Backbone dynamics of trp repressor, a 25 kDa DNA binding protein, have been studied using 15N relaxation data measured by proton-detected two-dimensional 1H-15N NMR spectroscopy. 15N spin-lattice relaxation time (T1), spin-spin relaxation time (T2), and heteronuclear NOEs were determined for all visible backbone amide 15N nuclei. Monte Carlo simulations of the amplitudes of backbone motions led to the conclusion that a wobbling in a cone model with consideration of the anisotropic reorientation of the molecule was appropriate to describe the underlying motions, allowing us to derive the semiangle of the cone (alpha) and the effective correlation time for internal motions (tau e) for each N-H bond vector. The final optimized rotational diffusion coefficients parallel (D parallel) and perpendicular (D perpendicular) to the unique axis of the molecule were found to be 1.48 +/- 0.06 x 10(7) and 1.15 +/- 0.05 x 10(7) s-1, respectively. The average semiangle of the cone (alpha) describing the amplitude of NH vector motions on the picosecond time scale was found to be 20.9 +/- 5.7 degrees. Large amplitude motions on the picosecond time scale are found at both the N and C termini but are restricted in both the hydrophobic core and DNA-binding regions.

Due to the vibration of the phenazine unit, compound S1 exhibits dual fluorescence in solution but one peak in the solid state. Based on this novel phenomenon and combined with the intramolecular energy transfer (IET) effect, a colour-tunable luminescence, even near white emission from a single molecule could be achieved in two different ways: controlling the polarity of the solvent and the aggregation index.

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The "N chemical shift tensors of uracil are reported using I5N powder pattem techniques. The principal values of the I5N uracil tensors are obtained from the spectra of [l-'5N]uracil and [3-'jN]uracil, and the tensor orientations are determined from the spectrum of [ 1,3-'5N2,2-'3C]~ra~i1 by including the effects of the direct dipolar interaction in the spectral fitting routine. Ambiguities in the orientational assignments, which arise from the axial symmetry of the direct dipolar tensor, are resolved using molecular symmetry considerations and results of ab initio calculations of I5N chemical shielding tensors. The NI nitrogen has principal values of 196, 114, and 30 ppm and the N3 nitrogen 200, 131, and 79 ppm with respect to I5NH4N03. Assuming that the smallest (most shielded) chemical shift tensor components are oriented perpendicular to the molecular plane, the largest components are found to lie 18" and 9" off the NI-H and N3-H bonds, respectively, rotated toward CZ and Cq. These orientations are in good agreement with those calculated theoretically. In addition, inclusion of intermolecular hydrogen bond effects in the theoretical calculations significantly improves the correlation between the calculated and experimental principal values.

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A series of novel hole transport materials for organic light-emitting diodes (OLEDs) based on 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine were synthesized and characterized by 1H NMR and 13C NMR, mass spectrometry and single crystal structure analysis methodologies.

Binding of L-tryptophan to Escherichia coli trp repressor wild type (WT) and AV77 mutant was studied by 1H NMR spectroscopy. Ligand binding to the proteins resulted in changes in line widths and chemical shifts of ligand resonances, but no changes in the coupling constant were observed. Line width and chemical shift changes of the H4 L-tryptophan proton were monitored as a function of temperature and ligand and protein concentrations. For the WT repressor, the H4 proton displays slow exchange at low temperatures (20-35 degrees C), while fast exchange occurs in the range from 45 to 65 degrees C. From 35 to 40 degrees C, the range of intermediate exchange, lines are broadened beyond detection. For the AV77 mutant, the intermediate and fast exchange regions are shifted at least 5 degrees C to higher temperatures. Line shapes of L-tryptophan H4 proton resonances were simulated using a general expression based on McConnell's modified Bloch equations for a two-site exchange. From the simulations, an exchange frequency (upsilon exch) of about 3000 Hz was obtained at 45 degrees C for WT and about 1000 Hz for AV77 mutant. The activation energy for the process is 32.7 kcal K-1 mol-1 for the WT and 29.1 kcal K-1 mol-1 for AV77. At 45 degrees C, the dissociation and association rate constants (k-1 and K+1, respectively) were calculated to be 2.0 x 10(3) s-1 and 9.9 x 10(6) M-1 s-1, for the WT.(ABSTRACT TRUNCATED AT 250 WORDS)