Rotating-frame Overhauser Research Articles

Host–guest association of Morin with β-CD and C-hexylpyrogallol[4]arene: Structure of the complexes and the effect of pH

The study of the host–guest association of Morin hydrate (MO) with β-cyclodextrin (β-CD) and C-hexylpyrogllol[4]arene (C-HPA) is reported in this paper. The iInclusion complexation of MO is studied by ultraviolet-visible, steady-state fluorescence, time-resolved fluorescence, 1H nuclear magnetic resonance (NMR), and two dimentional rotating-frame nuclear overhauser effect correlation (2D ROESY) spectroscopic techniques. The stoichiometry and the binding constant for the MO–β-CD complex are derived from the linearity of the Benesi–Hildebrand equation. The binding constant for the MO–C-HPA complex is calculated from the nonlinear curve fitting of fluorescence intensities. The effects of the acid strength on the absorption and fluorescence spectra of MO are studied in the absence and the presence of β-CD/C-HPA host molecules. The pK a values of the ground and the excited states are reported.

C-hexylpyrogallol[4]arene and β-cyclodextrin as directors of the mode of binding of Coumarin 153 with DNA

The supramolecular interaction between calf thymus DNA (ctDNA) and Coumarin 153 in the presence of β-cyclodextrin (β-CD) or C-hexylpyrogallol[4]arene (C-HPA) was studied. Inclusion complexes of Coumarin 153 with β-CD and C-HPA were characterised by infrared spectroscopy, proton nuclear magnetic resonance spectroscopy and two-dimensional rotating-frame nuclear overhauser effect spectroscopy. The inclusion complexation was further followed by steady-state and time-resolved fluorescence measurements. The influence of β-CD or C-HPA in the binding strength and binding model of C153 with ctDNA was studied by UV–visible, fluorescence and molecular modelling technique. The possible group of interaction of Coumarin 153 with DNA, β-CD and C-HPA was shown by molecular modelling technique.

Identification and localization of bound internal water in the solution structure of interleukin 1.beta. by heteronuclear three-dimensional proton rotating-fram Overhauser nitrogen-15-proton multiple quantum coherence NMR spectroscopy

The presence and location of bound internal water molecules in the solution structure of interleukin 1 beta have been investigated by means of three-dimensional 1H rotating-frame Overhauser 1H-15N multiple quantum coherence spectroscopy (ROESY-HMQC). In this experiment through-space rotating-frame Overhauser (ROE) interactions between NH protons and bound water separated by less than or equal to 3.5 A are clearly distinguished from chemical exchange effects, as the cross-peaks for these two processes are of opposite sign. The identification of ROEs between NH protons and water is rendered simple by spreading out the spectrum into a third dimension according to the 15N chemical shift of the directly bonded nitrogen atoms. By this means, the problems that prevent, in all but a very few limited cases, the interpretation, identification, and assignment of ROE peaks between NH protons and water in a 2D 1H-1H ROESY spectrum of a large protein such as interleukin 1 beta, namely, extensive NH chemical shift degeneracy and ROE peaks obscured by much stronger chemical exchange peaks, are completely circumvented. We demonstrate the existence of 15 NH protons that are close to bound water molecules. From an examination of the crystal structure of interleukin 1 beta [Finzel, B. C., Clancy, L. L., Holland, D. R., Muchmore, S. W., Watenpaugh, K. D., & Einspahr, H. M. (1989) J. Mol. Biol. 209, 779-791], the results can be attributed to 11 water molecules that are involved in interactions bridging hydrogen-bonding interactions with backbone amide and carbonyl groups which stabilize the 3-fold pseudosymmetric topology of interleukin 1 beta and thus constitute an integral part of the protein structure in solution.

Rotating-frame nuclear overhauser enhancement spectroscopy of aqueous solutions with elimination of the water resonance by transverse relaxation

We report here that the water resonance can be completely and selectively eliminated from ROESY spectra by the WATR (water attenuation by transverse relaxation) method. Elimination of the water resonance by the WATR method is achieved by selectively decreasing the transverse relaxation time of the water protons by addition of a water proton exchange reagent, and then measuring the spectrum with a delay for transverse relaxation prior to acquisition of the free induction decay