Fluorescence energy transfer as a probe for tetraplex formation: the i-motif

The secondary structure of cytosine-rich oligodeoxynucleotides has been investigated with fluorescent probes. Intramolecular folding of an oligonucleotide into an i-DNA motif led to fluorescence excitation energy transfer between a donor (fluorescein) and an acceptor (tetramethylrhodamine) covalently attached to the 5' and 3' ends of the DNA, respectively, provided that a suitable linker was chosen. The conjugation of the dyes to the oligonucleotide had an influence on the thermodynamics of i-motif formation as well as on the kinetics of folding. Intramolecular folding was demonstrated from the concentration independence of FRET over a wide concentration range. Folding of the oligonucleotide was confirmed by UV absorption melting experiments. The folding of the i-motif could be followed at concentrations as low as 50 pM. Fluorescence energy transfer can thus be used to reveal the formation of multistranded DNA structures.     

High-resolution imaging of protein phosphorylation in squid axons and synapse by electron energy loss spectroscopy

We demonstrate that clusters of phosphorus atoms can be detected in energy loss spectroscopic images (ESI) of cytoskeletal proteins of squid axons. In series of images taken at four energy windows below and three windows above the phosphorus P-L2,3 ionization edge, signal-to-background intensity differences were analyzed by videodensitometry. A distinct increase of relative intensities was recorded above the phosphorus edge in neurofilaments of the peripheral giant axon and in those of the presynaptic terminal. A high level of neurofilament phosphorylation in the peripheral axon supports previous biochemical and immunochemical results, but our finding of phosphorylated neurofilaments in the presynaptic axon conflicts with these studies. Our method may be advantageous for analysis with high elemental and spatial resolution of the phosphorylation state of cytoskeletal protein molecules in situ.     

Low energy loss electron microscopy of chromophores

A novel prism-mirror-prism imaging electron spectrometer with 1 eV energy resolution for a transmission electron microscope permits imaging with spectral energies corresponding to light-optical colour absorptions. The instrument selects the molecular orbital excitations of natural chromophores or of specific dyes normally used in biological light microscopy for delineation and chemical identification, but images them with electron microscopic detail. Heavy atom contrast agents customarily used in electron microscopy are not required. The first results exploit the intrinsic red colour of hematin molecules to demonstrate the potential of the technique and address its spatial resolution. Glycosaminoglycans in cartilage stained with Alcian blue are selectively depicted in situ by means of the electron-induced molecular absorption of this chromophore. Thus, with the use of specific colours the direct or indirect analysis of local chemistry by electron microscopy is possible, and can be carried out with a depiction of spatial detail as small as 16 A, or at least 100-fold finer than observed by light microscopy.     

Analytical electron microscopy of internally oxidized low Si-Al steel

Analytical electron microscopy was used to study the precipitates in internally oxidized low Si-Al steels, of the type used for electric motor laminations. After oxidizing heat treatments of one and five hours at 788 °C, the internally precipitated particles were about 0.1 to 0.2 μm in diameter. At the internal-oxidation reaction front, thin plates of Al₂O₃ precipitated. Subsequently, a shell of SiO₂ precipitated on the Al₂O₃ core. Depth of internal oxidation was predicted from the knowledge of precipitate composition, treatment time and temperature, and published information.     

Characterization of palladium hydride films by electron energy loss spectroscopy and electron diffraction

Electrolytic charging is used to hydrogenate Pd films to full stoichiometry PdH, which is checked by making use of the relation between the lattice constant of the Pd-H system and its hydrogen content. The role of the surface barrier in preventing hydrogen escape from fully charged specimens is studied with EELS technique. Electron energy loss spectra collected at different collector aperture deviation angles in a STEM are used to separate the volume loss component from the surface loss component. The results are compared with those of Pd metal and results of PdH obtained with other techniques.     

低碳低硅铝镇静钢低成本冶炼工艺优化

针对电炉炼钢的成本、电耗、钢水洁净度及可浇性的控制问题,对三种工艺路线进行了对比。分析认为：不经过LF和RH的工艺路线的生产成本最低,吨钢冶炼工艺成本约为70~75元,电耗为50~55 kWh,但钢水洁净度控制较差,钢中w（T.O）为35×10-6~45×10-6,夹杂物等级为B类不大于2.0级,Ds类不大于1.5级;...     

Calcium distribution in high-pressure frozen bone cells by electron energy loss spectroscopy and electron spectroscopic imaging

Glucose utilization of four cerebral cortex and 35 subcortical regions (CGU) was analyzed in three models of cholinergic seizures induced by the following compounds: 1) soman (pinacolylmethylphosphonofluoridate) an organophosphorus cholinesterase inhibitor, 100 microg/kg SC after pretreatment with pyridostigmine 26 microg/kg IM (n = 6); 2) physostigmine, a carbamate cholinesterase inhibitor, 1.31 mg/kg infused IV over 75 min (n = 6); and 3) pilocarpine, a direct cholinergic agonist, 30 mg/kg SC (n = 6). Physostigmine and pilocarpine were preceded by 3 mmol/kg LiCl IP 20 hrs earlier. Animals injected with saline SC (n = 6) were used as controls. Step-wise discriminant analysis successfully classified 100% of the cases into the four experimental groups with data from only six regions. Pyridostigmine-soman induced the most widespread and greatest increases in CGU. More restricted and lower levels of activation were observed with Li-pilocarpine while Li-physostigmine induced significant increases in CGU only in globus pallidus, entopeduncular nucleus, and substantia nigra. These three regions, which are functionally related, were also activated in the other two models of cholinergic convulsions and may represent the initial step in cholinergic activation of the CNS. Li-pilocarpine failed to activate most of the brainstem and the superior colliculus. All cortical regions were activated by Li-pilocarpine and pyridostigmine-soman, while they were inhibited by Li-physostigmine. This phenomenon may be due in part to the lack of activation with physostigmine of the basal forebrain nuclei (lateral septum, medial septum, vertical and horizontal limbs of the diagonal band, and substantia innominata) resulting in a decreased drive of cortical metabolism.