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331.
Markus Niederberger Georg Garnweitner Jelena Buha Julien Polleux Jianhua Ba Nicola Pinna 《Journal of Sol-Gel Science and Technology》2006,40(2-3):259-266
Nonaqueous solution routes to metal oxide nanoparticles are a valuable alternative to the well-known aqueous sol-gel processes,
offering advantages such as high crystallinity at low temperatures, robust synthesis parameters and ability to control the
crystal growth without the use of surfactants. In the first part of the review, we give an overview of the various nonaqueous
routes to metal oxides, their surface functionalization and their assembly into well-defined nanostructures. However, we will
strongly focus on surfactant-free processes developed in our group. Within the various reaction systems such as metal halides—benzyl
alcohol, metal alkoxides—benzyl alcohol, metal alkoxides—ketones, metal acetylacetonates—benzyl alcohol and metal acetylacetonates—benzylamine
we will discuss representative examples in order to show the versatility of this approach. The careful characterization of
the organic species in the final reaction mixtures provides information about possible condensation mechanisms. Depending
on the system several reaction pathways have been postulated: (i) elimination of organic ethers as result of condensation
between two metal alkoxide precursors; (ii) C–C bond formation between the alkoxy ligand of the metal alkoxide precursor and
the solvent benzyl alcohol under formation of a metal hydroxyl species, which can undergo further condensation; (iii) ketimine
and aldol-like condensation steps, which in the metal acetylacetonate systems are preceded by a solvolysis of the precursor,
involving C–C bond cleavage.
In the second part of the paper we will focus on the synthesis of indium oxide nanoparticles using different precursors and
solvents. Indium oxide represents an instructive example how the oxide precursors and the solvents influence the particle
morphology. These findings make it possible to tailor particle size and shape of a particular metal oxide by the appropriate
choice of the reaction system. 相似文献
332.
Asnuzilawati Asari 《Tetrahedron letters》2007,48(14):2631-2634
An enantioselective synthesis of the tricyclic core structure of the immunosuppressant natural product (−)-FR901483 has been achieved. A palladium-catalysed (Pd2(dba)3, Xantphos, KOPh) intramolecular enolate alkenylation reaction was used as the key ring forming step for the construction of the bicyclo-[3,3,1]-azanonane ring system. An alkylidene carbene 1,5-CH insertion reaction was used to construct the nitrogen-bearing stereocentre in the vinyl bromide cyclisation precursor. 相似文献
333.
Bennati M Weber A Antonic J Perlstein DL Robblee J Stubbe J 《Journal of the American Chemical Society》2003,125(49):14988-14989
Escherichia coli ribonucleotide reductase (RNR) catalyzes the conversion of nucleoside diphosphates (NDPs) to deoxynucleoside diphosphates (dNDPs). This RNR is composed of two homodimeric subunits: R1 and R2. R1 binds the NDPs in the active site, and R2 harbors the essential di-iron tyrosyl radical (Y*) cofactor. In this paper, we used PELDOR, a method that detects weak electron-electron dipolar coupling, to make the first direct measurement of the distance between the two Y*'s on each monomer of R2. In the crystal structure of R2, the Y*'s are reduced to tyrosines, and consequently R2 is inactive. In R2, where the Y*'s assume a well-defined geometry with respect to the protein backbone, the PELDOR method allows measurement of a distance of 33.1 +/- 0.2 A that compares favorably to the distance (32.4 A) between the center of mass of the spin density distribution of each Y* on each R2 monomer from the structure. The experiments provide the first direct experimental evidence for two Y*'s in a single R2 in solution. 相似文献
334.
Wang XB Dacres JE Yang X Broadus KM Lis L Wang LS Kass SR 《Journal of the American Chemical Society》2003,125(1):296-304
Zwitterions are critically important in many biological transformations and are used in numerous chemical processes. The consequences of electrostatic effects on reactivity and physical properties, however, are largely unknown. In this work, we report the results of negative ion photoelectron spectra of nine isomeric pyridinium dicarboxylate zwitterions and three nonzwitterionic methoxycarbonylpyridine carboxylate isomers (-O(2)CPyrCO(2)CH(3)). Information about the intramolecular electrostatic interactions was directly obtained from the photoelectron spectra. The adiabatic and vertical detachment energies were measured and understood in terms of intramolecular Coulombic forces. Calculations at the B3LYP and CCSD(T) level were performed and compared to the experimental electron binding energies. Structures, relative stabilities, and the electron detachment sites also were obtained from the calculations. 相似文献
335.
Excited Fluorophores Enhance the Opening of Vesicles at Electrode Surfaces in Vesicle Electrochemical Cytometry
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Neda Najafinobar Jelena Lovrić Dr. Soodabeh Majdi Johan Dunevall Prof. Ann‐Sofie Cans Prof. Andrew Ewing 《Angewandte Chemie (International ed. in English)》2016,55(48):15081-15085
Electrochemical cytometry is a method developed recently to determine the content of an individual cell vesicle. The mechanism of vesicle rupture at the electrode surface involves the formation of a pore at the interface between a vesicle and the electrode through electroporation, which leads to the release and oxidation of the vesicle's chemical cargo. We have manipulated the membrane properties using excited fluorophores conjugated to lipids, which appears to make the membrane more susceptible to electroporation. We propose that by having excited fluorophores in close contact with the membrane, membrane lipids (and perhaps proteins) are oxidized upon production of reactive oxygen species, which then leads to changes in membrane properties and the formation of water defects. This is supported by experiments in which the fluorophores were placed on the lipid tail instead of the headgroup, which leads to a more rapid onset of vesicle opening. Additionally, application of DMSO to the vesicles, which increases the membrane area per lipid, and decreasing the membrane thickness result in the same enhancement in vesicle opening, which confirms the mechanism of vesicle opening with excited fluorophores in the membrane. Light‐induced manipulation of membrane vesicle pore opening might be an attractive means of controlling cell activity and exocytosis. Additionally, our data confirm that in experiments in which cells or vesicle membranes are labeled for fluorescence monitoring, the properties of the excited membrane change substantially. 相似文献
336.
Janjic JM Srinivas M Kadayakkara DK Ahrens ET 《Journal of the American Chemical Society》2008,130(9):2832-2841
We report the design, synthesis, and biological testing of highly stable, nontoxic perfluoropolyether (PFPE) nanoemulsions for dual 19F MRI-fluorescence detection. A linear PFPE polymer was covalently conjugated to common fluorescent dyes (FITC, Alexa647 and BODIPy-TR), mixed with pluronic F68 and linear polyethyleneimine (PEI), and emulsified by microfluidization. Prepared nanoemulsions (<200 nm) were readily taken up by both phagocytic and non-phagocytic cells in vitro after a short (approximately 3 h) co-incubation. Following cell administration in vivo, 19F MRI selectively visualizes cell migration. Exemplary in vivo MRI images are presented of T cells labeled with a dual-mode nanoemulsion in a BALB/c mouse. Fluorescence detection enables fluorescent microscopy and FACS analysis of labeled cells, as demonstrated in several immune cell types including Jurkat cells, primary T cells and dendritic cells. The intracellular fluorescence signal is directly proportional to the 19F NMR signal and can be used to calibrate cell loading in vitro. 相似文献
337.
Kramar Ana D. Ilic-Tomic Tatjana R. Lađarević Jelena M. Nikodinovic-Runic Jasmina B. Kostic Mirjana M. 《Cellulose (London, England)》2021,28(13):8771-8784
Cellulose - Halochromic (pH-responsive) material was obtained by dyeing functionalized viscose fabric with a crude extract from Streptomyces sp. strain NP4. The functionalization of the fabric... 相似文献
338.
Lucija Kneevi Dario Omanovi Niko Ba
i Jelena Mandi Elvira Bura-Naki 《Molecules (Basel, Switzerland)》2021,26(9)
An improved methodology was developed for V redox speciation in estuarine waters using a hyphenated technique consisting of ion chromatograph (IC) with an anion exchange column and a high-resolution inductively coupled plasma mass spectrometer (HR ICP-MS). This approach enables the direct determination of V(V), whereas reduced species (mainly V(IV)) are calculated by subtracting V(V) concentrations from the measured total V concentration. Based on the “on-column” V(V) chelation mechanism by EDTA, with the eluent composed of 40 mmol L−1 ammonium bicarbonate, 40 mmol L−1 ammonium sulphate, 8 mmol L−1 ethylenediaminetetraacetic acid and 3% acetonitrile, the method was successfully used for analyses of V redox speciation in samples taken in the vertical salinity gradient of the highly stratified Krka River estuary. Due to the matrix effects causing different sensitivities, a standard addition method was used for V(V) quantification purposes. The limit of detection (LOD) was also found to be matrix related: 101.68 ng L−1 in the seawater and 30.56 µg L−1 in the freshwater. Performed stability tests showed that V redox speciation is preserved at least 7 days in un-treated samples, possibly due to the stabilization of V-reduced species with natural organic matter (NOM). The dominant V form in the analysed samples was V(V) with the reduced V(IV) accounting for up to 26% of the total dissolved pool. The concentration of V(IV) was found to correlate negatively with the oxygen concentration. Significant removal of dissolved V was detected in oxygen depleted zones possibly related to the particle scavenging. 相似文献
339.
Veljkovic N Glisic S Prljic J Perovic V Botta M Veljkovic V 《Current protein & peptide science》2008,9(5):493-506
The field of bioinformatics has become a major part of the drug discovery pipeline playing a key role in improvement and acceleration of this time and money consuming process. Here we review the application of the informational spectrum method (ISM), a virtual spectroscopy method for structure/function analysis of proteins, in identification of functional protein domains representing candidate therapeutic targets for drugs against human immunodeficiency virus (HIV)-1, anthrax, highly pathogenic influenza virus H5N1 and cardiovascular diseases. 相似文献
340.
Jelena Miladinović Rozalija Ninković Milica Todorović Joseph A. Rard 《Journal of solution chemistry》2008,37(3):307-329
Isopiestic vapor-pressure measurements were made for {yMgCl2+(1−y)MgSO4}(aq) solutions with MgCl2 ionic strength fractions of y=(0,0.1997,0.3989,0.5992,0.8008, and 1) at the temperature 298.15 K, using KCl(aq) as the reference standard. These measurements
for the mixtures cover the ionic strength range I=0.9794 to 9.4318 mol⋅kg−1. In addition, isopiestic measurements were made with NaCl(aq) as reference standard for mixtures of {xNa2SO4+(1−x)MgSO4}(aq) with the molality fraction x=0.5000 that correspond to solutions of the evaporite mineral bloedite (astrakanite), Na2Mg(SO4)2⋅4H2O(cr). The total molalities, m
T=m(Na2SO4)+m(MgSO4), range from m
T=1.4479 to 4.4312 mol⋅kg−1 (I=5.0677 to 15.509 mol⋅kg−1), where the uppermost concentration is the highest oversaturation molality that could be achieved by isothermal evaporation
of the solvent at 298.15 K. The parameters of an extended ion-interaction (Pitzer) model for MgCl2(aq) at 298.15 K, which were required for an analysis of the {yMgCl2+(1−y)MgSO4}(aq) mixture results, were evaluated up to I=12.075 mol⋅kg−1 from published isopiestic data together with the six new osmotic coefficients obtained in this study. Osmotic coefficients
of {yMgCl2+(1−y)MgSO4}(aq) solutions from the present study, along with critically-assessed values from previous studies, were used to evaluate
the mixing parameters of the extended ion-interaction model. 相似文献