Electrophilic substitution at the δ-methine bridge of pheophorbide a and a′

A chloro-substituted derivative was prepared from chlorophyll $\text{a}$′. The derivative was shown to be δ-chloro-methyl pheophorbide $\text{a}$ by UV/VIS, MS and ′H NMR.     

Research advances in the use of tetrapyrrolic photosensitizers for photodynamic therapy

Photodynamic therapy (PDT) is a promising new treatment modality for several diseases, most notably cancer. In PDT, light, O2, and a photosensitizing drug are combined to produce a selective therapeutic effect. Lately, there has been active research on new photosensitizer candidates, because the most commonly used porphyrin photosensitizers are far from ideal with respect to PDT. Finding a suitable photosensitizer is crucial in improving the efficacy of PDT. Recent synthetic activity has created such a great number of potential photosensitizers for PDT that it is difficult to decide which ones are suitable for which pathological conditions, such as various cancer species. To facilitate the choice of photosensitizer, this review presents a thorough survey of the photophysical and chemical properties of the developed tetrapyrrolic photosensitizers. Special attention is paid to the singlet-oxygen yield (PhiDelta) of each photosensitizer, because it is one of the most important photodynamic parameters in PDT. Also, in the survey, emphasis is placed on those photosensitizers that can easily be prepared by partial syntheses starting from the abundant natural precursors, protoheme and the chlorophylls. Such emphasis is justified by economical and environmental reasons. Several of the most promising photosensitizer candidates are chlorins or bacteriochlorins. Consequently, chlorophyll-related chlorins, whose PhiDelta have been determined, are discussed in detail as potential photosensitizers for PDT. Finally, PDT is briefly discussed as a treatment modality, including its clinical aspects, light sources, targeting of the photosensitizer, and opportunities.     

Studies on coordination compounds: V. A chromatographic,mass spectrometric and infrared spectroscopic investigation of the thermal decomposition products of some nickel(II) aniline chloride,bromide, iodide,nitrate and sulphate compounds

Using chromatographic, infrared and mass spectrometric methods. 44 different organic compounds, besides water and ammonia have been separated and identified from the pyrolysis products of nickel(II) aniline nitrate hydrate. The nickel(II) aniline chloride, bromide, iodide and sulphate complexes, however, showed only aniline, formed by dissociation as an organic pyrolysis product; this is in accordance with previous conclusions drawn from thermogravimetric (TG) curves.On the basis of these results it is advisable to proceed with a certain caution when drawing conclusions from TG curves on pyrolysis processes without specification analyses of the process products. This should be specially noted when the reaction is abrupt and not calculable from the corresponding part of the TG curve, that is not smooth, preferably of S-shape.The formation of the main pyrolysis products through radical reactions is duscussed.     

Deswelling of microfibril bundles in drying wood studied by small-angle neutron scattering and molecular dynamics

Cellulose - Structural changes of cellulose microfibrils and microfibril bundles in unmodified spruce cell wall due to drying in air were investigated using time-resolved small-angle neutron...     

Dynamic response of chlorine atoms on a RuO(2)(110) model catalyst surface

The dynamic behavior of surface accommodated chlorine atoms on RuO(2)(110) was studied by a variety of experimental methods including high resolution core level shift, thermal desorption-, and in situ infrared spectroscopy as well as in situ surface X-ray diffraction in combination with state-of-the-art density functional theory calculations. On the chlorinated RuO(2)(110) surface the undercoordinated oxygen atoms have been selectively replaced by chlorine. These strongly bound surface chlorine atoms shift from bridging to on-top sites when the sample is annealed in oxygen, while the reverse shift of Cl from on-top into bridge positions is observed during CO exposure; the vacant bridge position is then occupied by either chlorine or CO. For the CO oxidation reaction over chlorinated RuO(2)(110), the reactant induced site switching of chlorine causes a site-blocking of the catalytically active one-fold coordinatively unsaturated (1f-cus) Ru sites. This site blocking reduces the number of active sites and, even more important, on-top Cl blocks the free migration of the adsorbed reactants along the one-dimensional 1f-cus Ru rows, thus leading to a loss of catalytic activity.     

Determination of Pt from coke samples by ICP-MS after microwave assisted digestion and microwave assisted cloud point extraction

Platinum in coke samples was determined by inductively coupled plasma mass spectrometry (ICP-MS) after microwave-assisted sample digestion and temperature controlled microwave assisted cloud point extraction (MW-CPE). Interferences due to hafnium (¹⁷⁹Hf¹⁶O) were successfully eliminated using MW-CPE with 2-MBT prior to the determination of platinum by ICP-MS. The validity of the method was studied by spike recovery tests and by analyzing certified reference material (BCR-723 street dust). The results obtained for platinum in the BCR-723 were generally in good agreement with the certified values. Furthermore, the preliminary platinum results obtained for coke sample by ICP-MS after MW-CPE were compared to those obtained by a reference method (NiS-Fire Assay preconcentration/Te coprecipitation and ICP-MS determination).     

Degradation and Crystallization of Cellulose in Hydrogen Chloride Vapor for High‐Yield Isolation of Cellulose Nanocrystals

Despite the structural, load‐bearing role of cellulose in the plant kingdom, countless efforts have been devoted to degrading this recalcitrant polysaccharide, particularly in the context of biofuels and renewable nanomaterials. Herein, we show how the exposure of plant‐based fibers to HCl vapor results in rapid degradation with simultaneous crystallization. Because of the unchanged sample texture and the lack of mass transfer out of the substrate in the gas/solid system, the changes in the crystallinity could be reliably monitored. Furthermore, we describe the preparation of cellulose nanocrystals in high yields and with minimal water consumption. The study serves as a starting point for the solid‐state tuning of the supramolecular properties of morphologically heterogeneous biological materials.     

On the excursion theory for linear diffusions

We present a number of important identities related to the excursion theory of linear diffusions. In particular, excursions straddling an independent exponential time are studied in detail. Letting the parameter of the exponential time tend to zero it is seen that these results connect to the corresponding results for excursions of stationary diffusions (in stationary state). We characterize also the laws of the diffusion prior and posterior to the last zero before the exponential time. It is proved using Krein’s representations that, e.g. the law of the length of the excursion straddling an exponential time is infinitely divisible. As an illustration of the results we discuss the Ornstein–Uhlenbeck processes.     

Determination of Mercury Species by Capillary Column GC-QTAAS with Purge and Trap Preconcentration Technique

 A GC-QTAAS procedure was developed for the determination of methylmercury and inorganic mercury(II) in biological samples. A capillary column DB-1 (J&W Scientific) was used for the separation of ethylated mercury species. Sodium tetraethylborate was used as derivatization reagent. When direct sample introduction did not provide low enough detection limits, a purge and trap preconcentration technique was developed, where the evolved mercury species were concentrated on Tenax-ta adsorbent. With this system the measuring range was between 0–5 ng (as Hg) for the different species (dimethylmercury, methylmercury and inorganic mercury(II)) in a 100 μl sample. The detection limits obtained for a 250 mg sample with the standard addition method were 72 μg/kg, 136 μg/kg and 224 μg/kg for dimethylmercury, monomethylmercury and inorganic mercury(II), respectively. The method was successfully applied to the determination of mercury species in the dogfish certified standard reference material (DOLT-2). Received November 13, 2000. Revision June 12, 2001.