Analysis of organoselenium compounds in human urine using active carbon and chemically modified silica sol-gel surface-assisted laser desorption/ionization high-resolution time-of-flight mass spectrometry

Laser desorption/ionization time-of-flight mass spectra of three thermally labile low molecular weight organoselenium compounds (selenomethionine, selenoethionine, trimethylselenonium iodide) in human urine matrix have been obtained by using surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). Four active layers, active carbon, silica sol-gel, and silica sol-gel impregnated with crown ether and with active carbon, were deposited on three different support substrates: (i) microscope slide coverslips; (ii) Al foil; and (iii) Cu tapes. Primarily protonated molecular ions and alkali metal adducts were observed in the mass spectra. A mixed-silica sol-gel and active carbon substrate active layer gave the best signal response for all compounds. Sol-gel substrates offered very clean backgrounds compared to the pure active carbon layers; however, the mass spectral signal intensities acquired were substantially lower for the sol-gel surfaces than those of the pure active carbon under the same conditions. Cu tape and Al foil support materials gave strong mass spectra of molecular ions and alkali metal molecular ion adducts, with lower Na and K adducts found with the Cu tape than with Al foil. Glass coverslips gave no response under all experimental conditions examined. Aerosol deposition was used to prepare SALDI substrates to avoid the localized "sweet spot" phenomenon encountered in conventional SALDI substrate preparation. Various nebulizers were examined and found to be effective in producing SALDI films with controlled and reproducible thicknesses. We were able to obtain exact mass identification of all three selenium species by high-resolution TOF-MS. To the best of our knowledge, this is the first time low molecular weight organoselenium compounds have been identified by SALDI-high-resolution TOF-MS.     

Molecular factor analysis applied to collections of NMR spectra

It is often useful to identify and quantify mixture components by analyzing collections of NMR spectra. Such collections arise in metabonomics and many other applications. Many mixtures studied by NMR can contain hundreds of compounds, and it is challenging to analyze the resulting complex spectra. We have approached the problem of separating signals from different molecules in complex mixtures by using self-modeling curve resolution as implemented by the alternating least-squares algorithm. Alternating least squares uses nonnegativity criteria to generate spectra and concentrations from a collection of mixture spectra. Compared to previous applications of alternating least squares, NMR spectra of complex mixtures possess unique features, such as large numbers of components and sample-to-sample variability in peak positions. To deal with these features, we developed a set of data preprocessing methods, and we made modifications to the alternating least-squares algorithm. We use the term "molecular factor analysis" to refer to the preprocessing and modified alternating least-squares methods. Molecular factor analysis was tested using an artificial data set and spectra from a metabonomics study. The results show that the tools can extract valuable information on sample composition from sets of NMR spectra.     

Lineage of non-cranial neural crest cell in the dental mesenchyme: using a lacZ reporter gene during early tooth development

The tooth is one of the ectodermal organs controlled by reciprocal interactions between the epithelium and the mesenchyme. Mesenchymal cells in the developing tooth, so-called dental mesenchymal cells, are derived from two different origins: the cranial neural crest (CNC) and the non-CNC. These CNC-derived cells migrate, proliferate and differentiate into odontoblasts, cementoblasts, fibroblasts, osteoblasts and chondroblasts. Tooth germs of wild-type mice were transplanted into the kidney of adult lacZ-transgenic mice. After 1 week of transplantation, a few lacZ-expressing cells and many red blood cells were found near or inside the blood vessels in the pulp of wild-type tooth germs. This result shows that circulating cells of the adult host could invade the dental pulp during tooth development, through the blood vessels, and be a part of dental pulp tissue. Therefore, it can be suggested that these circulating progenitor cells could be the origin of non-CNC-derived cells in tooth germ and their migration pathways would be the blood vessels invading the dental pulp during tooth development. If variations of this experiment were suitably adjusted, such as the embryonic stage of the tooth germ, duration of transplantation, etc., this transplantation experiment using adult lacZ-transgenic mice could be a good system to reveal the origin and migration pathway of cells in developing organs as well as in dental mesenchymal cells.     

Enhanced three-dimensional integral imaging system by use of double display devices

We propose an enhanced three-dimensional (3D) integral imaging system using multiple display devices. Experimental results with double devices prove the improvement in the image depth for a given image quality. We present experiments on an enhanced 3D integral imaging system using double display devices, in which two 3D subimages that cover different depth ranges are separately generated in each device, and then they are combined with a beam splitter to reconstruct the whole 3D image with an enhanced depth of view. In a similar manner, the double-device system can also be used to obtain a wider viewing angle by combining two images with different viewing angle ranges. We discuss the possibility of 3D integral imaging systems using multiple display devices as extensions of the system with double display devices.     

Phosphorylcholine-based polymer coatings for stent drug delivery

Phosphorylcholine-based polymers have been used commercially to improve the biocompatibility of coronary stents. In this study, one particular polymer is assessed for its suitability as a drug delivery vehicle. Membranes of the material are characterized in terms of water content and molecular weight cut-off, and the presence of hydrophilic and hydrophobic domains investigated by use of the hydrophobic probe pyrene. The in vitro loading and elution of a variety of drugs was assessed using stents coated with the polymer. The rate of a drug's release was shown not to be simply a function of its water solubility, but rather more closely related to the drug oil/water partition coefficient. This finding was explained in terms of the more hydrophobic drugs partitioning into, and interacting with, the hydrophobic domains of the polymer coating. The suitability of the coated stent as a drug delivery vehicle was assessed in vivo using a radiolabeled analog of one of the more rapidly eluting drugs, angiopeptin. Autoradiography showed that the drug was released locally to the wall of the stented artery, and could be detected up to 28 days after implantation.     

Carbon tetrachloride dechlorination by the bacterial transition metal chelator pyridine-2,6-bis(thiocarboxylic acid)

A reaction pathway is proposed to explain the formation of end products during defined chemical reactions between carbon tetrachloride (CCl4) and either metal complexes of pyridine-2,6-bis(thiocarboxylic acid) (PDTC) or pure cultures of Pseudomonas stutzeri KC. The pathway includes one-electron reduction of CCl4 by the Cu(II):PDTC complex, condensation of trichloromethyl and thiyl radicals, and hydrolysis of a labile thioester intermediate. Products detected were carbon dioxide, chloride, carbonyl sulfide, carbon disulfide, and dipicolinic acid. Spin-trapping and electrospray MS/MS experiments gave evidence of trichloromethyl and thiyl radicals generated by reaction of CCl4 with PDTC and copper. Experiments testing the effects of transition metals showed that dechlorination by PDTC requires copper and is inhibited by cobalt but not by iron or nickel. PDTC was shown to react stoichiometrically rather than catalytically without added reducing equivalents. With added reductants, an increased turnover was seen along with increased chloroform production.     

Changes in deposition of phytoplankton constituents in a Ca2+ polluted lake

Systematic reductions in the deposition rate of organic C, N, P, and chlorophyll (Chl) are documented for Ca2+ polluted, culturally eutrophic, Onondaga Lake, NY, based on analyses of weekly sediment trap collections over the May-October interval for 10 years of the 1980-1992 period. Inputs of both nutrient-rich domestic waste and industrial salt waste (including Ca2+) decreased over this period. Constituent ratios of the collected sediment indicate phytoplankton biomass was the dominant source of the deposited organic C, N, and Chl. Substantial decreases in downward fluxes of these constituents occurred starting in 1987: 37, 42, 25, and 54%, on average, for organic C, N, P, and Chl, respectively. These reductions were driven primarily by the decreases in the lake's salinity and Ca2+ concentration, that resulted from the closure of a soda ash manufacturing facility (1986), rather than decreases in water column P concentrations from reductions in domestic waste loading. Three different mechanisms for the decreased deposition, related to the reductions in salinity and Ca2+ concentration, are considered: (i) decrease in coating of phytoplankton with CaCO3 precipitate, (ii) increased grazing of phytoplankton by large cladocerans, and (iii) decreases in coagulation of phytoplankton. The greater loss of phytoplankton biomass through deposition, driven by salt waste inputs from the industry, exacerbated the lake's problem of high primary production. This response is consistent with ecological theory for nutrient saturated phytoplankton growth but has not previously been demonstrated on a whole-lake basis.     

浅谈CFG桩复合地基技术

简述了CFG桩复合地基技术，并对CFG桩复合地基的基本原理进行了论述，说明了它是一种具有材料来源方便。环保、工程造价低等优点，并可大为推广的地基处理形式，为施工与设计人员提供了技术参考。