1,721,016 research outputs found
Nuclear magnetic resonance investigations of calcium-antagonist drugs. Part 1. Conformational and dynamic features of nimodipine {3-[(2-methoxyethoxy)carbonyl]-5-(isopropoxycarbonyl)-4-(3-nitrophenyl)-2,6-dimethyl-1,4-dihydropyridine} in [2H6]dimethyl sulphoxide
No full textConformational and dynamic features of nimodipine in [2H6]DMSO solution were investigated by 1D and 2D n.m.r. techniques. 1H and 13C n.m.r. relaxation rates, 13C-{1H} n.O.e.s, and 2D n.O.e. proton spectra were used to build up a Dreiding model of the preferred conformation. Folding of the two side-chains in opposite directions was indicated. Complete anisotropic motion was assumed wherefrom internal reorientational times within the phenyl ring and the side-chains were evaluated. Folding of the isopropoxycarbonyl side-chain was also demonstrated by motional constraints undergone by carbon atoms within it
Velocità di rilassamento nucleare e conformazione in soluzione di molecole biologicamente attive
No full textConformational Features of Penicillin G in Solution as Revealed by 13C-{1H} Selective Nuclear Overhauser Effects
No full textC-13-(H-1) nuclear Overhauser effects (n.O.e.) were measured for penicillin G in H-2(6) -DMSO upon selective presaturation of proton resonances and interpreted on the basis of effective correlation times as calculated by analysis of C-13 and H-1 spin-lattice relaxation rates. Preferential occurrence of a compact C2 puckered conformation with folding of the benzoylamino side chain towards the methyl at C2 was given evidence. A Dreiding model of such conformation was built
1H and 13C NMR conformational analysis in solution of isoproterenol a pure β-agonist drug
No full text13C and 1H NMR parameters were measured for isoproterenol in solution. Spin-lattice relaxation rates were considered and C-H and H-H J couplings were determined. The t rotamer was shown to occur in a much greater abundance than the two g rotamers. Dynamics in solution were interpreted in terms of a nearly isotropic motion of the α-hydroxyphenethyl moiety and of a high degree of flexibility of the isopropyl moiety, Relevant distances and dipolar connectivities were measured and used to build up a Dreiding model of the most probable conformation
1H NMR relaxation investigation of herbicides interacting with photosystem II preparations from Spinacia oleracea L.
No full textThe interaction of three common herbicides, paraquat, acifluorfen and alachlor, with spinach chloroplast photosystem II (PS II) was investigated by measuring LH nuclear magnetic resonance spin-lattice relaxation rates, transient nuclear Overhauser effect (NOE) and NOE spectroscopy (NOESY) spectra. Binding to PS II was detected by (i) the enhancement of single-selective relaxation rates and (ii) the decrease in the optimal mixing time providing maximal cross-peak intensity in NOESY spectra. Titration of relaxation enhancements was used to calculate the dissociation constants (K-d) from the bound state for paraquat (K-d = 292 +/- 71 mu M-1) and acifluorfen (K-d = 311 +/- 58 mu M-1). A similar K-d was apparent for alachlor. Double-selective relaxation rates allowed the isolation of dipolar relaxation terms between selected proton pairs wherefrom dynamic features of the bound state were evaluated. In all cases the motional correlation time of bound herbicide (tau(c) = 0.1-0.4 ns at 300 K) was found two orders of magnitude slower than in the free-solution state. In the case of alachlor the E and Z isomers were observed to bind differently to PS II and a change in conformation could be hypothesized
Cross relaxation effects on the longitudinal relaxation rate of water in protein solutions
No full textNon-selective and selective longitudinal relaxation rates were measured for water protons in protein solutions. The perturbations on water spin-lattice relaxation from cross relaxation between water and protein protons were shown to be significant at low temperature and small isotopic dilution. © 1981
Manganese(II) as magnetic relaxation probe in the study of biomechanisms and of biomacromolecules
No full textConformational dynamics of Cytochalasin B in solution as detected by 13C and 1H-NMR relaxation rates.
No full text13C and 1H NMR spin-lattice relaxation rates have been measured for cytochalasin B in [2H]6DMSO. Motional features have been interpreted in terms of nearly isotropic reorientation of the whole molecule with few additional internal motions. The 'isotropic' reorientational correlation time was evaluated at 0.21 ns at room temperature. By using selective and double-selective excitation techniques, relevant cross-relaxation terms have been obtained wherefrom proton-proton distances have been calculated. A Dreiding model of the 'preferred' conformation in solution has been built, yielding evidence of a strong similarity between solution and solid state structures of cytochalasin B
1H and 13C-NMR conformational analysis of adrenergic drugs. Part 3. Dichloroisoproterenol. A nonselective β-blocking agent
No full text13C and 1H NMR parameters were measured for dichloroisoproterenol in solution. Spin-lattice relaxation rates, nuclear Overhauser effects and J couplings were determined and compared to those obtained from isoproterenol. The t rotamer was shown to occur with a much higher probability than the two g rotamers. Dynamics in solution were interpreted in terms of a nearly isotropic motion of an extended molecular backbone. Some interesting differences were given evidence between the ‘preferred’ conformations in solution of dichloroisoproterenol and isoproterenol
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