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991.
《Comptes Rendus Chimie》2017,20(2):140-145
An aqueous microwave (mw)-assisted DMAP catalyzed one-pot highly efficient route to synthesize β-phosphonomalonates and 2-amino-4H-chromen-4-yl phosphonates has been demonstrated via the domino Knoevenagel-phospha-Michael reaction of aryl aldehyde/salicylaldehyde, malononitrile/ethyl cyanoacetate and alkyl phosphite ester. Optimization of reaction conditions were performed by using conventional and microwave synthetic approaches. This conversion proceeded smoothly to deliver the desired product in good to excellent yields (75–95%) in a short reaction time (10–12 min). The present methodology is very simple, environmentally benign, high yielding and has very well demonstrated the synergistic effect of water and microwaves. 相似文献
992.
《Macromolecular bioscience》2017,17(12)
Microfibers have received much attention due to their promise for creating flexible and highly relevant tissue models for use in biomedical applications such as 3D cell culture, tissue modeling, and clinical treatments. A generated tissue or implanted material should mimic the natural microenvironment in terms of structural and mechanical properties as well as cell adhesion, differentiation, and growth rate. Therefore, the mechanical and biological properties of the fibers are of importance. This paper briefly introduces common fiber fabrication approaches, provides examples of polymers used in biomedical applications, and then reviews the methods applied to modify the mechanical and biological properties of fibers fabricated using different approaches for creating a highly controlled microenvironment for cell culturing. It is shown that microfibers are a highly tunable and versatile tool with great promise for creating 3D cell cultures with specific properties. 相似文献
993.
《Comptes Rendus Chimie》2017,20(3):230-236
Long-range electron transfer reactions play a key role in biological photosynthesis, and they are likely to play an important role for future artificial photosynthetic endeavors as well. The possibility to control the rates for long-range electron transfer with external stimuli is of particular interest in this context. In the work presented herein, we explored a donor–bridge–acceptor compound in which intramolecular electron transfer from a triarylamine donor to a photoexcited Ru(bpy)32+ (bpy = 2,2′-bipyridine) acceptor occurs across an organoboron bridge over a distance of approximately 22 Å. Fluoride has a high binding affinity to the organoboron bridge in apolar solutions, and the resulting organofluoroborate has a significantly different electronic structure. We explored to what extent the change from an electron-deficient organoboron wire to an electron-rich organofluoroborate bridge affects long-range electron transfer between the distant triarylamine donor and the Ru(bpy)32+ acceptor. 相似文献
994.
Coherent Exciton-Phonon Coupling in CdSe/ZnS Nanocrystals Studied by Two-Dimensional Electronic Spectroscopy 下载免费PDF全文
Coherent exciton-phonon coupling in CdSe/ZnS nanocrystals have been investigated by temperature-dependent two-dimensional electronic spectroscopy (2DES) measurements. Benefiting from the ability of 2DES to dissect assembles in nanocrystal films, we have clearly identified experimental evidences of coherent coupling between exciton and phonon in CdSe/ZnS nanocrystals. In time domain, 2DES signals of excitonic transitions beat at a frequency resonant to a longitudinal optical phonon mode; in energy domain, phonon side bands are distinct at both Stokes and anti-Stokes sides. When temperature increases, phonon-induced exciton dephasing is observed with dramatic broadening of homogeneous linewidth. The results suggest exciton-phonon coupling is essential in elucidating the quantum dynamics of excitonic transitions in semiconductor nanocrystals. 相似文献
995.
The physical properties, namely structural, mechanical, and thermodynamic properties, of Pd2Al intermetallic compound were explored through first-principles calculations within the framework of density functional theory. The calculated lattice constants were consistent with the available experimental data. The calculated elastic constants revealed that Pd2Al was mechanically stable. By the predicted elastic constants, several related properties, namely Cauchy pressures, shear anisotropy factors, directional Young's modulus, bulk, shear and Young's moduli, the ratio of K/G, Vickers hardness, sound velocity, and minimum thermal conductivity for Pd2Al were evaluated. According to the calculated results, it was found that Pd2Al possesses a highly anisotropic feature and behaves in a ductile manner with low stiffness. Finally, temperature-dependence of thermodynamic properties, namely Debye temperature and heat capacity, were also evaluated through the quasi-harmonic Debye model. 相似文献
996.
《Angewandte Chemie (International ed. in English)》2017,56(1):384-388
A 13mer DNA duplex containing the artificial 4‐aminophthalimide:2,4‐diaminopyrimidine (4AP:DAP) base pair in the central position was characterized by optical and NMR spectroscopy. The fluorescence of 4AP in the duplex has a large Stokes shift of Δλ =124 nm and a quantum yield of Φ F=24 %. The NMR structure shows that two interstrand hydrogen bonds are formed and confirms the artificial base pairing. In contrast, the 4‐N ,N ‐dimethylaminophthalimide moiety prefers the syn conformation in DNA. The fluorescence intensity of this chromophore in DNA is very low and the NMR structure shows no significant interaction with DAP. Primer‐extension experiments with DNA polymerases showed that not only is the 4AP C nucleotide incorporated at the desired position opposite DAP in the template, but also that the polymerase is able to progress past this position to give the full‐length product. The observed selectivity supports the NMR results. 相似文献
997.
998.
《Angewandte Chemie (International ed. in English)》2017,56(20):5471-5474
We present a proof of concept that ultrafast dynamics combined with photochemical stability information of molecular photocatalysts can be acquired by electrospray ionization mass spectrometry combined with time‐resolved femtosecond laser spectroscopy in an ion trap. This pump‐probe “fragmentation action spectroscopy” gives straightforward access to information that usually requires high purity compounds and great experimental efforts. Results of gas‐phase studies on the electronic dynamics of two supramolecular photocatalysts compare well to previous findings in solution and give further evidence for a directed electron transfer, a key process for photocatalytic hydrogen generation. 相似文献
999.
《Angewandte Chemie (International ed. in English)》2017,56(1):239-242
Because arginine residues in proteins are expected to be in their protonated form almost without exception, reports demonstrating that a protein arginine residue is charge‐neutral are rare and potentially controversial. Herein, we present a 13C‐detected NMR experiment for probing individual arginine residues in proteins notwithstanding the presence of chemical and conformational exchange effects. In the experiment, the 15Nη and 15Nϵ chemical shifts of an arginine head group are correlated with that of the directly attached 13Cζ. In the resulting spectrum, the number of protons in the arginine head group can be obtained directly from the 15N–1H scalar coupling splitting pattern. We applied this method to unambiguously determine the ionization state of the R52 side chain in the photoactive yellow protein from Halorhodospira halophila . Although only three Hη atoms were previously identified by neutron crystallography, we show that R52 is predominantly protonated in solution. 相似文献
1000.
《Angewandte Chemie (International ed. in English)》2017,56(8):2208-2211
To understand the molecular details of O2‐tolerant hydrogen cycling by a soluble NAD+‐reducing [NiFe] hydrogenase, we herein present the first bioinspired heterobimetallic S‐oxygenated [NiFe] complex as a structural and vibrational spectroscopic model for the oxygen‐inhibited [NiFe] active site. This compound and its non‐S‐oxygenated congener were fully characterized, and their electronic structures were elucidated in a combined experimental and theoretical study with emphasis on the bridging sulfenato moiety. Based on the vibrational spectroscopic properties of these complexes, we also propose novel strategies for exploring S‐oxygenated intermediates in hydrogenases and similar enzymes. 相似文献