نتایج جستجو برای: prototropic shift

تعداد نتایج: 136852  

Journal: :Journal of the American Chemical Society 2011
Wait R Griswold Michael D Toney

Pyridoxal 5'-phosphate (PLP; vitamin B(6))-catalyzed reactions have been well studied, both on enzymes and in solution, due to the variety of important reactions this cofactor catalyzes in nitrogen metabolism. Three functional groups are central to PLP catalysis: the C4' aldehyde, the O3' phenol, and the N1 pyridine nitrogen. In the literature, the pyridine nitrogen has traditionally been assum...

Journal: :Journal of the American Chemical Society 2002
Hartmut Komber Hans-Heinrich Limbach Frank Böhme Christoph Kunert

Two novel cyclo-tris(4-R-2,6-pyridylformamidine)s (R = H, CH(3)) have been studied by solution- and solid-state NMR. Both compounds show fast exchange of NH protons in dimethyl sulfoxide at room temperature. The E-syn configuration of the formamidine group with the NH protons in the outer ring position could be proved by low-temperature (1)H NMR experiments. The influence of deuteration of the ...

2014
Carla I Nieto Pilar Cabildo M Ángeles García Rosa M Claramunt Ibon Alkorta José Elguero

This paper reports the (1)H, (13)C and (15)N NMR experimental study of five benzimidazoles in solution and in the solid state ((13)C and (15)N CPMAS NMR) as well as the theoretically calculated (GIAO/DFT) chemical shifts. We have assigned unambiguously the "tautomeric positions" (C3a/C7a, C4/C7 and C5/C6) of NH-benzimidazoles that, in some solvents and in the solid state, appear different (bloc...

Journal: :Molecules 2006
Mehdi Ghandi Abolfazl Olyaei Farshid Salimi

The acid-catalyzed cyclocondensation in refluxing acetonitrile of aqueous glyoxal with N-heteroaryl-N'-phenylureas 4a-f (heteroaryl = 2-thiazolyl, 2-pyrimidinyl,2-pyrazinyl, 2-pyridinyl, 3-pyridinyl and 2-benzimidazolyl) led to the formation of the corresponding 1-heteroaryl-3-phenyl-4,5-dihydroxy-2-imidazolidinones 5a-f. All the products were characterized by elemental and spectroscopic analys...

1996
Steven A. EVERETT Madeleine F. DENNIS Kantilal B. PATEL Michael R. L. STRATFORD Peter WARDMAN

The superoxide radical anion (O # −d) produced during the catalytic activity of nitric oxide synthase (NOS) and cytochrome P-450 has been implicated in the oxidative denitrification of hydroxyguanidines ("C ̄NOH). The reactivity of the radiolytically generated O # −d radical with N-hydroxy--arginine (NHA) is pH dependent and appears to parallel the prototropic equilibrium of the hydroxyguanidin...

Journal: :Drug discovery today 2010
Pier G De Benedetti Francesca Fanelli

Drugs are adaptive molecules. They realize this peculiarity by generating different ensembles of prototropic forms and conformers that depend on the environment. Among the impressive amount of available computational drug discovery technologies, quantitative structure-activity relationship approaches that rely on computational quantum chemistry descriptors are the most appropriate to model adap...

2013
Jan Szabo Gerhard Maas

Dedicated to Professor Gerhard Müller on the occasion of his 60th birthday The title compound, C10H20N6 (2), was prepared from N,N′,N′′-triaminoguanidinium chloride. Solventand temperature-dependent 1H NMR spectra indicating prototropic tautomerism were observed in solution. The crystal and molecular structure was determined by X-ray diffraction analysis. The compound crystallizes in the hexago...

2003
Nitin Chattopadhyay

Excited state proton transfer of carbazole gives rise to dual fluorescence from the two prototropic species. Simultaneous consideration of the two emissions takes care of many of the instrumental artifacts. The relative intensity of the two emissions of carbazole is sensitive not only to the pH of the bulk medium but also the microenvironment around the probe. Hence, excited state proton transf...

2012
Mihaela-Liliana Tinţaş Richard A. Varga Ion Grosu Elena Bogdan

The title compound, C(21)H(17)ClO(3), which crystallizes as one of two possible oxo/hy-droxy-fulvene prototropic tautomers, possesses a strong intra-molecular O-H⋯O hydrogen bond that closes a seven-membered ring. The dihedral angles between the central five-membered ring and two pendant rings are 55.05 (9) and 44.51 (10)°. The crystal packing is characterized by weak inter-molecular C-H⋯O inte...

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