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911.
912.
913.
Prof. Dr. Peter Schwerdtfeger Dr. Ralf Tonner Dr. Gloria E. Moyano Dr. Elke Pahl 《Angewandte Chemie (International ed. in English)》2016,55(40):12200-12205
The cohesive energies of argon in its cubic and hexagonal closed packed structures are computed with an unprecedented accuracy of about 5 J mol?1 (corresponding to 0.05 % of the total cohesive energy). The same relative accuracy with respect to experimental data is also found for the face‐centered cubic lattice constant deviating by ca. 0.003 Å. This level of accuracy was enabled by using high‐level theoretical, wave‐function‐based methods within a many‐body decomposition of the interaction energy. Static contributions of two‐, three‐, and four‐body fragments of the crystal are all individually converged to sub‐J mol?1 accuracy and complemented by harmonic and anharmonic vibrational corrections. Computational chemistry is thus achieving or even surpassing experimental accuracy for the solid‐state rare gases. 相似文献
914.
Britta Lange Sebastian Recknagel Michael Czerwensky Ralf Matschat Matthias Michaelis Burkhard Peplinski Ulrich Panne 《Mikrochimica acta》2008,160(1-2):97-107
The reliability and performance of various analytical methods for the determination of 22 trace elements in pure copper is
compared and discussed. The work was performed in the framework of an interlaboratory comparison for the preparation of four
pure copper reference materials with graded element mass fractions of Ag, Al, As, Bi, Cd, Co, Cr, Fe, Mg, Mn, Ni, P, Pb, S,
Sb, Se, Si, Sn, Te, Ti, Zn, and Zr. Special analytical results (ET-AAS, ICP-MS) obtained by the authors were described in
more detail and were compared to the certified values. Special regard was paid to the influence of the copper matrix on performance
and sensitivity of each analytical method and to the dissolution procedure of copper matrix and interferences from insoluble
residues. For a generalized evaluation of the figures of merit for each applied elemental analytical method results from several
independent laboratories were included in the discussion.
Correspondence: Britta Lange, Department of Analytical Chemistry, Reference Materials, Federal Institute for Materials Research
and Testing (BAM), Richard-Willstaetter-Str. 11, D-12489 Berlin, Germany 相似文献
915.
916.
The dynamic multicomponent syntheses of nanometer-sized chiral molecular cubes 1a and 1b from 8 tritopic 90 degree corner units and 12 linear spacers using an edge-directed approach is described. Thus, the TFA-catalyzed reaction of 8 equiv C3-trihexadecyloxy-triformylcyclotribenzylene 2 as corner unit with 12 equiv of 1,4-phenylenediamine 3a or benzidine 3b as spacers yields nanocubes 1a and 1b, respectively in close to quantitative yield. The same reactions carried out with enantiomerically pure (P)-2 (>99% ee) gave the homochiral cubes (all-P)-1a and (all-P)-1b. Force field calculations predict an edge length of 17 A and 21 A for 1a and 1b, which is consistent with their dimensions estimated from DOSY experiments. Furthermore, the asymmetric synthesis of (P)-2 through a dynamic thermodynamic resolution is described. This approach is based on the TFA-catalyzed reaction of racemic 2 with (R,R)-1,2-diaminocyclohexane (R)-5, which leads to a chiral cryptophane (>90% yield) that is built-up from two (P)-2 linked together with three diamines (R)-5. Hydrolysis of this cryptophane provides (P)-2 with >99% ee. 相似文献
917.
Jessica Tschirch Ralf Dillert Detlef Bahnemann Bernd Proft Andreas Biedermann Bernhard Goer 《Research on Chemical Intermediates》2008,34(4):381-392
The degradation of methylene blue (MB) in aqueous solutions has been re-examined as a method to characterize the photocatalytic
activity of transparent TiO2 coatings. Increasing irradiation intensities leads to a change in the observed kinetic behavior from zero-order to pseudo-first-order
regarding the concentration of MB. This is due to a diffusion inhibition of MB. In order to obtain data within a zero-order
kinetic regime at an initial MB concentration of 10 μmol/l and, thus, to avoid the diffusion control, irradiation intensities
below E=5 W/m2 for substrates comprising higher photonic efficiencies than ζ=0.09% have to be applied. Recommendations for a standard protocol
are given. 相似文献
918.
A new fluorescent calix crown ether: synthesis and complex formation with alkali metal ions 总被引:1,自引:0,他引:1
Stoll I Eberhard J Brodbeck R Eisfeld W Mattay J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(4):1155-1163
We synthesised a new N-benzylaza-21-crown-7 ether 5 with a dihydroxy coumarin as a fluorescence sensor and investigated the binding behaviour towards alkali metal cations in methanol by fluorescence titrations. The association constants are within one order of magnitude, with the exception of sodium. Potassium is the preferred binding partner (K(Na)=330 M(-1); K(K)=8600 M(-1); K(Rb)=8200 M(-1); K(Cs)=4400 M(-1)). The corresponding aza-21-crown-7 ether (6) was attached by a methylene unit to a resorcarene to give fluorescent calix crown ether 12. The binding abilities of the calix crown ether towards alkali metal ions in methanol have also been investigated, and an increasing complex stability, distinct for potassium and rubidium in comparison with 5, was found: K(Na)=440 M(-1); K(K)=110,000 M(-1); K(Rb)=63,000 M(-1); K(Cs)=20,000 M(-1). Like bis(crown ether)s, a cooperative complexation of the crown ether and the cavitand scaffold can be assumed. The proposed complex geometry is supported by Kohn-Sham DFT calculations for the potassium and caesium complexes. 相似文献
919.
Zinc chemicals are used as activators in the vulcanization of organic polymers with sulfur to produce elastic rubbers. In this work, the reactions of Zn(2+), ZnMe(2), Zn(OMe)(2), Zn(OOCMe)(2), and the heterocubane cluster Zn(4)O(4) with the vulcanization accelerator tetramethylthiuram disulfide (TMTD) and with the related radicals and anions Me(2)NCS(2)(*), Me(2)NCS(3)(*), Me(2)NCS(2)(-), and Me(2)NCS(3)(-) have been studied by quantum chemical methods at the MP2/6-31+G(2df,p)//B3LYP/6-31+G* level of theory. More than 35 zinc complexes have been structurally characterized and the energies of formation from their components calculated for the first time. The binding energy of TMTD as a bidendate ligand increases in the order ZnMe(2)相似文献
920.
Andreazza HJ Fitzgerald M Bilusich D Hoffmann R Hoffmann P Eichinger PC Bowie JH 《Rapid communications in mass spectrometry : RCM》2008,22(20):3305-3312
Peptides and proteins may contain post-translationally modified phosphorylated amino acid residues, in particular phosphorylated serine (pSer), threonine (pThr) and tyrosine (pTyr). Following earlier work by Lehmann et al., the [M-H]- anions of peptides containing pSer and pThr functionality show loss of the elements of H3PO4. This process, illustrated for Ser (and using a model system), is CH3CONH-C(CH2OPO3H2)CONHCH(3) --> [CH3CONHC(==CH2)CONHCH3 (-OPO3H2)] (a) --> [CH3CONHC(==CH2)CONHCH3-H]- + H3PO4, a process endothermic by 83 kJ mol(-1) at the MP2/6-31++G(d,p)//HF/6-31++G(d,p) level of theory. In addition, intermediate (a) may decompose to yield CH3CONHC(==CH2)CONHCH3 + H2PO4 - in a process exothermic by 3 kJ mol(-1). The barrier to the transition state for these two processes is 49 kJ mol(-1). Characteristic cleavages of pSer and pThr are more energetically favourable than the negative ion backbone cleavages of peptides described previously. In contrast, loss of HPO3 from [M-H]- is characteristic of pTyr. The cleavage [NH2CH(CH2-C6H4-OPO3H-)CO2H] --> [NH2C(CH2-C6H4-O-)CO2H (HPO3)] (b) --> NH2CH(CH2-C6H4-O-)CO2H + HPO3 is endothermic by 318 kJ mol(-1) at the HF/6-31+G(d)//AM1 level of theory. In addition, intermediate (b) also yields NH2CH(CH2-C6H4-OH)CO2H + PO3 - (reaction endothermic by 137 kJ mol(-1)). The two negative ion cleavages of pTyr have a barrier to the transition state of 198 kJ mol(-1) (at the HF/6-31+G(d)//AM1 level of theory) comparable with those already reported for negative ion backbone cleavages. 相似文献