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51.
Chow DC Lee WK Zauscher S Chilkoti A 《Journal of the American Chemical Society》2005,127(41):14122-14123
Nucleic acid nanostructures are useful as templates for bionanofabrication of composite molecular nanostructures in materials science, molecular electronics, and biosensing. Here, we demonstrate that terminal deoxynucleotidyl transferase, which repetitively adds mononucleotides to the 3' end of a short DNA initiator, can be used to rapidly fabricate DNA nanostructures up to 121 nm high with lateral dimensions from 0.1 to 4 mum in 2 h. These programmable scaffolds can potentially be employed to build more complex nanostructures consisting of natural or unnatural nucleotides with selective docking sites along the single-stranded DNA. 相似文献
52.
The ultrafast N-O bond fragmentation in a series of N-methoxypyridyl radicals, formed by one-electron reduction of the corresponding N-methoxypyridiniums, has been investigated as potentially barrierless electron-transfer-initiated chemical reactions. A model for the reaction involving the electronic and geometric factors that control the shape of the potential energy surface for the reaction is described. On the basis of this model, molecular structural features appropriate for ultrafast reactivity are proposed. Femtosecond kinetic measurements on these reactions are consistent with a kinetic definition of an essentially barrierless reaction, i.e., that the lifetime of the radical is a few vibrational periods of the fragmenting bond, for the p-methoxy-N-methoxypyridyl radical. 相似文献
53.
Liane M. Moreau Alexandre Herve Mark D. Straub Dominic R. Russo Rebecca J. Abergel Selim Alayoglu John Arnold Augustin Braun Gauthier J. P. Deblonde Yangdongling Liu Trevor D. Lohrey Daniel T. Olive Yusen Qiao Julian A. Rees David K. Shuh Simon J. Teat Corwin H. Booth Stefan G. Minasian 《Chemical science》2020,11(18):4648
We report the structural properties of ultra-small ThO2 and UO2 nanoparticles (NPs), which were synthesized without strong binding surface ligands by employing a covalent organic framework (COF-5) as an inert template. The resultant NPs were used to observe how structural properties are affected by decreasing grain size within bulk actinide oxides, which has implications for understanding the behavior of nuclear fuel materials. Through a comprehensive characterization strategy, we gain insight regarding how structure at the NP surface differs from the interior. Characterization using electron microscopy and small-angle X-ray scattering indicates that growth of the ThO2 and UO2 NPs was confined by the pores of the COF template, resulting in sub-3 nm particles. X-ray absorption fine structure spectroscopy results indicate that the NPs are best described as ThO2 and UO2 materials with unpassivated surfaces. The surface layers of these particles compensate for high surface energy by exhibiting a broader distribution of Th–O and U–O bond distances despite retaining average bond lengths that are characteristic of bulk ThO2 and UO2. The combined synthesis and physical characterization efforts provide a detailed picture of actinide oxide structure at the nanoscale, which remains highly underexplored compared to transition metal counterparts.ThO2 and UO2 nanoparticles synthesized using a COF-5 template exhibit unpassivated surfaces and provide insight into nanoscale properties of actinides. 相似文献
54.
S. Caroli O. Senofonte S. Caimi P. Pucci J. Pauwels G. N. Kramer 《Analytical and bioanalytical chemistry》1998,360(3-4):410-414
The preparation of new Certified Reference Materials (CRMs) of antarctic matrices forms the backbone of an ongoing project
in the framework of the Italian National Program for Antarctic Research. The first CRM of this kind (MURST-ISS-A1 Antarctic
Marine Sediment) is already available. The second phase focuses on the certification of antarctic krill, a small shrimp extremely
abundant in the Southern Ocean. The total mass of krill available for this purpose is approximately 44 kg and results from
the combination of three different catches (Ross Sea, Marguerite Bay and Livingston Island, respectively). The quantification
of the following elements in the raw mass appears to be affordable by current analytical techniques, values being in the range
of (in μg/g) 0.11–0.30 for As, 0.03–0.12 for Cd, 0.06–0.23 for Cr, 6.1–21 for Cu, 5.7–7.6 for Fe, 0.005–0.008 for Hg, 0.7–1.2
for Mn, 0.013– 0.077 for Ni, 0.04–0.57 for Pb and 12–16 for Zn. On the other hand, the average values ascertained in freeze-dried
krill are as a rule one order of magnitude higher, i.e., (in μg/g), 3.2 for As, 0.6 for Cd, 1.8 for Cr, 75 for Cu, 61 for
Fe, 0.025 for Hg, 4.6 for Mn, 0.7 for Ni, 2.1 for Pb and 81 for Zn. Information on the pretreatment of krill and details on
the planned certification campaign are also given.
Received: 10 June 1997 / Revised: 24 September 1997 / Accepted: 28 September 1997 相似文献
55.
U. Steiner M. Hafner S. Schreiner H. E. A. Kramer 《Photochemistry and photobiology》1974,19(2):119-128
Abstract— While studying the photoreduction of some dyes (D) by reducing agents (R), it was observed that the quantum yield of the photoreduction increases considerably upon addition of a third substance (C), whereas it is very small when the dye is photoreduced by C alone (catalytic effect), (see Table 1).
The system thionine (D), allylthiourea (R), and azulene (C) was investigated in detail using both flash photolysis and continuous illumination. On photolysis, thionine is converted into its photo-reduced form, leucothionine. Azulene reacts with the basic form of the thionine triplet3 TH + to produce the semithionine radical. In the system thionine and azulene, most of these radicals revert back to thionine. When ATU (˜ 102- M ) is added to thionine and azulene (3 × 10-4 M ), the semithionine radicals are reduced to leucothionine; the quantum yield of this reduction is considerably higher than in the system thionine and allylthiourea. Flash experiments demonstrate that allylthiourea does not react with the semithionine radicals.
At very high ATU concentrations (≥ 10-1 M ), however, the primary reaction is between thionine triplet and allylthiourea; under these conditions the quantum yield is not influenced by azulene (3 × 10-4 M ). 相似文献
The system thionine (D), allylthiourea (R), and azulene (C) was investigated in detail using both flash photolysis and continuous illumination. On photolysis, thionine is converted into its photo-reduced form, leucothionine. Azulene reacts with the basic form of the thionine triplet
At very high ATU concentrations (≥ 10
56.
Thedc-conductivity of the one-dimensional Anderson model of a disordered system is investigated with two independent numerical methods for systems as large as 104 sites starting from Kubo's formula. In contradiction to the conventional theory of one-dimensional disordered systems a non zero conductivity for finite values of the disorder parameterW/V is found. the eigenstates of the system are investigated. Results for the inverse participation number and the mean square extension of the states are given and compared with the results for the conductivity.Work supported by the Deutsche Forschungsgemeinschaft (SFB 125 Köln and Project No. Kr627/2) 相似文献
57.
Zusammenfassung Aus der Gruppe der Dibenzoazepinderivate wurden die Hydrochloride von Clomipramin, Imipramin und Desipramin miteinander kombiniert und aus der Gruppe der Dibenzocykloheptadiene bzw.-triene die Hydrochloride von Amitriptylin, Nortriptylin, Noxiptilin und Protriptylin.Bei fünf der untersuchten binären Systeme liegt Mischkristallbildung aufgrund von Isomorphiebeziehungen mit instabilen Modifikationen vor: Imipraminhydrochlorid — Clomipraminhydrochlorid, Imipraminhydrochlorid — Desipraminhydrochlorid, Clomipraminhydrochlorid — Desipraminhydrochlorid, Nortriptylinhydrochlorid — Protriptylinhydrochlorid und Noxiptilinhydrochlorid-Amitriptylinhydrochlorid. Das Substanzpaar Protriptylinhydrochlorid — Noxiptilinhydrochlorid bildet eine Molekülverbindung im Verhältnis 11. In drei Fällen werden einfache Eutektika gebildet.
Thermoanalytical investigations of psychotropic substances derived from phenothiazine and butyrophenones for isomorphism and polymorphism. II
Summary From the group of dibenzoazepine derivatives, the hydrochlorides of clomipramine, imipramine and desipramine were combined with each other and from the group of dibenzocycloheptadienes or -trienes the hydrochlorides of amitriptyline, nortriptyline, noxiptiline and protryptiline. In five of the binary systems investigated, there is formation of mixed crystals due to isomorphism with unstable modifications: imipramine hydrochloride — clomipramine hydrochloride, imipramine hydrochloride — desipramine hydrochloride, clomipramine hydrochloride 3- desipramine hydrochloride, nortriptyline hydrochloride — protriptyline hydrochloride and noxiptiline hydrochloride — amitriptyline hydrochloride. The substance pair protriptyline hydrochloride — noxiptiline hydrochloride forms a molecular compound in the ratio 11. In three cases, simple eutectics are formed.相似文献
58.
Garcia F Goodman JM Kowenicki RA McPartlin M Riera L Silva MA Wirsing A Wright DS 《Dalton transactions (Cambridge, England : 2003)》2005,(10):1764-1773
The 1 : 1 reactions of [ClP(mu-NtBu)]2 with the difunctional aromatic amines 1,2-1-YH-2-NH2-C6H4 in the presence of Et3N give the dimeric phosph(III)azane macrocycles [{P(mu-NtBu)2(1-Y-2-HN-C6H4)]2, predominantly as the cis isomer in the case of Y=O (1.cis) and as the trans isomer for Y=S (2.trans). Model M.O. calculations suggest that the selection of the cis and trans isomers is not thermodynamically controlled. The alternative isomers 1.trans and 2.cis are generated exclusively by the deprotonation of the model intermediates [(1-Y-2-NH2-C6H4)P(mu-NtBu)]2[Y=O (3), S (4)] with nBuLi followed by cyclisation with [ClP(mu-NtBu)]2. The solid-state structures of 1.cis/trans(50 : 50), 2.cis, 3 and 4 are reported. 相似文献
59.
Bond AD Doyle EL García F Kowenicki RA McPartlin M Riera L Wright DS 《Chemical communications (Cambridge, England)》2003,(24):2990-2991
The in situ reaction of the phosphazane dimer [CIP(mu-N-2-NC5H4)]2 (2) with CuCl in the presence of CsH5N/H2O gives the title complex [(P(mu-N-2-NC5H4))2(mu-O)]2(CuCl x (C5H5N)2)4 (1), containing a tricyclic [(P(mu-N-2-NC5H4))2(mu-O)]2 ligand which is isoelectronic with species of the type [(P(mu-NR))2NR]2. 相似文献
60.
H. Kaupp H. -P. Didra C. Kramer M. Baumann 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,27(4):307-312
Depolarization of excited114Cd 5s5p 3 P 1 atoms induced by collisions with various molecular gases (N2, H2, D2, CO, CO2, CH4, C2H6, C2H4) has been investigated using polarized fluorescence spectroscopy. After pulsed optical excitation of the Cd 53 P 1 level with appropriately polarized light the temporal behaviour of Zeeman quantum beats has been observed showing the influence of collisional destruction of orientation and alignment. By analyzing the signal curves at different molecular gas pressures the corresponding depolarization cross sections for114Cd atoms in the 53 P 1 state have been obtained. With regard to a test of a nuclear spin decoupling model for the collisions the cross sections were compared with previously measured hyperfine structure transfer cross sections of113Cd 5s5p 3 P 1 atoms. 相似文献