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41.
A series of novel mono-1,2,3-triazole and bis-1,2,3-triazole acyclonucleoside analogues of 9-(4-hydroxybutyl)guanine was prepared via copper(I)-catalyzed 1,3-dipolar cycloaddition of N-9 propargylpurine, N-1-propargylpyrimidines/as-triazine with the azido-pseudo-sugar 4-azidobutylacetate under solvent-free microwave conditions, followed by treatment with K(2)CO(3)/MeOH, or NH(3)/MeOH. All compounds studied in this work were screened for their antiviral activities [against human rhinovirus (HRV) and hepatitis C virus (HCV)] and antibacterial activities against a series of Gram positive and negative bacteria. 相似文献
42.
Schon C Roth W Fischer I Pfister J Fink RF Engels B 《Physical chemistry chemical physics : PCCP》2011,13(23):11076-11082
The structure of the electronic ground- and first excited state of mono-hydroxy [2.2]paracyclophane (MHPC) and the S(1)← S(0) electronic transition have been investigated by resonance-enhanced multiphoton ionisation (REMPI) and by quantum chemical spin-component-scaled-approximate coupled cluster second order (SCS-CC2) computations. The origin of the S(1)← S(0) transition was located at 30,772 cm(-1) (3.815 eV) in the REMPI spectrum. The value has to be compared with a computed excitation energy of 3.79 eV. The vibrational structure of the spectrum confirms a significant geometry change upon excitation along the coordinates corresponding to twist- and shift-motions in the molecule. It gives rise to an experimentally observed progression with a fundamental of +30 cm(-1) and an inverse anharmonicity. From the experimental data a shallow potential along the twist coordinate was derived for the S(1) state. For the shift vibration a wavenumber of +91 cm(-1) was observed, while +85 cm(-1) was computed. The ionisation energy of MHPC was determined to be 7.63 ± 0.05 eV using synchrotron radiation. When compared to earlier results on the parent compound [2.2]paracyclophane and pseudo-ortho-dihydroxy[2.2]paracyclophane it can be seen that already small variations in the substitution pattern have a significant impact on the shapes of the involved potential energy surfaces leading to strong variations in ground and excited state geometries and opto-electronic properties governing the exciton transfer processes. 相似文献
43.
The results of ab initio calculations of the vibronically averaged components of the anisotropic magnetic hyperfine tensor in the low-lying vibronic species of the X2Π electronic state of the HCCS radical are reported. The electronically averaged hyperfine coupling constants for hydrogen, deuterium, 13C and 33S are obtained as functions of two bending vibrational modes by the density functional theory method. The vibronic wave functions are calculated with the help of a variational approach which takes into account the Renner–Teller effect and spin-orbit coupling. The results of ab initio calculations are compared to the corresponding experimental findings. 相似文献
44.
We derive an analytic expression for point-to-point correlation functions of the Polyakov loop based on the transfer matrix formalism. For the 21) Ising model we show that the results deduced from point-point spin correlators are coinciding with those from zero momentum correlators. We investigate the contributions from eigenvalues of the transfer matrix beyond the mass gap and discuss the limitations and possibilities of such an analysis. The finite size behaviour of the obtained 21) Ising model matrix elements is examined. The point-to-point correlator formula is then applied to Polyakov loop data in finite temperature SU(2) gauge theory. The leading matrix element shows all expected scaling properties. Just above the critical point we find a Debye screening mass μD/T ≈ 4 , independent of the volume. 相似文献
45.
46.
Hermann Engels 《Historia Mathematica》1977,4(2):137-140
The mathematicians of ancient Egypt approximated the area of a circle by a square with astonishing accuracy. The way to find this approximation is not handed down. In this paper a conjecture is given which seems to be much more simple than earlier attempts. 相似文献
47.
Continuing our previous work we determined the gluonic vacuum state up to sixth order and the lowest states with external quark-antiquark and (unscreened) gluon-gluon sources up to fourth order in the strong coupling 1/N c expansion on the lattice. Unlike previously, we used here the colour electric flux operators on the links to define the colour electric energy. Additional remarks concerning the screening of external gluon sources and the analytic continuation toN c =3 and zero lattice spacing are also included. 相似文献
48.
49.
Influence of Modification of γ-Alumina by Halides on the Acidic Behaviour The influence of modification of γ-alumina by Cl and F on the acidic properties was studied by means of i.r. spectroscopic methods using ammonia as probe molecule. The measurements show a significant rise in Lewis acidity. 相似文献
50.
By Monte Carlo simulation on the lattice, we calculate the high-temperature behaviour of the energy density ? in SU(2) and SU(3) QCD with Wilson fermions. From the leading term of the hopping parameter expansion, we find that ? converges very rapidly to the Stefan-Boltzmann limit of an asymptotically free quark-gluon gas. The behaviour in the non-asymptotic region indicates that chiral symmetry restoration occurs at a higher temperature (Tch) than colour deconfinement (Tc), with . 相似文献