning electron microscopy, staining with an isopropanol solution of methylene blue and Sudan III, colourimetry, Fourier transform infrared (FTIR) spectroscopy and density measurements. Although the bonded areas formed under complex thermal and mechanical deformations during the fabric production, no localized staining was observed. The colour of the irradiated and stained fabrics changed uniformly due to the even production of polar groups in the process of irradiation. It was found that the change of redness and blueness of degraded and stained samples can be correlated linearly with the evolution of POOH groups as determined by FTIR spectroscopy. Products containing carbonyl (CO), hydroxyl and/or hydroperoxide (POOH) groups increase with time of degradation with a non-linear relation. It was also observed that the density and 997 cm⁻¹/972 cm⁻¹ FTIR absorbance ratio increases with degradation time. Density fluctuation and the build up of degradation products caused fibre cracks and embrittlement.     

Identification of the pathological prion protein allotypes in scrapie-infected heterozygous bank voles (Clethrionomys glareolus) by high-performance liquid chromatography-mass spectrometry

Cerebral formation of the pathological isoform of the prion protein (PrP) is a crucial molecular event in prion diseases. The bank vole (Clethrionomys glareolus) is a rodent species highly susceptible to natural scrapie. The PrP gene of bank vole is polymorphic (Met/Ile) at codon 109. Here we show that homozygous 109Met/Met voles have incubation times shorter than heterozygous 109Met/Ile voles after experimental challenge with three different scrapie isolates. An HPLC-MS/MS method was optimized and applied to investigate whether in heterozygous animals both PrP allotypes are able to undergo pathological conversion. The results demonstrate that both allotypes of the prion protein participate to pathological deposition.