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171.
Sawomir J. Grabowski Maciej A. Walczak T. Marek Krygowski 《Chemical physics letters》2004,400(4-6):362-367
The calculations on disubstituted ethylenes YCHCHX with Y = Li, H, F and X = H, F, Li, Na, OH, BeH, NH2, BH2, NO2 were performed at MP2/6-311++G(d,p) level of theory. The analysis of bond lengths and atoms in molecules based theory (AIM) topological parameters such as the characteristics of bond critical points (electron densities and their Laplacians) and atomic radii leads to the conclusion that the AIM parameters are much more sensitive to the action of intramolecular perturbations like substituents than traditional structural parameters such as bond lengths. A comparison of substituted ethylenes with the previously analyzed substituted acetylenes is also given. 相似文献
172.
[structure: see text]. The synthesis of a hetero-bis-metallo 1,3-butadiene is reported, and its use as an orthogonal Stille and Suzuki-Miyaura coupling partner is detailed. The tin/boron diene participated successfully in a one-pot, sequential Stille and Suzuki-Miyaura coupling protocol, and its utility was demonstrated in the two-step construction of the pentaene side chain of the Fusarium metabolite lucilactaene. 相似文献
173.
Friedrich J Walczak K Dolg M Piestert F Lauterbach T Worgull D Gansäuer A 《Journal of the American Chemical Society》2008,130(5):1788-1796
A method for the preparation of a variety of cyclobutanes via 4-exo cyclization of radicals is presented. Radical generation is carried out by electron transfer from titanocene(III) chlorides to epoxides. The reaction relies on the acceleration of the cyclization through the use of alpha,beta-unsaturated carbonyl compounds as radical traps and the thermodynamic stabilization of the cyclobutylcarbinyl radicals through conjugation. The mechanism of the transformation was investigated by a combined theoretical and experimental study. The computational results provide the crucial energetic and structural features of pertinent intermediates and transition structures. Moreover, the origins of the diastereoselectivity of the 4-exo cyclization are outlined for the first time. Catalysts for those cases where "Cp2TiCl" did not perform in a satisfactory manner have been devised. Through the introduction of tert-butyl or cyclo-hexyl substituted cyclopentadienyl ligands the longevity of the pivotal beta-titanoxy radicals is increased sufficiently enough to enable the slow but often surprisingly diastereoselective formation of the cyclobutylcarbinyl radical. The resulting transformation constitutes the first general approach to cyclobutanes using radical chemistry. 相似文献
174.
Missing elements and outliers can often occur in experimental data. The presence of outliers makes the evaluation of any least squares model parameters difficult, while the missing values influence the adequate identification of outliers. Therefore, approaches that can handle incomplete data containing outliers are highly valued. In this paper, we present the expectation-maximization robust soft independent modeling of class analogy approach (EM-S-SIMCA) based on the recently introduced spherical SIMCA method. Several important issues like the possibility of choosing the complexity of the model with the leverage correction procedure, the selection of training and test sets using methods of uniform design for incomplete data and prediction of new samples containing missing elements are discussed. The results of a comparison study showed that EM-S-SIMCA outperforms the classic expectation-maximization SIMCA method. The performance of the method was illustrated on simulated and real data sets and led to satisfactory results. 相似文献
175.
Malgorzata Walczak Mohamed Oujja José Francisco Marco Mikel Sanz Marta Castillejo 《Applied Physics A: Materials Science & Processing》2008,93(3):735-740
Promising applications of TiO2 nanostructures include the development of optical devices, sensors, photocatalysts and self-cleaning coatings. In view of
their importance, research on the synthesis of nanosized TiO2 is a particularly active field. In this work we report on the investigation of the effect of laser irradiation wavelength
(Q-switched Nd:YAG laser at 532, 355 and 266 nm), the temperature of the substrate and the atmosphere of deposition (vacuum,
Ar and O2) that are suitable for obtaining nanostructured deposits from TiO2 sintered targets. The ablation plume emission is characterized with spectral and temporal resolution by optical emission
spectroscopy (OES), while the surface morphology and chemical states of the material deposited on a Si (100) substrate are
examined by environmental scanning electron microscopy (ESEM) and atomic force microscopy (AFM) and by X-ray photoelectron
spectroscopy (XPS), respectively. Deposits with nanostructured morphology with grain size down to 40 nm and keeping the stoichiometry
of the targets were obtained at high temperature, while the highest concentration of particulates was observed at the longest
laser wavelength of 532 nm on a substrate heated up to 650°C. In situ characterization of the ablation plume, carried out
by OES, indicated the presence of emissions assigned to Ti I, Ti II and O I. 相似文献
176.
Łukasz Piskorski Magdalena Marciniak Jarosław Walczak 《Optical and Quantum Electronics》2017,49(5):199
We present the simulation results of threshold operation of mid-infrared GaSb-based vertical-cavity surface-emitting lasers (VCSELs) obtained with the use of comprehensive fully self-consistent optical-electrical-thermal-recombination numerical model. The results show that by a proper design of VCSEL structure and composition of the active region it is theoretically possible to achieve room-temperature (RT) threshold operation for wavelength of 2.8 μm which is about 0.2 μm longer than those reported so far in the literature for III-V VCSELs with type-I quantum wells. Calculated values of the RT threshold current were equal to 2.5 and 4.0 mA for tunnel-junction diameters of 2 and 4 μm, respectively. 相似文献
177.
Qing Qin Yun Zhao Max Schmallegger Tobias Heil Johannes Schmidt Ralf Walczak Georg Gescheidt‐Demner Haijun Jiao Martin Oschatz 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(37):13235-13240
The electrochemical conversion of N2 at ambient conditions using renewably generated electricity is an attractive approach for sustainable ammonia (NH3) production. Considering the chemical inertness of N2, rational design of efficient and stable catalysts is required. Therefore, in this work, it is demonstrated that a C‐doped TiO2/C (C‐TixOy/C) material derived from the metal–organic framework (MOF) MIL‐125(Ti) can achieve a high Faradaic efficiency (FE) of 17.8 %, which even surpasses most of the established noble metal‐based catalysts. On the basis of the experimental results and theoretical calculations, the remarkable properties of the catalysts can be attributed to the doping of carbon atoms into oxygen vacancies (OVs) and the formation of Ti?C bonds in C‐TixOy. This binding motive is found to be energetically more favorable for N2 activation compared to the non‐substituted OVs in TiO2. This work elucidates that electrochemical N2 reduction reaction (NRR) performance can be largely improved by creating catalytically active centers through rational substitution of anions into metal oxides. 相似文献
178.
Bacillus mycoides, Bacillus pseudomycoides, Bacillus weihenstephanensis, Bacillus anthracis, Bacillus thuringiensis, and Bacillus cereus belong to the B. cereus group. The last three species are characterized by different phenotype features and pathogenicity spectrum, but it has been shown that these species are genetically closely related. The macrorestriction analysis of the genomic DNA with the NotI enzyme was used to generate polymorphism of restriction profiles for 39 food‐borne isolates (B. cereus, B. mycoides) and seven reference strains (B. mycoides, B. thuringiensis, B. weihenstephanensis, and B. cereus). The PFGE method was applied to differentiate the examined strains of the B. cereus group. On the basis of the unweighted pair group method with the arithmetic mean method and Dice coefficient, the strains were divided into five clusters (types A–E), and the most numerous group was group A (25 strains). A total of 21 distinct pulsotypes were observed. The RFLP‐PFGE analysis was successfully used for the differentiation and characterization of B. cereus and B. mycoides strains isolated from different food products. 相似文献
179.
Summary The retention of a group of 38 E-s-cis and Z-s-cis chalcones on silica vs. nine polar chemically bonded phases is discussed.
It was established that the relatively greatest similarity to silica is observed with the NH2, DIOL and CN phases, whereas the chargetransfer type phases and the NO2 one offer a different separation selectivity. 相似文献
180.
Abstract— Face-to-profile chloroplast movement in Mougeotia was induced by sequences of strong blue and red short irradiations. This type of response occured only when blue light was applied prior to or simultaneously with red light, and far-red irradiation was necessary after the sequence to cancel the remaining gradient of the far-red absorbing form of phytochrome Pfr. The dependence of the response magnitude on blue and red light sequences was studied for a wide range of light durations and dark intervals. The relationship between the response and the dark interval points to the lack of direct coupling between phytochrome and blue-absorbing “cryptochrome”. It was postulated that a photoproduct having a life-time of2–3 min is formed by the blue-light-mediated reaction. This photoproduct interacts with phytochrome during its transformation or with its final Pfr form. 相似文献