2D NMR Methods for Structural Delineation of Copper(II) Complexes of Penicillin and Pilocarpine

A method was developed for delineating the structure of paramagnetic metal complexes. The selective disappearance of cross-peaks in proton-carbon shift correlated 2D NMR maps was shown to uniquely depend upon the scalar and/or dipolar interaction between ligand nuclei and the unpaired electron(s), thus providing a means of identifying binding sites. Copper(II) was shown to form metal complexes with both Penicillin (PNC) and Pilocarpine (PLC) and the structure of the two 1:2 complexes in water solution at physiological pH were determined

Probing the role of metal ions on reversible peptide–protein interactions by NMR

This work provides evidence that paramagnetic lanthanide ions constitute ideal probes suitable for investigations of metal effects upon peptide–receptor interactions with the use of NMR methods. Cerium(III) is herein used for assessing metal effects upon the interaction between angiotensin II and a fragment from the AT1Areceptor. Angiotensin II forms a complex with cerium(III) in water while the fCT300–320receptor fragment is poorly affected by cerium(III). However, the addition of the fragment displaces cerium(III) from the complex, thus directly demonstrating the higher affinity of angiotensin II for the receptor and probing the peptide residues involved in receptor binding

Inferences on the Nature of a Cr(V) or Cr(IV) Species Formed by Reduction of Dichromate by a Bovine Liver Homogenate: NMR and Mass-Spectrometric Studies

A low-molecular weight chromium-containing fraction of the material resulting from dichromate reduction by bovine liver homogenate was investigated by NMR and ES-MS. The ES-MS spectrum showed a readily detectable peak at m/z = 786.1. The same molecular weight reasonably agreed with the relatively low diffusion coefficient measured by NMR-DOSY experiments on the main species observed in the 1H NMR spectrum. At least two downfield shifted and broad paramagnetic signals were apparent in the 1H NMR spectrum. Temperature dependence of chemical shift was exploited in order to estimate the diamagnetic shift of the signals in the diamagnetic region of the spectrum. 2D TOCSY, NOESY, COSY and 1H-3C HMQC spectra revealed the presence of aromatic protons (which were assigned as His residues), Gly and some other short chain amino-acids. Combinations of the molecular masses of such components together with acetate (which is present in the solution) and chromium atoms allowed a tentative proposal of a model for the compound

Calcium ions affect the exchange network but not the structure of a small peptide (melanostatin) in solution: a 1H- and 13C-NMR study

The interaction of calcium ions with the peptide hormone melanostatin (Pro-Leu-Gly-NH2) was investigated by H-1 and C-13 NMR spectroscopy in [D-6]DMSO containing H2O (1%). Chemical shifts, spin-lattice relaxation rates, H-1 NOESY maps and the temperature coefficients of the amide 1H NMR chemical shifts were measured at increasing concentrations of calcium. A 1:1 complex with the metal coordinated to the carbonyl moieties of Pro and Gly (K-d = 17 +/- 2 mM(-1)) was shown to be the major species in solution, although evidence was also provided for the occurrence of a minor species with the metal bound to the Leu carbonyl and with different stoichiometry. Upon metal complexation, substantial changes in the intrinsic chain flexibility of the peptide and in the exchange rates between water and amide protons were detected

Identification of copper(II) binding sites in the aminoglycosidic antibiotic Neomycin B

Protonation and copper(II) coordination properties of neomycin B were studied in solution by potentiometry, NMR, UV/Vis, CD, and EPR spectroscopy, XAS and mass spectrometry. Mono- and dinuclear complexes were found depending on the metal-to-ligand molar ratio. Neomycin B anchors CuII ions above pH 5.0 with an NH2 group from ring B. Simultaneously, the second amino group of the same ring and the hydroxyl group of ring A complete the binding set of donors. With an increase in pH the remaining –NH3+ functional groups in the neomycin B molecule are deprotonated without affecting the complexation pattern. However, these groups, particularly the ones located in the D-ring of the antibiotic, may coordinate the second copper(II) ion when the metal is present in excess. We have proved this process with the use of potentiometry, CD and especially mass spectrometry