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71.
Hans R. Kricheldorf Colin V. Lossow Nino Lomadze Gert Schwarz 《Journal of polymer science. Part A, Polymer chemistry》2008,46(12):4012-4020
The NCAs of the following five amino acids were polymerized in bulk at 120 °C without addition of a catalyst or initiator: sarcosine (Sar), L ‐alanine (L ‐Ala), D ,L ‐phenylalanine (D ,L ‐Phe), D ,L ‐leucine (D ,L ‐Leu) and D ,L ‐valine (D,L ‐Val). The virgin reaction products were characterized by viscosity measurements 13C NMR spectroscopy and MALDI‐TOF mass spectrometry. In addition to numerous low molar mass byproducts cyclic polypeptides were formed as the main reaction products in the mass range above 800 Da. Two types of cyclic oligo‐ and polypeptides were detected in all cases with exception of sarcosine NCA, which only yielded one class of cyclic polypeptides. The efficient formation of cyclic oligo‐ and polypeptides explains why high molar mass polymers cannot be obtained by thermal polymerizations of α‐amino acid NCAs. Various polymerization mechanisms were discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4012–4020, 2008 相似文献
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Bohmian mechanics is a quantum theory with a clear ontology. To make clear what we mean by this, we shall proceed by recalling first what are the problems of quantum mechanics. We shall then briefly sketch the basics of Bohmian mechanics and indicate how Bohmian mechanics solves these problems and clarifies the status and the role of the quantum formalism. 相似文献
75.
Vincenzo Barone Francesco Lelj Nino Russo Yves Ellinger Robert Subra 《Chemical physics》1983,76(3):385-396
Non-empirical calculations have been performed to analyze the effects of fluorine substitution on the geometry and electronic properties of two series of π and σ radicals. Both UHF and RHF + perturbation methods have been used and the results are compared as a function of the basis set quality. As concerns geometry and spin-free electronic properties the results are independent of the UHF or RHF formalism, but highly sensitive to the basis set. The STO-3G basis is unable to reproduce even general trends. Polarization functions always play a relevant role and correlation effects seem not negligible at least for fluorine-containing radicals. The molecular shape of π radicals changes from a planar to a pyramidal geometry when increasing the electronegativity of the substituents. On the contrary, σ radicals always remain planar. Unprojected UHF spin densities are closer to the RHF + perturbation results for small spin contamination (X2NO). On the contrary, it is the projected UHF spin density which is in better agreement with the RHF + perturbation value for large spin contamination (X2CN). No simple correlation can be found between spin densities and gross atomic spin populations. For H2NO the spin density at nitrogen is smaller than at the oxygen nucleus, but substitution may enhance or reverse this trend. 相似文献
76.
Density functional theory (DFT) in its B3LYP implementation is used to investigate the reaction of ammonia with the late (Co(+), Ni(+), and Cu(+)) first-row transition metal cations in both high- and low-spin states. The potential energy surfaces (PES's) leading to three different exit channels are closely examined. The binding energies for the reaction products are calculated and compared with the corresponding experimental values. A comparison with our earlier works covering the reactivity of the Sc-Fe series of cations is made in order to underline similarities and differences of the reaction mechanisms as well as to establish trends along the row. 相似文献
77.
We discuss a recently proposed extension of Bohmian mechanics to quantum field theory. For more or less any regularized quantum field theory there is a corresponding theory of particle motion, which, in particular, ascribes trajectories to the electrons or whatever sort of particles the quantum field theory is about. Corresponding to the nonconservation of the particle number operator in the quantum field theory, the theory describes explicit creation and annihilation events: the world lines for the particles can begin and end. 相似文献
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Nonlinear Dynamics - A homogeneous continuous viscoelastic beam, describing the dynamics of a base-isolated tower, exposed to a uniformly distributed turbulent wind flow, is studied. The beam is... 相似文献
80.
Bruna Clara De Simone Angelo Domenico Quartarolo Sante Cospito Lucia Veltri Giuseppe Chidichimo Nino Russo 《Theoretical chemistry accounts》2012,131(5):1225
A new triarylamine derivative, N,N′-Bis(4-heptanoylamidophenyl)-N,N′-di(4-methoxyphenyl)-1,4-phenylenediamine, with stable electrochromism in near-infrared and visible light regions, has been
synthesized and characterized at theoretical and experimental level. The detected and simulated spectra, with and without
the presence of an external potential at different values, clearly show that this mixed-valence system undergoes ionization
at a low value of the applied potential, and the formed radical cation absorbs in the near-infrared region with an intense
peak located at 1,040 nm. Density functional computations give the geometrical structure and absorption properties in very
good agreement with experiment, allowing assigning the electronic transition and contributing to an understanding of the electron-transfer
process between the two redox centers. 相似文献